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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IETF Mobile IP Working Group C. Perkins (Ed.) 3 Internet-Draft Tellabs Inc. 4 Obsoletes: 3775 (if approved) D. Johnson 5 Intended status: Standards Track Rice University 6 Expires: August 12, 2011 J. Arkko 7 Ericsson 8 Feb 08, 2011 10 Mobility Support in IPv6 11 draft-ietf-mext-rfc3775bis-12.txt 13 Abstract 15 This document specifies Mobile IPv6, a protocol which allows nodes to 16 remain reachable while moving around in the IPv6 Internet. Each 17 mobile node is always identified by its home address, regardless of 18 its current point of attachment to the Internet. While situated away 19 from its home, a mobile node is also associated with a care-of 20 address, which provides information about the mobile node's current 21 location. IPv6 packets addressed to a mobile node's home address are 22 transparently routed to its care-of address. The protocol enables 23 IPv6 nodes to cache the binding of a mobile node's home address with 24 its care-of address, and to then send any packets destined for the 25 mobile node directly to it at this care-of address. To support this 26 operation, Mobile IPv6 defines a new IPv6 protocol and a new 27 destination option. All IPv6 nodes, whether mobile or stationary, 28 can communicate with mobile nodes. This document obsoletes RFC 3775. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on August 12, 2011. 47 Copyright Notice 48 Copyright (c) 2011 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 This document may contain material from IETF Documents or IETF 62 Contributions published or made publicly available before November 63 10, 2008. The person(s) controlling the copyright in some of this 64 material may not have granted the IETF Trust the right to allow 65 modifications of such material outside the IETF Standards Process. 66 Without obtaining an adequate license from the person(s) controlling 67 the copyright in such materials, this document may not be modified 68 outside the IETF Standards Process, and derivative works of it may 69 not be created outside the IETF Standards Process, except to format 70 it for publication as an RFC or to translate it into languages other 71 than English. 73 Table of Contents 75 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7 76 2. Comparison with Mobile IP for IPv4 . . . . . . . . . . . . . 9 77 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 10 78 3.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 10 79 3.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 12 80 4. Overview of Mobile IPv6 . . . . . . . . . . . . . . . . . . . 16 81 4.1. Basic Operation . . . . . . . . . . . . . . . . . . . . . 16 82 4.2. New IPv6 Protocol . . . . . . . . . . . . . . . . . . . . 18 83 4.3. New IPv6 Destination Option . . . . . . . . . . . . . . . 19 84 4.4. New IPv6 ICMP Messages . . . . . . . . . . . . . . . . . 19 85 4.5. Conceptual Data Structure Terminology . . . . . . . . . . 20 86 4.6. Unique-Local Addressability . . . . . . . . . . . . . . . 20 87 5. Overview of Mobile IPv6 Security . . . . . . . . . . . . . . 22 88 5.1. Binding Updates to Home Agents . . . . . . . . . . . . . 22 89 5.2. Binding Updates to Correspondent Nodes . . . . . . . . . 23 90 5.2.1. Node Keys . . . . . . . . . . . . . . . . . . . . . . 23 91 5.2.2. Nonces . . . . . . . . . . . . . . . . . . . . . . . 24 92 5.2.3. Cookies and Tokens . . . . . . . . . . . . . . . . . 24 93 5.2.4. Cryptographic Functions . . . . . . . . . . . . . . . 25 94 5.2.5. Return Routability Procedure . . . . . . . . . . . . 25 95 5.2.6. Authorizing Binding Management Messages . . . . . . . 30 96 5.2.7. Updating Node Keys and Nonces . . . . . . . . . . . . 32 97 5.2.8. Preventing Replay Attacks . . . . . . . . . . . . . . 33 98 5.2.9. Handling Interruptions to Return Routability . . . . 33 99 5.3. Dynamic Home Agent Address Discovery . . . . . . . . . . 34 100 5.4. Mobile Prefix Discovery . . . . . . . . . . . . . . . . . 34 101 5.5. Payload Packets . . . . . . . . . . . . . . . . . . . . . 34 102 6. New IPv6 Protocol, Message Types, and Destination Option . . 36 103 6.1. Mobility Header . . . . . . . . . . . . . . . . . . . . . 36 104 6.1.1. Format . . . . . . . . . . . . . . . . . . . . . . . 36 105 6.1.2. Binding Refresh Request Message . . . . . . . . . . . 38 106 6.1.3. Home Test Init Message . . . . . . . . . . . . . . . 39 107 6.1.4. Care-of Test Init Message . . . . . . . . . . . . . . 40 108 6.1.5. Home Test Message . . . . . . . . . . . . . . . . . . 41 109 6.1.6. Care-of Test Message . . . . . . . . . . . . . . . . 42 110 6.1.7. Binding Update Message . . . . . . . . . . . . . . . 44 111 6.1.8. Binding Acknowledgement Message . . . . . . . . . . . 46 112 6.1.9. Binding Error Message . . . . . . . . . . . . . . . . 49 113 6.2. Mobility Options . . . . . . . . . . . . . . . . . . . . 50 114 6.2.1. Format . . . . . . . . . . . . . . . . . . . . . . . 50 115 6.2.2. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 51 116 6.2.3. PadN . . . . . . . . . . . . . . . . . . . . . . . . 52 117 6.2.4. Binding Refresh Advice . . . . . . . . . . . . . . . 52 118 6.2.5. Alternate Care-of Address . . . . . . . . . . . . . . 52 119 6.2.6. Nonce Indices . . . . . . . . . . . . . . . . . . . . 53 120 6.2.7. Binding Authorization Data . . . . . . . . . . . . . 54 122 6.3. Home Address Option . . . . . . . . . . . . . . . . . . . 55 123 6.4. Type 2 Routing Header . . . . . . . . . . . . . . . . . . 57 124 6.4.1. Format . . . . . . . . . . . . . . . . . . . . . . . 57 125 6.5. ICMP Home Agent Address Discovery Request Message . . . . 59 126 6.6. ICMP Home Agent Address Discovery Reply Message . . . . . 60 127 6.7. ICMP Mobile Prefix Solicitation Message Format . . . . . 61 128 6.8. ICMP Mobile Prefix Advertisement Message Format . . . . . 62 129 7. Modifications to IPv6 Neighbor Discovery . . . . . . . . . . 66 130 7.1. Modified Router Advertisement Message Format . . . . . . 66 131 7.2. Modified Prefix Information Option Format . . . . . . . . 66 132 7.3. New Advertisement Interval Option Format . . . . . . . . 68 133 7.4. New Home Agent Information Option Format . . . . . . . . 69 134 7.5. Changes to Sending Router Advertisements . . . . . . . . 71 135 8. Requirements for Types of IPv6 Nodes . . . . . . . . . . . . 73 136 8.1. All IPv6 Nodes . . . . . . . . . . . . . . . . . . . . . 73 137 8.2. IPv6 Nodes with Support for Route Optimization . . . . . 73 138 8.3. All IPv6 Routers . . . . . . . . . . . . . . . . . . . . 75 139 8.4. IPv6 Home Agents . . . . . . . . . . . . . . . . . . . . 75 140 8.5. IPv6 Mobile Nodes . . . . . . . . . . . . . . . . . . . . 77 141 9. Correspondent Node Operation . . . . . . . . . . . . . . . . 79 142 9.1. Conceptual Data Structures . . . . . . . . . . . . . . . 79 143 9.2. Processing Mobility Headers . . . . . . . . . . . . . . . 80 144 9.3. Packet Processing . . . . . . . . . . . . . . . . . . . . 80 145 9.3.1. Receiving Packets with Home Address Option . . . . . 80 146 9.3.2. Sending Packets to a Mobile Node . . . . . . . . . . 81 147 9.3.3. Sending Binding Error Messages . . . . . . . . . . . 83 148 9.3.4. Receiving ICMP Error Messages . . . . . . . . . . . . 83 149 9.4. Return Routability Procedure . . . . . . . . . . . . . . 84 150 9.4.1. Receiving Home Test Init Messages . . . . . . . . . . 84 151 9.4.2. Receiving Care-of Test Init Messages . . . . . . . . 84 152 9.4.3. Sending Home Test Messages . . . . . . . . . . . . . 85 153 9.4.4. Sending Care-of Test Messages . . . . . . . . . . . . 85 154 9.5. Processing Bindings . . . . . . . . . . . . . . . . . . . 85 155 9.5.1. Receiving Binding Updates . . . . . . . . . . . . . . 85 156 9.5.2. Requests to Cache a Binding . . . . . . . . . . . . . 88 157 9.5.3. Requests to Delete a Binding . . . . . . . . . . . . 88 158 9.5.4. Sending Binding Acknowledgements . . . . . . . . . . 89 159 9.5.5. Sending Binding Refresh Requests . . . . . . . . . . 90 160 9.6. Cache Replacement Policy . . . . . . . . . . . . . . . . 90 161 10. Home Agent Operation . . . . . . . . . . . . . . . . . . . . 92 162 10.1. Conceptual Data Structures . . . . . . . . . . . . . . . 92 163 10.2. Processing Mobility Headers . . . . . . . . . . . . . . . 93 164 10.3. Processing Bindings . . . . . . . . . . . . . . . . . . . 93 165 10.3.1. Primary Care-of Address Registration . . . . . . . . 93 166 10.3.2. Primary Care-of Address De-Registration . . . . . . . 97 167 10.4. Packet Processing . . . . . . . . . . . . . . . . . . . . 98 168 10.4.1. Intercepting Packets for a Mobile Node . . . . . . . 98 169 10.4.2. Processing Intercepted Packets . . . . . . . . . . . 100 170 10.4.3. Multicast Membership Control . . . . . . . . . . . . 101 171 10.4.4. Stateful Address Autoconfiguration . . . . . . . . . 102 172 10.4.5. Handling Reverse Tunneled Packets . . . . . . . . . . 103 173 10.4.6. Protecting Return Routability Packets . . . . . . . . 103 174 10.5. Dynamic Home Agent Address Discovery . . . . . . . . . . 104 175 10.5.1. Receiving Router Advertisement Messages . . . . . . . 104 176 10.6. Sending Prefix Information to the Mobile Node . . . . . . 107 177 10.6.1. List of Home Network Prefixes . . . . . . . . . . . . 107 178 10.6.2. Scheduling Prefix Deliveries . . . . . . . . . . . . 107 179 10.6.3. Sending Advertisements . . . . . . . . . . . . . . . 109 180 10.6.4. Lifetimes for Changed Prefixes . . . . . . . . . . . 110 181 11. Mobile Node Operation . . . . . . . . . . . . . . . . . . . . 111 182 11.1. Conceptual Data Structures . . . . . . . . . . . . . . . 111 183 11.2. Processing Mobility Headers . . . . . . . . . . . . . . . 112 184 11.3. Packet Processing . . . . . . . . . . . . . . . . . . . . 113 185 11.3.1. Sending Packets While Away from Home . . . . . . . . 113 186 11.3.2. Interaction with Outbound IPsec Processing . . . . . 116 187 11.3.3. Receiving Packets While Away from Home . . . . . . . 118 188 11.3.4. Routing Multicast Packets . . . . . . . . . . . . . . 119 189 11.3.5. Receiving ICMP Error Messages . . . . . . . . . . . . 121 190 11.3.6. Receiving Binding Error Messages . . . . . . . . . . 121 191 11.4. Home Agent and Prefix Management . . . . . . . . . . . . 122 192 11.4.1. Dynamic Home Agent Address Discovery . . . . . . . . 122 193 11.4.2. Sending Mobile Prefix Solicitations . . . . . . . . . 123 194 11.4.3. Receiving Mobile Prefix Advertisements . . . . . . . 124 195 11.5. Movement . . . . . . . . . . . . . . . . . . . . . . . . 125 196 11.5.1. Movement Detection . . . . . . . . . . . . . . . . . 125 197 11.5.2. Home Link Detection . . . . . . . . . . . . . . . . . 128 198 11.5.3. Forming New Care-of Addresses . . . . . . . . . . . . 128 199 11.5.4. Using Multiple Care-of Addresses . . . . . . . . . . 129 200 11.5.5. Returning Home . . . . . . . . . . . . . . . . . . . 130 201 11.6. Return Routability Procedure . . . . . . . . . . . . . . 132 202 11.6.1. Sending Test Init Messages . . . . . . . . . . . . . 132 203 11.6.2. Receiving Test Messages . . . . . . . . . . . . . . . 133 204 11.6.3. Protecting Return Routability Packets . . . . . . . . 134 205 11.7. Processing Bindings . . . . . . . . . . . . . . . . . . . 134 206 11.7.1. Sending Binding Updates to the Home Agent . . . . . . 134 207 11.7.2. Correspondent Registration . . . . . . . . . . . . . 137 208 11.7.3. Receiving Binding Acknowledgements . . . . . . . . . 140 209 11.7.4. Receiving Binding Refresh Requests . . . . . . . . . 142 210 11.8. Retransmissions and Rate Limiting . . . . . . . . . . . . 143 211 12. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 145 212 13. Protocol Configuration Variables . . . . . . . . . . . . . . 146 213 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 147 214 15. Security Considerations . . . . . . . . . . . . . . . . . . . 150 215 15.1. Threats . . . . . . . . . . . . . . . . . . . . . . . . . 150 216 15.2. Features . . . . . . . . . . . . . . . . . . . . . . . . 152 217 15.3. Binding Updates to Home Agent . . . . . . . . . . . . . . 154 218 15.4. Binding Updates to Correspondent Nodes . . . . . . . . . 156 219 15.4.1. Overview . . . . . . . . . . . . . . . . . . . . . . 156 220 15.4.2. Achieved Security Properties . . . . . . . . . . . . 157 221 15.4.3. Comparison to Regular IPv6 Communications . . . . . . 158 222 15.4.4. Replay Attacks . . . . . . . . . . . . . . . . . . . 160 223 15.4.5. Denial-of-Service Attacks . . . . . . . . . . . . . . 160 224 15.4.6. Key Lengths . . . . . . . . . . . . . . . . . . . . . 161 225 15.5. Dynamic Home Agent Address Discovery . . . . . . . . . . 162 226 15.6. Mobile Prefix Discovery . . . . . . . . . . . . . . . . . 163 227 15.7. Tunneling via the Home Agent . . . . . . . . . . . . . . 163 228 15.8. Home Address Option . . . . . . . . . . . . . . . . . . . 164 229 15.9. Type 2 Routing Header . . . . . . . . . . . . . . . . . . 164 230 16. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 166 231 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 167 232 18. References . . . . . . . . . . . . . . . . . . . . . . . . . 168 233 18.1. Normative References . . . . . . . . . . . . . . . . . . 168 234 18.2. Informative References . . . . . . . . . . . . . . . . . 169 235 Appendix A. Future Extensions . . . . . . . . . . . . . . . . . 172 236 A.1. Piggybacking . . . . . . . . . . . . . . . . . . . . . . 172 237 A.2. Triangular Routing . . . . . . . . . . . . . . . . . . . 172 238 A.3. New Authorization Methods . . . . . . . . . . . . . . . . 172 239 A.4. Neighbor Discovery Extensions . . . . . . . . . . . . . . 172 240 Appendix B. Changes since RFC 3775 . . . . . . . . . . . . . . . 174 241 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 177 243 1. Introduction 245 This document specifies a protocol which allows nodes to remain 246 reachable while moving around in the IPv6 Internet. Without specific 247 support for mobility in IPv6 [6], packets destined to a mobile node 248 would not be able to reach it while the mobile node is away from its 249 home link. In order to continue communication in spite of its 250 movement, a mobile node could change its IP address each time it 251 moves to a new link, but the mobile node would then not be able to 252 maintain transport and higher-layer connections when it changes 253 location. Mobility support in IPv6 is particularly important, as 254 mobile computers are likely to account for a majority or at least a 255 substantial fraction of the population of the Internet during the 256 lifetime of IPv6. 258 The protocol defined in this document, known as Mobile IPv6, allows a 259 mobile node to move from one link to another without changing the 260 mobile node's "home address". Packets may be routed to the mobile 261 node using this address regardless of the mobile node's current point 262 of attachment to the Internet. The mobile node may also continue to 263 communicate with other nodes (stationary or mobile) after moving to a 264 new link. The movement of a mobile node away from its home link is 265 thus transparent to transport and higher-layer protocols and 266 applications. 268 The Mobile IPv6 protocol is just as suitable for mobility across 269 homogeneous media as for mobility across heterogeneous media. For 270 example, Mobile IPv6 facilitates node movement from one Ethernet 271 segment to another as well as it facilitates node movement from an 272 Ethernet segment to a wireless LAN cell, with the mobile node's IP 273 address remaining unchanged in spite of such movement. 275 One can think of the Mobile IPv6 protocol as solving the network- 276 layer mobility management problem. Some mobility management 277 applications -- for example, handover among wireless transceivers, 278 each of which covers only a very small geographic area -- have been 279 solved using link-layer techniques. For example, in many current 280 wireless LAN products, link-layer mobility mechanisms allow a 281 "handover" of a mobile node from one cell to another, re-establishing 282 link-layer connectivity to the node in each new location. 284 Mobile IPv6 does not attempt to solve all general problems related to 285 the use of mobile computers or wireless networks. In particular, 286 this protocol does not attempt to solve: 288 o Handling links with unidirectional connectivity or partial 289 reachability, such as the hidden terminal problem where a host is 290 hidden from only some of the routers on the link. 292 o Access control on a link being visited by a mobile node. 294 o Local or hierarchical forms of mobility management (similar to 295 many current link-layer mobility management solutions). 297 o Assistance for adaptive applications. 299 o Mobile routers. 301 o Service Discovery. 303 o Distinguishing between packets lost due to bit errors vs. network 304 congestion. 306 This document obsoletes RFC 3775. Issues with the original document 307 have been observed during integration, testing and deployment of RFC 308 3775. A more detailed list of the changes since RFC 3775 may be 309 found in Appendix B. 311 2. Comparison with Mobile IP for IPv4 313 The design of Mobile IP support in IPv6 (Mobile IPv6) benefits both 314 from the experiences gained from the development of Mobile IP support 315 in IPv4 (Mobile IPv4) [31] [25] [26], and from the opportunities 316 provided by IPv6. Mobile IPv6 thus shares many features with Mobile 317 IPv4, but is integrated into IPv6 and offers many other improvements. 318 This section summarizes the major differences between Mobile IPv4 and 319 Mobile IPv6: 321 o There is no need to deploy special routers as "foreign agents", as 322 in Mobile IPv4. Mobile IPv6 operates in any location without any 323 special support required from the local router. 325 o Support for route optimization is a fundamental part of the 326 protocol, rather than a nonstandard set of extensions. 328 o Mobile IPv6 route optimization can operate securely even without 329 pre-arranged security associations. It is expected that route 330 optimization can be deployed on a global scale between all mobile 331 nodes and correspondent nodes. 333 o Support is also integrated into Mobile IPv6 for allowing route 334 optimization to coexist efficiently with routers that perform 335 "ingress filtering" [27]. 337 o The IPv6 Neighbor Unreachability Detection assures symmetric 338 reachability between the mobile node and its default router in the 339 current location. 341 o Most packets sent to a mobile node while away from home in Mobile 342 IPv6 are sent using an IPv6 routing header rather than IP 343 encapsulation, reducing the amount of resulting overhead compared 344 to Mobile IPv4. 346 o Mobile IPv6 is decoupled from any particular link layer, as it 347 uses IPv6 Neighbor Discovery [18] instead of ARP. This also 348 improves the robustness of the protocol. 350 o The use of IPv6 encapsulation (and the routing header) removes the 351 need in Mobile IPv6 to manage "tunnel soft state". 353 o The dynamic home agent address discovery mechanism in Mobile IPv6 354 returns a single reply to the mobile node. The directed broadcast 355 approach used in IPv4 returns separate replies from each home 356 agent. 358 3. Terminology 360 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 361 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 362 document are to be interpreted as described in RFC 2119 [2]. 364 3.1. General Terms 366 IP 368 Internet Protocol Version 6 (IPv6). 370 node 372 A device that implements IP. 374 router 376 A node that forwards IP packets not explicitly addressed to 377 itself. 379 unicast routable address 381 An identifier for a single interface such that a packet sent to it 382 from another IPv6 subnet is delivered to the interface identified 383 by that address. Accordingly, a unicast routable address must 384 either be global IPv6 address or a unique local IPv6 address. 386 host 388 Any node that is not a router. 390 link 392 A communication facility or medium over which nodes can 393 communicate at the link layer, such as an Ethernet (simple or 394 bridged). A link is the layer immediately below IP. 396 interface 398 A node's attachment to a link. 400 subnet prefix 402 A bit string that consists of some number of initial bits of an IP 403 address. 405 interface identifier 407 A number used to identify a node's interface on a link. The 408 interface identifier is the remaining low-order bits in the node's 409 IP address after the subnet prefix. 411 link-layer address 413 A link-layer identifier for an interface, such as IEEE 802 414 addresses on Ethernet links. 416 packet 418 An IP header plus payload. 420 security association 422 An IPsec security association is a cooperative relationship formed 423 by the sharing of cryptographic keying material and associated 424 context. Security associations are simplex. That is, two 425 security associations are needed to protect bidirectional traffic 426 between two nodes, one for each direction. 428 security policy database 430 A database that specifies what security services are to be offered 431 to IP packets and in what fashion. 433 destination option 435 Destination options are carried by the IPv6 Destination Options 436 extension header. Destination options include optional 437 information that need be examined only by the IPv6 node given as 438 the destination address in the IPv6 header, not by routers in 439 between. Mobile IPv6 defines one new destination option, the Home 440 Address destination option (see Section 6.3). 442 routing header 444 A routing header may be present as an IPv6 header extension, and 445 indicates that the payload has to be delivered to a destination 446 IPv6 address in some way that is different from what would be 447 carried out by standard Internet routing. In this document, use 448 of the term "routing header" typically refers to use of a type 2 449 routing header, as specified in Section 6.4. 451 "|" (concatenation) 453 Some formulas in this specification use the symbol "|" to indicate 454 bytewise concatenation, as in A | B. This concatenation requires 455 that all of the octets of the datum A appear first in the result, 456 followed by all of the octets of the datum B. 458 First (size, input) 460 Some formulas in this specification use a functional form "First 461 (size, input)" to indicate truncation of the "input" data so that 462 only the first "size" bits remain to be used. 464 3.2. Mobile IPv6 Terms 466 These terms are intended to be compatible with the definitions given 467 in RFC 3753[38]. However, if there is any conflict, the definitions 468 given here should be considered to supersede those in RFC 3753. 470 home address 472 A unicast routable address assigned to a mobile node, used as the 473 permanent address of the mobile node. This address is within the 474 mobile node's home link. Standard IP routing mechanisms will 475 deliver packets destined for a mobile node's home address to its 476 home link. Mobile nodes can have multiple home addresses, for 477 instance when there are multiple home prefixes on the home link. 479 home subnet prefix 481 The IP subnet prefix corresponding to a mobile node's home 482 address. 484 home link 486 The link on which a mobile node's home subnet prefix is defined. 488 mobile node 490 A node that can change its point of attachment from one link to 491 another, while still being reachable via its home address. 493 movement 495 A change in a mobile node's point of attachment to the Internet 496 such that it is no longer connected to the same link as it was 497 previously. If a mobile node is not currently attached to its 498 home link, the mobile node is said to be "away from home". 500 L2 handover 502 A process by which the mobile node changes from one link-layer 503 connection to another. For example, a change of wireless access 504 point is a L2 handover. 506 L3 handover 508 Subsequent to a L2 handover, a mobile node detects a change in an 509 on-link subnet prefix that would require a change in the primary 510 care-of address. For example, a change of access router 511 subsequent to a change of wireless access point typically results 512 in an L3 handover. 514 correspondent node 516 A peer node with which a mobile node is communicating. The 517 correspondent node may be either mobile or stationary. 519 foreign subnet prefix 521 Any IP subnet prefix other than the mobile node's home subnet 522 prefix. 524 foreign link 526 Any link other than the mobile node's home link. 528 care-of address 530 A unicast routable address associated with a mobile node while 531 visiting a foreign link; the subnet prefix of this IP address is a 532 foreign subnet prefix. Among the multiple care-of addresses that 533 a mobile node may have at any given time (e.g., with different 534 subnet prefixes), the one registered with the mobile node's home 535 agent for a given home address is called its "primary" care-of 536 address. 538 home agent 540 A router on a mobile node's home link with which the mobile node 541 has registered its current care-of address. While the mobile node 542 is away from home, the home agent intercepts packets on the home 543 link destined to the mobile node's home address, encapsulates 544 them, and tunnels them to the mobile node's registered care-of 545 address. 547 binding 549 The association of the home address of a mobile node with a 550 care-of address for that mobile node, along with the remaining 551 lifetime of that association. 553 registration 555 The process during which a mobile node sends a Binding Update to 556 its home agent or a correspondent node, causing a binding for the 557 mobile node to be registered. 559 mobility message 561 A message containing a Mobility Header (see Section 6.1). 563 binding authorization 565 Correspondent registration needs to be authorized to allow the 566 recipient to believe that the sender has the right to specify a 567 new binding. 569 return routability procedure 571 The return routability procedure authorizes registrations by the 572 use of a cryptographic token exchange. 574 correspondent registration 576 A return routability procedure followed by a registration, run 577 between the mobile node and a correspondent node. 579 home registration 581 A registration between the mobile node and its home agent, 582 authorized by the use of IPsec. 584 nonce 586 Nonces are random numbers used internally by the correspondent 587 node in the creation of keygen tokens related to the return 588 routability procedure. The nonces are not specific to a mobile 589 node, and are kept secret within the correspondent node. 591 nonce index 593 A nonce index is used to indicate which nonces have been used when 594 creating keygen token values, without revealing the nonces 595 themselves. 597 cookie 599 A cookie is a random number used by a mobile node to prevent 600 spoofing by a bogus correspondent node in the return routability 601 procedure. 603 care-of init cookie 605 A cookie sent to the correspondent node in the Care-of Test Init 606 message, to be returned in the Care-of Test message. 608 home init cookie 610 A cookie sent to the correspondent node in the Home Test Init 611 message, to be returned in the Home Test message. 613 keygen token 615 A keygen token is a number supplied by a correspondent node in the 616 return routability procedure to enable the mobile node to compute 617 the necessary binding management key for authorizing a Binding 618 Update. 620 care-of keygen token 622 A keygen token sent by the correspondent node in the Care-of Test 623 message. 625 home keygen token 627 A keygen token sent by the correspondent node in the Home Test 628 message. 630 binding management key (Kbm) 632 A binding management key (Kbm) is a key used for authorizing a 633 binding cache management message (e.g., Binding Update or Binding 634 Acknowledgement). Return routability provides a way to create a 635 binding management key. 637 4. Overview of Mobile IPv6 639 4.1. Basic Operation 641 A mobile node is always expected to be addressable at its home 642 address, whether it is currently attached to its home link or is away 643 from home. The "home address" is an IP address assigned to the 644 mobile node within its home subnet prefix on its home link. While a 645 mobile node is at home, packets addressed to its home address are 646 routed to the mobile node's home link, using conventional Internet 647 routing mechanisms. 649 While a mobile node is attached to some foreign link away from home, 650 it is also addressable at one or more care-of addresses. A care-of 651 address is an IP address associated with a mobile node that has the 652 subnet prefix of a particular foreign link. The mobile node can 653 acquire its care-of address through conventional IPv6 mechanisms, 654 such as stateless or stateful auto-configuration. As long as the 655 mobile node stays in this location, packets addressed to this care-of 656 address will be routed to the mobile node. The mobile node may also 657 accept packets from several care-of addresses, such as when it is 658 moving but still reachable at the previous link. 660 The association between a mobile node's home address and care-of 661 address is known as a "binding" for the mobile node. While away from 662 home, a mobile node registers its primary care-of address with a 663 router on its home link, requesting this router to function as the 664 "home agent" for the mobile node. The mobile node performs this 665 binding registration by sending a "Binding Update" message to the 666 home agent. The home agent replies to the mobile node by returning a 667 "Binding Acknowledgement" message. The operation of the mobile node 668 is specified in Section 11, and the operation of the home agent is 669 specified in Section 10. 671 Any node communicating with a mobile node is referred to in this 672 document as a "correspondent node" of the mobile node, and may itself 673 be either a stationary node or a mobile node. Mobile nodes can 674 provide information about their current location to correspondent 675 nodes. This happens through the correspondent registration. As a 676 part of this procedure, a return routability test is performed in 677 order to authorize the establishment of the binding. The operation 678 of the correspondent node is specified in Section 9. 680 There are two possible modes for communications between the mobile 681 node and a correspondent node. The first mode, bidirectional 682 tunneling, does not require Mobile IPv6 support from the 683 correspondent node and is available even if the mobile node has not 684 registered its current binding with the correspondent node. Packets 685 from the correspondent node are routed to the home agent and then 686 tunneled to the mobile node. Packets to the correspondent node are 687 tunneled from the mobile node to the home agent ("reverse tunneled") 688 and then routed normally from the home network to the correspondent 689 node. In this mode, the home agent uses proxy Neighbor Discovery to 690 intercept any IPv6 packets addressed to the mobile node's home 691 address (or home addresses) on the home link. Each intercepted 692 packet is tunneled to the mobile node's primary care-of address. 693 This tunneling is performed using IPv6 encapsulation [7]. 695 The second mode, "route optimization", requires the mobile node to 696 register its current binding at the correspondent node. Packets from 697 the correspondent node can be routed directly to the care-of address 698 of the mobile node. When sending a packet to any IPv6 destination, 699 the correspondent node checks its cached bindings for an entry for 700 the packet's destination address. If a cached binding for this 701 destination address is found, the node uses a new type of IPv6 702 routing header [6] (see Section 6.4) to route the packet to the 703 mobile node by way of the care-of address indicated in this binding. 705 Routing packets directly to the mobile node's care-of address allows 706 the shortest communications path to be used. It also eliminates 707 congestion at the mobile node's home agent and home link. In 708 addition, the impact of temporary failures of the home agent or 709 networks on the path to or from the home agent is reduced. 711 When routing packets directly to the mobile node, the correspondent 712 node sets the Destination Address in the IPv6 header to the care-of 713 address of the mobile node. A new type of IPv6 routing header (see 714 Section 6.4) is also added to the packet to carry the desired home 715 address. Similarly, the mobile node sets the Source Address in the 716 packet's IPv6 header to its current care-of addresses. The mobile 717 node adds a new IPv6 "Home Address" destination option (see 718 Section 6.3) to carry its home address. The inclusion of home 719 addresses in these packets makes the use of the care-of address 720 transparent above the network layer (e.g., at the transport layer). 722 Mobile IPv6 also provides support for multiple home agents, and a 723 limited support for the reconfiguration of the home network. In 724 these cases, the mobile node may not know the IP address of its own 725 home agent, and even the home subnet prefixes may change over time. 726 A mechanism, known as "dynamic home agent address discovery" allows a 727 mobile node to dynamically discover the IP address of a home agent on 728 its home link, even when the mobile node is away from home. Mobile 729 nodes can also learn new information about home subnet prefixes 730 through the "mobile prefix discovery" mechanism. These mechanisms 731 are described starting from Section 6.5. 733 This document is written under the assumption that the mobile node is 734 configured with the home prefix for the mobile node to be able to 735 discover a home agent and configure a home address. This might be 736 limiting in deployments where the home agent and the home address for 737 the mobile node needs to be assigned dynamically. Additional 738 mechanisms have been specified for the mobile node to dynamically 739 configure a home agent, a home address and the home prefix. These 740 mechanisms are described in "Mobile IPv6 Bootstrapping in Split 741 Scenario" [22] and "MIP6 bootstrapping for the Integrated Scenario" 742 [35]. 744 4.2. New IPv6 Protocol 746 Mobile IPv6 defines a new IPv6 protocol, using the Mobility Header 747 (see Section 6.1). This Header is used to carry the following 748 messages: 750 Home Test Init 752 Home Test 754 Care-of Test Init 756 Care-of Test 758 These four messages are used to perform the return routability 759 procedure from the mobile node to a correspondent node. This 760 ensures authorization of subsequent Binding Updates, as described 761 in Section 5.2.5. 763 Binding Update 765 A Binding Update is used by a mobile node to notify a 766 correspondent node or the mobile node's home agent of its current 767 binding. The Binding Update sent to the mobile node's home agent 768 to register its primary care-of address is marked as a "home 769 registration". 771 Binding Acknowledgement 773 A Binding Acknowledgement is used to acknowledge receipt of a 774 Binding Update, if an acknowledgement was requested in the Binding 775 Update (e.g., the Binding Update was sent to a home agent), or an 776 error occurred. 778 Binding Refresh Request 780 A Binding Refresh Request is used by a correspondent node to 781 request that a mobile node re-establish its binding with the 782 correspondent node. This message is typically used when the 783 cached binding is in active use but the binding's lifetime is 784 close to expiration. The correspondent node may use, for 785 instance, recent traffic and open transport layer connections as 786 an indication of active use. 788 Binding Error 790 The Binding Error is used by the correspondent node to signal an 791 error related to mobility, such as an inappropriate attempt to use 792 the Home Address destination option without an existing binding. 793 The Binding Error message is also used by the Home Agent to signal 794 an error to the mobile node, if it receives an unrecognized 795 Mobility Header Message Type from the mobile node. 797 4.3. New IPv6 Destination Option 799 Mobile IPv6 defines a new IPv6 destination option, the Home Address 800 destination option. This option is described in detail in 801 Section 6.3. 803 4.4. New IPv6 ICMP Messages 805 Mobile IPv6 also introduces four new ICMP message types, two for use 806 in the dynamic home agent address discovery mechanism, and two for 807 renumbering and mobile configuration mechanisms. As described in 808 Section 10.5 and Section 11.4.1, the following two new ICMP message 809 types are used for home agent address discovery: 811 o Home Agent Address Discovery Request, described in Section 6.5. 813 o Home Agent Address Discovery Reply, described in Section 6.6. 815 The next two message types are used for network renumbering and 816 address configuration on the mobile node, as described in 817 Section 10.6: 819 o Mobile Prefix Solicitation, described in Section 6.7. 821 o Mobile Prefix Advertisement, described in Section 6.8. 823 4.5. Conceptual Data Structure Terminology 825 This document describes the Mobile IPv6 protocol in terms of the 826 following conceptual data structures: 828 Binding Cache 830 A cache of bindings for other nodes. This cache is maintained by 831 home agents and correspondent nodes. The cache contains both 832 "correspondent registration" entries (see Section 9.1) and "home 833 registration" entries (see Section 10.1). 835 Binding Update List 837 This list is maintained by each mobile node. The list has an item 838 for every binding that the mobile node has or is trying to 839 establish with a specific other node. Both correspondent and home 840 registrations are included in this list. Entries from the list 841 are deleted as the lifetime of the binding expires. See 842 Section 11.1. 844 Home Agents List 846 Home agents need to know which other home agents are on the same 847 link. This information is stored in the Home Agents List, as 848 described in more detail in Section 10.1. The list is used for 849 informing mobile nodes during dynamic home agent address 850 discovery. 852 4.6. Unique-Local Addressability 854 This specification requires that home and care-of addresses MUST be 855 unicast routable addresses. Unique-local IPv6 unicast addresses 856 (ULAs) RFC4193 [15] may be usable on networks that use such non- 857 globally routable addresses but this specification does not define 858 when such usage is safe and when it is not. Mobile nodes may not be 859 able to distinguish between their home site and the site at which 860 they are currently located. This can make it hard to prevent 861 accidental attachment to other sites, because the mobile node might 862 use the ULA at another site, which could not be used to successfully 863 send packets to the mobile node's HA. This would result in 864 unreachability between the MN and the HA, when unique-local IPv6 865 routable addresses are used as care-of addresses. Similarly, CNs 866 outside the MN's own site will not be reachable when ULAs are used as 867 home addresses. Therefore, unique-local IPv6 unicast addresses 868 SHOULD NOT be used as home or care-of addresses when other address 869 choices are available. If such addresses are used, however, 870 according to RFC4193 [15], they are treated as any global unicast 871 IPv6 address so, for the remainder of this specification, use of 872 unique-local IPv6 unicast addresses is not differentiated from other 873 globally unique IPv6 addresses. 875 5. Overview of Mobile IPv6 Security 877 This specification provides a number of security features. These 878 include the protection of Binding Updates both to home agents and 879 correspondent nodes, the protection of mobile prefix discovery, and 880 the protection of the mechanisms that Mobile IPv6 uses for 881 transporting data packets. 883 Binding Updates are protected by the use of IPsec extension headers, 884 or by the use of the Binding Authorization Data option. This option 885 employs a binding management key, Kbm, which can be established 886 through the return routability procedure. Mobile prefix discovery is 887 protected through the use of IPsec extension headers. Mechanisms 888 related to transporting payload packets - such as the Home Address 889 destination option and type 2 routing header - have been specified in 890 a manner which restricts their use in attacks. 892 5.1. Binding Updates to Home Agents 894 The mobile node and the home agent MUST use an IPsec security 895 association to protect the integrity and authenticity of the Binding 896 Updates and Acknowledgements. Both the mobile nodes and the home 897 agents MUST support and SHOULD use the Encapsulating Security Payload 898 (ESP) [5] header in transport mode and MUST use a non-NULL payload 899 authentication algorithm to provide data origin authentication, 900 connectionless integrity and optional anti-replay protection. Note 901 that Authentication Header (AH) [4] is also possible but for brevity 902 not discussed in this specification. 904 In order to protect messages exchanged between the mobile node and 905 the home agent with IPsec, appropriate security policy database 906 entries must be created. A mobile node must be prevented from using 907 its security association to send a Binding Update on behalf of 908 another mobile node using the same home agent. This MUST be achieved 909 by having the home agent check that the given home address has been 910 used with the right security association. Such a check is provided 911 in the IPsec processing, by having the security policy database 912 entries unequivocally identify a single security association for 913 protecting Binding Updates between any given home address and home 914 agent. In order to make this possible, it is necessary that the home 915 address of the mobile node is visible in the Binding Updates and 916 Acknowledgements. The home address is used in these packets as a 917 source or destination, or in the Home Address destination option or 918 the type 2 routing header. 920 As with all IPsec security associations in this specification, manual 921 configuration of security associations MUST be supported. The shared 922 secrets used MUST be random and unique for different mobile nodes, 923 and MUST be distributed off-line to the mobile nodes. Automatic key 924 management with IKEv2 [24] MAY be supported as described in [20]. 926 Section 11.3.2 discusses how IKEv2 connections to the home agent need 927 a careful treatment of the addresses used for transporting IKEv2. 928 This is necessary to ensure that a Binding Update is not needed 929 before the IKEv2 exchange which is needed for securing the Binding 930 Update. 932 More detailed descriptions and examples using IPsec to protect 933 communications between the mobile node and the home agent have been 934 published [12][20]. 936 5.2. Binding Updates to Correspondent Nodes 938 The protection of Binding Updates sent to correspondent nodes does 939 not require the configuration of security associations or the 940 existence of an authentication infrastructure between the mobile 941 nodes and correspondent nodes. Instead, a method called the return 942 routability procedure is used to assure that the right mobile node is 943 sending the message. This method does not protect against attackers 944 who are on the path between the home network and the correspondent 945 node. However, attackers in such a location are capable of 946 performing the same attacks even without Mobile IPv6. The main 947 advantage of the return routability procedure is that it limits the 948 potential attackers to those having an access to one specific path in 949 the Internet, and avoids forged Binding Updates from anywhere else in 950 the Internet. For a more in depth explanation of the security 951 properties of the return routability procedure, see Section 15. 952 Also, consult [41] 954 The integrity and authenticity of the Binding Update messages to 955 correspondent nodes is protected by using a keyed-hash algorithm. 956 The binding management key, Kbm, is used to key the hash algorithm 957 for this purpose. Kbm is established using data exchanged during the 958 return routability procedure. The data exchange is accomplished by 959 use of node keys, nonces, cookies, tokens, and certain cryptographic 960 functions. Section 5.2.5 outlines the basic return routability 961 procedure. Section 5.2.6 shows how the results of this procedure are 962 used to authorize a Binding Update to a correspondent node. 964 5.2.1. Node Keys 966 Each correspondent node has a secret key, Kcn, called the "node key", 967 which it uses to produce the keygen tokens sent to the mobile nodes. 968 The node key MUST be a random number, 20 octets in length. The node 969 key allows the correspondent node to verify that the keygen tokens 970 used by the mobile node in authorizing a Binding Update are indeed 971 its own. This key MUST NOT be shared with any other entity. 973 A correspondent node MAY generate a fresh node key at any time; this 974 avoids the need for secure persistent key storage. Procedures for 975 optionally updating the node key are discussed later in 976 Section 5.2.7. 978 5.2.2. Nonces 980 Each correspondent node also generates nonces at regular intervals. 981 The nonces should be generated by using a random number generator 982 that is known to have good randomness properties [14]. A 983 correspondent node may use the same Kcn and nonce with all the 984 mobiles it is in communication with. 986 Each nonce is identified by a nonce index. When a new nonce is 987 generated, it must be associated with a new nonce index; this may be 988 done, for example, by incrementing the value of the previous nonce 989 index, if the nonce index is used as an array pointer into a linear 990 array of nonces. However, there is no requirement that nonces be 991 stored that way, or that the values of subsequent nonce indices have 992 any particular relationship to each other. The index value is 993 communicated in the protocol, so that if a nonce is replaced by new 994 nonce during the run of a protocol, the correspondent node can 995 distinguish messages that should be checked against the old nonce 996 from messages that should be checked against the new nonce. Strictly 997 speaking, indices are not necessary in the authentication, but allow 998 the correspondent node to efficiently find the nonce value that it 999 used in creating a keygen token. 1001 Correspondent nodes keep both the current nonce and a small set of 1002 valid previous nonces whose lifetime has not yet expired. Expired 1003 values MUST be discarded, and messages using stale or unknown indices 1004 will be rejected. 1006 The specific nonce index values cannot be used by mobile nodes to 1007 determine the validity of the nonce. Expected validity times for the 1008 nonces values and the procedures for updating them are discussed 1009 later in Section 5.2.7. 1011 A nonce is an octet string of any length. The recommended length is 1012 64 bits. 1014 5.2.3. Cookies and Tokens 1016 The return routability address test procedure uses cookies and keygen 1017 tokens as opaque values within the test init and test messages, 1018 respectively. 1020 o The "home init cookie" and "care-of init cookie" are 64 bit values 1021 sent to the correspondent node from the mobile node, and later 1022 returned to the mobile node. The home init cookie is sent in the 1023 Home Test Init message, and returned in the Home Test message. 1024 The care-of init cookie is sent in the Care-of Test Init message, 1025 and returned in the Care-of Test message. 1027 o The "home keygen token" and "care-of keygen token" are 64-bit 1028 values sent by the correspondent node to the mobile node via the 1029 home agent (via the Home Test message) and the care-of address (by 1030 the Care-of Test message), respectively. 1032 The mobile node should set the home init or care-of init cookie to a 1033 newly generated random number in every Home or Care-of Test Init 1034 message it sends. The cookies are used to verify that the Home Test 1035 or Care-of Test message matches the Home Test Init or Care-of Test 1036 Init message, respectively. These cookies also serve to ensure that 1037 parties who have not seen the request cannot spoof responses. 1039 Home and care-of keygen tokens are produced by the correspondent node 1040 based on its currently active secret key (Kcn) and nonces, as well as 1041 the home or care-of address (respectively). A keygen token is valid 1042 as long as both the secret key (Kcn) and the nonce used to create it 1043 are valid. 1045 5.2.4. Cryptographic Functions 1047 By default in this specification, the function used to compute hash 1048 values is SHA1 [11]. Message Authentication Codes (MACs) are then 1049 computed using HMAC_SHA1 [1][11]. HMAC_SHA1(K,m) denotes such a MAC 1050 computed on message m with key K. 1052 5.2.5. Return Routability Procedure 1054 The Return Routability Procedure enables the correspondent node to 1055 obtain some reasonable assurance that the mobile node is in fact 1056 addressable at its claimed care-of address as well as at its home 1057 address. Only with this assurance is the correspondent node able to 1058 accept Binding Updates from the mobile node which would then instruct 1059 the correspondent node to direct that mobile node's data traffic to 1060 its claimed care-of address. 1062 This is done by testing whether packets addressed to the two claimed 1063 addresses are routed to the mobile node. The mobile node can pass 1064 the test only if it is able to supply proof that it received certain 1065 data (the "keygen tokens") which the correspondent node sends to 1066 those addresses. These data are combined by the mobile node into a 1067 binding management key, denoted Kbm. 1069 The figure below shows the message flow for the return routability 1070 procedure. 1072 Mobile node Home agent Correspondent node 1073 | | 1074 | Home Test Init (HoTI) | | 1075 |------------------------->|------------------------->| 1076 | | | 1077 | Care-of Test Init (CoTI) | 1078 |---------------------------------------------------->| 1079 | | 1080 | | Home Test (HoT) | 1081 |<-------------------------|<-------------------------| 1082 | | | 1083 | Care-of Test (CoT) | 1084 |<----------------------------------------------------| 1085 | | 1087 The Home and Care-of Test Init messages are sent at the same time. 1088 The procedure requires very little processing at the correspondent 1089 node, and the Home and Care-of Test messages can be returned quickly, 1090 perhaps nearly simultaneously. These four messages form the return 1091 routability procedure. 1093 Home Test Init 1095 A mobile node sends a Home Test Init message to the correspondent 1096 node (via the home agent) to acquire the home keygen token. The 1097 contents of the message can be summarized as follows: 1099 * Source Address = home address 1101 * Destination Address = correspondent 1103 * Parameters: 1105 + home init cookie 1107 The Home Test Init message conveys the mobile node's home address 1108 to the correspondent node. The mobile node also sends along a 1109 home init cookie that the correspondent node must return later. 1110 The Home Test Init message is reverse tunneled through the home 1111 agent. (The headers and addresses related to reverse tunneling 1112 have been omitted from the above discussion of the message 1113 contents.) The mobile node remembers these cookie values to 1114 obtain some assurance that its protocol messages are being 1115 processed by the desired correspondent node. 1117 Care-of Test Init 1119 The mobile node sends a Care-of Test Init message to the 1120 correspondent node (directly, not via the home agent) to acquire 1121 the care-of keygen token. The contents of this message can be 1122 summarized as follows: 1124 * Source Address = care-of address 1126 * Destination Address = correspondent 1128 * Parameters: 1130 + care-of init cookie 1132 The Care-of Test Init message conveys the mobile node's care-of 1133 address to the correspondent node. The mobile node also sends 1134 along a care-of init cookie that the correspondent node must 1135 return later. The Care-of Test Init message is sent directly to 1136 the correspondent node. 1138 Home Test 1140 The Home Test message is sent in response to a Home Test Init 1141 message. It is sent via the home agent. The contents of the 1142 message are: 1144 * Source Address = correspondent 1146 * Destination Address = home address 1148 * Parameters: 1150 + home init cookie 1152 + home keygen token 1154 + home nonce index 1156 When the correspondent node receives the Home Test Init message, 1157 it generates a home keygen token as follows: 1159 home keygen token := 1160 First (64, HMAC_SHA1 (Kcn, (home address | nonce | 0))) 1162 where | denotes concatenation. The final "0" inside the HMAC_SHA1 1163 function is a single zero octet, used to distinguish home and 1164 care-of cookies from each other. 1166 The home keygen token is formed from the first 64 bits of the MAC. 1167 The home keygen token tests that the mobile node can receive 1168 messages sent to its home address. Kcn is used in the production 1169 of home keygen token in order to allow the correspondent node to 1170 verify that it generated the home and care-of nonces, without 1171 forcing the correspondent node to remember a list of all tokens it 1172 has handed out. 1174 The Home Test message is sent to the mobile node via the home 1175 network, where it is presumed that the home agent will tunnel the 1176 message to the mobile node. This means that the mobile node needs 1177 to already have sent a Binding Update to the home agent, so that 1178 the home agent will have received and authorized the new care-of 1179 address for the mobile node before the return routability 1180 procedure. For improved security, the data passed between the 1181 home agent and the mobile node is made immune to inspection and 1182 passive attacks. Such protection is gained by encrypting the home 1183 keygen token as it is tunneled from the home agent to the mobile 1184 node as specified in Section 10.4.6. The security properties of 1185 this additional security are discussed in Section 15.4.1. 1187 The home init cookie from the mobile node is returned in the Home 1188 Test message, to ensure that the message comes from a node on the 1189 route between the home agent and the correspondent node. 1191 The home nonce index is delivered to the mobile node to later 1192 allow the correspondent node to efficiently find the nonce value 1193 that it used in creating the home keygen token. 1195 Care-of Test 1197 This message is sent in response to a Care-of Test Init message. 1198 This message is not sent via the home agent, it is sent directly 1199 to the mobile node. The contents of the message are: 1201 * Source Address = correspondent 1203 * Destination Address = care-of address 1204 * Parameters: 1206 + care-of init cookie 1208 + care-of keygen token 1210 + care-of nonce index 1212 When the correspondent node receives the Care-of Test Init 1213 message, it generates a care-of keygen token as follows: 1215 care-of keygen token := 1216 First (64, HMAC_SHA1 (Kcn, (care-of address | nonce | 1))) 1218 Here, the final "1" inside the HMAC_SHA1 function is a single 1219 octet containing the hex value 0x01, and is used to distinguish 1220 home and care-of cookies from each other. The keygen token is 1221 formed from the first 64 bits of the MAC, and sent directly to the 1222 mobile node at its care-of address. The care-of init cookie from 1223 the Care-of Test Init message is returned to ensure that the 1224 message comes from a node on the route to the correspondent node. 1226 The care-of nonce index is provided to identify the nonce used for 1227 the care-of keygen token. The home and care-of nonce indices MAY 1228 be the same, or different, in the Home and Care-of Test messages. 1230 When the mobile node has received both the Home and Care-of Test 1231 messages, the return routability procedure is complete. As a result 1232 of the procedure, the mobile node has the data it needs to send a 1233 Binding Update to the correspondent node. The mobile node hashes the 1234 tokens together to form a 20 octet binding key Kbm: 1236 Kbm = SHA1 (home keygen token | care-of keygen token) 1238 A Binding Update may also be used to delete a previously established 1239 binding (Section 6.1.7). In this case, the care-of keygen token is 1240 not used. Instead, the binding management key is generated as 1241 follows: 1243 Kbm = SHA1(home keygen token) 1245 Note that the correspondent node does not create any state specific 1246 to the mobile node, until it receives the Binding Update from that 1247 mobile node. The correspondent node does not maintain the value for 1248 the binding management key Kbm; it creates Kbm when given the nonce 1249 indices and the mobile node's addresses. 1251 5.2.6. Authorizing Binding Management Messages 1253 After the mobile node has created the binding management key (Kbm), 1254 it can supply a verifiable Binding Update to the correspondent node. 1255 This section provides an overview of this registration. The below 1256 figure shows the message flow. 1258 Mobile node Correspondent node 1259 | | 1260 | Binding Update (BU) | 1261 |---------------------------------------------->| 1262 | (MAC, seq#, nonce indices, care-of address) | 1263 | | 1264 | | 1265 | Binding Acknowledgement (BA) (if sent) | 1266 |<----------------------------------------------| 1267 | (MAC, seq#, status) | 1269 Binding Update 1271 To authorize a Binding Update, the mobile node creates a binding 1272 management key Kbm from the keygen tokens as described in the 1273 previous section. The contents of the Binding Update include the 1274 following: 1276 * Source Address = care-of address 1278 * Destination Address = correspondent 1280 * Parameters: 1282 + home address (within the Home Address destination option if 1283 different from the Source Address) 1285 + sequence number (within the Binding Update message header) 1287 + home nonce index (within the Nonce Indices option) 1289 + care-of nonce index (within the Nonce Indices option) 1291 + First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent 1292 | BU))) 1294 The Binding Update contains a Nonce Indices option, indicating to 1295 the correspondent node which home and care-of nonces to use to 1296 recompute Kbm, the binding management key. The MAC is computed as 1297 described in Section 6.2.7, using the correspondent node's address 1298 as the destination address and the Binding Update message itself 1299 ("BU" above) as the MH Data. 1301 Once the correspondent node has verified the MAC, it can create a 1302 Binding Cache entry for the mobile. 1304 Binding Acknowledgement 1306 The Binding Update is in some cases acknowledged by the 1307 correspondent node. The contents of the message are as follows: 1309 * Source Address = correspondent 1311 * Destination Address = care-of address 1313 * Parameters: 1315 + sequence number (within the Binding Update message header) 1317 + First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent 1318 | BA))) 1320 The Binding Acknowledgement contains the same sequence number as 1321 the Binding Update. The MAC is computed as described in 1322 Section 6.2.7, using the correspondent node's address as the 1323 destination address and the message itself ("BA" above) as the MH 1324 Data. 1326 Bindings established with correspondent nodes using keys created by 1327 way of the return routability procedure MUST NOT exceed 1328 MAX_RR_BINDING_LIFETIME seconds (see Section 12). 1330 The value in the Source Address field in the IPv6 header carrying the 1331 Binding Update is normally also the care-of address which is used in 1332 the binding. However, a different care-of address MAY be specified 1333 by including an Alternate Care-of Address mobility option in the 1334 Binding Update (see Section 6.2.5). When such a message is sent to 1335 the correspondent node and the return routability procedure is used 1336 as the authorization method, the Care-of Test Init and Care-of Test 1337 messages MUST have been performed for the address in the Alternate 1338 Care-of Address option (not the Source Address). The nonce indices 1339 and MAC value MUST be based on information gained in this test. 1341 Binding Updates may also be sent to delete a previously established 1342 binding. In this case, generation of the binding management key 1343 depends exclusively on the home keygen token and the care-of nonce 1344 index is ignored. 1346 5.2.7. Updating Node Keys and Nonces 1348 Correspondent nodes generate nonces at regular intervals. It is 1349 recommended to keep each nonce (identified by a nonce index) 1350 acceptable for at least MAX_TOKEN_LIFETIME seconds (see Section 12) 1351 after it has been first used in constructing a return routability 1352 message response. However, the correspondent node MUST NOT accept 1353 nonces beyond MAX_NONCE_LIFETIME seconds (see Section 12) after the 1354 first use. As the difference between these two constants is 30 1355 seconds, a convenient way to enforce the above lifetimes is to 1356 generate a new nonce every 30 seconds. The node can then continue to 1357 accept tokens that have been based on the last 8 (MAX_NONCE_LIFETIME 1358 / 30) nonces. This results in tokens being acceptable 1359 MAX_TOKEN_LIFETIME to MAX_NONCE_LIFETIME seconds after they have been 1360 sent to the mobile node, depending on whether the token was sent at 1361 the beginning or end of the first 30 second period. Note that the 1362 correspondent node may also attempt to generate new nonces on demand, 1363 or only if the old nonces have been used. This is possible, as long 1364 as the correspondent node keeps track of how long a time ago the 1365 nonces were used for the first time, and does not generate new nonces 1366 on every return routability request. 1368 Due to resource limitations, rapid deletion of bindings, or reboots 1369 the correspondent node may not in all cases recognize the nonces that 1370 the tokens were based on. If a nonce index is unrecognized, the 1371 correspondent node replies with an error code in the Binding 1372 Acknowledgement (either 136, 137, or 138 as discussed in 1373 Section 6.1.8). The mobile node can then retry the return 1374 routability procedure. 1376 An update of Kcn SHOULD be done at the same time as an update of a 1377 nonce, so that nonce indices can identify both the nonce and the key. 1378 Old Kcn values have to be therefore remembered as long as old nonce 1379 values. 1381 Given that the tokens are normally expected to be usable for 1382 MAX_TOKEN_LIFETIME seconds, the mobile node MAY use them beyond a 1383 single run of the return routability procedure until 1384 MAX_TOKEN_LIFETIME expires. After this the mobile node SHOULD NOT 1385 use the tokens. A fast moving mobile node MAY reuse a recent home 1386 keygen token from a correspondent node when moving to a new location, 1387 and just acquire a new care-of keygen token to show routability in 1388 the new location. 1390 While this does not save the number of round-trips due to the 1391 simultaneous processing of home and care-of return routability tests, 1392 there are fewer messages being exchanged, and a potentially long 1393 round-trip through the home agent is avoided. Consequently, this 1394 optimization is often useful. A mobile node that has multiple home 1395 addresses, MAY also use the same care-of keygen token for Binding 1396 Updates concerning all of these addresses. 1398 5.2.8. Preventing Replay Attacks 1400 The return routability procedure also protects the participants 1401 against replayed Binding Updates through the use of the sequence 1402 number and a MAC. Care must be taken when removing bindings at the 1403 correspondent node, however. Correspondent nodes must retain 1404 bindings and the associated sequence number information at least as 1405 long as the nonces used in the authorization of the binding are still 1406 valid. Alternatively, if memory is very constrained, the 1407 correspondent node MAY invalidate the nonces that were used for the 1408 binding being deleted (or some larger group of nonces that they 1409 belong to). This may, however, impact the ability to accept Binding 1410 Updates from mobile nodes that have recently received keygen tokens. 1411 This alternative is therefore recommended only as a last measure. 1413 5.2.9. Handling Interruptions to Return Routability 1415 In some scenarios, such as simultaneous mobility, where both 1416 correspondent host and mobile host move at the same time, or in the 1417 case where the correspondent node reboots and loses data, route 1418 optimization may not complete, or relevant data in the binding cache 1419 might be lost. 1421 o Return Routability signalling MUST be sent to the correspondent 1422 node's home address if it has one (i.e. not to the correspondent 1423 nodes care-of address if the correspondent node is also mobile). 1425 o If Return Routability signalling timed out after MAX_RO_FAILURE 1426 attempts, the mobile node MUST revert to sending packets to the 1427 correspondent node's home address through its home agent. 1429 The mobile node may run the bidirectional tunnelling in parallel with 1430 the return routability procedure until it is successful. Exponential 1431 backoff SHOULD be used for retransmission of return routability 1432 messages. 1434 The return routability procedure may be triggered by movement of the 1435 mobile node or by sustained loss of end-to-end communication with a 1436 correspondent node (e.g. based on indications from upper-layers) that 1437 has been using a route optimised connection to the mobile node. If 1438 such indications are received, the mobile node MAY revert to bi- 1439 directional tunnelling while re-starting the return routability 1440 procedure. 1442 5.3. Dynamic Home Agent Address Discovery 1444 Dynamic home agent address discovery has been designed for use in 1445 deployments where security is not needed. For this reason, no 1446 security solution is provided in this document for dynamic home agent 1447 address discovery. 1449 5.4. Mobile Prefix Discovery 1451 The mobile node and the home agent SHOULD use an IPsec security 1452 association to protect the integrity and authenticity of the Mobile 1453 Prefix Solicitations and Advertisements. Both the mobile nodes and 1454 the home agents MUST support and SHOULD use the Encapsulating 1455 Security Payload (ESP) header in transport mode with a non-NULL 1456 payload authentication algorithm to provide data origin 1457 authentication, connectionless integrity and optional anti-replay 1458 protection. 1460 5.5. Payload Packets 1462 Payload packets exchanged with mobile nodes can be protected in the 1463 usual manner, in the same way as stationary hosts can protect them. 1464 However, Mobile IPv6 introduces the Home Address destination option, 1465 a routing header, and tunneling headers in the payload packets. In 1466 the following we define the security measures taken to protect these, 1467 and to prevent their use in attacks against other parties. 1469 This specification limits the use of the Home Address destination 1470 option to the situation where the correspondent node already has a 1471 Binding Cache entry for the given home address. This avoids the use 1472 of the Home Address option in attacks described in Section 15.1. 1474 Mobile IPv6 uses a type of routing header specific to Mobile IPv6. 1475 This type provides the necessary functionality but does not open 1476 vulnerabilities discussed in Section 15.1 and RFC 5095 [43]. 1478 Tunnels between the mobile node and the home agent are protected by 1479 ensuring proper use of source addresses, and optional cryptographic 1480 protection. The mobile node verifies that the outer IP address 1481 corresponds to its home agent. The home agent verifies that the 1482 outer IP address corresponds to the current location of the mobile 1483 node (Binding Updates sent to the home agents are secure). The home 1484 agent identifies the mobile node through the source address of the 1485 inner packet. (Typically, this is the home address of the mobile 1486 node, but it can also be a link-local address, as discussed in 1487 Section 10.4.2. To recognize the latter type of addresses, the home 1488 agent requires that the Link-Local Address Compatibility (L) was set 1489 in the Binding Update.) These measures protect the tunnels against 1490 vulnerabilities discussed in Section 15.1. 1492 For traffic tunneled via the home agent, additional IPsec ESP 1493 encapsulation MAY be supported and used. If multicast group 1494 membership control protocols or stateful address autoconfiguration 1495 protocols are supported, payload data protection MUST be supported. 1497 6. New IPv6 Protocol, Message Types, and Destination Option 1499 6.1. Mobility Header 1501 The Mobility Header is an extension header used by mobile nodes, 1502 correspondent nodes, and home agents in all messaging related to the 1503 creation and management of bindings. The subsections within this 1504 section describe the message types that may be sent using the 1505 Mobility Header. 1507 Mobility Header messages MUST NOT be sent with a type 2 routing 1508 header, except as described in Section 9.5.4 for Binding 1509 Acknowledgement. Mobility Header messages also MUST NOT be used with 1510 a Home Address destination option, except as described in 1511 Section 11.7.1 and Section 11.7.2 for Binding Update. Binding Update 1512 List or Binding Cache information (when present) for the destination 1513 MUST NOT be used in sending Mobility Header messages. That is, 1514 Mobility Header messages bypass both the Binding Cache check 1515 described in Section 9.3.2 and the Binding Update List check 1516 described in Section 11.3.1 which are normally performed for all 1517 packets. This applies even to messages sent to or from a 1518 correspondent node which is itself a mobile node. 1520 6.1.1. Format 1522 The Mobility Header is identified by a Next Header value of 135 in 1523 the immediately preceding header, and has the following format: 1525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1526 | Payload Proto | Header Len | MH Type | Reserved | 1527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1528 | Checksum | | 1529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1530 | | 1531 . . 1532 . Message Data . 1533 . . 1534 | | 1535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1537 Payload Proto 1539 8-bit selector. Identifies the type of header immediately 1540 following the Mobility Header. Uses the same values as the IPv6 1541 Next Header field [6]. 1543 This field is intended to be used by a future extension (see 1544 Appendix A.1). 1546 Implementations conforming to this specification SHOULD set the 1547 payload protocol type to IPPROTO_NONE (59 decimal). 1549 Header Len 1551 8-bit unsigned integer, representing the length of the Mobility 1552 Header in units of 8 octets, excluding the first 8 octets. 1554 The length of the Mobility Header MUST be a multiple of 8 octets. 1556 MH Type 1558 8-bit selector. Identifies the particular mobility message in 1559 question. Current values are specified in Section 6.1.2 and 1560 onward. An unrecognized MH Type field causes an error indication 1561 to be sent. 1563 Reserved 1565 8-bit field reserved for future use. The value MUST be 1566 initialized to zero by the sender, and MUST be ignored by the 1567 receiver. 1569 Checksum 1571 16-bit unsigned integer. This field contains the checksum of the 1572 Mobility Header. The checksum is calculated from the octet string 1573 consisting of a "pseudo-header" followed by the entire Mobility 1574 Header starting with the Payload Proto field. The checksum is the 1575 16-bit one's complement of the one's complement sum of this 1576 string. 1578 The pseudo-header contains IPv6 header fields, as specified in 1579 Section 8.1 of RFC 2460 [6]. The Next Header value used in the 1580 pseudo-header is 135. The addresses used in the pseudo-header are 1581 the addresses that appear in the Source and Destination Address 1582 fields in the IPv6 packet carrying the Mobility Header. 1584 Note that the procedures of calculating upper layer checksums 1585 while away from home described in Section 11.3.1 apply even for 1586 the Mobility Header. If a mobility message has a Home Address 1587 destination option, then the checksum calculation uses the home 1588 address in this option as the value of the IPv6 Source Address 1589 field. The type 2 routing header is treated as explained in [6]. 1591 The Mobility Header is considered as the upper layer protocol for 1592 the purposes of calculating the pseudo-header. The Upper-Layer 1593 Packet Length field in the pseudo-header MUST be set to the total 1594 length of the Mobility Header. 1596 For computing the checksum, the checksum field is set to zero. 1598 Message Data 1600 A variable length field containing the data specific to the 1601 indicated Mobility Header type. 1603 Mobile IPv6 also defines a number of "mobility options" for use 1604 within these messages; if included, any options MUST appear after the 1605 fixed portion of the message data specified in this document. The 1606 presence of such options will be indicated by the Header Len field 1607 within the message. When the Header Len value is greater than the 1608 length required for the message specified here, the remaining octets 1609 are interpreted as mobility options. These options include padding 1610 options that can be used to ensure that other options are aligned 1611 properly, and that the total length of the message is divisible by 8. 1612 The encoding and format of defined options are described in 1613 Section 6.2. 1615 Alignment requirements for the Mobility Header are the same as for 1616 any IPv6 protocol Header. That is, they MUST be aligned on an 1617 8-octet boundary. 1619 6.1.2. Binding Refresh Request Message 1621 The Binding Refresh Request (BRR) message requests a mobile node to 1622 update its mobility binding. This message is sent by correspondent 1623 nodes according to the rules in Section 9.5.5. When a mobile node 1624 receives a packet containing a Binding Refresh Request message it 1625 processes the message according to the rules in Section 11.7.4. 1627 The Binding Refresh Request message uses the MH Type value 0. When 1628 this value is indicated in the MH Type field, the format of the 1629 Message Data field in the Mobility Header is as follows: 1631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1632 | Reserved | 1633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1634 | | 1635 . . 1636 . Mobility options . 1637 . . 1638 | | 1639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1641 Reserved 1643 16-bit field reserved for future use. The value MUST be 1644 initialized to zero by the sender, and MUST be ignored by the 1645 receiver. 1647 Mobility Options 1649 Variable-length field of such length that the complete Mobility 1650 Header is an integer multiple of 8 octets long. This field 1651 contains zero or more TLV-encoded mobility options. The encoding 1652 and format of defined options are described in Section 6.2. The 1653 receiver MUST ignore and skip any options which it does not 1654 understand. 1656 There MAY be additional information, associated with this Binding 1657 Refresh Request message that need not be present in all Binding 1658 Refresh Request messages sent. Mobility options allow future 1659 extensions to the format of the Binding Refresh Request message to 1660 be defined. This specification does not define any options valid 1661 for the Binding Refresh Request message. 1663 If no actual options are present in this message, no padding is 1664 necessary and the Header Len field will be set to 0. 1666 6.1.3. Home Test Init Message 1668 A mobile node uses the Home Test Init (HoTI) message to initiate the 1669 return routability procedure and request a home keygen token from a 1670 correspondent node (see Section 11.6.1). The Home Test Init message 1671 uses the MH Type value 1. When this value is indicated in the MH 1672 Type field, the format of the Message Data field in the Mobility 1673 Header is as follows: 1675 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1676 | Reserved | 1677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1678 | | 1679 + Home Init Cookie + 1680 | | 1681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1682 | | 1683 . . 1684 . Mobility Options . 1685 . . 1686 | | 1687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1689 Reserved 1691 16-bit field reserved for future use. This value MUST be 1692 initialized to zero by the sender, and MUST be ignored by the 1693 receiver. 1695 Home Init Cookie 1697 64-bit field which contains a random value, the home init cookie. 1699 Mobility Options 1701 Variable-length field of such length that the complete Mobility 1702 Header is an integer multiple of 8 octets long. This field 1703 contains zero or more TLV-encoded mobility options. The receiver 1704 MUST ignore and skip any options which it does not understand. 1705 This specification does not define any options valid for the Home 1706 Test Init message. 1708 If no actual options are present in this message, no padding is 1709 necessary and the Header Len field will be set to 1. 1711 This message is tunneled through the home agent when the mobile node 1712 is away from home. Such tunneling SHOULD employ IPsec ESP in tunnel 1713 mode between the home agent and the mobile node. This protection is 1714 indicated by the IPsec security policy database. The protection of 1715 Home Test Init messages is unrelated to the requirement to protect 1716 regular payload traffic, which MAY use such tunnels as well. 1718 6.1.4. Care-of Test Init Message 1720 A mobile node uses the Care-of Test Init (CoTI) message to initiate 1721 the return routability procedure and request a care-of keygen token 1722 from a correspondent node (see Section 11.6.1). The Care-of Test 1723 Init message uses the MH Type value 2. When this value is indicated 1724 in the MH Type field, the format of the Message Data field in the 1725 Mobility Header is as follows: 1727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1728 | Reserved | 1729 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1730 | | 1731 + Care-of Init Cookie + 1732 | | 1733 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1734 | | 1735 . . 1736 . Mobility Options . 1737 . . 1738 | | 1739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1741 Reserved 1743 16-bit field reserved for future use. The value MUST be 1744 initialized to zero by the sender, and MUST be ignored by the 1745 receiver. 1747 Care-of Init Cookie 1749 64-bit field which contains a random value, the care-of init 1750 cookie. 1752 Mobility Options 1754 Variable-length field of such length that the complete Mobility 1755 Header is an integer multiple of 8 octets long. This field 1756 contains zero or more TLV-encoded mobility options. The receiver 1757 MUST ignore and skip any options which it does not understand. 1758 This specification does not define any options valid for the 1759 Care-of Test Init message. 1761 If no actual options are present in this message, no padding is 1762 necessary and the Header Len field will be set to 1. 1764 6.1.5. Home Test Message 1766 The Home Test (HoT) message is a response to the Home Test Init 1767 message, and is sent from the correspondent node to the mobile node 1768 (see Section 5.2.5). The Home Test message uses the MH Type value 3. 1769 When this value is indicated in the MH Type field, the format of the 1770 Message Data field in the Mobility Header is as follows: 1772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1773 | Home Nonce Index | 1774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1775 | | 1776 + Home Init Cookie + 1777 | | 1778 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1779 | | 1780 + Home Keygen Token + 1781 | | 1782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1783 | | 1784 . . 1785 . Mobility options . 1786 . . 1787 | | 1788 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1790 Home Nonce Index 1792 This field will be echoed back by the mobile node to the 1793 correspondent node in a subsequent Binding Update. 1795 Home Init Cookie 1797 64-bit field which contains the home init cookie. 1799 Home Keygen Token 1801 This field contains the 64 bit home keygen token used in the 1802 return routability procedure. 1804 Mobility Options 1806 Variable-length field of such length that the complete Mobility 1807 Header is an integer multiple of 8 octets long. This field 1808 contains zero or more TLV-encoded mobility options. The receiver 1809 MUST ignore and skip any options which it does not understand. 1810 This specification does not define any options valid for the Home 1811 Test message. 1813 If no actual options are present in this message, no padding is 1814 necessary and the Header Len field will be set to 2. 1816 6.1.6. Care-of Test Message 1818 The Care-of Test (CoT) message is a response to the Care-of Test Init 1819 message, and is sent from the correspondent node to the mobile node 1820 (see Section 11.6.2). The Care-of Test message uses the MH Type 1821 value 4. When this value is indicated in the MH Type field, the 1822 format of the Message Data field in the Mobility Header is as 1823 follows: 1825 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1826 | Care-of Nonce Index | 1827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1828 | | 1829 + Care-of Init Cookie + 1830 | | 1831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1832 | | 1833 + Care-of Keygen Token + 1834 | | 1835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1836 | | 1837 . . 1838 . Mobility Options . 1839 . . 1840 | | 1841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1843 Care-of Nonce Index 1845 This value will be echoed back by the mobile node to the 1846 correspondent node in a subsequent Binding Update. 1848 Care-of Init Cookie 1850 64-bit field which contains the care-of init cookie. 1852 Care-of Keygen Token 1854 This field contains the 64 bit care-of keygen token used in the 1855 return routability procedure. 1857 Mobility Options 1859 Variable-length field of such length that the complete Mobility 1860 Header is an integer multiple of 8 octets long. This field 1861 contains zero or more TLV-encoded mobility options. The receiver 1862 MUST ignore and skip any options which it does not understand. 1863 This specification does not define any options valid for the 1864 Care-of Test message. 1866 If no actual options are present in this message, no padding is 1867 necessary and the Header Len field will be set to 2. 1869 6.1.7. Binding Update Message 1871 The Binding Update (BU) message is used by a mobile node to notify 1872 other nodes of a new care-of address for itself. Binding Updates are 1873 sent as described in Section 11.7.1 and Section 11.7.2. 1875 The Binding Update uses the MH Type value 5. When this value is 1876 indicated in the MH Type field, the format of the Message Data field 1877 in the Mobility Header is as follows: 1879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1880 | Sequence # | 1881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1882 |A|H|L|K| Reserved | Lifetime | 1883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1884 | | 1885 . . 1886 . Mobility options . 1887 . . 1888 | | 1889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1891 Acknowledge (A) 1893 The Acknowledge (A) bit is set by the sending mobile node to 1894 request a Binding Acknowledgement (Section 6.1.8) be returned upon 1895 receipt of the Binding Update. 1897 Home Registration (H) 1899 The Home Registration (H) bit is set by the sending mobile node to 1900 request that the receiving node should act as this node's home 1901 agent. The destination of the packet carrying this message MUST 1902 be that of a router sharing the same subnet prefix as the home 1903 address of the mobile node in the binding. 1905 Link-Local Address Compatibility (L) 1907 The Link-Local Address Compatibility (L) bit is set when the home 1908 address reported by the mobile node has the same interface 1909 identifier as the mobile node's link-local address. 1911 Key Management Mobility Capability (K) 1913 If this bit is cleared, the protocol used for establishing the 1914 IPsec security associations between the mobile node and the home 1915 agent does not survive movements. It may then have to be rerun. 1916 (Note that the IPsec security associations themselves are expected 1917 to survive movements.) If manual IPsec configuration is used, the 1918 bit MUST be cleared. 1920 This bit is valid only in Binding Updates sent to the home agent, 1921 and MUST be cleared in other Binding Updates. Correspondent nodes 1922 MUST ignore this bit. 1924 Reserved 1926 These fields are unused. They MUST be initialized to zero by the 1927 sender and MUST be ignored by the receiver. 1929 Sequence # 1931 A 16-bit unsigned integer used by the receiving node to sequence 1932 Binding Updates and by the sending node to match a returned 1933 Binding Acknowledgement with this Binding Update. 1935 Lifetime 1937 16-bit unsigned integer. The number of time units remaining 1938 before the binding MUST be considered expired. A value of zero 1939 indicates that the Binding Cache entry for the mobile node MUST be 1940 deleted. One time unit is 4 seconds. 1942 Mobility Options 1944 Variable-length field of such length that the complete Mobility 1945 Header is an integer multiple of 8 octets long. This field 1946 contains zero or more TLV-encoded mobility options. The encoding 1947 and format of defined options are described in Section 6.2. The 1948 receiver MUST ignore and skip any options which it does not 1949 understand. 1951 The following options are valid in a Binding Update: 1953 * Binding Authorization Data option (this option is mandatory in 1954 Binding Updates sent to a correspondent node) 1956 * Nonce Indices option. 1958 * Alternate Care-of Address option 1960 If no options are present in this message, 4 octets of padding are 1961 necessary and the Header Len field will be set to 1. 1963 The care-of address is specified either by the Source Address field 1964 in the IPv6 header or by the Alternate Care-of Address option, if 1965 present. The care-of address MUST be a unicast routable address. 1966 IPv6 Source Address MUST be a topologically correct source address. 1967 Binding Updates for a care-of address which is not a unicast routable 1968 address MUST be silently discarded. 1970 The deletion of a binding MUST be indicated by setting the Lifetime 1971 field to 0. In deletion, the generation of the binding management 1972 key depends exclusively on the home keygen token, as explained in 1973 Section 5.2.5. 1975 Correspondent nodes SHOULD NOT delete the Binding Cache entry before 1976 the lifetime expires, if any application hosted by the correspondent 1977 node is still likely to require communication with the mobile node. 1978 A Binding Cache entry that is de-allocated prematurely might cause 1979 subsequent packets to be dropped from the mobile node, if they 1980 contain the Home Address destination option. This situation is 1981 recoverable, since a Binding Error message is sent to the mobile node 1982 (see Section 6.1.9); however, it causes unnecessary delay in the 1983 communications. 1985 6.1.8. Binding Acknowledgement Message 1987 The Binding Acknowledgement is used to acknowledge receipt of a 1988 Binding Update (Section 6.1.7). This packet is sent as described in 1989 Section 9.5.4 and Section 10.3.1. 1991 The Binding Acknowledgement has the MH Type value 6. When this value 1992 is indicated in the MH Type field, the format of the Message Data 1993 field in the Mobility Header is as follows: 1995 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1996 | Status |K| Reserved | 1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1998 | Sequence # | Lifetime | 1999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2000 | | 2001 . . 2002 . Mobility options . 2003 . . 2004 | | 2005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2007 Status 2009 8-bit unsigned integer indicating the disposition of the Binding 2010 Update. Values of the Status field less than 128 indicate that 2011 the Binding Update was accepted by the receiving node. Values 2012 greater than or equal to 128 indicate that the Binding Update was 2013 rejected by the receiving node. The following Status values are 2014 currently defined: 2016 0 Binding Update accepted 2018 1 Accepted but prefix discovery necessary 2020 128 Reason unspecified 2022 129 Administratively prohibited 2024 130 Insufficient resources 2026 131 Home registration not supported 2028 132 Not home subnet 2030 133 Not home agent for this mobile node 2032 134 Duplicate Address Detection failed 2034 135 Sequence number out of window 2036 136 Expired home nonce index 2038 137 Expired care-of nonce index 2040 138 Expired nonces 2042 139 Registration type change disallowed 2044 TBD Invalid Care-of Address 2046 Up-to-date values of the Status field are to be specified in the 2047 IANA registry of assigned numbers [29]. 2049 Key Management Mobility Capability (K) 2051 If this bit is cleared, the protocol used by the home agent for 2052 establishing the IPsec security associations between the mobile 2053 node and the home agent does not survive movements. It may then 2054 have to be rerun. (Note that the IPsec security associations 2055 themselves are expected to survive movements.) 2057 Correspondent nodes MUST set the K bit to 0. 2059 Reserved 2061 This field is unused. It MUST be initialized to zero by the 2062 sender and MUST be ignored by the receiver. 2064 Sequence # 2066 The Sequence Number in the Binding Acknowledgement is copied from 2067 the Sequence Number field in the Binding Update. It is used by 2068 the mobile node in matching this Binding Acknowledgement with an 2069 outstanding Binding Update. 2071 Lifetime 2073 The granted lifetime, in time units of 4 seconds, for which this 2074 node SHOULD retain the entry for this mobile node in its Binding 2075 Cache. 2077 The value of this field is undefined if the Status field indicates 2078 that the Binding Update was rejected. 2080 Mobility Options 2082 Variable-length field of such length that the complete Mobility 2083 Header is an integer multiple of 8 octets long. This field 2084 contains zero or more TLV-encoded mobility options. The encoding 2085 and format of defined options are described in Section 6.2. The 2086 receiver MUST ignore and skip any options which it does not 2087 understand. 2089 There MAY be additional information, associated with this Binding 2090 Acknowledgement that need not be present in all Binding 2091 Acknowledgements sent. Mobility options allow future extensions 2092 to the format of the Binding Acknowledgement to be defined. The 2093 following options are valid for the Binding Acknowledgement: 2095 * Binding Authorization Data option (this option is mandatory in 2096 Binding Acknowledgements sent by a correspondent node, except 2097 where otherwise noted in Section 9.5.4) 2099 * Binding Refresh Advice option 2101 If no options are present in this message, 4 octets of padding are 2102 necessary and the Header Len field will be set to 1. 2104 6.1.9. Binding Error Message 2106 The Binding Error (BE) message is used by the correspondent node to 2107 signal an error related to mobility, such as an inappropriate attempt 2108 to use the Home Address destination option without an existing 2109 binding; see Section 9.3.3 for details. 2111 The Binding Error message uses the MH Type value 7. When this value 2112 is indicated in the MH Type field, the format of the Message Data 2113 field in the Mobility Header is as follows: 2115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2116 | Status | Reserved | 2117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2118 | | 2119 + + 2120 | | 2121 + Home Address + 2122 | | 2123 + + 2124 | | 2125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2126 . . 2127 . Mobility Options . 2128 . . 2129 | | 2130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2132 Status 2134 8-bit unsigned integer indicating the reason for this message. 2135 The following values are currently defined: 2137 1 Unknown binding for Home Address destination option 2139 2 Unrecognized MH Type value 2141 Reserved 2143 A 8-bit field reserved for future use. The value MUST be 2144 initialized to zero by the sender, and MUST be ignored by the 2145 receiver. 2147 Home Address 2149 The home address that was contained in the Home Address 2150 destination option. The mobile node uses this information to 2151 determine which binding does not exist, in cases where the mobile 2152 node has several home addresses. 2154 Mobility Options 2156 Variable-length field of such length that the complete Mobility 2157 Header is an integer multiple of 8 octets long. This field 2158 contains zero or more TLV-encoded mobility options. The receiver 2159 MUST ignore and skip any options which it does not understand. 2161 There MAY be additional information, associated with this Binding 2162 Error message that need not be present in all Binding Error 2163 messages sent. Mobility options allow future extensions to the 2164 format of the Binding Error message to be defined. The encoding 2165 and format of defined options are described in Section 6.2. This 2166 specification does not define any options valid for the Binding 2167 Error message. 2169 If no actual options are present in this message, no padding is 2170 necessary and the Header Len field will be set to 2. 2172 6.2. Mobility Options 2174 Mobility messages can include zero or more mobility options. This 2175 allows optional fields that may not be needed in every use of a 2176 particular Mobility Header, as well as future extensions to the 2177 format of the messages. Such options are included in the Message 2178 Data field of the message itself, after the fixed portion of the 2179 message data specified in the message subsections of Section 6.1. 2181 The presence of such options will be indicated by the Header Len of 2182 the Mobility Header. If included, the Binding Authorization Data 2183 option (Section 6.2.7) MUST be the last option and MUST NOT have 2184 trailing padding. Otherwise, options can be placed in any order. 2186 6.2.1. Format 2188 Mobility options are encoded within the remaining space of the 2189 Message Data field of a mobility message, using a type-length-value 2190 (TLV) format as follows: 2192 0 1 2 3 2193 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2195 | Option Type | Option Length | Option Data... 2196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2198 Option Type 2200 8-bit identifier of the type of mobility option. When processing 2201 a Mobility Header containing an option for which the Option Type 2202 value is not recognized by the receiver, the receiver MUST quietly 2203 ignore and skip over the option, correctly handling any remaining 2204 options in the message. 2206 Option Length 2208 8-bit unsigned integer, representing the length in octets of the 2209 mobility option, not including the Option Type and Option Length 2210 fields. 2212 Option Data 2214 A variable length field that contains data specific to the option. 2216 The following subsections specify the Option types which are 2217 currently defined for use in the Mobility Header. 2219 Implementations MUST silently ignore any mobility options that they 2220 do not understand. 2222 Mobility options may have alignment requirements. Following the 2223 convention in IPv6, these options are aligned in a packet so that 2224 multi-octet values within the Option Data field of each option fall 2225 on natural boundaries (i.e., fields of width n octets are placed at 2226 an integer multiple of n octets from the start of the header, for n = 2227 1, 2, 4, or 8) [6]. 2229 6.2.2. Pad1 2231 The Pad1 option does not have any alignment requirements. Its format 2232 is as follows: 2234 0 2235 0 1 2 3 4 5 6 7 2236 +-+-+-+-+-+-+-+-+ 2237 | Type = 0 | 2238 +-+-+-+-+-+-+-+-+ 2240 NOTE! the format of the Pad1 option is a special case - it has 2241 neither Option Length nor Option Data fields. 2243 The Pad1 option is used to insert one octet of padding in the 2244 Mobility Options area of a Mobility Header. If more than one octet 2245 of padding is required, the PadN option, described next, should be 2246 used rather than multiple Pad1 options. 2248 6.2.3. PadN 2250 The PadN option does not have any alignment requirements. Its format 2251 is as follows: 2253 0 1 2254 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 2256 | Type = 1 | Option Length | Option Data 2257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 2259 The PadN option is used to insert two or more octets of padding in 2260 the Mobility Options area of a mobility message. For N octets of 2261 padding, the Option Length field contains the value N-2, and the 2262 Option Data consists of N-2 zero-valued octets. PadN Option data 2263 MUST be ignored by the receiver. 2265 6.2.4. Binding Refresh Advice 2267 The Binding Refresh Advice option has an alignment requirement of 2n. 2268 Its format is as follows: 2270 0 1 2 3 2271 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2273 | Type = 2 | Length = 2 | 2274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2275 | Refresh Interval | 2276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2278 The Binding Refresh Advice option is only valid in the Binding 2279 Acknowledgement, and only on Binding Acknowledgements sent from the 2280 mobile node's home agent in reply to a home registration. The 2281 Refresh Interval is measured in units of four seconds, and indicates 2282 remaining time until the mobile node SHOULD send a new home 2283 registration to the home agent. The Refresh Interval MUST be set to 2284 indicate a smaller time interval than the Lifetime value of the 2285 Binding Acknowledgement. 2287 6.2.5. Alternate Care-of Address 2289 The Alternate Care-of Address option has an alignment requirement of 2290 8n+6. Its format is as follows: 2292 0 1 2 3 2293 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2295 | Type = 3 | Length = 16 | 2296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2297 | | 2298 + + 2299 | | 2300 + Alternate Care-of Address + 2301 | | 2302 + + 2303 | | 2304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2306 Normally, a Binding Update specifies the desired care-of address in 2307 the Source Address field of the IPv6 header. However, this is not 2308 possible in some cases, such as when the mobile node wishes to 2309 indicate a care-of address which it cannot use as a topologically 2310 correct source address (Section 6.1.7 and Section 11.7.2) or when the 2311 used security mechanism does not protect the IPv6 header 2312 (Section 11.7.1). 2314 The Alternate Care-of Address option is provided for these 2315 situations. This option is valid only in Binding Update. The 2316 Alternate Care-of Address field contains an address to use as the 2317 care-of address for the binding, rather than using the Source Address 2318 of the packet as the care-of address. 2320 6.2.6. Nonce Indices 2322 The Nonce Indices option has an alignment requirement of 2n. Its 2323 format is as follows: 2325 0 1 2 3 2326 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2328 | Type = 4 | Length = 4 | 2329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2330 | Home Nonce Index | Care-of Nonce Index | 2331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2333 The Nonce Indices option is valid only in the Binding Update message 2334 sent to a correspondent node, and only when present together with a 2335 Binding Authorization Data option. When the correspondent node 2336 authorizes the Binding Update, it needs to produce home and care-of 2337 keygen tokens from its stored random nonce values. 2339 The Home Nonce Index field tells the correspondent node which nonce 2340 value to use when producing the home keygen token. 2342 The Care-of Nonce Index field is ignored in requests to delete a 2343 binding. Otherwise, it tells the correspondent node which nonce 2344 value to use when producing the care-of keygen token. 2346 6.2.7. Binding Authorization Data 2348 The Binding Authorization Data option does not have alignment 2349 requirements as such. However, since this option must be the last 2350 mobility option, an implicit alignment requirement is 8n + 2. The 2351 format of this option is as follows: 2353 0 1 2 3 2354 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2356 | Type = 5 | Option Length | 2357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2358 | | 2359 + + 2360 | Authenticator | 2361 + + 2362 | | 2363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2365 The Binding Authorization Data option is valid in the Binding Update 2366 and Binding Acknowledgement. 2368 The Option Length field contains the length of the authenticator in 2369 octets. 2371 The Authenticator field contains a cryptographic value which can be 2372 used to determine that the message in question comes from the right 2373 authority. Rules for calculating this value depends on the used 2374 authorization procedure. 2376 For the return routability procedure, this option can appear in the 2377 Binding Update and Binding Acknowledgements. Rules for calculating 2378 the Authenticator value are the following: 2380 Mobility Data = care-of address | correspondent | MH Data 2381 Authenticator = First (96, HMAC_SHA1 (Kbm, Mobility Data)) 2383 Where | denotes concatenation. "Care-of address" is the care-of 2384 address which will be registered for the mobile node if the Binding 2385 Update succeeds, or the home address of the mobile node if this 2386 option is used in de-registration. Note also that this address might 2387 be different from the source address of the Binding Update message, 2388 if the Alternative Care-of Address mobility option is used, or when 2389 the lifetime of the binding is set to zero. 2391 The "correspondent" is the IPv6 address of the correspondent node. 2392 Note that, if the message is sent to a destination which is itself 2393 mobile, the "correspondent" address may not be the address found in 2394 the Destination Address field of the IPv6 header; instead the home 2395 address from the type 2 Routing header should be used. 2397 "MH Data" is the content of the Mobility Header, excluding the 2398 Authenticator field itself. The Authenticator value is calculated as 2399 if the Checksum field in the Mobility Header was zero. The Checksum 2400 in the transmitted packet is still calculated in the usual manner, 2401 with the calculated Authenticator being a part of the packet 2402 protected by the Checksum. Kbm is the binding management key, which 2403 is typically created using nonces provided by the correspondent node 2404 (see Section 9.4). Note that while the contents of a potential Home 2405 Address destination option are not covered in this formula, the rules 2406 for the calculation of the Kbm do take the home address in account. 2407 This ensures that the MAC will be different for different home 2408 addresses. 2410 The first 96 bits from the MAC result are used as the Authenticator 2411 field. 2413 6.3. Home Address Option 2415 The Home Address option is carried by the Destination Option 2416 extension header (Next Header value = 60). It is used in a packet 2417 sent by a mobile node while away from home, to inform the recipient 2418 of the mobile node's home address. 2420 The Home Address option is encoded in type-length-value (TLV) format 2421 as follows: 2423 0 1 2 3 2424 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2426 | Option Type | Option Length | 2427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2428 | | 2429 + + 2430 | | 2431 + Home Address + 2432 | | 2433 + + 2434 | | 2435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2437 Option Type 2439 201 = 0xC9 2441 Option Length 2443 8-bit unsigned integer. Length of the option, in octets, 2444 excluding the Option Type and Option Length fields. This field 2445 MUST be set to 16. 2447 Home Address 2449 The home address of the mobile node sending the packet. This 2450 address MUST be a unicast routable address. 2452 The alignment requirement [6] for the Home Address option is 8n+6. 2454 The three highest-order bits of the Option Type field are encoded to 2455 indicate specific processing of the option [6]; for the Home Address 2456 option, these three bits are set to 110. This indicates the 2457 following processing requirements: 2459 o Any IPv6 node that does not recognize the Option Type must discard 2460 the packet, and if the packet's Destination Address was not a 2461 multicast address, return an ICMP Parameter Problem, Code 2, 2462 message to the packet's Source Address. The Pointer field in the 2463 ICMP message SHOULD point at the Option Type field. Otherwise, 2464 for multicast addresses, the ICMP message MUST NOT be sent. 2466 o The data within the option cannot change en route to the packet's 2467 final destination. 2469 The Home Address option MUST be placed as follows: 2471 o After the routing header, if that header is present 2473 o Before the Fragment Header, if that header is present 2475 o Before the AH Header or ESP Header, if either one of those headers 2476 are present 2478 For each IPv6 packet header, the Home Address Option MUST NOT appear 2479 more than once. However, an encapsulated packet [7] MAY contain a 2480 separate Home Address option associated with each encapsulating IP 2481 header. 2483 The inclusion of a Home Address destination option in a packet 2484 affects the receiving node's processing of only this single packet. 2486 No state is created or modified in the receiving node as a result of 2487 receiving a Home Address option in a packet. In particular, the 2488 presence of a Home Address option in a received packet MUST NOT alter 2489 the contents of the receiver's Binding Cache and MUST NOT cause any 2490 changes in the routing of subsequent packets sent by this receiving 2491 node. 2493 6.4. Type 2 Routing Header 2495 Mobile IPv6 defines a new routing header variant, the type 2 routing 2496 header, to allow the packet to be routed directly from a 2497 correspondent to the mobile node's care-of address. The mobile 2498 node's care-of address is inserted into the IPv6 Destination Address 2499 field. Once the packet arrives at the care-of address, the mobile 2500 node retrieves its home address from the routing header, and this is 2501 used as the final destination address for the packet. 2503 The new routing header uses a different type than defined for 2504 "regular" IPv6 source routing, enabling firewalls to apply different 2505 rules to source routed packets than to Mobile IPv6. This routing 2506 header type (type 2) is restricted to carry only one IPv6 address. 2507 All IPv6 nodes which process this routing header MUST verify that the 2508 address contained within is the node's own home address in order to 2509 prevent packets from being forwarded outside the node. The IP 2510 address contained in the routing header, since it is the mobile 2511 node's home address, MUST be a unicast routable address. 2512 Furthermore, if the scope of the home address is smaller than the 2513 scope of the care-of address, the mobile node MUST discard the packet 2514 (see Section 4.6). 2516 6.4.1. Format 2518 The type 2 routing header has the following format: 2520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2521 | Next Header | Hdr Ext Len=2 | Routing Type=2|Segments Left=1| 2522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2523 | Reserved | 2524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2525 | | 2526 + + 2527 | | 2528 + Home Address + 2529 | | 2530 + + 2531 | | 2532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2534 Next Header 2536 8-bit selector. Identifies the type of header immediately 2537 following the routing header. Uses the same values as the IPv6 2538 Next Header field [6]. 2540 Hdr Ext Len 2542 2 (8-bit unsigned integer); length of the routing header in 2543 8-octet units, not including the first 8 octets. 2545 Routing Type 2547 2 (8-bit unsigned integer). 2549 Segments Left 2551 1 (8-bit unsigned integer). 2553 Reserved 2555 32-bit reserved field. The value MUST be initialized to zero by 2556 the sender, and MUST be ignored by the receiver. 2558 Home Address 2560 The Home Address of the destination Mobile Node. 2562 For a type 2 routing header, the Hdr Ext Len MUST be 2. The Segments 2563 Left value describes the number of route segments remaining; i.e., 2564 number of explicitly listed intermediate nodes still to be visited 2565 before reaching the final destination. Segments Left MUST be 1. The 2566 ordering rules for extension headers in an IPv6 packet are described 2567 in Section 4.1 of RFC 2460 [6]. The type 2 routing header defined 2568 for Mobile IPv6 follows the same ordering as other routing headers. 2569 If another routing header is present along with a type 2 routing 2570 header, the type 2 routing header should follow the other routing 2571 header. A packet containing such nested encapsulation should be 2572 created as if the inner (type 2) routing header was constructed first 2573 and then treated as an original packet by header construction process 2574 for the other routing header. 2576 In addition, the general procedures defined by IPv6 for routing 2577 headers suggest that a received routing header MAY be automatically 2578 "reversed" to construct a routing header for use in any response 2579 packets sent by upper-layer protocols, if the received packet is 2580 authenticated [6]. This MUST NOT be done automatically for type 2 2581 routing headers. 2583 6.5. ICMP Home Agent Address Discovery Request Message 2585 The ICMP Home Agent Address Discovery Request message is used by a 2586 mobile node to initiate the dynamic home agent address discovery 2587 mechanism, as described in Section 11.4.1. The mobile node sends the 2588 Home Agent Address Discovery Request message to the Mobile IPv6 Home- 2589 Agents anycast address [8] for its own home subnet prefix. (Note 2590 that the currently defined anycast addresses may not work with all 2591 prefix lengths other than those defined in RFC 4291 [16] [36].) 2593 0 1 2 3 2594 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2596 | Type | Code | Checksum | 2597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2598 | Identifier | Reserved | 2599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2601 Type 2603 144 2605 Code 2607 0 2609 Checksum 2611 The ICMP checksum [17]. 2613 Identifier 2615 An identifier to aid in matching Home Agent Address Discovery 2616 Reply messages to this Home Agent Address Discovery Request 2617 message. 2619 Reserved 2621 This field is unused. It MUST be initialized to zero by the 2622 sender and MUST be ignored by the receiver. 2624 The Source Address of the Home Agent Address Discovery Request 2625 message packet is typically one of the mobile node's current care-of 2626 addresses. At the time of performing this dynamic home agent address 2627 discovery procedure, it is likely that the mobile node is not 2628 registered with any home agent. Therefore, neither the nature of the 2629 address nor the identity of the mobile node can be established at 2630 this time. The home agent MUST then return the Home Agent Address 2631 Discovery Reply message directly to the Source Address chosen by the 2632 mobile node. 2634 6.6. ICMP Home Agent Address Discovery Reply Message 2636 The ICMP Home Agent Address Discovery Reply message is used by a home 2637 agent to respond to a mobile node that uses the dynamic home agent 2638 address discovery mechanism, as described in Section 10.5. 2640 0 1 2 3 2641 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2642 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2643 | Type | Code | Checksum | 2644 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2645 | Identifier | Reserved | 2646 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2647 | | 2648 + + 2649 . . 2650 . Home Agent Addresses . 2651 . . 2652 + + 2653 | | 2654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2656 Type 2658 145 2660 Code 2662 0 2664 Checksum 2666 The ICMP checksum [17]. 2668 Identifier 2670 The identifier from the invoking Home Agent Address Discovery 2671 Request message. 2673 Reserved 2675 This field is unused. It MUST be initialized to zero by the 2676 sender and MUST be ignored by the receiver. 2678 Home Agent Addresses 2680 A list of addresses of home agents on the home link for the mobile 2681 node. The number of addresses presented in the list is indicated 2682 by the remaining length of the IPv6 packet carrying the Home Agent 2683 Address Discovery Reply message. 2685 6.7. ICMP Mobile Prefix Solicitation Message Format 2687 The ICMP Mobile Prefix Solicitation Message is sent by a mobile node 2688 to its home agent while it is away from home. The purpose of the 2689 message is to solicit a Mobile Prefix Advertisement from the home 2690 agent, which will allow the mobile node to gather prefix information 2691 about its home network. This information can be used to configure 2692 and update home address(es) according to changes in prefix 2693 information supplied by the home agent. 2695 0 1 2 3 2696 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2698 | Type | Code | Checksum | 2699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2700 | Identifier | Reserved | 2701 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2703 IP Fields: 2705 Source Address 2707 The mobile node's care-of address. 2709 Destination Address 2711 The address of the mobile node's home agent. This home agent must 2712 be on the link that the mobile node wishes to learn prefix 2713 information about. 2715 Hop Limit 2717 Set to an initial hop limit value, similarly to any other unicast 2718 packet sent by the mobile node. 2720 Destination Option: 2722 A Home Address destination option MUST be included. 2724 ESP header: 2726 IPsec headers MUST be supported and SHOULD be used as described in 2727 Section 5.4. 2729 ICMP Fields: 2731 Type 2733 146 2735 Code 2737 0 2739 Checksum 2741 The ICMP checksum [17]. 2743 Identifier 2745 An identifier to aid in matching a future Mobile Prefix 2746 Advertisement to this Mobile Prefix Solicitation. 2748 Reserved 2750 This field is unused. It MUST be initialized to zero by the 2751 sender and MUST be ignored by the receiver. 2753 The Mobile Prefix Solicitation messages may have options. These 2754 options MUST use the option format defined in Neighbor Discovery (RFC 2755 4861 [18]). This document does not define any option types for the 2756 Mobile Prefix Solicitation message, but future documents may define 2757 new options. Home agents MUST silently ignore any options they do 2758 not recognize and continue processing the message. 2760 6.8. ICMP Mobile Prefix Advertisement Message Format 2762 A home agent will send a Mobile Prefix Advertisement to a mobile node 2763 to distribute prefix information about the home link while the mobile 2764 node is traveling away from the home network. This will occur in 2765 response to a Mobile Prefix Solicitation with an Advertisement, or by 2766 an unsolicited Advertisement sent according to the rules in 2767 Section 10.6. 2769 0 1 2 3 2770 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2771 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2772 | Type | Code | Checksum | 2773 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2774 | Identifier |M|O| Reserved | 2775 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2776 | Options ... 2777 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2779 IP Fields: 2781 Source Address 2783 The home agent's address as the mobile node would expect to see it 2784 (i.e., same network prefix). 2786 Destination Address 2788 If this message is a response to a Mobile Prefix Solicitation, 2789 this field contains the Source Address field from that packet. 2790 For unsolicited messages, the mobile node's care-of address SHOULD 2791 be used. Note that unsolicited messages can only be sent if the 2792 mobile node is currently registered with the home agent. 2794 Routing header: 2796 A type 2 routing header MUST be included. 2798 ESP header: 2800 IPsec headers MUST be supported and SHOULD be used as described in 2801 Section 5.4. 2803 ICMP Fields: 2805 Type 2807 147 2809 Code 2811 0 2813 Checksum 2815 The ICMP checksum [17]. 2817 Identifier 2819 An identifier to aid in matching this Mobile Prefix Advertisement 2820 to a previous Mobile Prefix Solicitation. 2822 M 2824 1-bit Managed Address Configuration flag. When set, hosts use the 2825 administered (stateful) protocol for address autoconfiguration in 2826 addition to any addresses autoconfigured using stateless address 2827 autoconfiguration. The use of this flag is described in [18] 2828 [19]. 2830 O 2832 1-bit Other Stateful Configuration flag. When set, hosts use the 2833 administered (stateful) protocol for autoconfiguration of other 2834 (non-address) information. The use of this flag is described in 2835 [18] [19]. 2837 Reserved 2839 This field is unused. It MUST be initialized to zero by the 2840 sender and MUST be ignored by the receiver. 2842 The Mobile Prefix Advertisement messages may have options. These 2843 options MUST use the option format defined in Neighbor Discovery (RFC 2844 4861 [18]). This document defines one option which may be carried in 2845 a Mobile Prefix Advertisement message, but future documents may 2846 define new options. Mobile nodes MUST silently ignore any options 2847 they do not recognize and continue processing the message. 2849 Prefix Information 2851 Each message contains one or more Prefix Information options. 2852 Each option carries the prefix(es) that the mobile node should use 2853 to configure its home address(es). Section 10.6 describes which 2854 prefixes should be advertised to the mobile node. 2856 The Prefix Information option is defined in Section 4.6.2 of 2857 Neighbor Discovery (RFC 4861 [18]), with modifications defined in 2858 Section 7.2 of this specification. The home agent MUST use this 2859 modified Prefix Information option to send home network prefixes 2860 as defined in Section 10.6.1. 2862 If the Advertisement is sent in response to a Mobile Prefix 2863 Solicitation, the home agent MUST copy the Identifier value from that 2864 message into the Identifier field of the Advertisement. 2866 The home agent MUST NOT send more than one Mobile Prefix 2867 Advertisement message per second to any mobile node. 2869 The M and O bits MUST be cleared if the Home Agent DHCPv6 support is 2870 not provided. If such support is provided then they are set in 2871 concert with the home network's administrative settings. 2873 7. Modifications to IPv6 Neighbor Discovery 2875 7.1. Modified Router Advertisement Message Format 2877 Mobile IPv6 modifies the format of the Router Advertisement message 2878 [18] by the addition of a single flag bit to indicate that the router 2879 sending the Advertisement message is serving as a home agent on this 2880 link. The format of the Router Advertisement message is as follows: 2882 0 1 2 3 2883 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2885 | Type | Code | Checksum | 2886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2887 | Cur Hop Limit |M|O|H| Reserved| Router Lifetime | 2888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2889 | Reachable Time | 2890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2891 | Retrans Timer | 2892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2893 | Options ... 2894 +-+-+-+-+-+-+-+-+-+-+-+- 2896 This format represents the following changes over that originally 2897 specified for Neighbor Discovery [18]: 2899 Home Agent (H) 2901 The Home Agent (H) bit is set in a Router Advertisement to 2902 indicate that the router sending this Router Advertisement is also 2903 functioning as a Mobile IPv6 home agent on this link. 2905 Reserved 2907 Reduced from a 6-bit field to a 5-bit field to account for the 2908 addition of the above bit. 2910 7.2. Modified Prefix Information Option Format 2912 Mobile IPv6 requires knowledge of a router's global address in 2913 building a Home Agents List as part of the dynamic home agent address 2914 discovery mechanism. 2916 However, Neighbor Discovery [18] only advertises a router's link- 2917 local address, by requiring this address to be used as the IP Source 2918 Address of each Router Advertisement. 2920 Mobile IPv6 extends Neighbor Discovery to allow a router to advertise 2921 its global address, by the addition of a single flag bit in the 2922 format of a Prefix Information option for use in Router Advertisement 2923 messages. The format of the Prefix Information option is as follows: 2925 0 1 2 3 2926 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2928 | Type | Length | Prefix Length |L|A|R|Reserved1| 2929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2930 | Valid Lifetime | 2931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2932 | Preferred Lifetime | 2933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2934 | Reserved2 | 2935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2936 | | 2937 + + 2938 | | 2939 + Prefix + 2940 | | 2941 + + 2942 | | 2943 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2945 This format represents the following changes over that originally 2946 specified for Neighbor Discovery [18]: 2948 Router Address (R) 2950 1-bit router address flag. When set, indicates that the Prefix 2951 field contains a complete IP address assigned to the sending 2952 router. The indicated prefix is given by the first Prefix Length 2953 bits of the Prefix field. The router IP address has the same 2954 scope and conforms to the same lifetime values as the advertised 2955 prefix. This use of the Prefix field is compatible with its use 2956 in advertising the prefix itself, since Prefix Advertisement uses 2957 only the leading bits. Interpretation of this flag bit is thus 2958 independent of the processing required for the On-Link (L) and 2959 Autonomous Address-Configuration (A) flag bits. 2961 Reserved1 2963 Reduced from a 6-bit field to a 5-bit field to account for the 2964 addition of the above bit. 2966 In a Router Advertisement, a home agent MUST, and all other routers 2967 MAY, include at least one Prefix Information option with the Router 2968 Address (R) bit set. Neighbor Discovery (RFC 4861 [18]) specifies 2969 that, when including all options in a Router Advertisement causes the 2970 size of the Advertisement to exceed the link MTU, multiple 2971 Advertisements can be sent, each containing a subset of the Neighbor 2972 Discovery options. Also, when sending unsolicited multicast Router 2973 Advertisements more frequently than the limit specified in RFC 4861, 2974 the sending router need not include all options in each of these 2975 Advertisements. However, in both of these cases the router SHOULD 2976 include at least one Prefix Information option with the Router 2977 Address (R) bit set in each such advertisement, if this bit is set in 2978 some advertisement sent by the router. 2980 In addition, the following requirement can assist mobile nodes in 2981 movement detection. Barring changes in the prefixes for the link, 2982 routers that send multiple Router Advertisements with the Router 2983 Address (R) bit set in some of the included Prefix Information 2984 options SHOULD provide at least one option and router address which 2985 stays the same in all of the Advertisements. 2987 7.3. New Advertisement Interval Option Format 2989 Mobile IPv6 defines a new Advertisement Interval option, used in 2990 Router Advertisement messages to advertise the interval at which the 2991 sending router sends unsolicited multicast Router Advertisements. 2992 The format of the Advertisement Interval option is as follows: 2994 0 1 2 3 2995 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2996 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2997 | Type | Length | Reserved | 2998 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2999 | Advertisement Interval | 3000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3002 Type 3004 7 3006 Length 3008 8-bit unsigned integer. The length of the option (including the 3009 type and length fields) is in units of 8 octets. The value of 3010 this field MUST be 1. 3012 Reserved 3014 This field is unused. It MUST be initialized to zero by the 3015 sender and MUST be ignored by the receiver. 3017 Advertisement Interval 3019 32-bit unsigned integer. The maximum time, in milliseconds, 3020 between successive unsolicited Router Advertisement messages sent 3021 by this router on this network interface. Using the conceptual 3022 router configuration variables defined by Neighbor Discovery [18], 3023 this field MUST be equal to the value MaxRtrAdvInterval, expressed 3024 in milliseconds. 3026 Routers MAY include this option in their Router Advertisements. A 3027 mobile node receiving a Router Advertisement containing this option 3028 SHOULD utilize the specified Advertisement Interval for that router 3029 in its movement detection algorithm, as described in Section 11.5.1. 3031 This option MUST be silently ignored for other Neighbor Discovery 3032 messages. 3034 7.4. New Home Agent Information Option Format 3036 Mobile IPv6 defines a new Home Agent Information option, used in 3037 Router Advertisements sent by a home agent to advertise information 3038 specific to this router's functionality as a home agent. The format 3039 of the Home Agent Information option is as follows: 3041 0 1 2 3 3042 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 3043 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3044 | Type | Length | Reserved | 3045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3046 | Home Agent Preference | Home Agent Lifetime | 3047 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3049 Type 3051 8 3053 Length 3055 8-bit unsigned integer. The length of the option (including the 3056 type and length fields) in units of 8 octets. The value of this 3057 field MUST be 1. 3059 Reserved 3061 This field is unused. It MUST be initialized to zero by the 3062 sender and MUST be ignored by the receiver. 3064 Home Agent Preference 3066 16-bit unsigned integer. The preference for the home agent 3067 sending this Router Advertisement, for use in ordering the 3068 addresses returned to a mobile node in the Home Agent Addresses 3069 field of a Home Agent Address Discovery Reply message. Higher 3070 values mean more preferable. If this option is not included in a 3071 Router Advertisement in which the Home Agent (H) bit is set, the 3072 preference value for this home agent MUST be considered to be 0. 3073 Greater values indicate a more preferable home agent than lower 3074 values. 3076 The manual configuration of the Home Agent Preference value is 3077 described in Section 8.4. In addition, the sending home agent MAY 3078 dynamically set the Home Agent Preference value, for example 3079 basing it on the number of mobile nodes it is currently serving or 3080 on its remaining resources for serving additional mobile nodes; 3081 such dynamic settings are beyond the scope of this document. Any 3082 such dynamic setting of the Home Agent Preference, however, MUST 3083 set the preference appropriately, relative to the default Home 3084 Agent Preference value of 0 that may be in use by some home agents 3085 on this link (i.e., a home agent not including a Home Agent 3086 Information option in its Router Advertisements will be considered 3087 to have a Home Agent Preference value of 0). 3089 Home Agent Lifetime 3091 16-bit unsigned integer. The lifetime associated with the home 3092 agent in units of seconds. The default value is the same as the 3093 Router Lifetime, as specified in the main body of the Router 3094 Advertisement. The maximum value corresponds to 18.2 hours. A 3095 value of 0 MUST NOT be used. The Home Agent Lifetime applies only 3096 to this router's usefulness as a home agent; it does not apply to 3097 information contained in other message fields or options. 3099 Home agents MAY include this option in their Router Advertisements. 3100 This option MUST NOT be included in a Router Advertisement in which 3101 the Home Agent (H) bit (see Section 7.1) is not set. If this option 3102 is not included in a Router Advertisement in which the Home Agent (H) 3103 bit is set, the lifetime for this home agent MUST be considered to be 3104 the same as the Router Lifetime in the Router Advertisement. If 3105 multiple Advertisements are being sent instead of a single larger 3106 unsolicited multicast Advertisement, all of the multiple 3107 Advertisements with the Router Address (R) bit set MUST include this 3108 option with the same contents, otherwise this option MUST be omitted 3109 from all Advertisements. 3111 This option MUST be silently ignored for other Neighbor Discovery 3112 messages. 3114 If both the Home Agent Preference and Home Agent Lifetime are set to 3115 their default values specified above, this option SHOULD NOT be 3116 included in the Router Advertisement messages sent by this home 3117 agent. 3119 7.5. Changes to Sending Router Advertisements 3121 The Neighbor Discovery protocol specification [18] limits routers to 3122 a minimum interval of 3 seconds between sending unsolicited multicast 3123 Router Advertisement messages from any given network interface 3124 (limited by MinRtrAdvInterval and MaxRtrAdvInterval), stating that: 3126 "Routers generate Router Advertisements frequently enough that 3127 hosts will learn of their presence within a few minutes, but not 3128 frequently enough to rely on an absence of advertisements to 3129 detect router failure; a separate Neighbor Unreachability 3130 Detection algorithm provides failure detection." 3132 This limitation, however, is not suitable to providing timely 3133 movement detection for mobile nodes. Mobile nodes detect their own 3134 movement by learning the presence of new routers as the mobile node 3135 moves into wireless transmission range of them (or physically 3136 connects to a new wired network), and by learning that previous 3137 routers are no longer reachable. Mobile nodes MUST be able to 3138 quickly detect when they move to a link served by a new router, so 3139 that they can acquire a new care-of address and send Binding Updates 3140 to register this care-of address with their home agent and to notify 3141 correspondent nodes as needed. 3143 One method which can provide for faster movement detection, is to 3144 increase the rate at which unsolicited Router Advertisements are 3145 sent. Mobile IPv6 relaxes this limit such that routers MAY send 3146 unsolicited multicast Router Advertisements more frequently. This 3147 method can be applied where the router is expecting to provide 3148 service to visiting mobile nodes (e.g., wireless network interfaces), 3149 or on which it is serving as a home agent to one or more mobile nodes 3150 (who may return home and need to hear its Advertisements). 3152 Routers supporting mobility SHOULD be able to be configured with a 3153 smaller MinRtrAdvInterval value and MaxRtrAdvInterval value to allow 3154 sending of unsolicited multicast Router Advertisements more often. 3155 The minimum allowed values are: 3157 o MinRtrAdvInterval 0.03 seconds 3158 o MaxRtrAdvInterval 0.07 seconds 3160 In the case where the minimum intervals and delays are used, the mean 3161 time between unsolicited multicast router advertisements is 50ms. 3162 Use of these modified limits MUST be configurable (see also the 3163 configuration variable MinDelayBetweenRas in Section 13 which may 3164 also have to be modified accordingly). Systems where these values 3165 are available MUST NOT default to them, and SHOULD default to values 3166 specified in Neighbor Discovery (RFC 4861 [18]). Knowledge of the 3167 type of network interface and operating environment SHOULD be taken 3168 into account in configuring these limits for each network interface. 3169 This is important with some wireless links, where increasing the 3170 frequency of multicast beacons can cause considerable overhead. 3171 Routers SHOULD adhere to the intervals specified in RFC 4861 [18], if 3172 this overhead is likely to cause service degradation. 3174 Additionally, the possible low values of MaxRtrAdvInterval may cause 3175 some problems with movement detection in some mobile nodes. To 3176 ensure that this is not a problem, Routers SHOULD add 20ms to any 3177 Advertisement Intervals sent in RAs, which are below 200 ms, in order 3178 to account for scheduling granularities on both the MN and the 3179 Router. 3181 Note that multicast Router Advertisements are not always required in 3182 certain wireless networks that have limited bandwidth. Mobility 3183 detection or link changes in such networks may be done at lower 3184 layers. Router advertisements in such networks SHOULD be sent only 3185 when solicited. In such networks it SHOULD be possible to disable 3186 unsolicited multicast Router Advertisements on specific interfaces. 3187 The MinRtrAdvInterval and MaxRtrAdvInterval in such a case can be set 3188 to some high values. 3190 Home agents MUST include the Source Link-Layer Address option in all 3191 Router Advertisements they send. This simplifies the process of 3192 returning home, as discussed in Section 11.5.5. 3194 Note that according to Neighbor Discovery (RFC 4861 [18]), 3195 AdvDefaultLifetime is by default based on the value of 3196 MaxRtrAdvInterval. AdvDefaultLifetime is used in the Router Lifetime 3197 field of Router Advertisements. Given that this field is expressed 3198 in seconds, a small MaxRtrAdvInterval value can result in a zero 3199 value for this field. To prevent this, routers SHOULD keep 3200 AdvDefaultLifetime in at least one second, even if the use of 3201 MaxRtrAdvInterval would result in a smaller value. 3203 8. Requirements for Types of IPv6 Nodes 3205 Mobile IPv6 places some special requirements on the functions 3206 provided by different types of IPv6 nodes. This section summarizes 3207 those requirements, identifying the functionality each requirement is 3208 intended to support. 3210 The requirements are set for the following groups of nodes: 3212 o All IPv6 nodes. 3214 o All IPv6 nodes with support for route optimization. 3216 o All IPv6 routers. 3218 o All Mobile IPv6 home agents. 3220 o All Mobile IPv6 mobile nodes. 3222 It is outside the scope of this specification to specify which of 3223 these groups are mandatory in IPv6. We only describe what is 3224 mandatory for a node that supports, for instance, route optimization. 3225 Other specifications are expected to define the extent of IPv6. 3227 8.1. All IPv6 Nodes 3229 Any IPv6 node may at any time be a correspondent node of a mobile 3230 node, either sending a packet to a mobile node or receiving a packet 3231 from a mobile node. There are no Mobile IPv6 specific MUST 3232 requirements for such nodes, and basic IPv6 techniques are 3233 sufficient. If a mobile node attempts to set up route optimization 3234 with a node with only basic IPv6 support, an ICMP error will signal 3235 that the node does not support such optimizations (Section 11.3.5), 3236 and communications will flow through the home agent . 3238 An IPv6 node MUST NOT support the Home Address destination option, 3239 type 2 routing header, or the Mobility Header unless it fully 3240 supports the requirements listed in the next sections for either 3241 route optimization, mobile node, or home agent functionality. 3243 8.2. IPv6 Nodes with Support for Route Optimization 3245 Nodes that implement route optimization are a subset of all IPv6 3246 nodes on the Internet. The ability of a correspondent node to 3247 participate in route optimization is essential for the efficient 3248 operation of the IPv6 Internet, for the following reasons: 3250 o Avoidance of congestion in the home network, and enabling the use 3251 of lower-performance home agent equipment even for supporting 3252 thousands of mobile nodes. 3254 o Reduced network load across the entire Internet, as mobile devices 3255 begin to predominate. 3257 o Reduction of jitter and latency for the communications. 3259 o Greater likelihood of success for QoS signaling as tunneling is 3260 avoided and, again, fewer sources of congestion. 3262 o Improved robustness against network partitions, congestion, and 3263 other problems, since fewer routing path segments are traversed. 3265 These effects combine to enable much better performance and 3266 robustness for communications between mobile nodes and IPv6 3267 correspondent nodes. Route optimization introduces a small amount of 3268 additional state for the peers, some additional messaging, and up to 3269 1.5 roundtrip delays before it can be turned on. However, it is 3270 believed that the benefits far outweigh the costs in most cases. 3271 Section 11.3.1 discusses how mobile nodes may avoid route 3272 optimization for some of the remaining cases, such as very short-term 3273 communications. 3275 The following requirements apply to all correspondent nodes that 3276 support route optimization: 3278 o The node MUST be able to validate a Home Address option using an 3279 existing Binding Cache entry, as described in Section 9.3.1. 3281 o The node MUST be able to insert a type 2 routing header into 3282 packets to be sent to a mobile node, as described in 3283 Section 9.3.2. 3285 o Unless the correspondent node is also acting as a mobile node, it 3286 MUST ignore type 2 routing headers and silently discard all 3287 packets that it has received with such headers. 3289 o The node SHOULD be able to interpret ICMP messages as described in 3290 Section 9.3.4. 3292 o The node MUST be able to send Binding Error messages as described 3293 in Section 9.3.3. 3295 o The node MUST be able to process Mobility Headers as described in 3296 Section 9.2. 3298 o The node MUST be able to participate in a return routability 3299 procedure (Section 9.4). 3301 o The node MUST be able to process Binding Update messages 3302 (Section 9.5). 3304 o The node MUST be able to return a Binding Acknowledgement 3305 (Section 9.5.4). 3307 o The node MUST be able to maintain a Binding Cache of the bindings 3308 received in accepted Binding Updates, as described in Section 9.1 3309 and Section 9.6. 3311 o The node SHOULD allow route optimization to be administratively 3312 enabled or disabled. The default SHOULD be enabled. 3314 8.3. All IPv6 Routers 3316 All IPv6 routers, even those not serving as a home agent for Mobile 3317 IPv6, have an effect on how well mobile nodes can communicate: 3319 o Every IPv6 router SHOULD be able to send an Advertisement Interval 3320 option (Section 7.3) in each of its Router Advertisements [18], to 3321 aid movement detection by mobile nodes (as in Section 11.5.1). 3322 The use of this option in Router Advertisements SHOULD be 3323 configurable. 3325 o Every IPv6 router SHOULD be able to support sending unsolicited 3326 multicast Router Advertisements at the faster rate described in 3327 Section 7.5. If the router supports a faster rate, the used rate 3328 MUST be configurable. 3330 o Each router SHOULD include at least one prefix with the Router 3331 Address (R) bit set and with its full IP address in its Router 3332 Advertisements (as described in Section 7.2). 3334 o Routers supporting filtering packets with routing headers SHOULD 3335 support different rules for type 0 and type 2 routing headers (see 3336 Section 6.4) so that filtering of source routed packets (type 0) 3337 will not necessarily limit Mobile IPv6 traffic which is delivered 3338 via type 2 routing headers. 3340 8.4. IPv6 Home Agents 3342 In order for a mobile node to operate correctly while away from home, 3343 at least one IPv6 router on the mobile node's home link must function 3344 as a home agent for the mobile node. The following additional 3345 requirements apply to all IPv6 routers that serve as a home agent: 3347 o Every home agent MUST be able to maintain an entry in its Binding 3348 Cache for each mobile node for which it is serving as the home 3349 agent (Section 10.1 and Section 10.3.1). 3351 o Every home agent MUST be able to intercept packets (using proxy 3352 Neighbor Discovery [18]) addressed to a mobile node for which it 3353 is currently serving as the home agent, on that mobile node's home 3354 link, while the mobile node is away from home (Section 10.4.1). 3356 o Every home agent MUST be able to encapsulate [7] such intercepted 3357 packets in order to tunnel them to the primary care-of address for 3358 the mobile node indicated in its binding in the home agent's 3359 Binding Cache (Section 10.4.2). 3361 o Every home agent MUST support decapsulating [7] reverse tunneled 3362 packets sent to it from a mobile node's home address. Every home 3363 agent MUST also check that the source address in the tunneled 3364 packets corresponds to the currently registered location of the 3365 mobile node (Section 10.4.5). 3367 o The node MUST be able to process Mobility Headers as described in 3368 Section 10.2. 3370 o Every home agent MUST be able to return a Binding Acknowledgement 3371 in response to a Binding Update (Section 10.3.1). 3373 o Every home agent MUST maintain a separate Home Agents List for 3374 each link on which it is serving as a home agent, as described in 3375 Section 10.1 and Section 10.5.1. 3377 o Every home agent MUST be able to accept packets addressed to the 3378 Mobile IPv6 Home-Agents anycast address [8] for the subnet on 3379 which it is serving as a home agent, and MUST be able to 3380 participate in dynamic home agent address discovery 3381 (Section 10.5). 3383 o Every home agent SHOULD support a configuration mechanism to allow 3384 a system administrator to manually set the value to be sent by 3385 this home agent in the Home Agent Preference field of the Home 3386 Agent Information Option in Router Advertisements that it sends 3387 (Section 7.4). 3389 o Every home agent SHOULD support sending ICMP Mobile Prefix 3390 Advertisements (Section 6.8), and SHOULD respond to Mobile Prefix 3391 Solicitations (Section 6.7). If supported, this behavior MUST be 3392 configurable, so that home agents can be configured to avoid 3393 sending such Prefix Advertisements according to the needs of the 3394 network administration in the home domain. 3396 o Every home agent MUST support IPsec ESP for protection of packets 3397 belonging to the return routability procedure (Section 10.4.6). 3399 o Every home agent SHOULD support the multicast group membership 3400 control protocols as described in Section 10.4.3. If this support 3401 is provided, the home agent MUST be capable of using it to 3402 determine which multicast data packets to forward via the tunnel 3403 to the mobile node. 3405 o Home agents MAY support stateful address autoconfiguration for 3406 mobile nodes as described in Section 10.4.4. 3408 8.5. IPv6 Mobile Nodes 3410 Finally, the following requirements apply to all IPv6 nodes capable 3411 of functioning as mobile nodes: 3413 o The node MUST maintain a Binding Update List (Section 11.1). 3415 o The node MUST support sending packets containing a Home Address 3416 option (Section 11.3.1), and follow the required IPsec interaction 3417 (Section 11.3.2). 3419 o The node MUST be able to perform IPv6 encapsulation and 3420 decapsulation [7]. 3422 o The node MUST be able to process type 2 routing header as defined 3423 in Section 6.4 and Section 11.3.3. 3425 o The node MUST support receiving a Binding Error message 3426 (Section 11.3.6). 3428 o The node MUST support receiving ICMP errors (Section 11.3.5). 3430 o The node MUST support movement detection, care-of address 3431 formation, and returning home (Section 11.5). 3433 o The node MUST be able to process Mobility Headers as described in 3434 Section 11.2. 3436 o The node MUST support the return routability procedure 3437 (Section 11.6). 3439 o The node MUST be able to send Binding Updates, as specified in 3440 Section 11.7.1 and Section 11.7.2. 3442 o The node MUST be able to receive and process Binding 3443 Acknowledgements, as specified in Section 11.7.3. 3445 o The node MUST support receiving a Binding Refresh Request 3446 (Section 6.1.2), by responding with a Binding Update. 3448 o The node MUST support receiving Mobile Prefix Advertisements 3449 (Section 11.4.3) and reconfiguring its home address based on the 3450 prefix information contained therein. 3452 o The node SHOULD support use of the dynamic home agent address 3453 discovery mechanism, as described in Section 11.4.1. 3455 o The node MUST allow route optimization to be administratively 3456 enabled or disabled. The default SHOULD be enabled. 3458 o The node MAY support the multicast address listener part of a 3459 multicast group membership protocol as described in 3460 Section 11.3.4. If this support is provided, the mobile node MUST 3461 be able to receive tunneled multicast packets from the home agent. 3463 o The node MAY support stateful address autoconfiguration mechanisms 3464 such as DHCPv6 [30] on the interface represented by the tunnel to 3465 the home agent. 3467 9. Correspondent Node Operation 3469 9.1. Conceptual Data Structures 3471 IPv6 nodes with route optimization support maintain a Binding Cache 3472 of bindings for other nodes. A separate Binding Cache SHOULD be 3473 maintained by each IPv6 node for each of its unicast routable 3474 addresses. The Binding Cache MAY be implemented in any manner 3475 consistent with the external behavior described in this document, for 3476 example by being combined with the node's Destination Cache as 3477 maintained by Neighbor Discovery [18]. When sending a packet, the 3478 Binding Cache is searched before the Neighbor Discovery conceptual 3479 Destination Cache [18]. 3481 Each Binding Cache entry conceptually contains the following fields: 3483 o The home address of the mobile node for which this is the Binding 3484 Cache entry. This field is used as the key for searching the 3485 Binding Cache for the destination address of a packet being sent. 3487 o The care-of address for the mobile node indicated by the home 3488 address field in this Binding Cache entry. 3490 o A lifetime value, indicating the remaining lifetime for this 3491 Binding Cache entry. The lifetime value is initialized from the 3492 Lifetime field in the Binding Update that created or last modified 3493 this Binding Cache entry. A correspondent node MAY select a 3494 smaller lifetime for the Binding Cache entry, and supply that 3495 value to the mobile node in the Binding Acknowledgment message. 3497 o A flag indicating whether or not this Binding Cache entry is a 3498 home registration entry (applicable only on nodes which support 3499 home agent functionality). 3501 o The maximum value of the Sequence Number field received in 3502 previous Binding Updates for this home address. The Sequence 3503 Number field is 16 bits long. Sequence Number values MUST be 3504 compared modulo 2**16 as explained in Section 9.5.1. 3506 o Usage information for this Binding Cache entry. This is needed to 3507 implement the cache replacement policy in use in the Binding 3508 Cache. Recent use of a cache entry also serves as an indication 3509 that a Binding Refresh Request should be sent when the lifetime of 3510 this entry nears expiration. 3512 Binding Cache entries not marked as home registrations MAY be 3513 replaced at any time by any reasonable local cache replacement policy 3514 but SHOULD NOT be unnecessarily deleted. The Binding Cache for any 3515 one of a node's IPv6 addresses may contain at most one entry for each 3516 mobile node home address. The contents of a node's Binding Cache 3517 MUST NOT be changed in response to a Home Address option in a 3518 received packet. 3520 9.2. Processing Mobility Headers 3522 Mobility Header processing MUST observe the following rules: 3524 o The checksum must be verified as per Section 6.1. If invalid, the 3525 node MUST silently discard the message. 3527 o The MH Type field MUST have a known value (Section 6.1.1). 3528 Otherwise, the node MUST discard the message and issue a Binding 3529 Error message as described in Section 9.3.3, with Status field set 3530 to 2 (unrecognized MH Type value). 3532 o The Payload Proto field MUST be IPPROTO_NONE (59 decimal). 3533 Otherwise, the node MUST discard the message and SHOULD send ICMP 3534 Parameter Problem, Code 0, directly to the Source Address of the 3535 packet as specified in RFC 4443 [17]. Thus no Binding Cache 3536 information is used in sending the ICMP message. The Pointer 3537 field in the ICMP message SHOULD point at the Payload Proto field. 3539 o The Header Len field in the Mobility Header MUST NOT be less than 3540 the length specified for this particular type of message in 3541 Section 6.1. Otherwise, the node MUST discard the message and 3542 SHOULD send ICMP Parameter Problem, Code 0, directly to the Source 3543 Address of the packet as specified in RFC 4443 [17]. (The Binding 3544 Cache information is again not used.) The Pointer field in the 3545 ICMP message SHOULD point at the Header Len field. 3547 Subsequent checks depend on the particular Mobility Header. 3549 9.3. Packet Processing 3551 This section describes how the correspondent node sends packets to 3552 the mobile node, and receives packets from it. 3554 9.3.1. Receiving Packets with Home Address Option 3556 Packets containing a Home Address option MUST be dropped if the given 3557 home address is not a unicast routable address. 3559 Mobile nodes can include a Home Address destination option in a 3560 packet if they believe the correspondent node has a Binding Cache 3561 entry for the home address of a mobile node. If the Next Header 3562 value of the Destination Option is one of the following: {50 (ESP), 3563 51 (AH), 135 (Mobility Header)}, the packet SHOULD be processed 3564 normally. Otherwise, the packet MUST be dropped if there is no 3565 corresponding Binding Cache entry. A corresponding Binding Cache 3566 entry MUST have the same home address as appears in the Home Address 3567 destination option, and the currently registered care-of address MUST 3568 be equal to the source address of the packet. 3570 If the packet is dropped due to the above tests, the correspondent 3571 node MUST send the Binding Error message as described in 3572 Section 9.3.3. The Status field in this message should be set to 1 3573 (unknown binding for Home Address destination option). 3575 The correspondent node MUST process the option in a manner consistent 3576 with exchanging the Home Address field from the Home Address option 3577 into the IPv6 header and replacing the original value of the Source 3578 Address field there. After all IPv6 options have been processed, it 3579 MUST be possible for upper layers to process the packet without the 3580 knowledge that it came originally from a care-of address or that a 3581 Home Address option was used. 3583 The use of IPsec Authentication Header (AH) for the Home Address 3584 option is not required, except that if the IPv6 header of a packet is 3585 covered by AH, then the authentication MUST also cover the Home 3586 Address option; this coverage is achieved automatically by the 3587 definition of the Option Type code for the Home Address option, since 3588 it indicates that the data within the option cannot change en route 3589 to the packet's final destination, and thus the option is included in 3590 the AH computation. By requiring that any authentication of the IPv6 3591 header also cover the Home Address option, the security of the Source 3592 Address field in the IPv6 header is not compromised by the presence 3593 of a Home Address option. 3595 When attempting to verify AH authentication data in a packet that 3596 contains a Home Address option, the receiving node MUST calculate the 3597 AH authentication data as if the following were true: The Home 3598 Address option contains the care-of address, and the source IPv6 3599 address field of the IPv6 header contains the home address. This 3600 conforms with the calculation specified in Section 11.3.2. 3602 9.3.2. Sending Packets to a Mobile Node 3604 Before sending any packet, the sending node SHOULD examine its 3605 Binding Cache for an entry for the destination address to which the 3606 packet is being sent. If the sending node has a Binding Cache entry 3607 for this address, the sending node SHOULD use a type 2 routing header 3608 to route the packet to this mobile node (the destination node) by way 3609 of its care-of address. However, the sending node MUST NOT do this 3610 in the following cases: 3612 o When sending an IPv6 Neighbor Discovery [18] packet. 3614 o Where otherwise noted in Section 6.1. 3616 When calculating authentication data in a packet that contains a type 3617 2 routing header, the correspondent node MUST calculate the AH 3618 authentication data as if the following were true: The routing header 3619 contains the care-of address, the destination IPv6 address field of 3620 the IPv6 header contains the home address, and the Segments Left 3621 field is zero. The IPsec Security Policy Database lookup MUST based 3622 on the mobile node's home address. 3624 For instance, assuming there are no additional routing headers in 3625 this packet beyond those needed by Mobile IPv6, the correspondent 3626 node could set the fields in the packet's IPv6 header and routing 3627 header as follows: 3629 o The Destination Address in the packet's IPv6 header is set to the 3630 mobile node's home address (the original destination address to 3631 which the packet was being sent). 3633 o The routing header is initialized to contain a single route 3634 segment, containing the mobile node's care-of address copied from 3635 the Binding Cache entry. The Segments Left field is, however, 3636 temporarily set to zero. 3638 The IP layer will insert the routing header before performing any 3639 necessary IPsec processing. Once all IPsec processing has been 3640 performed, the node swaps the IPv6 destination field with the Home 3641 Address field in the routing header, sets the Segments Left field to 3642 one, and sends the packet. This ensures the AH calculation is done 3643 on the packet in the form it will have on the receiver after 3644 advancing the routing header. 3646 Following the definition of a type 2 routing header in Section 6.4, 3647 this packet will be routed to the mobile node's care-of address, 3648 where it will be delivered to the mobile node (the mobile node has 3649 associated the care-of address with its network interface). 3651 Note that following the above conceptual model in an implementation 3652 creates some additional requirements for path MTU discovery since the 3653 layer that determines the packet size (e.g., TCP and applications 3654 using UDP) needs to be aware of the size of the headers added by the 3655 IP layer on the sending node. 3657 If, instead, the sending node has no Binding Cache entry for the 3658 destination address to which the packet is being sent, the sending 3659 node simply sends the packet normally, with no routing header. If 3660 the destination node is not a mobile node (or is a mobile node that 3661 is currently at home), the packet will be delivered directly to this 3662 node and processed normally by it. If, however, the destination node 3663 is a mobile node that is currently away from home, the packet will be 3664 intercepted by the mobile node's home agent and tunneled to the 3665 mobile node's current primary care-of address. 3667 9.3.3. Sending Binding Error Messages 3669 Section 9.2 and Section 9.3.1 describe error conditions that lead to 3670 a need to send a Binding Error message. 3672 A Binding Error message is sent directly to the address that appeared 3673 in the IPv6 Source Address field of the offending packet. If the 3674 Source Address field does not contain a unicast address, the Binding 3675 Error message MUST NOT be sent. 3677 The Home Address field in the Binding Error message MUST be copied 3678 from the Home Address field in the Home Address destination option of 3679 the offending packet, or set to the unspecified address if no such 3680 option appeared in the packet. 3682 Note that the IPv6 Source Address and Home Address field values 3683 discussed above are the values from the wire, i.e., before any 3684 modifications possibly performed as specified in Section 9.3.1. 3686 Binding Error messages SHOULD be subject to rate limiting in the same 3687 manner as is done for ICMPv6 messages [17]. 3689 9.3.4. Receiving ICMP Error Messages 3691 When the correspondent node has a Binding Cache entry for a mobile 3692 node, all traffic destined to the mobile node goes directly to the 3693 current care-of address of the mobile node using a routing header. 3694 Any ICMP error message caused by packets on their way to the care-of 3695 address will be returned in the normal manner to the correspondent 3696 node. 3698 On the other hand, if the correspondent node has no Binding Cache 3699 entry for the mobile node, the packet will be routed through the 3700 mobile node's home link. Any ICMP error message caused by the packet 3701 on its way to the mobile node while in the tunnel, will be 3702 transmitted to the mobile node's home agent. By the definition of 3703 IPv6 encapsulation [7], the home agent MUST relay certain ICMP error 3704 messages back to the original sender of the packet, which in this 3705 case is the correspondent node. 3707 Thus, in all cases, any meaningful ICMP error messages caused by 3708 packets from a correspondent node to a mobile node will be returned 3709 to the correspondent node. If the correspondent node receives 3710 persistent ICMP Destination Unreachable messages after sending 3711 packets to a mobile node based on an entry in its Binding Cache, the 3712 correspondent node SHOULD delete this Binding Cache entry. Note that 3713 if the mobile node continues to send packets with the Home Address 3714 destination option to this correspondent node, they will be dropped 3715 due to the lack of a binding. For this reason it is important that 3716 only persistent ICMP messages lead to the deletion of the Binding 3717 Cache entry. 3719 9.4. Return Routability Procedure 3721 This subsection specifies actions taken by a correspondent node 3722 during the return routability procedure. 3724 9.4.1. Receiving Home Test Init Messages 3726 Upon receiving a Home Test Init message, the correspondent node 3727 verifies the following: 3729 o The packet MUST NOT include a Home Address destination option. 3731 Any packet carrying a Home Test Init message which fails to satisfy 3732 this test MUST be silently ignored. 3734 Otherwise, in preparation for sending the corresponding Home Test 3735 Message, the correspondent node checks that it has the necessary 3736 material to engage in a return routability procedure, as specified in 3737 Section 5.2. The correspondent node MUST have a secret Kcn and a 3738 nonce. If it does not have this material yet, it MUST produce it 3739 before continuing with the return routability procedure. 3741 Section 9.4.3 specifies further processing. 3743 9.4.2. Receiving Care-of Test Init Messages 3745 Upon receiving a Care-of Test Init message, the correspondent node 3746 verifies the following: 3748 o The packet MUST NOT include a Home Address destination option. 3750 Any packet carrying a Care-of Test Init message which fails to 3751 satisfy this test MUST be silently ignored. 3753 Otherwise, in preparation for sending the corresponding Care-of Test 3754 Message, the correspondent node checks that it has the necessary 3755 material to engage in a return routability procedure in the manner 3756 described in Section 9.4.1. 3758 Section 9.4.4 specifies further processing. 3760 9.4.3. Sending Home Test Messages 3762 The correspondent node creates a home keygen token and uses the 3763 current nonce index as the Home Nonce Index. It then creates a Home 3764 Test message (Section 6.1.5) and sends it to the mobile node at the 3765 latter's home address. 3767 9.4.4. Sending Care-of Test Messages 3769 The correspondent node creates a care-of keygen token and uses the 3770 current nonce index as the Care-of Nonce Index. It then creates a 3771 Care-of Test message (Section 6.1.6) and sends it to the mobile node 3772 at the latter's care-of address. 3774 9.5. Processing Bindings 3776 This section explains how the correspondent node processes messages 3777 related to bindings. These messages are: 3779 o Binding Update 3781 o Binding Refresh Request 3783 o Binding Acknowledgement 3785 o Binding Error 3787 9.5.1. Receiving Binding Updates 3789 Before accepting a Binding Update, the receiving node MUST validate 3790 the Binding Update according to the following tests: 3792 o The packet MUST contain a unicast routable home address, either in 3793 the Home Address option or in the Source Address, if the Home 3794 Address option is not present. 3796 o The Sequence Number field in the Binding Update is greater than 3797 the Sequence Number received in the previous valid Binding Update 3798 for this home address, if any. 3800 If the receiving node has no Binding Cache entry for the indicated 3801 home address, it MUST accept any Sequence Number value in a 3802 received Binding Update from this mobile node. 3804 This Sequence Number comparison MUST be performed modulo 2**16, 3805 i.e., the number is a free running counter represented modulo 3806 65536. A Sequence Number in a received Binding Update is 3807 considered less than or equal to the last received number if its 3808 value lies in the range of the last received number and the 3809 preceding 32768 values, inclusive. For example, if the last 3810 received sequence number was 15, then messages with sequence 3811 numbers 0 through 15, as well as 32783 through 65535, would be 3812 considered less than or equal. 3814 When the Home Registration (H) bit is not set, the following are also 3815 required: 3817 o A Nonce Indices mobility option MUST be present, and the Home and 3818 Care-of Nonce Index values in this option MUST be recent enough to 3819 be recognized by the correspondent node. (Care-of Nonce Index 3820 values are not inspected for requests to delete a binding.) 3822 o The correspondent node MUST re-generate the home keygen token and 3823 the care-of keygen token from the information contained in the 3824 packet. It then generates the binding management key Kbm and uses 3825 it to verify the authenticator field in the Binding Update as 3826 specified in Section 6.1.7. 3828 o The Binding Authorization Data mobility option MUST be present, 3829 and its contents MUST satisfy rules presented in Section 5.2.6. 3830 Note that a care-of address different from the Source Address MAY 3831 have been specified by including an Alternate Care-of Address 3832 mobility option in the Binding Update. When such a message is 3833 received and the return routability procedure is used as an 3834 authorization method, the correspondent node MUST verify the 3835 authenticator by using the address within the Alternate Care-of 3836 Address in the calculations. 3838 o The Binding Authorization Data mobility option MUST be the last 3839 option and MUST NOT have trailing padding. 3841 If the Home Registration (H) bit is set, the Nonce Indices mobility 3842 option MUST NOT be present. 3844 If the mobile node sends a sequence number which is not greater than 3845 the sequence number from the last valid Binding Update for this home 3846 address, then the receiving node MUST send back a Binding 3847 Acknowledgement with status code 135, and the last accepted sequence 3848 number in the Sequence Number field of the Binding Acknowledgement. 3850 If a binding already exists for the given home address and the home 3851 registration flag has a different value than the Home Registration 3852 (H) bit in the Binding Update, then the receiving node MUST send back 3853 a Binding Acknowledgement with status code 139 (registration type 3854 change disallowed). The home registration flag stored in the Binding 3855 Cache entry MUST NOT be changed. 3857 If the receiving node no longer recognizes the Home Nonce Index 3858 value, Care-of Nonce Index value, or both values from the Binding 3859 Update, then the receiving node MUST send back a Binding 3860 Acknowledgement with status code 136, 137, or 138, respectively. 3862 Packets carrying Binding Updates that fail to satisfy all of these 3863 tests for any reason other than insufficiency of the Sequence Number, 3864 registration type change, or expired nonce index values, MUST be 3865 silently discarded. 3867 If the Binding Update is valid according to the tests above, then the 3868 Binding Update is processed further as follows: 3870 o The Sequence Number value received from a mobile node in a Binding 3871 Update is stored by the receiving node in its Binding Cache entry 3872 for the given home address. 3874 o If the Lifetime specified in the Binding Update is not zero, then 3875 this is a request to cache a binding for the home address. If the 3876 Home Registration (H) bit is set in the Binding Update, the 3877 Binding Update is processed according to the procedure specified 3878 in Section 10.3.1; otherwise, it is processed according to the 3879 procedure specified in Section 9.5.2. 3881 o If the Lifetime specified in the Binding Update is zero, then this 3882 is a request to delete the cached binding for the home address. 3883 In this case, the Binding Update MUST include a valid home nonce 3884 index, and the care-of nonce index MUST be ignored by the 3885 correspondent node. The generation of the binding management key 3886 depends then exclusively on the home keygen token (Section 5.2.5). 3887 If the Home Registration (H) bit is set in the Binding Update, the 3888 Binding Update is processed according to the procedure specified 3889 in Section 10.3.2; otherwise, it is processed according to the 3890 procedure specified in Section 9.5.3. 3892 The specified care-of address MUST be determined as follows: 3894 o If the Alternate Care-of Address option is present, the care-of 3895 address is the address in that option. 3897 o Otherwise, the care-of address is the Source Address field in the 3898 packet's IPv6 header. 3900 The home address for the binding MUST be determined as follows: 3902 o If the Home Address destination option is present, the home 3903 address is the address in that option. 3905 o Otherwise, the home address is the Source Address field in the 3906 packet's IPv6 header. 3908 9.5.2. Requests to Cache a Binding 3910 This section describes the processing of a valid Binding Update that 3911 requests a node to cache a binding, for which the Home Registration 3912 (H) bit is not set in the Binding Update. 3914 In this case, the receiving node SHOULD create a new entry in its 3915 Binding Cache for this home address, or update its existing Binding 3916 Cache entry for this home address, if such an entry already exists. 3917 The lifetime for the Binding Cache entry is initialized from the 3918 Lifetime field specified in the Binding Update, although this 3919 lifetime MAY be reduced by the node caching the binding; the lifetime 3920 for the Binding Cache entry MUST NOT be greater than the Lifetime 3921 value specified in the Binding Update. Any Binding Cache entry MUST 3922 be deleted after the expiration of its lifetime. 3924 Note that if the mobile node did not request a Binding 3925 Acknowledgement, then it is not aware of the selected shorter 3926 lifetime. The mobile node may thus use route optimization and send 3927 packets with the Home Address destination option. As discussed in 3928 Section 9.3.1, such packets will be dropped if there is no binding. 3929 This situation is recoverable, but can cause temporary packet loss. 3931 The correspondent node MAY refuse to accept a new Binding Cache entry 3932 if it does not have sufficient resources. A new entry MAY also be 3933 refused if the correspondent node believes its resources are utilized 3934 more efficiently in some other purpose, such as serving another 3935 mobile node with higher amount of traffic. In both cases the 3936 correspondent node SHOULD return a Binding Acknowledgement with 3937 status value 130. 3939 9.5.3. Requests to Delete a Binding 3941 This section describes the processing of a valid Binding Update that 3942 requests a node to delete a binding when the Home Registration (H) 3943 bit is not set in the Binding Update. 3945 Any existing binding for the given home address MUST be deleted. A 3946 Binding Cache entry for the home address MUST NOT be created in 3947 response to receiving the Binding Update. 3949 If the Binding Cache entry was created by use of return routability 3950 nonces, the correspondent node MUST ensure that the same nonces are 3951 not used again with the particular home and care-of address. If both 3952 nonces are still valid, the correspondent node has to remember the 3953 particular combination of nonce indexes, addresses, and sequence 3954 number as illegal until at least one of the nonces has become too 3955 old. 3957 9.5.4. Sending Binding Acknowledgements 3959 A Binding Acknowledgement may be sent to indicate receipt of a 3960 Binding Update as follows: 3962 o If the Binding Update was discarded as described in Section 9.2 or 3963 Section 9.5.1, a Binding Acknowledgement MUST NOT be sent. 3964 Otherwise the treatment depends on the following rules. 3966 o If the Acknowledge (A) bit is set in the Binding Update, a Binding 3967 Acknowledgement MUST be sent. Otherwise, the treatment depends on 3968 the next rule. 3970 o If the node rejects the Binding Update due to an expired nonce 3971 index, sequence number being out of window (Section 9.5.1), or 3972 insufficiency of resources (Section 9.5.2), a Binding 3973 Acknowledgement MUST be sent. If the node accepts the Binding 3974 Update, the Binding Acknowledgement SHOULD NOT be sent. 3976 If the node accepts the Binding Update and creates or updates an 3977 entry for this binding, the Status field in the Binding 3978 Acknowledgement MUST be set to a value less than 128. Otherwise, the 3979 Status field MUST be set to a value greater than or equal to 128. 3980 Values for the Status field are described in Section 6.1.8 and in the 3981 IANA registry of assigned numbers [29]. 3983 If the Status field in the Binding Acknowledgement contains the value 3984 136 (expired home nonce index), 137 (expired care-of nonce index), or 3985 138 (expired nonces) then the message MUST NOT include the Binding 3986 Authorization Data mobility option. Otherwise, the Binding 3987 Authorization Data mobility option MUST be included, and MUST meet 3988 the specific authentication requirements for Binding Acknowledgements 3989 as defined in Section 5.2. 3991 If the Source Address field of the IPv6 header that carried the 3992 Binding Update does not contain a unicast address, the Binding 3993 Acknowledgement MUST NOT be sent and the Binding Update packet MUST 3994 be silently discarded. Otherwise, the acknowledgement MUST be sent 3995 to the Source Address. Unlike the treatment of regular packets, this 3996 addressing procedure does not use information from the Binding Cache. 3998 However, a routing header is needed in some cases. If the Source 3999 Address is the home address of the mobile node, i.e., the Binding 4000 Update did not contain a Home Address destination option, then the 4001 Binding Acknowledgement MUST be sent to that address and the routing 4002 header MUST NOT be used. Otherwise, the Binding Acknowledgement MUST 4003 be sent using a type 2 routing header which contains the mobile 4004 node's home address. 4006 9.5.5. Sending Binding Refresh Requests 4008 If a Binding Cache entry being deleted is still in active use when 4009 sending packets to a mobile node, then the next packet sent to the 4010 mobile node will be routed normally to the mobile node's home link. 4011 Communication with the mobile node continues, but the tunneling from 4012 the home network creates additional overhead and latency in 4013 delivering packets to the mobile node. 4015 If the sender knows that the Binding Cache entry is still in active 4016 use, it MAY send a Binding Refresh Request message to the mobile node 4017 in an attempt to avoid this overhead and latency due to deleting and 4018 recreating the Binding Cache entry. This message is always sent to 4019 the home address of the mobile node. 4021 The correspondent node MAY retransmit Binding Refresh Request 4022 messages as long as the rate limitation is applied. The 4023 correspondent node MUST stop retransmitting when it receives a 4024 Binding Update. 4026 9.6. Cache Replacement Policy 4028 Conceptually, a node maintains a separate timer for each entry in its 4029 Binding Cache. When creating or updating a Binding Cache entry in 4030 response to a received and accepted Binding Update, the node sets the 4031 timer for this entry to the specified Lifetime period. Any entry in 4032 a node's Binding Cache MUST be deleted after the expiration of the 4033 Lifetime specified in the Binding Update from which the entry was 4034 created or last updated. 4036 Each node's Binding Cache will, by necessity, have a finite size. A 4037 node MAY use any reasonable local policy for managing the space 4038 within its Binding Cache. 4040 A node MAY choose to drop any entry already in its Binding Cache in 4041 order to make space for a new entry. For example, a "least-recently 4042 used" (LRU) strategy for cache entry replacement among entries should 4043 work well, unless the size of the Binding Cache is substantially 4044 insufficient. When entries are deleted, the correspondent node MUST 4045 follow the rules in Section 5.2.8 in order to guard the return 4046 routability procedure against replay attacks. 4048 If the node sends a packet to a destination for which it has dropped 4049 the entry from its Binding Cache, the packet will be routed through 4050 the mobile node's home link. The mobile node can detect this and 4051 establish a new binding if necessary. 4053 However, if the mobile node believes that the binding still exists, 4054 it may use route optimization and send packets with the Home Address 4055 destination option. This can create temporary packet loss, as 4056 discussed earlier, in the context of binding lifetime reductions 4057 performed by the correspondent node (Section 9.5.2). 4059 10. Home Agent Operation 4061 10.1. Conceptual Data Structures 4063 Each home agent MUST maintain a Binding Cache and Home Agents List. 4065 The rules for maintaining a Binding Cache are the same for home 4066 agents and correspondent nodes and have already been described in 4067 Section 9.1. 4069 The Home Agents List is maintained by each home agent, recording 4070 information about each router on the same link that is acting as a 4071 home agent. This list is used by the dynamic home agent address 4072 discovery mechanism. A router is known to be acting as a home agent, 4073 if it sends a Router Advertisement in which the Home Agent (H) bit is 4074 set. When the lifetime for a list entry (defined below) expires, 4075 that entry is removed from the Home Agents List. The Home Agents 4076 List is similar to the Default Router List conceptual data structure 4077 maintained by each host for Neighbor Discovery [18]. The Home Agents 4078 List MAY be implemented in any manner consistent with the external 4079 behavior described in this document. 4081 Each home agent maintains a separate Home Agents List for each link 4082 on which it is serving as a home agent. A new entry is created or an 4083 existing entry is updated in response to receipt of a valid Router 4084 Advertisement in which the Home Agent (H) bit is set. Each Home 4085 Agents List entry conceptually contains the following fields: 4087 o The link-local IP address of a home agent on the link. This 4088 address is learned through the Source Address of the Router 4089 Advertisements [18] received from the router. 4091 o One or more global IP addresses for this home agent. Global 4092 addresses are learned through Prefix Information options with the 4093 Router Address (R) bit set and received in Router Advertisements 4094 from this link-local address. Global addresses for the router in 4095 a Home Agents List entry MUST be deleted once the prefix 4096 associated with that address is no longer valid [18]. 4098 o The remaining lifetime of this Home Agents List entry. If a Home 4099 Agent Information Option is present in a Router Advertisement 4100 received from a home agent, the lifetime of the Home Agents List 4101 entry representing that home agent is initialized from the Home 4102 Agent Lifetime field in the option (if present); otherwise, the 4103 lifetime is initialized from the Router Lifetime field in the 4104 received Router Advertisement. If Home Agents List entry lifetime 4105 reaches zero, the entry MUST be deleted from the Home Agents List. 4107 o The preference for this home agent; higher values indicate a more 4108 preferable home agent. The preference value is taken from the 4109 Home Agent Preference field in the received Router Advertisement, 4110 if the Router Advertisement contains a Home Agent Information 4111 Option and is otherwise set to the default value of 0. A home 4112 agent uses this preference in ordering the Home Agents List when 4113 it sends an ICMP Home Agent Address Discovery message. 4115 10.2. Processing Mobility Headers 4117 All IPv6 home agents MUST observe the rules described in Section 9.2 4118 when processing Mobility Headers. 4120 10.3. Processing Bindings 4122 10.3.1. Primary Care-of Address Registration 4124 When a node receives a Binding Update, it MUST validate it and 4125 determine the type of Binding Update according to the steps described 4126 in Section 9.5.1. Furthermore, it MUST authenticate the Binding 4127 Update as described in Section 5.1. An authorization step specific 4128 for the home agent is also needed to ensure that only the right node 4129 can control a particular home address. This is provided through the 4130 home address unequivocally identifying the security association that 4131 must be used. 4133 This section describes the processing of a valid and authorized 4134 Binding Update when it requests the registration of the mobile node's 4135 primary care-of address. 4137 To begin processing the Binding Update, the home agent MUST perform 4138 the following sequence of tests: 4140 o If the node implements only correspondent node functionality, or 4141 has not been configured to act as a home agent, then the node MUST 4142 reject the Binding Update. The node MUST also return a Binding 4143 Acknowledgement to the mobile node, in which the Status field is 4144 set to 131 (home registration not supported). 4146 o Else, if the home address for the binding (the Home Address field 4147 in the packet's Home Address option) is not an on-link IPv6 4148 address with respect to the home agent's current Prefix List, then 4149 the home agent MUST reject the Binding Update and SHOULD return a 4150 Binding Acknowledgement to the mobile node, in which the Status 4151 field is set to 132 (not home subnet). 4153 o Else, if the home agent chooses to reject the Binding Update for 4154 any other reason (e.g., insufficient resources to serve another 4155 mobile node as a home agent), then the home agent SHOULD return a 4156 Binding Acknowledgement to the mobile node, in which the Status 4157 field is set to an appropriate value to indicate the reason for 4158 the rejection. 4160 o A Home Address destination option MUST be present in the message. 4161 It MUST be validated as described in Section 9.3.1 with the 4162 following additional rule. The Binding Cache entry existence test 4163 MUST NOT be done for IPsec packets when the Home Address option 4164 contains an address for which the receiving node could act as a 4165 home agent. 4167 If home agent accepts the Binding Update, it MUST then create a new 4168 entry in its Binding Cache for this mobile node or update its 4169 existing Binding Cache entry, if such an entry already exists. The 4170 Home Address field as received in the Home Address option provides 4171 the home address of the mobile node. 4173 The home agent MUST mark this Binding Cache entry as a home 4174 registration to indicate that the node is serving as a home agent for 4175 this binding. Binding Cache entries marked as a home registration 4176 MUST be excluded from the normal cache replacement policy used for 4177 the Binding Cache (Section 9.6) and MUST NOT be removed from the 4178 Binding Cache until the expiration of the Lifetime period. 4180 Unless this home agent already has a binding for the given home 4181 address, the home agent MUST perform Duplicate Address Detection [19] 4182 on the mobile node's home link before returning the Binding 4183 Acknowledgement. This ensures that no other node on the home link 4184 was using the mobile node's home address when the Binding Update 4185 arrived. If this Duplicate Address Detection fails for the given 4186 home address or an associated link local address, then the home agent 4187 MUST reject the complete Binding Update and MUST return a Binding 4188 Acknowledgement to the mobile node, in which the Status field is set 4189 to 134 (Duplicate Address Detection failed). When the home agent 4190 sends a successful Binding Acknowledgement to the mobile node, the 4191 home agent assures to the mobile node that its address(es) will be 4192 kept unique by the home agent for as long as the lifetime was granted 4193 for the binding. 4195 The specific addresses, which are to be tested before accepting the 4196 Binding Update and later to be defended by performing Duplicate 4197 Address Detection, depend on the setting of the Link-Local Address 4198 Compatibility (L) bit, as follows: 4200 o L=0: Defend only the given address. Do not derive a link-local 4201 address. 4203 o L=1: Defend both the given non link-local unicast (home) address 4204 and the derived link-local. The link-local address is derived by 4205 replacing the subnet prefix in the mobile node's home address with 4206 the link-local prefix. 4208 The lifetime of the Binding Cache entry depends on a number of 4209 factors: 4211 o The lifetime for the Binding Cache entry MUST NOT be greater than 4212 the Lifetime value specified in the Binding Update. 4214 o The lifetime for the Binding Cache entry MUST NOT be greater than 4215 the remaining valid lifetime for the subnet prefix in the mobile 4216 node's home address specified with the Binding Update. The 4217 remaining valid lifetime for this prefix is determined by the home 4218 agent based on its own Prefix List entry [18]. 4220 The remaining preferred lifetime SHOULD NOT have any impact on the 4221 lifetime for the Binding Cache entry. 4223 The home agent MUST remove a binding when the valid lifetime of 4224 the prefix associated with it expires. 4226 o The home agent MAY further decrease the specified lifetime for the 4227 binding, for example based on a local policy. The resulting 4228 lifetime is stored by the home agent in the Binding Cache entry, 4229 and this Binding Cache entry MUST be deleted by the home agent 4230 after the expiration of this lifetime. 4232 Regardless of the setting of the Acknowledge (A) bit in the Binding 4233 Update, the home agent MUST return a Binding Acknowledgement to the 4234 mobile node constructed as follows: 4236 o The Status field MUST be set to a value indicating success. The 4237 value 1 (accepted but prefix discovery necessary) MUST be used if 4238 the subnet prefix of the specified home address is deprecated, or 4239 becomes deprecated during the lifetime of the binding, or becomes 4240 invalid at the end of the lifetime. The value 0 MUST be used 4241 otherwise. For the purposes of comparing the binding and prefix 4242 lifetimes, the prefix lifetimes are first converted into units of 4243 four seconds by ignoring the two least significant bits. 4245 o The Key Management Mobility Capability (K) bit is set if the 4246 following conditions are all fulfilled, and cleared otherwise: 4248 * The Key Management Mobility Capability (K) bit was set in the 4249 Binding Update. 4251 * The IPsec security associations between the mobile node and the 4252 home agent have been established dynamically. 4254 * The home agent has the capability to update its endpoint in the 4255 used key management protocol to the new care-of address every 4256 time it moves. 4258 Depending on the final value of the bit in the Binding 4259 Acknowledgement, the home agent SHOULD perform the following 4260 actions: 4262 K = 0 4264 Discard key management connections, if any, to the old care-of 4265 address. If the mobile node did not have a binding before 4266 sending this Binding Update, discard the connections to the 4267 home address. 4269 K = 1 4271 Move the peer endpoint of the key management protocol 4272 connection, if any, to the new care-of address. 4274 o The Sequence Number field MUST be copied from the Sequence Number 4275 given in the Binding Update. 4277 o The Lifetime field MUST be set to the remaining lifetime for the 4278 binding as set by the home agent in its home registration Binding 4279 Cache entry for the mobile node, as described above. 4281 o If the home agent stores the Binding Cache entry in nonvolatile 4282 storage, then the Binding Refresh Advice mobility option MUST be 4283 omitted. Otherwise, the home agent MAY include this option to 4284 suggest that the mobile node refreshes its binding before the 4285 actual lifetime of the binding ends. 4287 If the Binding Refresh Advice mobility option is present, the 4288 Refresh Interval field in the option MUST be set to a value less 4289 than the Lifetime value being returned in the Binding 4290 Acknowledgement. This indicates that the mobile node SHOULD 4291 attempt to refresh its home registration at the indicated shorter 4292 interval. The home agent MUST still retain the registration for 4293 the Lifetime period, even if the mobile node does not refresh its 4294 registration within the Refresh period. 4296 The rules for selecting the Destination IP address (and possibly 4297 routing header construction) for the Binding Acknowledgement to the 4298 mobile node are the same as in Section 9.5.4. 4300 In addition, the home agent MUST follow the procedure defined in 4301 Section 10.4.1 to intercept packets on the mobile node's home link 4302 addressed to the mobile node, while the home agent is serving as the 4303 home agent for this mobile node. The home agent MUST also be 4304 prepared to accept reverse tunneled packets from the new care-of 4305 address of the mobile node, as described in Section 10.4.5. Finally, 4306 the home agent MUST also propagate new home network prefixes, as 4307 described in Section 10.6. 4309 10.3.2. Primary Care-of Address De-Registration 4311 A binding may need to be de-registered when the mobile node returns 4312 home or when the mobile node knows that it will not have any care-of 4313 addresses in the visited network. 4315 A Binding Update is validated and authorized in the manner described 4316 in the previous section; note that when the mobile node de-registers 4317 when it is at home, it MAY choose to omit the Home Address 4318 destination option, in which case the mobile node's home address is 4319 the source IP address of the de-registration Binding Update. This 4320 section describes the processing of a valid Binding Update that 4321 requests the receiving node to no longer serve as its home agent, de- 4322 registering its primary care-of address. 4324 To begin processing the Binding Update, the home agent MUST perform 4325 the following test: 4327 o If the receiving node has no entry marked as a home registration 4328 in its Binding Cache for this mobile node, then this node MUST 4329 reject the Binding Update and SHOULD return a Binding 4330 Acknowledgement to the mobile node, in which the Status field is 4331 set to 133 (not home agent for this mobile node). 4333 If the home agent does not reject the Binding Update as described 4334 above, then the home agent MUST return a Binding Acknowledgement to 4335 the mobile node, constructed as follows: 4337 o The Status field MUST be set to a value 0, indicating success. 4339 o The Key Management Mobility Capability (K) bit is set or cleared 4340 and actions based on its value are performed as described in the 4341 previous section. The mobile node's home address is used as its 4342 new care-of address for the purposes of moving the key management 4343 connection to a new endpoint. 4345 o The Sequence Number field MUST be copied from the Sequence Number 4346 given in the Binding Update. 4348 o The Lifetime field MUST be set to zero. 4350 o The Binding Refresh Advice mobility option MUST be omitted. 4352 The rules for selecting the Destination IP address (and, if required, 4353 routing header construction) for the Binding Acknowledgement to the 4354 mobile node are the same as in the previous section. When the Status 4355 field in the Binding Acknowledgement is greater than or equal to 128 4356 and the Source Address of the Binding Update is on the home link, and 4357 the Binding Update came from a mobile node on the same link, the home 4358 agent MUST send it to the mobile node's link layer address (retrieved 4359 either from the Binding Update or through Neighbor Solicitation). 4361 When a mobile node sends a Binding Update to refresh the binding from 4362 the visited link and soon after moves to the home link and sends a 4363 de-registration Binding Update, a race condition can happen if the 4364 first Binding Update gets delayed. The delayed Binding Update can 4365 cause the home agent to create a new Binding Cache entry for a mobile 4366 node that had just attached to the home link and successfully deleted 4367 the binding. This would prevent the mobile node from using its home 4368 address from the home link. 4370 In order to prevent this, the home agent SHOULD NOT remove the 4371 Binding Cache entry immediately after receiving the deregistration 4372 Binding Update from the mobile node. It SHOULD mark the Binding 4373 Cache entry as invalid, and MUST stop intercepting packets on the 4374 mobile node's home link that are addressed to the mobile node 4375 (Section 10.4.1). The home agent should wait for 4376 MAX_DELETE_BCE_TIMEOUT (Section 12) seconds before removing the 4377 Binding Cache entry completely. In the scenario described above, if 4378 the home agent receives the delayed Binding Update that the mobile 4379 node sent from the visited link, it would reject the message since 4380 the sequence number would be less than the last received 4381 deregistration Binding Update from the home link. The home agent 4382 would then send a Binding Acknowledgment with status '135' (Sequence 4383 number out of window) to the care of address on the visited link. 4384 The mobile node can continue using the home address from the home 4385 link. 4387 10.4. Packet Processing 4389 10.4.1. Intercepting Packets for a Mobile Node 4391 While a node is serving as the home agent for a mobile node it MUST 4392 attempt to intercept packets on the mobile node's home link that are 4393 addressed to the mobile node. 4395 In order to do this, when a node begins serving as the home agent it 4396 MUST have performed Duplicate Address Detection (as specified in 4397 Section 10.3.1), and subsequently it MUST multicast onto the home 4398 link a Neighbor Advertisement message [18] on behalf of the mobile 4399 node. For the home address specified in the Binding Update, the home 4400 agent sends a Neighbor Advertisement message [18] to the all-nodes 4401 multicast address on the home link to advertise the home agent's own 4402 link-layer address for this IP address on behalf of the mobile node. 4403 If the Link-Layer Address Compatibility (L) flag has been specified 4404 in the Binding Update, the home agent MUST do the same for the link- 4405 local address of the mobile node. 4407 All fields in each Neighbor Advertisement message SHOULD be set in 4408 the same way they would be set by the mobile node if it was sending 4409 this Neighbor Advertisement [18] while at home, with the following 4410 exceptions: 4412 o The Target Address in the Neighbor Advertisement MUST be set to 4413 the specific IP address for the mobile node. 4415 o The Advertisement MUST include a Target Link-layer Address option 4416 specifying the home agent's link-layer address. 4418 o The Router (R) bit in the Advertisement MUST be set to zero. 4420 o The Solicited Flag (S) in the Advertisement MUST NOT be set, since 4421 it was not solicited by any Neighbor Solicitation. 4423 o The Override Flag (O) in the Advertisement MUST be set, indicating 4424 that the Advertisement SHOULD override any existing Neighbor Cache 4425 entry at any node receiving it. 4427 o The Source Address in the IPv6 header MUST be set to the home 4428 agent's IP address on the interface used to send the 4429 advertisement. 4431 Any node on the home link that receives one of the Neighbor 4432 Advertisement messages (described above) will update its Neighbor 4433 Cache to associate the mobile node's address with the home agent's 4434 link layer address, causing it to transmit any future packets 4435 normally destined to the mobile node to the mobile node's home agent. 4436 Since multicasting on the local link (such as Ethernet) is typically 4437 not guaranteed to be reliable, the home agent MAY retransmit this 4438 Neighbor Advertisement message up to MAX_NEIGHBOR_ADVERTISEMENT (see 4439 [18]) times to increase its reliability. It is still possible that 4440 some nodes on the home link will not receive any of the Neighbor 4441 Advertisements, but these nodes will eventually be able to detect the 4442 link-layer address change for the mobile node's address through use 4443 of Neighbor Unreachability Detection [18]. 4445 While a node is serving as a home agent for some mobile node, the 4446 home agent uses IPv6 Neighbor Discovery [18] to intercept unicast 4447 packets on the home link addressed to the mobile node. In order to 4448 intercept packets in this way, the home agent MUST act as a proxy for 4449 this mobile node and reply to any received Neighbor Solicitations for 4450 it. When a home agent receives a Neighbor Solicitation, it MUST 4451 check if the Target Address specified in the message matches the 4452 address of any mobile node for which it has a Binding Cache entry 4453 marked as a home registration. 4455 If such an entry exists in the home agent's Binding Cache, the home 4456 agent MUST reply to the Neighbor Solicitation with a Neighbor 4457 Advertisement giving the home agent's own link-layer address as the 4458 link-layer address for the specified Target Address. In addition, 4459 the Router (R) bit in the Advertisement MUST be set to zero. Acting 4460 as a proxy in this way allows other nodes on the mobile node's home 4461 link to resolve the mobile node's address and for the home agent to 4462 defend these addresses on the home link for Duplicate Address 4463 Detection [18]. 4465 10.4.2. Processing Intercepted Packets 4467 For any packet sent to a mobile node from the mobile node's home 4468 agent (in which the home agent is the original sender of the packet), 4469 the home agent is operating as a correspondent node of the mobile 4470 node for this packet and the procedures described in Section 9.3.2 4471 apply. The home agent then uses a routing header to route the packet 4472 to the mobile node by way of the primary care-of address in the home 4473 agent's Binding Cache. 4475 While the mobile node is away from home, the home agent intercepts 4476 any packets on the home link addressed to the mobile node's home 4477 address, as described in Section 10.4.1. In order to forward each 4478 intercepted packet to the mobile node, the home agent MUST tunnel the 4479 packet to the mobile node using IPv6 encapsulation [7]. When a home 4480 agent encapsulates an intercepted packet for forwarding to the mobile 4481 node, the home agent sets the Source Address in the new tunnel IP 4482 header to the home agent's own IP address and sets the Destination 4483 Address in the tunnel IP header to the mobile node's primary care-of 4484 address. When received by the mobile node, normal processing of the 4485 tunnel header [7] will result in decapsulation and processing of the 4486 original packet by the mobile node. 4488 However, packets addressed to the mobile node's link-local address 4489 MUST NOT be tunneled to the mobile node. Instead, these packets MUST 4490 be discarded and the home agent SHOULD return an ICMP Destination 4491 Unreachable, Code 3, message to the packet's Source Address (unless 4492 this Source Address is a multicast address). 4494 Interception and tunneling of the following multicast addressed 4495 packets on the home network are only done if the home agent supports 4496 multicast group membership control messages from the mobile node as 4497 described in the next section. Tunneling of multicast packets to a 4498 mobile node follows similar limitations to those defined above for 4499 unicast packets addressed to the mobile node's link-local address. 4500 Multicast packets addressed to a multicast address with link-local 4501 scope [16], to which the mobile node is subscribed, MUST NOT be 4502 tunneled to the mobile node. These packets SHOULD be silently 4503 discarded (after delivering to other local multicast recipients). 4504 Multicast packets addressed to a multicast address with a scope 4505 larger than link-local, but smaller than global (e.g., site-local and 4506 organization-local [16]), to which the mobile node is subscribed, 4507 SHOULD NOT be tunneled to the mobile node. Multicast packets 4508 addressed with a global scope, to which the mobile node has 4509 successfully subscribed, MUST be tunneled to the mobile node. 4511 Before tunneling a packet to the mobile node, the home agent MUST 4512 perform any IPsec processing as indicated by the security policy data 4513 base. 4515 10.4.3. Multicast Membership Control 4517 This section is a prerequisite for the multicast data packet 4518 forwarding, described in the previous section. If this support is 4519 not provided, multicast group membership control messages are 4520 silently ignored. 4522 In order to forward multicast data packets from the home network to 4523 all the proper mobile nodes, the home agent SHOULD be capable of 4524 receiving tunneled multicast group membership control information 4525 from the mobile node in order to determine which groups the mobile 4526 node has subscribed to. These multicast group membership messages 4527 are Listener Report messages specified in MLD [9] or in other 4528 protocols such as [39]. 4530 The messages are issued by the mobile node, but sent through the 4531 reverse tunnel to the home agent. These messages are issued whenever 4532 the mobile node decides to enable reception of packets for a 4533 multicast group or in response to an MLD Query from the home agent. 4534 The mobile node will also issue multicast group control messages to 4535 disable reception of multicast packets when it is no longer 4536 interested in receiving multicasts for a particular group. 4538 To obtain the mobile node's current multicast group membership the 4539 home agent must periodically transmit MLD Query messages through the 4540 tunnel to the mobile node. These MLD periodic transmissions will 4541 ensure the home agent has an accurate record of the groups in which 4542 the mobile node is interested despite packet losses of the mobile 4543 node's MLD group membership messages. 4545 All MLD packets are sent directly between the mobile node and the 4546 home agent. Since all of these packets are destined to a link-scope 4547 multicast address and have a hop limit of 1, there is no direct 4548 forwarding of such packets between the home network and the mobile 4549 node. The MLD packets between the mobile node and the home agent are 4550 encapsulated within the same tunnel header used for other packet 4551 flows between the mobile node and home agent. 4553 Note that at this time, even though a link-local source is used on 4554 MLD packets, no functionality depends on these addresses being 4555 unique, nor do they elicit direct responses. All MLD messages are 4556 sent to multicast destinations. To avoid ambiguity on the home 4557 agent, due to mobile nodes which may choose identical link-local 4558 source addresses for their MLD function, it is necessary for the home 4559 agent to identify which mobile node was actually the issuer of a 4560 particular MLD message. This may be accomplished by noting which 4561 tunnel such an MLD arrived by, which IPsec SA was used, or by other 4562 distinguishing means. 4564 This specification puts no requirement on how the functions in this 4565 section and the multicast forwarding in Section 10.4.2 are to be 4566 achieved. At the time of this writing it was thought that a full 4567 IPv6 multicast router function would be necessary on the home agent, 4568 but it may be possible to achieve the same effects through a "proxy 4569 MLD" application coupled with kernel multicast forwarding. This may 4570 be the subject of future specifications. 4572 10.4.4. Stateful Address Autoconfiguration 4574 This section describes how home agents support the use of stateful 4575 address autoconfiguration mechanisms such as DHCPv6 [30] from the 4576 mobile nodes. If this support is not provided, then the M and O bits 4577 must remain cleared on the Mobile Prefix Advertisement Messages. Any 4578 mobile node which sends DHCPv6 messages to the home agent without 4579 this support will not receive a response. 4581 If DHCPv6 is used, packets are sent with link-local source addresses 4582 either to a link-scope multicast address or a link-local address. 4583 Mobile nodes desiring to locate a DHCPv6 service may reverse tunnel 4584 standard DHCPv6 packets to the home agent. Since these link-scope 4585 packets cannot be forwarded onto the home network, it is necessary 4586 for the home agent to either implement a DHCPv6 relay agent or a 4587 DHCPv6 server function itself. The arriving tunnel or IPsec SA of 4588 DHCPv6 link-scope messages from the mobile node must be noted so that 4589 DHCPv6 responses may be sent back to the appropriate mobile node. 4590 DHCPv6 messages sent to the mobile node with a link-local destination 4591 must be tunneled within the same tunnel header used for other packet 4592 flows. 4594 10.4.5. Handling Reverse Tunneled Packets 4596 Unless a binding has been established between the mobile node and a 4597 correspondent node, traffic from the mobile node to the correspondent 4598 node goes through a reverse tunnel. Home agents MUST support reverse 4599 tunneling as follows: 4601 o The tunneled traffic arrives to the home agent's address using 4602 IPv6 encapsulation [7]. 4604 o Depending on the security policies used by the home agent, reverse 4605 tunneled packets MAY be discarded unless accompanied by a valid 4606 ESP header. The support for authenticated reverse tunneling 4607 allows the home agent to protect the home network and 4608 correspondent nodes from malicious nodes masquerading as a mobile 4609 node. 4611 o Otherwise, when a home agent decapsulates a tunneled packet from 4612 the mobile node, the home agent MUST verify that the Source 4613 Address in the tunnel IP header is the mobile node's primary 4614 care-of address. Otherwise, any node in the Internet could send 4615 traffic through the home agent and escape ingress filtering 4616 limitations. This simple check forces the attacker to know the 4617 current location of the real mobile node and be able to defeat 4618 ingress filtering. This check is not necessary if the reverse- 4619 tunneled packet is protected by ESP in tunnel mode. 4621 10.4.6. Protecting Return Routability Packets 4623 The return routability procedure, described in Section 5.2.5, assumes 4624 that the confidentiality of the Home Test Init and Home Test messages 4625 is protected as they are tunneled between the home agent and the 4626 mobile node. Therefore, the home agent MUST support tunnel mode 4627 IPsec ESP for the protection of packets belonging to the return 4628 routability procedure. Support for a non-null encryption transform 4629 and authentication algorithm MUST be available. It is not necessary 4630 to distinguish between different kinds of packets during the return 4631 routability procedure. 4633 Security associations are needed to provide this protection. When 4634 the care-of address for the mobile node changes as a result of an 4635 accepted Binding Update, special treatment is needed for the next 4636 packets sent using these security associations. The home agent MUST 4637 set the new care-of address as the destination address of these 4638 packets, as if the outer header destination address in the security 4639 association had changed. 4641 The above protection SHOULD be used with all mobile nodes. The use 4642 is controlled by configuration of the IPsec security policy database 4643 both at the mobile node and at the home agent. 4645 As described earlier, the Binding Update and Binding Acknowledgement 4646 messages require protection between the home agent and the mobile 4647 node. The Mobility Header protocol carries both these messages as 4648 well as the return routability messages. From the point of view of 4649 the security policy database these messages are indistinguishable. 4650 When IPsec is used to protect return routability signaling or payload 4651 packets, this protection MUST only be applied to the return 4652 routability packets entering the IPv6 encapsulated tunnel interface 4653 between the mobile node and the home agent. This can be achieved, 4654 for instance, by defining the security policy database entries 4655 specifically for the tunnel interface. That is, the policy entries 4656 are not generally applied on all traffic on the physical interface(s) 4657 of the nodes, but rather only on traffic that enters the tunnel. 4658 This makes use of per-interface security policy database entries [3] 4659 specific to the tunnel interface (the node's attachment to the tunnel 4660 [6]). 4662 10.5. Dynamic Home Agent Address Discovery 4664 This section describes an optional mechanism by which a home agent 4665 can help mobile nodes to discover the addresses of other home agents 4666 on the mobile node's home network. The home agent keeps track of the 4667 other home agents on the same link and responds to queries sent by 4668 the mobile node. 4670 10.5.1. Receiving Router Advertisement Messages 4672 For each link on which a router provides service as a home agent, the 4673 router maintains a Home Agents List recording information about all 4674 other home agents on that link. This list is used in the dynamic 4675 home agent address discovery mechanism; the mobile node uses the list 4676 as described in Section 11.4.1. The information for the list is 4677 learned through receipt of the periodic unsolicited multicast Router 4678 Advertisements, in a manner similar to the Default Router List 4679 conceptual data structure maintained by each host for Neighbor 4680 Discovery [18]. In the construction of the Home Agents List, the 4681 Router Advertisements are from each (other) home agent on the link 4682 and the Home Agent (H) bit is set in them. 4684 On receipt of a valid Router Advertisement, as defined in the 4685 processing algorithm specified for Neighbor Discovery [18], the home 4686 agent performs the following steps in addition to any steps already 4687 required of it by Neighbor Discovery: 4689 o If the Home Agent (H) bit in the Router Advertisement is not set, 4690 delete the sending node's entry in the current Home Agents List 4691 (if one exists). Skip all the following steps. 4693 o Otherwise, extract the Source Address from the IP header of the 4694 Router Advertisement. This is the link-local IP address on this 4695 link of the home agent sending this Advertisement [18]. 4697 o Determine the preference for this home agent. If the Router 4698 Advertisement contains a Home Agent Information Option, then the 4699 preference is taken from the Home Agent Preference field in the 4700 option; otherwise, the default preference of 0 MUST be used. 4702 o Determine the lifetime for this home agent. If the Router 4703 Advertisement contains a Home Agent Information Option, then the 4704 lifetime is taken from the Home Agent Lifetime field in the 4705 option; otherwise, the lifetime specified by the Router Lifetime 4706 field in the Router Advertisement SHOULD be used. 4708 o If the link-local address of the home agent sending this 4709 Advertisement is already present in this home agent's Home Agents 4710 List and the received home agent lifetime value is zero, 4711 immediately delete this entry in the Home Agents List. 4713 o Otherwise, if the link-local address of the home agent sending 4714 this Advertisement is already present in the receiving home 4715 agent's Home Agents List, reset its lifetime and preference to the 4716 values determined above. 4718 o If the link-local address of the home agent sending this 4719 Advertisement is not already present in the Home Agents List 4720 maintained by the receiving home agent, and the lifetime for the 4721 sending home agent is non-zero, create a new entry in the list, 4722 and initialize its lifetime and preference to the values 4723 determined above. 4725 o If the Home Agents List entry for the link-local address of the 4726 home agent sending this Advertisement was not deleted as described 4727 above, determine any global address(es) of the home agent based on 4728 each Prefix Information option received in this Advertisement in 4729 which the Router Address (R) bit is set (Section 7.2). Add all 4730 such global addresses to the list of global addresses in this Home 4731 Agents List entry. 4733 A home agent SHOULD maintain an entry in its Home Agents List for 4734 each valid home agent address until that entry's lifetime expires, 4735 after which time the entry MUST be deleted. 4737 As described in Section 11.4.1, a mobile node attempts dynamic home 4738 agent address discovery by sending an ICMP Home Agent Address 4739 Discovery Request message to the Mobile IPv6 Home-Agents anycast 4740 address [8] for its home IP subnet prefix. A home agent receiving a 4741 Home Agent Address Discovery Request message that serves this subnet 4742 SHOULD return an ICMP Home Agent Address Discovery Reply message to 4743 the mobile node with the Source Address of the Reply packet set to 4744 one of the global unicast addresses of the home agent. The Home 4745 Agent Addresses field in the Reply message is constructed as follows: 4747 o The Home Agent Addresses field SHOULD contain all global IP 4748 addresses for each home agent currently listed in this home 4749 agent's own Home Agents List (Section 10.1). 4751 o The IP addresses in the Home Agent Addresses field SHOULD be 4752 listed in order of decreasing preference values, based either on 4753 the respective advertised preference from a Home Agent Information 4754 option or on the default preference of 0 if no preference is 4755 advertised (or on the configured home agent preference for this 4756 home agent itself). 4758 o Among home agents with equal preference, their IP addresses in the 4759 Home Agent Addresses field SHOULD be listed in an order randomized 4760 with respect to other home agents with equal preference every time 4761 a Home Agent Address Discovery Reply message is returned by this 4762 home agent. 4764 o If more than one global IP address is associated with a home 4765 agent, these addresses SHOULD be listed in a randomized order. 4767 o The home agent SHOULD reduce the number of home agent IP addresses 4768 so that the packet fits within the minimum IPv6 MTU [6]. The home 4769 agent addresses selected for inclusion in the packet SHOULD be 4770 those from the complete list with the highest preference. This 4771 limitation avoids the danger of the Reply message packet being 4772 fragmented (or rejected by an intermediate router with an ICMP 4773 Packet Too Big message [17]). 4775 10.6. Sending Prefix Information to the Mobile Node 4777 10.6.1. List of Home Network Prefixes 4779 Mobile IPv6 arranges to propagate relevant prefix information to the 4780 mobile node when it is away from home, so that it may be used in 4781 mobile node home address configuration and in network renumbering. 4782 In this mechanism, mobile nodes away from home receive Mobile Prefix 4783 Advertisement messages. These messages include Prefix Information 4784 Options for the prefixes configured on the home subnet interface(s) 4785 of the home agent. 4787 If there are multiple home agents, differences in the advertisements 4788 sent by different home agents can lead to an inability to use a 4789 particular home address when changing to another home agent. In 4790 order to ensure that the mobile nodes get the same information from 4791 different home agents, it is preferred that all of the home agents on 4792 the same link be configured in the same manner. 4794 To support this, the home agent monitors prefixes advertised by 4795 itself and other home agents on the home link. In Neighbor Discovery 4796 (RFC 4861 [18]) it is acceptable for two routers to advertise 4797 different sets of prefixes on the same link. For home agents, the 4798 differences should be detected for a given home address because the 4799 mobile node communicates only with one home agent at a time and the 4800 mobile node needs to know the full set of prefixes assigned to the 4801 home link. All other comparisons of Router Advertisements are as 4802 specified in Section 6.2.7 of RFC 4861. 4804 10.6.2. Scheduling Prefix Deliveries 4806 A home agent serving a mobile node will schedule the delivery of the 4807 new prefix information to that mobile node when any of the following 4808 conditions occur: 4810 MUST: 4812 o The state of the flags changes for the prefix of the mobile node's 4813 registered home address. 4815 o The valid or preferred lifetime is reconfigured or changes for any 4816 reason other than advancing real time. 4818 o The mobile node requests the information with a Mobile Prefix 4819 Solicitation (see Section 11.4.2). 4821 SHOULD: 4823 o A new prefix is added to the home subnet interface(s) of the home 4824 agent. 4826 MAY: 4828 o The valid or preferred lifetime or the state of the flags changes 4829 for a prefix which is not used in any Binding Cache entry for this 4830 mobile node. 4832 The home agent uses the following algorithm to determine when to send 4833 prefix information to the mobile node. 4835 o If a mobile node sends a solicitation, answer right away. 4837 o If no Mobile Prefix Advertisement has been sent to the mobile node 4838 in the last MaxMobPfxAdvInterval seconds (see Section 13), then 4839 ensure that a transmission is scheduled. The actual transmission 4840 time is randomized as described below. 4842 o If a prefix matching the mobile node's home registration is added 4843 on the home subnet interface or if its information changes in any 4844 way that does not deprecate the mobile node's address, ensure that 4845 a transmission is scheduled. The actual transmission time is 4846 randomized as described below. 4848 o If a home registration expires, cancel any scheduled 4849 advertisements to the mobile node. 4851 The list of prefixes is sent in its entirety in all cases. 4853 If the home agent has already scheduled the transmission of a Mobile 4854 Prefix Advertisement to the mobile node, then the home agent will 4855 replace the advertisement with a new one to be sent at the scheduled 4856 time. 4858 Otherwise, the home agent computes a fresh value for RAND_ADV_DELAY 4859 which offsets from the current time for the scheduled transmission. 4860 First calculate the maximum delay for the scheduled Advertisement: 4862 MaxScheduleDelay = min (MaxMobPfxAdvInterval, Preferred Lifetime), 4864 where MaxMobPfxAdvInterval is as defined in Section 12. Then compute 4865 the final delay for the advertisement: 4867 RAND_ADV_DELAY = MinMobPfxAdvInterval + 4868 (rand() % abs(MaxScheduleDelay - MinMobPfxAdvInterval)) 4870 Here rand() returns a random integer value in the range of 0 to the 4871 maximum possible integer value. This computation is expected to 4872 alleviate bursts of advertisements when prefix information changes. 4873 In addition, a home agent MAY further reduce the rate of packet 4874 transmission by further delaying individual advertisements, when 4875 necessary to avoid overwhelming local network resources. The home 4876 agent SHOULD periodically continue to retransmit an unsolicited 4877 Advertisement to the mobile node, until it is acknowledged by the 4878 receipt of a Mobile Prefix Solicitation from the mobile node. 4880 The home agent MUST wait PREFIX_ADV_TIMEOUT (see Section 12) before 4881 the first retransmission and double the retransmission wait time for 4882 every succeeding retransmission until a maximum number of 4883 PREFIX_ADV_RETRIES attempts (see Section 12) has been tried. If the 4884 mobile node's bindings expire before the matching Binding Update has 4885 been received, then the home agent MUST NOT attempt any more 4886 retransmissions, even if not all PREFIX_ADV_RETRIES have been 4887 retransmitted. In the mean time, if the mobile node sends another 4888 Binding Update without returning home, then the home agent SHOULD 4889 begin transmitting the unsolicited Advertisement again. 4891 If some condition, as described above, occurs on the home link and 4892 causes another Prefix Advertisement to be sent to the mobile node, 4893 before the mobile node acknowledges a previous transmission, the home 4894 agent SHOULD combine any Prefix Information options in the 4895 unacknowledged Mobile Prefix Advertisement into a new Advertisement. 4896 The home agent then discards the old Advertisement. 4898 10.6.3. Sending Advertisements 4900 When sending a Mobile Prefix Advertisement to the mobile node, the 4901 home agent MUST construct the packet as follows: 4903 o The Source Address in the packet's IPv6 header MUST be set to the 4904 home agent's IP address to which the mobile node addressed its 4905 current home registration or its default global home agent address 4906 if no binding exists. 4908 o If the advertisement was solicited, it MUST be destined to the 4909 source address of the solicitation. If it was triggered by prefix 4910 changes or renumbering, the advertisement's destination will be 4911 the mobile node's home address in the binding which triggered the 4912 rule. 4914 o A type 2 routing header MUST be included with the mobile node's 4915 home address. 4917 o IPsec headers MUST be supported and SHOULD be used. 4919 o The home agent MUST send the packet as it would any other unicast 4920 IPv6 packet that it originates. 4922 o Set the Managed Address Configuration (M) flag if the 4923 corresponding flag has been set in any of the Router 4924 Advertisements from which the prefix information has been learned 4925 (including the ones sent by this home agent). 4927 o Set the Other Stateful Configuration (O) flag if the corresponding 4928 flag has been set in any of the Router Advertisements from which 4929 the prefix information has been learned (including the ones sent 4930 by this home agent). 4932 10.6.4. Lifetimes for Changed Prefixes 4934 As described in Section 10.3.1, the lifetime returned by the home 4935 agent in a Binding Acknowledgement MUST NOT be greater than the 4936 remaining valid lifetime for the subnet prefix in the mobile node's 4937 home address. This limit on the binding lifetime serves to prohibit 4938 use of a mobile node's home address after it becomes invalid. 4940 11. Mobile Node Operation 4942 11.1. Conceptual Data Structures 4944 Each mobile node MUST maintain a Binding Update List. 4946 The Binding Update List records information for each Binding Update 4947 sent by this mobile node, in which the lifetime of the binding has 4948 not yet expired. The Binding Update List includes all bindings sent 4949 by the mobile node either to its home agent or correspondent nodes. 4950 It also contains Binding Updates which are waiting for the completion 4951 of the return routability procedure before they can be sent. 4952 However, for multiple Binding Updates sent to the same destination 4953 address, the Binding Update List contains only the most recent 4954 Binding Update (i.e., with the greatest Sequence Number value) sent 4955 to that destination. The Binding Update List MAY be implemented in 4956 any manner consistent with the external behavior described in this 4957 document. 4959 Each Binding Update List entry conceptually contains the following 4960 fields: 4962 o The IP address of the node to which a Binding Update was sent. 4964 o The home address for which that Binding Update was sent. 4966 o The care-of address sent in that Binding Update. This value is 4967 necessary for the mobile node to determine if it has sent a 4968 Binding Update while giving its new care-of address to this 4969 destination after changing its care-of address. 4971 o The initial value of the Lifetime field sent in that Binding 4972 Update. 4974 o The remaining lifetime of that binding. This lifetime is 4975 initialized from the Lifetime value sent in the Binding Update and 4976 is decremented until it reaches zero, at which time this entry 4977 MUST be deleted from the Binding Update List. 4979 o The maximum value of the Sequence Number field sent in previous 4980 Binding Updates to this destination. The Sequence Number field is 4981 16 bits long and all comparisons between Sequence Number values 4982 MUST be performed modulo 2**16 (see Section 9.5.1). 4984 o The time at which a Binding Update was last sent to this 4985 destination, as needed to implement the rate limiting restriction 4986 for sending Binding Updates. 4988 o The state of any retransmissions needed for this Binding Update. 4989 This state includes the time remaining until the next 4990 retransmission attempt for the Binding Update and the current 4991 state of the exponential back-off mechanism for retransmissions. 4993 o A flag specifying whether or not future Binding Updates should be 4994 sent to this destination. The mobile node sets this flag in the 4995 Binding Update List entry when it receives an ICMP Parameter 4996 Problem, Code 1, error message in response to a return routability 4997 message or Binding Update sent to that destination, as described 4998 in Section 11.3.5. 5000 The Binding Update List is used to determine whether a particular 5001 packet is sent directly to the correspondent node or tunneled via the 5002 home agent (see Section 11.3.1). 5004 The Binding Update list also conceptually contains the following data 5005 related to running the return routability procedure. This data is 5006 relevant only for Binding Updates sent to correspondent nodes. 5008 o The time at which a Home Test Init or Care-of Test Init message 5009 was last sent to this destination, as needed to implement the rate 5010 limiting restriction for the return routability procedure. 5012 o The state of any retransmissions needed for this return 5013 routability procedure. This state includes the time remaining 5014 until the next retransmission attempt and the current state of the 5015 exponential back-off mechanism for retransmissions. 5017 o Cookie values used in the Home Test Init and Care-of Test Init 5018 messages. 5020 o Home and care-of keygen tokens received from the correspondent 5021 node. 5023 o Home and care-of nonce indices received from the correspondent 5024 node. 5026 o The time at which each of the tokens and nonces were received from 5027 the correspondent node, as needed to implement reuse while moving. 5029 11.2. Processing Mobility Headers 5031 All IPv6 mobile nodes MUST observe the rules described in Section 9.2 5032 when processing Mobility Headers. 5034 11.3. Packet Processing 5036 11.3.1. Sending Packets While Away from Home 5038 While a mobile node is away from home, it continues to use its home 5039 address, as well as also using one or more care-of addresses. When 5040 sending a packet while away from home, a mobile node MAY choose among 5041 these in selecting the address that it will use as the source of the 5042 packet, as follows: 5044 o Protocols layered over IP will generally treat the mobile node's 5045 home address as its IP source address for most packets. For 5046 packets sent that are part of transport-level connections 5047 established while the mobile node was at home, the mobile node 5048 MUST use its home address. Likewise, for packets sent that are 5049 part of transport-level connections that the mobile node may still 5050 be using after moving to a new location, the mobile node SHOULD 5051 use its home address in this way. If a binding exists, the mobile 5052 node SHOULD send the packets directly to the correspondent node. 5053 Otherwise, if a binding does not exist, the mobile node MUST use 5054 reverse tunneling. 5056 o The mobile node MAY choose to directly use one of its care-of 5057 addresses as the source of the packet, not requiring the use of a 5058 Home Address option in the packet. This is particularly useful 5059 for short-term communication that may easily be retried if it 5060 fails. Using the mobile node's care-of address as the source for 5061 such queries will generally have a lower overhead than using the 5062 mobile node's home address, since no extra options need to be used 5063 in either the query or its reply. Such packets can be routed 5064 normally, directly between their source and destination without 5065 relying on Mobile IPv6. If application running on the mobile node 5066 has no particular knowledge that the communication being sent fits 5067 within this general type of communication, however, the mobile 5068 node should not use its care-of address as the source of the 5069 packet in this way. 5071 The choice of the most efficient communications method is 5072 application specific, and outside the scope of this specification. 5073 The APIs necessary for controlling the choice are also out of 5074 scope. One example of such an API is described in the IPv6 Socket 5075 API for Source Address Selection specification [42]. 5077 o While not at its home link, the mobile node MUST NOT use the Home 5078 Address destination option when communicating with link-local 5079 peers. 5081 Similarly, the mobile node MUST NOT use the Home Address 5082 destination option for IPv6 Neighbor Discovery [18] packets. 5084 Detailed operation of these cases is described later in this section 5085 and also discussed in [32]. 5087 For packets sent by a mobile node while it is at home, no special 5088 Mobile IPv6 processing is required. Likewise, if the mobile node 5089 uses any address other than one of its home addresses as the source 5090 of a packet sent while away from home, no special Mobile IPv6 5091 processing is required. In either case, the packet is simply 5092 addressed and transmitted in the same way as any normal IPv6 packet. 5094 For packets sent by the mobile node sent while away from home using 5095 the mobile node's home address as the source, special Mobile IPv6 5096 processing of the packet is required. This can be done in the 5097 following two ways: 5099 Route Optimization 5101 This manner of delivering packets does not require going through 5102 the home network, and typically will enable faster and more 5103 reliable transmission. 5105 The mobile node needs to ensure that a Binding Cache entry exists 5106 for its home address so that the correspondent node can process 5107 the packet (Section 9.3.1 specifies the rules for Home Address 5108 Destination Option Processing at a correspondent node). The 5109 mobile node SHOULD examine its Binding Update List for an entry 5110 which fulfills the following conditions: 5112 * The Source Address field of the packet being sent is equal to 5113 the home address in the entry. 5115 * The Destination Address field of the packet being sent is equal 5116 to the address of the correspondent node in the entry. 5118 * One of the current care-of addresses of the mobile node appears 5119 as the care-of address in the entry. 5121 * The entry indicates that a binding has been successfully 5122 created. 5124 * The remaining lifetime of the binding is greater than zero. 5126 When these conditions are met, the mobile node knows that the 5127 correspondent node has a suitable Binding Cache entry. 5129 A mobile node SHOULD arrange to supply the home address in a Home 5130 Address option, and MUST set the IPv6 header's Source Address 5131 field to the care-of address which the mobile node has registered 5132 to be used with this correspondent node. The correspondent node 5133 will then use the address supplied in the Home Address option to 5134 serve the function traditionally done by the Source IP address in 5135 the IPv6 header. The mobile node's home address is then supplied 5136 to higher protocol layers and applications. 5138 Specifically: 5140 * Construct the packet using the mobile node's home address as 5141 the packet's Source Address, in the same way as if the mobile 5142 node were at home. This includes the calculation of upper 5143 layer checksums using the home address as the value of the 5144 source. 5146 * Insert a Home Address option into the packet with the Home 5147 Address field copied from the original value of the Source 5148 Address field in the packet. 5150 * Change the Source Address field in the packet's IPv6 header to 5151 one of the mobile node's care-of addresses. This will 5152 typically be the mobile node's current primary care-of address, 5153 but MUST be an address assigned to the interface on the link 5154 being used. 5156 By using the care-of address as the Source Address in the IPv6 5157 header, with the mobile node's home address instead in the Home 5158 Address option, the packet will be able to safely pass through any 5159 router implementing ingress filtering [27]. 5161 Reverse Tunneling 5163 This is the mechanism which tunnels the packets via the home 5164 agent. It is not as efficient as the above mechanism, but is 5165 needed if there is no binding yet with the correspondent node. 5167 This mechanism is used for packets that have the mobile node's 5168 home address as the Source Address in the IPv6 header, or with 5169 multicast control protocol packets as described in Section 11.3.4. 5170 Specifically: 5172 * The packet is sent to the home agent using IPv6 encapsulation 5173 [7]. 5175 * The Source Address in the tunnel packet is the primary care-of 5176 address as registered with the home agent. 5178 * The Destination Address in the tunnel packet is the home 5179 agent's address. 5181 Then, the home agent will pass the encapsulated packet to the 5182 correspondent node. 5184 11.3.2. Interaction with Outbound IPsec Processing 5186 This section sketches the interaction between outbound Mobile IPv6 5187 processing and outbound IP Security (IPsec) processing for packets 5188 sent by a mobile node while away from home. Any specific 5189 implementation MAY use algorithms and data structures other than 5190 those suggested here, but its processing MUST be consistent with the 5191 effect of the operation described here and with the relevant IPsec 5192 specifications. In the steps described below, it is assumed that 5193 IPsec is being used in transport mode [3] and that the mobile node is 5194 using its home address as the source for the packet (from the point 5195 of view of higher protocol layers or applications, as described in 5196 Section 11.3.1): 5198 o The packet is created by higher layer protocols and applications 5199 (e.g., by TCP) as if the mobile node were at home and Mobile IPv6 5200 were not being used. 5202 o Determine the outgoing interface for the packet. (Note that the 5203 selection between reverse tunneling and route optimization may 5204 imply different interfaces, particularly if tunnels are considered 5205 interfaces as well.) 5207 o As part of outbound packet processing in IP, the packet is 5208 compared against the IPsec security policy database to determine 5209 what processing is required for the packet [3]. 5211 o If IPsec processing is required, the packet is either mapped to an 5212 existing Security Association (or SA bundle), or a new SA (or SA 5213 bundle) is created for the packet, according to the procedures 5214 defined for IPsec. 5216 o Since the mobile node is away from home, the mobile is either 5217 using reverse tunneling or route optimization to reach the 5218 correspondent node. 5220 If reverse tunneling is used, the packet is constructed in the 5221 normal manner and then tunneled through the home agent. 5223 If route optimization is in use, the mobile node inserts a Home 5224 Address destination option into the packet, replacing the Source 5225 Address in the packet's IP header with the care-of address used 5226 with this correspondent node, as described in Section 11.3.1. The 5227 Destination Options header in which the Home Address destination 5228 option is inserted MUST appear in the packet after the routing 5229 header, if present, and before the IPsec (AH [4] or ESP [5]) 5230 header, so that the Home Address destination option is processed 5231 by the destination node before the IPsec header is processed. 5233 Finally, once the packet is fully assembled, the necessary IPsec 5234 authentication (and encryption, if required) processing is 5235 performed on the packet, initializing the Authentication Data in 5236 the IPsec header. 5238 RFC 4302 treatment of destination options is extended as follows. 5239 The AH authentication data MUST be calculated as if the following 5240 were true: 5242 * the IPv6 source address in the IPv6 header contains the mobile 5243 node's home address, 5245 * the Home Address field of the Home Address destination option 5246 (Section 6.3) contains the new care-of address. 5248 o This allows, but does not require, the receiver of the packet 5249 containing a Home Address destination option to exchange the two 5250 fields of the incoming packet to reach the above situation, 5251 simplifying processing for all subsequent packet headers. 5252 However, such an exchange is not required, as long as the result 5253 of the authentication calculation remains the same. 5255 When an automated key management protocol is used to create new 5256 security associations for a peer, it is important to ensure that the 5257 peer can send the key management protocol packets to the mobile node. 5258 This may not be possible if the peer is the home agent of the mobile 5259 node and the purpose of the security associations would be to send a 5260 Binding Update to the home agent. Packets addressed to the home 5261 address of the mobile node cannot be used before the Binding Update 5262 has been processed. For the default case of using IKEv2 [24] as the 5263 automated key management protocol, such problems can be avoided by 5264 the following requirements when communicating with its home agent: 5266 o When the mobile node is away from home, it MUST use its care-of 5267 address as the Source Address of all packets it sends as part of 5268 the key management protocol (without use of Mobile IPv6 for these 5269 packets, as suggested in Section 11.3.1). 5271 The Key Management Mobility Capability (K) bit in Binding Updates and 5272 Acknowledgements can be used to avoid the need to rerun IKEv2 upon 5273 movements. 5275 11.3.3. Receiving Packets While Away from Home 5277 While away from home, a mobile node will receive packets addressed to 5278 its home address, by one of two methods: 5280 o Packets sent by a correspondent node, that does not have a Binding 5281 Cache entry for the mobile node, will be sent to the home address, 5282 captured by the home agent and tunneled to the mobile node. 5284 o Packets sent by a correspondent node that has a Binding Cache 5285 entry for the mobile node that contains the mobile node's current 5286 care-of address, will be sent by the correspondent node using a 5287 type 2 routing header. The packet will be addressed to the mobile 5288 node's care-of address, with the final hop in the routing header 5289 directing the packet to the mobile node's home address; the 5290 processing of this last hop of the routing header is entirely 5291 internal to the mobile node, since the care-of address and home 5292 address are both addresses within the mobile node. 5294 For packets received by the first method, the mobile node MUST check 5295 that the IPv6 source address of the tunneled packet is the IP address 5296 of its home agent. In this method, the mobile node may also send a 5297 Binding Update to the original sender of the packet as described in 5298 Section 11.7.2 and subject to the rate limiting defined in 5299 Section 11.8. The mobile node MUST also process the received packet 5300 in the manner defined for IPv6 encapsulation [7], which will result 5301 in the encapsulated (inner) packet being processed normally by upper- 5302 layer protocols within the mobile node as if it had been addressed 5303 (only) to the mobile node's home address. 5305 For packets received by the second method, the following rules will 5306 result in the packet being processed normally by upper-layer 5307 protocols within the mobile node as if it had been addressed to the 5308 mobile node's home address. 5310 A node receiving a packet addressed to itself (i.e., one of the 5311 node's addresses is in the IPv6 destination field) follows the next 5312 header chain of headers and processes them. When it encounters a 5313 type 2 routing header during this processing, it performs the 5314 following checks. If any of these checks fail, the node MUST 5315 silently discard the packet. 5317 o The length field in the routing header is exactly 2. 5319 o The segments left field in the routing header is 1 on the wire. 5320 (But implementations may process the routing header so that the 5321 value may become 0 after the routing header has been processed, 5322 but before the rest of the packet is processed.) 5324 o The Home Address field in the routing header is one of the node's 5325 home addresses, if the segments left field was 1. Thus, in 5326 particular the address field is required to be a unicast routable 5327 address. 5329 Once the above checks have been performed, the node swaps the IPv6 5330 destination field with the Home Address field in the routing header, 5331 decrements segments left by one from the value it had on the wire, 5332 and resubmits the packet to IP for processing the next header. 5333 Conceptually, this follows the same model as in RFC 2460. However, 5334 in the case of type 2 routing header this can be simplified since it 5335 is known that the packet will not be forwarded to a different node. 5337 The definition of AH requires the sender to calculate the AH 5338 integrity check value of a routing header in the same way it appears 5339 in the receiver after it has processed the header. Since IPsec 5340 headers follow the routing header, any IPsec processing will operate 5341 on the packet with the home address in the IP destination field and 5342 segments left being zero. Thus, the AH calculations at the sender 5343 and receiver will have an identical view of the packet. 5345 11.3.4. Routing Multicast Packets 5347 A mobile node that is connected to its home link functions in the 5348 same way as any other (stationary) node. Thus, when it is at home, a 5349 mobile node functions identically to other multicast senders and 5350 receivers. Therefore, this section describes the behavior of a 5351 mobile node that is not on its home link. 5353 In order to receive packets sent to some multicast group, a mobile 5354 node must join that multicast group. One method, in which a mobile 5355 node MAY join the group, is via a (local) multicast router on the 5356 foreign link being visited. In this case, the mobile node MUST use 5357 its care-of address and MUST NOT use the Home Address destination 5358 option when sending MLD packets [9]. 5360 Alternatively, a mobile node MAY join multicast groups via a bi- 5361 directional tunnel to its home agent. The mobile node tunnels its 5362 multicast group membership control packets (such as those defined in 5363 [9] or in [39]) to its home agent, and the home agent forwards 5364 multicast packets down the tunnel to the mobile node. A mobile node 5365 MUST NOT tunnel multicast group membership control packets until (1) 5366 the mobile node has a binding in place at the home agent, and (2) the 5367 latter sends at least one multicast group membership control packet 5368 via the tunnel. Once this condition is true, the mobile node SHOULD 5369 assume it does not change as long as the binding does not expire. 5371 A mobile node that wishes to send packets to a multicast group also 5372 has two options: 5374 1. Send directly on the foreign link being visited. 5376 To do this, the application uses the care-of address as a source 5377 address for multicast traffic, just as it would use a stationary 5378 address. This requires that the application either knows the 5379 care-of address, or uses an API such as the IPv6 Socket API for 5380 Source Address Selection specification [42] to request that the 5381 care-of address be used as the source address in transmitted 5382 packets. The mobile node MUST NOT use Home Address destination 5383 option in such traffic. 5385 2. Send via a tunnel to its home agent. 5387 Because multicast routing in general depends upon the Source 5388 Address used in the IPv6 header of the multicast packet, a mobile 5389 node that tunnels a multicast packet to its home agent MUST use 5390 its home address as the IPv6 Source Address of the inner 5391 multicast packet. 5393 Note that direct sending from the foreign link is only applicable 5394 while the mobile node is at that foreign link. This is because the 5395 associated multicast tree is specific to that source location and any 5396 change of location and source address will invalidate the source 5397 specific tree or branch and the application context of the other 5398 multicast group members. 5400 This specification does not provide mechanisms to enable such local 5401 multicast session to survive hand-off and to seamlessly continue from 5402 a new care-of address on each new foreign link. Any such mechanism, 5403 developed as an extension to this specification, needs to take into 5404 account the impact of fast moving mobile nodes on the Internet 5405 multicast routing protocols and their ability to maintain the 5406 integrity of source specific multicast trees and branches. 5408 While the use of bidirectional tunneling can ensure that multicast 5409 trees are independent of the mobile nodes movement, in some case such 5410 tunneling can have adverse affects. The latency of specific types of 5411 multicast applications (such as multicast based discovery protocols) 5412 will be affected when the round-trip time between the foreign subnet 5413 and the home agent is significant compared to that of the topology to 5414 be discovered. In addition, the delivery tree from the home agent in 5415 such circumstances relies on unicast encapsulation from the agent to 5416 the mobile node. Therefore, bandwidth usage is inefficient compared 5417 to the native multicast forwarding in the foreign multicast system. 5419 11.3.5. Receiving ICMP Error Messages 5421 Any node that does not recognize the Mobility header will return an 5422 ICMP Parameter Problem, Code 1, message to the sender of the packet. 5423 If the mobile node receives such an ICMP error message in response to 5424 a return routability procedure or Binding Update, it SHOULD record in 5425 its Binding Update List that future Binding Updates SHOULD NOT be 5426 sent to this destination. Such Binding Update List entries SHOULD be 5427 removed after a period of time in order to allow for retrying route 5428 optimization. 5430 New Binding Update List entries MUST NOT be created as a result of 5431 receiving ICMP error messages. 5433 Correspondent nodes that have participated in the return routability 5434 procedure MUST implement the ability to correctly process received 5435 packets containing a Home Address destination option. Therefore, 5436 correctly implemented correspondent nodes should always be able to 5437 recognize Home Address options. If a mobile node receives an ICMP 5438 Parameter Problem, Code 2, message from some node indicating that it 5439 does not support the Home Address option, the mobile node SHOULD log 5440 the error and then discard the ICMP message. 5442 11.3.6. Receiving Binding Error Messages 5444 When a mobile node receives a packet containing a Binding Error 5445 message, it should first check if the mobile node has a Binding 5446 Update List entry for the source of the Binding Error message. If 5447 the mobile node does not have such an entry, it MUST ignore the 5448 message. This is necessary to prevent a waste of resources on, e.g., 5449 return routability procedure due to spoofed Binding Error messages. 5451 Otherwise, if the message Status field was 1 (unknown binding for 5452 Home Address destination option), the mobile node should perform one 5453 of the following three actions: 5455 o If the Binding Error Message was sent by the Home Agent, the 5456 Mobile Node SHOULD send a Binding Update to the Home Agent 5457 according to Section 11.7.1. 5459 o If the mobile node has recent upper layer progress information, 5460 which indicates that communications with the correspondent node 5461 are progressing, it MAY ignore the message. This can be done in 5462 order to limit the damage that spoofed Binding Error messages can 5463 cause to ongoing communications. 5465 o If the mobile node has no upper layer progress information, it 5466 MUST remove the entry and route further communications through the 5467 home agent. It MAY also optionally start a return routability 5468 procedure (see Section 5.2). 5470 If the message Status field was 2 (unrecognized MH Type value), the 5471 mobile node should perform one of the following two actions: 5473 o If the mobile node is not expecting an acknowledgement or response 5474 from the correspondent node, the mobile node SHOULD ignore this 5475 message. 5477 o Otherwise, the mobile node SHOULD cease the use of any extensions 5478 to this specification. If no extensions had been used, the mobile 5479 node should cease the attempt to use route optimization. 5481 11.4. Home Agent and Prefix Management 5483 11.4.1. Dynamic Home Agent Address Discovery 5485 Sometimes when the mobile node needs to send a Binding Update to its 5486 home agent to register its new primary care-of address, as described 5487 in Section 11.7.1, the mobile node may not know the address of any 5488 router on its home link that can serve as a home agent for it. For 5489 example, some nodes on its home link may have been reconfigured while 5490 the mobile node has been away from home, such that the router that 5491 was operating as the mobile node's home agent has been replaced by a 5492 different router serving this role. 5494 In this case, the mobile node MAY attempt to discover the address of 5495 a suitable home agent on its home link. To do so, the mobile node 5496 sends an ICMP Home Agent Address Discovery Request message to the 5497 Mobile IPv6 Home-Agents anycast address [8] for its home subnet 5498 prefix. As described in Section 10.5, the home agent on its home 5499 link that receives this Request message will return an ICMP Home 5500 Agent Address Discovery Reply message. This message gives the 5501 addresses for the home agents operating on the home link. 5503 The mobile node, upon receiving this Home Agent Address Discovery 5504 Reply message, MAY then send its home registration Binding Update to 5505 any of the unicast IP addresses listed in the Home Agent Addresses 5506 field in the Reply. For example, the mobile node MAY attempt its 5507 home registration to each of these addresses, in turn, until its 5508 registration is accepted. The mobile node sends a Binding Update to 5509 an address and waits for the matching Binding Acknowledgement, moving 5510 on to the next address if there is no response. The mobile node 5511 MUST, however, wait at least InitialBindackTimeoutFirstReg seconds 5512 (see Section 13) before sending a Binding Update to the next home 5513 agent. In trying each of the returned home agent addresses, the 5514 mobile node SHOULD try each of them in the order they appear in the 5515 Home Agent Addresses field in the received Home Agent Address 5516 Discovery Reply message. In order to do this, the mobile node SHOULD 5517 store the list of home agents for later use in case the home agent 5518 currently managing the mobile node's care-of address forwarding 5519 should become unavailable. The list MAY be stored, along with any 5520 available lifetime information for the home agent addresses, in 5521 nonvolatile memory to survive reboots by the mobile node. 5523 If the mobile node has a current registration with some home agent 5524 (the Lifetime for that registration has not yet expired), then the 5525 mobile node MUST attempt any new registration first with that home 5526 agent. If that registration attempt fails (e.g., timed out or 5527 rejected), the mobile node SHOULD then reattempt this registration 5528 with another home agent. If the mobile node knows of no other 5529 suitable home agent, then it MAY attempt the dynamic home agent 5530 address discovery mechanism described above. 5532 If, after a mobile node transmits a Home Agent Address Discovery 5533 Request message to the Home Agents Anycast address, it does not 5534 receive a corresponding Home Agent Address Discovery Reply message 5535 within INITIAL_DHAAD_TIMEOUT (see Section 12) seconds, the mobile 5536 node MAY retransmit the same Request message to the same anycast 5537 address. This retransmission MAY be repeated up to a maximum of 5538 DHAAD_RETRIES (see Section 12) attempts. Each retransmission MUST be 5539 delayed by twice the time interval of the previous retransmission. 5541 11.4.2. Sending Mobile Prefix Solicitations 5543 When a mobile node has a home address that is about to become 5544 invalid, it SHOULD send a Mobile Prefix Solicitation to its home 5545 agent in an attempt to acquire fresh routing prefix information. The 5546 new information also enables the mobile node to participate in 5547 renumbering operations affecting the home network, as described in 5548 Section 10.6. 5550 The mobile node MUST use the Home Address destination option to carry 5551 its home address. The mobile node MUST support and SHOULD use IPsec 5552 to protect the solicitation. The mobile node MUST set the Identifier 5553 field in the ICMP header to a random value. 5555 As described in Section 11.7.2, Binding Updates sent by the mobile 5556 node to other nodes MUST use a lifetime no greater than the remaining 5557 lifetime of its home registration of its primary care-of address. 5558 The mobile node SHOULD further limit the lifetimes that it sends on 5559 any Binding Updates to be within the remaining valid lifetime (see 5560 Section 10.6.2) for the prefix in its home address. 5562 When the lifetime for a changed prefix decreases, and the change 5563 would cause cached bindings at correspondent nodes in the Binding 5564 Update List to be stored past the newly shortened lifetime, the 5565 mobile node MUST issue a Binding Update to all such correspondent 5566 nodes. 5568 These limits on the binding lifetime serve to prohibit use of a 5569 mobile node's home address after it becomes invalid. 5571 11.4.3. Receiving Mobile Prefix Advertisements 5573 Section 10.6 describes the operation of a home agent to support boot 5574 time configuration and renumbering a mobile node's home subnet while 5575 the mobile node is away from home. The home agent sends Mobile 5576 Prefix Advertisements to the mobile node while away from home, giving 5577 "important" Prefix Information options that describe changes in the 5578 prefixes in use on the mobile node's home link. 5580 The Mobile Prefix Solicitation is similar to the Router Solicitation 5581 used in Neighbor Discovery [18], except it is routed from the mobile 5582 node on the visited network to the home agent on the home network by 5583 usual unicast routing rules. 5585 When a mobile node receives a Mobile Prefix Advertisement, it MUST 5586 validate it according to the following test: 5588 o The Source Address of the IP packet carrying the Mobile Prefix 5589 Advertisement is the same as the home agent address to which the 5590 mobile node last sent an accepted home registration Binding Update 5591 to register its primary care-of address. Otherwise, if no such 5592 registrations have been made, it SHOULD be the mobile node's 5593 stored home agent address, if one exists. Otherwise, if the 5594 mobile node has not yet discovered its home agent's address, it 5595 MUST NOT accept Mobile Prefix Advertisements. 5597 o The packet MUST have a type 2 routing header and SHOULD be 5598 protected by an IPsec header as described in Section 5.4 and 5599 Section 6.8. 5601 o If the ICMP Identifier value matches the ICMP Identifier value of 5602 the most recently sent Mobile Prefix Solicitation and no other 5603 advertisement has yet been received for this value, then the 5604 advertisement is considered to be solicited and will be processed 5605 further. 5607 Otherwise, the advertisement is unsolicited, and MUST be 5608 discarded. In this case the mobile node SHOULD send a Mobile 5609 Prefix Solicitation. 5611 Any received Mobile Prefix Advertisement not meeting these tests MUST 5612 be silently discarded. 5614 For an accepted Mobile Prefix Advertisement, the mobile node MUST 5615 process Managed Address Configuration (M), Other Stateful 5616 Configuration (O), and the Prefix Information Options as if they 5617 arrived in a Router Advertisement [18] on the mobile node's home 5618 link. (This specification does not, however, describe how to acquire 5619 home addresses through stateful protocols.) Such processing may 5620 result in the mobile node configuring a new home address, although 5621 due to separation between preferred lifetime and valid lifetime, such 5622 changes should not affect most communications by the mobile node, in 5623 the same way as for nodes that are at home. 5625 This specification assumes that any security associations and 5626 security policy entries that may be needed for new prefixes have been 5627 pre-configured in the mobile node. Note that while dynamic key 5628 management avoids the need to configure new security associations, it 5629 is still necessary to add policy entries to protect the 5630 communications involving the home address(es). Mechanisms for 5631 setting up these entries are outside the scope of this specification. 5633 11.5. Movement 5635 11.5.1. Movement Detection 5637 The primary goal of movement detection is to detect L3 handovers. 5638 This section does not attempt to specify a fast movement detection 5639 algorithm which will function optimally for all types of 5640 applications, link-layers and deployment scenarios; instead, it 5641 describes a generic method that uses the facilities of IPv6 Neighbor 5642 Discovery, including Router Discovery and Neighbor Unreachability 5643 Detection. At the time of this writing, this method is considered 5644 well enough understood to recommend for standardization, however it 5645 is expected that future versions of this specification or other 5646 specifications may contain updated versions of the movement detection 5647 algorithm that have better performance. 5649 Generic movement detection uses Neighbor Unreachability Detection to 5650 detect when the default router is no longer bi-directionally 5651 reachable, in which case the mobile node must discover a new default 5652 router (usually on a new link). However, this detection only occurs 5653 when the mobile node has packets to send, and in the absence of 5654 frequent Router Advertisements or indications from the link-layer, 5655 the mobile node might become unaware of an L3 handover that occurred. 5656 Therefore, the mobile node should supplement this method with other 5657 information whenever it is available to the mobile node (e.g., from 5658 lower protocol layers). 5660 When the mobile node detects an L3 handover, it performs Duplicate 5661 Address Detection [19] on its link-local address, selects a new 5662 default router as a consequence of Router Discovery, and then 5663 performs Prefix Discovery with that new router to form new care-of 5664 address(es) as described in Section 11.5.3. It then registers its 5665 new primary care-of address with its home agent as described in 5666 Section 11.7.1. After updating its home registration, the mobile 5667 node then updates associated mobility bindings in correspondent nodes 5668 that it is performing route optimization with as specified in 5669 Section 11.7.2. 5671 Due to the temporary packet flow disruption and signaling overhead 5672 involved in updating mobility bindings, the mobile node should avoid 5673 performing an L3 handover until it is strictly necessary. 5674 Specifically, when the mobile node receives a Router Advertisement 5675 from a new router that contains a different set of on-link prefixes, 5676 if the mobile node detects that the currently selected default router 5677 on the old link is still bi-directionally reachable, it should 5678 generally continue to use the old router on the old link rather than 5679 switch away from it to use a new default router. 5681 Mobile nodes can use the information in received Router 5682 Advertisements to detect L3 handovers. In doing so the mobile node 5683 needs to consider the following issues: 5685 o There might be multiple routers on the same link, thus hearing a 5686 new router does not necessarily constitute an L3 handover. 5688 o When there are multiple routers on the same link they might 5689 advertise different prefixes. Thus even hearing a new router with 5690 a new prefix might not be a reliable indication of an L3 handover. 5692 o The link-local addresses of routers are not globally unique, hence 5693 after completing an L3 handover the mobile node might continue to 5694 receive Router Advertisements with the same link-local source 5695 address. This might be common if routers use the same link-local 5696 address on multiple interfaces. This issue can be avoided when 5697 routers use the Router Address (R) bit, since that provides a 5698 global address of the router. 5700 In addition, the mobile node should consider the following events as 5701 indications that an L3 handover may have occurred. Upon receiving 5702 such indications, the mobile node needs to perform Router Discovery 5703 to discover routers and prefixes on the new link, as described in 5704 Section 6.3.7 of Neighbor Discovery (RFC 4861 [18]). 5706 o If Router Advertisements that the mobile node receives include an 5707 Advertisement Interval option, the mobile node may use its 5708 Advertisement Interval field as an indication of the frequency 5709 with which it should expect to continue to receive future 5710 Advertisements from that router. This field specifies the minimum 5711 rate (the maximum amount of time between successive 5712 Advertisements) that the mobile node should expect. If this 5713 amount of time elapses without the mobile node receiving any 5714 Advertisement from this router, the mobile node can be sure that 5715 at least one Advertisement sent by the router has been lost. The 5716 mobile node can then implement its own policy to determine how 5717 many lost Advertisements from its current default router 5718 constitute an L3 handover indication. 5720 o Neighbor Unreachability Detection determines that the default 5721 router is no longer reachable. 5723 o With some types of networks, notification that a L2 handover has 5724 occurred might be obtained from lower layer protocols or device 5725 driver software within the mobile node. While further details 5726 around handling L2 indications as movement hints is an item for 5727 further study, at the time of writing this specification the 5728 following is considered reasonable: 5730 A L2 handover indication may or may not imply L2 movement and L2 5731 movement may or may not imply L3 movement; the correlations might 5732 be a function of the type of L2 but might also be a function of 5733 actual deployment of the wireless topology. 5735 Unless it is well-known that a L2 handover indication is likely to 5736 imply L3 movement, instead of immediately multicasting a router 5737 solicitation it may be better to attempt to verify whether the 5738 default router is still bi-directionally reachable. This can be 5739 accomplished by sending a unicast Neighbor Solicitation and 5740 waiting for a Neighbor Advertisement with the solicited flag set. 5741 Note that this is similar to Neighbor Unreachability detection but 5742 it does not have the same state machine, such as the STALE state. 5744 If the default router does not respond to the Neighbor 5745 Solicitation it makes sense to proceed to multicasting a Router 5746 Solicitation. 5748 11.5.2. Home Link Detection 5750 When an MN detects that it has arrived on a new link using the 5751 movement detection algorithm in use (Section 11.5.1,) or on 5752 bootstrapping, it performs the following steps to determine if it is 5753 on the home link. 5755 o The MN performs the procedure described in Section 11.5.3 and 5756 configures an address. It also keeps track of all the on-link 5757 prefix(es) received in the RA along with their prefix lengths. 5759 o If the home prefix has not been statically configured the MN uses 5760 some form of bootstrapping procedure (e.g. RFC5026 [22]) to 5761 determine the home prefix. 5763 o Given the availability of the home prefix, the MN checks whether 5764 or not the home prefix matches one of the prefixes received in the 5765 RA. If it does, the MN concludes that it is connected to the home 5766 link. 5768 11.5.3. Forming New Care-of Addresses 5770 After detecting that it has moved a mobile node SHOULD generate a new 5771 primary care-of address using normal IPv6 mechanisms. This SHOULD 5772 also be done when the current primary care-of address becomes 5773 deprecated. A mobile node MAY form a new primary care-of address at 5774 any time, but a mobile node MUST NOT send a Binding Update about a 5775 new care-of address to its home agent more than MAX_UPDATE_RATE times 5776 within a second. 5778 In addition, a mobile node MAY form new non-primary care-of addresses 5779 even when it has not switched to a new default router. A mobile node 5780 can have only one primary care-of address at a time (which is 5781 registered with its home agent), but it MAY have an additional 5782 care-of address for any or all of the prefixes on its current link. 5783 Furthermore, since a wireless network interface may actually allow a 5784 mobile node to be reachable on more than one link at a time (i.e., 5785 within wireless transmitter range of routers on more than one 5786 separate link), a mobile node MAY have care-of addresses on more than 5787 one link at a time. The use of more than one care-of address at a 5788 time is described in Section 11.5.4. 5790 As described in Section 4, in order to form a new care-of address, a 5791 mobile node MAY use either stateless [19] or stateful (e.g., DHCPv6 5792 [30]) Address Autoconfiguration. If a mobile node needs to use a 5793 source address (other than the unspecified address) in packets sent 5794 as a part of address autoconfiguration, it MUST use an IPv6 link- 5795 local address rather than its own IPv6 home address. 5797 RFC 4862 [19] specifies that in normal processing for Duplicate 5798 Address Detection, the node SHOULD delay sending the initial Neighbor 5799 Solicitation message by a random delay between 0 and 5800 MAX_RTR_SOLICITATION_DELAY. Since delaying DAD can result in 5801 significant delays in configuring a new care-of address when the 5802 Mobile Node moves to a new link, the Mobile Node preferably SHOULD 5803 NOT delay DAD when configuring a new care-of address. The Mobile 5804 Node SHOULD delay according to the mechanisms specified in RFC 4862 5805 unless the implementation has a behavior that desynchronizes the 5806 steps that happen before the DAD in the case that multiple nodes 5807 experience handover at the same time. Such desynchronizing behaviors 5808 might be due to random delays in the L2 protocols or device drivers, 5809 or due to the movement detection mechanism that is used. 5811 11.5.4. Using Multiple Care-of Addresses 5813 As described in Section 11.5.3, a mobile node MAY use more than one 5814 care-of address at a time. Particularly in the case of many wireless 5815 networks, a mobile node effectively might be reachable through 5816 multiple links at the same time (e.g., with overlapping wireless 5817 cells), on which different on-link subnet prefixes may exist. The 5818 mobile node MUST ensure that its primary care-of address always has a 5819 prefix that is advertised by its current default router. After 5820 selecting a new primary care-of address, the mobile node MUST send a 5821 Binding Update containing that care-of address to its home agent. 5822 The Binding Update MUST have the Home Registration (H) and 5823 Acknowledge (A) bits set its home agent, as described on 5824 Section 11.7.1. 5826 To assist with smooth handovers, a mobile node SHOULD retain its 5827 previous primary care-of address as a (non-primary) care-of address, 5828 and SHOULD still accept packets at this address, even after 5829 registering its new primary care-of address with its home agent. 5830 This is reasonable, since the mobile node could only receive packets 5831 at its previous primary care-of address if it were indeed still 5832 connected to that link. If the previous primary care-of address was 5833 allocated using stateful Address Autoconfiguration [30], the mobile 5834 node may not wish to release the address immediately upon switching 5835 to a new primary care-of address. 5837 Whenever a mobile node determines that it is no longer reachable 5838 through a given link, it SHOULD invalidate all care-of addresses 5839 associated with address prefixes that it discovered from routers on 5840 the unreachable link which are not in the current set of address 5841 prefixes advertised by the (possibly new) current default router. 5843 11.5.5. Returning Home 5845 A mobile node detects that it has returned to its home link through 5846 the movement detection algorithm in use (Section 11.5.2), when the 5847 mobile node detects that its home subnet prefix is again on-link. To 5848 be able to send and receive packets using its home address from the 5849 home link, the mobile node MUST send a Binding Update to its home 5850 agent to instruct its home agent to no longer intercept or tunnel 5851 packets for it. Until the mobile node sends such a de-registration 5852 Binding Update, it MUST NOT attempt to send and receive packets using 5853 its home address from the home link. The home agent will continue to 5854 intercept all packets sent to the mobile's home address and tunnel 5855 them to the previously registered care-of address. 5857 In this home registration, the mobile node MUST set the Acknowledge 5858 (A) and Home Registration (H) bits, set the Lifetime field to zero, 5859 and set the care-of address for the binding to the mobile node's own 5860 home address. The mobile node MUST use its home address as the 5861 source address in the Binding Update. 5863 When sending this Binding Update to its home agent, the mobile node 5864 must be careful in how it uses Neighbor Solicitation [18] (if needed) 5865 to learn the home agent's link-layer address, since the home agent 5866 will be currently configured to intercept packets to the mobile 5867 node's home address using Proxy Neighbor Discovery (Proxy ND). In 5868 particular, the mobile node is unable to use its home address as the 5869 Source Address in the Neighbor Solicitation until the home agent 5870 stops defending the home address. 5872 Neighbor Solicitation by the mobile node for the home agent's address 5873 will normally not be necessary, since the mobile node has already 5874 learned the home agent's link-layer address from a Source Link-Layer 5875 Address option in a Router Advertisement. However, if there are 5876 multiple home agents it may still be necessary to send a 5877 solicitation. In this special case of the mobile node returning 5878 home, the mobile node MUST multicast the packet, and in addition set 5879 the Source Address of this Neighbor Solicitation to the unspecified 5880 address (0:0:0:0:0:0:0:0). The target of the Neighbor Solicitation 5881 MUST be set to the mobile node's home address. The destination IP 5882 address MUST be set to the Solicited-Node multicast address [16]. 5883 The home agent will send a multicast Neighbor Advertisement back to 5884 the mobile node with the Solicited flag (S) set to zero. In any 5885 case, the mobile node SHOULD record the information from the Source 5886 Link-Layer Address option or from the advertisement, and set the 5887 state of the Neighbor Cache entry for the home agent to REACHABLE. 5889 The mobile node then sends its Binding Update to the home agent's 5890 link-layer address, instructing its home agent to no longer serve as 5891 a home agent for it. By processing this Binding Update, the home 5892 agent will cease defending the mobile node's home address for 5893 Duplicate Address Detection and will no longer respond to Neighbor 5894 Solicitations for the mobile node's home address. The mobile node is 5895 then the only node on the link receiving packets at the mobile node's 5896 home address. In addition, when returning home prior to the 5897 expiration of a current binding for its home address, and configuring 5898 its home address on its network interface on its home link, the 5899 mobile node MUST NOT perform Duplicate Address Detection on its own 5900 home address, in order to avoid confusion or conflict with its home 5901 agent's use of the same address. This rule also applies to the 5902 derived link-local address of the mobile node, if the Link Local 5903 Address Compatibility (L) bit was set when the binding was created. 5904 If the mobile node returns home after the bindings for all of its 5905 care-of addresses have expired, then it SHOULD perform DAD. 5907 After the Mobile Node sends the Binding Update, it MUST be prepared 5908 to reply to Neighbor Solicitations for its home address. Such 5909 replies MUST be sent using a unicast Neighbor Advertisement to the 5910 sender's link-layer address. It is necessary to reply, since sending 5911 the Binding Acknowledgement from the home agent may require 5912 performing Neighbor Discovery, and the mobile node may not be able to 5913 distinguish Neighbor Solicitations coming from the home agent from 5914 other Neighbor Solicitations. Note that a race condition exists 5915 where both the mobile node and the home agent respond to the same 5916 solicitations sent by other nodes; this will be only temporary, 5917 however, until the Binding Update is accepted. 5919 After receiving the Binding Acknowledgement for its Binding Update to 5920 its home agent, the mobile node MUST multicast onto the home link (to 5921 the all-nodes multicast address) a Neighbor Advertisement [18], to 5922 advertise the mobile node's own link-layer address for its own home 5923 address. The Target Address in this Neighbor Advertisement MUST be 5924 set to the mobile node's home address, and the Advertisement MUST 5925 include a Target Link-layer Address option specifying the mobile 5926 node's link-layer address. The mobile node MUST multicast such a 5927 Neighbor Advertisement for each of its home addresses, as defined by 5928 the current on-link prefixes, including its link-local address. The 5929 Solicited Flag (S) in these Advertisements MUST NOT be set, since 5930 they were not solicited by any Neighbor Solicitation. The Override 5931 Flag (O) in these Advertisements MUST be set, indicating that the 5932 Advertisements SHOULD override any existing Neighbor Cache entries at 5933 any node receiving them. 5935 Since multicasting on the local link (such as Ethernet) is typically 5936 not guaranteed to be reliable, the mobile node MAY retransmit these 5937 Neighbor Advertisements [18] up to MAX_NEIGHBOR_ADVERTISEMENT times 5938 to increase their reliability. It is still possible that some nodes 5939 on the home link will not receive any of these Neighbor 5940 Advertisements, but these nodes will eventually be able to recover 5941 through use of Neighbor Unreachability Detection [18]. 5943 Note that the tunnel via the home agent typically stops operating at 5944 the same time that the home registration is deleted. 5946 11.6. Return Routability Procedure 5948 This section defines the rules that the mobile node must follow when 5949 performing the return routability procedure. Section 11.7.2 5950 describes the rules when the return routability procedure needs to be 5951 initiated. 5953 11.6.1. Sending Test Init Messages 5955 A mobile node that initiates a return routability procedure MUST send 5956 (in parallel) a Home Test Init message and a Care-of Test Init 5957 messages. However, if the mobile node has recently received (see 5958 Section 5.2.7) one or both home or care-of keygen tokens, and 5959 associated nonce indices for the desired addresses, it MAY reuse 5960 them. Therefore, the return routability procedure may in some cases 5961 be completed with only one message pair. It may even be completed 5962 without any messages at all, if the mobile node has a recent home 5963 keygen token and has previously visited the same care-of address so 5964 that it also has a recent care-of keygen token. If the mobile node 5965 intends to send a Binding Update with the Lifetime set to zero and 5966 the care-of address equal to its home address - such as when 5967 returning home - sending a Home Test Init message is sufficient. In 5968 this case, generation of the binding management key depends 5969 exclusively on the home keygen token (Section 5.2.5). 5971 A Home Test Init message MUST be created as described in 5972 Section 6.1.3. 5974 A Care-of Test Init message MUST be created as described in 5975 Section 6.1.4. When sending a Home Test Init or Care-of Test Init 5976 message the mobile node MUST record in its Binding Update List the 5977 following fields from the messages: 5979 o The IP address of the node to which the message was sent. 5981 o The home address of the mobile node. This value will appear in 5982 the Source Address field of the Home Test Init message. When 5983 sending the Care-of Test Init message, this address does not 5984 appear in the message, but represents the home address for which 5985 the binding is desired. 5987 o The time at which each of these messages was sent. 5989 o The cookies used in the messages. 5991 Note that a single Care-of Test Init message may be sufficient even 5992 when there are multiple home addresses. In this case the mobile node 5993 MAY record the same information in multiple Binding Update List 5994 entries. 5996 11.6.2. Receiving Test Messages 5998 Upon receiving a packet carrying a Home Test message, a mobile node 5999 MUST validate the packet according to the following tests: 6001 o The Source Address of the packet belongs to a correspondent node 6002 for which the mobile node has a Binding Update List entry with a 6003 state indicating that return routability procedure is in progress. 6004 Note that there may be multiple such entries. 6006 o The Binding Update List indicates that no home keygen token has 6007 been received yet. 6009 o The Destination Address of the packet has the home address of the 6010 mobile node, and the packet has been received in a tunnel from the 6011 home agent. 6013 o The Home Init Cookie field in the message matches the value stored 6014 in the Binding Update List. 6016 Any Home Test message not satisfying all of these tests MUST be 6017 silently ignored. Otherwise, the mobile node MUST record the Home 6018 Nonce Index and home keygen token in the Binding Update List. If the 6019 Binding Update List entry does not have a care-of keygen token, the 6020 mobile node SHOULD continue waiting for the Care-of Test message. 6022 Upon receiving a packet carrying a Care-of Test message, a mobile 6023 node MUST validate the packet according to the following tests: 6025 o The Source Address of the packet belongs to a correspondent node 6026 for which the mobile node has a Binding Update List entry with a 6027 state indicating that return routability procedure is in progress. 6028 Note that there may be multiple such entries. 6030 o The Binding Update List indicates that no care-of keygen token has 6031 been received yet. 6033 o The Destination Address of the packet is the current care-of 6034 address of the mobile node. 6036 o The Care-of Init Cookie field in the message matches the value 6037 stored in the Binding Update List. 6039 Any Care-of Test message not satisfying all of these tests MUST be 6040 silently ignored. Otherwise, the mobile node MUST record the Care-of 6041 Nonce Index and care-of keygen token in the Binding Update List. If 6042 the Binding Update List entry does not have a home keygen token, the 6043 mobile node SHOULD continue waiting for the Home Test message. 6045 If after receiving either the Home Test or the Care-of Test message 6046 and performing the above actions, the Binding Update List entry has 6047 both the home and the care-of keygen tokens, the return routability 6048 procedure is complete. The mobile node SHOULD then proceed with 6049 sending a Binding Update as described in Section 11.7.2. 6051 Correspondent nodes from the time before this specification was 6052 published may not support the Mobility Header protocol. These nodes 6053 will respond to Home Test Init and Care-of Test Init messages with an 6054 ICMP Parameter Problem code 1. The mobile node SHOULD take such 6055 messages as an indication that the correspondent node cannot provide 6056 route optimization, and revert back to the use of bidirectional 6057 tunneling. 6059 11.6.3. Protecting Return Routability Packets 6061 The mobile node MUST support the protection of Home Test and Home 6062 Test Init messages as described in Section 10.4.6. 6064 When IPsec is used to protect return routability signaling or payload 6065 packets, the mobile node MUST set the source address it uses for the 6066 outgoing tunnel packets to the current primary care-of address. The 6067 mobile node starts to use a new primary care-of address immediately 6068 after sending a Binding Update to the home agent to register this new 6069 address. 6071 11.7. Processing Bindings 6073 11.7.1. Sending Binding Updates to the Home Agent 6075 In order to change its primary care-of address as described in 6076 Section 11.5.1 and Section 11.5.3, a mobile node MUST register this 6077 care-of address with its home agent in order to make this its primary 6078 care-of address. 6080 Also, if the mobile node wants the services of the home agent beyond 6081 the current registration period, the mobile node should send a new 6082 Binding Update to it well before the expiration of this period, even 6083 if it is not changing its primary care-of address. However, if the 6084 home agent returned a Binding Acknowledgement for the current 6085 registration with Status field set to 1 (accepted but prefix 6086 discovery necessary), the mobile node should not try to register 6087 again before it has learned the validity of its home prefixes through 6088 mobile prefix discovery. This is typically necessary every time this 6089 Status value is received, because information learned earlier may 6090 have changed. 6092 To register a care-of address or to extend the lifetime of an 6093 existing registration, the mobile node sends a packet to its home 6094 agent containing a Binding Update, with the packet constructed as 6095 follows: 6097 o The Home Registration (H) bit MUST be set in the Binding Update. 6099 o The Acknowledge (A) bit MUST be set in the Binding Update. 6101 o The packet MUST contain a Home Address destination option, giving 6102 the mobile node's home address for the binding. 6104 o The care-of address for the binding MUST be used as the Source 6105 Address in the packet's IPv6 header, unless an Alternate Care-of 6106 Address mobility option is included in the Binding Update. This 6107 option MUST be included in all home registrations, as the ESP 6108 protocol will not be able to protect care-of addresses in the IPv6 6109 header. (Mobile IPv6 implementations that know they are using 6110 IPsec AH to protect a particular message might avoid this option. 6111 For brevity the usage of AH is not discussed in this document.) 6113 o If the mobile node's link-local address has the same interface 6114 identifier as the home address for which it is supplying a new 6115 care-of address, then the mobile node SHOULD set the Link-Local 6116 Address Compatibility (L) bit. 6118 o If the home address was generated using RFC 4941 [21], then the 6119 link local address is unlikely to have a compatible interface 6120 identifier. In this case, the mobile node MUST clear the Link- 6121 Local Address Compatibility (L) bit. 6123 o If the IPsec security associations between the mobile node and the 6124 home agent have been established dynamically, and the mobile node 6125 has the capability to update its endpoint in the used key 6126 management protocol to the new care-of address every time it 6127 moves, the mobile node SHOULD set the Key Management Mobility 6128 Capability (K) bit in the Binding Update. Otherwise, the mobile 6129 node MUST clear the bit. 6131 o The value specified in the Lifetime field MUST be non-zero and 6132 SHOULD be less than or equal to the remaining valid lifetime of 6133 the home address and the care-of address specified for the 6134 binding. 6136 Mobile nodes that use dynamic home agent address discovery should 6137 be careful with long lifetimes. If the mobile node loses the 6138 knowledge of its binding with a specific home agent, registering a 6139 new binding with another home agent may be impossible as the 6140 previous home agent is still defending the existing binding. 6141 Therefore, to ensure that mobile nodes using home agent address 6142 discovery do not lose information about their binding, they SHOULD 6143 de-register before losing this information, or use small 6144 lifetimes. 6146 The Acknowledge (A) bit in the Binding Update requests the home agent 6147 to return a Binding Acknowledgement in response to this Binding 6148 Update. As described in Section 6.1.8, the mobile node SHOULD 6149 retransmit this Binding Update to its home agent until it receives a 6150 matching Binding Acknowledgement. Once reaching a retransmission 6151 timeout period of MAX_BINDACK_TIMEOUT, the mobile node SHOULD restart 6152 the process of delivering the Binding Update, but trying instead the 6153 next home agent returned during dynamic home agent address discovery 6154 (see Section 11.4.1). If there was only one home agent, the mobile 6155 node instead SHOULD continue to periodically retransmit the Binding 6156 Update at this rate until acknowledged (or until it begins attempting 6157 to register a different primary care-of address). See Section 11.8 6158 for information about retransmitting Binding Updates. 6160 With the Binding Update, the mobile node requests the home agent to 6161 serve as the home agent for the given home address. Until the 6162 lifetime of this registration expires, the home agent considers 6163 itself the home agent for this home address. 6165 Each Binding Update MUST be authenticated as coming from the right 6166 mobile node, as defined in Section 5.1. The mobile node MUST use its 6167 home address - either in the Home Address destination option or in 6168 the Source Address field of the IPv6 header - in Binding Updates sent 6169 to the home agent. This is necessary in order to allow the IPsec 6170 policies to be matched with the correct home address. 6172 When sending a Binding Update to its home agent, the mobile node MUST 6173 also create or update the corresponding Binding Update List entry, as 6174 specified in Section 11.7.2. 6176 The last Sequence Number value sent to the home agent in a Binding 6177 Update is stored by the mobile node. If the sending mobile node has 6178 no knowledge of the correct Sequence Number value, it may start at 6179 any value. If the home agent rejects the value, it sends back a 6180 Binding Acknowledgement with a status code 135, and the last accepted 6181 sequence number in the Sequence Number field of the Binding 6182 Acknowledgement. The mobile node MUST store this information and use 6183 the next Sequence Number value for the next Binding Update it sends. 6185 If the mobile node has additional home addresses, then the mobile 6186 node SHOULD send an additional packet containing a Binding Update to 6187 its home agent to register the care-of address for each such other 6188 home address. 6190 The home agent will only perform DAD for the mobile node's home 6191 address when the mobile node has supplied a valid binding between its 6192 home address and a care-of address. If some time elapses during 6193 which the mobile node has no binding at the home agent, it might be 6194 possible for another node to autoconfigure the mobile node's home 6195 address. Therefore, the mobile node MUST treat the creation of a new 6196 binding with the home agent using an existing home address, the same 6197 as creation of a new home address. In the unlikely event that the 6198 mobile node's home address is autoconfigured as the IPv6 address of 6199 another network node on the home network, the home agent will reply 6200 to the mobile node's subsequent Binding Update with a Binding 6201 Acknowledgement containing a Status of 134 (Duplicate Address 6202 Detection failed). In this case, the mobile node MUST NOT attempt to 6203 re-use the same home address. It SHOULD continue to register the 6204 care-of addresses for its other home addresses, if any. Mechanisms 6205 outlined in "Mobile IPv6 Bootstrapping in Split Scenario" [22] allow 6206 mobile nodes to acquire new home addresses to replace the one for 6207 which Status 134 was received. 6209 11.7.2. Correspondent Registration 6211 When the mobile node is assured that its home address is valid, it 6212 can initiate a correspondent registration with the purpose of 6213 allowing the correspondent node to cache the mobile node's current 6214 care-of address. This procedure consists of the return routability 6215 procedure followed by a registration. 6217 This section defines when the correspondent registration is to be 6218 initiated and the rules to follow while it is being performed. 6220 After the mobile node has sent a Binding Update to its home agent, 6221 registering a new primary care-of address (as described in 6222 Section 11.7.1), the mobile node SHOULD initiate a correspondent 6223 registration for each node that already appears in the mobile node's 6224 Binding Update List. The initiated procedures can be used to either 6225 update or delete binding information in the correspondent node. 6227 For nodes that do not appear in the mobile node's Binding Update 6228 List, the mobile node MAY initiate a correspondent registration at 6229 any time after sending the Binding Update to its home agent. 6230 Considerations regarding when (and if) to initiate the procedure 6231 depend on the specific movement and traffic patterns of the mobile 6232 node and are outside the scope of this document. 6234 In addition, the mobile node MAY initiate the correspondent 6235 registration in response to receiving a packet that meets all of the 6236 following tests: 6238 o The packet was tunneled using IPv6 encapsulation. 6240 o The Destination Address in the tunnel (outer) IPv6 header is equal 6241 to any of the mobile node's care-of addresses. 6243 o The Destination Address in the original (inner) IPv6 header is 6244 equal to one of the mobile node's home addresses. 6246 o The Source Address in the tunnel (outer) IPv6 header differs from 6247 the Source Address in the original (inner) IPv6 header. 6249 o The packet does not contain a Home Test, Home Test Init, Care-of 6250 Test, or Care-of Test Init message. 6252 If a mobile node has multiple home addresses, it becomes important to 6253 select the right home address to use in the correspondent 6254 registration. The used home address MUST be the Destination Address 6255 of the original (inner) packet. 6257 The peer address used in the procedure MUST be determined as follows: 6259 o If a Home Address destination option is present in the original 6260 (inner) packet, the address from this option is used. 6262 o Otherwise, the Source Address in the original (inner) IPv6 header 6263 of the packet is used. 6265 Note that the validity of the original packet is checked before 6266 attempting to initiate a correspondent registration. For instance, 6267 if a Home Address destination option appeared in the original packet, 6268 then rules in Section 9.3.1 are followed. 6270 A mobile node MAY also choose to keep its topological location 6271 private from certain correspondent nodes, and thus need not initiate 6272 the correspondent registration. 6274 Upon successfully completing the return routability procedure, and 6275 after receiving a successful Binding Acknowledgement from the Home 6276 Agent, a Binding Update MAY be sent to the correspondent node. 6278 In any Binding Update sent by a mobile node, the care-of address 6279 (either the Source Address in the packet's IPv6 header or the Care-of 6280 Address in the Alternate Care-of Address mobility option of the 6281 Binding Update) MUST be set to one of the care-of addresses currently 6282 in use by the mobile node or to the mobile node's home address. A 6283 mobile node MAY set the care-of address differently for sending 6284 Binding Updates to different correspondent nodes. 6286 A mobile node MAY also send a Binding Update to such a correspondent 6287 node, instructing it to delete any existing binding for the mobile 6288 node from its Binding Cache, as described in Section 6.1.7. Even in 6289 this case a successful completion of the return routability procedure 6290 is required first. 6292 If the care-of address is not set to the mobile node's home address, 6293 the Binding Update requests that the correspondent node create or 6294 update an entry for the mobile node in the correspondent node's 6295 Binding Cache. This is done in order to record a care-of address for 6296 use in sending future packets to the mobile node. In this case, the 6297 value specified in the Lifetime field sent in the Binding Update 6298 SHOULD be less than or equal to the remaining lifetime of the home 6299 registration and the care-of address specified for the binding. The 6300 care-of address given in the Binding Update MAY differ from the 6301 mobile node's primary care-of address. 6303 If the Binding Update is sent to the correspondent node, requesting 6304 the deletion of any existing Binding Cache entry it has for the 6305 mobile node, the care-of address is set to the mobile node's home 6306 address and the Lifetime field set to zero. In this case, generation 6307 of the binding management key depends exclusively on the home keygen 6308 token (Section 5.2.5). The care-of nonce index SHOULD be set to zero 6309 in this case. In keeping with the Binding Update creation rules 6310 below, the care-of address MUST be set to the home address if the 6311 mobile node is at home, or to the current care-of address if it is 6312 away from home. 6314 If the mobile node wants to ensure that its new care-of address has 6315 been entered into a correspondent node's Binding Cache, the mobile 6316 node needs to request an acknowledgement by setting the Acknowledge 6317 (A) bit in the Binding Update. 6319 A Binding Update is created as follows: 6321 o The current care-of address of the mobile node MUST be sent either 6322 in the Source Address of the IPv6 header, or in the Alternate 6323 Care-of Address mobility option. 6325 o The Destination Address of the IPv6 header MUST contain the 6326 address of the correspondent node. 6328 o The Mobility Header is constructed according to rules in 6329 Section 6.1.7 and Section 5.2.6, including the Binding 6330 Authorization Data (calculated as defined in Section 6.2.7) and 6331 possibly the Nonce Indices mobility options. 6333 o The home address of the mobile node MUST be added to the packet in 6334 a Home Address destination option, unless the Source Address is 6335 the home address. 6337 Each Binding Update MUST have a Sequence Number greater than the 6338 Sequence Number value sent in the previous Binding Update to the same 6339 destination address (if any). The sequence numbers are compared 6340 modulo 2**16, as described in Section 9.5.1. There is no 6341 requirement, however, that the Sequence Number value strictly 6342 increase by 1 with each new Binding Update sent or received, as long 6343 as the value stays within the window. The last Sequence Number value 6344 sent to a destination in a Binding Update is stored by the mobile 6345 node in its Binding Update List entry for that destination. If the 6346 sending mobile node has no Binding Update List entry, the Sequence 6347 Number SHOULD start at a random value. The mobile node MUST NOT use 6348 the same Sequence Number in two different Binding Updates to the same 6349 correspondent node, even if the Binding Updates provide different 6350 care-of addresses. 6352 The mobile node is responsible for the completion of the 6353 correspondent registration, as well as any retransmissions that may 6354 be needed (subject to the rate limitation defined in Section 11.8). 6356 11.7.3. Receiving Binding Acknowledgements 6358 Upon receiving a packet carrying a Binding Acknowledgement, a mobile 6359 node MUST validate the packet according to the following tests: 6361 o The packet meets the authentication requirements for Binding 6362 Acknowledgements defined in Section 6.1.8 and Section 5. That is, 6363 if the Binding Update was sent to the home agent, the underlying 6364 IPsec protection is used. If the Binding Update was sent to the 6365 correspondent node, the Binding Authorization Data mobility option 6366 MUST be present and have a valid value. 6368 o The Binding Authorization Data mobility option, if present, MUST 6369 be the last option and MUST NOT have trailing padding. 6371 o The Sequence Number field matches the Sequence Number sent by the 6372 mobile node to this destination address in an outstanding Binding 6373 Update, and the Status field is not 135. 6375 Any Binding Acknowledgement not satisfying all of these tests MUST be 6376 silently ignored. 6378 When a mobile node receives a packet carrying a valid Binding 6379 Acknowledgement, the mobile node MUST examine the Status field as 6380 follows: 6382 o If the Status field indicates that the Binding Update was accepted 6383 (the Status field is less than 128), then the mobile node MUST 6384 update the corresponding entry in its Binding Update List to 6385 indicate that the Binding Update has been acknowledged; the mobile 6386 node MUST then stop retransmitting the Binding Update. In 6387 addition, if the value specified in the Lifetime field in the 6388 Binding Acknowledgement is less than the Lifetime value sent in 6389 the Binding Update being acknowledged, the mobile node MUST 6390 subtract the difference between these two Lifetime values from the 6391 remaining lifetime for the binding as maintained in the 6392 corresponding Binding Update List entry (with a minimum value for 6393 the Binding Update List entry lifetime of 0). That is, if the 6394 Lifetime value sent in the Binding Update was L_update, the 6395 Lifetime value received in the Binding Acknowledgement was L_ack, 6396 and the current remaining lifetime of the Binding Update List 6397 entry is L_remain, then the new value for the remaining lifetime 6398 of the Binding Update List entry should be 6400 max((L_remain - (L_update - L_ack)), 0) 6402 where max(X, Y) is the maximum of X and Y. The effect of this step 6403 is to correctly manage the mobile node's view of the binding's 6404 remaining lifetime (as maintained in the corresponding Binding 6405 Update List entry) so that it correctly counts down from the 6406 Lifetime value given in the Binding Acknowledgement, but with the 6407 timer countdown beginning at the time that the Binding Update was 6408 sent. 6410 Mobile nodes SHOULD send a new Binding Update well before the 6411 expiration of this period in order to extend the lifetime. This 6412 helps to avoid disruptions in communications which might otherwise 6413 be caused by network delays or clock drift. 6415 o If the Binding Acknowledgement correctly passes authentication and 6416 the Status field value is 135 (Sequence Number out of window), 6417 then the mobile node MUST update its binding sequence number 6418 appropriately to match the sequence number given in the Binding 6419 Acknowledgement. Otherwise, if the Status field value is 135 but 6420 the Binding Acknowledgement does not pass authentication, the 6421 message MUST be silently ignored. 6423 o If the Status field value is 1 (accepted but prefix discovery 6424 necessary), the mobile node SHOULD send a Mobile Prefix 6425 Solicitation message to update its information about the available 6426 prefixes. 6428 o If the Status field indicates that the Binding Update was rejected 6429 (the Status field is greater than or equal to 128), then the 6430 mobile node can take steps to correct the cause of the error and 6431 retransmit the Binding Update (with a new Sequence Number value), 6432 subject to the rate limiting restriction specified in 6433 Section 11.8. If this is not done or it fails, then the mobile 6434 node SHOULD record in its Binding Update List that future Binding 6435 Updates SHOULD NOT be sent to this destination. 6437 The treatment of a Binding Refresh Advice mobility option within the 6438 Binding Acknowledgement depends on where the acknowledgement came 6439 from. This option MUST be ignored if the acknowledgement came from a 6440 correspondent node. If it came from the home agent, the mobile node 6441 uses the Refresh Interval field in the option as a suggestion that it 6442 SHOULD attempt to refresh its home registration at the indicated 6443 shorter interval. 6445 If the acknowledgement came from the home agent, the mobile node 6446 examines the value of the Key Management Mobility Capability (K) bit. 6447 If this bit is not set, the mobile node SHOULD discard key management 6448 protocol connections, if any, to the home agent. The mobile node MAY 6449 also initiate a new key management connection. 6451 If this bit is set, the mobile node SHOULD move its own endpoint in 6452 the key management protocol connections to the home agent, if any. 6453 The mobile node's new endpoint should be the new care-of address. 6455 11.7.4. Receiving Binding Refresh Requests 6457 When a mobile node receives a packet containing a Binding Refresh 6458 Request message, if the mobile node has a Binding Update List entry 6459 for the source of the Binding Refresh Request, and the mobile node 6460 wants to retain its Binding Cache entry at the correspondent node, 6461 then the mobile node should start a return routability procedure. If 6462 the mobile node wants to have its Binding Cache entry removed, it can 6463 either ignore the Binding Refresh Request and wait for the binding to 6464 time out, or at any time, it can delete its binding from a 6465 correspondent node with an explicit Binding Update with a zero 6466 lifetime and the care-of address set to the home address. If the 6467 mobile node does not know if it needs the Binding Cache entry, it can 6468 make the decision in an implementation dependent manner, such as 6469 based on available resources. 6471 Note that the mobile node should be careful to not respond to Binding 6472 Refresh Requests for addresses not in the Binding Update List to 6473 avoid being subjected to a denial of service attack. 6475 If the return routability procedure completes successfully, a Binding 6476 Update message SHOULD be sent, as described in Section 11.7.2. The 6477 Lifetime field in this Binding Update SHOULD be set to a new 6478 lifetime, extending any current lifetime remaining from a previous 6479 Binding Update sent to this node (as indicated in any existing 6480 Binding Update List entry for this node), and the lifetime SHOULD 6481 again be less than or equal to the remaining lifetime of the home 6482 registration and the care-of address specified for the binding. When 6483 sending this Binding Update, the mobile node MUST update its Binding 6484 Update List in the same way as for any other Binding Update sent by 6485 the mobile node. 6487 11.8. Retransmissions and Rate Limiting 6489 The mobile node is responsible for retransmissions and rate limiting 6490 in the return routability procedure, registrations, and in solicited 6491 prefix discovery. 6493 When the mobile node sends a Mobile Prefix Solicitation, Home Test 6494 Init, Care-of Test Init or Binding Update for which it expects a 6495 response, the mobile node has to determine a value for the initial 6496 retransmission timer: 6498 o If the mobile node is sending a Mobile Prefix Solicitation, it 6499 SHOULD use an initial retransmission interval of 6500 INITIAL_SOLICIT_TIMER (see Section 12). 6502 o If the mobile node is sending a Binding Update and does not have 6503 an existing binding at the home agent, it SHOULD use 6504 InitialBindackTimeoutFirstReg (see Section 13) as a value for the 6505 initial retransmission timer. This long retransmission interval 6506 will allow the home agent to complete the Duplicate Address 6507 Detection procedure mandated in this case, as detailed in 6508 Section 11.7.1. 6510 o Otherwise, the mobile node should use the specified value of 6511 INITIAL_BINDACK_TIMEOUT for the initial retransmission timer. 6513 If the mobile node fails to receive a valid matching response within 6514 the selected initial retransmission interval, the mobile node SHOULD 6515 retransmit the message until a response is received. 6517 The retransmissions by the mobile node MUST use an exponential back- 6518 off process in which the timeout period is doubled upon each 6519 retransmission, until either the node receives a response or the 6520 timeout period reaches the value MAX_BINDACK_TIMEOUT. The mobile 6521 node MAY continue to send these messages at this slower rate 6522 indefinitely. 6524 The mobile node SHOULD start a separate back-off process for 6525 different message types, different home addresses and different 6526 care-of addresses. However, in addition an overall rate limitation 6527 applies for messages sent to a particular correspondent node. This 6528 ensures that the correspondent node has a sufficient amount of time 6529 to respond when bindings for multiple home addresses are registered, 6530 for instance. The mobile node MUST NOT send Mobility Header messages 6531 of a particular type to a particular correspondent node more than 6532 MAX_UPDATE_RATE times within a second. 6534 Retransmitted Binding Updates MUST use a Sequence Number value 6535 greater than that used for the previous transmission of this Binding 6536 Update. Retransmitted Home Test Init and Care-of Test Init messages 6537 MUST use new cookie values. 6539 12. Protocol Constants 6541 DHAAD_RETRIES 4 retransmissions 6542 INITIAL_BINDACK_TIMEOUT 1 second 6543 INITIAL_DHAAD_TIMEOUT 3 seconds 6544 INITIAL_SOLICIT_TIMER 3 seconds 6545 MAX_BINDACK_TIMEOUT 32 seconds 6546 MAX_DELETE_BCE_TIMEOUT 10 seconds 6547 MAX_NONCE_LIFETIME 240 seconds 6548 MAX_TOKEN_LIFETIME 210 seconds 6549 MAX_RO_FAILURE 3 retries 6550 MAX_RR_BINDING_LIFETIME 420 seconds 6551 MAX_UPDATE_RATE 3 times 6552 PREFIX_ADV_RETRIES 3 retransmissions 6553 PREFIX_ADV_TIMEOUT 3 seconds 6555 13. Protocol Configuration Variables 6557 MaxMobPfxAdvInterval Default: 86,400 seconds 6558 MinDelayBetweenRAs Default: 3 seconds, 6559 Min: 0.03 seconds 6560 MinMobPfxAdvInterval Default: 600 seconds 6561 InitialBindackTimeoutFirstReg Default: 1.5 seconds 6563 Home agents MUST allow the first three variables to be configured by 6564 system management, and mobile nodes MUST allow the last variable to 6565 be configured by system management. 6567 The default value for InitialBindackTimeoutFirstReg has been 6568 calculated as 1.5 times the default value of RetransTimer, as 6569 specified in Neighbor Discovery (RFC 4861 [18]) times the default 6570 value of DupAddrDetectTransmits, as specified in Stateless Address 6571 Autoconfiguration (RFC 4862 [19]) 6573 The value MinDelayBetweenRAs overrides the value of the protocol 6574 constant MIN_DELAY_BETWEEN_RAS, as specified in Neighbor Discovery 6575 (RFC 4861 [18]). This variable SHOULD be set to MinRtrAdvInterval, 6576 if MinRtrAdvInterval is less than 3 seconds. 6578 14. IANA Considerations 6580 This document defines a new IPv6 protocol, the Mobility Header, 6581 described in Section 6.1. This protocol has been assigned protocol 6582 number 135. 6584 This document also creates a new name space "Mobility Header Type", 6585 for the MH Type field in the Mobility Header. The current message 6586 types are described starting from Section 6.1.2, and are the 6587 following: 6589 0 Binding Refresh Request 6591 1 Home Test Init 6593 2 Care-of Test Init 6595 3 Home Test 6597 4 Care-of Test 6599 5 Binding Update 6601 6 Binding Acknowledgement 6603 7 Binding Error 6605 Future values of the MH Type can be allocated using Standards Action 6606 or IESG Approval [23]. 6608 Furthermore, each mobility message may contain mobility options as 6609 described in Section 6.2. This document defines a new name space 6610 "Mobility Option" to identify these options. The current mobility 6611 options are defined starting from Section 6.2.2 and are the 6612 following: 6614 0 Pad1 6616 1 PadN 6618 2 Binding Refresh Advice 6620 3 Alternate Care-of Address 6622 4 Nonce Indices 6623 5 Authorization Data 6625 Future values of the Option Type can be allocated using Standards 6626 Action or IESG Approval [23]. 6628 Finally, this document creates a third new name space "Status Code" 6629 for the Status field in the Binding Acknowledgement message. The 6630 current values are listed in Section 6.1.8 and are the following: 6632 0 Binding Update accepted 6634 1 Accepted but prefix discovery necessary 6636 128 Reason unspecified 6638 129 Administratively prohibited 6640 130 Insufficient resources 6642 131 Home registration not supported 6644 132 Not home subnet 6646 133 Not home agent for this mobile node 6648 134 Duplicate Address Detection failed 6650 135 Sequence number out of window 6652 136 Expired home nonce index 6654 137 Expired care-of nonce index 6656 138 Expired nonces 6658 139 Registration type change disallowed 6660 TBD Invalid Care-of Address 6662 Future values of the Status field can be allocated using Standards 6663 Action or IESG Approval [23]. 6665 All fields labeled "Reserved" are only to be assigned through 6666 Standards Action or IESG Approval. 6668 This document also defines a new IPv6 destination option, the Home 6669 Address option, described in Section 6.3. This option has been 6670 assigned the Option Type value 0xC9. 6672 This document also defines a new IPv6 type 2 routing header, 6673 described in Section 6.4. The value 2 has been allocated by IANA. 6675 In addition, this document defines four ICMP message types, two used 6676 as part of the dynamic home agent address discovery mechanism, and 6677 two used in lieu of Router Solicitations and Advertisements when the 6678 mobile node is away from the home link. These messages have been 6679 assigned ICMPv6 type numbers from the informational message range: 6681 o The Home Agent Address Discovery Request message, described in 6682 Section 6.5; 6684 o The Home Agent Address Discovery Reply message, described in 6685 Section 6.6; 6687 o The Mobile Prefix Solicitation, described in Section 6.7; and 6689 o The Mobile Prefix Advertisement, described in Section 6.8. 6691 This document also defines two new Neighbor Discovery [18] options, 6692 which have been assigned Option Type values within the option 6693 numbering space for Neighbor Discovery messages: 6695 o The Advertisement Interval option, described in Section 7.3; and 6697 o The Home Agent Information option, described in Section 7.4. 6699 15. Security Considerations 6701 15.1. Threats 6703 Any mobility solution must protect itself against misuses of the 6704 mobility features and mechanisms. In Mobile IPv6, most of the 6705 potential threats are concerned with false Bindings, usually 6706 resulting in Denial-of-Service attacks. Some of the threats also 6707 pose potential for Man-in-the-Middle, Hijacking, Confidentiality, and 6708 Impersonation attacks. The main threats this protocol protects 6709 against are the following: 6711 o Threats involving Binding Updates sent to home agents and 6712 correspondent nodes. For instance, an attacker might claim that a 6713 certain mobile node is currently at a different location than it 6714 really is. If a home agent accepts such spoofed information sent 6715 to it, the mobile node might not get traffic destined to it. 6716 Similarly, a malicious (mobile) node might use the home address of 6717 a victim node in a forged Binding Update sent to a correspondent 6718 node. 6720 These pose threats against confidentiality, integrity, and 6721 availability. That is, an attacker might learn the contents of 6722 packets destined to another node by redirecting the traffic to 6723 itself. Furthermore, an attacker might use the redirected packets 6724 in an attempt to set itself as a Man-in-the-Middle between a 6725 mobile and a correspondent node. This would allow the attacker to 6726 impersonate the mobile node, leading to integrity and availability 6727 problems. 6729 A malicious (mobile) node might also send Binding Updates in which 6730 the care-of address is set to the address of a victim node. If 6731 such Binding Updates were accepted, the malicious node could lure 6732 the correspondent node into sending potentially large amounts of 6733 data to the victim; the correspondent node's replies to messages 6734 sent by the malicious mobile node will be sent to the victim host 6735 or network. This could be used to cause a Distributed Denial-of- 6736 Service attack. For example, the correspondent node might be a 6737 site that will send a high-bandwidth stream of video to anyone who 6738 asks for it. Note that the use of flow-control protocols such as 6739 TCP does not necessarily defend against this type of attack, 6740 because the attacker can fake the acknowledgements. Even keeping 6741 TCP initial sequence numbers secret does not help, because the 6742 attacker can receive the first few segments (including the ISN) at 6743 its own address, and only then redirect the stream to the victim's 6744 address. These types of attacks may also be directed to networks 6745 instead of nodes. Further variations of this threat are described 6746 elsewhere [28] [34]. 6748 An attacker might also attempt to disrupt a mobile node's 6749 communications by replaying a Binding Update that the node had 6750 sent earlier. If the old Binding Update was accepted, packets 6751 destined for the mobile node would be sent to its old location as 6752 opposed to its current location. 6754 A malicious mobile node associated to multiple home agents could 6755 create a routing loop amongst them. This can be achieved when a 6756 mobile node binds one home address located on a first home agent 6757 to another home address on a second home agent. This type of 6758 binding will force the home agents to route the same packet among 6759 each other without knowledge that a routing loop has been created. 6760 Such looping problem is limited to cases where a mobile node has 6761 multiple home agents and is permitted to be associated with the 6762 multiple home agents. For the single home agent case, a policy at 6763 the home agent would prevent the binding of one home address to 6764 another home address hosted by the same home agent. 6766 The potential problems caused by such routing loops in this 6767 scenario can be substantially reduced by use of the Tunnel-Limit 6768 Option specified in RFC 2473 [7]. 6770 In conclusion, there are Denial-of-Service, Man-in-the-Middle, 6771 Confidentiality, and Impersonation threats against the parties 6772 involved in sending legitimate Binding Updates, the threat of 6773 routing loops when there are multiple home agents, and Denial-of- 6774 Service threats against any other party. 6776 o Threats associated with payload packets: Payload packets exchanged 6777 with mobile nodes are exposed to similar threats as that of 6778 regular IPv6 traffic. However, Mobile IPv6 introduces the Home 6779 Address destination option, a new routing header type (type 2), 6780 and uses tunneling headers in the payload packets. The protocol 6781 must protect against potential new threats involving the use of 6782 these mechanisms. 6784 Third parties become exposed to a reflection threat via the Home 6785 Address destination option, unless appropriate security 6786 precautions are followed. The Home Address destination option 6787 could be used to direct response traffic toward a node whose IP 6788 address appears in the option. In this case, ingress filtering 6789 would not catch the forged "return address" [37] [41]. 6791 A similar threat exists with the tunnels between the mobile node 6792 and the home agent. An attacker might forge tunnel packets 6793 between the mobile node and the home agent, making it appear that 6794 the traffic is coming from the mobile node when it is not. Note 6795 that an attacker who is able to forge tunnel packets would 6796 typically also be able to forge packets that appear to come 6797 directly from the mobile node. This is not a new threat as such. 6798 However, it may make it easier for attackers to escape detection 6799 by avoiding ingress filtering and packet tracing mechanisms. 6800 Furthermore, spoofed tunnel packets might be used to gain access 6801 to the home network. 6803 Finally, a routing header could also be used in reflection 6804 attacks, and in attacks designed to bypass firewalls. The 6805 generality of the regular routing header would allow circumvention 6806 of IP-address based rules in firewalls. It would also allow 6807 reflection of traffic to other nodes. These threats exist with 6808 routing headers in general, even if the usage that Mobile IPv6 6809 requires is safe. 6811 o Threats associated with dynamic home agent and mobile prefix 6812 discovery. 6814 o Threats against the Mobile IPv6 security mechanisms themselves: An 6815 attacker might, for instance, lure the participants into executing 6816 expensive cryptographic operations or allocating memory for the 6817 purpose of keeping state. The victim node would have no resources 6818 left to handle other tasks. 6820 As a fundamental service in an IPv6 stack, Mobile IPv6 is expected to 6821 be deployed in most nodes of the IPv6 Internet. The above threats 6822 should therefore be considered as being applicable to the whole 6823 Internet. 6825 It should also be noted that some additional threats result from 6826 movements as such, even without the involvement of mobility 6827 protocols. Mobile nodes must be capable to defend themselves in the 6828 networks that they visit, as typical perimeter defenses applied in 6829 the home network no longer protect them. 6831 15.2. Features 6833 This specification provides a series of features designed to mitigate 6834 the risk introduced by the threats listed above. The main security 6835 features are the following: 6837 o Reverse Tunneling as a mandatory feature. 6839 o Protection of Binding Updates sent to home agents. 6841 o Protection of Binding Updates sent to correspondent nodes. 6843 o Protection against reflection attacks that use the Home Address 6844 destination option. 6846 o Protection of tunnels between the mobile node and the home agent. 6848 o Closing routing header vulnerabilities. 6850 o Mitigating Denial-of-Service threats to the Mobile IPv6 security 6851 mechanisms themselves. 6853 The support for encrypted reverse tunneling (see Section 11.3.1) 6854 allows mobile nodes to defeat certain kinds of traffic analysis. 6856 Protecting those Binding Updates that are sent to home agents and 6857 those that are sent to arbitrary correspondent nodes requires very 6858 different security solutions due to the different situations. Mobile 6859 nodes and home agents are naturally expected to be subject to the 6860 network administration of the home domain. 6862 Thus, they can and are supposed to have a security association that 6863 can be used to reliably authenticate the exchanged messages. See 6864 Section 5.1 for the description of the protocol mechanisms, and 6865 Section 15.3 below for a discussion of the resulting level of 6866 security. 6868 It is expected that Mobile IPv6 route optimization will be used on a 6869 global basis between nodes belonging to different administrative 6870 domains. It would be a very demanding task to build an 6871 authentication infrastructure on this scale. Furthermore, a 6872 traditional authentication infrastructure cannot be easily used to 6873 authenticate IP addresses because IP addresses can change often. It 6874 is not sufficient to just authenticate the mobile nodes; 6875 Authorization to claim the right to use an address is needed as well. 6876 Thus, an "infrastructureless" approach is necessary. The chosen 6877 infrastructureless method is described in Section 5.2, and 6878 Section 15.4 discusses the resulting security level and the design 6879 rationale of this approach. 6881 Specific rules guide the use of the Home Address destination option, 6882 the routing header, and the tunneling headers in the payload packets. 6883 These rules are necessary to remove the vulnerabilities associated 6884 with their unrestricted use. The effect of the rules is discussed in 6885 Section 15.7, Section 15.8, and Section 15.9. 6887 Denial-of-Service threats against Mobile IPv6 security mechanisms 6888 themselves concern mainly the Binding Update procedures with 6889 correspondent nodes. The protocol has been designed to limit the 6890 effects of such attacks, as will be described in Section 15.4.5. 6892 15.3. Binding Updates to Home Agent 6894 Signaling between the mobile node and the home agent requires message 6895 integrity. This is necessary to assure the home agent that a Binding 6896 Update is from a legitimate mobile node. In addition, correct 6897 ordering and anti-replay protection are optionally needed. 6899 IPsec ESP protects the integrity of the Binding Updates and Binding 6900 Acknowledgements by securing mobility messages between the mobile 6901 node and the home agent. 6903 IPsec can provide anti-replay protection only if dynamic keying is 6904 used (which may not always be the case). IPsec does not guarantee 6905 correct ordering of packets, only that they have not been replayed. 6906 Because of this, sequence numbers within the Mobile IPv6 messages are 6907 used to ensure correct ordering (see Section 5.1). However, if the 6908 16 bit Mobile IPv6 sequence number space is cycled through, or the 6909 home agent reboots and loses its state regarding the sequence 6910 numbers, replay and reordering attacks become possible. The use of 6911 dynamic keying, IPsec anti-replay protection, and the Mobile IPv6 6912 sequence numbers can together prevent such attacks. It is also 6913 recommended that use of non-volatile storage be considered for home 6914 agents, to avoid losing their state. 6916 A sliding window scheme is used for the sequence numbers. The 6917 protection against replays and reordering attacks without a key 6918 management mechanism works when the attacker remembers up to a 6919 maximum of 2**15 Binding Updates. 6921 The above mechanisms do not show that the care-of address given in 6922 the Binding Update is correct. This opens the possibility for 6923 Denial-of-Service attacks against third parties. However, since the 6924 mobile node and home agent have a security association, the home 6925 agent can always identify an ill-behaving mobile node. This allows 6926 the home agent operator to discontinue the mobile node's service, and 6927 possibly take further actions based on the business relationship with 6928 the mobile node's owner. 6930 Note that the use of a single pair of manually keyed security 6931 associations conflicts with the generation of a new home address [21] 6932 for the mobile node, or with the adoption of a new home subnet 6933 prefix. This is because IPsec security associations are bound to the 6934 used addresses. While certificate-based automatic keying alleviates 6935 this problem to an extent, it is still necessary to ensure that a 6936 given mobile node cannot send Binding Updates for the address of 6937 another mobile node. In general, this leads to the inclusion of home 6938 addresses in certificates in the Subject AltName field. This again 6939 limits the introduction of new addresses without either manual or 6940 automatic procedures to establish new certificates. Therefore, this 6941 specification restricts the generation of new home addresses (for any 6942 reason) to those situations where a security association or 6943 certificate for the new address already exists. 6945 Support for IKEv2 has been specified as optional. The following 6946 should be observed about the use of manual keying: 6948 o As discussed above, with manually keyed IPsec, only a limited form 6949 of protection exists against replay and reordering attacks. A 6950 vulnerability exists if either the sequence number space is cycled 6951 through, or if the home agent reboots and forgets its sequence 6952 numbers (and uses volatile memory to store the sequence numbers). 6954 Assuming the mobile node moves continuously every 10 minutes, it 6955 takes roughly 455 days before the sequence number space has been 6956 cycled through. Typical movement patterns rarely reach this high 6957 frequency today. 6959 o A mobile node and its home agent belong to the same domain. If 6960 this were not the case, manual keying would not be possible [40], 6961 but in Mobile IPv6 only these two parties need to know the 6962 manually configured keys. Similarly, we note that Mobile IPv6 6963 employs standard block ciphers in IPsec, and is not vulnerable to 6964 problems associated with stream ciphers and manual keying. 6966 o It is expected that the owner of the mobile node and the 6967 administrator of the home agent agree on the used keys and other 6968 parameters with some off-line mechanism. 6970 The use of IKEv2 with Mobile IPv6 is documented in more detail in 6971 [20]. The following should be observed regarding the use of IKEv2: 6973 o It is necessary to prevent a mobile node from claiming another 6974 mobile node's home address. The home agent must verify that the 6975 mobile node trying to negotiate the SA for a particular home 6976 address is authorized for that home address. This implies that 6977 even with the use of IKEv2, a policy entry needs to be configured 6978 for each home address served by the home agent. 6980 It may be possible to include home addresses in the Subject 6981 AltName field of certificate to avoid this. However, 6982 implementations are not guaranteed to support the use of a 6983 particular IP address (care-of address) while another address 6984 (home address) appears in the certificate. In any case, even this 6985 approach would require user-specific tasks in the certificate 6986 authority. 6988 o Due to the problems outlined in Section 11.3.2, the IKEv2 SA 6989 between the mobile node and its home agent is established using 6990 the mobile node's current care-of address. This implies that when 6991 the mobile node moves to a new location, it may have to re- 6992 establish an IKEv2 Security Association. A Key Management 6993 Mobility Capability (K) flag is provided for implementations that 6994 can update the IKEv2 endpoints without re-establishing an IKEv2 6995 Security Association, but the support for this behavior is 6996 optional. 6998 o Nevertheless, even if per-mobile node configuration is required 6999 with IKEv2, an important benefit of IKEv2 is that it automates the 7000 negotiation of cryptographic parameters, including the SPIs, 7001 cryptographic algorithms, and so on. Thus, less configuration 7002 information is needed. 7004 o The frequency of movements in some link layers or deployment 7005 scenarios may be high enough to make replay and reordering attacks 7006 possible, if only manual keying is used. IKEv2 SHOULD be used in 7007 such cases. Potentially vulnerable scenarios involve continuous 7008 movement through small cells, or uncontrolled alternation between 7009 available network attachment points. 7011 o Similarly, in some deployment scenarios the number of mobile nodes 7012 may be very large. In these cases, it can be necessary to use 7013 automatic mechanisms to reduce the management effort in the 7014 administration of cryptographic parameters, even if some per- 7015 mobile node configuration is always needed. IKEv2 SHOULD also be 7016 used in such cases. 7018 15.4. Binding Updates to Correspondent Nodes 7020 The motivation for designing the return routability procedure was to 7021 have sufficient support for Mobile IPv6, without creating significant 7022 new security problems. The goal for this procedure was not to 7023 protect against attacks that were already possible before the 7024 introduction of Mobile IPv6. 7026 The next sections will describe the security properties of the used 7027 method, both from the point of view of possible on-path attackers who 7028 can see those cryptographic values that have been sent in the clear 7029 (Section 15.4.2 and Section 15.4.3) and from the point of view of 7030 other attackers (Section 15.4.6). 7032 15.4.1. Overview 7034 The chosen infrastructureless method verifies that the mobile node is 7035 "live" (that is, it responds to probes) at its home and care-of 7036 addresses. Section 5.2 describes the return routability procedure in 7037 detail. The procedure uses the following principles: 7039 o A message exchange verifies that the mobile node is reachable at 7040 its addresses, i.e., is at least able to transmit and receive 7041 traffic at both the home and care-of addresses. 7043 o The eventual Binding Update is cryptographically bound to the 7044 tokens supplied in the exchanged messages. 7046 o Symmetric exchanges are employed to avoid the use of this protocol 7047 in reflection attacks. In a symmetric exchange, the responses are 7048 always sent to the same address the request was sent from. 7050 o The correspondent node operates in a stateless manner until it 7051 receives a fully authorized Binding Update. 7053 o Some additional protection is provided by encrypting the tunnels 7054 between the mobile node and home agent with IPsec ESP. As the 7055 tunnel also transports the nonce exchanges, the ability of 7056 attackers to see these nonces is limited. For instance, this 7057 prevents attacks from being launched from the mobile node's 7058 current foreign link, even when no link-layer confidentiality is 7059 available. 7061 The resulting level of security is in theory the same even without 7062 this additional protection: the return routability tokens are 7063 still exposed only to one path within the whole Internet. 7064 However, the mobile nodes are often found on an insecure link, 7065 such as a public access Wireless LAN. Thus, in many cases, this 7066 addition makes a practical difference. 7068 For further information about the design rationale of the return 7069 routability procedure, see [28] [34] [33] [41]. The mechanisms used 7070 have been adopted from these documents. 7072 15.4.2. Achieved Security Properties 7074 The return routability procedure protects Binding Updates against all 7075 attackers who are unable to monitor the path between the home agent 7076 and the correspondent node. The procedure does not defend against 7077 attackers who can monitor this path. Note that such attackers are in 7078 any case able to mount an active attack against the mobile node when 7079 it is at its home location. The possibility of such attacks is not 7080 an impediment to the deployment of Mobile IPv6 because these attacks 7081 are possible regardless of whether or not Mobile IPv6 is in use. 7083 This procedure also protects against Denial-of-Service attacks in 7084 which the attacker pretends to be mobile, but uses the victim's 7085 address as the care-of address. This would cause the correspondent 7086 node to send the victim some unexpected traffic. This procedure 7087 defends against these attacks by requiring at least the passive 7088 presence of the attacker at the care-of address or on the path from 7089 the correspondent to the care-of address. Normally, this will be the 7090 mobile node. 7092 15.4.3. Comparison to Regular IPv6 Communications 7094 This section discusses the protection offered by the return 7095 routability method by comparing it to the security of regular IPv6 7096 communications. We will divide vulnerabilities into three classes: 7097 (1) those related to attackers on the local network of the mobile 7098 node, home agent, or the correspondent node, (2) those related to 7099 attackers on the path between the home network and the correspondent 7100 node, and (3) off-path attackers, i.e., the rest of the Internet. 7102 We will now discuss the vulnerabilities of regular IPv6 7103 communications. The on-link vulnerabilities of IPv6 communications 7104 include Denial-of-Service, Masquerading, Man-in-the-Middle, 7105 Eavesdropping, and other attacks. These attacks can be launched 7106 through spoofing Router Discovery, Neighbor Discovery and other IPv6 7107 mechanisms. Some of these attacks can be prevented with the use of 7108 cryptographic protection in the packets. 7110 A similar situation exists with on-path attackers. That is, without 7111 cryptographic protection, the traffic is completely vulnerable. 7113 Assuming that attackers have not penetrated the security of the 7114 Internet routing protocols, attacks are much harder to launch from 7115 off-path locations. Attacks that can be launched from these 7116 locations are mainly Denial-of-Service attacks, such as flooding 7117 and/or reflection attacks. It is not possible for an off-path 7118 attacker to become a Man-in-the-Middle. 7120 Next, we will consider the vulnerabilities that exist when IPv6 is 7121 used together with Mobile IPv6 and the return routability procedure. 7122 On the local link, the vulnerabilities are the same as those in IPv6, 7123 but Masquerade and Man-in-the-Middle attacks can now also be launched 7124 against future communications, and not just against current 7125 communications. If a Binding Update was sent while the attacker was 7126 present on the link, its effects remain for the lifetime of the 7127 binding. This happens even if the attacker moves away from the link. 7128 In contrast, an attacker who uses only plain IPv6 generally has to 7129 stay on the link in order to continue the attack. Note that in order 7130 to launch these new attacks, the IP address of the victim must be 7131 known. This makes this attack feasible, mainly in the context of 7132 well-known interface IDs, such as those already appearing in the 7133 traffic on the link or registered in the DNS. 7135 On-path attackers can exploit similar vulnerabilities as in regular 7136 IPv6. There are some minor differences, however. Masquerade, Man- 7137 in-the-Middle, and Denial-of-Service attacks can be launched with 7138 just the interception of a few packets, whereas in regular IPv6 it is 7139 necessary to intercept every packet. The effect of the attacks is 7140 the same regardless of the method, however. In any case, the most 7141 difficult task an attacker faces in these attacks is getting on the 7142 right path. 7144 The vulnerabilities for off-path attackers are the same as in regular 7145 IPv6. Those nodes that are not on the path between the home agent 7146 and the correspondent node will not be able to receive the home 7147 address probe messages. 7149 In conclusion, we can state the following main results from this 7150 comparison: 7152 o Return routability prevents any off-path attacks beyond those that 7153 are already possible in regular IPv6. This is the most important 7154 result, preventing attackers on the Internet from exploiting any 7155 vulnerabilities. 7157 o Vulnerabilities to attackers on the home agent link, the 7158 correspondent node link, and the path between them are roughly the 7159 same as in regular IPv6. 7161 o However, one difference is that in basic IPv6 an on-path attacker 7162 must be constantly present on the link or the path, whereas with 7163 Mobile IPv6, an attacker can leave a binding behind after moving 7164 away. 7166 For this reason, this specification limits the creation of 7167 bindings to at most MAX_TOKEN_LIFETIME seconds after the last 7168 routability check has been performed, and limits the duration of a 7169 binding to at most MAX_RR_BINDING_LIFETIME seconds. With these 7170 limitations, attackers cannot take any practical advantages of 7171 this vulnerability. 7173 o There are some other minor differences, such as an effect to the 7174 Denial-of-Service vulnerabilities. These can be considered to be 7175 insignificant. 7177 o The path between the home agent and a correspondent node is 7178 typically easiest to attack on the links at either end, in 7179 particular if these links are publicly accessible wireless LANs. 7181 Attacks against the routers or switches on the path are typically 7182 harder to accomplish. The security on layer 2 of the links plays 7183 then a major role in the resulting overall network security. 7184 Similarly, security of IPv6 Neighbor and Router Discovery on these 7185 links has a large impact. If these were secured using some new 7186 technology in the future, this could change the situation 7187 regarding the easiest point of attack. 7189 For a more in-depth discussion of these issues, see [41]. 7191 15.4.4. Replay Attacks 7193 The return routability procedure also protects the participants 7194 against replayed Binding Updates. The attacker is unable replay the 7195 same message due to the sequence number which is a part of the 7196 Binding Update. It is also unable to modify the Binding Update since 7197 the MAC verification would fail after such a modification. 7199 Care must be taken when removing bindings at the correspondent node, 7200 however. If a binding is removed while the nonce used in its 7201 creation is still valid, an attacker could replay the old Binding 7202 Update. Rules outlined in Section 5.2.8 ensure that this cannot 7203 happen. 7205 15.4.5. Denial-of-Service Attacks 7207 The return routability procedure has protection against resource 7208 exhaustion Denial-of-Service attacks. The correspondent nodes do not 7209 retain any state about individual mobile nodes until an authentic 7210 Binding Update arrives. This is achieved through the construct of 7211 keygen tokens from the nonces and node keys that are not specific to 7212 individual mobile nodes. The keygen tokens can be reconstructed by 7213 the correspondent node, based on the home and care-of address 7214 information that arrives with the Binding Update. This means that 7215 the correspondent nodes are safe against memory exhaustion attacks 7216 except where on-path attackers are concerned. Due to the use of 7217 symmetric cryptography, the correspondent nodes are relatively safe 7218 against CPU resource exhaustion attacks as well. 7220 Nevertheless, as [28] describes, there are situations in which it is 7221 impossible for the mobile and correspondent nodes to determine if 7222 they actually need a binding or whether they just have been fooled 7223 into believing so by an attacker. Therefore, it is necessary to 7224 consider situations where such attacks are being made. 7226 Even if route optimization is a very important optimization, it is 7227 still only an optimization. A mobile node can communicate with a 7228 correspondent node even if the correspondent refuses to accept any 7229 Binding Updates. However, performance will suffer because packets 7230 from the correspondent node to the mobile node will be routed via the 7231 mobile's home agent rather than a more direct route. A correspondent 7232 node can protect itself against some of these resource exhaustion 7233 attacks as follows. If the correspondent node is flooded with a 7234 large number of Binding Updates that fail the cryptographic integrity 7235 checks, it can stop processing Binding Updates. If a correspondent 7236 node finds that it is spending more resources on checking bogus 7237 Binding Updates than it is likely to save by accepting genuine 7238 Binding Updates, then it may silently discard some or all Binding 7239 Updates without performing any cryptographic operations. 7241 Layers above IP can usually provide additional information to help 7242 determine whether there is a need to establish a binding with a 7243 specific peer. For example, TCP knows if the node has a queue of 7244 data that it is trying to send to a peer. An implementation of this 7245 specification is not required to make use of information from higher 7246 protocol layers, but some implementations are likely to be able to 7247 manage resources more effectively by making use of such information. 7249 We also require that all implementations be capable of 7250 administratively disabling route optimization. 7252 15.4.6. Key Lengths 7254 Attackers can try to break the return routability procedure in many 7255 ways. Section 15.4.2 discusses the situation where the attacker can 7256 see the cryptographic values sent in the clear, and Section 15.4.3 7257 discusses the impact this has on IPv6 communications. This section 7258 discusses whether attackers can guess the correct values without 7259 seeing them. 7261 While the return routability procedure is in progress, 64 bit cookies 7262 are used to protect spoofed responses. This is believed to be 7263 sufficient, given that to blindly spoof a response a very large 7264 number of messages would have to be sent before success would be 7265 probable. 7267 The tokens used in the return routability procedure provide together 7268 128 bits of information. This information is used internally as 7269 input to a hash function to produce a 160 bit quantity suitable for 7270 producing the keyed hash in the Binding Update using the HMAC_SHA1 7271 algorithm. The final keyed hash length is 96 bits. The limiting 7272 factors in this case are the input token lengths and the final keyed 7273 hash length. The internal hash function application does not reduce 7274 the entropy. 7276 The 96 bit final keyed hash is of typical size and is believed to be 7277 secure. The 128 bit input from the tokens is broken in two pieces, 7278 the home keygen token and the care-of keygen token. An attacker can 7279 try to guess the correct cookie value, but again this would require a 7280 large number of messages (an the average 2**63 messages for one or 7281 2**127 for two). Furthermore, given that the cookies are valid only 7282 for a short period of time, the attack has to keep a high constant 7283 message rate to achieve a lasting effect. This does not appear 7284 practical. 7286 When the mobile node is returning home, it is allowed to use just the 7287 home keygen token of 64 bits. This is less than 128 bits, but 7288 attacking it blindly would still require a large number of messages 7289 to be sent. If the attacker is on the path and capable of seeing the 7290 Binding Update, it could conceivably break the keyed hash with brute 7291 force. However, in this case the attacker has to be on the path, 7292 which appears to offer easier ways for denial-of-service than 7293 preventing route optimization. 7295 15.5. Dynamic Home Agent Address Discovery 7297 The dynamic home agent address discovery function could be used to 7298 learn the addresses of home agents in the home network. 7300 The ability to learn addresses of nodes may be useful to attackers 7301 because brute-force scanning of the address space is not practical 7302 with IPv6. Thus, they could benefit from any means which make 7303 mapping the networks easier. For example, if a security threat 7304 targeted at routers or even home agents is discovered, having a 7305 simple ICMP mechanism to easily find out possible targets may prove 7306 to be an additional (though minor) security risk. 7308 This document does not define any authentication mechanism for 7309 dynamic home agent address discovery messages. Therefore the home 7310 agent cannot verify the home address of the mobile node that 7311 requested the list of home agents. 7313 Apart from discovering the address(es) of home agents, attackers will 7314 not be able to learn much from this information, and mobile nodes 7315 cannot be tricked into using wrong home agents, as all other 7316 communication with the home agents is secure. 7318 In cases where additional security is needed, one may consider 7319 instead the use of MIPv6 bootstrapping [22], (based on DNS SRV 7320 Resource Records [10]) in conjunction with security mechanisms 7321 suggested in these specifications. In that solution, security is 7322 provided by the DNSSEC [13] framework. The needed pre-configured 7323 data on the mobile node for this mechanism is the domain name of the 7324 mobile service provider, which is marginally better than the home 7325 subnet prefix. For the security, a trust anchor which dominates the 7326 domain is needed. 7328 15.6. Mobile Prefix Discovery 7330 The mobile prefix discovery function may leak interesting information 7331 about network topology and prefix lifetimes to eavesdroppers; for 7332 this reason, requests for this information have to be authenticated. 7333 Responses and unsolicited prefix information needs to be 7334 authenticated to prevent the mobile nodes from being tricked into 7335 believing false information about the prefixes and possibly 7336 preventing communications with the existing addresses. Optionally, 7337 encryption may be applied to prevent leakage of the prefix 7338 information. 7340 15.7. Tunneling via the Home Agent 7342 Tunnels between the mobile node and the home agent can be protected 7343 by ensuring proper use of source addresses, and optional 7344 cryptographic protection. These procedures are discussed in 7345 Section 5.5. 7347 Binding Updates to the home agents are secure. When receiving 7348 tunneled traffic, the home agent verifies that the outer IP address 7349 corresponds to the current location of the mobile node. This acts as 7350 a weak form of protection against spoofing packets that appear to 7351 come from the mobile node. This is particularly useful, if no end- 7352 to-end security is being applied between the mobile and correspondent 7353 nodes. The outer IP address check prevents attacks where the 7354 attacker is controlled by ingress filtering. It also prevents 7355 attacks when the attacker does not know the current care-of address 7356 of the mobile node. Attackers who know the care-of address and are 7357 not controlled by ingress filtering could still send traffic through 7358 the home agent. This includes attackers on the same local link as 7359 the mobile node is currently on. But such attackers could send 7360 packets that appear to come from the mobile node without attacking 7361 the tunnel; the attacker could simply send packets with the source 7362 address set to the mobile node's home address. However, this attack 7363 does not work if the final destination of the packet is in the home 7364 network, and some form of perimeter defense is being applied for 7365 packets sent to those destinations. In such cases it is recommended 7366 that either end-to-end security or additional tunnel protection be 7367 applied, as is usual in remote access situations. 7369 Home agents and mobile nodes may use IPsec ESP to protect payload 7370 packets tunneled between themselves. This is useful for protecting 7371 communications against attackers on the path of the tunnel. 7373 When a Unique-Local Address (ULA) RFC4193 [15] is used as a home 7374 address, reverse tunneling can be used to send local traffic from 7375 another location. Administrators should be aware of this when 7376 allowing such home addresses. In particular, the outer IP address 7377 check described above is not sufficient against all attackers. The 7378 use of encrypted tunnels is particularly useful for these kinds of 7379 home addresses. 7381 15.8. Home Address Option 7383 When the mobile node sends packets directly to the correspondent 7384 node, the Source Address field of the packet's IPv6 header is the 7385 care-of address. Therefore, ingress filtering [27] works in the 7386 usual manner even for mobile nodes, as the Source Address is 7387 topologically correct. The Home Address option is used to inform the 7388 correspondent node of the mobile node's home address. 7390 However, the care-of address in the Source Address field does not 7391 survive in replies sent by the correspondent node unless it has a 7392 binding for this mobile node. Also, not all attacker tracing 7393 mechanisms work when packets are being reflected through 7394 correspondent nodes using the Home Address option. For these 7395 reasons, this specification restricts the use of the Home Address 7396 option. It may only be used when a binding has already been 7397 established with the participation of the node at the home address, 7398 as described in Section 5.5 and Section 6.3. This prevents 7399 reflection attacks through the use of the Home Address option. It 7400 also ensures that the correspondent nodes reply to the same address 7401 that the mobile node sends traffic from. 7403 No special authentication of the Home Address option is required 7404 beyond the above, but note that if the IPv6 header of a packet is 7405 covered by IPsec Authentication Header, then that authentication 7406 covers the Home Address option as well. Thus, even when 7407 authentication is used in the IPv6 header, the security of the Source 7408 Address field in the IPv6 header is not compromised by the presence 7409 of a Home Address option. Without authentication of the packet, any 7410 field in the IPv6 header, including the Source Address field or any 7411 other part of the packet and the Home Address option can be forged or 7412 modified in transit. In this case, the contents of the Home Address 7413 option is no more suspect than any other part of the packet. 7415 15.9. Type 2 Routing Header 7417 The definition of the type 2 routing header is described in 7418 Section 6.4. This definition and the associated processing rules 7419 have been chosen so that the header cannot be used for what is 7420 traditionally viewed as source routing. In particular, the Home 7421 Address in the routing header will always have to be assigned to the 7422 home address of the receiving node; otherwise the packet will be 7423 dropped. 7425 Generally, source routing has a number of security concerns. These 7426 include the automatic reversal of unauthenticated source routes 7427 (which is an issue for IPv4, but not for IPv6). Another concern is 7428 the ability to use source routing to "jump" between nodes inside, as 7429 well as outside a firewall. These security concerns are not issues 7430 in Mobile IPv6, due to the rules mentioned above. 7432 In essence the semantics of the type 2 routing header is the same as 7433 a special form of IP-in-IP tunneling where the inner and outer source 7434 addresses are the same. 7436 This implies that a device which implements the filtering of packets 7437 should be able to distinguish between a type 2 routing header and 7438 other routing headers, as required in Section 8.3. This is necessary 7439 in order to allow Mobile IPv6 traffic while still having the option 7440 of filtering out other uses of routing headers. 7442 16. Contributors 7444 Work done by Tuomas Aura, Mike Roe, Greg O'Shea, Pekka Nikander, Erik 7445 Nordmark, and Michael Thomas shaped the return routability protocols 7446 described in [34]. 7448 Significant contributions were made by members of the Mobile IPv6 7449 Security Design Team, including (in alphabetical order) Gabriel 7450 Montenegro, Erik Nordmark and Pekka Nikander. 7452 17. Acknowledgements 7454 We would like to thank the members of the Mobile IP, Mobility 7455 Extensions for IPv6, and IPng Working Groups for their comments and 7456 suggestions on this work. We would particularly like to thank (in 7457 alphabetical order) Fred Baker, Josh Broch, Samita Chakrabarti, 7458 Robert Chalmers, Noel Chiappa, Jean-Michel Combes, Greg Daley, Vijay 7459 Devarapalli, Rich Draves, Francis Dupont, Ashutosh Dutta, Arnaud 7460 Ebalard, Wesley Eddy, Thomas Eklund, Jun-Ichiro Itojun Hagino, Brian 7461 Haley, Marc Hasson, John Ioannidis, James Kempf, Rajeev Koodli, 7462 Suresh Krishnan, Krishna Kumar, T.J. Kniveton, Joe Lau, Aime Le 7463 Rouzic, Julien Laganier, Jiwoong Lee, Benjamin Lim, Vesa-Matti 7464 Mantyla, Kevin Miles, Glenn Morrow, Ahmad Muhanna, Thomas Narten, 7465 Karen Nielsen, Simon Nybroe, David Oran, Mohan Parthasarathy, 7466 Basavaraj Patil, Brett Pentland, Lars Henrik Petander, Alexandru 7467 Petrescu, Mattias Petterson, Ken Powell, Ed Remmell, Phil Roberts, 7468 Patrice Romand, Luis A. Sanchez, Pekka Savola, Jeff Schiller, Arvind 7469 Sevalkar, Keiichi Shima, Tom Soderlund, Hesham Soliman, Jim Solomon, 7470 Tapio Suihko, Dave Thaler, Pascal Thubert, Benny Van Houdt, Jon-Olov 7471 Vatn, Ryuji Wakikawa, Kilian Weniger, Carl E. Williams, Vladislav 7472 Yasevich, Alper Yegin, and Xinhua Zhao, for their detailed reviews of 7473 earlier versions of this document. Their suggestions have helped to 7474 improve both the design and presentation of the protocol. 7476 We would also like to thank the participants of the Mobile IPv6 7477 testing event (1999), implementors who participated in Mobile IPv6 7478 interoperability testing at Connectathons (2000, 2001, 2002, and 7479 2003), and the participants at the ETSI interoperability testing 7480 (2000, 2002). Finally, we would like to thank the TAHI project who 7481 has provided test suites for Mobile IPv6. 7483 18. References 7485 18.1. Normative References 7487 [1] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing 7488 for Message Authentication", RFC 2104, February 1997. 7490 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement 7491 Levels", BCP 14, RFC 2119, March 1997. 7493 [3] Kent, S. and K. Seo, "Security Architecture for the Internet 7494 Protocol", RFC 4301, December 2005. 7496 [4] Kent, S., "IP Authentication Header", RFC 4302, December 2005. 7498 [5] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, 7499 December 2005. 7501 [6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 7502 Specification", RFC 2460, December 1998. 7504 [7] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 7505 Specification", RFC 2473, December 1998. 7507 [8] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast 7508 Addresses", RFC 2526, March 1999. 7510 [9] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener 7511 Discovery (MLD) for IPv6", RFC 2710, October 1999. 7513 [10] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 7514 specifying the location of services (DNS SRV)", RFC 2782, 7515 February 2000. 7517 [11] National Institute of Standards and Technology, "Secure Hash 7518 Standard", FIPS PUB 180-1, April 1995, 7519 . 7521 [12] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to 7522 Protect Mobile IPv6 Signaling Between Mobile Nodes and Home 7523 Agents", RFC 3776, June 2004. 7525 [13] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, 7526 "DNS Security Introduction and Requirements", RFC 4033, 7527 March 2005. 7529 [14] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 7530 Requirements for Security", BCP 106, RFC 4086, June 2005. 7532 [15] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 7533 Addresses", RFC 4193, October 2005. 7535 [16] Hinden, R. and S. Deering, "IP Version 6 Addressing 7536 Architecture", RFC 4291, February 2006. 7538 [17] Conta, A., Deering, S., and M. Gupta, "Internet Control Message 7539 Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) 7540 Specification", RFC 4443, March 2006. 7542 [18] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 7543 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 7544 September 2007. 7546 [19] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address 7547 Autoconfiguration", RFC 4862, September 2007. 7549 [20] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with 7550 IKEv2 and the Revised IPsec Architecture", RFC 4877, 7551 April 2007. 7553 [21] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions 7554 for Stateless Address Autoconfiguration in IPv6", RFC 4941, 7555 September 2007. 7557 [22] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6 7558 Bootstrapping in Split Scenario", RFC 5026, October 2007. 7560 [23] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 7561 Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. 7563 [24] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, "Internet Key 7564 Exchange Protocol Version 2 (IKEv2)", RFC 5996, September 2010. 7566 18.2. Informative References 7568 [25] Perkins, C., "IP Encapsulation within IP", RFC 2003, 7569 October 1996. 7571 [26] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 7572 October 1996. 7574 [27] Ferguson, P. and D. Senie, "Network Ingress Filtering: 7575 Defeating Denial of Service Attacks which employ IP Source 7576 Address Spoofing", BCP 38, RFC 2827, May 2000. 7578 [28] Aura, T. and J. Arkko, "MIPv6 BU Attacks and Defenses", 7579 draft-aura-mipv6-bu-attacks-01 (work in progress), March 2002. 7581 [29] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On- 7582 line Database", RFC 3232, January 2002. 7584 [30] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. 7585 Carney, "Dynamic Host Configuration Protocol for IPv6 7586 (DHCPv6)", RFC 3315, July 2003. 7588 [31] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, 7589 August 2002. 7591 [32] Draves, R., "Default Address Selection for Internet Protocol 7592 version 6 (IPv6)", RFC 3484, February 2003. 7594 [33] Nordmark, E., "Securing MIPv6 BUs using return routability 7595 (BU3WAY)", draft-nordmark-mobileip-bu3way-00 (work in 7596 progress), November 2001. 7598 [34] Roe, M., "Authentication of Mobile IPv6 Binding Updates and 7599 Acknowledgments", draft-roe-mobileip-updateauth-02 (work in 7600 progress), March 2002. 7602 [35] Chowdhury, K. and A. Yegin, "MIP6-bootstrapping for the 7603 Integrated Scenario", 7604 draft-ietf-mip6-bootstrapping-integrated-dhc-06 (work in 7605 progress), April 2008. 7607 [36] Savola, P., "Use of /127 Prefix Length Between Routers 7608 Considered Harmful", RFC 3627, September 2003. 7610 [37] Savola, P., "Security of IPv6 Routing Header and Home Address 7611 Options", draft-savola-ipv6-rh-ha-security-02 (work in 7612 progress), March 2002. 7614 [38] Manner, J. and M. Kojo, "Mobility Related Terminology", 7615 RFC 3753, June 2004. 7617 [39] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 7618 (MLDv2) for IPv6", RFC 3810, June 2004. 7620 [40] Bellovin, S. and R. Housley, "Guidelines for Cryptographic Key 7621 Management", BCP 107, RFC 4107, June 2005. 7623 [41] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. 7624 Nordmark, "Mobile IP Version 6 Route Optimization Security 7625 Design Background", RFC 4225, December 2005. 7627 [42] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6 Socket 7628 API for Source Address Selection", RFC 5014, September 2007. 7630 [43] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation of 7631 Type 0 Routing Headers in IPv6", RFC 5095, December 2007. 7633 Appendix A. Future Extensions 7635 A.1. Piggybacking 7637 This document does not specify how to piggyback payload packets on 7638 the binding related messages. However, it is envisioned that this 7639 can be specified in a separate document when issues such as the 7640 interaction between piggybacking and IPsec are fully resolved (see 7641 also Appendix A.3). The return routability messages can indicate 7642 support for piggybacking with a new mobility option. 7644 A.2. Triangular Routing 7646 Due to the concerns about opening reflection attacks with the Home 7647 Address destination option, this specification requires that this 7648 option be verified against the Binding Cache, i.e., there must be a 7649 Binding Cache entry for the Home Address and Care-of Address. 7651 Future extensions may be specified that allow the use of unverified 7652 Home Address destination options in ways that do not introduce 7653 security issues. 7655 A.3. New Authorization Methods 7657 While the return routability procedure provides a good level of 7658 security, there exist methods that have even higher levels of 7659 security. Secondly, as discussed in Section 15.4, future 7660 enhancements of IPv6 security may cause a need to also improve the 7661 security of the return routability procedure. Using IPsec as the 7662 sole method for authorizing Binding Updates to correspondent nodes is 7663 also possible. The protection of the Mobility Header for this 7664 purpose is easy, though one must ensure that the IPsec SA was created 7665 with appropriate authorization to use the home address referenced in 7666 the Binding Update. For instance, a certificate used by IKEv2 to 7667 create the security association might contain the home address. A 7668 future specification may specify how this is done. 7670 A.4. Neighbor Discovery Extensions 7672 Future specifications may improve the efficiency of Neighbor 7673 Discovery tasks, which could be helpful for fast movements. One 7674 factor is currently being looked at: the delays caused by the 7675 Duplicate Address Detection mechanism. Currently, Duplicate Address 7676 Detection needs to be performed for every new care-of address as the 7677 mobile node moves, and for the mobile node's link-local address on 7678 every new link. In particular, the need and the trade-offs of re- 7679 performing Duplicate Address Detection for the link-local address 7680 every time the mobile node moves on to new links will need to be 7681 examined. Improvements in this area are, however, generally 7682 applicable and progress independently from the Mobile IPv6 7683 specification. 7685 Future functional improvements may also be relevant for Mobile IPv6 7686 and other applications. For instance, mechanisms that would allow 7687 recovery from a Duplicate Address Detection collision would be useful 7688 for link-local, care-of, and home addresses. 7690 Appendix B. Changes since RFC 3775 7692 The following issues were identified during the evolution of the 7693 current document. Discussion about the issues can be found on the 7694 [mext] working group page 7695 http://trac.tools.ietf.org/wg/mext/trac/report/6 7697 Issue #1 Last Accepted SQN [Ahmad Muhanna] 7699 Solution: specify that the mobile node update its binding sequence 7700 number to match the sequence number given in the Binding 7701 Acknowledgement (if the Binding Acknowledgement correctly passes 7702 authentication and the status is 135 (Sequence Number out of 7703 window). See Section 11.7.3. 7705 Issue #4 Remove references to site-local addresses [George 7706 Tsirtsis]. 7708 Fixed. 7710 Issue #5 Wrong protocol number (2 instead of 135) used in discussion 7711 about checksum pseudo-header. 7713 Fixed. See Section 6.1.1. 7715 Issue #8 Application using the care-of address [Julien Laganier] 7717 Cite IPv6 Socket API for Source Address Selection specification 7718 [42]. See Section 11.3.4. 7720 Issue #10 The usage of "HA lifetime" [Ryuji Wakikawa] 7722 The mobile node SHOULD store the list of home agents for later use 7723 in case the home agent currently managing the mobile node's 7724 care-of address forwarding should become unavailable. See 7725 Section 11.4.1. 7727 Issue #11 De-registration when returning home [Vijay Devarapalli] 7729 To be able to send and receive packets using its home address from 7730 the home link, the mobile node MUST send a Binding Update to its 7731 home agent to instruct its home agent to no longer intercept or 7732 tunnel packets for it. Until the mobile node sends such a de- 7733 registration Binding Update, it MUST NOT attempt to send and 7734 receive packets using its home address from the home link. See 7735 Section 11.5.5. 7737 Issue #12 BErr sent by HA too, not only by CN [Alexandru Petrescu] 7739 Fixed. See Section 4.2. 7741 Issue #13 Home Link Detection [Suresh Krishnan] 7743 Proposal: add Section 11.5.2 for Home Link Detection, drawing on 7744 Internet Draft draft-krishnan-mext-hld. 7746 Issue #14 References to Bootstrapping [Vijay Devarapalli] 7748 Cite "Mobile IPv6 Bootstrapping in Split Scenario" [22] and "MIP6 7749 bootstrapping for the Integrated Scenario" [35]. See Section 4.1. 7751 Issue #17 Multi-homed mobile node can cause routing loop between 7752 home agents [Benjamin Lim] 7754 Added security advisory in Section 15.1, to highlight risk of 7755 routing loop among HAs (e.g., in 3GPP): 7757 A malicious mobile node associated to multiple home agents could 7758 create a routing loop amongst them. This would happen when a 7759 mobile node binds one home address located on a first home agent 7760 to another home address on a second home agent. 7762 Issue #18 Subject: Issues regarding Home Address Option and ICMP / 7763 Binding Errors [Fabian Mauchle] 7765 Proposal: Use the value in the Next Header field {50 (ESP), 51 7766 (AH), 135 (Mobility Header)} to determine, if a Binding Cache 7767 entry is required. See Section 9.3.1. 7769 Proposal: If the Binding Error Message was sent by the Home Agent, 7770 the Mobile Node SHOULD send a Binding Update to the Home Agent 7771 according to Section 11.7.1. See Section 11.3.6. 7773 Issue #19 BU de-registration race condition [Kilian Weniger] 7775 Problem arises if de-registration arrives at Home Agent before an 7776 immediately preceding Binding Update. 7778 Solution: Home Agent defers BCE removal after sending the Binding 7779 Acknowledgement. See Section 10.3.2. 7781 Issue #6 Minor editorial corrections and updates. 7783 Update IPsec and IKE references to the revised IPsec architecture 7784 and IKEv2. 7786 Update HMAC_SHA1 [1] to Normative instead of Informational. 7788 Authors' Addresses 7790 Charles E. Perkins 7791 Tellabs Inc. 7792 4555 Great America Parkway, Suite 150 7793 Santa Clara CA 95054 7794 USA 7796 Email: charliep@computer.org 7798 David B. Johnson 7799 Rice University 7800 Dept. of Computer Science, MS 132 7801 6100 Main Street 7802 Houston TX 77005-1892 7803 USA 7805 Email: dbj@cs.rice.edu 7807 Jari Arkko 7808 Ericsson 7809 Jorvas 02420 7810 Finland 7812 Email: jari.arkko@ericsson.com