idnits 2.17.1 draft-templin-aerolink-04.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == The 'Obsoletes: ' line in the draft header should list only the _numbers_ of the RFCs which will be obsoleted by this document (if approved); it should not include the word 'RFC' in the list. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (January 28, 2014) is 3741 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) == Unused Reference: 'RFC0768' is defined on line 1064, but no explicit reference was found in the text == Unused Reference: 'RFC0791' is defined on line 1067, but no explicit reference was found in the text == Unused Reference: 'RFC0792' is defined on line 1070, but no explicit reference was found in the text == Unused Reference: 'RFC2460' is defined on line 1076, but no explicit reference was found in the text == Unused Reference: 'RFC4862' is defined on line 1089, but no explicit reference was found in the text == Unused Reference: 'RFC3315' is defined on line 1106, but no explicit reference was found in the text == Unused Reference: 'RFC6204' is defined on line 1137, but no explicit reference was found in the text == Unused Reference: 'RFC6980' is defined on line 1161, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 6434 (Obsoleted by RFC 8504) -- Obsolete informational reference (is this intentional?): RFC 879 (Obsoleted by RFC 7805, RFC 9293) -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 3633 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 6204 (Obsoleted by RFC 7084) -- Obsolete informational reference (is this intentional?): RFC 6691 (Obsoleted by RFC 9293) Summary: 2 errors (**), 0 flaws (~~), 10 warnings (==), 6 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Obsoletes: rfc6706 (if approved) January 28, 2014 5 Intended status: Standards Track 6 Expires: August 1, 2014 8 Transmission of IPv6 Packets over AERO Links 9 draft-templin-aerolink-04.txt 11 Abstract 13 This document specifies the operation of IPv6 over tunnel virtual 14 Non-Broadcast, Multiple Access (NBMA) links using Asymmetric Extended 15 Route Optimization (AERO). Nodes attached to AERO links can exchange 16 packets via trusted intermediate routers on the link that provide 17 forwarding services to reach off-link destinations and/or redirection 18 services to inform the node of an on-link neighbor that is closer to 19 the final destination. Operation of the IPv6 Neighbor Discovery (ND) 20 protocol over AERO links is based on an IPv6 link local address 21 format known as the AERO address. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on August 1, 2014. 40 Copyright Notice 42 Copyright (c) 2014 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 5 60 3.1. AERO Interface Configuration . . . . . . . . . . . . . . . 5 61 3.2. AERO Interface Encapsulation, Re-encapsulation and 62 Decapsulation . . . . . . . . . . . . . . . . . . . . . . 7 63 3.3. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 8 64 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . . 9 65 3.5. AERO Reference Operational Scenario . . . . . . . . . . . 9 66 3.6. AERO Router Discovery and Prefix Delegation . . . . . . . 11 67 3.6.1. AERO Client Behavior . . . . . . . . . . . . . . . . . 11 68 3.6.2. AERO Server Behavior . . . . . . . . . . . . . . . . . 11 69 3.7. AERO Neighbor Solicitation and Advertisement . . . . . . . 12 70 3.8. AERO Redirection . . . . . . . . . . . . . . . . . . . . . 13 71 3.8.1. Classical Redirection Approaches . . . . . . . . . . . 13 72 3.8.2. AERO Redirection Concept of Operations . . . . . . . . 14 73 3.8.3. AERO Redirection Message Format . . . . . . . . . . . 15 74 3.8.4. Sending Predirects . . . . . . . . . . . . . . . . . . 16 75 3.8.5. Processing Predirects and Sending Redirects . . . . . 17 76 3.8.6. Re-encapsulating and Relaying Redirects . . . . . . . 18 77 3.8.7. Processing Redirects . . . . . . . . . . . . . . . . . 18 78 3.9. Neighbor Reachability Considerations . . . . . . . . . . . 19 79 3.10. MTU Considerations . . . . . . . . . . . . . . . . . . . . 19 80 3.11. Mobility and Link-Layer Address Change Considerations . . 21 81 3.12. Underlying Protocol Version Considerations . . . . . . . . 21 82 3.13. Multicast Considerations . . . . . . . . . . . . . . . . . 21 83 3.14. Operation on Server-less AERO Links . . . . . . . . . . . 21 84 3.15. Other Considerations . . . . . . . . . . . . . . . . . . . 22 85 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 22 86 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 87 6. Security Considerations . . . . . . . . . . . . . . . . . . . 22 88 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 89 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 90 8.1. Normative References . . . . . . . . . . . . . . . . . . . 23 91 8.2. Informative References . . . . . . . . . . . . . . . . . . 24 92 Appendix A. AERO Server and Relay Interworking . . . . . . . . . 25 93 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 27 95 1. Introduction 97 This document specifies the operation of IPv6 over tunnel virtual 98 Non-Broadcast, Multiple Access (NBMA) links using Asymmetric Extended 99 Route Optimization (AERO). Nodes attached to AERO links can exchange 100 packets via trusted intermediate routers on the link that provide 101 forwarding services to reach off-link destinations and/or redirection 102 services to inform the node of an on-link neighbor that is closer to 103 the final destination. 105 Nodes on AERO links use an IPv6 link-local address format known as 106 the AERO Address. This address type has properties that statelessly 107 link IPv6 Neighbor Discovery (ND) to IPv6 routing. The AERO link can 108 be used for tunneling to neighboring nodes on either IPv6 or IPv4 109 networks, i.e., AERO views the IPv6 and IPv4 networks as equivalent 110 links for tunneling. The remainder of this document presents the 111 AERO specification. 113 2. Terminology 115 The terminology in the normative references applies; the following 116 terms are defined within the scope of this document: 118 AERO link 119 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 120 configured over a node's attached IPv6 and/or IPv4 networks. All 121 nodes on the AERO link appear as single-hop neighbors from the 122 perspective of IPv6. 124 AERO interface 125 a node's attachment to an AERO link. 127 AERO address 128 an IPv6 link-local address assigned to an AERO interface and 129 constructed as specified in Section 3.3. 131 AERO node 132 a node that is connected to an AERO link and that participates in 133 IPv6 Neighbor Discovery over the link. 135 AERO Client ("client") 136 a node that configures either a host interface or a router 137 interface on an AERO link. 139 AERO Server ("server") 140 a node that configures a router interface on an AERO link over 141 which it can provide default forwarding and redirection services 142 for other AERO nodes. 144 AERO Relay ("relay") 145 a node that relays IPv6 packets between Servers on the same AERO 146 link, and/or that forwards IPv6 packets between the AERO link and 147 the IPv6 Internet. An AERO Relay may or may not also be 148 configured as an AERO Server. 150 ingress tunnel endpoint (ITE) 151 an AERO interface endpoint that injects packets into an AERO link. 153 egress tunnel endpoint (ETE) 154 an AERO interface endpoint that receives tunneled packets from an 155 AERO link. 157 underlying network 158 a connected IPv6 or IPv4 network routing region over which AERO 159 nodes tunnel IPv6 packets. 161 underlying interface 162 an AERO node's interface point of attachment to an underlying 163 network. 165 underlying address 166 an IPv6 or IPv4 address assigned to an AERO node's underlying 167 interface. When UDP encapsulation is used, the UDP port number is 168 also considered as part of the underlying address. Underlying 169 addresses are used as the source and destination addresses of the 170 AERO encapsulation header. 172 link-layer address 173 the same as defined for "underlying address" above. 175 network layer address 176 an IPv6 address used as the source or destination address of the 177 inner IPv6 packet header. 179 end user network (EUN) 180 an IPv6 network attached to a downstream interface of an AERO 181 Client (where the AERO interface is seen as the upstream 182 interface). 184 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 185 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 186 document are to be interpreted as described in [RFC2119]. 188 3. Asymmetric Extended Route Optimization (AERO) 190 The following sections specify the operation of IPv6 over Asymmetric 191 Extended Route Optimization (AERO) links: 193 3.1. AERO Interface Configuration 195 AERO hosts configure their AERO interfaces as host interfaces, while 196 AERO routers configure their AERO interfaces as (non-advertising) 197 router interfaces. End system applications on AERO hosts bind 198 directly to the AERO interface, while applications on AERO routers 199 (or IPv6 hosts served by an AERO router) bind to end user network 200 (EUN) interfaces beyond which their packets may be forwarded over an 201 AERO interface. 203 AERO interfaces use IPv6-in-IPv6 encapsulation [RFC2473] to exchange 204 tunneled packets with AERO neighbors attached to an underlying IPv6 205 network, and use IPv6-in-IPv4 encapsulation [RFC4213] to exchange 206 tunneled packets with AERO neighbors attached to an underlying IPv4 207 network. AERO interfaces can also use IPsec encapsulation [RFC4301] 208 (either IPv6-in-IPv6 or IPv6-in-IPv4) in environments where strong 209 authentication and confidentiality are required. When NAT traversal 210 and/or filtering middlebox traversal is necessary, a UDP header is 211 further inserted between the outer IP encapsulation header and the 212 inner packet. 214 AERO interfaces configure a Maximum Transmission Unit (MTU) that is 215 the larger of 1500 bytes and the MTU of the underlying interface 216 minus the encapsulation overhead (where the largest possible sizes 217 are 64KB minus encapsulation overhead over IPv4, and 4GB minus 218 encapsulation overhead over IPv6). 220 AERO interfaces maintain a neighbor cache and use a variation of 221 standard unicast IPv6 ND messaging. AERO interfaces use Neighbor 222 Solicitation (NS), Neighbor Advertisement (NA) and Redirect messages 223 the same as for any IPv6 link. They do not use Router Solicitation 224 (RS) and Router Advertisement (RA) messages for several reasons. 225 First, default router discovery is supported through other means more 226 appropriate for AERO links as described below. Second, discovery of 227 more-specific routes is through the receipt of NS, NA and Redirect 228 messages. Finally, AERO nodes receive IPv6 prefix delegations via 229 DHCPv6; hence, there is no need for RA-based prefix discovery. 231 AERO Neighbor Solicitation (NS) and Neighbor Advertisement (NA) 232 messages do not include Source/Target Link Layer Address Options 233 (S/TLLAO). Instead, AERO nodes determine the link-layer addresses of 234 neighbors by examining the encapsulation source address of any NS/NA 235 messages they receive and ignore any S/TLLAOs included in these 236 messages. This is vital to the operation of AERO links for which 237 neighbors are separated by Network Address Translators (NATs) - 238 either IPv4 or IPv6. 240 AERO Redirect messages include a TLLAO the same as for any IPv6 link. 241 The TLLAO includes the link-layer address of the target node, 242 including both the IP address and the UDP source port number used by 243 the target when it sends UDP-encapsulated packets over the AERO 244 interface (the TLLAO instead encodes the value 0 when the target does 245 not use UDP encapsulation). TLLAOs for target nodes that use an IPv6 246 underlying address include the full 16 bytes of the IPv6 address as 247 shown in Figure 1, while TLLAOs for target nodes that use an IPv4 248 underlying address include only the 4 bytes of the IPv4 address as 249 shown in Figure 2. 251 0 1 2 3 252 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 1 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 | Type = 2 | Length = 3 | UDP Source Port (or 0) | 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 | Reserved | 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 258 | | 259 +-- --+ 260 | | 261 +-- IPv6 Address --+ 262 | | 263 +-- --+ 264 | | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 267 Figure 1: AERO TLLAO Format for IPv6 269 0 1 2 3 270 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 1 271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 272 | Type = 2 | Length = 1 | UDP Source Port (or 0) | 273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 274 | IPv4 Address | 275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 Figure 2: AERO TLLAO Format for IPv4 279 Finally, nodes on AERO interfaces use a simple data origin 280 authentication for encapsulated packets they receive from other 281 nodes. In particular, AERO Clients accept encapsulated packets with 282 a link-layer source address belonging to their current AERO Server. 283 AERO nodes also accept encapsulated packets with a link-layer source 284 address that is correct for the network-layer source address. The 285 AERO node considers the link-layer source address correct for the 286 network-layer source address if there is an IPv6 route that matches 287 the network-layer source address as well as a neighbor cache entry 288 corresponding to the next hop that includes the link-layer address. 289 (An exception is that NS, NA and Redirect messages may include a 290 different link-layer address than the one currently in the neighbor 291 cache, and the new link-layer address updates the neighbor cache 292 entry.) 294 3.2. AERO Interface Encapsulation, Re-encapsulation and Decapsulation 296 AERO interfaces encapsulate IPv6 packets according to whether they 297 are entering the AERO interface for the first time or if they are 298 being forwarded out the same AERO interface that they arrived on. 299 This latter form of encapsulation is known as "re-encapsulation". 301 AERO interfaces encapsulate packets per the specifications in , 302 [RFC2473], [RFC4213] except that the interface copies the "TTL/Hop 303 Limit", "Type of Service/Traffic Class" and "Congestion Experienced" 304 values in the inner network layer header into the corresponding 305 fields in the outer IP header. For packets undergoing re- 306 encapsulation, the AERO interface instead copies the "TTL/Hop Limit", 307 "Type of Service/Traffic Class" and "Congestion Experienced" values 308 in the original outer IP header into the corresponding fields in the 309 new outer IP header (i.e., the values are transferred between outer 310 headers and *not* copied from the inner network layer header). 312 When UDP encapsulation is used, the AERO interface inserts a UDP 313 header between the inner header and outer IP header. The AERO 314 interface sets the UDP source port to a constant value that it will 315 use in each successive packet it sends, sets the UDP destination port 316 to 8060 (i.e., the IANA-registered port number for AERO), sets the 317 UDP checksum field to zero (see: [RFC6935][RFC6936]) and sets the UDP 318 length field to the length of the inner packet plus 8 bytes for the 319 UDP header itself. 321 The AERO interface next sets the outer IP protocol number to the 322 appropriate value for the first protocol layer within the 323 encapsulation (e.g., IPv6, IPv6 Fragment Header, UDP, etc.). When 324 IPv6 is used as the outer IP protocol, the ITE then sets the flow 325 label value in the outer IPv6 header the same as described in 326 [RFC6438]. When IPv4 is used as the outer IP protocol, the AERO 327 interface sets the DF bit as discussed in Section 3.10. 329 AERO interfaces decapsulate packets destined either to the localhost 330 or to a destination reached via an interface other than the receiving 331 AERO interface per the specifications in , [RFC2473], [RFC4213]. 332 When the encapsulated packet includes a UDP header, the AERO 333 interfaces examines the first octet of data following the UDP header 334 to determine the inner header type. If the most significant four 335 bits of the first octet encode the value '0110', the inner header is 336 an IPv6 header. Otherwise, the interface considers the first octet 337 as an IP protocol type that encodes the value '44' for IPv6 fragment 338 header, the value '50' for Encapsulating Security Payload, the value 339 '51' for Authentication Header etc. (If the first octet encodes the 340 value '0', the interface instead discards the packet, since this is 341 the value reserved for experimentation under , [RFC6706]). During 342 the decapsulation, the AERO interface records the UDP source port in 343 the neighbor cache entry for this neighbor then discards the UDP 344 header. 346 3.3. AERO Node Types 348 AERO Relays relay packets between nodes connected to the same AERO 349 link and also forward packets between the AERO link and the native 350 IPv6 network. The relaying process entails re-encapsulation of IPv6 351 packets that were received from a first AERO node and are to be 352 forwarded without modification to a second AERO node. 354 AERO Servers configure their AERO link interfaces as router 355 interfaces, and provide default routing services to AERO Clients. An 356 AERO Server may also act as an AERO Relay. 358 AERO Clients are provisioned with IPv6 Prefix Delegations either 359 through a DHCPv6 Prefix Delegation exchange with an AERO Server over 360 the AERO link or via a static delegation obtained through an out-of- 361 band exchange with an AERO link prefix delegation authority. Each 362 AERO Client receives at least a /64 prefix delegation, and may 363 receive even shorter prefixes. 365 AERO Clients that act as routers configure their AERO link interfaces 366 as router interfaces, i.e., even if the AERO Client otherwise 367 displays the outward characteristics of an ordinary host (for 368 example, the Client may internally configure both an AERO interface 369 and (internal virtual) EUN interfaces). AERO Clients that act as 370 routers sub-delegate portions of their received prefix delegations to 371 links on EUNs. 373 AERO Clients that act as ordinary hosts configure their AERO link 374 interfaces as host interfaces and assign one or more IPv6 addresses 375 taken from their received prefix delegations to their AERO interfaces 376 but DO NOT assign the delegated prefix itself to the AERO interface. 377 Instead, the host assigns the delegated prefix to a "black hole" 378 route so that unused portions of the prefix are nullified. 380 3.4. AERO Addresses 382 An AERO address is an IPv6 link-local address assigned to an AERO 383 interface and with an IPv6 prefix embedded within the interface 384 identifier. The AERO address is formatted as: 386 fe80::[IPv6 prefix] 388 Each AERO Client configures an AERO address based on the delegated 389 prefix it has received from the AERO link prefix delegation 390 authority. The address begins with the prefix fe80::/64 and includes 391 in its interface identifier the base /64 prefix taken from the 392 Client's delegated IPv6 prefix. The base prefix is determined by 393 masking the delegated prefix with the prefix length. For example, if 394 an AERO Client has received the prefix delegation: 396 2001:db8:1000:2000::/56 398 it would construct its AERO address as: 400 fe80::2001:db8:1000:2000 402 An AERO Client may receive multiple non-contiguous IPv6 prefix 403 delegations, in which case it would configure multiple AERO addresses 404 - one for each prefix. 406 Each AERO Server configures the special AERO address fe80::1 to 407 support the operation of IPv6 Neighbor Discovery over the AERO link; 408 the address therefore has the properties of an IPv6 Anycast address. 409 While all Servers configure the same AERO address and therefore 410 cannot be distinguished from one another at the network layer, 411 Clients can still distinguish Servers at the link layer by examining 412 the Servers' link-layer addresses. 414 Nodes that are configured as pure AERO Relays (i.e., and that do not 415 also act as Servers) do not configure an IPv6 address of any kind on 416 their AERO interfaces. The Relay's AERO interface is therefore used 417 purely for transit and does not participate in IPv6 ND message 418 exchanges. 420 3.5. AERO Reference Operational Scenario 422 Figure 3 depicts the AERO reference operational scenario. The figure 423 shows an AERO Server('A'), two AERO Clients ('B', 'D') and three 424 ordinary IPv6 hosts ('C', 'E', 'F'): 426 .-(::::::::) 427 .-(::: IPv6 :::)-. +-------------+ 428 (:::: Internet ::::)--| Host F | 429 `-(::::::::::::)-' +-------------+ 430 `-(::::::)-' 2001:db8:3::1 431 | 432 +--------------+ 433 | AERO Server A| 434 | (C->B; E->D) | 435 +--------------+ 436 fe80::1 437 L2(A) 438 | 439 X-----+-----------+-----------+--------X 440 | AERO Link | 441 L2(B) L2(D) 442 fe80::2001:db8:0:0 fe80::2001:db8:1:0 .-. 443 +--------------+ +--------------+ ,-( _)-. 444 | AERO Client B| | AERO Client D| .-(_ IPv6 )-. 445 | (default->A) | | (default->A) |--(__ EUN ) 446 +--------------+ +--------------+ `-(______)-' 447 2001:DB8:0::/48 2001:DB8:1::/48 | 448 | 2001:db8:1::1 449 .-. +-------------+ 450 ,-( _)-. 2001:db8:0::1 | Host E | 451 .-(_ IPv6 )-. +-------------+ +-------------+ 452 (__ EUN )--| Host C | 453 `-(______)-' +-------------+ 455 Figure 3: AERO Reference Operational Scenario 457 In Figure 3, AERO Server ('A') connects to the AERO link and connects 458 to the IPv6 Internet, either directly or via other IPv6 routers (not 459 shown). Server ('A') assigns the address fe80::1 to its AERO 460 interface with link-layer address L2(A). Server ('A') next arranges 461 to add L2(A) to a published list of valid Servers for the AERO link. 463 AERO Client ('B') assigns the address fe80::2001:db8:0:0 to its AERO 464 interface with link-layer address L2(B). Client ('B') configures a 465 default route via the AERO interface with next-hop network-layer 466 address fe80::1 and link-layer address L2(A), then sub-delegates the 467 prefix 2001:db8:0::/48 to its attached EUNs. IPv6 host ('C') 468 connects to the EUN, and configures the network-layer address 2001: 469 db8:0::1. 471 AERO Client ('D') assigns the address fe80::2001:db8:1:0 to its AERO 472 interface with link-layer address L2(D). Client ('D') configures a 473 default route via the AERO interface with next-hop network-layer 474 address fe80::1 and link-layer address L2(A), then sub-delegates the 475 network-layer prefix 2001:db8:1::/48 to its attached EUNs. IPv6 host 476 ('E') connects to the EUN, and configures the network-layer address 477 2001:db8:1::1. 479 Finally, IPv6 host ('F') connects to an IPv6 network outside of the 480 AERO link domain. Host ('F') configures its IPv6 interface in a 481 manner specific to its attached IPv6 link, and assigns the network- 482 layer address 2001:db8:3::1 to its IPv6 link interface. 484 3.6. AERO Router Discovery and Prefix Delegation 486 3.6.1. AERO Client Behavior 488 AERO Clients observe the IPv6 router requirements defined in 489 [RFC6434]. AERO Clients first discover the link-layer address of an 490 AERO Server via static configuration, or through an automated means 491 such as DNS name resolution. In the absence of other information, 492 the Client resolves the Fully-Qualified Domain Name (FQDN) 493 "linkupnetworks.domainname", where "domainname" is the DNS domain 494 appropriate for the Client's attached underlying network. The Client 495 then creates a neighbor cache entry with the IPv6 link-local address 496 fe80::1 and the discovered address as the link-layer address. The 497 Client further creates a default route with the link-local address 498 fe80::1 as the next hop. 500 Next, the Client acts as a requesting router to obtain IPv6 prefixes 501 through DHCPv6 Prefix Delegation [RFC3633] via the Server. After the 502 Client acquires prefixes, it sub-delegates them to nodes and links 503 within its attached EUNs. It also assigns the link-local AERO 504 address(es) taken from its delegated prefix(es) to the AERO interface 505 (see: Section 3.3). 507 After configuring a default route and obtaining prefixes, the Client 508 sends periodic NS messages to the server to obtain new NAs in order 509 to keep neighbor cache entries alive. The Client can also forward 510 IPv6 packets destined to networks beyond its local EUNs via the 511 Server as an IPv6 default router. The Server may in turn return a 512 Redirect message informing the Client of a neighbor on the AERO link 513 that is topologically closer to the final destination as specified in 514 Section 3.8. 516 3.6.2. AERO Server Behavior 518 AERO Servers observe the IPv6 router requirements defined in 519 [RFC6434]. They further configure a DHCPv6 relay/server function on 520 their AERO links. When the Server delegates prefixes, it also 521 establishes forwarding table and neighbor cache entries that list the 522 AERO address of the Client as the next hop toward the delegated IPv6 523 prefixes (where the AERO address is constructed as specified in 524 Section 3.3). 526 Servers respond to NS messages from Clients on their AERO interfaces 527 by returning an NA message. When the Server receives an NS message, 528 it updates the neighbor cache entry using the network layer source 529 address as the neighbor's network layer address and using the link- 530 layer source address of the NS message as the neighbor's link-layer 531 address. 533 When the Server forwards a packet via the same AERO interface on 534 which it arrived, it initiates an AERO route optimization procedure 535 as specified in Section 3.8. 537 3.7. AERO Neighbor Solicitation and Advertisement 539 After an AERO node has received a prefix delegation, it creates an 540 AERO address as specified in Section 3.3. It can then send NS 541 messages to elicit NA messages from other AERO nodes. When the AERO 542 node sends NS/NA messages, however, it must also include the length 543 of the prefix corresponding to the AERO address. AERO NS/NA messages 544 therefore include an 8-bit "Prefix Length" field take from the low- 545 order 8 bits of the Reserved field as shown in Figure 4 and Figure 5. 547 0 1 2 3 548 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 1 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 550 | Type (=135) | Code | Checksum | 551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 552 | Reserved | Prefix Length | 553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 554 | | 555 + + 556 | | 557 + Target Address + 558 | | 559 + + 560 | | 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 562 | Options ... 563 +-+-+-+-+-+-+-+-+-+-+-+- 565 Figure 4: AERO Neighbor Solicitation (NS) Message Format 567 0 1 2 3 568 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 1 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 | Type (=136) | Code | Checksum | 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 572 | R|S|O| Reserved | Prefix Length | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | | 575 + + 576 | | 577 + Target Address + 578 | | 579 + + 580 | | 581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 582 | Options ... 583 +-+-+-+-+-+-+-+-+-+-+-+- 585 Figure 5: AERO Neighbor Advertisement (NA) Message Format 587 When an AERO node sends an NS/NA message, it MUST use its AERO 588 address as the IPv6 source address and MUST include its AERO address 589 prefix length in the Prefix Length field. 591 When an AERO node receives an NS/NA message, it accepts the message 592 if the Prefix Length applied to the source address is correct for the 593 neighbor; otherwise, it ignores the message. 595 3.8. AERO Redirection 597 Section 3.5 describes the AERO reference operational scenario. We 598 now discuss the operation and protocol details of AERO Redirection 599 with respect to this reference scenario. 601 3.8.1. Classical Redirection Approaches 603 With reference to Figure 3, when the IPv6 source host ('C') sends a 604 packet to an IPv6 destination host ('E'), the packet is first 605 forwarded via the EUN to AERO Client ('B'). Client ('B') then 606 forwards the packet over its AERO interface to AERO Server ('A'), 607 which then re-encapsulates and forwards the packet to AERO Client 608 ('D'), where the packet is finally forwarded to the IPv6 destination 609 host ('E'). When Server ('A') re-encapsulates and forwards the 610 packet back out on its advertising AERO interface, it must arrange to 611 redirect Client ('B') toward Client ('D') as a better next-hop node 612 on the AERO link that is closer to the final destination. However, 613 this redirection process applied to AERO interfaces must be more 614 carefully orchestrated than on ordinary links since the parties may 615 be separated by potentially many underlying network routing hops. 617 Consider a first alternative in which Server ('A') informs Client 618 ('B') only and does not inform Client ('D') (i.e., "classical 619 redirection"). In that case, Client ('D') has no way of knowing that 620 Client ('B') is authorized to forward packets from their claimed 621 network-layer source addresses, and it may simply elect to drop the 622 packets. Also, Client ('B') has no way of knowing whether Client 623 ('D') is performing some form of source address filtering that would 624 reject packets arriving from a node other than a trusted default 625 router, nor whether Client ('D') is even reachable via a direct path 626 that does not involve Server ('A'). 628 Consider a second alternative in which Server ('A') informs both 629 Client ('B') and Client ('D') separately, via independent redirection 630 control messages (i.e., "augmented redirection"). In that case, if 631 Client ('B') receives the redirection control message but Client 632 ('D') does not, subsequent packets sent by Client ('B') could be 633 dropped due to filtering since Client ('D') would not have a route to 634 verify their source network-layer addresses. Also, if Client ('D') 635 receives the redirection control message but Client ('B') does not, 636 subsequent packets sent in the reverse direction by Client ('D') 637 would be lost. 639 Since both of these alternatives have shortcomings, a new redirection 640 technique (i.e., "AERO redirection") is needed. 642 3.8.2. AERO Redirection Concept of Operations 644 Again, with reference to Figure 3, when source host ('C') sends a 645 packet to destination host ('E'), the packet is first forwarded over 646 the source host's attached EUN to Client ('B'), which then forwards 647 the packet via its AERO interface to Server ('A'). 649 Server ('A') then re-encapsulates forwards the packet out the same 650 AERO interface toward Client ('D') and also sends an AERO "Predirect" 651 message forward to Client ('D') as specified in Section 3.8.4. The 652 Predirect message includes Client ('B')'s network- and link-layer 653 addresses as well as information that Client ('D') can use to 654 determine the IPv6 prefix used by Client ('B') . After Client ('D') 655 receives the Predirect message, it process the message and returns an 656 AERO Redirect message destined for Client ("B") via Server ('A') as 657 specified in Section 3.8.5. During the process, Client ('D') also 658 creates or updates a neighbor cache entry for Client ('B'), and 659 creates an IPv6 route for Client ('B')'s IPv6 prefix. 661 When Server ('A') receives the Redirect message, it re-encapsulates 662 the message and forwards it on to Client ('B') as specified in 663 Section 3.8.6. The message includes Client ('D')'s network- and 664 link-layer addresses as well as information that Client ('B') can use 665 to determine the IPv6 prefix used by Client ('D'). After Client 666 ('B') receives the Redirect message, it processes the message as 667 specified in Section 3.8.7. During the process, Client ('B') also 668 creates or updates a neighbor cache entry for Client ('D'), and 669 creates an IPv6 route for Client ('D')'s IPv6 prefix. 671 Following the above Predirect/Redirect message exchange, forwarding 672 of packets from Client ('B') to Client ('D') without involving Server 673 ('A) as an intermediary is enabled. The mechanisms that support this 674 exchange are specified in the following sections. 676 3.8.3. AERO Redirection Message Format 678 AERO Redirect/Predirect messages use the same format as for ICMPv6 679 Redirect messages depicted in Section 4.5 of [RFC4861], but also 680 include a new "Prefix Length" field taken from the low-order 8 bits 681 of the Redirect message Reserved field. The Redirect/Predirect 682 messages are formatted as shown in Figure 6: 683 0 1 2 3 684 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 1 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 686 | Type (=137) | Code (=0/1) | Checksum | 687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 688 | Reserved | Prefix Length | 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 690 | | 691 + + 692 | | 693 + Target Address + 694 | | 695 + + 696 | | 697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 698 | | 699 + + 700 | | 701 + Destination Address + 702 | | 703 + + 704 | | 705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 | Options ... 707 +-+-+-+-+-+-+-+-+-+-+-+- 709 Figure 6: AERO Redirect/Predirect Message Format 711 3.8.4. Sending Predirects 713 When an AERO Server forwards a packet out the same AERO interface 714 that it arrived on, the Server sends a Predirect message forward 715 toward the AERO Client nearest the destination instead of sending a 716 Redirect message back to AERO Client nearest the source. 718 In the reference operational scenario, when Server ('A') forwards a 719 packet sent by Client ('B') toward Client ('D'), it also sends a 720 Predirect message forward toward Client ('D'), subject to rate 721 limiting (see Section 8.2 of [RFC4861]). Server ('A') prepares the 722 Predirect message as follows: 724 o the link-layer source address is set to 'L2(A)' (i.e., the 725 underlying address of Server ('A')). 727 o the link-layer destination address is set to 'L2(D)' (i.e., the 728 underlying address of Client ('D')). 730 o the network-layer source address is set to fe80::1 (i.e., the AERO 731 address of Server ('A')). 733 o the network-layer destination address is set to fe80::2001:db8:1:0 734 (i.e., the AERO address of Client ('D')). 736 o the Type is set to 137. 738 o the Code is set to 1 to indicate "Predirect". 740 o the Prefix Length is set to the length of the prefix to be applied 741 to Target address. 743 o the Target Address is set to fe80::2001:db8:0::0 (i.e., the AERO 744 address of Client ('B')). 746 o the Destination Address is set to the IPv6 source address of the 747 packet that triggered the Predirection event. 749 o the message includes a TLLAO set to 'L2(B)' (i.e., the underlying 750 address of Client ('B')). 752 o the message includes a Redirected Header Option (RHO) that 753 contains the originating packet truncated to ensure that at least 754 the network-layer header is included but the size of the message 755 does not exceed 1280 bytes. 757 Server ('A') then sends the message forward to Client ('D'). 759 3.8.5. Processing Predirects and Sending Redirects 761 When Client ('D') receives a Predirect message, it accepts the 762 message only if it has a link-layer source address of the Server, 763 i.e. 'L2(A)'. Client ('D') further accepts the message only if it 764 is willing to serve as a redirection target. Next, Client ('D') 765 validates the message according to the ICMPv6 Redirect message 766 validation rules in Section 8.1 of [RFC4861]. 768 In the reference operational scenario, when the Client ('D') receives 769 a valid Predirect message, it either creates or updates a neighbor 770 cache entry that stores the Target Address of the message as the 771 network-layer address of Client ('B') and stores the link-layer 772 address found in the TLLAO as the link-layer address of Client ('B'). 773 Client ('D') then applies the Prefix Length to the Interface 774 Identifier portion of the Target Address and records the resulting 775 IPv6 prefix in its IPv6 forwarding table. 777 After processing the message, Client ('D') prepares a Redirect 778 message response as follows: 780 o the link-layer source address is set to 'L2(D)' (i.e., the link- 781 layer address of Client ('D')). 783 o the link-layer destination address is set to 'L2(A)' (i.e., the 784 link-layer address of Server ('A')). 786 o the network-layer source address is set to 'L3(D)' (i.e., the AERO 787 address of Client ('D')). 789 o the network-layer destination address is set to 'L3(B)' (i.e., the 790 AERO address of Client ('B')). 792 o the Type is set to 137. 794 o the Code is set to 0 to indicate "Redirect". 796 o the Prefix Length is set to the length of the prefix to be applied 797 to the Target and Destination address. 799 o the Target Address is set to fe80::2001:db8:1::1 (i.e., the AERO 800 address of Client ('D')). 802 o the Destination Address is set to the IPv6 destination address of 803 the packet that triggered the Redirection event. 805 o the message includes a TLLAO set to 'L2(D)' (i.e., the underlying 806 address of Client ('D')). 808 o the message includes as much of the RHO copied from the 809 corresponding AERO Predirect message as possible such that at 810 least the network-layer header is included but the size of the 811 message does not exceed 1280 bytes. 813 After Client ('D') prepares the Redirect message, it sends the 814 message to Server ('A'). 816 3.8.6. Re-encapsulating and Relaying Redirects 818 When Server ('A') receives a Redirect message, it accepts the message 819 only if it has a neighbor cache entry that associates the message's 820 link-layer source address with the network-layer source address. 821 Next, Server ('A') validates the message according to the ICMPv6 822 Redirect message validation rules in Section 8.1 of [RFC4861]. 823 Following validation, Server ('A') re-encapsulates the Redirect then 824 relays the re-encapsulated Redirect on to Client ('B') as follows. 826 In the reference operational scenario, Server ('A') receives the 827 Redirect message from Client ('D') and prepares to re-encapsulate and 828 forward the message to Client ('B'). Server ('A') first verifies 829 that Client ('D') is authorized to use the Prefix Length in the 830 Redirect message when applied to the AERO address in the network- 831 layer source of the Redirect message, and discards the message if 832 verification fails. Otherwise, Server ('A') re-encapsulates the 833 message by changing the link-layer source address of the message to 834 'L2(A)', changing the network-layer source address of the message to 835 fe80::1, and changing the link-layer destination address to 'L2(B)' . 836 Server ('A') finally relays the re-encapsulated message to the 837 ingress node ('B') without decrementing the network-layer IPv6 header 838 Hop Limit field. 840 While not shown in Figure 3, AERO Relays relay Redirect and Predirect 841 messages in exactly this same fashion described above. See Figure 7 842 in Appendix A for an extension of the reference operational scenario 843 that includes Relays. 845 3.8.7. Processing Redirects 847 When Client ('B') receives the Redirect message, it accepts the 848 message only if it has a link-layer source address of the Server, 849 i.e. 'L2(A)'. Next, Client ('B') validates the message according to 850 the ICMPv6 Redirect message validation rules in Section 8.1 of 851 [RFC4861]. Following validation, Client ('B') then processes the 852 message as follows. 854 In the reference operational scenario, when Client ('B') receives the 855 Redirect message, it either creates or updates a neighbor cache entry 856 that stores the Target Address of the message as the network-layer 857 address of Client ('D') and stores the link-layer address found in 858 the TLLAO as the link-layer address of Client ('D'). Client ('B') 859 then applies the Prefix Length to the Interface Identifier portion of 860 the Target Address and records the resulting IPv6 prefix in its IPv6 861 forwarding table. 863 Now, Client ('B') has an IPv6 forwarding table entry for 864 Client('D')'s prefix, and Client ('D') has an IPv6 forwarding table 865 entry for Client ('B')'s prefix. Thereafter, the clients may 866 exchange ordinary network-layer data packets directly without 867 forwarding through Server ('A'). 869 3.9. Neighbor Reachability Considerations 871 When a source Client discovers a target neighbor (either through 872 redirection or some other means) it MUST test the direct path to the 873 target by sending an initial NS message to elicit a solicited NA 874 response. While testing the path, the Client SHOULD continue sending 875 packets via the Server until target reachability has been confirmed. 876 The Client MUST thereafter follow the Neighbor Unreachability 877 Detection (NUD) procedures in Section 7.3 of [RFC4861], and can 878 resume sending packets via the Server at any time the direct path 879 appears to be failing. 881 If the Client is unable to elicit an NA response after MAX_RETRY 882 attempts, it SHOULD consider the direct path unusable for forwarding 883 purposes but still viable for ingress filtering purposes. 885 If reachability is confirmed, the Client SHOULD thereafter process 886 any link-layer errors as a hint that the direct path to the target 887 has either failed or has become intermittent. 889 3.10. MTU Considerations 891 The base tunneling specifications for IPv4 and IPv6 typically set a 892 static MTU on the tunnel interface to 1500 bytes minus the 893 encapsulation overhead or smaller still if the tunnel is likely to 894 incur additional encapsulations such as IPsec on the path. This can 895 result in path MTU related black holes when packets that are too 896 large to be accommodated over the AERO link are dropped, but the 897 resulting ICMP Packet Too Big (PTB) messages are lost on the return 898 path. As a result, AERO nodes MUST use the following MTU mitigations 899 to accommodate larger packets. 901 First, the node sets the AERO interface MTU to the larger of 1500 902 bytes and the underlying interface MTU minus the encapsulation 903 overhead. The node also optionallly caches per-neighbor MTU values 904 in the underlying IP path MTU discovery cache initialized to the 905 underlying interface MTU. The node then admits packets that are no 906 larger than 1280 bytes minus the encapsulation overhead as well as 907 packets that are larger than 1500 bytes into the tunnel without 908 fragmentation. (For IPv4, the node sets the DF bit to 0 for packets 909 no larger than 1280 bytes and sets the DF but to 1 for packets larger 910 than 1500 bytes.) If a large packet is lost in the path, the node 911 may optionally cache the MTU reported in the resulting PTB message or 912 may ignore the message, e.g., if there is a possibility that the 913 message is spurious. 915 For packets larger than 1280 bytes minus the encapsulation overhead 916 but no larger than 1500 bytes, if the outer protocol is IPv6 the node 917 uses outer IPv6 fragmentation to fragment the packet into two pieces 918 where the first fragment contains at least 1024 bytes of the 919 fragmented inner packet then admits the fragments into the tunnel. 920 If the outer protocol is IPv4, the node instead admits the packet 921 into the tunnel with DF set to 0 subject to rate limiting to ensure 922 that any fragmentation resulting in the path does not result in 923 reassembly errors [RFC4963][RFC6864]. For both IPv4 and IPv6, the 924 node also sends a 1500 byte probe message to the neighbor, subject to 925 rate limiting. To construct a probe, the node prepares an ICMPv6 926 Neighbor Solicitation (NS) message with trailing null padding added. 927 The node then encapsulates the NS in the outer encapsulation headers 928 with length set to 1500 plus the encapsulation overhead, sets DF to 1 929 (for IPv4) and sends the padded NS message to the neighbor. If the 930 neighbor returns an NA message, the node may then send whole packets 931 within this size range and (for IPv4) relax the rate limiting 932 requirement. 934 In addition to these MTU mitigations, AERO nodes rewrite the TCP 935 Maximum Segment Size (MSS) value in any TCP connection handshakes 936 they originate over the AERO interface [RFC0879][RFC6691]. The nodes 937 perform this "MSS clamping" by rewriting the MSS to a size that is no 938 larger than 1500 bytes minus the length of the TCP and IPv6 headers 939 minus the encapsulation overhead minus the length of any additional 940 encapsulations (e.g., IPsec) expected on the path. 942 By writing a reduced value in the TCP MSS, the AERO Client ensures 943 that the resulting TCP session will use packet sizes small enough to 944 avoid fragmentation. The communicating endpoints can subsequently 945 probe for larger packet sizes using Packetization Layer Path MTU 946 Discovery (PLMPMTUD) [RFC4821], which searches for successful packet 947 sizes larger than the original MSS. Other protocol types that do not 948 include an MSS exchange in their connection establishment (e.g., UDP) 949 will still see a 1500 byte minimum MTU even if a small amount of 950 fragmentation and reassembly are required. 952 3.11. Mobility and Link-Layer Address Change Considerations 954 When a Client needs to change its link-layer address (e.g., due to a 955 mobility event, due to a change in underlying network interface, 956 etc.), it sends an immediate NA message forward to any of its 957 correspondents (including the Server and any other Clients) which 958 then discover the new link-layer address. 960 If two Clients change their link-layer addresses simultaneously, the 961 NA messages may be lost. In that case, the Clients follow the same 962 NUD procedures specified in Section 3.8. 964 3.12. Underlying Protocol Version Considerations 966 A source Client may connect only to an IPvX underlying network, while 967 the target Client connects only to an IPvY underlying network. In 968 that case, the source Client has no means for reaching the target 969 directly (since they connect to underlying networks of different IP 970 protocol versions) and so must ignore any Redirects and continue to 971 send packets via the Server. 973 3.13. Multicast Considerations 975 When the underlying network does not support multicast AERO nodes map 976 IPv6 link-scoped multicast addresses (including 977 "All_DHCP_Relay_Agents_and_Servers" to the underlying IP address of 978 the AERO Server. 980 When the underlying network supports multicast, AERO nodes use the 981 multicast address mapping specification found in [RFC2529] for IPv4 982 underlying networks and use a direct multicast mapping for IPv6 983 underlying networks. (In the latter case, "direct multicast mapping" 984 means that if the IPv6 multicast destination address of the inner 985 packet is "M", then the IPv6 multicast destination address of the 986 encapsulating header is also "M".) 988 3.14. Operation on Server-less AERO Links 990 In some AERO link scenarios, there may be no Server on the link 991 and/or no need for Clients to use a Server as an intermediary trust 992 anchor. In that case, Clients can establish neighbor cache entries 993 and IPv6 routes by performing direct NS/NA exchanges, and some other 994 form of trust basis must be applied so that each Client can verify 995 that the prospective neighbor is authorized to use its claimed 996 prefix. 998 When there is no Server on the link, Clients must arrange to receive 999 prefix delegations and publish the delegations via a secure prefix 1000 discovery service through some means outside the scope of this 1001 document. 1003 3.15. Other Considerations 1005 AERO nodes that connect to an IPv4 underlying network can configure a 1006 NAT64 function [RFC6146] to support any IPv6 nodes on their attached 1007 EUNs. 1009 AERO nodes can use the Default Address Selection Policy with DHCPv6 1010 option[RFC7078] the same as on any IPv6 link. 1012 4. Implementation Status 1014 An early implementation is available at: 1015 http://linkupnetworks.com/seal/sealv2-1.0.tgz. 1017 5. IANA Considerations 1019 This document uses the UDP Service Port Number 8060 reserved by IANA 1020 for AERO in [RFC6706]. Therefore, there are no new IANA actions 1021 required for this document. 1023 6. Security Considerations 1025 AERO link security considerations are the same as for standard IPv6 1026 Neighbor Discovery [RFC4861] except that AERO improves on some 1027 aspects. In particular, AERO is dependent on a trust basis between 1028 AERO Clients and Servers, where the Clients only engage in the AERO 1029 mechanism when it is facilitated by a trust anchor. 1031 AERO links must be protected against link-layer address spoofing 1032 attacks in which an attacker on the link pretends to be a trusted 1033 neighbor. Links that provide link-layer securing mechanisms (e.g., 1034 WiFi networks) and links that provide physical security (e.g., 1035 enterprise network LANs) provide a first line of defense that is 1036 often sufficient. In other instances, securing mechanisms such as 1037 Secure Neighbor Discovery (SeND) [RFC3971] or IPsec [RFC4301] must be 1038 used. 1040 7. Acknowledgements 1042 Discussions both on the v6ops list and in private exchanges helped 1043 shape some of the concepts in this work. Individuals who contributed 1044 insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant, 1045 Brian Carpenter, Brian Haberman, Joel Halpern, and Lee Howard. 1046 Members of the IESG also provided valuable input during their review 1047 process that greatly improved the document. Special thanks go to 1048 Stewart Bryant, Joel Halpern and Brian Haberman for their shepherding 1049 guidance. 1051 This work has further been encouraged and supported by Boeing 1052 colleagues including Balaguruna Chidambaram, Jeff Holland, Cam 1053 Brodie, Yueli Yang, Wen Fang, Ed King, Mike Slane, Kent Shuey, Gen 1054 MacLean, and other members of the BR&T and BIT mobile networking 1055 teams. 1057 Earlier works on NBMA tunneling approaches are found in 1058 [RFC2529][RFC5214][RFC5569]. 1060 8. References 1062 8.1. Normative References 1064 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1065 August 1980. 1067 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1068 September 1981. 1070 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 1071 RFC 792, September 1981. 1073 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1074 Requirement Levels", BCP 14, RFC 2119, March 1997. 1076 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1077 (IPv6) Specification", RFC 2460, December 1998. 1079 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1080 IPv6 Specification", RFC 2473, December 1998. 1082 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 1083 for IPv6 Hosts and Routers", RFC 4213, October 2005. 1085 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1086 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1087 September 2007. 1089 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1090 Address Autoconfiguration", RFC 4862, September 2007. 1092 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 1093 Requirements", RFC 6434, December 2011. 1095 8.2. Informative References 1097 [IRON] Templin, F., "The Internet Routing Overlay Network 1098 (IRON)", Work in Progress, June 2012. 1100 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 1101 RFC 879, November 1983. 1103 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 1104 Domains without Explicit Tunnels", RFC 2529, March 1999. 1106 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 1107 and M. Carney, "Dynamic Host Configuration Protocol for 1108 IPv6 (DHCPv6)", RFC 3315, July 2003. 1110 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 1111 Host Configuration Protocol (DHCP) version 6", RFC 3633, 1112 December 2003. 1114 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 1115 Neighbor Discovery (SEND)", RFC 3971, March 2005. 1117 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1118 Internet Protocol", RFC 4301, December 2005. 1120 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 1121 Discovery", RFC 4821, March 2007. 1123 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 1124 Errors at High Data Rates", RFC 4963, July 2007. 1126 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1127 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1128 March 2008. 1130 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 1131 Infrastructures (6rd)", RFC 5569, January 2010. 1133 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 1134 NAT64: Network Address and Protocol Translation from IPv6 1135 Clients to IPv4 Servers", RFC 6146, April 2011. 1137 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 1138 Troan, "Basic Requirements for IPv6 Customer Edge 1139 Routers", RFC 6204, April 2011. 1141 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 1142 for Equal Cost Multipath Routing and Link Aggregation in 1143 Tunnels", RFC 6438, November 2011. 1145 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 1146 RFC 6691, July 2012. 1148 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 1149 (AERO)", RFC 6706, August 2012. 1151 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 1152 RFC 6864, February 2013. 1154 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 1155 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 1157 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1158 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1159 RFC 6936, April 2013. 1161 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 1162 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 1164 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 1165 Address Selection Policy Using DHCPv6", RFC 7078, 1166 January 2014. 1168 Appendix A. AERO Server and Relay Interworking 1170 Figure 3 depicts a reference AERO operational scenario with a single 1171 Server on the AERO link. In order to support scaling to larger 1172 numbers of nodes, the AERO link can deploy multiple Servers and 1173 Relays, e.g., as shown in Figure 7. 1175 .-(::::::::) 1176 .-(::: IPv6 :::)-. 1177 (:: Internetwork ::) 1178 `-(::::::::::::)-' 1179 `-(::::::)-' 1180 | 1181 +--------------+ +------+-------+ +--------------+ 1182 |AERO Server C | | AERO Relay D | |AERO Server E | 1183 | (default->D) | | (A->C; G->E) | | (default->D) | 1184 | (A->B) | +-------+------+ | (G->F) | 1185 +-------+------+ | +------+-------+ 1186 | | | 1187 X---+---+-------------------+------------------+---+---X 1188 | AERO Link | 1189 +-----+--------+ +--------+-----+ 1190 |AERO Client B | |AERO Client F | 1191 | (default->C) | | (default->E) | 1192 +--------------+ +--------------+ 1193 .-. .-. 1194 ,-( _)-. ,-( _)-. 1195 .-(_ IPv6 )-. .-(_ IPv6 )-. 1196 (__ EUN ) (__ EUN ) 1197 `-(______)-' `-(______)-' 1198 | | 1199 +--------+ +--------+ 1200 | Host A | | Host G | 1201 +--------+ +--------+ 1203 Figure 7: AERO Server/Relay Interworking 1205 In this example, AERO Client ('B') associates with AERO Server ('C'), 1206 while AERO Client ('F') associates with AERO Server ('E'). 1207 Furthermore, AERO Servers ('C') and ('E') do not associate with each 1208 other directly, but rather have an association with AERO Relay ('D') 1209 (i.e., a router that has full topology information concerning its 1210 associated Servers and their Clients). Relay ('D') connects to the 1211 AERO link, and also connects to the native IPv6 Internetwork. 1213 When host ('A') sends a packet toward destination host ('G'), IPv6 1214 forwarding directs the packet through the EUN to Client ('B'), which 1215 forwards the packet to Server ('C') in absence of more-specific 1216 forwarding information. Server ('C') forwards the packet, and it 1217 also generates an AERO Predirect message that is then forwarded 1218 through Relay ('D') to Server ('E'). When Server ('E') receives the 1219 message, it forwards the message to Client ('F'). 1221 After processing the AERO Predirect message, Client ('F') sends an 1222 AERO Redirect message to Server ('E'). Server ('E'), in turn, 1223 forwards the message through Relay ('D') to Server ('C'). When 1224 Server ('C') receives the message, it forwards the message to Client 1225 ('B') informing it that host 'G's EUN can be reached via Client 1226 ('F'), thus completing the AERO redirection. 1228 The network layer routing information shared between Servers and 1229 Relays must be carefully coordinated in a manner outside the scope of 1230 this document. In particular, Relays require full topology 1231 information, while individual Servers only require partial topology 1232 information (i.e., they only need to know the EUN prefixes associated 1233 with their current set of Clients). See [IRON] for an architectural 1234 discussion of routing coordination between Relays and Servers. 1236 Author's Address 1238 Fred L. Templin (editor) 1239 Boeing Research & Technology 1240 P.O. Box 3707 1241 Seattle, WA 98124 1242 USA 1244 Email: fltemplin@acm.org