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'I-D.templin-intarea-seal') ** 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: 3 errors (**), 0 flaws (~~), 9 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 20, 2014 5 Intended status: Standards Track 6 Expires: July 24, 2014 8 Transmission of IPv6 Packets over AERO Links 9 draft-templin-aerolink-03.txt 11 Abstract 13 This document specifies the operation of IPv6 over tunnel virtual 14 Non-Broadcast, Multiple Access (NBMA) links using Automatic 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 July 24, 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 Characteristics . . . . . . . . . . . . . . 5 61 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 7 62 3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . . 7 63 3.4. AERO Reference Operational Scenario . . . . . . . . . . . 8 64 3.5. AERO Prefix Delegation and Router Discovery . . . . . . . 10 65 3.5.1. AERO Client Behavior . . . . . . . . . . . . . . . . . 10 66 3.5.2. AERO Server Behavior . . . . . . . . . . . . . . . . . 10 67 3.6. AERO Neighbor Solicitation and Advertisement . . . . . . . 11 68 3.7. AERO Redirection . . . . . . . . . . . . . . . . . . . . . 12 69 3.7.1. Classical Redirection Approaches . . . . . . . . . . . 12 70 3.7.2. AERO Redirection Concept of Operations . . . . . . . . 13 71 3.7.3. AERO Redirection Message Format . . . . . . . . . . . 14 72 3.7.4. Sending Predirects . . . . . . . . . . . . . . . . . . 15 73 3.7.5. Processing Predirects and Sending Redirects . . . . . 16 74 3.7.6. Re-encapsulating and Relaying Redirects . . . . . . . 17 75 3.7.7. Processing Redirects . . . . . . . . . . . . . . . . . 17 76 3.8. Neighbor Reachability Considerations . . . . . . . . . . . 18 77 3.9. MTU Considerations . . . . . . . . . . . . . . . . . . . . 18 78 3.10. Mobility and Link-Layer Address Change Considerations . . 19 79 3.11. Underlying Protocol Version Considerations . . . . . . . . 19 80 3.12. Multicast Considerations . . . . . . . . . . . . . . . . . 19 81 3.13. Operation on Server-less AERO Links . . . . . . . . . . . 19 82 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 20 83 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 84 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20 85 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20 86 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 87 8.1. Normative References . . . . . . . . . . . . . . . . . . . 21 88 8.2. Informative References . . . . . . . . . . . . . . . . . . 22 89 Appendix A. AERO Server and Relay Interworking . . . . . . . . . 23 90 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 24 92 1. Introduction 94 This document specifies the operation of IPv6 over tunnel virtual 95 Non-Broadcast, Multiple Access (NBMA) links using Automatic Extended 96 Route Optimization (AERO). Nodes attached to AERO links can exchange 97 packets via trusted intermediate routers on the link that provide 98 forwarding services to reach off-link destinations and/or redirection 99 services to inform the node of an on-link neighbor that is closer to 100 the final destination. 102 Nodes on AERO links use an IPv6 link-local address format known as 103 the AERO Address. This address type has properties that statelessly 104 link IPv6 Neighbor Discovery (ND) to IPv6 routing. The AERO link can 105 be used for tunneling to neighboring nodes on either IPv6 or IPv4 106 networks, i.e., AERO views the IPv6 and IPv4 networks as equivalent 107 links for tunneling. The remainder of this document presents the 108 AERO specification. 110 2. Terminology 112 The terminology in the normative references applies; the following 113 terms are defined within the scope of this document: 115 AERO link 116 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 117 configured over a node's attached IPv6 and/or IPv4 networks. All 118 nodes on the AERO link appear as single-hop neighbors from the 119 perspective of IPv6. 121 AERO interface 122 a node's attachment to an AERO link. 124 AERO address 125 an IPv6 link-local address assigned to an AERO interface and 126 constructed as specified in Section 3.3. 128 AERO node 129 a node that is connected to an AERO link and that participates in 130 IPv6 Neighbor Discovery over the link. 132 AERO Server ("server") 133 a node that configures an advertising router interface on an AERO 134 link over which it can provide default forwarding and redirection 135 services for other AERO nodes. 137 AERO Client ("client") 138 a node that configures a non-advertising router interface on an 139 AERO link over which it can connect End User Networks (EUNs) to 140 the AERO link. 142 AERO Relay ("relay") 143 a node that relays IPv6 packets between Servers on the same AERO 144 link, and/or that forwards IPv6 packets between the AERO link and 145 the IPv6 Internet. An AERO Relay may or may not also be 146 configured as an AERO Server. 148 ingress tunnel endpoint (ITE) 149 an AERO interface endpoint that injects packets into an AERO link. 151 egress tunnel endpoint (ETE) 152 an AERO interface endpoint that receives tunneled packets from an 153 AERO link. 155 underlying network 156 a connected IPv6 or IPv4 network routing region over which AERO 157 nodes tunnel IPv6 packets. 159 underlying interface 160 an AERO node's interface point of attachment to an underlying 161 network. 163 underlying address 164 an IPv6 or IPv4 address assigned to an AERO node's underlying 165 interface. When UDP encapsulation is used, the UDP port number is 166 also considered as part of the underlying address. Underlying 167 addresses are used as the source and destination addresses of the 168 AERO encapsulation header. 170 link-layer address 171 the same as defined for "underlying address" above. 173 network layer address 174 an IPv6 address used as the source or destination address of the 175 inner IPv6 packet header. 177 end user network (EUN) 178 an IPv6 network attached to a downstream interface of an AERO 179 Client (where the AERO interface is seen as the upstream 180 interface). 182 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 183 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 184 document are to be interpreted as described in [RFC2119]. 186 3. Asymmetric Extended Route Optimization (AERO) 188 The following sections specify the operation of IPv6 over Automatic 189 Extended Route Optimization (AERO) links: 191 3.1. AERO Interface Characteristics 193 All nodes connected to an AERO link configure their AERO interfaces 194 as router interfaces (not host interfaces). End system applications 195 therefore do not bind directly to the AERO interface, but rather bind 196 to end user network (EUN) interfaces beyond which their packets may 197 be forwarded over an AERO interface. 199 AERO interfaces use IPv6-in-IPv6 encapsulation [RFC2473] to exchange 200 tunneled packets with AERO neighbors attached to an underlying IPv6 201 network, and use IPv6-in-IPv4 encapsulation [RFC4213] to exchange 202 tunneled packets with AERO neighbors attached to an underlying IPv4 203 network. AERO interfaces can also use IPsec encapsulation [RFC4301] 204 (either IPv6-in-IPv6 or IPv6-in-IPv4) in environments where strong 205 authentication and confidentiality are required. 207 AERO interfaces further use the Subnetwork Encapsulation and 208 Adaptation Layer (SEAL) [I-D.templin-intarea-seal] and can therefore 209 configure an unlimited Maximum Transmission Unit (MTU). This entails 210 the insertion of a SEAL header (i.e., an IPv6 fragment header with 211 the S bit set to 1) between the inner IPv6 header and the outer IP 212 encapsulation header. When NAT traversal and/or filtering middlebox 213 traversal is necessary, a UDP header is further inserted between the 214 outer IP encapsulation header and the SEAL header. (Note that while 215 [RFC6980] forbids fragmentation of IPv6 ND messages, the SEAL 216 fragmentation header applies only to the outer tunnel encapsulation 217 and not the inner IPv6 ND packet.) 219 AERO interfaces maintain a neighbor cache and use a variation of 220 standard unicast IPv6 ND messaging. AERO interfaces use Neighbor 221 Solicitation (NS), Neighbor Advertisement (NA) and Redirect messages 222 the same as for any IPv6 link. They do not use Router Solicitation 223 (RS) and Router Advertisement (RA) messages for several reasons. 224 First, default router discovery is supported through other means more 225 appropriate for AERO links as described below. Second, discovery of 226 more-specific routes is through the receipt of NS, NA and Redirect 227 messages. Finally, AERO links do not use any on-link prefixes other 228 than link-local; hence, there is no need for prefix discovery. 230 AERO Neighbor Solicitation (NS) and Neighbor Advertisement (NA) 231 messages do not include Source/Target Link Layer Address Options 232 (S/TLLAO). Instead, AERO nodes determine the link-layer addresses of 233 neighbors by examining the encapsulation source address of any NS/NA 234 messages they receive and ignore any S/TLLAOs included in these 235 messages. This is vital to the operation of AERO links for which 236 neighbors are separated by Network Address Translators (NATs) - 237 either IPv4 or IPv6. 239 AERO Redirect messages include a TLLAO the same as for any IPv6 link. 240 The TLLAO includes the link-layer address of the target node, 241 including both the IP address and the UDP source port number used by 242 the target when it sends UDP-encapsulated packets over the AERO 243 interface (the TLLAO instead encodes the value 0 when the target does 244 not use UDP encapsulation). TLLAOs for target nodes that use an IPv6 245 underlying address include the full 16 bytes of the IPv6 address as 246 shown in Figure 1, while TLLAOs for target nodes that use an IPv4 247 underlying address include only the 4 bytes of the IPv4 address as 248 shown in Figure 2. 250 0 1 2 3 251 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 1 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 | Type = 2 | Length = 3 | UDP Source Port (or 0) | 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 | Reserved | 256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 257 | | 258 +-- --+ 259 | | 260 +-- IPv6 Address --+ 261 | | 262 +-- --+ 263 | | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 Figure 1: AERO TLLAO Format for IPv6 268 0 1 2 3 269 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 1 270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 271 | Type = 2 | Length = 1 | UDP Source Port (or 0) | 272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 273 | IPv4 Address | 274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 276 Figure 2: AERO TLLAO Format for IPv4 278 Finally, nodes on AERO interfaces use a simple data origin 279 authentication for encapsulated packets they receive from other 280 nodes. In particular, AERO Clients accept encapsulated packets with 281 a link-layer source address belonging to their current AERO Server. 282 AERO nodes also accept encapsulated packets with a link-layer source 283 address that is correct for the network-layer source address. The 284 AERO node considers the link-layer source address correct for the 285 network-layer source address if there is an IPv6 route that matches 286 the network-layer source address as well as a neighbor cache entry 287 corresponding to the next hop that includes the link-layer address. 289 3.2. AERO Node Types 291 AERO Servers configure their AERO link interfaces as router 292 interfaces, and provide default routing services to AERO Clients. 294 AERO Clients also configure their AERO link interfaces as router 295 interfaces, i.e., even if the AERO Client otherwise displays the 296 outward characteristics of an ordinary host (for example, the Client 297 may internally configure both an AERO interface and (virtual) EUN 298 interfaces). AERO Clients are provisioned with IPv6 Prefix 299 Delegations either through a DHCPv6 Prefix Delegation exchange with 300 an AERO Server over the AERO link or via a static delegation obtained 301 through an out-of-band exchange with an AERO link prefix delegation 302 authority. Each AERO Client receives at least a /64 prefix 303 delegation, and may receive even shorter prefixes. 305 AERO Relays relay packets between nodes connected to the same AERO 306 link and also forward packets between the AERO link and the native 307 IPv6 network. The relaying process entails re-encapsulation of IPv6 308 packets that were received from a first AERO node and are to be 309 forwarded without modification to a second AERO node. 311 3.3. AERO Addresses 313 An AERO address is an IPv6 link-local address assigned to an AERO 314 interface and with an IPv6 prefix embedded within the interface 315 identifier. The AERO address is formatted as: 317 fe80::[IPv6 prefix] 319 Each AERO Client configures an AERO address based on the delegated 320 prefix it has received from the AERO link prefix delegation 321 authority. The address begins with the prefix fe80::/64 and includes 322 in its interface identifier the base /64 prefix taken from the 323 Client's delegated IPv6 prefix. The base prefix is determined by 324 masking the delegated prefix with the prefix length. For example, if 325 an AERO Client has received the prefix delegation: 327 2001:db8:1000:2000::/56 329 it would construct its AERO address as: 331 fe80::2001:db8:1000:2000 333 An AERO Client may receive multiple discontiguous IPv6 prefix 334 delegations, in which case it would configure multiple AERO addresses 335 - one for each prefix. 337 Each AERO Server configures the special AERO address fe80::1 to 338 support the operation of IPv6 Neighbor Discovery over the AERO link; 339 the address therefore has the properties of an IPv6 Anycast address. 340 While all Servers configure the same AERO address and therefore 341 cannot be distinguished from one another at the network layer, 342 Clients can still distinguish Servers at the link layer by examining 343 the Servers' link-layer addresses. 345 Nodes that are configured as pure AERO Relays (i.e., and that do not 346 also act as Servers) do not configure an IPv6 address of any kind on 347 their AERO interfaces. The Relay's AERO interface is therefore used 348 purely for transit and does not participate in IPv6 ND message 349 exchanges. 351 3.4. AERO Reference Operational Scenario 353 Figure 3 depicts the AERO reference operational scenario. The figure 354 shows an AERO Server('A'), two AERO Clients ('B', 'D') and three 355 ordinary IPv6 hosts ('C', 'E', 'F'): 357 .-(::::::::) 358 .-(::: IPv6 :::)-. +-------------+ 359 (:::: Internet ::::)--| Host F | 360 `-(::::::::::::)-' +-------------+ 361 `-(::::::)-' 2001:db8:3::1 362 | 363 +--------------+ 364 | AERO Server A| 365 | (C->B; E->D) | 366 +--------------+ 367 fe80::1 368 L2(A) 369 | 370 X-----+-----------+-----------+--------X 371 | AERO Link | 372 L2(B) L2(D) 373 fe80::2001:db8:0:0 fe80::2001:db8:1:0 .-. 374 +--------------+ +--------------+ ,-( _)-. 375 | AERO Client B| | AERO Client D| .-(_ IPv6 )-. 376 | (default->A) | | (default->A) |--(__ EUN ) 377 +--------------+ +--------------+ `-(______)-' 378 2001:DB8:0::/48 2001:DB8:1::/48 | 379 | 2001:db8:1::1 380 .-. +-------------+ 381 ,-( _)-. 2001:db8:0::1 | Host E | 382 .-(_ IPv6 )-. +-------------+ +-------------+ 383 (__ EUN )--| Host C | 384 `-(______)-' +-------------+ 386 Figure 3: AERO Reference Operational Scenario 388 In Figure 3, AERO Server ('A') connects to the AERO link and connects 389 to the IPv6 Internet, either directly or via other IPv6 routers (not 390 shown). Server ('A') assigns the address fe80::1 to its AERO 391 interface with link-layer address L2(A). Server ('A') next arranges 392 to add L2(A) to a published list of valid Servers for the AERO link. 394 AERO Client ('B') assigns the address fe80::2001:db8:0:0 to its AERO 395 interface with link-layer address L2(B). Client ('B') configures a 396 default route via the AERO interface with next-hop network-layer 397 address fe80::1 and link-layer address L2(A), then sub-delegates the 398 prefix 2001:db8:0::/48 to its attached EUNs. IPv6 host ('C') 399 connects to the EUN, and configures the network-layer address 2001: 400 db8:0::1. 402 AERO Client ('D') assigns the address fe80::2001:db8:1:0 to its AERO 403 interface with link-layer address L2(D). Client ('D') configures a 404 default route via the AERO interface with next-hop network-layer 405 address fe80::1 and link-layer address L2(A), then sub-delegates the 406 network-layer prefix 2001:db8:1::/48 to its attached EUNs. IPv6 host 407 ('E') connects to the EUN, and configures the network-layer address 408 2001:db8:1::1. 410 Finally, IPv6 host ('F') connects to an IPv6 network outside of the 411 AERO link domain. Host ('F') configures its IPv6 interface in a 412 manner specific to its attached IPv6 link, and assigns the network- 413 layer address 2001:db8:3::1 to its IPv6 link interface. 415 3.5. AERO Prefix Delegation and Router Discovery 417 3.5.1. AERO Client Behavior 419 AERO Clients observe the IPv6 router requirements defined in 420 [RFC6434]. AERO Clients first discover the link-layer address of an 421 AERO Server via static configuration, or through an automated means 422 such as DNS name resolution. In the absence of other information, 423 the Client resolves the name "linkupnetworks.[domainname]", where 424 [domainname] is the DNS domain appropriate for the Client's attached 425 underlying network. The Client then creates a neighbor cache entry 426 with the IPv6 link-local address fe80::1 and the discovered address 427 as the link-layer address. The Client further creates a default 428 route with the link-local address fe80::1 as the next hop. 430 Next, the Client acts as a requesting router to obtain IPv6 prefixes 431 through DHCPv6 Prefix Delegation [RFC3633] via the Server. After the 432 Client acquires prefixes, it sub-delegates them to nodes and links 433 within its attached EUNs. It also assigns the link-local AERO 434 address(es) taken from its delegated prefix(es) to the AERO interface 435 (see: Section 3.3). 437 After configuring a default route and obtaining prefixes, the Client 438 sends periodic NS messages to the server to obtain new NAs in order 439 to keep neighbor cache entries alive. The Client can also forward 440 IPv6 packets destined to networks beyond its local EUNs via the 441 Server as an IPv6 default router. The Server may in turn return a 442 Redirect message informing the Client of a neighbor on the AERO link 443 that is topologically closer to the final destination as specified in 444 Section 3.7. 446 3.5.2. AERO Server Behavior 448 AERO Servers observe the IPv6 router requirements defined in 449 [RFC6434]. They further configure a DHCPv6 relay/server function on 450 their AERO links. When the Server delegates prefixes, it also 451 establishes forwarding table and neighbor cache entries that list the 452 AERO address of the Client as the next hop toward the delegated IPv6 453 prefixes (where the AERO address is constructed as specified in 454 Section 3.3). 456 Servers respond to NS messages from Clients on their AERO interfaces 457 by returning an NA message. When the Server receives an NS message, 458 it updates the neighbor cache entry using the network layer source 459 address as the neighbor's network layer address and using the link- 460 layer source address of the NS message as the neighbor's link-layer 461 address. 463 When the Server forwards a packet via the same AERO interface on 464 which it arrived, it initiates an AERO route optimization procedure 465 as specified in Section 3.7. 467 3.6. AERO Neighbor Solicitation and Advertisement 469 After an AERO node has received a prefix delegation, it creates an 470 AERO address as specified in Section 3.3. It can then send NS 471 messages to elicit NA messages from other AERO nodes. When the AERO 472 node sends NS/NA messages, however, it must also include the length 473 of the prefix corresponding to the AERO address. AERO NS/NA messages 474 therefore include a new 8-bit "Prefix Length" field take from the 475 low-order 8 bits of the Reserved field as shown in Figure 4 and 476 Figure 5. 478 0 1 2 3 479 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 1 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 | Type (=135) | Code | Checksum | 482 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 483 | Reserved | Prefix Length | 484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 485 | | 486 + + 487 | | 488 + Target Address + 489 | | 490 + + 491 | | 492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 493 | Options ... 494 +-+-+-+-+-+-+-+-+-+-+-+- 496 Figure 4: AERO Neighbor Solicitation (NS) Message Format 498 0 1 2 3 499 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 1 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 501 | Type (=136) | Code | Checksum | 502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 503 | R|S|O| Reserved | Prefix Length | 504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 505 | | 506 + + 507 | | 508 + Target Address + 509 | | 510 + + 511 | | 512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 513 | Options ... 514 +-+-+-+-+-+-+-+-+-+-+-+- 516 Figure 5: AERO Neighbor Advertisement (NA) Message Format 518 When an AERO node sends an NS/NA message, it MUST use its AERO 519 address as the IPv6 source address and MUST include its AERO address 520 prefix length in the Prefix Length field. 522 When an AERO node receives an NS/NA message, it accepts the message 523 if the Prefix Length applied to the source address is correct for the 524 neighbor; otherwise, it ignores the message. 526 3.7. AERO Redirection 528 Section 3.4 describes the AERO reference operational scenario. We 529 now discuss the operation and protocol details of AERO Redirection 530 with respect to this reference scenario. 532 3.7.1. Classical Redirection Approaches 534 With reference to Figure 3, when the IPv6 source host ('C') sends a 535 packet to an IPv6 destination host ('E'), the packet is first 536 forwarded via the EUN to AERO Client ('B'). Client ('B') then 537 forwards the packet over its AERO interface to AERO Server ('A'), 538 which then forwards the packet to AERO Client ('D'), where the packet 539 is finally forwarded to the IPv6 destination host ('E'). When Server 540 ('A') forwards the packet back out on its advertising AERO interface, 541 it must arrange to redirect Client ('B') toward Client ('D') as a 542 better next-hop node on the AERO link that is closer to the final 543 destination. However, this redirection process applied to AERO 544 interfaces must be more carefully orchestrated than on ordinary links 545 since the parties may be separated by potentially many underlying 546 network routing hops. 548 Consider a first alternative in which Server ('A') informs Client 549 ('B') only and does not inform Client ('D') (i.e., "classical 550 redirection"). In that case, Client ('D') has no way of knowing that 551 Client ('B') is authorized to forward packets from their claimed 552 network-layer source addresses, and it may simply elect to drop the 553 packets. Also, Client ('B') has no way of knowing whether Client 554 ('D') is performing some form of source address filtering that would 555 reject packets arriving from a node other than a trusted default 556 router, nor whether Client ('D') is even reachable via a direct path 557 that does not involve Server ('A'). 559 Consider a second alternative in which Server ('A') informs both 560 Client ('B') and Client ('D') separately, via independent redirection 561 control messages (i.e., "augmented redirection"). In that case, if 562 Client ('B') receives the redirection control message but Client 563 ('D') does not, subsequent packets sent by Client ('B') could be 564 dropped due to filtering since Client ('D') would not have a route to 565 verify their source network-layer addresses. Also, if Client ('D') 566 receives the redirection control message but Client ('B') does not, 567 subsequent packets sent in the reverse direction by Client ('D') 568 would be lost. 570 Since both of these alternatives have shortcomings, a new redirection 571 technique (i.e., "AERO redirection") is needed. 573 3.7.2. AERO Redirection Concept of Operations 575 Again, with reference to Figure 3, when source host ('C') sends a 576 packet to destination host ('E'), the packet is first forwarded over 577 the source host's attached EUN to Client ('B'), which then forwards 578 the packet via its AERO interface to Server ('A'). 580 Using AERO redirection, Server ('A') then forwards the packet out the 581 same AERO interface toward Client ('D') and also sends an AERO 582 "Predirect" message forward to Client ('D') as specified in 583 Section 3.7.4. The Predirect message includes Client ('B')'s 584 network- and link-layer addresses as well as information that Client 585 ('D') can use to determine the IPv6 prefix used by Client ('B') . 586 After Client ('D') receives the Predirect message, it process the 587 message and returns an AERO Redirect message destined for Client 588 ("B") via Server ('A') as specified in Section 3.7.5. During the 589 process, Client ('D') also creates or updates a neighbor cache entry 590 for Client ('B'), and creates an IPv6 route for Client ('B')'s IPv6 591 prefix. 593 When Server ('A') receives the Redirect message, it processes the 594 message and forwards it on to Client ('B') as specified in 595 Section 3.7.6. The message includes Client ('D')'s network- and 596 link-layer addresses as well as information that Client ('B') can use 597 to determine the IPv6 prefix used by Client ('D'). After Client 598 ('B') receives the Redirect message, it processes the message as 599 specified in Section 3.7.7. During the process, Client ('B') also 600 creates or updates a neighbor cache entry for Client ('D'), and 601 creates an IPv6 route for Client ('D')'s IPv6 prefix. 603 Following the above Predirect/Redirect message exchange, forwarding 604 of packets from Client ('B') to Client ('D') without involving Server 605 ('A) as an intermediary is enabled. The mechanisms that support this 606 exchange are specified in the following sections. 608 3.7.3. AERO Redirection Message Format 610 AERO Redirect/Predirect messages use the same format as for ICMPv6 611 Redirect messages depicted in Section 4.5 of [RFC4861], but also 612 include a new "Prefix Length" field taken from the low-order 8 bits 613 of the Redirect message Reserved field. The Redirect/Predirect 614 messages are formatted as shown in Figure 6: 615 0 1 2 3 616 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 1 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | Type (=137) | Code (=0/1) | Checksum | 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 | Reserved | Prefix Length | 621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 622 | | 623 + + 624 | | 625 + Target Address + 626 | | 627 + + 628 | | 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 | | 631 + + 632 | | 633 + Destination Address + 634 | | 635 + + 636 | | 637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 638 | Options ... 639 +-+-+-+-+-+-+-+-+-+-+-+- 641 Figure 6: AERO Redirect/Predirect Message Format 643 3.7.4. Sending Predirects 645 When an AERO Server forwards a packet out the same AERO interface 646 that it arrived on, the Server sends a Predirect message forward 647 toward the AERO Client nearest the destination instead of sending a 648 Redirect message back to AERO Client nearest the source. 650 In the reference operational scenario, when Server ('A') forwards a 651 packet sent by Client ('B') toward Client ('D'), it also sends a 652 Predirect message forward toward Client ('D'), subject to rate 653 limiting (see Section 8.2 of [RFC4861]). Server ('A') prepares the 654 Predirect message as follows: 656 o the link-layer source address is set to 'L2(A)' (i.e., the 657 underlying address of Server ('A')). 659 o the link-layer destination address is set to 'L2(D)' (i.e., the 660 underlying address of Client ('D')). 662 o the network-layer source address is set to fe80::1 (i.e., the AERO 663 address of Server ('A')). 665 o the network-layer destination address is set to fe80::2001:db8:1:0 666 (i.e., the AERO address of Client ('D')). 668 o the Type is set to 137. 670 o the Code is set to 1 to indicate "Predirect". 672 o the Prefix Length is set to the length of the prefix to be applied 673 to Target address. 675 o the Target Address is set to fe80::2001:db8:0::0 (i.e., the AERO 676 address of Client ('B')). 678 o the Destination Address is set to the IPv6 source address of the 679 packet that triggered the Predirection event. 681 o the message includes a TLLAO set to 'L2(B)' (i.e., the underlying 682 address of Client ('B')). 684 o the message includes a Redirected Header Option (RHO) that 685 contains the originating packet truncated to ensure that at least 686 the network-layer header is included but the size of the message 687 does not exceed 1280 bytes. 689 Server ('A') then sends the message forward to Client ('D'). 691 3.7.5. Processing Predirects and Sending Redirects 693 When Client ('D') receives a Predirect message, it accepts the 694 message only if it has a link-layer source address of the Server, 695 i.e. 'L2(A)'. Client ('D') further accepts the message only if it 696 is willing to serve as a redirection target. Next, Client ('D') 697 validates the message according to the ICMPv6 Redirect message 698 validation rules in Section 8.1 of [RFC4861]. 700 In the reference operational scenario, when the Client ('D') receives 701 a valid Predirect message, it either creates or updates a neighbor 702 cache entry that stores the Target Address of the message as the 703 network-layer address of Client ('B') and stores the link-layer 704 address found in the TLLAO as the link-layer address of Client ('B'). 705 Client ('D') then applies the Prefix Length to the Interface 706 Identifier portion of the Target Address and records the resulting 707 IPv6 prefix in its IPv6 forwarding table. 709 After processing the message, Client ('D') prepares a Redirect 710 message response as follows: 712 o the link-layer source address is set to 'L2(D)' (i.e., the link- 713 layer address of Client ('D')). 715 o the link-layer destination address is set to 'L2(A)' (i.e., the 716 link-layer address of Server ('A')). 718 o the network-layer source address is set to 'L3(D)' (i.e., the AERO 719 address of Client ('D')). 721 o the network-layer destination address is set to 'L3(B)' (i.e., the 722 AERO address of Client ('B')). 724 o the Type is set to 137. 726 o the Code is set to 0 to indicate "Redirect". 728 o the Prefix Length is set to the length of the prefix to be applied 729 to the Target and Destination address. 731 o the Target Address is set to fe80::2001:db8:1::1 (i.e., the AERO 732 address of Client ('D')). 734 o the Destination Address is set to the IPv6 destination address of 735 the packet that triggered the Redirection event. 737 o the message includes a TLLAO set to 'L2(D)' (i.e., the underlying 738 address of Client ('D')). 740 o the message includes as much of the RHO copied from the 741 corresponding AERO Predirect message as possible such that at 742 least the network-layer header is included but the size of the 743 message does not exceed 1280 bytes. 745 After Client ('D') prepares the Redirect message, it sends the 746 message to Server ('A'). 748 3.7.6. Re-encapsulating and Relaying Redirects 750 When Server ('A') receives a Redirect message, it accepts the message 751 only if it has a neighbor cache entry that associates the message's 752 link-layer source address with the network-layer source address. 753 Next, Server ('A') validates the message according to the ICMPv6 754 Redirect message validation rules in Section 8.1 of [RFC4861]. 755 Following validation, Server ('A') re-encapsulates the Redirect as 756 discussed in [I-D.templin-intarea-seal], and then relays the re- 757 encapsulated Redirect on to Client ('B') as follows. 759 In the reference operational scenario, Server ('A') receives the 760 Redirect message from Client ('D') and prepares to forward a 761 corresponding Redirect message to Client ('B'). Server ('A') then 762 verifies that Client ('D') is authorized to use the Prefix Length in 763 the Redirect message when applied to the AERO address in the network- 764 layer source of the Redirect message, and discards the message if 765 verification fails. Otherwise, Server ('A') re-encapsulates the 766 redirect by changing the link-layer source address of the message to 767 'L2(A)', changing the network-layer source address of the message to 768 fe80::1, and changing the link-layer destination address to 'L2(B)' . 769 Server ('A') finally relays the re-encapsulated message to the 770 ingress node ('B') without decrementing the network-layer IPv6 header 771 Hop Limit field. 773 While not shown in Figure 3, AERO Relays relay Redirect and Predirect 774 messages in exactly this same fashion described above. See Figure 7 775 in Appendix A for an extension of the reference operational scenario 776 that includes Relays. 778 3.7.7. Processing Redirects 780 When Client ('B') receives the Redirect message, it accepts the 781 message only if it has a link-layer source address of the Server, 782 i.e. 'L2(A)'. Next, Client ('B') validates the message according to 783 the ICMPv6 Redirect message validation rules in Section 8.1 of 784 [RFC4861]. Following validation, Client ('B') then processes the 785 message as follows. 787 In the reference operational scenario, when Client ('B') receives the 788 Redirect message, it either creates or updates a neighbor cache entry 789 that stores the Target Address of the message as the network-layer 790 address of Client ('D') and stores the link-layer address found in 791 the TLLAO as the link-layer address of Client ('D'). Client ('B') 792 then applies the Prefix Length to the Interface Identifier portion of 793 the Target Address and records the resulting IPv6 prefix in its IPv6 794 forwarding table. 796 Now, Client ('B') has an IPv6 forwarding table entry for 797 Client('D')'s prefix, and Client ('D') has an IPv6 forwarding table 798 entry for Client ('B')'s prefix. Thereafter, the clients may 799 exchange ordinary network-layer data packets directly without 800 forwarding through Server ('A'). 802 3.8. Neighbor Reachability Considerations 804 When a source Client discovers a target neighbor (either through 805 redirection or some other means) it MUST test the direct path to the 806 target by sending an initial NS message to elicit a solicited NA 807 response. While testing the path, the Client SHOULD continue sending 808 packets via the Server until target reachability has been confirmed. 809 The Client MUST thereafter follow the Neighbor Unreachability 810 Detection (NUD) procedures in Section 7.3 of [RFC4861], and can 811 resume sending packets via the Server at any time the direct path 812 appears to be failing. 814 If the Client is unable to elicit an NA response after MAX_RETRY 815 attempts, it SHOULD consider the direct path unusable for forwarding 816 purposes but still viable for ingress filtering purposes. 818 If reachability is confirmed, the Client SHOULD thereafter process 819 any link-layer errors as a hint that the direct path to the target 820 has either failed or has become intermittent. 822 3.9. MTU Considerations 824 As specified in Section 3.1, AERO interfaces configure an unlimited 825 MTU (here, "unlimited' means 64KB minus overhead for encapsulation 826 over IPv4, and 4GB minus overhead for encapsulation over IPv6). The 827 use of SEAL also ensures that packets up to 1500 bytes in length are 828 delivered over the AERO link, while larger packets can still be used 829 when the AERO link can support the larger size without fragmentation. 831 AERO Clients SHOULD examine the Maximum Segment Size (MSS) value in 832 TCP connection requests involving a host on their attached end user 833 network. The Client SHOULD rewrite the MSS value to a size that 834 would avoid SEAL fragmentation and path MTU black holes in the vast 835 majority of cases, i.e., at most 1500 bytes minus the TCP, IPv6 and 836 encapsulation header lengths (see: [RFC0879][RFC6691]). 838 By writing a reduced value in the TCP MSS, the AERO Client ensures 839 that the resulting TCP session will use packet sizes small enough to 840 avoid SEAL fragmentation and reassembly. The communicating endpoints 841 can subsequently negotiate for larger packet sizes using 842 Packetization Layer Path MTU Discovery (PLMPMTUD) [RFC4821], which 843 searches for successful packet sizes larger than the original MSS. 844 Other protocol types that do not include an MSS exchange in their 845 connection establishment (e.g., UDP) will still see a 1500 byte 846 minimum MTU even if a small amount of fragmentation and reassembly 847 are necessary. 849 3.10. Mobility and Link-Layer Address Change Considerations 851 When a Client needs to change its link-layer address (e.g., due to a 852 mobility event, due to a change in underlying network interface, 853 etc.), it sends an immediate NS message forward to any of its 854 correspondents (including the Server and any other Clients) which 855 then discover the new link-layer address. 857 If two Clients change their link-layer addresses simultaneously, the 858 NS/NA exchange(s) may fail. In that case, the Clients follow the 859 same NUD procedures specified in Section 3.8. 861 3.11. Underlying Protocol Version Considerations 863 A source Client may connect only to an IPvX underlying network, while 864 the target Client connects only to an IPvY underlying network. In 865 that case, the source Client has no means for reaching the target 866 directly (since they connect to underlying networks of different IP 867 protocol versions) and so must ignore any Redirects and continue to 868 send packets via the Server. 870 3.12. Multicast Considerations 872 When the underlying network supports multicast, AERO nodes use the 873 multicast address mapping specification found in [RFC2529] for IPv4 874 underlying networks and use a direct multicast mapping for IPv6 875 underlying networks. (In the latter case, "direct multicast mapping" 876 means that if the IPv6 multicast destination address of the inner 877 packet is "M", then the IPv6 multicast destination address of the 878 encapsulating header is also "M".) 880 3.13. Operation on Server-less AERO Links 882 In some AERO link scenarios, there may be no Server on the link 883 and/or no need for Clients to use a Server as an intermediary trust 884 anchor. In that case, Clients can establish neighbor cache entries 885 and IPv6 routes by performing direct NS/NA exchanges, and some other 886 form of trust basis must be applied so that each Client can verify 887 that the prospective neighbor is authorized to use its claimed 888 prefix. 890 When there is no Server on the link, Clients must arrange to receive 891 prefix delegations and publish the delegations via a secure prefix 892 discovery service through some means outside the scope of this 893 document. 895 4. Implementation Status 897 An early implementation is available at: 898 http://linkupnetworks.com/seal/sealv2-1.0.tgz. 900 5. IANA Considerations 902 There are no IANA actions required for this document. 904 6. Security Considerations 906 AERO link security considerations are the same as for standard IPv6 907 Neighbor Discovery [RFC4861] except that AERO improves on some 908 aspects. In particular, AERO is dependent on a trust basis between 909 AERO Clients and Servers, where the Clients only engage in the AERO 910 mechanism when it is facilitated by a trust anchor. 912 AERO links must be protected against link-layer address spoofing 913 attacks in which an attacker on the link pretends to be a trusted 914 neighbor. Links that provide link-layer securing mechanisms (e.g., 915 WiFi networks) and links that provide physical security (e.g., 916 enterprise network LANs) provide a first line of defense that is 917 often sufficient. In other instances, securing mechanisms such as 918 Secure Neighbor Discovery (SeND) [RFC3971] or IPsec [RFC4301] must be 919 used. 921 7. Acknowledgements 923 Discussions both on the v6ops list and in private exchanges helped 924 shape some of the concepts in this work. Individuals who contributed 925 insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant, 926 Brian Carpenter, Brian Haberman, Joel Halpern, and Lee Howard. 927 Members of the IESG also provided valuable input during their review 928 process that greatly improved the document. Special thanks go to 929 Stewart Bryant, Joel Halpern and Brian Haberman for their shepherding 930 guidance. 932 This work has further been encouraged and supported by Boeing 933 colleagues including Balaguruna Chidambaram, Jeff Holland, Cam 934 Brodie, Yueli Yang, Wen Fang, Ed King, Mike Slane, Kent Shuey, Gen 935 MacLean, and other members of the BR&T and BIT mobile networking 936 teams. 938 Earlier works on NBMA tunneling approaches are found in 939 [RFC2529][RFC5214][RFC5569]. 941 8. References 943 8.1. Normative References 945 [I-D.templin-intarea-seal] 946 Templin, F., "The Subnetwork Encapsulation and Adaptation 947 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 948 progress), January 2014. 950 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 951 August 1980. 953 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 954 September 1981. 956 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 957 RFC 792, September 1981. 959 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 960 Requirement Levels", BCP 14, RFC 2119, March 1997. 962 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 963 (IPv6) Specification", RFC 2460, December 1998. 965 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 966 IPv6 Specification", RFC 2473, December 1998. 968 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 969 for IPv6 Hosts and Routers", RFC 4213, October 2005. 971 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 972 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 973 September 2007. 975 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 976 Address Autoconfiguration", RFC 4862, September 2007. 978 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 979 Requirements", RFC 6434, December 2011. 981 8.2. Informative References 983 [IRON] Templin, F., "The Internet Routing Overlay Network 984 (IRON)", Work in Progress, June 2012. 986 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 987 RFC 879, November 1983. 989 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 990 Domains without Explicit Tunnels", RFC 2529, March 1999. 992 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 993 and M. Carney, "Dynamic Host Configuration Protocol for 994 IPv6 (DHCPv6)", RFC 3315, July 2003. 996 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 997 Host Configuration Protocol (DHCP) version 6", RFC 3633, 998 December 2003. 1000 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 1001 Neighbor Discovery (SEND)", RFC 3971, March 2005. 1003 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1004 Internet Protocol", RFC 4301, December 2005. 1006 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 1007 Discovery", RFC 4821, March 2007. 1009 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1010 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1011 March 2008. 1013 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 1014 Infrastructures (6rd)", RFC 5569, January 2010. 1016 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 1017 Troan, "Basic Requirements for IPv6 Customer Edge 1018 Routers", RFC 6204, April 2011. 1020 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 1021 RFC 6691, July 2012. 1023 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 1024 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 1026 Appendix A. AERO Server and Relay Interworking 1028 Figure 3 depicts a reference AERO operational scenario with a single 1029 Server on the AERO link. In order to support scaling to larger 1030 numbers of nodes, the AERO link can deploy multiple Servers and 1031 Relays, e.g., as shown in Figure 7. 1033 .-(::::::::) 1034 .-(::: IPv6 :::)-. 1035 (:: Internetwork ::) 1036 `-(::::::::::::)-' 1037 `-(::::::)-' 1038 | 1039 +--------------+ +------+-------+ +--------------+ 1040 |AERO Server C | | AERO Relay D | |AERO Server E | 1041 | (default->D) | | (A->C; G->E) | | (default->D) | 1042 | (A->B) | +-------+------+ | (G->F) | 1043 +-------+------+ | +------+-------+ 1044 | | | 1045 X---+---+-------------------+------------------+---+---X 1046 | AERO Link | 1047 +-----+--------+ +--------+-----+ 1048 |AERO Client B | |AERO Client F | 1049 | (default->C) | | (default->E) | 1050 +--------------+ +--------------+ 1051 .-. .-. 1052 ,-( _)-. ,-( _)-. 1053 .-(_ IPv6 )-. .-(_ IPv6 )-. 1054 (__ EUN ) (__ EUN ) 1055 `-(______)-' `-(______)-' 1056 | | 1057 +--------+ +--------+ 1058 | Host A | | Host G | 1059 +--------+ +--------+ 1061 Figure 7: AERO Server/Relay Interworking 1063 In this example, AERO Client ('B') associates with AERO Server ('C'), 1064 while AERO Client ('F') associates with AERO Server ('E'). 1065 Furthermore, AERO Servers ('C') and ('E') do not associate with each 1066 other directly, but rather have an association with AERO Relay ('D') 1067 (i.e., a router that has full topology information concerning its 1068 associated Servers and their Clients). Relay ('D') connects to the 1069 AERO link, and also connects to the native IPv6 Internetwork. 1071 When host ('A') sends a packet toward destination host ('G'), IPv6 1072 forwarding directs the packet through the EUN to Client ('B'), which 1073 forwards the packet to Server ('C') in absence of more-specific 1074 forwarding information. Server ('C') forwards the packet, and it 1075 also generates an AERO Predirect message that is then forwarded 1076 through Relay ('D') to Server ('E'). When Server ('E') receives the 1077 message, it forwards the message to Client ('F'). 1079 After processing the AERO Predirect message, Client ('F') sends an 1080 AERO Redirect message to Server ('E'). Server ('E'), in turn, 1081 forwards the message through Relay ('D') to Server ('C'). When 1082 Server ('C') receives the message, it forwards the message to Client 1083 ('B') informing it that host 'G's EUN can be reached via Client 1084 ('F'), thus completing the AERO redirection. 1086 The network layer routing information shared between Servers and 1087 Relays must be carefully coordinated in a manner outside the scope of 1088 this document. In particular, Relays require full topology 1089 information, while individual Servers only require partial topology 1090 information (i.e., they only need to know the EUN prefixes associated 1091 with their current set of Clients). See [IRON] for an architectural 1092 discussion of routing coordination between Relays and Servers. 1094 Author's Address 1096 Fred L. Templin (editor) 1097 Boeing Research & Technology 1098 P.O. Box 3707 1099 Seattle, WA 98124 1100 USA 1102 Email: fltemplin@acm.org