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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == Line 1071 has weird spacing: '...ated to rever...' == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: Before sending any packet, the sending node SHOULD examine its Binding Cache for an entry for the destination address to which the packet is being sent. If the sending node has a Binding Cache entry for this address, the sending node SHOULD use a type 2 routing header to route the packet to this mobile node (the destination node) by way of its care-of address. However, the mobile node MUST not do this in the following cases: == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: o The Binding Authorization Data mobility option, if present, MUST be the last option and MUST not have trailing padding. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 30, 2003) is 7598 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 1750 (ref. '1') (Obsoleted by RFC 4086) ** Obsolete normative reference: RFC 2373 (ref. '3') (Obsoleted by RFC 3513) ** Obsolete normative reference: RFC 2401 (ref. '4') (Obsoleted by RFC 4301) ** Obsolete normative reference: RFC 2402 (ref. '5') (Obsoleted by RFC 4302, RFC 4305) ** Obsolete normative reference: RFC 2406 (ref. '6') (Obsoleted by RFC 4303, RFC 4305) ** Obsolete normative reference: RFC 2407 (ref. '7') (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2408 (ref. '8') (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2409 (ref. '9') (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2434 (ref. '10') (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 2460 (ref. '11') (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 2461 (ref. '12') (Obsoleted by RFC 4861) ** Obsolete normative reference: RFC 2462 (ref. '13') (Obsoleted by RFC 4862) ** Obsolete normative reference: RFC 2463 (ref. '14') (Obsoleted by RFC 4443) ** Obsolete normative reference: RFC 3041 (ref. '18') (Obsoleted by RFC 4941) ** Downref: Normative reference to an Informational RFC: RFC 3232 (ref. '19') -- Possible downref: Non-RFC (?) normative reference: ref. '20' -- Obsolete informational reference (is this intentional?): RFC 2002 (ref. '22') (Obsoleted by RFC 3220) -- Obsolete informational reference (is this intentional?): RFC 2267 (ref. '26') (Obsoleted by RFC 2827) == Outdated reference: A later version (-03) exists of draft-bellovin-mandate-keymgmt-00 == Outdated reference: A later version (-17) exists of draft-ietf-ipsec-ikev2-07 -- Unexpected draft version: The latest known version of draft-ietf-ipv6-default-addr-select is -08, but you're referring to -09. == Outdated reference: A later version (-02) exists of draft-nikander-mobileip-v6-ro-sec-00 == Outdated reference: A later version (-08) exists of draft-vida-mld-v2-06 Summary: 17 errors (**), 0 flaws (~~), 10 warnings (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IETF Mobile IP Working Group D. Johnson 3 Internet-Draft Rice University 4 Expires: December 29, 2003 C. Perkins 5 Nokia Research Center 6 J. Arkko 7 Ericsson 8 June 30, 2003 10 Mobility Support in IPv6 11 draft-ietf-mobileip-ipv6-24.txt 13 Status of this Memo 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as 21 Internet-Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at http:// 29 www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on December 29, 2003. 36 Copyright Notice 38 Copyright (C) The Internet Society (2003). All Rights Reserved. 40 Abstract 42 This document specifies a protocol which allows nodes to remain 43 reachable while moving around in the IPv6 Internet. Each mobile node 44 is always identified by its home address, regardless of its current 45 point of attachment to the Internet. While situated away from its 46 home, a mobile node is also associated with a care-of address, which 47 provides information about the mobile node's current location. IPv6 48 packets addressed to a mobile node's home address are transparently 49 routed to its care-of address. The protocol enables IPv6 nodes to 50 cache the binding of a mobile node's home address with its care-of 51 address, and to then send any packets destined for the mobile node 52 directly to it at this care-of address. To support this operation, 53 Mobile IPv6 defines a new IPv6 protocol and a new destination option. 54 All IPv6 nodes, whether mobile or stationary can communicate with 55 mobile nodes. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 6 60 2. Comparison with Mobile IP for IPv4 . . . . . . . . . . . . 8 61 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 9 62 3.1 General Terms . . . . . . . . . . . . . . . . . . . 9 63 3.2 Mobile IPv6 Terms . . . . . . . . . . . . . . . . . 11 64 4. Overview of Mobile IPv6 . . . . . . . . . . . . . . . . . 15 65 4.1 Basic Operation . . . . . . . . . . . . . . . . . . 15 66 4.2 New IPv6 Protocol . . . . . . . . . . . . . . . . . 17 67 4.3 New IPv6 Destination Option . . . . . . . . . . . . 18 68 4.4 New IPv6 ICMP Messages . . . . . . . . . . . . . . . 18 69 4.5 Conceptual Data Structure Terminology . . . . . . . 18 70 4.6 Site-Local Addressability . . . . . . . . . . . . . 19 71 5. Overview of Mobile IPv6 Security . . . . . . . . . . . . . 20 72 5.1 Binding Updates to Home Agents . . . . . . . . . . . 20 73 5.2 Binding Updates to Correspondent Nodes . . . . . . . 21 74 5.2.1 Node Keys . . . . . . . . . . . . . . . . . 22 75 5.2.2 Nonces . . . . . . . . . . . . . . . . . . . 22 76 5.2.3 Cookies and Tokens . . . . . . . . . . . . . 23 77 5.2.4 Cryptographic Functions . . . . . . . . . . 23 78 5.2.5 Return Routability Procedure . . . . . . . . 23 79 5.2.6 Authorizing Binding Management Messages . . 28 80 5.2.7 Updating Node Keys and Nonces . . . . . . . 30 81 5.2.8 Preventing Replay Attacks . . . . . . . . . 31 82 5.3 Dynamic Home Agent Address Discovery . . . . . . . . 31 83 5.4 Mobile Prefix Discovery . . . . . . . . . . . . . . 31 84 5.5 Payload Packets . . . . . . . . . . . . . . . . . . 32 85 6. New IPv6 Protocol, Message Types, and Destination Option . 33 86 6.1 Mobility Header . . . . . . . . . . . . . . . . . . 33 87 6.1.1 Format . . . . . . . . . . . . . . . . . . . 33 88 6.1.2 Binding Refresh Request Message . . . . . . 35 89 6.1.3 Home Test Init Message . . . . . . . . . . . 36 90 6.1.4 Care-of Test Init Message . . . . . . . . . 37 91 6.1.5 Home Test Message . . . . . . . . . . . . . 38 92 6.1.6 Care-of Test Message . . . . . . . . . . . . 39 93 6.1.7 Binding Update Message . . . . . . . . . . . 41 94 6.1.8 Binding Acknowledgement Message . . . . . . 43 95 6.1.9 Binding Error Message . . . . . . . . . . . 46 96 6.2 Mobility Options . . . . . . . . . . . . . . . . . . 47 97 6.2.1 Format . . . . . . . . . . . . . . . . . . . 48 98 6.2.2 Pad1 . . . . . . . . . . . . . . . . . . . . 48 99 6.2.3 PadN . . . . . . . . . . . . . . . . . . . . 49 100 6.2.4 Binding Refresh Advice . . . . . . . . . . . 49 101 6.2.5 Alternate Care-of Address . . . . . . . . . 50 102 6.2.6 Nonce Indices . . . . . . . . . . . . . . . 50 103 6.2.7 Binding Authorization Data . . . . . . . . . 51 104 6.3 Home Address Option . . . . . . . . . . . . . . . . 52 105 6.4 Type 2 Routing Header . . . . . . . . . . . . . . . 54 106 6.4.1 Format . . . . . . . . . . . . . . . . . . . 54 107 6.5 ICMP Home Agent Address Discovery Request Message . 56 108 6.6 ICMP Home Agent Address Discovery Reply Message . . 57 109 6.7 ICMP Mobile Prefix Solicitation Message Format . . . 58 110 6.8 ICMP Mobile Prefix Advertisement Message Format . . 60 111 7. Modifications to IPv6 Neighbor Discovery . . . . . . . . . 63 112 7.1 Modified Router Advertisement Message Format . . . . 63 113 7.2 Modified Prefix Information Option Format . . . . . 63 114 7.3 New Advertisement Interval Option Format . . . . . . 65 115 7.4 New Home Agent Information Option Format . . . . . . 66 116 7.5 Changes to Sending Router Advertisements . . . . . . 68 117 8. Requirements for Types of IPv6 Nodes . . . . . . . . . . . 70 118 8.1 All IPv6 Nodes . . . . . . . . . . . . . . . . . . . 70 119 8.2 IPv6 Nodes with Support for Route Optimization . . . 70 120 8.3 All IPv6 Routers . . . . . . . . . . . . . . . . . . 72 121 8.4 IPv6 Home Agents . . . . . . . . . . . . . . . . . . 72 122 8.5 IPv6 Mobile Nodes . . . . . . . . . . . . . . . . . 74 123 9. Correspondent Node Operation . . . . . . . . . . . . . . . 76 124 9.1 Conceptual Data Structures . . . . . . . . . . . . . 76 125 9.2 Processing Mobility Headers . . . . . . . . . . . . 77 126 9.3 Packet Processing . . . . . . . . . . . . . . . . . 77 127 9.3.1 Receiving Packets with Home Address Option . 77 128 9.3.2 Sending Packets to a Mobile Node . . . . . . 78 129 9.3.3 Sending Binding Error Messages . . . . . . . 80 130 9.3.4 Receiving ICMP Error Messages . . . . . . . 80 131 9.4 Return Routability Procedure . . . . . . . . . . . . 81 132 9.4.1 Receiving Home Test Init Messages . . . . . 81 133 9.4.2 Receiving Care-of Test Init Messages . . . . 81 134 9.4.3 Sending Home Test Messages . . . . . . . . . 82 135 9.4.4 Sending Care-of Test Messages . . . . . . . 82 136 9.5 Processing Bindings . . . . . . . . . . . . . . . . 82 137 9.5.1 Receiving Binding Updates . . . . . . . . . 82 138 9.5.2 Requests to Cache a Binding . . . . . . . . 85 139 9.5.3 Requests to Delete a Binding . . . . . . . . 85 140 9.5.4 Sending Binding Acknowledgements . . . . . . 86 141 9.5.5 Sending Binding Refresh Requests . . . . . . 87 142 9.6 Cache Replacement Policy . . . . . . . . . . . . . . 87 143 10. Home Agent Operation . . . . . . . . . . . . . . . . . . . 89 144 10.1 Conceptual Data Structures . . . . . . . . . . . . . 89 145 10.2 Processing Mobility Headers . . . . . . . . . . . . 90 146 10.3 Processing Bindings . . . . . . . . . . . . . . . . 90 147 10.3.1 Primary Care-of Address Registration . . . . 90 148 10.3.2 Primary Care-of Address De-Registration . . 94 149 10.4 Packet Processing . . . . . . . . . . . . . . . . . 95 150 10.4.1 Intercepting Packets for a Mobile Node . . . 95 151 10.4.2 Processing Intercepted Packets . . . . . . . 97 152 10.4.3 Multicast Membership Control . . . . . . . . 98 153 10.4.4 Stateful Address Autoconfiguration . . . . . 99 154 10.4.5 Handling Reverse Tunneled Packets . . . . . 99 155 10.4.6 Protecting Return Routability Packets . . . 100 156 10.5 Dynamic Home Agent Address Discovery . . . . . . . .101 157 10.5.1 Receiving Router Advertisement Messages . . 101 158 10.6 Sending Prefix Information to the Mobile Node . . .103 159 10.6.1 List of Home Network Prefixes . . . . . . . 103 160 10.6.2 Scheduling Prefix Deliveries . . . . . . . . 104 161 10.6.3 Sending Advertisements . . . . . . . . . . . 106 162 10.6.4 Lifetimes for Changed Prefixes . . . . . . . 107 163 11. Mobile Node Operation . . . . . . . . . . . . . . . . . . 108 164 11.1 Conceptual Data Structures . . . . . . . . . . . . .108 165 11.2 Processing Mobility Headers . . . . . . . . . . . .109 166 11.3 Packet Processing . . . . . . . . . . . . . . . . .110 167 11.3.1 Sending Packets While Away from Home . . . . 110 168 11.3.2 Interaction with Outbound IPsec Processing . 113 169 11.3.3 Receiving Packets While Away from Home . . . 115 170 11.3.4 Routing Multicast Packets . . . . . . . . . 116 171 11.3.5 Receiving ICMP Error Messages . . . . . . . 118 172 11.3.6 Receiving Binding Error Messages . . . . . . 118 173 11.4 Home Agent and Prefix Management . . . . . . . . . .119 174 11.4.1 Dynamic Home Agent Address Discovery . . . . 119 175 11.4.2 Sending Mobile Prefix Solicitations . . . . 120 176 11.4.3 Receiving Mobile Prefix Advertisements . . . 121 177 11.5 Movement . . . . . . . . . . . . . . . . . . . . . .122 178 11.5.1 Movement Detection . . . . . . . . . . . . . 122 179 11.5.2 Forming New Care-of Addresses . . . . . . . 124 180 11.5.3 Using Multiple Care-of Addresses . . . . . . 125 181 11.5.4 Returning Home . . . . . . . . . . . . . . . 126 182 11.6 Return Routability Procedure . . . . . . . . . . . .128 183 11.6.1 Sending Test Init Messages . . . . . . . . . 128 184 11.6.2 Receiving Test Messages . . . . . . . . . . 129 185 11.6.3 Protecting Return Routability Packets . . . 130 186 11.7 Processing Bindings . . . . . . . . . . . . . . . .130 187 11.7.1 Sending Binding Updates to the Home Agent . 131 188 11.7.2 Correspondent Registration . . . . . . . . . 133 189 11.7.3 Receiving Binding Acknowledgements . . . . . 136 190 11.7.4 Receiving Binding Refresh Requests . . . . . 138 191 11.8 Retransmissions and Rate Limiting . . . . . . . . .139 192 12. Protocol Constants . . . . . . . . . . . . . . . . . . . . 141 193 13. Protocol Configuration Variables . . . . . . . . . . . . . 142 194 14. IANA Considerations . . . . . . . . . . . . . . . . . . . 143 195 15. Security Considerations . . . . . . . . . . . . . . . . . 145 196 15.1 Threats . . . . . . . . . . . . . . . . . . . . . .145 197 15.2 Features . . . . . . . . . . . . . . . . . . . . . .147 198 15.3 Binding Updates to Home Agent . . . . . . . . . . .148 199 15.4 Binding Updates to Correspondent Nodes . . . . . . .151 200 15.4.1 Overview . . . . . . . . . . . . . . . . . . 151 201 15.4.2 Achieved Security Properties . . . . . . . . 152 202 15.4.3 Comparison to Regular IPv6 Communications . 153 203 15.4.4 Replay Attacks . . . . . . . . . . . . . . . 155 204 15.4.5 Denial-of-Service Attacks . . . . . . . . . 155 205 15.4.6 Key Lengths . . . . . . . . . . . . . . . . 156 206 15.5 Dynamic Home Agent Address Discovery . . . . . . . .157 207 15.6 Mobile Prefix Discovery . . . . . . . . . . . . . .157 208 15.7 Tunneling via the Home Agent . . . . . . . . . . . .158 209 15.8 Home Address Option . . . . . . . . . . . . . . . .158 210 15.9 Type 2 Routing Header . . . . . . . . . . . . . . .159 211 16. Contributors . . . . . . . . . . . . . . . . . . . . . . . 161 212 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 162 213 Normative References . . . . . . . . . . . . . . . . . . . 163 214 Informative References . . . . . . . . . . . . . . . . . . 165 215 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 166 216 A. Changes from Previous Version of the Draft . . . . . . . . 167 217 B. Future Extensions . . . . . . . . . . . . . . . . . . . . 168 218 B.1 Piggybacking . . . . . . . . . . . . . . . . . . . . . . . 168 219 B.2 Triangular Routing . . . . . . . . . . . . . . . . . . . . 168 220 B.3 New Authorization Methods . . . . . . . . . . . . . . . . 168 221 B.4 Dynamically Generated Home Addresses . . . . . . . . . . . 168 222 B.5 Remote Home Address Configuration . . . . . . . . . . . . 168 223 B.6 Neighbor Discovery Extensions . . . . . . . . . . . . . . 169 224 Intellectual Property and Copyright Statements . . . . . . 171 226 1. Introduction 228 This document specifies a protocol which allows nodes to remain 229 reachable while moving around in the IPv6 Internet. Without specific 230 support for mobility in IPv6 [11], packets destined to a mobile node 231 would not be able to reach it while the mobile node is away from its 232 home link. In order to continue communication in spite of its 233 movement, a mobile node could change its IP address each time it 234 moves to a new link, but the mobile node would then not be able to 235 maintain transport and higher-layer connections when it changes 236 location. Mobility support in IPv6 is particularly important, as 237 mobile computers are likely to account for a majority or at least a 238 substantial fraction of the population of the Internet during the 239 lifetime of IPv6. 241 The protocol defined in this document, known as Mobile IPv6, allows a 242 mobile node to move from one link to another without changing the 243 mobile node's "home address". Packets may be routed to the mobile 244 node using this address regardless of the mobile node's current point 245 of attachment to the Internet. The mobile node may also continue to 246 communicate with other nodes (stationary or mobile) after moving to a 247 new link. The movement of a mobile node away from its home link is 248 thus transparent to transport and higher-layer protocols and 249 applications. 251 The Mobile IPv6 protocol is just as suitable for mobility across 252 homogeneous media as for mobility across heterogeneous media. For 253 example, Mobile IPv6 facilitates node movement from one Ethernet 254 segment to another as well as it facilitates node movement from an 255 Ethernet segment to a wireless LAN cell, with the mobile node's IP 256 address remaining unchanged in spite of such movement. 258 One can think of the Mobile IPv6 protocol as solving the 259 network-layer mobility management problem. Some mobility management 260 applications -- for example, handover among wireless transceivers, 261 each of which covers only a very small geographic area -- have been 262 solved using link-layer techniques. For example, in many current 263 wireless LAN products, link-layer mobility mechanisms allow a 264 "handover" of a mobile node from one cell to another, re-establishing 265 link-layer connectivity to the node in each new location. 267 Mobile IPv6 does not attempt to solve all general problems related to 268 the use of mobile computers or wireless networks. In particular, 269 this protocol does not attempt to solve: 271 o Handling links with unidirectional connectivity or partial 272 reachability, such as the hidden terminal problem where a host is 273 hidden from only some of the routers on the link. 275 o Access control on a link being visited by a mobile node. 277 o Local or hierarchical forms of mobility management (similar to 278 many current link-layer mobility management solutions). 280 o Assistance for adaptive applications 282 o Mobile routers 284 o Service Discovery 286 o Distinguishing between packets lost due to bit errors vs. network 287 congestion 289 2. Comparison with Mobile IP for IPv4 291 The design of Mobile IP support in IPv6 (Mobile IPv6) benefits both 292 from the experiences gained from the development of Mobile IP support 293 in IPv4 (Mobile IPv4) [22, 23, 24], and from the opportunities 294 provided by IPv6. Mobile IPv6 thus shares many features with Mobile 295 IPv4, but is integrated into IPv6 and offers many other improvements. 296 This section summarizes the major differences between Mobile IPv4 and 297 Mobile IPv6: 299 o There is no need to deploy special routers as "foreign agents", as 300 in Mobile IPv4. Mobile IPv6 operates in any location without any 301 special support required from the local router. 303 o Support for route optimization is a fundamental part of the 304 protocol, rather than a nonstandard set of extensions. 306 o Mobile IPv6 route optimization can operate securely even without 307 pre-arranged security associations. It is expected that route 308 optimization can be deployed on a global scale between all mobile 309 nodes and correspondent nodes. 311 o Support is also integrated into Mobile IPv6 for allowing route 312 optimization to coexist efficiently with routers that perform 313 "ingress filtering" [26]. 315 o The IPv6 Neighbor Unreachability Detection assures symmetric 316 reachability between the mobile node and its default router in the 317 current location. 319 o Most packets sent to a mobile node while away from home in Mobile 320 IPv6 are sent using an IPv6 routing header rather than IP 321 encapsulation, reducing the amount of resulting overhead compared 322 to Mobile IPv4. 324 o Mobile IPv6 is decoupled from any particular link layer, as it 325 uses IPv6 Neighbor Discovery [12] instead of ARP. This also 326 improves the robustness of the protocol. 328 o The use of IPv6 encapsulation (and the routing header) removes the 329 need in Mobile IPv6 to manage "tunnel soft state". 331 o The dynamic home agent address discovery mechanism in Mobile IPv6 332 returns a single reply to the mobile node. The directed broadcast 333 approach used in IPv4 returns separate replies from each home 334 agent. 336 3. Terminology 338 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 339 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 340 document are to be interpreted as described in RFC 2119 [2]. 342 3.1 General Terms 344 IP 346 Internet Protocol Version 6 (IPv6). 348 node 350 A device that implements IP. 352 router 354 A node that forwards IP packets not explicitly addressed to 355 itself. 357 unicast routable address 359 An identifier for a single interface such that a packet sent to it 360 from another IPv6 subnet is delivered to the interface identified 361 by that address. Accordingly, a unicast routable address must 362 have either a global or site-local scope (but not link-local). 364 host 366 Any node that is not a router. 368 link 370 A communication facility or medium over which nodes can 371 communicate at the link layer, such as an Ethernet (simple or 372 bridged). A link is the layer immediately below IP. 374 interface 376 A node's attachment to a link. 378 subnet prefix 380 A bit string that consists of some number of initial bits of an IP 381 address. 383 interface identifier 385 A number used to identify a node's interface on a link. The 386 interface identifier is the remaining low-order bits in the node's 387 IP address after the subnet prefix. 389 link-layer address 391 A link-layer identifier for an interface, such as IEEE 802 392 addresses on Ethernet links. 394 packet 396 An IP header plus payload. 398 security association 400 An IPsec security association is a cooperative relationship formed 401 by the sharing of cryptographic keying material and associated 402 context. Security associations are simplex. That is, two 403 security associations are needed to protect bidirectional traffic 404 between two nodes, one for each direction. 406 security policy database 408 A database that specifies what security services are to be offered 409 to IP packets and in what fashion. 411 destination option 413 Destination options are carried by the IPv6 Destination Options 414 extension header. Destination options include optional 415 information that need be examined only by the IPv6 node given as 416 the destination address in the IPv6 header, not by routers in 417 between. Mobile IPv6 defines one new destination option, the Home 418 Address destination option (see Section 6.3). 420 routing header 422 A routing header may be present as an IPv6 header extension, and 423 indicates that the payload has to be delivered to a destination 424 IPv6 address in some way that is different from what would be 425 carried out by standard Internet routing. In this document, use 426 of the term "routing header" typically refers to use of a type 2 427 routing header, as specified in Section 6.4. 429 '|' (concatenation) 431 Some formulas in this specification use the symbol '|' indicate 432 bytewise concatenation, as in A | B. This concatenation requires 433 that all of the octets of the datum A appear first in the result, 434 followed by all of the octets of the datum B. 436 First (size, input) 438 Some formulas in this specification use a functional form "First 439 (size, input)" to indicate truncation of the "input" data so that 440 only the first "size" bits remain to be used. 442 3.2 Mobile IPv6 Terms 444 home address 446 A unicast routable address assigned to a mobile node, used as the 447 permanent address of the mobile node. This address is within the 448 mobile node's home link. Standard IP routing mechanisms will 449 deliver packets destined for a mobile node's home address to its 450 home link. Mobile nodes can have multiple home addresses, for 451 instance when there are multiple home prefixes on the home link. 453 home subnet prefix 455 The IP subnet prefix corresponding to a mobile node's home 456 address. 458 home link 460 The link on which a mobile node's home subnet prefix is defined. 462 mobile node 464 A node that can change its point of attachment from one link to 465 another, while still being reachable via its home address. 467 movement 469 A change in a mobile node's point of attachment to the Internet 470 such that it is no longer connected to the same link as it was 471 previously. If a mobile node is not currently attached to its 472 home link, the mobile node is said to be "away from home". 474 L2 handover 476 A process by which the mobile node changes from one link-layer 477 connection to another. For example, a change of wireless access 478 point is an L2 handover. 480 L3 handover 482 Subsequent to an L2 handover, a mobile node detects a change in an 483 on-link subnet prefix that would require a change in the primary 484 care-of address. For example, a change of access router 485 subsequent to a change of wireless access point typically results 486 in an L3 handover. 488 correspondent node 490 A peer node with which a mobile node is communicating. The 491 correspondent node may be either mobile or stationary. 493 foreign subnet prefix 495 Any IP subnet prefix other than the mobile node's home subnet 496 prefix. 498 foreign link 500 Any link other than the mobile node's home link. 502 care-of address 504 A unicast routable address associated with a mobile node while 505 visiting a foreign link; the subnet prefix of this IP address is a 506 foreign subnet prefix. Among the multiple care-of addresses that 507 a mobile node may have at any given time (e.g., with different 508 subnet prefixes), the one registered with the mobile node's home 509 agent for a given home address is called its "primary" care-of 510 address. 512 home agent 514 A router on a mobile node's home link with which the mobile node 515 has registered its current care-of address. While the mobile node 516 is away from home, the home agent intercepts packets on the home 517 link destined to the mobile node's home address, encapsulates 518 them, and tunnels them to the mobile node's registered care-of 519 address. 521 binding 523 The association of the home address of a mobile node with a 524 care-of address for that mobile node, along with the remaining 525 lifetime of that association. 527 registration 529 The process during which a mobile node sends a Binding Update to 530 its home agent or a correspondent node, causing a binding for the 531 mobile node to be registered. 533 mobility message 535 A message containing a Mobility Header (see Section 6.1). 537 binding authorization 539 Correspondent registration needs to be authorized to allow the 540 recipient to believe that the sender has the right to specify a 541 new binding. 543 return routability procedure 545 The return routability procedure authorizes registrations by the 546 use of a cryptographic token exchange. 548 correspondent registration 550 A return routability procedure followed by a registration, run 551 between the mobile node and a correspondent node. 553 home registration 555 A registration between the mobile node and its home agent, 556 authorized by the use of IPsec. 558 nonce 560 Nonces are random numbers used internally by the correspondent 561 node in the creation of keygen tokens related to the return 562 routability procedure. The nonces are not specific to a mobile 563 node, and are kept secret within the correspondent node. 565 nonce index 567 A nonce index is used to indicate which nonces have been used when 568 creating keygen token values, without revealing the nonces 569 themselves. 571 cookie 573 A cookie is a random number used by a mobile nodes to prevent 574 spoofing by a bogus correspondent node in the return routability 575 procedure. 577 care-of init cookie 579 A cookie sent to the correspondent node in the Care-of Test Init 580 message, to be returned in the Care-of Test message. 582 home init cookie 584 A cookie sent to the correspondent node in the Home Test Init 585 message, to be returned in the Home Test message. 587 keygen token 589 A keygen token is a number supplied by a correspondent node in the 590 return routability procedure to enable the mobile node to compute 591 the necessary binding management key for authorizing a Binding 592 Update. 594 care-of keygen token 596 A keygen token sent by the correspondent node in the Care-of Test 597 message. 599 home keygen token 601 A keygen token sent by the correspondent node in the Home Test 602 message. 604 binding management key (Kbm) 606 A binding management key (Kbm) is a key used for authorizing a 607 binding cache management message (e.g., Binding Update or Binding 608 Acknowledgement). Return routability provides a way to create a 609 binding management key. 611 4. Overview of Mobile IPv6 613 4.1 Basic Operation 615 A mobile node is always expected to be addressable at its home 616 address, whether it is currently attached to its home link or is away 617 from home. The "home address" is an IP address assigned to the 618 mobile node within its home subnet prefix on its home link. While a 619 mobile node is at home, packets addressed to its home address are 620 routed to the mobile node's home link, using conventional Internet 621 routing mechanisms. 623 While a mobile node is attached to some foreign link away from home, 624 it is also addressable at one or more care-of addresses. A care-of 625 address is an IP address associated with a mobile node that has the 626 subnet prefix of a particular foreign link. The mobile node can 627 acquire its care-of address through conventional IPv6 mechanisms, 628 such as stateless or stateful auto-configuration. As long as the 629 mobile node stays in this location, packets addressed to this care-of 630 address will be routed to the mobile node. The mobile node may also 631 accept packets from several care-of addresses, such as when it is 632 moving but still reachable at the previous link. 634 The association between a mobile node's home address and care-of 635 address is known as a "binding" for the mobile node. While away from 636 home, a mobile node registers its primary care-of address with a 637 router on its home link, requesting this router to function as the 638 "home agent" for the mobile node. The mobile node performs this 639 binding registration by sending a "Binding Update" message to the 640 home agent. The home agent replies to the mobile node by returning a 641 "Binding Acknowledgement" message. The operation of the mobile node 642 is specified in Section 11, and the operation of the home agent is 643 specified in Section 10. 645 Any node communicating with a mobile node is referred to in this 646 document as a "correspondent node" of the mobile node, and may itself 647 be either a stationary node or a mobile node. Mobile nodes can 648 provide information about their current location to correspondent 649 nodes. This happens through the correspondent registration. As a 650 part of this procedure, a return routability test is performed in 651 order to authorize the establishment of the binding. The operation 652 of the correspondent node is specified in Section 9. 654 There are two possible modes for communications between the mobile 655 node and a correspondent node. The first mode, bidirectional 656 tunneling, does not require Mobile IPv6 support from the 657 correspondent node and is available even if the mobile node has not 658 registered its current binding with the correspondent node. Packets 659 from the correspondent node are routed to the home agent and then 660 tunneled to the mobile node. Packets to the correspondent node are 661 tunneled from the mobile node to the home agent ("reverse tunneled") 662 and then routed normally from the home network to the correspondent 663 node. In this mode, the home agent uses proxy Neighbor Discovery to 664 intercept any IPv6 packets addressed to the mobile node's home 665 address (or home addresses) on the home link. Each intercepted 666 packet is tunneled to the mobile node's primary care-of address. 667 This tunneling is performed using IPv6 encapsulation [15]. 669 The second mode, "route optimization", requires the mobile node to 670 register its current binding at the correspondent node. Packets from 671 the correspondent node can be routed directly to the care-of address 672 of the mobile node. When sending a packet to any IPv6 destination, 673 the correspondent node checks its cached bindings for an entry for 674 the packet's destination address. If a cached binding for this 675 destination address is found, the node uses a new type of IPv6 676 routing header [11] (see Section 6.4) to route the packet to the 677 mobile node by way of the care-of address indicated in this binding. 679 Routing packets directly to the mobile node's care-of address allows 680 the shortest communications path to be used. It also eliminates 681 congestion at the mobile node's home agent and home link. In 682 addition, the impact of any possible failure of the home agent or 683 networks on the path to or from it is reduced. 685 When routing packets directly to the mobile node, the correspondent 686 node sets the Destination Address in the IPv6 header to the care-of 687 address of the mobile node. A new type of IPv6 routing header (see 688 Section 6.4) is also added to the packet to carry the desired home 689 address. Similarly, the mobile node sets the Source Address in the 690 packet's IPv6 header to its current care-of addresses. The mobile 691 node adds a new IPv6 "Home Address" destination option (see Section 692 6.3) to carry its home address. The inclusion of home addresses in 693 these packets makes the use of the care-of address transparent above 694 the network layer (e.g., at the transport layer). 696 Mobile IPv6 also provides support for multiple home agents, and a 697 limited support for the reconfiguration of the home network. In 698 these cases, the mobile node may not know the IP address of its own 699 home agent, and even the home subnet prefixes may change over time. 700 A mechanism, known as "dynamic home agent address discovery" allows a 701 mobile node to dynamically discover the IP address of a home agent on 702 its home link, even when the mobile node is away from home. Mobile 703 nodes can also learn new information about home subnet prefixes 704 through the "mobile prefix discovery" mechanism. These mechanisms 705 are described starting from Section 6.5. 707 4.2 New IPv6 Protocol 709 Mobile IPv6 defines a new IPv6 protocol, using the Mobility Header 710 (see Section 6.1). This Header is used to carry the following 711 messages: 713 Home Test Init 715 Home Test 717 Care-of Test Init 719 Care-of Test 721 These four messages are used to perform the return routability 722 procedure from the mobile node to a correspondent node. This 723 ensures authorization of subsequent Binding Updates, as described 724 in Section 5.2.5. 726 Binding Update 728 A Binding Update is used by a mobile node to notify a 729 correspondent node or the mobile node's home agent of its current 730 binding. The Binding Update sent to the mobile node's home agent 731 to register its primary care-of address is marked as a "home 732 registration". 734 Binding Acknowledgement 736 A Binding Acknowledgement is used to acknowledge receipt of a 737 Binding Update, if an acknowledgement was requested in the Binding 738 Update, the binding update was sent to a home agent, or an error 739 occurred. 741 Binding Refresh Request 743 A Binding Refresh Request is used by a correspondent node to 744 request a mobile node to re-establish its binding with the 745 correspondent node. This message is typically used when the 746 cached binding is in active use but the binding's lifetime is 747 close to expiration. The correspondent node may use, for 748 instance, recent traffic and open transport layer connections as 749 an indication of active use. 751 Binding Error 753 The Binding Error is used by the correspondent node to signal an 754 error related to mobility, such as an inappropriate attempt to use 755 the Home Address destination option without an existing binding. 757 4.3 New IPv6 Destination Option 759 Mobile IPv6 defines a new IPv6 destination option, the Home Address 760 destination option. This option is described in detail in Section 761 6.3. 763 4.4 New IPv6 ICMP Messages 765 Mobile IPv6 also introduces four new ICMP message types, two for use 766 in the dynamic home agent address discovery mechanism, and two for 767 renumbering and mobile configuration mechanisms. As described in 768 Section 10.5 and Section 11.4.1, the following two new ICMP message 769 types are used for home agent address discovery: 771 o Home Agent Address Discovery Request, described in Section 6.5. 773 o Home Agent Address Discovery Reply, described in Section 6.6. 775 The next two message types are used for network renumbering and 776 address configuration on the mobile node, as described in Section 777 10.6: 779 o Mobile Prefix Solicitation, described in Section 6.7. 781 o Mobile Prefix Advertisement, described in Section 6.8. 783 4.5 Conceptual Data Structure Terminology 785 This document describes the Mobile IPv6 protocol in terms of the 786 following conceptual data structures: 788 Binding Cache 790 A cache of bindings for other nodes. This cache is maintained by 791 home agents and correspondent nodes. The cache contains both 792 "correspondent registration" entries (see Section 9.1) and "home 793 registration" entries (see Section 10.1). 795 Binding Update List 797 This list is maintained by each mobile node. The list has an item 798 for every binding that the mobile node has or is trying to 799 establish with a specific other node. Both correspondent and home 800 registrations are included in this list. Entries from the list 801 are deleted as the lifetime of the binding expires. See Section 802 11.1. 804 Home Agents List 806 Home agents need to know which other home agents are on the same 807 link. This information is stored in the Home Agents List, as 808 described in more detail in Section 10.1. The list is used for 809 informing mobile nodes during dynamic home agent address 810 discovery. 812 4.6 Site-Local Addressability 814 This specification requires that home and care-of addresses MUST be 815 unicast routable addresses. Site-local addresses may be usable on 816 networks that are not connected to the Internet, but this 817 specification does not define when such usage is safe and when not. 818 Mobile nodes may not be aware of which site they are currently in, it 819 is hard to prevent accidental attachment to other sites, and 820 ambiguity of site-local addresses can cause problems if the home and 821 visited networks use the same addresses. Therefore, site-local 822 addresses SHOULD NOT be used as home or care-of addresses. 824 5. Overview of Mobile IPv6 Security 826 This specification provides a number of security features. These 827 include the protection of Binding Updates both to home agents and 828 correspondent nodes, the protection of mobile prefix discovery, and 829 the protection of the mechanisms that Mobile IPv6 uses for 830 transporting data packets. 832 Binding Updates are protected by the use of IPsec extension headers, 833 or by the use of the Binding Authorization Data option. This option 834 employs a binding management key, Kbm, which can be established 835 through the return routability procedure. Mobile prefix discovery is 836 protected through the use of IPsec extension headers. Mechanisms 837 related to transporting payload packets - such as the Home Address 838 destination option and type 2 routing header - have been specified in 839 a manner which restricts their use in attacks. 841 5.1 Binding Updates to Home Agents 843 The mobile node and the home agent MUST use an IPsec security 844 association to protect the integrity and authenticity of the Binding 845 Updates and Acknowledgements. Both the mobile nodes and the home 846 agents MUST support and SHOULD use the Encapsulating Security Payload 847 (ESP) [6] header in transport mode and MUST use a non-NULL payload 848 authentication algorithm to provide data origin authentication, 849 connectionless integrity and optional anti-replay protection. Note 850 that Authentication Header (AH) [5] is also possible but for brevity 851 not discussed in this specification. 853 In order to protect messages exchanged between the mobile node and 854 the home agent with IPsec, appropriate security policy database 855 entries must be created. A mobile node must be prevented from using 856 its security association to send a Binding Update on behalf of 857 another mobile node using the same home agent. This MUST be achieved 858 by having the home agent check that the given home address has been 859 used with the right security association. Such a check is provided 860 in the IPsec processing, by having the security policy database 861 entries unequivocally identify a single security association for 862 protecting Binding Updates between any given home address and home 863 agent. In order to make this possible, it is necessary that the home 864 address of the mobile node is visible in the Binding Updates and 865 Acknowledgements. The home address is used in these packets as a 866 source or destination, or in the Home Address Destination option or 867 the type 2 routing header. 869 As with all IPsec security associations in this specification, manual 870 configuration of security associations MUST be supported. The used 871 shared secrets MUST be random and unique for different mobile nodes, 872 and MUST be distributed off-line to the mobile nodes. 874 Automatic key management with IKE [9] MAY be supported. When IKE is 875 used, either the security policy database entries or the MIPv6 876 processing MUST unequivocally identify the IKE phase 1 credentials 877 which can be used to authorize the creation of security associations 878 for protecting Binding Updates for a particular home address. How 879 these mappings are maintained is outside the scope of this 880 specification, but they may be maintained, for instance, as a locally 881 administered table in the home agent. If the phase 1 identity is a 882 Fully Qualified Domain Name (FQDN), secure forms of DNS may also be 883 used. 885 Section 11.3.2 discusses how IKE connections to the home agent need a 886 careful treatment of the addresses used for transporting IKE. This 887 is necessary to ensure that a Binding Update is not needed before the 888 IKE exchange which is needed for securing the Binding Update. 890 When IKE version 1 is used with preshared secret authentication 891 between the mobile node and the home agent, aggressive mode MUST be 892 used. Similarly, the ID_IPV6_ADDR Identity Payload MUST NOT be used 893 in IKEv1 phase 1. 895 Reference [21] contains a more detailed description and examples on 896 using IPsec to protect the communications between the mobile node and 897 the home agent. 899 5.2 Binding Updates to Correspondent Nodes 901 The protection of Binding Updates sent to correspondent nodes does 902 not require the configuration of security associations or the 903 existence of an authentication infrastructure between the mobile 904 nodes and correspondent nodes. Instead, a method called the return 905 routability procedure is used to assure that the right mobile node is 906 sending the message. This method does not protect against attackers 907 who are on the path between the home network and the correspondent 908 node. However, attackers in such a location are capable of 909 performing the same attacks even without Mobile IPv6. The main 910 advantage of the return routability procedure is that it limits the 911 potential attackers to those having an access to one specific path in 912 the Internet, and avoids forged Binding Updates from anywhere else in 913 the Internet. For a more in depth explanation of the security 914 properties of the return routability procedure, see Section 15. 916 The integrity and authenticity of the Binding Updates messages to 917 correspondent nodes is protected by using a keyed-hash algorithm. 918 The binding management key, Kbm, is used to key the hash algorithm 919 for this purpose. Kbm is established using data exchanged during the 920 return routability procedure. The data exchange is accomplished by 921 use of node keys, nonces, cookies, tokens, and certain cryptographic 922 functions. Section 5.2.5 outlines the basic return routability 923 procedure. Section 5.2.6 shows how the results of this procedure are 924 used to authorize a Binding Update to a correspondent node. 926 5.2.1 Node Keys 928 Each correspondent node has a secret key, Kcn, called the "node key", 929 which it uses to produce the keygen tokens sent to the mobile nodes. 930 The node key MUST be a random number, 20 octets in length. The node 931 key allows the correspondent node to verify that the keygen tokens 932 used by the mobile node in authorizing a Binding Update are indeed 933 its own. This key MUST NOT be shared with any other entity. 935 A correspondent node MAY generate a fresh node key at any time; this 936 avoids the need for secure persistent key storage. Procedures for 937 optionally updating the node key are discussed later in Section 938 5.2.7. 940 5.2.2 Nonces 942 Each correspondent node also generates nonces at regular intervals. 943 The nonces should be generated by using a random number generator 944 that is known to have good randomness properties [1]. A 945 correspondent node may use the same Kcn and nonce with all the 946 mobiles it is in communication with. 948 Each nonce is identified by a nonce index. When a new nonce is 949 generated, it must be associated with a new nonce index; this may be 950 done, for example, by incrementing the value of the previous nonce 951 index, if the nonce index is used as an array pointer into a linear 952 array of nonces. However, there is no requirement that nonces be 953 stored that way, or that the values of subsequent nonce indices have 954 any particular relationship to each other. The index value is 955 communicated in the protocol, so that if a nonce is replaced by new 956 nonce during the run of a protocol, the correspondent node can 957 distinguish messages that should be checked against the old nonce 958 from messages that should be checked against the new nonce. Strictly 959 speaking, indices are not necessary in the authentication, but allow 960 the correspondent node to efficiently find the nonce value that it 961 used in creating a keygen token. 963 Correspondent nodes keep both the current nonce and a small set of 964 valid previous nonces whose lifetime has not yet expired. Expired 965 values MUST be discarded, and messages using stale or unknown indices 966 will be rejected. 968 The specific nonce index values cannot be used by mobile nodes to 969 determine the validity of the nonce. Expected validity times for the 970 nonces values and the procedures for updating them are discussed 971 later in Section 5.2.7. 973 A nonce is an octet string of any length. The recommended length is 974 64 bits. 976 5.2.3 Cookies and Tokens 978 The return routability address test procedure uses cookies and keygen 979 tokens as opaque values within the test init and test messages, 980 respectively. 982 o The "home init cookie" and "care-of init cookie" are 64 bit values 983 sent to the correspondent node from the mobile node, and later 984 returned to the mobile node. The home init cookie is sent in the 985 Home Test Init message, and returned in the Home Test message. 986 The care-of init cookie is sent in the Care-of Test Init message, 987 and returned in the Care-of Test message. 989 o The "home keygen token" and "care-of keygen token" are 64-bit 990 values sent by the correspondent node to the mobile node via the 991 home agent (via the Home Test message) and the care-of address (by 992 the Care-of Test message), respectively. 994 The mobile node should set the home init or care-of init cookie to a 995 newly generated random number in every Home or Care-of Test Init 996 message it sends. The cookies are used to verify that the Home Test 997 or Care-of Test message matches the Home Test Init or Care-of Test 998 Init message, respectively. These cookies also serve to ensure that 999 parties who have not seen the request cannot spoof responses. 1001 Home and care-of keygen tokens are produced by the correspondent node 1002 based on its currently active secret key (Kcn) and nonces, as well as 1003 the home or care-of address (respectively). A keygen token is valid 1004 as long as both the secret key (Kcn) and the nonce used to create it 1005 are valid. 1007 5.2.4 Cryptographic Functions 1009 In this specification, the function used to compute hash values is 1010 SHA1 [20]. Message Authentication Codes (MACs) are computed using 1011 HMAC_SHA1 [25, 20]. HMAC_SHA1(K,m) denotes such a MAC computed on 1012 message m with key K. 1014 5.2.5 Return Routability Procedure 1015 The Return Routability Procedure enables the correspondent node to 1016 obtain some reasonable assurance that the mobile node is in fact 1017 addressable at its claimed care-of address as well as at its home 1018 address. Only with this assurance is the correspondent node able to 1019 accept Binding Updates from the mobile node which would then instruct 1020 the correspondent node to direct that mobile node's data traffic to 1021 its claimed care-of address. 1023 This is done by testing whether packets addressed to the two claimed 1024 addresses are routed to the mobile node. The mobile node can pass 1025 the test only if it is able to supply proof that it received certain 1026 data (the "keygen tokens") which the correspondent node sends to 1027 those addresses. These data are combined by the mobile node into a 1028 binding management key, denoted Kbm. 1030 The below figure shows the message flow for the return routability 1031 procedure. 1033 Mobile node Home agent Correspondent node 1034 | | 1035 | Home Test Init (HoTI) | | 1036 |------------------------->|------------------------->| 1037 | | | 1038 | Care-of Test Init (CoTI) | 1039 |---------------------------------------------------->| 1040 | | 1041 | | Home Test (HoT) | 1042 |<-------------------------|<-------------------------| 1043 | | | 1044 | Care-of Test (CoT) | 1045 |<----------------------------------------------------| 1046 | | 1048 The Home and Care-of Test Init messages are sent at the same time. 1049 The procedure requires very little processing at the correspondent 1050 node, and the Home and Care-of Test messages can be returned quickly, 1051 perhaps nearly simultaneously. These four messages form the return 1052 routability procedure. 1054 Home Test Init 1056 A mobile node sends a Home Test Init message to the correspondent 1057 node (via the home agent) to acquire the home keygen token. The 1058 contents of the message can be summarized as follows: 1060 * Source Address = home address 1061 * Destination Address = correspondent 1063 * Parameters: 1065 + home init cookie 1067 The Home Test Init message conveys the mobile node's home address 1068 to the correspondent node. The mobile node also sends along a 1069 home init cookie that the correspondent node must return later. 1070 The Home Test Init message is reverse tunneled through the home 1071 agent. (The headers and addresses related to reverse tunneling 1072 have been omitted from the above discussion of the message 1073 contents.) The mobile node remembers these cookie values to obtain 1074 some assurance that its protocol messages are being processed by 1075 the desired correspondent node. 1077 Care-of Test Init 1079 The mobile node sends a Care-of Test Init message to the 1080 correspondent node (directly, not via the home agent) to acquire 1081 the care-of keygen token. The contents of this message can be 1082 summarized as follows: 1084 * Source Address = care-of address 1086 * Destination Address = correspondent 1088 * Parameters: 1090 + care-of init cookie 1092 The Care-of Test Init message conveys the mobile node's care-of 1093 address to the correspondent node. The mobile node also sends 1094 along a care-of init cookie that the correspondent node must 1095 return later. The Care-of Test Init message is sent directly to 1096 the correspondent node. 1098 Home Test 1100 The Home Test message is sent in response to a Home Test Init 1101 message. It is sent via the home agent. The contents of the 1102 message are: 1104 * Source Address = correspondent 1105 * Destination Address = home address 1107 * Parameters: 1109 + home init cookie 1111 + home keygen token 1113 + home nonce index 1115 When the correspondent node receives the Home Test Init message, 1116 it generates a home keygen token as follows: 1118 home keygen token := 1119 First (64, HMAC_SHA1 (Kcn, (home address | nonce | 0))) 1121 where | denotes concatenation. The final "0" inside the HMAC_SHA1 1122 function is a single zero octet, used to distinguish home and 1123 care-of cookies from each other. 1125 The home keygen token is formed from the first 64 bits of the MAC. 1126 The home keygen token tests that the mobile node can receive 1127 messages sent to its home address. Kcn is used in the production 1128 of home keygen token in order to allow the correspondent node to 1129 verify that it generated the home and care-of nonces, without 1130 forcing the correspondent node to remember a list of all tokens it 1131 has handed out. 1133 The Home Test message is sent to the mobile node via the home 1134 network, where it is presumed that the home agent will tunnel the 1135 message to the mobile node. This means that the mobile node needs 1136 to already have sent a Binding Update to the home agent, so that 1137 the home agent will have received and authorized the new care-of 1138 address for the mobile node before the return routability 1139 procedure. For improved security, the data passed between the 1140 home agent and the mobile node is made immune to inspection and 1141 passive attacks. Such protection is gained by encrypting the home 1142 keygen token as it is tunneled from the home agent to the mobile 1143 node as specified in Section 10.4.6. The security properties of 1144 this additional security are discussed in Section 15.4.1. 1146 The home init cookie from the mobile node is returned in the Home 1147 Test message, to ensure that the message comes from a node on the 1148 route between the home agent and the correspondent node. 1150 The home nonce index is delivered to the mobile node to later 1151 allow the correspondent node to efficiently find the nonce value 1152 that it used in creating the home keygen token. 1154 Care-of Test 1156 This message is sent in response to a Care-of Test Init message. 1157 This message is not sent via the home agent, it is sent directly 1158 to the mobile node. The contents of the message are: 1160 * Source Address = correspondent 1162 * Destination Address = care-of address 1164 * Parameters: 1166 + care-of init cookie 1168 + care-of keygen token 1170 + care-of nonce index 1172 When the correspondent node receives the Care-of Test Init 1173 message, it generates a care-of keygen token as follows: 1175 care-of keygen token := 1176 First (64, HMAC_SHA1 (Kcn, (care-of address | nonce | 1))) 1178 Here, the final "1" inside the HMAC_SHA1 function is a single 1179 octet containing the hex value 0x01, and is used to distinguish 1180 home and care-of cookies from each other. The keygen token is 1181 formed from the first 64 bits of the MAC, and sent directly to the 1182 mobile node at its care-of address. The care-of init cookie from 1183 the Care-of Test Init message is returned to ensure that the 1184 message comes from a node on the route to the correspondent node. 1186 The care-of nonce index is provided to identify the nonce used for 1187 the care-of keygen token. The home and care-of nonce indices MAY 1188 be the same, or different, in the Home and Care-of Test messages. 1190 When the mobile node has received both the Home and Care-of Test 1191 messages, the return routability procedure is complete. As a result 1192 of the procedure, the mobile node has the data it needs to send a 1193 Binding Update to the correspondent node. The mobile node hashes the 1194 tokens together to form a 20 octet binding key Kbm: 1196 Kbm = SHA1 (home keygen token | care-of keygen token) 1198 A Binding Update may also be used to delete a previously established 1199 binding (Section 6.1.7). In this case, the care-of keygen token is 1200 not used. Instead, the binding management key is generated as 1201 follows: 1203 Kbm = SHA1(home keygen token) 1205 Note that the correspondent node does not create any state specific 1206 to the mobile node, until it receives the Binding Update from that 1207 mobile node. The correspondent node does not maintain the value for 1208 the binding management key Kbm; it creates Kbm when given the nonce 1209 indices and the mobile node's addresses. 1211 5.2.6 Authorizing Binding Management Messages 1213 After the mobile node has created the binding management key (Kbm), 1214 it can supply a verifiable Binding Update to the correspondent node. 1215 This section provides an overview of this registration. The below 1216 figure shows the message flow. 1218 Mobile node Correspondent node 1219 | | 1220 | Binding Update (BU) | 1221 |---------------------------------------------->| 1222 | (MAC, seq#, nonce indices, care-of address) | 1223 | | 1224 | | 1225 | Binding Acknowledgement (BA) (if sent) | 1226 |<----------------------------------------------| 1227 | (MAC, seq#, status) | 1229 Binding Update 1231 To authorize a Binding Update, the mobile node creates a binding 1232 management key Kbm from the keygen tokens as described in the 1233 previous section. The contents of the Binding Update include the 1234 following: 1236 * Source Address = care-of address 1238 * Destination Address = correspondent 1240 * Parameters: 1242 + home address (within the Home Address destination option if 1243 different from the Source Address) 1245 + sequence number (within the Binding Update message header) 1247 + home nonce index (within the Nonce Indices option) 1249 + care-of nonce index (within the Nonce Indices option) 1251 + First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent 1252 | BU))) 1254 The Binding Update contains a Nonce Indices option, indicating to 1255 the correspondent node which home and care-of nonces to use to 1256 recompute Kbm, the binding management key. The MAC is computed as 1257 described in Section 6.2.7, using the correspondent node's address 1258 as the destination address and the Binding Update message itself 1259 ("BU" above) as the MH Data. 1261 Once the correspondent node has verified the MAC, it can create a 1262 Binding Cache entry for the mobile. 1264 Binding Acknowledgement 1266 The Binding Update is in some cases acknowledged by the 1267 correspondent node. The contents of the message are as follows: 1269 * Source Address = correspondent 1271 * Destination Address = care-of address 1273 * Parameters: 1275 + sequence number (within the Binding Update message header) 1277 + First (96, HMAC_SHA1 (Kbm, (care-of address | correspondent 1278 | BA))) 1280 The Binding Acknowledgement contains the same sequence number as 1281 the Binding Update. The MAC is computed as described in Section 1282 6.2.7, using the correspondent node's address as the destination 1283 address and the message itself ("BA" above) as the MH Data. 1285 Bindings established with correspondent nodes using keys created by 1286 way of the return routability procedure MUST NOT exceed 1287 MAX_RR_BINDING_LIFETIME seconds (see Section 12). 1289 The value in the Source Address field in the IPv6 header carrying the 1290 Binding Update is normally also the care-of address which is used in 1291 the binding. However, a different care-of address MAY be specified 1292 by including an Alternate Care-of Address mobility option in the 1293 Binding Update (see Section 6.2.5). When such a message is sent to 1294 the correspondent node and the return routability procedure is used 1295 as the authorization method, the Care-of Test Init and Care-of Test 1296 messages MUST have been performed for the address in the Alternate 1297 Care-of Address option (not the Source Address). The nonce indices 1298 and MAC value MUST be based on information gained in this test. 1300 Binding Updates may also be sent to delete a previously established 1301 binding. In this case, generation of the binding management key 1302 depends exclusively on the home keygen token and the care-of nonce 1303 index is ignored. 1305 5.2.7 Updating Node Keys and Nonces 1307 Correspondent nodes generate nonces at regular intervals. It is 1308 recommended to keep each nonce (identified by a nonce index) 1309 acceptable for at least MAX_TOKEN_LIFETIME seconds (see Section 12) 1310 after it has been first used in constructing a return routability 1311 message response. However, the correspondent node MUST NOT accept 1312 nonces beyond MAX_NONCE_LIFETIME seconds (see Section 12) after the 1313 first use. As the difference between these two constants is 30 1314 seconds, a convenient way to enforce the above lifetimes is to 1315 generate a new nonce every 30 seconds. The node can then continue to 1316 accept tokens that have been based on the last 8 (MAX_NONCE_LIFETIME 1317 / 30) nonces. This results in tokens being acceptable 1318 MAX_TOKEN_LIFETIME to MAX_NONCE_LIFETIME seconds after they have been 1319 sent to the mobile node, depending on whether the token was sent at 1320 the beginning or end of the first 30 second period. Note that the 1321 correspondent node may also attempt to generate new nonces on demand, 1322 or only if the old nonces have been used. This is possible, as long 1323 as the correspondent node keeps track of how long a time ago the 1324 nonces were used for the first time, and does not generate new nonces 1325 on every return routability request. 1327 Due to resource limitations, rapid deletion of bindings, or reboots 1328 the correspondent node may not in all cases recognize the nonces that 1329 the tokens were based on. If a nonce index is unrecognized, the 1330 correspondent node replies with an an error code in the Binding 1331 Acknowledgement (either 136, 137, or 138 as discussed in Section 1332 6.1.8). The mobile node can then retry the return routability 1333 procedure. 1335 An update of Kcn SHOULD be done at the same time as an update of a 1336 nonce, so that nonce indices can identify both the nonce and the key. 1338 Old Kcn values have to be therefore remembered as long as old nonce 1339 values. 1341 Given that the tokens are normally expected to be usable for 1342 MAX_TOKEN_LIFETIME seconds, the mobile node MAY use them beyond a 1343 single run of the return routability procedure until 1344 MAX_TOKEN_LIFETIME expires. After this the mobile node SHOULD NOT 1345 use the tokens. A fast moving mobile node MAY reuse a recent home 1346 keygen token from a correspondent node when moving to a new location, 1347 and just acquire a new care-of keygen token to show routability in 1348 the new location. 1350 While this does not save the number of round-trips due to the 1351 simultaneous processing of home and care-of return routability tests, 1352 there are fewer messages being exchanged, and a potentially long 1353 round-trip through the home agent is avoided. Consequently, this 1354 optimization is often useful. A mobile node that has multiple home 1355 addresses, MAY also use the same care-of keygen token for Binding 1356 Updates concerning all of these addresses. 1358 5.2.8 Preventing Replay Attacks 1360 The return routability procedure also protects the participants 1361 against replayed Binding Updates through the use of the sequence 1362 number and a MAC. Care must be taken when removing bindings at the 1363 correspondent node, however. Correspondent nodes must retain 1364 bindings and the associated sequence number information at least as 1365 long as the nonces used in the authorization of the binding are still 1366 valid. Alternatively, if memory is very constrained, the 1367 correspondent node MAY invalidate the nonces that were used for the 1368 binding being deleted (or some larger group of nonces that they 1369 belong to). This may, however, impact the ability to accept Binding 1370 Updates from mobile nodes that have recently received keygen tokens. 1371 This alternative is therefore recommended only as a last measure. 1373 5.3 Dynamic Home Agent Address Discovery 1375 No security is required for dynamic home agent address discovery. 1377 5.4 Mobile Prefix Discovery 1379 The mobile node and the home agent SHOULD use an IPsec security 1380 association to protect the integrity and authenticity of the Mobile 1381 Prefix Solicitations and Advertisements. Both the mobile nodes and 1382 the home agents MUST support and SHOULD use the Encapsulating 1383 Security Payload (ESP) header in transport mode with a non-NULL 1384 payload authentication algorithm to provide data origin 1385 authentication, connectionless integrity and optional anti-replay 1386 protection. 1388 5.5 Payload Packets 1390 Payload packets exchanged with mobile nodes can be protected in the 1391 usual manner, in the same way as stationary hosts can protect them. 1392 However, Mobile IPv6 introduces the Home Address destination option, 1393 a routing header, and tunneling headers in the payload packets. In 1394 the following we define the security measures taken to protect these, 1395 and to prevent their use in attacks against other parties. 1397 This specification limits the use of the Home Address destination 1398 option to the situation where the correspondent node already has a 1399 Binding Cache entry for the given home address. This avoids the use 1400 of the Home Address option in attacks described in Section 15.1. 1402 Mobile IPv6 uses a Mobile IPv6 specific type of a routing header. 1403 This type provides the necessary functionality but does not open 1404 vulnerabilities discussed in Section 15.1. 1406 Tunnels between the mobile node and the home agent are protected by 1407 ensuring proper use of source addresses, and optional cryptographic 1408 protection. The mobile node verifies that the outer IP address 1409 corresponds to its home agent. The home agent verifies that the 1410 outer IP address corresponds to the current location of the mobile 1411 node (Binding Updates sent to the home agents are secure). The home 1412 agent identifies the mobile node through the source address of the 1413 inner packet. (Typically, this is the home address of the mobile 1414 node, but it can also be a link-local address, as discussed in 1415 Section 10.4.2. To recognize the latter type of addresses, the home 1416 agent requires that the Link-Local Address Compatibility (L) was set 1417 in the Binding Update.) These measures protect the tunnels against 1418 vulnerabilities discussed in Section 15.1. 1420 For traffic tunneled via the home agent, additional IPsec ESP 1421 encapsulation MAY be supported and used. If multicast group 1422 membership control protocols or stateful address autoconfiguration 1423 protocols are supported, payload data protection MUST be supported. 1425 6. New IPv6 Protocol, Message Types, and Destination Option 1427 6.1 Mobility Header 1429 The Mobility Header is an extension header used by mobile nodes, 1430 correspondent nodes, and home agents in all messaging related to the 1431 creation and management of bindings. The subsections within this 1432 section describe the message types that may be sent using the 1433 Mobility Header. 1435 Mobility Header messages MUST NOT be sent with a type 2 routing 1436 header, except as described in Section 9.5.4 for Binding 1437 Acknowledgement. Mobility Header messages also MUST NOT be used with 1438 a Home Address destination option, except as described in Section 1439 11.7.1 and Section 11.7.2 for Binding Update. Binding Update List or 1440 Binding Cache information (when present) for the destination MUST NOT 1441 be used in sending Mobility Header messages. That is, Mobility 1442 Header messages bypass both the Binding Cache check described in 1443 Section 9.3.2 and the Binding Update List check described in Section 1444 11.3.1 which are normally performed for all packets. This applies 1445 even to messages sent to or from a correspondent node which is itself 1446 a mobile node. 1448 6.1.1 Format 1450 The Mobility Header is identified by a Next Header value of TBD in the immediately preceding header, and has the 1452 following format: 1454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1455 | Payload Proto | Header Len | MH Type | Reserved | 1456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1457 | Checksum | | 1458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1459 | | 1460 . . 1461 . Message Data . 1462 . . 1463 | | 1464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1466 Payload Proto 1468 8-bit selector. Identifies the type of header immediately 1469 following the Mobility Header. Uses the same values as the IPv6 1470 Next Header field [11]. 1472 This field is intended to be used by a future extension (see 1473 Appendix B.1). 1475 Implementations conforming to this specification SHOULD set the 1476 payload protocol type to IPPROTO_NONE (59 decimal). 1478 Header Len 1480 8-bit unsigned integer, representing the length of the Mobility 1481 Header in units of 8 octets, excluding the first 8 octets. 1483 The length of the Mobility Header MUST be a multiple of 8 octets. 1485 MH Type 1487 8-bit selector. Identifies the particular mobility message in 1488 question. Current values are specified in Section 6.1.2 and 1489 onward. An unrecognized MH Type field causes an error indication 1490 to be sent. 1492 Reserved 1494 8-bit field reserved for future use. The value MUST be 1495 initialized to zero by the sender, and MUST be ignored by the 1496 receiver. 1498 Checksum 1500 16-bit unsigned integer. This field contains the checksum of the 1501 Mobility Header. The checksum is calculated from the octet string 1502 consisting of a "pseudo-header" followed by the entire Mobility 1503 Header starting with the Payload Proto field. The checksum is the 1504 16-bit one's complement of the one's complement sum of this 1505 string. 1507 The pseudo-header contains IPv6 header fields, as specified in 1508 Section 8.1 of RFC 2460 [11]. The Next Header value used in the 1509 pseudo-header is TBD . The addresses used 1510 in the pseudo-header are the addresses that appear in the Source 1511 and Destination Address fields in the IPv6 packet carrying the 1512 Mobility Header. 1514 Note that the procedures of calculating upper layer checksums 1515 while away from home described in Section 11.3.1 apply even for 1516 the Mobility Header. If a mobility message has a Home Address 1517 destination option, then the checksum calculation uses the home 1518 address in this option as the value of the IPv6 Source Address 1519 field. The type 2 routing header is treated as explained in [11]. 1521 The Mobility Header is considered as the upper layer protocol for 1522 the purposes of calculating the pseudo-header. The Upper-Layer 1523 Packet Length field in the pseudo-header MUST be set to the total 1524 length of the Mobility Header. 1526 For computing the checksum, the checksum field is set to zero. 1528 Message Data 1530 A variable length field containing the data specific to the 1531 indicated Mobility Header type. 1533 Mobile IPv6 also defines a number of "mobility options" for use 1534 within these messages; if included, any options MUST appear after the 1535 fixed portion of the message data specified in this document. The 1536 presence of such options will be indicated by the Header Len field 1537 within the message. When the Header Len value is greater than the 1538 length required for the message specified here, the remaining octets 1539 are interpreted as mobility options. These options include padding 1540 options that can be used to ensure that other options are aligned 1541 properly, and that the total length of the message is divisible by 8. 1542 The encoding and format of defined options are described in Section 1543 6.2. 1545 Alignment requirements for the Mobility Header are the same as for 1546 any IPv6 protocol Header. That is, they MUST be aligned on an 1547 8-octet boundary. 1549 6.1.2 Binding Refresh Request Message 1551 The Binding Refresh Request (BRR) message requests a mobile node to 1552 update its mobility binding. This message is sent by correspondent 1553 nodes according to the rules in Section 9.5.5. When a mobile node 1554 receives a packet containing a Binding Refresh Request message it 1555 processes the message according to the rules in Section 11.7.4. 1557 The Binding Refresh Request message uses the MH Type value 0. When 1558 this value is indicated in the MH Type field, the format of the 1559 Message Data field in the Mobility Header is as follows: 1561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1562 | Reserved | 1563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1564 | | 1565 . . 1566 . Mobility options . 1567 . . 1568 | | 1569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1571 Reserved 1573 16-bit field reserved for future use. The value MUST be 1574 initialized to zero by the sender, and MUST be ignored by the 1575 receiver. 1577 Mobility Options 1579 Variable-length field of such length that the complete Mobility 1580 Header is an integer multiple of 8 octets long. This field 1581 contains zero or more TLV-encoded mobility options. The encoding 1582 and format of defined options are described in Section 6.2. The 1583 receiver MUST ignore and skip any options which it does not 1584 understand. 1586 There MAY be additional information, associated with this Binding 1587 Refresh Request message that need not be present in all Binding 1588 Refresh Request messages sent. Mobility options allow future 1589 extensions to the format of the Binding Refresh Request message to 1590 be defined. This specification does not define any options valid 1591 for the Binding Refresh Request message. 1593 If no actual options are present in this message, no padding is 1594 necessary and the Header Len field will be set to 0. 1596 6.1.3 Home Test Init Message 1598 A mobile node uses the Home Test Init (HoTI) message to initiate the 1599 return routability procedure and request a home keygen token from a 1600 correspondent node (see Section 11.6.1). The Home Test Init message 1601 uses the MH Type value 1. When this value is indicated in the MH 1602 Type field, the format of the Message Data field in the Mobility 1603 Header is as follows: 1605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1606 | Reserved | 1607 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1608 | | 1609 + Home Init Cookie + 1610 | | 1611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1612 | | 1613 . . 1614 . Mobility Options . 1615 . . 1616 | | 1617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1619 Reserved 1621 16-bit field reserved for future use. This value MUST be 1622 initialized to zero by the sender, and MUST be ignored by the 1623 receiver. 1625 Home Init Cookie 1627 64-bit field which contains a random value, the home init cookie. 1629 Mobility Options 1631 Variable-length field of such length that the complete Mobility 1632 Header is an integer multiple of 8 octets long. This field 1633 contains zero or more TLV-encoded mobility options. The receiver 1634 MUST ignore and skip any options which it does not understand. 1635 This specification does not define any options valid for the Home 1636 Test Init message. 1638 If no actual options are present in this message, no padding is 1639 necessary and the Header Len field will be set to 1. 1641 This message is tunneled through the home agent when the mobile node 1642 is away from home. Such tunneling SHOULD employ IPsec ESP in tunnel 1643 mode between the home agent and the mobile node. This protection is 1644 indicated by the IPsec security policy database. The protection of 1645 Home Test Init messages is unrelated to the requirement to protect 1646 regular payload traffic, which MAY use such tunnels as well. 1648 6.1.4 Care-of Test Init Message 1650 A mobile node uses the Care-of Test Init (CoTI) message to initiate 1651 the return routability procedure and request a care-of keygen token 1652 from a correspondent node (see Section 11.6.1). The Care-of Test 1653 Init message uses the MH Type value 2. When this value is indicated 1654 in the MH Type field, the format of the Message Data field in the 1655 Mobility Header is as follows: 1657 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1658 | Reserved | 1659 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1660 | | 1661 + Care-of Init Cookie + 1662 | | 1663 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1664 | | 1665 . . 1666 . Mobility Options . 1667 . . 1668 | | 1669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1671 Reserved 1673 16-bit field reserved for future use. The value MUST be 1674 initialized to zero by the sender, and MUST be ignored by the 1675 receiver. 1677 Care-of Init Cookie 1679 64-bit field which contains a random value, the care-of init 1680 cookie. 1682 Mobility Options 1684 Variable-length field of such length that the complete Mobility 1685 Header is an integer multiple of 8 octets long. This field 1686 contains zero or more TLV-encoded mobility options. The receiver 1687 MUST ignore and skip any options which it does not understand. 1688 This specification does not define any options valid for the 1689 Care-of Test Init message. 1691 If no actual options are present in this message, no padding is 1692 necessary and the Header Len field will be set to 1. 1694 6.1.5 Home Test Message 1696 The Home Test (HoT) message is a response to the Home Test Init 1697 message, and is sent from the correspondent node to the mobile node 1698 (see Section 5.2.5). The Home Test message uses the MH Type value 3. 1699 When this value is indicated in the MH Type field, the format of the 1700 Message Data field in the Mobility Header is as follows: 1702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1703 | Home Nonce Index | 1704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1705 | | 1706 + Home Init Cookie + 1707 | | 1708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1709 | | 1710 + Home Keygen Token + 1711 | | 1712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1713 | | 1714 . . 1715 . Mobility options . 1716 . . 1717 | | 1718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1720 Home Nonce Index 1722 This field will be echoed back by the mobile node to the 1723 correspondent node in a subsequent Binding Update. 1725 Home Init Cookie 1727 64-bit field which contains the home init cookie. 1729 Home Keygen Token 1731 This field contains the 64 bit home keygen token used in the 1732 return routability procedure. 1734 Mobility Options 1736 Variable-length field of such length that the complete Mobility 1737 Header is an integer multiple of 8 octets long. This field 1738 contains zero or more TLV-encoded mobility options. The receiver 1739 MUST ignore and skip any options which it does not understand. 1740 This specification does not define any options valid for the Home 1741 Test message. 1743 If no actual options are present in this message, no padding is 1744 necessary and the Header Len field will be set to 2. 1746 6.1.6 Care-of Test Message 1748 The Care-of Test (CoT) message is a response to the Care-of Test Init 1749 message, and is sent from the correspondent node to the mobile node 1750 (see Section 11.6.2). The Care-of Test message uses the MH Type 1751 value 4. When this value is indicated in the MH Type field, the 1752 format of the Message Data field in the Mobility Header is as 1753 follows: 1755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1756 | Care-of Nonce Index | 1757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1758 | | 1759 + Care-of Init Cookie + 1760 | | 1761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1762 | | 1763 + Care-of Keygen Token + 1764 | | 1765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1766 | | 1767 . . 1768 . Mobility Options . 1769 . . 1770 | | 1771 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1773 Care-of Nonce Index 1775 This value will be echoed back by the mobile node to the 1776 correspondent node in a subsequent Binding Update. 1778 Care-of Init Cookie 1780 64-bit field which contains the care-of init cookie. 1782 Care-of Keygen Token 1784 This field contains the 64 bit care-of keygen token used in the 1785 return routability procedure. 1787 Mobility Options 1789 Variable-length field of such length that the complete Mobility 1790 Header is an integer multiple of 8 octets long. This field 1791 contains zero or more TLV-encoded mobility options. The receiver 1792 MUST ignore and skip any options which it does not understand. 1793 This specification does not define any options valid for the 1794 Care-of Test message. 1796 If no actual options are present in this message, no padding is 1797 necessary and the Header Len field will be set to 2. 1799 6.1.7 Binding Update Message 1801 The Binding Update (BU) message is used by a mobile node to notify 1802 other nodes of a new care-of address for itself. Binding Updates are 1803 sent as described in Section 11.7.1 and Section 11.7.2. 1805 The Binding Update uses the MH Type value 5. When this value is 1806 indicated in the MH Type field, the format of the Message Data field 1807 in the Mobility Header is as follows: 1809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1810 | Sequence # | 1811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1812 |A|H|L|K| Reserved | Lifetime | 1813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1814 | | 1815 . . 1816 . Mobility options . 1817 . . 1818 | | 1819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1821 Acknowledge (A) 1823 The Acknowledge (A) bit is set by the sending mobile node to 1824 request a Binding Acknowledgement (Section 6.1.8) be returned upon 1825 receipt of the Binding Update. 1827 Home Registration (H) 1829 The Home Registration (H) bit is set by the sending mobile node to 1830 request that the receiving node should act as this node's home 1831 agent. The destination of the packet carrying this message MUST 1832 be that of a router sharing the same subnet prefix as the home 1833 address of the mobile node in the binding. 1835 Link-Local Address Compatibility (L) 1837 The Link-Local Address Compatibility (L) bit is set when the home 1838 address reported by the mobile node has the same interface 1839 identifier as the mobile node's link-local address. 1841 Key Management Mobility Capability (K) 1843 If this bit is cleared, the protocol used for establishing the 1844 IPsec security associations between the mobile node and the home 1845 agent does not survive movements. It may then have to be rerun. 1846 (Note that the IPsec security associations themselves are expected 1847 to survive movements.) If manual IPsec configuration is used, the 1848 bit MUST be cleared. 1850 This bit is valid only in Binding Updates sent to the home agent, 1851 and MUST be cleared in other Binding Updates. Correspondent nodes 1852 MUST ignore this bit. 1854 Reserved 1856 These fields are unused. They MUST be initialized to zero by the 1857 sender and MUST be ignored by the receiver. 1859 Sequence # 1861 A 16-bit unsigned integer used by the receiving node to sequence 1862 Binding Updates and by the sending node to match a returned 1863 Binding Acknowledgement with this Binding Update. 1865 Lifetime 1867 16-bit unsigned integer. The number of time units remaining 1868 before the binding MUST be considered expired. A value of zero 1869 indicates that the Binding Cache entry for the mobile node MUST be 1870 deleted. (In this case the specified care-of address MUST also be 1871 set equal to the home address.) One time unit is 4 seconds. 1873 Mobility Options 1875 Variable-length field of such length that the complete Mobility 1876 Header is an integer multiple of 8 octets long. This field 1877 contains zero or more TLV-encoded mobility options. The encoding 1878 and format of defined options are described in Section 6.2. The 1879 receiver MUST ignore and skip any options which it does not 1880 understand. 1882 The following options are valid in a Binding Update: 1884 * Binding Authorization Data option (this option is mandatory in 1885 Binding Updates sent to a correspondent node) 1887 * Nonce Indices option. 1889 * Alternate Care-of Address option 1891 If no options are present in this message, 4 octets of padding is 1892 necessary and the Header Len field will be set to 1. 1894 The care-of address is specified either by the Source Address field 1895 in the IPv6 header or by the Alternate Care-of Address option, if 1896 present. The care-of address MUST be a unicast routable address. 1897 IPv6 Source Address MUST be a topologically correct source address. 1898 Binding Updates for a care-of address which is not a unicast routable 1899 address MUST be silently discarded. Similarly, the Binding Update 1900 MUST be silently discarded if the care-of address appears as a home 1901 address in an existing Binding Cache entry, with its current location 1902 creating a circular reference back to the home address specified in 1903 the Binding Update (possibly through additional entries). 1905 The deletion of a binding can be indicated by setting the Lifetime 1906 field to 0 and by setting the care-of address equal to the home 1907 address. In deletion, the generation of the binding management key 1908 depends exclusively on the home keygen token, as explained in Section 1909 5.2.5. (Note that while the senders are required to set both the 1910 Lifetime field to 0 and the care-of address equal to the home 1911 address, Section 9.5.1 rules for receivers are more liberal, and 1912 interpret either condition as a deletion.) 1914 Correspondent nodes SHOULD NOT expire the Binding Cache entry before 1915 the lifetime expires, if any application hosted by the correspondent 1916 node is still likely to require communication with the mobile node. 1917 A Binding Cache entry that is deallocated prematurely might cause 1918 subsequent packets to be dropped from the mobile node, if they 1919 contain the Home Address destination option. This situation is 1920 recoverable, since an Binding Error message is sent to the mobile 1921 node (see Section 6.1.9); however, it causes unnecessary delay in the 1922 communications. 1924 6.1.8 Binding Acknowledgement Message 1926 The Binding Acknowledgement is used to acknowledge receipt of a 1927 Binding Update (Section 6.1.7). This packet is sent as described in 1928 Section 9.5.4 and Section 10.3.1. 1930 The Binding Acknowledgement has the MH Type value 6. When this value 1931 is indicated in the MH Type field, the format of the Message Data 1932 field in the Mobility Header is as follows: 1934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1935 | Status |K| Reserved | 1936 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1937 | Sequence # | Lifetime | 1938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1939 | | 1940 . . 1941 . Mobility options . 1942 . . 1943 | | 1944 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1946 Key Management Mobility Capability (K) 1948 If this bit is cleared, the protocol used by the home agent for 1949 establishing the IPsec security associations between the mobile 1950 node and the home agent does not survive movements. It may then 1951 have to be rerun. (Note that the IPsec security associations 1952 themselves are expected to survive movements.) 1954 Correspondent nodes MUST set the K bit to 0. 1956 Reserved 1958 These fields are unused. They MUST be initialized to zero by the 1959 sender and MUST be ignored by the receiver. 1961 Status 1963 8-bit unsigned integer indicating the disposition of the Binding 1964 Update. Values of the Status field less than 128 indicate that 1965 the Binding Update was accepted by the receiving node. Values 1966 greater than or equal to 128 indicate that the Binding Update was 1967 rejected by the receiving node. The following Status values are 1968 currently defined: 1970 0 Binding Update accepted 1972 1 Accepted but prefix discovery necessary 1974 128 Reason unspecified 1976 129 Administratively prohibited 1978 130 Insufficient resources 1979 131 Home registration not supported 1981 132 Not home subnet 1983 133 Not home agent for this mobile node 1985 134 Duplicate Address Detection failed 1987 135 Sequence number out of window 1989 136 Expired home nonce index 1991 137 Expired care-of nonce index 1993 138 Expired nonces 1995 139 Registration type change disallowed 1997 Up-to-date values of the Status field are to be specified in the 1998 IANA registry of assigned numbers [19]. 2000 Sequence # 2002 The Sequence Number in the Binding Acknowledgement is copied from 2003 the Sequence Number field in the Binding Update. It is used by 2004 the mobile node in matching this Binding Acknowledgement with an 2005 outstanding Binding Update. 2007 Lifetime 2009 The granted lifetime, in time units of 4 seconds, for which this 2010 node SHOULD retain the entry for this mobile node in its Binding 2011 Cache. 2013 The value of this field is undefined if the Status field indicates 2014 that the Binding Update was rejected. 2016 Mobility Options 2018 Variable-length field of such length that the complete Mobility 2019 Header is an integer multiple of 8 octets long. This field 2020 contains zero or more TLV-encoded mobility options. The encoding 2021 and format of defined options are described in Section 6.2. The 2022 receiver MUST ignore and skip any options which it does not 2023 understand. 2025 There MAY be additional information, associated with this Binding 2026 Acknowledgement that need not be present in all Binding 2027 Acknowledgements sent. Mobility options allow future extensions 2028 to the format of the Binding Acknowledgement to be defined. The 2029 following options are valid for the Binding Acknowledgement: 2031 * Binding Authorization Data option (this option is mandatory in 2032 Binding Acknowledgements sent by a correspondent node, except 2033 where otherwise noted in Section 9.5.4) 2035 * Binding Refresh Advice option 2037 If no options are present in this message, 4 octets of padding is 2038 necessary and the Header Len field will be set to 1. 2040 6.1.9 Binding Error Message 2042 The Binding Error (BE) message is used by the correspondent node to 2043 signal an error related to mobility, such as an inappropriate attempt 2044 to use the Home Address destination option without an existing 2045 binding; see Section 9.3.3 for details. 2047 The Binding Error message uses the MH Type value 7. When this value 2048 is indicated in the MH Type field, the format of the Message Data 2049 field in the Mobility Header is as follows: 2051 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2052 | Status | Reserved | 2053 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2054 | | 2055 + + 2056 | | 2057 + Home Address + 2058 | | 2059 + + 2060 | | 2061 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2062 . . 2063 . Mobility Options . 2064 . . 2065 | | 2066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2068 Status 2070 8-bit unsigned integer indicating the reason for this message. 2071 The following values are currently defined: 2073 1 Unknown binding for Home Address destination option 2075 2 Unrecognized MH Type value 2077 Reserved 2079 A 8-bit field reserved for future use. The value MUST be 2080 initialized to zero by the sender, and MUST be ignored by the 2081 receiver. 2083 Home Address 2085 The home address that was contained in the Home Address 2086 destination option. The mobile node uses this information to 2087 determine which binding does not exist, in cases where the mobile 2088 node has several home addresses. 2090 Mobility Options 2092 Variable-length field of such length that the complete Mobility 2093 Header is an integer multiple of 8 octets long. This field 2094 contains zero or more TLV-encoded mobility options. The receiver 2095 MUST ignore and skip any options which it does not understand. 2097 There MAY be additional information, associated with this Binding 2098 Error message that need not be present in all Binding Error 2099 messages sent. Mobility options allow future extensions to the 2100 format of the format of the Binding Error message to be defined. 2101 The encoding and format of defined options are described in 2102 Section 6.2. This specification does not define any options valid 2103 for the Binding Error message. 2105 If no actual options are present in this message, no padding is 2106 necessary and the Header Len field will be set to 2. 2108 6.2 Mobility Options 2110 Mobility messages can include zero or more mobility options. This 2111 allows optional fields that may not be needed in every use of a 2112 particular Mobility Header, as well as future extensions to the 2113 format of the messages. Such options are included in the Message 2114 Data field of the message itself, after the fixed portion of the 2115 message data specified in the message subsections of Section 6.1. 2117 The presence of such options will be indicated by the Header Len of 2118 the Mobility Header. If included, the Binding Authorization Data 2119 option (Section 6.2.7) MUST be the last option and MUST NOT have 2120 trailing padding. Otherwise, options can be placed in any order. 2122 6.2.1 Format 2124 Mobility options are encoded within the remaining space of the 2125 Message Data field of a mobility message, using a type-length-value 2126 (TLV) format as follows: 2128 0 1 2 3 2129 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 2130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2131 | Option Type | Option Length | Option Data... 2132 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2134 Option Type 2136 8-bit identifier of the type of mobility option. When processing 2137 a Mobility Header containing an option for which the Option Type 2138 value is not recognized by the receiver, the receiver MUST quietly 2139 ignore and skip over the option, correctly handling any remaining 2140 options in the message. 2142 Option Length 2144 8-bit unsigned integer, representing the length in octets of the 2145 mobility option, not including the Option Type and Option Length 2146 fields. 2148 Option Data 2150 A variable length field that contains data specific to the option. 2152 The following subsections specify the Option types which are 2153 currently defined for use in the Mobility Header. 2155 Implementations MUST silently ignore any mobility options that they 2156 do not understand. 2158 Mobility options may have alignment requirements. Following the 2159 convention in IPv6, these options are aligned in a packet so that 2160 multi-octet values within the Option Data field of each option fall 2161 on natural boundaries (i.e., fields of width n octets are placed at 2162 an integer multiple of n octets from the start of the header, for n = 2163 1, 2, 4, or 8) [11]. 2165 6.2.2 Pad1 2167 The Pad1 option does not have any alignment requirements. Its format 2168 is as follows: 2170 0 2171 0 1 2 3 4 5 6 7 2172 +-+-+-+-+-+-+-+-+ 2173 | Type = 0 | 2174 +-+-+-+-+-+-+-+-+ 2176 NOTE! the format of the Pad1 option is a special case - it has 2177 neither Option Length nor Option Data fields. 2179 The Pad1 option is used to insert one octet of padding in the 2180 Mobility Options area of a Mobility Header. If more than one octet 2181 of padding is required, the PadN option, described next, should be 2182 used rather than multiple Pad1 options. 2184 6.2.3 PadN 2186 The PadN option does not have any alignment requirements. Its format 2187 is as follows: 2189 0 1 2190 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 2192 | Type = 1 | Option Length | Option Data 2193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - 2195 The PadN option is used to insert two or more octets of padding in 2196 the Mobility Options area of a mobility message. For N octets of 2197 padding, the Option Length field contains the value N-2, and the 2198 Option Data consists of N-2 zero-valued octets. PadN Option data 2199 MUST be ignored by the receiver. 2201 6.2.4 Binding Refresh Advice 2203 The Binding Refresh Advice option has an alignment requirement of 2n. 2204 Its format is as follows: 2206 0 1 2 3 2207 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 2208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2209 | Type = 2 | Length = 2 | 2210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2211 | Refresh Interval | 2212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2214 The Binding Refresh Advice option is only valid in the Binding 2215 Acknowledgement, and only on Binding Acknowledgements sent from the 2216 mobile node's home agent in reply to a home registration. The 2217 Refresh Interval is measured in units of four seconds, and indicates 2218 how long before the mobile node SHOULD send a new home registration 2219 to the home agent. The Refresh Interval MUST be set to indicate a 2220 smaller time interval than the Lifetime value of the Binding 2221 Acknowledgement. 2223 6.2.5 Alternate Care-of Address 2225 The Alternate Care-of Address option has an alignment requirement of 2226 8n+6. Its format is as follows: 2228 0 1 2 3 2229 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 2230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2231 | Type = 3 | Length = 16 | 2232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2233 | | 2234 + + 2235 | | 2236 + Alternate Care-of Address + 2237 | | 2238 + + 2239 | | 2240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2242 Normally, a Binding Update specifies the desired care-of address in 2243 the Source Address field of the IPv6 header. However, this is not 2244 possible in some cases, such as when the mobile node wishes to 2245 indicate a care-of address which it cannot use as a topologically 2246 correct source address (Section 6.1.7 and Section 11.7.2) or when the 2247 used security mechanism does not protect the IPv6 header (Section 2248 11.7.1). 2250 The Alternate Care-of Address option is provided for these 2251 situations. This option is valid only in Binding Update. The 2252 Alternate Care-of Address field contains an address to use as the 2253 care-of address for the binding, rather than using the Source Address 2254 of the packet as the care-of address. 2256 6.2.6 Nonce Indices 2258 The Nonce Indices option has an alignment requirement of 2n. Its 2259 format is as follows: 2261 0 1 2 3 2262 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 2263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2264 | Type = 4 | Length = 4 | 2265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2266 | Home Nonce Index | Care-of Nonce Index | 2267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2269 The Nonce Indices option is valid only in the Binding Update message 2270 sent to a correspondent node, and only when present together with a 2271 Binding Authorization Data option. When the correspondent node 2272 authorizes the Binding Update, it needs to produce home and care-of 2273 keygen tokens from its stored random nonce values. 2275 The Home Nonce Index field tells the correspondent node which nonce 2276 value to use when producing the home keygen token. 2278 The Care-of Nonce Index field is ignored in requests to delete a 2279 binding. Otherwise, it tells the correspondent node which nonce 2280 value to use when producing the care-of keygen token. 2282 6.2.7 Binding Authorization Data 2284 The Binding Authorization Data option does not have alignment 2285 requirements as such. However, since this option must be the last 2286 mobility option, an implicit alignment requirement is 8n + 2. The 2287 format of this option is as follows: 2289 0 1 2 3 2290 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 2291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2292 | Type = 5 | Option Length | 2293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2294 | | 2295 + + 2296 | Authenticator | 2297 + + 2298 | | 2299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2301 The Binding Authorization Data option is valid in the Binding Update 2302 and Binding Acknowledgement. 2304 The Option Length field contains the length of the authenticator in 2305 octets. 2307 The Authenticator field contains a cryptographic value which can be 2308 used to determine that the message in question comes from the right 2309 authority. Rules for calculating this value depend on the used 2310 authorization procedure. 2312 For the return routability procedure, this option can appear in the 2313 Binding Update and Binding Acknowledgements. Rules for calculating 2314 the Authenticator value are the following: 2316 Mobility Data = care-of address | correspondent | MH Data 2317 Authenticator = First (96, HMAC_SHA1 (Kbm, Mobility Data)) 2319 Where | denotes concatenation and "correspondent" is the IPv6 address 2320 of the correspondent node. Note that, if the message is sent to a 2321 destination which is itself mobile, the "correspondent" address may 2322 not be the address found in the Destination Address field of the IPv6 2323 header; instead the home address from the type 2 Routing header 2324 should be used. 2326 "MH Data" is the content of the Mobility Header, excluding the 2327 Authenticator field itself. The Authenticator value is calculated as 2328 if the Checksum field in the Mobility Header was zero. The Checksum 2329 in the transmitted packet is still calculated in the usual manner, 2330 with the calculated Authenticator being a part of the packet 2331 protected by the Checksum. Kbm is the binding management key, which 2332 is typically created using nonces provided by the correspondent node 2333 (see Section 9.4). Note that while the contents of a potential Home 2334 Address destination option are not covered in this formula, the rules 2335 for the calculation of the Kbm do take the home address in account. 2336 This ensures that the MAC will be different for different home 2337 addresses. 2339 The first 96 bits from the MAC result are used as the Authenticator 2340 field. 2342 6.3 Home Address Option 2344 The Home Address option is carried by the Destination Option 2345 extension header (Next Header value = 60). It is used in a packet 2346 sent by a mobile node while away from home, to inform the recipient 2347 of the mobile node's home address. 2349 The Home Address option is encoded in type-length-value (TLV) format 2350 as follows: 2352 0 1 2 3 2353 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 2354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2355 | Option Type | Option Length | 2356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2357 | | 2358 + + 2359 | | 2360 + Home Address + 2361 | | 2362 + + 2363 | | 2364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2366 Option Type 2368 201 = 0xC9 2370 Option Length 2372 8-bit unsigned integer. Length of the option, in octets, 2373 excluding the Option Type and Option Length fields. This field 2374 MUST be set to 16. 2376 Home Address 2378 The home address of the mobile node sending the packet. This 2379 address MUST be a unicast routable address. 2381 The alignment requirement [11] for the Home Address option is 8n+6. 2383 The three highest-order bits of the Option Type field are encoded to 2384 indicate specific processing of the option [11]; for the Home Address 2385 option, these three bits are set to 110. This indicates the 2386 following processing requirements: 2388 o Any IPv6 node that does not recognize the Option Type must discard 2389 the packet, and if the packet's Destination Address was not a 2390 multicast address, return an ICMP Parameter Problem, Code 2, 2391 message to the packet's Source Address. The Pointer field in the 2392 ICMP message SHOULD point at the Option Type field. Otherwise, 2393 for multicast addresses, the ICMP message MUST NOT be sent. 2395 o The data within the option cannot change en-route to the packet's 2396 final destination. 2398 The Home Address option MUST be placed as follows: 2400 o After the routing header, if that header is present 2402 o Before the Fragment Header, if that header is present 2404 o Before the AH Header or ESP Header, if either one of those headers 2405 is present 2407 For each IPv6 packet header, the Home Address Option MUST NOT appear 2408 more than once. However, an encapsulated packet [15] MAY contain a 2409 separate Home Address option associated with each encapsulating IP 2410 header. 2412 The inclusion of a Home Address destination option in a packet 2413 affects the receiving node's processing of only this single packet. 2414 No state is created or modified in the receiving node as a result of 2415 receiving a Home Address option in a packet. In particular, the 2416 presence of a Home Address option in a received packet MUST NOT alter 2417 the contents of the receiver's Binding Cache and MUST NOT cause any 2418 changes in the routing of subsequent packets sent by this receiving 2419 node. 2421 6.4 Type 2 Routing Header 2423 Mobile IPv6 defines a new routing header variant, the type 2 routing 2424 header, to allow the packet to be routed directly from a 2425 correspondent to the mobile node's care-of address. The mobile 2426 node's care-of address is inserted into the IPv6 Destination Address 2427 field. Once the packet arrives at the care-of address, the mobile 2428 node retrieves its home address from the routing header, and this is 2429 used as the final destination address for the packet. 2431 The new routing header uses a different type than defined for 2432 "regular" IPv6 source routing, enabling firewalls to apply different 2433 rules to source routed packets than to Mobile IPv6. This routing 2434 header type (type 2) is restricted to carry only one IPv6 address. 2435 All IPv6 nodes which process this routing header MUST verify that the 2436 address contained within is the node's own home address in order to 2437 prevent packets from being forwarded outside the node. The IP 2438 address contained in the routing header, since it is the mobile 2439 node's home address, MUST be a unicast routable address. 2440 Furthermore, if the scope of the home address is smaller than the 2441 scope of the care-of address, the mobile node MUST discard the packet 2442 (see Section 4.6). 2444 6.4.1 Format 2446 The type 2 routing header has the following format: 2448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2449 | Next Header | Hdr Ext Len=2 | Routing Type=2|Segments Left=1| 2450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2451 | Reserved | 2452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2453 | | 2454 + + 2455 | | 2456 + Home Address + 2457 | | 2458 + + 2459 | | 2460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2462 Next Header 2464 8-bit selector. Identifies the type of header immediately 2465 following the routing header. Uses the same values as the IPv6 2466 Next Header field [11]. 2468 Hdr Ext Len 2470 2 (8-bit unsigned integer); length of the routing header in 2471 8-octet units, not including the first 8 octets 2473 Routing Type 2475 2 (8-bit unsigned integer). 2477 Segments Left 2479 1 (8-bit unsigned integer). 2481 Reserved 2483 32-bit reserved field. The value MUST be initialized to zero by 2484 the sender, and MUST be ignored by the receiver. 2486 Home Address 2488 The Home Address of the destination Mobile Node. 2490 For a type 2 routing header, the Hdr Ext Len MUST be 2. The Segments 2491 Left value describes the number of route segments remaining; i.e., 2492 number of explicitly listed intermediate nodes still to be visited 2493 before reaching the final destination. Segments Left MUST be 1. The 2494 ordering rules for extension headers in an IPv6 packet are described 2495 in Section 4.1 of RFC 2460 [11]. The type 2 routing header defined 2496 for Mobile IPv6 follows the same ordering as other routing headers. 2497 If both a type 0 and a type 2 routing header are present, the type 2 2498 routing header should follow the other routing header. A packet 2499 containing such nested encapsulation should be created as if the 2500 inner (type 2) routing header was constructed first and then treated 2501 as an original packet by the outer (type 0) routing header 2502 construction process. 2504 In addition, the general procedures defined by IPv6 for routing 2505 headers suggest that a received routing header MAY be automatically 2506 "reversed" to construct a routing header for use in any response 2507 packets sent by upper-layer protocols, if the received packet is 2508 authenticated [6]. This MUST NOT be done automatically for type 2 2509 routing headers. 2511 6.5 ICMP Home Agent Address Discovery Request Message 2513 The ICMP Home Agent Address Discovery Request message is used by a 2514 mobile node to initiate the dynamic home agent address discovery 2515 mechanism, as described in Section 11.4.1. The mobile node sends the 2516 Home Agent Address Discovery Request message to the Mobile IPv6 2517 Home-Agents anycast address [16] for its own home subnet prefix. 2518 (Note that the currently defined anycast addresses may not work with 2519 all prefix lengths other than those defined in RFC 2373 [3, 35].) 2521 0 1 2 3 2522 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 2523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2524 | Type | Code | Checksum | 2525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2526 | Identifier | Reserved | 2527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2529 Type 2531 150 2533 Code 2535 0 2537 Checksum 2539 The ICMP checksum [14]. 2541 Identifier 2543 An identifier to aid in matching Home Agent Address Discovery 2544 Reply messages to this Home Agent Address Discovery Request 2545 message. 2547 Reserved 2549 This field is unused. It MUST be initialized to zero by the 2550 sender and MUST be ignored by the receiver. 2552 The Source Address of the Home Agent Address Discovery Request 2553 message packet is typically one of the mobile node's current care-of 2554 addresses. At the time of performing this dynamic home agent address 2555 discovery procedure, it is likely that the mobile node is not 2556 registered with any home agent. Therefore, neither the nature of the 2557 address nor the identity of the mobile node can be established at 2558 this time. The home agent MUST then return the Home Agent Address 2559 Discovery Reply message directly to the Source Address chosen by the 2560 mobile node. 2562 6.6 ICMP Home Agent Address Discovery Reply Message 2564 The ICMP Home Agent Address Discovery Reply message is used by a home 2565 agent to respond to a mobile node that uses the dynamic home agent 2566 address discovery mechanism, as described in Section 10.5. 2568 0 1 2 3 2569 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 2570 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2571 | Type | Code | Checksum | 2572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2573 | Identifier | Reserved | 2574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2575 | | 2576 + + 2577 . . 2578 . Home Agent Addresses . 2579 . . 2580 + + 2581 | | 2582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2584 Type 2586 151 2588 Code 2590 0 2592 Checksum 2594 The ICMP checksum [14]. 2596 Identifier 2598 The identifier from the invoking Home Agent Address Discovery 2599 Request message. 2601 Reserved 2603 This field is unused. It MUST be initialized to zero by the 2604 sender and MUST be ignored by the receiver. 2606 Home Agent Addresses 2608 A list of addresses of home agents on the home link for the mobile 2609 node. The number of addresses present in the list is indicated by 2610 the remaining length of the IPv6 packet carrying the Home Agent 2611 Address Discovery Reply message. 2613 6.7 ICMP Mobile Prefix Solicitation Message Format 2615 The ICMP Mobile Prefix Solicitation Message is sent by a mobile node 2616 to its home agent while it is away from home. The purpose of the 2617 message is to solicit a Mobile Prefix Advertisement from the home 2618 agent, which will allow the mobile node to gather prefix information 2619 about its home network. This information can be used to configure 2620 and update home address(es) according to changes in prefix 2621 information supplied by the home agent. 2623 0 1 2 3 2624 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 2625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2626 | Type | Code | Checksum | 2627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2628 | Identifier | Reserved | 2629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2631 IP Fields: 2633 Source Address 2635 The mobile node's care-of address. 2637 Destination Address 2639 The address of the mobile node's home agent. This home agent must 2640 be on the link which the mobile node wishes to learn prefix 2641 information about. 2643 Hop Limit 2645 Set to an initial hop limit value, similarly to any other unicast 2646 packet sent by the mobile node. 2648 Destination Option: 2650 A Home Address destination option MUST be included. 2652 ESP header: 2654 IPsec headers MUST be supported and SHOULD be used as described in 2655 Section 5.4. 2657 ICMP Fields: 2659 Type 2661 152 2663 Code 2665 0 2667 Checksum 2669 The ICMP checksum [14]. 2671 Identifier 2673 An identifier to aid in matching a future Mobile Prefix 2674 Advertisement to this Mobile Prefix Solicitation. 2676 Reserved 2678 This field is unused. It MUST be initialized to zero by the 2679 sender and MUST be ignored by the receiver. 2681 The Mobile Prefix Solicitation messages may have options. These 2682 options MUST use the option format defined in RFC 2461 [12]. This 2683 document does not define any option types for the Mobile Prefix 2684 Solicitation message, but future documents may define new options. 2685 Home agents MUST silently ignore any options they do not recognize 2686 and continue processing the message. 2688 6.8 ICMP Mobile Prefix Advertisement Message Format 2690 A home agent will send a Mobile Prefix Advertisement to a mobile node 2691 to distribute prefix information about the home link while the mobile 2692 node is traveling away from the home network. This will occur in 2693 response to a Mobile Prefix Solicitation with an Advertisement, or by 2694 an unsolicited Advertisement sent according to the rules in Section 2695 10.6. 2697 0 1 2 3 2698 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 2699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2700 | Type | Code | Checksum | 2701 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2702 | Identifier |M|O| Reserved | 2703 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2704 | Options ... 2705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2707 IP Fields: 2709 Source Address 2711 The home agent's address as the mobile node would expect to see it 2712 (i.e., same network prefix). 2714 Destination Address 2716 If this message is a response to a Mobile Prefix Solicitation, 2717 this field contains the Source Address field from that packet. 2718 For unsolicited messages, the mobile node's care-of address SHOULD 2719 be used. Note that unsolicited messages can only be sent if the 2720 mobile node is currently registered with the home agent. 2722 Routing header: 2724 A type 2 routing header MUST be included. 2726 ESP header: 2728 IPsec headers MUST be supported and SHOULD be used as described in 2729 Section 5.4. 2731 ICMP Fields: 2733 Type 2735 153 2737 Code 2739 0 2741 Checksum 2743 The ICMP checksum [14]. 2745 Identifier 2747 An identifier to aid in matching this Mobile Prefix Advertisement 2748 to a previous Mobile Prefix Solicitation. 2750 M 2752 1-bit Managed Address Configuration flag. When set, hosts use the 2753 administered (stateful) protocol for address autoconfiguration in 2754 addition to any addresses autoconfigured using stateless address 2755 autoconfiguration. The use of this flag is described in [12, 13]. 2757 O 2759 1-bit Other Stateful Configuration flag. When set, hosts use the 2760 administered (stateful) protocol for autoconfiguration of other 2761 (non-address) information. The use of this flag is described in 2762 [12, 13]. 2764 Reserved 2766 This field is unused. It MUST be initialized to zero by the 2767 sender and MUST be ignored by the receiver. 2769 The Mobile Prefix Advertisement messages may have options. These 2770 options MUST use the option format defined in RFC 2461 [12]. This 2771 document defines one option which may be carried in a Mobile Prefix 2772 Advertisement message, but future documents may define new options. 2773 Mobile nodes MUST silently ignore any options they do not recognize 2774 and continue processing the message. 2776 Prefix Information 2778 Each message contains one or more Prefix Information options. 2779 Each option carries the prefix(es) that the mobile node should use 2780 to configure its home address(es). Section 10.6 describes which 2781 prefixes should be advertised to the mobile node. 2783 The Prefix Information option is defined in Section 4.6.2 of RFC 2784 2461 [12], with modifications defined in Section 7.2 of this 2785 specification. The home agent MUST use this modified Prefix 2786 Information option to send home network prefixes as defined in 2787 Section 10.6.1. 2789 If the Advertisement is sent in response to a Mobile Prefix 2790 Solicitation, the home agent MUST copy the Identifier value from that 2791 message into the Identifier field of the Advertisement. 2793 The home agent MUST NOT send more than one Mobile Prefix 2794 Advertisement message per second to any mobile node. 2796 The M and O bits MUST be cleared if the Home Agent DHCPv6 support is 2797 not provided. If such support is provided then they are set in 2798 concert with the home network's administrative settings. 2800 7. Modifications to IPv6 Neighbor Discovery 2802 7.1 Modified Router Advertisement Message Format 2804 Mobile IPv6 modifies the format of the Router Advertisement message 2805 [12] by the addition of a single flag bit to indicate that the router 2806 sending the Advertisement message is serving as a home agent on this 2807 link. The format of the Router Advertisement message is as follows: 2809 0 1 2 3 2810 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 2811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2812 | Type | Code | Checksum | 2813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2814 | Cur Hop Limit |M|O|H| Reserved| Router Lifetime | 2815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2816 | Reachable Time | 2817 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2818 | Retrans Timer | 2819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2820 | Options ... 2821 +-+-+-+-+-+-+-+-+-+-+-+- 2823 This format represents the following changes over that originally 2824 specified for Neighbor Discovery [12]: 2826 Home Agent (H) 2828 The Home Agent (H) bit is set in a Router Advertisement to 2829 indicate that the router sending this Router Advertisement is also 2830 functioning as a Mobile IPv6 home agent on this link. 2832 Reserved 2834 Reduced from a 6-bit field to a 5-bit field to account for the 2835 addition of the above bit. 2837 7.2 Modified Prefix Information Option Format 2839 Mobile IPv6 requires knowledge of a router's global address in 2840 building a Home Agents List as part of the dynamic home agent address 2841 discovery mechanism. 2843 However, Neighbor Discovery [12] only advertises a router's 2844 link-local address, by requiring this address to be used as the IP 2845 Source Address of each Router Advertisement. 2847 Mobile IPv6 extends Neighbor Discovery to allow a router to advertise 2848 its global address, by the addition of a single flag bit in the 2849 format of a Prefix Information option for use in Router Advertisement 2850 messages. The format of the Prefix Information option is as follows: 2852 0 1 2 3 2853 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 2854 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2855 | Type | Length | Prefix Length |L|A|R|Reserved1| 2856 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2857 | Valid Lifetime | 2858 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2859 | Preferred Lifetime | 2860 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2861 | Reserved2 | 2862 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2863 | | 2864 + + 2865 | | 2866 + Prefix + 2867 | | 2868 + + 2869 | | 2870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2872 This format represents the following changes over that originally 2873 specified for Neighbor Discovery [12]: 2875 Router Address (R) 2877 1-bit router address flag. When set, indicates that the Prefix 2878 field contains a complete IP address assigned to the sending 2879 router. The indicated prefix is the first Prefix Length bits of 2880 the Prefix field. The router IP address has the same scope and 2881 conforms to the same lifetime values as the advertised prefix. 2882 This use of the Prefix field is compatible with its use in 2883 advertising the prefix itself, since Prefix Advertisement uses 2884 only the leading bits. Interpretation of this flag bit is thus 2885 independent of the processing required for the On-Link (L) and 2886 Autonomous Address-Configuration (A) flag bits. 2888 Reserved1 2890 Reduced from a 6-bit field to a 5-bit field to account for the 2891 addition of the above bit. 2893 In a Router Advertisement, a home agent MUST, and all other routers 2894 MAY, include at least one Prefix Information option with the Router 2895 Address (R) bit set. Neighbor Discovery specifies that, if including 2896 all options in a Router Advertisement causes the size of the 2897 Advertisement to exceed the link MTU, multiple Advertisements can be 2898 sent, each containing a subset of the options [12]. Also, when 2899 sending unsolicited multicast Router Advertisements more frequently 2900 than the limit specified in RFC 2461 [12], the sending router need 2901 not include all options in each of these Advertisements. However, in 2902 both of these cases the router SHOULD include at least one Prefix 2903 Information option with the Router Address (R) bit set in each such 2904 advertisement, if this bit is set in some advertisement sent by the 2905 router. 2907 In addition, the following requirement can assist mobile nodes in 2908 movement detection. Barring changes in the prefixes for the link, 2909 routers that send multiple Router Advertisements with the Router 2910 Address (R) bit set in some of the included Prefix Information 2911 options SHOULD provide at least one option and router address which 2912 stays the same in all of the Advertisements. 2914 7.3 New Advertisement Interval Option Format 2916 Mobile IPv6 defines a new Advertisement Interval option, used in 2917 Router Advertisement messages to advertise the interval at which the 2918 sending router sends unsolicited multicast Router Advertisements. 2919 The format of the Advertisement Interval option is as follows: 2921 0 1 2 3 2922 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 2923 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2924 | Type | Length | Reserved | 2925 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2926 | Advertisement Interval | 2927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2929 Type 2931 7 2933 Length 2935 8-bit unsigned integer. The length of the option (including the 2936 type and length fields) in units of 8 octets. The value of this 2937 field MUST be 1. 2939 Reserved 2941 This field is unused. It MUST be initialized to zero by the 2942 sender and MUST be ignored by the receiver. 2944 Advertisement Interval 2946 32-bit unsigned integer. The maximum time, in milliseconds, 2947 between successive unsolicited router Router Advertisement 2948 messages sent by this router on this network interface. Using the 2949 conceptual router configuration variables defined by Neighbor 2950 Discovery [12], this field MUST be equal to the value 2951 MaxRtrAdvInterval, expressed in milliseconds. 2953 Routers MAY include this option in their Router Advertisements. A 2954 mobile node receiving a Router Advertisement containing this option 2955 SHOULD utilize the specified Advertisement Interval for that router 2956 in its movement detection algorithm, as described in Section 11.5.1. 2958 This option MUST be silently ignored for other Neighbor Discovery 2959 messages. 2961 7.4 New Home Agent Information Option Format 2963 Mobile IPv6 defines a new Home Agent Information option, used in 2964 Router Advertisements sent by a home agent to advertise information 2965 specific to this router's functionality as a home agent. The format 2966 of the Home Agent Information option is as follows: 2968 0 1 2 3 2969 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 2970 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2971 | Type | Length | Reserved | 2972 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2973 | Home Agent Preference | Home Agent Lifetime | 2974 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2976 Type 2978 8 2980 Length 2982 8-bit unsigned integer. The length of the option (including the 2983 type and length fields) in units of 8 octets. The value of this 2984 field MUST be 1. 2986 Reserved 2988 This field is unused. It MUST be initialized to zero by the 2989 sender and MUST be ignored by the receiver. 2991 Home Agent Preference 2993 16-bit unsigned integer. The preference for the home agent 2994 sending this Router Advertisement, for use in ordering the 2995 addresses returned to a mobile node in the Home Agent Addresses 2996 field of a Home Agent Address Discovery Reply message. Higher 2997 values mean more preferable. If this option is not included in a 2998 Router Advertisement in which the Home Agent (H) bit is set, the 2999 preference value for this home agent MUST be considered to be 0. 3000 Greater values indicate a more preferable home agent than lower 3001 values. 3003 The manual configuration of the Home Agent Preference value is 3004 described in Section 8.4. In addition, the sending home agent MAY 3005 dynamically set the Home Agent Preference value, for example 3006 basing it on the number of mobile nodes it is currently serving or 3007 on its remaining resources for serving additional mobile nodes; 3008 such dynamic settings are beyond the scope of this document. Any 3009 such dynamic setting of the Home Agent Preference, however, MUST 3010 set the preference appropriately, relative to the default Home 3011 Agent Preference value of 0 that may be in use by some home agents 3012 on this link (i.e., a home agent not including a Home Agent 3013 Information option in its Router Advertisements will be considered 3014 to have a Home Agent Preference value of 0). 3016 Home Agent Lifetime 3018 16-bit unsigned integer. The lifetime associated with the home 3019 agent in units of seconds. The default value is the same as the 3020 Router Lifetime, as specified in the main body of the Router 3021 Advertisement. The maximum value corresponds to 18.2 hours. A 3022 value of 0 MUST NOT be used. The Home Agent Lifetime applies only 3023 to this router's usefulness as a home agent; it does not apply to 3024 information contained in other message fields or options. 3026 Home agents MAY include this option in their Router Advertisements. 3027 This option MUST NOT be included in a Router Advertisement in which 3028 the Home Agent (H) bit (see Section 7.1) is not set. If this option 3029 is not included in a Router Advertisement in which the Home Agent (H) 3030 bit is set, the lifetime for this home agent MUST be considered to be 3031 the same as the Router Lifetime in the Router Advertisement. If 3032 multiple Advertisements are being sent instead of a single larger 3033 unsolicited multicast Advertisement, all of the multiple 3034 Advertisements with the Router Address (R) bit set MUST include this 3035 option with the same contents, otherwise this option MUST be omitted 3036 from all Advertisements. 3038 This option MUST be silently ignored for other Neighbor Discovery 3039 messages. 3041 If both the Home Agent Preference and Home Agent Lifetime are set to 3042 their default values specified above, this option SHOULD NOT be 3043 included in the Router Advertisement messages sent by this home 3044 agent. 3046 7.5 Changes to Sending Router Advertisements 3048 The Neighbor Discovery protocol specification [12] limits routers to 3049 a minimum interval of 3 seconds between sending unsolicited multicast 3050 Router Advertisement messages from any given network interface 3051 (limited by MinRtrAdvInterval and MaxRtrAdvInterval), stating that: 3053 "Routers generate Router Advertisements frequently enough that 3054 hosts will learn of their presence within a few minutes, but not 3055 frequently enough to rely on an absence of advertisements to 3056 detect router failure; a separate Neighbor Unreachability 3057 Detection algorithm provides failure detection." 3059 This limitation, however, is not suitable to providing timely 3060 movement detection for mobile nodes. Mobile nodes detect their own 3061 movement by learning the presence of new routers as the mobile node 3062 moves into wireless transmission range of them (or physically 3063 connects to a new wired network), and by learning that previous 3064 routers are no longer reachable. Mobile nodes MUST be able to 3065 quickly detect when they move to a link served by a new router, so 3066 that they can acquire a new care-of address and send Binding Updates 3067 to register this care-of address with their home agent and to notify 3068 correspondent nodes as needed. 3070 One method which can provide for faster movement detection, is to 3071 increase the rate at which unsolicited Router Advertisements are 3072 sent. Mobile IPv6 relaxes this limit such that routers MAY send 3073 unsolicited multicast Router Advertisements more frequently. This 3074 method can be applied where the router is expecting to provide 3075 service to visiting mobile nodes (e.g., wireless network interfaces), 3076 or on which it is serving as a home agent to one or more mobile nodes 3077 (who may return home and need to hear its Advertisements). 3079 Routers supporting mobility SHOULD be able to be configured with a 3080 smaller MinRtrAdvInterval value and MaxRtrAdvInterval value to allow 3081 sending of unsolicited multicast Router Advertisements more often. 3082 The minimum allowed values are: 3084 o MinRtrAdvInterval 0.03 seconds 3086 o MaxRtrAdvInterval 0.07 seconds 3087 In the case where the minimum intervals and delays are used, the mean 3088 time between unsolicited multicast router advertisements is 50ms. 3089 Use of these modified limits MUST be configurable (see also the 3090 configuration variable MinDelayBetweenRas in Section 13 which may 3091 also have to be modified accordingly). Systems where these values 3092 are available MUST NOT default to them, and SHOULD default to values 3093 specified in RFC 2461. Knowledge of the type of network interface 3094 and operating environment SHOULD be taken into account in configuring 3095 these limits for each network interface. This is important with some 3096 wireless links, where increasing the frequency of multicast beacons 3097 can cause considerable overhead. Routers SHOULD adhere to the 3098 intervals specified in RFC 2461 [12], if this overhead is likely to 3099 cause service degradation. 3101 Additionally, the possible low values of MaxRtrAdvInterval may cause 3102 some problems with movement detection in some mobile nodes. To 3103 ensure that this is not a problem, Routers SHOULD add 20ms to any 3104 Advertisement Intervals sent in RAs, which are below 200 ms, in order 3105 to account for scheduling granularities on both the MN and the 3106 Router. 3108 Note that multicast Router Advertisements are not always required in 3109 certain wireless networks that have limited bandwidth. Mobility 3110 detection or link changes in such networks may be done at lower 3111 layers. Router advertisements in such networks SHOULD be sent only 3112 when solicited. In such networks it SHOULD be possible to disable 3113 unsolicited multicast Router Advertisements on specific interfaces. 3114 The MinRtrAdvInterval and MaxRtrAdvInterval in such a case can be set 3115 to some high values. 3117 Home agents MUST include the Source Link-Layer Address option in all 3118 Router Advertisements they send. This simplifies the process of 3119 returning home, as discussed in Section 11.5.4. 3121 Note that according to RFC 2461 [12], AdvDefaultLifetime is by 3122 default based on the value of MaxRtrAdvInterval. AdvDefaultLifetime 3123 is used in the Router Lifetime field of Router Advertisements. Given 3124 that this field is expressed in seconds, a small MaxRtrAdvInterval 3125 value can result in a zero value for this field. To prevent this, 3126 routers SHOULD keep AdvDefaultLifetime in at least one second, even 3127 if the use of MaxRtrAdvInterval would result in a smaller value. 3129 8. Requirements for Types of IPv6 Nodes 3131 Mobile IPv6 places some special requirements on the functions 3132 provided by different types of IPv6 nodes. This section summarizes 3133 those requirements, identifying the functionality each requirement is 3134 intended to support. 3136 The requirements are set for the following groups of nodes: 3138 o All IPv6 nodes. 3140 o All IPv6 nodes with support for route optimization. 3142 o All IPv6 routers. 3144 o All Mobile IPv6 home agents. 3146 o All Mobile IPv6 mobile nodes. 3148 It is outside the scope of this specification to specify which of 3149 these groups are mandatory in IPv6. We only describe what is 3150 mandatory for a node that supports, for instance, route optimization. 3151 Other specifications are expected to define the extent of IPv6. 3153 8.1 All IPv6 Nodes 3155 Any IPv6 node may at any time be a correspondent node of a mobile 3156 node, either sending a packet to a mobile node or receiving a packet 3157 from a mobile node. There are no Mobile IPv6 specific MUST 3158 requirements for such nodes, and basic IPv6 techniques are 3159 sufficient. If a mobile node attempts to set up route optimization 3160 with a node with only basic IPv6 support, an ICMP error will signal 3161 that the node does not support such optimizations (Section 11.3.5), 3162 and communications will flow through the home agent . 3164 An IPv6 node MUST NOT support the Home Address destination option, 3165 type 2 routing header, or the Mobility Header unless it fully 3166 supports the requirements listed in the next sections for either 3167 route optimization, mobile node, or home agent functionality. 3169 8.2 IPv6 Nodes with Support for Route Optimization 3171 Nodes that implement route optimization are a subset of all IPv6 3172 nodes on the Internet. The ability of a correspondent node to 3173 participate in route optimization is essential for the efficient 3174 operation of the IPv6 Internet, for the following reasons: 3176 o Avoidance of congestion in the home network, and enabling the use 3177 of lower-performance home agent equipment even for supporting 3178 thousands of mobile nodes. 3180 o Reduced network load across the entire Internet, as mobile devices 3181 begin to predominate. 3183 o Reduction of jitter and latency for the communications. 3185 o Greater likelihood of success for QoS signaling as tunneling is 3186 avoided and, again, fewer sources of congestion. 3188 o Improved robustness against network partitions, congestion, and 3189 other problems, since fewer routing path segments are traversed. 3191 These effects combine to enable much better performance and 3192 robustness for communications between mobile nodes and IPv6 3193 correspondent nodes. Route optimization introduces a small amount of 3194 additional state for the peers, some additional messaging, and up to 3195 1.5 roundtrip delays before it can be turned on. However, it is 3196 believed that the benefits far outweigh the costs in most cases. 3197 Section 11.3.1 discusses how mobile nodes may avoid route 3198 optimization for some of the remaining cases, such as very short-term 3199 communications. 3201 The following requirements apply to all correspondent nodes that 3202 support route optimization: 3204 o The node MUST be able validate a Home Address option using an 3205 existing Binding Cache entry, as described in Section 9.3.1. 3207 o The node MUST be able to insert a type 2 routing header into 3208 packets to be sent to a mobile node, as described in Section 3209 9.3.2. 3211 o Unless the correspondent node is also acting as a mobile node, it 3212 MUST ignore type 2 routing headers and silently discard all 3213 packets that it has received with such headers. 3215 o The node SHOULD be able to interpret ICMP messages as described in 3216 Section 9.3.4. 3218 o The node MUST be able to send Binding Error messages as described 3219 in Section 9.3.3. 3221 o The node MUST be able to process Mobility Headers as described in 3222 Section 9.2. 3224 o The node MUST be able to participate in a return routability 3225 procedure (Section 9.4). 3227 o The node MUST be able to process Binding Update messages (Section 3228 9.5). 3230 o The node MUST be able to return a Binding Acknowledgement (Section 3231 9.5.4). 3233 o The node MUST be able to maintain a Binding Cache of the bindings 3234 received in accepted Binding Updates, as described in Section 9.1 3235 and Section 9.6. 3237 o The node SHOULD allow route optimization to be administratively 3238 enabled or disabled. The default SHOULD be enabled. 3240 8.3 All IPv6 Routers 3242 All IPv6 routers, even those not serving as a home agent for Mobile 3243 IPv6, have an effect on how well mobile nodes can communicate: 3245 o Every IPv6 router SHOULD be able to send an Advertisement Interval 3246 option (Section 7.3) in each of its Router Advertisements [12], to 3247 aid movement detection by mobile nodes (as in Section 11.5.1). 3248 The use of this option in Router Advertisements SHOULD be 3249 configurable. 3251 o Every IPv6 router SHOULD be able to support sending unsolicited 3252 multicast Router Advertisements at the faster rate described in 3253 Section 7.5. If the router supports a faster rate, the used rate 3254 MUST be configurable. 3256 o Each router SHOULD include at least one prefix with the Router 3257 Address (R) bit set and with its full IP address in its Router 3258 Advertisements (as described in Section 7.2). 3260 o Routers supporting filtering packets with routing headers SHOULD 3261 support different rules for type 0 and type 2 routing headers (see 3262 Section 6.4) so that filtering of source routed packets (type 0) 3263 will not necessarily limit Mobile IPv6 traffic which is delivered 3264 via type 2 routing headers. 3266 8.4 IPv6 Home Agents 3268 In order for a mobile node to operate correctly while away from home, 3269 at least one IPv6 router on the mobile node's home link must function 3270 as a home agent for the mobile node. The following additional 3271 requirements apply to all IPv6 routers that serve as a home agent: 3273 o Every home agent MUST be able to maintain an entry in its Binding 3274 Cache for each mobile node for which it is serving as the home 3275 agent (Section 10.1 and Section 10.3.1). 3277 o Every home agent MUST be able to intercept packets (using proxy 3278 Neighbor Discovery [12]) addressed to a mobile node for which it 3279 is currently serving as the home agent, on that mobile node's home 3280 link, while the mobile node is away from home (Section 10.4.1). 3282 o Every home agent MUST be able to encapsulate [15] such intercepted 3283 packets in order to tunnel them to the primary care-of address for 3284 the mobile node indicated in its binding in the home agent's 3285 Binding Cache (Section 10.4.2). 3287 o Every home agent MUST support decapsulating [15] reverse tunneled 3288 packets sent to it from a mobile node's home address. Every home 3289 agent MUST also check that the source address in the tunneled 3290 packets corresponds to the currently registered location of the 3291 mobile node (Section 10.4.5). 3293 o The node MUST be able to process Mobility Headers as described in 3294 Section 10.2. 3296 o Every home agent MUST be able to return a Binding Acknowledgement 3297 in response to a Binding Update (Section 10.3.1). 3299 o Every home agent MUST maintain a separate Home Agents List for 3300 each link on which it is serving as a home agent, as described in 3301 Section 10.1 and Section 10.5.1. 3303 o Every home agent MUST be able to accept packets addressed to the 3304 Mobile IPv6 Home-Agents anycast address [16] for the subnet on 3305 which it is serving as a home agent, and MUST be able to 3306 participate in dynamic home agent address discovery (Section 3307 10.5). 3309 o Every home agent SHOULD support a configuration mechanism to allow 3310 a system administrator to manually set the value to be sent by 3311 this home agent in the Home Agent Preference field of the Home 3312 Agent Information Option in Router Advertisements that it sends 3313 (Section 7.4). 3315 o Every home agent SHOULD support sending ICMP Mobile Prefix 3316 Advertisements (Section 6.8), and SHOULD respond to Mobile Prefix 3317 Solicitations (Section 6.7). If supported, this behavior MUST be 3318 configurable, so that home agents can be configured to avoid 3319 sending such Prefix Advertisements according to the needs of the 3320 network administration in the home domain. 3322 o Every home agent MUST support IPsec ESP for protection of packets 3323 belonging to the return routability procedure (Section 10.4.6). 3325 o Every home agent SHOULD support the multicast group membership 3326 control protocols as described in Section 10.4.3. If this support 3327 is provided, the home agent MUST be capable of using it to 3328 determine which multicast data packets to forward via the tunnel 3329 to the mobile node. 3331 o Home agents MAY support stateful address autoconfiguration for 3332 mobile nodes as described in Section 10.4.4. 3334 8.5 IPv6 Mobile Nodes 3336 Finally, the following requirements apply to all IPv6 nodes capable 3337 of functioning as mobile nodes: 3339 o The node MUST maintain a Binding Update List (Section 11.1). 3341 o The node MUST support sending packets containing a Home Address 3342 option (Section 11.3.1), and follow the required IPsec interaction 3343 (Section 11.3.2). 3345 o The node MUST be able to perform IPv6 encapsulation and 3346 decapsulation [15]. 3348 o The node MUST be able to process type 2 routing header as defined 3349 in Section 6.4 and Section 11.3.3. 3351 o The node MUST support receiving a Binding Error message (Section 3352 11.3.6). 3354 o The node MUST support receiving ICMP errors (Section 11.3.5). 3356 o The node MUST support movement detection, care-of address 3357 formation, and returning home (Section 11.5). 3359 o The node MUST be able to process Mobility Headers as described in 3360 Section 11.2. 3362 o The node MUST support the return routability procedure (Section 3363 11.6). 3365 o The node MUST be able to send Binding Updates, as specified in 3366 Section 11.7.1 and Section 11.7.2. 3368 o The node MUST be able to receive and process Binding 3369 Acknowledgements, as specified in Section 11.7.3. 3371 o The node MUST support receiving a Binding Refresh Request (Section 3372 6.1.2), by responding with a Binding Update. 3374 o The node MUST support receiving Mobile Prefix Advertisements 3375 (Section 11.4.3) and reconfiguring its home address based on the 3376 prefix information contained therein. 3378 o The node SHOULD support use of the dynamic home agent address 3379 discovery mechanism, as described in Section 11.4.1. 3381 o The node MUST allow route optimization to be administratively 3382 enabled or disabled. The default SHOULD be enabled. 3384 o The node MAY support the multicast address listener part of a 3385 multicast group membership protocol as described in Section 3386 11.3.4. If this support is provided, the mobile node MUST be able 3387 to receive tunneled multicast packets from the home agent. 3389 o The node MAY support stateful address autoconfiguration mechanisms 3390 such as DHCPv6 [29] on the interface represented by the tunnel to 3391 the home agent. 3393 9. Correspondent Node Operation 3395 9.1 Conceptual Data Structures 3397 IPv6 nodes with route optimization support maintain a Binding Cache 3398 of bindings for other nodes. A separate Binding Cache SHOULD be 3399 maintained by each IPv6 node for each of its unicast routable 3400 addresses. The Binding Cache MAY be implemented in any manner 3401 consistent with the external behavior described in this document, for 3402 example by being combined with the node's Destination Cache as 3403 maintained by Neighbor Discovery [12]. When sending a packet, the 3404 Binding Cache is searched before the Neighbor Discovery conceptual 3405 Destination Cache [12]. 3407 Each Binding Cache entry conceptually contains the following fields: 3409 o The home address of the mobile node for which this is the Binding 3410 Cache entry. This field is used as the key for searching the 3411 Binding Cache for the destination address of a packet being sent. 3413 o The care-of address for the mobile node indicated by the home 3414 address field in this Binding Cache entry. 3416 o A lifetime value, indicating the remaining lifetime for this 3417 Binding Cache entry. The lifetime value is initialized from the 3418 Lifetime field in the Binding Update that created or last modified 3419 this Binding Cache entry. 3421 o A flag indicating whether or not this Binding Cache entry is a 3422 home registration entry (applicable only on nodes which support 3423 home agent functionality). 3425 o The maximum value of the Sequence Number field received in 3426 previous Binding Updates for this home address. The Sequence 3427 Number field is 16 bits long. Sequence Number values MUST be 3428 compared modulo 2**16 as explained in Section 9.5.1. 3430 o Usage information for this Binding Cache entry. This is needed to 3431 implement the cache replacement policy in use in the Binding 3432 Cache. Recent use of a cache entry also serves as an indication 3433 that a Binding Refresh Request should be sent when the lifetime of 3434 this entry nears expiration. 3436 Binding Cache entries not marked as home registrations MAY be 3437 replaced at any time by any reasonable local cache replacement policy 3438 but SHOULD NOT be unnecessarily deleted. The Binding Cache for any 3439 one of a node's IPv6 addresses may contain at most one entry for each 3440 mobile node home address. The contents of a node's Binding Cache 3441 MUST NOT be changed in response to a Home Address option in a 3442 received packet. 3444 9.2 Processing Mobility Headers 3446 Mobility Header processing MUST observe the following rules: 3448 o The checksum must be verified as per Section 6.1. Otherwise, the 3449 node MUST silently discard the message. 3451 o The MH Type field MUST have a known value (Section 6.1.1). 3452 Otherwise, the node MUST discard the message and issue a Binding 3453 Error message as described in Section 9.3.3, with Status field set 3454 to 2 (unrecognized MH Type value). 3456 o The Payload Proto field MUST be IPPROTO_NONE (59 decimal). 3457 Otherwise, the node MUST discard the message and SHOULD send ICMP 3458 Parameter Problem, Code 0, directly to the Source Address of the 3459 packet as specified in RFC 2463 [14]. Thus no Binding Cache 3460 information is used in sending the ICMP message. The Pointer 3461 field in the ICMP message SHOULD point at the Payload Proto field. 3463 o The Header Len field in the Mobility Header MUST NOT be less than 3464 the length specified for this particular type of message in 3465 Section 6.1. Otherwise, the node MUST discard the message and 3466 SHOULD send ICMP Parameter Problem, Code 0, directly to the Source 3467 Address of the packet as specified in RFC 2463 [14]. (The Binding 3468 Cache information is again not used.) The Pointer field in the 3469 ICMP message SHOULD point at the Header Len field. 3471 Subsequent checks depend on the particular Mobility Header. 3473 9.3 Packet Processing 3475 This section describes how the correspondent node sends packets to 3476 the mobile node, and receives packets from it. 3478 9.3.1 Receiving Packets with Home Address Option 3480 Packets containing a Home Address option MUST be dropped if the given 3481 home address is not a unicast routable address. 3483 Mobile nodes can include a Home Address destination option in a 3484 packet if they believe the correspondent node has a Binding Cache 3485 entry for the home address of a mobile node. Packets containing a 3486 Home Address option MUST be dropped if there is no corresponding 3487 Binding Cache entry. A corresponding Binding Cache entry MUST have 3488 the same home address as appears in the Home Address destination 3489 option, and the currently registered care-of address MUST be equal to 3490 the source address of the packet. These tests MUST NOT be done for 3491 packets that contain a Home Address option and a Binding Update. 3493 If the packet is dropped due the above tests, the correspondent node 3494 MUST send the Binding Error message as described in Section 9.3.3. 3495 The Status field in this message should be set to 1 (unknown binding 3496 for Home Address destination option). 3498 The correspondent node MUST process the option in a manner consistent 3499 with exchanging the Home Address field from the Home Address option 3500 into the IPv6 header and replacing the original value of the Source 3501 Address field there. After all IPv6 options have been processed, it 3502 MUST be possible for upper layers to process the packet without the 3503 knowledge that it came originally from a care-of address or that a 3504 Home Address option was used. 3506 The use of IPsec Authentication Header (AH) for the Home Address 3507 option is not required, except that if the IPv6 header of a packet is 3508 covered by AH, then the authentication MUST also cover the Home 3509 Address option; this coverage is achieved automatically by the 3510 definition of the Option Type code for the Home Address option, since 3511 it indicates that the data within the option cannot change en-route 3512 to the packet's final destination, and thus the option is included in 3513 the AH computation. By requiring that any authentication of the IPv6 3514 header also cover the Home Address option, the security of the Source 3515 Address field in the IPv6 header is not compromised by the presence 3516 of a Home Address option. 3518 When attempting to verify AH authentication data in a packet that 3519 contains a Home Address option, the receiving node MUST calculate the 3520 AH authentication data as if the following were true: The Home 3521 Address option contains the care-of address, and the source IPv6 3522 address field of the IPv6 header contains the home address. This 3523 conforms with the calculation specified in Section 11.3.2. 3525 9.3.2 Sending Packets to a Mobile Node 3527 Before sending any packet, the sending node SHOULD examine its 3528 Binding Cache for an entry for the destination address to which the 3529 packet is being sent. If the sending node has a Binding Cache entry 3530 for this address, the sending node SHOULD use a type 2 routing header 3531 to route the packet to this mobile node (the destination node) by way 3532 of its care-of address. However, the mobile node MUST not do this in 3533 the following cases: 3535 o When sending an IPv6 Neighbor Discovery [12] packet. 3537 o Where otherwise noted in Section 6.1. 3539 When calculating authentication data in a packet that contains a type 3540 2 routing header, the correspondent node MUST calculate the AH 3541 authentication data as if the following were true: The routing header 3542 contains the care-of address, the destination IPv6 address field of 3543 the IPv6 header contains the home address, and the Segments Left 3544 field is zero. The IPsec Security Policy Database lookup MUST based 3545 on the mobile node's home address. 3547 For instance, assuming there are no additional routing headers in 3548 this packet beyond those needed by Mobile IPv6, the correspondent 3549 node could set the fields in the packet's IPv6 header and routing 3550 header as follows: 3552 o The Destination Address in the packet's IPv6 header is set to the 3553 mobile node's home address (the original destination address to 3554 which the packet was being sent). 3556 o The routing header is initialized to contain a single route 3557 segment, containing the mobile node's care-of address copied from 3558 the Binding Cache entry. The Segments Left field is, however, 3559 temporarily set to zero. 3561 The IP layer will insert the routing header before performing any 3562 necessary IPsec processing. Once all IPsec processing has been 3563 performed, the node swaps the IPv6 destination field with the Home 3564 Address field in the routing header, sets the Segments Left field to 3565 one, and sends the packet. This ensures the AH calculation is done 3566 on the packet in the form it will have on the receiver after 3567 advancing the routing header. 3569 Following the definition of a type 2 routing header in Section 6.4, 3570 this packet will be routed to the mobile node's care-of address, 3571 where it will be delivered to the mobile node (the mobile node has 3572 associated the care-of address with its network interface). 3574 Note that following the above conceptual model in an implementation 3575 creates some additional requirements for path MTU discovery since the 3576 layer that decides the packet size (e.g., TCP and applications using 3577 UDP) needs to be aware of the size of the headers added by the IP 3578 layer on the sending node. 3580 If, instead, the sending node has no Binding Cache entry for the 3581 destination address to which the packet is being sent, the sending 3582 node simply sends the packet normally, with no routing header. If 3583 the destination node is not a mobile node (or is a mobile node that 3584 is currently at home), the packet will be delivered directly to this 3585 node and processed normally by it. If, however, the destination node 3586 is a mobile node that is currently away from home, the packet will be 3587 intercepted by the mobile node's home agent and tunneled to the 3588 mobile node's current primary care-of address. 3590 9.3.3 Sending Binding Error Messages 3592 Section 9.2 and Section 9.3.1 describe error conditions that lead to 3593 a need to send a Binding Error message. 3595 A Binding Error message is sent directly to the address that appeared 3596 in the IPv6 Source Address field of the offending packet. If the 3597 Source Address field does not contain a unicast address, the Binding 3598 Error message MUST NOT be sent. 3600 The Home Address field in the Binding Error message MUST be copied 3601 from the Home Address field in the Home Address destination option of 3602 the offending packet, or set to the unspecified address if no such 3603 option appeared in the packet. 3605 Note that the IPv6 Source Address and Home Address field values 3606 discussed above are the values from the wire, i.e., before any 3607 modifications possibly performed as specified in Section 9.3.1. 3609 Binding Error messages SHOULD be subject to rate limiting in the same 3610 manner as is done for ICMPv6 messages [14]. 3612 9.3.4 Receiving ICMP Error Messages 3614 When the correspondent node has a Binding Cache entry for a mobile 3615 node, all traffic destined to the mobile node goes directly to the 3616 current care-of address of the mobile node using a routing header. 3617 Any ICMP error message caused by packets on their way to the care-of 3618 address will be returned in the normal manner to the correspondent 3619 node. 3621 On the other hand, if the correspondent node has no Binding Cache 3622 entry for the mobile node, the packet will be routed through the 3623 mobile node's home link. Any ICMP error message caused by the packet 3624 on its way to the mobile node while in the tunnel, will be 3625 transmitted to the mobile node's home agent. By the definition of 3626 IPv6 encapsulation [15], the home agent MUST relay certain ICMP error 3627 messages back to the original sender of the packet, which in this 3628 case is the correspondent node. 3630 Thus, in all cases, any meaningful ICMP error messages caused by 3631 packets from a correspondent node to a mobile node will be returned 3632 to the correspondent node. If the correspondent node receives 3633 persistent ICMP Destination Unreachable messages after sending 3634 packets to a mobile node based on an entry in its Binding Cache, the 3635 correspondent node SHOULD delete this Binding Cache entry. Note that 3636 if the mobile node continues to send packets with the Home Address 3637 destination option to this correspondent node, they will be dropped 3638 due to the lack of a binding. For this reason it is important that 3639 only persistent ICMP messages lead to the deletion of the Binding 3640 Cache entry. 3642 9.4 Return Routability Procedure 3644 This subsection specifies actions taken by a correspondent node 3645 during the return routability procedure. 3647 9.4.1 Receiving Home Test Init Messages 3649 Upon receiving a Home Test Init message, the correspondent node 3650 verifies the following: 3652 o The packet MUST NOT include a Home Address destination option. 3654 Any packet carrying a Home Test Init message which fails to satisfy 3655 all of these tests MUST be silently ignored. 3657 Otherwise, in preparation for sending the corresponding Home Test 3658 Message, the correspondent node checks that it has the necessary 3659 material to engage in a return routability procedure, as specified in 3660 Section 5.2. The correspondent node MUST have a secret Kcn and a 3661 nonce. If it does not have this material yet, it MUST produce it 3662 before continuing with the return routability procedure. 3664 Section 9.4.3 specifies further processing. 3666 9.4.2 Receiving Care-of Test Init Messages 3668 Upon receiving a Care-of Test Init message, the correspondent node 3669 verifies the following: 3671 o The packet MUST NOT include a Home Address destination option. 3673 Any packet carrying a Care-of Test Init message which fails to 3674 satisfy all of these tests MUST be silently ignored. 3676 Otherwise, in preparation for sending the corresponding Care-of Test 3677 Message, the correspondent node checks that it has the necessary 3678 material to engage in a return routability procedure in the manner 3679 described in Section 9.4.1. 3681 Section 9.4.4 specifies further processing. 3683 9.4.3 Sending Home Test Messages 3685 The correspondent node creates a home keygen token and uses the 3686 current nonce index as the Home Nonce Index. It then creates a Home 3687 Test message (Section 6.1.5) and sends it to the mobile node at the 3688 latter's home address. 3690 9.4.4 Sending Care-of Test Messages 3692 The correspondent node creates a care-of nonce and uses the current 3693 nonce index as the Care-of Nonce Index. It then creates a Care-of 3694 Test message (Section 6.1.6) and sends it to the mobile node at the 3695 latter's care-of address. 3697 9.5 Processing Bindings 3699 This section explains how the correspondent node processes messages 3700 related to bindings. These messages are: 3702 o Binding Update 3704 o Binding Refresh Request 3706 o Binding Acknowledgement 3708 o Binding Error 3710 9.5.1 Receiving Binding Updates 3712 Before accepting a Binding Update, the receiving node MUST validate 3713 the Binding Update according to the following tests: 3715 o The packet MUST contain a unicast routable home address, either in 3716 the Home Address option or in the Source Address, if the Home 3717 Address option is not present. 3719 o The Sequence Number field in the Binding Update is greater than 3720 the Sequence Number received in the previous valid Binding Update 3721 for this home address, if any. 3723 If the receiving node has no Binding Cache entry for the indicated 3724 home address, it MUST accept any Sequence Number value in a 3725 received Binding Update from this mobile node. 3727 This Sequence Number comparison MUST be performed modulo 2**16, 3728 i.e., the number is a free running counter represented modulo 3729 65536. A Sequence Number in a received Binding Update is 3730 considered less than or equal to the last received number if its 3731 value lies in the range of the last received number and the 3732 preceding 32768 values, inclusive. For example, if the last 3733 received sequence number was 15, then messages with sequence 3734 numbers 0 through 15, as well as 32783 through 65535, would be 3735 considered less than or equal. 3737 When the Home Registration (H) bit is not set, the following are also 3738 required: 3740 o A Nonce Indices mobility option MUST be present, and the Home and 3741 Care-of Nonce Index values in this option MUST be recent enough to 3742 be recognized by the correspondent node. (Care-of Nonce Index 3743 values are not inspected for requests to delete a binding.) 3745 o The correspondent node MUST re-generate the home keygen token and 3746 the care-of keygen token from the information contained in the 3747 packet. It then generates the binding management key Kbm and uses 3748 it to verify the authenticator field in the Binding Update as 3749 specified in Section 6.1.7. 3751 o The Binding Authorization Data mobility option MUST be present, 3752 and its contents MUST satisfy rules presented in Section 5.2.6. 3753 Note that a care-of address different from the Source Address MAY 3754 have been specified by including an Alternate Care-of Address 3755 mobility option in the Binding Update. When such a message is 3756 received and the return routability procedure is used as an 3757 authorization method, the correspondent node MUST verify the 3758 authenticator by using the address within the Alternate Care-of 3759 Address in the calculations. 3761 o The Binding Authorization Data mobility option MUST be the last 3762 option and MUST NOT have trailing padding. 3764 If the Home Registration (H) bit is set, the Nonce Indices mobility 3765 option MUST NOT be present. 3767 If the mobile node sends a sequence number which is not greater than 3768 the sequence number from the last valid Binding Update for this home 3769 address, then the receiving node MUST send back a Binding 3770 Acknowledgement with status code 135, and the last accepted sequence 3771 number in the Sequence Number field of the Binding Acknowledgement. 3773 If a binding already exists for the given home address and the home 3774 registration flag has a different value than the Home Registration 3775 (H) bit in the Binding Update, then the receiving node MUST send back 3776 a Binding Acknowledgement with status code 139 (registration type 3777 change disallowed). The home registration flag stored in the Binding 3778 Cache entry MUST NOT be changed. 3780 If the receiving node no longer recognizes the Home Nonce Index 3781 value, Care-of Nonce Index value, or both values from the Binding 3782 Update, then the receiving node MUST send back a Binding 3783 Acknowledgement with status code 136, 137, or 138, respectively. 3785 For packets carrying Binding Updates that fail to satisfy all of 3786 these tests for any reason other than insufficiency of the Sequence 3787 Number, registration type change, or expired nonce index values, they 3788 MUST be silently discarded. 3790 If the Binding Update is valid according to the tests above, then the 3791 Binding Update is processed further as follows: 3793 o The Sequence Number value received from a mobile node in a Binding 3794 Update is stored by the receiving node in its Binding Cache entry 3795 for the given home address. 3797 o If the Lifetime specified in the Binding Update is nonzero and the 3798 specified care-of address is not equal to the home address for the 3799 binding, then this is a request to cache a binding for the home 3800 address. If the Home Registration (H) bit is set in the Binding 3801 Update, the Binding Update is processed according to the procedure 3802 specified in Section 10.3.1; otherwise, it is processed according 3803 to the procedure specified in Section 9.5.2. 3805 o If the Lifetime specified in the Binding Update is zero or the 3806 specified care-of address matches the home address for the 3807 binding, then this is a request to delete the cached binding for 3808 the home address. In this case, the Binding Update MUST include a 3809 valid home nonce index, and the care-of nonce index MUST be 3810 ignored by the correspondent node. The generation of the binding 3811 management key depends then exclusively on the home keygen token 3812 (Section 5.2.5). If the Home Registration (H) bit is set in the 3813 Binding Update, the Binding Update is processed according to the 3814 procedure specified in Section 10.3.2; otherwise, it is processed 3815 according to the procedure specified in Section 9.5.3. 3817 The specified care-of address MUST be determined as follows: 3819 o If the Alternate Care-of Address option is present, the care-of 3820 address is the address in that option. 3822 o Otherwise, the care-of address is the Source Address field in the 3823 packet's IPv6 header. 3825 The home address for the binding MUST be determined as follows: 3827 o If the Home Address destination option is present, the home 3828 address is the address in that option. 3830 o Otherwise, the home address is the Source Address field in the 3831 packet's IPv6 header. 3833 9.5.2 Requests to Cache a Binding 3835 This section describes the processing of a valid Binding Update that 3836 requests a node to cache a binding, for which the Home Registration 3837 (H) bit is not set in the Binding Update. 3839 In this case, the receiving node SHOULD create a new entry in its 3840 Binding Cache for this home address, or update its existing Binding 3841 Cache entry for this home address, if such an entry already exists. 3842 The lifetime for the Binding Cache entry is initialized from the 3843 Lifetime field specified in the Binding Update, although this 3844 lifetime MAY be reduced by the node caching the binding; the lifetime 3845 for the Binding Cache entry MUST NOT be greater than the Lifetime 3846 value specified in the Binding Update. Any Binding Cache entry MUST 3847 be deleted after the expiration of its lifetime. 3849 Note that if the mobile node did not request a Binding 3850 Acknowledgement, it is not aware of the selected shorter lifetime. 3851 The mobile node may thus use route optimization and send packets with 3852 the Home Address destination option. As discussed in Section 9.3.1, 3853 such packets will be dropped if there is no binding. This situation 3854 is recoverable, but can cause temporary packet loss. 3856 The correspondent node MAY refuse to accept a new Binding Cache 3857 entry, if it does not have sufficient resources. A new entry MAY 3858 also be refused if the correspondent node believes its resources are 3859 utilized more efficiently in some other purpose, such as serving 3860 another mobile node with higher amount of traffic. In both cases the 3861 correspondent node SHOULD return a Binding Acknowledgement with 3862 status value 130. 3864 9.5.3 Requests to Delete a Binding 3866 This section describes the processing of a valid Binding Update that 3867 requests a node to delete a binding, when the Home Registration (H) 3868 bit is not set in the Binding Update. 3870 Any existing binding for the given home address MUST be deleted. A 3871 Binding Cache entry for the home address MUST NOT be created in 3872 response to receiving the Binding Update. 3874 If the Binding Cache entry was created by use of return routability 3875 nonces, the correspondent node MUST ensure that the same nonces are 3876 not used again with the particular home and care-of address. If both 3877 nonces are still valid, the correspondent node has to remember the 3878 particular combination of nonce indexes, addresses, and sequence 3879 number as illegal, until at least one of the nonces has become too 3880 old. 3882 9.5.4 Sending Binding Acknowledgements 3884 A Binding Acknowledgement may be sent to indicate receipt of a 3885 Binding Update as follows: 3887 o If the Binding Update was discarded as described in Section 9.2 or 3888 Section 9.5.1, a Binding Acknowledgement MUST NOT be sent. 3889 Otherwise the treatment depends on the below rules. 3891 o If the Acknowledge (A) bit set is set in the Binding Update, a 3892 Binding Acknowledgement MUST be sent. Otherwise, the treatment 3893 depends on the below rule. 3895 o If the node rejects the Binding Update due to an expired nonce 3896 index, sequence number being out of window (Section 9.5.1), or 3897 insufficiency of resources (Section 9.5.2), a Binding 3898 Acknowledgement MUST be sent. If the node accepts the Binding 3899 Update, the Binding Acknowledgement SHOULD NOT be sent. 3901 If the node accepts the Binding Update and creates or updates an 3902 entry for this binding, the Status field in the Binding 3903 Acknowledgement MUST be set to a value less than 128. Otherwise, the 3904 Status field MUST be set to a value greater than or equal to 128. 3905 Values for the Status field are described in Section 6.1.8 and in the 3906 IANA registry of assigned numbers [19]. 3908 If the Status field in the Binding Acknowledgement contains the value 3909 136 (expired home nonce index), 137 (expired care-of nonce index), or 3910 138 (expired nonces) then the message MUST NOT include the Binding 3911 Authorization Data mobility option. Otherwise, the Binding 3912 Authorization Data mobility option MUST be included, and MUST meet 3913 the specific authentication requirements for Binding Acknowledgements 3914 as defined in Section 5.2. 3916 If the Source Address field of the IPv6 header that carried the 3917 Binding Update does not contain a unicast address, the Binding 3918 Acknowledgement MUST NOT be sent, and the Binding Update packet MUST 3919 be silently discarded. Otherwise, the acknowledgement MUST be sent 3920 to the Source Address. Unlike the treatment of regular packets, this 3921 addressing procedure does not use information from the Binding Cache. 3922 However, a routing header is needed in some cases. If the Source 3923 Address is the home address of the mobile node, i.e., the Binding 3924 Update did not contain a Home Address destination option, then the 3925 Binding Acknowledgement MUST be sent to that address, and the routing 3926 header MUST NOT be used. Otherwise, the Binding Acknowledgement MUST 3927 be sent using a type 2 routing header which contains the mobile 3928 node's home address. 3930 9.5.5 Sending Binding Refresh Requests 3932 If a Binding Cache entry being deleted is still in active use in 3933 sending packets to a mobile node, the next packet sent to the mobile 3934 node will be routed normally to the mobile node's home link. 3935 Communication with the mobile node continues, but the tunneling from 3936 the home network creates additional overhead and latency in 3937 delivering packets to the mobile node. 3939 If the sender knows that the Binding Cache entry is still in active 3940 use, it MAY send a Binding Refresh Request message to the mobile node 3941 in an attempt to avoid this overhead and latency due to deleting and 3942 recreating the Binding Cache entry. 3944 The correspondent node MAY retransmit Binding Refresh Request 3945 messages provided that rate limitation is applied. The correspondent 3946 node MUST stop retransmitting when it receives a Binding Update. 3948 9.6 Cache Replacement Policy 3950 Conceptually, a node maintains a separate timer for each entry in its 3951 Binding Cache. When creating or updating a Binding Cache entry in 3952 response to a received and accepted Binding Update, the node sets the 3953 timer for this entry to the specified Lifetime period. Any entry in 3954 a node's Binding Cache MUST be deleted after the expiration of the 3955 Lifetime specified in the Binding Update from which the entry was 3956 created or last updated. 3958 Each node's Binding Cache will, by necessity, have a finite size. A 3959 node MAY use any reasonable local policy for managing the space 3960 within its Binding Cache. 3962 A node MAY choose to drop any entry already in its Binding Cache in 3963 order to make space for a new entry. For example, a "least-recently 3964 used" (LRU) strategy for cache entry replacement among entries is 3965 likely to work well unless the size of the Binding Cache is 3966 substantially insufficient. When entries are deleted, the 3967 correspondent node MUST follow the rules in Section 5.2.8 in order to 3968 guard the return routability procedure against replay attacks. 3970 If the node sends a packet to a destination for which it has dropped 3971 the entry from its Binding Cache, the packet will be routed through 3972 the mobile node's home link. The mobile node can detect this, and 3973 establish a new binding if necessary. 3975 However, if the mobile node believes that the binding still exists, 3976 it may use route optimization and send packets with the Home Address 3977 destination option. This can create temporary packet loss, as 3978 discussed earlier in the context of binding lifetime reductions 3979 performed by the correspondent node (Section 9.5.2). 3981 10. Home Agent Operation 3983 10.1 Conceptual Data Structures 3985 Each home agent MUST maintain a Binding Cache and Home Agents List. 3987 The rules for maintaining a Binding Cache are the same for home 3988 agents and correspondent nodes, and have already been described in 3989 Section 9.1. 3991 The Home Agents List is maintained by each home agent, recording 3992 information about each router on the same link which is acting as a 3993 home agent; this list is used by the dynamic home agent address 3994 discovery mechanism. A router is known to be acting as a home agent, 3995 if it sends a Router Advertisement in which the Home Agent (H) bit is 3996 set. When the lifetime for a list entry (defined below) expires, 3997 that entry is removed from the Home Agents List. The Home Agents 3998 List is thus similar to the Default Router List conceptual data 3999 structure maintained by each host for Neighbor Discovery [12]. The 4000 Home Agents List MAY be implemented in any manner consistent with the 4001 external behavior described in this document. 4003 Each home agent maintains a separate Home Agents List for each link 4004 on which it is serving as a home agent. A new entry is created or an 4005 existing entry is updated in response to receipt of a valid Router 4006 Advertisement in which the Home Agent (H) bit is set. Each Home 4007 Agents List entry conceptually contains the following fields: 4009 o The link-local IP address of a home agent on the link. This 4010 address is learned through the Source Address of the Router 4011 Advertisements [12] received from the router. 4013 o One or more global IP addresses for this home agent. Global 4014 addresses are learned through Prefix Information options with the 4015 Router Address (R) bit set, received in Router Advertisements from 4016 this link-local address. Global addresses for the router in a 4017 Home Agents List entry MUST be deleted once the prefix associated 4018 with that address is no longer valid [12]. 4020 o The remaining lifetime of this Home Agents List entry. If a Home 4021 Agent Information Option is present in a Router Advertisement 4022 received from a home agent, the lifetime of the Home Agents List 4023 entry representing that home agent is initialized from the Home 4024 Agent Lifetime field in the option (if present); otherwise, the 4025 lifetime is initialized from the Router Lifetime field in the 4026 received Router Advertisement. If Home Agents List entry lifetime 4027 reaches zero, the entry MUST be deleted from the Home Agents List. 4029 o The preference for this home agent; higher values indicate a more 4030 preferable home agent. The preference value is taken from the 4031 Home Agent Preference field in the received Router Advertisement, 4032 if the Router Advertisement contains a Home Agent Information 4033 Option, and is otherwise set to the default value of 0. A home 4034 agent uses this preference in ordering the Home Agents List when 4035 it sends an ICMP Home Agent Address Discovery message. 4037 10.2 Processing Mobility Headers 4039 All IPv6 home agents MUST observe the rules described in Section 9.2 4040 when processing Mobility Headers. 4042 10.3 Processing Bindings 4044 10.3.1 Primary Care-of Address Registration 4046 When a node receives a Binding Update, it MUST validate it and 4047 determine the type of Binding Update according to the steps described 4048 in Section 9.5.1. Furthermore, it MUST authenticate the Binding 4049 Update as described in Section 5.1. An authorization step specific 4050 for the home agent is also needed to ensure that only the right node 4051 can control a particular home address. This is provided through the 4052 home address unequivocally identifying the security association that 4053 must be used. 4055 This section describes the processing of a valid and authorized 4056 Binding Update, when it requests the registration of the mobile 4057 node's primary care-of address. 4059 To begin processing the Binding Update, the home agent MUST perform 4060 the following sequence of tests: 4062 o If the node implements only correspondent node functionality, or 4063 has not been configured to act as a home agent, then the node MUST 4064 reject the Binding Update. The node MUST then also return a 4065 Binding Acknowledgement to the mobile node, in which the Status 4066 field is set to 131 (home registration not supported). 4068 o Else, if the home address for the binding (the Home Address field 4069 in the packet's Home Address option) is not an on-link IPv6 4070 address with respect to the home agent's current Prefix List, then 4071 the home agent MUST reject the Binding Update and SHOULD return a 4072 Binding Acknowledgement to the mobile node, in which the Status 4073 field is set to 132 (not home subnet). 4075 o Else, if the home agent chooses to reject the Binding Update for 4076 any other reason (e.g., insufficient resources to serve another 4077 mobile node as a home agent), then the home agent SHOULD return a 4078 Binding Acknowledgement to the mobile node, in which the Status 4079 field is set to an appropriate value to indicate the reason for 4080 the rejection. 4082 o A Home Address destination option MUST be present in the message. 4083 It MUST be validated as described in Section 9.3.1 with the 4084 following additional rule. The Binding Cache entry existence test 4085 MUST NOT be done for IPsec packets when the Home Address option 4086 contains an address for which the receiving node could act as a 4087 home agent. 4089 If home agent accepts the Binding Update, it MUST then create a new 4090 entry in its Binding Cache for this mobile node, or update its 4091 existing Binding Cache entry, if such an entry already exists. The 4092 Home Address field as received in the Home Address option provides 4093 the home address of the mobile node. 4095 The home agent MUST mark this Binding Cache entry as a home 4096 registration to indicate that the node is serving as a home agent for 4097 this binding. Binding Cache entries marked as a home registration 4098 MUST be excluded from the normal cache replacement policy used for 4099 the Binding Cache (Section 9.6) and MUST NOT be removed from the 4100 Binding Cache until the expiration of the Lifetime period. 4102 Unless this home agent already has a binding for the given home 4103 address, the home agent MUST perform Duplicate Address Detection [13] 4104 on the mobile node's home link before returning the Binding 4105 Acknowledgement. This ensures that no other node on the home link 4106 was using the mobile node's home address when the Binding Update 4107 arrived. If this Duplicate Address Detection fails for the given 4108 home address or an associated link local address, then the home agent 4109 MUST reject the complete Binding Update and MUST return a Binding 4110 Acknowledgement to the mobile node, in which the Status field is set 4111 to 134 (Duplicate Address Detection failed). When the home agent 4112 sends a successful Binding Acknowledgement to the mobile node, the 4113 home agent assures to the mobile node that its address(es) will 4114 continue to be kept unique by the home agent at least as long as the 4115 lifetime granted for the binding is not over. 4117 The specific addresses which are to be tested before accepting the 4118 Binding Update, and later to be defended by performing Duplicate 4119 Address Detection, depend on the setting of the Link-Local Address 4120 Compatibility (L) bit, as follows: 4122 o L=0: Defend only the given address. Do not derive a link-local 4123 address. 4125 o L=1: Defend both the given non link-local unicast (home) address 4126 and the derived link-local. The link-local address is derived by 4127 replacing the subnet prefix in the mobile node's home address with 4128 the link-local prefix. 4130 The lifetime of the Binding Cache entry depends on a number of 4131 factors: 4133 o The lifetime for the Binding Cache entry MUST NOT be greater than 4134 the Lifetime value specified in the Binding Update. 4136 o The lifetime for the Binding Cache entry MUST NOT be greater than 4137 the remaining valid lifetime for the subnet prefix in the mobile 4138 node's home address specified with the Binding Update. The 4139 remaining valid lifetime for this prefix is determined by the home 4140 agent based on its own Prefix List entry for this prefix [12]. 4142 The remaining preferred lifetime SHOULD NOT have any impact on the 4143 lifetime for the binding cache entry. 4145 The home agent MUST remove a binding when the valid lifetime of 4146 the prefix associated with it expires. 4148 o The home agent MAY further decrease the specified lifetime for the 4149 binding, for example based on a local policy. The resulting 4150 lifetime is stored by the home agent in the Binding Cache entry, 4151 and this Binding Cache entry MUST be deleted by the home agent 4152 after the expiration of this lifetime. 4154 Regardless of the setting of the Acknowledge (A) bit in the Binding 4155 Update, the home agent MUST return a Binding Acknowledgement to the 4156 mobile node, constructed as follows: 4158 o The Status field MUST be set to a value indicating success. The 4159 value 1 (accepted but prefix discovery necessary) MUST be used if 4160 the subnet prefix of the specified home address is deprecated, 4161 becomes deprecated during the lifetime of the binding, or becomes 4162 invalid at the end of the lifetime. The value 0 MUST be used 4163 otherwise. For the purposes of comparing the binding and prefix 4164 lifetimes, the prefix lifetimes are first converted into units of 4165 four seconds by ignoring the two least significant bits. 4167 o The Key Management Mobility Capability (K) bit is set if the 4168 following conditions are all fulfilled, and cleared otherwise: 4170 * The Key Management Mobility Capability (K) bit was set in the 4171 Binding Update. 4173 * The IPsec security associations between the mobile node and the 4174 home agent have been established dynamically. 4176 * The home agent has the capability to update its endpoint in the 4177 used key management protocol to the new care-of address every 4178 time it moves 4180 Depending on the final value of the bit in the Binding 4181 Acknowledgement, the home agent SHOULD perform the following 4182 actions: 4184 K = 0 4186 Discard key management connections, if any, to the old care-of 4187 address. If the mobile node did not have a binding before 4188 sending this Binding Update, discard the connections to the 4189 home address. 4191 K = 1 4193 Move the peer endpoint of the key management protocol 4194 connection, if any, to the new care-of address. For an IKE 4195 phase 1 connection, this means that any IKE packets sent to the 4196 peer are sent to this address, and packets from this address 4197 with the original ISAKMP cookies are accepted. 4199 Note that Section 2.5.3 in RFC 2408 [8] Section 2.5.3 states 4200 three specifies rules that ISAKMP cookies must satisfy: they 4201 must depend on specific parties and they can only have been 4202 generated by the entity itself. Then it recommends a 4203 particular way to do this, namely a hash of IP addresses. With 4204 the K bit set to 1, the recommended implementation technique 4205 does not work directly. To satisfy the two rules, the specific 4206 parties must be treated as the original IP addresses, not the 4207 ones in use at the specific moment. 4209 o The Sequence Number field MUST be copied from the Sequence Number 4210 given in the Binding Update. 4212 o The Lifetime field MUST be set to the remaining lifetime for the 4213 binding as set by the home agent in its home registration Binding 4214 Cache entry for the mobile node, as described above. 4216 o If the home agent stores the Binding Cache entry in nonvolatile 4217 storage, then the Binding Refresh Advice mobility option MUST be 4218 omitted. Otherwise, the home agent MAY include this option to 4219 suggest that the mobile node refreshes its binding sooner than the 4220 actual lifetime of the binding ends. 4222 If the Binding Refresh Advice mobility option is present, the 4223 Refresh Interval field in the option MUST be set to a value less 4224 than the Lifetime value being returned in the Binding 4225 Acknowledgement. This indicates that the mobile node SHOULD 4226 attempt to refresh its home registration at the indicated shorter 4227 interval. The home agent MUST still retain the registration for 4228 the Lifetime period, even if the mobile node does not refresh its 4229 registration within the Refresh period. 4231 The rules for selecting the Destination IP address (and possibly 4232 routing header construction) for the Binding Acknowledgement to the 4233 mobile node are the same as in Section 9.5.4. 4235 In addition, the home agent MUST follow the procedure defined in 4236 Section 10.4.1 to intercept packets on the mobile node's home link 4237 addressed to the mobile node, while the home agent is serving as the 4238 home agent for this mobile node. The home agent MUST also be 4239 prepared to accept reverse tunneled packets from the new care-of 4240 address of the mobile node, as described in Section 10.4.5. Finally, 4241 the home agent MUST also propagate new home network prefixes, as 4242 described in Section 10.6. 4244 10.3.2 Primary Care-of Address De-Registration 4246 A binding may need to be de-registered when the mobile node returns 4247 home, or when the mobile node knows that it will soon not have any 4248 care-of addresses in the visited network. 4250 A Binding Update is validated and authorized in the manner described 4251 in the previous section. This section describes the processing of a 4252 valid Binding Update that requests the receiving node to no longer 4253 serve as its home agent, de-registering its primary care-of address. 4255 To begin processing the Binding Update, the home agent MUST perform 4256 the following test: 4258 o If the receiving node has no entry marked as a home registration 4259 in its Binding Cache for this mobile node, then this node MUST 4260 reject the Binding Update and SHOULD return a Binding 4261 Acknowledgement to the mobile node, in which the Status field is 4262 set to 133 (not home agent for this mobile node). 4264 If the home agent does not reject the Binding Update as described 4265 above, then it MUST delete any existing entry in its Binding Cache 4266 for this mobile node. Then, the home agent MUST return a Binding 4267 Acknowledgement to the mobile node, constructed as follows: 4269 o The Status field MUST be set to a value 0, indicating success. 4271 o The Key Management Mobility Capability (K) bit is set or cleared, 4272 and actions based on its value are performed as described in the 4273 previous section. The mobile node's home address is used as its 4274 new care-of address for the purposes of moving the key management 4275 connection to a new endpoint. 4277 o The Sequence Number field MUST be copied from the Sequence Number 4278 given in the Binding Update. 4280 o The Lifetime field MUST be set to zero. 4282 o The Binding Refresh Advice mobility option MUST be omitted. 4284 In addition, the home agent MUST stop intercepting packets on the 4285 mobile node's home link that are addressed to the mobile node 4286 (Section 10.4.1). 4288 The rules for selecting the Destination IP address (and, if required, 4289 routing header construction) for the Binding Acknowledgement to the 4290 mobile node are the same as in the previous section. When the Status 4291 field in the Binding Acknowledgement is greater than or equal to 128 4292 and the Source Address of the Binding Update is on the home link, the 4293 home agent MUST send it to the mobile node's link layer address 4294 (retrieved either from the Binding Update or through Neighbor 4295 Solicitation). 4297 10.4 Packet Processing 4299 10.4.1 Intercepting Packets for a Mobile Node 4301 While a node is serving as the home agent for mobile node it MUST 4302 attempt to intercept packets on the mobile node's home link that are 4303 addressed to the mobile node. 4305 In order to do this, when a node begins serving as the home agent it 4306 MUST multicast onto the home link a Neighbor Advertisement message 4307 [12] on behalf of the mobile node. For the home address specified in 4308 the Binding Update, the home agent sends a Neighbor Advertisement 4309 message [12] to the all-nodes multicast address on the home link, to 4310 advertise the home agent's own link-layer address for this IP address 4311 on behalf of the mobile node. If the Link-Layer Address 4312 Compatibility (L) flag has been specified in the Binding Update, the 4313 home agent MUST do the same for the link-local address of the mobile 4314 node. 4316 All fields in each such Neighbor Advertisement message SHOULD be set 4317 in the same way they would be set by the mobile node itself if 4318 sending this Neighbor Advertisement [12] while at home, with the 4319 following exceptions: 4321 o The Target Address in the Neighbor Advertisement MUST be set to 4322 the specific IP address for the mobile node. 4324 o The Advertisement MUST include a Target Link-layer Address option 4325 specifying the home agent's link-layer address. 4327 o The Router (R) bit in the Advertisement MUST be set to zero. 4329 o The Solicited Flag (S) in the Advertisement MUST NOT be set, since 4330 it was not solicited by any Neighbor Solicitation. 4332 o The Override Flag (O) in the Advertisement MUST be set, indicating 4333 that the Advertisement SHOULD override any existing Neighbor Cache 4334 entry at any node receiving it. 4336 o The Source Address in the IPv6 header MUST be set to the home 4337 agent's IP address on the interface used to send the 4338 advertisement. 4340 Any node on the home link receiving one of the Neighbor Advertisement 4341 messages described above will thus update its Neighbor Cache to 4342 associate the mobile node's address with the home agent's link layer 4343 address, causing it to transmit any future packets normally destined 4344 to the mobile node to the mobile node's home agent. Since 4345 multicasting on the local link (such as Ethernet) is typically not 4346 guaranteed to be reliable, the home agent MAY retransmit this 4347 Neighbor Advertisement message up to MAX_NEIGHBOR_ADVERTISEMENT (see 4348 [12]) times to increase its reliability. It is still possible that 4349 some nodes on the home link will not receive any of these Neighbor 4350 Advertisements, but these nodes will eventually be able to detect the 4351 link-layer address change for the mobile node's address, through use 4352 of Neighbor Unreachability Detection [12]. 4354 While a node is serving as a home agent for some mobile node, the 4355 home agent uses IPv6 Neighbor Discovery [12] to intercept unicast 4356 packets on the home link addressed to the mobile node. In order to 4357 intercept packets in this way, the home agent MUST act as a proxy for 4358 this mobile node, and reply to any received Neighbor Solicitations 4359 for it. When a home agent receives a Neighbor Solicitation, it MUST 4360 check if the Target Address specified in the message matches the 4361 address of any mobile node for which it has a Binding Cache entry 4362 marked as a home registration. 4364 If such an entry exists in the home agent's Binding Cache, the home 4365 agent MUST reply to the Neighbor Solicitation with a Neighbor 4366 Advertisement, giving the home agent's own link-layer address as the 4367 link-layer address for the specified Target Address. In addition, 4368 the Router (R) bit in the Advertisement MUST be set to zero. Acting 4369 as a proxy in this way allows other nodes on the mobile node's home 4370 link to resolve the mobile node's address, and allows the home agent 4371 to defend these addresses on the home link for Duplicate Address 4372 Detection [12]. 4374 10.4.2 Processing Intercepted Packets 4376 For any packet sent to a mobile node from the mobile node's home 4377 agent (for which the home agent is the original sender of the 4378 packet), the home agent is operating as a correspondent node of the 4379 mobile node for this packet and the procedures described in Section 4380 9.3.2 apply. The home agent then uses a routing header to route the 4381 packet to the mobile node by way of the primary care-of address in 4382 the home agent's Binding Cache. 4384 While the mobile node is away from home, the home agent intercepts 4385 any packets on the home link addressed to the mobile node's home 4386 address, as described in Section 10.4.1. In order to forward each 4387 intercepted packet to the mobile node, the home agent MUST tunnel the 4388 packet to the mobile node using IPv6 encapsulation [15]. When a home 4389 agent encapsulates an intercepted packet for forwarding to the mobile 4390 node, the home agent sets the Source Address in the new tunnel IP 4391 header to the home agent's own IP address, and sets the Destination 4392 Address in the tunnel IP header to the mobile node's primary care-of 4393 address. When received by the mobile node, normal processing of the 4394 tunnel header [15] will result in decapsulation and processing of the 4395 original packet by the mobile node. 4397 However, packets addressed to the mobile node's link-local address 4398 MUST NOT be tunneled to the mobile node. Instead, such a packet MUST 4399 be discarded, and the home agent SHOULD return an ICMP Destination 4400 Unreachable, Code 3, message to the packet's Source Address (unless 4401 this Source Address is a multicast address). Packets addressed to 4402 the mobile node's site-local address SHOULD NOT be tunneled to the 4403 mobile node by default. 4405 Interception and tunneling of the following multicast addressed 4406 packets on the home network are only done if the home agent supports 4407 multicast group membership control messages from the mobile node as 4408 described in the next section. Tunneling of multicast packets to a 4409 mobile node follows similar limitations to those defined above for 4410 unicast packets addressed to the mobile node's link-local and 4411 site-local addresses. Multicast packets addressed to a multicast 4412 address with link-local scope [3], to which the mobile node is 4413 subscribed, MUST NOT be tunneled to the mobile node; such packets 4414 SHOULD be silently discarded (after delivering to other local 4415 multicast recipients). Multicast packets addressed to a multicast 4416 address with scope larger than link-local but smaller than global 4417 (e.g., site-local and organization-local [3]), to which the mobile 4418 node is subscribed, SHOULD NOT be tunneled to the mobile node. 4419 Multicast packets addressed with a global scope to which the mobile 4420 node has successfully subscribed MUST be tunneled to the mobile node. 4422 Before tunneling a packet to the mobile node, the home agent MUST 4423 perform any IPsec processing as indicated by the security policy data 4424 base. 4426 10.4.3 Multicast Membership Control 4428 This section is a prerequisite for the multicast data packet 4429 forwarding described in the previous section. If this support is not 4430 provided, multicast group membership control messages are silently 4431 ignored. 4433 In order to forward multicast data packets from the home network to 4434 all the proper mobile nodes the home agent SHOULD be capable of 4435 receiving tunneled multicast group membership control information 4436 from the mobile node in order to determine which groups the mobile 4437 node has subscribed to. These multicast group membership messages 4438 are Listener Report messages specified MLD [17] or in other protocols 4439 such as [37]. 4441 The messages are issued by the mobile node but sent through the 4442 reverse tunnel to the home agent. These messages are issued whenever 4443 the mobile node decides to enable reception of packets for a 4444 multicast group or in response to an MLD Query from the home agent. 4445 The mobile node will also issue multicast group control messages to 4446 disable reception of multicast packets when it is no longer 4447 interested in receiving multicasts for a particular group. 4449 To obtain the mobile node's current multicast group membership the 4450 home agent must periodically transmit MLD Query messages through the 4451 tunnel to the mobile node. These MLD periodic transmissions will 4452 ensure the home agent has an accurate record of the groups in which 4453 the mobile node is interested despite packet losses of the mobile 4454 node's MLD group membership messages. 4456 All MLD packets are sent directly between the mobile node and the 4457 home agent. Since all these packets are destined to a link-scope 4458 multicast address and have a hop limit of 1, there is no direct 4459 forwarding of such packets between the home network and the mobile 4460 node. The MLD packets between the mobile node and the home agent are 4461 encapsulated within the same tunnel header used for other packet 4462 flows between the mobile node and home agent. 4464 Note that at this time, even though a link-local source is used on 4465 MLD packets, no functionality depends on these addresses being 4466 unique, nor do they elicit direct responses. All MLD messages are 4467 sent to multicast destinations. To avoid ambiguity on the home agent 4468 due to mobile nodes which may choose identical link-local source 4469 addresses for their MLD function it is necessary for the home agent 4470 to identify which mobile node was actually the issuer of a particular 4471 MLD message. This may be accomplished by noting which tunnel such an 4472 MLD arrived by, which IPsec SA was used, or by other distinguishing 4473 means. 4475 This specification puts no requirement on how the functions in this 4476 section and the multicast forwarding in Section 10.4.2 are to be 4477 achieved. At the time of this writing it was thought that a full 4478 IPv6 multicast router function would be necessary on the home agent, 4479 but it may be possible to achieve the same effects through a "proxy 4480 MLD" application coupled with kernel multicast forwarding. This may 4481 be the subject of future specifications. 4483 10.4.4 Stateful Address Autoconfiguration 4485 This section describes how home agents support the use of stateful 4486 address autoconfiguration mechanisms such as DHCPv6 [29] from the 4487 mobile nodes. If this support is not provided, then the M and O bits 4488 must remain cleared on the Mobile Prefix Advertisement Messages. Any 4489 mobile node which sends DHCPv6 messages to the home agent without 4490 this support will not receive a response. 4492 If DHCPv6 is used, packets are sent with link-local source addresses 4493 either to a link-scope multicast address or a link-local address. 4494 Mobile nodes desiring to locate a DHCPv6 service may reverse tunnel 4495 standard DHCPv6 packets to the home agent. Since these link-scope 4496 packets cannot be forwarded onto the home network it is necessary for 4497 the home agent to either implement a DHCPv6 relay agent or a DHCPv6 4498 server function itself. The arriving tunnel or IPsec SA of DHCPv6 4499 link-scope messages from the mobile node must be noted so that DHCPv6 4500 responses may be sent back to the appropriate mobile node. DHCPv6 4501 messages sent to the mobile node with a link-local destination must 4502 be tunneled within the same tunnel header used for other packet 4503 flows. 4505 10.4.5 Handling Reverse Tunneled Packets 4507 Unless a binding has been established between the mobile node and a 4508 correspondent node, traffic from the mobile node to the correspondent 4509 node goes through a reverse tunnel. Home agents MUST support reverse 4510 tunneling as follows: 4512 o The tunneled traffic arrives to the home agent's address using 4513 IPv6 encapsulation [15]. 4515 o Depending on the security policies used by the home agent, reverse 4516 tunneled packets MAY be discarded unless accompanied by a valid 4517 ESP header. The support for authenticated reverse tunneling 4518 allows the home agent to protect the home network and 4519 correspondent nodes from malicious nodes masquerading as a mobile 4520 node. 4522 o Otherwise, when a home agent decapsulates a tunneled packet from 4523 the mobile node, the home agent MUST verify that the Source 4524 Address in the tunnel IP header is the mobile node's primary 4525 care-of address. Otherwise any node in the Internet could send 4526 traffic through the home agent and escape ingress filtering 4527 limitations. This simple check forces the attacker to at least 4528 know the current location of the real mobile node and be able to 4529 defeat ingress filtering. 4531 10.4.6 Protecting Return Routability Packets 4533 The return routability procedure described in Section 5.2.5 assumes 4534 that the confidentiality of the Home Test Init and Home Test messages 4535 is protected as they are tunneled between the home agent to the 4536 mobile node. Therefore, the home agent MUST support tunnel mode 4537 IPsec ESP for the protection of packets belonging to the return 4538 routability procedure. Support for a non-null encryption transform 4539 and authentication algorithm MUST be available. It is not necessary 4540 to distinguish between different kinds of packets within the return 4541 routability procedure. 4543 Security associations are needed to provide this protection. When 4544 the care-of address for the mobile node changes as a result of an 4545 accepted Binding Update, special treatment is needed for the next 4546 packets sent using these security associations. The home agent MUST 4547 set the new care-of address as the destination address of these 4548 packets, as if the outer header destination address in the security 4549 association had changed [21]. 4551 The above protection SHOULD be used with all mobile nodes. The use 4552 is controlled by configuration of the IPsec security policy database 4553 both at the mobile node and at the home agent. 4555 As described earlier, the Binding Update and Binding Acknowledgement 4556 messages require protection between the home agent and the mobile 4557 node. The Mobility Header protocol carries both these messages as 4558 well as the return routability messages. From the point of view of 4559 the security policy database these messages are indistinguishable. 4560 When IPsec is used to protect return routability signaling or payload 4561 packets, this protection MUST only be applied to the return 4562 routability packets entering the IPv6 encapsulated tunnel interface 4563 between the mobile node and the home agent. This can be achieved, 4564 for instance, by defining the security policy database entries 4565 specifically for the tunnel interface. That is, the policy entries 4566 are not generally applied on all traffic on the physical interface(s) 4567 of the nodes, but rather only on traffic that enters the tunnel. 4568 This makes use of per-interface security policy database entries [4], 4569 specific to the tunnel interface (the node's attachment to the tunnel 4570 [11]). 4572 10.5 Dynamic Home Agent Address Discovery 4574 This section describes how a home agent can help mobile nodes to 4575 discover the addresses of the home agents. The home agent keeps 4576 track of the other home agents on the same link, and responds to 4577 queries sent by the mobile node. 4579 10.5.1 Receiving Router Advertisement Messages 4581 For each link on which a router provides service as a home agent, the 4582 router maintains a Home Agents List recording information about all 4583 other home agents on that link. This list is used in the dynamic 4584 home agent address discovery mechanism, described in Section 10.5. 4585 The information for the list is learned through receipt of the 4586 periodic unsolicited multicast Router Advertisements, in a manner 4587 similar to the Default Router List conceptual data structure 4588 maintained by each host for Neighbor Discovery [12]. In the 4589 construction of the Home Agents List, the Router Advertisements are 4590 from each other home agent on the link, and the Home Agent (H) bit is 4591 set in them. 4593 On receipt of a valid Router Advertisement, as defined in the 4594 processing algorithm specified for Neighbor Discovery [12], the home 4595 agent performs the following steps, in addition to any steps already 4596 required of it by Neighbor Discovery: 4598 o If the Home Agent (H) bit in the Router Advertisement is not set, 4599 delete the sending node's entry in the current Home Agents List 4600 (if one exists). Skip all the following steps. 4602 o Otherwise, extract the Source Address from the IP header of the 4603 Router Advertisement. This is the link-local IP address on this 4604 link of the home agent sending this Advertisement [12]. 4606 o Determine the preference for this home agent. If the Router 4607 Advertisement contains a Home Agent Information Option, then the 4608 preference is taken from the Home Agent Preference field in the 4609 option; otherwise, the default preference of 0 MUST be used. 4611 o Determine the lifetime for this home agent. If the Router 4612 Advertisement contains a Home Agent Information Option, then the 4613 lifetime is taken from the Home Agent Lifetime field in the 4614 option; otherwise, the lifetime specified by the Router Lifetime 4615 field in the Router Advertisement SHOULD be used. 4617 o If the link-local address of the home agent sending this 4618 Advertisement is already present in this home agent's Home Agents 4619 List and the received home agent lifetime value is zero, 4620 immediately delete this entry in the Home Agents List. 4622 o Otherwise, if the link-local address of the home agent sending 4623 this Advertisement is already present in the receiving home 4624 agent's Home Agents List, reset its lifetime and preference to the 4625 values determined above. 4627 o If the link-local address of the home agent sending this 4628 Advertisement is not already present in the Home Agents List 4629 maintained by the receiving home agent, and the lifetime for the 4630 sending home agent is non-zero, create a new entry in the list, 4631 and initialize its lifetime and preference to the values 4632 determined above. 4634 o If the Home Agents List entry for the link-local address of the 4635 home agent sending this Advertisement was not deleted as described 4636 above, determine any global address(es) of the home agent based on 4637 each Prefix Information option received in this Advertisement in 4638 which the Router Address (R) bit is set (Section 7.2). Add all 4639 such global addresses to the list of global addresses in this Home 4640 Agents List entry. 4642 A home agent SHOULD maintain an entry in its Home Agents List for 4643 each valid home agent address until that entry's lifetime expires, 4644 after which time the entry MUST be deleted. 4646 As described in Section 11.4.1, a mobile node attempts dynamic home 4647 agent address discovery by sending an ICMP Home Agent Address 4648 Discovery Request message to the Mobile IPv6 Home-Agents anycast 4649 address [16] for its home IP subnet prefix. A home agent receiving 4650 such a Home Agent Address Discovery Request message that is serving 4651 this subnet SHOULD return an ICMP Home Agent Address Discovery Reply 4652 message to the mobile node, with the Source Address of the Reply 4653 packet set to one of the global unicast addresses of the home agent. 4654 The Home Agent Addresses field in the Reply message is constructed as 4655 follows: 4657 o The Home Agent Addresses field SHOULD contain all global IP 4658 addresses for each home agent currently listed in this home 4659 agent's own Home Agents List (Section 10.1). 4661 o The IP addresses in the Home Agent Addresses field SHOULD be 4662 listed in order of decreasing preference values, based either on 4663 the respective advertised preference from a Home Agent Information 4664 option or on the default preference of 0 if no preference is 4665 advertised (or on the configured home agent preference for this 4666 home agent itself). 4668 o Among home agents with equal preference, their IP addresses in the 4669 Home Agent Addresses field SHOULD be listed in an order randomized 4670 with respect to other home agents with equal preference, each time 4671 a Home Agent Address Discovery Reply message is returned by this 4672 home agent. 4674 o If more than one global IP address is associated with a home 4675 agent, these addresses SHOULD be listed in a randomized order. 4677 o The home agent SHOULD reduce the number of home agent IP addresses 4678 so that the packet fits within the minimum IPv6 MTU [11]. The 4679 home agent addresses selected for inclusion in the packet SHOULD 4680 be those from the complete list with the highest preference. This 4681 limitation avoids the danger of the Reply message packet being 4682 fragmented (or rejected by an intermediate router with an ICMP 4683 Packet Too Big message [14]). 4685 10.6 Sending Prefix Information to the Mobile Node 4687 10.6.1 List of Home Network Prefixes 4689 Mobile IPv6 arranges to propagate relevant prefix information to the 4690 mobile node when it is away from home, so that it may be used in 4691 mobile node home address configuration, and in network renumbering. 4692 In this mechanism, mobile nodes away from home receive Mobile Prefix 4693 Advertisements messages. These messages include Prefix Information 4694 Options for the prefixes configured on the home subnet interface(s) 4695 of the home agent. 4697 If there are multiple home agents, differences in the advertisements 4698 sent by different home agents can lead to an inability to use a 4699 particular home address when changing to another home agent. In 4700 order to ensure that the mobile nodes get the same information from 4701 different home agents, it is desired that all the home agents on the 4702 same link be configured in the same manner. 4704 To support this, the home agent monitors prefixes advertised by 4705 itself and other home agents on the home link. In RFC 2461 [12] it 4706 is acceptable for two routers to advertise different sets of prefixes 4707 on the same link. For home agents such differences should be 4708 detected since for a given home address the mobile node communicates 4709 only with one home agent at a time and the mobile node needs to know 4710 the full set of prefixes assigned to the home link. All other 4711 comparisons of Router Advertisements are as specified in Section 4712 6.2.7 of RFC 2461. 4714 10.6.2 Scheduling Prefix Deliveries 4716 A home agent serving a mobile node will schedule the delivery of new 4717 prefix information to that mobile node when any of the following 4718 conditions occur: 4720 MUST: 4722 o The state of the flags changes for the prefix of the mobile node's 4723 registered home address. 4725 o The valid or preferred lifetime is reconfigured or changes for any 4726 reason other than advancing real time. 4728 o The mobile node requests the information with a Mobile Prefix 4729 Solicitation (see Section 11.4.2). 4731 SHOULD: 4733 o A new prefix is added to the home subnet interface(s) of the home 4734 agent. 4736 MAY: 4738 o The valid or preferred lifetime or the state of the flags changes 4739 for a prefix which is not used in any Binding Cache entry for this 4740 mobile node. 4742 The home agent uses the following algorithm to determine when to send 4743 prefix information to the mobile node. 4745 o If a mobile node sends a solicitation, answer right away. 4747 o If no Mobile Prefix Advertisement has been sent to the mobile node 4748 in the last MaxMobPfxAdvInterval (see Section 13) seconds, then 4749 ensure that a transmission is scheduled. The actual transmission 4750 time is randomized as described below. 4752 o If a prefix matching the mobile node's home registration is added 4753 on the home subnet interface, or if its information changes in any 4754 way that does not deprecate the mobile node's address, ensure that 4755 a transmission is scheduled. The actual transmission time is 4756 randomized as described below. 4758 o If a home registration expires, cancel any scheduled 4759 advertisements to the mobile node. 4761 The list of prefixes is sent in its entirety in all cases. 4763 If the home agent already has scheduled the transmission of a Mobile 4764 Prefix Advertisement to the mobile node, the home agent replaces the 4765 advertisement with a new one, to be sent at the scheduled time. 4767 Otherwise, the home agent computes a fresh value for RAND_ADV_DELAY, 4768 the offset from the current time for the scheduled transmission as 4769 follows. First calculate the maximum delay for the scheduled 4770 Advertisement: 4772 MaxScheduleDelay = min (MaxMobPfxAdvInterval, Preferred Lifetime), 4774 where MaxMobPfxAdvInterval is as defined in Section 12. Then compute 4775 the final delay for the advertisement: 4777 RAND_ADV_DELAY = MinMobPfxAdvInterval + 4778 (rand() % abs(MaxScheduleDelay - MinMobPfxAdvInterval)) 4780 Here rand() returns a random integer value in the range of 0 to the 4781 maximum possible integer value. This computation is expected to 4782 alleviate bursts of advertisements when prefix information changes. 4783 In addition, a home agent MAY further reduce the rate of packet 4784 transmission by further delaying individual advertisements, if needed 4785 to avoid overwhelming local network resources. The home agent SHOULD 4786 periodically continue to retransmit an unsolicited Advertisement to 4787 the mobile node, until it is acknowledged by the receipt of a Mobile 4788 Prefix Solicitation from the mobile node. 4790 The home agent MUST wait PREFIX_ADV_TIMEOUT (see Section 12) before 4791 the first retransmission, and double the retransmission wait time for 4792 every succeeding retransmission, up until a maximum of 4793 PREFIX_ADV_RETRIES attempts (see Section 12). If the mobile node's 4794 bindings expire before the matching Binding Update has been received, 4795 then the home agent MUST NOT attempt any more retransmissions, even 4796 if not all PREFIX_ADV_RETRIES have been retransmitted. If the mobile 4797 node sends another Binding Update without returning home in the 4798 meantime, the home agent SHOULD again begin transmitting the 4799 unsolicited Advertisement. 4801 If some condition as described above occurs on the home link and 4802 causes another Prefix Advertisement to be sent to the mobile node, 4803 before the mobile node acknowledges a previous transmission, the home 4804 agent SHOULD combine any Prefix Information options in the 4805 unacknowledged Mobile Prefix Advertisement into a new Advertisement. 4806 The home agent discards the old Advertisement. 4808 10.6.3 Sending Advertisements 4810 When sending a Mobile Prefix Advertisement to the mobile node, the 4811 home agent MUST construct the packet as follows: 4813 o The Source Address in the packet's IPv6 header MUST be set to the 4814 home agent's IP address to which the mobile node addressed its 4815 current home registration, or its default global home agent 4816 address if no binding exists. 4818 o If the advertisement was solicited, it MUST be destined to the 4819 source address of the solicitation. If it was triggered by prefix 4820 changes or renumbering, the advertisement's destination will be 4821 the mobile node's home address in the binding which triggered the 4822 rule. 4824 o A type 2 routing header MUST be included with the mobile node's 4825 home address. 4827 o IPsec headers MUST be supported and SHOULD be used. 4829 o The home agent MUST send the packet as it would any other unicast 4830 IPv6 packet that it originates. 4832 o Set the Managed Address Configuration (M) flag if the 4833 corresponding flag has been set in any of the Router 4834 Advertisements from which the prefix information has been learned 4835 (including the ones sent by this home agent). 4837 o Set the Other Stateful Configuration (O) flag if the corresponding 4838 flag has been set in any of the Router Advertisements from which 4839 the prefix information has been learned (including the ones sent 4840 by this home agent). 4842 10.6.4 Lifetimes for Changed Prefixes 4844 As described in Section 10.3.1, the lifetime returned by the home 4845 agent in a Binding Acknowledgement MUST be no greater than the 4846 remaining valid lifetime for the subnet prefix in the mobile node's 4847 home address. This limit on the binding lifetime serves to prohibit 4848 use of a mobile node's home address after it becomes invalid. 4850 11. Mobile Node Operation 4852 11.1 Conceptual Data Structures 4854 Each mobile node MUST maintain a Binding Update List. 4856 The Binding Update List records information for each Binding Update 4857 sent by this mobile node, for which the lifetime of the binding has 4858 not yet expired. The Binding Update List includes all bindings sent 4859 by the mobile node either to its home agent or correspondent nodes. 4860 It also contains Binding Updates which are waiting for the completion 4861 of the return routability procedure before they can be sent. 4862 However, for multiple Binding Updates sent to the same destination 4863 address, the Binding Update List contains only the most recent 4864 Binding Update (i.e., with the greatest Sequence Number value) sent 4865 to that destination. The Binding Update List MAY be implemented in 4866 any manner consistent with the external behavior described in this 4867 document. 4869 Each Binding Update List entry conceptually contains the following 4870 fields: 4872 o The IP address of the node to which a Binding Update was sent. 4874 o The home address for which that Binding Update was sent. 4876 o The care-of address sent in that Binding Update. This value is 4877 necessary for the mobile node to determine if it has sent a 4878 Binding Update giving its new care-of address to this destination 4879 after changing its care-of address. 4881 o The initial value of the Lifetime field sent in that Binding 4882 Update. 4884 o The remaining lifetime of that binding. This lifetime is 4885 initialized from the Lifetime value sent in the Binding Update and 4886 is decremented until it reaches zero, at which time this entry 4887 MUST be deleted from the Binding Update List. 4889 o The maximum value of the Sequence Number field sent in previous 4890 Binding Updates to this destination. The Sequence Number field is 4891 16 bits long, and all comparisons between Sequence Number values 4892 MUST be performed modulo 2**16 (see Section 9.5.1). 4894 o The time at which a Binding Update was last sent to this 4895 destination, as needed to implement the rate limiting restriction 4896 for sending Binding Updates. 4898 o The state of any retransmissions needed for this Binding Update. 4899 This state includes the time remaining until the next 4900 retransmission attempt for the Binding Update, and the current 4901 state of the exponential back-off mechanism for retransmissions. 4903 o A flag specifying whether or not future Binding Updates should be 4904 sent to this destination. The mobile node sets this flag in the 4905 Binding Update List entry when it receives an ICMP Parameter 4906 Problem, Code 1, error message in response to a return routability 4907 message or Binding Update sent to that destination, as described 4908 in Section 11.3.5. 4910 The Binding Update List is used to determine whether a particular 4911 packet is sent directly to the correspondent node or tunneled via the 4912 home agent (see Section 11.3.1). 4914 The Binding Update list also conceptually contains the following data 4915 related to running the return routability procedure. This data is 4916 relevant only for Binding Updates sent to correspondent nodes. 4918 o The time at which a Home Test Init or Care-of Test Init message 4919 was last sent to this destination, as needed to implement the rate 4920 limiting restriction for the return routability procedure. 4922 o The state of any retransmissions needed for this return 4923 routability procedure. This state includes the time remaining 4924 until the next retransmission attempt and the current state of the 4925 exponential back-off mechanism for retransmissions. 4927 o Cookie values used in the Home Test Init and Care-of Test Init 4928 messages. 4930 o Home and care-of keygen tokens received from the correspondent 4931 node. 4933 o Home and care-of nonce indices received from the correspondent 4934 node. 4936 o The time at which each of the tokens and nonces was received from 4937 this correspondent node, as needed to implement reuse while 4938 moving. 4940 11.2 Processing Mobility Headers 4942 All IPv6 mobile nodes MUST observe the rules described in Section 9.2 4943 when processing Mobility Headers. 4945 11.3 Packet Processing 4947 11.3.1 Sending Packets While Away from Home 4949 While a mobile node is away from home, it continues to use its home 4950 address, as well as also using one or more care-of addresses. When 4951 sending a packet while away from home, a mobile node MAY choose among 4952 these in selecting the address that it will use as the source of the 4953 packet, as follows: 4955 o Protocols layered over IP will generally treat the mobile node's 4956 home address as its IP address for most packets. For packets sent 4957 that are part of transport-level connections established while the 4958 mobile node was at home, the mobile node MUST use its home 4959 address. Likewise, for packets sent that are part of 4960 transport-level connections that the mobile node may still be 4961 using after moving to a new location, the mobile node SHOULD use 4962 its home address in this way. If a binding exists, the mobile 4963 node SHOULD send the packets directly to the correspondent node. 4964 Otherwise, if a binding does not exist, the mobile node MUST use 4965 reverse tunneling. 4967 o The mobile node MAY choose to directly use one of its care-of 4968 addresses as the source of the packet, not requiring the use of a 4969 Home Address option in the packet. This is particularly useful 4970 for short-term communication that may easily be retried if it 4971 fails. Using the mobile node's care-of address as the source for 4972 such queries will generally have a lower overhead than using the 4973 mobile node's home address, since no extra options need be used in 4974 either the query or its reply. Such packets can be routed 4975 normally, directly between their source and destination without 4976 relying on Mobile IPv6. If application running on the mobile node 4977 has no particular knowledge that the communication being sent fits 4978 within this general type of communication, however, the mobile 4979 node should not use its care-of address as the source of the 4980 packet in this way. 4982 The choice of the most efficient communications method is 4983 application specific, and outside the scope of this specification. 4984 The APIs necessary for controlling the choice are also out of 4985 scope. 4987 o While not at its home link, the mobile node MUST NOT use the Home 4988 Address destination option when communicating with link-local or 4989 site-local peers, if the scope of the home address is larger than 4990 the scope of the peer's address. 4992 Similarly, the mobile node MUST NOT use the Home Address 4993 destination option for IPv6 Neighbor Discovery [12] packets. 4995 Detailed operation of these cases is described later in this section 4996 and also discussed in [31]. 4998 For packets sent by a mobile node while it is at home, no special 4999 Mobile IPv6 processing is required. Likewise, if the mobile node 5000 uses any address other than any of its home addresses as the source 5001 of a packet sent while away from home no special Mobile IPv6 5002 processing is required. In either case, the packet is simply 5003 addressed and transmitted in the same way as any normal IPv6 packet. 5005 For packets sent by the mobile node sent while away from home using 5006 the mobile node's home address as the source, special Mobile IPv6 5007 processing of the packet is required. This can be done in the 5008 following two ways: 5010 Route Optimization 5012 This manner of delivering packets does not require going through 5013 the home network, and typically will enable faster and more 5014 reliable transmission. 5016 The mobile node needs to ensure that there exists a Binding Cache 5017 entry for its home address so that the correspondent node can 5018 process the packet (Section 9.3.1 specifies the rules for Home 5019 Address Destination Option Processing at a correspondent node). 5020 The mobile node SHOULD examine its Binding Update List for an 5021 entry which fulfills the following conditions: 5023 * The Source Address field of the packet being sent is equal to 5024 the home address in the entry. 5026 * The Destination Address field of the packet being sent is equal 5027 to the address of the correspondent node in the entry. 5029 * One of the current care-of addresses of the mobile node appears 5030 as the care-of address in the entry. 5032 * The entry indicates that a binding has been successfully 5033 created. 5035 * The remaining lifetime of the binding is greater than zero. 5037 When these conditions are met, the mobile node knows that the 5038 correspondent node has a suitable Binding Cache entry. 5040 A mobile node SHOULD arrange to supply the home address in a Home 5041 Address option, and MUST set the IPv6 header's Source Address 5042 field to the care-of address which the mobile node has registered 5043 to be used with this correspondent node. The correspondent node 5044 will then use the address supplied in the Home Address option to 5045 serve the function traditionally done by the Source IP address in 5046 the IPv6 header. The mobile node's home address is then supplied 5047 to higher protocol layers and applications. 5049 Specifically: 5051 * Construct the packet using the mobile node's home address as 5052 the packet's Source Address, in the same way as if the mobile 5053 node were at home. This includes the calculation of upper 5054 layer checksums using the home address as the value of the 5055 source. 5057 * Insert a Home Address option into the packet, with the Home 5058 Address field copied from the original value of the Source 5059 Address field in the packet. 5061 * Change the Source Address field in the packet's IPv6 header to 5062 one of the mobile node's care-of addresses. This will 5063 typically be the mobile node's current primary care-of address, 5064 but MUST be an address assigned to the interface on the link 5065 being used. 5067 By using the care-of address as the Source Address in the IPv6 5068 header, with the mobile node's home address instead in the Home 5069 Address option, the packet will be able to safely pass through any 5070 router implementing ingress filtering [26]. 5072 Reverse Tunneling 5074 This is the mechanism which tunnels the packets via the home 5075 agent. It is not as efficient as the above mechanism, but is 5076 needed if there is no binding yet with the correspondent node. 5078 This mechanism is used for packets that have the mobile node's 5079 home address as the Source Address in the IPv6 header, or with 5080 multicast control protocol packets as described in Section 11.3.4. 5081 Specifically: 5083 * The packet is sent to the home agent using IPv6 encapsulation 5084 [15]. 5086 * The Source Address in the tunnel packet is the primary care-of 5087 address as registered with the home agent. 5089 * The Destination Address in the tunnel packet is the home 5090 agent's address. 5092 Then, the home agent will pass the encapsulated packet to the 5093 correspondent node. 5095 11.3.2 Interaction with Outbound IPsec Processing 5097 This section sketches the interaction between outbound Mobile IPv6 5098 processing and outbound IP Security (IPsec) processing for packets 5099 sent by a mobile node while away from home. Any specific 5100 implementation MAY use algorithms and data structures other than 5101 those suggested here, but its processing MUST be consistent with the 5102 effect of the operation described here and with the relevant IPsec 5103 specifications. In the steps described below, it is assumed that 5104 IPsec is being used in transport mode [4] and that the mobile node is 5105 using its home address as the source for the packet (from the point 5106 of view of higher protocol layers or applications, as described in 5107 Section 11.3.1): 5109 o The packet is created by higher layer protocols and applications 5110 (e.g., by TCP) as if the mobile node were at home and Mobile IPv6 5111 were not being used. 5113 o Determine the outgoing interface for the packet. (Note that the 5114 selection between reverse tunneling and route optimization may 5115 imply different interfaces, particularly if tunnels are considered 5116 interfaces as well.) 5118 o As part of outbound packet processing in IP, the packet is 5119 compared against the IPsec security policy database to determine 5120 what processing is required for the packet [4]. 5122 o If IPsec processing is required, the packet is either mapped to an 5123 existing Security Association (or SA bundle), or a new SA (or SA 5124 bundle) is created for the packet, according to the procedures 5125 defined for IPsec. 5127 o Since the mobile node is away from home, the mobile is either 5128 using reverse tunneling or route optimization to reach the 5129 correspondent node. 5131 If reverse tunneling is used, the packet is constructed in the 5132 normal manner and then tunneled through the home agent. 5134 If route optimization is in use, the mobile node inserts a Home 5135 Address destination option into the packet, replacing the Source 5136 Address in the packet's IP header with the care-of address used 5137 with this correspondent node, as described in Section 11.3.1. The 5138 Destination Options header in which the Home Address destination 5139 option is inserted MUST appear in the packet after the routing 5140 header, if present, and before the IPsec (AH [5] or ESP [6]) 5141 header, so that the Home Address destination option is processed 5142 by the destination node before the IPsec header is processed. 5144 Finally, once the packet is fully assembled, the necessary IPsec 5145 authentication (and encryption, if required) processing is 5146 performed on the packet, initializing the Authentication Data in 5147 the IPsec header. 5149 RFC 2402 treatment of destination options is extended as follows. 5150 The AH authentication data MUST be calculated as if the following 5151 were true: 5153 * the IPv6 source address in the IPv6 header contains the mobile 5154 node's home address, 5156 * the Home Address field of the Home Address destination option 5157 (Section 6.3) contains the new care-of address. 5159 o This allows, but does not require, the receiver of the packet 5160 containing a Home Address destination option to exchange the two 5161 fields of the incoming packet to reach the above situation, 5162 simplifying processing for all subsequent packet headers. 5163 However, such an exchange is not required, as long as the result 5164 of the authentication calculation remains the same. 5166 When an automated key management protocol is used to create new 5167 security associations for a peer, it is important to ensure that the 5168 peer can send the key management protocol packets to the mobile node. 5169 This may not be possible if the peer is the home agent of the mobile 5170 node, and the purpose of the security associations would be to send a 5171 Binding Update to the home agent. Packets addressed to the home 5172 address of the mobile node cannot be used before the Binding Update 5173 has been processed. For the default case of using IKE [9] as the 5174 automated key management protocol, such problems can be avoided by 5175 the following requirements when communicating with its home agent: 5177 o When the mobile node is away from home, it MUST use its care-of 5178 address as the Source Address of all packets it sends as part of 5179 the key management protocol (without use of Mobile IPv6 for these 5180 packets, as suggested in Section 11.3.1). 5182 o In addition, for all security associations bound to the mobile 5183 node's home address established by IKE, the mobile node MUST 5184 include an ISAKMP Identification Payload [8] in the IKE exchange, 5185 giving the mobile node's home address as the initiator of the 5186 Security Association [7]. 5188 The Key Management Mobility Capability (K) bit in Binding Updates and 5189 Acknowledgements can be used avoid the need to rerun IKE upon 5190 movements. 5192 11.3.3 Receiving Packets While Away from Home 5194 While away from home, a mobile node will receive packets addressed to 5195 its home address, by one of two methods: 5197 o Packets sent by a correspondent node that does not have a Binding 5198 Cache entry for the mobile node, will be sent to the home address, 5199 captured by the home agent and tunneled to the mobile node 5201 o Packets sent by a correspondent node that has a Binding Cache 5202 entry for the mobile node that contains the mobile node's current 5203 care-of address, will be sent by the correspondent node using a 5204 type 2 routing header. The packet will be addressed to the mobile 5205 node's care-of address, with the final hop in the routing header 5206 directing the packet to the mobile node's home address; the 5207 processing of this last hop of the routing header is entirely 5208 internal to the mobile node, since the care-of address and home 5209 address are both addresses within the mobile node. 5211 For packets received by the first method, the mobile node MUST check 5212 that the IPv6 source address of the tunneled packet is the IP address 5213 of its home agent. In this method the mobile node may also send a 5214 Binding Update to the original sender of the packet, as described in 5215 Section 11.7.2, subject to the rate limiting defined in Section 11.8. 5216 The mobile node MUST also process the received packet in the manner 5217 defined for IPv6 encapsulation [15], which will result in the 5218 encapsulated (inner) packet being processed normally by upper-layer 5219 protocols within the mobile node, as if it had been addressed (only) 5220 to the mobile node's home address. 5222 For packets received by the second method, the following rules will 5223 result in the packet being processed normally by upper-layer 5224 protocols within the mobile node, as if it had been addressed to the 5225 mobile node's home address. 5227 A node receiving a packet addressed to itself (i.e., one of the 5228 node's addresses is in the IPv6 destination field) follows the next 5229 header chain of headers and processes them. When it encounters a 5230 type 2 routing header during this processing it performs the 5231 following checks. If any of these checks fail the node MUST silently 5232 discard the packet. 5234 o The length field in the routing header is exactly 2. 5236 o The segments left field in the routing header is 1 on the wire. 5237 (But implementations may process the routing header so that the 5238 value may become 0 after the routing header has been processed, 5239 but before the rest of the packet is processed.) 5241 o The Home Address field in the routing header is one of the node's 5242 home addresses, if the segments left field was 1. Thus, in 5243 particular the address field is required to be a unicast routable 5244 address. 5246 Once the above checks have been performed, the node swaps the IPv6 5247 destination field with the Home Address field in the routing header, 5248 decrements segments left by one from the value it had on the wire, 5249 and resubmits the packet to IP for processing the next header. 5250 Conceptually this follows the same model as in RFC 2460. However, in 5251 the case of type 2 routing header this can be simplified since it is 5252 known that the packet will not be forwarded to a different node. 5254 The definition of AH requires the sender to calculate the AH 5255 integrity check value of a routing header in a way as it appears in 5256 the receiver after it has processed the header. Since IPsec headers 5257 follow the routing header, any IPsec processing will operate on the 5258 packet with the home address in the IP destination field and segments 5259 left being zero. Thus, the AH calculations at the sender and 5260 receiver will have an identical view of the packet. 5262 11.3.4 Routing Multicast Packets 5264 A mobile node that is connected to its home link functions in the 5265 same way as any other (stationary) node. Thus, when it is at home, a 5266 mobile node functions identically to other multicast senders and 5267 receivers. This section therefore describes the behavior of a mobile 5268 node that is not on its home link. 5270 In order to receive packets sent to some multicast group, a mobile 5271 node must join that multicast group. One method by which a mobile 5272 node MAY join the group is via a (local) multicast router on the 5273 foreign link being visited. In this case, the mobile node MUST use 5274 its care-of address and MUST NOT use the Home Address destination 5275 option when sending MLD packets [17]. 5277 Alternatively, a mobile node MAY join multicast groups via a 5278 bi-directional tunnel to its home agent. The mobile node tunnels its 5279 multicast group membership control packets (such as those defined in 5280 [17] or in [37]) to its home agent, and the home agent forwards 5281 multicast packets down the tunnel to the mobile node. A mobile node 5282 MUST NOT tunnel multicast group membership control packets until (1) 5283 the mobile node has a binding in place at the home agent, and (2) the 5284 latter sends at least one such multicast group membership control 5285 packet via the tunnel. Once this condition is true, the mobile node 5286 SHOULD assume it does not change as long as the binding does not 5287 expire. 5289 A mobile node that wishes to send packets to a multicast group also 5290 has two options: 5292 1. Send directly on the foreign link being visited. 5294 The application is aware of the care-of address and uses it as a 5295 source address for multicast traffic, just like it would use a 5296 stationary address. The mobile node MUST NOT use Home Address 5297 destination option in such traffic. 5299 2. Send via a tunnel to its home agent. 5301 Because multicast routing in general depends upon the Source 5302 Address used in the IPv6 header of the multicast packet, a mobile 5303 node that tunnels a multicast packet to its home agent MUST use 5304 its home address as the IPv6 Source Address of the inner 5305 multicast packet. 5307 Note that direct sending from the foreign link is only applicable 5308 while the mobile node is at that foreign link. This is because the 5309 associated multicast tree is specific to that source location and any 5310 change of location and source address will invalidate the source 5311 specific tree or branch and the application context of the other 5312 multicast group members. 5314 This specification does not provide mechanisms to enable such local 5315 multicast session to survive hand-off, and to seamlessly continue 5316 from a new care-of address on each new foreign link. Any such 5317 mechanism, developed as an extension to this specification, needs to 5318 take into account the impact of fast moving mobile nodes on the 5319 Internet multicast routing protocols and their ability to maintain 5320 the integrity of source specific multicast trees and branches. 5322 While the use of bidirectional tunneling can ensure that multicast 5323 trees are independent of the mobile nodes movement, in some case such 5324 tunneling can have adverse affects. The latency of specific types of 5325 multicast applications such as multicast based discovery protocols 5326 will be affected when the round-trip time between the foreign subnet 5327 and the home agent is significant compared to that of the topology to 5328 be discovered. In addition, the delivery tree from the home agent in 5329 such circumstances relies on unicast encapsulation from the agent to 5330 the mobile node and is therefore bandwidth inefficient compared to 5331 the native multicast forwarding in the foreign multicast system. 5333 11.3.5 Receiving ICMP Error Messages 5335 Any node that does not recognize the Mobility header will return an 5336 ICMP Parameter Problem, Code 1, message to the sender of the packet. 5337 If the mobile node receives such an ICMP error message in response to 5338 a return routability procedure or Binding Update, it SHOULD record in 5339 its Binding Update List that future Binding Updates SHOULD NOT be 5340 sent to this destination. Such Binding Update List entries SHOULD be 5341 removed after a period of time, in order to allow for retrying route 5342 optimization. 5344 New Binding Update List entries MUST NOT be created as a result of 5345 receiving ICMP error messages. 5347 Correspondent nodes that have participated in the return routability 5348 procedure MUST implement the ability to correctly process received 5349 packets containing a Home Address destination option. Therefore, 5350 correctly implemented correspondent nodes should always be able to 5351 recognize Home Address options. If a mobile node receives an ICMP 5352 Parameter Problem, Code 2, message from some node indicating that it 5353 does not support the Home Address option, the mobile node SHOULD log 5354 the error and then discard the ICMP message. 5356 11.3.6 Receiving Binding Error Messages 5358 When a mobile node receives a packet containing a Binding Error 5359 message, it should first check if the mobile node has a Binding 5360 Update List entry for the source of the Binding Error message. If 5361 the mobile node does not have such an entry, it MUST ignore the 5362 message. This is necessary to prevent a waste of resources on e.g. 5363 return routability procedure due to spoofed Binding Error messages. 5365 Otherwise, if the message Status field was 1 (unknown binding for 5366 Home Address destination option), the mobile node should perform one 5367 of the following two actions: 5369 o If the mobile node has recent upper layer progress information 5370 that indicates communications with the correspondent node are 5371 progressing, it MAY ignore the message. This can be done in order 5372 to limit the damage that spoofed Binding Error messages can cause 5373 to ongoing communications. 5375 o If the mobile node has no upper layer progress information, it 5376 MUST remove the entry and route further communications through the 5377 home agent. It MAY also optionally start a return routability 5378 procedure (see Section 5.2). 5380 If the message Status field was 2 (unrecognized MH Type value), the 5381 mobile node should perform one of the following two actions: 5383 o If the mobile node is not expecting an acknowledgement or response 5384 from the correspondent node, the mobile node SHOULD ignore this 5385 message. 5387 o Otherwise, the mobile node SHOULD cease the use of any extensions 5388 to this specification. If no extensions had been used, the mobile 5389 node should cease the attempt to use route optimization. 5391 11.4 Home Agent and Prefix Management 5393 11.4.1 Dynamic Home Agent Address Discovery 5395 Sometimes, when the mobile node needs to send a Binding Update to its 5396 home agent to register its new primary care-of address, as described 5397 in Section 11.7.1, the mobile node may not know the address of any 5398 router on its home link that can serve as a home agent for it. For 5399 example, some nodes on its home link may have been reconfigured while 5400 the mobile node has been away from home, such that the router that 5401 was operating as the mobile node's home agent has been replaced by a 5402 different router serving this role. 5404 In this case, the mobile node MAY attempt to discover the address of 5405 a suitable home agent on its home link. To do so, the mobile node 5406 sends an ICMP Home Agent Address Discovery Request message to the 5407 Mobile IPv6 Home-Agents anycast address [16] for its home subnet 5408 prefix. As described in Section 10.5, the home agent on its home 5409 link that receives this Request message will return an ICMP Home 5410 Agent Address Discovery Reply message. This message gives the 5411 addresses for the home agents operating on the home link. 5413 The mobile node, upon receiving this Home Agent Address Discovery 5414 Reply message, MAY then send its home registration Binding Update to 5415 any of the unicast IP addresses listed in the Home Agent Addresses 5416 field in the Reply. For example, the mobile node MAY attempt its 5417 home registration to each of these addresses, in turn, until its 5418 registration is accepted. The mobile node sends a Binding Update to 5419 an address and waits for the matching Binding Acknowledgement, moving 5420 on to the next address if there is no response. The mobile node 5421 MUST, however, wait at least InitialBindackTimeoutFirstReg seconds 5422 (see Section 13) before sending a Binding Update to the next home 5423 agent. In trying each of the returned home agent addresses, the 5424 mobile node SHOULD try each in the order listed in the Home Agent 5425 Addresses field in the received Home Agent Address Discovery Reply 5426 message. 5428 If the mobile node has a current registration with some home agent 5429 (the Lifetime for that registration has not yet expired), then the 5430 mobile node MUST attempt any new registration first with that home 5431 agent. If that registration attempt fails (e.g., times out or is 5432 rejected), the mobile node SHOULD then reattempt this registration 5433 with another home agent. If the mobile node knows of no other 5434 suitable home agent, then it MAY attempt the dynamic home agent 5435 address discovery mechanism described above. 5437 If, after a mobile node transmits a Home Agent Address Discovery 5438 Request message to the Home Agents Anycast address, it does not 5439 receive a corresponding Home Agent Address Discovery Reply message 5440 within INITIAL_DHAAD_TIMEOUT (see Section 12) seconds, the mobile 5441 node MAY retransmit the same Request message to the same anycast 5442 address. This retransmission MAY be repeated up to a maximum of 5443 DHAAD_RETRIES (see Section 12) attempts. Each retransmission MUST be 5444 delayed by twice the time interval of the previous retransmission. 5446 11.4.2 Sending Mobile Prefix Solicitations 5448 When a mobile node has a home address that is about to become 5449 invalid, it SHOULD send a Mobile Prefix Solicitation to its home 5450 agent in an attempt to acquire fresh routing prefix information. The 5451 new information also enables the mobile node to participate in 5452 renumbering operations affecting the home network, as described in 5453 Section 10.6. 5455 The mobile node MUST use the Home Address destination option to carry 5456 its home address. The mobile node MUST support and SHOULD use IPsec 5457 to protect the solicitation. The mobile node MUST set the Identifier 5458 field in the ICMP header to a random value. 5460 As described in Section 11.7.2, Binding Updates sent by the mobile 5461 node to other nodes MUST use a lifetime no greater than the remaining 5462 lifetime of its home registration of its primary care-of address. 5463 The mobile node SHOULD further limit the lifetimes that it sends on 5464 any Binding Updates to be within the remaining valid lifetime (see 5465 Section 10.6.2) for the prefix in its home address. 5467 When the lifetime for a changed prefix decreases, and the change 5468 would cause cached bindings at correspondent nodes in the Binding 5469 Update List to be stored past the newly shortened lifetime, the 5470 mobile node MUST issue a Binding Update to all such correspondent 5471 nodes. 5473 These limits on the binding lifetime serve to prohibit use of a 5474 mobile node's home address after it becomes invalid. 5476 11.4.3 Receiving Mobile Prefix Advertisements 5478 Section 10.6 describes the operation of a home agent to support boot 5479 time configuration and renumbering a mobile node's home subnet while 5480 the mobile node is away from home. The home agent sends Mobile 5481 Prefix Advertisements to the mobile node while away from home, giving 5482 "important" Prefix Information options that describe changes in the 5483 prefixes in use on the mobile node's home link. 5485 The Mobile Prefix Solicitation is similar to the Router Solicitation 5486 used in Neighbor Discovery [12], except it is routed from the mobile 5487 node on the visited network to the home agent on the home network by 5488 usual unicast routing rules. 5490 When a mobile node receives a Mobile Prefix Advertisement, it MUST 5491 validate it according to the following test: 5493 o The Source Address of the IP packet carrying the Mobile Prefix 5494 Advertisement is the same as the home agent address to which the 5495 mobile node last sent an accepted home registration Binding Update 5496 to register its primary care-of address. Otherwise, if no such 5497 registrations have been made, it SHOULD be the mobile node's 5498 stored home agent address, if one exists. Otherwise, if the 5499 mobile node has not yet discovered its home agent's address, it 5500 MUST NOT accept Mobile Prefix Advertisements. 5502 o The packet MUST have a type 2 routing header and SHOULD be 5503 protected by an IPsec header as described in Section 5.4 and 5504 Section 6.8. 5506 o If the ICMP Identifier value matches the ICMP Identifier value of 5507 the most recently sent Mobile Prefix Solicitation and no other 5508 advertisement has yet been received for this value, then the 5509 advertisement is considered to be solicited and will be processed 5510 further. 5512 Otherwise, the advertisement is unsolicited, and MUST be silently 5513 discarded. In this case the mobile node SHOULD send a Mobile 5514 Prefix Solicitation. 5516 Any received Mobile Prefix Advertisement not meeting these tests MUST 5517 be silently discarded. 5519 For an accepted Mobile Prefix Advertisement, the mobile node MUST 5520 process Managed Address Configuration (M), Other Stateful 5521 Configuration (O), and the Prefix Information Options as if they 5522 arrived in a Router Advertisement [12] on the mobile node's home 5523 link. (This specification does not, however, describe how to acquire 5524 home addresses through stateful protocols.) Such processing may 5525 result in the mobile node configuring a new home address, although 5526 due to separation between preferred lifetime and valid lifetime, such 5527 changes should not affect most communications by the mobile node, in 5528 the same way as for nodes that are at home. 5530 This specification assumes that any security associations and 5531 security policy entries that may be needed for new prefixes have been 5532 pre-configured in the mobile node. Note that while dynamic key 5533 management avoids the need to create new security associations, it is 5534 still necessary to add policy entries to protect the communications 5535 involving the home address(es). Mechanisms for automatic set-up of 5536 these entries are outside the scope of this specification. 5538 11.5 Movement 5540 11.5.1 Movement Detection 5542 The primary goal of movement detection is to detect L3 handovers. 5543 This section does not attempt to specify a fast movement detection 5544 algorithm which will function optimally for all types of 5545 applications, link-layers and deployment scenarios; instead, it 5546 describes a generic method that uses the facilities of IPv6 Neighbor 5547 Discovery, including Router Discovery and Neighbor Unreachability 5548 Detection. At the time of this writing, this method is considered 5549 well enough understood to recommend for standardization, however it 5550 is expected that future versions of this specification or other 5551 specifications may contain updated versions of the movement detection 5552 algorithm that have better performance. 5554 Generic movement detection uses Neighbor Unreachability Detection to 5555 detect when the default router is no longer bi-directionally 5556 reachable, in which case the mobile node must discover a new default 5557 router (usually on a new link). However, this detection only occurs 5558 when the mobile node has packets to send, and in the absence of 5559 frequent Router Advertisements or indications from the link-layer, 5560 the mobile node might become unaware of an L3 handover that occurred. 5561 Therefore, the mobile node should supplement this method with other 5562 information whenever it is available to the mobile node (e.g., from 5563 lower protocol layers). 5565 When the mobile node detects an L3 handover, it performs Duplicate 5566 Address Detection [13] on its link-local address, selects a new 5567 default router as a consequence of Router Discovery, and then 5568 performs Prefix Discovery with that new router to form new care-of 5569 address(es) as described in Section 11.5.2. It then registers its 5570 new primary care-of address with its home agent as described in 5571 Section 11.7.1. After updating its home registration, the mobile 5572 node then updates associated mobility bindings in correspondent nodes 5573 that it is performing route optimization with as specified in Section 5574 11.7.2. 5576 Due to the temporary packet flow disruption and signaling overhead 5577 involved in updating mobility bindings, the mobile node should avoid 5578 performing an L3 handover until it is strictly necessary. 5579 Specifically, when the mobile node receives a Router Advertisement 5580 from a new router that contains a different set of on-link prefixes, 5581 if the mobile node detects that the currently selected default router 5582 on the old link is still bi-directionally reachable, it should 5583 generally continue to use the old router on the old link rather than 5584 switch away from it to use a new default router. 5586 Mobile nodes can use the information in received Router 5587 Advertisements to detect L3 handovers. In doing so the mobile node 5588 needs to consider the following issues: 5590 o There might be multiple routers on the same link, thus hearing a 5591 new router does not necessarily constitute an L3 handover. 5593 o When there are multiple routers on the same link they might 5594 advertise different prefixes. Thus even hearing a new router with 5595 a new prefix might not be a reliable indication of an L3 handover. 5597 o The link-local addresses of routers are not globally unique, hence 5598 after completing an L3 handover the mobile node might continue to 5599 receive Router Advertisements with the same link-local source 5600 address. This might be common if routers use the same link-local 5601 address on multiple interfaces. This issue can be avoided when 5602 routers use the Router Address (R) bit, since that provides a 5603 global address of the router. 5605 In addition, the mobile node should consider the following events as 5606 indications that an L3 handover may have occurred. Upon receiving 5607 such indications, the mobile node needs to perform Router Discovery 5608 to discover routers and prefixes on the new link, as described in 5609 Section 6.3.7 of RFC 2461 [12]. 5611 o If Router Advertisements that the mobile node receives include an 5612 Advertisement Interval option, the mobile node may use its 5613 Advertisement Interval field as an indication of the frequency 5614 with which it should expect to continue to receive future 5615 Advertisements from that router. This field specifies the minimum 5616 rate (the maximum amount of time between successive 5617 Advertisements) that the mobile node should expect. If this 5618 amount of time elapses without the mobile node receiving any 5619 Advertisement from this router, the mobile node can be sure that 5620 at least one Advertisement sent by the router has been lost. The 5621 mobile node can then implement its own policy to determine how 5622 many lost Advertisements from its current default router 5623 constitute an L3 handover indication. 5625 o Neighbor Unreachability Detection determines that the default 5626 router is no longer reachable. 5628 o With some types of networks, notification that an L2 handover has 5629 occurred might be obtained from lower layer protocols or device 5630 driver software within the mobile node. While further details 5631 around handling L2 indications as movement hints is an item for 5632 further study, at the time of writing this specification the 5633 following is considered reasonable: 5635 An L2 handover indication may or may not imply L2 movement and L2 5636 movement may or may not imply L3 movement; the correlations might 5637 be a function of the type of L2 but might also be a function of 5638 actual deployment of the wireless topology. 5640 Unless it is well-known that an L2 handover indication is likely 5641 to imply L3 movement, instead of immediately multicasting a router 5642 solicitation it may be better to attempt to verify whether the 5643 default router is still bi-directionally reachable. This can be 5644 accomplished by sending a unicast Neighbor Solicitation and 5645 waiting for a Neighbor Advertisement with the solicited flag set. 5646 Note that this is similar to Neighbor Unreachability detection but 5647 it does not have the same state machine, such as the STALE state. 5649 If the default router does not respond to the Neighbor 5650 Solicitation it makes sense to proceed to multicasting a Router 5651 Solicitation. 5653 11.5.2 Forming New Care-of Addresses 5655 After detecting that it has moved a mobile node SHOULD generate a new 5656 primary care-of address using normal IPv6 mechanisms. This SHOULD 5657 also be done when the current primary care-of address becomes 5658 deprecated. A mobile node MAY form a new primary care-of address at 5659 any time, but a mobile node MUST NOT send a Binding Update about a 5660 new care-of address to its home agent more than MAX_UPDATE_RATE times 5661 within a second. 5663 In addition, a mobile node MAY form new non-primary care-of addresses 5664 even when it has not switched to a new default router. A mobile node 5665 can have only one primary care-of address at a time (which is 5666 registered with its home agent), but it MAY have an additional 5667 care-of address for any or all of the prefixes on its current link. 5668 Furthermore, since a wireless network interface may actually allow a 5669 mobile node to be reachable on more than one link at a time (i.e., 5670 within wireless transmitter range of routers on more than one 5671 separate link), a mobile node MAY have care-of addresses on more than 5672 one link at a time. The use of more than one care-of address at a 5673 time is described in Section 11.5.3. 5675 As described in Section 4, in order to form a new care-of address, a 5676 mobile node MAY use either stateless [13] or stateful (e.g., DHCPv6 5677 [29]) Address Autoconfiguration. If a mobile node needs to use a 5678 source address (other than the unspecified address) in packets sent 5679 as a part of address autoconfiguration, it MUST use an IPv6 5680 link-local address rather than its own IPv6 home address. 5682 RFC 2462 [13] specifies that in normal processing for Duplicate 5683 Address Detection, the node SHOULD delay sending the initial Neighbor 5684 Solicitation message by a random delay between 0 and 5685 MAX_RTR_SOLICITATION_DELAY. Since delaying DAD can result in 5686 significant delays in configuring a new care-of address when the 5687 Mobile Node moves to a new link, the Mobile Node preferably SHOULD 5688 NOT delay DAD when configuring a new care-of address. The Mobile 5689 Node SHOULD delay according to the mechanisms specified in RFC 2462 5690 unless the implementation has a behavior that desynchronizes the 5691 steps that happen before the DAD in the case that multiple nodes 5692 experience handover at the same time. Such desynchronizing behaviors 5693 might be due to random delays in the L2 protocols or device drivers, 5694 or due to the movement detection mechanism that is used. 5696 11.5.3 Using Multiple Care-of Addresses 5698 As described in Section 11.5.2, a mobile node MAY use more than one 5699 care-of address at a time. Particularly in the case of many wireless 5700 networks, a mobile node effectively might be reachable through 5701 multiple links at the same time (e.g., with overlapping wireless 5702 cells), on which different on-link subnet prefixes may exist. The 5703 mobile node MUST ensure that its primary care-of address always has a 5704 prefix that is considered on-link by its current default router, 5705 i.e., advertised by its current default router in a solicited Router 5706 Advertisement. After selecting a new primary care-of address, the 5707 mobile node MUST send a Binding Update containing that care-of 5708 address to its home agent. The Binding Update MUST have the Home 5709 Registration (H) and Acknowledge (A) bits set its home agent, as 5710 described on Section 11.7.1. 5712 To assist with smooth handovers, a mobile node SHOULD retain its 5713 previous primary care-of address as a (non-primary) care-of address, 5714 and SHOULD still accept packets at this address, even after 5715 registering its new primary care-of address with its home agent. 5716 This is reasonable, since the mobile node could only receive packets 5717 at its previous primary care-of address if it were indeed still 5718 connected to that link. If the previous primary care-of address was 5719 allocated using stateful Address Autoconfiguration [29], the mobile 5720 node may not wish to release the address immediately upon switching 5721 to a new primary care-of address. 5723 Whenever a mobile node determines that it is no longer reachable 5724 through a given link, it SHOULD invalidate all care-of addresses 5725 associated with address prefixes that it discovered from routers on 5726 the unreachable link which are not in the current set of address 5727 prefixes advertised by the (possibly new) current default router. 5729 11.5.4 Returning Home 5731 A mobile node detects that it has returned to its home link through 5732 the movement detection algorithm in use (Section 11.5.1), when the 5733 mobile node detects that its home subnet prefix is again on-link. 5734 The mobile node SHOULD then send a Binding Update to its home agent, 5735 to instruct its home agent to no longer intercept or tunnel packets 5736 for it. In this home registration, the mobile node MUST set the 5737 Acknowledge (A) and Home Registration (H) bits, set the Lifetime 5738 field to zero, and set the care-of address for the binding to the 5739 mobile node's own home address. The mobile node MUST use its home 5740 address as the source address in the Binding Update. 5742 When sending this Binding Update to its home agent, the mobile node 5743 must be careful in how it uses Neighbor Solicitation [12] (if needed) 5744 to learn the home agent's link-layer address, since the home agent 5745 will be currently configured to intercept packets to the mobile 5746 node's home address using Duplicate Address Detection (DAD). In 5747 particular, the mobile node is unable to use its home address as the 5748 Source Address in the Neighbor Solicitation until the home agent 5749 stops defending the home address. 5751 Neighbor Solicitation by the mobile node for the home agent's address 5752 will normally not be necessary, since the mobile node has already 5753 learned the home agent's link-layer address from a Source Link-Layer 5754 Address option in a Router Advertisement. However, if there are 5755 multiple home agents it may still be necessary to send a 5756 solicitation. In this special case of the mobile node returning 5757 home, the mobile node MUST multicast the packet, and in addition set 5758 the Source Address of this Neighbor Solicitation to the unspecified 5759 address (0:0:0:0:0:0:0:0). The target of the Neighbor Solicitation 5760 MUST be set to the mobile node's home address. The destination IP 5761 address MUST be set to the Solicited-Node multicast address [3]. The 5762 home agent will send a multicast Neighbor Advertisement back to the 5763 mobile node with the Solicited flag (S) set to zero. In any case, 5764 the mobile node SHOULD record the information from the Source 5765 Link-Layer Address option or from the advertisement, and set the 5766 state of the Neighbor Cache entry for the home agent to REACHABLE. 5768 The mobile node then sends its Binding Update to the home agent's 5769 link-layer address, instructing its home agent to no longer serve as 5770 a home agent for it. By processing this Binding Update, the home 5771 agent will cease defending the mobile node's home address for 5772 Duplicate Address Detection and will no longer respond to Neighbor 5773 Solicitations for the mobile node's home address. The mobile node is 5774 then the only node on the link receiving packets at the mobile node's 5775 home address. In addition, when returning home prior to the 5776 expiration of a current binding for its home address, and configuring 5777 its home address on its network interface on its home link, the 5778 mobile node MUST NOT perform Duplicate Address Detection on its own 5779 home address, in order to avoid confusion or conflict with its home 5780 agent's use of the same address. This rule also applies to the 5781 derived link-local address of the mobile node, if the Link Local 5782 Address Compatibility (L) bit was set when the binding was created. 5783 If the mobile node returns home after the bindings for all of its 5784 care-of addresses have expired, then it SHOULD perform DAD. 5786 After the Mobile Node sends the Binding Update, it MUST be prepared 5787 to reply to Neighbor Solicitations for its home address. Such 5788 replies MUST be sent using a unicast Neighbor Advertisement to the 5789 sender's link-layer address. It is necessary to reply, since sending 5790 the Binding Acknowledgement from the home agent may require 5791 performing Neighbor Discovery, and the mobile node may not be able to 5792 distinguish Neighbor Solicitations coming from the home agent from 5793 other Neighbor Solicitations. Note that a race condition exists 5794 where both the mobile node and the home agent respond to the same 5795 solicitations sent by other nodes; this will be only temporary, 5796 however, until the Binding Update is accepted. 5798 After receiving the Binding Acknowledgement for its Binding Update to 5799 its home agent, the mobile node MUST multicast onto the home link (to 5800 the all-nodes multicast address) a Neighbor Advertisement [12], to 5801 advertise the mobile node's own link-layer address for its own home 5802 address. The Target Address in this Neighbor Advertisement MUST be 5803 set to the mobile node's home address, and the Advertisement MUST 5804 include a Target Link-layer Address option specifying the mobile 5805 node's link-layer address. The mobile node MUST multicast such a 5806 Neighbor Advertisement for each of its home addresses, as defined by 5807 the current on-link prefixes, including its link-local address and 5808 site-local address. The Solicited Flag (S) in these Advertisements 5809 MUST NOT be set, since they were not solicited by any Neighbor 5810 Solicitation. The Override Flag (O) in these Advertisements MUST be 5811 set, indicating that the Advertisements SHOULD override any existing 5812 Neighbor Cache entries at any node receiving them. 5814 Since multicasting on the local link (such as Ethernet) is typically 5815 not guaranteed to be reliable, the mobile node MAY retransmit these 5816 Neighbor Advertisements [12] up to MAX_NEIGHBOR_ADVERTISEMENT times 5817 to increase their reliability. It is still possible that some nodes 5818 on the home link will not receive any of these Neighbor 5819 Advertisements, but these nodes will eventually be able to recover 5820 through use of Neighbor Unreachability Detection [12]. 5822 11.6 Return Routability Procedure 5824 This section defines the rules that the mobile node must follow when 5825 performing the return routability procedure. Section 11.7.2 5826 describes the rules when the return routability procedure needs to be 5827 initiated. 5829 11.6.1 Sending Test Init Messages 5831 A mobile node that initiates a return routability procedure MUST send 5832 (in parallel) a Home Test Init message and a Care-of Test Init 5833 messages. However, if the mobile node has recently received (see 5834 Section 5.2.7) one or both home or care-of keygen tokens, and 5835 associated nonce indices for the desired addresses, it MAY reuse 5836 them. Therefore, the return routability procedure may in some cases 5837 be completed with only one message pair. It may even be completed 5838 without any messages at all, if the mobile node has a recent home 5839 keygen token and and has previously visited the same care-of address 5840 so that it also has a recent care-of keygen token. If the mobile 5841 node intends to send a Binding Update with the Lifetime set to zero 5842 and the care-of address equal to its home address - such as when 5843 returning home - sending a Home Test Init message is sufficient. In 5844 this case, generation of the binding management key depends 5845 exclusively on the home keygen token (Section 5.2.5). 5847 A Home Test Init message MUST be created as described in Section 5848 6.1.3. 5850 A Care-of Test Init message MUST be created as described in Section 5851 6.1.4. When sending a Home Test Init or Care-of Test Init message 5852 the mobile node MUST record in its Binding Update List the following 5853 fields from the messages: 5855 o The IP address of the node to which the message was sent. 5857 o The home address of the mobile node. This value will appear in 5858 the Source Address field of the Home Test Init message. When 5859 sending the Care-of Test Init message, this address does not 5860 appear in the message, but represents the home address for which 5861 the binding is desired. 5863 o The time at which each of these messages was sent. 5865 o The cookies used in the messages. 5867 Note that a single Care-of Test Init message may be sufficient even 5868 when there are multiple home addresses. In this case the mobile node 5869 MAY record the same information in multiple Binding Update List 5870 entries. 5872 11.6.2 Receiving Test Messages 5874 Upon receiving a packet carrying a Home Test message, a mobile node 5875 MUST validate the packet according to the following tests: 5877 o The Source Address of the packet belongs to a correspondent node 5878 for which the mobile node has a Binding Update List entry with a 5879 state indicating that return routability procedure is in progress. 5880 Note that there may be multiple such entries. 5882 o The Binding Update List indicates that no home keygen token has 5883 been received yet. 5885 o The Destination Address of the packet has the home address of the 5886 mobile node, and the packet has been received in a tunnel from the 5887 home agent. 5889 o The Home Init Cookie field in the message matches the value stored 5890 in the Binding Update List. 5892 Any Home Test message not satisfying all of these tests MUST be 5893 silently ignored. Otherwise, the mobile node MUST record the Home 5894 Nonce Index and home keygen token in the Binding Update List. If the 5895 Binding Update List entry does not have a care-of keygen token, the 5896 mobile node SHOULD continue waiting for the Care-of Test message. 5898 Upon receiving a packet carrying a Care-of Test message, a mobile 5899 node MUST validate the packet according to the following tests: 5901 o The Source Address of the packet belongs to a correspondent node 5902 for which the mobile node has a Binding Update List entry with a 5903 state indicating that return routability procedure is in progress. 5904 Note that there may be multiple such entries. 5906 o The Binding Update List indicates that no care-of keygen token has 5907 been received yet. 5909 o The Destination Address of the packet is the current care-of 5910 address of the mobile node. 5912 o The Care-of Init Cookie field in the message matches the value 5913 stored in the Binding Update List. 5915 Any Care-of Test message not satisfying all of these tests MUST be 5916 silently ignored. Otherwise, the mobile node MUST record the Care-of 5917 Nonce Index and care-of keygen token in the Binding Update List. If 5918 the Binding Update List entry does not have a home keygen token, the 5919 mobile node SHOULD continue waiting for the Home Test message. 5921 If after receiving either the Home Test or the Care-of Test message 5922 and performing the above actions, the Binding Update List entry has 5923 both the home and the care-of keygen tokens, the return routability 5924 procedure is complete. The mobile node SHOULD then proceed with 5925 sending a Binding Update as described in Section 11.7.2. 5927 Correspondent nodes from the time before this specification was 5928 published may not support the Mobility Header protocol. These nodes 5929 will respond to Home Test Init and Care-of Test Init messages with an 5930 ICMP Parameter Problem code 1. The mobile node SHOULD take such 5931 messages as an indication that the correspondent node cannot provide 5932 route optimization, and revert back to the use of bidirectional 5933 tunneling. 5935 11.6.3 Protecting Return Routability Packets 5937 The mobile node MUST support the protection of Home Test and Home 5938 Test Init messages as described in Section 10.4.6. 5940 When IPsec is used to protect return routability signaling or payload 5941 packets, the mobile node MUST set the source address it uses for the 5942 outgoing tunnel packets to the current primary care-of address. The 5943 mobile node starts to use a new primary care-of address immediately 5944 after sending a Binding Update to the home agent to register this new 5945 address. 5947 11.7 Processing Bindings 5948 11.7.1 Sending Binding Updates to the Home Agent 5950 After deciding to change its primary care-of address as described in 5951 Section 11.5.1 and Section 11.5.2, a mobile node MUST register this 5952 care-of address with its home agent in order to make this its primary 5953 care-of address. 5955 Also, if the mobile node wants the services of the home agent beyond 5956 the current registration period, the mobile node should send a new 5957 Binding Update to it well before the expiration of this period, even 5958 if it is not changing its primary care-of address. However, if the 5959 home agent returned a Binding Acknowledgement for the current 5960 registration with Status field set to 1 (accepted but prefix 5961 discovery necessary), the mobile node should not try to register 5962 again before it has learned the validity of its home prefixes through 5963 mobile prefix discovery. This is typically necessary every time this 5964 Status value is received, because information learned earlier may 5965 have changed. 5967 To register a care-of address or to extend the lifetime of an 5968 existing registration, the mobile node sends a packet to its home 5969 agent containing a Binding Update, with the packet constructed as 5970 follows: 5972 o The Home Registration (H) bit MUST be set in the Binding Update. 5974 o The Acknowledge (A) bit MUST be set in the Binding Update. 5976 o The packet MUST contain a Home Address destination option, giving 5977 the mobile node's home address for the binding. 5979 o The care-of address for the binding MUST be used as the Source 5980 Address in the packet's IPv6 header, unless an Alternate Care-of 5981 Address mobility option is included in the Binding Update. This 5982 option MUST be included in all home registrations, as the ESP 5983 protocol will not be able to protect care-of addresses in the IPv6 5984 header. (Mobile IPv6 implementations that know they are using 5985 IPsec AH to protect a particular message might avoid this option. 5986 For brevity the usage of AH is not discussed in this document.) 5988 o If the mobile node's link-local address has the same interface 5989 identifier as the home address for which it is supplying a new 5990 care-of address, then the mobile node SHOULD set the Link-Local 5991 Address Compatibility (L) bit. 5993 o If the home address was generated using RFC 3041 [18], then the 5994 link local address is unlikely to have a compatible interface 5995 identifier. In this case, the mobile node MUST clear the 5996 Link-Local Address Compatibility (L) bit. 5998 o If the IPsec security associations between the mobile node and the 5999 home agent have been established dynamically, and the mobile node 6000 has the capability to update its endpoint in the used key 6001 management protocol to the new care-of address every time it 6002 moves, the mobile node SHOULD set the Key Management Mobility 6003 Capability (K) bit in the Binding Update. Otherwise, the mobile 6004 node MUST clear the bit. 6006 o The value specified in the Lifetime field SHOULD be less than or 6007 equal to the remaining valid lifetime of the home address and the 6008 care-of address specified for the binding. 6010 Mobile nodes that use dynamic home agent address discovery should 6011 be careful with long lifetimes. If the mobile node loses the 6012 knowledge of its binding with a specific home agent, registering a 6013 new binding with another home agent may be impossible as the 6014 previous home agent is still defending the existing binding. 6015 Therefore, mobile nodes that use home agent address discovery 6016 SHOULD ensure information about their bindings is not lost, 6017 de-register before losing this information, or use small 6018 lifetimes. 6020 The Acknowledge (A) bit in the Binding Update requests the home agent 6021 to return a Binding Acknowledgement in response to this Binding 6022 Update. As described in Section 6.1.8, the mobile node SHOULD 6023 retransmit this Binding Update to its home agent until it receives a 6024 matching Binding Acknowledgement. Once reaching a retransmission 6025 timeout period of MAX_BINDACK_TIMEOUT, the mobile node SHOULD restart 6026 the process of delivering the Binding Update, but trying instead the 6027 next home agent returned during dynamic home agent address discovery 6028 (see Section 11.4.1). If there was only one home agent, the mobile 6029 node instead SHOULD continue to periodically retransmit the Binding 6030 Update at this rate until acknowledged (or until it begins attempting 6031 to register a different primary care-of address). See Section 11.8 6032 for information about retransmitting Binding Updates. 6034 With the Binding Update, the mobile node requests the home agent to 6035 serve as the home agent for the given home address. Until the 6036 lifetime of this registration expires, the home agent considers 6037 itself the home agent for this home address. 6039 Each Binding Update MUST be authenticated as coming from the right 6040 mobile node, as defined in Section 5.1. The mobile node MUST use its 6041 home address - either in the Home Address destination option or in 6042 the Source Address field of the IPv6 header - in Binding Updates sent 6043 to the home agent. This is necessary in order to allow the IPsec 6044 policies to be matched with the right home address. 6046 When sending a Binding Update to its home agent, the mobile node MUST 6047 also create or update the corresponding Binding Update List entry, as 6048 specified in Section 11.7.2. 6050 The last Sequence Number value sent to the home agent in a Binding 6051 Update is stored by the mobile node. If the sending mobile node has 6052 no knowledge of the right Sequence Number value, it may start at any 6053 value. If the home agent rejects the value, it sends back a Binding 6054 Acknowledgement with status code 135, and the last accepted sequence 6055 number in the Sequence Number field of the Binding Acknowledgement. 6056 The mobile node MUST store this information and use the next Sequence 6057 Number value for the next Binding Update it sends. 6059 If the mobile node has additional home addresses, then the mobile 6060 node SHOULD send an additional packet containing a Binding Update to 6061 its home agent to register the care-of address for each such other 6062 home address. 6064 The home agent will only perform DAD for the mobile node's home 6065 address when the mobile node has supplied a valid binding between its 6066 home address and a care-of address. If some time elapses during 6067 which the mobile node has no binding at the home agent, it might be 6068 possible for another node to autoconfigure the mobile node's home 6069 address. Therefore, the mobile node MUST treat creation of a new 6070 binding with the home agent using an existing home address the same 6071 as creation of a new home address. In the unlikely event that the 6072 mobile node's home address is autoconfigured as the IPv6 address of 6073 another network node on the home network, the home agent will reply 6074 to the mobile node's subsequent Binding Update with a Binding 6075 Acknowledgement containing a Status of 134 (Duplicate Address 6076 Detection failed). In this case, the mobile node MUST NOT attempt to 6077 re-use the same home address. It SHOULD continue to register care-of 6078 addresses for its other home addresses, if any. (Mechanisms outlined 6079 in Appendix B.5 may in the future allow mobile nodes to acquire new 6080 home addresses to replace the one for which Status 134 was received.) 6082 11.7.2 Correspondent Registration 6084 When the mobile node is assured that its home address is valid, it 6085 can initiate a correspondent registration with the purpose of 6086 allowing the correspondent node to cache the mobile node's current 6087 care-of address. This procedure consists of the return routability 6088 procedure followed by a registration. 6090 This section defines when to initiate the correspondent registration, 6091 and rules to follow when performing it. 6093 After the mobile node has sent a Binding Update to its home agent to 6094 register a new primary care-of address (as described in Section 6095 11.7.1), the mobile node SHOULD initiate a correspondent registration 6096 for each node that already appears in the mobile node's Binding 6097 Update List. The initiated procedures can be used to either update 6098 or delete binding information in the correspondent node. 6100 For nodes that do not appear in the mobile node's Binding Update 6101 List, the mobile node MAY initiate a correspondent registration at 6102 any time after sending the Binding Update to its home agent. 6103 Considerations regarding when (and if) to initiate the procedure 6104 depend on the specific movement and traffic patterns of the mobile 6105 node and are outside the scope of this document. 6107 In addition, the mobile node MAY initiate the procedure in response 6108 to receiving a packet that meets all of the following tests: 6110 o The packet was tunneled using IPv6 encapsulation. 6112 o The Destination Address in the tunnel (outer) IPv6 header is equal 6113 to any of the mobile node's care-of addresses. 6115 o The Destination Address in the original (inner) IPv6 header is 6116 equal to one of the mobile node's home addresses. 6118 o The Source Address in the tunnel (outer) IPv6 header differs from 6119 the Source Address in the original (inner) IPv6 header. 6121 o The packet does not contain a Home Test, Home Test Init, Care-of 6122 Test, or Care-of Test Init message. 6124 If a mobile node has multiple home addresses, it becomes important to 6125 select the right home address to use in the correspondent 6126 registration. The used home address MUST be the Destination Address 6127 of the original (inner) packet. 6129 The peer address used in the procedure MUST be determined as follows: 6131 o If a Home Address destination option is present in the original 6132 (inner) packet, the address from this option is used. 6134 o Otherwise, the Source Address in the original (inner) IPv6 header 6135 of the packet is used. 6137 Note that the validity of the original packet is checked before 6138 attempting to initiate a correspondent registration. For instance, 6139 if a Home Address destination option appeared in the original packet, 6140 then rules in Section 9.3.1 are followed. 6142 A mobile node MAY also choose to keep its topological location 6143 private from certain correspondent nodes, and thus need not initiate 6144 the correspondent registration. 6146 Upon successfully completing the return routability procedure, and 6147 after receiving a successful Binding Acknowledgement from the Home 6148 Agent, a Binding Update MAY be sent to the correspondent node. 6150 In any Binding Update sent by a mobile node, the care-of address 6151 (either the Source Address in the packet's IPv6 header or the Care-of 6152 Address in the Alternate Care-of Address mobility option of the 6153 Binding Update) MUST be set to one of the care-of addresses currently 6154 in use by the mobile node or to the mobile node's home address. A 6155 mobile node MAY set the care-of address differently for sending 6156 Binding Updates to different correspondent nodes. 6158 A mobile node MAY also send a Binding Update to such a correspondent 6159 node to instruct it to delete any existing binding for the mobile 6160 node from its Binding Cache, as described in Section 6.1.7. Even in 6161 this case a successful completion of the return routability procedure 6162 is required first. 6164 If the care-of address is not set to the mobile node's home address, 6165 the Binding Update requests the correspondent node to create or 6166 update an entry for the mobile node in the correspondent node's 6167 Binding Cache. This is done in order to record a care-of address for 6168 use in sending future packets to the mobile node. In this case, the 6169 value specified in the Lifetime field sent in the Binding Update 6170 SHOULD be less than or equal to the remaining lifetime of the home 6171 registration and the care-of address specified for the binding. The 6172 care-of address given in the Binding Update MAY differ from the 6173 mobile node's primary care-of address. 6175 If the Binding Update is sent to request the correspondent node to 6176 delete any existing Binding Cache entry that it has for the mobile 6177 node, the care-of address is set to the mobile node's home address 6178 and the Lifetime field set to zero. In this case, generation of the 6179 binding management key depends exclusively on the home keygen token 6180 (Section 5.2.5). The care-of nonce index SHOULD be set to zero in 6181 this case. In keeping with the Binding Update creation rules below, 6182 the care-of address MUST be set to the home address if the mobile 6183 node is at home, or to the current care-of address if it is away from 6184 home. 6186 If the mobile node wants to ensure that its new care-of address has 6187 been entered into a correspondent node's Binding Cache, the mobile 6188 node needs to request an acknowledgement by setting the Acknowledge 6189 (A) bit in the Binding Update. 6191 A Binding Update is created as follows: 6193 o The current care-of address of the mobile node MUST be sent either 6194 in the Source Address of the IPv6 header or in the Alternate 6195 Care-of Address mobility option. 6197 o The Destination Address of the IPv6 header MUST contain the 6198 address of the correspondent node. 6200 o The Mobility Header is constructed according to rules in Section 6201 6.1.7 and Section 5.2.6, including the Binding Authorization Data 6202 (calculated as defined in Section 6.2.7) and possibly the Nonce 6203 Indices mobility options. 6205 o The home address of the mobile node MUST be added to the packet in 6206 a Home Address destination option, unless the Source Address is 6207 the home address. 6209 Each Binding Update MUST have a Sequence Number greater than the 6210 Sequence Number value sent in the previous Binding Update to the same 6211 destination address (if any). The sequence numbers are compared 6212 modulo 2**16, as described in Section 9.5.1. There is no 6213 requirement, however, that the Sequence Number value strictly 6214 increase by 1 with each new Binding Update sent or received, as long 6215 as the value stays within the window. The last Sequence Number value 6216 sent to a destination in a Binding Update is stored by the mobile 6217 node in its Binding Update List entry for that destination. If the 6218 sending mobile node has no Binding Update List entry, the Sequence 6219 Number SHOULD start at a random value. The mobile node MUST NOT use 6220 the same Sequence Number in two different Binding Updates to the same 6221 correspondent node, even if the Binding Updates provide different 6222 care-of addresses. 6224 The mobile node is responsible for the completion of the 6225 correspondent registration, as well as any retransmissions that may 6226 be needed (subject to the rate limiting defined in Section 11.8). 6228 11.7.3 Receiving Binding Acknowledgements 6230 Upon receiving a packet carrying a Binding Acknowledgement, a mobile 6231 node MUST validate the packet according to the following tests: 6233 o The packet meets the authentication requirements for Binding 6234 Acknowledgements, defined in Section 6.1.8 and Section 5. That 6235 is, if the Binding Update was sent to the home agent, underlying 6236 IPsec protection is used. If the Binding Update was sent to the 6237 correspondent node, the Binding Authorization Data mobility option 6238 MUST be present and have a valid value. 6240 o The Binding Authorization Data mobility option, if present, MUST 6241 be the last option and MUST not have trailing padding. 6243 o The Sequence Number field matches the Sequence Number sent by the 6244 mobile node to this destination address in an outstanding Binding 6245 Update. 6247 Any Binding Acknowledgement not satisfying all of these tests MUST be 6248 silently ignored. 6250 When a mobile node receives a packet carrying a valid Binding 6251 Acknowledgement, the mobile node MUST examine the Status field as 6252 follows: 6254 o If the Status field indicates that the Binding Update was accepted 6255 (the Status field is less than 128), then the mobile node MUST 6256 update the corresponding entry in its Binding Update List to 6257 indicate that the Binding Update has been acknowledged; the mobile 6258 node MUST then stop retransmitting the Binding Update. In 6259 addition, if the value specified in the Lifetime field in the 6260 Binding Acknowledgement is less than the Lifetime value sent in 6261 the Binding Update being acknowledged, then the mobile node MUST 6262 subtract the difference between these two Lifetime values from the 6263 remaining lifetime for the binding as maintained in the 6264 corresponding Binding Update List entry (with a minimum value for 6265 the Binding Update List entry lifetime of 0). That is, if the 6266 Lifetime value sent in the Binding Update was L_update, the 6267 Lifetime value received in the Binding Acknowledgement was L_ack, 6268 and the current remaining lifetime of the Binding Update List 6269 entry is L_remain, then the new value for the remaining lifetime 6270 of the Binding Update List entry should be 6272 max((L_remain - (L_update - L_ack)), 0) 6274 where max(X, Y) is the maximum of X and Y. The effect of this 6275 step is to correctly manage the mobile node's view of the 6276 binding's remaining lifetime (as maintained in the corresponding 6277 Binding Update List entry) so that it correctly counts down from 6278 the Lifetime value given in the Binding Acknowledgement, but with 6279 the timer countdown beginning at the time that the Binding Update 6280 was sent. 6282 Mobile nodes SHOULD send a new Binding Update well before the 6283 expiration of this period in order to extend the lifetime. This 6284 helps to avoid disruptions in communications, which might 6285 otherwise be caused by network delays or clock drift. 6287 o Additionally, if the Status field value is 1 (Accepted but prefix 6288 discovery necessary), the mobile node SHOULD send a Mobile Prefix 6289 Solicitation message to update its information about the available 6290 prefixes. 6292 o If the Status field indicates that the Binding Update was rejected 6293 (the Status field is greater than or equal to 128), then the 6294 mobile node can take steps to correct the cause of the error and 6295 retransmit the Binding Update (with a new Sequence Number value), 6296 subject to the rate limiting restriction specified in Section 6297 11.8. If this is not done, or it fails, then the mobile node 6298 SHOULD record in its Binding Update List that future Binding 6299 Updates SHOULD NOT be sent to this destination. 6301 The treatment of a Binding Refresh Advice mobility option within the 6302 Binding Acknowledgement depends on the where the acknowledgement came 6303 from. This option MUST be ignored if the acknowledgement came from a 6304 correspondent node. If it came from the home agent, the mobile node 6305 uses Refresh Interval field in the option as a suggestion that it 6306 SHOULD attempt to refresh its home registration at the indicated 6307 shorter interval. 6309 If the acknowledgement came from the home agent, the mobile node 6310 examines the value of the Key Management Mobility Capability (K) bit. 6311 If this bit is not set, the mobile node SHOULD discard key management 6312 protocol connections, if any, to the home agent. The mobile node MAY 6313 also initiate a new key management connection. 6315 If this bit is set, the mobile node SHOULD move its own endpoint in 6316 the key management protocol connections to the home agent, if any. 6317 The mobile node's new endpoint should be the new care-of address. 6318 For an IKE phase 1 connection, this means packets sent to this 6319 address with the original ISAKMP cookies are accepted. 6321 11.7.4 Receiving Binding Refresh Requests 6323 When a mobile node receives a packet containing a Binding Refresh 6324 Request message, the mobile node has a Binding Update List entry for 6325 the source of the Binding Refresh Request, and the mobile node wants 6326 to retain its binding cache entry at the correspondent node, then the 6327 mobile node should start a return routability procedure. If the 6328 mobile node wants to have its binding cache entry removed it can 6329 either ignore the Binding Refresh Request and wait for the binding to 6330 time out, or it can at any time delete its binding from a 6331 correspondent node with an explicit binding update with zero lifetime 6332 and the care-of address set to the home address. If the mobile node 6333 does not know if it needs the binding cache entry, it can make the 6334 decision in an implementation dependent manner, such as based on 6335 available resources. 6337 Note that the mobile node should be careful to not respond to Binding 6338 Refresh Requests for addresses not in the Binding Update List to 6339 avoid being subjected to a denial of service attack. 6341 If the return routability procedure completes successfully, a Binding 6342 Update message SHOULD be sent as described in Section 11.7.2. The 6343 Lifetime field in this Binding Update SHOULD be set to a new 6344 lifetime, extending any current lifetime remaining from a previous 6345 Binding Update sent to this node (as indicated in any existing 6346 Binding Update List entry for this node), and lifetime SHOULD again 6347 be less than or equal to the remaining lifetime of the home 6348 registration and the care-of address specified for the binding. When 6349 sending this Binding Update, the mobile node MUST update its Binding 6350 Update List in the same way as for any other Binding Update sent by 6351 the mobile node. 6353 11.8 Retransmissions and Rate Limiting 6355 The mobile node is responsible for retransmissions and rate limiting 6356 in the return routability procedure, registrations, and in solicited 6357 prefix discovery. 6359 When the mobile node sends a Mobile Prefix Solicitation, Home Test 6360 Init, Care-of Test Init or Binding Update for which it expects a 6361 response, the mobile node has to determine a value for the initial 6362 retransmission timer: 6364 o If the mobile node is sending a Mobile Prefix Solicitation, it 6365 SHOULD use an initial retransmission interval of 6366 INITIAL_SOLICIT_TIMER (see Section 12). 6368 o If the mobile node is sending a Binding Update and it does not 6369 have an existing binding at the home agent, it SHOULD use 6370 InitialBindackTimeoutFirstReg (see Section 13) as a value for the 6371 initial retransmission timer. This long retransmission interval 6372 will allow the home agent to complete the Duplicate Address 6373 Detection procedure which is mandated in this case, as detailed in 6374 Section 11.7.1. 6376 o Otherwise, the mobile node should use the specified value of 6377 INITIAL_BINDACK_TIMEOUT for the initial retransmission timer. 6379 If the mobile node fails to receive a valid, matching response within 6380 the selected initial retransmission interval, the mobile node SHOULD 6381 retransmit the message, until a response is received. 6383 The retransmissions by the mobile node MUST use an exponential 6384 back-off process, in which the timeout period is doubled upon each 6385 retransmission until either the node receives a response or the 6386 timeout period reaches the value MAX_BINDACK_TIMEOUT. The mobile 6387 node MAY continue to send these messages at this slower rate 6388 indefinitely. 6390 The mobile node SHOULD start a separate back-off process for 6391 different message types, different home addresses and different 6392 care-of addresses. However, in addition an overall rate limitation 6393 applies for messages sent to a particular correspondent node. This 6394 ensures that the correspondent node has sufficient amount of time to 6395 answer when bindings for multiple home addresses are registered, for 6396 instance. The mobile node MUST NOT send Mobility Header messages of 6397 a particular type to a particular correspondent node more than 6398 MAX_UPDATE_RATE times within a second. 6400 Retransmitted Binding Updates MUST use a Sequence Number value 6401 greater than that used for the previous transmission of this Binding 6402 Update. Retransmitted Home Test Init and Care-of Test Init messages 6403 MUST use new cookie values. 6405 12. Protocol Constants 6407 DHAAD_RETRIES 4 retransmissions 6408 INITIAL_BINDACK_TIMEOUT 1 second 6409 INITIAL_DHAAD_TIMEOUT 3 seconds 6410 INITIAL_SOLICIT_TIMER 3 seconds 6411 MAX_BINDACK_TIMEOUT 32 seconds 6412 MAX_NONCE_LIFETIME 240 seconds 6413 MAX_TOKEN_LIFETIME 210 seconds 6414 MAX_RR_BINDING_LIFETIME 420 seconds 6415 MAX_UPDATE_RATE 3 times 6416 PREFIX_ADV_RETRIES 3 retransmissions 6417 PREFIX_ADV_TIMEOUT 3 seconds 6419 13. Protocol Configuration Variables 6421 MaxMobPfxAdvInterval Default: 86,400 seconds 6422 MinDelayBetweenRAs Default: 3 seconds, 6423 Min: 0.03 seconds 6424 MinMobPfxAdvInterval Default: 600 seconds 6425 InitialBindackTimeoutFirstReg Default: 1.5 seconds 6427 Home agents MUST allow the first three variables to be configured by 6428 system management, and mobile nodes MUST allow the last variable to 6429 be configured by system management. 6431 The default value for InitialBindackTimeoutFirstReg has been 6432 calculated as 1.5 times the default value of RetransTimer [12] times 6433 the default value of DupAddrDetectTransmits [13]. 6435 The value MinDelayBetweenRAs overrides the value of the protocol 6436 constant MIN_DELAY_BETWEEN_RAS, as specified in RFC 2461 [12]. This 6437 variable SHOULD be set to MinRtrAdvInterval, if MinRtrAdvInterval is 6438 less than 3 seconds. 6440 14. IANA Considerations 6442 This document defines a new IPv6 protocol, the Mobility Header, 6443 described in Section 6.1. This protocol must be assigned a protocol 6444 number. 6446 This document also creates a new name space "Mobility Header Type", 6447 for the MH Type field in the Mobility Header. The current message 6448 types are described starting from Section 6.1.2, and are the 6449 following: 6451 0 Binding Refresh Request 6453 1 Home Test Init 6455 2 Care-of Test Init 6457 3 Home Test 6459 4 Care-of Test 6461 5 Binding Update 6463 6 Binding Acknowledgement 6465 7 Binding Error 6467 Future values of the MH Type can be allocated using standards action 6468 [10]. 6470 Furthermore, each mobility message may contain mobility options as 6471 described in Section 6.2. This document defines a new name space 6472 "Mobility Option" to identify these options. The current mobility 6473 options are defined starting from Section 6.2.2 and are the 6474 following: 6476 0 Pad1 6478 1 PadN 6480 2 Binding Refresh Advice 6482 3 Alternate Care-of Address 6484 4 Nonce Indices 6485 5 Authorization Data 6487 Future values of the Option Type can be allocated using standards 6488 action [10]. 6490 This document also defines a new IPv6 destination option, the Home 6491 Address option, described in Section 6.3. This option has already 6492 been assigned the Option Type value 0xC9. 6494 This document also defines a new IPv6 type 2 routing header, 6495 described in Section 6.4. The value 2 is to be allocated by IANA 6496 when this specification becomes an RFC. 6498 In addition, this document defines four ICMP message types, two used 6499 as part of the dynamic home agent address discovery mechanism and two 6500 used in lieu of Router Solicitations and Advertisements when the 6501 mobile node is away from the home link. These messages must be 6502 assigned ICMPv6 type numbers from the informational message range: 6504 o The Home Agent Address Discovery Request message, described in 6505 Section 6.5; 6507 o The Home Agent Address Discovery Reply message, described in 6508 Section 6.6; 6510 o The Mobile Prefix Solicitation, described in Section 6.7; and 6512 o The Mobile Prefix Advertisement, described in Section 6.8. 6514 This document also defines two new Neighbor Discovery [12] options, 6515 which must be assigned Option Type values within the option numbering 6516 space for Neighbor Discovery messages: 6518 o The Advertisement Interval option, described in Section 7.3; and 6520 o The Home Agent Information option, described in Section 7.4. 6522 15. Security Considerations 6524 15.1 Threats 6526 Any mobility solution must protect itself against misuses of the 6527 mobility features and mechanisms. In Mobile IPv6, most of the 6528 potential threats are concerned with false Bindings, usually 6529 resulting in Denial-of-Service attacks. Some of the threats also 6530 pose potential for Man-in-the-Middle, Hijacking, Confidentiality, and 6531 Impersonation attacks. The main threats this protocol protects 6532 against are the following: 6534 o Threats involving Binding Updates sent to home agents and 6535 correspondent nodes. For instance, an attacker might claim that a 6536 certain mobile node is currently at a different location than it 6537 really is. If a home agent accepts such spoofed information sent 6538 to it, the mobile node might not get traffic destined to it. 6539 Similarly, a malicious (mobile) node might use the home address of 6540 a victim node in a forged Binding Update sent to a correspondent 6541 node. 6543 These pose threats against confidentiality, integrity, and 6544 availability. That is, an attacker might learn the contents of 6545 packets destined to another node by redirecting the traffic to 6546 itself. Furthermore, an attacker might use the redirected packets 6547 in an attempt to set itself as a Man-in-the-Middle between a 6548 mobile and a correspondent node. This would allow the attacker to 6549 impersonate the mobile node, leading to integrity and availability 6550 problems. 6552 A malicious (mobile) node might also send Binding Updates in which 6553 the care-of address is set to the address of a victim node. If 6554 such Binding Updates were accepted, the malicious node could lure 6555 the correspondent node into sending potentially large amounts of 6556 data to the victim; the correspondent node's replies to messages 6557 sent by the malicious mobile node will be sent to the victim host 6558 or network. This could be used to cause a Distributed 6559 Denial-of-Service attack. For example, the correspondent node 6560 might be a site that will send a high-bandwidth stream of video to 6561 anyone who asks for it. Note that the use of flow-control 6562 protocols such as TCP does not necessarily defend against this 6563 type of attack, because the attacker can fake the 6564 acknowledgements. Even keeping TCP initial sequence numbers 6565 secret does not help, because the attacker can receive the first 6566 few segments (including the ISN) at its own address, and only then 6567 redirect the stream to the victim's address. These types of 6568 attacks may also be directed to networks instead of nodes. 6569 Further variations of this threat are described elsewhere 6571 [27, 34]. 6573 An attacker might also attempt to disrupt a mobile node's 6574 communications by replaying a Binding Update that the node had 6575 sent earlier. If the old Binding Update was accepted, packets 6576 destined for the mobile node would be sent to its old location and 6577 not its current location. 6579 In conclusion, there are Denial-of-Service, Man-in-the-Middle, 6580 Confidentiality, and Impersonation threats against the parties 6581 involved in sending legitimate Binding Updates, and 6582 Denial-of-Service threats against any other party. 6584 o Threats associated with payload packets: Payload packets exchanged 6585 with mobile nodes are exposed to similar threats as regular IPv6 6586 traffic is. However, Mobile IPv6 introduces the Home Address 6587 destination option, a new routing header type (type 2), and uses 6588 tunneling headers in the payload packets. The protocol must 6589 protect against potential new threats involving the use of these 6590 mechanisms. 6592 Third parties become exposed to a reflection threat via the Home 6593 Address destination option, unless appropriate security 6594 precautions are followed. The Home Address destination option 6595 could be used to direct response traffic toward a node whose IP 6596 address appears in the option. In this case, ingress filtering 6597 would not catch the forged "return address" [36, 32]. 6599 A similar threat exists with the tunnels between the mobile node 6600 and the home agent. An attacker might forge tunnel packets 6601 between the mobile node and the home agent, making it appear that 6602 the traffic is coming from the mobile node when it is not. Note 6603 that an attacker who is able to forge tunnel packets would 6604 typically be able forge also packets that appear to come directly 6605 from the mobile node. This is not a new threat as such. However, 6606 it may make it easier for attackers to escape detection by 6607 avoiding ingress filtering and packet tracing mechanisms. 6608 Furthermore, spoofed tunnel packets might be used to gain access 6609 to the home network. 6611 Finally, a routing header could also be used in reflection 6612 attacks, and in attacks designed to bypass firewalls. The 6613 generality of the regular routing header would allow circumvention 6614 of IP-address based rules in firewalls. It would also allow 6615 reflection of traffic to other nodes. These threats exist with 6616 routing headers in general, even if the usage that Mobile IPv6 6617 requires is safe. 6619 o Threats associated with dynamic home agent and mobile prefix 6620 discovery. 6622 o Threats against the Mobile IPv6 security mechanisms themselves: An 6623 attacker might, for instance, lure the participants into executing 6624 expensive cryptographic operations or allocating memory for the 6625 purpose of keeping state. The victim node would have no resources 6626 left to handle other tasks. 6628 As a fundamental service in an IPv6 stack, Mobile IPv6 is expected to 6629 be deployed in most nodes of the IPv6 Internet. The above threats 6630 should therefore be considered in the light of being applicable to 6631 the whole Internet. 6633 It should also be noted that some additional threats result from 6634 movements as such, even without the involvement of mobility 6635 protocols. Mobile nodes must be capable to defend themselves in the 6636 networks that they visit, as typical perimeter defenses applied in 6637 the home network no longer protect them. 6639 15.2 Features 6641 This specification provides a series of features designed to mitigate 6642 the risk introduced by the threats listed above. The main security 6643 features are the following: 6645 o Reverse Tunneling as a mandatory feature. 6647 o Protection of Binding Updates sent to home agents. 6649 o Protection of Binding Updates sent to correspondent nodes. 6651 o Protection against reflection attacks that use the Home Address 6652 destination option. 6654 o Protection of tunnels between the mobile node and the home agent. 6656 o Closing routing header vulnerabilities. 6658 o Mitigating Denial-of-Service threats to the Mobile IPv6 security 6659 mechanisms themselves. 6661 The support for encrypted reverse tunneling (see Section 11.3.1) 6662 allows mobile nodes to defeat certain kinds of traffic analysis. 6664 Protecting those Binding Updates that are sent to home agents and 6665 those that are sent to arbitrary correspondent nodes requires very 6666 different security solutions due to the different situations. Mobile 6667 nodes and home agents are expected to be naturally subject to the 6668 network administration of the home domain. 6670 Thus, they can and are supposed to have a security association that 6671 can be used to reliably authenticate the exchanged messages. See 6672 Section 5.1 for the description of the protocol mechanisms, and 6673 Section 15.3 below for a discussion of the resulting level of 6674 security. 6676 It is expected that Mobile IPv6 route optimization will be used on a 6677 global basis between nodes belonging to different administrative 6678 domains. It would be a very demanding task to build an 6679 authentication infrastructure on this scale. Furthermore, a 6680 traditional authentication infrastructure cannot be easily used to 6681 authenticate IP addresses, because IP addresses can change often. It 6682 is not sufficient to just authenticate the mobile nodes. 6683 Authorization to claim the right to use an address is needed as well. 6684 Thus, an "infrastructureless" approach is necessary. The chosen 6685 infrastructureless method is described in Section 5.2 and Section 6686 15.4 discusses the resulting security level and the design rationale 6687 of this approach. 6689 Specific rules guide the use of the Home Address destination option, 6690 the routing header, and the tunneling headers in the payload packets. 6691 These rules are necessary to remove the vulnerabilities associated 6692 with their unrestricted use. The effect of the rules is discussed in 6693 Section 15.7, Section 15.8, and Section 15.9. 6695 Denial-of-Service threats against Mobile IPv6 security mechanisms 6696 themselves concern mainly the Binding Update procedures with 6697 correspondent nodes. The protocol has been designed to limit the 6698 effects of such attacks, as will be described in Section 15.4.5. 6700 15.3 Binding Updates to Home Agent 6702 Signaling between the mobile node and the home agent requires message 6703 integrity. This is necessary to assure the home agent that a Binding 6704 Update is from a legitimate mobile node. In addition, correct 6705 ordering and anti-replay protection are optionally needed. 6707 IPsec ESP protects the integrity of the Binding Updates and Binding 6708 Acknowledgements, by securing mobility messages between the mobile 6709 node and the home agent. 6711 IPsec can provide anti-replay protection only if dynamic keying is 6712 used (which may not always be the case). IPsec also does not 6713 guarantee correct ordering of packets, only that they have not been 6714 replayed. Because of this, sequence numbers within the Mobile IPv6 6715 messages are used to ensure correct ordering (see Section 5.1). 6716 However, if the 16 bit Mobile IPv6 sequence number space is cycled 6717 through, or the home agent reboots and loses its state regarding the 6718 sequence numbers, replay and reordering attacks become possible. The 6719 use of dynamic keying, IPsec anti-replay protection, and the Mobile 6720 IPv6 sequence numbers can together prevent such attacks. It is also 6721 recommended that use of non-volatile storage is considered for home 6722 agents, to avoid losing their state. 6724 A sliding window scheme is used for the sequence numbers. The 6725 protection against replays and reordering attacks without a key 6726 management mechanism works when the attacker remembers up to a 6727 maximum of 2**15 Binding Updates. 6729 The above mechanisms do not show that the care-of address given in 6730 the Binding Update is correct. This opens the possibility for 6731 Denial-of-Service attacks against third parties. However, since the 6732 mobile node and home agent have a security association, the home 6733 agent can always identify an ill-behaving mobile node. This allows 6734 the home agent operator to discontinue the mobile node's service, and 6735 possibly take further actions based on the business relationship with 6736 the mobile node's owner. 6738 Note that the use of a single pair of manually keyed security 6739 associations conflicts with the generation of a new home addresses 6740 [18] for the mobile node, or with the adoption of a new home subnet 6741 prefix. This is because IPsec security associations are bound to the 6742 used addresses. While certificate-based automatic keying alleviates 6743 this problem to an extent, it is still necessary to ensure that a 6744 given mobile node cannot send Binding Updates for the address of 6745 another mobile node. In general, this leads to the inclusion of home 6746 addresses in certificates in the Subject AltName field. This again 6747 limits the introduction of new addresses without either manual or 6748 automatic procedures to establish new certificates. Therefore, this 6749 specification restricts the generation of new home addresses (for any 6750 reason) to those situations where there already exists a security 6751 association or certificate for the new address. (Appendix B.4 lists 6752 the improvement of security for new addresses as one of the future 6753 developments for Mobile IPv6.) 6755 Support for IKE has been specified as optional. The following should 6756 be observed about the use of manual keying: 6758 o As discussed above, with manually keyed IPsec only a limited form 6759 of protection exists against replay and reordering attacks. A 6760 vulnerability exists if either the sequence number space is cycled 6761 through, or if the home agent reboots and forgets its sequence 6762 numbers (and uses volatile memory to store the sequence numbers). 6764 Assuming the mobile node moves continuously every 10 minutes, it 6765 takes roughly 455 days before the sequence number space has been 6766 cycled through. Typical movement patterns rarely reach this high 6767 frequency today. 6769 o A mobile node and its home agent belong to the same domain. If 6770 this were not the case, manual keying would not be possible [28], 6771 but in Mobile IPv6 only these two parties need to know the 6772 manually configured keys. Similarly, we note that Mobile IPv6 6773 employs standard block ciphers in IPsec, and is not vulnerable to 6774 problems associated with stream ciphers and manual keying. 6776 o It is expected that the owner of the mobile node and the 6777 administrator of the home agent agree on the used keys and other 6778 parameters with some off-line mechanism. 6780 The use of IKEv1 with Mobile IPv6 is documented in more detail in 6781 [21]. The following should be observed from the use of IKEv1: 6783 o It is necessary to prevent a mobile node from claiming another 6784 mobile node's home address. The home agent must verify that the 6785 mobile node trying to negotiate the SA for a particular home 6786 address is authorized for that home address. This implies that 6787 even with the use of IKE, a policy entry needs to be configured 6788 for each home address served by the home agent. 6790 It may be possible to include home addresses in the Subject 6791 AltName field of certificate to avoid this. However, 6792 implementations are not guaranteed to support the use of a 6793 particular IP address (care-of address) while another address 6794 (home address) appears in the certificate. In any case, even this 6795 approach would require user-specific tasks in the certificate 6796 authority. 6798 o If preshared secret authentication is used, IKEv1 main mode cannot 6799 be used. Aggressive mode or group preshared secrets need to be 6800 used instead, with corresponding security implications. 6802 Note that like many other issues, this is a general IKEv1 issue 6803 related to the ability to use different IP addresses, and not 6804 specifically related to Mobile IPv6. For further information, see 6805 Section 4.4 in [21]. 6807 o Due to the problems outlined in Section 11.3.2, IKE phase 1 6808 between the mobile node and its home agent is established using 6809 the mobile node's current care-of address. This implies that when 6810 the mobile node moves to a new location, it may have to 6811 re-establish phase 1. A Key Management Mobility Capability (K) 6812 flag is provided for implementations that can update the IKE phase 6813 1 endpoints without re-establishing phase 1, but the support for 6814 this behavior is optional. 6816 o When certificates are used, IKE fragmentation can occur as 6817 discussed in Section 7 in [21]. 6819 o Nevertheless, even if per-mobile node configuration is required 6820 even with IKE, an important benefit of IKE is that it automates 6821 the negotiation of cryptographic parameters, including the SPIs, 6822 cryptographic algorithms, and so on. Thus less configuration 6823 information is needed. 6825 o The frequency of movements in some link layers or deployment 6826 scenarios may be high enough to make replay and reordering attacks 6827 possible, if only manual keying is used. IKE SHOULD be used in 6828 such cases. Potentially vulnerable scenarios involve continuous 6829 movement through small cells, or uncontrolled alternation between 6830 available network attachment points. 6832 o Similarly, in some deployment scenarios the number of mobile nodes 6833 may be very large. It these cases it can be necessary to use 6834 automatic mechanisms to reduce the management effort in the 6835 administration of cryptographic parameters, even if some 6836 per-mobile node configuration is always needed. IKE SHOULD also 6837 be used in such cases. 6839 o Other automatic key management mechanisms exist beyond IKEv1, but 6840 this document does not address the issues related to them. We 6841 note, however, that most of the above discussion applies to IKEv2 6842 [30] as well, at least as it is currently specified. 6844 15.4 Binding Updates to Correspondent Nodes 6846 The motivation for designing the return routability procedure was to 6847 have sufficient support for Mobile IPv6, without creating significant 6848 new security problems. The goal for this procedure was not to 6849 protect against attacks that were already possible before the 6850 introduction of Mobile IPv6. 6852 The next sections will describe the security properties of the used 6853 method, both from the point of view of possible on-path attackers who 6854 can see those cryptographic values that have been sent in the clear 6855 (Section 15.4.2 and Section 15.4.3) or from the point of view of 6856 other attackers (Section 15.4.6). 6858 15.4.1 Overview 6860 The chosen infrastructureless method verifies that the mobile node is 6861 "live" (that is, it responds to probes) at its home and care-of 6862 addresses. Section 5.2 describes the return routability procedure in 6863 detail. The procedure uses the following principles: 6865 o A message exchange verifies that the mobile node is reachable at 6866 its addresses i.e. is at least able to transmit and receive 6867 traffic at both the home and care-of addresses. 6869 o The eventual Binding Update is cryptographically bound to the 6870 tokens supplied in the exchanged messages. 6872 o Symmetric exchanges are employed to avoid the use of this protocol 6873 in reflection attacks. In a symmetric exchange, the responses are 6874 always sent to the same address as the request was sent from. 6876 o The correspondent node operates in a stateless manner until it 6877 receives a fully authorized Binding Update. 6879 o Some additional protection is provided by encrypting the tunnels 6880 between the mobile node and home agent with IPsec ESP. As the 6881 tunnel transports also the nonce exchanges, this limits the 6882 ability of attackers to see these nonces. For instance, this 6883 prevents attacks launched from the mobile node's current foreign 6884 link even when no link-layer confidentiality is available. 6886 The resulting level of security is in theory the same even without 6887 this additional protection: the return routability tokens are 6888 still exposed only to one path within the whole Internet. 6889 However, the mobile nodes are often found on an insecure link, 6890 such as a public access Wireless LAN. Thus this addition makes a 6891 practical difference in many cases. 6893 For further information about the design rationale of the return 6894 routability procedure, see [27, 34, 33, 32]. The used mechanisms 6895 have been adopted from these documents. 6897 15.4.2 Achieved Security Properties 6899 The return routability procedure protects Binding Updates against all 6900 attackers who are unable to monitor the path between the home agent 6901 and the correspondent node. The procedure does not defend against 6902 attackers who can monitor this path. Note that such attackers are in 6903 any case able to mount an active attack against the mobile node when 6904 it is at its home location. The possibility of such attacks is not 6905 an impediment to the deployment of Mobile IPv6, because these attacks 6906 are possible regardless of whether Mobile IPv6 is in use. 6908 This procedure also protects against Denial-of-Service attacks in 6909 which the attacker pretends to be a mobile, but uses the victim's 6910 address as the care-of address. This would cause the correspondent 6911 node to send the victim some unexpected traffic. The procedure 6912 defends against these attacks by requiring at least passive presence 6913 of the attacker at the care-of address or on the path from the 6914 correspondent to the care-of address. Normally, this will be the 6915 mobile node. 6917 15.4.3 Comparison to Regular IPv6 Communications 6919 This section discusses the protection offered by the return 6920 routability method by comparing it to the security of regular IPv6 6921 communications. We will divide vulnerabilities in three classes: (1) 6922 those related to attackers on the local network of the mobile node, 6923 home agent, or the correspondent node, (2) those related to attackers 6924 on the path between the home network and the correspondent node, and 6925 (3) off-path attackers, i.e. the rest of the Internet. 6927 We will now discuss the vulnerabilities of regular IPv6 6928 communications. The on-link vulnerabilities of IPv6 communications 6929 include Denial-of-Service, Masquerading, Man-in-the-Middle, 6930 Eavesdropping, and other attacks. These attacks can be launched 6931 through spoofing Router Discovery, Neighbor Discovery and other IPv6 6932 mechanisms. Some of these attacks can be prevented with the use of 6933 cryptographic protection in the packets. 6935 A similar situation exists with on-path attackers. That is, without 6936 cryptographic protection the traffic is completely vulnerable. 6938 Assuming that attackers have not penetrated the security of the 6939 Internet routing protocols, attacks are much harder to launch from 6940 off-path locations. Attacks that can be launched from these 6941 locations are mainly Denial-of-Service attacks, such as flooding and/ 6942 or reflection attacks. It is not possible for an off-path attacker 6943 to become a Man-in-the-Middle. 6945 Next, we will consider the vulnerabilities that exist when IPv6 is 6946 used together with Mobile IPv6 and the return routability procedure. 6947 On the local link the vulnerabilities are same as those as in IPv6, 6948 but Masquerade and Man-in-the-Middle attacks can now be launched also 6949 against future communications, and not just against current 6950 communications. If a Binding Update was sent while the attacker was 6951 present on the link, its effects stay during the lifetime of the 6952 binding. This happens even if the attacker moves away from the link. 6953 In contrast, an attacker who uses only plain IPv6 generally has to 6954 stay on the link in order to continue the attack. Note that in order 6955 to launch these new attacks, the IP address of the victim must be 6956 known. This makes this attack feasible mainly in the context of 6957 well-known interface IDs, such as those already appearing in the 6958 traffic on the link or registered in the DNS. 6960 On-path attackers can exploit similar vulnerabilities as in regular 6961 IPv6. There are some minor differences, however. Masquerade, 6962 Man-in-the-Middle, and Denial-of-Service attacks can be launched with 6963 just the interception of a few packets, whereas in regular IPv6 it is 6964 necessary to intercept every packet. The effect of the attacks is 6965 the same regardless of the method, however. In any case, the most 6966 difficult task attacker faces in these attacks is getting on the 6967 right path. 6969 The vulnerabilities for off-path attackers are the same as in regular 6970 IPv6. Those nodes that are not on the path between the home agent 6971 and the correspondent node will not be able to receive the home 6972 address probe messages. 6974 In conclusion, we can state the following main results from this 6975 comparison: 6977 o Return routability procedure prevents any off-path attacks beyond 6978 those that are already possible in regular IPv6. This is the most 6979 important result, and prevents attackers from the Internet from 6980 exploiting any vulnerabilities. 6982 o Vulnerabilities to attackers on the home agent link, the 6983 correspondent node link, and the path between them are roughly the 6984 same as in regular IPv6. 6986 o However, one difference is that in basic IPv6 an on-path attacker 6987 must be constantly present on the link or the path, whereas with 6988 Mobile IPv6 an attacker can leave a binding behind after moving 6989 away. 6991 For this reason, this specification limits the creation of 6992 bindings to at most MAX_TOKEN_LIFETIME seconds after the last 6993 routability check has been performed, and limits the duration of a 6994 binding to at most MAX_RR_BINDING_LIFETIME seconds. With these 6995 limitation, attackers cannot take practical advantages of this 6996 vulnerability. 6998 o There are some other minor differences, such as an effect to the 6999 Denial-of-Service vulnerabilities. These can be considered to be 7000 insignificant. 7002 o The path between the home agent and a correspondent node is 7003 typically easiest to attack on the links at either end, in 7004 particular if these links are publicly accessible wireless LANs. 7006 Attacks against the routers or switches on the path are typically 7007 harder to accomplish. The security on layer 2 of the links plays 7008 then a major role in the resulting overall network security. 7009 Similarly, security of IPv6 Neighbor and Router Discovery on these 7010 links has a large impact. If these were secured using some new 7011 technology in the future, this could change the situation 7012 regarding the easiest point of attack. 7014 For a more in-depth discussion of these issues, see [32]. 7016 15.4.4 Replay Attacks 7018 The return routability procedure also protects the participants 7019 against replayed Binding Updates. The attacker is unable replay the 7020 same message due to the sequence number which is a part of the 7021 Binding Update. It is also unable to modify the Binding Update since 7022 the MAC verification would fail after such a modification. 7024 Care must be taken when removing bindings at the correspondent node, 7025 however. If a binding is removed while the nonce used in its 7026 creation is still valid, an attacker could replay the old Binding 7027 Update. Rules outlined in Section 5.2.8 ensure that this cannot 7028 happen. 7030 15.4.5 Denial-of-Service Attacks 7032 The return routability procedure has protection against resource 7033 exhaustion Denial-of-Service attacks. The correspondent nodes do not 7034 retain any state about individual mobile nodes until an authentic 7035 Binding Update arrives. This is achieved through the construct of 7036 keygen tokens from the nonces and node keys that are not specific to 7037 individual mobile nodes. The keygen tokens can be reconstructed by 7038 the correspondent node, based on the home and care-of address 7039 information that arrives with the Binding Update. This means that 7040 the correspondent nodes are safe against memory exhaustion attacks 7041 except where on-path attackers are concerned. Due to the use of 7042 symmetric cryptography, the correspondent nodes are relatively safe 7043 against CPU resource exhaustion attacks as well. 7045 Nevertheless, as [27] describes, there are situations in which it is 7046 impossible for the mobile and correspondent nodes to determine if 7047 they actually need a binding or whether they just have been fooled 7048 into believing so by an attacker. Therefore, it is necessary to 7049 consider situations where such attacks are being made. 7051 Even if route optimization is a very important optimization, it is 7052 still only an optimization. A mobile node can communicate with a 7053 correspondent node even if the correspondent refuses to accept any 7054 Binding Updates. However, performance will suffer because packets 7055 from the correspondent node to the mobile node will be routed via the 7056 mobile's home agent rather than a more direct route. A correspondent 7057 node can protect itself against some of these resource exhaustion 7058 attacks as follows. If the correspondent node is flooded with a 7059 large number of Binding Updates that fail the cryptographic integrity 7060 checks, it can stop processing Binding Updates. If a correspondent 7061 node finds that it is spending more resources on checking bogus 7062 Binding Updates than it is likely to save by accepting genuine 7063 Binding Updates, then it may silently discard some or all Binding 7064 Updates without performing any cryptographic operations. 7066 Layers above IP can usually provide additional information to decide 7067 if there is a need to establish a binding with a specific peer. For 7068 example, TCP knows if the node has a queue of data that it is trying 7069 to send to a peer. An implementation of this specification is not 7070 required to make use of information from higher protocol layers, but 7071 some implementations are likely to be able to manage resources more 7072 effectively by making use of such information. 7074 We also require that all implementations be capable of 7075 administratively disabling route optimization. 7077 15.4.6 Key Lengths 7079 Attackers can try to break the return routability procedure in many 7080 ways. Section 15.4.2 discusses the situation where the attacker can 7081 see the cryptographic values sent in the clear, and Section 15.4.3 7082 discusses the impact this has on IPv6 communications. This section 7083 discusses whether attackers can guess the right values without seeing 7084 them. 7086 While the return routability procedure is in progress, 64 bit cookies 7087 are used to protect spoofed responses. This is believed to be 7088 sufficient, given that to blindly spoof a response a very large 7089 number of messages would have to be sent before success would be 7090 probable. 7092 The tokens used in the return routability procedure provide together 7093 128 bits of information. This information is used internally as an 7094 input to a hash function to produce a 160 bit quantity suitable for 7095 producing the keyed hash in the Binding Update using the HMAC_SHA1 7096 algorithm. The final keyed hash length is 96 bits. The limiting 7097 factors in this case are the input token lengths and the final keyed 7098 hash length. The internal hash function application does not reduce 7099 the entropy. 7101 The 96 bit final keyed hash is of typical size and believed to be 7102 secure. The 128 bit input from the tokens is broken in two pieces, 7103 the home keygen token and the care-of keygen token. An attacker can 7104 try to guess the right cookie value, but again this would require a 7105 large number of messages, in the average 2**63 messages for one or 7106 2**127 for two. Furthermore, given that the cookies are valid only 7107 for a short period of time, the attack has to keep a high constant 7108 message rate to achieve a lasting effect. This does not appear 7109 practical. 7111 When the mobile node is returning home, it is allowed to use just the 7112 home keygen token of 64 bits. This is less than 128 bits, but 7113 attacking it blindly would still require a large number of messages 7114 to be sent. If the attacker is on the path and capable of seeing the 7115 Binding Update, it could conceivably break the keyed hash with brute 7116 force. However, in this case the attacker has to be on path, which 7117 appears to offer easier ways for denial-of-service than preventing 7118 route optimization. 7120 15.5 Dynamic Home Agent Address Discovery 7122 The dynamic home agent address discovery function could be used to 7123 learn the addresses of home agents in the home network. 7125 The ability to learn addresses of nodes may be useful to attackers, 7126 because brute-force scanning of the address space is not practical 7127 with IPv6. Thus, they could benefit from any means which make 7128 mapping the networks easier. For example, if a security threat 7129 targeted at routers or even home agents is discovered, having a 7130 simple ICMP mechanism to find out possible targets easily may prove 7131 to be an additional (though minor) security risk. 7133 Apart from discovering the address(es) of home agents, attackers will 7134 not be able to learn much from this information, however, and mobile 7135 nodes cannot be tricked into using wrong home agents as all other 7136 communication with the home agents is secure. 7138 15.6 Mobile Prefix Discovery 7140 The mobile prefix discovery function may leak interesting information 7141 about network topology and prefix lifetimes to eavesdroppers, and for 7142 this reason requests for this information have to be authenticated. 7143 Responses and unsolicited prefix information needs to be 7144 authenticated to prevent the mobile nodes from being tricked into 7145 believing false information about the prefixes, and possibly 7146 preventing communications with the existing addresses. Optionally, 7147 encryption may be applied to prevent leakage of the prefix 7148 information. 7150 15.7 Tunneling via the Home Agent 7152 Tunnels between the mobile node and the home agent can be protected 7153 by ensuring proper use of source addresses, and optional 7154 cryptographic protection. These procedures are discussed in Section 7155 5.5. 7157 Binding Updates to the home agents are secure. When receiving 7158 tunneled traffic the home agent verifies the outer IP address 7159 corresponds to the current location of the mobile node. This acts as 7160 a weak form of protection against spoofing packets that appear to 7161 come from the mobile node. This is particularly useful, if no 7162 end-to-end security is being applied between the mobile and 7163 correspondent nodes. The outer IP address check prevents attacks 7164 where the attacker is controlled by ingress filtering. It also 7165 prevents attacks when the attacker does not know the current care-of 7166 address of the mobile node. Attackers who know the care-of address 7167 and are not controlled by ingress filtering could still send traffic 7168 through the home agent. This includes attackers on the same local 7169 link as the mobile node is currently on. But such attackers could in 7170 any case send packets that appear to come from the mobile node, 7171 without attacking the tunnel; the attacker could simply send packets 7172 with the source address set to the mobile node's home address. 7173 However, this attack does not work if the final destination of the 7174 packet is in the home network, and some form of perimeter defense is 7175 being applied for packets sent to those destinations. In such cases 7176 it is recommended that either end-to-end security or additional 7177 tunnel protection is applied, as is usual in remote access 7178 situations. 7180 Home agents and mobile nodes may use IPsec ESP to protect payload 7181 packets tunneled between themselves. This is useful to protect 7182 communications against attackers on the path of the tunnel. 7184 When site local home address are used, reverse tunneling can be used 7185 to send site local traffic from another location. Administrators 7186 should be aware of this when allowing such home addresses. In 7187 particular, the outer IP address check described above is not 7188 sufficient against all attackers. The use of encrypted tunnels is 7189 particularly useful for this kind of home addresses. 7191 15.8 Home Address Option 7193 When the mobile node sends packets directly to the correspondent 7194 node, the Source Address field of the packet's IPv6 header is the 7195 care-of address. Ingress filtering [26] works therefore in the usual 7196 manner even for mobile nodes, as the Source Address is topologically 7197 correct. The Home Address option is used to inform the correspondent 7198 node of the mobile node's home address. 7200 However, the care-of address in the Source Address field does not 7201 survive in replies sent by the correspondent node unless it has a 7202 binding for this mobile node. Also, not all attacker tracing 7203 mechanisms work when packets are being reflected through 7204 correspondent nodes using the Home Address option. For these 7205 reasons, this specification restricts the use of the Home Address 7206 option. It may only used when a binding has already been established 7207 with the participation of the node at the home address, as described 7208 in Section 5.5 and Section 6.3. This prevents reflection attacks 7209 through the use of the Home Address option. It also ensures that the 7210 correspondent nodes reply to the same address as the mobile node 7211 sends traffic from. 7213 No special authentication of the Home Address option is required 7214 beyond the above, but note that if the IPv6 header of a packet is 7215 covered by IPsec Authentication Header, then that authentication 7216 covers the Home Address option as well. Thus, even when 7217 authentication is used in the IPv6 header, the security of the Source 7218 Address field in the IPv6 header is not compromised by the presence 7219 of a Home Address option. Without authentication of the packet, then 7220 any field in the IPv6 header, including the Source Address field, and 7221 any other parts of the packet, including the Home Address option, can 7222 be forged or modified in transit. In this case, the contents of the 7223 Home Address option is no more suspect than any other part of the 7224 packet. 7226 15.9 Type 2 Routing Header 7228 The definition of the type 2 routing header is described in Section 7229 6.4. This definition and the associated processing rules have been 7230 chosen so that the header cannot be used for what is traditionally 7231 viewed as source routing. In particular, the Home Address in the 7232 routing header will always have to be assigned to the home address of 7233 the receiving node. Otherwise the packet will be dropped. 7235 Generally, source routing has a number of security concerns. These 7236 include the automatic reversal of unauthenticated source routes 7237 (which is an issue for IPv4, but not for IPv6). Another concern is 7238 the ability to use source routing to "jump" between nodes inside, as 7239 well as outside a firewall. These security concerns are not issues 7240 in Mobile IPv6, due to the rules mentioned above. 7242 In essence the semantics of the type 2 routing header is the same as 7243 a special form of IP-in-IP tunneling where the inner and outer source 7244 addresses are the same. 7246 This implies that a device which implements filtering of packets 7247 should be able to distinguish between a type 2 routing header and 7248 other routing headers, as required in Section 8.3. This is necessary 7249 in order to allow Mobile IPv6 traffic while still having the option 7250 to filter out other uses of routing headers. 7252 16. Contributors 7254 Tuomas Aura, Mike Roe, Greg O'Shea, Pekka Nikander, Erik Nordmark, 7255 and Michael Thomas worked on the return routability protocols which 7256 eventually led to the procedures used in this protocol. The 7257 procedures described in [34] were adopted in the protocol. 7259 Significant contributions were made by members of the Mobile IPv6 7260 Security Design Team, including (in alphabetical order) Gabriel 7261 Montenegro, Erik Nordmark and Pekka Nikander, who have contributed 7262 volumes of text to this specification. 7264 17. Acknowledgements 7266 We would like to thank the members of the Mobile IP and IPng Working 7267 Groups for their comments and suggestions on this work. We would 7268 particularly like to thank (in alphabetical order) Fred Baker, Josh 7269 Broch, Samita Chakrabarti, Robert Chalmers, Noel Chiappa, Greg Daley, 7270 Vijay Devarapalli, Rich Draves, Francis Dupont, Thomas Eklund, 7271 Jun-Ichiro Itojun Hagino, Brian Haley, Marc Hasson, John Ioannidis, 7272 James Kempf, Rajeev Koodli, Krishna Kumar, T.J. Kniveton, Joe Lau, 7273 Jiwoong Lee, Aime Le Rouzic, Vesa-Matti Mantyla, Kevin Miles, Glenn 7274 Morrow, Thomas Narten, Karen Nielsen, Simon Nybroe, David Oran, Brett 7275 Pentland, Lars Henrik Petander, Basavaraj Patil, Mohan Parthasarathy, 7276 Alexandru Petrescu, Mattias Petterson, Ken Powell, Phil Roberts, Ed 7277 Remmell, Patrice Romand, Luis A. Sanchez, Jeff Schiller, Pekka 7278 Savola, Arvind Sevalkar, Keiichi Shima, Tom Soderlund, Hesham 7279 Soliman, Jim Solomon, Tapio Suihko, Dave Thaler, Benny Van Houdt, 7280 Jon-Olov Vatn, Carl E. Williams, Vladislav Yasevich, Alper Yegin, 7281 and Xinhua Zhao, for their detailed reviews of earlier versions of 7282 this document. Their suggestions have helped to improve both the 7283 design and presentation of the protocol. 7285 We would also like to thank the participants of the Mobile IPv6 7286 testing event (1999), implementors who participated Mobile IPv6 7287 interoperability testing at Connectathons (2000, 2001, 2002, and 7288 2003), and the participants at the ETSI interoperability testing 7289 (2000, 2002). Finally, we would like to thank the TAHI project who 7290 has provided test suites for Mobile IPv6. 7292 Normative References 7294 [1] Eastlake, D., Crocker, S. and J. Schiller, "Randomness 7295 Recommendations for Security", RFC 1750, December 1994. 7297 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement 7298 Levels", BCP 14, RFC 2119, March 1997. 7300 [3] Hinden, R. and S. Deering, "IP Version 6 Addressing 7301 Architecture", RFC 2373, July 1998. 7303 [4] Kent, S. and R. Atkinson, "Security Architecture for the 7304 Internet Protocol", RFC 2401, November 1998. 7306 [5] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, 7307 November 1998. 7309 [6] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload 7310 (ESP)", RFC 2406, November 1998. 7312 [7] Piper, D., "The Internet IP Security Domain of Interpretation 7313 for ISAKMP", RFC 2407, November 1998. 7315 [8] Maughan, D., Schertler, M., Schneider, M. and J. Turner, 7316 "Internet Security Association and Key Management Protocol 7317 (ISAKMP)", RFC 2408, November 1998. 7319 [9] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", 7320 RFC 2409, November 1998. 7322 [10] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 7323 Considerations Section in RFCs", BCP 26, RFC 2434, October 7324 1998. 7326 [11] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 7327 Specification", RFC 2460, December 1998. 7329 [12] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery 7330 for IP Version 6 (IPv6)", RFC 2461, December 1998. 7332 [13] Thomson, S. and T. Narten, "IPv6 Stateless Address 7333 Autoconfiguration", RFC 2462, December 1998. 7335 [14] Conta, A. and S. Deering, "Internet Control Message Protocol 7336 (ICMPv6) for the Internet Protocol Version 6 (IPv6) 7337 Specification", RFC 2463, December 1998. 7339 [15] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 7340 Specification", RFC 2473, December 1998. 7342 [16] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast 7343 Addresses", RFC 2526, March 1999. 7345 [17] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener 7346 Discovery (MLD) for IPv6", RFC 2710, October 1999. 7348 [18] Narten, T. and R. Draves, "Privacy Extensions for Stateless 7349 Address Autoconfiguration in IPv6", RFC 3041, January 2001. 7351 [19] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an 7352 On-line Database", RFC 3232, January 2002. 7354 [20] National Institute of Standards and Technology, "Secure Hash 7355 Standard", FIPS PUB 180-1, April 1995, . 7358 [21] Arkko, J., Devarapalli, V. and F. Dupont, "Using IPsec to 7359 Protect Mobile IPv6 Signaling betweenMobile Nodes and Home 7360 Agents", draft-ietf-mobileip-mipv6-ha-ipsec-06 (work in 7361 progress), June 2003. 7363 Informative References 7365 [22] Perkins, C., "IP Mobility Support", RFC 2002, October 1996. 7367 [23] Perkins, C., "IP Encapsulation within IP", RFC 2003, October 7368 1996. 7370 [24] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 7371 October 1996. 7373 [25] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing 7374 for Message Authentication", RFC 2104, February 1997. 7376 [26] Ferguson, P. and D. Senie, "Network Ingress Filtering: 7377 Defeating Denial of Service Attacks which employ IP Source 7378 Address Spoofing", RFC 2267, January 1998. 7380 [27] Aura, T. and J. Arkko, "MIPv6 BU Attacks and Defenses", 7381 draft-aura-mipv6-bu-attacks-01 (work in progress), March 2002. 7383 [28] Bellovin, S., "Guidelines for Mandating Automated Key 7384 Management", draft-bellovin-mandate-keymgmt-00 (work in 7385 progress), August 2003. 7387 [29] Droms, R., "Dynamic Host Configuration Protocol for IPv6 7388 (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), 7389 November 2002. 7391 [30] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 7392 draft-ietf-ipsec-ikev2-07 (work in progress), April 2003. 7394 [31] Draves, R., "Default Address Selection for IPv6", 7395 draft-ietf-ipv6-default-addr-select-09 (work in progress), 7396 August 2002. 7398 [32] Nikander, P., Aura, T., Arkko, J., Montenegro, G. and E. 7399 Nordmark, "Mobile IP version 6 Route Optimization Security 7400 Design Background", draft-nikander-mobileip-v6-ro-sec-00.txt 7401 (work in progress), April 2003. 7403 [33] Nordmark, E., "Securing MIPv6 BUs using return routability 7404 (BU3WAY)", draft-nordmark-mobileip-bu3way-00 (work in 7405 progress), November 2001. 7407 [34] Roe, M., Aura, T., O'Shea, G. and J. Arkko, "Authentication of 7408 Mobile IPv6 Binding Updates and Acknowledgments", 7409 draft-roe-mobileip-updateauth-02 (work in progress), March 7410 2002. 7412 [35] Savola, P., "Use of /127 Prefix Length Between Routers 7413 Considered Harmful", draft-savola-ipv6-127-prefixlen-04 (work 7414 in progress), June 2002. 7416 [36] Savola, P., "Security of IPv6 Routing Header and Home Address 7417 Options", draft-savola-ipv6-rh-ha-security-03 (work in 7418 progress), December 2002. 7420 [37] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 7421 (MLDv2) for IPv6", draft-vida-mld-v2-06 (work in progress), 7422 December 2002. 7424 Authors' Addresses 7426 David B. Johnson 7427 Rice University 7428 Dept. of Computer Science, MS 132 7429 6100 Main Street 7430 Houston TX 77005-1892 7431 USA 7433 EMail: dbj@cs.rice.edu 7435 Charles E. Perkins 7436 Nokia Research Center 7437 313 Fairchild Drive 7438 Mountain View CA 94043 7439 USA 7441 EMail: charliep@iprg.nokia.com 7443 Jari Arkko 7444 Ericsson 7445 Jorvas 02420 7446 Finland 7448 EMail: jari.arkko@ericsson.com 7450 Appendix A. Changes from Previous Version of the Draft 7452 This appendix briefly lists some of the major changes in this draft 7453 relative to the previous version of this same draft, 7454 draft-ietf-mobileip-ipv6-23.txt: 7456 o A typo in Section 6.8 has been corrected; rules regarding 7457 reception of Mobile Prefix Advertisements apply to mobile nodes, 7458 not home agents (tracked issue 317). 7460 o A sentence has been removed from Section 10.3.1, since it dealt 7461 with the tracking of router advertisements by other home agents, 7462 which is a function that was already removed earlier in an IESG 7463 review (tracked issue 316). 7465 Appendix B. Future Extensions 7467 B.1 Piggybacking 7469 This document does not specify how to piggyback payload packets on 7470 the binding related messages. However, it is envisioned that this 7471 can be specified in a separate document when currently discussed 7472 issues such as the interaction between piggybacking and IPsec are 7473 fully resolved (see also Appendix B.3). The return routability 7474 messages can indicate support for piggybacking with a new mobility 7475 option. 7477 B.2 Triangular Routing 7479 Due to the concerns about opening reflection attacks with the Home 7480 Address destination option, this specification requires that this 7481 option must be verified against the Binding Cache, i.e., there must 7482 be a Binding Cache entry for the Home Address and Care-of Address. 7484 Future extensions may be specified that allow the use of unverified 7485 Home Address destination options in ways that do not introduce 7486 security issues. 7488 B.3 New Authorization Methods 7490 While the return routability procedure provides a good level of 7491 security, there exists methods that have even higher levels of 7492 security. Secondly, as discussed in Section 15.4, future 7493 enhancements of IPv6 security may cause a need to improve also the 7494 security of the return routability procedure. Using IPsec as the 7495 sole method for authorizing Binding Updates to correspondent nodes is 7496 also possible. The protection of the Mobility Header for this 7497 purpose is easy, though one must ensure that the IPsec SA was created 7498 with appropriate authorization to use the home address referenced in 7499 the Binding Update. For instance, a certificate used by IKE to 7500 create the security association might contain the home address. A 7501 future specification may specify how this is done. 7503 B.4 Dynamically Generated Home Addresses 7505 A future version of this specification may include functionality that 7506 allows the generation of new home addresses without requiring 7507 pre-arranged security associations or certificates even for the new 7508 addresses. 7510 B.5 Remote Home Address Configuration 7512 The method for initializing a mobile node's home addresses on 7513 power-up or after an extended period of being disconnected from the 7514 network is beyond the scope of this specification. Whatever 7515 procedure is used should result in the mobile node having the same 7516 stateless or stateful (e.g., DHCPv6) home address autoconfiguration 7517 information it would have if it were attached to the home network. 7518 Due to the possibility that the home network could be renumbered 7519 while the mobile node is disconnected, a robust mobile node would not 7520 rely solely on storing these addresses locally. 7522 Such a mobile node could initialize by using the following procedure: 7524 1. Generate a care-of address. 7526 2. Query DNS for an anycast address associated with the FQDN of the 7527 home agent(s). 7529 3. Perform home agent address discovery, and select a home agent. 7531 4. Configure one home address based on the selected home agent's 7532 subnet prefix and the interface identifier of the mobile node. 7534 5. Create security associations and security policy database entries 7535 for protecting the traffic between the selected home address and 7536 home agent. 7538 6. Perform a home registration to the selected home agent. 7540 7. Perform mobile prefix discovery. 7542 8. Make a decision if further home addresses need to be configured. 7544 This procedure is restricted to those situations where the home 7545 prefix is 64 bits and the mobile node knows its own interface 7546 identifier of also 64 bits. 7548 B.6 Neighbor Discovery Extensions 7550 Future specifications may improve the efficiency of Neighbor 7551 Discovery tasks, which could be helpful for fast movements. One 7552 factor which is currently being looked at is the delays caused by the 7553 Duplicate Address Detection mechanism. Currently, Duplicate Address 7554 Detection needs to be performed for every new care-of address as the 7555 mobile node moves, and for the mobile node's link-local address on 7556 every new link. In particular, the need and the trade-offs of 7557 re-performing Duplicate Address Detection for the link-local address 7558 every time when the mobile node moves on to new links will need to be 7559 examined. Improvements in this area are, however, generally 7560 applicable and progressed independently from Mobile IPv6 7561 specification. 7563 Future functional improvements may also be relevant for Mobile IPv6 7564 and other applications. For instance, mechanisms that would allow 7565 recovery from a Duplicate Address Detection collision would be useful 7566 for link-local, care-of, and home addresses. 7568 Intellectual Property Statement 7570 The IETF takes no position regarding the validity or scope of any 7571 intellectual property or other rights that might be claimed to 7572 pertain to the implementation or use of the technology described in 7573 this document or the extent to which any license under such rights 7574 might or might not be available; neither does it represent that it 7575 has made any effort to identify any such rights. Information on the 7576 IETF's procedures with respect to rights in standards-track and 7577 standards-related documentation can be found in BCP-11. Copies of 7578 claims of rights made available for publication and any assurances of 7579 licenses to be made available, or the result of an attempt made to 7580 obtain a general license or permission for the use of such 7581 proprietary rights by implementors or users of this specification can 7582 be obtained from the IETF Secretariat. 7584 The IETF invites any interested party to bring to its attention any 7585 copyrights, patents or patent applications, or other proprietary 7586 rights which may cover technology that may be required to practice 7587 this standard. Please address the information to the IETF Executive 7588 Director. 7590 Full Copyright Statement 7592 Copyright (C) The Internet Society (2003). All Rights Reserved. 7594 This document and translations of it may be copied and furnished to 7595 others, and derivative works that comment on or otherwise explain it 7596 or assist in its implementation may be prepared, copied, published 7597 and distributed, in whole or in part, without restriction of any 7598 kind, provided that the above copyright notice and this paragraph are 7599 included on all such copies and derivative works. However, this 7600 document itself may not be modified in any way, such as by removing 7601 the copyright notice or references to the Internet Society or other 7602 Internet organizations, except as needed for the purpose of 7603 developing Internet standards in which case the procedures for 7604 copyrights defined in the Internet Standards process must be 7605 followed, or as required to translate it into languages other than 7606 English. 7608 The limited permissions granted above are perpetual and will not be 7609 revoked by the Internet Society or its successors or assignees. 7611 This document and the information contained herein is provided on an 7612 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 7613 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 7614 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 7615 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 7616 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 7618 Acknowledgement 7620 Funding for the RFC Editor function is currently provided by the 7621 Internet Society.