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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, July 27, 2016 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: January 28, 2017 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-aerolink-70.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, address/prefix provisioning 23 and mobility are supported by the Dynamic Host Configuration Protocol 24 for IPv6 (DHCPv6), and route optimization is naturally supported 25 through dynamic neighbor cache updates. Although DHCPv6 and IPv6 ND 26 messaging are used in the control plane, both IPv4 and IPv6 are 27 supported in the data plane. AERO is a widely-applicable tunneling 28 solution using standard control messaging exchanges as described in 29 this document. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at http://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on January 28, 2017. 48 Copyright Notice 50 Copyright (c) 2016 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 6 68 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 6 69 3.2. AERO Link Node Types . . . . . . . . . . . . . . . . . . 8 70 3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 9 71 3.4. AERO Interface Characteristics . . . . . . . . . . . . . 10 72 3.5. AERO Link Registration . . . . . . . . . . . . . . . . . 11 73 3.6. AERO Interface Initialization . . . . . . . . . . . . . . 12 74 3.6.1. AERO Relay Behavior . . . . . . . . . . . . . . . . . 12 75 3.6.2. AERO Server Behavior . . . . . . . . . . . . . . . . 12 76 3.6.3. AERO Client Behavior . . . . . . . . . . . . . . . . 13 77 3.6.4. AERO Forwarding Agent Behavior . . . . . . . . . . . 13 78 3.7. AERO Routing System . . . . . . . . . . . . . . . . . . . 13 79 3.8. AERO Interface Neighbor Cache Maintenace . . . . . . . . 15 80 3.9. AERO Interface Sending Algorithm . . . . . . . . . . . . 16 81 3.10. AERO Interface Encapsulation and Re-encapsulation . . . . 18 82 3.11. AERO Interface Decapsulation . . . . . . . . . . . . . . 19 83 3.12. AERO Interface Data Origin Authentication . . . . . . . . 19 84 3.13. AERO Interface Packet Size Issues . . . . . . . . . . . . 20 85 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 22 86 3.15. AERO Router Discovery, Prefix Delegation and Address 87 Configuration . . . . . . . . . . . . . . . . . . . . . . 25 88 3.15.1. AERO DHCPv6 Service Model . . . . . . . . . . . . . 25 89 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 25 90 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 28 91 3.15.4. Deleting Link Registrations . . . . . . . . . . . . 32 92 3.16. AERO Forwarding Agent Behavior . . . . . . . . . . . . . 32 93 3.17. AERO Intradomain Route Optimization . . . . . . . . . . . 33 94 3.17.1. Reference Operational Scenario . . . . . . . . . . . 33 95 3.17.2. Concept of Operations . . . . . . . . . . . . . . . 35 96 3.17.3. Message Format . . . . . . . . . . . . . . . . . . . 35 97 3.17.4. Sending Predirects . . . . . . . . . . . . . . . . . 36 98 3.17.5. Re-encapsulating and Relaying Predirects . . . . . . 37 99 3.17.6. Processing Predirects and Sending Redirects . . . . 38 100 3.17.7. Re-encapsulating and Relaying Redirects . . . . . . 40 101 3.17.8. Processing Redirects . . . . . . . . . . . . . . . . 40 102 3.17.9. Server-Oriented Redirection . . . . . . . . . . . . 41 103 3.17.10. Route Optimization Policy . . . . . . . . . . . . . 41 104 3.17.11. Route Optimization and Multiple ACPs . . . . . . . . 42 105 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 42 106 3.19. Mobility Management . . . . . . . . . . . . . . . . . . . 43 107 3.19.1. Announcing Link-Layer Address Changes . . . . . . . 43 108 3.19.2. Bringing New Links Into Service . . . . . . . . . . 43 109 3.19.3. Removing Existing Links from Service . . . . . . . . 43 110 3.19.4. Moving to a New Server . . . . . . . . . . . . . . . 44 111 3.19.5. Packet Queueing for Mobility . . . . . . . . . . . . 44 112 3.20. Proxy AERO . . . . . . . . . . . . . . . . . . . . . . . 45 113 3.21. Extending AERO Links Through Security Gateways . . . . . 47 114 3.22. Extending IPv6 AERO Links to the Internet . . . . . . . . 49 115 3.23. Encapsulation Protocol Version Considerations . . . . . . 52 116 3.24. Multicast Considerations . . . . . . . . . . . . . . . . 53 117 3.25. Operation on AERO Links Without DHCPv6 Services . . . . . 53 118 3.26. Operation on Server-less AERO Links . . . . . . . . . . . 53 119 3.27. Manually-Configured AERO Tunnels . . . . . . . . . . . . 53 120 3.28. Intradomain Routing . . . . . . . . . . . . . . . . . . . 54 121 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 54 122 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 54 123 6. Security Considerations . . . . . . . . . . . . . . . . . . . 54 124 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 55 125 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 56 126 8.1. Normative References . . . . . . . . . . . . . . . . . . 56 127 8.2. Informative References . . . . . . . . . . . . . . . . . 58 128 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 65 129 Appendix B. When to Insert an Encapsulation Fragment Header . . 66 130 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 67 132 1. Introduction 134 This document specifies the operation of IP over tunnel virtual links 135 using Asymmetric Extended Route Optimization (AERO). The AERO link 136 can be used for tunneling to neighboring nodes over either IPv6 or 137 IPv4 networks, i.e., AERO views the IPv6 and IPv4 networks as 138 equivalent links for tunneling. Nodes attached to AERO links can 139 exchange packets via trusted intermediate routers that provide 140 forwarding services to reach off-link destinations and redirection 141 services for route optimization [RFC5522]. 143 AERO provides an IPv6 link-local address format known as the AERO 144 address that supports operation of the IPv6 Neighbor Discovery (ND) 145 [RFC4861] protocol and links IPv6 ND to IP forwarding. Admission 146 control, address/prefix provisioning and mobility are supported by 147 the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315], 148 and route optimization is naturally supported through dynamic 149 neighbor cache updates. Although DHCPv6 and IPv6 ND messaging are 150 used in the control plane, both IPv4 and IPv6 can be used in the data 151 plane. AERO is a widely-applicable tunneling solution using standard 152 control messaging exchanges as described in this document. The 153 remainder of this document presents the AERO specification. 155 2. Terminology 157 The terminology in the normative references applies; the following 158 terms are defined within the scope of this document: 160 AERO link 161 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 162 configured over a node's attached IPv6 and/or IPv4 networks. All 163 nodes on the AERO link appear as single-hop neighbors from the 164 perspective of the virtual overlay even though they may be 165 separated by many underlying network hops. AERO can also operate 166 over native multiple access link types (e.g., Ethernet, WiFi etc.) 167 when a tunnel virtual overlay is not needed. 169 AERO interface 170 a node's attachment to an AERO link. Nodes typically have a 171 single AERO interface; support for multiple AERO interfaces is 172 also possible but out of scope for this document. AERO interfaces 173 do not require Duplicate Address Detection (DAD) and therefore set 174 the administrative variable DupAddrDetectTransmits to zero 175 [RFC4862]. 177 AERO address 178 an IPv6 link-local address constructed as specified in Section 3.3 179 and assigned to a Client's AERO interface. 181 AERO node 182 a node that is connected to an AERO link and that participates in 183 IPv6 ND and DHCPv6 messaging over the link. 185 AERO Client ("Client") 186 a node that issues DHCPv6 messages to receive IP Prefix 187 Delegations (PDs) from one or more AERO Servers. Following PD, 188 the Client assigns an AERO address to the AERO interface for use 189 in DHCPv6 and IPv6 ND exchanges with other AERO nodes. 191 AERO Server ("Server") 192 a node that configures an AERO interface to provide default 193 forwarding and DHCPv6 services for AERO Clients. The Server 194 assigns an administratively provisioned IPv6 link-local unicast 195 address to support the operation of DHCPv6 and the IPv6 ND 196 protocol. An AERO Server can also act as an AERO Relay. 198 AERO Relay ("Relay") 199 a node that configures an AERO interface to relay IP packets 200 between nodes on the same AERO link and/or forward IP packets 201 between the AERO link and the native Internetwork. The Relay 202 assigns an administratively provisioned IPv6 link-local unicast 203 address to the AERO interface the same as for a Server. An AERO 204 Relay can also act as an AERO Server. 206 AERO Forwarding Agent ("Forwarding Agent") 207 a node that performs data plane forwarding services as a companion 208 to an AERO Server. 210 ingress tunnel endpoint (ITE) 211 an AERO interface endpoint that injects tunneled packets into an 212 AERO link. 214 egress tunnel endpoint (ETE) 215 an AERO interface endpoint that receives tunneled packets from an 216 AERO link. 218 underlying network 219 a connected IPv6 or IPv4 network routing region over which the 220 tunnel virtual overlay is configured. A typical example is an 221 enterprise network, but many other use cases are also in scope. 223 underlying interface 224 an AERO node's interface point of attachment to an underlying 225 network. 227 link-layer address 228 an IP address assigned to an AERO node's underlying interface. 229 When UDP encapsulation is used, the UDP port number is also 230 considered as part of the link-layer address; otherwise, UDP port 231 number is set to the constant value '0'. Link-layer addresses are 232 used as the encapsulation header source and destination addresses. 234 network layer address 235 the source or destination address of the encapsulated IP packet. 237 end user network (EUN) 238 an internal virtual or external edge IP network that an AERO 239 Client connects to the rest of the network via the AERO interface. 241 AERO Service Prefix (ASP) 242 an IP prefix associated with the AERO link and from which AERO 243 Client Prefixes (ACPs) are derived (for example, the IPv6 ACP 244 2001:db8:1:2::/64 is derived from the IPv6 ASP 2001:db8::/32). 246 AERO Client Prefix (ACP) 247 a more-specific IP prefix taken from an ASP and delegated to a 248 Client. 250 Throughout the document, the simple terms "Client", "Server" and 251 "Relay" refer to "AERO Client", "AERO Server" and "AERO Relay", 252 respectively. Capitalization is used to distinguish these terms from 253 DHCPv6 client/server/relay [RFC3315]. 255 The terminology of DHCPv6 [RFC3315] and IPv6 ND [RFC4861] (including 256 the names of node variables and protocol constants) applies to this 257 document. Also throughout the document, the term "IP" is used to 258 generically refer to either Internet Protocol version (i.e., IPv4 or 259 IPv6). 261 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 262 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 263 document are to be interpreted as described in [RFC2119]. Lower case 264 uses of these words are not to be interpreted as carrying RFC2119 265 significance. 267 3. Asymmetric Extended Route Optimization (AERO) 269 The following sections specify the operation of IP over Asymmetric 270 Extended Route Optimization (AERO) links: 272 3.1. AERO Link Reference Model 273 .-(::::::::) 274 .-(:::: IP ::::)-. 275 (:: Internetwork ::) 276 `-(::::::::::::)-' 277 `-(::::::)-' 278 | 279 +--------------+ +--------+-------+ +--------------+ 280 |AERO Server S1| | AERO Relay R1 | |AERO Server S2| 281 | Nbr: C1; R1 | | Nbr: S1; S2 | | Nbr: C2; R1 | 282 | default->R1 | |(P1->S1; P2->S2)| | default->R1 | 283 | P1->C1 | | ASP A1 | | P2->C2 | 284 +-------+------+ +--------+-------+ +------+-------+ 285 | | | 286 X---+---+-------------------+------------------+---+---X 287 | AERO Link | 288 +-----+--------+ +--------+-----+ 289 |AERO Client C1| |AERO Client C2| 290 | Nbr: S1 | | Nbr: S2 | 291 | default->S1 | | default->S2 | 292 | ACP P1 | | ACP P2 | 293 +--------------+ +--------------+ 294 .-. .-. 295 ,-( _)-. ,-( _)-. 296 .-(_ IP )-. .-(_ IP )-. 297 (__ EUN ) (__ EUN ) 298 `-(______)-' `-(______)-' 299 | | 300 +--------+ +--------+ 301 | Host H1| | Host H2| 302 +--------+ +--------+ 304 Figure 1: AERO Link Reference Model 306 Figure 1 presents the AERO link reference model. In this model: 308 o AERO Relay R1 aggregates AERO Service Prefix (ASP) A1, acts as a 309 default router for its associated Servers S1 and S2, and connects 310 the AERO link to the rest of the IP Internetwork. 312 o AERO Servers S1 and S2 associate with Relay R1 and also act as 313 default routers for their associated Clients C1 and C2. 315 o AERO Clients C1 and C2 associate with Servers S1 and S2, 316 respectively. They receive AERO Client Prefix (ACP) delegations 317 P1 and P2, and also act as default routers for their associated 318 physical or internal virtual EUNs. (Alternatively, clients can 319 act as multi-addressed hosts without serving any EUNs). 321 o Simple hosts H1 and H2 attach to the EUNs served by Clients C1 and 322 C2, respectively. 324 Each AERO node maintains an AERO interface neighbor cache and an IP 325 forwarding table. For example, AERO Relay R1 in the diagram has 326 neighbor cache entries for Servers S1 and S2 as well as IP forwarding 327 table entries for the ACPs delegated to Clients C1 and C2. In common 328 operational practice, there may be many additional Relays, Servers 329 and Clients. (Although not shown in the figure, AERO Forwarding 330 Agents may also be provided for data plane forwarding offload 331 services.) 333 3.2. AERO Link Node Types 335 AERO Relays provide default forwarding services to AERO Servers. 336 Relays forward packets between neighbors connected to the same AERO 337 link and also forward packets between the AERO link and the native IP 338 Internetwork. Relays present the AERO link to the native 339 Internetwork as a set of one or more AERO Service Prefixes (ASPs) and 340 serve as a gateway between the AERO link and the Internetwork. AERO 341 Relays maintain an AERO interface neighbor cache entry for each AERO 342 Server, and maintain an IP forwarding table entry for each AERO 343 Client Prefix (ACP). AERO Relays can also be configured to act as 344 AERO Servers. 346 AERO Servers provide default forwarding services to AERO Clients. 347 Each Server also peers with each Relay in a dynamic routing protocol 348 instance to advertise its list of associated ACPs. Servers configure 349 a DHCPv6 server function to facilitate Prefix Delegation (PD) 350 exchanges with Clients. Each delegated prefix becomes an ACP taken 351 from an ASP. Servers forward packets between AERO interface 352 neighbors, and maintain an AERO interface neighbor cache entry for 353 each AERO Relay. They also maintain both neighbor cache entries and 354 IP forwarding table entries for each of their associated Clients. 355 AERO Servers can also be configured to act as AERO Relays. 357 AERO Clients act as requesting routers to receive ACPs through DHCPv6 358 PD exchanges with AERO Servers over the AERO link. Each Client MAY 359 associate with a single Server or with multiple Servers, e.g., for 360 fault tolerance, load balancing, etc. Each IPv6 Client receives at 361 least a /64 IPv6 ACP, and may receive even shorter prefixes. 362 Similarly, each IPv4 Client receives at least a /32 IPv4 ACP (i.e., a 363 singleton IPv4 address), and may receive even shorter prefixes. AERO 364 Clients maintain an AERO interface neighbor cache entry for each of 365 their associated Servers as well as for each of their correspondent 366 Clients. 368 AERO Forwarding Agents provide data plane forwarding services as 369 companions to AERO Servers. Note that while Servers are required to 370 perform both control and data plane operations on their own behalf, 371 they may optionally enlist the services of special-purpose Forwarding 372 Agents to offload data plane traffic. 374 3.3. AERO Addresses 376 An AERO address is an IPv6 link-local address with an embedded ACP 377 and assigned to a Client's AERO interface. The AERO address is 378 formed as follows: 380 fe80::[ACP] 382 For IPv6, the AERO address begins with the prefix fe80::/64 and 383 includes in its interface identifier the base prefix taken from the 384 Client's IPv6 ACP. The base prefix is determined by masking the ACP 385 with the prefix length. For example, if the AERO Client receives the 386 IPv6 ACP: 388 2001:db8:1000:2000::/56 390 it constructs its AERO address as: 392 fe80::2001:db8:1000:2000 394 For IPv4, the AERO address is formed from the lower 64 bits of an 395 IPv4-mapped IPv6 address [RFC4291] that includes the base prefix 396 taken from the Client's IPv4 ACP. For example, if the AERO Client 397 receives the IPv4 ACP: 399 192.0.2.32/28 401 it constructs its AERO address as: 403 fe80::FFFF:192.0.2.32 405 The AERO address remains stable as the Client moves between 406 topological locations, i.e., even if its link-layer addresses change. 408 NOTE: In some cases, prospective neighbors may not have advanced 409 knowledge of the Client's ACP length and may therefore send initial 410 IPv6 ND messages with an AERO destination address that matches the 411 ACP but does not correspond to the base prefix. For example, if the 412 Client receives the IPv6 ACP 2001:db8:1000:2000::/56 then 413 subsequently receives an IPv6 ND message with destination address 414 fe80::2001:db8:1000:2001, it accepts the message as though it were 415 addressed to fe80::2001:db8:1000:2000. 417 3.4. AERO Interface Characteristics 419 AERO interfaces use encapsulation (see: Section 3.10) to exchange 420 packets with neighbors attached to the AERO link. AERO interfaces 421 maintain a neighbor cache, and AERO nodes use both DHCPv6 PD and IPv6 422 ND control messaging. AERO Clients send DHCPv6 Solicit, Rebind, 423 Renew and Release messages to AERO Servers, which respond with DHCPv6 424 Reply messages. These messages result in the creation, modification 425 and deletion of neighbor cache entries. 427 AERO interfaces use unicast IPv6 ND Neighbor Solicitation (NS), 428 Neighbor Advertisement (NA), Router Solicitation (RS) and Router 429 Advertisement (RA) messages the same as for any IPv6 link. AERO 430 interfaces use two IPv6 ND redirection message types -- the first 431 known as a Predirect message and the second being the standard 432 Redirect message (see Section 3.17). AERO links further use link- 433 local-only addressing; hence, AERO nodes ignore any Prefix 434 Information Options (PIOs) they may receive in RA messages over an 435 AERO interface. 437 AERO interface ND messages include one or more Source/Target Link- 438 Layer Address Options (S/TLLAOs) formatted as shown in Figure 2: 440 0 1 2 3 441 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 1 442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 443 | Type = 2 | Length = 3 | Reserved | 444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 445 | Link ID | NDSCPs | DSCP #1 |Prf| DSCP #2 |Prf| 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 | DSCP #3 |Prf| DSCP #4 |Prf| .... 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 | UDP Port Number | | 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 451 | | 452 + + 453 | IP Address | 454 + + 455 | | 456 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 457 | | 458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 460 Figure 2: AERO Source/Target Link-Layer Address Option (S/TLLAO) 461 Format 463 In this format, Link ID is an integer value between 0 and 255 464 corresponding to an underlying interface of the target node, NDSCPs 465 encodes an integer value between 0 and 64 indicating the number of 466 Differentiated Services Code Point (DSCP) octets that follow. Each 467 DSCP octet is a 6-bit integer DSCP value followed by a 2-bit 468 Preference ("Prf") value. Each DSCP value encodes an integer between 469 0 and 63 associated with this Link ID, where the value 0 means 470 "default" and other values are interpreted as specified in [RFC2474]. 471 The 'Prf' qualifier for each DSCP value is set to the value 0 472 ("deprecated'), 1 ("low"), 2 ("medium"), or 3 ("high") to indicate a 473 preference level for packet forwarding purposes. When a particular 474 DSCP value is not specified, its preference level is set to "medium" 475 by default. 477 UDP Port Number and IP Address are set to the addresses used by the 478 target node when it sends encapsulated packets over the underlying 479 interface. When UDP is not used as part of the encapsulation, UDP 480 Port Number is set to the value '0'. When the encapsulation IP 481 address family is IPv4, IP Address is formed as an IPv4-mapped IPv6 482 address [RFC4291]. 484 AERO interfaces may be configured over multiple underlying 485 interfaces. For example, common mobile handheld devices have both 486 wireless local area network ("WLAN") and cellular wireless links. 487 These links are typically used "one at a time" with low-cost WLAN 488 preferred and highly-available cellular wireless as a standby. In a 489 more complex example, aircraft frequently have many wireless data 490 link types (e.g. satellite-based, terrestrial, air-to-air 491 directional, etc.) with diverse performance and cost properties. 493 If a Client's multiple underlying interfaces are used "one at a time" 494 (i.e., all other interfaces are in standby mode while one interface 495 is active), then Redirect, Predirect and unsolicited NA messages 496 include only a single TLLAO with Link ID set to a constant value. 498 If the Client has multiple active underlying interfaces, then from 499 the perspective of IPv6 ND it would appear to have multiple link- 500 layer addresses. In that case, Redirect and Predirect messages MAY 501 include multiple TLLAOs -- each with a Link ID that corresponds to a 502 specific underlying interface of the Client. 504 3.5. AERO Link Registration 506 When an administrative authority first deploys a set of AERO Relays 507 and Servers that comprise an AERO link, they also assign a unique 508 domain name for the link, e.g., "linkupnetworks.example.com". Next, 509 if administrative policy permits Clients within the domain to serve 510 as correspondent nodes for Internet mobile nodes, the administrative 511 authority adds a Fully Qualified Domain Name (FQDN) for each of the 512 AERO link's ASPs to the Domain Name System (DNS) [RFC1035]. The FQDN 513 is based on the suffix "aero.linkupnetworks.net" with a prefix formed 514 from the wildcard-terminated reverse mapping of the ASP 515 [RFC3596][RFC4592], and resolves to a DNS PTR resource record. For 516 example, for the ASP '2001:db8:1::/48' within the domain name 517 "linkupnetworks.example.com", the DNS database contains: 519 '*.1.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net. PTR 520 linkupnetworks.example.com' 522 This DNS registration advertises the AERO link's ASPs to prospective 523 correspondent nodes. 525 3.6. AERO Interface Initialization 527 3.6.1. AERO Relay Behavior 529 When a Relay enables an AERO interface, it first assigns an 530 administratively provisioned link-local address fe80::ID to the 531 interface. Each fe80::ID address MUST be unique among all AERO nodes 532 on the link, and MUST NOT collide with any potential AERO addresses 533 nor the special addresses fe80:: and fe80::ffff:ffff:ffff:ffff. (The 534 fe80::ID addresses are typically taken from the available range 535 fe80::/96, e.g., as fe80::1, fe80::2, fe80::3, etc.) The Relay then 536 engages in a dynamic routing protocol session with all Servers on the 537 link (see: Section 3.7), and advertises its assigned ASP prefixes 538 into the native IP Internetwork. 540 Each Relay subsequently maintains an IP forwarding table entry for 541 each ACP covered by its ASP(s), and maintains a neighbor cache entry 542 for each Server on the link. Relays exchange NS/NA messages with 543 AERO link neighbors the same as for any AERO node, however they 544 typically do not perform explicit Neighbor Unreachability Detection 545 (NUD) (see: Section 3.18) since the dynamic routing protocol already 546 provides reachability confirmation. 548 3.6.2. AERO Server Behavior 550 When a Server enables an AERO interface, it assigns an 551 administratively provisioned link-local address fe80::ID the same as 552 for Relays. The Server further configures a DHCPv6 server function 553 to facilitate DHCPv6 PD exchanges with AERO Clients. The Server 554 maintains a neighbor cache entry for each Relay on the link, and 555 manages per-ACP neighbor cache entries and IP forwarding table 556 entries based on control message exchanges. Each Server also engages 557 in a dynamic routing protocol with each Relay on the link (see: 558 Section 3.7). 560 When the Server receives an NS/RS message from a Client on the AERO 561 interface it returns an NA/RA message. The Server further provides a 562 simple link-layer conduit between AERO interface neighbors. 563 Therefore, packets enter the Server's AERO interface from the link 564 layer and are forwarded back out the link layer without ever leaving 565 the AERO interface and therefore without ever disturbing the network 566 layer. 568 3.6.3. AERO Client Behavior 570 When a Client enables an AERO interface, it uses the special address 571 fe80::ffff:ffff:ffff:ffff to obtain one or more ACPs from an AERO 572 Server via DHCPv6 PD. Next, it assigns the corresponding AERO 573 address(es) to the AERO interface and creates a neighbor cache entry 574 for the Server, i.e., the DHCPv6 PD exchange bootstraps 575 autoconfiguration of unique link-local address(es). The Client 576 maintains a neighbor cache entry for each of its Servers and each of 577 its active correspondent Clients. When the Client receives Redirect/ 578 Predirect messages on the AERO interface it updates or creates 579 neighbor cache entries, including link-layer address information. 581 3.6.4. AERO Forwarding Agent Behavior 583 When a Forwarding Agent enables an AERO interface, it assigns the 584 same link-local address(es) as the companion AERO Server. The 585 Forwarding Agent thereafter provides data plane forwarding services 586 based solely on the forwarding information assigned to it by the 587 companion AERO Server. 589 3.7. AERO Routing System 591 The AERO routing system is based on a private instance of the Border 592 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 593 and Servers and does not interact with either the public Internet BGP 594 routing system or the native IP Internetwork interior routing system. 595 Relays advertise only a small and unchanging set of ASPs to the 596 native routing system instead of the full dynamically changing set of 597 ACPs. 599 In a reference deployment, each AERO Server is configured as an 600 Autonomous System Border Router (ASBR) for a stub Autonomous System 601 (AS) using an AS Number (ASN) that is unique within the BGP instance, 602 and each Server further peers with each Relay but does not peer with 603 other Servers. Similarly, Relays do not peer with each other, since 604 they will reliably receive all updates from all Servers and will 605 therefore have a consistent view of the AERO link ACP delegations. 607 Each Server maintains a working set of associated ACPs, and 608 dynamically announces new ACPs and withdraws departed ACPs in its BGP 609 updates to Relays. Clients are expected to remain associated with 610 their current Servers for extended timeframes, however Servers SHOULD 611 selectively suppress BGP updates for impatient Clients that 612 repeatedly associate and disassociate with them in order to dampen 613 routing churn. 615 Each Relay configures a black-hole route for each of its ASPs. By 616 black-holing the ASPs, the Relay will maintain forwarding table 617 entries only for the ACPs that are currently active, and all other 618 ACPs will correctly result in destination unreachable failures due to 619 the black hole route. 621 Scaling properties of the AERO routing system are limited by the 622 number of BGP routes that can be carried by Relays. Assuming O(10^6) 623 as a reasonable maximum number of BGP routes, this means that O(10^6) 624 Clients can be serviced by a single set of Relays. A means of 625 increasing scaling would be to assign a different set of Relays for 626 each set of ASPs. In that case, each Server still peers with each 627 Relay, but the Server institutes route filters so that each set of 628 Relays only receives BGP updates for the ASPs they aggregate. For 629 example, if the ASP for the AERO link is 2001:db8::/32, a first set 630 of Relays could service the ASP segment 2001:db8::/40, a second set 631 of Relays could service 2001:db8:0100::/40, a third set could service 632 2001:db8:0200::/40, etc. 634 Assuming up to O(10^3) sets of Relays, the AERO routing system can 635 then accommodate O(10^9) ACPs with no additional overhead for Servers 636 and Relays (for example, it should be possible to service 4 billion 637 /64 ACPs taken from a /32 ASP and even more for shorter ASPs). In 638 this way, each set of Relays services a specific set of ASPs that 639 they advertise to the native routing system, and each Server 640 configures ASP-specific routes that list the correct set of Relays as 641 next hops. This arrangement also allows for natural incremental 642 deployment, and can support small scale initial deployments followed 643 by dynamic deployment of additional Clients, Servers and Relays 644 without disturbing the already-deployed base. 646 Note that in an alternate routing arrangement each set of Relays 647 could advertise the aggregated ASP for the link into the native 648 routing system even though each Relay services only a segment of the 649 ASP. In that case, a Relay upon receiving a packet with a 650 destination address covered by the ASP segment of another Relay can 651 simply tunnel the packet to the correct Relay. The tradeoff then is 652 the penalty for Relay-to-Relay tunneling compared with reduced 653 routing information in the native routing system. 655 3.8. AERO Interface Neighbor Cache Maintenace 657 Each AERO interface maintains a conceptual neighbor cache that 658 includes an entry for each neighbor it communicates with on the AERO 659 link, the same as for any IPv6 interface [RFC4861]. AERO interface 660 neighbor cache entires are said to be one of "permanent", "static" or 661 "dynamic". 663 Permanent neighbor cache entries are created through explicit 664 administrative action; they have no timeout values and remain in 665 place until explicitly deleted. AERO Relays maintain a permanent 666 neighbor cache entry for each Server on the link, and AERO Servers 667 maintain a permanent neighbor cache entry for each Relay. Each entry 668 maintains the mapping between the neighbor's fe80::ID network-layer 669 address and corresponding link-layer address. 671 Static neighbor cache entries are created through DHCPv6 PD exchanges 672 and remain in place for durations bounded by prefix lifetimes. AERO 673 Servers maintain static neighbor cache entries for the ACPs of each 674 of their associated Clients, and AERO Clients maintain a static 675 neighbor cache entry for each of their associated Servers. When an 676 AERO Server sends a Reply message response to a Client's Solicit, 677 Rebind or Renew message, it creates or updates a static neighbor 678 cache entry based on the Client's DHCP Unique Identifier (DUID) as 679 the Client identifier, the AERO address(es) corresponding to the 680 Client's ACP(s) as the network-layer address(es), the prefix lifetime 681 as the neighbor cache entry lifetime, the Client's encapsulation IP 682 address and UDP port number as the link-layer address and the prefix 683 length(s) as the length to apply to the AERO address(es). When an 684 AERO Client receives a Reply message from a Server, it creates or 685 updates a static neighbor cache entry based on the Reply message 686 link-local source address as the network-layer address, the prefix 687 lifetime as the neighbor cache entry lifetime, and the encapsulation 688 IP source address and UDP source port number as the link-layer 689 address. 691 Dynamic neighbor cache entries are created or updated based on 692 receipt of a Predirect/Redirect message, and are garbage-collected if 693 not used within a bounded timescale. AERO Clients maintain dynamic 694 neighbor cache entries for each of their active correspondent Client 695 ACPs with lifetimes based on IPv6 ND messaging constants. When an 696 AERO Client receives a valid Predirect message it creates or updates 697 a dynamic neighbor cache entry for the Predirect target network-layer 698 and link-layer addresses plus prefix length. The node then sets an 699 "AcceptTime" variable in the neighbor cache entry to ACCEPT_TIME 700 seconds and uses this value to determine whether packets received 701 from the correspondent can be accepted. When an AERO Client receives 702 a valid Redirect message it creates or updates a dynamic neighbor 703 cache entry for the Redirect target network-layer and link-layer 704 addresses plus prefix length. The Client then sets a "ForwardTime" 705 variable in the neighbor cache entry to FORWARD_TIME seconds and uses 706 this value to determine whether packets can be sent directly to the 707 correspondent. The Client also sets a "MaxRetry" variable to 708 MAX_RETRY to limit the number of keepalives sent when a correspondent 709 may have gone unreachable. 711 It is RECOMMENDED that FORWARD_TIME be set to the default constant 712 value 30 seconds to match the default REACHABLE_TIME value specified 713 for IPv6 ND [RFC4861]. 715 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 716 value 40 seconds to allow a 10 second window so that the AERO 717 redirection procedure can converge before AcceptTime decrements below 718 FORWARD_TIME. 720 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 721 for IPv6 ND address resolution in Section 7.3.3 of [RFC4861]. 723 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 724 administratively set, if necessary, to better match the AERO link's 725 performance characteristics; however, if different values are chosen, 726 all nodes on the link MUST consistently configure the same values. 727 Most importantly, ACCEPT_TIME SHOULD be set to a value that is 728 sufficiently longer than FORWARD_TIME to allow the AERO redirection 729 procedure to converge. 731 When there may be a Network Address Translator (NAT) between the 732 Client and the Server, or if the path from the Client to the Server 733 should be tested for reachability, the Client can send periodic RS 734 messages to the Server to receive RA replies. The RS/RA messaging 735 will keep NAT state alive and test Server reachability without 736 disturbing the DHCPv6 server. 738 3.9. AERO Interface Sending Algorithm 740 IP packets enter a node's AERO interface either from the network 741 layer (i.e., from a local application or the IP forwarding system), 742 or from the link layer (i.e., from the AERO tunnel virtual link). 743 Packets that enter the AERO interface from the network layer are 744 encapsulated and admitted into the AERO link, i.e., they are 745 tunnelled to an AERO interface neighbor. Packets that enter the AERO 746 interface from the link layer are either re-admitted into the AERO 747 link or delivered to the network layer where they are subject to 748 either local delivery or IP forwarding. Since each AERO node may 749 have only partial information about neighbors on the link, AERO 750 interfaces may forward packets with link-local destination addresses 751 at a layer below the network layer. This means that AERO nodes act 752 as both IP routers/hosts and sub-IP layer forwarding nodes. AERO 753 interface sending considerations for Clients, Servers and Relays are 754 given below. 756 When an IP packet enters a Client's AERO interface from the network 757 layer, if the destination is covered by an ASP the Client searches 758 for a dynamic neighbor cache entry with a non-zero ForwardTime and an 759 AERO address that matches the packet's destination address. (The 760 destination address may be either an address covered by the 761 neighbor's ACP or the (link-local) AERO address itself.) If there is 762 a match, the Client uses a link-layer address in the entry as the 763 link-layer address for encapsulation then admits the packet into the 764 AERO link. If there is no match, the Client instead uses the link- 765 layer address of a neighboring Server as the link-layer address for 766 encapsulation. 768 When an IP packet enters a Server's AERO interface from the link 769 layer, if the destination is covered by an ASP the Server searches 770 for a neighbor cache entry with an AERO address that matches the 771 packet's destination address. (The destination address may be either 772 an address covered by the neighbor's ACP or the AERO address itself.) 773 If there is a match, the Server uses a link-layer address in the 774 entry as the link-layer address for encapsulation and re-admits the 775 packet into the AERO link. If there is no match, the Server instead 776 uses the link-layer address in a permanent neighbor cache entry for a 777 Relay selected through longest-prefix-match as the link-layer address 778 for encapsulation. 780 When an IP packet enters a Relay's AERO interface from the network 781 layer, the Relay searches its IP forwarding table for an entry that 782 is covered by an ASP and also matches the destination. If there is a 783 match, the Relay uses the link-layer address in the corresponding 784 neighbor cache entry as the link-layer address for encapsulation and 785 admits the packet into the AERO link. When an IP packet enters a 786 Relay's AERO interface from the link-layer, if the destination is not 787 a link-local address and does not match an ASP the Relay removes the 788 packet from the AERO interface and uses IP forwarding to forward the 789 packet to the Internetwork. If the destination address is a link- 790 local address or a non-link-local address that matches an ASP, and 791 there is a more-specific ACP entry in the IP forwarding table, the 792 Relay uses the link-layer address in the corresponding neighbor cache 793 entry as the link-layer address for encapsulation and re-admits the 794 packet into the AERO link. When an IP packet enters a Relay's AERO 795 interface from either the network layer or link-layer, and the 796 packet's destination address matches an ASP but there is no more- 797 specific ACP entry, the Relay drops the packet and returns an ICMP 798 Destination Unreachable message (see: Section 3.14). 800 When an AERO Server receives a packet from a Relay via the AERO 801 interface, the Server MUST NOT forward the packet back to the same or 802 a different Relay. 804 When an AERO Relay receives a packet from a Server via the AERO 805 interface, the Relay MUST NOT forward the packet back to the same 806 Server. 808 When an AERO node re-admits a packet into the AERO link without 809 involving the network layer, the node MUST NOT decrement the network 810 layer TTL/Hop-count. 812 When an AERO node forwards a data packet to the primary link-layer 813 address of a Server, it may receive Redirect messages with an SLLAO 814 that include the link-layer address of an AERO Forwarding Agent. The 815 AERO node SHOULD record the link-layer address in the neighbor cache 816 entry for the neighbor and send subsequent data packets via this 817 address instead of the Server's primary address (see: Section 3.16). 819 3.10. AERO Interface Encapsulation and Re-encapsulation 821 AERO interfaces encapsulate IP packets according to whether they are 822 entering the AERO interface from the network layer or if they are 823 being re-admitted into the same AERO link they arrived on. This 824 latter form of encapsulation is known as "re-encapsulation". 826 The AERO interface encapsulates packets per the Generic UDP 827 Encapsulation (GUE) encapsulation procedures in 828 [I-D.ietf-nvo3-gue][I-D.herbert-gue-fragmentation], or through an 829 alternate encapsulation format (see: Appendix A). For packets 830 entering the AERO link from the IP layer, the AERO interface copies 831 the "TTL/Hop Limit", "Type of Service/Traffic Class" [RFC2983], "Flow 832 Label"[RFC6438].(for IPv6) and "Congestion Experienced" [RFC3168] 833 values in the packet's IP header into the corresponding fields in the 834 encapsulation IP header. For packets undergoing re-encapsulation 835 within the AERO link, the AERO interface instead copies the "TTL/Hop 836 Limit", "Type of Service/Traffic Class", "Flow Label" and "Congestion 837 Experienced" values in the original encapsulation IP header into the 838 corresponding fields in the new encapsulation IP header, i.e., the 839 values are transferred between encapsulation headers and *not* copied 840 from the encapsulated packet's network-layer header. 842 When GUE encapsulation is used, the AERO interface next sets the UDP 843 source port to a constant value that it will use in each successive 844 packet it sends, and sets the UDP length field to the length of the 845 encapsulated packet plus 8 bytes for the UDP header itself plus the 846 length of the GUE header (or 0 if GUE direct IP encapsulation is 847 used). For packets sent to a Server, the AERO interface sets the UDP 848 destination port to 8060, i.e., the IANA-registered port number for 849 AERO. For packets sent to a correspondent Client, the AERO interface 850 sets the UDP destination port to the port value stored in the 851 neighbor cache entry for this correspondent. The AERO interface then 852 either includes or omits the UDP checksum according to the GUE 853 specification. 855 For IPv4 encapsulation, the AERO interface sets the DF bit as 856 discussed in Section 3.13. 858 3.11. AERO Interface Decapsulation 860 AERO interfaces decapsulate packets destined either to the AERO node 861 itself or to a destination reached via an interface other than the 862 AERO interface the packet was received on. Decapsulation is per the 863 procedures specified for the appropriate encapsulation format. 865 3.12. AERO Interface Data Origin Authentication 867 AERO nodes employ simple data origin authentication procedures for 868 encapsulated packets they receive from other nodes on the AERO link. 869 In particular: 871 o AERO Servers and Relays accept encapsulated packets with a link- 872 layer source address that matches a permanent neighbor cache 873 entry. 875 o AERO Servers accept authentic encapsulated DHCPv6 messages from 876 Clients, and create or update a static neighbor cache entry for 877 the Client based on the specific DHCPv6 message type. 879 o AERO Clients and Servers accept encapsulated packets if there is a 880 static neighbor cache entry with a link-layer address that matches 881 the packet's link-layer source address. 883 o AERO Clients, Servers and Relays accept encapsulated packets if 884 there is a dynamic neighbor cache entry with an AERO address that 885 matches the packet's network-layer source address, with a link- 886 layer address that matches the packet's link-layer source address, 887 and with a non-zero AcceptTime. 889 Note that this simple data origin authentication is effective in 890 environments in which link-layer addresses cannot be spoofed. In 891 other environments, each AERO message must include a signature that 892 the recipient can use to authenticate the message origin. 894 3.13. AERO Interface Packet Size Issues 896 The AERO interface is the node's attachment to the AERO link. The 897 AERO interface acts as a tunnel ingress when it sends a packet to an 898 AERO link neighbor and as a tunnel egress when it receives a packet 899 from an AERO link neighbor. AERO interfaces observe the packet 900 sizing considerations for tunnels discussed in 901 [I-D.ietf-intarea-tunnels] and as specified below. 903 IPv6 specifies a minimum link Maximum Transmission Unit (MTU) of 1280 904 bytes [RFC2460]. Although IPv4 specifies a smaller minimum link MTU 905 of 68 bytes [RFC0791], AERO interfaces also observe the IPv6 minimum 906 for IPv4 even if the packet may incur fragmentation in the network. 908 IPv6 specifies a minimum Maximum Reassembly Unit (MRU) of 1500 bytes 909 [RFC2460], while the minimum MRU for IPv4 is only 576 bytes [RFC1122] 910 (note that IPv6 over IPv4 tunnels assume a larger MRU than the IPv4 911 minimum). 913 Original sources expect that IP packets will either be delivered to 914 the final destination or a suitable Packet Too Big (PTB) message 915 returned. However, PTB messages may be crafted for malicious 916 purposes such as denial of service, or lost in the network [RFC2923] 917 resulting in failure of the IP Path MTU Discovery (PMTUD) mechanisms 918 [RFC1191][RFC1981]. For these reasons, AERO links employ operational 919 procedures that avoid all interactions with PMTUD. 921 AERO Servers advertise an MTU that MUST be no smaller than 1280 922 bytes, MUST be no larger than the minimum MRU among all nodes on the 923 AERO link minus the encapsulation overhead ("ENCAPS"), and SHOULD be 924 no smaller than 1500 bytes. AERO Servers advertise a Maximum 925 Fragment Unit (MFU) as the maximum size for the fragments of an 926 encapsulated packet that require fragmentation. The MFU value MUST 927 be no larger than 1280 bytes unless there is operational assurance 928 that a larger size can traverse the link along all paths without 929 fragmentation, and MUST be no larger than (MTU+ENCAPS). 931 AERO Clients set the AERO interface MTU/MFU based on the values 932 advertised by their Server, and configure an MRU large enough to 933 reassemble packets up to (MTU+ENCAPS) bytes. 935 All AERO nodes on the link MUST configure the same MTU/MFU values for 936 reasons cited in [RFC3819][RFC4861], e.g., to support multicast. 938 All AERO nodes on the link MUST configure a minimum MRU of 939 (1500+ENCAPS) bytes, and SHOULD be capable of setting a larger MRU 940 accoding to the Server's advertised MTU. 942 In accordnace with these requirements, the ingress accommodates 943 packets of various sizes as follows: 945 o First, for original IPv4 packets that are larger than the AERO 946 interface MTU and with the DF bit set to 0, the ingress uses IPv4 947 fragmentation to break the packet into a minimum number of non- 948 overlapping fragments where the first fragment is no larger than 949 (MFU-ENCAPS) bytes and the remaining fragments are no larger than 950 the first. 952 o Next, for each original IP packet or fragment that is no larger 953 than (MFU-ENCAPS) bytes, the ingress encapsulates the packet and 954 admits it into the tunnel. For IPv4 AERO links, the ingress sets 955 the Don't Fragment (DF) bit to 0 so that these packets will be 956 delivered to the egress even if some fragmentation occurs in the 957 network. 959 o For all other original IP packets or fragments, if the packet is 960 larger than the AERO interface MTU, the ingress drops the packet 961 and returns a PTB message to the original source. Otherwise, the 962 ingress encapsulates the packet and fragments the encapsulated 963 packet into a minimum number of non-overlapping fragments where 964 the first fragment is no larger than MFU bytes and the remaining 965 fragments are no larger than the first. The ingress then admits 966 the fragments into the tunnel, and for IPv4 sets the DF bit to 0 967 in the IP encapsulation header. These fragmented encapsulated 968 packets will be delivered to the egress, which reassembles them 969 into a whole packet. 971 Several factors must be considered when fragmentation of the 972 encapsulated packet is needed. For AERO links over IPv4, the IP ID 973 field is only 16 bits in length, meaning that fragmentation at high 974 data rates could result in data corruption due to reassembly 975 misassociations [RFC6864][RFC4963]. For AERO links over both IPv4 976 and IPv6, studies have also shown that IP fragments are dropped 977 unconditionally over some network paths [I-D.taylor-v6ops-fragdrop]. 978 In environments where IP fragmentation issues could result in 979 operational problems, the ingress SHOULD employ intermediate-layer 980 fragmentation (see: [RFC2764] and [I-D.herbert-gue-fragmentation]) 981 before appending the outer encapsulation headers to each fragment. 983 Since the encapsulation fragment header reduces the room available 984 for packet data, but the original source has no way to control its 985 insertion, the ingress MUST include the fragment header length in the 986 ENCAPS length even for packets in which the header is absent. 988 3.14. AERO Interface Error Handling 990 When an AERO node admits encapsulated packets into the AERO 991 interface, it may receive link-layer (L2) or network-layer (L3) error 992 indications. 994 An L2 error indication is an ICMP error message generated by a router 995 on the path to the neighbor or by the neighbor itself. The message 996 includes an IP header with the address of the node that generated the 997 error as the source address and with the link-layer address of the 998 AERO node as the destination address. 1000 The IP header is followed by an ICMP header that includes an error 1001 Type, Code and Checksum. Valid type values include "Destination 1002 Unreachable", "Time Exceeded" and "Parameter Problem" 1003 [RFC0792][RFC4443]. (AERO interfaces ignore all L2 IPv4 1004 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1005 only emit packets that are guaranteed to be no larger than the IP 1006 minimum link MTU.) 1008 The ICMP header is followed by the leading portion of the packet that 1009 generated the error, also known as the "packet-in-error". For 1010 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1011 much of invoking packet as possible without the ICMPv6 packet 1012 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1013 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1014 "Internet Header + 64 bits of Original Data Datagram", however 1015 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1016 ICMP datagram SHOULD contain as much of the original datagram as 1017 possible without the length of the ICMP datagram exceeding 576 1018 bytes". 1020 The L2 error message format is shown in Figure 3: 1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 ~ ~ 1024 | L2 IP Header of | 1025 | error message | 1026 ~ ~ 1027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1028 | L2 ICMP Header | 1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1030 ~ ~ P 1031 | IP and other encapsulation | a 1032 | headers of original L3 packet | c 1033 ~ ~ k 1034 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1035 ~ ~ t 1036 | IP header of | 1037 | original L3 packet | i 1038 ~ ~ n 1039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1040 ~ ~ e 1041 | Upper layer headers and | r 1042 | leading portion of body | r 1043 | of the original L3 packet | o 1044 ~ ~ r 1045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1047 Figure 3: AERO Interface L2 Error Message Format 1049 The AERO node rules for processing these L2 error messages is as 1050 follows: 1052 o When an AERO node receives an L2 Parameter Problem message, it 1053 processes the message the same as described as for ordinary ICMP 1054 errors in the normative references [RFC0792][RFC4443]. 1056 o When an AERO node receives persistent L2 IPv4 Time Exceeded 1057 messages, the IP ID field may be wrapping before earlier fragments 1058 have been processed. In that case, the node SHOULD begin 1059 including integrity checks and/or institute rate limits for 1060 subseqent packets. 1062 o When an AERO Client receives persistent L2 Destination Unreachable 1063 messages in response to tunneled packets that it sends to one of 1064 its dynamic neighbor correspondents, the Client SHOULD test the 1065 path to the correspondent using Neighbor Unreachability Detection 1066 (NUD) (see Section 3.18). If NUD fails, the Client SHOULD set 1067 ForwardTime for the corresponding dynamic neighbor cache entry to 1068 0 and allow future packets destined to the correspondent to flow 1069 through a Server. 1071 o When an AERO Client receives persistent L2 Destination Unreachable 1072 messages in response to tunneled packets that it sends to one of 1073 its static neighbor Servers, the Client SHOULD test the path to 1074 the Server using NUD. If NUD fails, the Client SHOULD delete the 1075 neighbor cache entry and attempt to associate with a new Server. 1077 o When an AERO Server receives persistent L2 Destination Unreachable 1078 messages in response to tunneled packets that it sends to one of 1079 its static neighbor Clients, the Server SHOULD test the path to 1080 the Client using NUD. If NUD fails, the Server SHOULD cancel the 1081 DHCPv6 PD for the Client's ACP, withdraw its route for the ACP 1082 from the AERO routing system and delete the neighbor cache entry 1083 (see Section 3.18 and Section 3.19). 1085 o When an AERO Relay or Server receives an L2 Destination 1086 Unreachable message in response to a tunneled packet that it sends 1087 to one of its permanent neighbors, it discards the message since 1088 the AERO routing system is likely in a temporary transitional 1089 state that will soon re-converge. In case of a prolonged outage, 1090 however, the AERO routing system will compensate for Relays or 1091 Servers that have fallen silent. 1093 When an AERO Relay receives an L3 packet for which the destination 1094 address is covered by an ASP, if there is no more-specific routing 1095 information for the destination the Relay drops the packet and 1096 returns an L3 Destination Unreachable message. The Relay first 1097 writes the IP source address of the original L3 packet as the 1098 destination address of the L3 Destination Unreachable message and 1099 determines the next hop to the destination. If the next hop is 1100 reached via the AERO interface, the Relay uses the IPv6 address "::" 1101 or the IPv4 address "0.0.0.0" as the IP source address of the L3 1102 Destination Unreachable message and forwards the message to the next 1103 hop within the AERO interface. Otherwise, the Relay uses one of its 1104 non link-local addresses as the source address of the L3 Destination 1105 Unreachable message and forwards the message via a link outside the 1106 AERO interface. 1108 When an AERO node receives an encapsulated packet for which the 1109 reassembly buffer it too small, it drops the packet and returns an L3 1110 Packet To Big (PTB) message. The node first writes the IP source 1111 address of the original L3 packet as the destination address of the 1112 L3 PTB message and determines the next hop to the destination. If 1113 the next hop is reached via the AERO interface, the node uses the 1114 IPv6 address "::" or the IPv4 address "0.0.0.0" as the IP source 1115 address of the L3 PTB message and forwards the message to the next 1116 hop within the AERO interface. Otherwise, the node uses one of its 1117 non link-local addresses as the source address of the L3 PTB message 1118 and forwards the message via a link outside the AERO interface. 1120 When an AERO node receives any L3 error message via the AERO 1121 interface, it examines the destination address in the L3 IP header of 1122 the message. If the next hop toward the destination address of the 1123 error message is via the AERO interface, the node re-encapsulates and 1124 forwards the message to the next hop within the AERO interface. 1125 Otherwise, if the source address in the L3 IP header of the message 1126 is the IPv6 address "::" or the IPv4 address "0.0.0.0", the node 1127 writes one of its non link-local addresses as the source address of 1128 the L3 message and recalculates the IP and/or ICMP checksums. The 1129 node finally forwards the message via a link outside of the AERO 1130 interface. 1132 3.15. AERO Router Discovery, Prefix Delegation and Address 1133 Configuration 1135 3.15.1. AERO DHCPv6 Service Model 1137 Each AERO Server configures a DHCPv6 server function to facilitate PD 1138 requests from Clients. Each Server is provisioned with a database of 1139 ACP-to-Client ID mappings for all Clients enrolled in the AERO 1140 system, as well as any information necessary to authenticate each 1141 Client. The Client database is maintained by a central 1142 administrative authority for the AERO link and securely distributed 1143 to all Servers, e.g., via the Lightweight Directory Access Protocol 1144 (LDAP) [RFC4511] or a similar distributed database service. 1146 Therefore, no Server-to-Server DHCPv6 PD delegation state 1147 synchronization is necessary, and Clients can optionally hold 1148 separate delegations for the same ACPs from multiple Servers. In 1149 this way, Clients can associate with multiple Servers, and can 1150 receive new delegations from new Servers before deprecating 1151 delegations received from existing Servers. This provides the Client 1152 with a natural fault-tolerance and/or load balancing profile. 1154 AERO Clients and Servers exchange Client link-layer address 1155 information using an option format similar to the Client Link Layer 1156 Address Option (CLLAO) defined in [RFC6939]. Due to practical 1157 limitations of CLLAO, however, AERO interfaces instead use Vendor- 1158 Specific Information Options as described in the following sections. 1160 3.15.2. AERO Client Behavior 1162 AERO Clients discover the link-layer addresses of AERO Servers via 1163 static configuration (e.g., from a flat-file map of Server addresses 1164 and locations), or through an automated means such as DNS name 1165 resolution. In the absence of other information, the Client resolves 1166 the FQDN "linkupnetworks.[domainname]" where "linkupnetworks" is a 1167 constant text string and "[domainname]" is a DNS suffix for the 1168 Client's underlying network (e.g., "example.com"). After discovering 1169 the link-layer addresses, the Client associates with one or more of 1170 the corresponding Servers. 1172 To associate with a Server, the Client acts as a requesting router to 1173 request ACPs through a two-message (i.e., Solicit/Reply) DHCPv6 PD 1174 exchange [RFC3315][RFC3633]. The Client's Solicit message includes 1175 fe80::ffff:ffff:ffff:ffff as the IPv6 source address, 1176 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address 1177 and the link-layer address of the Server as the link-layer 1178 destination address. The Solicit message also includes a Client 1179 Identifier option with a DUID and an Identity Association for Prefix 1180 Delegation (IA_PD) option. If the Client is pre-provisioned with 1181 ACPs associated with the AERO service, it MAY also include the ACPs 1182 in the IA_PD to indicate its preferences to the DHCPv6 server. 1184 The Client also SHOULD include an AERO Link-registration Request 1185 (ALREQ) option in the Solicit message to register one or more links 1186 with the Server. The Server will include an AERO Link-registration 1187 Reply (ALREP) option in the corresponding Reply message as specified 1188 in Section 3.15.3. (The Client MAY omit the ALREQ option, in which 1189 case the Server will still include an ALREP option in its Reply with 1190 "Link ID" set to 0.) 1192 The format for the ALREQ option is shown in Figure 4: 1194 0 1 2 3 1195 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 1196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1197 | OPTION_VENDOR_OPTS | option-len (1) | 1198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1199 | enterprise-number = 45282 | 1200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1201 | opt-code = OPTION_ALREQ (0) | option-len (2) | 1202 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1203 | Link ID | DSCP #1 |Prf| DSCP #2 |Prf| ... 1204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1206 Figure 4: AERO Link-registration Request (ALREQ) Option 1208 In the above format, the Client sets 'option-code' to 1209 OPTION_VENDOR_OPTS, sets 'option-len (1)' to the length of the option 1210 following this field, sets 'enterprise-number' to 45282 (see: "IANA 1211 Considerations"), sets opt-code to the value 0 ("OPTION_ALREQ") and 1212 sets 'option-len (2)' to the length of the remainder of the option. 1213 The Client includes appropriate 'Link ID, 'DSCP' and 'Prf' values for 1214 the underlying interface over which the Solicit message will be 1215 issued the same as specified for an S/TLLAO Section 3.4. The Server 1216 will register each value with the Link ID in the Client's neighbor 1217 cache entry. The Client finally includes any necessary 1218 authentication options to identify itself to the DHCPv6 server, and 1219 sends the encapsulated Solicit message via the underlying interface 1220 corresponding to Link ID. (Note that this implies that the Client 1221 must send additional Rebind messages with ALREQ options to the server 1222 following the initial PD exchange using different underlying 1223 interfaces and their corresponding Link IDs if it wishes to register 1224 additional link-layer addresses and their associated DSCPs.) 1226 When the Client receives its ACP via a Reply from the AERO Server, it 1227 creates a static neighbor cache entry with the Server's link-local 1228 address as the network-layer address and the Server's encapsulation 1229 address as the link-layer address. The Client then considers the 1230 link-layer address of the Server as the primary default encapsulation 1231 address for forwarding packets for which no more-specific forwarding 1232 information is available. The Client further applies the MTU value 1233 in the ALREP option to its AERO interface, then caches any ASPs 1234 included in the ALREP option as ASPs to apply to the AERO link. 1236 Next, the Client autoconfigures an AERO address for each of the 1237 delegated ACPs, assigns the address(es) to the AERO interface and 1238 sub-delegates the ACPs to its attached EUNs and/or the Client's own 1239 internal virtual interfaces. Alternatively, the Client can configure 1240 as many addresses as it wants from /64 prefixes taken from the ACPs 1241 and assign them to either an internal virtual interface ("weak end- 1242 system") or to the AERO interface itself ("strong end-system") 1243 [RFC1122] while black-holing the remaining portions of the /64s. 1244 Finally, the Client assigns one or more default IP routes to the AERO 1245 interface with the link-local address of a Server as the next hop. 1247 After AERO address autoconfiguration, the Client SHOULD begin using 1248 the AERO address as the source address for further DHCPv6 messaging. 1249 The Client subsequently renews its ACP delegations through each of 1250 its Servers by sending Renew messages with the link-layer address of 1251 a Server as the link-layer destination address and the same options 1252 that were used in the initial PD request. Note that if the Client 1253 does not issue a Renew before the delegations expire (e.g., if the 1254 Client has been out of touch with the Server for a considerable 1255 amount of time) it must re-initiate the DHCPv6 PD procedure. 1257 Since the addresses assigned to the Client's AERO interface are 1258 obtained from the unique ACP delegations it receives, there is no 1259 need for DAD on AERO links. Other nodes maliciously attempting to 1260 hijack addresses from an authorized Client's ACPs will be denied 1261 access to the network by the Server due to an unacceptable link-layer 1262 address and/or security parameters (see: Security Considerations). 1264 When a Client attempts to perform a DHCPv6 PD exchange with a Server 1265 that is too busy to service the request, the Client may receive 1266 either a "NoPrefixAvail" status code in the Server's Reply per 1267 [RFC3633] or no reply at all. In that case, the Client SHOULD 1268 discontinue DHCPv6 PD attempts through this Server and try another 1269 Server. 1271 3.15.2.1. Autoconfiguration for Constrained Platforms 1273 On some platforms (e.g., popular cell phone operating systems), the 1274 act of assigning a default IPv6 route and/or assigning an address to 1275 an interface may not be permitted from a user application due to 1276 security policy. Typically, those platforms include a TUN/TAP 1277 interface [TUNTAP] that acts as a point-to-point conduit between user 1278 applications and the AERO interface. In that case, the Client can 1279 instead generate a "synthesized RA" message. The message conforms to 1280 [RFC4861] and is prepared as follows: 1282 o the IPv6 source address is the Client's AERO address 1284 o the IPv6 destination address is all-nodes multicast 1286 o the Router Lifetime is set to a time that is no longer than the 1287 ACP DHCPv6 lifetime 1289 o the message does not include a Source Link Layer Address Option 1290 (SLLAO) 1292 o the message includes a Prefix Information Option (PIO) with a /64 1293 prefix taken from the ACP as the prefix for autoconfiguration 1295 The Client then sends the synthesized RA message via the TUN/TAP 1296 interface, where the operating system kernel will interpret it as 1297 though it were generated by an actual router. The operating system 1298 will then install a default route and use StateLess Address 1299 AutoConfiguration (SLAAC) to configure an IPv6 address on the TUN/TAP 1300 interface. Methods for similarly installing an IPv4 default route 1301 and IPv4 address on the TUN/TAP interface are based on synthesized 1302 DHCPv4 messages [RFC2131]. 1304 3.15.3. AERO Server Behavior 1306 AERO Servers configure a DHCPv6 server function on their AERO links. 1307 AERO Servers arrange to add their encapsulation layer IP addresses 1308 (i.e., their link-layer addresses) to a static map of Server 1309 addresses for the link and/or the DNS resource records for the FQDN 1310 "linkupnetworks.[domainname]" before entering service. 1312 When an AERO Server receives a prospective Client's Solicit on its 1313 AERO interface, and the Server is too busy to service the message, it 1314 SHOULD return a Reply with status code "NoPrefixAvail" per [RFC3633]. 1315 Otherwise, the Server authenticates the message. If authentication 1316 succeeds, the Server determines the correct ACPs to delegate to the 1317 Client by searching the Client database. 1319 When the Server delegates the ACPs, it also creates IP forwarding 1320 table entries so that the AERO routing system will propagate the ACPs 1321 to all Relays that aggregate the corresponding ASP (see: 1322 Section 3.7). Next, the Server prepares a Reply message to send to 1323 the Client while using fe80::ID as the IPv6 source address, the link- 1324 local address taken from the Client's Solicit as the IPv6 destination 1325 address, the Server's link-layer address as the source link-layer 1326 address, and the Client's link-layer address as the destination link- 1327 layer address. The server also includes IA_PD options with the 1328 delegated ACPs. Since the Client may experience a fault that 1329 prevents it from issuing a Release before departing from the network, 1330 Servers should set a short prefix lifetime (e.g., 40 seconds) so that 1331 stale prefix delegation state can be flushed out of the network. 1333 The Server also includes an ALREP option that includes configuration 1334 information pertaining to the Client's ALREQ. (Note that if the 1335 Client did not include an ALREQ option in its DHCPv6 message, the 1336 Server MUST still include an ALREP option in the corresponding 1337 reply.)The ALREP option is formatted as shown in Figure 5: 1339 0 1 2 3 1340 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 1341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1342 | OPTION_VENDOR_OPTS | option-len (1) | 1343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1344 | enterprise-number = 45282 | 1345 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1346 | opt-code = OPTION_ALREP (1) | option-len (2) | 1347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1348 | Link ID | Reserved | UDP Port Number | 1349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1350 | | 1351 + + 1352 | | 1353 + IP Address + 1354 | | 1355 + + 1356 | | 1357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1358 |Maximum Transmission Unit (MTU)| Maximum Fragment Unit (MFU) | 1359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1360 | | 1361 + AERO Service Prefix (ASP) #1 +-+-+-+-+-+-+-+-+ 1362 | | Prefix Len | 1363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1364 | | 1365 + AERO Service Prefix (ASP) #2 +-+-+-+-+-+-+-+-+ 1366 | | Prefix Len | 1367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1368 ~ ~ 1369 ~ ~ 1371 Figure 5: AERO Link-registration Reply (ALREP) Option 1373 In the ALREP, the Server sets 'option-code' to OPTION_VENDOR_OPTS, 1374 sets 'option-length (1)' to the length of the option, sets 1375 'enterprise-number' to 45282 (see: "IANA Considerations"), sets opt- 1376 code to OPTION_ALREP (1), and sets 'option-len (2)' to the length of 1377 the remainder of the option. Next, the Server sets 'Link ID' to the 1378 same value that appeared in the ALREQ (or '0' if the Client did not 1379 include an ALREQ), sets Reserved to 0 and sets 'UDP Port Number' and 1380 'IP address' to the link-layer address observed in the Client's 1381 DHCPv6 message. 1383 The Server next sets MTU and MFU according to the considerations 1384 specified in Section 3.13. 1386 The Server finally includes one or more ASP with the IP prefix as it 1387 would appear in the interface identifier portion of the corresponding 1388 AERO address (see: Section 3.3), except that the low-order 8 bits of 1389 the ASP field encode the prefix length instead of the low-order 8 1390 bits of the prefix. The longest prefix that can therefore appear as 1391 an ASP is /56 for IPv6 or /24 for IPv4. 1393 When the Server admits the Reply message into the AERO interface, it 1394 creates a static neighbor cache entry for the Client based on the 1395 DUID and AERO addresses with lifetime set to no more than the 1396 delegation lifetimes and the Client's link-layer address as the link- 1397 layer address for the Link ID specified in the ALREQ. The Server 1398 then uses the Client link-layer address information in the ALREQ 1399 option as the link-layer address for encapsulation based on the 1400 (DSCP, Prf) information. 1402 After the initial DHCPv6 PD exchange, the AERO Server maintains the 1403 neighbor cache entry for the Client until the delegation lifetimes 1404 expire. If the Client issues a Renew, the Server extends the 1405 lifetimes. If the Client issues a Release, or if the Client does not 1406 issue a Renew before the lifetime expires, the Server deletes the 1407 neighbor cache entry for the Client and withdraws the IP routes from 1408 the AERO routing system. 1410 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1412 AERO Clients and Servers are always on the same link (i.e., the AERO 1413 link) from the perspective of DHCPv6. However, in some 1414 implementations the DHCPv6 server and AERO interface driver may be 1415 located in separate modules. In that case, the Server's AERO 1416 interface driver module can act as a Lightweight DHCPv6 Relay Agent 1417 (LDRA)[RFC6221] to relay DHCPv6 messages to and from the DHCPv6 1418 server module. 1420 When the LDRA receives a DHCPv6 message from a client, it prepares an 1421 ALREP option the same as described above then wraps the option in a 1422 Relay-Supplied DHCP Option option (RSOO) [RFC6422]. The LDRA then 1423 incorporates the option into the Relay-Forward message and forwards 1424 the message to the DHCPv6 server. 1426 When the DHCPv6 server receives the Relay-Forward message, it caches 1427 the ALREP option and authenticates the encapsulated DHCPv6 message. 1428 The DHCPv6 server subsequently ignores the ALREQ option itself, since 1429 the relay has already included the ALREP option. 1431 When the DHCPv6 server prepares a Reply message, it then includes the 1432 ALREP option in the body of the message along with any other options, 1433 then wraps the message in a Relay-Reply message. The DHCPv6 server 1434 then delivers the Relay-Reply message to the LDRA, which discards the 1435 Relay-Reply wrapper and delivers the DHCPv6 message to the Client. 1437 3.15.4. Deleting Link Registrations 1439 After an AERO Client registers its Link IDs and their associated 1440 (DSCP,Prf) values with the AERO Server, the Client may wish to delete 1441 one or more Link registrations, e.g., if an underlying link becomes 1442 unavailable. To do so, the Client prepares a Rebind message that 1443 includes an AERO Link-registration Delete (ALDEL) option and sends 1444 the Rebind message to the Server over any available underlying link. 1445 The ALDEL option is formatted as shown in Figure 6: 1447 0 1 2 3 1448 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 1449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1450 | OPTION_VENDOR_OPTS | option-len (1) | 1451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1452 | enterprise-number = 45282 | 1453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1454 | opt-code = OPTION_ALDEL (2) | option-len (2) | 1455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1456 | Link ID #1 | Link ID #2 | Link ID #3 | ... 1457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1459 Figure 6: AERO Link-registration Delete (ALDEL) Option 1461 In the ALDEL, the Client sets 'option-code' to OPTION_VENDOR_OPTS, 1462 sets 'option-length (1)' to the length of the option, sets 1463 'enterprise-number' to 45282 (see: "IANA Considerations"), sets 1464 optcode to OPTION_ALDEL (2), and sets 'option-len (2)' to the length 1465 of the remainder of the option. Next, the Server includes each 'Link 1466 ID' value that it wishes to delete. 1468 If the Client wishes to discontinue use of a Server and thereby 1469 delete all of its Link ID associations, it must issue a Release to 1470 delete the entire neighbor cache entry, i.e., instead of issuing a 1471 Rebind with one or more ALDEL options. 1473 3.16. AERO Forwarding Agent Behavior 1475 AERO Servers MAY associate with one or more companion AERO Forwarding 1476 Agents as platforms for offloading high-speed data plane traffic. 1477 When an AERO Server receives a Client's Solicit/Renew/Rebind/Release 1478 message, it services the message then forwards the corresponding 1479 Reply message to the Forwarding Agent. When the Forwarding Agent 1480 receives the Reply message, it creates, updates or deletes a neighbor 1481 cache entry with the Client's AERO address and link-layer information 1482 included in the Reply message. The Forwarding Agent then forwards 1483 the Reply message back to the AERO Server, which forwards the message 1484 to the Client. In this way, Forwarding Agent state is managed in 1485 conjunction with Server state, with the Client responsible for 1486 reliability. 1488 When an AERO Server receives a data packet on an AERO interface with 1489 a network layer destination address for which it has distributed 1490 forwarding information to a Forwarding Agent, the Server returns a 1491 Redirect message to the source neighbor (subject to rate limiting) 1492 then forwards the data packet as usual. The Redirect message 1493 includes a TLLAO with the link-layer address of the Forwarding 1494 Engine. 1496 When the source neighbor receives the Redirect message, it SHOULD 1497 record the link-layer address in the TLLAO as the encapsulation 1498 addresses to use for sending subsequent data packets. However, the 1499 source MUST continue to use the primary link-layer address of the 1500 Server as the encapsulation address for sending control messages. 1502 3.17. AERO Intradomain Route Optimization 1504 When a source Client forwards packets to a prospective correspondent 1505 Client within the same AERO link domain (i.e., one for which the 1506 packet's destination address is covered by an ASP), the source Client 1507 MAY initiate an intra-domain AERO route optimization procedure. It 1508 is important to note that this procedure is initiated by the Client; 1509 if the procedure were initiated by the Server, the Server would have 1510 no way of knowing whether the Client was actually able to contact the 1511 correspondent over the route-optimized path. 1513 The procedure is based on an exchange of IPv6 ND messages using a 1514 chain of AERO Servers and Relays as a trust basis. This procedure is 1515 in contrast to the Return Routability procedure required for route 1516 optimization to a correspondent Client located in the Internet as 1517 described in Section 3.22. The following sections specify the AERO 1518 intradomain route optimization procedure. 1520 3.17.1. Reference Operational Scenario 1522 Figure 7 depicts the AERO intradomain route optimization reference 1523 operational scenario, using IPv6 addressing as the example (while not 1524 shown, a corresponding example for IPv4 addressing can be easily 1525 constructed). The figure shows an AERO Relay ('R1'), two AERO 1526 Servers ('S1', 'S2'), two AERO Clients ('C1', 'C2') and two ordinary 1527 IPv6 hosts ('H1', 'H2'): 1529 +--------------+ +--------------+ +--------------+ 1530 | Server S1 | | Relay R1 | | Server S2 | 1531 +--------------+ +--------------+ +--------------+ 1532 fe80::2 fe80::1 fe80::3 1533 L2(S1) L2(R1) L2(S2) 1534 | | | 1535 X-----+-----+------------------+-----------------+----+----X 1536 | AERO Link | 1537 L2(A) L2(B) 1538 fe80::2001:db8:0:0 fe80::2001:db8:1:0 1539 +--------------+ +--------------+ 1540 |AERO Client C1| |AERO Client C2| 1541 +--------------+ +--------------+ 1542 2001:DB8:0::/48 2001:DB8:1::/48 1543 | | 1544 .-. .-. 1545 ,-( _)-. 2001:db8:0::1 2001:db8:1::1 ,-( _)-. 1546 .-(_ IP )-. +---------+ +---------+ .-(_ IP )-. 1547 (__ EUN )--| Host H1 | | Host H2 |--(__ EUN ) 1548 `-(______)-' +---------+ +---------+ `-(______)-' 1550 Figure 7: AERO Reference Operational Scenario 1552 In Figure 7, Relay ('R1') assigns the address fe80::1 to its AERO 1553 interface with link-layer address L2(R1), Server ('S1') assigns the 1554 address fe80::2 with link-layer address L2(S1),and Server ('S2') 1555 assigns the address fe80::3 with link-layer address L2(S2). Servers 1556 ('S1') and ('S2') next arrange to add their link-layer addresses to a 1557 published list of valid Servers for the AERO link. 1559 AERO Client ('C1') receives the ACP 2001:db8:0::/48 in a DHCPv6 PD 1560 exchange via AERO Server ('S1') then assigns the address 1561 fe80::2001:db8:0:0 to its AERO interface with link-layer address 1562 L2(C1). Client ('C1') configures a default route and neighbor cache 1563 entry via the AERO interface with next-hop address fe80::2 and link- 1564 layer address L2(S1), then sub-delegates the ACP to its attached 1565 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1566 address 2001:db8:0::1. 1568 AERO Client ('C2') receives the ACP 2001:db8:1::/48 in a DHCPv6 PD 1569 exchange via AERO Server ('S2') then assigns the address 1570 fe80::2001:db8:1:0 to its AERO interface with link-layer address 1571 L2(C2). Client ('C2') configures a default route and neighbor cache 1572 entry via the AERO interface with next-hop address fe80::3 and link- 1573 layer address L2(S2), then sub-delegates the ACP to its attached 1574 EUNs. IPv6 host ('H2') connects to the EUN, and configures the 1575 address 2001:db8:1::1. 1577 3.17.2. Concept of Operations 1579 Again, with reference to Figure 7, when source host ('H1') sends a 1580 packet to destination host ('H2'), the packet is first forwarded over 1581 the source host's attached EUN to Client ('C1'). Client ('C1') then 1582 forwards the packet via its AERO interface to Server ('S1') and also 1583 sends a Predirect message toward Client ('C2') via Server ('S1'). 1584 Server ('S1') then re-encapsulates and forwards both the packet and 1585 the Predirect message out the same AERO interface toward Client 1586 ('C2') via Relay ('R1'). 1588 When Relay ('R1') receives the packet and Predirect message, it 1589 consults its forwarding table to discover Server ('S2') as the next 1590 hop toward Client ('C2'). Relay ('R1') then forwards both the packet 1591 and the Predirect message to Server ('S2'), which then forwards them 1592 to Client ('C2'). 1594 After Client ('C2') receives the Predirect message, it process the 1595 message and returns a Redirect message toward Client ('C1') via 1596 Server ('S2'). During the process, Client ('C2') also creates or 1597 updates a dynamic neighbor cache entry for Client ('C1'). 1599 When Server ('S2') receives the Redirect message, it re-encapsulates 1600 the message and forwards it on to Relay ('R1'), which forwards the 1601 message on to Server ('S1') which forwards the message on to Client 1602 ('C1'). After Client ('C1') receives the Redirect message, it 1603 processes the message and creates or updates a dynamic neighbor cache 1604 entry for Client ('C2'). 1606 Following the above Predirect/Redirect message exchange, forwarding 1607 of packets from Client ('C1') to Client ('C2') without involving any 1608 intermediate nodes is enabled. The mechanisms that support this 1609 exchange are specified in the following sections. 1611 3.17.3. Message Format 1613 AERO Redirect/Predirect messages use the same format as for IPv6 ND 1614 Redirect messages depicted in Section 4.5 of [RFC4861], but also 1615 include a new "Prefix Length" field taken from the low-order 8 bits 1616 of the Redirect message Reserved field. For IPv6, valid values for 1617 the Prefix Length field are 0 through 64; for IPv4, valid values are 1618 0 through 32. The Redirect/Predirect messages are formatted as shown 1619 in Figure 8: 1621 0 1 2 3 1622 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 1623 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1624 | Type (=137) | Code (=0/1) | Checksum | 1625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1626 | Reserved | Prefix Length | 1627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1628 | | 1629 + + 1630 | | 1631 + Target Address + 1632 | | 1633 + + 1634 | | 1635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1636 | | 1637 + + 1638 | | 1639 + Destination Address + 1640 | | 1641 + + 1642 | | 1643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1644 | Options ... 1645 +-+-+-+-+-+-+-+-+-+-+-+- 1647 Figure 8: AERO Redirect/Predirect Message Format 1649 3.17.4. Sending Predirects 1651 When a Client forwards a packet with a source address from one of its 1652 ACPs toward a destination address covered by an ASP (i.e., toward 1653 another AERO Client connected to the same AERO link), the source 1654 Client MAY send a Predirect message forward toward the destination 1655 Client via the Server. 1657 In the reference operational scenario, when Client ('C1') forwards a 1658 packet toward Client ('C2'), it MAY also send a Predirect message 1659 forward toward Client ('C2'), subject to rate limiting (see 1660 Section 8.2 of [RFC4861]). Client ('C1') prepares the Predirect 1661 message as follows: 1663 o the link-layer source address is set to 'L2(C1)' (i.e., the link- 1664 layer address of Client ('C1')). 1666 o the link-layer destination address is set to 'L2(S1)' (i.e., the 1667 link-layer address of Server ('S1')). 1669 o the network-layer source address is set to fe80::2001:db8:0:0 1670 (i.e., the AERO address of Client ('C1')). 1672 o the network-layer destination address is set to fe80::2001:db8:1:0 1673 (i.e., the AERO address of Client ('C2')). 1675 o the Type is set to 137. 1677 o the Code is set to 1 to indicate "Predirect". 1679 o the Prefix Length is set to the length of the prefix to be 1680 assigned to the Target Address. 1682 o the Target Address is set to fe80::2001:db8:0:0 (i.e., the AERO 1683 address of Client ('C1')). 1685 o the Destination Address is set to the source address of the 1686 originating packet that triggered the Predirection event. (If the 1687 originating packet is an IPv4 packet, the address is constructed 1688 in IPv4-compatible IPv6 address format). 1690 o the message includes one or more TLLAOs with Link ID and DSCPs set 1691 to appropriate values for Client ('C1')'s underlying interfaces, 1692 and with UDP Port Number and IP Address set to 0'. 1694 o the message SHOULD include a Timestamp option and a Nonce option. 1696 o the message includes a Redirected Header Option (RHO) that 1697 contains the originating packet truncated if necessary to ensure 1698 that at least the network-layer header is included but the size of 1699 the message does not exceed 1280 bytes. 1701 Note that the act of sending Predirect messages is cited as "MAY", 1702 since Client ('C1') may have advanced knowledge that the direct path 1703 to Client ('C2') would be unusable or otherwise undesirable. If the 1704 direct path later becomes unusable after the initial route 1705 optimization, Client ('C1') simply allows packets to again flow 1706 through Server ('S1'). 1708 3.17.5. Re-encapsulating and Relaying Predirects 1710 When Server ('S1') receives a Predirect message from Client ('C1'), 1711 it first verifies that the TLLAOs in the Predirect are a proper 1712 subset of the Link IDs in Client ('C1')'s neighbor cache entry. If 1713 the Client's TLLAOs are not acceptable, Server ('S1') discards the 1714 message. Otherwise, Server ('S1') validates the message according to 1715 the Redirect message validation rules in Section 8.1 of [RFC4861], 1716 except that the Predirect has Code=1. Server ('S1') also verifies 1717 that Client ('C1') is authorized to use the Prefix Length in the 1718 Predirect when applied to the AERO address in the network-layer 1719 source address by searching for the AERO address in the neighbor 1720 cache. If validation fails, Server ('S1') discards the Predirect; 1721 otherwise, it copies the correct UDP Port numbers and IP Addresses 1722 for Client ('C1')'s links into the (previously empty) TLLAOs. 1724 Server ('S1') then examines the network-layer destination address of 1725 the Predirect to determine the next hop toward Client ('C2') by 1726 searching for the AERO address in the neighbor cache. Since Client 1727 ('C2') is not one of its neighbors, Server ('S1') re-encapsulates the 1728 Predirect and relays it via Relay ('R1') by changing the link-layer 1729 source address of the message to 'L2(S1)' and changing the link-layer 1730 destination address to 'L2(R1)'. Server ('S1') finally forwards the 1731 re-encapsulated message to Relay ('R1') without decrementing the 1732 network-layer TTL/Hop Limit field. 1734 When Relay ('R1') receives the Predirect message from Server ('S1') 1735 it determines that Server ('S2') is the next hop toward Client ('C2') 1736 by consulting its forwarding table. Relay ('R1') then re- 1737 encapsulates the Predirect while changing the link-layer source 1738 address to 'L2(R1)' and changing the link-layer destination address 1739 to 'L2(S2)'. Relay ('R1') then relays the Predirect via Server 1740 ('S2'). 1742 When Server ('S2') receives the Predirect message from Relay ('R1') 1743 it determines that Client ('C2') is a neighbor by consulting its 1744 neighbor cache. Server ('S2') then re-encapsulates the Predirect 1745 while changing the link-layer source address to 'L2(S2)' and changing 1746 the link-layer destination address to 'L2(C2)'. Server ('S2') then 1747 forwards the message to Client ('C2'). 1749 3.17.6. Processing Predirects and Sending Redirects 1751 When Client ('C2') receives the Predirect message, it accepts the 1752 Predirect only if the message has a link-layer source address of one 1753 of its Servers (e.g., L2(S2)). Client ('C2') further accepts the 1754 message only if it is willing to serve as a redirection target. 1755 Next, Client ('C2') validates the message according to the Redirect 1756 message validation rules in Section 8.1 of [RFC4861], except that it 1757 accepts the message even though Code=1 and even though the network- 1758 layer source address is not that of it's current first-hop router. 1760 In the reference operational scenario, when Client ('C2') receives a 1761 valid Predirect message, it either creates or updates a dynamic 1762 neighbor cache entry that stores the Target Address of the message as 1763 the network-layer address of Client ('C1') , stores the link-layer 1764 addresses found in the TLLAOs as the link-layer addresses of Client 1765 ('C1') and stores the Prefix Length as the length to be applied to 1766 the network-layer address for forwarding purposes. Client ('C2') 1767 then sets AcceptTime for the neighbor cache entry to ACCEPT_TIME. 1769 After processing the message, Client ('C2') prepares a Redirect 1770 message response as follows: 1772 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 1773 layer address of Client ('C2')). 1775 o the link-layer destination address is set to 'L2(S2)' (i.e., the 1776 link-layer address of Server ('S2')). 1778 o the network-layer source address is set to fe80::2001:db8:1:0 1779 (i.e., the AERO address of Client ('C2')). 1781 o the network-layer destination address is set to fe80::2001:db8:0:0 1782 (i.e., the AERO address of Client ('C1')). 1784 o the Type is set to 137. 1786 o the Code is set to 0 to indicate "Redirect". 1788 o the Prefix Length is set to the length of the prefix to be applied 1789 to the Target Address. 1791 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 1792 address of Client ('C2')). 1794 o the Destination Address is set to the destination address of the 1795 originating packet that triggered the Redirection event. (If the 1796 originating packet is an IPv4 packet, the address is constructed 1797 in IPv4-compatible IPv6 address format). 1799 o the message includes one or more TLLAOs with Link ID and DSCPs set 1800 to appropriate values for Client ('C2')'s underlying interfaces, 1801 and with UDP Port Number and IP Address set to '0'. 1803 o the message SHOULD include a Timestamp option and MUST echo the 1804 Nonce option received in the Predirect (i.e., if a Nonce option is 1805 included). 1807 o the message includes as much of the RHO copied from the 1808 corresponding Predirect message as possible such that at least the 1809 network-layer header is included but the size of the message does 1810 not exceed 1280 bytes. 1812 After Client ('C2') prepares the Redirect message, it sends the 1813 message to Server ('S2'). 1815 3.17.7. Re-encapsulating and Relaying Redirects 1817 When Server ('S2') receives a Redirect message from Client ('C2'), it 1818 first verifies that the TLLAOs in the Redirect are a proper subset of 1819 the Link IDs in Client ('C2')'s neighbor cache entry. If the 1820 Client's TLLAOs are not acceptable, Server ('S2') discards the 1821 message. Otherwise, Server ('S2') validates the message according to 1822 the Redirect message validation rules in Section 8.1 of [RFC4861]. 1823 Server ('S2') also verifies that Client ('C2') is authorized to use 1824 the Prefix Length in the Redirect when applied to the AERO address in 1825 the network-layer source address by searching for the AERO address in 1826 the neighbor cache. If validation fails, Server ('S2') discards the 1827 Redirect; otherwise, it copies the correct UDP Port numbers and IP 1828 Addresses for Client ('C2')'s links into the (previously empty) 1829 TLLAOs. 1831 Server ('S2') then examines the network-layer destination address of 1832 the Redirect to determine the next hop toward Client ('C1') by 1833 searching for the AERO address in the neighbor cache. Since Client 1834 ('C1') is not a neighbor, Server ('S2') re-encapsulates the Redirect 1835 and relays it via Relay ('R1') by changing the link-layer source 1836 address of the message to 'L2(S2)' and changing the link-layer 1837 destination address to 'L2(R1)'. Server ('S2') finally forwards the 1838 re-encapsulated message to Relay ('R1') without decrementing the 1839 network-layer TTL/Hop Limit field. 1841 When Relay ('R1') receives the Redirect message from Server ('S2') it 1842 determines that Server ('S1') is the next hop toward Client ('C1') by 1843 consulting its forwarding table. Relay ('R1') then re-encapsulates 1844 the Redirect while changing the link-layer source address to 'L2(R1)' 1845 and changing the link-layer destination address to 'L2(S1)'. Relay 1846 ('R1') then relays the Redirect via Server ('S1'). 1848 When Server ('S1') receives the Redirect message from Relay ('R1') it 1849 determines that Client ('C1') is a neighbor by consulting its 1850 neighbor cache. Server ('S1') then re-encapsulates the Redirect 1851 while changing the link-layer source address to 'L2(S1)' and changing 1852 the link-layer destination address to 'L2(C1)'. Server ('S1') then 1853 forwards the message to Client ('C1'). 1855 3.17.8. Processing Redirects 1857 When Client ('C1') receives the Redirect message, it accepts the 1858 message only if it has a link-layer source address of one of its 1859 Servers (e.g., ''L2(S1)'). Next, Client ('C1') validates the message 1860 according to the Redirect message validation rules in Section 8.1 of 1861 [RFC4861], except that it accepts the message even though the 1862 network-layer source address is not that of it's current first-hop 1863 router. Following validation, Client ('C1') then processes the 1864 message as follows. 1866 In the reference operational scenario, when Client ('C1') receives 1867 the Redirect message, it either creates or updates a dynamic neighbor 1868 cache entry that stores the Target Address of the message as the 1869 network-layer address of Client ('C2'), stores the link-layer 1870 addresses found in the TLLAOs as the link-layer addresses of Client 1871 ('C2') and stores the Prefix Length as the length to be applied to 1872 the network-layer address for forwarding purposes. Client ('C1') 1873 then sets ForwardTime for the neighbor cache entry to FORWARD_TIME. 1875 Now, Client ('C1') has a neighbor cache entry with a valid 1876 ForwardTime value, while Client ('C2') has a neighbor cache entry 1877 with a valid AcceptTime value. Thereafter, Client ('C1') may forward 1878 ordinary network-layer data packets directly to Client ('C2') without 1879 involving any intermediate nodes, and Client ('C2') can verify that 1880 the packets came from an acceptable source. (In order for Client 1881 ('C2') to forward packets to Client ('C1'), a corresponding 1882 Predirect/Redirect message exchange is required in the reverse 1883 direction; hence, the mechanism is asymmetric.) 1885 3.17.9. Server-Oriented Redirection 1887 In some environments, the Server nearest the target Client may need 1888 to serve as the redirection target, e.g., if direct Client-to-Client 1889 communications are not possible. In that case, the Server prepares 1890 the Redirect message the same as if it were the destination Client 1891 (see: Section 3.17.6), except that it writes its own link-layer 1892 address in the TLLAO option. The Server must then maintain a dynamic 1893 neighbor cache entry for the redirected source Client. 1895 3.17.10. Route Optimization Policy 1897 Although the Client is responsible for initiating route optimization 1898 through the transmission of Predirect messages, the Server is the 1899 policy enforcement point that determines whether route optimization 1900 is permitted. For example, on some AERO links route optimization 1901 would allow traffic to circumvent critical network-based traffic 1902 interception points. In those cases, the Server can deny route 1903 optimization requests by simply discarding any Predirect messages 1904 instead of forwarding them. 1906 3.17.11. Route Optimization and Multiple ACPs 1908 Clients that receive multiple non-contiguous ACP delegations must 1909 perform route optimization for each of the individual ACPs based on 1910 demand of traffic with source addresses taken from those prefixes. 1911 For example, if Client C1 has already performed route optimization 1912 for destination ACP X on behalf of its source ACP Y, it must also 1913 perform route optimization for X on behalf of its source ACP Z. As a 1914 result, source route optimization state cannot be shared between non- 1915 contiguous ACPs and must be managed separately. 1917 3.18. Neighbor Unreachability Detection (NUD) 1919 AERO nodes perform Neighbor Unreachability Detection (NUD) by sending 1920 unicast NS messages to elicit solicited NA messages from neighbors 1921 the same as described in [RFC4861]. NUD is performed either 1922 reactively in response to persistent L2 errors (see Section 3.14) or 1923 proactively to test existing neighbor cache entries. 1925 When an AERO node sends an NS/NA message, it MUST use its link-local 1926 address as the IPv6 source address and the link-local address of the 1927 neighbor as the IPv6 destination address. When an AERO node receives 1928 an NS message or a solicited NA message, it accepts the message if it 1929 has a neighbor cache entry for the neighbor; otherwise, it ignores 1930 the message. 1932 When a source Client is redirected to a target Client it SHOULD 1933 proactively test the direct path by sending an initial NS message to 1934 elicit a solicited NA response. While testing the path, the source 1935 Client can optionally continue sending packets via the Server, 1936 maintain a small queue of packets until target reachability is 1937 confirmed, or (optimistically) allow packets to flow directly to the 1938 target. The source Client SHOULD thereafter continue to test the 1939 direct path to the target Client (see Section 7.3 of [RFC4861]) 1940 periodically in order to keep dynamic neighbor cache entries alive. 1942 In particular, while the source Client is actively sending packets to 1943 the target Client it SHOULD also send NS messages separated by 1944 RETRANS_TIMER milliseconds in order to receive solicited NA messages. 1945 If the source Client is unable to elicit a solicited NA response from 1946 the target Client after MAX_RETRY attempts, it SHOULD set ForwardTime 1947 to 0 and resume sending packets via one of its Servers. Otherwise, 1948 the source Client considers the path usable and SHOULD thereafter 1949 process any link-layer errors as a hint that the direct path to the 1950 target Client has either failed or has become intermittent. 1952 When ForwardTime for a dynamic neighbor cache entry expires, the 1953 source Client resumes sending any subsequent packets via a Server and 1954 may (eventually) attempt to re-initiate the AERO redirection process. 1955 When AcceptTime for a dynamic neighbor cache entry expires, the 1956 target Client discards any subsequent packets received directly from 1957 the source Client. When both ForwardTime and AcceptTime for a 1958 dynamic neighbor cache entry expire, the Client deletes the neighbor 1959 cache entry. 1961 3.19. Mobility Management 1963 3.19.1. Announcing Link-Layer Address Changes 1965 When a Client needs to change its link-layer address, e.g., due to a 1966 mobility event, it issues an immediate Rebind to each of its Servers 1967 using the new link-layer address as the source address and with an 1968 ALREQ that includes the correct Link ID and DSCP values. If 1969 authentication succeeds, the Server then updates its neighbor cache 1970 and sends a Reply. Note that if the Client does not issue a Rebind 1971 before the prefix delegation lifetime expires (e.g., if the Client 1972 has been out of touch with the Server for a considerable amount of 1973 time), the Server's Reply will report NoBinding and the Client must 1974 re-initiate the DHCPv6 PD procedure. 1976 Next, the Client sends Predirect messages to each of its 1977 correspondent Client neighbors using the same procedures as specified 1978 in Section 3.17.4. The Client sends the Predirect messages via a 1979 Server the same as if it was performing the initial route 1980 optimization procedure with the correspondent. The Predirect message 1981 will update the correspondent' link layer address mapping for the 1982 Client. 1984 3.19.2. Bringing New Links Into Service 1986 When a Client needs to bring a new underlying interface into service 1987 (e.g., when it activates a new data link), it issues an immediate 1988 Rebind to each of its Servers using the new link-layer address as the 1989 source address and with an ALREQ that includes the new Link ID and 1990 DSCP values. If authentication succeeds, the Server then updates its 1991 neighbor cache and sends a Reply. The Client MAY then send Predirect 1992 messages to each of its correspondent Clients to inform them of the 1993 new link-layer address as described in Section 3.19.1. 1995 3.19.3. Removing Existing Links from Service 1997 When a Client needs to remove an existing underlying interface from 1998 service (e.g., when it de-activates an existing data link), it issues 1999 an immediate Rebind to each of its Servers over any available link 2000 with an ALDEL that includes the deprecated Link ID. If 2001 authentication succeeds, the Server then updates its neighbor cache 2002 and sends a Reply. The Client SHOULD then send Predirect messages to 2003 each of its correspondent Clients to inform them of the deprecated 2004 link-layer address as described in Section 3.19.1. 2006 3.19.4. Moving to a New Server 2008 When a Client associates with a new Server, it performs the Client 2009 procedures specified in Section 3.15.2. 2011 When a Client disassociates with an existing Server, it sends a 2012 Release message via a new Server to the unicast link-local network 2013 layer address of the old Server. The new Server then writes its own 2014 link-layer address in the Release message IP source address and 2015 forwards the message to the old Server. 2017 When the old Server receives the Release, it first authenticates the 2018 message. Next, it resets the Client's neighbor cache entry lifetime 2019 to 3 seconds, rewrites the link-layer address in the neighbor cache 2020 entry to the address of the new Server, then returns a Reply message 2021 to the Client via the old Server. When the lifetime expires, the old 2022 Server withdraws the IP route from the AERO routing system and 2023 deletes the neighbor cache entry for the Client. The Client can then 2024 use the Reply message to verify that the termination signal has been 2025 processed, and can delete both the default route and the neighbor 2026 cache entry for the old Server. (Note that since Release/Reply 2027 messages may be lost in the network the Client MUST retry until it 2028 gets a Reply indicating that the Release was successful. If the 2029 Client does not receive a Reply after MAX_RETRY attempts, the old 2030 Server may have failed and the Client should discontinue its Release 2031 attempts.) 2033 Clients SHOULD NOT move rapidly between Servers in order to avoid 2034 causing excessive oscillations in the AERO routing system. Such 2035 oscillations could result in intermittent reachability for the Client 2036 itself, while causing little harm to the network. Examples of when a 2037 Client might wish to change to a different Server include a Server 2038 that has gone unreachable, topological movements of significant 2039 distance, etc. 2041 3.19.5. Packet Queueing for Mobility 2043 AERO Clients and Servers should maintain a samll queue of packets 2044 they have recently sent to an AERO neighbor, e.g., a 1 second window. 2045 If the AERO neighbor moves, the AERO node MAY retransmit the queued 2046 packets to ensure that they are delviered to the AERO neighbor's new 2047 location. 2049 Note that this may have performance implications for asymmetric 2050 paths. For example, if the AERO neighbor moves from a 50mbps link to 2051 a 128kbps link, retransmitting a 1 second window could lead to 2052 significant congestion. 2054 3.20. Proxy AERO 2056 Proxy Mobile IPv6 (PMIPv6) [RFC5213][RFC5844][RFC5949] presents a 2057 network-based localized mobility management scheme for use within an 2058 access network domain. It is typically used in WiFi and cellular 2059 wireless access networks, and allows Mobile Nodes (MNs) to receive 2060 and retain an IP address that remains stable within the access 2061 network domain without needing to implement any special mobility 2062 protocols. In the PMIPv6 architecture, access network devices known 2063 as Mobility Access Gateways (MAGs) provide MNs with an access link 2064 abstraction and receive prefixes for the MNs from a Local Mobility 2065 Anchor (LMA). 2067 In a proxy AERO domain, a proxy AERO Client (acting as a MAG) can 2068 similarly provide proxy services for MNs that do not participate in 2069 AERO messaging. The proxy Client presents an access link abstraction 2070 to MNs, and performs DHCPv6 PD exchanges over the AERO interface with 2071 an AERO Server (acting as an LMA) to receive ACPs for address 2072 provisioning of new MNs that come onto an access link. This scheme 2073 assumes that proxy Clients act as fixed (non-mobile) infrastructure 2074 elements under the same administrative trust basis as for Relays and 2075 Servers. 2077 When an MN comes onto an access link within a proxy AERO domain for 2078 the first time, the proxy Client authenticates the MN and obtains a 2079 unique identifier that it can use as a DHCPv6 DUID then sends a 2080 Solicit message to its Server. When the Server delegates an ACP and 2081 returns a Reply, the proxy Client creates an AERO address for the MN 2082 and assigns the ACP to the MN's access link. The proxy Client then 2083 configures itself as a default router for the MN and provides address 2084 autoconfiguration services (e.g., SLAAC, DHCPv6, DHCPv4, etc.) for 2085 provisioning MN addresses from the ACP over the access link. Since 2086 the proxy Client may serve many such MNs simultaneously, it may 2087 receive multiple ACP prefix delegations and configure multiple AERO 2088 addresses, i.e., one for each MN. 2090 When two MNs are associated with the same proxy Client, the Client 2091 can forward traffic between the MNs without involving a Server since 2092 it configures the AERO addresses of both MNs and therefore also has 2093 the necessary routing information. When two MNs are associated with 2094 different proxy Clients, the source MN's Client can initiate standard 2095 AERO intradomain route optimization to discover a direct path to the 2096 target MN's Client through the exchange of Predirect/Redirect 2097 messages. 2099 When an MN in a proxy AERO domain leaves an access link provided by 2100 an old proxy Client, the MN issues an access link-specific "leave" 2101 message that informs the old Client of the link-layer address of a 2102 new Client on the planned new access link. This is known as a 2103 "predictive handover". When an MN comes onto an access link provided 2104 by a new proxy Client, the MN issues an access link-specific "join" 2105 message that informs the new Client of the link-layer address of the 2106 old Client on the actual old access link. This is known as a 2107 "reactive handover". 2109 Upon receiving a predictive handover indication, the old proxy Client 2110 sends a Solicit message directly to the new Client and queues any 2111 arriving data packets addressed to the departed MN. The Solicit 2112 message includes the MN's ID as the DUID, the ACP in an IA_PD option, 2113 the old Client's address as the link-layer source address and the new 2114 Client's address as the link-layer destination address. When the new 2115 Client receives the Solicit message, it changes the link-layer source 2116 address to its own address, changes the link-layer destination 2117 address to the address of its Server, and forwards the message to the 2118 Server. At the same time, the new Client creates access link state 2119 for the ACP in anticipation of the MN's arrival (while queuing any 2120 data packets until the MN arrives), creates a neighbor cache entry 2121 for the old Client with AcceptTime set to ACCEPT_TIME, then sends a 2122 Redirect message back to the old Client. When the old Client 2123 receives the Redirect message, it creates a neighbor cache entry for 2124 the new Client with ForwardTime set to FORWARD_TIME, then forwards 2125 any queued data packets to the new Client. At the same time, the old 2126 Client sends a Release message to its Server. Finally, the old 2127 Client sends unsolicited Redirect messages to any of the ACP's 2128 correspondents with a TLLAO containing the link-layer address of the 2129 new Client. 2131 Upon receiving a reactive handover indication, the new proxy Client 2132 creates access link state for the MN's ACP, sends a Solicit message 2133 to its Server, and sends a Release message directly to the old 2134 Client. The Release message includes the MN's ID as the DUID, the 2135 ACP in an IA_PD option, the new Client's address as the link-layer 2136 source address and the old Client's address as the link-layer 2137 destination address. When the old Client receives the Release 2138 message, it changes the link-layer source address to its own address, 2139 changes the link-layer destination address to the address of its 2140 Server, and forwards the message to the Server. At the same time, 2141 the old Client sends a Predirect message back to the new Client and 2142 queues any arriving data packets addressed to the departed MN. When 2143 the new Client receives the Predirect, it creates a neighbor cache 2144 entry for the old Client with AcceptTime set to ACCEPT_TIME, then 2145 sends a Redirect message back to the old Client. When the old Client 2146 receives the Redirect message, it creates a neighbor cache entry for 2147 the new Client with ForwardTime set to FORWARD_TIME, then forwards 2148 any queued data packets to the new Client. Finally, the old Client 2149 sends unsolicited Redirect messages to correspondents the same as for 2150 the predictive case. 2152 When a Server processes a Solicit message, it creates a neighbor 2153 cache entry for this ACP if none currently exists. If a neighbor 2154 cache entry already exists, however, the Server changes the link- 2155 layer address to the address of the new proxy Client (this satisfies 2156 the case of both the old Client and new Client using the same 2157 Server). 2159 When a Server processes a Release message, it resets the neighbor 2160 cache entry lifetime for this ACP to 3 seconds if the cached link- 2161 layer address matches the old proxy Client's address. Otherwise, the 2162 Server ignores the Release message (this satisfies the case of both 2163 the old Client and new Client using the same Server). 2165 When a correspondent Client receives an unsolicited Redirect message, 2166 it changes the link-layer address for the ACP's neighbor cache entry 2167 to the address of the new proxy Client. 2169 From an architectural perspective, in addition to the use of DHCPv6 2170 PD and IPv6 ND signaling the AERO approach differs from PMIPv6 in its 2171 use of the NBMA virtual link model instead of point-to-point tunnels. 2172 This provides a more agile interface for Client/Server and Client/ 2173 Client coordinations, and also facilitates simple route optimization. 2174 The AERO routing system is also arranged in such a fashion that 2175 Clients get the same service from any Server they happen to associate 2176 with. This provides a natural fault tolerance and load balancing 2177 capability such as desired for distributed mobility management. 2179 3.21. Extending AERO Links Through Security Gateways 2181 When an enterprise mobile device moves from a campus LAN connection 2182 to a public Internet link, it must re-enter the enterprise via a 2183 security gateway that has both a physical interface connection to the 2184 Internet and a physical interface connection to the enterprise 2185 internetwork. This most often entails the establishment of a Virtual 2186 Private Network (VPN) link over the public Internet from the mobile 2187 device to the security gateway. During this process, the mobile 2188 device supplies the security gateway with its public Internet address 2189 as the link-layer address for the VPN. The mobile device then acts 2190 as an AERO Client to negotiate with the security gateway to obtain 2191 its ACP. 2193 In order to satisfy this need, the security gateway also operates as 2194 an AERO Server with support for AERO Client proxying. In particular, 2195 when a mobile device (i.e., the Client) connects via the security 2196 gateway (i.e., the Server), the Server provides the Client with an 2197 ACP in a DHCPv6 PD exchange the same as if it were attached to an 2198 enterprise campus access link. The Server then replaces the Client's 2199 link-layer source address with the Server's enterprise-facing link- 2200 layer address in all AERO messages the Client sends toward neighbors 2201 on the AERO link. The AERO messages are then delivered to other 2202 devices on the AERO link as if they were originated by the security 2203 gateway instead of by the AERO Client. In the reverse direction, the 2204 AERO messages sourced by devices within the enterprise network can be 2205 forwarded to the security gateway, which then replaces the link-layer 2206 destination address with the Client's link-layer address and replaces 2207 the link-layer source address with its own (Internet-facing) link- 2208 layer address. 2210 After receiving the ACP, the Client can send IP packets that use an 2211 address taken from the ACP as the network layer source address, the 2212 Client's link-layer address as the link-layer source address, and the 2213 Server's Internet-facing link-layer address as the link-layer 2214 destination address. The Server will then rewrite the link-layer 2215 source address with the Server's own enterprise-facing link-layer 2216 address and rewrite the link-layer destination address with the 2217 target AERO node's link-layer address, and the packets will enter the 2218 enterprise network as though they were sourced from a device located 2219 within the enterprise. In the reverse direction, when a packet 2220 sourced by a node within the enterprise network uses a destination 2221 address from the Client's ACP, the packet will be delivered to the 2222 security gateway which then rewrites the link-layer destination 2223 address to the Client's link-layer address and rewrites the link- 2224 layer source address to the Server's Internet-facing link-layer 2225 address. The Server then delivers the packet across the VPN to the 2226 AERO Client. In this way, the AERO virtual link is essentially 2227 extended *through* the security gateway to the point at which the VPN 2228 link and AERO link are effectively grafted together by the link-layer 2229 address rewriting performed by the security gateway. All AERO 2230 messaging services (including route optimization and mobility 2231 signaling) are therefore extended to the Client. 2233 In order to support this virtual link grafting, the security gateway 2234 (acting as an AERO Server) must keep static neighbor cache entries 2235 for all of its associated Clients located on the public Internet. 2236 The neighbor cache entry is keyed by the AERO Client's AERO address 2237 the same as if the Client were located within the enterprise 2238 internetwork. The neighbor cache is then managed in all ways as 2239 though the Client were an ordinary AERO Client. This includes the 2240 AERO IPv6 ND messaging signaling for Route Optimization and Neighbor 2241 Unreachability Detection. 2243 Note that the main difference between a security gateway acting as an 2244 AERO Server and an enterprise-internal AERO Server is that the 2245 security gateway has at least one enterprise-internal physical 2246 interface and at least one public Internet physical interface. 2247 Conversely, the enterprise-internal AERO Server has only enterprise- 2248 internal physical interfaces. For this reason security gateway 2249 proxying is needed to ensure that the public Internet link-layer 2250 addressing space is kept separate from the enterprise-internal link- 2251 layer addressing space. This is afforded through a natural extension 2252 of the security association caching already performed for each VPN 2253 client by the security gateway. 2255 3.22. Extending IPv6 AERO Links to the Internet 2257 When an IPv6 host ('H1') with an address from an ACP owned by AERO 2258 Client ('C1') sends packets to a correspondent IPv6 host ('H2'), the 2259 packets eventually arrive at the IPv6 router that owns ('H2')s 2260 prefix. This IPv6 router may or may not be an AERO Client ('C2') 2261 either within the same home network as ('C1') or in a different home 2262 network. 2264 If Client ('C1') is currently located outside the boundaries of its 2265 home network, it will connect back into the home network via a 2266 security gateway acting as an AERO Server. The packets sent by 2267 ('H1') via ('C1') will then be forwarded through the security gateway 2268 then through the home network and finally to ('C2') where they will 2269 be delivered to ('H2'). This could lead to sub-optimal performance 2270 when ('C2') could instead be reached via a more direct route without 2271 involving the security gateway. 2273 Consider the case when host ('H1') has the IPv6 address 2274 2001:db8:1::1, and Client ('C1') has the ACP 2001:db8:1::/64 with 2275 underlying IPv6 Internet address of 2001:db8:1000::1. Also, host 2276 ('H2') has the IPv6 address 2001:db8:2::1, and Client ('C2') has the 2277 ACP 2001:db8:2::/64 with underlying IPv6 address of 2001:db8:2000::1. 2278 Client ('C1') can determine whether 'C2' is indeed also an AERO 2279 Client willing to serve as a route optimization correspondent by 2280 resolving the AAAA records for the DNS FQDN that matches ('H2')s 2281 prefix, i.e.: 2283 '0.0.0.0.2.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net' 2285 If ('C2') is indeed a candidate correspondent, the FQDN lookup will 2286 return a PTR resource record that contains the domain name for the 2287 AERO link that manages ('C2')s ASP. Client ('C1') can then attempt 2288 route optimization using an approach similar to the Return 2289 Routability procedure specified for Mobile IPv6 (MIPv6) [RFC6275]. 2290 In order to support this process, both Clients MUST intercept and 2291 decapsulate packets that have a subnet router anycast address 2292 corresponding to any of the /64 prefixes covered by their respective 2293 ACPs. 2295 To initiate the process, Client ('C1') creates a specially-crafted 2296 encapsulated Predirect message that will be routed through its home 2297 network then through ('C2')s home network and finally to ('C2') 2298 itself. Client ('C1') prepares the initial message in the exchange 2299 as follows: 2301 o The encapsulating IPv6 header source address is set to 2302 2001:db8:1:: (i.e., the IPv6 subnet router anycast address for 2303 ('C1')s ACP) 2305 o The encapsulating IPv6 header destination address is set to 2306 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2307 ('C2')s ACP) 2309 o The encapsulating IPv6 header is followed by any additional 2310 encapsulation headers 2312 o The encapsulated IPv6 header source address is set to 2313 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2315 o The encapsulated IPv6 header destination address is set to 2316 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2318 o The encapsulated Predirect message includes all of the securing 2319 information that would occur in a MIPv6 "Home Test Init" message 2320 (format TBD) 2322 Client ('C1') then further encapsulates the message in the 2323 encapsulating headers necessary to convey the packet to the security 2324 gateway (e.g., through IPsec encapsulation) so that the message now 2325 appears "double-encapsulated". ('C1') then sends the message to the 2326 security gateway, which re-encapsulates and forwards it over the home 2327 network from where it will eventually reach ('C2'). 2329 At the same time, ('C1') creates and sends a second encapsulated 2330 Predirect message that will be routed through the IPv6 Internet 2331 without involving the security gateway. Client ('C1') prepares the 2332 message as follows: 2334 o The encapsulating IPv6 header source address is set to 2335 2001:db8:1000:1 (i.e., the Internet IPv6 address of ('C1')) 2337 o The encapsulating IPv6 header destination address is set to 2338 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2339 ('C2')s ACP) 2341 o The encapsulating IPv6 header is followed by any additional 2342 encapsulation headers 2344 o The encapsulated IPv6 header source address is set to 2345 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2347 o The encapsulated IPv6 header destination address is set to 2348 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2350 o The encapsulated Predirect message includes all of the securing 2351 information that would occur in a MIPv6 "Care-of Test Init" 2352 message (format TBD) 2354 ('C2') will receive both Predirect messages through its home network 2355 then return a corresponding Redirect for each of the Predirect 2356 messages with the source and destination addresses in the inner and 2357 outer headers reversed. The first message includes all of the 2358 securing information that would occur in a MIPv6 "Home Test" message, 2359 while the second message includes all of the securing information 2360 that would occur in a MIPv6 "Care-of Test" message (formats TBD). 2362 When ('C1') receives the Redirect messages, it performs the necessary 2363 security procedures per the MIPv6 specification. It then prepares an 2364 encapsulated NS message that includes the same source and destination 2365 addresses as for the "Care-of Test Init" Predirect message, and 2366 includes all of the securing information that would occur in a MIPv6 2367 "Binding Update" message (format TBD) and sends the message to 2368 ('C2'). 2370 When ('C2') receives the NS message, if the securing information is 2371 correct it creates or updates a neighbor cache entry for ('C1') with 2372 fe80::2001:db8:1:0 as the network-layer address, 2001:db8:1000::1 as 2373 the link-layer address and with AcceptTime set to ACCEPT_TIME. 2374 ('C2') then sends an encapsulated NA message back to ('C1') that 2375 includes the same source and destination addresses as for the "Care- 2376 of Test" Redirect message, and includes all of the securing 2377 information that would occur in a MIPv6 "Binding Acknowledgement" 2378 message (format TBD) and sends the message to ('C1'). 2380 When ('C1') receives the NA message, it creates or updates a neighbor 2381 cache entry for ('C2') with fe80::2001:db8:2:0 as the network-layer 2382 address and 2001:db8:2:: as the link-layer address and with 2383 ForwardTime set to FORWARD_TIME, thus completing the route 2384 optimization in the forward direction. 2386 ('C1') subsequently forwards encapsulated packets with outer source 2387 address 2001:db8:1000::1, with outer destination address 2388 2001:db8:2::, with inner source address taken from the 2001:db8:1::, 2389 and with inner destination address taken from 2001:db8:2:: due to the 2390 fact that it has a securely-established neighbor cache entry with 2391 non-zero ForwardTime. ('C2') subsequently accepts any such 2392 encapsulated packets due to the fact that it has a securely- 2393 established neighbor cache entry with non-zero AcceptTime. 2395 In order to keep neighbor cache entries alive, ('C1') periodically 2396 sends additional NS messages to ('C2') and receives any NA responses. 2397 If ('C1') moves to a different point of attachment after the initial 2398 route optimization, it sends a new secured NS message to ('C2') as 2399 above to update ('C2')s neighbor cache. 2401 If ('C2') has packets to send to ('C1'), it performs a corresponding 2402 route optimization in the opposite direction following the same 2403 procedures described above. In the process, the already-established 2404 unidirectional neighbor cache entries within ('C1') and ('C2') are 2405 updated to include the now-bidirectional information. In particular, 2406 the AcceptTime and ForwardTime variables for both neighbor cache 2407 entries are updated to non-zero values, and the link-layer address 2408 for ('C1')s neighbor cache entry for ('C2') is reset to 2409 2001:db8:2000::1. 2411 Note that two AERO Clients can use full security protocol messaging 2412 instead of Return Routability, e.g., if strong authentication and/or 2413 confidentiality are desired. In that case, security protocol key 2414 exchanges such as specified for MOBIKE [RFC4555] would be used to 2415 establish security associations and neighbor cache entries between 2416 the AERO clients. Thereafter, NS/NA messaging can be used to 2417 maintain neighbor cache entries, test reachability, and to announce 2418 mobility events. If reachability testing fails, e.g., if both 2419 Clients move at roughly the same time, the Clients can tear down the 2420 security association and neighbor cache entries and again allow 2421 packets to flow through their home network. 2423 3.23. Encapsulation Protocol Version Considerations 2425 A source Client may connect only to an IPvX underlying network, while 2426 the target Client connects only to an IPvY underlying network. In 2427 that case, the target and source Clients have no means for reaching 2428 each other directly (since they connect to underlying networks of 2429 different IP protocol versions) and so must ignore any redirection 2430 messages and continue to send packets via their Servers. 2432 3.24. Multicast Considerations 2434 When the underlying network does not support multicast, AERO Clients 2435 map link-scoped multicast addresses to the link-layer address of a 2436 Server, which acts as a multicast forwarding agent. The AERO Client 2437 also serves as an IGMP/MLD Proxy for its EUNs and/or hosted 2438 applications per [RFC4605] while using the link-layer address of the 2439 Server as the link-layer address for all multicast packets. 2441 When the underlying network supports multicast, AERO nodes use the 2442 multicast address mapping specification found in [RFC2529] for IPv4 2443 underlying networks and use a TBD site-scoped multicast mapping for 2444 IPv6 underlying networks. In that case, border routers must ensure 2445 that the encapsulated site-scoped multicast packets do not leak 2446 outside of the site spanned by the AERO link. 2448 3.25. Operation on AERO Links Without DHCPv6 Services 2450 When Servers on the AERO link do not provide DHCPv6 services, 2451 operation can still be accommodated through administrative 2452 configuration of ACPs on AERO Clients. In that case, administrative 2453 configurations of AERO interface neighbor cache entries on both the 2454 Server and Client are also necessary. However, this may interfere 2455 with the ability for Clients to dynamically change to new Servers, 2456 and can expose the AERO link to misconfigurations unless the 2457 administrative configurations are carefully coordinated. 2459 3.26. Operation on Server-less AERO Links 2461 In some AERO link scenarios, there may be no Servers on the link and/ 2462 or no need for Clients to use a Server as an intermediary trust 2463 anchor. In that case, each Client acts as a Server unto itself to 2464 establish neighbor cache entries by performing direct Client-to- 2465 Client IPv6 ND message exchanges, and some other form of trust basis 2466 must be applied so that each Client can verify that the prospective 2467 neighbor is authorized to use its claimed ACP. 2469 When there is no Server on the link, Clients must arrange to receive 2470 ACPs and publish them via a secure alternate prefix delegation 2471 authority through some means outside the scope of this document. 2473 3.27. Manually-Configured AERO Tunnels 2475 In addition to the dynamic neighbor discovery procedures for AERO 2476 link neighbors described above, AERO encapsulation can be applied to 2477 manually-configured tunnels. In that case, the tunnel endpoints use 2478 an administratively-assigned link-local address and exchange NS/NA 2479 messages the same as for dynamically-established tunnels. 2481 3.28. Intradomain Routing 2483 After a tunnel neighbor relationship has been established, neighbors 2484 can use a traditional dynamic routing protocol over the tunnel to 2485 exchange routing information without having to inject the routes into 2486 the AERO routing system. 2488 4. Implementation Status 2490 User-level and kernel-level AERO implementations have been developed 2491 and are undergoing internal testing within Boeing. 2493 An initial public release of the AERO source code was announced on 2494 the intarea mailing list on August 21, 2015, and a pointer to the 2495 code is available in the list archives. 2497 5. IANA Considerations 2499 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2500 AERO in the "enterprise-numbers" registry. 2502 The IANA has assigned the UDP port number "8060" for an earlier 2503 experimental version of AERO [RFC6706]. This document obsoletes 2504 [RFC6706] and claims the UDP port number "8060" for all future use. 2506 No further IANA actions are required. 2508 6. Security Considerations 2510 AERO link security considerations are the same as for standard IPv6 2511 Neighbor Discovery [RFC4861] except that AERO improves on some 2512 aspects. In particular, AERO uses a trust basis between Clients and 2513 Servers, where the Clients only engage in the AERO mechanism when it 2514 is facilitated by a trust anchor. Unless there is some other means 2515 of authenticating the Client's identity (e.g., link-layer security), 2516 AERO nodes SHOULD also use DHCPv6 securing services (e.g., DHCPv6 2517 authentication, Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6], etc.) for 2518 Client authentication and network admission control. In particular, 2519 Clients SHOULD include authenticating information on each 2520 Solicit/Rebind/Release message they send, but omit authenticating 2521 information on Renew messages. Renew messages are exempt due to the 2522 fact that the Renew must already be checked for having a correct 2523 link-layer address and does not update any link-layer addresses. 2524 Therefore, asking the Server to also authenticate the Renew message 2525 would be unnecessary and could result in excessive processing 2526 overhead. 2528 Redirect, Predirect and unsolicited NA messages SHOULD include a 2529 Timestamp option (see Section 5.3 of [RFC3971]) that other AERO nodes 2530 can use to verify the message time of origin. Predirect, NS and RS 2531 messages SHOULD include a Nonce option (see Section 5.3 of [RFC3971]) 2532 that recipients echo back in corresponding responses. 2534 AERO links must be protected against link-layer address spoofing 2535 attacks in which an attacker on the link pretends to be a trusted 2536 neighbor. Links that provide link-layer securing mechanisms (e.g., 2537 IEEE 802.1X WLANs) and links that provide physical security (e.g., 2538 enterprise network wired LANs) provide a first line of defense that 2539 is often sufficient. In other instances, additional securing 2540 mechanisms such as Secure Neighbor Discovery (SeND) [RFC3971], IPsec 2541 [RFC4301] or TLS [RFC5246] may be necessary. 2543 AERO Clients MUST ensure that their connectivity is not used by 2544 unauthorized nodes on their EUNs to gain access to a protected 2545 network, i.e., AERO Clients that act as routers MUST NOT provide 2546 routing services for unauthorized nodes. (This concern is no 2547 different than for ordinary hosts that receive an IP address 2548 delegation but then "share" the address with unauthorized nodes via 2549 some form of Internet connection sharing.) 2551 On some AERO links, establishment and maintenance of a direct path 2552 between neighbors requires secured coordination such as through the 2553 Internet Key Exchange (IKEv2) protocol [RFC5996] to establish a 2554 security association. 2556 An AERO Client's link-layer address could be rewritten by a link- 2557 layer switching element on the path from the Client to the Server and 2558 not detected by the DHCPv6 security mechanism. However, such a 2559 condition would only be a matter of concern on unmanaged/unsecured 2560 links where the link-layer switching elements themselves present a 2561 man-in-the-middle attack threat. For this reason, IP security MUST 2562 be used when AERO is employed over unmanaged/unsecured links. 2564 7. Acknowledgements 2566 Discussions both on IETF lists and in private exchanges helped shape 2567 some of the concepts in this work. Individuals who contributed 2568 insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, 2569 Stewart Bryant, Brian Carpenter, Wojciech Dec, Ralph Droms, Adrian 2570 Farrel, Sri Gundavelli, Brian Haberman, Joel Halpern, Tom Herbert, 2571 Sascha Hlusiak, Lee Howard, Andre Kostur, Ted Lemon, Andy Malis, 2572 Satoru Matsushima, Tomek Mrugalski, Alexandru Petrescu, Behcet 2573 Saikaya, Joe Touch, Bernie Volz, Ryuji Wakikawa and Lloyd Wood. 2574 Members of the IESG also provided valuable input during their review 2575 process that greatly improved the document. Discussions on the v6ops 2576 list in the December 2015 through January 2016 timeframe further 2577 helped clarify AERO multi-addressing capabilities. Special thanks go 2578 to Stewart Bryant, Joel Halpern and Brian Haberman for their 2579 shepherding guidance during the publication of the AERO first 2580 edition. 2582 This work has further been encouraged and supported by Boeing 2583 colleagues including M. Wayne Benson, Dave Bernhardt, Cam Brodie, 2584 Balaguruna Chidambaram, Irene Chin, Bruce Cornish, Claudiu Danilov, 2585 Wen Fang, Anthony Gregory, Jeff Holland, Ed King, Gen MacLean, Rob 2586 Muszkiewicz, Sean O'Sullivan, Kent Shuey, Brian Skeen, Mike Slane, 2587 Brendan Williams, Julie Wulff, Yueli Yang, and other members of the 2588 BR&T and BIT mobile networking teams. Wayne Benson is especially 2589 acknowledged for his outstanding work in converting the AERO proof- 2590 of-concept implementation into production-ready code. 2592 Earlier works on NBMA tunneling approaches are found in 2593 [RFC2529][RFC5214][RFC5569]. 2595 Many of the constructs presented in this second edition of AERO are 2596 based on the author's earlier works, including: 2598 o The Internet Routing Overlay Network (IRON) 2599 [RFC6179][I-D.templin-ironbis] 2601 o Virtual Enterprise Traversal (VET) 2602 [RFC5558][I-D.templin-intarea-vet] 2604 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2605 [RFC5320][I-D.templin-intarea-seal] 2607 o AERO, First Edition [RFC6706] 2609 Note that these works cite numerous earlier efforts that are not also 2610 cited here due to space limitations. The authors of those earlier 2611 works are acknowledged for their insights. 2613 8. References 2615 8.1. Normative References 2617 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2618 DOI 10.17487/RFC0768, August 1980, 2619 . 2621 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2622 DOI 10.17487/RFC0791, September 1981, 2623 . 2625 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2626 RFC 792, DOI 10.17487/RFC0792, September 1981, 2627 . 2629 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 2630 DOI 10.17487/RFC2003, October 1996, 2631 . 2633 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2634 Requirement Levels", BCP 14, RFC 2119, 2635 DOI 10.17487/RFC2119, March 1997, 2636 . 2638 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2639 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 2640 December 1998, . 2642 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2643 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2644 December 1998, . 2646 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2647 "Definition of the Differentiated Services Field (DS 2648 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2649 DOI 10.17487/RFC2474, December 1998, 2650 . 2652 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 2653 C., and M. Carney, "Dynamic Host Configuration Protocol 2654 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2655 2003, . 2657 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2658 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2659 DOI 10.17487/RFC3633, December 2003, 2660 . 2662 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2663 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2664 DOI 10.17487/RFC3971, March 2005, 2665 . 2667 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 2668 for IPv6 Hosts and Routers", RFC 4213, 2669 DOI 10.17487/RFC4213, October 2005, 2670 . 2672 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2673 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2674 DOI 10.17487/RFC4861, September 2007, 2675 . 2677 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2678 Address Autoconfiguration", RFC 4862, 2679 DOI 10.17487/RFC4862, September 2007, 2680 . 2682 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 2683 Requirements", RFC 6434, DOI 10.17487/RFC6434, December 2684 2011, . 2686 8.2. Informative References 2688 [I-D.herbert-gue-fragmentation] 2689 Herbert, T. and F. Templin, "Fragmentation option for 2690 Generic UDP Encapsulation", draft-herbert-gue- 2691 fragmentation-02 (work in progress), October 2015. 2693 [I-D.ietf-dhc-sedhcpv6] 2694 Jiang, S., Li, L., Cui, Y., Jinmei, T., Lemon, T., and D. 2695 Zhang, "Secure DHCPv6", draft-ietf-dhc-sedhcpv6-13 (work 2696 in progress), July 2016. 2698 [I-D.ietf-intarea-tunnels] 2699 Touch, D. and W. Townsley, "IP Tunnels in the Internet 2700 Architecture", draft-ietf-intarea-tunnels-03 (work in 2701 progress), July 2016. 2703 [I-D.ietf-nvo3-gue] 2704 Herbert, T., Yong, L., and O. Zia, "Generic UDP 2705 Encapsulation", draft-ietf-nvo3-gue-04 (work in progress), 2706 July 2016. 2708 [I-D.templin-intarea-grefrag] 2709 Templin, F., "GRE Tunnel Fragmentation", draft-templin- 2710 intarea-grefrag-02 (work in progress), January 2016. 2712 [I-D.templin-intarea-seal] 2713 Templin, F., "The Subnetwork Encapsulation and Adaptation 2714 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 2715 progress), January 2014. 2717 [I-D.templin-intarea-vet] 2718 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 2719 templin-intarea-vet-40 (work in progress), May 2013. 2721 [I-D.templin-ironbis] 2722 Templin, F., "The Interior Routing Overlay Network 2723 (IRON)", draft-templin-ironbis-16 (work in progress), 2724 March 2014. 2726 [RFC0879] Postel, J., "The TCP Maximum Segment Size and Related 2727 Topics", RFC 879, DOI 10.17487/RFC0879, November 1983, 2728 . 2730 [RFC1035] Mockapetris, P., "Domain names - implementation and 2731 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 2732 November 1987, . 2734 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2735 Communication Layers", STD 3, RFC 1122, 2736 DOI 10.17487/RFC1122, October 1989, 2737 . 2739 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2740 DOI 10.17487/RFC1191, November 1990, 2741 . 2743 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 2744 RFC 1812, DOI 10.17487/RFC1812, June 1995, 2745 . 2747 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 2748 selection, and registration of an Autonomous System (AS)", 2749 BCP 6, RFC 1930, DOI 10.17487/RFC1930, March 1996, 2750 . 2752 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 2753 for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 2754 1996, . 2756 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 2757 RFC 2131, DOI 10.17487/RFC2131, March 1997, 2758 . 2760 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2761 Domains without Explicit Tunnels", RFC 2529, 2762 DOI 10.17487/RFC2529, March 1999, 2763 . 2765 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 2766 RFC 2675, DOI 10.17487/RFC2675, August 1999, 2767 . 2769 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 2770 Malis, "A Framework for IP Based Virtual Private 2771 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 2772 . 2774 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 2775 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 2776 DOI 10.17487/RFC2784, March 2000, 2777 . 2779 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 2780 RFC 2890, DOI 10.17487/RFC2890, September 2000, 2781 . 2783 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 2784 RFC 2923, DOI 10.17487/RFC2923, September 2000, 2785 . 2787 [RFC2983] Black, D., "Differentiated Services and Tunnels", 2788 RFC 2983, DOI 10.17487/RFC2983, October 2000, 2789 . 2791 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 2792 of Explicit Congestion Notification (ECN) to IP", 2793 RFC 3168, DOI 10.17487/RFC3168, September 2001, 2794 . 2796 [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, 2797 "DNS Extensions to Support IP Version 6", RFC 3596, 2798 DOI 10.17487/RFC3596, October 2003, 2799 . 2801 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 2802 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2803 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2804 RFC 3819, DOI 10.17487/RFC3819, July 2004, 2805 . 2807 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 2808 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 2809 DOI 10.17487/RFC4271, January 2006, 2810 . 2812 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2813 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2814 2006, . 2816 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2817 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 2818 December 2005, . 2820 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 2821 Control Message Protocol (ICMPv6) for the Internet 2822 Protocol Version 6 (IPv6) Specification", RFC 4443, 2823 DOI 10.17487/RFC4443, March 2006, 2824 . 2826 [RFC4459] Savola, P., "MTU and Fragmentation Issues with In-the- 2827 Network Tunneling", RFC 4459, DOI 10.17487/RFC4459, April 2828 2006, . 2830 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 2831 Protocol (LDAP): The Protocol", RFC 4511, 2832 DOI 10.17487/RFC4511, June 2006, 2833 . 2835 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 2836 (MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006, 2837 . 2839 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 2840 System", RFC 4592, DOI 10.17487/RFC4592, July 2006, 2841 . 2843 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 2844 "Internet Group Management Protocol (IGMP) / Multicast 2845 Listener Discovery (MLD)-Based Multicast Forwarding 2846 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 2847 August 2006, . 2849 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2850 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 2851 . 2853 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2854 Errors at High Data Rates", RFC 4963, 2855 DOI 10.17487/RFC4963, July 2007, 2856 . 2858 [RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski, 2859 "DHCPv6 Relay Agent Echo Request Option", RFC 4994, 2860 DOI 10.17487/RFC4994, September 2007, 2861 . 2863 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 2864 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 2865 RFC 5213, DOI 10.17487/RFC5213, August 2008, 2866 . 2868 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2869 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2870 DOI 10.17487/RFC5214, March 2008, 2871 . 2873 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 2874 (TLS) Protocol Version 1.2", RFC 5246, 2875 DOI 10.17487/RFC5246, August 2008, 2876 . 2878 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 2879 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 2880 February 2010, . 2882 [RFC5494] Arkko, J. and C. Pignataro, "IANA Allocation Guidelines 2883 for the Address Resolution Protocol (ARP)", RFC 5494, 2884 DOI 10.17487/RFC5494, April 2009, 2885 . 2887 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 2888 Route Optimization Requirements for Operational Use in 2889 Aeronautics and Space Exploration Mobile Networks", 2890 RFC 5522, DOI 10.17487/RFC5522, October 2009, 2891 . 2893 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 2894 RFC 5558, DOI 10.17487/RFC5558, February 2010, 2895 . 2897 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 2898 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 2899 January 2010, . 2901 [RFC5720] Templin, F., "Routing and Addressing in Networks with 2902 Global Enterprise Recursion (RANGER)", RFC 5720, 2903 DOI 10.17487/RFC5720, February 2010, 2904 . 2906 [RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy 2907 Mobile IPv6", RFC 5844, DOI 10.17487/RFC5844, May 2010, 2908 . 2910 [RFC5949] Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F. 2911 Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949, 2912 DOI 10.17487/RFC5949, September 2010, 2913 . 2915 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 2916 "Internet Key Exchange Protocol Version 2 (IKEv2)", 2917 RFC 5996, DOI 10.17487/RFC5996, September 2010, 2918 . 2920 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 2921 NAT64: Network Address and Protocol Translation from IPv6 2922 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 2923 April 2011, . 2925 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 2926 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 2927 . 2929 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 2930 Troan, Ed., "Basic Requirements for IPv6 Customer Edge 2931 Routers", RFC 6204, DOI 10.17487/RFC6204, April 2011, 2932 . 2934 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 2935 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 2936 DOI 10.17487/RFC6221, May 2011, 2937 . 2939 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 2940 and A. Bierman, Ed., "Network Configuration Protocol 2941 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 2942 . 2944 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2945 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2946 2011, . 2948 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2949 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 2950 DOI 10.17487/RFC6355, August 2011, 2951 . 2953 [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", 2954 RFC 6422, DOI 10.17487/RFC6422, December 2011, 2955 . 2957 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 2958 for Equal Cost Multipath Routing and Link Aggregation in 2959 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 2960 . 2962 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 2963 RFC 6691, DOI 10.17487/RFC6691, July 2012, 2964 . 2966 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 2967 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 2968 . 2970 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 2971 RFC 6864, DOI 10.17487/RFC6864, February 2013, 2972 . 2974 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 2975 UDP Checksums for Tunneled Packets", RFC 6935, 2976 DOI 10.17487/RFC6935, April 2013, 2977 . 2979 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 2980 for the Use of IPv6 UDP Datagrams with Zero Checksums", 2981 RFC 6936, DOI 10.17487/RFC6936, April 2013, 2982 . 2984 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 2985 Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939, 2986 May 2013, . 2988 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 2989 with IPv6 Neighbor Discovery", RFC 6980, 2990 DOI 10.17487/RFC6980, August 2013, 2991 . 2993 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 2994 Address Selection Policy Using DHCPv6", RFC 7078, 2995 DOI 10.17487/RFC7078, January 2014, 2996 . 2998 [TUNTAP] Wikipedia, W., "http://en.wikipedia.org/wiki/TUN/TAP", 2999 October 2014. 3001 Appendix A. AERO Alternate Encapsulations 3003 When GUE encapsulation is not needed, AERO can use common 3004 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3005 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3006 encapsulation is therefore only differentiated from non-AERO tunnels 3007 through the application of AERO control messaging and not through, 3008 e.g., a well-known UDP port number. 3010 As for GUE encapsulation, alternate AERO encapsulation formats may 3011 require encapsulation layer fragmentation. For simple IP-in-IP 3012 encapsulation, an IPv6 fragment header is inserted directly between 3013 the inner and outer IP headers when needed, i.e., even if the outer 3014 header is IPv4. The IPv6 Fragment Header is identified to the outer 3015 IP layer by its IP protocol number, and the Next Header field in the 3016 IPv6 Fragment Header identifies the inner IP header version. For GRE 3017 encapsulation, a GRE fragment header is inserted within the GRE 3018 header [I-D.templin-intarea-grefrag]. 3020 Figure 9 shows the AERO IP-in-IP encapsulation format before any 3021 fragmentation is applied: 3023 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3024 | Outer IPv4 Header | | Outer IPv6 Header | 3025 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3026 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3028 | Inner IP Header | | Inner IP Header | 3029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3030 | | | | 3031 ~ ~ ~ ~ 3032 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3033 ~ ~ ~ ~ 3034 | | | | 3035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3037 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3039 Figure 9: Minimal Encapsulation Format using IP-in-IP 3041 Figure 10 shows the AERO GRE encapsulation format before any 3042 fragmentation is applied: 3044 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3045 | Outer IP Header | 3046 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3047 | GRE Header | 3048 | (with checksum, key, etc..) | 3049 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3050 | GRE Fragment Header (optional)| 3051 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3052 | Inner IP Header | 3053 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3054 | | 3055 ~ ~ 3056 ~ Inner Packet Body ~ 3057 ~ ~ 3058 | | 3059 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3061 Figure 10: Minimal Encapsulation Using GRE 3063 Alternate encapsulation may be preferred in environments where GUE 3064 encapsulation would add unnecessary overhead. For example, certain 3065 low-bandwidth wireless data links may benefit from a reduced 3066 encapsulation overhead. 3068 GUE encapsulation can traverse network paths that are inaccessible to 3069 non-UDP encapsulations, e.g., for crossing Network Address 3070 Translators (NATs). More and more, network middleboxes are also 3071 being configured to discard packets that include anything other than 3072 a well-known IP protocol such as UDP and TCP. It may therefore be 3073 necessary to determine the potential for middlebox filtering before 3074 enabling alternate encapsulation in a given environment. 3076 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3077 encapsulations such as IPsec and SSL/TLS. In that case, AERO control 3078 messaging and route determination occur before security encapsulation 3079 is applied for outgoing packets and after security decapsulation is 3080 applied for incoming packets. 3082 Appendix B. When to Insert an Encapsulation Fragment Header 3084 An encapsulation fragment header is inserted when the AERO tunnel 3085 ingress needs to apply fragmentation to accommodate packets that must 3086 be delivered without loss due to a size restriction. Fragmentation 3087 is performed on the inner packet while encapsulating each inner 3088 packet fragment in outer IP and encapsulation layer headers that 3089 differ only in the fragment header fields. 3091 The fragment header can also be inserted in order to include a 3092 coherent Identification value with each packet, e.g., to aid in 3093 Duplicate Packet Detection (DPD). In this way, network nodes can 3094 cache the Identification values of recently-seen packets and use the 3095 cached values to determine whether a newly-arrived packet is in fact 3096 a duplicate. The Identification value within each packet could 3097 further provide a rough indicator of packet reordering, e.g., in 3098 cases when the tunnel egress wishes to discard packets that are 3099 grossly out of order. 3101 In some use cases, there may be operational assurance that no 3102 fragmentation of any kind will be necessary, or that only occasional 3103 large control messages will require fragmentation. In that case, the 3104 encapsulation fragment header can be omitted and ordinary 3105 fragmentation of the outer IP protocol version can be applied when 3106 necessary. 3108 Author's Address 3110 Fred L. Templin (editor) 3111 Boeing Research & Technology 3112 P.O. Box 3707 3113 Seattle, WA 98124 3114 USA 3116 Email: fltemplin@acm.org