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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, June 8, 2015 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: December 10, 2015 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-aerolink-55.txt 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). Nodes attached 17 to AERO links can exchange packets via trusted intermediate routers 18 that provide forwarding services to reach off-link destinations and 19 redirection services for route optimization. AERO provides an IPv6 20 link-local address format known as the AERO address that supports 21 operation of the IPv6 Neighbor Discovery (ND) protocol and links IPv6 22 ND to IP forwarding. Admission control and provisioning are 23 supported by the Dynamic Host Configuration Protocol for IPv6 24 (DHCPv6), and node mobility is naturally supported through dynamic 25 neighbor cache updates. Although DHCPv6 and IPv6 ND messaging are 26 used in the control plane, both IPv4 and IPv6 are supported in the 27 data plane. AERO is a widely-applicable tunneling solution using 28 standard control messaging exchanges as described in this document. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on December 10, 2015. 47 Copyright Notice 49 Copyright (c) 2015 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 6 67 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 6 68 3.2. AERO Link Node Types . . . . . . . . . . . . . . . . . . 8 69 3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 9 70 3.4. AERO Interface Characteristics . . . . . . . . . . . . . 10 71 3.5. AERO Link Registration . . . . . . . . . . . . . . . . . 11 72 3.6. AERO Interface Initialization . . . . . . . . . . . . . . 12 73 3.6.1. AERO Relay Behavior . . . . . . . . . . . . . . . . . 12 74 3.6.2. AERO Server Behavior . . . . . . . . . . . . . . . . 12 75 3.6.3. AERO Client Behavior . . . . . . . . . . . . . . . . 13 76 3.6.4. AERO Forwarding Agent Behavior . . . . . . . . . . . 13 77 3.7. AERO Link Routing System . . . . . . . . . . . . . . . . 13 78 3.8. AERO Interface Neighbor Cache Maintenace . . . . . . . . 15 79 3.9. AERO Interface Sending Algorithm . . . . . . . . . . . . 16 80 3.10. AERO Interface Encapsulation and Re-encapsulation . . . . 18 81 3.11. AERO Interface Decapsulation . . . . . . . . . . . . . . 20 82 3.12. AERO Interface Data Origin Authentication . . . . . . . . 21 83 3.13. AERO Interface MTU and Fragmentation . . . . . . . . . . 21 84 3.13.1. Accommodating Large Control Messages . . . . . . . . 24 85 3.13.2. Integrity . . . . . . . . . . . . . . . . . . . . . 25 86 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 26 87 3.15. AERO Router Discovery, Prefix Delegation and Address 88 Configuration . . . . . . . . . . . . . . . . . . . . . . 30 89 3.15.1. AERO DHCPv6 Service Model . . . . . . . . . . . . . 30 90 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 31 91 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 34 92 3.15.4. Deleting Link Registrations . . . . . . . . . . . . 37 93 3.16. AERO Forwarding Agent Behavior . . . . . . . . . . . . . 37 94 3.17. AERO Intradomain Route Optimization . . . . . . . . . . . 38 95 3.17.1. Reference Operational Scenario . . . . . . . . . . . 38 96 3.17.2. Concept of Operations . . . . . . . . . . . . . . . 40 97 3.17.3. Message Format . . . . . . . . . . . . . . . . . . . 40 98 3.17.4. Sending Predirects . . . . . . . . . . . . . . . . . 41 99 3.17.5. Re-encapsulating and Relaying Predirects . . . . . . 42 100 3.17.6. Processing Predirects and Sending Redirects . . . . 43 101 3.17.7. Re-encapsulating and Relaying Redirects . . . . . . 45 102 3.17.8. Processing Redirects . . . . . . . . . . . . . . . . 46 103 3.17.9. Server-Oriented Redirection . . . . . . . . . . . . 46 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 46 105 3.19. Mobility Management . . . . . . . . . . . . . . . . . . . 48 106 3.19.1. Announcing Link-Layer Address Changes . . . . . . . 48 107 3.19.2. Bringing New Links Into Service . . . . . . . . . . 49 108 3.19.3. Removing Existing Links from Service . . . . . . . . 49 109 3.19.4. Moving to a New Server . . . . . . . . . . . . . . . 50 110 3.20. Proxy AERO . . . . . . . . . . . . . . . . . . . . . . . 50 111 3.21. Extending AERO Links Through Security Gateways . . . . . 53 112 3.22. Extending IPv6 AERO Links to the Internet . . . . . . . . 55 113 3.23. Encapsulation Protocol Version Considerations . . . . . . 58 114 3.24. Multicast Considerations . . . . . . . . . . . . . . . . 58 115 3.25. Operation on AERO Links Without DHCPv6 Services . . . . . 59 116 3.26. Operation on Server-less AERO Links . . . . . . . . . . . 59 117 3.27. Manually-Configured AERO Tunnels . . . . . . . . . . . . 59 118 3.28. Intradomain Routing . . . . . . . . . . . . . . . . . . . 59 119 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 59 120 5. Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . 60 121 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60 122 7. Security Considerations . . . . . . . . . . . . . . . . . . . 60 123 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 61 124 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 62 125 9.1. Normative References . . . . . . . . . . . . . . . . . . 62 126 9.2. Informative References . . . . . . . . . . . . . . . . . 63 127 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 68 129 1. Introduction 131 This document specifies the operation of IP over tunnel virtual links 132 using Asymmetric Extended Route Optimization (AERO). The AERO link 133 can be used for tunneling to neighboring nodes over either IPv6 or 134 IPv4 networks, i.e., AERO views the IPv6 and IPv4 networks as 135 equivalent links for tunneling. Nodes attached to AERO links can 136 exchange packets via trusted intermediate routers that provide 137 forwarding services to reach off-link destinations and redirection 138 services for route optimization that addresses the requirements 139 outlined in [RFC5522]. 141 AERO provides an IPv6 link-local address format known as the AERO 142 address that supports operation of the IPv6 Neighbor Discovery (ND) 144 [RFC4861] protocol and links IPv6 ND to IP forwarding. Admission 145 control and provisioning are supported by the Dynamic Host 146 Configuration Protocol for IPv6 (DHCPv6) [RFC3315], and node mobility 147 is naturally supported through dynamic neighbor cache updates. 148 Although DHCPv6 and IPv6 ND messaging are used in the control plane, 149 both IPv4 and IPv6 can be used in the data plane. AERO is a widely- 150 applicable tunneling solution using standard control messaging 151 exchanges as described in this document. The remainder of this 152 document presents the AERO specification. 154 2. Terminology 156 The terminology in the normative references applies; the following 157 terms are defined within the scope of this document: 159 AERO link 160 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 161 configured over a node's attached IPv6 and/or IPv4 networks. All 162 nodes on the AERO link appear as single-hop neighbors from the 163 perspective of the virtual overlay. 165 AERO interface 166 a node's attachment to an AERO link. Nodes typically have a 167 single AERO interface; support for multiple AERO interfaces is 168 also possible but out of scope for this document. 170 AERO address 171 an IPv6 link-local address constructed as specified in Section 3.3 172 and assigned to a Client's AERO interface. 174 AERO node 175 a node that is connected to an AERO link and that participates in 176 IPv6 ND and DHCPv6 messaging over the link. 178 AERO Client ("Client") 179 a node that issues DHCPv6 messages using the special IPv6 link- 180 local address 'fe80::ffff:ffff:ffff:ffff' to receive IP Prefix 181 Delegations (PD) from one or more AERO Servers. Following PD, the 182 Client assigns an AERO address to the AERO interface which it uses 183 in IPv6 ND messaging to coordinate with other AERO nodes. 185 AERO Server ("Server") 186 a node that configures an AERO interface to provide default 187 forwarding and DHCPv6 services for AERO Clients. The Server 188 assigns an administratively provisioned IPv6 link-local unicast 189 address to support the operation of DHCPv6 and the IPv6 ND 190 protocol. An AERO Server can also act as an AERO Relay. 192 AERO Relay ("Relay") 193 a node that configures an AERO interface to relay IP packets 194 between nodes on the same AERO link and/or forward IP packets 195 between the AERO link and the native Internetwork. The Relay 196 assigns an administratively provisioned IPv6 link-local unicast 197 address to the AERO interface the same as for a Server. An AERO 198 Relay can also act as an AERO Server. 200 AERO Forwarding Agent ("Forwarding Agent") 201 a node that performs data plane forwarding services as a companion 202 to an AERO Server. 204 ingress tunnel endpoint (ITE) 205 an AERO interface endpoint that injects tunneled packets into an 206 AERO link. 208 egress tunnel endpoint (ETE) 209 an AERO interface endpoint that receives tunneled packets from an 210 AERO link. 212 underlying network 213 a connected IPv6 or IPv4 network routing region over which the 214 tunnel virtual overlay is configured. A typical example is an 215 enterprise network. 217 underlying interface 218 an AERO node's interface point of attachment to an underlying 219 network. 221 link-layer address 222 an IP address assigned to an AERO node's underlying interface. 223 When UDP encapsulation is used, the UDP port number is also 224 considered as part of the link-layer address. Link-layer 225 addresses are used as the encapsulation header source and 226 destination addresses. 228 network layer address 229 the source or destination address of the encapsulated IP packet. 231 end user network (EUN) 232 an internal virtual or external edge IP network that an AERO 233 Client connects to the rest of the network via the AERO interface. 235 AERO Service Prefix (ASP) 236 an IP prefix associated with the AERO link and from which AERO 237 Client Prefixes (ACPs) are derived (for example, the IPv6 ACP 238 2001:db8:1:2::/64 is derived from the IPv6 ASP 2001:db8::/32). 240 AERO Client Prefix (ACP) 241 a more-specific IP prefix taken from an ASP and delegated to a 242 Client. 244 Throughout the document, the simple terms "Client", "Server" and 245 "Relay" refer to "AERO Client", "AERO Server" and "AERO Relay", 246 respectively. Capitalization is used to distinguish these terms from 247 DHCPv6 client/server/relay [RFC3315]. 249 The terminology of [RFC4861] (including the names of node variables 250 and protocol constants) applies to this document. Also throughout 251 the document, the term "IP" is used to generically refer to either 252 Internet Protocol version (i.e., IPv4 or IPv6). 254 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 255 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 256 document are to be interpreted as described in [RFC2119]. Lower case 257 uses of these words are not to be interpreted as carrying RFC2119 258 significance. 260 3. Asymmetric Extended Route Optimization (AERO) 262 The following sections specify the operation of IP over Asymmetric 263 Extended Route Optimization (AERO) links: 265 3.1. AERO Link Reference Model 266 .-(::::::::) 267 .-(:::: IP ::::)-. 268 (:: Internetwork ::) 269 `-(::::::::::::)-' 270 `-(::::::)-' 271 | 272 +--------------+ +--------+-------+ +--------------+ 273 |AERO Server S1| | AERO Relay R1 | |AERO Server S2| 274 | Nbr: C1; R1 | | Nbr: S1; S2 | | Nbr: C2; R1 | 275 | default->R1 | |(H1->S1; H2->S2)| | default->R1 | 276 | H1->C1 | +--------+-------+ | H2->C2 | 277 +-------+------+ | +------+-------+ 278 | | | 279 X---+---+-------------------+------------------+---+---X 280 | AERO Link | 281 +-----+--------+ +--------+-----+ 282 |AERO Client C1| |AERO Client C2| 283 | Nbr: S1 | | Nbr: S2 | 284 | default->S1 | | default->S2 | 285 +--------------+ +--------------+ 286 .-. .-. 287 ,-( _)-. ,-( _)-. 288 .-(_ IP )-. .-(_ IP )-. 289 (__ EUN ) (__ EUN ) 290 `-(______)-' `-(______)-' 291 | | 292 +--------+ +--------+ 293 | Host H1| | Host H2| 294 +--------+ +--------+ 296 Figure 1: AERO Link Reference Model 298 Figure 1 presents the AERO link reference model. In this model: 300 o Relay R1 acts as a default router for its associated Servers S1 301 and S2, and connects the AERO link to the rest of the IP 302 Internetwork 304 o Servers S1 and S2 associate with Relay R1 and also act as default 305 routers for their associated Clients C1 and C2. 307 o Clients C1 and C2 associate with Servers S1 and S2, respectively 308 and also act as default routers for their associated EUNs 310 o Hosts H1 and H2 attach to the EUNs served by Clients C1 and C2, 311 respectively 313 Each node maintains a neighbor cache and IP forwarding table. (For 314 example, AERO Relay R1 in the diagram has neighbor cache entries for 315 Servers S1 and S2 and IP forwarding table entries for ACPs H1 and 316 H2.) In common operational practice, there may be many additional 317 Relays, Servers and Clients. (Although not shown in the figure, AERO 318 Forwarding Agents may also be provided for data plane forwarding 319 offload services.) 321 3.2. AERO Link Node Types 323 AERO Relays provide default forwarding services to AERO Servers. 324 Relays forward packets between Servers connected to the same AERO 325 link and also forward packets between the AERO link and the native IP 326 Internetwork. Relays present the AERO link to the native 327 Internetwork as a set of one or more AERO Service Prefixes (ASPs) and 328 serve as a gateway between the AERO link and the Internetwork. AERO 329 Relays maintain an AERO interface neighbor cache entry for each AERO 330 Server, and maintain an IP forwarding table entry for each AERO 331 Client Prefix (ACP). AERO Relays can also be configured to act as 332 AERO Servers. 334 AERO Servers provide default forwarding services to AERO Clients. 335 Each Server also peers with each Relay in a dynamic routing protocol 336 instance to advertise its list of associated ACPs. Servers configure 337 a DHCPv6 server function to facilitate Prefix Delegation (PD) 338 exchanges with Clients. Each delegated prefix becomes an ACP taken 339 from an ASP. Servers forward packets between AERO interface 340 neighbors only, i.e., and not between the AERO link and the native IP 341 Internetwork. AERO Servers maintain an AERO interface neighbor cache 342 entry for each AERO Relay. They also maintain both a neighbor cache 343 entry and an IP forwarding table entry for each of their associated 344 Clients. AERO Servers can also be configured to act as AERO Relays. 346 AERO Clients act as requesting routers to receive ACPs through DHCPv6 347 PD exchanges with AERO Servers over the AERO link and sub-delegate 348 portions of their ACPs to EUN interfaces. (Each Client MAY associate 349 with a single Server or with multiple Servers, e.g., for fault 350 tolerance, load balancing, etc.) Each IPv6 Client receives at least 351 a /64 IPv6 ACP, and may receive even shorter prefixes. Similarly, 352 each IPv4 Client receives at least a /32 IPv4 ACP (i.e., a singleton 353 IPv4 address), and may receive even shorter prefixes. AERO Clients 354 maintain an AERO interface neighbor cache entry for each of their 355 associated Servers as well as for each of their correspondent 356 Clients. 358 AERO Clients typically configure a TUN/TAP interface [TUNTAP] as a 359 point-to-point linkage between the IP layer and the AERO interface. 360 The IP layer therefore sees only the TUN/TAP interface, while the 361 AERO interface provides an intermediate conduit between the TUN/TAP 362 interface and the underlying interfaces. AERO Clients that act as 363 hosts assign one or more IP addresses from their ACPs to the TUN/TAP 364 interface, i.e., and not to the AERO interface. 366 AERO Forwarding Agents provide data plane forwarding services as 367 companions to AERO Servers. Note that while Servers are required to 368 perform both control and data plane operations on their own behalf, 369 they may optionally enlist the services of special-purpose Forwarding 370 Agents to offload data plane traffic. 372 3.3. AERO Addresses 374 An AERO address is an IPv6 link-local address with an embedded ACP 375 and assigned to a Client's AERO interface. The AERO address is 376 formed as follows: 378 fe80::[ACP] 380 For IPv6, the AERO address begins with the prefix fe80::/64 and 381 includes in its interface identifier the base prefix taken from the 382 Client's IPv6 ACP. The base prefix is determined by masking the ACP 383 with the prefix length. For example, if the AERO Client receives the 384 IPv6 ACP: 386 2001:db8:1000:2000::/56 388 it constructs its AERO address as: 390 fe80::2001:db8:1000:2000 392 For IPv4, the AERO address is formed from the lower 64 bits of an 393 IPv4-mapped IPv6 address [RFC4291] that includes the base prefix 394 taken from the Client's IPv4 ACP. For example, if the AERO Client 395 receives the IPv4 ACP: 397 192.0.2.32/28 399 it constructs its AERO address as: 401 fe80::FFFF:192.0.2.32 403 The AERO address remains stable as the Client moves between 404 topological locations, i.e., even if its link-layer addresses change. 406 NOTE: In some cases, prospective neighbors may not have advanced 407 knowledge of the Client's ACP length and may therefore send initial 408 IPv6 ND messages with an AERO destination address that matches the 409 ACP but does not correspond to the base prefix. In that case, the 410 Client MUST accept the address as equivalent to the base address, but 411 then use the base address as the source address of any IPv6 ND 412 message replies. For example, if the Client receives the IPv6 ACP 413 2001:db8:1000:2000::/56 then subsequently receives an IPv6 ND message 414 with destination address fe80::2001:db8:1000:2001, it accepts the 415 message but uses fe80::2001:db8:1000:2000 as the source address of 416 any IPv6 ND replies. 418 3.4. AERO Interface Characteristics 420 AERO interfaces use encapsulation (see Section 3.10) to exchange 421 packets with neighbors attached to the AERO link. AERO interfaces 422 maintain a neighbor cache, and AERO Clients and Servers use unicast 423 IPv6 ND messaging. AERO interfaces use unicast Neighbor Solicitation 424 (NS), Neighbor Advertisement (NA), Router Solicitation (RS) and 425 Router Advertisement (RA) messages the same as for any IPv6 link. 426 AERO interfaces use two redirection message types -- the first known 427 as a Predirect message and the second being the standard Redirect 428 message (see Section 3.17). AERO links further use link-local-only 429 addressing; hence, AERO nodes ignore any Prefix Information Options 430 (PIOs) they may receive in RA messages over an AERO interface. 432 AERO interface ND messages include one or more Source/Target Link- 433 Layer Address Options (S/TLLAOs) formatted as shown in Figure 2: 435 0 1 2 3 436 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 1 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 438 | Type = 2 | Length = 3 | Reserved | 439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 440 | Link ID | NDSCPs | DSCP #1 |Prf| DSCP #2 |Prf| 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 442 | DSCP #3 |Prf| DSCP #4 |Prf| .... 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | UDP Port Number | | 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 446 | | 447 + + 448 | IP Address | 449 + + 450 | | 451 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 452 | | 453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 455 Figure 2: AERO Source/Target Link-Layer Address Option (S/TLLAO) 456 Format 458 In this format, Link ID is an integer value between 0 and 255 459 corresponding to an underlying interface of the target node, NDSCPs 460 encodes an integer value between 1 and 64 indicating the number of 461 Differentiated Services Code Point (DSCP) octets that follow. Each 462 DSCP octet is a 6-bit integer DSCP value followed by a 2-bit 463 Preference ("Prf") value. Each DSCP value encodes an integer between 464 0 and 63 associated with this Link ID, where the value 0 means 465 "default" and other values are interpreted as specified in [RFC2474]. 466 The 'Prf' qualifier for each DSCP value is set to the value 0 467 ("deprecated'), 1 ("low"), 2 ("medium"), or 3 ("high") to indicate a 468 preference level for packet forwarding purposes. UDP Port Number and 469 IP Address are set to the addresses used by the target node when it 470 sends encapsulated packets over the underlying interface. When the 471 encapsulation IP address family is IPv4, IP Address is formed as an 472 IPv4-mapped IPv6 address [RFC4291]. 474 AERO interfaces may be configured over multiple underlying 475 interfaces. For example, common mobile handheld devices have both 476 wireless local area network ("WLAN") and cellular wireless links. 477 These links are typically used "one at a time" with low-cost WLAN 478 preferred and highly-available cellular wireless as a standby. In a 479 more complex example, aircraft frequently have many wireless data 480 link types (e.g. satellite-based, terrestrial, air-to-air 481 directional, etc.) with diverse performance and cost properties. 483 If a Client's multiple underlying interfaces are used "one at a time" 484 (i.e., all other interfaces are in standby mode while one interface 485 is active), then Redirect, Predirect and unsolicited NA messages 486 include only a single TLLAO with Link ID set to a constant value. 488 If the Client has multiple active underlying interfaces, then from 489 the perspective of IPv6 ND it would appear to have a single link- 490 local address with multiple link-layer addresses. In that case, 491 Redirect, Predirect and unsolicited NA messages MAY include multiple 492 TLLAOs -- each with a different Link ID that corresponds to a 493 specific underlying interface of the Client. 495 3.5. AERO Link Registration 497 When an administrative authority first deploys a set of AERO Relays 498 and Servers that comprise an AERO link, they also assign a unique 499 domain name for the link, e.g., "linkupnetworks.example.com". Next, 500 if administrative policy permits Clients within the domain to serve 501 as correspondent nodes for Internet mobile nodes, the administrative 502 authority adds a Fully Qualified Domain Name (FQDN) for each of the 503 AERO link's ASPs to the Domain Name System (DNS) [RFC1035]. The FQDN 504 is based on the suffix "aero.linkupnetworks.net" with a prefix formed 505 from the wildcard-terminated reverse mapping of the ASP 507 [RFC3596][RFC4592], and resolves to a DNS PTR resource record. For 508 example, for the ASP '2001:db8:1::/48' within the domain name 509 "linkupnetworks.example.com", the DNS database contains: 511 '*.1.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net. PTR 512 linkupnetworks.example.com' 514 This DNS registration advertises the AERO link's ASPs to prospective 515 mobile nodes. 517 3.6. AERO Interface Initialization 519 3.6.1. AERO Relay Behavior 521 When a Relay enables an AERO interface, it first assigns an 522 administratively provisioned link-local address fe80::ID to the 523 interface. Each fe80::ID address MUST be unique among all AERO nodes 524 on the link, and MUST NOT collide with any potential AERO addresses 525 nor the special addresses fe80:: and fe80::ffff:ffff:ffff:ffff. (The 526 fe80::ID addresses are typically taken from the available range 527 fe80::/96, e.g., as fe80::1, fe80::2, fe80::3, etc.) The Relay then 528 engages in a dynamic routing protocol session with all Servers on the 529 link (see: Section 3.7), and advertises the set of ASPs into the 530 native IP Internetwork. 532 Each Relay subsequently maintains an IP forwarding table entry for 533 each Client-Server association, and maintains a neighbor cache entry 534 for each Server on the link. Relays exchange NS/NA messages with 535 AERO link neighbors the same as for any AERO node, however they 536 typically do not perform explicit Neighbor Unreachability Detection 537 (NUD) (see: Section 3.18) since the dynamic routing protocol already 538 provides reachability confirmation. 540 3.6.2. AERO Server Behavior 542 When a Server enables an AERO interface, it assigns an 543 administratively provisioned link-local address fe80::ID the same as 544 for Relays. The Server further configures a DHCPv6 server function 545 to facilitate DHCPv6 PD exchanges with AERO Clients. The Server 546 maintains a neighbor cache entry for each Relay on the link, and 547 manages per-Client neighbor cache entries and IP forwarding table 548 entries based on control message exchanges. Each Server also engages 549 in a dynamic routing protocol with each Relay on the link (see: 550 Section 3.7). 552 When the Server receives an NS/RS message on the AERO interface it 553 returns an NA/RA message but does not update the neighbor cache. The 554 Server further provides a simple conduit between AERO interface 555 neighbors. Therefore, packets enter the Server's AERO interface from 556 the link layer and are forwarded back out the link layer without ever 557 leaving the AERO interface and therefore without ever disturbing the 558 network layer. 560 3.6.3. AERO Client Behavior 562 When a Client enables an AERO interface, it uses the special address 563 fe80::ffff:ffff:ffff:ffff to obtain an ACP from an AERO Server via 564 DHCPv6 PD. Next, it assigns the corresponding AERO address to the 565 AERO interface and creates a neighbor cache entry for the Server, 566 i.e., the PD exchange bootstraps autoconfiguration of a unique link- 567 local address. The Client maintains a neighbor cache entry for each 568 of its Servers and each of its active correspondent Clients. When 569 the Client receives Redirect/Predirect messages on the AERO interface 570 it updates or creates neighbor cache entries, including link-layer 571 address information. Unsolicited NA messages update the cached link- 572 layer addresses for correspondent Clients (e.g., following a link- 573 layer address change due to node mobility) but do not create new 574 neighbor cache entries. NS/NA messages used for NUD update timers in 575 existing neighbor cache entires but do not update link-layer 576 addresses nor create new neighbor cache entries. 578 Finally, the Client need not maintain any IP forwarding table entries 579 for its Servers or correspondent Clients. Instead, it can set a 580 single "route-to-interface" default route in the IP forwarding table, 581 and all forwarding decisions can be made within the AERO interface 582 based on neighbor cache entries. (On systems in which adding a 583 default route would violate security policy, the default route could 584 instead be installed via a "synthesized RA", e.g., as discussed in 585 Section 3.15.2.) 587 3.6.4. AERO Forwarding Agent Behavior 589 When a Forwarding Agent enables an AERO interface, it assigns the 590 same link-local address(es) as the companion AERO Server. The 591 Forwarding Agent thereafter provides data plane forwarding services 592 based solely on the forwarding information assigned to it by the 593 companion AERO Server. AERO Forwarding Agents perform NS/NA 594 messaging, i.e., the same as for any AERO node. 596 3.7. AERO Link Routing System 598 Relays require full topology knowledge of all ACP/Server 599 associations, while individual Servers at a minimum only need to know 600 the ACPs for their current set of associated Clients. This is 601 accomplished through the use of an internal instance of the Border 602 Gateway Protocol (BGP) [RFC4271] coordinated between Servers and 603 Relays. This internal BGP instance does not interact with the public 604 Internet BGP instance; therefore, the AERO link is presented to the 605 IP Internetwork as a small set of ASPs as opposed to the full set of 606 individual ACPs. 608 In a reference BGP arrangement, each AERO Server is configured as an 609 Autonomous System Border Router (ASBR) for a stub Autonomous System 610 (AS) using an AS Number (ASN) that is unique within the BGP instance, 611 and each Server further peers with each Relay but does not peer with 612 other Servers. Similarly, Relays do not peer with each other, since 613 they will reliably receive all updates from all Servers and will 614 therefore have a consistent view of the AERO link ACP delegations. 616 Each Server maintains a working set of associated ACPs, and 617 dynamically announces new ACPs and withdraws departed ACPs in its BGP 618 updates to Relays. Clients are expected to remain associated with 619 their current Servers for extended timeframes, however Servers SHOULD 620 selectively suppress BGP updates for impatient Clients that 621 repeatedly associate and disassociate with them in order to dampen 622 routing churn. 624 In some environments, Relays need not send BGP updates to Servers 625 since Servers can always use Relays as default routers, however this 626 presents a data/control plane performance tradeoff. In environments 627 where sustained packet forwarding over Relays is undesirable, Relays 628 can instead report ACPs to Servers while including a BGP Remote-Next- 629 Hop [I-D.vandevelde-idr-remote-next-hop]. The Server then creates a 630 neighbor cache entry for each ACP with the Remote-Next-Hop as the 631 link-layer address to enable Server-to-Server route optimization. 633 Scaling properties of the AERO routing system are therefore limited 634 by the number of BGP routes that can be carried by Relays. Assuming 635 O(10^6) as a maximum number of BGP routes, this means that at most 636 O(10^6) Clients can be serviced by Relays within a single BGP 637 instance. A means of increasing scaling would be to assign a 638 different set of Relays for each set of ASPs, and still have each 639 Server peer with each Relay but with a distinct BGP instance for each 640 Relay set. Another possibility would be for Servers to institute 641 route flters within a single BGP instance so that each set of Relays 642 only receives BGP updates for the ASPs they aggregate. 644 Assuming up to O(10^3) sets of Relays, scaling can then accomodate 645 O(10^9) Clients with no additional overhead for Servers and Relays. 646 In this way, each set of Relays services a specific set of ASPs that 647 they advertise to peers outside of the AERO link, and each Server 648 configures ASP-specific routes that list the correct set of Relays as 649 next hops. 651 3.8. AERO Interface Neighbor Cache Maintenace 653 Each AERO interface maintains a conceptual neighbor cache that 654 includes an entry for each neighbor it communicates with on the AERO 655 link, the same as for any IPv6 interface [RFC4861]. AERO interface 656 neighbor cache entires are said to be one of "permanent", "static" or 657 "dynamic". 659 Permanent neighbor cache entries are created through explicit 660 administrative action; they have no timeout values and remain in 661 place until explicitly deleted. AERO Relays maintain a permanent 662 neighbor cache entry for each Server on the link, and AERO Servers 663 maintain a permanent neighbor cache entry for each Relay. Each entry 664 maintains the mapping between the neighbor's fe80::ID network-layer 665 address and corresponding link-layer address. 667 Static neighbor cache entries are created though DHCPv6 PD exchanges 668 and remain in place for durations bounded by prefix lifetimes. AERO 669 Servers maintain static neighbor cache entries for the ACPs of each 670 of their associated Clients, and AERO Clients maintain a static 671 neighbor cache entry for each of their associated Servers. When an 672 AERO Server sends a DHCPv6 Reply message response to a Client's 673 DHCPv6 Solicit/Request, Rebind or Renew message, it creates or 674 updates a static neighbor cache entry based on the AERO address 675 corresponding to the Client's ACP as the network-layer address, the 676 prefix lifetime as the neighbor cache entry lifetime, the Client's 677 encapsulation IP address and UDP port number as the link-layer 678 address and the prefix length as the length to apply to the AERO 679 address. When an AERO Client receives a DHCPv6 Reply message from a 680 Server, it creates or updates a static neighbor cache entry based on 681 the Reply message link-local source address as the network-layer 682 address, the prefix lifetime as the neighbor cache entry lifetime, 683 and the encapsulation IP source address and UDP source port number as 684 the link-layer address. 686 Dynamic neighbor cache entries are created or updated based on 687 receipt of an IPv6 ND message, and are garbage-collected if not used 688 within a bounded timescale. AERO Clients maintain dynamic neighbor 689 cache entries for each of their active correspondent Client ACPs with 690 lifetimes based on IPv6 ND messaging constants. When an AERO Client 691 receives a valid Predirect message it creates or updates a dynamic 692 neighbor cache entry for the Predirect target network-layer and link- 693 layer addresses plus prefix length. The node then sets an 694 "AcceptTime" variable in the neighbor cache entry to ACCEPT_TIME 695 seconds and uses this value to determine whether packets received 696 from the correspondent can be accepted. When an AERO Client receives 697 a valid Redirect message it creates or updates a dynamic neighbor 698 cache entry for the Redirect target network-layer and link-layer 699 addresses plus prefix length. The Client then sets a "ForwardTime" 700 variable in the neighbor cache entry to FORWARD_TIME seconds and uses 701 this value to determine whether packets can be sent directly to the 702 correspondent. The Client also sets a "MaxRetry" variable to 703 MAX_RETRY to limit the number of keepalives sent when a correspondent 704 may have gone unreachable. 706 For dynamic neighbor cache entries, when an AERO Client receives a 707 valid NS message it (re)sets AcceptTime for the neighbor to 708 ACCEPT_TIME. When an AERO Client receives a valid solicited NA 709 message, it (re)sets ForwardTime for the neighbor to FORWARD_TIME and 710 sets MaxRetry to MAX_RETRY. When an AERO Client receives a valid 711 unsolicited NA message, it updates the correspondent's link-layer 712 addresses but DOES NOT reset AcceptTime, ForwardTime or MaxRetry. 714 It is RECOMMENDED that FORWARD_TIME be set to the default constant 715 value 30 seconds to match the default REACHABLE_TIME value specified 716 for IPv6 ND [RFC4861]. 718 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 719 value 40 seconds to allow a 10 second window so that the AERO 720 redirection procedure can converge before AcceptTime decrements below 721 FORWARD_TIME. 723 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 724 for IPv6 ND address resolution in Section 7.3.3 of [RFC4861]. 726 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 727 administratively set, if necessary, to better match the AERO link's 728 performance characteristics; however, if different values are chosen, 729 all nodes on the link MUST consistently configure the same values. 730 Most importantly, ACCEPT_TIME SHOULD be set to a value that is 731 sufficiently longer than FORWARD_TIME to allow the AERO redirection 732 procedure to converge. 734 3.9. AERO Interface Sending Algorithm 736 IP packets enter a node's AERO interface either from the network 737 layer (i.e., from a local application or the IP forwarding system), 738 or from the link layer (i.e., from the AERO tunnel virtual link). 739 Packets that enter the AERO interface from the network layer are 740 encapsulated and admitted into the AERO link, i.e., they are 741 tunnelled to an AERO interface neighbor. Packets that enter the AERO 742 interface from the link layer are either re-admitted into the AERO 743 link or delivered to the network layer where they are subject to 744 either local delivery or IP forwarding. Since each AERO node may 745 have only partial information about neighbors on the link, AERO 746 interfaces may forward packets with link-local destination addresses 747 at a layer below the network layer. This means that AERO nodes act 748 as both IP routers and sub-IP layer forwarding agents. AERO 749 interface sending considerations for Clients, Servers and Relays are 750 given below. 752 When an IP packet enters a Client's AERO interface from the network 753 layer, if the destination is covered by an ASP the Client searches 754 for a dynamic neighbor cache entry with a non-zero ForwardTime and an 755 AERO address that matches the packet's destination address. (The 756 destination address may be either an address covered by the 757 neighbor's ACP or the (link-local) AERO address itself.) If there is 758 a match, the Client uses a link-layer address in the entry as the 759 link-layer address for encapsulation then admits the packet into the 760 AERO link. If there is no match, the Client instead uses the link- 761 layer address of a neighboring Server as the link-layer address for 762 encapsulation. 764 When an IP packet enters a Server's AERO interface from the link 765 layer, if the destination is covered by an ASP the Server searches 766 for a neighbor cache entry with an AERO address that matches the 767 packet's destination address. (The destination address may be either 768 an address covered by the neighbor's ACP or the AERO address itself.) 769 If there is a match, the Server uses a link-layer address in the 770 entry as the link-layer address for encapsulation and re-admits the 771 packet into the AERO link. If there is no match, the Server instead 772 uses the link-layer address in a permanent neighbor cache entry for a 773 Relay as the link-layer address for encapsulation. 775 When an IP packet enters a Relay's AERO interface from the network 776 layer, the Relay searches its IP forwarding table for an entry that 777 is covered by an ASP and also matches the destination. If there is a 778 match, the Relay uses the link-layer address in a permanent neighbor 779 cache entry for a Server as the link-layer address for encapsulation 780 and admits the packet into the AERO link. When an IP packet enters a 781 Relay's AERO interface from the link-layer, if the destination is not 782 a link-local address and does not match an ASP the Relay removes the 783 packet from the AERO interface and uses IP forwarding to forward the 784 packet to the Internetwork. If the destination address is a link- 785 local address or a non-link-local address that matches an ASP, and 786 there is a more-specific ACP entry in the IP forwarding table, the 787 Relay uses the link-layer address in the corresponding neighbor cache 788 entry as the link-layer address for encapsulation and re-admits the 789 packet into the AERO link. When an IP packet enters a Relay's AERO 790 interface from either the network layer or link-layer, and the 791 packet's destination address matches an ASP but there is no more- 792 specific ACP entry, the Relay drops the packet and returns an ICMP 793 Destination Unreachable message (see: Section 3.14). 795 When an AERO Server receives a packet from a Relay via the AERO 796 interface, the Server MUST NOT forward the packet back to the same or 797 a different Relay. 799 When an AERO Relay receives a packet from a Server via the AERO 800 interface, the Relay MUST NOT forward the packet back to the same 801 Server. 803 When an AERO node re-admits a packet into the AERO link without 804 involving the network layer, the node MUST NOT decrement the network 805 layer TTL/Hop-count. 807 When an AERO node forwards a data packet to the primary link-layer 808 address of a Server, it may receive Redirect messages with an SLLAO 809 that include the link-layer address of an AERO Forwarding Agent. The 810 AERO node SHOULD record the link-layer address in the neighbor cache 811 entry for the neighbor and send subsequent data packets via this 812 address instead of the Server's primary address (see: Section 3.16). 814 3.10. AERO Interface Encapsulation and Re-encapsulation 816 AERO interfaces encapsulate IP packets according to whether they are 817 entering the AERO interface from the network layer or if they are 818 being re-admitted into the same AERO link they arrived on. This 819 latter form of encapsulation is known as "re-encapsulation". 821 The AERO interface encapsulates packets per the base tunneling 822 specifications (e.g., [RFC2003], [RFC2473], [RFC2784], [RFC4213], 823 [RFC4301], [RFC5246], etc.) except that it inserts a UDP header 824 immediately following the IP encapsulation header. If there are no 825 additional encapsulation headers (and no fragmentation, 826 identification, checksum or signature is needed), the AERO interface 827 next encapsulates the IPv4 or IPv6 packet immediately following the 828 UDP header. In that case, the most significant four bits of the 829 encapsulated packet encode the value '4' for IPv4 or '6' for IPv6. 831 For all other encapsulations, the AERO interface MUST insert an AERO 832 Header between the UDP header and the next encapsulation header as 833 shown in Figure 3: 835 0 1 2 3 836 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 1 837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 838 |Version|N|F|C|S| Next Header |Fragment Offset (13 bits)|Res|M| 839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 840 | Identification (32 bits) | 841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 842 | Checksum (16 bits) | Signature (variable length) : 843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 845 Figure 3: AERO Header 847 Version a 4-bit "Version" field. MUST be 0 for the purpose of this 848 specification. 850 N a 1-bit "Next Header" flag. MUST be 1 for the purpose of this 851 specification to indicate that "Next Header" field is present. 852 "Next Header" encodes the IP protocol number corresponding to the 853 next header in the encapsulation immediately following the AERO 854 header. For example, "Next Header" encodes the value '4' for 855 IPv4, '17' for UDP, '41' for IPv6, '47' for GRE, '50' for ESP, 856 '51' for AH, etc. 858 F a 1-bit "Fragment Header" flag. Set to '1' if the "Fragment 859 Offset", "Res", "M", and "Identification" fields are present and 860 collectively referred to as the "AERO Fragment Header"; otherwise, 861 set to '0'. 863 C a 1-bit "Checksum" flag. Set to '1' if the "Checksum" field is 864 present; otherwise, set to '0'. When present, the Checksum field 865 contains a checksum of the IP/UDP/AERO encapsulation headers prior 866 to the Checksum field. 868 S a 1-bit "Signature" flag. Set to '1' if the "Signature" field is 869 present; otherwise, set to '0'. When present, the Signature field 870 contains a cryptographic signature of the encapsulated packet 871 following the Signature field. The signature is applied prior to 872 any fragmentation; hence' the Signature field only appears in the 873 first fragment of a fragmented packet. 875 (Note: [RFC6706] defines an experimental use in which the bits 876 corresponding to (Version, N, F, C, S) are all zero, which can be 877 unambiguously distinguished from the values permitted by this 878 specification.) 880 During encapsulation, the AERO interface copies the "TTL/Hop Limit", 881 "Type of Service/Traffic Class" [RFC2983] and "Congestion 882 Experienced" [RFC3168] values in the packet's IP header into the 883 corresponding fields in the encapsulation IP header. (When IPv6 is 884 used as the encapsulation protocol, the interface also sets the Flow 885 Label value in the encapsulation header per [RFC6438].) For packets 886 undergoing re-encapsulation, the AERO interface instead copies the 887 "TTL/Hop Limit", "Type of Service/Traffic Class", "Flow Label" and 888 "Congestion Experienced" values in the original encapsulation IP 889 header into the corresponding fields in the new encapsulation IP 890 header, i.e., the values are transferred between encapsulation 891 headers and *not* copied from the encapsulated packet's network-layer 892 header. 894 The AERO interface next sets the UDP source port to a constant value 895 that it will use in each successive packet it sends, and sets the UDP 896 length field to the length of the encapsulated packet plus 8 bytes 897 for the UDP header itself, plus the length of the AERO header. For 898 packets sent via a Server, the AERO interface sets the UDP 899 destination port to 8060, i.e., the IANA-registered port number for 900 AERO. For packets sent to a correspondent Client, the AERO interface 901 sets the UDP destination port to the port value stored in the 902 neighbor cache entry for this correspondent. The AERO interface also 903 sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) unless 904 an integrity check is required (see: Section 3.13.2). 906 The AERO interface next sets the IP protocol number in the 907 encapsulation header to 17 (i.e., the IP protocol number for UDP). 908 When IPv4 is used as the encapsulation protocol, the AERO interface 909 sets the DF bit as discussed in Section 3.13. The AERO interface 910 finally sets the AERO header fields as described in Figure 3. 912 3.11. AERO Interface Decapsulation 914 AERO interfaces decapsulate packets destined either to the node 915 itself or to a destination reached via an interface other than the 916 AERO interface the packet was received on. When the AERO interface 917 receives a UDP packet, it examines the first octet of the 918 encapsulated packet. 920 If the most significant four bits of the first octet encode the value 921 '4' (i.e., the IP version number value for IPv4) or the value '6' 922 (i.e., the IP version number value for IPv6), the AERO interface 923 discards the encapsulation headers and accepts the encapsulated 924 packet as an ordinary IPv6 or IPv4 data packet, respectively. If the 925 most significant four bits encode the value '0', however, the AERO 926 interface processes the packet according to the appropriate AERO 927 Header fields as specified in Figure 3. 929 3.12. AERO Interface Data Origin Authentication 931 AERO nodes employ simple data origin authentication procedures for 932 encapsulated packets they receive from other nodes on the AERO link. 933 In particular: 935 o AERO Relays and Servers accept encapsulated packets with a link- 936 layer source address that matches a permanent neighbor cache 937 entry. 939 o AERO Servers accept authentic encapsulated DHCPv6 messages from 940 Clients, and create or update a static neighbor cache entry for 941 the source based on the specific message type. 943 o AERO Servers accept encapsulated packets if there is a neighbor 944 cache entry with an AERO address that matches the packet's 945 network-layer source address and with a link-layer address that 946 matches the packet's link-layer source address. 948 o AERO Clients accept encapsulated packets if there is a static 949 neighbor cache entry with a link-layer source address that matches 950 the packet's link-layer source address. 952 o AERO Clients and Servers accept encapsulated packets if there is a 953 dynamic neighbor cache entry with an AERO address that matches the 954 packet's network-layer source address, with a link-layer address 955 that matches the packet's link-layer source address, and with a 956 non-zero AcceptTime. 958 Note that this simple data origin authentication is effective in 959 environments in which link-layer addresses cannot be spoofed. In 960 other environments, each AERO message must include a signature that 961 the recipient can use to authenticate the message origin. 963 3.13. AERO Interface MTU and Fragmentation 965 The AERO interface is the node's point of attachment to the AERO 966 link. AERO links over IP networks have a maximum link MTU of 64KB 967 minus the encapsulation overhead (termed here "ENCAPS"), since the 968 maximum packet size in the base IP specifications is 64KB 969 [RFC0791][RFC2460] (while IPv6 jumbograms can be up to 4GB, they are 970 considered optional for IPv6 nodes [RFC2675][RFC6434]). 972 IPv6 specifies a minimum link MTU of 1280 bytes [RFC2460]. This is 973 the minimum packet size the AERO interface MUST admit without 974 returning an ICMP Packet Too Big (PTB) message. Although IPv4 975 specifies a smaller minimum link MTU of 68 bytes [RFC0791], AERO 976 interfaces also observe a 1280 byte minimum for IPv4. Additionally, 977 the vast majority of links in the Internet configure an MTU of at 978 least 1500 bytes. Original source hosts have therefore become 979 conditioned to expect that IP packets up to 1500 bytes in length will 980 either be delivered to the final destination or a suitable PTB 981 message returned. However, PTB messages may be lost in the network 982 [RFC2923] resulting in failure of the IP Path MTU Discovery (PMTUD) 983 mechanisms [RFC1191][RFC1981]. 985 For these reasons, the source AERO interface (i.e., the tunnel 986 ingress)admit packets into the tunnel subject to their reasonable 987 expectation that PMTUD will convey the correct information to the 988 original source in the event that the packet is too large. In 989 particular, if the original source is within the same well-managed 990 administrative domain as the tunnel ingress, the ingress drops the 991 packet and sends a PTB message back to the original source if the 992 packet is too large to traverse the tunnel in one piece. Similarly, 993 if the tunnel ingress is within the same well-managed administrative 994 domain as the to the destination AERO interface (i.e., the tunnel 995 egress), the ingress can cache MTU values reported in PTB messages 996 received from a router on the path to the egress. 998 In all other cases, AERO interfaces admit all packets up to 1500 999 bytes in length even if some fragmentation is necessary, and admit 1000 larger packets without fragmentation in case they are able to 1001 traverse the tunnel in one piece. AERO interfaces are therefore 1002 considered to have an indefinite MTU, i.e., instead of clamping the 1003 MTU to a finite size. 1005 For AERO links over IPv4, the IP ID field is only 16 bits in length, 1006 meaning that fragmentation at high data rates could result in data 1007 corruption due to reassembly misassociations [RFC6864][RFC4963] (see: 1008 Section 3.13.2). For AERO links over both IPv4 and IPv6, studies 1009 have also shown that IP fragments are dropped unconditionally over 1010 some network paths [I-D.taylor-v6ops-fragdrop]. For these reasons, 1011 when fragmentation is needed it is performed through insertion of an 1012 AERO fragment header (see: Section 3.10) and application of tunnel 1013 fragmentation as described in Section 3.1.7 of [RFC2764]. Since the 1014 AERO fragment header reduces the room available for packet data, but 1015 the original source has no way to control its insertion, the header 1016 length MUST be included in the ENCAPS length even for packets in 1017 which the header does not appear. 1019 The tunnel ingress therefore sends encapsulated packets to the tunnel 1020 egress according to the following algorithm: 1022 o For IP packets that are no larger than (1280-ENCAPS) bytes, the 1023 tunnel ingress encapsulates the packet and admits it into the 1024 tunnel without fragmentation. For IPv4 AERO links, the tunnel 1025 ingress sets the Don't Fragment (DF) bit to 0 so that these 1026 packets will be delivered to the tunnel egress even if there is a 1027 restricting link in the path, i.e., unless lost due to congestion 1028 or routing errors. 1030 o For IP packets that are larger than (1280-ENCAPS) bytes but no 1031 larger than 1500 bytes, the tunnel ingress encapsulates the packet 1032 and inserts an AERO fragment header. Next, the tunnel ingress 1033 uses the fragmentation algorithm in [RFC2460] to break the packet 1034 into two non-overlapping fragments where the first fragment 1035 (including ENCAPS) is no larger than 1024 bytes and the second is 1036 no larger than the first. Each fragment consists of identical 1037 UDP/IP encapsulation headers, followed by the AERO header followed 1038 by the fragment of the encapsulated packet itself. The tunnel 1039 ingress then admits both fragments into the tunnel, and for IPv4 1040 sets the DF bit to 0 in the IP encapsulation header. These 1041 fragmented encapsulated packets will be delivered to the tunnel 1042 egress. When the tunnel egress receives the fragments, it 1043 reassembles them into a whole packet per the reassembly algorithm 1044 in [RFC2460]. The tunnel egress therefore MUST be capable of 1045 reassembling packets up to 1500+ENCAPS bytes in length; hence, it 1046 is RECOMMENDED that the tunnel egress be capable of reassembling 1047 at least 2KB. 1049 o For IPv4 packets that are larger than 1500 bytes and with the DF 1050 bit set to 0, the tunnel ingress uses ordinary IPv4 fragmentation 1051 to break the unencapsulated packet into a minimum number of non- 1052 overlapping fragments where the first fragment is no larger than 1053 1024-ENCAPS and all other fragments are no larger than the first 1054 fragment. The tunnel ingress then encapsulates each fragment (and 1055 for IPv4 sets the DF bit to 0) then admits them into the tunnel. 1056 These fragments will be delivered to the final destination via the 1057 tunnel egress. 1059 o For all other IP packets, if the packet is too large to enter the 1060 underlying interface following encapsulation, the tunnel ingress 1061 drops the packet and returns a network-layer (L3) PTB message to 1062 the original source with MTU set to the larger of 1500 bytes or 1063 the underlying interface MTU minus ENCAPS. Otherwise, the tunnel 1064 ingress encapsulates the packet and admits it into the tunnel 1065 without fragmentation (and for IPv4 sets the DF bit to 1) and 1066 translates any link-layer (L2) PTB messages it may receive from 1067 the network into corresponding L3 PTB messages to send to the 1068 original source as specified in Section 3.14. Since both L2 and 1069 L3 PTB messages may be either lost or contain insufficient 1070 information, however, it is RECOMMENDED that original sources that 1071 send unfragmentable IP packets larger than 1500 bytes use 1072 Packetization Layer Path MTU Discovery (PLPMTUD) [RFC4821]. 1074 While sending packets according to the above algorithm, the tunnel 1075 ingress MAY also send 1500 byte or larger probe packets to determine 1076 whether they can reach the tunnel egress without fragmentation. If 1077 the probes succeed, the tunnel ingress can discontinue fragmentation 1078 and (for IPv4) set DF to 1. Since the path MTU within the tunnel may 1079 fluctuate due to routing changes, the tunnel ingress SHOULD continue 1080 to send additional probes subject to rate limiting and SHOULD process 1081 any L2 PTB messages as an indication that the path MTU may have 1082 decreased. If the path MTU within the tunnel becomes insufficient, 1083 the source MUST resume fragmentation. 1085 To construct a probe, the tunnel ingress prepares an NS message with 1086 a Nonce option plus trailing NULL padding octets added to the probe 1087 length without including the length of the padding in the IPv6 1088 Payload Length field, but with the length included in the 1089 encapsulating IP header. The tunnel ingress then encapsulates the 1090 padded NS message in the encapsulation headers (and for IPv4 sets DF 1091 to 1) then sends the message to the tunnel egress. If the tunnel 1092 egress returns a solicited NA message with a matching Nonce option, 1093 the tunnel ingress deems the probe successful. Note that in this 1094 process it is essential that probes follow equivalent paths to those 1095 used to convey actual data packets. This means that Equal Cost 1096 MultiPath (ECMP) and Link Aggregation Gateway (LAG) equipment in the 1097 path would need to ensure that probes and data packets follow the 1098 same path, which is outside the scope of this specification. 1100 3.13.1. Accommodating Large Control Messages 1102 Control messages (i.e., IPv6 ND, DHCPv6, etc.) MUST be accommodated 1103 even if some fragmentation is necessary. These packets are therefore 1104 accommodated through a modification of the second rule in the above 1105 algorithm as follows: 1107 o For control messages that are larger than (1280-ENCAPS) bytes, the 1108 tunnel ingress encapsulates the packet and inserts an AERO 1109 fragment header. Next, the tunnel ingress uses the fragmentation 1110 algorithm in [RFC2460] to break the packet into a minimum number 1111 of non-overlapping fragments where the first fragment (including 1112 ENCAPS) is no larger than 1024 bytes and the remaining fragments 1113 are no larger than the first. The tunnel ingress then 1114 encapsulates each fragment (and for IPv4 sets the DF bit to 0) 1115 then admits them into the tunnel. 1117 Control messages that exceed the 2KB minimum reassembly size rarely 1118 occur in the modern era, however the tunnel egress SHOULD be able to 1119 reassemble them if they do. This means that the tunnel egress SHOULD 1120 include a configuration knob allowing the operator to set a larger 1121 reassembly buffer size if large control messages become more common 1122 in the future. 1124 The tunnel ingress can send large control messages without 1125 fragmentation if there is assurance that large packets can traverse 1126 the tunnel without fragmentation. The tunnel ingress MAY send 1500 1127 byte or larger probe packets as specified above to determine a size 1128 for which fragmentation can be avoided. 1130 3.13.2. Integrity 1132 When fragmentation is needed, there must be assurance that reassembly 1133 can be safely conducted without incurring data corruption. Sources 1134 of corruption can include implementation errors, memory errors and 1135 misassociation of fragments from a first datagram with fragments of 1136 another datagram. The first two conditions (implementation and 1137 memory errors) are mitigated by modern systems and implementations 1138 that have demonstrated integrity through decades of operational 1139 practice. The third condition (reassembly misassociations) must be 1140 accounted for by AERO. 1142 The AERO fragmentation procedure described in the above algorithms 1143 reuses standard IPv6 fragmentation and reassembly code. Since the 1144 AERO fragment header includes a 32-bit ID field, there would need to 1145 be 2^32 packets alive in the network before a second packet with a 1146 duplicate ID enters the system with the (remote) possibility for a 1147 reassembly misassociation. For 1280 byte packets, and for a maximum 1148 network lifetime value of 60 seconds[RFC2460], this means that the 1149 tunnel ingress would need to produce ~(7 *10^12) bits/sec in order 1150 for a duplication event to be possible. This exceeds the bandwidth 1151 of data link technologies of the modern era, but not necessarily so 1152 going forward into the future. Although wireless data links commonly 1153 used by AERO Clients support vastly lower data rates, the aggregate 1154 data rates between AERO Servers and Relays may be substantial. 1155 However, high speed data links in the network core are expected to 1156 configure larger MTUs, e.g., 4KB, 8KB or even larger such that 1157 unfragmented packets can be used. Hence, no integrity check is 1158 included to cover the AERO fragmentation and reassembly procedures. 1160 When the tunnel ingress sends an IPv4-encapsulated packet with the DF 1161 bit set to 0 in the above algorithms, there is a chance that the 1162 packet may be fragmented by an IPv4 router somewhere within the 1163 tunnel. Since the largest such packet is only 1280 bytes, however, 1164 it is very likely that the packet will traverse the tunnel without 1165 incurring a restricting link. Even when a link within the tunnel 1166 configures an MTU smaller than 1280 bytes, it is very likely that it 1167 does so due to limited performance characteristics [RFC3819]. This 1168 means that the tunnel would not be able to convey fragmented 1169 IPv4-encapsulated packets fast enough to produce reassembly 1170 misassociations, as discussed above. However, AERO must also account 1171 for the possibility of tunnel paths that include "poorly managed" 1172 IPv4 link MTUs due to misconfigurations. 1174 Since the IPv4 header includes only a 16-bit ID field, there would 1175 only need to be 2^16 packets alive in the network before a second 1176 packet with a duplicate ID enters the system. For 1280 byte packets, 1177 and for a maximum network lifetime value of 120 seconds[RFC0791], 1178 this means that the tunnel ingress would only need to produce ~(5 1179 *10^6) bits/sec in order for a duplication event to be possible - a 1180 value that is well within range for many modern wired and wireless 1181 data link technologies. 1183 Therefore, if there is strong operational assurance that no IPv4 1184 links capable of supporting data rates of 5Mbps or more configure an 1185 MTU smaller than 1280 the tunnel ingress MAY omit an integrity check 1186 for the IPv4 fragmentation and reassembly procedures; otherwise, the 1187 tunnel ingress SHOULD include an integrity check. When an upper 1188 layer encapsulation (e.g., IPsec) already includes an integrity 1189 check, the tunnel ingress need not include an additional check. 1190 Otherwise, the tunnel ingress calculates the UDP checksum over the 1191 encapsulated packet and writes the value into the UDP encapsulation 1192 header, i.e., instead of writing the value 0. The tunnel egress will 1193 then verify the UDP checksum and discard the packet if the checksum 1194 is incorrect. 1196 3.14. AERO Interface Error Handling 1198 When an AERO node admits encapsulated packets into the AERO 1199 interface, it may receive link-layer (L2) or network-layer (L3) error 1200 indications. 1202 An L2 error indication is an ICMP error message generated by a router 1203 on the path to the neighbor or by the neighbor itself. The message 1204 includes an IP header with the address of the node that generated the 1205 error as the source address and with the link-layer address of the 1206 AERO node as the destination address. 1208 The IP header is followed by an ICMP header that includes an error 1209 Type, Code and Checksum. For ICMPv6 [RFC4443], the error Types 1210 include "Destination Unreachable", "Packet Too Big (PTB)", "Time 1211 Exceeded" and "Parameter Problem". For ICMPv4 [RFC0792], the error 1212 Types include "Destination Unreachable", "Fragmentation Needed" (a 1213 Destination Unreachable Code that is analogous to the ICMPv6 PTB), 1214 "Time Exceeded" and "Parameter Problem". 1216 The ICMP header is followed by the leading portion of the packet that 1217 generated the error, also known as the "packet-in-error". For 1218 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1219 much of invoking packet as possible without the ICMPv6 packet 1220 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1221 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1222 "Internet Header + 64 bits of Original Data Datagram", however 1223 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1224 ICMP datagram SHOULD contain as much of the original datagram as 1225 possible without the length of the ICMP datagram exceeding 576 1226 bytes". 1228 The L2 error message format is shown in Figure 4: 1230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1231 ~ ~ 1232 | L2 IP Header of | 1233 | error message | 1234 ~ ~ 1235 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1236 | L2 ICMP Header | 1237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1238 ~ ~ P 1239 | IP and other encapsulation | a 1240 | headers of original L3 packet | c 1241 ~ ~ k 1242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1243 ~ ~ t 1244 | IP header of | 1245 | original L3 packet | i 1246 ~ ~ n 1247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1248 ~ ~ e 1249 | Upper layer headers and | r 1250 | leading portion of body | r 1251 | of the original L3 packet | o 1252 ~ ~ r 1253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1255 Figure 4: AERO Interface L2 Error Message Format 1257 The AERO node rules for processing these L2 error messages is as 1258 follows: 1260 o When an AERO node receives an L2 Parameter Problem message, it 1261 processes the message the same as described as for ordinary ICMP 1262 errors in the normative references [RFC0792][RFC4443]. 1264 o When an AERO node receives persistent L2 IPv4 Time Exceeded 1265 messages, the IP ID field may be wrapping before earlier fragments 1266 have been processed. In that case, the node SHOULD begin 1267 including IPv4 integrity checks (see: Section 3.13.2). 1269 o When an AERO Client receives persistent L2 Destination Unreachable 1270 messages in response to tunneled packets that it sends to one of 1271 its dynamic neighbor correspondents, the Client SHOULD test the 1272 path to the correspondent using Neighbor Unreachability Detection 1273 (NUD) (see Section 3.18). If NUD fails, the Client SHOULD set 1274 ForwardTime for the corresponding dynamic neighbor cache entry to 1275 0 and allow future packets destined to the correspondent to flow 1276 through a Server. 1278 o When an AERO Client receives persistent L2 Destination Unreachable 1279 messages in response to tunneled packets that it sends to one of 1280 its static neighbor Servers, the Client SHOULD test the path to 1281 the Server using NUD. If NUD fails, the Client SHOULD delete the 1282 neighbor cache entry and attempt to associate with a new Server. 1284 o When an AERO Server receives persistent L2 Destination Unreachable 1285 messages in response to tunneled packets that it sends to one of 1286 its static neighbor Clients, the Server SHOULD test the path to 1287 the Client using NUD. If NUD fails, the Server SHOULD cancel the 1288 DHCPv6 PD for the Client's ACP, withdraw its route for the ACP 1289 from the AERO routing system and delete the neighbor cache entry 1290 (see Section 3.18 and Section 3.19). 1292 o When an AERO Relay or Server receives an L2 Destination 1293 Unreachable message in response to a tunneled packet that it sends 1294 to one of its permanent neighbors, it discards the message since 1295 the routing system is likely in a temporary transitional state 1296 that will soon re-converge. 1298 o When an AERO node receives an L2 PTB message, it translates the 1299 message into an L3 PTB message if possible (*) and forwards the 1300 message toward the original source as described below. 1302 To translate an L2 PTB message to an L3 PTB message, the AERO node 1303 first caches the MTU field value of the L2 ICMP header. The node 1304 next discards the L2 IP and ICMP headers, and also discards the 1305 encapsulation headers of the original L3 packet. Next the node 1306 encapsulates the included segment of the original L3 packet in an L3 1307 IP and ICMP header, and sets the ICMP header Type and Code values to 1308 appropriate values for the L3 IP protocol. In the process, the node 1309 writes the maximum of 1500 bytes and (L2 MTU - ENCAPS) into the MTU 1310 field of the L3 ICMP header. 1312 The node next writes the IP source address of the original L3 packet 1313 as the destination address of the L3 PTB message and determines the 1314 next hop to the destination. If the next hop is reached via the AERO 1315 interface, the node uses the IPv6 address "::" or the IPv4 address 1316 "0.0.0.0" as the IP source address of the L3 PTB message. Otherwise, 1317 the node uses one of its non link-local addresses as the source 1318 address of the L3 PTB message. The node finally calculates the ICMP 1319 checksum over the L3 PTB message and writes the Checksum in the 1320 corresponding field of the L3 ICMP header. The L3 PTB message 1321 therefore is formatted as follows: 1323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1324 ~ ~ 1325 | L3 IP Header of | 1326 | error message | 1327 ~ ~ 1328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1329 | L3 ICMP Header | 1330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1331 ~ ~ p 1332 | IP header of | k 1333 | original L3 packet | t 1334 ~ ~ 1335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i 1336 ~ ~ n 1337 | Upper layer headers and | 1338 | leading portion of body | e 1339 | of the original L3 packet | r 1340 ~ ~ r 1341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1343 Figure 5: AERO Interface L3 Error Message Format 1345 After the node has prepared the L3 PTB message, it either forwards 1346 the message via a link outside of the AERO interface without 1347 encapsulation, or encapsulates and forwards the message to the next 1348 hop via the AERO interface. 1350 When an AERO Relay receives an L3 packet for which the destination 1351 address is covered by an ASP, if there is no more-specific routing 1352 information for the destination the Relay drops the packet and 1353 returns an L3 Destination Unreachable message. The Relay first 1354 writes the IP source address of the original L3 packet as the 1355 destination address of the L3 Destination Unreachable message and 1356 determines the next hop to the destination. If the next hop is 1357 reached via the AERO interface, the Relay uses the IPv6 address "::" 1358 or the IPv4 address "0.0.0.0" as the IP source address of the L3 1359 Destination Unreachable message and forwards the message to the next 1360 hop within the AERO interface. Otherwise, the Relay uses one of its 1361 non link-local addresses as the source address of the L3 Destination 1362 Unreachable message and forwards the message via a link outside the 1363 AERO interface. 1365 When an AERO node receives any L3 error message via the AERO 1366 interface, it examines the destination address in the L3 IP header of 1367 the message. If the next hop toward the destination address of the 1368 error message is via the AERO interface, the node re-encapsulates and 1369 forwards the message to the next hop within the AERO interface. 1370 Otherwise, if the source address in the L3 IP header of the message 1371 is the IPv6 address "::" or the IPv4 address "0.0.0.0", the node 1372 writes one of its non link-local addresses as the source address of 1373 the L3 message and recalculates the IP and/or ICMP checksums. The 1374 node finally forwards the message via a link outside of the AERO 1375 interface. 1377 (*) Note that in some instances the packet-in-error field of an L2 1378 PTB message may not include enough information for translation to an 1379 L3 PTB message. In that case, the AERO interface simply discards the 1380 L2 PTB message. It can therefore be said that translation of L2 PTB 1381 messages to L3 PTB messages can provide a useful optimization when 1382 possible, but is not critical for sources that correctly use PLPMTUD. 1384 3.15. AERO Router Discovery, Prefix Delegation and Address 1385 Configuration 1387 3.15.1. AERO DHCPv6 Service Model 1389 Each AERO Server configures a DHCPv6 server function to facilitate PD 1390 requests from Clients. Each Server is provisioned with a database of 1391 ACP-to-Client ID mappings for all Clients enrolled in the AERO 1392 system, as well as any information necessary to authenticate each 1393 Client. The Client database is maintained by a central 1394 administrative authority for the AERO link and securely distributed 1395 to all Servers, e.g., via the Lightweight Directory Access Protocol 1396 (LDAP) [RFC4511] or a similar distributed database service. 1398 Therefore, no Server-to-Server DHCPv6 PD delegation state 1399 synchronization is necessary, and Clients can optionally hold 1400 separate delegations for the same ACP from multiple Servers. In this 1401 way, Clients can associate with multiple Servers, and can receive new 1402 delegations from new Servers before deprecating delegations received 1403 from existing Servers. 1405 AERO Clients and Servers exchange Client link-layer address 1406 information using an option format similar to the Client Link Layer 1407 Address Option (CLLAO) defined in [RFC6939]. Due to practical 1408 limitations of CLLAO, however, AERO interfaces instead use Vendor- 1409 Specific Information Options as described in the following sections. 1411 3.15.2. AERO Client Behavior 1413 AERO Clients discover the link-layer addresses of AERO Servers via 1414 static configuration, or through an automated means such as DNS name 1415 resolution. In the absence of other information, the Client resolves 1416 the FQDN "linkupnetworks.[domainname]" where "linkupnetworks" is a 1417 constant text string and "[domainname]" is the connection-specific 1418 DNS suffix for the Client's underlying network connection (e.g., 1419 "example.com"). After discovering the link-layer addresses, the 1420 Client associates with one or more of the corresponding Servers. 1422 To associate with a Server, the Client acts as a requesting router to 1423 request an ACP through a two-message (i.e., Request/Reply) DHCPv6 PD 1424 exchange [RFC3315][RFC3633]. The Client's Request message includes 1425 fe80::ffff:ffff:ffff:ffff as the IPv6 source address, 1426 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address 1427 and the link-layer address of the Server as the link-layer 1428 destination address. The Request message also includes a Client 1429 Identifier option with a DHCP Unique Identifier (DUID) and an 1430 Identity Association for Prefix Delegation (IA_PD) option. If the 1431 Client is pre-provisioned with an ACP associated with the AERO 1432 service, it MAY also include the ACP in the IA_PD to indicate its 1433 preference to the DHCPv6 server. 1435 The Client also SHOULD include an AERO Link-registration Request 1436 (ALREQ) option to register one or more links with the Server. The 1437 Server will include an AERO Link-registration Reply (ALREP) option in 1438 the corresponding DHCPv6 Reply message as specified in 1439 Section 3.15.3. (The Client MAY omit the ALREQ option, in which case 1440 the Server will still include an ALREP option in its Reply with "Link 1441 ID" set to 0, "DSCP" set to 0, and "Prf" set to 3.) 1443 The format for the ALREQ option is shown in Figure 6: 1445 0 1 2 3 1446 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 1447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1448 | OPTION_VENDOR_OPTS | option-len (1) | 1449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1450 | enterprise-number = 45282 | 1451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1452 | opt-code = OPTION_ALREQ (0) | option-len (2) | 1453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1454 | Link ID | DSCP #1 |Prf| DSCP #2 |Prf| ... 1455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1457 Figure 6: AERO Link-registration Request (ALREQ) Option 1459 In the above format, the Client sets 'option-code' to 1460 OPTION_VENDOR_OPTS, sets 'option-len (1)' to the length of the option 1461 following this field, sets 'enterprise-number' to 45282 (see: "IANA 1462 Considerations"), sets opt-code to the value 0 ("OPTION_ALREQ") and 1463 sets 'option-len (2)' to the length of the remainder of the option. 1464 The Client includes appropriate 'Link ID, 'DSCP' and 'Prf' values for 1465 the underlying interface over which the DHCPv6 PD Request will be 1466 issued the same as specified for an S/TLLAO Section 3.4. The Client 1467 MAY include multiple (DSCP, Prf) values with this Link ID, with the 1468 number of values indicated by option-len (2). The Server will 1469 register each value with the Link ID in the Client's neighbor cache 1470 entry. The Client finally includes any necessary authentication 1471 options to identify itself to the DHCPv6 server, and sends the 1472 encapsulated DHCPv6 PD Request via the underlying interface 1473 corresponding to Link ID. (Note that this implies that the Client 1474 must perform additional Renew/Reply DHCPv6 exchanges with the server 1475 following the initial Request/Reply using different underlying 1476 interfaces and their corresponding Link IDs if it wishes to register 1477 additional link-layer addresses and their associated DSCPs.) 1479 When the Client receives its ACP via a DHCPv6 Reply from the AERO 1480 Server, it creates a static neighbor cache entry with the Server's 1481 link-local address as the network-layer address and the Server's 1482 encapsulation address as the link-layer address. The Client then 1483 considers the link-layer address of the Server as the primary default 1484 encapsulation address for forwarding packets for which no more- 1485 specific forwarding information is available. The Client further 1486 caches any ASPs included in the ALREP option as ASPs to apply to the 1487 AERO link. 1489 Next, the Client autoconfigures an AERO address from the delegated 1490 ACP, assigns the AERO address to the AERO interface and sub-delegates 1491 the ACP to its attached EUNs and/or the Client's own internal virtual 1492 interfaces. The Client also assigns a default IP route to the AERO 1493 interface as a route-to-interface, i.e., with no explicit next-hop. 1494 The Client can then determine the correct next hops for packets 1495 submitted to the AERO interface by inspecting the neighbor cache. 1497 The Client subsequently renews its ACP delegation through each of its 1498 Servers by performing DHCPv6 Renew/Reply exchanges with the link- 1499 layer address of a Server as the link-layer destination address and 1500 the same options that were used in the initial PD request. Note that 1501 if the Client does not issue a DHCPv6 Renew before the delegation 1502 expires (e.g., if the Client has been out of touch with the Server 1503 for a considerable amount of time) it must re-initiate the DHCPv6 PD 1504 procedure. 1506 Since the Client's AERO address is obtained from the unique ACP 1507 delegation it receives, there is no need for Duplicate Address 1508 Detection (DAD) on AERO links. Other nodes maliciously attempting to 1509 hijack an authorized Client's AERO address will be denied access to 1510 the network by the DHCPv6 server due to an unacceptable link-layer 1511 address and/or security parameters (see: Security Considerations). 1513 3.15.2.1. Autoconfiguration for Constrained Platforms 1515 On some platforms (e.g., popular cell phone operating systems), the 1516 act of assigning a default IPv6 route and/or assigning an address to 1517 an interface may not be permitted from a user application due to 1518 security policy. Typically, those platforms include a TUN/TAP 1519 interface that acts as a point-to-point conduit between user 1520 applications and the AERO interface. In that case, the Client can 1521 instead generate a "synthesized RA" message. The message conforms to 1522 [RFC4861] and is prepared as follows: 1524 o the IPv6 source address is the Client's AERO address 1526 o the IPv6 destination address is all-nodes multicast 1528 o the Router Lifetime is set to a time that is no longer than the 1529 ACP DHCPv6 lifetime 1531 o the message does not include a Source Link Layer Address Option 1532 (SLLAO) 1534 o the message includes a Prefix Information Option (PIO) with a /64 1535 prefix taken from the ACP as the prefix for autoconfiguration 1537 The Client then sends the synthesized RA message via the TUN/TAP 1538 interface, where the operating system kernel will interpret it as 1539 though it were generated by an actual router. The operating system 1540 will then install a default route and use StateLess Address 1541 AutoConfiguration (SLAAC) to configure an IPv6 address on the TUN/TAP 1542 interface. Methods for similarly installing an IPv4 default route 1543 and IPv4 address on the TUN/TAP interface are based on synthesized 1544 DHCPv4 messages [RFC2131]. 1546 3.15.2.2. Client DHCPv6 Message Source Address 1548 In the initial DHCPv6 PD message exchanges, AERO Clients use the 1549 special IPv6 source address 'fe80::ffff:ffff:ffff:ffff' since their 1550 AERO addresses are not yet configured. After AERO address 1551 autoconfiguration, however, AERO Clients can either continue to use 1552 'fe80::ffff:ffff:ffff:ffff' as the source address for further DHCPv6 1553 messaging or begin using their AERO address as the source address. 1555 3.15.3. AERO Server Behavior 1557 AERO Servers configure a DHCPv6 server function on their AERO links. 1558 AERO Servers arrange to add their encapsulation layer IP addresses 1559 (i.e., their link-layer addresses) to the DNS resource records for 1560 the FQDN "linkupnetworks.[domainname]" before entering service. 1562 When an AERO Server receives a prospective Client's DHCPv6 PD Request 1563 on its AERO interface, it first authenticates the message. If 1564 authentication succeeds, the Server determines the correct ACP to 1565 delegate to the Client by searching the Client database. In 1566 environments where spoofing is not considered a threat, the Server 1567 MAY use the Client's DUID as the identification value. Otherwise, 1568 the Server SHOULD use a signed certificate provided by the Client. 1570 When the Server delegates the ACP, it also creates an IP forwarding 1571 table entry so that the AERO routing system will propagate the ACP to 1572 all Relays that aggregate the corresponding ASP (see: Section 3.7). 1573 Next, the Server prepares a DHCPv6 Reply message to send to the 1574 Client while using fe80::ID as the IPv6 source address, the link- 1575 local address taken from the Client's Request as the IPv6 destination 1576 address, the Server's link-layer address as the source link-layer 1577 address, and the Client's link-layer address as the destination link- 1578 layer address. The server also includes an IA_PD option with the 1579 delegated ACP. 1581 The Server also includes an ALREP option that includes the UDP Port 1582 Number and IP Address values it observed when it received the ALREQ 1583 in the Client's original DHCPv6 message (if present) followed by the 1584 ASP(s) for the AERO link. The ALREP option is formatted as shown in 1585 Figure 7: 1587 0 1 2 3 1588 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 1589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1590 | OPTION_VENDOR_OPTS | option-len (1) | 1591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1592 | enterprise-number = 45282 | 1593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1594 | opt-code = OPTION_ALREP (1) | option-len (2) | 1595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1596 | Link ID | Reserved | UDP Port Number | 1597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1598 | | 1599 + + 1600 | | 1601 + IP Address + 1602 | | 1603 + + 1604 | | 1605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1606 | | 1607 + AERO Service Prefix (ASP) #1 +-+-+-+-+-+-+-+-+ 1608 | | Prefix Len | 1609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1610 | | 1611 + AERO Service Prefix (ASP) #2 +-+-+-+-+-+-+-+-+ 1612 | | Prefix Len | 1613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1614 ~ ~ 1615 ~ ~ 1617 Figure 7: AERO Link-registration Reply (ALREP) Option 1619 In the ALREP, the Server sets 'option-code' to OPTION_VENDOR_OPTS, 1620 sets 'option-length (1)' to the length of the option, sets 1621 'enterprise-number' to 45282 (see: "IANA Considerations"), sets opt- 1622 code to OPTION_ALREP (1), and sets 'option-len (2)' to the length of 1623 the remainder of the option. Next, the Server sets 'Link ID' to the 1624 same value that appeared in the ALREQ, sets Reserved to 0 and sets 1625 'UDP Port Number' and 'IP address' to the Client's link-layer 1626 address. The Server next includes one or more ASP with the IP prefix 1627 as it would appear in the interface identifier portion of the 1628 corresponding AERO address (see: Section 3.3), except that the low- 1629 order 8 bits of the ASP field encode the prefix length instead of the 1630 low-order 8 bits of the prefix. The longest prefix that can 1631 therefore appear as an ASP is /56 for IPv6 or /24 for IPv4. (Note 1632 that if the Client did not include an ALREQ option in its DHCPv6 1633 message, the Server MUST still include an ALREP option in the 1634 corresponding reply with 'Link ID' set to 0.) 1636 When the Server admits the DHCPv6 Reply message into the AERO 1637 interface, it creates a static neighbor cache entry for the Client's 1638 AERO address with lifetime set to no more than the delegation 1639 lifetime and the Client's link-layer address as the link-layer 1640 address for the Link ID specified in the ALREQ. The Server then uses 1641 the Client link-layer address information in the ALREQ option as the 1642 link-layer address for encapsulation based on the (DSCP, Prf) 1643 information. 1645 After the initial DHCPv6 PD exchange, the AERO Server maintains the 1646 neighbor cache entry for the Client until the delegation lifetime 1647 expires. If the Client issues a Renew/Reply exchange, the Server 1648 extends the lifetime. If the Client issues a Release/Reply, or if 1649 the Client does not issue a Renew/Reply before the lifetime expires, 1650 the Server deletes the neighbor cache entry for the Client and 1651 withdraws the IP route from the AERO routing system. 1653 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1655 AERO Clients and Servers are always on the same link (i.e., the AERO 1656 link) from the perspective of DHCPv6. However, in some 1657 implementations the DHCPv6 server and AERO interface driver may be 1658 located in separate modules. In that case, the Server's AERO 1659 interface driver module acts as a Lightweight DHCPv6 Relay Agent 1660 (LDRA)[RFC6221] to relay DHCPv6 messages to and from the DHCPv6 1661 server module. 1663 When the LDRA receives a DHCPv6 message from a client, it prepares an 1664 ALREP option the same as described above then wraps the option in a 1665 Relay-Supplied DHCP Option option (RSOO) [RFC6422]. The LDRA then 1666 incorporates the option into the Relay-Forward message and forwards 1667 the message to the DHCPv6 server. 1669 When the DHCPv6 server receives the Relay-Forward message, it caches 1670 the ALREP option and authenticates the encapsulated DHCPv6 message. 1671 The DHCPv6 server subsequently ignores the ALREQ option itself, since 1672 the relay has already included the ALREP option. 1674 When the DHCPv6 server prepares a Reply message, it then includes the 1675 ALREP option in the body of the message along with any other options, 1676 then wraps the message in a Relay-Reply message. The DHCPv6 server 1677 then delivers the Relay-Reply message to the LDRA, which discards the 1678 Relay-Reply wrapper and delivers the DHCPv6 message to the Client. 1680 3.15.4. Deleting Link Registrations 1682 After an AERO Client registers its Link IDs and their associated 1683 (DSCP,Prf) values with the AERO Server, the Client may wish to delete 1684 one or more Link registrations, e.g., if an underlying link becomes 1685 unavailable. To do so, the Client prepares a DHCPv6 Renew message 1686 that includes an AERO Link-registration Delete (ALDEL) option and 1687 sends the Renew message to the Server over any available underlying 1688 link. The ALDEL option is formatted as shown in Figure 8: 1690 0 1 2 3 1691 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 1692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1693 | OPTION_VENDOR_OPTS | option-len (1) | 1694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1695 | enterprise-number = 45282 | 1696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1697 | opt-code = OPTION_ALDEL (2) | option-len (2) | 1698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1699 | Link ID #1 | Link ID #2 | Link ID #3 | ... 1700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1702 Figure 8: AERO Link-registration Delete (ALDEL) Option 1704 In the ALDEL, the Client sets 'option-code' to OPTION_VENDOR_OPTS, 1705 sets 'option-length (1)' to the length of the option, sets 1706 'enterprise-number' to 45282 (see: "IANA Considerations"), sets 1707 optcode to OPTION_ALDEL (2), and sets 'option-len (2)' to the length 1708 of the remainder of the option. Next, the Server includes each 'Link 1709 ID' value that it wishes to delete. 1711 If the Client wishes to discontinue use of a Server and thereby 1712 delete all of its Link ID associations, it must use a DHCPv6 Release/ 1713 Reply exchange to delete the entire neighbor cache entry, i.e., 1714 instead of using a DHCPv6 Renew/Reply exchange with one or more ALDEL 1715 options. 1717 3.16. AERO Forwarding Agent Behavior 1719 AERO Servers MAY associate with one or more companion AERO Forwarding 1720 Agents as platforms for offloading high-speed data plane traffic. 1721 When an AERO Server receives a Client's DHCPv6 Request/Renew/Rebind/ 1722 Release message, it services the message then forwards the 1723 corresponding Reply message to the Forwarding Agent. When the 1724 Forwarding Agent receives the Reply message, it creates or updates a 1725 neighbor cache entry with the Client's AERO address and link-layer 1726 information included in the Reply message. The Forwarding Agent then 1727 forwards the Reply message back to the AERO Server, which forwards 1728 the message to the Client. In this way, Forwarding Agent state is 1729 managed in conjunction with Server state, with the Client responsible 1730 for reliability. If the Client subsequently disappears without 1731 issuing a Release, the Server is responsible for purging the 1732 Forwarding Agent state by sending synthesized Reply messages. 1734 When an AERO Server receives a data packet on an AERO interface with 1735 a network layer destination address for which it has distributed 1736 forwarding information to a Forwarding Agent, the Server returns a 1737 Redirect message to the source neighbor (subject to rate limiting) 1738 then forwards the data packet as usual. The Redirect message 1739 includes a TLLAO with the link-layer address of the Forwarding 1740 Engine. 1742 When the source neighbor receives the Redirect message, it SHOULD 1743 record the link-layer address in the TLLAO as the encapsulation 1744 addresses to use for sending subsequent data packets. However, the 1745 source MUST continue to use the primary link-layer address of the 1746 Server as the encapsulation address for sending control messages. 1748 3.17. AERO Intradomain Route Optimization 1750 When a source Client forwards packets to a prospective correspondent 1751 Client within the same AERO link domain (i.e., one for which the 1752 packet's destination address is covered by an ASP), the source Client 1753 initiates an intra-domain AERO route optimization procedure. The 1754 procedure is based on an exchange of IPv6 ND messages using a chain 1755 of AERO Servers and Relays as a trust basis. This procedure is in 1756 contrast to the Return Routability procedure required for route 1757 optimization to a correspondent Client located in the Internet as 1758 described in Section 3.22. The following sections specify the AERO 1759 intradomain route optimization procedure. 1761 3.17.1. Reference Operational Scenario 1763 Figure 9 depicts the AERO intradomain route optimization reference 1764 operational scenario, using IPv6 addressing as the example (while not 1765 shown, a corresponding example for IPv4 addressing can be easily 1766 constructed). The figure shows an AERO Relay ('R1'), two AERO 1767 Servers ('S1', 'S2'), two AERO Clients ('C1', 'C2') and two ordinary 1768 IPv6 hosts ('H1', 'H2'): 1770 +--------------+ +--------------+ +--------------+ 1771 | Server S1 | | Relay R1 | | Server S2 | 1772 +--------------+ +--------------+ +--------------+ 1773 fe80::2 fe80::1 fe80::3 1774 L2(S1) L2(R1) L2(S2) 1775 | | | 1776 X-----+-----+------------------+-----------------+----+----X 1777 | AERO Link | 1778 L2(A) L2(B) 1779 fe80::2001:db8:0:0 fe80::2001:db8:1:0 1780 +--------------+ +--------------+ 1781 |AERO Client C1| |AERO Client C2| 1782 +--------------+ +--------------+ 1783 2001:DB8:0::/48 2001:DB8:1::/48 1784 | | 1785 .-. .-. 1786 ,-( _)-. 2001:db8:0::1 2001:db8:1::1 ,-( _)-. 1787 .-(_ IP )-. +---------+ +---------+ .-(_ IP )-. 1788 (__ EUN )--| Host H1 | | Host H2 |--(__ EUN ) 1789 `-(______)-' +---------+ +---------+ `-(______)-' 1791 Figure 9: AERO Reference Operational Scenario 1793 In Figure 9, Relay ('R1') assigns the address fe80::1 to its AERO 1794 interface with link-layer address L2(R1), Server ('S1') assigns the 1795 address fe80::2 with link-layer address L2(S1),and Server ('S2') 1796 assigns the address fe80::3 with link-layer address L2(S2). Servers 1797 ('S1') and ('S2') next arrange to add their link-layer addresses to a 1798 published list of valid Servers for the AERO link. 1800 AERO Client ('C1') receives the ACP 2001:db8:0::/48 in a DHCPv6 PD 1801 exchange via AERO Server ('S1') then assigns the address 1802 fe80::2001:db8:0:0 to its AERO interface with link-layer address 1803 L2(C1). Client ('C1') configures a default route and neighbor cache 1804 entry via the AERO interface with next-hop address fe80::2 and link- 1805 layer address L2(S1), then sub-delegates the ACP to its attached 1806 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1807 address 2001:db8:0::1. 1809 AERO Client ('C2') receives the ACP 2001:db8:1::/48 in a DHCPv6 PD 1810 exchange via AERO Server ('S2') then assigns the address 1811 fe80::2001:db8:1:0 to its AERO interface with link-layer address 1812 L2(C2). Client ('C2') configures a default route and neighbor cache 1813 entry via the AERO interface with next-hop address fe80::3 and link- 1814 layer address L2(S2), then sub-delegates the ACP to its attached 1815 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1816 address 2001:db8:1::1. 1818 3.17.2. Concept of Operations 1820 Again, with reference to Figure 9, when source host ('H1') sends a 1821 packet to destination host ('H2'), the packet is first forwarded over 1822 the source host's attached EUN to Client ('C1'). Client ('C1') then 1823 forwards the packet via its AERO interface to Server ('S1') and also 1824 sends a Predirect message toward Client ('C2') via Server ('S1'). 1825 Server ('S1') then re-encapsulates and forwards both the packet and 1826 the Predirect message out the same AERO interface toward Client 1827 ('C2') via Relay ('R1'). 1829 When Relay ('R1') receives the packet and Predirect message, it 1830 consults its forwarding table to discover Server ('S2') as the next 1831 hop toward Client ('C2'). Relay ('R1') then forwards both the packet 1832 and the Predirect message to Server ('S2'), which then forwards them 1833 to Client ('C2'). 1835 After Client ('C2') receives the Predirect message, it process the 1836 message and returns a Redirect message toward Client ('C1') via 1837 Server ('S2'). During the process, Client ('C2') also creates or 1838 updates a dynamic neighbor cache entry for Client ('C1'). 1840 When Server ('S2') receives the Redirect message, it re-encapsulates 1841 the message and forwards it on to Relay ('R1'), which forwards the 1842 message on to Server ('S1') which forwards the message on to Client 1843 ('C1'). After Client ('C1') receives the Redirect message, it 1844 processes the message and creates or updates a dynamic neighbor cache 1845 entry for Client ('C2'). 1847 Following the above Predirect/Redirect message exchange, forwarding 1848 of packets from Client ('C1') to Client ('C2') without involving any 1849 intermediate nodes is enabled. The mechanisms that support this 1850 exchange are specified in the following sections. 1852 3.17.3. Message Format 1854 AERO Redirect/Predirect messages use the same format as for ICMPv6 1855 Redirect messages depicted in Section 4.5 of [RFC4861], but also 1856 include a new "Prefix Length" field taken from the low-order 8 bits 1857 of the Redirect message Reserved field. For IPv6, valid values for 1858 the Prefix Length field are 0 through 64; for IPv4, valid values are 1859 0 through 32. The Redirect/Predirect messages are formatted as shown 1860 in Figure 10: 1862 0 1 2 3 1863 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 1864 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1865 | Type (=137) | Code (=0/1) | Checksum | 1866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1867 | Reserved | Prefix Length | 1868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1869 | | 1870 + + 1871 | | 1872 + Target Address + 1873 | | 1874 + + 1875 | | 1876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1877 | | 1878 + + 1879 | | 1880 + Destination Address + 1881 | | 1882 + + 1883 | | 1884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1885 | Options ... 1886 +-+-+-+-+-+-+-+-+-+-+-+- 1888 Figure 10: AERO Redirect/Predirect Message Format 1890 3.17.4. Sending Predirects 1892 When a Client forwards a packet with a source address from one of its 1893 ACPs toward a destination address covered by an ASP (i.e., toward 1894 another AERO Client connected to the same AERO link), the source 1895 Client MAY send a Predirect message forward toward the destination 1896 Client via the Server. 1898 In the reference operational scenario, when Client ('C1') forwards a 1899 packet toward Client ('C2'), it MAY also send a Predirect message 1900 forward toward Client ('C2'), subject to rate limiting (see 1901 Section 8.2 of [RFC4861]). Client ('C1') prepares the Predirect 1902 message as follows: 1904 o the link-layer source address is set to 'L2(C1)' (i.e., the link- 1905 layer address of Client ('C1')). 1907 o the link-layer destination address is set to 'L2(S1)' (i.e., the 1908 link-layer address of Server ('S1')). 1910 o the network-layer source address is set to fe80::2001:db8:0:0 1911 (i.e., the AERO address of Client ('C1')). 1913 o the network-layer destination address is set to fe80::2001:db8:1:0 1914 (i.e., the AERO address of Client ('C2')). 1916 o the Type is set to 137. 1918 o the Code is set to 1 to indicate "Predirect". 1920 o the Prefix Length is set to the length of the prefix to be 1921 assigned to the Target Address. 1923 o the Target Address is set to fe80::2001:db8:0:0 (i.e., the AERO 1924 address of Client ('C1')). 1926 o the Destination Address is set to the source address of the 1927 originating packet that triggered the Predirection event. (If the 1928 originating packet is an IPv4 packet, the address is constructed 1929 in IPv4-compatible IPv6 address format). 1931 o the message includes one or more TLLAOs with Link ID and DSCPs set 1932 to appropriate values for Client ('C1')'s underlying interfaces, 1933 and with UDP Port Number and IP Address set to 0'. 1935 o the message SHOULD include a Timestamp option and a Nonce option. 1937 o the message includes a Redirected Header Option (RHO) that 1938 contains the originating packet truncated if necessary to ensure 1939 that at least the network-layer header is included but the size of 1940 the message does not exceed 1280 bytes. 1942 Note that the act of sending Predirect messages is cited as "MAY", 1943 since Client ('C1') may have advanced knowledge that the direct path 1944 to Client ('C2') would be unusable or otherwise undesirable. If the 1945 direct path later becomes unusable after the initial route 1946 optimization, Client ('C1') simply allows packets to again flow 1947 through Server ('S1'). 1949 3.17.5. Re-encapsulating and Relaying Predirects 1951 When Server ('S1') receives a Predirect message from Client ('C1'), 1952 it first verifies that the TLLAOs in the Predirect are a proper 1953 subset of the Link IDs in Client ('C1')'s neighbor cache entry. If 1954 the Client's TLLAOs are not acceptable, Server ('S1') discards the 1955 message. Otherwise, Server ('S1') validates the message according to 1956 the ICMPv6 Redirect message validation rules in Section 8.1 of 1957 [RFC4861], except that the Predirect has Code=1. Server ('S1') also 1958 verifies that Client ('C1') is authorized to use the Prefix Length in 1959 the Predirect when applied to the AERO address in the network-layer 1960 source address by searching for the AERO address in the neighbor 1961 cache. If validation fails, Server ('S1') discards the Predirect; 1962 otherwise, it copies the correct UDP Port numbers and IP Addresses 1963 for Client ('C1')'s links into the (previously empty) TLLAOs. 1965 Server ('S1') then examines the network-layer destination address of 1966 the Predirect to determine the next hop toward Client ('C2') by 1967 searching for the AERO address in the neighbor cache. Since Client 1968 ('C2') is not one of its neighbors, Server ('S1') re-encapsulates the 1969 Predirect and relays it via Relay ('R1') by changing the link-layer 1970 source address of the message to 'L2(S1)' and changing the link-layer 1971 destination address to 'L2(R1)'. Server ('S1') finally forwards the 1972 re-encapsulated message to Relay ('R1') without decrementing the 1973 network-layer TTL/Hop Limit field. 1975 When Relay ('R1') receives the Predirect message from Server ('S1') 1976 it determines that Server ('S2') is the next hop toward Client ('C2') 1977 by consulting its forwarding table. Relay ('R1') then re- 1978 encapsulates the Predirect while changing the link-layer source 1979 address to 'L2(R1)' and changing the link-layer destination address 1980 to 'L2(S2)'. Relay ('R1') then relays the Predirect via Server 1981 ('S2'). 1983 When Server ('S2') receives the Predirect message from Relay ('R1') 1984 it determines that Client ('C2') is a neighbor by consulting its 1985 neighbor cache. Server ('S2') then re-encapsulates the Predirect 1986 while changing the link-layer source address to 'L2(S2)' and changing 1987 the link-layer destination address to 'L2(C2)'. Server ('S2') then 1988 forwards the message to Client ('C2'). 1990 3.17.6. Processing Predirects and Sending Redirects 1992 When Client ('C2') receives the Predirect message, it accepts the 1993 Predirect only if the message has a link-layer source address of one 1994 of its Servers (e.g., L2(S2)). Client ('C2') further accepts the 1995 message only if it is willing to serve as a redirection target. 1996 Next, Client ('C2') validates the message according to the ICMPv6 1997 Redirect message validation rules in Section 8.1 of [RFC4861], except 1998 that it accepts the message even though Code=1 and even though the 1999 network-layer source address is not that of it's current first-hop 2000 router. 2002 In the reference operational scenario, when Client ('C2') receives a 2003 valid Predirect message, it either creates or updates a dynamic 2004 neighbor cache entry that stores the Target Address of the message as 2005 the network-layer address of Client ('C1') , stores the link-layer 2006 addresses found in the TLLAOs as the link-layer addresses of Client 2007 ('C1') and stores the Prefix Length as the length to be applied to 2008 the network-layer address for forwarding purposes. Client ('C2') 2009 then sets AcceptTime for the neighbor cache entry to ACCEPT_TIME. 2011 After processing the message, Client ('C2') prepares a Redirect 2012 message response as follows: 2014 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 2015 layer address of Client ('C2')). 2017 o the link-layer destination address is set to 'L2(S2)' (i.e., the 2018 link-layer address of Server ('S2')). 2020 o the network-layer source address is set to fe80::2001:db8:1:0 2021 (i.e., the AERO address of Client ('C2')). 2023 o the network-layer destination address is set to fe80::2001:db8:0:0 2024 (i.e., the AERO address of Client ('C1')). 2026 o the Type is set to 137. 2028 o the Code is set to 0 to indicate "Redirect". 2030 o the Prefix Length is set to the length of the prefix to be applied 2031 to the Target Address. 2033 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 2034 address of Client ('C2')). 2036 o the Destination Address is set to the destination address of the 2037 originating packet that triggered the Redirection event. (If the 2038 originating packet is an IPv4 packet, the address is constructed 2039 in IPv4-compatible IPv6 address format). 2041 o the message includes one or more TLLAOs with Link ID and DSCPs set 2042 to appropriate values for Client ('C2')'s underlying interfaces, 2043 and with UDP Port Number and IP Address set to '0'. 2045 o the message SHOULD include a Timestamp option and MUST echo the 2046 Nonce option received in the Predirect (i.e., if a Nonce option is 2047 included). 2049 o the message includes as much of the RHO copied from the 2050 corresponding AERO Predirect message as possible such that at 2051 least the network-layer header is included but the size of the 2052 message does not exceed 1280 bytes. 2054 After Client ('C2') prepares the Redirect message, it sends the 2055 message to Server ('S2'). 2057 3.17.7. Re-encapsulating and Relaying Redirects 2059 When Server ('S2') receives a Redirect message from Client ('C2'), it 2060 first verifies that the TLLAOs in the Redirect are a proper subset of 2061 the Link IDs in Client ('C2')'s neighbor cache entry. If the 2062 Client's TLLAOs are not acceptable, Server ('S2') discards the 2063 message. Otherwise, Server ('S2') validates the message according to 2064 the ICMPv6 Redirect message validation rules in Section 8.1 of 2065 [RFC4861]. Server ('S2') also verifies that Client ('C2') is 2066 authorized to use the Prefix Length in the Redirect when applied to 2067 the AERO address in the network-layer source address by searching for 2068 the AERO address in the neighbor cache. If validation fails, Server 2069 ('S2') discards the Predirect; otherwise, it copies the correct UDP 2070 Port numbers and IP Addresses for Client ('C2')'s links into the 2071 (previously empty) TLLAOs. 2073 Server ('S2') then examines the network-layer destination address of 2074 the Predirect to determine the next hop toward Client ('C2') by 2075 searching for the AERO address in the neighbor cache. Since Client 2076 ('C2') is not a neighbor, Server ('S2') re-encapsulates the Predirect 2077 and relays it via Relay ('R1') by changing the link-layer source 2078 address of the message to 'L2(S2)' and changing the link-layer 2079 destination address to 'L2(R1)'. Server ('S2') finally forwards the 2080 re-encapsulated message to Relay ('R1') without decrementing the 2081 network-layer TTL/Hop Limit field. 2083 When Relay ('R1') receives the Predirect message from Server ('S2') 2084 it determines that Server ('S1') is the next hop toward Client ('C1') 2085 by consulting its forwarding table. Relay ('R1') then re- 2086 encapsulates the Predirect while changing the link-layer source 2087 address to 'L2(R1)' and changing the link-layer destination address 2088 to 'L2(S1)'. Relay ('R1') then relays the Predirect via Server 2089 ('S1'). 2091 When Server ('S1') receives the Predirect message from Relay ('R1') 2092 it determines that Client ('C1') is a neighbor by consulting its 2093 neighbor cache. Server ('S1') then re-encapsulates the Predirect 2094 while changing the link-layer source address to 'L2(S1)' and changing 2095 the link-layer destination address to 'L2(C1)'. Server ('S1') then 2096 forwards the message to Client ('C1'). 2098 3.17.8. Processing Redirects 2100 When Client ('C1') receives the Redirect message, it accepts the 2101 message only if it has a link-layer source address of one of its 2102 Servers (e.g., ''L2(S1)'). Next, Client ('C1') validates the message 2103 according to the ICMPv6 Redirect message validation rules in 2104 Section 8.1 of [RFC4861], except that it accepts the message even 2105 though the network-layer source address is not that of it's current 2106 first-hop router. Following validation, Client ('C1') then processes 2107 the message as follows. 2109 In the reference operational scenario, when Client ('C1') receives 2110 the Redirect message, it either creates or updates a dynamic neighbor 2111 cache entry that stores the Target Address of the message as the 2112 network-layer address of Client ('C2'), stores the link-layer 2113 addresses found in the TLLAOs as the link-layer addresses of Client 2114 ('C2') and stores the Prefix Length as the length to be applied to 2115 the network-layer address for forwarding purposes. Client ('C1') 2116 then sets ForwardTime for the neighbor cache entry to FORWARD_TIME. 2118 Now, Client ('C1') has a neighbor cache entry with a valid 2119 ForwardTime value, while Client ('C2') has a neighbor cache entry 2120 with a valid AcceptTime value. Thereafter, Client ('C1') may forward 2121 ordinary network-layer data packets directly to Client ('C2') without 2122 involving any intermediate nodes, and Client ('C2') can verify that 2123 the packets came from an acceptable source. (In order for Client 2124 ('C2') to forward packets to Client ('C1'), a corresponding 2125 Predirect/Redirect message exchange is required in the reverse 2126 direction; hence, the mechanism is asymmetric.) 2128 3.17.9. Server-Oriented Redirection 2130 In some environments, the Server nearest the target Client may need 2131 to serve as the redirection target, e.g., if direct Client-to-Client 2132 communications are not possible. In that case, the Server prepares 2133 the Redirect message the same as if it were the destination Client 2134 (see: Section 3.17.6), except that it writes its own link-layer 2135 address in the TLLAO option. The Server must then maintain a dynamic 2136 neighbor cache entry for the redirected source Client. 2138 3.18. Neighbor Unreachability Detection (NUD) 2140 AERO nodes perform Neighbor Unreachability Detection (NUD) by sending 2141 unicast NS messages to elicit solicited NA messages from neighbors 2142 the same as described in [RFC4861]. NUD is performed either 2143 reactively in response to persistent L2 errors (see Section 3.14) or 2144 proactively to refresh existing neighbor cache entries. 2146 When an AERO node sends an NS/NA message, it MUST use its link-local 2147 address as the IPv6 source address and the link-local address of the 2148 neighbor as the IPv6 destination address. When an AERO node receives 2149 an NS message or a solicited NA message, it accepts the message if it 2150 has a neighbor cache entry for the neighbor; otherwise, it ignores 2151 the message. 2153 When a source Client is redirected to a target Client it SHOULD 2154 proactively test the direct path by sending an initial NS message to 2155 elicit a solicited NA response. While testing the path, the source 2156 Client can optionally continue sending packets via the Server, 2157 maintain a small queue of packets until target reachability is 2158 confirmed, or (optimistically) allow packets to flow directly to the 2159 target. The source Client SHOULD thereafter continue to proactively 2160 test the direct path to the target Client (see Section 7.3 of 2161 [RFC4861]) periodically in order to keep dynamic neighbor cache 2162 entries alive. 2164 In particular, while the source Client is actively sending packets to 2165 the target Client it SHOULD also send NS messages separated by 2166 RETRANS_TIMER milliseconds in order to receive solicited NA messages. 2167 If the source Client is unable to elicit a solicited NA response from 2168 the target Client after MAX_RETRY attempts, it SHOULD set ForwardTime 2169 to 0 and resume sending packets via one of its Servers. Otherwise, 2170 the source Client considers the path usable and SHOULD thereafter 2171 process any link-layer errors as a hint that the direct path to the 2172 target Client has either failed or has become intermittent. 2174 When a target Client receives an NS message from a source Client, it 2175 resets AcceptTime to ACCEPT_TIME if a neighbor cache entry exists; 2176 otherwise, it discards the NS message. If ForwardTime is non-zero, 2177 the target Client then sends a solicited NA message to the link-layer 2178 address of the source Client; otherwise, it sends the solicited NA 2179 message to the link-layer address of one of its Servers. 2181 When a source Client receives a solicited NA message from a target 2182 Client, it resets ForwardTime to FORWARD_TIME if a neighbor cache 2183 entry exists; otherwise, it discards the NA message. 2185 When ForwardTime for a dynamic neighbor cache entry expires, the 2186 source Client resumes sending any subsequent packets via a Server and 2187 may (eventually) attempt to re-initiate the AERO redirection process. 2188 When AcceptTime for a dynamic neighbor cache entry expires, the 2189 target Client discards any subsequent packets received directly from 2190 the source Client. When both ForwardTime and AcceptTime for a 2191 dynamic neighbor cache entry expire, the Client deletes the neighbor 2192 cache entry. 2194 3.19. Mobility Management 2196 3.19.1. Announcing Link-Layer Address Changes 2198 When a Client needs to change its link-layer address, e.g., due to a 2199 mobility event, it performs an immediate DHCPv6 Rebind/Reply exchange 2200 via each of its Servers using the new link-layer address as the 2201 source address and with an ALREQ that includes the correct Link ID 2202 and DSCP values. If authentication succeeds, the Server then update 2203 its neighbor cache and sends a DHCPv6 Reply. Note that if the Client 2204 does not issue a DHCPv6 Rebind before the prefix delegation lifetime 2205 expires (e.g., if the Client has been out of touch with the Server 2206 for a considerable amount of time), the Server's Reply will report 2207 NoBinding and the Client must re-initiate the DHCPv6 PD procedure. 2209 Next, the Client sends unsolicited NA messages to each of its 2210 correspondent Client neighbors using the same procedures as specified 2211 in Section 7.2.6 of [RFC4861], except that it sends the messages as 2212 unicast to each neighbor via a Server instead of multicast. In this 2213 process, the Client should send no more than 2214 MAX_NEIGHBOR_ADVERTISEMENT messages separated by no less than 2215 RETRANS_TIMER seconds to each neighbor. 2217 With reference to Figure 9, when Client ('C2') needs to change its 2218 link-layer address it sends unicast unsolicited NA messages to Client 2219 ('C1') via Server ('S2') as follows: 2221 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 2222 layer address of Client ('C2')). 2224 o the link-layer destination address is set to 'L2(S2)' (i.e., the 2225 link-layer address of Server ('S2')). 2227 o the network-layer source address is set to fe80::2001:db8:1:0 2228 (i.e., the AERO address of Client ('C2')). 2230 o the network-layer destination address is set to fe80::2001:db8:0:0 2231 (i.e., the AERO address of Client ('C1')). 2233 o the Type is set to 136. 2235 o the Code is set to 0. 2237 o the Solicited flag is set to 0. 2239 o the Override flag is set to 1. 2241 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 2242 address of Client ('C2')). 2244 o the message includes one or more TLLAOs with Link ID and DSCPs set 2245 to appropriate values for Client ('C2')'s underlying interfaces, 2246 and with UDP Port Number and IP Address set to '0'. 2248 o the message SHOULD include a Timestamp option. 2250 When Server ('S1') receives the NA message, it relays the message in 2251 the same way as described for relaying Redirect messages in 2252 Section 3.17.7. In particular, Server ('S1') copies the correct UDP 2253 port numbers and IP addresses into the TLLAOs, changes the link-layer 2254 source address to its own address, changes the link-layer destination 2255 address to the address of Relay ('R1'), then forwards the NA message 2256 via the relaying chain the same as for a Redirect. 2258 When Client ('C1') receives the NA message, it accepts the message 2259 only if it already has a neighbor cache entry for Client ('C2') then 2260 updates the link-layer addresses for Client ('C2') based on the 2261 addresses in the TLLAOs. Next, Client ('C1') SHOULD initiate the NUD 2262 procedures specified in Section 3.18 to provide Client ('C2') with an 2263 indication that the link-layer source address has been updated, and 2264 to refresh ('C2')'s AcceptTime and ('C1')'s ForwardTime timers. 2266 If Client ('C2') receives an NS message from Client ('C1') indicating 2267 that an unsolicited NA has updated its neighbor cache, Client ('C2') 2268 need not send additional unsolicited NAs. If Client ('C2')'s 2269 unsolicited NA messages are somehow lost, however, Client ('C1') will 2270 soon learn of the mobility event via NUD. 2272 3.19.2. Bringing New Links Into Service 2274 When a Client needs to bring a new underlying interface into service 2275 (e.g., when it activates a new data link), it performs an immediate 2276 Renew/Reply exchange via each of its Servers using the new link-layer 2277 address as the source address and with an ALREQ that includes the new 2278 Link ID and DSCP values. If authentication succeeds, the Server then 2279 updates its neighbor cache and sends a DHCPv6 Reply. The Client MAY 2280 then send unsolicited NA messages to each of its correspondent 2281 Clients to inform them of the new link-layer address as described in 2282 Section 3.19.1. 2284 3.19.3. Removing Existing Links from Service 2286 When a Client needs to remove an existing underlying interface from 2287 service (e.g., when it de-activates an existing data link), it 2288 performs an immediate Renew/Reply exchange via each of its Servers 2289 over any available link with an ALDEL that includes the deprecated 2290 Link ID. If authentication succeeds, the Server then updates its 2291 neighbor cache and sends a DHCPv6 Reply. The Client SHOULD then send 2292 unsolicited NA messages to each of its correspondent Clients to 2293 inform them of the deprecated link-layer address as described in 2294 Section 3.19.1. 2296 3.19.4. Moving to a New Server 2298 When a Client associates with a new Server, it performs the Client 2299 procedures specified in Section 3.15.2. 2301 When a Client disassociates with an existing Server, it sends a 2302 DHCPv6 Release message via a new Server to the unicast link-local 2303 network layer address of the old Server. The new Server then writes 2304 its own link-layer address in the DHCPv6 Release message IP source 2305 address and forwards the message to the old Server. 2307 When the old Server receives the DHCPv6 Release, it first 2308 authenticates the message. The Server then resets the Client's 2309 neighbor cache entry lifetime to 5 seconds, rewrites the link-layer 2310 address in the neighbor cache entry to the address of the new Server, 2311 then returns a DHCPv6 Reply message to the Client via the old Server. 2312 When the lifetime expires, the old Server withdraws the IP route from 2313 the AERO routing system and deletes the neighbor cache entry for the 2314 Client. The Client can then use the Reply message to verify that the 2315 termination signal has been processed, and can delete both the 2316 default route and the neighbor cache entry for the old Server. (Note 2317 that since Release/Reply messages may be lost in the network the 2318 Client MUST retry until it gets Reply indicating that the Release was 2319 successful.) 2321 Clients SHOULD NOT move rapidly between Servers in order to avoid 2322 causing excessive oscillations in the AERO routing system. Such 2323 oscillations could result in intermittent reachability for the Client 2324 itself, while causing little harm to the network. Examples of when a 2325 Client might wish to change to a different Server include a Server 2326 that has gone unreachable, topological movements of significant 2327 distance, etc. 2329 3.20. Proxy AERO 2331 Proxy Mobile IPv6 (PMIPv6) [RFC5213][RFC5844][RFC5949] presents a 2332 localized mobility management scheme for use within an access network 2333 domain. It is typically used in WiFi and cellular wireless access 2334 networks, and allows Mobile Nodes (MNs) to receive and retain an IP 2335 address that remains stable within the access network domain without 2336 needing to implement any special mobility protocols. In the PMIPv6 2337 architecture, access network devices known as Mobility Access 2338 Gateways (MAGs) provide MNs with an access link abstraction and 2339 receive prefixes for the MNs from a Local Mobility Anchor (LMA). 2341 In a proxy AERO domain, a proxy AERO Client (acting as a MAG) can 2342 similarly provide proxy services for MNs that do not participate in 2343 AERO messaging. The proxy Client presents an access link abstraction 2344 to MNs, and performs DHCPv6 PD exchanges over the AERO interface with 2345 an AERO Server (acting as an LMA) to receive ACPs for address 2346 provisioning of new MNs that come onto an access link. This scheme 2347 assumes that proxy Clients act as fixed (non-mobile) infrastructure 2348 elements under the same administrative trust basis as for Relays and 2349 Servers. 2351 When an MN comes onto an access link within a proxy AERO domain for 2352 the first time, the proxy Client authenticates the MN and obtains a 2353 unique identifier that it can use as a DHCPv6 DUID then issues a 2354 DHCPv6 PD Request to its Server. When the Server delegates an ACP, 2355 the proxy Client creates an AERO address for the MN and assigns the 2356 ACP to the MN's access link. The proxy Client then configures itself 2357 as a default router for the MN and provides address autoconfiguration 2358 services (e.g., SLAAC, DHCPv6, DHCPv4, etc.) for provisioning MN 2359 addresses from the ACP over the access link. Since the proxy Client 2360 may serve many such MNs simultaneously, it may receive multiple ACP 2361 prefix delegations and configure multiple AERO addresses, i.e., one 2362 for each MN. 2364 When two MNs are associated with the same proxy Client, the Client 2365 can forward traffic between the MNs without involving a Server since 2366 it configures the AERO addresses of both MNs and therefore also has 2367 the necessary routing information. When two MNs are associated with 2368 different proxy Clients, the source MN's Client can initiate standard 2369 AERO route optimization to discover a direct path to the target MN's 2370 Client through the exchange of Predirect/Redirect messages. 2372 When an MN in a proxy AERO domain leaves an access link provided by 2373 an old proxy Client, the MN issues an access link-specific "leave" 2374 message that informs the old Client of the link-layer address of a 2375 new Client on the planned new access link. This is known as a 2376 "predictive handover". When an MN comes onto an access link provided 2377 by a new proxy Client, the MN issues an access link-specific "join" 2378 message that informs the new Client of the link-layer address of the 2379 old Client on the actual old access link. This is known as a 2380 "reactive handover". 2382 Upon receiving a predictive handover indication, the old proxy Client 2383 sends a DHCPv6 PD Request message directly to the new Client and 2384 queues any arriving data packets addressed to the departed MN. The 2385 Request message includes the MN's ID as the DUID, the ACP in an IA_PD 2386 option, the old Client's address as the link-layer source address and 2387 the new Client's address as the link-layer destination address. When 2388 the new Client receives the Request message, it changes the link- 2389 layer source address to its own address, changes the link-layer 2390 destination address to the address of its Server, and forwards the 2391 message to the Server. At the same time, the new Client creates 2392 access link state for the ACP in anticipation of the MN's arrival 2393 (while queuing any data packets until the MN arrives), creates a 2394 neighbor cache entry for the old Client with AcceptTime set to 2395 ACCEPT_TIME, then sends a Redirect message back to the old Client. 2396 When the old Client receives the Redirect message, it creates a 2397 neighbor cache entry for the new Client with ForwardTime set to 2398 FORWARD_TIME, then forwards any queued data packets to the new 2399 Client. At the same time, the old Client sends a DHCPv6 PD Release 2400 message to its Server. Finally, the old Client sends unsolicited NA 2401 messages to any of the ACP's correspondents with a TLLAO containing 2402 the link-layer address of the new Client. This follows the procedure 2403 specified in Section 3.19.1, except that it is the old Client and not 2404 the Server that supplies the link-layer address. 2406 Upon receiving a reactive handover indication, the new proxy Client 2407 creates access link state for the MN's ACP, sends a DHCPv6 PD Request 2408 message to its Server, and sends a DHCPv6 PD Release message directly 2409 to the old Client. The Release message includes the MN's ID as the 2410 DUID, the ACP in an IA_PD option, the new Client's address as the 2411 link-layer source address and the old Client's address as the link- 2412 layer destination address. When the old Client receives the Release 2413 message, it changes the link-layer source address to its own address, 2414 changes the link-layer destination address to the address of its 2415 Server, and forwards the message to the Server. At the same time, 2416 the old Client sends a Predirect message back to the new Client and 2417 queues any arriving data packets addressed to the departed MN. When 2418 the new Client receives the Predirect, it creates a neighbor cache 2419 entry for the old Client with AcceptTime set to ACCEPT_TIME, then 2420 sends a Redirect message back to the old Client. When the old Client 2421 receives the Redirect message, it creates a neighbor cache entry for 2422 the new Client with ForwardTime set to FORWARD_TIME, then forwards 2423 any queued data packets to the new Client. Finally, the old Client 2424 sends unsolicited NA messages to correspondents the same as for the 2425 predictive case. 2427 When a Server processes a DHCPv6 Request message, it creates a 2428 neighbor cache entry for this ACP if none currently exists. If a 2429 neighbor cache entry already exists, however, the Server changes the 2430 link-layer address to the address of the new proxy Client (this 2431 satisfies the case of both the old Client and new Client using the 2432 same Server). 2434 When a Server processes a DHCPv6 Release message, it resets the 2435 neighbor cache entry lifetime for this ACP to 5 seconds if the cached 2436 link-layer address matches the old proxy Client's address. 2437 Otherwise, the Server ignores the Release message (this satisfies the 2438 case of both the old Client and new Client using the same Server). 2440 When a correspondent Client receives an unsolicited NA message, it 2441 changes the link-layer address for the ACP's neighbor cache entry to 2442 the address of the new proxy Client. The correspondent Client then 2443 issues a Predirect/Redirect exchange to establish a new neighbor 2444 cache entry in the new Client. 2446 From an architectural perspective, in addition to the use of DHCPv6 2447 PD and IPv6 ND signaling the AERO approach differs from PMIPv6 in its 2448 use of the NBMA virtual link model instead of point-to-point tunnels. 2449 This provides a more agile interface for Client/Server and Client/ 2450 Client coordinations, and also facilitates simple route optimization. 2451 The AERO routing system is also arranged in such a fashion that 2452 Clients get the same service from any Server they happen to associate 2453 with. This provides a natural fault tolerance and load balancing 2454 capability such as desired for distributed mobility management. 2456 3.21. Extending AERO Links Through Security Gateways 2458 When an enterprise mobile device moves from a campus LAN connection 2459 to a public Internet link, it must re-enter the enterprise via a 2460 security gateway that has both a physical interface connection to the 2461 Internet and a physical interface connection to the enterprise 2462 internetwork. This most often entails the establishment of a Virtual 2463 Private Network (VPN) link over the public Internet from the mobile 2464 device to the security gateway. During this process, the mobile 2465 device supplies the security gateway with its public Internet address 2466 as the link-layer address for the VPN. The mobile device then acts 2467 as an AERO Client to negotiate with the security gateway to obtain 2468 its ACP. 2470 In order to satisfy this need, the security gateway also operates as 2471 an AERO Server with support for AERO Client proxying. In particular, 2472 when a mobile device (i.e., the Client) connects via the security 2473 gateway (i.e., the Server), the Server provides the Client with an 2474 ACP in a DHCPv6 PD exchange the same as if it were attached to an 2475 enterprise campus access link. The Server then replaces the Client's 2476 link-layer source address with the Server's enterprise-facing link- 2477 layer address in all AERO messages the Client sends toward neighbors 2478 on the AERO link. The AERO messages are then delivered to other 2479 devices on the AERO link as if they were originated by the security 2480 gateway instead of by the AERO Client. In the reverse direction, the 2481 AERO messages sourced by devices within the enterprise network can be 2482 forwarded to the security gateway, which then replaces the link-layer 2483 destination address with the Client's link-layer address and replaces 2484 the link-layer source address with its own (Internet-facing) link- 2485 layer address. 2487 After receiving the ACP, the Client can send IP packets that use an 2488 address taken from the ACP as the network layer source address, the 2489 Client's link-layer address as the link-layer source address, and the 2490 Server's Internet-facing link-layer address as the link-layer 2491 destination address. The Server will then rewrite the link-layer 2492 source address with the Server's own enterprise-facing link-layer 2493 address and rewrite the link-layer destination address with the 2494 target AERO node's link-layer address, and the packets will enter the 2495 enterprise network as though they were sourced from a device located 2496 within the enterprise. In the reverse direction, when a packet 2497 sourced by a node within the enterprise network uses a destination 2498 address from the Client's ACP, the packet will be delivered to the 2499 security gateway which then rewrites the link-layer destination 2500 address to the Client's link-layer address and rewrites the link- 2501 layer source address to the Server's Internet-facing link-layer 2502 address. The Server then delivers the packet across the VPN to the 2503 AERO Client. In this way, the AERO virtual link is essentially 2504 extended *through* the security gateway to the point at which the VPN 2505 link and AERO link are effectively grafted together by the link-layer 2506 address rewriting performed by the security gateway. All AERO 2507 messaging services (including route optimization and mobility 2508 signaling) are therefore extended to the Client. 2510 In order to support this virtual link grafting, the security gateway 2511 (acting as an AERO Server) must keep static neighbor cache entries 2512 for all of its associated Clients located on the public Internet. 2513 The neighbor cache entry is keyed by the AERO Client's AERO address 2514 the same as if the Client were located within the enterprise 2515 internetwork. The neighbor cache is then managed in all ways as 2516 though the Client were an ordinary AERO Client. This includes the 2517 AERO IPv6 ND messaging signaling for Route Optimization and Neighbor 2518 Unreachability Detection. 2520 Note that the main difference between a security gateway acting as an 2521 AERO Server and an enterprise-internal AERO Server is that the 2522 security gateway has at least one enterprise-internal physical 2523 interface and at least one public Internet physical interface. 2524 Conversely, the enterprise-internal AERO Server has only enterprise- 2525 internal physical interfaces. For this reason security gateway 2526 proxying is needed to ensure that the public Internet link-layer 2527 addressing space is kept separate from the enterprise-internal link- 2528 layer addressing space. This is afforded through a natural extension 2529 of the security association caching already performed for each VPN 2530 client by the security gateway. 2532 3.22. Extending IPv6 AERO Links to the Internet 2534 When an IPv6 host ('H1') with an address from an ACP owned by AERO 2535 Client ('C1') sends packets to a correspondent IPv6 host ('H2'), the 2536 packets eventually arrive at the IPv6 router that owns ('H2')s 2537 prefix. This IPv6 router may or may not be an AERO Client ('C2') 2538 either within the same home network as ('C1') or in a different home 2539 network. 2541 If Client ('C1') is currently located outside the boundaries of its 2542 home network, it will connect back into the home network via a 2543 security gateway acting as an AERO Server. The packets sent by 2544 ('H1') via ('C1') will then be forwarded through the security gateway 2545 then through the home network and finally to ('C2') where they will 2546 be delivered to ('H2'). This could lead to sub-optimal performance 2547 when ('C2') could instead be reached via a more direct route without 2548 involving the security gateway. 2550 Consider the case when host ('H1') has the IPv6 address 2551 2001:db8:1::1, and Client ('C1') has the ACP 2001:db8:1::/64 with 2552 underlying IPv6 Internet address of 2001:db8:1000::1. Also, host 2553 ('H2') has the IPv6 address 2001:db8:2::1, and Client ('C2') has the 2554 ACP 2001:db8:2::/64 with underlying IPv6 address of 2001:db8:2000::1. 2555 Client ('C1') can determine whether 'C2' is indeed also an AERO 2556 Client willing to serve as a route optimization correspondent by 2557 resolving the AAAA records for the DNS FQDN that matches ('H2')s 2558 prefix, i.e.: 2560 '0.0.0.0.2.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net' 2562 If ('C2') is indeed a candidate correspondent, the FQDN lookup will 2563 return a PTR resource record that contains the domain name for the 2564 AERO link that manages ('C2')s ASP. Client ('C1') can then attempt 2565 route optimization using an approach similar to the Return 2566 Routability procedure specified for Mobile IPv6 (MIPv6) [RFC6275]. 2567 In order to support this process, both Clients MUST intercept and 2568 decapsulate packets that have a subnet router anycast address 2569 corresponding to any of the /64 prefixes covered by their respective 2570 ACPs. 2572 To initiate the process, Client ('C1') creates a specially-crafted 2573 encapsulated AERO Predirect message that will be routed through its 2574 home network then through ('C2')s home network and finally to ('C2') 2575 itself. Client ('C1') prepares the initial message in the exchange 2576 as follows: 2578 o The encapsulating IPv6 header source address is set to 2579 2001:db8:1:: (i.e., the IPv6 subnet router anycast address for 2580 ('C1')s ACP) 2582 o The encapsulating IPv6 header destination address is set to 2583 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2584 ('C2')s ACP) 2586 o The encapsulating IPv6 header is followed by a UDP header with 2587 source and destination port set to 8060 2589 o The encapsulated IPv6 header source address is set to 2590 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2592 o The encapsulated IPv6 header destination address is set to 2593 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2595 o The encapsulated AERO Predirect message includes all of the 2596 securing information that would occur in a MIPv6 "Home Test Init" 2597 message (format TBD) 2599 Client ('C1') then further encapsulates the message in the 2600 encapsulating headers necessary to convey the packet to the security 2601 gateway (e.g., through IPsec encapsulation) so that the message now 2602 appears "double-encapsulated". ('C1') then sends the message to the 2603 security gateway, which re-encapsulates and forwards it over the home 2604 network from where it will eventually reach ('C2'). 2606 At the same time, ('C1') creates and sends a second encapsulated AERO 2607 Predirect message that will be routed through the IPv6 Internet 2608 without involving the security gateway. Client ('C1') prepares the 2609 message as follows: 2611 o The encapsulating IPv6 header source address is set to 2612 2001:db8:1000:1 (i.e., the Internet IPv6 address of ('C1')) 2614 o The encapsulating IPv6 header destination address is set to 2615 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2616 ('C2')s ACP) 2618 o The encapsulating IPv6 header is followed by a UDP header with 2619 source and destination port set to 8060 2621 o The encapsulated IPv6 header source address is set to 2622 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2624 o The encapsulated IPv6 header destination address is set to 2625 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2627 o The encapsulated AERO Predirect message includes all of the 2628 securing information that would occur in a MIPv6 "Care-of Test 2629 Init" message (format TBD) 2631 ('C2') will receive both Predirect messages through its home network 2632 then return a corresponding Redirect for each of the Predirect 2633 messages with the source and destination addresses in the inner and 2634 outer headers reversed. The first message includes all of the 2635 securing information that would occur in a MIPv6 "Home Test" message, 2636 while the second message includes all of the securing information 2637 that would occur in a MIPv6 "Care-of Test" message (formats TBD). 2639 When ('C1') receives the Redirect messages, it performs the necessary 2640 security procedures per the MIPv6 specification. It then prepares an 2641 encapsulated NS message that includes the same source and destination 2642 addresses as for the "Care-of Test Init" Predirect message, and 2643 includes all of the securing information that would occur in a MIPv6 2644 "Binding Update" message (format TBD) and sends the message to 2645 ('C2'). 2647 When ('C2') receives the NS message, if the securing information is 2648 correct it creates or updates a neighbor cache entry for ('C1') with 2649 fe80::2001:db8:1:0 as the network-layer address, 2001:db8:1000::1 as 2650 the link-layer address and with AcceptTime set to ACCEPT_TIME. 2651 ('C2') then sends an encapsulated NA message back to ('C1') that 2652 includes the same source and destination addresses as for the "Care- 2653 of Test" Redirect message, and includes all of the securing 2654 information that would occur in a MIPv6 "Binding Acknowledgement" 2655 message (format TBD) and sends the message to ('C1'). 2657 When ('C1') receives the NA message, it creates or updates a neighbor 2658 cache entry for ('C2') with fe80::2001:db8:2:0 as the network-layer 2659 address and 2001:db8:2:: as the link-layer address and with 2660 ForwardTime set to FORWARD_TIME, thus completing the route 2661 optimization in the forward direction. 2663 ('C1') subsequently forwards encapsulated packets with outer source 2664 address 2001:db8:1000::1, with outer destination address 2665 2001:db8:2::, with inner source address taken from the 2001:db8:1::, 2666 and with inner destination address taken from 2001:db8:2:: due to the 2667 fact that it has a securely-established neighbor cache entry with 2668 non-zero ForwardTime. ('C2') subsequently accepts any such 2669 encapsulated packets due to the fact that it has a securely- 2670 established neighbor cache entry with non-zero AcceptTime. 2672 In order to keep neighbor cache entries alive, ('C1') periodically 2673 sends additional NS messages to ('C2') and receives any NA responses. 2674 If ('C1') moves to a different point of attachment after the initial 2675 route optimization, it sends a new secured NS message to ('C2') as 2676 above to update ('C2')s neighbor cache. 2678 If ('C2') has packets to send to ('C1'), it performs a corresponding 2679 route optimization in the opposite direction following the same 2680 procedures described above. In the process, the already-established 2681 unidirectional neighbor cache entries within ('C1') and ('C2') are 2682 updated to include the now-bidirectional information. In particular, 2683 the AcceptTime and ForwardTime variables for both neighbor cache 2684 entries are updated to non-zero values, and the link-layer address 2685 for ('C1')s neighbor cache entry for ('C2') is reset to 2686 2001:db8:2000::1. 2688 Note that two AERO Clients can use full security protocol messaging 2689 instead of Return Routability, e.g., if strong authentication and/or 2690 confidentiality are desired. In that case, security protocol key 2691 exchanges such as specified for MOBIKE [RFC4555] would be used to 2692 establish security associations and neighbor cache entries between 2693 the AERO clients. Thereafter, AERO NS/NA messaging can be used to 2694 maintain neighbor cache entries, test reachability, and to announce 2695 mobility events. If reachability testing fails, e.g., if both 2696 Clients move at roughly the same time, the Clients can tear down the 2697 security association and neighbor cache entries and again allow 2698 packets to flow through their home network. 2700 3.23. Encapsulation Protocol Version Considerations 2702 A source Client may connect only to an IPvX underlying network, while 2703 the target Client connects only to an IPvY underlying network. In 2704 that case, the target and source Clients have no means for reaching 2705 each other directly (since they connect to underlying networks of 2706 different IP protocol versions) and so must ignore any redirection 2707 messages and continue to send packets via the Server. 2709 3.24. Multicast Considerations 2711 When the underlying network does not support multicast, AERO nodes 2712 map IPv6 link-scoped multicast addresses (including 2713 'All_DHCP_Relay_Agents_and_Servers') to the link-layer address of a 2714 Server. 2716 When the underlying network supports multicast, AERO nodes use the 2717 multicast address mapping specification found in [RFC2529] for IPv4 2718 underlying networks and use a direct multicast mapping for IPv6 2719 underlying networks. (In the latter case, "direct multicast mapping" 2720 means that if the IPv6 multicast destination address of the 2721 encapsulated packet is "M", then the IPv6 multicast destination 2722 address of the encapsulating header is also "M".) 2724 3.25. Operation on AERO Links Without DHCPv6 Services 2726 When Servers on the AERO link do not provide DHCPv6 services, 2727 operation can still be accommodated through administrative 2728 configuration of ACPs on AERO Clients. In that case, administrative 2729 configurations of AERO interface neighbor cache entries on both the 2730 Server and Client are also necessary. However, this may interfere 2731 with the ability for Clients to dynamically change to new Servers, 2732 and can expose the AERO link to misconfigurations unless the 2733 administrative configurations are carefully coordinated. 2735 3.26. Operation on Server-less AERO Links 2737 In some AERO link scenarios, there may be no Servers on the link and/ 2738 or no need for Clients to use a Server as an intermediary trust 2739 anchor. In that case, each Client acts as a Server unto itself to 2740 establish neighbor cache entries by performing direct Client-to- 2741 Client IPv6 ND message exchanges, and some other form of trust basis 2742 must be applied so that each Client can verify that the prospective 2743 neighbor is authorized to use its claimed ACP. 2745 When there is no Server on the link, Clients must arrange to receive 2746 ACPs and publish them via a secure alternate prefix delegation 2747 authority through some means outside the scope of this document. 2749 3.27. Manually-Configured AERO Tunnels 2751 In addition to the dynamic neighbor discovery procedures for AERO 2752 link neighbors described above, AERO encapsulation can be applied to 2753 manually-configured tunnels. In that case, the tunnel endpoints use 2754 an administratively-assigned link-local address and exchange NS/NA 2755 messages the same as for dynamically-established tunnels. 2757 3.28. Intradomain Routing 2759 After a tunnel neighbor relationship has been established, neighbors 2760 can use a traditional dynamic routing protocol over the tunnel to 2761 exchange routing information without having to inject the routes into 2762 the AERO routing system. 2764 4. Implementation Status 2766 User-level and kernel-level AERO implementations have been developed 2767 and are undergoing internal testing within Boeing. 2769 5. Next Steps 2771 A new Generic UDP Encapsulation (GUE) format has been specified in 2772 [I-D.herbert-gue-fragmentation] [I-D.ietf-nvo3-gue]. The GUE 2773 encapsulation format will eventually supplant the native AERO UDP 2774 encapsulation format. 2776 Future versions of the spec will explore the subject of DSCP marking 2777 in more detail. 2779 6. IANA Considerations 2781 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2782 AERO in the "enterprise-numbers" registry. 2784 The IANA has assigned the UDP port number "8060" for an earlier 2785 experimental version of AERO [RFC6706]. This document obsoletes 2786 [RFC6706] and claims the UDP port number "8060" for all future use. 2788 No further IANA actions are required. 2790 7. Security Considerations 2792 AERO link security considerations are the same as for standard IPv6 2793 Neighbor Discovery [RFC4861] except that AERO improves on some 2794 aspects. In particular, AERO uses a trust basis between Clients and 2795 Servers, where the Clients only engage in the AERO mechanism when it 2796 is facilitated by a trust anchor. Unless there is some other means 2797 of authenticating the Client's identity (e.g., link-layer security), 2798 AERO nodes SHOULD also use DHCPv6 securing services (e.g., DHCPv6 2799 authentication, Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6], etc.) for 2800 Client authentication and network admission control. 2802 AERO Redirect, Predirect and unsolicited NA messages SHOULD include a 2803 Timestamp option (see Section 5.3 of [RFC3971]) that other AERO nodes 2804 can use to verify the message time of origin. AERO Predirect, NS and 2805 RS messages SHOULD include a Nonce option (see Section 5.3 of 2806 [RFC3971]) that recipients echo back in corresponding responses. 2808 AERO links must be protected against link-layer address spoofing 2809 attacks in which an attacker on the link pretends to be a trusted 2810 neighbor. Links that provide link-layer securing mechanisms (e.g., 2811 IEEE 802.1X WLANs) and links that provide physical security (e.g., 2812 enterprise network wired LANs) provide a first line of defense that 2813 is often sufficient. In other instances, additional securing 2814 mechanisms such as Secure Neighbor Discovery (SeND) [RFC3971], IPsec 2815 [RFC4301] or TLS [RFC5246] may be necessary. 2817 AERO Clients MUST ensure that their connectivity is not used by 2818 unauthorized nodes on their EUNs to gain access to a protected 2819 network, i.e., AERO Clients that act as routers MUST NOT provide 2820 routing services for unauthorized nodes. (This concern is no 2821 different than for ordinary hosts that receive an IP address 2822 delegation but then "share" the address with unauthorized nodes via a 2823 NAT function.) 2825 On some AERO links, establishment and maintenance of a direct path 2826 between neighbors requires secured coordination such as through the 2827 Internet Key Exchange (IKEv2) protocol [RFC5996] to establish a 2828 security association. 2830 An AERO Client's link-layer address could be rewritten by a link- 2831 layer switching element on the path from the Client to the Server and 2832 not detected by the DHCPv6 security mechanism. However, such a 2833 condition would only be a matter of concern on unmanaged/unsecured 2834 links where the link-layer switching elements themselves present a 2835 man-in-the-middle attack threat. For this reason, IP security MUST 2836 be used when AERO is employed over unmanaged/unsecured links. 2838 8. Acknowledgements 2840 Discussions both on IETF lists and in private exchanges helped shape 2841 some of the concepts in this work. Individuals who contributed 2842 insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, 2843 Stewart Bryant, Brian Carpenter, Wojciech Dec, Ralph Droms, Adrian 2844 Farrel, Sri Gundavelli, Brian Haberman, Joel Halpern, Tom Herbert, 2845 Sascha Hlusiak, Lee Howard, Andre Kostur, Ted Lemon, Andy Malis, 2846 Satoru Matsushima, Tomek Mrugalski, Behcet Saikaya, Joe Touch, Bernie 2847 Volz, Ryuji Wakikawa and Lloyd Wood. Members of the IESG also 2848 provided valuable input during their review process that greatly 2849 improved the document. Special thanks go to Stewart Bryant, Joel 2850 Halpern and Brian Haberman for their shepherding guidance. 2852 This work has further been encouraged and supported by Boeing 2853 colleagues including Dave Bernhardt, Cam Brodie, Balaguruna 2854 Chidambaram, Bruce Cornish, Claudiu Danilov, Wen Fang, Anthony 2855 Gregory, Jeff Holland, Ed King, Gen MacLean, Rob Muszkiewicz, Sean 2856 O'Sullivan, Kent Shuey, Brian Skeen, Mike Slane, Brendan Williams, 2857 Julie Wulff, Yueli Yang, and other members of the BR&T and BIT mobile 2858 networking teams. 2860 Earlier works on NBMA tunneling approaches are found in 2861 [RFC2529][RFC5214][RFC5569]. 2863 Many of the constructs presented in this second edition of AERO are 2864 based on the author's earlier works, including: 2866 o The Internet Routing Overlay Network (IRON) 2867 [RFC6179][I-D.templin-ironbis] 2869 o Virtual Enterprise Traversal (VET) 2870 [RFC5558][I-D.templin-intarea-vet] 2872 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2873 [RFC5320][I-D.templin-intarea-seal] 2875 o AERO, First Edition [RFC6706] 2877 Note that these works cite numerous earlier efforts that are not also 2878 cited here due to space limitations. The authors of those earlier 2879 works are acknowledged for their insights. 2881 9. References 2883 9.1. Normative References 2885 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2886 August 1980. 2888 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 2889 1981. 2891 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2892 RFC 792, September 1981. 2894 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 2895 October 1996. 2897 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2898 Requirement Levels", BCP 14, RFC 2119, March 1997. 2900 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2901 (IPv6) Specification", RFC 2460, December 1998. 2903 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2904 IPv6 Specification", RFC 2473, December 1998. 2906 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2907 "Definition of the Differentiated Services Field (DS 2908 Field) in the IPv4 and IPv6 Headers", RFC 2474, December 2909 1998. 2911 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2912 and M. Carney, "Dynamic Host Configuration Protocol for 2913 IPv6 (DHCPv6)", RFC 3315, July 2003. 2915 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2916 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2917 December 2003. 2919 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2920 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2922 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 2923 for IPv6 Hosts and Routers", RFC 4213, October 2005. 2925 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2926 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2927 September 2007. 2929 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2930 Address Autoconfiguration", RFC 4862, September 2007. 2932 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 2933 Requirements", RFC 6434, December 2011. 2935 9.2. Informative References 2937 [I-D.herbert-gue-fragmentation] 2938 Herbert, T. and F. Templin, "Fragmentation option for 2939 Generic UDP Encapsulation", draft-herbert-gue- 2940 fragmentation-00 (work in progress), March 2015. 2942 [I-D.ietf-dhc-sedhcpv6] 2943 Jiang, S., Shen, S., Zhang, D., and T. Jinmei, "Secure 2944 DHCPv6", draft-ietf-dhc-sedhcpv6-07 (work in progress), 2945 March 2015. 2947 [I-D.ietf-nvo3-gue] 2948 Herbert, T., Yong, L., and O. Zia, "Generic UDP 2949 Encapsulation", draft-ietf-nvo3-gue-00 (work in progress), 2950 April 2015. 2952 [I-D.templin-intarea-seal] 2953 Templin, F., "The Subnetwork Encapsulation and Adaptation 2954 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 2955 progress), January 2014. 2957 [I-D.templin-intarea-vet] 2958 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 2959 templin-intarea-vet-40 (work in progress), May 2013. 2961 [I-D.templin-ironbis] 2962 Templin, F., "The Interior Routing Overlay Network 2963 (IRON)", draft-templin-ironbis-16 (work in progress), 2964 March 2014. 2966 [I-D.vandevelde-idr-remote-next-hop] 2967 Velde, G., Patel, K., Rao, D., Raszuk, R., and R. Bush, 2968 "BGP Remote-Next-Hop", draft-vandevelde-idr-remote-next- 2969 hop-09 (work in progress), March 2015. 2971 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 2972 RFC 879, November 1983. 2974 [RFC1035] Mockapetris, P., "Domain names - implementation and 2975 specification", STD 13, RFC 1035, November 1987. 2977 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2978 November 1990. 2980 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 2981 1812, June 1995. 2983 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 2984 selection, and registration of an Autonomous System (AS)", 2985 BCP 6, RFC 1930, March 1996. 2987 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 2988 for IP version 6", RFC 1981, August 1996. 2990 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2991 2131, March 1997. 2993 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2994 Domains without Explicit Tunnels", RFC 2529, March 1999. 2996 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 2997 RFC 2675, August 1999. 2999 [RFC2764] Gleeson, B., Heinanen, J., Lin, A., Armitage, G., and A. 3000 Malis, "A Framework for IP Based Virtual Private 3001 Networks", RFC 2764, February 2000. 3003 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3004 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3005 March 2000. 3007 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 3008 2923, September 2000. 3010 [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 3011 2983, October 2000. 3013 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3014 of Explicit Congestion Notification (ECN) to IP", RFC 3015 3168, September 2001. 3017 [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, 3018 "DNS Extensions to Support IP Version 6", RFC 3596, 3019 October 2003. 3021 [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., 3022 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3023 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3024 RFC 3819, July 2004. 3026 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 3027 Protocol 4 (BGP-4)", RFC 4271, January 2006. 3029 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3030 Architecture", RFC 4291, February 2006. 3032 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3033 Internet Protocol", RFC 4301, December 2005. 3035 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 3036 Message Protocol (ICMPv6) for the Internet Protocol 3037 Version 6 (IPv6) Specification", RFC 4443, March 2006. 3039 [RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol 3040 (LDAP): The Protocol", RFC 4511, June 2006. 3042 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 3043 (MOBIKE)", RFC 4555, June 2006. 3045 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 3046 System", RFC 4592, July 2006. 3048 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 3049 Discovery", RFC 4821, March 2007. 3051 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3052 Errors at High Data Rates", RFC 4963, July 2007. 3054 [RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski, 3055 "DHCPv6 Relay Agent Echo Request Option", RFC 4994, 3056 September 2007. 3058 [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., 3059 and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. 3061 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3062 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3063 March 2008. 3065 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3066 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 3068 [RFC5320] Templin, F., "The Subnetwork Encapsulation and Adaptation 3069 Layer (SEAL)", RFC 5320, February 2010. 3071 [RFC5494] Arkko, J. and C. Pignataro, "IANA Allocation Guidelines 3072 for the Address Resolution Protocol (ARP)", RFC 5494, 3073 April 2009. 3075 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3076 Route Optimization Requirements for Operational Use in 3077 Aeronautics and Space Exploration Mobile Networks", RFC 3078 5522, October 2009. 3080 [RFC5558] Templin, F., "Virtual Enterprise Traversal (VET)", RFC 3081 5558, February 2010. 3083 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3084 Infrastructures (6rd)", RFC 5569, January 2010. 3086 [RFC5720] Templin, F., "Routing and Addressing in Networks with 3087 Global Enterprise Recursion (RANGER)", RFC 5720, February 3088 2010. 3090 [RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy 3091 Mobile IPv6", RFC 5844, May 2010. 3093 [RFC5949] Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F. 3094 Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949, 3095 September 2010. 3097 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 3098 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 3099 5996, September 2010. 3101 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3102 NAT64: Network Address and Protocol Translation from IPv6 3103 Clients to IPv4 Servers", RFC 6146, April 2011. 3105 [RFC6179] Templin, F., "The Internet Routing Overlay Network 3106 (IRON)", RFC 6179, March 2011. 3108 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 3109 Troan, "Basic Requirements for IPv6 Customer Edge 3110 Routers", RFC 6204, April 2011. 3112 [RFC6221] Miles, D., Ooghe, S., Dec, W., Krishnan, S., and A. 3113 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, May 3114 2011. 3116 [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A. 3117 Bierman, "Network Configuration Protocol (NETCONF)", RFC 3118 6241, June 2011. 3120 [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support 3121 in IPv6", RFC 6275, July 2011. 3123 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3124 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, August 3125 2011. 3127 [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", RFC 3128 6422, December 2011. 3130 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3131 for Equal Cost Multipath Routing and Link Aggregation in 3132 Tunnels", RFC 6438, November 2011. 3134 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 3135 RFC 6691, July 2012. 3137 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 3138 (AERO)", RFC 6706, August 2012. 3140 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3141 RFC 6864, February 2013. 3143 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3144 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 3146 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3147 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3148 RFC 6936, April 2013. 3150 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 3151 Address Option in DHCPv6", RFC 6939, May 2013. 3153 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 3154 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 3156 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 3157 Address Selection Policy Using DHCPv6", RFC 7078, January 3158 2014. 3160 [TUNTAP] Wikipedia, W., "http://en.wikipedia.org/wiki/TUN/TAP", 3161 October 2014. 3163 Author's Address 3165 Fred L. Templin (editor) 3166 Boeing Research & Technology 3167 P.O. Box 3707 3168 Seattle, WA 98124 3169 USA 3171 Email: fltemplin@acm.org