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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 Obsoletes: rfc5320, rfc5558, rfc5720, September 22, 2014 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: March 26, 2015 10 Transmission of IP Packets over AERO Links 11 draft-templin-aerolink-39.txt 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). Nodes attached 17 to AERO links can exchange packets via trusted intermediate routers 18 that provide forwarding services to reach off-link destinations and 19 redirection services for route optimization. AERO provides an IPv6 20 link-local address format known as the AERO address that supports 21 operation of the IPv6 Neighbor Discovery (ND) protocol and links IPv6 22 ND to IP forwarding. Admission control and provisioning are 23 supported by the Dynamic Host Configuration Protocol for IPv6 24 (DHCPv6), and node mobility is naturally supported through dynamic 25 neighbor cache updates. Although DHCPv6 and IPv6 ND messaging is 26 used in the control plane, both IPv4 and IPv6 are supported in the 27 data plane. 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 March 26, 2015. 46 Copyright Notice 48 Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 6 66 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 6 67 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 7 68 3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 8 69 3.4. AERO Interface Characteristics . . . . . . . . . . . . . 9 70 3.4.1. Coordination of Multiple Underlying Interfaces . . . 11 71 3.5. AERO Interface Neighbor Cache Maintenace . . . . . . . . 11 72 3.6. AERO Interface Sending Algorithm . . . . . . . . . . . . 13 73 3.7. AERO Interface Encapsulation, Re-encapsulation and 74 Decapsulation . . . . . . . . . . . . . . . . . . . . . . 15 75 3.8. AERO Interface Data Origin Authentication . . . . . . . . 16 76 3.9. AERO Interface MTU and Fragmentation . . . . . . . . . . 17 77 3.10. AERO Interface Error Handling . . . . . . . . . . . . . . 20 78 3.11. AERO Router Discovery, Prefix Delegation and Address 79 Configuration . . . . . . . . . . . . . . . . . . . . . . 24 80 3.11.1. AERO DHCPv6 Service Model . . . . . . . . . . . . . 24 81 3.11.2. AERO Client Behavior . . . . . . . . . . . . . . . . 24 82 3.11.3. AERO Server Behavior . . . . . . . . . . . . . . . . 27 83 3.12. AERO Relay/Server Routing System . . . . . . . . . . . . 29 84 3.13. AERO Redirection . . . . . . . . . . . . . . . . . . . . 30 85 3.13.1. Reference Operational Scenario . . . . . . . . . . . 30 86 3.13.2. Concept of Operations . . . . . . . . . . . . . . . 31 87 3.13.3. Message Format . . . . . . . . . . . . . . . . . . . 32 88 3.13.4. Sending Predirects . . . . . . . . . . . . . . . . . 32 89 3.13.5. Re-encapsulating and Relaying Predirects . . . . . . 34 90 3.13.6. Processing Predirects and Sending Redirects . . . . 35 91 3.13.7. Re-encapsulating and Relaying Redirects . . . . . . 36 92 3.13.8. Processing Redirects . . . . . . . . . . . . . . . . 37 93 3.13.9. Server-Oriented Redirection . . . . . . . . . . . . 37 95 3.14. Neighbor Unreachability Detection (NUD) . . . . . . . . . 38 96 3.15. Mobility Management . . . . . . . . . . . . . . . . . . . 39 97 3.15.1. Announcing Link-Layer Address Changes . . . . . . . 39 98 3.15.2. Bringing New Links Into Service . . . . . . . . . . 41 99 3.15.3. Removing Existing Links from Service . . . . . . . . 41 100 3.15.4. Moving to a New Server . . . . . . . . . . . . . . . 41 101 3.16. Encapsulation Protocol Version Considerations . . . . . . 42 102 3.17. Multicast Considerations . . . . . . . . . . . . . . . . 42 103 3.18. Operation on AERO Links Without DHCPv6 Services . . . . . 42 104 3.19. Operation on Server-less AERO Links . . . . . . . . . . . 43 105 3.20. Proxy AERO . . . . . . . . . . . . . . . . . . . . . . . 43 106 3.21. Extending AERO Links Through Security Gateways . . . . . 44 107 3.22. Extending IPv6 AERO Links to the Internet . . . . . . . . 46 108 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 49 109 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49 110 6. Security Considerations . . . . . . . . . . . . . . . . . . . 49 111 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 50 112 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 51 113 8.1. Normative References . . . . . . . . . . . . . . . . . . 51 114 8.2. Informative References . . . . . . . . . . . . . . . . . 52 115 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 55 117 1. Introduction 119 This document specifies the operation of IP over tunnel virtual links 120 using Asymmetric Extended Route Optimization (AERO). The AERO link 121 can be used for tunneling to neighboring nodes over either IPv6 or 122 IPv4 networks, i.e., AERO views the IPv6 and IPv4 networks as 123 equivalent links for tunneling. Nodes attached to AERO links can 124 exchange packets via trusted intermediate routers that provide 125 forwarding services to reach off-link destinations and redirection 126 services for route optimization that addresses the requirements 127 outlined in [RFC5522]. 129 AERO provides an IPv6 link-local address format known as the AERO 130 address that supports operation of the IPv6 Neighbor Discovery (ND) 131 [RFC4861] protocol and links IPv6 ND to IP forwarding. Admission 132 control and provisioning are supported by the Dynamic Host 133 Configuration Protocol for IPv6 (DHCPv6) [RFC3315], and node mobility 134 is naturally supported through dynamic neighbor cache updates. 135 Although DHCPv6 and IPv6 ND message signalling is used in the control 136 plane, both IPv4 and IPv6 can be used in the data plane. The 137 remainder of this document presents the AERO specification. 139 2. Terminology 141 The terminology in the normative references applies; the following 142 terms are defined within the scope of this document: 144 AERO link 145 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 146 configured over a node's attached IPv6 and/or IPv4 networks. All 147 nodes on the AERO link appear as single-hop neighbors from the 148 perspective of the virtual overlay. 150 AERO interface 151 a node's attachment to an AERO link. 153 AERO address 154 an IPv6 link-local address constructed as specified in Section 3.2 155 and assigned to a Client's AERO interface. 157 AERO node 158 a node that is connected to an AERO link and that participates in 159 IPv6 ND and DHCPv6 messaging over the link. 161 AERO Client ("Client") 162 a node that applies an AERO address to an AERO interface and 163 receives an IP prefix via a DHCPv6 Prefix Delegation (PD) exchange 164 with one or more AERO Servers. 166 AERO Server ("Server") 167 a node that configures an AERO interface to provide default 168 forwarding and DHCPv6 services for AERO Clients. The Server 169 applies the IPv6 link-local subnet router anycast address (fe80::) 170 to the AERO interface and also applies an administratively 171 assigned IPv6 link-local unicast address used for operation of 172 DHCPv6 and the IPv6 ND protocol. 174 AERO Relay ("Relay") 175 a node that configures an AERO interface to relay IP packets 176 between nodes on the same AERO link and/or forward IP packets 177 between the AERO link and the native Internetwork. The Relay 178 applies an administratively assigned IPv6 link-local unicast 179 address to the AERO interface the same as for a Server. 181 ingress tunnel endpoint (ITE) 182 an AERO interface endpoint that injects tunneled packets into an 183 AERO link. 185 egress tunnel endpoint (ETE) 186 an AERO interface endpoint that receives tunneled packets from an 187 AERO link. 189 underlying network 190 a connected IPv6 or IPv4 network routing region over which the 191 tunnel virtual overlay is configured. A typical example is an 192 enterprise network. 194 underlying interface 195 an AERO node's interface point of attachment to an underlying 196 network. 198 link-layer address 199 an IP address assigned to an AERO node's underlying interface. 200 When UDP encapsulation is used, the UDP port number is also 201 considered as part of the link-layer address. Link-layer 202 addresses are used as the encapsulation header source and 203 destination addresses. 205 network layer address 206 the source or destination address of the encapsulated IP packet. 208 end user network (EUN) 209 an internal virtual or external edge IP network that an AERO 210 Client connects to the rest of the network via the AERO interface. 212 AERO Service Prefix (ASP) 213 an IP prefix associated with the AERO link and from which AERO 214 Client Prefixes (ACPs) are derived (for example, the IPv6 ACP 215 2001:db8:1:2::/64 is derived from the IPv6 ASP 2001:db8::/32). 217 AERO Client Prefix (ACP) 218 a more-specific IP prefix taken from an ASP and delegated to a 219 Client. 221 Throughout the document, the simple terms "Client", "Server" and 222 "Relay" refer to "AERO Client", "AERO Server" and "AERO Relay", 223 respectively. Capitalization is used to distinguish these terms from 224 DHCPv6 client/server/relay. 226 The terminology of [RFC4861] (including the names of node variables 227 and protocol constants) applies to this document. Also throughout 228 the document, the term "IP" is used to generically refer to either 229 Internet Protocol version (i.e., IPv4 or IPv6). 231 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 232 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 233 document are to be interpreted as described in [RFC2119]. 235 3. Asymmetric Extended Route Optimization (AERO) 237 The following sections specify the operation of IP over Asymmetric 238 Extended Route Optimization (AERO) links: 240 3.1. AERO Link Reference Model 242 .-(::::::::) 243 .-(:::: IP ::::)-. 244 (:: Internetwork ::) 245 `-(::::::::::::)-' 246 `-(::::::)-' 247 | 248 +--------------+ +--------+-------+ +--------------+ 249 |AERO Server S1| | AERO Relay R1 | |AERO Server S2| 250 | Nbr: C1; R1 | | Nbr: S1; S2 | | Nbr: C2; R1 | 251 | default->R1 | |(H1->S1; H2->S2)| | default->R1 | 252 | H1->C1 | +--------+-------+ | H2->C2 | 253 +-------+------+ | +------+-------+ 254 | | | 255 X---+---+-------------------+------------------+---+---X 256 | AERO Link | 257 +-----+--------+ +--------+-----+ 258 |AERO Client C1| |AERO Client C2| 259 | Nbr: S1 | | Nbr: S2 | 260 | default->S1 | | default->S2 | 261 +--------------+ +--------------+ 262 .-. .-. 263 ,-( _)-. ,-( _)-. 264 .-(_ IP )-. .-(_ IP )-. 265 (__ EUN ) (__ EUN ) 266 `-(______)-' `-(______)-' 267 | | 268 +--------+ +--------+ 269 | Host H1| | Host H2| 270 +--------+ +--------+ 272 Figure 1: AERO Link Reference Model 274 Figure 1 above presents the AERO link reference model. In this 275 model: 277 o Relay R1 acts as a default router for its associated Servers S1 278 and S2, and connects the AERO link to the rest of the IP 279 Internetwork 281 o Servers S1 and S2 associate with Relay R1 and also act as default 282 routers for their associated Clients C1 and C2. 284 o Clients C1 and C2 associate with Servers S1 and S2, respectively 285 and also act as default routers for their associated EUNs 287 o Hosts H1 and H2 attach to the EUNs served by Clients C1 and C2, 288 respectively 290 In common operational practice, there may be many additional Relays, 291 Servers and Clients. 293 3.2. AERO Node Types 295 AERO Relays provide default forwarding services to AERO Servers. 296 Relays forward packets between Servers connected to the same AERO 297 link and also forward packets between the AERO link and the native 298 Internetwork. Relays present the AERO link to the native 299 Internetwork as a set of one or more AERO Service Prefixes (ASPs). 300 Each Relay advertises the ASPs for the AERO link into the native IP 301 Internetwork and serves as a gateway between the AERO link and the 302 Internetwork. AERO Relays maintain an AERO interface neighbor cache 303 entry for each AERO Server, and maintain an IP forwarding table entry 304 for each AERO Client Prefix (ACP). 306 AERO Servers provide default forwarding services to AERO Clients. 307 Each Server also peers with each Relay in a dynamic routing protocol 308 instance to advertise its list of associated ACPs. Servers configure 309 a DHCPv6 server function to facilitate Prefix Delegation (PD) 310 exchanges with Clients. Each delegated prefix becomes an ACP taken 311 from an ASP. Servers forward packets between Clients and Relays, as 312 well as between Clients and other Clients associated with the same 313 Server. AERO Servers maintain an AERO interface neighbor cache entry 314 for each AERO Relay. They also maintain both a neighbor cache entry 315 and an IP forwarding table entry for each of their associated 316 Clients. 318 AERO Clients act as requesting routers to receive ACPs through DHCPv6 319 PD exchanges with AERO Servers over the AERO link and sub-delegate 320 portions of their ACPs to EUN interfaces. (Each Client MAY associate 321 with a single Server or with multiple Servers, e.g., for fault 322 tolerance and/or load balancing.) Each IPv6 Client receives at least 323 a /64 IPv6 ACP, and may receive even shorter prefixes. Similarly, 324 each IPv4 Client receives at least a /32 IPv4 ACP (i.e., a singleton 325 IPv4 address), and may receive even shorter prefixes. AERO Clients 326 maintain an AERO interface neighbor cache entry for each of their 327 associated Servers as well as for each of their correspondent 328 Clients. 330 AERO Clients that act as hosts typically configure a TUN/TAP 331 interface as a point-to-point linkage between the IP layer and the 332 AERO interface. The IP layer therefore sees only the TUN/TAP 333 interface, while the AERO interface provides an intermediate conduit 334 between the TUN/TAP interface and the underlying interfaces. AERO 335 Clients that act as hosts assign one or more IP addresses from their 336 ACPs to the TUN/TAP interface. 338 3.3. AERO Addresses 340 An AERO address is an IPv6 link-local address with an embedded ACP 341 and assigned to a Client's AERO interface. The AERO address is 342 formed as follows: 344 fe80::[ACP] 346 For IPv6, the AERO address begins with the prefix fe80::/64 and 347 includes in its interface identifier the base prefix taken from the 348 Client's IPv6 ACP. The base prefix is determined by masking the ACP 349 with the prefix length. For example, if the AERO Client receives the 350 IPv6 ACP: 352 2001:db8:1000:2000::/56 354 it constructs its AERO address as: 356 fe80::2001:db8:1000:2000 358 For IPv4, the AERO address is formed from the lower 64 bits of an 359 IPv4-mapped IPv6 address [RFC4291] that includes the base prefix 360 taken from the Client's IPv4 ACP. For example, if the AERO Client 361 receives the IPv4 ACP: 363 192.0.2.32/28 365 it constructs its AERO address as: 367 fe80::FFFF:192.0.2.32 369 The AERO address remains stable as the Client moves between 370 topological locations, i.e., even if its link-layer addresses change. 372 NOTE: In some cases, prospective neighbors may not have advanced 373 knowledge of the Client's ACP length and may therefore send initial 374 IPv6 ND messages with an AERO destination address that matches the 375 ACP but does not correspond to the base prefix. In that case, the 376 Client MUST accept the address as equivalent to the base address, but 377 then use the base address as the source address of any IPv6 ND 378 message replies. For example, if the Client receives the IPv6 ACP 379 2001:db8:1000:2000::/56 then subsequently receives an IPv6 ND message 380 with destination address fe80::2001:db8:1000:2001, it accepts the 381 message but uses fe80::2001:db8:1000:2000 as the source address of 382 any IPv6 ND replies. 384 3.4. AERO Interface Characteristics 386 AERO interfaces use IP-in-IPv6 encapsulation [RFC2473] to exchange 387 tunneled packets with AERO neighbors attached to an underlying IPv6 388 network, and use IP-in-IPv4 encapsulation [RFC2003][RFC4213] to 389 exchange tunneled packets with AERO neighbors attached to an 390 underlying IPv4 network. AERO interfaces can also coordinate secured 391 tunnel types such as IPsec [RFC4301] or TLS [RFC5246]. When Network 392 Address Translator (NAT) traversal and/or filtering middlebox 393 traversal may be necessary, a UDP header is further inserted 394 immediately above the IP encapsulation header. 396 AERO interfaces maintain a neighbor cache, and AERO Clients and 397 Servers use an adaptation of standard unicast IPv6 ND messaging. 398 AERO interfaces use unicast Neighbor Solicitation (NS), Neighbor 399 Advertisement (NA), Router Solicitation (RS) and Router Advertisement 400 (RA) messages the same as for any IPv6 link. AERO interfaces use two 401 redirection message types -- the first known as a Predirect message 402 and the second being the standard Redirect message (see Section 3.9). 403 AERO links further use link-local-only addressing; hence, AERO nodes 404 ignore any Prefix Information Options (PIOs) they may receive in RA 405 messages over an AERO interface. 407 AERO interface ND messages include one or more Target Link-Layer 408 Address Options (TLLAOs) formatted as shown in Figure 2: 410 0 1 2 3 411 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 1 412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 413 | Type = 2 | Length = 3 | Reserved | 414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 415 | Link ID | Preference | UDP Port Number | 416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 417 | | 418 +-- --+ 419 | | 420 +-- IP Address --+ 421 | | 422 +-- --+ 423 | | 424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 Figure 2: AERO Target Link-Layer Address Option (TLLAO) Format 428 In this format, Link ID is an integer value between 0 and 255 429 corresponding to an underlying interface of the target node, and 430 Preference is an integer value between 0 and 255 indicating the 431 node's preference for this underlying interface (with 255 being the 432 highest preference, 1 being the lowest, and 0 meaning "link 433 disabled"). UDP Port Number and IP Address are set to the addresses 434 used by the target node when it sends encapsulated packets over the 435 underlying interface. When the encapsulation IP address family is 436 IPv4, IP Address is formed as an IPv4-mapped IPv6 address [RFC4291]. 438 When a Relay enables an AERO interface, it assigns an 439 administratively assigned link-local address fe80::ID to the 440 interface. Each fe80::ID address MUST be unique among all Relays and 441 Servers on the link, and MUST NOT collide with any potential AERO 442 addresses. The addresses are typically taken from the range 443 fe80::/96, e.g., as fe80::1, fe80::2, fe80::3, etc. The Relay also 444 maintains an IP forwarding table entry for each Client-Server 445 association and maintains a neighbor cache entry for each Server on 446 the link. Relays do not require the use of IPv6 ND messaging for 447 reachability determination since Relays and Servers engage in a 448 dynamic routing protocol over the AERO interface. At a minimum, 449 however, Relays respond to NS messages by returning an NA. 451 When a Server enables an AERO interface, it assigns the address 452 fe80:: to the interface as a link-local Subnet Router Anycast 453 address, and also assigns an administratively assigned link-local 454 address fe80::ID the same as for Relays. (The Server then accepts 455 DHCPv6 and IPv6 ND solicitation messages destined to either the 456 fe80:: or fe80::ID addresses, but always uses fe80::ID as the source 457 address in the replies it generates.) The Server further configures 458 a DHCPv6 server function to facilitate DHCPv6 PD exchanges with AERO 459 Clients. The Server maintains a neighbor cache entry for each Relay 460 on the link, and manages per-Client neighbor cache entries and IP 461 forwarding table entries based on DHCPv6 exchanges. When the Server 462 receives an NS/RS message on the AERO interface it returns an NA/RA 463 message but does not update the neighbor cache. Each Server also 464 engages in a dynamic routing protocol with all Relays on the link. 465 Finally, the Server provides a simple conduit between Clients and 466 Relays, or between Clients and other Clients. Therefore, packets 467 enter the Server's AERO interface from the link layer and are 468 forwarded back out the link layer without ever leaving the AERO 469 interface and therefore without ever disturbing the network layer. 471 When a Client enables an AERO interface, it invokes DHCPv6 PD to 472 receive an ACP from an AERO Server. Next, it assigns the 473 corresponding AERO address to the AERO interface and creates a 474 neighbor cache entry for the Server, i.e., the PD exchange bootstraps 475 the provisioning of a unique link-local address. The Client 476 maintains a neighbor cache entry for each of its Servers and each of 477 its active correspondent Clients. When the Client receives Redirect/ 478 Predirect messages on the AERO interface it updates or creates 479 neighbor cache entries, including link-layer address information. 480 Unsolicited NA messages update the cached link-layer addresses for 481 correspondent Clients (e.g., following a link-layer address change 482 due to node mobility) but do not create new neighbor cache entries. 483 NS/NA messages used for Neighbor Unreachability Detection (NUD) 484 update timers in existing neighbor cache entires but do not update 485 link-layer addresses nor create new neighbor cache entries. Finally, 486 the Client need not maintain any IP forwarding table entries for its 487 Servers or correspondent Clients. Instead, it can set a single 488 "route-to-interface" default route in the IP forwarding table 489 pointing to the AERO interface, and all forwarding decisions can be 490 made within the AERO interface based on neighbor cache entries. (On 491 systems in which adding a default route would violate security 492 policy, the default route could instead be installed via a 493 "synthesized RA", e.g., as discussed in Section 3.11.2.) 495 3.4.1. Coordination of Multiple Underlying Interfaces 497 AERO interfaces may be configured over multiple underlying 498 interfaces. For example, common mobile handheld devices have both 499 wireless local area network ("WLAN") and cellular wireless links. 500 These links are typically used "one at a time" with low-cost WLAN 501 preferred and highly-available cellular wireless as a standby. In a 502 more complex example, aircraft frequently have many wireless data 503 link types (e.g. satellite-based, terrestrial, air-to-air 504 directional, etc.) with diverse performance and cost properties. 506 If a Client's multiple underlying interfaces are used "one at a time" 507 (i.e., all other interfaces are in standby mode while one interface 508 is active), then Redirect, Predirect and unsolicited NA messages 509 include only a single TLLAO with Link ID set to a constant value. 511 If the Client has multiple active underlying interfaces, then from 512 the perspective of IPv6 ND it would appear to have a single link- 513 local address with multiple link-layer addresses. In that case, 514 Redirect, Predirect and unsolicited NA messages MAY include multiple 515 TLLAOs -- each with a different Link ID that corresponds to a 516 specific underlying interface of the Client. 518 3.5. AERO Interface Neighbor Cache Maintenace 520 Each AERO interface maintains a conceptual neighbor cache that 521 includes an entry for each neighbor it communicates with on the AERO 522 link, the same as for any IPv6 interface [RFC4861]. AERO interface 523 neighbor cache entires are said to be one of "permanent", "static" or 524 "dynamic". 526 Permanent neighbor cache entries are created through explicit 527 administrative action; they have no timeout values and remain in 528 place until explicitly deleted. AERO Relays maintain a permanent 529 neighbor cache entry for each Server on the link, and AERO Servers 530 maintain a permanent neighbor cache entry for each Relay on the link. 532 Static neighbor cache entries are created though DHCPv6 PD exchanges 533 and remain in place for durations bounded by prefix lifetimes. AERO 534 Servers maintain a static neighbor cache entry for each of their 535 associated Clients, and AERO Clients maintain a static neighbor cache 536 for each of their associated Servers. When an AERO Server sends a 537 DHCPv6 Reply message response to a Client's DHCPv6 Solicit/Request or 538 Renew message, it creates or updates a static neighbor cache entry 539 based on the Client's AERO address as the network-layer address, the 540 prefix lifetime as the neighbor cache entry lifetime, the Client's 541 encapsulation IP address and UDP port number as the link-layer 542 address and the prefix length as the length to apply to the AERO 543 address. When an AERO Client receives a DHCPv6 Reply message from a 544 Server, it creates or updates a static neighbor cache entry based on 545 the Reply message link-local source address as the network-layer 546 address, the prefix lifetime as the neighbor cache entry lifetime, 547 and the encapsulation IP source address and UDP source port number as 548 the link-layer address. 550 Dynamic neighbor cache entries are created based on receipt of an 551 IPv6 ND message, and are garbage-collected if not used within a short 552 timescale. AERO Clients maintain dynamic neighbor cache entries for 553 each of their active correspondent Clients with lifetimes based on 554 IPv6 ND messaging constants. When an AERO Client receives a valid 555 Predirect message it creates or updates a dynamic neighbor cache 556 entry for the Predirect target network-layer and link-layer addresses 557 plus prefix length. The node then sets an "AcceptTime" variable in 558 the neighbor cache entry and uses this value to determine whether 559 packets received from the correspondent can be accepted. When an 560 AERO Client receives a valid Redirect message it creates or updates a 561 dynamic neighbor cache entry for the Redirect target network-layer 562 and link-layer addresses plus prefix length. The Client then sets a 563 "ForwardTime" variable in the neighbor cache entry and uses this 564 value to determine whether packets can be sent directly to the 565 correspondent. The Client also maintains a "MaxRetry" variable to 566 limit the number of keepalives sent when a correspondent may have 567 gone unreachable. 569 For dynamic neighbor cache entries, when an AERO Client receives a 570 valid NS message it (re)sets AcceptTime for the neighbor to 571 ACCEPT_TIME. When an AERO Client receives a valid solicited NA 572 message, it (re)sets ForwardTime for the neighbor to FORWARD_TIME and 573 sets MaxRetry to MAX_RETRY. When an AERO Client receives a valid 574 unsolicited NA message, it updates the correspondent's link-layer 575 addresses but DOES NOT reset AcceptTime, ForwardTime or MaxRetry. 577 It is RECOMMENDED that FORWARD_TIME be set to the default constant 578 value 30 seconds to match the default REACHABLE_TIME value specified 579 for IPv6 ND [RFC4861]. 581 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 582 value 40 seconds to allow a 10 second window so that the AERO 583 redirection procedure can converge before AcceptTime decrements below 584 FORWARD_TIME. 586 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 587 for IPv6 ND address resolution in Section 7.3.3 of [RFC4861]. 589 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 590 administratively set, if necessary, to better match the AERO link's 591 performance characteristics; however, if different values are chosen, 592 all nodes on the link MUST consistently configure the same values. 593 Most importantly, ACCEPT_TIME SHOULD be set to a value that is 594 sufficiently longer than FORWARD_TIME to allow the AERO redirection 595 procedure to converge. 597 3.6. AERO Interface Sending Algorithm 599 IP packets enter a node's AERO interface either from the network 600 layer (i.e., from a local application or the IP forwarding system), 601 or from the link layer (i.e., from the AERO tunnel virtual link). 602 Packets that enter the AERO interface from the network layer are 603 encapsulated and admitted into the AERO link, i.e., they are 604 tunnelled to an AERO interface neighbor. Packets that enter the AERO 605 interface from the link layer are either re-admitted into the AERO 606 link or delivered to the network layer where they are subject to 607 either local delivery or IP forwarding. Since each AERO node has 608 only partial information about neighbors on the link, AERO interfaces 609 may forward packets with link-local destination addresses at a layer 610 below the network layer. This means that AERO nodes act as both IP 611 routers and sub-IP layer forwarding agents. AERO interface sending 612 considerations for Clients, Servers and Relays are given below. 614 When an IP packet enters a Client's AERO interface from the network 615 layer, if the destination is covered by an ASP the Client searches 616 for a dynamic neighbor cache entry with a non-zero ForwardTime and an 617 AERO address that matches the packet's destination address. (The 618 destination address may be either an address covered by the 619 neighbor's ACP or the (link-local) AERO address itself.) If there is 620 a match, the Client uses a link-layer address in the entry as the 621 link-layer address for encapsulation then admits the packet into the 622 AERO link. If there is no match, the Client instead uses the link- 623 layer address of a neighboring Server as the link-layer address for 624 encapsulation. 626 When an IP packet enters a Server's AERO interface from the link 627 layer, if the destination is covered by an ASP the Server searches 628 for a static neighbor cache entry with an AERO address that matches 629 the packet's destination address. (The destination address may be 630 either an address covered by the neighbor's ACP or the AERO address 631 itself.) If there is a match, the Server uses a link-layer address 632 in the entry as the link-layer address for encapsulation and re- 633 admits the packet into the AERO link. If there is no match, the 634 Server instead uses the link-layer address in any permanent neighbor 635 cache entry as the link-layer address for encapsulation. 637 When an IP packet enters a Relay's AERO interface from the network 638 layer, the Relay searches its IP forwarding table for an entry that 639 is covered by an ASP and also matches the destination. If there is a 640 match, the Relay uses the link-layer address in the neighbor cache 641 entry for the next-hop Server as the link-layer address for 642 encapsulation and admits the packet into the AERO link. When an IP 643 packet enters a Relay's AERO interface from the link-layer, if the 644 destination is not a link-local address and is does not match an ASP 645 the Relay removes the packet from the AERO interface and uses IP 646 forwarding to forward the packet to the Internetwork. If the 647 destination address is a link-local or non-link-local address that 648 matches an ASP, and there is a more-specific ACP entry in the IP 649 forwarding table, the Relay uses the link-layer address in the 650 corresponding neighbor cache entry for the next-hop Server as the 651 link-layer address for encapsulation and re-admits the packet into 652 the AERO link. When an IP packet enters a Relay's AERO interface 653 from either the network layer or link-layer, and the packet's 654 destination address matches an ASP but there is no more-specific ACP 655 entry, the Relay drops the packet and returns an ICMP Destination 656 Unreachable message (see: Section 3.10). 658 When an AERO Server receives a packet from a Relay via the AERO 659 interface, the Server MUST NOT forward the packet back to the same or 660 a different Relay. 662 When an AERO Relay receives a packet from a Server via the AERO 663 interface, the Relay MUST NOT forward the packet back to the same 664 Server. 666 When an AERO node re-admits a packet into the AERO link without 667 involving the network layer, the node MUST NOT decrement the network 668 layer TTL/Hop-count. 670 Note that in the above that the link-layer address for encapsulation 671 may be determined through consulting either the neighbor cache or the 672 IP forwarding table. IP forwarding is therefore linked to IPv6 ND 673 via the AERO address. 675 3.7. AERO Interface Encapsulation, Re-encapsulation and Decapsulation 677 AERO interfaces encapsulate IP packets according to whether they are 678 entering the AERO interface from the network layer or if they are 679 being re-admitted into the same AERO link they arrived on. This 680 latter form of encapsulation is known as "re-encapsulation". 682 AERO interfaces encapsulate packets per the base tunneling 683 specifications (e.g., [RFC2003][RFC2473][RFC4213][RFC4301][RFC5246], 684 etc.) except that the interface copies the "TTL/Hop Limit", "Type of 685 Service/Traffic Class" and "Congestion Experienced" values in the 686 packet's IP header into the corresponding fields in the encapsulation 687 header. For packets undergoing re-encapsulation, the AERO interface 688 instead copies the "TTL/Hop Limit", "Type of Service/Traffic Class" 689 and "Congestion Experienced" values in the original encapsulation 690 header into the corresponding fields in the new encapsulation header 691 (i.e., the values are transferred between encapsulation headers and 692 *not* copied from the encapsulated packet's network-layer header). 694 The AERO interface encapsulates the packet per the base tunneling 695 specification except that it inserts a UDP header between the 696 encapsulation header and the packet's IP header. The AERO interface 697 sets the UDP source port to a constant value that it will use in each 698 successive packet it sends and sets the UDP length field to the 699 length of the IP packet plus 8 bytes for the UDP header itself. For 700 packets sent via a Server, the AERO interface sets the UDP 701 destination port to 8060, i.e., the IANA-registered port number for 702 AERO. For packets sent to a correspondent Client, the AERO interface 703 sets the UDP destination port to the port value stored in the 704 neighbor cache entry for this correspondent. The AERO interface also 705 sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) unless 706 an integrity check is required (see: Section 3.9). 708 The AERO interface next sets the IP protocol number in the 709 encapsulation header to 17 (i.e., the IP protocol number for UDP). 710 When IPv6 is used as the encapsulation protocol, the interface then 711 sets the flow label value in the encapsulation header the same as 712 described in [RFC6438]. When IPv4 is used as the encapsulation 713 protocol, the AERO interface sets the DF bit as discussed in 714 Section 3.9. 716 AERO interfaces decapsulate packets destined either to the node 717 itself or to a destination reached via an interface other than the 718 AERO interface the packet was received on. When the AERO interface 719 receives a UDP packet, it examines the first octet of the 720 encapsulated packet. The packet is accepted if the most significant 721 four bits of the first octet encode the value '0110' (i.e., the 722 version number value for IPv6) or the value '0100' (i.e., the version 723 number value for IPv4). Otherwise, the packet is accepted if the 724 first octet encodes a valid IP protocol number per the IANA 725 "protocol-numbers" registry that matches a supported encapsulation 726 type. Otherwise, the packet is discarded. 728 Further decapsulation then proceeds according to the appropriate base 729 tunneling specification. 731 3.8. AERO Interface Data Origin Authentication 733 AERO nodes employ simple data origin authentication procedures for 734 encapsulated packets they receive from other nodes on the AERO link. 735 In particular: 737 o AERO Relays and Servers accept encapsulated packets with a link- 738 layer source address that matches a permanent neighbor cache 739 entry. 741 o AERO Servers accept authentic encapsulated DHCPv6 messages, and 742 create or update a static neighbor cache entry for the source 743 based on the specific message type. 745 o AERO Servers accept encapsulated packets if there is a static 746 neighbor cache entry with an AERO address that matches the 747 packet's network-layer source address and with a link-layer 748 address that matches the packet's link-layer source address. 750 o AERO Clients accept encapsulated packets if there is a static 751 neighbor cache entry with a link-layer source address that matches 752 the packet's link-layer source address. 754 o AERO Clients and Servers accept encapsulated packets if there is a 755 dynamic neighbor cache entry with an AERO address that matches the 756 packet's network-layer source address, with a link-layer address 757 that matches the packet's link-layer source address, and with a 758 non-zero AcceptTime. 760 Note that this simple data origin authentication only applies to 761 environments in which link-layer addresses cannot be spoofed. 762 Additional security mitigations may be necessary in other 763 environments. 765 3.9. AERO Interface MTU and Fragmentation 767 The AERO interface is the node's point of attachment to the AERO 768 link. AERO links over IP networks have a maximum link MTU of 64KB 769 minus the encapsulation overhead (i.e., "64KB-ENCAPS"), since the 770 maximum packet size in the base IP specifications is 64KB 771 [RFC0791][RFC2460]. AERO interfaces therefore set a maximum MTU of 772 64KB-ENCAPS. (Note that AERO links over IPv6 networks have a 773 theoretical maximum link MTU of 4GB-ENCAPS [RFC2675], however IPv6 774 Jumbograms are considered optional for IPv6 nodes [RFC6434] and 775 therefore out of scope for this document.) 777 IPv6 specifies a minimum link MTU of 1280 bytes [RFC2460]. This is 778 the minimum packet size an AERO interface MUST be capable of 779 forwarding without returning an ICMP Packet Too Big (PTB) message. 780 Although IPv4 specifies a smaller minimum link MTU of 68 bytes 781 [RFC0791], AERO interfaces also observe a 1280 byte minimum for IPv4. 782 Additionally, the vast majority of links in the Internet configure an 783 MTU of at least 1500 bytes. Hosts have therefore become conditioned 784 to expect that IP packets up to 1500 bytes in length will either be 785 delivered to the final destination or a suitable ICMP Packet Too Big 786 (PTB) message returned, however such PTB messages are often lost 787 [RFC2923]. Therefore, AERO interfaces MUST set a minimum MTU of 1500 788 bytes, meaning that they MUST pass IP packets of at least 1500 bytes 789 even if some fragmentation is necessary. 791 PTB messages may be generated by the IP layer of the AERO node if the 792 packet is too large to enter the AERO interface, from within the AERO 793 interface itself if the packet is larger than 1500 bytes and also 794 larger than the MTU of the underlying interface to be used for 795 tunneling minus ENCAPS, or from a router within the AERO link (i.e., 796 the "tunnel") after the encapsulated packet has been admitted. The 797 latter condition would result in a link-layer (L2) PTB message 798 delivered to the AERO interface, while the former two conditions 799 would result in a network-layer (L3) PTB message delivered to the 800 original source. 802 For AERO links over IPv4, the IP ID field is only 16 bits in length, 803 meaning that fragmentation at high data rates could result in 804 dangerous reassembly misassociations [RFC6864][RFC4963]. For AERO 805 links over both IPv4 and IPv6, studies have shown that IP fragments 806 may be dropped unconditionally over some Internet paths [I-D.taylor- 807 v6ops-fragdrop]. For these reasons, when fragmentation is needed it 808 is performed within the AERO interface itself before the fragments 809 are encapsulated and admitted into the tunnel. This fragmentation is 810 supported through the insertion of an IPv6 Fragment Header [RFC2460] 811 that is not associated with either the encapsulating nor encapsulated 812 IP headers. Since the IPv6 Fragment Header reduces the room 813 available for packet data, but the source node has no way to control 814 its insertion, the Fragment Header length MUST be included in 815 "ENCAPS" even for packets in which the header does not appear. 817 The AERO interface therefore admits encapsulated packets into the 818 tunnel (using fragmentation as necessary) as follows: 820 o For IP packets that are no larger than (1280-ENCAPS) bytes, the 821 AERO interface admits the packet into the tunnel without 822 fragmentation. For IPv4 AERO links, the AERO interface sets the 823 Don't Fragment (DF) bit to 0 so that these packets will be 824 deterministically delivered even if there is a restricting link in 825 the path and also calculates the UDP checksum over the 826 encapsulated packet. The tunnel egress will then verify the 827 checksum as an integrity check to detect reassembly errors. 829 o For IP packets that are larger than (1280-ENCAPS) bytes but no 830 larger than 1500 bytes, the AERO interface prepends an IPv6 831 Fragment Header before the packet header. Next, the AERO 832 interface uses the fragmentation algorithm in [RFC2460] to break 833 the packet into two pieces where the first piece is no larger than 834 1024 bytes and the second piece is no larger than the first. 835 (This fragmentation is conducted without a leading IPv6 header; 836 hence, the AERO interface must keep track of the fragment lengths 837 through some other means.) The AERO interface then encapsulates 838 both pieces (and for IPv4 sets the DF bit to 0 and calculates the 839 UDP checksum) then admits them into the tunnel. 841 o For IPv4 packets that are larger than 1500 bytes and with the DF 842 bit set to 0, the AERO interface uses ordinary IP fragmentation to 843 break the packet into a minimum number of fragments where the 844 first fragment is no larger than 1024 bytes and all other 845 fragments are no larger than the first fragment. The AERO 846 interface then encapsulates each fragment (and for IPv4 sets the 847 DF bit to 0 and calculates the UDP checksum) then admits the 848 fragments into the tunnel. These encapsulated fragments will be 849 deterministically delivered to the final destination. 851 o For all other IP packets, if the packet is larger than the AERO 852 interface MTU the AERO node drops the packet and returns an L3 PTB 853 message with MTU set to the AERO interface MTU; otherwise, the 854 node admits the packet into the AERO interface. Next, if the 855 packet length is larger than the MTU of the underlying interface 856 to be used for tunneling minus ENCAPS, the AERO interface drops 857 the packet and returns an L3 PTB message with MTU set to the 858 larger of 1500 or the underlying interface MTU minus ENCAPS. 859 Otherwise, the AERO interface encapsulates the packet and admits 860 it into the tunnel without fragmentation (and for IPv4 sets the DF 861 bit to 1) and translates any L2 PTB messages it may receive from 862 the network into corresponding L3 PTB messages to send to the 863 original source as specified in Section 3.10. Since both L2 and 864 L3 PTB messages may be either lost or contain insufficient 865 information, however, it is RECOMMENDED that sources that send 866 unfragmentable IP packets larger than 1500 bytes use Packetization 867 Layer Path MTU Discovery (PLPMTUD) [RFC4821]. 869 While sending packets according to the above specifications, the 870 source AERO interface (i.e., the tunnel ingress) MAY also send 1500 871 byte probe packets to the destination AERO interface (i.e., the 872 tunnel egress) to determine whether the probes can traverse the 873 tunnel without fragmentation. If the probes succeed, the tunnel 874 ingress can begin sending packets that are larger than 1280-ENCAPS 875 bytes but no larger than 1500 bytes without fragmentation (and for 876 IPv4 with DF set to 1). Since the path MTU within the tunnel may 877 fluctuate due to routing changes, the tunnel ingress SHOULD 878 continually send additional probes subject to rate limiting in case 879 L2 PTB messages are lost. If the path MTU within the tunnel later 880 becomes insufficient, the tunnel ingress MUST resume fragmentation. 882 To construct a probe, the tunnel ingress prepares an NS message with 883 a Nonce option plus trailing padding octets added to a length of 1500 884 bytes without including the length of the padding in the IPv6 Payload 885 Length field. The tunnel ingress then encapsulates the padded NS 886 message in the encapsulation headers (and for IPv4 sets DF to 1) then 887 sends the message to the tunnel egress. If the tunnel egress returns 888 a solicited NA message with a matching Nonce option, the tunnel 889 ingress deems the probe successful. Note that the tunnel ingress 890 SHOULD NOT include the trailing padding within the Nonce option 891 itself but rather as padding beyond the last option in the NS 892 message; otherwise, the (large) Nonce option would be echoed back in 893 the solicited NA message and may be lost at a link with a small MTU 894 along the reverse path. 896 When the tunnel egress receives the fragments of a fragmented packet, 897 it reassembles them into a whole packet per the reassembly algorithm 898 in [RFC2460] then discards the IPv6 fragment header. The tunnel 899 egress MUST be capable of reassembling packets up to 1500+ENCAPS 900 bytes in length, hence it is RECOMMENDED that the tunnel egress be 901 capable of reassembling at least 2KB. 903 As an exception to the above procedures, IPv6 ND and DHCPv6 messages 904 of all sizes MUST be accommodated even if some fragmentation is 905 necessary. These packets are therefore accommodated through a 906 modification of the second rule in the above algorithm as follows: 908 o For IPv6 ND and DHCPv6 messages that are larger than (1280-ENCAPS) 909 bytes, the AERO interface prepends an IPv6 Fragment Header before 910 the message header. Next, the AERO interface uses the 911 fragmentation algorithm in [RFC2460] to break the packet into a 912 minimum number of pieces where the first piece is no larger than 913 1024 bytes and the remaining pieces are no larger than the first. 914 The AERO interface then encapsulates both pieces (and for IPv4 915 sets the DF bit to 0 and calculates the UDP checksum) and admits 916 them into the tunnel. 918 In that case, the tunnel egress MAY be required to reassemble 919 fragmented IPv6 ND or DHCPv6 messages that are larger than 2KB-ENCAPS 920 but no larger than 64KB-ENCAPS. 922 3.10. AERO Interface Error Handling 924 When an AERO node admits encapsulated packets into the AERO 925 interface, it may receive link-layer (L2) or network-layer (L3) error 926 indications. 928 An L2 error indication is an ICMP error message generated by a router 929 on the path to the neighbor or by the neighbor itself. The message 930 includes an IP header with the address of the node that generated the 931 error as the source address and with the link-layer address of the 932 AERO node as the destination address. 934 The IP header is followed by an ICMP header that includes an error 935 Type, Code and Checksum. For ICMPv6 [RFC4443], the error Types 936 include "Destination Unreachable", "Packet Too Big (PTB)", "Time 937 Exceeded" and "Parameter Problem". For ICMPv4 [RFC0792], the error 938 Types include "Destination Unreachable", "Fragmentation Needed" (a 939 Destination Unreachable Code that is analogous to the ICMPv6 PTB), 940 "Time Exceeded" and "Parameter Problem". 942 The ICMP header is followed by the leading portion of the packet that 943 generated the error, also known as the "packet-in-error". For 944 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 945 much of invoking packet as possible without the ICMPv6 packet 946 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 947 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 948 "Internet Header + 64 bits of Original Data Datagram", however 949 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 950 ICMP datagram SHOULD contain as much of the original datagram as 951 possible without the length of the ICMP datagram exceeding 576 952 bytes". 954 The L2 error message format is shown in Figure 3: 956 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 957 ~ ~ 958 | L2 IP Header of | 959 | error message | 960 ~ ~ 961 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 962 | L2 ICMP Header | 963 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 964 ~ ~ P 965 | IP and other encapsulation | a 966 | headers of original L3 packet | c 967 ~ ~ k 968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 969 ~ ~ t 970 | IP header of | 971 | original L3 packet | i 972 ~ ~ n 973 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 974 ~ ~ e 975 | Upper layer headers and | r 976 | leading portion of body | r 977 | of the original L3 packet | o 978 ~ ~ r 979 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 981 Figure 3: AERO Interface L2 Error Message Format 983 The AERO node rules for processing these L2 error messages is as 984 follows: 986 o When an AERO node receives an L2 "Parameter Problem", it processes 987 the message the same as described as for ordinary ICMP errors in 988 the normative references [RFC0792][RFC4443]. 990 o When an AERO node receives persistent L2 Time Exceeded messages, 991 the IP ID field may be wrapping before earlier fragments have been 992 processed due to high data rates. Since the AERO node includes a 993 UDP integrity check, however, it MAY ignore the messages and 994 continue sending packets without rate limiting. 996 o When an AERO Client receives persistent L2 Destination Unreachable 997 messages in response to tunneled packets that it sends to one of 998 its dynamic neighbor correspondents, the Client SHOULD test the 999 path to the correspondent using Neighbor Unreachability Detection 1000 (NUD) (see Section 3.14). If NUD fails, the Client SHOULD set 1001 ForwardTime for the corresponding dynamic neighbor cache entry to 1002 0 and allow future packets destined to the correspondent to flow 1003 through a Server. 1005 o When an AERO Client receives persistent L2 Destination Unreachable 1006 messages in response to tunneled packets that it sends to one of 1007 its static neighbor Servers, the Client SHOULD test the path to 1008 the Server using NUD. If NUD fails, the Client SHOULD delete the 1009 neighbor cache entry and attempt to associate with a new Server. 1011 o When an AERO Server receives persistent L2 Destination Unreachable 1012 messages in response to tunneled packets that it sends to one of 1013 its static neighbor Clients, the Server SHOULD test the path to 1014 the Client using NUD. If NUD fails, the Server SHOULD cancel the 1015 DHCPv6 PD lease for the Client's ACP, withdraw its route for the 1016 ACP from the AERO routing system and delete the neighbor cache 1017 entry (see Sections 3.11 and 3.12). 1019 o When an AERO Relay or Server receives an L2 Destination 1020 Unreachable message in response to a tunneled packet that it sends 1021 to one of its permanent neighbors, it discards the message since 1022 the routing system is likely in a temporary transitional state 1023 that will soon re-converge. 1025 o When an AERO node receives an L2 PTB message, it translates the 1026 message into an L3 PTB message if possible (*) and forwards the 1027 message toward the original source as described below. 1029 To translate an L2 PTB message to an L3 PTB message, the AERO node 1030 first caches the MTU field value of the L2 ICMP header. The node 1031 next discards the L2 IP and ICMP headers, and also discards the 1032 encapsulation headers of the original L3 packet. Next the node 1033 encapsulates the included segment of the original L3 packet in an L3 1034 IP and ICMP header, and sets the ICMP header Type and Code values to 1035 appropriate values for the L3 IP protocol. In the process, the node 1036 writes the maximum of 1500 bytes and (L2 MTU - ENCAPS) into the MTU 1037 field of the L3 ICMP header. 1039 The node next writes the IP source address of the original L3 packet 1040 as the destination address of the L3 PTB message and determines the 1041 next hop to the destination. If the next hop is reached via the AERO 1042 interface, the node uses the IPv6 address "::" or the IPv4 address 1043 "0.0.0.0" as the IP source address of the L3 PTB message. Otherwise, 1044 the node uses one of its non link-local addresses as the source 1045 address of the L3 PTB message. The node finally calculates the ICMP 1046 checksum over the L3 PTB message and writes the Checksum in the 1047 corresponding field of the L3 ICMP header. The L3 PTB message 1048 therefore is formatted as follows: 1050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1051 ~ ~ 1052 | L3 IP Header of | 1053 | error message | 1054 ~ ~ 1055 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1056 | L3 ICMP Header | 1057 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1058 ~ ~ p 1059 | IP header of | k 1060 | original L3 packet | t 1061 ~ ~ 1062 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i 1063 ~ ~ n 1064 | Upper layer headers and | 1065 | leading portion of body | e 1066 | of the original L3 packet | r 1067 ~ ~ r 1068 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1070 Figure 4: AERO Interface L3 Error Message Format 1072 After the node has prepared the L3 PTB message, it either forwards 1073 the message via a link outside of the AERO interface without 1074 encapsulation, or encapsulates and forwards the message to the next 1075 hop via the AERO interface. 1077 When an AERO Relay receives an L3 packet for which the destination 1078 address is covered by an ASP, if there is no more-specific routing 1079 information for the destination the Relay drops the packet and 1080 returns an L3 Destination Unreachable message. The Relay first 1081 writes the IP source address of the original L3 packet as the 1082 destination address of the L3 Destination Unreachable message and 1083 determines the next hop to the destination. If the next hop is 1084 reached via the AERO interface, the Relay uses the IPv6 address "::" 1085 or the IPv4 address "0.0.0.0" as the IP source address of the L3 1086 Destination Unreachable message and forwards the message to the next 1087 hop within the AERO interface. Otherwise, the Relay uses one of its 1088 non link-local addresses as the source address of the L3 Destination 1089 Unreachable message and forwards the message via a link outside the 1090 AERO interface. 1092 When an AERO node receives any L3 error message via the AERO 1093 interface, it examines the destination address in the L3 IP header of 1094 the message. If the next hop toward the destination address of the 1095 error message is via the AERO interface, the node re-encapsulates and 1096 forwards the message to the next hop within the AERO interface. 1097 Otherwise, if the source address in the L3 IP header of the message 1098 is the IPv6 address "::" or the IPv4 address "0.0.0.0", the node 1099 writes one of its non link-local addresses as the source address of 1100 the L3 message and recalculates the IP and/or ICMP checksums. The 1101 node finally forwards the message via a link outside of the AERO 1102 interface. 1104 (*) Note that in some instances the packet-in-error field of an L2 1105 PTB message may not include enough information for translation to an 1106 L3 PTB message. In that case, the AERO interface simply discards the 1107 L2 PTB message. It can therefore be said that translation of L2 PTB 1108 messages to L3 PTB messages can provide a useful optimization when 1109 possible, but is not critical for sources that correctly use PLPMTUD. 1111 3.11. AERO Router Discovery, Prefix Delegation and Address 1112 Configuration 1114 3.11.1. AERO DHCPv6 Service Model 1116 Each AERO Server configures a DHCPv6 server function to facilitate PD 1117 requests from Clients. Each Server is pre-configured with an 1118 identical list of ACP-to-Client ID mappings for all Clients enrolled 1119 in the AERO system, as well as any information necessary to 1120 authenticate Clients. The configuration information is maintained by 1121 a central administrative authority for the AERO link and securely 1122 propagated to all Servers whenever a new Client is enrolled or an 1123 existing Client is withdrawn. 1125 With these identical configurations, each Server can function 1126 independently of all other Servers, including the maintenance of 1127 active leases. Therefore, no Server-to-Server DHCPv6 state 1128 synchronization is necessary, and Clients can optionally hold 1129 separate leases for the same ACP from multiple Servers. 1131 In this way, Clients can easily associate with multiple Servers, and 1132 can receive new leases from new Servers before deprecating leases 1133 held through old Servers. This enables a graceful "make-before- 1134 break" capability. 1136 3.11.2. AERO Client Behavior 1138 AERO Clients discover the link-layer addresses of AERO Servers via 1139 static configuration, or through an automated means such as DNS name 1140 resolution. In the absence of other information, the Client resolves 1141 the Fully-Qualified Domain Name (FQDN) "linkupnetworks.[domainname]" 1142 where "linkupnetworks" is a constant text string and "[domainname]" 1143 is the connection-specific DNS suffix for the Client's underlying 1144 network connection (e.g., "example.com"). After discovering the 1145 link-layer addresses, the Client associates with one or more of the 1146 corresponding Servers. 1148 To associate with a Server, the Client acts as a requesting router to 1149 request an ACP through a DHCPv6 PD exchange[RFC3315][RFC3633] in 1150 which the Client's Solicit/Request messages use the IPv6 1151 "unspecified" address (i.e., "::") as the IPv6 source address, 1152 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address 1153 and the link-layer address of the Server as the link-layer 1154 destination address. The Client also includes a Client Identifier 1155 option with a DHCP Unique Identifier (DUID) plus any necessary 1156 authentication options to identify itself to the DHCPv6 server, and 1157 includes a Client Link Layer Address Option (CLLAO) [RFC6939] with 1158 the format shown in Figure 5: 1160 0 1 2 3 1161 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 1162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1163 | OPTION_CLIENT_LINKLAYER_ADDR | option-length | 1164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1165 | link-layer type (16 bits) | Link ID | Preference | 1166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1168 Figure 5: AERO Client Link-Layer Address Option (CLLAO) Format 1170 The Client sets the CLLAO 'option-length' field to 4 and sets the 1171 'link-layer type' field to TBD1 (see: IANA Considerations), then 1172 includes appropriate Link ID and Preference values for the underlying 1173 interface over which the Solicit/Request will be issued (note that 1174 these are the same values that would be included in a TLLAO as shown 1175 in Figure 2). If the Client is pre-provisioned with an ACP 1176 associated with the AERO service, it MAY also include the ACP in the 1177 Solicit/Request message Identity Association (IA) option to indicate 1178 its preferred ACP to the DHCPv6 server. The Client then sends the 1179 encapsulated DHCPv6 request via the underlying interface. 1181 When the Client receives its ACP and the set of ASPs via a DHCPv6 1182 Reply from the AERO Server, it creates a static neighbor cache entry 1183 with the Server's link-local address as the network-layer address and 1184 the Server's encapsulation address as the link-layer address. The 1185 Client then records the lifetime for the ACP in the neighbor cache 1186 entry and marks the neighbor cache entry as "default", i.e., the 1187 Client considers the Server as a default router. If the Reply 1188 message contains a Vendor-Specific Information Option (see: 1189 Section 3.10.3) the Client also caches each ASP in the option. 1191 The Client then applies the AERO address to the AERO interface and 1192 sub-delegates the ACP to nodes and links within its attached EUNs 1193 (the AERO address thereafter remains stable as the Client moves). 1194 The Client also assigns a default IP route to the AERO interface as a 1195 route-to-interface, i.e., with no explicit next-hop. The next hop 1196 will then be determined after a packet has been submitted to the AERO 1197 interface by inspecting the neighbor cache (see above). 1199 On some platforms (e.g., popular cell phone operating systems), the 1200 act of assigning a default IPv6 route to the AERO interface may not 1201 be permitted from a user application due to security policy. 1202 Typically, those platforms include a TUN/TAP interface that acts as a 1203 point-to-point conduit between user applications and the AERO 1204 interface. In that case, the Client can instead generate a 1205 "synthesized RA" message. The message conforms to [RFC4861] and is 1206 prepared as follows: 1208 o the IPv6 source address is fe80:: 1210 o the IPv6 destination address is all-nodes multicast 1212 o the Router Lifetime is set to a time that is no longer than the 1213 ACP DHCPv6 lifetime 1215 o the message does not include a Source Link Layer Address Option 1216 (SLLAO) 1218 o the message includes a Prefix Information Option (PIO) with a /64 1219 prefix taken from the ACP as the prefix for autoconfiguration 1221 The Client then sends the synthesized RA message via the TUN/TAP 1222 interface, where the operating system kernel will interpret it as 1223 though it were generated by an actual router. The operating system 1224 will then install a default route and use StateLess Address 1225 AutoConfiguration (SLAAC) to configure an IPv6 address on the TUN/TAP 1226 interface. Methods for similarly installing an IPv4 default route 1227 and IPv4 address on the TUN/TAP interface are based on synthesized 1228 DHCPv4 messages [RFC2131]. Note that in this method, the Client 1229 appears as a mobility proxy for applications that bind to the (point- 1230 to-point) TUN/TAP interface. The arrangement can be likened to a 1231 Proxy AERO scenario in which the mobile node and Client are located 1232 within the same physical platform (see Section 3.20 for further 1233 details on Proxy AERO). 1235 The Client subsequently renews its ACP delegation through each of its 1236 Servers by performing DHCPv6 Renew/Reply exchanges with its AERO 1237 address as the IPv6 source address, 1238 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address, 1239 the link-layer address of a Server as the link-layer destination 1240 address and the same Client identifier, authentication options and 1241 CLLAO option as was used in the initial PD request. Note that if the 1242 Client does not issue a DHCPv6 Renew before the Server has terminated 1243 the lease (e.g., if the Client has been out of touch with the Server 1244 for a considerable amount of time), the Server's Reply will report 1245 NoBinding and the Client must re-initiate the DHCPv6 PD procedure. 1246 If the Client sends synthesized RA and/or DHCPv4 messages (see 1247 above), it also sends a new synthesized message when issuing a DHCPv6 1248 Renew or when re-initiating the DHCPv6 PD procedure. 1250 Since the Client's AERO address is configured from the unique ACP 1251 delegation it receives, there is no need for Duplicate Address 1252 Detection (DAD) on AERO links. Other nodes maliciously attempting to 1253 hijack an authorized Client's AERO address will be denied access to 1254 the network by the DHCPv6 server due to an unacceptable link-layer 1255 address and/or security parameters (see: Security Considerations). 1257 AERO Clients ignore the IP address and UDP port number in any S/TLLAO 1258 options in ND messages they receive directly from another AERO 1259 Client, but examine the Link ID and Preference values to match the 1260 message with the correct link-layer address information. 1262 When a source Client forwards a packet to a prospective destination 1263 Client (i.e., one for which the packet's destination address is 1264 covered by an ASP), the source Client initiates an AERO route 1265 optimization procedure as specified in Section 3.13. 1267 3.11.3. AERO Server Behavior 1269 AERO Servers configure a DHCPv6 server function on their AERO links. 1270 AERO Servers arrange to add their encapsulation layer IP addresses 1271 (i.e., their link-layer addresses) to the DNS resource records for 1272 the FQDN "linkupnetworks.[domainname]" before entering service. 1274 When an AERO Server receives a prospective Client's DHCPv6 PD 1275 Solicit/Request message, it first authenticates the message. If 1276 authentication succeeds, the Server determines the correct ACP to 1277 delegate to the Client by matching the Client's DUID within an online 1278 directory service (e.g., LDAP). The Server then delegates the ACP 1279 and creates a static neighbor cache entry for the Client's AERO 1280 address with lifetime set to no more than the lease lifetime and the 1281 Client's link-layer address as the link-layer address for the Link ID 1282 specified in the CLLAO option. The Server then creates an IP 1283 forwarding table entry so that the AERO routing system will propagate 1284 the ACP to all Relays (see: Section 3.12). Finally, the Server sends 1285 a DHCPv6 Reply message to the Client while using fe80::ID as the IPv6 1286 source address, the Client's AERO address as the IPv6 destination 1287 address, and the Client's link-layer address as the destination link- 1288 layer address. The Server also includes a Server Unicast option with 1289 server-address set to fe80::ID so that all future Client/Server 1290 transactions will be link-local-only unicast over the AERO link. 1292 When the Server sends the DHCPv6 Reply message, it also includes a 1293 DHCPv6 Vendor-Specific Information Option with 'enterprise-number' 1294 set to "TBD2" (see: IANA Considerations). The option is formatted as 1295 shown in[RFC3315] and with the AERO enterprise-specific format shown 1296 in Figure 6: 1298 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 1299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1300 | OPTION_VENDOR_OPTS | option-len | 1301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1302 | enterprise-number ("TBD2") | 1303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1304 | Reserved | Prefix Length | 1305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1306 | | 1307 + ASP (1) + 1308 | | 1309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1310 | Reserved | Prefix Length | 1311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1312 | | 1313 + ASP (2) + 1314 | | 1315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1316 | Reserved | Prefix Length | 1317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1318 | | 1319 + ASP (3) + 1320 | | 1321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1322 . (etc.) . 1323 . . 1324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1326 Figure 6: AERO Vendor-Specific Information Option 1328 Per Figure 6, the option includes one or more ASP. The ASP field 1329 contains the IP prefix as it would appear in the interface identifier 1330 portion of the corresponding AERO address (see: Section 3.3). For 1331 IPv6, valid values for the Prefix Length field are 0 through 64; for 1332 IPv4, valid values are 0 through 32. 1334 After the initial DHCPv6 PD exchange, the AERO Server maintains the 1335 neighbor cache entry for the Client as long as the lease lifetime 1336 remains current. If the Client issues a Renew/Reply exchange, the 1337 Server extends the lifetime. If the Client issues a Release/Reply 1338 exchange, or if the Client does not issue a Renew/Reply within the 1339 lease lifetime, the Server deletes the neighbor cache entry for the 1340 Client and withdraws the IP route from the AERO routing system. 1342 3.12. AERO Relay/Server Routing System 1344 Relays require full topology information of all Client/Server 1345 associations, while individual Servers only require partial topology 1346 information, i.e., they only need to know the ACPs associated with 1347 their current set of associated Clients. This is accomplished 1348 through the use of an internal instance of the Border Gateway 1349 Protocol (BGP) [RFC4271] coordinated between Servers and Relays. 1350 This internal BGP instance does not interact with the public Internet 1351 BGP instance; therefore, the AERO link is presented to the IP 1352 Internetwork as a small set of ASPs as opposed to the full set of 1353 individual ACPs. 1355 In a reference BGP arrangement, each AERO Server is configured as an 1356 Autonomous System Border Router (ASBR) for a stub Autonomous System 1357 (AS) (possibly using a private AS Number (ASN) [RFC1930]), and each 1358 Server further peers with each Relay but does not peer with other 1359 Servers. Similarly, Relays need not peer with each other, since they 1360 will receive all updates from all Servers and will therefore have a 1361 consistent view of the AERO link ACP delegations. 1363 Each Server maintains a working set of associated Clients, and 1364 dynamically announces new ACPs and withdraws departed ACPs in its BGP 1365 updates to Relays (this is typically accomplished via a "redistribute 1366 static" routing directive). Relays do not send BGP updates to 1367 Servers, however, such that the BGP route reporting is unidirectional 1368 from the Servers to the Relays. 1370 The Relays therefore discover the full topology of the AERO link in 1371 terms of the working set of ACPs associated with each Server, while 1372 the Servers only discover the ACPs of their associated Clients. 1373 Since Clients are expected to remain associated with their current 1374 set of Servers for extended timeframes, the amount of BGP control 1375 messaging between Servers and Relays should be minimal. However, BGP 1376 peers SHOULD dampen any route oscillations caused by impatient 1377 Clients that repeatedly associate and disassociate with Servers. 1379 3.13. AERO Redirection 1381 3.13.1. Reference Operational Scenario 1383 Figure 7 depicts the AERO redirection reference operational scenario, 1384 using IPv6 addressing as the example (while not shown, a 1385 corresponding example for IPv4 addressing can be easily constructed). 1386 The figure shows an AERO Relay ('R1'), two AERO Servers ('S1', 'S2'), 1387 two AERO Clients ('C1', 'C2') and two ordinary IPv6 hosts ('H1', 1388 'H2'): 1390 +--------------+ +--------------+ +--------------+ 1391 | Server S1 | | Relay R1 | | Server S2 | 1392 +--------------+ +--------------+ +--------------+ 1393 fe80::2 fe80::1 fe80::3 1394 L2(S1) L2(R1) L2(S2) 1395 | | | 1396 X-----+-----+------------------+-----------------+----+----X 1397 | AERO Link | 1398 L2(A) L2(B) 1399 fe80::2001:db8:0:0 fe80::2001:db8:1:0 1400 +--------------+ +--------------+ 1401 |AERO Client C1| |AERO Client C2| 1402 +--------------+ +--------------+ 1403 2001:DB8:0::/48 2001:DB8:1::/48 1404 | | 1405 .-. .-. 1406 ,-( _)-. 2001:db8:0::1 2001:db8:1::1 ,-( _)-. 1407 .-(_ IP )-. +---------+ +---------+ .-(_ IP )-. 1408 (__ EUN )--| Host H1 | | Host H2 |--(__ EUN ) 1409 `-(______)-' +---------+ +---------+ `-(______)-' 1411 Figure 7: AERO Reference Operational Scenario 1413 In Figure 7, Relay ('R1') applies the address fe80::1 to its AERO 1414 interface with link-layer address L2(R1), Server ('S1') applies the 1415 address fe80::2 with link-layer address L2(S1),and Server ('S2') 1416 applies the address fe80::3 with link-layer address L2(S2). Servers 1417 ('S1') and ('S2') next arrange to add their link-layer addresses to a 1418 published list of valid Servers for the AERO link. 1420 AERO Client ('C1') receives the ACP 2001:db8:0::/48 in a DHCPv6 PD 1421 exchange via AERO Server ('S1') then applies the address 1422 fe80::2001:db8:0:0 to its AERO interface with link-layer address 1423 L2(C1). Client ('C1') configures a default route and neighbor cache 1424 entry via the AERO interface with next-hop address fe80::2 and link- 1425 layer address L2(S1), then sub-delegates the ACP to its attached 1426 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1427 address 2001:db8:0::1. 1429 AERO Client ('C2') receives the ACP 2001:db8:1::/48 in a DHCPv6 PD 1430 exchange via AERO Server ('S2') then applies the address 1431 fe80::2001:db8:1:0 to its AERO interface with link-layer address 1432 L2(C2). Client ('C2') configures a default route and neighbor cache 1433 entry via the AERO interface with next-hop address fe80::3 and link- 1434 layer address L2(S2), then sub-delegates the ACP to its attached 1435 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1436 address 2001:db8:1::1. 1438 3.13.2. Concept of Operations 1440 Again, with reference to Figure 7, when source host ('H1') sends a 1441 packet to destination host ('H2'), the packet is first forwarded over 1442 the source host's attached EUN to Client ('C1'). Client ('C1') then 1443 forwards the packet via its AERO interface to Server ('S1') and also 1444 sends a Predirect message toward Client ('C2') via Server ('S1'). 1445 Server ('S1') then re-encapsulates and forwards both the packet and 1446 the Predirect message out the same AERO interface toward Client 1447 ('C2') via Relay ('R1'). 1449 When Relay ('R1') receives the packet and Predirect message, it 1450 consults its forwarding table to discover Server ('S2') as the next 1451 hop toward Client ('C2'). Relay ('R1') then forwards both the packet 1452 and the Predirect message to Server ('S2'), which then forwards them 1453 to Client ('C2'). 1455 After Client ('C2') receives the Predirect message, it process the 1456 message and returns a Redirect message toward Client ('C1') via 1457 Server ('S2'). During the process, Client ('C2') also creates or 1458 updates a dynamic neighbor cache entry for Client ('C1'). 1460 When Server ('S2') receives the Redirect message, it re-encapsulates 1461 the message and forwards it on to Relay ('R1'), which forwards the 1462 message on to Server ('S1') which forwards the message on to Client 1463 ('C1'). After Client ('C1') receives the Redirect message, it 1464 processes the message and creates or updates a dynamic neighbor cache 1465 entry for Client ('C2'). 1467 Following the above Predirect/Redirect message exchange, forwarding 1468 of packets from Client ('C1') to Client ('C2') without involving any 1469 intermediate nodes is enabled. The mechanisms that support this 1470 exchange are specified in the following sections. 1472 3.13.3. Message Format 1474 AERO Redirect/Predirect messages use the same format as for ICMPv6 1475 Redirect messages depicted in Section 4.5 of [RFC4861], but also 1476 include a new "Prefix Length" field taken from the low-order 8 bits 1477 of the Redirect message Reserved field. For IPv6, valid values for 1478 the Prefix Length field are 0 through 64; for IPv4, valid values are 1479 0 through 32. The Redirect/Predirect messages are formatted as shown 1480 in Figure 8: 1482 0 1 2 3 1483 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 1484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1485 | Type (=137) | Code (=0/1) | Checksum | 1486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1487 | Reserved | Prefix Length | 1488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1489 | | 1490 + + 1491 | | 1492 + Target Address + 1493 | | 1494 + + 1495 | | 1496 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1497 | | 1498 + + 1499 | | 1500 + Destination Address + 1501 | | 1502 + + 1503 | | 1504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1505 | Options ... 1506 +-+-+-+-+-+-+-+-+-+-+-+- 1508 Figure 8: AERO Redirect/Predirect Message Format 1510 3.13.4. Sending Predirects 1512 When a Client forwards a packet with a source address from one of its 1513 ACPs toward a destination address covered by an ASP (i.e., toward 1514 another AERO Client connected to the same AERO link), the source 1515 Client MAY send a Predirect message forward toward the destination 1516 Client via the Server. 1518 In the reference operational scenario, when Client ('C1') forwards a 1519 packet toward Client ('C2'), it MAY also send a Predirect message 1520 forward toward Client ('C2'), subject to rate limiting (see 1521 Section 8.2 of [RFC4861]). Client ('C1') prepares the Predirect 1522 message as follows: 1524 o the link-layer source address is set to 'L2(C1)' (i.e., the link- 1525 layer address of Client ('C1')). 1527 o the link-layer destination address is set to 'L2(S1)' (i.e., the 1528 link-layer address of Server ('S1')). 1530 o the network-layer source address is set to fe80::2001:db8:0:0 1531 (i.e., the AERO address of Client ('C1')). 1533 o the network-layer destination address is set to fe80::2001:db8:1:0 1534 (i.e., the AERO address of Client ('C2')). 1536 o the Type is set to 137. 1538 o the Code is set to 1 to indicate "Predirect". 1540 o the Prefix Length is set to the length of the prefix to be 1541 assigned to the Target Address. 1543 o the Target Address is set to fe80::2001:db8:0:0 (i.e., the AERO 1544 address of Client ('C1')). 1546 o the Destination Address is set to the source address of the 1547 originating packet that triggered the Predirection event. (If the 1548 originating packet is an IPv4 packet, the address is constructed 1549 in IPv4-compatible IPv6 address format). 1551 o the message includes one or more TLLAOs with Link ID and 1552 Preference set to appropriate values for Client ('C1')'s 1553 underlying interfaces, and with UDP Port Number and IP Address set 1554 to 0'. 1556 o the message SHOULD include a Timestamp option and a Nonce option. 1558 o the message includes a Redirected Header Option (RHO) that 1559 contains the originating packet truncated if necessary to ensure 1560 that at least the network-layer header is included but the size of 1561 the message does not exceed 1280 bytes. 1563 Note that the act of sending Predirect messages is cited as "MAY", 1564 since Client ('C1') may have advanced knowledge that the direct path 1565 to Client ('C2') would be unusable or otherwise undesirable. If the 1566 direct path later becomes unusable after the initial route 1567 optimization, Client ('C1') simply allows packets to again flow 1568 through Server ('S1'). 1570 3.13.5. Re-encapsulating and Relaying Predirects 1572 When Server ('S1') receives a Predirect message from Client ('C1'), 1573 it first verifies that the TLLAOs in the Predirect are a proper 1574 subset of the Link IDs in Client ('C1')'s neighbor cache entry. If 1575 the Client's TLLAOs are not acceptable, Server ('S1') discards the 1576 message. Otherwise, Server ('S1') validates the message according to 1577 the ICMPv6 Redirect message validation rules in Section 8.1 of 1578 [RFC4861], except that the Predirect has Code=1. Server ('S1') also 1579 verifies that Client ('C1') is authorized to use the Prefix Length in 1580 the Predirect when applied to the AERO address in the network-layer 1581 source address by searching for the AERO address in the neighbor 1582 cache. If validation fails, Server ('S1') discards the Predirect; 1583 otherwise, it copies the correct UDP Port numbers and IP Addresses 1584 for Client ('C1')'s links into the (previously empty) TLLAOs. 1586 Server ('S1') then examines the network-layer destination address of 1587 the Predirect to determine the next hop toward Client ('C2') by 1588 searching for the AERO address in the neighbor cache. Since Client 1589 ('C2') is not one of its neighbors, Server ('S1') re-encapsulates the 1590 Predirect and relays it via Relay ('R1') by changing the link-layer 1591 source address of the message to 'L2(S1)' and changing the link-layer 1592 destination address to 'L2(R1)'. Server ('S1') finally forwards the 1593 re-encapsulated message to Relay ('R1') without decrementing the 1594 network-layer TTL/Hop Limit field. 1596 When Relay ('R1') receives the Predirect message from Server ('S1') 1597 it determines that Server ('S2') is the next hop toward Client ('C2') 1598 by consulting its forwarding table. Relay ('R1') then re- 1599 encapsulates the Predirect while changing the link-layer source 1600 address to 'L2(R1)' and changing the link-layer destination address 1601 to 'L2(S2)'. Relay ('R1') then relays the Predirect via Server 1602 ('S2'). 1604 When Server ('S2') receives the Predirect message from Relay ('R1') 1605 it determines that Client ('C2') is a neighbor by consulting its 1606 neighbor cache. Server ('S2') then re-encapsulates the Predirect 1607 while changing the link-layer source address to 'L2(S2)' and changing 1608 the link-layer destination address to 'L2(C2)'. Server ('S2') then 1609 forwards the message to Client ('C2'). 1611 3.13.6. Processing Predirects and Sending Redirects 1613 When Client ('C2') receives the Predirect message, it accepts the 1614 Predirect only if the message has a link-layer source address of one 1615 of its Servers (e.g., L2(S2)). Client ('C2') further accepts the 1616 message only if it is willing to serve as a redirection target. 1617 Next, Client ('C2') validates the message according to the ICMPv6 1618 Redirect message validation rules in Section 8.1 of [RFC4861], except 1619 that it accepts the message even though Code=1 and even though the 1620 network-layer source address is not that of it's current first-hop 1621 router. 1623 In the reference operational scenario, when Client ('C2') receives a 1624 valid Predirect message, it either creates or updates a dynamic 1625 neighbor cache entry that stores the Target Address of the message as 1626 the network-layer address of Client ('C1') , stores the link-layer 1627 addresses found in the TLLAOs as the link-layer addresses of Client 1628 ('C1') and stores the Prefix Length as the length to be applied to 1629 the network-layer address for forwarding purposes. Client ('C2') 1630 then sets AcceptTime for the neighbor cache entry to ACCEPT_TIME. 1632 After processing the message, Client ('C2') prepares a Redirect 1633 message response as follows: 1635 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 1636 layer address of Client ('C2')). 1638 o the link-layer destination address is set to 'L2(S2)' (i.e., the 1639 link-layer address of Server ('S2')). 1641 o the network-layer source address is set to fe80::2001:db8:1:0 1642 (i.e., the AERO address of Client ('C2')). 1644 o the network-layer destination address is set to fe80::2001:db8:0:0 1645 (i.e., the AERO address of Client ('C1')). 1647 o the Type is set to 137. 1649 o the Code is set to 0 to indicate "Redirect". 1651 o the Prefix Length is set to the length of the prefix to be applied 1652 to the Target Address. 1654 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 1655 address of Client ('C2')). 1657 o the Destination Address is set to the destination address of the 1658 originating packet that triggered the Redirection event. (If the 1659 originating packet is an IPv4 packet, the address is constructed 1660 in IPv4-compatible IPv6 address format). 1662 o the message includes one or more TLLAOs with Link ID and 1663 Preference set to appropriate values for Client ('C2')'s 1664 underlying interfaces, and with UDP Port Number and IP Address set 1665 to '0'. 1667 o the message SHOULD include a Timestamp option and MUST echo the 1668 Nonce option received in the Predirect (i.e., if a Nonce option is 1669 included). 1671 o the message includes as much of the RHO copied from the 1672 corresponding AERO Predirect message as possible such that at 1673 least the network-layer header is included but the size of the 1674 message does not exceed 1280 bytes. 1676 After Client ('C2') prepares the Redirect message, it sends the 1677 message to Server ('S2'). 1679 3.13.7. Re-encapsulating and Relaying Redirects 1681 When Server ('S2') receives a Redirect message from Client ('C2'), it 1682 first verifies that the TLLAOs in the Redirect are a proper subset of 1683 the Link IDs in Client ('C2')'s neighbor cache entry. If the 1684 Client's TLLAOs are not acceptable, Server ('S2') discards the 1685 message. Otherwise, Server ('S2') validates the message according to 1686 the ICMPv6 Redirect message validation rules in Section 8.1 of 1687 [RFC4861]. Server ('S2') also verifies that Client ('C2') is 1688 authorized to use the Prefix Length in the Redirect when applied to 1689 the AERO address in the network-layer source address by searching for 1690 the AERO address in the neighbor cache. If validation fails, Server 1691 ('S2') discards the Predirect; otherwise, it copies the correct UDP 1692 Port numbers and IP Addresses for Client ('C2')'s links into the 1693 (previously empty) TLLAOs. 1695 Server ('S2') then examines the network-layer destination address of 1696 the Predirect to determine the next hop toward Client ('C2') by 1697 searching for the AERO address in the neighbor cache. Since Client 1698 ('C2') is not a neighbor, Server ('S2') re-encapsulates the Predirect 1699 and relays it via Relay ('R1') by changing the link-layer source 1700 address of the message to 'L2(S2)' and changing the link-layer 1701 destination address to 'L2(R1)'. Server ('S2') finally forwards the 1702 re-encapsulated message to Relay ('R1') without decrementing the 1703 network-layer TTL/Hop Limit field. 1705 When Relay ('R1') receives the Predirect message from Server ('S2') 1706 it determines that Server ('S1') is the next hop toward Client ('C1') 1707 by consulting its forwarding table. Relay ('R1') then re- 1708 encapsulates the Predirect while changing the link-layer source 1709 address to 'L2(R1)' and changing the link-layer destination address 1710 to 'L2(S1)'. Relay ('R1') then relays the Predirect via Server 1711 ('S1'). 1713 When Server ('S1') receives the Predirect message from Relay ('R1') 1714 it determines that Client ('C1') is a neighbor by consulting its 1715 neighbor cache. Server ('S1') then re-encapsulates the Predirect 1716 while changing the link-layer source address to 'L2(S1)' and changing 1717 the link-layer destination address to 'L2(C1)'. Server ('S1') then 1718 forwards the message to Client ('C1'). 1720 3.13.8. Processing Redirects 1722 When Client ('C1') receives the Redirect message, it accepts the 1723 message only if it has a link-layer source address of one of its 1724 Servers (e.g., ''L2(S1)'). Next, Client ('C1') validates the message 1725 according to the ICMPv6 Redirect message validation rules in 1726 Section 8.1 of [RFC4861], except that it accepts the message even 1727 though the network-layer source address is not that of it's current 1728 first-hop router. Following validation, Client ('C1') then processes 1729 the message as follows. 1731 In the reference operational scenario, when Client ('C1') receives 1732 the Redirect message, it either creates or updates a dynamic neighbor 1733 cache entry that stores the Target Address of the message as the 1734 network-layer address of Client ('C2'), stores the link-layer 1735 addresses found in the TLLAOs as the link-layer addresses of Client 1736 ('C2') and stores the Prefix Length as the length to be applied to 1737 the network-layer address for forwarding purposes. Client ('C1') 1738 then sets ForwardTime for the neighbor cache entry to FORWARD_TIME. 1740 Now, Client ('C1') has a neighbor cache entry with a valid 1741 ForwardTime value, while Client ('C2') has a neighbor cache entry 1742 with a valid AcceptTime value. Thereafter, Client ('C1') may forward 1743 ordinary network-layer data packets directly to Client ('C2') without 1744 involving any intermediate nodes, and Client ('C2') can verify that 1745 the packets came from an acceptable source. (In order for Client 1746 ('C2') to forward packets to Client ('C1'), a corresponding 1747 Predirect/Redirect message exchange is required in the reverse 1748 direction; hence, the mechanism is asymmetric.) 1750 3.13.9. Server-Oriented Redirection 1752 In some environments, the Server nearest the target Client may need 1753 to serve as the redirection target, e.g., if direct Client-to-Client 1754 communications are not possible. In that case, the Server prepares 1755 the Redirect message the same as if it were the destination Client 1756 (see: Section 3.9.6), except that it writes its own link-layer 1757 address in the TLLAO option. The Server must then maintain a 1758 neighbor cache entry for the redirected source Client. 1760 3.14. Neighbor Unreachability Detection (NUD) 1762 AERO nodes perform Neighbor Unreachability Detection (NUD) by sending 1763 unicast NS messages to elicit solicited NA messages from neighbors 1764 the same as described in [RFC4861]. NUD is performed either 1765 reactively in response to persistent L2 errors (see Section 3.10) or 1766 proactively to refresh existing neighbor cache entries. 1768 When an AERO node sends an NS/NA message, it MUST use its link-local 1769 address as the IPv6 source address and the link-local address of the 1770 neighbor as the IPv6 destination address. When an AERO node receives 1771 an NS message or a solicited NA message, it accepts the message if it 1772 has a neighbor cache entry for the neighbor; otherwise, it ignores 1773 the message. 1775 When a source Client is redirected to a target Client it SHOULD 1776 proactively test the direct path by sending an initial NS message to 1777 elicit a solicited NA response. While testing the path, the source 1778 Client can optionally continue sending packets via the Server, 1779 maintain a small queue of packets until target reachability is 1780 confirmed, or (optimistically) allow packets to flow directly to the 1781 target. The source Client SHOULD thereafter continue to proactively 1782 test the direct path to the target Client (see Section 7.3 of 1783 [RFC4861]) periodically in order to keep dynamic neighbor cache 1784 entries alive. 1786 In particular, while the source Client is actively sending packets to 1787 the target Client it SHOULD also send NS messages separated by 1788 RETRANS_TIMER milliseconds in order to receive solicited NA messages. 1789 If the source Client is unable to elicit a solicited NA response from 1790 the target Client after MAX_RETRY attempts, it SHOULD set ForwardTime 1791 to 0 and resume sending packets via one of its Servers. Otherwise, 1792 the source Client considers the path usable and SHOULD thereafter 1793 process any link-layer errors as a hint that the direct path to the 1794 target Client has either failed or has become intermittent. 1796 When a target Client receives an NS message from a source Client, it 1797 resets AcceptTime to ACCEPT_TIME if a neighbor cache entry exists; 1798 otherwise, it discards the NS message. If ForwardTime is non-zero, 1799 the target Client then sends a solicited NA message to the link-layer 1800 address of the source Client; otherwise, it sends the solicited NA 1801 message to the link-layer address of one of its Servers. 1803 When a source Client receives a solicited NA message from a target 1804 Client, it resets ForwardTime to FORWARD_TIME if a neighbor cache 1805 entry exists; otherwise, it discards the NA message. 1807 When ForwardTime for a dynamic neighbor cache entry expires, the 1808 source Client resumes sending any subsequent packets via a Server and 1809 may (eventually) attempt to re-initiate the AERO redirection process. 1810 When AcceptTime for a dynamic neighbor cache entry expires, the 1811 target Client discards any subsequent packets received directly from 1812 the source Client. When both ForwardTime and AcceptTime for a 1813 dynamic neighbor cache entry expire, the Client deletes the neighbor 1814 cache entry. 1816 3.15. Mobility Management 1818 3.15.1. Announcing Link-Layer Address Changes 1820 When a Client needs to change its link-layer address, e.g., due to a 1821 mobility event, it performs an immediate DHCPv6 Rebind/Reply exchange 1822 via each of its Servers using the new link-layer address as the 1823 source and with a CLLAO that includes the correct Link ID and 1824 Preference values. If authentication succeeds, the Server then 1825 update its neighbor cache and sends a DHCPv6 Reply. Note that if the 1826 Client does not issue a DHCPv6 Rebind before the Server has 1827 terminated the lease (e.g., if the Client has been out of touch with 1828 the Server for a considerable amount of time), the Server's Reply 1829 will report NoBinding and the Client must re-initiate the DHCPv6 PD 1830 procedure. 1832 Next, the Client sends unsolicited NA messages to each of its 1833 correspondent Client neighbors using the same procedures as specified 1834 in Section 7.2.6 of [RFC4861], except that it sends the messages as 1835 unicast to each neighbor via a Server instead of multicast. In this 1836 process, the Client should send no more than 1837 MAX_NEIGHBOR_ADVERTISEMENT messages separated by no less than 1838 RETRANS_TIMER seconds to each neighbor. 1840 With reference to Figure 7, when Client ('C2') needs to change its 1841 link-layer address it sends unicast unsolicited NA messages to Client 1842 ('C1') via Server ('S2') as follows: 1844 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 1845 layer address of Client ('C2')). 1847 o the link-layer destination address is set to 'L2(S2)' (i.e., the 1848 link-layer address of Server ('S2')). 1850 o the network-layer source address is set to fe80::2001:db8:1:0 1851 (i.e., the AERO address of Client ('C2')). 1853 o the network-layer destination address is set to fe80::2001:db8:0:0 1854 (i.e., the AERO address of Client ('C1')). 1856 o the Type is set to 136. 1858 o the Code is set to 0. 1860 o the Solicited flag is set to 0. 1862 o the Override flag is set to 1. 1864 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 1865 address of Client ('C2')). 1867 o the message includes one or more TLLAOs with Link ID and 1868 Preference set to appropriate values for Client ('C2')'s 1869 underlying interfaces, and with UDP Port Number and IP Address set 1870 to '0'. 1872 o the message SHOULD include a Timestamp option. 1874 When Server ('S1') receives the NA message, it relays the message in 1875 the same way as described for relaying Redirect messages in 1876 Section 3.12.7. In particular, Server ('S1') copies the correct UDP 1877 port numbers and IP addresses into the TLLAOs, changes the link-layer 1878 source address to its own address, changes the link-layer destination 1879 address to the address of Relay ('R1'), then forwards the NA message 1880 via the relaying chain the same as for a Redirect. 1882 When Client ('C1') receives the NA message, it accepts the message 1883 only if it already has a neighbor cache entry for Client ('C2') then 1884 updates the link-layer addresses for Client ('C2') based on the 1885 addresses in the TLLAOs. However, Client ('C1') MUST NOT update 1886 ForwardTime since Client ('C2') will not have updated AcceptTime. 1888 Note that these unsolicited NA messages are unacknowledged; hence, 1889 Client ('C2') has no way of knowing whether Client ('C1') has 1890 received them. If the messages are somehow lost, however, Client 1891 ('C1') will soon learn of the mobility event via the NUD procedures 1892 specified in Section 3.14. 1894 3.15.2. Bringing New Links Into Service 1896 When a Client needs to bring a new underlying interface into service 1897 (e.g., when it activates a new data link), it performs an immediate 1898 Rebind/Reply exchange via each of its Servers using the new link- 1899 layer address as the source address and with a CLLAO that includes 1900 the new Link ID and Preference values. If authentication succeeds, 1901 the Server then updates its neighbor cache and sends a DHCPv6 Reply. 1902 The Client MAY then send unsolicited NA messages to each of its 1903 correspondent Clients to inform them of the new link-layer address as 1904 described in Section 3.15.1. 1906 3.15.3. Removing Existing Links from Service 1908 When a Client needs to remove an existing underlying interface from 1909 service (e.g., when it de-activates an existing data link), it 1910 performs an immediate Rebind/Reply exchange via each of its Servers 1911 over any available link with a CLLAO that includes the deprecated 1912 Link ID and a Preference value of 0. If authentication succeeds, the 1913 Server then updates its neighbor cache and sends a DHCPv6 Reply. The 1914 Client SHOULD then send unsolicited NA messages to each of its 1915 correspondent Clients to inform them of the deprecated link-layer 1916 address as described in Section 3.15.1. 1918 3.15.4. Moving to a New Server 1920 When a Client associates with a new Server, it performs the Client 1921 procedures specified in Section 3.10. 1923 When a Client disassociates with an existing Server, it sends a 1924 DHCPv6 Release message to the unicast link-local network layer 1925 address of the old Server. The Client SHOULD send the message via a 1926 new Server (i.e., by setting the link-layer destination address to 1927 the address of the new Server) in case the old Server is unreachable 1928 at the link layer, e.g., if the old Server is in a different network 1929 partition. The new Server will forward the message to a Relay, which 1930 will in turn forward the message to the old Server. 1932 When the old Server receives the DHCPv6 Release, it first 1933 authenticates the message. If authentication succeeds, the old 1934 Server withdraws the IP route from the AERO routing system and 1935 deletes the neighbor cache entry for the Client. (The old Server MAY 1936 impose a small delay before deleting the neighbor cache entry so that 1937 any packets already in the system can still be delivered to the 1938 Client.) The old Server then returns a DHCPv6 Reply message via a 1939 Relay. The Client can then use the Reply message to verify that the 1940 termination signal has been processed, and can delete both the 1941 default route and the neighbor cache entry for the old Server. (Note 1942 that the Server's Reply to the Client's Release message may be lost, 1943 e.g., if the AERO routing system has not yet converged. Since the 1944 Client is responsible for reliability, however, it will retry until 1945 it gets an indication that the Release was successful.) 1947 Clients SHOULD NOT move rapidly between Servers in order to avoid 1948 causing excessive oscillations in the AERO routing system. Such 1949 oscillations could result in intermittent reachability for the Client 1950 itself, while causing little harm to the network due to routing 1951 protocol dampening. Examples of when a Client might wish to change 1952 to a different Server include a Server that has gone unreachable, 1953 topological movements of significant distance, etc. 1955 3.16. Encapsulation Protocol Version Considerations 1957 A source Client may connect only to an IPvX underlying network, while 1958 the target Client connects only to an IPvY underlying network. In 1959 that case, the target and source Clients have no means for reaching 1960 each other directly (since they connect to underlying networks of 1961 different IP protocol versions) and so must ignore any redirection 1962 messages and continue to send packets via the Server. 1964 3.17. Multicast Considerations 1966 When the underlying network does not support multicast, AERO nodes 1967 map IPv6 link-scoped multicast addresses (including 1968 'All_DHCP_Relay_Agents_and_Servers') to the link-layer address of a 1969 Server. 1971 When the underlying network supports multicast, AERO nodes use the 1972 multicast address mapping specification found in [RFC2529] for IPv4 1973 underlying networks and use a direct multicast mapping for IPv6 1974 underlying networks. (In the latter case, "direct multicast mapping" 1975 means that if the IPv6 multicast destination address of the 1976 encapsulated packet is "M", then the IPv6 multicast destination 1977 address of the encapsulating header is also "M".) 1979 3.18. Operation on AERO Links Without DHCPv6 Services 1981 When Servers on the AERO link do not provide DHCPv6 services, 1982 operation can still be accommodated through administrative 1983 configuration of ACPs on AERO Clients. In that case, administrative 1984 configurations of AERO interface neighbor cache entries on both the 1985 Server and Client are also necessary. However, this may interfere 1986 with the ability for Clients to dynamically change to new Servers, 1987 and can expose the AERO link to misconfigurations unless the 1988 administrative configurations are carefully coordinated. 1990 3.19. Operation on Server-less AERO Links 1992 In some AERO link scenarios, there may be no Servers on the link and/ 1993 or no need for Clients to use a Server as an intermediary trust 1994 anchor. In that case, each Client acts as a Server unto itself to 1995 establish neighbor cache entries by performing direct Client-to- 1996 Client IPv6 ND message exchanges, and some other form of trust basis 1997 must be applied so that each Client can verify that the prospective 1998 neighbor is authorized to use its claimed ACP. 2000 When there is no Server on the link, Clients must arrange to receive 2001 ACPs and publish them via a secure alternate prefix delegation 2002 authority through some means outside the scope of this document. 2004 3.20. Proxy AERO 2006 Proxy Mobile IPv6 (PMIPv6) [RFC5213][RFC5844] presents a localized 2007 mobility management scheme for use within an access network domain. 2008 It is typically used in cellular wireless service provider networks, 2009 and allows mobile nodes to receive and retain a stable IP address 2010 without needing to implement any special mobility protocols. In the 2011 PMIPv6 architecture, access network devices known as Mobility Access 2012 Gateways (MAGs) provide mobile nodes with an access link abstraction 2013 and receive prefixes for the mobile nodes from a Local Mobility 2014 Anchor (LMA). 2016 The AERO Client (acting as a MAG) can similarly provide proxy 2017 services for mobile nodes that do not participate in AERO messaging. 2018 The proxy Client presents an access link abstraction to mobile nodes, 2019 and performs DHCPv6 PD exchanges over the AERO interface with an AERO 2020 Server (acting as an LMA) to receive a prefix for address 2021 provisioning of the mobile node. 2023 When a mobile node comes onto an access link presented by a proxy 2024 Client, the Client authenticates the node and obtains a unique 2025 identifier that it can use as the DUID in its DHCPv6 PD messages to 2026 the Server. When the Server delegates a prefix, the Client creates a 2027 new AERO address for the mobile node and assigns the delegated prefix 2028 to the mobile node's access link. The Client then generates address 2029 autoconfiguration messages (e.g., IPv6 RA, DHCPv6, DHCPv4, etc.) over 2030 the access link and configures itself as a default router for the 2031 mobile node. Since the Client may serve many such mobile nodes 2032 simultaneously, it may configure multiple AERO addresses, i.e., one 2033 for each mobile node. 2035 When two mobile nodes are associated with the same proxy Client, the 2036 Client can forward traffic between the mobiles without involving the 2037 Server since it configures the AERO addresses of each mobile and 2038 therefore also has the necessary routing information. When two 2039 mobiles are associated with different Clients, the first mobile 2040 node's Client can initiate standard AERO route optimization using the 2041 mobile's AERO address as the source for route optimization messaging. 2042 This may result in a route optimization where the first mobile node's 2043 Client discovers a direct path to the second mobile node's Client. 2045 When a mobile node moves to a new proxy Client, the old proxy Client 2046 issues a DHCPv6 Release message and sends unsolicited NA messages to 2047 any of the mobile node's correspondents the same as specified for 2048 announcing link-layer address changes in Section 3.15.1. However, 2049 since the old Client has no way of knowing where the mobile has moved 2050 to, it sets the Code field in the NA message to 1. When the 2051 correspondent receives such an NA message, it deletes the neighbor 2052 cache entry for the departed mobile node and again allows packets to 2053 flow through its Server. 2055 In addition to the use of DHCPv6 PD signaling, the AERO approach 2056 differs from PMIPv6 in its use of the NBMA virtual link model instead 2057 of point-to-point tunnels. This provides a more agile interface for 2058 Client-to-Server coordinations, and also facilitates simple route 2059 optimization. The AERO routing system is also arranged in such a 2060 fashion that Clients get the same service from any Server they happen 2061 to associate with. This provides a natural fault tolerance and load 2062 balancing capability such as desired for distributed mobility 2063 management. All other considerations are the same as specified in 2064 [RFC5213][RFC5844]. 2066 3.21. Extending AERO Links Through Security Gateways 2068 When an enterprise mobile device moves from a campus LAN connection 2069 to a public Internet link, it must re-enter the enterprise via a 2070 security gateway that has both a physical interface connection to the 2071 Internet and a physical interface connection to the enterprise 2072 internetwork. This most often entails the establishment of a Virtual 2073 Private Network (VPN) link over the public Internet from the mobile 2074 device to the security gateway. During this process, the mobile 2075 device supplies the security gateway with its public Internet address 2076 as the link-layer address for the VPN. The mobile device then acts 2077 as an AERO Client to negotiate with the security gateway to obtain 2078 its ACP. 2080 In order to satisfy this need, the security gateway also operates as 2081 an AERO Server with support for AERO Client proxying. In particular, 2082 when a mobile device (i.e., the Client) connects via the security 2083 gateway (i.e., the Server), the Server provides the Client with an 2084 ACP in a DHCPv6 PD exchange the same as if it were attached to an 2085 enterprise campus access link. The Server then replaces the Client's 2086 link-layer source address with the Server's enterprise-facing link- 2087 layer address in all AERO messages the Client sends toward neighbors 2088 on the AERO link. The AERO messages are then delivered to other 2089 devices on the AERO link as if they were originated by the security 2090 gateway instead of by the AERO Client. In the reverse direction, the 2091 AERO messages sourced by devices within the enterprise network can be 2092 forwarded to the security gateway, which then replaces the link-layer 2093 destination address with the Client's link-layer address and replaces 2094 the link-layer source address with its own (Internet-facing) link- 2095 layer address. 2097 After receiving the ACP, the Client can send IP packets that use an 2098 address taken from the ACP as the network layer source address, the 2099 Client's link-layer address as the link-layer source address, and the 2100 Server's Internet-facing link-layer address as the link-layer 2101 destination address. The Server will then rewrite the link-layer 2102 source address with the Server's own enterprise-facing link-layer 2103 address and rewrite the link-layer destination address with the 2104 target AERO node's link-layer address, and the packets will enter the 2105 enterprise network as though they were sourced from a device located 2106 within the enterprise. In the reverse direction, when a packet 2107 sourced by a node within the enterprise network uses a destination 2108 address from the Client's ACP, the packet will be delivered to the 2109 security gateway which then rewrites the link-layer destination 2110 address to the Client's link-layer address and rewrites the link- 2111 layer source address to the Server's Internet-facing link-layer 2112 address. The Server then delivers the packet across the VPN to the 2113 AERO Client. In this way, the AERO virtual link is essentially 2114 extended *through* the security gateway to the point at which the VPN 2115 link and AERO link are effectively grafted together by the link-layer 2116 address rewriting performed by the security gateway. All AERO 2117 messaging services (including route optimization and mobility 2118 signaling) are therefore extended to the Client. 2120 In order to support this virtual link grafting, the security gateway 2121 (acting as an AERO Server) must keep static neighbor cache entries 2122 for all of its associated Clients located on the public Internet. 2123 The neighbor cache entry is keyed by the AERO Client's AERO address 2124 the same as if the Client were located within the enterprise 2125 internetwork. The neighbor cache is then managed in all ways as 2126 though the Client were an ordinary AERO Client. This includes the 2127 AERO IPv6 ND messaging signaling for Route Optimization and Neighbor 2128 Unreachability Detection. 2130 Note that the main difference between a security gateway acting as an 2131 AERO Server and an enterprise-internal AERO Server is that the 2132 security gateway has at least one enterprise-internal physical 2133 interface and at least one public Internet physical interface. 2135 Conversely, the enterprise-internal AERO Server has only enterprise- 2136 internal physical interfaces. For this reason security gateway 2137 proxying is needed to ensure that the public Internet link-layer 2138 addressing space is kept separate from the enterprise-internal link- 2139 layer addressing space. This is afforded through a natural extension 2140 of the security association caching already performed for each VPN 2141 client by the security gateway. 2143 3.22. Extending IPv6 AERO Links to the Internet 2145 When an IPv6 host ('H1') with an address from an ACP owned by AERO 2146 Client ('C1') sends packets to a correspondent IPv6 host ('H2'), the 2147 packets eventually arrive at the IPv6 router that owns ('H2')s 2148 prefix. This IPv6 router may or may not be an AERO Client ('C2') 2149 either within the same home network as ('C1') or in a different home 2150 network. 2152 If Client ('C1') is currently located outside the boundaries of its 2153 home network, it will connect back into the home network via a 2154 security gateway acting as an AERO Server. The packets sent by 2155 ('H1') via ('C1') will then be forwarded through the security gateway 2156 then through the home network and finally to ('C2') where they will 2157 be delivered to ('H2'). This could lead to sub-optimal performance 2158 when ('C2') could instead be reached via a more direct route without 2159 involving the security gateway. 2161 Consider the case when host ('H1') has the IPv6 address 2162 2001:db8:1::1, and Client ('C1') has the ACP 2001:db8:1::/64 with 2163 underlying IPv6 Internet address of 2001:db8:1000::1. Also, host 2164 ('H2') has the IPv6 address 2001:db8:2::1, and Client ('C2') has the 2165 ACP 2001:db8:2::/64 with underlying IPv6 Internet address of 2166 2001:db8:2000::1. While Client ('C1') may not initially know whether 2167 ('C2') is in fact an AERO Client, it can attempt route optimization 2168 using an approach similar to the Return Routability procedure 2169 specified for Mobile IPv6 (MIPv6) [RFC6275]. In order to support 2170 this process, both Clients MUST intercept and decapsulate packets 2171 that have a subnet router anycast address corresponding to any of the 2172 /64 prefixes covered by their respective ACPs. 2174 To initiate the process, Client ('C1') creates a specially-crafted 2175 encapsulated AERO Predirect message that will be routed through its 2176 home network then through ('C2')s home network and finally to ('C2') 2177 itself. Client ('C1') prepares the initial message in the exchange 2178 as follows: 2180 o The encapsulating IPv6 header source address is set to 2181 2001:db8:1:: (i.e., the IPv6 subnet router anycast address for 2182 ('C1')s ACP) 2184 o The encapsulating IPv6 header destination address is set to 2185 2001:db8:2:: (i.e., the presumed IPv6 subnet router anycast 2186 address for ('C2')s ACP) 2188 o The encapsulating IPv6 header is followed by a UDP header with 2189 source and destination port set to 8060 2191 o The encapsulated IPv6 header source address is set to 2192 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2194 o The encapsulated IPv6 header destination address is set to 2195 fe80::2001:db8:2:0 (i.e., the presumed AERO address for ('C2')) 2197 o The encapsulated AERO Predirect message includes all of the 2198 securing information that would occur in a MIPv6 "Home Test Init" 2199 message (format TBD) 2201 Client ('C1') then further encapsulates the message in the 2202 encapsulating headers necessary to convey the packet to the security 2203 gateway (e.g., through IPsec encapsulation) so that the message now 2204 appears "double-encapsulated". ('C1') then sends the message to the 2205 security gateway, which re-encapsulates and forwards it over the home 2206 network from where it will eventually reach ('C2'). 2208 At the same time, ('C1') creates and sends a second encapsulated AERO 2209 Predirect message that will be routed through the IPv6 Internet 2210 without involving the security gateway. Client ('C1') prepares the 2211 message as follows: 2213 o The encapsulating IPv6 header source address is set to 2214 2001:db8:1000:1 (i.e., the Internet IPv6 address of ('C1')) 2216 o The encapsulating IPv6 header destination address is set to 2217 2001:db8:2:: (i.e., the presumed IPv6 subnet router anycast 2218 address for ('C2')s ACP) 2220 o The encapsulating IPv6 header is followed by a UDP header with 2221 source and destination port set to 8060 2223 o The encapsulated IPv6 header source address is set to 2224 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2226 o The encapsulated IPv6 header destination address is set to 2227 fe80::2001:db8:2:0 (i.e., the presumed AERO address for ('C2')) 2229 o The encapsulated AERO Predirect message includes all of the 2230 securing information that would occur in a MIPv6 "Care-of Test 2231 Init" message (format TBD) 2233 If ('C2') is indeed an AERO Client, it will receive both Predirect 2234 messages through its home network. ('C2') then return a 2235 corresponding Redirect for each of the Predirect messages with the 2236 source and destination addresses in the inner and outer headers 2237 reversed. The first message includes all of the securing information 2238 that would occur in a MIPv6 "Home Test" message, while the second 2239 message includes all of the securing information that would occur in 2240 a MIPv6 "Care-of Test" message (formats TBD). 2242 When ('C1') receives the Redirect messages, it performs the necessary 2243 security procedures per the MIPv6 specification. It then prepares an 2244 encapsulated NS message that includes the same source and destination 2245 addresses as for the "Care-of Test Init" Predirect message, and 2246 includes all of the securing information that would occur in a MIPv6 2247 "Binding Update" message (format TBD) and sends the message to 2248 ('C2'). 2250 When ('C2') receives the NS message, if the securing information is 2251 correct it creates or updates a neighbor cache entry for ('C1') with 2252 fe80::2001:db8:1:0 as the network-layer address, 2001:db8:1000::1 as 2253 the link-layer address and with AcceptTime set to ACCEPT_TIME. 2254 ('C2') then sends an encapsulated NA message back to ('C1') that 2255 includes the same source and destination addresses as for the "Care- 2256 of Test" Redirect message, and includes all of the securing 2257 information that would occur in a MIPv6 "Binding Acknowledgement" 2258 message (format TBD) and sends the message to ('C1'). 2260 When ('C1') receives the NA message, it creates or updates a neighbor 2261 cache entry for ('C2') with fe80::2001:db8:2:0 as the network-layer 2262 address and 2001:db8:2:: as the link-layer address and with 2263 ForwardTime set to FORWARD_TIME, thus completing the route 2264 optimization in the forward direction. 2266 ('C1') subsequently forwards encapsulated packets with outer source 2267 address 2001:db8:1000::1, with outer destination address 2268 2001:db8:2::, with inner source address taken from the 2001:db8:1::, 2269 and with inner destination address taken from 2001:db8:2:: due to the 2270 fact that it has a securely-established neighbor cache entry with 2271 non-zero ForwardTime. ('C2') subsequently accepts any such 2272 encapsulated packets due to the fact that it has a securely- 2273 established neighbor cache entry with non-zero AcceptTime.. 2275 In order to keep neighbor cache entries alive, ('C1') periodically 2276 sends additional NS messages to ('C2') and receives any NA responses. 2277 If ('C1') moves to a different point of attachment after the initial 2278 route optimization, it sends a new secured NS message to ('C2') as 2279 above to update ('C2')s neighbor cache. 2281 If ('C2') has packets to send to ('C1'), it performs a corresponding 2282 route optimization in the opposite direction following the same 2283 procedures described above. In the process, the already-established 2284 unidirectional neighbor cache entries within ('C1') and ('C2') are 2285 updated to include the now-bidirectional information. In particular, 2286 the AcceptTime and ForwardTime variables for both neighbor cache 2287 entries are updated to non-zero values, and the link-layer address 2288 for ('C1')s neighbor cache entry for ('C2') is reset to 2289 2001:db8:2000::1. 2291 Note that two AERO Clients can use full security protocol messaging 2292 instead of Return Routability, e.g., if strong authentication and/or 2293 confidentiality are desired. In that case, security protocol key 2294 exchanges such as specified for MOBIKE [RFC4555] would be used to 2295 establish security associations and neighbor cache entries between 2296 the AERO clients. Thereafter, AERO NS/NA messaging can be used to 2297 maintain neighbor cache entries, test reachability, and to announce 2298 mobility events. If reachability testing fails, e.g., if both 2299 Clients move at roughly the same time, the Clients can tear down the 2300 security association and neighbor cache entries and again allow 2301 packets to flow through their home network (which may result in a new 2302 route optimization event). 2304 4. Implementation Status 2306 An application-layer implementation is in progress. 2308 5. IANA Considerations 2310 IANA is instructed to assign a new 2-octet Hardware Type number 2311 "TBD1" for AERO in the "arp-parameters" registry per Section 2 of 2312 [RFC5494]. The number is assigned from the 2-octet Unassigned range 2313 with Hardware Type "AERO" and with this document as the reference. 2315 IANA is instructed to assign a 4-octet Enterprise Number "TBD2" for 2316 AERO in the "enterprise-numbers" registry per [RFC3315]. 2318 6. Security Considerations 2320 AERO link security considerations are the same as for standard IPv6 2321 Neighbor Discovery [RFC4861] except that AERO improves on some 2322 aspects. In particular, AERO uses a trust basis between Clients and 2323 Servers, where the Clients only engage in the AERO mechanism when it 2324 is facilitated by a trust anchor. Unless there is some other means 2325 of authenticating the Client's identity (e.g., link-layer security), 2326 AERO nodes SHOULD also use DHCPv6 securing services (e.g., DHCPv6 2327 authentication, Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6], etc.) for 2328 Client authentication and network admission control. 2330 AERO Redirect, Predirect and unsolicited NA messages SHOULD include a 2331 Timestamp option (see Section 5.3 of [RFC3971]) that other AERO nodes 2332 can use to verify the message time of origin. AERO Predirect, NS and 2333 RS messages SHOULD include a Nonce option (see Section 5.3 of 2334 [RFC3971]) that recipients echo back in corresponding responses. 2336 AERO links must be protected against link-layer address spoofing 2337 attacks in which an attacker on the link pretends to be a trusted 2338 neighbor. Links that provide link-layer securing mechanisms (e.g., 2339 IEEE 802.1X WLANs) and links that provide physical security (e.g., 2340 enterprise network wired LANs) provide a first line of defense that 2341 is often sufficient. In other instances, additional securing 2342 mechanisms such as Secure Neighbor Discovery (SeND) [RFC3971], IPsec 2343 [RFC4301] or TLS [RFC5246] may be necessary. 2345 AERO Clients MUST ensure that their connectivity is not used by 2346 unauthorized nodes on their EUNs to gain access to a protected 2347 network, i.e., AERO Clients that act as routers MUST NOT provide 2348 routing services for unauthorized nodes. (This concern is no 2349 different than for ordinary hosts that receive an IP address 2350 delegation but then "share" the address with unauthorized nodes via a 2351 NAT function.) 2353 On some AERO links, establishment and maintenance of a direct path 2354 between neighbors requires secured coordination such as through the 2355 Internet Key Exchange (IKEv2) protocol [RFC5996] to establish a 2356 security association. 2358 7. Acknowledgements 2360 Discussions both on IETF lists and in private exchanges helped shape 2361 some of the concepts in this work. Individuals who contributed 2362 insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, 2363 Stewart Bryant, Brian Carpenter, Wojciech Dec, Ralph Droms, Sri 2364 Gundavelli, Brian Haberman, Joel Halpern, Sascha Hlusiak, Lee Howard, 2365 Andre Kostur, Ted Lemon, Joe Touch and Bernie Volz. Members of the 2366 IESG also provided valuable input during their review process that 2367 greatly improved the document. Special thanks go to Stewart Bryant, 2368 Joel Halpern and Brian Haberman for their shepherding guidance. 2370 This work has further been encouraged and supported by Boeing 2371 colleagues including Keith Bartley, Dave Bernhardt, Cam Brodie, 2372 Balaguruna Chidambaram, Claudiu Danilov, Wen Fang, Anthony Gregory, 2373 Jeff Holland, Ed King, Gen MacLean, Kent Shuey, Brian Skeen, Mike 2374 Slane, Julie Wulff, Yueli Yang, and other members of the BR&T and BIT 2375 mobile networking teams. 2377 Earlier works on NBMA tunneling approaches are found in 2378 [RFC2529][RFC5214][RFC5569]. 2380 8. References 2382 8.1. Normative References 2384 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2385 August 1980. 2387 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 2388 1981. 2390 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2391 RFC 792, September 1981. 2393 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 2394 October 1996. 2396 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2397 Requirement Levels", BCP 14, RFC 2119, March 1997. 2399 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2400 (IPv6) Specification", RFC 2460, December 1998. 2402 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2403 IPv6 Specification", RFC 2473, December 1998. 2405 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2406 and M. Carney, "Dynamic Host Configuration Protocol for 2407 IPv6 (DHCPv6)", RFC 3315, July 2003. 2409 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2410 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2411 December 2003. 2413 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2414 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2416 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 2417 for IPv6 Hosts and Routers", RFC 4213, October 2005. 2419 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2420 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2421 September 2007. 2423 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2424 Address Autoconfiguration", RFC 4862, September 2007. 2426 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 2427 Requirements", RFC 6434, December 2011. 2429 8.2. Informative References 2431 [I-D.ietf-dhc-sedhcpv6] 2432 Jiang, S., Shen, S., Zhang, D., and T. Jinmei, "Secure 2433 DHCPv6 with Public Key", draft-ietf-dhc-sedhcpv6-03 (work 2434 in progress), June 2014. 2436 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 2437 RFC 879, November 1983. 2439 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 2440 1812, June 1995. 2442 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 2443 selection, and registration of an Autonomous System (AS)", 2444 BCP 6, RFC 1930, March 1996. 2446 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2447 2131, March 1997. 2449 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2450 Domains without Explicit Tunnels", RFC 2529, March 1999. 2452 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 2453 RFC 2675, August 1999. 2455 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 2456 2923, September 2000. 2458 [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., 2459 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2460 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2461 RFC 3819, July 2004. 2463 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 2464 Protocol 4 (BGP-4)", RFC 4271, January 2006. 2466 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2467 Architecture", RFC 4291, February 2006. 2469 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2470 Internet Protocol", RFC 4301, December 2005. 2472 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 2473 Message Protocol (ICMPv6) for the Internet Protocol 2474 Version 6 (IPv6) Specification", RFC 4443, March 2006. 2476 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 2477 (MOBIKE)", RFC 4555, June 2006. 2479 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2480 Discovery", RFC 4821, March 2007. 2482 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2483 Errors at High Data Rates", RFC 4963, July 2007. 2485 [RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski, 2486 "DHCPv6 Relay Agent Echo Request Option", RFC 4994, 2487 September 2007. 2489 [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., 2490 and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. 2492 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2493 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2494 March 2008. 2496 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 2497 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 2499 [RFC5494] Arkko, J. and C. Pignataro, "IANA Allocation Guidelines 2500 for the Address Resolution Protocol (ARP)", RFC 5494, 2501 April 2009. 2503 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 2504 Route Optimization Requirements for Operational Use in 2505 Aeronautics and Space Exploration Mobile Networks", RFC 2506 5522, October 2009. 2508 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 2509 Infrastructures (6rd)", RFC 5569, January 2010. 2511 [RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy 2512 Mobile IPv6", RFC 5844, May 2010. 2514 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 2515 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 2516 5996, September 2010. 2518 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 2519 NAT64: Network Address and Protocol Translation from IPv6 2520 Clients to IPv4 Servers", RFC 6146, April 2011. 2522 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 2523 Troan, "Basic Requirements for IPv6 Customer Edge 2524 Routers", RFC 6204, April 2011. 2526 [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support 2527 in IPv6", RFC 6275, July 2011. 2529 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2530 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, August 2531 2011. 2533 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 2534 for Equal Cost Multipath Routing and Link Aggregation in 2535 Tunnels", RFC 6438, November 2011. 2537 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 2538 RFC 6691, July 2012. 2540 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 2541 (AERO)", RFC 6706, August 2012. 2543 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 2544 RFC 6864, February 2013. 2546 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 2547 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 2549 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 2550 for the Use of IPv6 UDP Datagrams with Zero Checksums", 2551 RFC 6936, April 2013. 2553 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 2554 Address Option in DHCPv6", RFC 6939, May 2013. 2556 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 2557 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 2559 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 2560 Address Selection Policy Using DHCPv6", RFC 7078, January 2561 2014. 2563 Author's Address 2565 Fred L. Templin (editor) 2566 Boeing Research & Technology 2567 P.O. Box 3707 2568 Seattle, WA 98124 2569 USA 2571 Email: fltemplin@acm.org