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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 Intended status: Experimental June 25, 2012 5 Expires: December 27, 2012 7 Asymmetric Extended Route Optimization (AERO) 8 draft-templin-aero-12.txt 10 Abstract 12 Nodes attached to common multi-access link types (e.g., multicast- 13 capable, shared media, non-broadcast multiple access (NBMA), etc.) 14 can exchange packets as neighbors on the link, but may not always be 15 provisioned with sufficient routing information for optimal neighbor 16 selection. Such nodes should therefore be able to discover a trusted 17 intermediate router on the link that provides both forwarding 18 services to reach off-link destinations and redirection services to 19 inform the node of an on-link neighbor that is closer to the final 20 destination. This redirection can provide a useful route 21 optimization, since the triangular path from the ingress link 22 neighbor, to the intermediate router, and finally to the egress link 23 neighbor may be considerably longer than the direct path from ingress 24 to egress. However, ordinary redirection may lead to operational 25 issues on certain link types and/or in certain deployment scenarios. 26 This document therefore introduces an Asymmetric Extended Route 27 Optimization (AERO) capability that addresses the issues. 29 Status of this Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on December 27, 2012. 46 Copyright Notice 48 Copyright (c) 2012 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 65 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 7 66 4. Example Use Cases . . . . . . . . . . . . . . . . . . . . . . 8 67 5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 9 68 6. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 69 6.1. AERO Link Dynamic Routing . . . . . . . . . . . . . . . . 10 70 6.2. AERO Node Behavior . . . . . . . . . . . . . . . . . . . . 11 71 6.2.1. AERO Node Types . . . . . . . . . . . . . . . . . . . 11 72 6.2.2. AERO Host Behavior . . . . . . . . . . . . . . . . . . 11 73 6.2.3. Edge AERO Router Behavior . . . . . . . . . . . . . . 11 74 6.2.4. Intermediate AERO Router Behavior . . . . . . . . . . 11 75 6.3. AERO Reference Operational Scenario . . . . . . . . . . . 12 76 6.4. AERO Specification . . . . . . . . . . . . . . . . . . . . 14 77 6.4.1. Classical Redirection Approaches . . . . . . . . . . . 14 78 6.4.2. AERO Concept of Operations . . . . . . . . . . . . . . 15 79 6.4.3. Conceptual Data Structures and Protocol Constants . . 16 80 6.4.4. Data Origin Authentication . . . . . . . . . . . . . . 17 81 6.4.5. AERO Redirection Message Format . . . . . . . . . . . 18 82 6.4.6. Sending Predirects . . . . . . . . . . . . . . . . . . 20 83 6.4.7. Processing Predirects and Sending Redirects . . . . . 21 84 6.4.8. Forwarding Redirects . . . . . . . . . . . . . . . . . 22 85 6.4.9. Processing Redirects . . . . . . . . . . . . . . . . . 23 86 6.4.10. Sending Periodic Predirect Keepalives . . . . . . . . 24 87 6.4.11. Neighbor Reachability Considerations . . . . . . . . . 26 88 6.4.12. Mobility Considerations . . . . . . . . . . . . . . . 26 89 6.4.13. Link-Layer Address Change Considerations . . . . . . . 27 90 6.4.14. Prefix Re-Provisioning Considerations . . . . . . . . 28 91 6.4.15. Backward Compatibility . . . . . . . . . . . . . . . . 28 92 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 93 8. Security Considerations . . . . . . . . . . . . . . . . . . . 29 94 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29 95 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 96 10.1. Normative References . . . . . . . . . . . . . . . . . . . 30 97 10.2. Informative References . . . . . . . . . . . . . . . . . . 30 98 Appendix A. Intermediate Router Interworking . . . . . . . . . . 31 99 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 33 101 1. Introduction 103 Nodes attached to common multi-access link types (e.g., multicast- 104 capable, shared media, non-broadcast multiple access (NBMA), etc.) 105 can exchange packets as neighbors on the link, but may not always be 106 provisioned with sufficient routing information for optimal neighbor 107 selection. Such nodes should therefore be able to discover a trusted 108 intermediate router on the link that provides both default forwarding 109 services to reach off-link destinations and redirection services to 110 inform the node of an on-link neighbor that is closer to the final 111 destination. 113 +--------------+ 114 | Router A | 115 | (D->C) | 116 +--------------+ 117 | 118 X--------+--------+--------+------X 119 | | 120 +----------+---+ +---+----------+ 121 | Node B | | Router C | 122 | (default->A) | +-------+------+ 123 +--------------+ .-. 124 ,-( _)-. 125 .-(_ IPv6 )-. 126 (__ EUN ) 127 `-(______)-' 128 +-------+------+ 129 | Node D | 130 +--------------+ 132 Figure 1: Classical Multi-Access Link Redirection 134 Figure 1 shows a classical multi-access link redirection scenario. 135 In this figure, Node 'B' is provisioned with only a default route 136 with Router 'A' as the next hop. Router 'A' in turn has a more- 137 specific route that lists Router 'C' as the next hop neighbor on the 138 link for Node 'D's attached End User Network (EUN). 140 If Node 'B' has a packet to send to Node 'D', 'B' is obliged to send 141 its initial packets via Router 'A'. Router 'A' then forwards the 142 packet to Router 'C' and also returns a redirection message to inform 143 'B' that 'C' is in fact an on-link neighbor that is closer to the 144 final destination 'D'. After receiving the redirection message, 'B' 145 can place a more-specific route in its forwarding table so that 146 future packets destined to 'D' can be sent directly via Router 'C', 147 as shown in Figure 2. 149 +--------------+ 150 | Router A | 151 | (D->C) | 152 +--------------+ 153 | 154 X--------+--------+--------+------X 155 | | 156 +----------+---+ +---+----------+ 157 | Node B | | Router C | 158 | (default->A) | +-------+------+ 159 | (D->C) | .-. 160 +--------------+ ,-( _)-. 161 .-(_ IPv6 )-. 162 (__ EUN ) 163 `-(______)-' 164 +-------+------+ 165 | Node D | 166 +--------------+ 168 Figure 2: More-Specific Routes Following Redirection 170 This classical redirection can provide a useful route optimization, 171 since the triangular path from the ingress link neighbor, to the 172 intermediate router, and finally to the egress link neighbor may be 173 considerably longer than the direct path from ingress to egress. 174 However, ordinary redirection may lead to operational issues on 175 certain link types and/or in certain deployment scenarios. 177 For example, when an ingress link neighbor accepts an ordinary 178 redirection message, it has no way of knowing whether the egress link 179 neighbor is ready and willing to accept packets directly without 180 forwarding through an intermediate router. Likewise, the egress has 181 no way of knowing that the ingress is authorized to forward packets 182 from the claimed network-layer source address. (This is especially 183 important for very large links, since any node on the link can spoof 184 the network-layer source address with low probability of detection 185 even if the link-layer source address cannot be spoofed.) 186 Additionally, the ingress would have no way of knowing whether the 187 direct path to the egress has failed, nor whether the final 188 destination has moved away from the egress to some other network 189 attachment point. 191 Therefore, a new approach is required that can enable redirection 192 signaling from the egress to the ingress link node under the 193 mediation of a trusted intermediate router. The mechanism is 194 asymmetric (since only the forward direction from the ingress to the 195 egress is optimized) and extended (since the redirection extends 196 forward to the egress before reaching back to the ingress). This 197 document therefore introduces an Asymmetric Extended Route 198 Optimization (AERO) capability that addresses the issues. 200 While the AERO mechanisms were initially designed for the specific 201 purpose of NBMA tunnel virtual interfaces (e.g., see: 202 [RFC2529][RFC5214][RFC5569][I-D.templin-intarea-vet]) they can also 203 be applied to any multiple access link types that support 204 redirection. The AERO techniques are discussed herein with reference 205 to IPv6 [RFC2460][RFC4861][RFC4862][RFC3315], however they can also 206 be applied to any other network layer protocol (e.g., IPv4 207 [RFC0791][RFC0792][RFC2131], etc.) that provides a redirection 208 service (details of operation for other network layer protocols are 209 out of scope.) 211 This document is intended for publication on the experimental track, 212 and therefore does not seek to define a new standard for the 213 Internet. Experimental instead of standards-track is requested since 214 the document proposes a new and different dynamic routing mechanism. 215 Experimentation will focus on candidate multiaccess link types that 216 can connect large numbers of neighboring nodes where the use of 217 existing dynamic routing protocols may be impractical. Examples 218 include NBMA tunnel virtual links, large bridged campus LANs, etc. 220 2. Terminology 222 The terminology in the normative references apply; the following 223 terms are defined within the scope of this document: 225 AERO link 226 any link (either physical or virtual) over which the AERO 227 mechanisms can be applied. (For example, a virtual overlay of 228 tunnels can serve as an AERO link.) 230 AERO interface 231 an node's attachment to an AERO link. 233 AERO node 234 a router or host connected to an AERO link, and that participates 235 in the AERO protocol on that link. 237 intermediate AERO router ("intermediate router") 238 a router that configures an advertising router interface on an 239 AERO link over which it can provide default forwarding and 240 redirection services for other AERO nodes. 242 edge AERO router ("edge router") 243 a router that configures a non-advertising router interface on an 244 AERO link over which it can connect End User Networks (EUNs) to 245 the AERO link. 247 AERO host 248 a simple host on an AERO link. 250 ingress AERO node ("ingress node") 251 a node that injects packets into an AERO link. 253 egress AERO node ("egress node") 254 a node that receives packets from an AERO link. 256 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 257 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this 258 document, are to be interpreted as described in [RFC2119]. 260 3. Motivation 262 AERO was designed to operate as an on-demand route optimization 263 function for nodes attached to a single multi-access link, i.e., 264 similar to the standard ICMPv6 redirect mechanism. However, AERO 265 differs in that the target of the redirection first receives a pre- 266 authorization notification, after which it returns route optimization 267 information to the source of the original packet. This scenario 268 calls into question whether a standard dynamic routing protocol could 269 be used instead of AERO, but a number of considerations indicate that 270 standard routing protocols may be poorly suited for the use cases 271 AERO was designed to address. 273 First, AERO is designed to work on very large multiple access links 274 that may connect a mix of many thousands of routers and hosts. 275 Classical proactive dynamic routing protocols such as OSPF, IS-IS, 276 RIP, OLSR and TBRPF may be inefficient in such environments due to 277 the control message overhead scaling when large numbers of routers 278 are present and/or when link capacity is low. 280 Secondly, AERO is designed to work on-demand of data packet arrival, 281 but only seeks to discover neighbors on the same link and not distant 282 nodes that may be located many link hops away. Reactive dynamic 283 routing protocols such as AODV and DSR also operate on-demand, 284 however they flood specialized route discovery messages that reach 285 all nodes on the link and may further traverse multiple link hops 286 before a route reply is received. This requires a multicast-capable 287 network and does not ensure delivery of the original data packet 288 which may be dropped or delayed during route discovery. 290 Additionally, AERO is designed to override an existing route to a 291 destination if the existing route directs traffic along a sub-optimal 292 path via an extraneous router on the shared link. AERO nodes send 293 data packets over a pre-existing working route, and may subsequently 294 receive notification of a better route based on route optimization 295 feedback from a trusted on-link neighbor. This stands in contrast to 296 on-demand routing protocols that were designed to operate when no 297 pre-existing working routes are present and that multicast explicit 298 route request messages to receive a route reply rather than simply 299 unicast forwarding the data packet via a pre-existing route. 301 Finally, AERO requires less control message and/or processing 302 overhead than standard dynamic routing protocols on links for which 303 the number of routes that must be maintained by each router is far 304 smaller than the total number of routers on the link, and the routes 305 maintained by each router may be changing over time. For example, on 306 a link that connects N nodes it will often be the case that each node 307 will only communicate with a small number link neighbors, and the set 308 of neighbors may change dynamically over time. Therefore, the number 309 of active neighbor pairs on the link is V*N (where V is a small 310 variable number) instead of N**2. This is especially important on 311 very large links, e.g., for values of N such as 1,000 or more. 313 4. Example Use Cases 315 AERO was designed to satisfy numerous operational use cases. As a 316 first example, a hypothetical major airline has deployed an overlay 317 network on top of the global Internet to track the aircraft in its 318 fleet. The global Internet therefore acts as the "link" over which 319 the overlay network is configured. Each aircraft acts as a mobile 320 router that fronts for an internal network that includes various 321 devices controlled and monitored by the airline. However, it would 322 be impractical for each aircraft to track the changing locations of 323 all other aircraft in the fleet due to control message overhead on 324 limited capacity communication links. 326 In this example, an aircraft 'A' en route to its destination needs to 327 report its ETA and communicate passenger itineraries to other en 328 route aircraft that will be servicing passenger connections. 'A' 329 knows the overlay network addresses of the other aircraft, but does 330 not know the current underlay address mappings. 'A' sends its 331 initial messages targeted to the other aircraft via an airline 332 central dispatch router 'D', which may be located in a far away 333 location. 'D' forwards the messages, but also initiates the AERO 334 redirection procedure to step out of the triangular path and allow 335 direct aircraft-to-aircraft communications. 337 In a second example, Mobile Ad-hoc Networks (MANETs) are often 338 deployed in environments with a high degree of mobility, attrition, 339 and very limited wireless communications link bandwidth. Such 340 environments typically also require the use of network layer security 341 mechanisms that view the MANET as a "link" over which encrypted 342 messages are forwarded in an overlay network. In such environments, 343 a dynamic routing protocol running in the overlay network may serve 344 to add unacceptable additional congestion to the already overtaxed 345 wireless links. In that case, the AERO route optimization mechanism 346 can eliminate costly extraneous routing hops without imparting 347 additional control message overhead. 349 In a further example, a large campus LAN that is joined by L2 bridges 350 may connect many thousands of routers and hosts that appear to share 351 a single common multi-access link. In that case, the AERO mechanisms 352 can be applied to satisfy the necessary intra-link route optimization 353 functions without employing an adjunct dynamic routing protocol that 354 may be inefficient for reasons mentioned above. 356 5. Requirements 358 The route optimization mechanism must satisfy the following 359 requirements: 361 Req 1: Off-load traffic from performance-critical gateways 362 The mechanism must offload sustained transit though an 363 intermediate AERO router that would otherwise become a traffic 364 concentrator. 366 Req 2: Support route optimization 367 The ingress AERO node should be able to send packets directly to 368 the egress node without forwarding through an intermediate router 369 for route optimization purposes. 371 Req 3: Support scaling 372 For scaling purposes, support interworking and control message 373 forwarding between multiple intermediate routers (see appendix A). 375 Req 4: Do not circumvent ingress filtering 376 The mechanism must not open an attack vector where network-layer 377 source address spoofing is enabled even when link-layer source 378 address spoofing is disabled. 380 Req 5: Do not expose packets to loss due to filtering 381 The ingress AERO node must have a way of knowing that the egress 382 AERO node will accept its forwarded packets. 384 Req 6: Do not expose packets to loss due to path failure 385 The ingress AERO node must have a way of discovering whether the 386 AERO egress node has gone unreachable on the route optimized path. 388 Req 7: Do not introduce routing loops 389 Intermediate routers must not invoke a route optimization that 390 would cause a routing loop to form. 392 Req 8: Support mobility 393 The mechanism must continue to work even if the final destination 394 node/network moves from a first egress node and re-associates with 395 a second egress node. 397 Req 9: Support link layer address changes 398 The mechanism must continue to work even if the Layer 2 addresses 399 of ingress and/or egress AERO nodes change. 401 Req 10: Support network renumbering 402 The mechanism must provide graceful transition when an AERO node's 403 attached EUN is renumbered. 405 6. Asymmetric Extended Route Optimization (AERO) 407 The following sections specify an Asymmetric Extended Route 408 Optimization (AERO) capability that fulfills the requirements 409 specified in Section 5. 411 6.1. AERO Link Dynamic Routing 413 In many AERO link use case scenarios (e.g., small enterprise 414 networks, small and stable MANETs, etc.), routers can engage in a 415 classical dynamic routing protocol so that routing/forwarding tables 416 can be populated and standard forwarding between routers can be used. 417 In other scenarios (e.g., large enterprise/ISP networks, cellular 418 service provider networks, dynamic MANETs, etc.), this might be 419 impractical due to routing protocol control message scaling issues. 421 When a classical dynamic routing protocol cannot be used, the 422 mechanisms specified in this section can provide a useful on-demand 423 route discovery capability. When both classical dynamic routing 424 protocols and the AERO mechanism are active on the same link, routes 425 discovered by the dynamic routing protocol should take precedence 426 over those discovered by AERO. 428 6.2. AERO Node Behavior 430 The following sections discuss characteristics of nodes attached to 431 links over which AERO can be used: 433 6.2.1. AERO Node Types 435 Intermediate AERO routers configure their AERO link interfaces as 436 advertising router interfaces (see: [RFC4861], Section 6.2.2), and 437 therefore may send Router Advertisement (RA) messages that include 438 non-zero Router Lifetimes. 440 Edge AERO routers configure their AERO link interfaces as non- 441 advertising router interfaces. 443 AERO hosts configure their AERO link interfaces as simple host 444 interfaces. 446 6.2.2. AERO Host Behavior 448 AERO hosts observe the IPv6 host requirements defined in [RFC6434], 449 except that AERO hosts also engage in the AERO route optimization 450 procedure as specified in Section 6.4. 452 6.2.3. Edge AERO Router Behavior 454 Edge AERO routers observe the IPv6 router requirements defined in 455 [RFC6434] except that they act as "hosts" on their non-advertising 456 AERO link router interfaces in the same fashion as for IPv6 CPE 457 routers [RFC6204]. Edge routers can then acquire managed prefix 458 delegations aggregated by an intermediate router through the use of, 459 e.g., DHCPv6 Prefix Delegation [RFC3633], administrative 460 configuration, etc. 462 After the edge router acquires prefixes, it can sub-delegate them to 463 nodes and links within its attached EUNs, then can forward any 464 outbound packets coming from its EUNs via the intermediate router. 465 The edge router also engages in the AERO route optimization procedure 466 as specified in Section 6.4. 468 6.2.4. Intermediate AERO Router Behavior 470 Intermediate AERO routers observe the IPv6 router requirements 471 defined in [RFC6434] and respond to RS messages from AERO hosts and 472 edge routers on their advertising AERO link router interfaces by 473 returning an RA message. Intermediate routers further configure a 474 DHCP relay/server function on their AERO links and/or provide an 475 administrative interface for delegation of network-layer addresses 476 and prefixes. 478 When the intermediate router completes a stateful network-layer 479 address or prefix delegation transaction (e.g., as a DHCPv6 relay/ 480 server, etc.), it establishes forwarding table entries that list the 481 link-layer address of the client AERO node as the link-layer address 482 of the next hop toward the delegated network-layer addresses/ 483 prefixes. 485 When the intermediate router forwards a packet out the same AERO 486 interface it arrived on, it initiates an AERO route optimization 487 procedure as specified in Section 6.4. 489 6.3. AERO Reference Operational Scenario 491 Figure 3 depicts the AERO reference operational scenario. The figure 492 shows an intermediate AERO router ('A'), two edge AERO routers ('B', 493 'D'), an AERO host ('F'), and three ordinary IPv6 hosts ('C', 'E', 494 'G'): 496 .-(::::::::) 497 .-(::: IPv6 :::)-. +-------------+ 498 (:::: Internet ::::)--| Host G | 499 `-(::::::::::::)-' +-------------+ 500 `-(::::::)-' 2001:db8:3::1 501 | 502 +--------------+ +--------------+ 503 | Intermediate | | AERO Host F | 504 | AERO Router A| | (default->A) | 505 | (C->B; E->D) | +--------------+ 506 +--------------+ 2001:db8:2:1 507 L3(A) L3(F) 508 L3(A) L2(F) 509 | | 510 X-----+-----------+-----------+-----------+---X 511 | AERO Link | 512 L2(B) L2(D) 513 L3(B) L3(D) 514 +--------------+ +--------------+ .-. 515 | AERO Edge | | AERO Edge | ,-( _)-. 516 | Router B | | Router D | .-(_ IPv6 )-. 517 | (default->A) | | (default->A) |--(__ EUN ) 518 +--------------+ +--------------+ `-(______)-' 519 2001:db8:0::/48 2001:db8:1::/48 | 520 | 2001:db8:1::1 521 .-. +-------------+ 522 ,-( _)-. 2001:db8:0::1 | Host E | 523 .-(_ IPv6 )-. +-------------+ +-------------+ 524 (__ EUN )--| Host C | 525 `-(______)-' +-------------+ 527 Figure 3: AERO Reference Operational Scenario 529 In Figure 3, intermediate AERO router ('A') connects to the AERO link 530 and also connects to the IPv6 Internet, either directly or via other 531 IPv6 routers (not shown). Intermediate router ('A') configures an 532 AERO link interface with a link-local network-layer address L3(A) and 533 with link-layer address L2(A). The intermediate router next arranges 534 to add L2(A) to a published list of valid intermediate routers for 535 the link. 537 AERO node ('B') is an AERO edge router that connects to the AERO link 538 via an interface with link-local network-layer address L3(B) and with 539 link-layer address L2(B). Node ('B') configures a default route with 540 next-hop network-layer address L3(A) via the AERO interface, and also 541 assigns the network-layer prefix 2001:db8:0::/48 to its attached EUN 542 link. IPv6 host ('C') attaches to the EUN, and configures the 543 network-layer address 2001:db8:0::1. 545 AERO node ('D') is an AERO edge router that connects to the AERO link 546 via an interface with link-local network-layer address L3(D) and with 547 link-layer address L2(D). Node ('D') configures a default route with 548 next-hop network-layer address L3(A) via the AERO interface, and also 549 assigns the network-layer prefix 2001:db8:1::/48 to its attached EUN 550 link. IPv6 host ('E') attaches to the EUN, and configures the 551 network-layer address 2001:db8:1::1. 553 AERO host ('F') connects to the AERO link via an interface with link- 554 local network-layer address L3(F) and with link-layer address L2(F). 555 Host ('F') configures a default route with next-hop network-layer 556 address L3(A) via the AERO interface, and also assigns the network- 557 layer address 2001:db8:2::1 to the AERO interface. 559 Finally, IPv6 host ('G') connects to an IPv6 network outside of the 560 AERO link domain. Host ('G') configures its IPv6 interface in a 561 manner specific to its attached IPv6 link, and assigns the network- 562 layer address 2001:db8:3::1 to its IPv6 link interface. 564 In these arrangements, intermediate router ('A') must maintain state 565 that associates the delegated network-layer addresses/prefixes with 566 the link-local network-layer addresses of the correct edge routers 567 and/or hosts on the AERO link. The nodes must in turn maintain at 568 least a default route that points to intermediate router ('A'), and 569 can discover more-specific routes either via a proactive dynamic 570 routing protocol or via the AERO mechanisms specified in Section 6.4. 572 6.4. AERO Specification 574 Section 6.3 describes the AERO reference operational scenario. We 575 now discuss the operation and protocol details of AERO with respect 576 to this reference scenario. 578 6.4.1. Classical Redirection Approaches 580 With reference to Figure 3, when IPv6 source host ('C') sends a 581 packet to an IPv6 destination host ('E'), the packet is first 582 forwarded via the EUN to ingress AERO node ('B'). The ingress node 583 ('B') then forwards the packet over its AERO interface to 584 intermediate router ('A'), which then forwards the packet to egress 585 AERO node ('D'), where the packet is finally forwarded to the IPv6 586 destination host ('E'). When intermediate router ('A') forwards the 587 packet back out on its advertising AERO interface, it must arrange to 588 redirect ingress node ('B') toward egress node ('D') as a better next 589 hop node on the AERO link that is closer to the final destination. 590 However, this redirection process should only occur if there is 591 assurance that both the ingress and egress nodes are willing 592 participants. 594 Consider a first alternative in which intermediate router ('A') 595 informs ingress node ('B') only and does not inform egress node ('D') 596 (i.e., "classic redirection"). In that case, the egress node has no 597 way of knowing that the ingress is authorized to forward packets from 598 their claimed source network-layer addresses, and may simply elect to 599 drop the packets. Also, the ingress node has no way of knowing 600 whether the egress is performing some form of source address 601 filtering that would reject packets arriving from a node other than a 602 trusted default router, nor whether the egress is even reachable via 603 a direct path that does not involve the intermediate router. 604 Finally, the ingress node has no way of knowing whether the final 605 destination has moved away from egress node. 607 Consider also a second alternative in which intermediate router ('A') 608 informs both ingress node ('B') and egress node ('D') separately via 609 independent redirection messages (i.e., "augmented redirection"). In 610 that case, several conditions can occur that could result in 611 communication failures. First, if the ingress receives the 612 redirection message but the egress does not, subsequent packets sent 613 by the ingress could be dropped due to filtering since the egress 614 would not have neighbor state to verify their source network-layer 615 addresses. Second, if the egress receives the redirection message 616 but the ingress does not, subsequent packets sent in the reverse 617 direction by the egress would be lost. Finally, timing issues 618 surrounding the establishment and garbage collection of neighbor 619 state at the ingress and egress nodes could yield unpredictable 620 behavior. For example, unless the timing were carefully coordinated 621 through some form of synchronization loop, there would invariably be 622 instances in which one node has the correct neighbor state and the 623 other node does not resulting in non-deterministic packet loss. 625 Since neither of these alternatives can satisfy the requirements 626 listed in Section 5, a new redirection technique (i.e., "AERO 627 redirection") is needed. 629 6.4.2. AERO Concept of Operations 631 AERO redirection is used on links for which the classical redirection 632 approaches described in Section 6.4.1 are insufficient to satisfy all 633 requirements. We now discuss the concept of operations for this new 634 approach. 636 Again with reference to Figure 3, when source host ('C') sends a 637 packet to destination host ('E'), the packet is first forwarded over 638 the source host's attached EUN to ingress node ('B'), which then 639 forwards the packet via its AERO interface to intermediate router 640 ('A'). 642 Using AERO redirection, intermediate router ('A') then forwards the 643 packet out the same AERO interface toward egress node ('D') and also 644 sends a "Predirect" message forward to the egress node as specified 645 in Section 6.4.6. The Predirect message includes the identity of 646 ingress node ('B') as well as information that egress node ('D') can 647 use to determine the longest-match prefixes that cover the source and 648 destination network-layer addresses of the packet that triggered the 649 Predirect. After egress node ('D') receives the Predirect, it 650 process the message and returns a Redirect message to the 651 intermediate router ('A') as specified in Section 6.4.7. (During the 652 process, it also creates or updates neighbor state for ingress node 653 ('B'), and retains this (src, dst) "prefix pair" as ingress filtering 654 information to accept future packets using addresses matched by the 655 prefixes from ingress node ('B').) 657 When the intermediate router ('A') receives the Redirect message, it 658 processes the message and forwards it on to ingress node ('B') as 659 specified in Section 6.4.8. The Redirect message includes the 660 identity of egress node ('D') as well as information that ingress 661 node ('B') can use to determine the longest-match prefixes that cover 662 the source and destination network-layer addresses of the packet that 663 triggered the Redirect. After ingress node ('B') receives the 664 Redirect, it processes the message as specified in Section 6.4.9. 665 (During the process, it also creates or updates neighbor state for 666 egress node ('D'), and retains this prefix pair as forwarding 667 information to forward future packets using addresses matched by the 668 prefixes to the egress node ('D').) 670 Following the above Predirect/Redirect message exchange, forwarding 671 of packets with source and destination network-layer addresses 672 covered by the longest-match prefix pair is enabled in the forward 673 direction from ingress node ('B') to egress node ('D'). The 674 mechanisms that enable this exchange are specified in the following 675 sections. 677 6.4.3. Conceptual Data Structures and Protocol Constants 679 Each AERO node maintains a per AERO interface conceptual neighbor 680 cache that includes an entry for each neighbor it communicates with 681 on the AERO link the same as for any IPv6 interface (see: [RFC4861]). 683 Each AERO interface neighbor cache entry further maintains two lists 684 of (src, dst) prefix pairs. The AERO node adds a prefix pair to the 685 ACCEPT list if it has been informed by a trusted intermediate router 686 that it is safe to accept packets from the neighbor using network- 687 layer source and destination addresses covered by the prefix pair. 688 The AERO node adds a prefix pair to the FORWARD list if it has been 689 informed by a trusted intermediate router that it is permitted to 690 forward packets to the neighbor using network-layer addresses covered 691 by the prefix pair. 693 When the node adds a prefix pair to a neighbor cache entry ACCEPT 694 list, it also sets an expiration timer for the prefix pair to 695 ACCEPT_TIME seconds. When the node adds a prefix pair to a neighbor 696 cache entry FORWARD list, it also sets an expiration timer for the 697 prefix pair to FORWARD_TIME seconds. The node further maintains a 698 keepalive interval KEEPALIVE_TIME used to limit the number of 699 keepalive control messages. Finally, the node maintains a constant 700 value MAX_RETRY to limit the number of keepalives sent when a 701 neighbor has gone unreachable. 703 It is RECOMMENDED that FORWARD_TIME be set to the default constant 704 value 30 seconds to match the default REACHABLE_TIME value specified 705 for IPv6 neighbor discovery [RFC4861]. 707 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 708 value 40 seconds to allow a 10 second window so that the AERO 709 redirection procedure can converge before the ACCEPT_TIME timer 710 decrements below FORWARD_TIME. 712 It is RECOMMENDED that KEEPALIVE_TIME be set to the default constant 713 value 5 seconds to providing timely reachability verification without 714 causing excessive control message overhead. 716 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 717 for IPv6 neighbor discovery address resolution in Section 7.3.3 of 718 [RFC4861]. 720 Different values for FORWARD_TIME, ACCEPT_TIME, KEEPALIVE_TIME and 721 MAX_RETRY MAY be administratively set if necessary to better match 722 the AERO link's performance characteristics; however, if different 723 values are chosen all nodes on the link MUST consistently configure 724 the same values. ACCEPT_TIME SHOULD further be set to a value that 725 is sufficiently longer than FORWARD time to allow the AERO 726 redirection procedure to converge. 728 6.4.4. Data Origin Authentication 730 AERO nodes MUST employ a data origin authentication check for the 731 packets they receive on an AERO interface. In particular, the node 732 considers the network-layer source address correct for the link-layer 733 source address if at least one of the following is true: 735 o the network-layer source address is an on-link address that embeds 736 the link-layer source address, or 738 o the network-layer source address is explicitly linked to the link- 739 layer source address through per-neighbor state, or 741 o the link-layer source address is the address of a trusted 742 intermediate AERO router. 744 When the AERO node receives a packet on an AERO interface, it 745 processed the packet further if it satisfies one of these data origin 746 authentication conditions; otherwise it drops the packet. 748 Note that on links in which link-layer address spoofing is possible, 749 AERO nodes may require additional securing mechanisms. To address 750 this, future work will define a strong data origin authentication 751 scheme such as the use of digital signatures. 753 6.4.5. AERO Redirection Message Format 755 AERO redirection messages use the same format as for ICMPv6 Redirect 756 messages depicted in Section 4.5 of [RFC4861], however the messages 757 are encapsulated in a UDP header [RFC0768] to distinguish them from 758 ordinary ICMPv6 Redirect messages. AERO Redirect messages therefore 759 require a new UDP service port number 'AERO_PORT'. 761 The AERO redirection message is formatted as shown in Figure 4: 763 0 1 2 3 764 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 1 765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 766 | Type (=0) | Code (=0) | Checksum (=0) | 767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 |P| Reserved | 769 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 770 | | 771 + + 772 | | 773 + Target Address + 774 | | 775 + + 776 | | 777 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 778 | | 779 + + 780 | | 781 + Destination Address + 782 | | 783 + + 784 | | 785 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 786 | Options ... 787 +-+-+-+-+-+-+-+-+-+-+-+- 789 Figure 4: AERO Redirection Message Format 791 The AERO redirection message sender sets the 'Type' field to 0 (since 792 this is not an actual ICMPv6 message), and also sets the 'Checksum' 793 field to 0 (since the UDP checksum will provide protection for the 794 entire packet). The sender further sets the 'P' bit to 1 if this is 795 a 'Predirect' message and sets the 'P' bit to 0 if this is a 796 'Redirect' message (as described below). 798 The sender then encapsulates the AERO Redirect message in IP/UDP 799 headers as shown in Figure 5: 801 +--------------------+ 802 ~ IP header ~ 803 +--------------------+ 804 ~ UDP header ~ 805 +--------------------+ 806 | | 807 ~ AERO Redirect ~ 808 ~ Message ~ 809 | | 810 +--------------------+ 812 Figure 5: AERO Message UDP Encapsulation Format 814 The AERO redirection message sender sets the UDP destination port 815 number to 'AERO_PORT" and sets the UDP source port number to a 816 (pseudo-)random value. The sender next sets the UDP length field to 817 the length of the UDP message, then calculates the checksum across 818 the message and writes the value into the UDP checksum field. Next, 819 the sender sets the IP TTL/Hop-limit field to a small integer value 820 chosen to provide a quick exit from any temporal routing loops. It 821 is RECOMMENDED that the sender set IP TTL/Hop-limit to the value 8 822 unless it has better knowledge of the AERO link characteristics. 824 6.4.6. Sending Predirects 826 When an intermediate AERO router forwards a packet out the same AERO 827 interface that it arrived on, the router sends an AERO Predirect 828 message forward toward the egress AERO node instead of sending an 829 ICMPv6 Redirect message back to the ingress AERO node. 831 In the reference operational scenario, when the intermediate router 832 ('A') forwards a packet sent by the ingress node ('B') toward the 833 egress node ('D'), it also sends an AERO Predirect message forward 834 toward the egress, subject to rate limiting (see Section 8.2 of 835 [RFC4861]). The intermediate router ('A') prepares the AERO 836 Predirect message as follows: 838 o the link-layer source address is set to 'L2(A)' (i.e., the link- 839 layer address of the intermediate router). 841 o the link-layer destination address is set to 'L2(D)' (i.e., the 842 link-layer address of the egress node). 844 o the network-layer source address is set to 'L3(A)' (i.e., the 845 link-local network-layer address of the intermediate router). 847 o the network-layer destination address is set to 'L3(D)'. (i.e., 848 the link-local network-layer address of the egress node). 850 o the UDP destination port is set to 'AERO_PORT'. 852 o the Target and Destination Addresses are both set to 'L3(B)' 853 (i.e., the link-local network-layer address of the ingress node). 855 o on links that require stateful address mapping, the message 856 includes a Target Link Layer Address Option (TLLAO) set to 'L2(B)' 857 (i.e., the link-layer address of the ingress node). 859 o the message includes a Route Information Option (RIO) [RFC4191] 860 that encodes the ingress node's network-layer address/prefix 861 delegation that covers the network-layer source address of the 862 originating packet. 864 o the message includes a Redirected Header Option (RHO) that 865 contains the originating packet truncated to ensure that at least 866 the network-layer header is included but the size of the message 867 does not exceed 1280 bytes. 869 o the 'P' bit is set to P=1. 871 The intermediate router ('A') then sends the message forward to the 872 egress node ('D'). 874 6.4.7. Processing Predirects and Sending Redirects 876 When the egress node ('D') receives an AERO Predirect message, it 877 accepts the message only if it satisfies the data origin 878 authentication requirements specified in Section 6.4.4. The egress 879 further accepts the message only if it is willing to serve as a 880 redirection target. 882 Next, the egress node ('D') validates the message according to the 883 ICMPv6 Redirect message validation rules in Section 8.1 of [RFC4861] 884 with the exception that the message includes a Type value of 0, a 885 Checksum value of 0 and a link-local address in the ICMP destination 886 field that differs from the destination address of the packet header 887 encapsulated in the RHO. 889 In the reference operational scenario, when the egress node ('D') 890 receives a valid AERO Predirect message it either creates or updates 891 a neighbor cache entry that stores the Target address of the message 892 (i.e., the link-local network-layer address of the ingress node 893 ('B')). The egress node ('D') then records the prefix found in the 894 RIO along with its own prefix that matches the network-layer 895 destination address in the packet header found in the RHO with the 896 neighbor cache entry as an acceptable (src, dst) prefix pair. The 897 egress node ('D') then adds the prefix pair to the neighbor cache 898 entry ACCEPT list, and sets/resets an expiration timer for the prefix 899 pair to ACCEPT_TIME seconds. If the timer later expires, the egress 900 node ('D') deletes the prefix pair. 902 After processing the message, the egress node ('D') prepares an AERO 903 Redirect message response as follows: 905 o the link-layer source address is set to 'L2(D)' (i.e., the link- 906 layer address of the egress node). 908 o the link-layer destination address is set to 'L2(A)' (i.e., the 909 link-layer address of the intermediate router). 911 o the network-layer source address is set to 'L3(D)' (i.e., the 912 link-local network-layer address of the egress node). 914 o the network-layer destination address is set to 'L3(B)' (i.e., the 915 link-local network-layer address of the ingress node). 917 o the UDP destination port is set to 'AERO_PORT'. 919 o the Target and the Destination Addresses are both set to 'L3(D)' 920 (i.e., the link-local network-layer address of the egress node). 922 o on links that require stateful address mapping, the message 923 includes a Target Link Layer Address Option (TLLAO) set to 924 'L2(D)'. 926 o the message includes an RIO that encodes the egress node's 927 network-layer address/prefix delegation that covers the network- 928 layer destination address of the originating packet. 930 o the message includes as much of the RHO copied from the 931 corresponding AERO Predirect message as possible such that at 932 least the network-layer header is included but the size of the 933 message does not exceed 1280 bytes. 935 o the 'P' bit is set to P=0. 937 After the egress node ('D') prepares the AERO Redirect message, it 938 sends the message to the intermediate router ('A'). 940 6.4.8. Forwarding Redirects 942 When the intermediate router ('A') receives an AERO Redirect message, 943 it accepts the message only if it satisfies the data origin 944 authentication requirements specified in Section 6.4.4. Next, the 945 intermediate router ('A') validates the message the same as described 946 in Section 6.4.7. Following validation, the intermediate router 947 ('A') processes the Redirect, and then forwards a corresponding 948 Redirect on to the ingress node ('B') as follows. 950 In the reference operational scenario, the intermediate router ('A') 951 receives the AERO Redirect message from the egress node ('D') and 952 prepares to forward a corresponding Redirect message to the ingress 953 node ('B'). The intermediate router ('A') then verifies that the RIO 954 encodes a network-layer address/prefix that the egress node ('D') is 955 authorized to use, and discards the message if verification fails. 956 Otherwise, the intermediate router ('A') changes the link-layer 957 source address of the message to 'L2(A)', changes the network-layer 958 source address of the message to the link-local network-layer address 959 'L3(A)', and changes the link-layer destination address to 'L2(B)' . 960 The intermediate router ('A') finally decrements the IP TTL/Hop-limit 961 and forwards the message to the ingress node ('B'). 963 6.4.9. Processing Redirects 965 When the ingress node ('B') receives an AERO Redirect message (i.e., 966 one with P=0), it accepts the message only if it satisfies the data 967 origin authentication requirements specified in Section 6.4.4. Next, 968 the ingress node ('B') validates the message the same as described in 969 Section 6.4.6. Following validation, the ingress node ('B') then 970 processes the message as follows. 972 In the reference operational scenario, when the ingress node ('B') 973 receives the AERO Redirect message it either creates or updates a 974 neighbor cache entry that stores the Target address of the message 975 (i.e., the link-local network-layer address of the egress node 976 'L3(D)'). The ingress node ('B') then records the (src, dst) prefix 977 pair associated with the triggering packet in the neighbor cache 978 entry FORWARD list, i.e., it records its prefix that matches the 979 redirected packet's network-layer source address and the prefix 980 listed in the RIO as the prefix pair. The ingress node ('B') then 981 sets/resets an expiration timer for the prefix pair to FORWARD_TIME 982 seconds. If the timer later expires, the ingress node ('B') deletes 983 the entry. 985 Now, the ingress node ('B') has a neighbor cache FORWARD list entry 986 for the prefix pair, and the egress node ('D') has a neighbor cache 987 ACCEPT list entry for the prefix pair. Therefore, the ingress node 988 ('B') may forward ordinary network-layer data packets with network- 989 layer source and destination addresses that match the prefix pair 990 directly to the egress node ('D') without forwarding through the 991 intermediate router ('A'). Note that the ingress node must have a 992 way of informing the network layer of a route that associates the 993 destination prefix with this neighbor cache entry. The manner of 994 establishing such a route (and deleting it when it is no longer 995 necessary) is left to the implementation. 997 To enable packet forwarding in the reverse direction, a separate AERO 998 redirection operation is required which is the mirror-image of the 999 forward operation described above but the link segments traversed in 1000 the forward and reverse directions may be different, i.e., the 1001 operations are asymmetric. 1003 6.4.10. Sending Periodic Predirect Keepalives 1005 In order to prevent prefix pairs from expiring while data packets are 1006 actively flowing, the ingress node ('B') can send AERO Predirect 1007 keepalive messages directly to the egress node ('D') to solicit AERO 1008 Redirect messages. The node should send a keepalive message only 1009 when a data packet covered by the prefix pair has been sent recently, 1010 and should wait for at least KEEPALIVE_TIME seconds before sending 1011 each successive keepalive message in order to limit control message 1012 overhead. 1014 In the reference operational scenario, when the ingress node ('B') 1015 needs to refresh the FORWARD timer for a specific prefix pair it can 1016 send an AERO Predirect keepalive message directly to the egress node 1017 ('D') prepared as follows: 1019 o the link-layer source address is set to 'L2(B)' (i.e., the link- 1020 layer address of the ingress node). 1022 o the link-layer destination address is set to 'L2(D)' (i.e., the 1023 link-layer address of the egress node). 1025 o the network-layer source address is set to 'L3(B)' (i.e., the 1026 link-local network-layer address of the ingress node). 1028 o the network-layer destination address is set to 'L3(D)' (i.e., the 1029 link-local network-layer address of the egress node). 1031 o the UDP destination port is set to 'AERO_PORT'. 1033 o the Predirect Target and Destination Addresses are both set to 1034 'L3(B)' (i.e., the link-local network-layer address of the ingress 1035 node). 1037 o the Predirect message includes an RHO that contains the 1038 originating packet truncated to ensure that at least the network- 1039 layer header is included but the size of the message does not 1040 exceed 1280 bytes. 1042 o the 'P' bit is set to P=1. 1044 When the egress node ('D') receives the AERO Predirect message, it 1045 validates the message the same as described in Section 6.4.6. 1046 Following validation, the egress node ('D') then resets its ACCEPT 1047 timer for the prefix pair that matches the originating packet's 1048 network-layer source and destination addresses to ACCEPT_TIME 1049 seconds, and sends an AERO Redirect message directly to the ingress 1050 node ('B') prepared as follows: 1052 o the link-layer source address is set to 'L2(D)' (i.e., the link- 1053 layer address of the egress node). 1055 o the link-layer destination address is set to 'L2(B)' (i.e., the 1056 link-layer address of the ingress node). 1058 o the network-layer source address is set to 'L3(D)' (i.e., the 1059 link-local network-layer address of the egress node). 1061 o the network-layer destination address is set to 'L3(B)' (i.e., the 1062 link-local network-layer address of the ingress node). 1064 o the UDP destination port is set to 'AERO_PORT'. 1066 o the Redirect Target and Destination Addresses are both set to 1067 'L3(D)' (i.e., the link-local network-layer address of the egress 1068 node). 1070 o the message includes as much of the RHO copied from the 1071 corresponding AERO Predirect message as possible such that at 1072 least the network-layer header is included but the size of the 1073 message does not exceed 1280 bytes. 1075 o the 'P' bit is set to P=0. 1077 When the ingress node ('B') receives the AERO Redirect message, it 1078 validates the message the same as described in Section 6.4.6. 1079 Following validation, the ingress node ('B') then resets its FORWARD 1080 timer for the prefix pair that matches the originating packet's 1081 network-layer source and destination addresses to FORWARD_TIME 1082 seconds. 1084 In this process, if the ingress node sends MAX_RETRY Predirect 1085 keepalive messages without receiving a Redirect reply it can either 1086 declare the prefix pair unreachable immediately or allow the pair to 1087 expire after FORWARD_TIME seconds. 1089 6.4.11. Neighbor Reachability Considerations 1091 When the ingress node ('B') receives an AERO Redirect message 1092 informing it of a direct path to a new egress node ('D'), there is a 1093 question in point as to whether the new egress node ('D') can be 1094 reached directly without forwarding through an intermediate router 1095 ('A'). On some AERO links, it may be reasonable for the ingress node 1096 ('B') to (optimistically) assume that reachability is transitive, and 1097 to immediately begin forwarding data packets to the egress node ('D') 1098 without testing reachability. 1100 On AERO links in which an optimistic assumption of transitive 1101 reachability may be unreasonable, however, the ingress node ('B') can 1102 defer the redirection until it tests the direct path to the egress 1103 node ('D'), e.g., by sending an IPv6 Neighbor Solicitation to elicit 1104 an IPv6 Neighbor Advertisement response. If the ingress node ('B') 1105 is unable to elicit a response after MAX_RETRY attempts, it should 1106 consider the direct path to the egress node ('D') as unusable. 1108 In either case, the ingress node ('B') can process any link errors 1109 corresponding to the data packets sent directly to the egress node 1110 ('D') as a hint that the direct path has either failed or has become 1111 intermittent. Conversely, the ingress node ('B') can further process 1112 any Redirect messages received as evidence of neighbor reachability. 1114 6.4.12. Mobility Considerations 1116 Again with reference to Figure 3, egress node ('D') can configure 1117 both a non-advertising router interface on a provider AERO link and 1118 advertising router interfaces on its connected EUN links. When an 1119 EUN node ('E') in one of the egress node's connected EUNs moves to a 1120 different network point of attachment, however, it can release its 1121 network-layer address/prefix delegations that were registered with 1122 egress node ('D' ) and re-establish them via a different router. 1124 When the EUN node ('E') releases its network-layer address/prefix 1125 delegations, the egress node ('D') marks its forwarding table entries 1126 corresponding to the network-layer addresses/prefixes as "departed" 1127 and no longer responds to AERO Predirect keepalive messages for the 1128 departed addresses/prefixes. When egress node ('D') receives packets 1129 from an ingress node ('B') with network-layer source and destination 1130 addresses that match a prefix pair on the ACCEPT list, it forwards 1131 them to the last-known link-layer address of EUN node ('E') as a 1132 means for avoiding mobility-related packet loss during routing 1133 changes. Egress node ('D') also returns a NULL AERO Redirect message 1134 to inform the ingress node ('B') of the departure. The message is 1135 prepared as follows: 1137 o the link-layer source address is set to 'L2(D)'. 1139 o the link-layer destination address is set to 'L2(B)'. 1141 o the network-layer source address is set to the link-local address 1142 'L3(D)'. 1144 o the network-layer destination address is set to the link-local 1145 address 'L3(B)'. 1147 o the UDP destination port is set to 'AERO_PORT'. 1149 o the Redirect Target and Destination Addresses are both set to 1150 NULL. 1152 o the message includes an RHO that contains as much of the original 1153 packet as possible such that at least the network-layer header is 1154 included but the size of the message does not exceed 1280 bytes. 1156 o the 'P' bit is set to P=0. 1158 When ingress node ('B') receives the NULL AERO Redirect message, it 1159 deletes the prefix pair associated with the packet in the RHO from 1160 its list of forwarding entries corresponding to egress node ('D'). 1161 When egress node ('D')s ACCEPT_TIME timer for the prefix pair 1162 corresponding to the departed prefix expires, it deletes the prefix 1163 pairs from its list of ingress filtering entries corresponding to 1164 ingress node ('B'). 1166 Eventually, any such correspondent AERO nodes will receive a NULL 1167 AERO Redirect message and will cease to use the egress node ('D') as 1168 a next hop. They will then revert to sending packets destined to the 1169 EUN node ('E') via a trusted intermediate router and may subsequently 1170 receive new AERO Redirect messages to discover that the EUN node ('E' 1171 ) is now associated with a new AERO edge router. 1173 Note that any packets forwarded by the egress node ('D') via a 1174 departed forwarding table entry may be lost if the (mobile) EUN node 1175 ('E') moves off-link with respect to its previous EUN point of 1176 attachment. This should not be a problem for large links (e.g., 1177 large cellular network deployments, large ISP networks, etc.) in 1178 which all/most mobility events are intra-link. 1180 6.4.13. Link-Layer Address Change Considerations 1182 When an ingress node needs to change its link-layer address, it 1183 deletes each FORWARD list entry that was established under the old 1184 link layer address, changes the link layer address, then allows 1185 packets to again flow through an intermediate router. Any egress 1186 node that receives the packets will also receive new Predirect 1187 messages from the intermediate router. The egress node then deletes 1188 the ACCEPT entry that included the ingress node's old link-layer 1189 address and installs a new ACCEPT entry that includes the ingress 1190 node's new link-layer address. The egress then returns a new 1191 Redirect message to the ingress node via the intermediate router, 1192 which the ingress node uses to establish a new FORWARD list entry. 1194 When an egress node needs to change its link-layer address, it 1195 deletes each entry in the ACCEPT list and SHOULD also send NULL AERO 1196 Redirect messages to the corresponding ingress node (i.e., the same 1197 as described for mobility operations in Section 6.4.12) before 1198 changing the link-layer address. Any ingress node that receives the 1199 NULL Redirect messages will delete any corresponding FORWARD list 1200 entries and again allow packets to flow through an intermediate 1201 router. The egress then changes the link-layer address, and sends 1202 new Redirect messages in response to any Predirect messages it 1203 receives from the intermediate router while using the new link-layer 1204 address. 1206 6.4.14. Prefix Re-Provisioning Considerations 1208 When an AERO node configures one or more FORWARD/ACCEPT list prefix 1209 pair entries, and the prefixes associated with the pair are somehow 1210 re-configured or renumbered, the stale FORWARD/ACCEPT list 1211 information must be deleted. 1213 When an ingress node ('B') re-configures it's network-layer source 1214 prefix in such a way that the ACCEPT list entry in the egress node 1215 ('D') would no longer be valid (e.g., the prefix length of the source 1216 prefix changes), the ingress node ('B') simply deletes the prefix 1217 pair form its FORWARD list and allows subsequent packets to again 1218 flow through an intermediate router ('A'). 1220 When the egress node ('D') re-configures it's network-layer 1221 destination prefix in such a way that the FORWARD list entry in the 1222 ingress node ('B') would no longer be valid, the egress node ('D') 1223 sends a NULL AERO Redirect message to the ingress node ('B') the same 1224 as described for mobility and link-layer address change 1225 considerations when it receives either an AERO Predirect message or a 1226 data packet (subject to rate limiting) from the ingress node ('B') . 1228 6.4.15. Backward Compatibility 1230 There are no backward compatibility considerations since AERO 1231 redirection messages use a new UDP port number that distinguishes 1232 them from other kinds of control messages. Therefore, legacy nodes 1233 will simply discard ant AERO redirection messages they may 1234 accidentally receive. 1236 Note however that AERO redirection requires that all three of the 1237 ingress, intermediate router and egress participate in the protocol. 1238 Additionally, the intermediate router SHOULD disable ordinary ICMPv6 1239 Redirects when AERO redirection is enabled. 1241 7. IANA Considerations 1243 IANA has assigned a UDP user port number TBD for this protocol via 1244 the expert review process [RFC5226]. 1246 8. Security Considerations 1248 AERO link security considerations are the same as for standard IPv6 1249 Neighbor Discovery [RFC4861] except that AERO improves on some 1250 aspects. In particular, AERO is dependent on a trust basis between 1251 AERO edge nodes and intermediate routers, where the edge nodes must 1252 only engage in the AERO mechanism when it is facilitated by a trusted 1253 intermediate router. 1255 AERO links must be protected against link-layer address spoofing 1256 attacks in which an attacker on the link pretends to be a trusted 1257 neighbor. Links that provide link-layer securing mechanisms (e.g., 1258 WiFi networks) and links that provide physical security (e.g., 1259 enterprise network LANs) provide a first-line of defense that is 1260 often sufficient. In other instances, sufficient assurances against 1261 link-layer address spoofing attacks are possible if the source can 1262 digitally sign its messages through means outside the scope of this 1263 document. 1265 9. Acknowledgements 1267 Discussions both on the v6ops list and in private exchanges helped 1268 shape some of the concepts in this work. Individuals who contributed 1269 insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant, 1270 Brian Carpenter, Brian Haberman, Joel Halpern, and Lee Howard. 1271 Members of the IESG also provided valuable input during their review 1272 process that greatly improved the document. 1274 10. References 1275 10.1. Normative References 1277 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1278 August 1980. 1280 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1281 Requirement Levels", BCP 14, RFC 2119, March 1997. 1283 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1284 (IPv6) Specification", RFC 2460, December 1998. 1286 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 1287 More-Specific Routes", RFC 4191, November 2005. 1289 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 1290 Message Protocol (ICMPv6) for the Internet Protocol 1291 Version 6 (IPv6) Specification", RFC 4443, March 2006. 1293 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1294 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1295 September 2007. 1297 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1298 Address Autoconfiguration", RFC 4862, September 2007. 1300 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1301 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1302 May 2008. 1304 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 1305 Requirements", RFC 6434, December 2011. 1307 10.2. Informative References 1309 [I-D.templin-intarea-vet] 1310 Templin, F., "Virtual Enterprise Traversal (VET)", 1311 draft-templin-intarea-vet-33 (work in progress), 1312 December 2011. 1314 [I-D.templin-ironbis] 1315 Templin, F., "The Internet Routing Overlay Network 1316 (IRON)", draft-templin-ironbis-10 (work in progress), 1317 December 2011. 1319 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1320 September 1981. 1322 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 1323 RFC 792, September 1981. 1325 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 1326 RFC 2131, March 1997. 1328 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 1329 Domains without Explicit Tunnels", RFC 2529, March 1999. 1331 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 1332 and M. Carney, "Dynamic Host Configuration Protocol for 1333 IPv6 (DHCPv6)", RFC 3315, July 2003. 1335 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 1336 Host Configuration Protocol (DHCP) version 6", RFC 3633, 1337 December 2003. 1339 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1340 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1341 March 2008. 1343 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 1344 Infrastructures (6rd)", RFC 5569, January 2010. 1346 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 1347 Troan, "Basic Requirements for IPv6 Customer Edge 1348 Routers", RFC 6204, April 2011. 1350 Appendix A. Intermediate Router Interworking 1352 Figure 3 depicts a reference AERO operational scenario with a single 1353 intermediate router on the AERO link. In order to support scaling to 1354 larger numbers of nodes, the AERO link can deploy multiple 1355 intermediate routers, e.g., as shown in Figure 6 1356 +--------------+ +--------------+ 1357 | Intermediate | +--------------+ | Intermediate | 1358 | Router C | | Core Router D| | Router E | 1359 | (default->D) | | (A->C; G->E) | | (default->D) | 1360 | (A->B) | +--------------+ | (G->F) | 1361 +-------+------+ +------+-------+ 1362 | | 1363 X---+---+--------------------------------------+---+---X 1364 | AERO Link | 1365 +-----+--------+ +--------+-----+ 1366 | Edge Router B| | Edge Router F| 1367 | (default->C) | | (default->E) | 1368 +--------------+ +--------------+ 1369 .-. .-. 1370 ,-( _)-. ,-( _)-. 1371 .-(_ IPv6 )-. .-(_ IPv6 )-. 1372 (__ EUN ) (__ EUN ) 1373 `-(______)-' `-(______)-' 1374 | | 1375 +--------+ +--------+ 1376 | Host A | | Host G | 1377 +--------+ +--------+ 1379 Figure 6: Multiple Intermediate Routers 1381 In this example, the ingress AERO node ('B') (in this case an edge 1382 router, but could also be a host) associates with intermediate AERO 1383 router ('C'), while the egress AERO node ('F') (in this case an edge 1384 router, but could also be a host) associates with intermediate AERO 1385 router ('E'). Furthermore, intermediate routers ('C') and ('E') do 1386 not associate with each other directly, but rather have an 1387 association with a "core" router ('D') (i.e., a router that has full 1388 topology information concerning its associated intermediate routers). 1389 Core router 'D' may connect to either the AERO link, or to other 1390 physical or virtual links (not shown) to which intermediate routers 1391 'C' and 'E' also connect. 1393 When host ('A') sends a packet toward destination host ('G'), IPv6 1394 forwarding directs the packet through the EUN to edge router ('B') 1395 which forwards the packet to intermediate router ('C') in absence of 1396 more-specific forwarding information. Intermediate router ('C') 1397 forwards the packet, and also generates an AERO Predirect message 1398 that is then forwarded through core router ('D') to intermediate 1399 router ('E'). When intermediate router ('E') receives the Predirect, 1400 it forwards the message to egress router ('F'). 1402 After processing the AERO Predirect message, egress router ('F') 1403 sends an AERO Redirect message to intermediate router ('E'). 1405 Intermediate router ('E') in turn forwards the message through core 1406 router ('D') to intermediate router ('C'). When intermediate router 1407 ('C') receives the Redirect, it forwards the message to ingress edge 1408 router ('B') informing it that host 'G's EUN can be reached via 1409 egress router 'F', thus completing the AERO redirection. 1411 The interworkings between intermediate and core routers (including 1412 the conveyance of pseudo Predirects and Redirects) must be carefully 1413 coordinated in a manner outside the scope of this document. In 1414 particular, the intermediate and core routers must ensure that any 1415 routing loops that may be formed are temporal in nature. See 1416 [I-D.templin-ironbis] for an architectural discussion of 1417 coordinations between intermediate and core routers. 1419 Author's Address 1421 Fred L. Templin (editor) 1422 Boeing Research & Technology 1423 P.O. Box 3707 MC 7L-49 1424 Seattle, WA 98124 1425 USA 1427 Email: fltemplin@acm.org