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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, May 20, 2015 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: November 21, 2015 10 Transmission of IP Packets over AERO Links 11 draft-templin-aerolink-53.txt 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). Nodes attached 17 to AERO links can exchange packets via trusted intermediate routers 18 that provide forwarding services to reach off-link destinations and 19 redirection services for route optimization. AERO provides an IPv6 20 link-local address format known as the AERO address that supports 21 operation of the IPv6 Neighbor Discovery (ND) protocol and links IPv6 22 ND to IP forwarding. Admission control and provisioning are 23 supported by the Dynamic Host Configuration Protocol for IPv6 24 (DHCPv6), and node mobility is naturally supported through dynamic 25 neighbor cache updates. Although DHCPv6 and IPv6 ND messaging is 26 used in the control plane, both IPv4 and IPv6 are supported in the 27 data plane. 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 November 21, 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 . . . . . . . . . . . . . . . . . 12 72 3.6. AERO Interface Initialization . . . . . . . . . . . . . . 12 73 3.6.1. AERO Relay Behavior . . . . . . . . . . . . . . . . . 12 74 3.6.2. AERO Server Behavior . . . . . . . . . . . . . . . . 13 75 3.6.3. AERO Client Behavior . . . . . . . . . . . . . . . . 13 76 3.6.4. AERO Forwarding Agent Behavior . . . . . . . . . . . 14 77 3.7. AERO Link Routing System . . . . . . . . . . . . . . . . 14 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 Discovery . . . . . . . . . . . . . 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 is 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 assigned 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 assigned 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 other AERO nodes. 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 Realys can also be configured to act as 332 AERO Servers. (By analogy, the AERO Relay and Server can be thought 333 of as two "halves" of a whole IP router with the Relay being the 334 "upper half" and the Server being the "lower half". These two halves 335 can be split out into different nodes or can be combined in a single 336 node.) 338 AERO Servers provide default forwarding services to AERO Clients. 339 Each Server also peers with each Relay in a dynamic routing protocol 340 instance to advertise its list of associated ACPs. Servers configure 341 a DHCPv6 server function to facilitate Prefix Delegation (PD) 342 exchanges with Clients. Each delegated prefix becomes an ACP taken 343 from an ASP. Servers forward packets between AERO interface 344 neighbors only, i.e., and not between the AERO link and the native IP 345 Internetwork. AERO Servers maintain an AERO interface neighbor cache 346 entry for each AERO Relay. They also maintain both a neighbor cache 347 entry and an IP forwarding table entry for each of their associated 348 Clients. AERO Servers can also be configured to act as AERO Relays. 350 AERO Clients act as requesting routers to receive ACPs through DHCPv6 351 PD exchanges with AERO Servers over the AERO link and sub-delegate 352 portions of their ACPs to EUN interfaces. (Each Client MAY associate 353 with a single Server or with multiple Servers, e.g., for fault 354 tolerance, load balancing, etc.) Each IPv6 Client receives at least 355 a /64 IPv6 ACP, and may receive even shorter prefixes. Similarly, 356 each IPv4 Client receives at least a /32 IPv4 ACP (i.e., a singleton 357 IPv4 address), and may receive even shorter prefixes. AERO Clients 358 maintain an AERO interface neighbor cache entry for each of their 359 associated Servers as well as for each of their correspondent 360 Clients. 362 AERO Clients typically configure a TUN/TAP interface [TUNTAP] as a 363 point-to-point linkage between the IP layer and the AERO interface. 364 The IP layer therefore sees only the TUN/TAP interface, while the 365 AERO interface provides an intermediate conduit between the TUN/TAP 366 interface and the underlying interfaces. AERO Clients that act as 367 hosts assign one or more IP addresses from their ACPs to the TUN/TAP 368 interface, i.e., and not to the AERO interface. 370 AERO Forwarding Agents provide data plane forwarding services as 371 companions to other AERO nodes. Note that while all Relays, Servers 372 and Clients are required to perform both control and data plane 373 operations on their own behalf, they may optionally enlist the 374 services of special-purpose Forwarding Agents to offload performance- 375 intensive traffic. 377 3.3. AERO Addresses 379 An AERO address is an IPv6 link-local address with an embedded ACP 380 and assigned to a Client's AERO interface. The AERO address is 381 formed as follows: 383 fe80::[ACP] 385 For IPv6, the AERO address begins with the prefix fe80::/64 and 386 includes in its interface identifier the base prefix taken from the 387 Client's IPv6 ACP. The base prefix is determined by masking the ACP 388 with the prefix length. For example, if the AERO Client receives the 389 IPv6 ACP: 391 2001:db8:1000:2000::/56 393 it constructs its AERO address as: 395 fe80::2001:db8:1000:2000 397 For IPv4, the AERO address is formed from the lower 64 bits of an 398 IPv4-mapped IPv6 address [RFC4291] that includes the base prefix 399 taken from the Client's IPv4 ACP. For example, if the AERO Client 400 receives the IPv4 ACP: 402 192.0.2.32/28 404 it constructs its AERO address as: 406 fe80::FFFF:192.0.2.32 408 The AERO address remains stable as the Client moves between 409 topological locations, i.e., even if its link-layer addresses change. 411 NOTE: In some cases, prospective neighbors may not have advanced 412 knowledge of the Client's ACP length and may therefore send initial 413 IPv6 ND messages with an AERO destination address that matches the 414 ACP but does not correspond to the base prefix. In that case, the 415 Client MUST accept the address as equivalent to the base address, but 416 then use the base address as the source address of any IPv6 ND 417 message replies. For example, if the Client receives the IPv6 ACP 418 2001:db8:1000:2000::/56 then subsequently receives an IPv6 ND message 419 with destination address fe80::2001:db8:1000:2001, it accepts the 420 message but uses fe80::2001:db8:1000:2000 as the source address of 421 any IPv6 ND replies. 423 3.4. AERO Interface Characteristics 425 AERO interfaces use encapsulation (see Section 3.10) to exchange 426 packets with neighbors attached to the AERO link. AERO interfaces 427 maintain a neighbor cache, and AERO Clients and Servers use unicast 428 IPv6 ND messaging. AERO interfaces use unicast Neighbor Solicitation 429 (NS), Neighbor Advertisement (NA), Router Solicitation (RS) and 430 Router Advertisement (RA) messages the same as for any IPv6 link. 431 AERO interfaces use two redirection message types -- the first known 432 as a Predirect message and the second being the standard Redirect 433 message (see Section 3.17). AERO links further use link-local-only 434 addressing; hence, AERO nodes ignore any Prefix Information Options 435 (PIOs) they may receive in RA messages over an AERO interface. 437 AERO interface ND messages include one or more Source/Target Link- 438 Layer Address Options (S/TLLAOs) formatted as shown in Figure 2: 440 0 1 2 3 441 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 443 | Type = 2 | Length = 3 | Reserved | 444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 445 | Link ID | NDSCPs | DSCP #1 |Prf| DSCP #2 |Prf| 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 | DSCP #3 |Prf| DSCP #4 |Prf| .... 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 | UDP Port Number | | 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 451 | | 452 + + 453 | IP Address | 454 + + 455 | | 456 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 457 | | 458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 460 Figure 2: AERO Source/Target Link-Layer Address Option (S/TLLAO) 461 Format 463 In this format, Link ID is an integer value between 0 and 255 464 corresponding to an underlying interface of the target node, NDSCPs 465 encodes an integer value between 1 and 64 indicating the number of 466 Differentiated Services Code Point (DSCP) octets that follow. Each 467 DSCP octet is a 6-bit integer DSCP value followed by a 2-bit 468 Preference ("Prf") value. Each DSCP value encodes an integer between 469 0 and 63 associated with this Link ID, where the value 0 means 470 "default" and other values are interpreted as specified in [RFC2474]. 471 The 'Prf' qualifier for each DSCP value is set to the value 0 472 ("deprecated'), 1 ("low"), 2 ("medium"), or 3 ("high") to indicate a 473 preference level for packet forwarding purposes. UDP Port Number and 474 IP Address are set to the addresses used by the target node when it 475 sends encapsulated packets over the underlying interface. When the 476 encapsulation IP address family is IPv4, IP Address is formed as an 477 IPv4-mapped IPv6 address [RFC4291]. 479 AERO interfaces may be configured over multiple underlying 480 interfaces. For example, common mobile handheld devices have both 481 wireless local area network ("WLAN") and cellular wireless links. 482 These links are typically used "one at a time" with low-cost WLAN 483 preferred and highly-available cellular wireless as a standby. In a 484 more complex example, aircraft frequently have many wireless data 485 link types (e.g. satellite-based, terrestrial, air-to-air 486 directional, etc.) with diverse performance and cost properties. 488 If a Client's multiple underlying interfaces are used "one at a time" 489 (i.e., all other interfaces are in standby mode while one interface 490 is active), then Redirect, Predirect and unsolicited NA messages 491 include only a single TLLAO with Link ID set to a constant value. 493 If the Client has multiple active underlying interfaces, then from 494 the perspective of IPv6 ND it would appear to have a single link- 495 local address with multiple link-layer addresses. In that case, 496 Redirect, Predirect and unsolicited NA messages MAY include multiple 497 TLLAOs -- each with a different Link ID that corresponds to a 498 specific underlying interface of the Client. 500 3.5. AERO Link Registration 502 When an administrative authority first deploys a set of AERO Relays 503 and Servers that comprise an AERO link, they also assign a unique 504 domain name for the link, e.g., "linkupnetworks.example.com". Next, 505 if administrative policy permits Clients within the domain to serve 506 as correspondent nodes for Internet mobile nodes, the administrative 507 authority adds a Fully Qualified Domain Name (FQDN) for each of the 508 AERO link's ASPs to the Domain Name System (DNS) [RFC1035]. The FQDN 509 is based on the suffix "aero.linkupnetworks.net" with a prefix formed 510 from the wildcard-terminated reverse mapping of the ASP 511 [RFC3596][RFC4592], and resolves to a DNS PTR resource record. For 512 example, for the ASP '2001:db8:1::/48' within the domain name 513 "linkupnetworks.example.com", the DNS database contains: 515 '*.1.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net. PTR 516 linkupnetworks.example.com' 518 This DNS registration advertises the AERO link's ASPs to prospective 519 mobile nodes. 521 3.6. AERO Interface Initialization 523 3.6.1. AERO Relay Behavior 525 When a Relay enables an AERO interface, it first assigns an 526 administratively-assigned link-local address fe80::ID to the 527 interface. Each fe80::ID address MUST be unique among all AERO nodes 528 on the link, and MUST NOT collide with any potential AERO addresses 529 nor the special addresses fe80:: and fe80::ffff:ffff:ffff:ffff. (The 530 fe80::ID addresses are typically taken from the available range 531 fe80::/96, e.g., as fe80::1, fe80::2, fe80::3, etc.) The Relay then 532 engages in a dynamic routing protocol session with all Servers on the 533 link (see: Section 3.7), and advertises the set of ASPs into the 534 native IP Internetwork. 536 Each Relay subsequently maintains an IP forwarding table entry for 537 each Client-Server association, and maintains a neighbor cache entry 538 for each Server on the link. Relays exchange NS/NA messages with 539 AERO link neighbors the same as for any AERO node, however they 540 typically do not perform explicit Neighbor Unreachability Detection 541 (NUD) (see: Section 3.18) since the dynamic routing protocol already 542 provides reachability confirmation. 544 3.6.2. AERO Server Behavior 546 When a Server enables an AERO interface, it assigns an 547 administratively assigned link-local address fe80::ID the same as for 548 Relays. The Server further configures a DHCPv6 server function to 549 facilitate DHCPv6 PD exchanges with AERO Clients. The Server 550 maintains a neighbor cache entry for each Relay on the link, and 551 manages per-Client neighbor cache entries and IP forwarding table 552 entries based on control message exchanges. Each Server also engages 553 in a dynamic routing protocol with each Relay on the link (see: 554 Section 3.7). 556 When the Server receives an NS/RS message on the AERO interface it 557 returns an NA/RA message but does not update the neighbor cache. The 558 Server further provides a simple conduit between AERO interface 559 neighbors. Therefore, packets enter the Server's AERO interface from 560 the link layer and are forwarded back out the link layer without ever 561 leaving the AERO interface and therefore without ever disturbing the 562 network layer. 564 3.6.3. AERO Client Behavior 566 When a Client enables an AERO interface, it uses the special address 567 fe80::ffff:ffff:ffff:ffff to obtain an ACP from an AERO Server via 568 DHCPv6 PD. Next, it assigns the corresponding AERO address to the 569 AERO interface and creates a neighbor cache entry for the Server, 570 i.e., the PD exchange bootstraps autoconfiguration of a unique link- 571 local address. The Client maintains a neighbor cache entry for each 572 of its Servers and each of its active correspondent Clients. When 573 the Client receives Redirect/Predirect messages on the AERO interface 574 it updates or creates neighbor cache entries, including link-layer 575 address information. Unsolicited NA messages update the cached link- 576 layer addresses for correspondent Clients (e.g., following a link- 577 layer address change due to node mobility) but do not create new 578 neighbor cache entries. NS/NA messages used for NUD update timers in 579 existing neighbor cache entires but do not update link-layer 580 addresses nor create new neighbor cache entries. 582 Finally, the Client need not maintain any IP forwarding table entries 583 for its Servers or correspondent Clients. Instead, it can set a 584 single "route-to-interface" default route in the IP forwarding table, 585 and all forwarding decisions can be made within the AERO interface 586 based on neighbor cache entries. (On systems in which adding a 587 default route would violate security policy, the default route could 588 instead be installed via a "synthesized RA", e.g., as discussed in 589 Section 3.15.2.) 591 3.6.4. AERO Forwarding Agent Behavior 593 When a Forwarding Agent enables an AERO interface, it assigns the 594 same link-local address(es) as the companion AERO node that manages 595 AERO control messaging services. The Forwarding Agent thereafter 596 provides data plane forwarding services based solely on the 597 forwarding information assigned to it by the companion AERO node. 598 AERO Forwarding Agents perform NS/NA messaging, i.e., the same as for 599 any AERO node. 601 3.7. AERO Link Routing System 603 Relays require full topology knowledge of all ACP/Server 604 associations, while individual Servers at a minimum only need to know 605 the ACPs for their current set of associated Clients. This is 606 accomplished through the use of an internal instance of the Border 607 Gateway Protocol (BGP) [RFC4271] coordinated between Servers and 608 Relays. This internal BGP instance does not interact with the public 609 Internet BGP instance; therefore, the AERO link is presented to the 610 IP Internetwork as a small set of ASPs as opposed to the full set of 611 individual ACPs. 613 In a reference BGP arrangement, each AERO Server is configured as an 614 Autonomous System Border Router (ASBR) for a stub Autonomous System 615 (AS) using an AS Number (ASN) that is unique within the BGP instance, 616 and each Server further peers with each Relay but does not peer with 617 other Servers. Similarly, Relays do not peer with each other, since 618 they will reliably receive all updates from all Servers and will 619 therefore have a consistent view of the AERO link ACP delegations. 621 Each Server maintains a working set of associated ACPs, and 622 dynamically announces new ACPs and withdraws departed ACPs in its BGP 623 updates to Relays. Clients are expected to remain associated with 624 their current Servers for extended timeframes, however Servers SHOULD 625 selectively suppress BGP updates for impatient Clients that 626 repeatedly associate and disassociate with them in order to dampen 627 routing churn. 629 In some environments, Relays need not send BGP updates to Servers 630 since Servers can always use Relays as default routers, however this 631 presents a data/control plane performance tradeoff. In environments 632 where sustained packet forwarding over Relays is undesirable, Relays 633 can instead report ACPs to Servers while including a BGP Remote-Next- 634 Hop [I-D.vandevelde-idr-remote-next-hop]. The Server then creates a 635 neighbor cache entry for each ACP with the Remote-Next-Hop as the 636 link-layer address to enable Server-to-Server route optimization. 638 3.8. AERO Interface Neighbor Cache Maintenace 640 Each AERO interface maintains a conceptual neighbor cache that 641 includes an entry for each neighbor it communicates with on the AERO 642 link, the same as for any IPv6 interface [RFC4861]. AERO interface 643 neighbor cache entires are said to be one of "permanent", "static" or 644 "dynamic". 646 Permanent neighbor cache entries are created through explicit 647 administrative action; they have no timeout values and remain in 648 place until explicitly deleted. AERO Relays maintain a permanent 649 neighbor cache entry for each Server on the link, and AERO Servers 650 maintain a permanent neighbor cache entry for each Relay. Each entry 651 maintains the mapping between the neighbor's fe80::ID network-layer 652 address and corresponding link-layer address. 654 Static neighbor cache entries are created though DHCPv6 PD exchanges 655 and remain in place for durations bounded by prefix lifetimes. AERO 656 Servers maintain static neighbor cache entries for the ACPs of each 657 of their associated Clients, and AERO Clients maintain a static 658 neighbor cache entry for each of their associated Servers. When an 659 AERO Server sends a DHCPv6 Reply message response to a Client's 660 DHCPv6 Solicit/Request, Rebind or Renew message, it creates or 661 updates a static neighbor cache entry based on the AERO address 662 corresponding to the Client's ACP as the network-layer address, the 663 prefix lifetime as the neighbor cache entry lifetime, the Client's 664 encapsulation IP address and UDP port number as the link-layer 665 address and the prefix length as the length to apply to the AERO 666 address. When an AERO Client receives a DHCPv6 Reply message from a 667 Server, it creates or updates a static neighbor cache entry based on 668 the Reply message link-local source address as the network-layer 669 address, the prefix lifetime as the neighbor cache entry lifetime, 670 and the encapsulation IP source address and UDP source port number as 671 the link-layer address. 673 Dynamic neighbor cache entries are created or updated based on 674 receipt of an IPv6 ND message, and are garbage-collected if not used 675 within a short timescale. AERO Clients maintain dynamic neighbor 676 cache entries for each of their active correspondent Client ACPs with 677 lifetimes based on IPv6 ND messaging constants. When an AERO Client 678 receives a valid Predirect message it creates or updates a dynamic 679 neighbor cache entry for the Predirect target network-layer and link- 680 layer addresses plus prefix length. The node then sets an 681 "AcceptTime" variable in the neighbor cache entry to ACCEPT_TIME 682 seconds and uses this value to determine whether packets received 683 from the correspondent can be accepted. When an AERO Client receives 684 a valid Redirect message it creates or updates a dynamic neighbor 685 cache entry for the Redirect target network-layer and link-layer 686 addresses plus prefix length. The Client then sets a "ForwardTime" 687 variable in the neighbor cache entry to FORWARD_TIME seconds and uses 688 this value to determine whether packets can be sent directly to the 689 correspondent. The Client also sets a "MaxRetry" variable to 690 MAX_RETRY to limit the number of keepalives sent when a correspondent 691 may have gone unreachable. 693 For dynamic neighbor cache entries, when an AERO Client receives a 694 valid NS message it (re)sets AcceptTime for the neighbor to 695 ACCEPT_TIME. When an AERO Client receives a valid solicited NA 696 message, it (re)sets ForwardTime for the neighbor to FORWARD_TIME and 697 sets MaxRetry to MAX_RETRY. When an AERO Client receives a valid 698 unsolicited NA message, it updates the correspondent's link-layer 699 addresses but DOES NOT reset AcceptTime, ForwardTime or MaxRetry. 701 It is RECOMMENDED that FORWARD_TIME be set to the default constant 702 value 30 seconds to match the default REACHABLE_TIME value specified 703 for IPv6 ND [RFC4861]. 705 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 706 value 40 seconds to allow a 10 second window so that the AERO 707 redirection procedure can converge before AcceptTime decrements below 708 FORWARD_TIME. 710 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 711 for IPv6 ND address resolution in Section 7.3.3 of [RFC4861]. 713 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 714 administratively set, if necessary, to better match the AERO link's 715 performance characteristics; however, if different values are chosen, 716 all nodes on the link MUST consistently configure the same values. 717 Most importantly, ACCEPT_TIME SHOULD be set to a value that is 718 sufficiently longer than FORWARD_TIME to allow the AERO redirection 719 procedure to converge. 721 3.9. AERO Interface Sending Algorithm 723 IP packets enter a node's AERO interface either from the network 724 layer (i.e., from a local application or the IP forwarding system), 725 or from the link layer (i.e., from the AERO tunnel virtual link). 726 Packets that enter the AERO interface from the network layer are 727 encapsulated and admitted into the AERO link, i.e., they are 728 tunnelled to an AERO interface neighbor. Packets that enter the AERO 729 interface from the link layer are either re-admitted into the AERO 730 link or delivered to the network layer where they are subject to 731 either local delivery or IP forwarding. Since each AERO node may 732 have only partial information about neighbors on the link, AERO 733 interfaces may forward packets with link-local destination addresses 734 at a layer below the network layer. This means that AERO nodes act 735 as both IP routers and sub-IP layer forwarding agents. AERO 736 interface sending considerations for Clients, Servers and Relays are 737 given below. 739 When an IP packet enters a Client's AERO interface from the network 740 layer, if the destination is covered by an ASP the Client searches 741 for a dynamic neighbor cache entry with a non-zero ForwardTime and an 742 AERO address that matches the packet's destination address. (The 743 destination address may be either an address covered by the 744 neighbor's ACP or the (link-local) AERO address itself.) If there is 745 a match, the Client uses a link-layer address in the entry as the 746 link-layer address for encapsulation then admits the packet into the 747 AERO link. If there is no match, the Client instead uses the link- 748 layer address of a neighboring Server as the link-layer address for 749 encapsulation. 751 When an IP packet enters a Server's AERO interface from the link 752 layer, if the destination is covered by an ASP the Server searches 753 for a neighbor cache entry with an AERO address that matches the 754 packet's destination address. (The destination address may be either 755 an address covered by the neighbor's ACP or the AERO address itself.) 756 If there is a match, the Server uses a link-layer address in the 757 entry as the link-layer address for encapsulation and re-admits the 758 packet into the AERO link. If there is no match, the Server instead 759 uses the link-layer address in a permanent neighbor cache entry for a 760 Relay as the link-layer address for encapsulation. 762 When an IP packet enters a Relay's AERO interface from the network 763 layer, the Relay searches its IP forwarding table for an entry that 764 is covered by an ASP and also matches the destination. If there is a 765 match, the Relay uses the link-layer address in a permanent neighbor 766 cache entry for a Server as the link-layer address for encapsulation 767 and admits the packet into the AERO link. When an IP packet enters a 768 Relay's AERO interface from the link-layer, if the destination is not 769 a link-local address and does not match an ASP the Relay removes the 770 packet from the AERO interface and uses IP forwarding to forward the 771 packet to the Internetwork. If the destination address is a link- 772 local address or a non-link-local address that matches an ASP, and 773 there is a more-specific ACP entry in the IP forwarding table, the 774 Relay uses the link-layer address in the corresponding neighbor cache 775 entry as the link-layer address for encapsulation and re-admits the 776 packet into the AERO link. When an IP packet enters a Relay's AERO 777 interface from either the network layer or link-layer, and the 778 packet's destination address matches an ASP but there is no more- 779 specific ACP entry, the Relay drops the packet and returns an ICMP 780 Destination Unreachable message (see: Section 3.14). 782 When an AERO Server receives a packet from a Relay via the AERO 783 interface, the Server MUST NOT forward the packet back to the same or 784 a different Relay. 786 When an AERO Relay receives a packet from a Server via the AERO 787 interface, the Relay MUST NOT forward the packet back to the same 788 Server. 790 When an AERO node re-admits a packet into the AERO link without 791 involving the network layer, the node MUST NOT decrement the network 792 layer TTL/Hop-count. 794 When an AERO node forwards a data packet to the primary link-layer 795 address of a neighbor, it may receive RA messages with one or more 796 SLLAOs that include the link-layer addresses of AERO Forwarding 797 Agents. The AERO node SHOULD record the link-layer addresses in the 798 neighbor cache entry for the neighbor and send subsequent data 799 packets via one of these addresses instead of the neighbor's primary 800 address (see: Section 3.16). 802 3.10. AERO Interface Encapsulation and Re-encapsulation 804 AERO interfaces encapsulate IP packets according to whether they are 805 entering the AERO interface from the network layer or if they are 806 being re-admitted into the same AERO link they arrived on. This 807 latter form of encapsulation is known as "re-encapsulation". 809 The AERO interface encapsulates packets per the base tunneling 810 specifications (e.g., [RFC2003], [RFC2473], [RFC2784], [RFC4213], 811 [RFC4301], [RFC5246], etc.) except that it inserts a UDP header 812 immediately following the IP encapsulation header. If there are no 813 additional encapsulation headers (and no fragmentation, 814 identification, checksum or signature is needed), the AERO interface 815 next encapsulates the IPv4 or IPv6 packet immediately following the 816 UDP header. In that case, the most significant four bits of the 817 encapsulated packet encode the value '4' for IPv4 or '6' for IPv6. 819 For all other encapsulations, the AERO interface MUST insert an AERO 820 Header between the UDP header and the next encapsulation header as 821 shown in Figure 3: 823 0 1 2 3 824 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 1 825 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 826 |Version|N|F|C|S| Next Header |Fragment Offset (13 bits)|Res|M| 827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 828 | Identification (32 bits) | 829 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 830 | Checksum (16 bits) | Signature (variable length) : 831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 833 Figure 3: AERO Header 835 Version a 4-bit "Version" field. MUST be 0 for the purpose of this 836 specification. 838 N a 1-bit "Next Header" flag. MUST be 1 for the purpose of this 839 specification to indicate that "Next Header" field is present. 840 "Next Header" encodes the IP protocol number corresponding to the 841 next header in the encapsulation immediately following the AERO 842 header. For example, "Next Header" encodes the value '4' for 843 IPv4, '17' for UDP, '41' for IPv6, '47' for GRE, '50' for ESP, 844 '51' for AH, etc. 846 F a 1-bit "Fragment Header" flag. Set to '1' if the "Fragment 847 Offset", "Res", "M", and "Identification" fields are present and 848 collectively referred to as the "AERO Fragment Header"; otherwise, 849 set to '0'. 851 C a 1-bit "Checksum" flag. Set to '1' if the "Checksum" field is 852 present; otherwise, set to '0'. When present, the Checksum field 853 contains a checksum of the IP/UDP/AERO encapsulation headers prior 854 to the Checksum field. 856 S a 1-bit "Signature" flag. Set to '1' if the "Signature" field is 857 present; otherwise, set to '0'. When present, the Signature field 858 contains a cryptographic signature of the encapsulated packet 859 following the Signature field. The signature is applied prior to 860 any fragmentation; hence' the Signature field only appears in the 861 first fragment of a fragmented packet. 863 (Note: [RFC6706] defines an experimental use in which the bits 864 corresponding to (Version, N, F, C, S) are all zero, which can be 865 unambiguously distinguished from the values permitted by this 866 specification.) 868 During encapsulation, the AERO interface copies the "TTL/Hop Limit", 869 "Type of Service/Traffic Class" [RFC2983] and "Congestion 870 Experienced" [RFC3168] values in the packet's IP header into the 871 corresponding fields in the encapsulation IP header. (When IPv6 is 872 used as the encapsulation protocol, the interface also sets the Flow 873 Label value in the encapsulation header per [RFC6438].) For packets 874 undergoing re-encapsulation, the AERO interface instead copies the 875 "TTL/Hop Limit", "Type of Service/Traffic Class", "Flow Label" and 876 "Congestion Experienced" values in the original encapsulation IP 877 header into the corresponding fields in the new encapsulation IP 878 header, i.e., the values are transferred between encapsulation 879 headers and *not* copied from the encapsulated packet's network-layer 880 header. 882 The AERO interface next sets the UDP source port to a constant value 883 that it will use in each successive packet it sends, and sets the UDP 884 length field to the length of the encapsulated packet plus 8 bytes 885 for the UDP header itself, plus the length of the AERO header. For 886 packets sent via a Server, the AERO interface sets the UDP 887 destination port to 8060, i.e., the IANA-registered port number for 888 AERO. For packets sent to a correspondent Client, the AERO interface 889 sets the UDP destination port to the port value stored in the 890 neighbor cache entry for this correspondent. The AERO interface also 891 sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) unless 892 an integrity check is required (see: Section 3.13.2). 894 The AERO interface next sets the IP protocol number in the 895 encapsulation header to 17 (i.e., the IP protocol number for UDP). 896 When IPv4 is used as the encapsulation protocol, the AERO interface 897 sets the DF bit as discussed in Section 3.13. The AERO interface 898 finally sets the AERO header fields as described in Figure 3. 900 3.11. AERO Interface Decapsulation 902 AERO interfaces decapsulate packets destined either to the node 903 itself or to a destination reached via an interface other than the 904 AERO interface the packet was received on. When the AERO interface 905 receives a UDP packet, it examines the first octet of the 906 encapsulated packet. 908 If the most significant four bits of the first octet encode the value 909 '4' (i.e., the IP version number value for IPv4) or the value '6' 910 (i.e., the IP version number value for IPv6), the AERO interface 911 discards the encapsulation headers and accepts the encapsulated 912 packet as an ordinary IPv6 or IPv4 data packet, respectively. If the 913 most significant four bits encode the value '0', however, the AERO 914 interface processes the packet according to the appropriate AERO 915 Header fields as specified in Figure 3. 917 3.12. AERO Interface Data Origin Authentication 919 AERO nodes employ simple data origin authentication procedures for 920 encapsulated packets they receive from other nodes on the AERO link. 921 In particular: 923 o AERO Relays and Servers accept encapsulated packets with a link- 924 layer source address that matches a permanent neighbor cache 925 entry. 927 o AERO Servers accept authentic encapsulated DHCPv6 messages from 928 Clients, and create or update a static neighbor cache entry for 929 the source based on the specific message type. 931 o AERO Servers accept encapsulated packets if there is a neighbor 932 cache entry with an AERO address that matches the packet's 933 network-layer source address and with a link-layer address that 934 matches the packet's link-layer source address. 936 o AERO Clients accept encapsulated packets if there is a static 937 neighbor cache entry with a link-layer source address that matches 938 the packet's link-layer source address. 940 o AERO Clients and Servers accept encapsulated packets if there is a 941 dynamic neighbor cache entry with an AERO address that matches the 942 packet's network-layer source address, with a link-layer address 943 that matches the packet's link-layer source address, and with a 944 non-zero AcceptTime. 946 Note that this simple data origin authentication is effective in 947 environments in which link-layer addresses cannot be spoofed. In 948 other environments, each AERO message must include a signature that 949 the recipient can use to authenticate the message origin. 951 3.13. AERO Interface MTU and Fragmentation 953 The AERO interface is the node's point of attachment to the AERO 954 link. AERO links over IP networks have a maximum link MTU of 64KB 955 minus the encapsulation overhead (termed here "ENCAPS"), since the 956 maximum packet size in the base IP specifications is 64KB 957 [RFC0791][RFC2460] (while IPv6 jumbograms can be up to 4GB, they are 958 considered optional for IPv6 nodes [RFC2675][RFC6434]). 960 IPv6 specifies a minimum link MTU of 1280 bytes [RFC2460]. This is 961 the minimum packet size the AERO interface MUST admit without 962 returning an ICMP Packet Too Big (PTB) message. Although IPv4 963 specifies a smaller minimum link MTU of 68 bytes [RFC0791], AERO 964 interfaces also observe a 1280 byte minimum for IPv4. Additionally, 965 the vast majority of links in the Internet configure an MTU of at 966 least 1500 bytes. Original source hosts have therefore become 967 conditioned to expect that IP packets up to 1500 bytes in length will 968 either be delivered to the final destination or a suitable PTB 969 message returned. However, PTB messages may be lost in the network 970 [RFC2923] resulting in failure of the IP Path MTU Discovery (PMTUD) 971 mechanisms [RFC1191][RFC1981]. 973 For these reasons, the source AERO interface (i.e., the tunnel 974 ingress)admit packets into the tunnel subject to their reasonable 975 expectation that PMTUD will convey the correct information to the 976 original source in the event that the packet is too large. In 977 particular, if the original source is within the same well-managed 978 administrative domain as the tunnel ingress, the ingress drops the 979 packet and sends a PTB message back to the original source if the 980 packet is too large to traverse the tunnel in one piece. Similarly, 981 if the tunnel ingress is within the same well-managed administrative 982 domain as the to the destination AERO interface (i.e., the tunnel 983 egress), the ingress can cache MTU values reported in PTB messages 984 received from a router on the path to the egress. 986 In all other cases, AERO interfaces admit all packets up to 1500 987 bytes in length even if some fragmentation is necessary, and admit 988 larger packets without fragmentation in case they are able to 989 traverse the tunnel in one piece. AERO interfaces are therefore 990 considered to have an indefinite MTU, i.e., instead of clamping the 991 MTU to a finite size. 993 For AERO links over IPv4, the IP ID field is only 16 bits in length, 994 meaning that fragmentation at high data rates could result in data 995 corruption due to reassembly misassociations [RFC6864][RFC4963] (see: 996 Section 3.13.2). For AERO links over both IPv4 and IPv6, studies 997 have also shown that IP fragments are dropped unconditionally over 998 some network paths [I-D.taylor-v6ops-fragdrop]. For these reasons, 999 when fragmentation is needed it is performed through insertion of an 1000 AERO fragment header (see: Section 3.10) and application of tunnel 1001 fragmentation as described in Section 3.1.7 of [RFC2764]. Since the 1002 AERO fragment header reduces the room available for packet data, but 1003 the original source has no way to control its insertion, the header 1004 length MUST be included in the ENCAPS length even for packets in 1005 which the header does not appear. 1007 The tunnel ingress therefore sends encapsulated packets to the tunnel 1008 egress according to the following algorithm: 1010 o For IP packets that are no larger than (1280-ENCAPS) bytes, the 1011 tunnel ingress encapsulates the packet and admits it into the 1012 tunnel without fragmentation. For IPv4 AERO links, the tunnel 1013 ingress sets the Don't Fragment (DF) bit to 0 so that these 1014 packets will be delivered to the tunnel egress even if there is a 1015 restricting link in the path, i.e., unless lost due to congestion 1016 or routing errors. 1018 o For IP packets that are larger than (1280-ENCAPS) bytes but no 1019 larger than 1500 bytes, the tunnel ingress encapsulates the packet 1020 and inserts an AERO fragment header. Next, the tunnel ingress 1021 uses the fragmentation algorithm in [RFC2460] to break the packet 1022 into two non-overlapping fragments where the first fragment 1023 (including ENCAPS) is no larger than 1024 bytes and the second is 1024 no larger than the first. Each fragment consists of identical 1025 UDP/IP encapsulation headers, followed by the AERO header followed 1026 by the fragment of the encapsulated packet itself. The tunnel 1027 ingress then admits both fragments into the tunnel, and for IPv4 1028 sets the DF bit to 0 in the IP encapsulation header. These 1029 fragmented encapsulated packets will be delivered to the tunnel 1030 egress. When the tunnel egress receives the fragments, it 1031 reassembles them into a whole packet per the reassembly algorithm 1032 in [RFC2460]. The tunnel egress therefore MUST be capable of 1033 reassembling packets up to 1500+ENCAPS bytes in length; hence, it 1034 is RECOMMENDED that the tunnel egress be capable of reassembling 1035 at least 2KB. 1037 o For IPv4 packets that are larger than 1500 bytes and with the DF 1038 bit set to 0, the tunnel ingress uses ordinary IPv4 fragmentation 1039 to break the unencapsulated packet into a minimum number of non- 1040 overlapping fragments where the first fragment is no larger than 1041 1024-ENCAPS and all other fragments are no larger than the first 1042 fragment. The tunnel ingress then encapsulates each fragment (and 1043 for IPv4 sets the DF bit to 0) then admits them into the tunnel. 1044 These fragments will be delivered to the final destination via the 1045 tunnel egress. 1047 o For all other IP packets, if the packet is too large to enter the 1048 underlying interface following encapsulation, the tunnel ingress 1049 drops the packet and returns a network-layer (L3) PTB message to 1050 the original source with MTU set to the larger of 1500 bytes or 1051 the underlying interface MTU minus ENCAPS. Otherwise, the tunnel 1052 ingress encapsulates the packet and admits it into the tunnel 1053 without fragmentation (and for IPv4 sets the DF bit to 1) and 1054 translates any link-layer (L2) PTB messages it may receive from 1055 the network into corresponding L3 PTB messages to send to the 1056 original source as specified in Section 3.14. Since both L2 and 1057 L3 PTB messages may be either lost or contain insufficient 1058 information, however, it is RECOMMENDED that original sources that 1059 send unfragmentable IP packets larger than 1500 bytes use 1060 Packetization Layer Path MTU Discovery (PLPMTUD) [RFC4821]. 1062 While sending packets according to the above algorithm, the tunnel 1063 ingress MAY also send 1500 byte or larger probe packets to determine 1064 whether they can reach the tunnel egress without fragmentation. If 1065 the probes succeed, the tunnel ingress can discontinue fragmentation 1066 and (for IPv4) set DF to 1. Since the path MTU within the tunnel may 1067 fluctuate due to routing changes, the tunnel ingress SHOULD continue 1068 to send additional probes subject to rate limiting and SHOULD process 1069 any L2 PTB messages as an indication that the path MTU may have 1070 decreased. If the path MTU within the tunnel becomes insufficient, 1071 the source MUST resume fragmentation. 1073 To construct a probe, the tunnel ingress prepares an NS message with 1074 a Nonce option plus trailing NULL padding octets added to the probe 1075 length without including the length of the padding in the IPv6 1076 Payload Length field, but with the length included in the 1077 encapsulating IP header. The tunnel ingress then encapsulates the 1078 padded NS message in the encapsulation headers (and for IPv4 sets DF 1079 to 1) then sends the message to the tunnel egress. If the tunnel 1080 egress returns a solicited NA message with a matching Nonce option, 1081 the tunnel ingress deems the probe successful. Note that in this 1082 process it is essential that probes follow equivalent paths to those 1083 used to convey actual data packets. This means that Equal Cost 1084 MultiPath (ECMP) and Link Aggregation Gateway (LAG) equipment in the 1085 path would need to ensure that probes and data packets follow the 1086 same path, which is outside the scope of this specification. 1088 3.13.1. Accommodating Large Control Messages 1090 Control messages (i.e., IPv6 ND, DHCPv6, etc.) MUST be accommodated 1091 even if some fragmentation is necessary. These packets are therefore 1092 accommodated through a modification of the second rule in the above 1093 algorithm as follows: 1095 o For control messages that are larger than (1280-ENCAPS) bytes, the 1096 tunnel ingress encapsulates the packet and inserts an AERO 1097 fragment header. Next, the tunnel ingress uses the fragmentation 1098 algorithm in [RFC2460] to break the packet into a minimum number 1099 of non-overlapping fragments where the first fragment (including 1100 ENCAPS) is no larger than 1024 bytes and the remaining fragments 1101 are no larger than the first. The tunnel ingress then 1102 encapsulates each fragment (and for IPv4 sets the DF bit to 0) 1103 then admits them into the tunnel. 1105 Control messages that exceed the 2KB minimum reassembly size rarely 1106 occur in the modern era, however the tunnel egress SHOULD be able to 1107 reassemble them if they do. This means that the tunnel egress SHOULD 1108 include a configuration knob allowing the operator to set a larger 1109 reassembly buffer size if large control messages become more common 1110 in the future. 1112 The tunnel ingress can send large control messages without 1113 fragmentation if there is assurance that large packets can traverse 1114 the tunnel without fragmentation. The tunnel ingress MAY send 1500 1115 byte or larger probe packets as specified above to determine a size 1116 for which fragmentation can be avoided. 1118 3.13.2. Integrity 1120 When fragmentation is needed, there must be assurance that reassembly 1121 can be safely conducted without incurring data corruption. Sources 1122 of corruption can include implementation errors, memory errors and 1123 misassociation of fragments from a first datagram with fragments of 1124 another datagram. The first two conditions (implementation and 1125 memory errors) are mitigated by modern systems and implementations 1126 that have demonstrated integrity through decades of operational 1127 practice. The third condition (reassembly misassociations) must be 1128 accounted for by AERO. 1130 The AERO fragmentation procedure described in the above algorithms 1131 reuses standard IPv6 fragmentation and reassembly code. Since the 1132 AERO fragment header includes a 32-bit ID field, there would need to 1133 be 2^32 packets alive in the network before a second packet with a 1134 duplicate ID enters the system with the (remote) possibility for a 1135 reassembly misassociation. For 1280 byte packets, and for a maximum 1136 network lifetime value of 60 seconds[RFC2460], this means that the 1137 tunnel ingress would need to produce ~(7 *10^12) bits/sec in order 1138 for a duplication event to be possible. This exceeds the bandwidth 1139 of data link technologies of the modern era, but not necessarily so 1140 going forward into the future. Although wireless data links commonly 1141 used by AERO Clients support vastly lower data rates, the aggregate 1142 data rates between AERO Servers and Relays may be substantial. 1143 However, high speed data links in the network core are expected to 1144 configure larger MTUs, e.g., 4KB, 8KB or even larger such that 1145 unfragmented packets can be used. Hence, no integrity check is 1146 included to cover the AERO fragmentation and reassembly procedures. 1148 When the tunnel ingress sends an IPv4-encapsulated packet with the DF 1149 bit set to 0 in the above algorithms, there is a chance that the 1150 packet may be fragmented by an IPv4 router somewhere within the 1151 tunnel. Since the largest such packet is only 1280 bytes, however, 1152 it is very likely that the packet will traverse the tunnel without 1153 incurring a restricting link. Even when a link within the tunnel 1154 configures an MTU smaller than 1280 bytes, it is very likely that it 1155 does so due to limited performance characteristics [RFC3819]. This 1156 means that the tunnel would not be able to convey fragmented 1157 IPv4-encapsulated packets fast enough to produce reassembly 1158 misassociations, as discussed above. However, AERO must also account 1159 for the possibility of tunnel paths that include "poorly managed" 1160 IPv4 link MTUs due to misconfigurations. 1162 Since the IPv4 header includes only a 16-bit ID field, there would 1163 only need to be 2^16 packets alive in the network before a second 1164 packet with a duplicate ID enters the system. For 1280 byte packets, 1165 and for a maximum network lifetime value of 120 seconds[RFC0791], 1166 this means that the tunnel ingress would only need to produce ~(5 1167 *10^6) bits/sec in order for a duplication event to be possible - a 1168 value that is well within range for many modern wired and wireless 1169 data link technologies. 1171 Therefore, if there is strong operational assurance that no IPv4 1172 links capable of supporting data rates of 5Mbps or more configure an 1173 MTU smaller than 1280 the tunnel ingress MAY omit an integrity check 1174 for the IPv4 fragmentation and reassembly procedures; otherwise, the 1175 tunnel ingress SHOULD include an integrity check. When an upper 1176 layer encapsulation (e.g., IPsec) already includes an integrity 1177 check, the tunnel ingress need not include an additional check. 1178 Otherwise, the tunnel ingress calculates the UDP checksum over the 1179 encapsulated packet and writes the value into the UDP encapsulation 1180 header, i.e., instead of writing the value 0. The tunnel egress will 1181 then verify the UDP checksum and discard the packet if the checksum 1182 is incorrect. 1184 3.14. AERO Interface Error Handling 1186 When an AERO node admits encapsulated packets into the AERO 1187 interface, it may receive link-layer (L2) or network-layer (L3) error 1188 indications. 1190 An L2 error indication is an ICMP error message generated by a router 1191 on the path to the neighbor or by the neighbor itself. The message 1192 includes an IP header with the address of the node that generated the 1193 error as the source address and with the link-layer address of the 1194 AERO node as the destination address. 1196 The IP header is followed by an ICMP header that includes an error 1197 Type, Code and Checksum. For ICMPv6 [RFC4443], the error Types 1198 include "Destination Unreachable", "Packet Too Big (PTB)", "Time 1199 Exceeded" and "Parameter Problem". For ICMPv4 [RFC0792], the error 1200 Types include "Destination Unreachable", "Fragmentation Needed" (a 1201 Destination Unreachable Code that is analogous to the ICMPv6 PTB), 1202 "Time Exceeded" and "Parameter Problem". 1204 The ICMP header is followed by the leading portion of the packet that 1205 generated the error, also known as the "packet-in-error". For 1206 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1207 much of invoking packet as possible without the ICMPv6 packet 1208 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1209 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1210 "Internet Header + 64 bits of Original Data Datagram", however 1211 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1212 ICMP datagram SHOULD contain as much of the original datagram as 1213 possible without the length of the ICMP datagram exceeding 576 1214 bytes". 1216 The L2 error message format is shown in Figure 4: 1218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1219 ~ ~ 1220 | L2 IP Header of | 1221 | error message | 1222 ~ ~ 1223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1224 | L2 ICMP Header | 1225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1226 ~ ~ P 1227 | IP and other encapsulation | a 1228 | headers of original L3 packet | c 1229 ~ ~ k 1230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1231 ~ ~ t 1232 | IP header of | 1233 | original L3 packet | i 1234 ~ ~ n 1235 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1236 ~ ~ e 1237 | Upper layer headers and | r 1238 | leading portion of body | r 1239 | of the original L3 packet | o 1240 ~ ~ r 1241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1243 Figure 4: AERO Interface L2 Error Message Format 1245 The AERO node rules for processing these L2 error messages is as 1246 follows: 1248 o When an AERO node receives an L2 Parameter Problem message, it 1249 processes the message the same as described as for ordinary ICMP 1250 errors in the normative references [RFC0792][RFC4443]. 1252 o When an AERO node receives persistent L2 IPv4 Time Exceeded 1253 messages, the IP ID field may be wrapping before earlier fragments 1254 have been processed. In that case, the node SHOULD begin 1255 including IPv4 integrity checks (see: Section 3.13.2). 1257 o When an AERO Client receives persistent L2 Destination Unreachable 1258 messages in response to tunneled packets that it sends to one of 1259 its dynamic neighbor correspondents, the Client SHOULD test the 1260 path to the correspondent using Neighbor Unreachability Detection 1261 (NUD) (see Section 3.18). If NUD fails, the Client SHOULD set 1262 ForwardTime for the corresponding dynamic neighbor cache entry to 1263 0 and allow future packets destined to the correspondent to flow 1264 through a Server. 1266 o When an AERO Client receives persistent L2 Destination Unreachable 1267 messages in response to tunneled packets that it sends to one of 1268 its static neighbor Servers, the Client SHOULD test the path to 1269 the Server using NUD. If NUD fails, the Client SHOULD delete the 1270 neighbor cache entry and attempt to associate with a new Server. 1272 o When an AERO Server receives persistent L2 Destination Unreachable 1273 messages in response to tunneled packets that it sends to one of 1274 its static neighbor Clients, the Server SHOULD test the path to 1275 the Client using NUD. If NUD fails, the Server SHOULD cancel the 1276 DHCPv6 PD for the Client's ACP, withdraw its route for the ACP 1277 from the AERO routing system and delete the neighbor cache entry 1278 (see Section 3.18 and Section 3.19). 1280 o When an AERO Relay or Server receives an L2 Destination 1281 Unreachable message in response to a tunneled packet that it sends 1282 to one of its permanent neighbors, it discards the message since 1283 the routing system is likely in a temporary transitional state 1284 that will soon re-converge. 1286 o When an AERO node receives an L2 PTB message, it translates the 1287 message into an L3 PTB message if possible (*) and forwards the 1288 message toward the original source as described below. 1290 To translate an L2 PTB message to an L3 PTB message, the AERO node 1291 first caches the MTU field value of the L2 ICMP header. The node 1292 next discards the L2 IP and ICMP headers, and also discards the 1293 encapsulation headers of the original L3 packet. Next the node 1294 encapsulates the included segment of the original L3 packet in an L3 1295 IP and ICMP header, and sets the ICMP header Type and Code values to 1296 appropriate values for the L3 IP protocol. In the process, the node 1297 writes the maximum of 1500 bytes and (L2 MTU - ENCAPS) into the MTU 1298 field of the L3 ICMP header. 1300 The node next writes the IP source address of the original L3 packet 1301 as the destination address of the L3 PTB message and determines the 1302 next hop to the destination. If the next hop is reached via the AERO 1303 interface, the node uses the IPv6 address "::" or the IPv4 address 1304 "0.0.0.0" as the IP source address of the L3 PTB message. Otherwise, 1305 the node uses one of its non link-local addresses as the source 1306 address of the L3 PTB message. The node finally calculates the ICMP 1307 checksum over the L3 PTB message and writes the Checksum in the 1308 corresponding field of the L3 ICMP header. The L3 PTB message 1309 therefore is formatted as follows: 1311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1312 ~ ~ 1313 | L3 IP Header of | 1314 | error message | 1315 ~ ~ 1316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1317 | L3 ICMP Header | 1318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1319 ~ ~ p 1320 | IP header of | k 1321 | original L3 packet | t 1322 ~ ~ 1323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i 1324 ~ ~ n 1325 | Upper layer headers and | 1326 | leading portion of body | e 1327 | of the original L3 packet | r 1328 ~ ~ r 1329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1331 Figure 5: AERO Interface L3 Error Message Format 1333 After the node has prepared the L3 PTB message, it either forwards 1334 the message via a link outside of the AERO interface without 1335 encapsulation, or encapsulates and forwards the message to the next 1336 hop via the AERO interface. 1338 When an AERO Relay receives an L3 packet for which the destination 1339 address is covered by an ASP, if there is no more-specific routing 1340 information for the destination the Relay drops the packet and 1341 returns an L3 Destination Unreachable message. The Relay first 1342 writes the IP source address of the original L3 packet as the 1343 destination address of the L3 Destination Unreachable message and 1344 determines the next hop to the destination. If the next hop is 1345 reached via the AERO interface, the Relay uses the IPv6 address "::" 1346 or the IPv4 address "0.0.0.0" as the IP source address of the L3 1347 Destination Unreachable message and forwards the message to the next 1348 hop within the AERO interface. Otherwise, the Relay uses one of its 1349 non link-local addresses as the source address of the L3 Destination 1350 Unreachable message and forwards the message via a link outside the 1351 AERO interface. 1353 When an AERO node receives any L3 error message via the AERO 1354 interface, it examines the destination address in the L3 IP header of 1355 the message. If the next hop toward the destination address of the 1356 error message is via the AERO interface, the node re-encapsulates and 1357 forwards the message to the next hop within the AERO interface. 1358 Otherwise, if the source address in the L3 IP header of the message 1359 is the IPv6 address "::" or the IPv4 address "0.0.0.0", the node 1360 writes one of its non link-local addresses as the source address of 1361 the L3 message and recalculates the IP and/or ICMP checksums. The 1362 node finally forwards the message via a link outside of the AERO 1363 interface. 1365 (*) Note that in some instances the packet-in-error field of an L2 1366 PTB message may not include enough information for translation to an 1367 L3 PTB message. In that case, the AERO interface simply discards the 1368 L2 PTB message. It can therefore be said that translation of L2 PTB 1369 messages to L3 PTB messages can provide a useful optimization when 1370 possible, but is not critical for sources that correctly use PLPMTUD. 1372 3.15. AERO Router Discovery, Prefix Delegation and Address 1373 Configuration 1375 3.15.1. AERO DHCPv6 Service Model 1377 Each AERO Server configures a DHCPv6 server function to facilitate PD 1378 requests from Clients. Each Server is provisioned with a database of 1379 ACP-to-Client ID mappings for all Clients enrolled in the AERO 1380 system, as well as any information necessary to authenticate each 1381 Client. The Client database is maintained by a central 1382 administrative authority for the AERO link and securely distributed 1383 to all Servers, e.g., via the Lightweight Directory Access Protocol 1384 (LDAP) [RFC4511] or a similar distributed database service. 1386 Therefore, no Server-to-Server DHCPv6 PD delegation state 1387 synchronization is necessary, and Clients can optionally hold 1388 separate delegations for the same ACP from multiple Servers. In this 1389 way, Clients can associate with multiple Servers, and can receive new 1390 delegations from new Servers before deprecating delegations received 1391 from existing Servers. 1393 AERO Clients and Servers exchange Client link-layer address 1394 information using an option format similar to the Client Link Layer 1395 Address Option (CLLAO) defined in [RFC6939]. Due to practical 1396 limitations of CLLAO, however, AERO interfaces instead use Vendor- 1397 Specific Information Options as described in the following sections. 1399 3.15.2. AERO Client Behavior 1401 AERO Clients discover the link-layer addresses of AERO Servers via 1402 static configuration, or through an automated means such as DNS name 1403 resolution. In the absence of other information, the Client resolves 1404 the FQDN "linkupnetworks.[domainname]" where "linkupnetworks" is a 1405 constant text string and "[domainname]" is the connection-specific 1406 DNS suffix for the Client's underlying network connection (e.g., 1407 "example.com"). After discovering the link-layer addresses, the 1408 Client associates with one or more of the corresponding Servers. 1410 To associate with a Server, the Client acts as a requesting router to 1411 request an ACP through a two-message (i.e., Request/Reply) DHCPv6 PD 1412 exchange [RFC3315][RFC3633]. The Client's Request message includes 1413 fe80::ffff:ffff:ffff:ffff as the IPv6 source address, 1414 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address 1415 and the link-layer address of the Server as the link-layer 1416 destination address. The Request message also includes a Client 1417 Identifier option with a DHCP Unique Identifier (DUID) and an 1418 Identity Association for Prefix Delegation (IA_PD) option. If the 1419 Client is pre-provisioned with an ACP associated with the AERO 1420 service, it MAY also include the ACP in the IA_PD to indicate its 1421 preference to the DHCPv6 server. 1423 The Client also SHOULD include an AERO Link-registration Request 1424 (ALREQ) option to register one or more links with the Server. The 1425 Server will include an AERO Link-registration Reply (ALREP) option in 1426 the corresponding DHCPv6 Reply message as specified in 1427 Section 3.15.3. (The Client MAY omit the ALREQ option, in which case 1428 the Server will still include an ALREP option in its Reply with "Link 1429 ID" set to 0, "DSCP" set to 0, and "Prf" set to 3.) 1431 The format for the ALREQ option is shown in Figure 6: 1433 0 1 2 3 1434 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 1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1436 | OPTION_VENDOR_OPTS | option-len (1) | 1437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1438 | enterprise-number = 45282 | 1439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1440 | opt-code = OPTION_ALREQ (0) | option-len (2) | 1441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1442 | Link ID | DSCP #1 |Prf| DSCP #2 |Prf| ... 1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1445 Figure 6: AERO Link-registration Request (ALREQ) Option 1447 In the above format, the Client sets 'option-code' to 1448 OPTION_VENDOR_OPTS, sets 'option-len (1)' to the length of the option 1449 following this field, sets 'enterprise-number' to 45282 (see: "IANA 1450 Considerations"), sets opt-code to the value 0 ("OPTION_ALREQ") and 1451 sets 'option-len (2)' to the length of the remainder of the option. 1452 The Client includes appropriate 'Link ID, 'DSCP' and 'Prf' values for 1453 the underlying interface over which the DHCPv6 PD Request will be 1454 issued the same as specified for an S/TLLAO Section 3.4. The Client 1455 MAY include multiple (DSCP, Prf) values with this Link ID, with the 1456 number of values indicated by option-len (2). The Server will 1457 register each value with the Link ID in the Client's neighbor cache 1458 entry. The Client finally includes any necessary authentication 1459 options to identify itself to the DHCPv6 server, and sends the 1460 encapsulated DHCPv6 PD Request via the underlying interface 1461 corresponding to Link ID. (Note that this implies that the Client 1462 must perform additional Renew/Reply DHCPv6 exchanges with the server 1463 following the initial Request/Reply using different underlying 1464 interfaces and their corresponding Link IDs if it wishes to register 1465 additional link-layer addresses and their associated DSCPs.) 1467 When the Client receives its ACP via a DHCPv6 Reply from the AERO 1468 Server, it creates a static neighbor cache entry with the Server's 1469 link-local address as the network-layer address and the Server's 1470 encapsulation address as the link-layer address. The Client then 1471 considers the link-layer address of the Server as the primary default 1472 encapsulation address for forwarding packets for which no more- 1473 specific forwarding information is available. The Client further 1474 caches any ASPs included in the ALREP option as ASPs to apply to the 1475 AERO link. 1477 Next, the Client autoconfigures an AERO address from the delegated 1478 ACP, assigns the AERO address to the AERO interface and sub-delegates 1479 the ACP to its attached EUNs and/or the Client's own internal virtual 1480 interfaces. The Client also assigns a default IP route to the AERO 1481 interface as a route-to-interface, i.e., with no explicit next-hop. 1482 The Client can then determine the correct next hops for packets 1483 submitted to the AERO interface by inspecting the neighbor cache. 1485 The Client subsequently renews its ACP delegation through each of its 1486 Servers by performing DHCPv6 Renew/Reply exchanges with the link- 1487 layer address of a Server as the link-layer destination address and 1488 the same options that were used in the initial PD request. Note that 1489 if the Client does not issue a DHCPv6 Renew before the delegation 1490 expires (e.g., if the Client has been out of touch with the Server 1491 for a considerable amount of time) it must re-initiate the DHCPv6 PD 1492 procedure. 1494 Since the Client's AERO address is obtained from the unique ACP 1495 delegation it receives, there is no need for Duplicate Address 1496 Detection (DAD) on AERO links. Other nodes maliciously attempting to 1497 hijack an authorized Client's AERO address will be denied access to 1498 the network by the DHCPv6 server due to an unacceptable link-layer 1499 address and/or security parameters (see: Security Considerations). 1501 3.15.2.1. Autoconfiguration for Constrained Platforms 1503 On some platforms (e.g., popular cell phone operating systems), the 1504 act of assigning a default IPv6 route and/or assigning an address to 1505 an interface may not be permitted from a user application due to 1506 security policy. Typically, those platforms include a TUN/TAP 1507 interface that acts as a point-to-point conduit between user 1508 applications and the AERO interface. In that case, the Client can 1509 instead generate a "synthesized RA" message. The message conforms to 1510 [RFC4861] and is prepared as follows: 1512 o the IPv6 source address is the Client's AERO address 1514 o the IPv6 destination address is all-nodes multicast 1516 o the Router Lifetime is set to a time that is no longer than the 1517 ACP DHCPv6 lifetime 1519 o the message does not include a Source Link Layer Address Option 1520 (SLLAO) 1522 o the message includes a Prefix Information Option (PIO) with a /64 1523 prefix taken from the ACP as the prefix for autoconfiguration 1525 The Client then sends the synthesized RA message via the TUN/TAP 1526 interface, where the operating system kernel will interpret it as 1527 though it were generated by an actual router. The operating system 1528 will then install a default route and use StateLess Address 1529 AutoConfiguration (SLAAC) to configure an IPv6 address on the TUN/TAP 1530 interface. Methods for similarly installing an IPv4 default route 1531 and IPv4 address on the TUN/TAP interface are based on synthesized 1532 DHCPv4 messages [RFC2131]. 1534 3.15.2.2. Client DHCPv6 Message Source Address 1536 In the initial DHCPv6 PD message exchanges, AERO Clients use the 1537 special IPv6 source address 'fe80::ffff:ffff:ffff:ffff' since their 1538 AERO addresses are not yet configured. After AERO address 1539 autoconfiguration, however, AERO Clients can continue to use 1540 'fe80::ffff:ffff:ffff:ffff' as the source address for further DHCPv6 1541 messaging or begin using their AERO address as the source address. 1543 3.15.3. AERO Server Behavior 1545 AERO Servers configure a DHCPv6 server function on their AERO links. 1546 AERO Servers arrange to add their encapsulation layer IP addresses 1547 (i.e., their link-layer addresses) to the DNS resource records for 1548 the FQDN "linkupnetworks.[domainname]" before entering service. 1550 When an AERO Server receives a prospective Client's DHCPv6 PD Request 1551 on its AERO interface, it first authenticates the message. If 1552 authentication succeeds, the Server determines the correct ACP to 1553 delegate to the Client by searching the Client database. In 1554 environments where spoofing is not considered a threat, the Server 1555 MAY use the Client's DUID as the identification value. Otherwise, 1556 the Server SHOULD use a signed certificate provided by the Client. 1558 When the Server delegates the ACP, it also creates an IP forwarding 1559 table entry so that the AERO routing system will propagate the ACP to 1560 all Relays (see: Section 3.7). Next, the Server prepares a DHCPv6 1561 Reply message to send to the Client while using fe80::ID as the IPv6 1562 source address, the link-local address taken from the Client's 1563 Request as the IPv6 destination address, the Server's link-layer 1564 address as the source link-layer address, and the Client's link-layer 1565 address as the destination link-layer address. The server also 1566 includes an IA_PD option with the delegated ACP. 1568 The Server also includes an ALREP option that includes the UDP Port 1569 Number and IP Address values it observed when it received the ALREQ 1570 in the Client's original DHCPv6 message (if present) followed by the 1571 ASP(s) for the AERO link. The ALREP option is formatted as shown in 1572 Figure 7: 1574 0 1 2 3 1575 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 1576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1577 | OPTION_VENDOR_OPTS | option-len (1) | 1578 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1579 | enterprise-number = 45282 | 1580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1581 | opt-code = OPTION_ALREP (1) | option-len (2) | 1582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1583 | Link ID | Reserved | UDP Port Number | 1584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1585 | | 1586 + + 1587 | | 1588 + IP Address + 1589 | | 1590 + + 1591 | | 1592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1593 | | 1594 + AERO Service Prefix (ASP) #1 +-+-+-+-+-+-+-+-+ 1595 | | Prefix Len | 1596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1597 | | 1598 + AERO Service Prefix (ASP) #2 +-+-+-+-+-+-+-+-+ 1599 | | Prefix Len | 1600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1601 ~ ~ 1602 ~ ~ 1604 Figure 7: AERO Link-registration Reply (ALREP) Option 1606 In the ALREP, the Server sets 'option-code' to OPTION_VENDOR_OPTS, 1607 sets 'option-length (1)' to the length of the option, sets 1608 'enterprise-number' to 45282 (see: "IANA Considerations"), sets opt- 1609 code to OPTION_ALREP (1), and sets 'option-len (2)' to the length of 1610 the remainder of the option. Next, the Server sets 'Link ID' to the 1611 same value that appeared in the ALREQ, sets Reserved to 0 and sets 1612 'UDP Port Number' and 'IP address' to the Client's link-layer 1613 address. The Server next includes one or more ASP with the IP prefix 1614 as it would appear in the interface identifier portion of the 1615 corresponding AERO address (see: Section 3.3), except that the low- 1616 order 8 bits of the ASP field encode the prefix length instead of the 1617 low-order 8 bits of the prefix. The longest prefix that can 1618 therefore appear as an ASP is /56 for IPv6 or /24 for IPv4. (Note 1619 that if the Client did not include an ALREQ option in its DHCPv6 1620 message, the Server MUST still include an ALREP option in the 1621 corresponding reply with 'Link ID' set to 0.) 1623 When the Server admits the DHCPv6 Reply message into the AERO 1624 interface, it creates a static neighbor cache entry for the Client's 1625 AERO address with lifetime set to no more than the delegation 1626 lifetime and the Client's link-layer address as the link-layer 1627 address for the Link ID specified in the ALREQ. The Server then uses 1628 the Client link-layer address information in the ALREQ option as the 1629 link-layer address for encapsulation based on the (DSCP, Prf) 1630 information. 1632 After the initial DHCPv6 PD exchange, the AERO Server maintains the 1633 neighbor cache entry for the Client until the delegation lifetime 1634 expires. If the Client issues a Renew/Reply exchange, the Server 1635 extends the lifetime. If the Client issues a Release/Reply, or if 1636 the Client does not issue a Renew/Reply before the lifetime expires, 1637 the Server deletes the neighbor cache entry for the Client and 1638 withdraws the IP route from the AERO routing system. 1640 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1642 AERO Clients and Servers are always on the same link (i.e., the AERO 1643 link) from the perspective of DHCPv6. However, in some 1644 implementations the DHCPv6 server and AERO interface driver may be 1645 located in separate modules. In that case, the Server's AERO 1646 interface driver module acts as a Lightweight DHCPv6 Relay Agent 1647 (LDRA)[RFC6221] to relay DHCPv6 messages to and from the DHCPv6 1648 server module. 1650 When the LDRA receives a DHCPv6 message from a client, it prepares an 1651 ALREP option the same as described above then wraps the option in a 1652 Relay-Supplied DHCP Option option (RSOO) [RFC6422]. The LDRA then 1653 incorporates the option into the Relay-Forward message and forwards 1654 the message to the DHCPv6 server. 1656 When the DHCPv6 server receives the Relay-Forward message, it caches 1657 the ALREP option and authenticates the encapsulated DHCPv6 message. 1658 The DHCPv6 server subsequently ignores the ALREQ option itself, since 1659 the relay has already included the ALREP option. 1661 When the DHCPv6 server prepares a Reply message, it then includes the 1662 ALREP option in the body of the message along with any other options, 1663 then wraps the message in a Relay-Reply message. The DHCPv6 server 1664 then delivers the Relay-Reply message to the LDRA, which discards the 1665 Relay-Reply wrapper and delivers the DHCPv6 message to the Client. 1667 3.15.4. Deleting Link Registrations 1669 After an AERO Client registers its Link IDs and their associated 1670 (DSCP,Prf) values with the AERO Server, the Client may wish to delete 1671 one or more Link registrations, e.g., if an underlying link becomes 1672 unavailable. To do so, the Client prepares a DHCPv6 Renew message 1673 that includes an AERO Link-registration Delete (ALDEL) option and 1674 sends the Renew message to the Server over any available underlying 1675 link. The ALDEL option is formatted as shown in Figure 8: 1677 0 1 2 3 1678 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 1679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1680 | OPTION_VENDOR_OPTS | option-len (1) | 1681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1682 | enterprise-number = 45282 | 1683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1684 | opt-code = OPTION_ALDEL (2) | option-len (2) | 1685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1686 | Link ID #1 | Link ID #2 | Link ID #3 | ... 1687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1689 Figure 8: AERO Link-registration Delete (ALDEL) Option 1691 In the ALDEL, the Client sets 'option-code' to OPTION_VENDOR_OPTS, 1692 sets 'option-length (1)' to the length of the option, sets 1693 'enterprise-number' to 45282 (see: "IANA Considerations"), sets 1694 optcode to OPTION_ALDEL (2), and sets 'option-len (2)' to the length 1695 of the remainder of the option. Next, the Server includes each 'Link 1696 ID' value that it wishes to delete. 1698 If the Client wishes to discontinue use of a Server and thereby 1699 delete all of its Link ID associations, it must use a DHCPv6 Release/ 1700 Reply exchange to delete the entire neighbor cache entry, i.e., 1701 instead of using a DHCPv6 Renew/Reply exchange with one or more ALDEL 1702 options. 1704 3.16. AERO Forwarding Agent Discovery 1706 AERO Relays, Servers and Clients MAY associate with one or more 1707 companion AERO Forwarding Agents as platforms for offloading high- 1708 speed data plane traffic. AERO nodes distribute forwarding 1709 information to Forwarding Agents via an out-of-band messaging service 1710 (e.g., NETCONF [RFC6241], etc.). 1712 When an AERO node receives a data packet on an AERO interface with a 1713 network layer destination address for which it has distributed 1714 forwarding information to one or more Forwarding Agents, the node 1715 returns an RA message to the source neighbor (subject to rate 1716 limiting) then forwards the data packet as usual. The RA message 1717 includes one or more SLLAOs with the link-layer addresses of 1718 candidate Forwarding Engines. 1720 If the forwarding information pertains only to a specific ACP, the 1721 AERO node sets the network-layer source address of the RA to the AERO 1722 address corresponding to the ACP, and sets the default router 1723 lifetime to 0. If the forwarding information pertains to all 1724 addresses, the AERO node instead sets the network-layer source 1725 address of the RA to its own link-local address and sets the default 1726 router lifetime to a non-zero value. 1728 When the source neighbor receives the RA message, it SHOULD record 1729 the link-layer addresses in the SLLAOs as the encapsulation addresses 1730 to use for sending subsequent data packets with addresses that match 1731 the information in the RA. However, the source MUST continue to use 1732 the primary link-layer address of the AERO node as the encapsulation 1733 address for sending control messages. 1735 3.17. AERO Intradomain Route Optimization 1737 When a source Client forwards packets to a prospective correspondent 1738 Client within the same AERO link domain (i.e., one for which the 1739 packet's destination address is covered by an ASP), the source Client 1740 initiates an intra-domain AERO route optimization procedure. The 1741 procedure is based on an exchange of IPv6 ND messages using a chain 1742 of AERO Servers and Relays as a trust basis. This procedure is in 1743 contrast to the Return Routability procedure required for route 1744 optimization to a correspondent Client located in the Internet as 1745 described in Section 3.22. The following sections specify the AERO 1746 intradomain route optimization procedure. 1748 3.17.1. Reference Operational Scenario 1750 Figure 9 depicts the AERO intradomain route optimization reference 1751 operational scenario, using IPv6 addressing as the example (while not 1752 shown, a corresponding example for IPv4 addressing can be easily 1753 constructed). The figure shows an AERO Relay ('R1'), two AERO 1754 Servers ('S1', 'S2'), two AERO Clients ('C1', 'C2') and two ordinary 1755 IPv6 hosts ('H1', 'H2'): 1757 +--------------+ +--------------+ +--------------+ 1758 | Server S1 | | Relay R1 | | Server S2 | 1759 +--------------+ +--------------+ +--------------+ 1760 fe80::2 fe80::1 fe80::3 1761 L2(S1) L2(R1) L2(S2) 1762 | | | 1763 X-----+-----+------------------+-----------------+----+----X 1764 | AERO Link | 1765 L2(A) L2(B) 1766 fe80::2001:db8:0:0 fe80::2001:db8:1:0 1767 +--------------+ +--------------+ 1768 |AERO Client C1| |AERO Client C2| 1769 +--------------+ +--------------+ 1770 2001:DB8:0::/48 2001:DB8:1::/48 1771 | | 1772 .-. .-. 1773 ,-( _)-. 2001:db8:0::1 2001:db8:1::1 ,-( _)-. 1774 .-(_ IP )-. +---------+ +---------+ .-(_ IP )-. 1775 (__ EUN )--| Host H1 | | Host H2 |--(__ EUN ) 1776 `-(______)-' +---------+ +---------+ `-(______)-' 1778 Figure 9: AERO Reference Operational Scenario 1780 In Figure 9, Relay ('R1') assigns the address fe80::1 to its AERO 1781 interface with link-layer address L2(R1), Server ('S1') assigns the 1782 address fe80::2 with link-layer address L2(S1),and Server ('S2') 1783 assigns the address fe80::3 with link-layer address L2(S2). Servers 1784 ('S1') and ('S2') next arrange to add their link-layer addresses to a 1785 published list of valid Servers for the AERO link. 1787 AERO Client ('C1') receives the ACP 2001:db8:0::/48 in a DHCPv6 PD 1788 exchange via AERO Server ('S1') then assigns the address 1789 fe80::2001:db8:0:0 to its AERO interface with link-layer address 1790 L2(C1). Client ('C1') configures a default route and neighbor cache 1791 entry via the AERO interface with next-hop address fe80::2 and link- 1792 layer address L2(S1), then sub-delegates the ACP to its attached 1793 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1794 address 2001:db8:0::1. 1796 AERO Client ('C2') receives the ACP 2001:db8:1::/48 in a DHCPv6 PD 1797 exchange via AERO Server ('S2') then assigns the address 1798 fe80::2001:db8:1:0 to its AERO interface with link-layer address 1799 L2(C2). Client ('C2') configures a default route and neighbor cache 1800 entry via the AERO interface with next-hop address fe80::3 and link- 1801 layer address L2(S2), then sub-delegates the ACP to its attached 1802 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1803 address 2001:db8:1::1. 1805 3.17.2. Concept of Operations 1807 Again, with reference to Figure 9, when source host ('H1') sends a 1808 packet to destination host ('H2'), the packet is first forwarded over 1809 the source host's attached EUN to Client ('C1'). Client ('C1') then 1810 forwards the packet via its AERO interface to Server ('S1') and also 1811 sends a Predirect message toward Client ('C2') via Server ('S1'). 1812 Server ('S1') then re-encapsulates and forwards both the packet and 1813 the Predirect message out the same AERO interface toward Client 1814 ('C2') via Relay ('R1'). 1816 When Relay ('R1') receives the packet and Predirect message, it 1817 consults its forwarding table to discover Server ('S2') as the next 1818 hop toward Client ('C2'). Relay ('R1') then forwards both the packet 1819 and the Predirect message to Server ('S2'), which then forwards them 1820 to Client ('C2'). 1822 After Client ('C2') receives the Predirect message, it process the 1823 message and returns a Redirect message toward Client ('C1') via 1824 Server ('S2'). During the process, Client ('C2') also creates or 1825 updates a dynamic neighbor cache entry for Client ('C1'). 1827 When Server ('S2') receives the Redirect message, it re-encapsulates 1828 the message and forwards it on to Relay ('R1'), which forwards the 1829 message on to Server ('S1') which forwards the message on to Client 1830 ('C1'). After Client ('C1') receives the Redirect message, it 1831 processes the message and creates or updates a dynamic neighbor cache 1832 entry for Client ('C2'). 1834 Following the above Predirect/Redirect message exchange, forwarding 1835 of packets from Client ('C1') to Client ('C2') without involving any 1836 intermediate nodes is enabled. The mechanisms that support this 1837 exchange are specified in the following sections. 1839 3.17.3. Message Format 1841 AERO Redirect/Predirect messages use the same format as for ICMPv6 1842 Redirect messages depicted in Section 4.5 of [RFC4861], but also 1843 include a new "Prefix Length" field taken from the low-order 8 bits 1844 of the Redirect message Reserved field. For IPv6, valid values for 1845 the Prefix Length field are 0 through 64; for IPv4, valid values are 1846 0 through 32. The Redirect/Predirect messages are formatted as shown 1847 in Figure 10: 1849 0 1 2 3 1850 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 1851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1852 | Type (=137) | Code (=0/1) | Checksum | 1853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1854 | Reserved | Prefix Length | 1855 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1856 | | 1857 + + 1858 | | 1859 + Target Address + 1860 | | 1861 + + 1862 | | 1863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1864 | | 1865 + + 1866 | | 1867 + Destination Address + 1868 | | 1869 + + 1870 | | 1871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1872 | Options ... 1873 +-+-+-+-+-+-+-+-+-+-+-+- 1875 Figure 10: AERO Redirect/Predirect Message Format 1877 3.17.4. Sending Predirects 1879 When a Client forwards a packet with a source address from one of its 1880 ACPs toward a destination address covered by an ASP (i.e., toward 1881 another AERO Client connected to the same AERO link), the source 1882 Client MAY send a Predirect message forward toward the destination 1883 Client via the Server. 1885 In the reference operational scenario, when Client ('C1') forwards a 1886 packet toward Client ('C2'), it MAY also send a Predirect message 1887 forward toward Client ('C2'), subject to rate limiting (see 1888 Section 8.2 of [RFC4861]). Client ('C1') prepares the Predirect 1889 message as follows: 1891 o the link-layer source address is set to 'L2(C1)' (i.e., the link- 1892 layer address of Client ('C1')). 1894 o the link-layer destination address is set to 'L2(S1)' (i.e., the 1895 link-layer address of Server ('S1')). 1897 o the network-layer source address is set to fe80::2001:db8:0:0 1898 (i.e., the AERO address of Client ('C1')). 1900 o the network-layer destination address is set to fe80::2001:db8:1:0 1901 (i.e., the AERO address of Client ('C2')). 1903 o the Type is set to 137. 1905 o the Code is set to 1 to indicate "Predirect". 1907 o the Prefix Length is set to the length of the prefix to be 1908 assigned to the Target Address. 1910 o the Target Address is set to fe80::2001:db8:0:0 (i.e., the AERO 1911 address of Client ('C1')). 1913 o the Destination Address is set to the source address of the 1914 originating packet that triggered the Predirection event. (If the 1915 originating packet is an IPv4 packet, the address is constructed 1916 in IPv4-compatible IPv6 address format). 1918 o the message includes one or more TLLAOs with Link ID and DSCPs set 1919 to appropriate values for Client ('C1')'s underlying interfaces, 1920 and with UDP Port Number and IP Address set to 0'. 1922 o the message SHOULD include a Timestamp option and a Nonce option. 1924 o the message includes a Redirected Header Option (RHO) that 1925 contains the originating packet truncated if necessary to ensure 1926 that at least the network-layer header is included but the size of 1927 the message does not exceed 1280 bytes. 1929 Note that the act of sending Predirect messages is cited as "MAY", 1930 since Client ('C1') may have advanced knowledge that the direct path 1931 to Client ('C2') would be unusable or otherwise undesirable. If the 1932 direct path later becomes unusable after the initial route 1933 optimization, Client ('C1') simply allows packets to again flow 1934 through Server ('S1'). 1936 3.17.5. Re-encapsulating and Relaying Predirects 1938 When Server ('S1') receives a Predirect message from Client ('C1'), 1939 it first verifies that the TLLAOs in the Predirect are a proper 1940 subset of the Link IDs in Client ('C1')'s neighbor cache entry. If 1941 the Client's TLLAOs are not acceptable, Server ('S1') discards the 1942 message. Otherwise, Server ('S1') validates the message according to 1943 the ICMPv6 Redirect message validation rules in Section 8.1 of 1944 [RFC4861], except that the Predirect has Code=1. Server ('S1') also 1945 verifies that Client ('C1') is authorized to use the Prefix Length in 1946 the Predirect when applied to the AERO address in the network-layer 1947 source address by searching for the AERO address in the neighbor 1948 cache. If validation fails, Server ('S1') discards the Predirect; 1949 otherwise, it copies the correct UDP Port numbers and IP Addresses 1950 for Client ('C1')'s links into the (previously empty) TLLAOs. 1952 Server ('S1') then examines the network-layer destination address of 1953 the Predirect to determine the next hop toward Client ('C2') by 1954 searching for the AERO address in the neighbor cache. Since Client 1955 ('C2') is not one of its neighbors, Server ('S1') re-encapsulates the 1956 Predirect and relays it via Relay ('R1') by changing the link-layer 1957 source address of the message to 'L2(S1)' and changing the link-layer 1958 destination address to 'L2(R1)'. Server ('S1') finally forwards the 1959 re-encapsulated message to Relay ('R1') without decrementing the 1960 network-layer TTL/Hop Limit field. 1962 When Relay ('R1') receives the Predirect message from Server ('S1') 1963 it determines that Server ('S2') is the next hop toward Client ('C2') 1964 by consulting its forwarding table. Relay ('R1') then re- 1965 encapsulates the Predirect while changing the link-layer source 1966 address to 'L2(R1)' and changing the link-layer destination address 1967 to 'L2(S2)'. Relay ('R1') then relays the Predirect via Server 1968 ('S2'). 1970 When Server ('S2') receives the Predirect message from Relay ('R1') 1971 it determines that Client ('C2') is a neighbor by consulting its 1972 neighbor cache. Server ('S2') then re-encapsulates the Predirect 1973 while changing the link-layer source address to 'L2(S2)' and changing 1974 the link-layer destination address to 'L2(C2)'. Server ('S2') then 1975 forwards the message to Client ('C2'). 1977 3.17.6. Processing Predirects and Sending Redirects 1979 When Client ('C2') receives the Predirect message, it accepts the 1980 Predirect only if the message has a link-layer source address of one 1981 of its Servers (e.g., L2(S2)). Client ('C2') further accepts the 1982 message only if it is willing to serve as a redirection target. 1983 Next, Client ('C2') validates the message according to the ICMPv6 1984 Redirect message validation rules in Section 8.1 of [RFC4861], except 1985 that it accepts the message even though Code=1 and even though the 1986 network-layer source address is not that of it's current first-hop 1987 router. 1989 In the reference operational scenario, when Client ('C2') receives a 1990 valid Predirect message, it either creates or updates a dynamic 1991 neighbor cache entry that stores the Target Address of the message as 1992 the network-layer address of Client ('C1') , stores the link-layer 1993 addresses found in the TLLAOs as the link-layer addresses of Client 1994 ('C1') and stores the Prefix Length as the length to be applied to 1995 the network-layer address for forwarding purposes. Client ('C2') 1996 then sets AcceptTime for the neighbor cache entry to ACCEPT_TIME. 1998 After processing the message, Client ('C2') prepares a Redirect 1999 message response as follows: 2001 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 2002 layer address of Client ('C2')). 2004 o the link-layer destination address is set to 'L2(S2)' (i.e., the 2005 link-layer address of Server ('S2')). 2007 o the network-layer source address is set to fe80::2001:db8:1:0 2008 (i.e., the AERO address of Client ('C2')). 2010 o the network-layer destination address is set to fe80::2001:db8:0:0 2011 (i.e., the AERO address of Client ('C1')). 2013 o the Type is set to 137. 2015 o the Code is set to 0 to indicate "Redirect". 2017 o the Prefix Length is set to the length of the prefix to be applied 2018 to the Target Address. 2020 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 2021 address of Client ('C2')). 2023 o the Destination Address is set to the destination address of the 2024 originating packet that triggered the Redirection event. (If the 2025 originating packet is an IPv4 packet, the address is constructed 2026 in IPv4-compatible IPv6 address format). 2028 o the message includes one or more TLLAOs with Link ID and DSCPs set 2029 to appropriate values for Client ('C2')'s underlying interfaces, 2030 and with UDP Port Number and IP Address set to '0'. 2032 o the message SHOULD include a Timestamp option and MUST echo the 2033 Nonce option received in the Predirect (i.e., if a Nonce option is 2034 included). 2036 o the message includes as much of the RHO copied from the 2037 corresponding AERO Predirect message as possible such that at 2038 least the network-layer header is included but the size of the 2039 message does not exceed 1280 bytes. 2041 After Client ('C2') prepares the Redirect message, it sends the 2042 message to Server ('S2'). 2044 3.17.7. Re-encapsulating and Relaying Redirects 2046 When Server ('S2') receives a Redirect message from Client ('C2'), it 2047 first verifies that the TLLAOs in the Redirect are a proper subset of 2048 the Link IDs in Client ('C2')'s neighbor cache entry. If the 2049 Client's TLLAOs are not acceptable, Server ('S2') discards the 2050 message. Otherwise, Server ('S2') validates the message according to 2051 the ICMPv6 Redirect message validation rules in Section 8.1 of 2052 [RFC4861]. Server ('S2') also verifies that Client ('C2') is 2053 authorized to use the Prefix Length in the Redirect when applied to 2054 the AERO address in the network-layer source address by searching for 2055 the AERO address in the neighbor cache. If validation fails, Server 2056 ('S2') discards the Predirect; otherwise, it copies the correct UDP 2057 Port numbers and IP Addresses for Client ('C2')'s links into the 2058 (previously empty) TLLAOs. 2060 Server ('S2') then examines the network-layer destination address of 2061 the Predirect to determine the next hop toward Client ('C2') by 2062 searching for the AERO address in the neighbor cache. Since Client 2063 ('C2') is not a neighbor, Server ('S2') re-encapsulates the Predirect 2064 and relays it via Relay ('R1') by changing the link-layer source 2065 address of the message to 'L2(S2)' and changing the link-layer 2066 destination address to 'L2(R1)'. Server ('S2') finally forwards the 2067 re-encapsulated message to Relay ('R1') without decrementing the 2068 network-layer TTL/Hop Limit field. 2070 When Relay ('R1') receives the Predirect message from Server ('S2') 2071 it determines that Server ('S1') is the next hop toward Client ('C1') 2072 by consulting its forwarding table. Relay ('R1') then re- 2073 encapsulates the Predirect while changing the link-layer source 2074 address to 'L2(R1)' and changing the link-layer destination address 2075 to 'L2(S1)'. Relay ('R1') then relays the Predirect via Server 2076 ('S1'). 2078 When Server ('S1') receives the Predirect message from Relay ('R1') 2079 it determines that Client ('C1') is a neighbor by consulting its 2080 neighbor cache. Server ('S1') then re-encapsulates the Predirect 2081 while changing the link-layer source address to 'L2(S1)' and changing 2082 the link-layer destination address to 'L2(C1)'. Server ('S1') then 2083 forwards the message to Client ('C1'). 2085 3.17.8. Processing Redirects 2087 When Client ('C1') receives the Redirect message, it accepts the 2088 message only if it has a link-layer source address of one of its 2089 Servers (e.g., ''L2(S1)'). Next, Client ('C1') validates the message 2090 according to the ICMPv6 Redirect message validation rules in 2091 Section 8.1 of [RFC4861], except that it accepts the message even 2092 though the network-layer source address is not that of it's current 2093 first-hop router. Following validation, Client ('C1') then processes 2094 the message as follows. 2096 In the reference operational scenario, when Client ('C1') receives 2097 the Redirect message, it either creates or updates a dynamic neighbor 2098 cache entry that stores the Target Address of the message as the 2099 network-layer address of Client ('C2'), stores the link-layer 2100 addresses found in the TLLAOs as the link-layer addresses of Client 2101 ('C2') and stores the Prefix Length as the length to be applied to 2102 the network-layer address for forwarding purposes. Client ('C1') 2103 then sets ForwardTime for the neighbor cache entry to FORWARD_TIME. 2105 Now, Client ('C1') has a neighbor cache entry with a valid 2106 ForwardTime value, while Client ('C2') has a neighbor cache entry 2107 with a valid AcceptTime value. Thereafter, Client ('C1') may forward 2108 ordinary network-layer data packets directly to Client ('C2') without 2109 involving any intermediate nodes, and Client ('C2') can verify that 2110 the packets came from an acceptable source. (In order for Client 2111 ('C2') to forward packets to Client ('C1'), a corresponding 2112 Predirect/Redirect message exchange is required in the reverse 2113 direction; hence, the mechanism is asymmetric.) 2115 3.17.9. Server-Oriented Redirection 2117 In some environments, the Server nearest the target Client may need 2118 to serve as the redirection target, e.g., if direct Client-to-Client 2119 communications are not possible. In that case, the Server prepares 2120 the Redirect message the same as if it were the destination Client 2121 (see: Section 3.17.6), except that it writes its own link-layer 2122 address in the TLLAO option. The Server must then maintain a dynamic 2123 neighbor cache entry for the redirected source Client. 2125 3.18. Neighbor Unreachability Detection (NUD) 2127 AERO nodes perform Neighbor Unreachability Detection (NUD) by sending 2128 unicast NS messages to elicit solicited NA messages from neighbors 2129 the same as described in [RFC4861]. NUD is performed either 2130 reactively in response to persistent L2 errors (see Section 3.14) or 2131 proactively to refresh existing neighbor cache entries. 2133 When an AERO node sends an NS/NA message, it MUST use its link-local 2134 address as the IPv6 source address and the link-local address of the 2135 neighbor as the IPv6 destination address. When an AERO node receives 2136 an NS message or a solicited NA message, it accepts the message if it 2137 has a neighbor cache entry for the neighbor; otherwise, it ignores 2138 the message. 2140 When a source Client is redirected to a target Client it SHOULD 2141 proactively test the direct path by sending an initial NS message to 2142 elicit a solicited NA response. While testing the path, the source 2143 Client can optionally continue sending packets via the Server, 2144 maintain a small queue of packets until target reachability is 2145 confirmed, or (optimistically) allow packets to flow directly to the 2146 target. The source Client SHOULD thereafter continue to proactively 2147 test the direct path to the target Client (see Section 7.3 of 2148 [RFC4861]) periodically in order to keep dynamic neighbor cache 2149 entries alive. 2151 In particular, while the source Client is actively sending packets to 2152 the target Client it SHOULD also send NS messages separated by 2153 RETRANS_TIMER milliseconds in order to receive solicited NA messages. 2154 If the source Client is unable to elicit a solicited NA response from 2155 the target Client after MAX_RETRY attempts, it SHOULD set ForwardTime 2156 to 0 and resume sending packets via one of its Servers. Otherwise, 2157 the source Client considers the path usable and SHOULD thereafter 2158 process any link-layer errors as a hint that the direct path to the 2159 target Client has either failed or has become intermittent. 2161 When a target Client receives an NS message from a source Client, it 2162 resets AcceptTime to ACCEPT_TIME if a neighbor cache entry exists; 2163 otherwise, it discards the NS message. If ForwardTime is non-zero, 2164 the target Client then sends a solicited NA message to the link-layer 2165 address of the source Client; otherwise, it sends the solicited NA 2166 message to the link-layer address of one of its Servers. 2168 When a source Client receives a solicited NA message from a target 2169 Client, it resets ForwardTime to FORWARD_TIME if a neighbor cache 2170 entry exists; otherwise, it discards the NA message. 2172 When ForwardTime for a dynamic neighbor cache entry expires, the 2173 source Client resumes sending any subsequent packets via a Server and 2174 may (eventually) attempt to re-initiate the AERO redirection process. 2175 When AcceptTime for a dynamic neighbor cache entry expires, the 2176 target Client discards any subsequent packets received directly from 2177 the source Client. When both ForwardTime and AcceptTime for a 2178 dynamic neighbor cache entry expire, the Client deletes the neighbor 2179 cache entry. 2181 3.19. Mobility Management 2183 3.19.1. Announcing Link-Layer Address Changes 2185 When a Client needs to change its link-layer address, e.g., due to a 2186 mobility event, it performs an immediate DHCPv6 Rebind/Reply exchange 2187 via each of its Servers using the new link-layer address as the 2188 source address and with an ALREQ that includes the correct Link ID 2189 and DSCP values. If authentication succeeds, the Server then update 2190 its neighbor cache and sends a DHCPv6 Reply. Note that if the Client 2191 does not issue a DHCPv6 Rebind before the prefix delegation lifetime 2192 expires (e.g., if the Client has been out of touch with the Server 2193 for a considerable amount of time), the Server's Reply will report 2194 NoBinding and the Client must re-initiate the DHCPv6 PD procedure. 2196 Next, the Client sends unsolicited NA messages to each of its 2197 correspondent Client neighbors using the same procedures as specified 2198 in Section 7.2.6 of [RFC4861], except that it sends the messages as 2199 unicast to each neighbor via a Server instead of multicast. In this 2200 process, the Client should send no more than 2201 MAX_NEIGHBOR_ADVERTISEMENT messages separated by no less than 2202 RETRANS_TIMER seconds to each neighbor. 2204 With reference to Figure 9, when Client ('C2') needs to change its 2205 link-layer address it sends unicast unsolicited NA messages to Client 2206 ('C1') via Server ('S2') as follows: 2208 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 2209 layer address of Client ('C2')). 2211 o the link-layer destination address is set to 'L2(S2)' (i.e., the 2212 link-layer address of Server ('S2')). 2214 o the network-layer source address is set to fe80::2001:db8:1:0 2215 (i.e., the AERO address of Client ('C2')). 2217 o the network-layer destination address is set to fe80::2001:db8:0:0 2218 (i.e., the AERO address of Client ('C1')). 2220 o the Type is set to 136. 2222 o the Code is set to 0. 2224 o the Solicited flag is set to 0. 2226 o the Override flag is set to 1. 2228 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 2229 address of Client ('C2')). 2231 o the message includes one or more TLLAOs with Link ID and DSCPs set 2232 to appropriate values for Client ('C2')'s underlying interfaces, 2233 and with UDP Port Number and IP Address set to '0'. 2235 o the message SHOULD include a Timestamp option. 2237 When Server ('S1') receives the NA message, it relays the message in 2238 the same way as described for relaying Redirect messages in 2239 Section 3.17.7. In particular, Server ('S1') copies the correct UDP 2240 port numbers and IP addresses into the TLLAOs, changes the link-layer 2241 source address to its own address, changes the link-layer destination 2242 address to the address of Relay ('R1'), then forwards the NA message 2243 via the relaying chain the same as for a Redirect. 2245 When Client ('C1') receives the NA message, it accepts the message 2246 only if it already has a neighbor cache entry for Client ('C2') then 2247 updates the link-layer addresses for Client ('C2') based on the 2248 addresses in the TLLAOs. Next, Client ('C1') SHOULD initiate the NUD 2249 procedures specified in Section 3.18 to provide Client ('C2') with an 2250 indication that the link-layer source address has been updated, and 2251 to refresh ('C2')'s AcceptTime and ('C1')'s ForwardTime timers. 2253 If Client ('C2') receives an NS message from Client ('C1') indicating 2254 that an unsolicited NA has updated its neighbor cache, Client ('C2') 2255 need not send additional unsolicited NAs. If Client ('C2')'s 2256 unsolicited NA messages are somehow lost, however, Client ('C1') will 2257 soon learn of the mobility event via NUD. 2259 3.19.2. Bringing New Links Into Service 2261 When a Client needs to bring a new underlying interface into service 2262 (e.g., when it activates a new data link), it performs an immediate 2263 Renew/Reply exchange via each of its Servers using the new link-layer 2264 address as the source address and with an ALREQ that includes the new 2265 Link ID and DSCP values. If authentication succeeds, the Server then 2266 updates its neighbor cache and sends a DHCPv6 Reply. The Client MAY 2267 then send unsolicited NA messages to each of its correspondent 2268 Clients to inform them of the new link-layer address as described in 2269 Section 3.19.1. 2271 3.19.3. Removing Existing Links from Service 2273 When a Client needs to remove an existing underlying interface from 2274 service (e.g., when it de-activates an existing data link), it 2275 performs an immediate Renew/Reply exchange via each of its Servers 2276 over any available link with an ALDEL that includes the deprecated 2277 Link ID. If authentication succeeds, the Server then updates its 2278 neighbor cache and sends a DHCPv6 Reply. The Client SHOULD then send 2279 unsolicited NA messages to each of its correspondent Clients to 2280 inform them of the deprecated link-layer address as described in 2281 Section 3.19.1. 2283 3.19.4. Moving to a New Server 2285 When a Client associates with a new Server, it performs the Client 2286 procedures specified in Section 3.15.2. 2288 When a Client disassociates with an existing Server, it sends a 2289 DHCPv6 Release message via a new Server to the unicast link-local 2290 network layer address of the old Server. The new Server then writes 2291 its own link-layer address in the DHCPv6 Release message IP source 2292 address and forwards the message to the old Server. 2294 When the old Server receives the DHCPv6 Release, it first 2295 authenticates the message. The Server then resets the Client's 2296 neighbor cache entry lifetime to 5 seconds, rewrites the link-layer 2297 address in the neighbor cache entry to the address of the new Server, 2298 then returns a DHCPv6 Reply message to the Client via the old Server. 2299 When the lifetime expires, the old Server withdraws the IP route from 2300 the AERO routing system and deletes the neighbor cache entry for the 2301 Client. The Client can then use the Reply message to verify that the 2302 termination signal has been processed, and can delete both the 2303 default route and the neighbor cache entry for the old Server. (Note 2304 that since Release/Reply messages may be lost in the network the 2305 Client MUST retry until it gets Reply indicating that the Release was 2306 successful.) 2308 Clients SHOULD NOT move rapidly between Servers in order to avoid 2309 causing excessive oscillations in the AERO routing system. Such 2310 oscillations could result in intermittent reachability for the Client 2311 itself, while causing little harm to the network. Examples of when a 2312 Client might wish to change to a different Server include a Server 2313 that has gone unreachable, topological movements of significant 2314 distance, etc. 2316 3.20. Proxy AERO 2318 Proxy Mobile IPv6 (PMIPv6) [RFC5213][RFC5844][RFC5949] presents a 2319 localized mobility management scheme for use within an access network 2320 domain. It is typically used in WiFi and cellular wireless access 2321 networks, and allows Mobile Nodes (MNs) to receive and retain an IP 2322 address that remains stable within the access network domain without 2323 needing to implement any special mobility protocols. In the PMIPv6 2324 architecture, access network devices known as Mobility Access 2325 Gateways (MAGs) provide MNs with an access link abstraction and 2326 receive prefixes for the MNs from a Local Mobility Anchor (LMA). 2328 In a proxy AERO domain, a proxy AERO Client (acting as a MAG) can 2329 similarly provide proxy services for MNs that do not participate in 2330 AERO messaging. The proxy Client presents an access link abstraction 2331 to MNs, and performs DHCPv6 PD exchanges over the AERO interface with 2332 an AERO Server (acting as an LMA) to receive ACPs for address 2333 provisioning of new MNs that come onto an access link. This scheme 2334 assumes that proxy Clients act as fixed (non-mobile) infrastructure 2335 elements under the same administrative trust basis as for Relays and 2336 Servers. 2338 When an MN comes onto an access link within a proxy AERO domain for 2339 the first time, the proxy Client authenticates the MN and obtains a 2340 unique identifier that it can use as a DHCPv6 DUID then issues a 2341 DHCPv6 PD Request to its Server. When the Server delegates an ACP, 2342 the proxy Client creates an AERO address for the MN and assigns the 2343 ACP to the MN's access link. The proxy Client then configures itself 2344 as a default router for the MN and provides address autoconfiguration 2345 services (e.g., SLAAC, DHCPv6, DHCPv4, etc.) for provisioning MN 2346 addresses from the ACP over the access link. Since the proxy Client 2347 may serve many such MNs simultaneously, it may receive multiple ACP 2348 prefix delegations and configure multiple AERO addresses, i.e., one 2349 for each MN. 2351 When two MNs are associated with the same proxy Client, the Client 2352 can forward traffic between the MNs without involving a Server since 2353 it configures the AERO addresses of both MNs and therefore also has 2354 the necessary routing information. When two MNs are associated with 2355 different proxy Clients, the source MN's Client can initiate standard 2356 AERO route optimization to discover a direct path to the target MN's 2357 Client through the exchange of Predirect/Redirect messages. 2359 When an MN in a proxy AERO domain leaves an access link provided by 2360 an old proxy Client, the MN issues an access link-specific "leave" 2361 message that informs the old Client of the link-layer address of a 2362 new Client on the planned new access link. This is known as a 2363 "predictive handover". When an MN comes onto an access link provided 2364 by a new proxy Client, the MN issues an access link-specific "join" 2365 message that informs the new Client of the link-layer address of the 2366 old Client on the actual old access link. This is known as a 2367 "reactive handover". 2369 Upon receiving a predictive handover indication, the old proxy Client 2370 sends a DHCPv6 PD Request message directly to the new Client and 2371 queues any arriving data packets addressed to the departed MN. The 2372 Request message includes the MN's ID as the DUID, the ACP in an IA_PD 2373 option, the old Client's address as the link-layer source address and 2374 the new Client's address as the link-layer destination address. When 2375 the new Client receives the Request message, it changes the link- 2376 layer source address to its own address, changes the link-layer 2377 destination address to the address of its Server, and forwards the 2378 message to the Server. At the same time, the new Client creates 2379 access link state for the ACP in anticipation of the MN's arrival 2380 (while queuing any data packets until the MN arrives), creates a 2381 neighbor cache entry for the old Client with AcceptTime set to 2382 ACCEPT_TIME, then sends a Redirect message back to the old Client. 2383 When the old Client receives the Redirect message, it creates a 2384 neighbor cache entry for the new Client with ForwardTime set to 2385 FORWARD_TIME, then forwards any queued data packets to the new 2386 Client. At the same time, the old Client sends a DHCPv6 PD Release 2387 message to its Server. Finally, the old Client sends unsolicited NA 2388 messages to any of the ACP's correspondents with a TLLAO containing 2389 the link-layer address of the new Client. This follows the procedure 2390 specified in Section 3.19.1, except that it is the old Client and not 2391 the Server that supplies the link-layer address. 2393 Upon receiving a reactive handover indication, the new proxy Client 2394 creates access link state for the MN's ACP, sends a DHCPv6 PD Request 2395 message to its Server, and sends a DHCPv6 PD Release message directly 2396 to the old Client. The Release message includes the MN's ID as the 2397 DUID, the ACP in an IA_PD option, the new Client's address as the 2398 link-layer source address and the old Client's address as the link- 2399 layer destination address. When the old Client receives the Release 2400 message, it changes the link-layer source address to its own address, 2401 changes the link-layer destination address to the address of its 2402 Server, and forwards the message to the Server. At the same time, 2403 the old Client sends a Predirect message back to the new Client and 2404 queues any arriving data packets addressed to the departed MN. When 2405 the new Client receives the Predirect, it creates a neighbor cache 2406 entry for the old Client with AcceptTime set to ACCEPT_TIME, then 2407 sends a Redirect message back to the old Client. When the old Client 2408 receives the Redirect message, it creates a neighbor cache entry for 2409 the new Client with ForwardTime set to FORWARD_TIME, then forwards 2410 any queued data packets to the new Client. Finally, the old Client 2411 sends unsolicited NA messages to correspondents the same as for the 2412 predictive case. 2414 When a Server processes a DHCPv6 Request message, it creates a 2415 neighbor cache entry for this ACP if none currently exists. If a 2416 neighbor cache entry already exists, however, the Server changes the 2417 link-layer address to the address of the new proxy Client (this 2418 satisfies the case of both the old Client and new Client using the 2419 same Server). 2421 When a Server processes a DHCPv6 Release message, it resets the 2422 neighbor cache entry lifetime for this ACP to 5 seconds if the cached 2423 link-layer address matches the old proxy Client's address. 2424 Otherwise, the Server ignores the Release message (this satisfies the 2425 case of both the old Client and new Client using the same Server). 2427 When a correspondent Client receives an unsolicited NA message, it 2428 changes the link-layer address for the ACP's neighbor cache entry to 2429 the address of the new proxy Client. The correspondent Client then 2430 issues a Predirect/Redirect exchange to establish a new neighbor 2431 cache entry in the new Client. 2433 From an architectural perspective, in addition to the use of DHCPv6 2434 PD and IPv6 ND signaling the AERO approach differs from PMIPv6 in its 2435 use of the NBMA virtual link model instead of point-to-point tunnels. 2436 This provides a more agile interface for Client/Server and Client/ 2437 Client coordinations, and also facilitates simple route optimization. 2438 The AERO routing system is also arranged in such a fashion that 2439 Clients get the same service from any Server they happen to associate 2440 with. This provides a natural fault tolerance and load balancing 2441 capability such as desired for distributed mobility management. 2443 3.21. Extending AERO Links Through Security Gateways 2445 When an enterprise mobile device moves from a campus LAN connection 2446 to a public Internet link, it must re-enter the enterprise via a 2447 security gateway that has both a physical interface connection to the 2448 Internet and a physical interface connection to the enterprise 2449 internetwork. This most often entails the establishment of a Virtual 2450 Private Network (VPN) link over the public Internet from the mobile 2451 device to the security gateway. During this process, the mobile 2452 device supplies the security gateway with its public Internet address 2453 as the link-layer address for the VPN. The mobile device then acts 2454 as an AERO Client to negotiate with the security gateway to obtain 2455 its ACP. 2457 In order to satisfy this need, the security gateway also operates as 2458 an AERO Server with support for AERO Client proxying. In particular, 2459 when a mobile device (i.e., the Client) connects via the security 2460 gateway (i.e., the Server), the Server provides the Client with an 2461 ACP in a DHCPv6 PD exchange the same as if it were attached to an 2462 enterprise campus access link. The Server then replaces the Client's 2463 link-layer source address with the Server's enterprise-facing link- 2464 layer address in all AERO messages the Client sends toward neighbors 2465 on the AERO link. The AERO messages are then delivered to other 2466 devices on the AERO link as if they were originated by the security 2467 gateway instead of by the AERO Client. In the reverse direction, the 2468 AERO messages sourced by devices within the enterprise network can be 2469 forwarded to the security gateway, which then replaces the link-layer 2470 destination address with the Client's link-layer address and replaces 2471 the link-layer source address with its own (Internet-facing) link- 2472 layer address. 2474 After receiving the ACP, the Client can send IP packets that use an 2475 address taken from the ACP as the network layer source address, the 2476 Client's link-layer address as the link-layer source address, and the 2477 Server's Internet-facing link-layer address as the link-layer 2478 destination address. The Server will then rewrite the link-layer 2479 source address with the Server's own enterprise-facing link-layer 2480 address and rewrite the link-layer destination address with the 2481 target AERO node's link-layer address, and the packets will enter the 2482 enterprise network as though they were sourced from a device located 2483 within the enterprise. In the reverse direction, when a packet 2484 sourced by a node within the enterprise network uses a destination 2485 address from the Client's ACP, the packet will be delivered to the 2486 security gateway which then rewrites the link-layer destination 2487 address to the Client's link-layer address and rewrites the link- 2488 layer source address to the Server's Internet-facing link-layer 2489 address. The Server then delivers the packet across the VPN to the 2490 AERO Client. In this way, the AERO virtual link is essentially 2491 extended *through* the security gateway to the point at which the VPN 2492 link and AERO link are effectively grafted together by the link-layer 2493 address rewriting performed by the security gateway. All AERO 2494 messaging services (including route optimization and mobility 2495 signaling) are therefore extended to the Client. 2497 In order to support this virtual link grafting, the security gateway 2498 (acting as an AERO Server) must keep static neighbor cache entries 2499 for all of its associated Clients located on the public Internet. 2500 The neighbor cache entry is keyed by the AERO Client's AERO address 2501 the same as if the Client were located within the enterprise 2502 internetwork. The neighbor cache is then managed in all ways as 2503 though the Client were an ordinary AERO Client. This includes the 2504 AERO IPv6 ND messaging signaling for Route Optimization and Neighbor 2505 Unreachability Detection. 2507 Note that the main difference between a security gateway acting as an 2508 AERO Server and an enterprise-internal AERO Server is that the 2509 security gateway has at least one enterprise-internal physical 2510 interface and at least one public Internet physical interface. 2511 Conversely, the enterprise-internal AERO Server has only enterprise- 2512 internal physical interfaces. For this reason security gateway 2513 proxying is needed to ensure that the public Internet link-layer 2514 addressing space is kept separate from the enterprise-internal link- 2515 layer addressing space. This is afforded through a natural extension 2516 of the security association caching already performed for each VPN 2517 client by the security gateway. 2519 3.22. Extending IPv6 AERO Links to the Internet 2521 When an IPv6 host ('H1') with an address from an ACP owned by AERO 2522 Client ('C1') sends packets to a correspondent IPv6 host ('H2'), the 2523 packets eventually arrive at the IPv6 router that owns ('H2')s 2524 prefix. This IPv6 router may or may not be an AERO Client ('C2') 2525 either within the same home network as ('C1') or in a different home 2526 network. 2528 If Client ('C1') is currently located outside the boundaries of its 2529 home network, it will connect back into the home network via a 2530 security gateway acting as an AERO Server. The packets sent by 2531 ('H1') via ('C1') will then be forwarded through the security gateway 2532 then through the home network and finally to ('C2') where they will 2533 be delivered to ('H2'). This could lead to sub-optimal performance 2534 when ('C2') could instead be reached via a more direct route without 2535 involving the security gateway. 2537 Consider the case when host ('H1') has the IPv6 address 2538 2001:db8:1::1, and Client ('C1') has the ACP 2001:db8:1::/64 with 2539 underlying IPv6 Internet address of 2001:db8:1000::1. Also, host 2540 ('H2') has the IPv6 address 2001:db8:2::1, and Client ('C2') has the 2541 ACP 2001:db8:2::/64 with underlying IPv6 address of 2001:db8:2000::1. 2542 Client ('C1') can determine whether 'C2' is indeed also an AERO 2543 Client willing to serve as a route optimization correspondent by 2544 resolving the AAAA records for the DNS FQDN that matches ('H2')s 2545 prefix, i.e.: 2547 '0.0.0.0.2.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net' 2549 If ('C2') is indeed a candidate correspondent, the FQDN lookup will 2550 return a PTR resource record that contains the domain name for the 2551 AERO link that manages ('C2')s ASP. Client ('C1') can then attempt 2552 route optimization using an approach similar to the Return 2553 Routability procedure specified for Mobile IPv6 (MIPv6) [RFC6275]. 2554 In order to support this process, both Clients MUST intercept and 2555 decapsulate packets that have a subnet router anycast address 2556 corresponding to any of the /64 prefixes covered by their respective 2557 ACPs. 2559 To initiate the process, Client ('C1') creates a specially-crafted 2560 encapsulated AERO Predirect message that will be routed through its 2561 home network then through ('C2')s home network and finally to ('C2') 2562 itself. Client ('C1') prepares the initial message in the exchange 2563 as follows: 2565 o The encapsulating IPv6 header source address is set to 2566 2001:db8:1:: (i.e., the IPv6 subnet router anycast address for 2567 ('C1')s ACP) 2569 o The encapsulating IPv6 header destination address is set to 2570 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2571 ('C2')s ACP) 2573 o The encapsulating IPv6 header is followed by a UDP header with 2574 source and destination port set to 8060 2576 o The encapsulated IPv6 header source address is set to 2577 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2579 o The encapsulated IPv6 header destination address is set to 2580 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2582 o The encapsulated AERO Predirect message includes all of the 2583 securing information that would occur in a MIPv6 "Home Test Init" 2584 message (format TBD) 2586 Client ('C1') then further encapsulates the message in the 2587 encapsulating headers necessary to convey the packet to the security 2588 gateway (e.g., through IPsec encapsulation) so that the message now 2589 appears "double-encapsulated". ('C1') then sends the message to the 2590 security gateway, which re-encapsulates and forwards it over the home 2591 network from where it will eventually reach ('C2'). 2593 At the same time, ('C1') creates and sends a second encapsulated AERO 2594 Predirect message that will be routed through the IPv6 Internet 2595 without involving the security gateway. Client ('C1') prepares the 2596 message as follows: 2598 o The encapsulating IPv6 header source address is set to 2599 2001:db8:1000:1 (i.e., the Internet IPv6 address of ('C1')) 2601 o The encapsulating IPv6 header destination address is set to 2602 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2603 ('C2')s ACP) 2605 o The encapsulating IPv6 header is followed by a UDP header with 2606 source and destination port set to 8060 2608 o The encapsulated IPv6 header source address is set to 2609 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2611 o The encapsulated IPv6 header destination address is set to 2612 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2614 o The encapsulated AERO Predirect message includes all of the 2615 securing information that would occur in a MIPv6 "Care-of Test 2616 Init" message (format TBD) 2618 ('C2') will receive both Predirect messages through its home network 2619 then return a corresponding Redirect for each of the Predirect 2620 messages with the source and destination addresses in the inner and 2621 outer headers reversed. The first message includes all of the 2622 securing information that would occur in a MIPv6 "Home Test" message, 2623 while the second message includes all of the securing information 2624 that would occur in a MIPv6 "Care-of Test" message (formats TBD). 2626 When ('C1') receives the Redirect messages, it performs the necessary 2627 security procedures per the MIPv6 specification. It then prepares an 2628 encapsulated NS message that includes the same source and destination 2629 addresses as for the "Care-of Test Init" Predirect message, and 2630 includes all of the securing information that would occur in a MIPv6 2631 "Binding Update" message (format TBD) and sends the message to 2632 ('C2'). 2634 When ('C2') receives the NS message, if the securing information is 2635 correct it creates or updates a neighbor cache entry for ('C1') with 2636 fe80::2001:db8:1:0 as the network-layer address, 2001:db8:1000::1 as 2637 the link-layer address and with AcceptTime set to ACCEPT_TIME. 2638 ('C2') then sends an encapsulated NA message back to ('C1') that 2639 includes the same source and destination addresses as for the "Care- 2640 of Test" Redirect message, and includes all of the securing 2641 information that would occur in a MIPv6 "Binding Acknowledgement" 2642 message (format TBD) and sends the message to ('C1'). 2644 When ('C1') receives the NA message, it creates or updates a neighbor 2645 cache entry for ('C2') with fe80::2001:db8:2:0 as the network-layer 2646 address and 2001:db8:2:: as the link-layer address and with 2647 ForwardTime set to FORWARD_TIME, thus completing the route 2648 optimization in the forward direction. 2650 ('C1') subsequently forwards encapsulated packets with outer source 2651 address 2001:db8:1000::1, with outer destination address 2652 2001:db8:2::, with inner source address taken from the 2001:db8:1::, 2653 and with inner destination address taken from 2001:db8:2:: due to the 2654 fact that it has a securely-established neighbor cache entry with 2655 non-zero ForwardTime. ('C2') subsequently accepts any such 2656 encapsulated packets due to the fact that it has a securely- 2657 established neighbor cache entry with non-zero AcceptTime. 2659 In order to keep neighbor cache entries alive, ('C1') periodically 2660 sends additional NS messages to ('C2') and receives any NA responses. 2661 If ('C1') moves to a different point of attachment after the initial 2662 route optimization, it sends a new secured NS message to ('C2') as 2663 above to update ('C2')s neighbor cache. 2665 If ('C2') has packets to send to ('C1'), it performs a corresponding 2666 route optimization in the opposite direction following the same 2667 procedures described above. In the process, the already-established 2668 unidirectional neighbor cache entries within ('C1') and ('C2') are 2669 updated to include the now-bidirectional information. In particular, 2670 the AcceptTime and ForwardTime variables for both neighbor cache 2671 entries are updated to non-zero values, and the link-layer address 2672 for ('C1')s neighbor cache entry for ('C2') is reset to 2673 2001:db8:2000::1. 2675 Note that two AERO Clients can use full security protocol messaging 2676 instead of Return Routability, e.g., if strong authentication and/or 2677 confidentiality are desired. In that case, security protocol key 2678 exchanges such as specified for MOBIKE [RFC4555] would be used to 2679 establish security associations and neighbor cache entries between 2680 the AERO clients. Thereafter, AERO NS/NA messaging can be used to 2681 maintain neighbor cache entries, test reachability, and to announce 2682 mobility events. If reachability testing fails, e.g., if both 2683 Clients move at roughly the same time, the Clients can tear down the 2684 security association and neighbor cache entries and again allow 2685 packets to flow through their home network. 2687 3.23. Encapsulation Protocol Version Considerations 2689 A source Client may connect only to an IPvX underlying network, while 2690 the target Client connects only to an IPvY underlying network. In 2691 that case, the target and source Clients have no means for reaching 2692 each other directly (since they connect to underlying networks of 2693 different IP protocol versions) and so must ignore any redirection 2694 messages and continue to send packets via the Server. 2696 3.24. Multicast Considerations 2698 When the underlying network does not support multicast, AERO nodes 2699 map IPv6 link-scoped multicast addresses (including 2700 'All_DHCP_Relay_Agents_and_Servers') to the link-layer address of a 2701 Server. 2703 When the underlying network supports multicast, AERO nodes use the 2704 multicast address mapping specification found in [RFC2529] for IPv4 2705 underlying networks and use a direct multicast mapping for IPv6 2706 underlying networks. (In the latter case, "direct multicast mapping" 2707 means that if the IPv6 multicast destination address of the 2708 encapsulated packet is "M", then the IPv6 multicast destination 2709 address of the encapsulating header is also "M".) 2711 3.25. Operation on AERO Links Without DHCPv6 Services 2713 When Servers on the AERO link do not provide DHCPv6 services, 2714 operation can still be accommodated through administrative 2715 configuration of ACPs on AERO Clients. In that case, administrative 2716 configurations of AERO interface neighbor cache entries on both the 2717 Server and Client are also necessary. However, this may interfere 2718 with the ability for Clients to dynamically change to new Servers, 2719 and can expose the AERO link to misconfigurations unless the 2720 administrative configurations are carefully coordinated. 2722 3.26. Operation on Server-less AERO Links 2724 In some AERO link scenarios, there may be no Servers on the link and/ 2725 or no need for Clients to use a Server as an intermediary trust 2726 anchor. In that case, each Client acts as a Server unto itself to 2727 establish neighbor cache entries by performing direct Client-to- 2728 Client IPv6 ND message exchanges, and some other form of trust basis 2729 must be applied so that each Client can verify that the prospective 2730 neighbor is authorized to use its claimed ACP. 2732 When there is no Server on the link, Clients must arrange to receive 2733 ACPs and publish them via a secure alternate prefix delegation 2734 authority through some means outside the scope of this document. 2736 3.27. Manually-Configured AERO Tunnels 2738 In addition to the dynamic neighbor discovery procedures for AERO 2739 link neighbors described above, AERO encapsulation can be applied to 2740 manually-configured tunnels. In that case, the tunnel endpoints use 2741 an administratively-assigned link-local address and exchange NS/NA 2742 messages the same as for dynamically-established tunnels. 2744 3.28. Intradomain Routing 2746 After a tunnel neighbor relationship has been established, neighbors 2747 can use a traditional dynamic routing protocol over the tunnel to 2748 exchange routing information without having to inject the routes into 2749 the AERO routing system. 2751 4. Implementation Status 2753 User-level and kernel-level AERO implementations have been developed 2754 and are undergoing internal testing within Boeing. 2756 5. Next Steps 2758 A new Generic UDP Encapsulation (GUE) format has been specified in 2759 [I-D.herbert-gue-fragmentation] [I-D.ietf-nvo3-gue]. The GUE 2760 encapsulation format will eventually supplant the native AERO UDP 2761 encapsulation format. 2763 Future versions of the spec will explore the subject of DSCP marking 2764 in more detail. 2766 6. IANA Considerations 2768 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2769 AERO in the "enterprise-numbers" registry. 2771 The IANA has assigned the UDP port number "8060" for [RFC6706], and 2772 this port will now be used for the current AERO version. 2774 No further IANA actions are required. 2776 7. Security Considerations 2778 AERO link security considerations are the same as for standard IPv6 2779 Neighbor Discovery [RFC4861] except that AERO improves on some 2780 aspects. In particular, AERO uses a trust basis between Clients and 2781 Servers, where the Clients only engage in the AERO mechanism when it 2782 is facilitated by a trust anchor. Unless there is some other means 2783 of authenticating the Client's identity (e.g., link-layer security), 2784 AERO nodes SHOULD also use DHCPv6 securing services (e.g., DHCPv6 2785 authentication, Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6], etc.) for 2786 Client authentication and network admission control. 2788 AERO Redirect, Predirect and unsolicited NA messages SHOULD include a 2789 Timestamp option (see Section 5.3 of [RFC3971]) that other AERO nodes 2790 can use to verify the message time of origin. AERO Predirect, NS and 2791 RS messages SHOULD include a Nonce option (see Section 5.3 of 2792 [RFC3971]) that recipients echo back in corresponding responses. 2794 AERO links must be protected against link-layer address spoofing 2795 attacks in which an attacker on the link pretends to be a trusted 2796 neighbor. Links that provide link-layer securing mechanisms (e.g., 2797 IEEE 802.1X WLANs) and links that provide physical security (e.g., 2798 enterprise network wired LANs) provide a first line of defense that 2799 is often sufficient. In other instances, additional securing 2800 mechanisms such as Secure Neighbor Discovery (SeND) [RFC3971], IPsec 2801 [RFC4301] or TLS [RFC5246] may be necessary. 2803 AERO Clients MUST ensure that their connectivity is not used by 2804 unauthorized nodes on their EUNs to gain access to a protected 2805 network, i.e., AERO Clients that act as routers MUST NOT provide 2806 routing services for unauthorized nodes. (This concern is no 2807 different than for ordinary hosts that receive an IP address 2808 delegation but then "share" the address with unauthorized nodes via a 2809 NAT function.) 2811 On some AERO links, establishment and maintenance of a direct path 2812 between neighbors requires secured coordination such as through the 2813 Internet Key Exchange (IKEv2) protocol [RFC5996] to establish a 2814 security association. 2816 An AERO Client's link-layer address could be rewritten by a link- 2817 layer switching element on the path from the Client to the Server and 2818 not detected by the DHCPv6 security mechanism. However, such a 2819 condition would only be a matter of concern on unmanaged/unsecured 2820 links where the link-layer switching elements themselves present a 2821 man-in-the-middle attack threat. For this reason, IP security MUST 2822 be used when AERO is employed over unmanaged/unsecured links. 2824 8. Acknowledgements 2826 Discussions both on IETF lists and in private exchanges helped shape 2827 some of the concepts in this work. Individuals who contributed 2828 insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, 2829 Stewart Bryant, Brian Carpenter, Wojciech Dec, Ralph Droms, Adrian 2830 Farrel, Sri Gundavelli, Brian Haberman, Joel Halpern, Tom Herbert, 2831 Sascha Hlusiak, Lee Howard, Andre Kostur, Ted Lemon, Andy Malis, 2832 Satoru Matsushima, Tomek Mrugalski, Behcet Saikaya, Joe Touch, Bernie 2833 Volz, Ryuji Wakikawa and Lloyd Wood. Members of the IESG also 2834 provided valuable input during their review process that greatly 2835 improved the document. Special thanks go to Stewart Bryant, Joel 2836 Halpern and Brian Haberman for their shepherding guidance. 2838 This work has further been encouraged and supported by Boeing 2839 colleagues including Dave Bernhardt, Cam Brodie, Balaguruna 2840 Chidambaram, Bruce Cornish, Claudiu Danilov, Wen Fang, Anthony 2841 Gregory, Jeff Holland, Ed King, Gen MacLean, Rob Muszkiewicz, Sean 2842 O'Sullivan, Kent Shuey, Brian Skeen, Mike Slane, Brendan Williams, 2843 Julie Wulff, Yueli Yang, and other members of the BR&T and BIT mobile 2844 networking teams. 2846 Earlier works on NBMA tunneling approaches are found in 2847 [RFC2529][RFC5214][RFC5569]. 2849 Many of the constructs presented in this second edition of AERO are 2850 based on the author's earlier works, including: 2852 o The Internet Routing Overlay Network (IRON) 2853 [RFC6179][I-D.templin-ironbis] 2855 o Virtual Enterprise Traversal (VET) 2856 [RFC5558][I-D.templin-intarea-vet] 2858 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2859 [RFC5320][I-D.templin-intarea-seal] 2861 o AERO, First Edition [RFC6706] 2863 Note that these works cite numerous earlier efforts that are not also 2864 cited here due to space limitations. The authors of those earlier 2865 works are acknowledged for their insights. 2867 9. References 2869 9.1. Normative References 2871 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2872 August 1980. 2874 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 2875 1981. 2877 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2878 RFC 792, September 1981. 2880 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 2881 October 1996. 2883 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2884 Requirement Levels", BCP 14, RFC 2119, March 1997. 2886 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2887 (IPv6) Specification", RFC 2460, December 1998. 2889 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2890 IPv6 Specification", RFC 2473, December 1998. 2892 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2893 "Definition of the Differentiated Services Field (DS 2894 Field) in the IPv4 and IPv6 Headers", RFC 2474, December 2895 1998. 2897 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2898 and M. Carney, "Dynamic Host Configuration Protocol for 2899 IPv6 (DHCPv6)", RFC 3315, July 2003. 2901 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2902 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2903 December 2003. 2905 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2906 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2908 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 2909 for IPv6 Hosts and Routers", RFC 4213, October 2005. 2911 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2912 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2913 September 2007. 2915 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2916 Address Autoconfiguration", RFC 4862, September 2007. 2918 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 2919 Requirements", RFC 6434, December 2011. 2921 9.2. Informative References 2923 [I-D.herbert-gue-fragmentation] 2924 Herbert, T. and F. Templin, "Fragmentation option for 2925 Generic UDP Encapsulation", draft-herbert-gue- 2926 fragmentation-00 (work in progress), March 2015. 2928 [I-D.ietf-dhc-sedhcpv6] 2929 Jiang, S., Shen, S., Zhang, D., and T. Jinmei, "Secure 2930 DHCPv6", draft-ietf-dhc-sedhcpv6-07 (work in progress), 2931 March 2015. 2933 [I-D.ietf-nvo3-gue] 2934 Herbert, T., Yong, L., and O. Zia, "Generic UDP 2935 Encapsulation", draft-ietf-nvo3-gue-00 (work in progress), 2936 April 2015. 2938 [I-D.templin-intarea-seal] 2939 Templin, F., "The Subnetwork Encapsulation and Adaptation 2940 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 2941 progress), January 2014. 2943 [I-D.templin-intarea-vet] 2944 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 2945 templin-intarea-vet-40 (work in progress), May 2013. 2947 [I-D.templin-ironbis] 2948 Templin, F., "The Interior Routing Overlay Network 2949 (IRON)", draft-templin-ironbis-16 (work in progress), 2950 March 2014. 2952 [I-D.vandevelde-idr-remote-next-hop] 2953 Velde, G., Patel, K., Rao, D., Raszuk, R., and R. Bush, 2954 "BGP Remote-Next-Hop", draft-vandevelde-idr-remote-next- 2955 hop-09 (work in progress), March 2015. 2957 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 2958 RFC 879, November 1983. 2960 [RFC1035] Mockapetris, P., "Domain names - implementation and 2961 specification", STD 13, RFC 1035, November 1987. 2963 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2964 November 1990. 2966 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 2967 1812, June 1995. 2969 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 2970 selection, and registration of an Autonomous System (AS)", 2971 BCP 6, RFC 1930, March 1996. 2973 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 2974 for IP version 6", RFC 1981, August 1996. 2976 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2977 2131, March 1997. 2979 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2980 Domains without Explicit Tunnels", RFC 2529, March 1999. 2982 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 2983 RFC 2675, August 1999. 2985 [RFC2764] Gleeson, B., Heinanen, J., Lin, A., Armitage, G., and A. 2986 Malis, "A Framework for IP Based Virtual Private 2987 Networks", RFC 2764, February 2000. 2989 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 2990 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 2991 March 2000. 2993 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 2994 2923, September 2000. 2996 [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 2997 2983, October 2000. 2999 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3000 of Explicit Congestion Notification (ECN) to IP", RFC 3001 3168, September 2001. 3003 [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, 3004 "DNS Extensions to Support IP Version 6", RFC 3596, 3005 October 2003. 3007 [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., 3008 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3009 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3010 RFC 3819, July 2004. 3012 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 3013 Protocol 4 (BGP-4)", RFC 4271, January 2006. 3015 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3016 Architecture", RFC 4291, February 2006. 3018 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3019 Internet Protocol", RFC 4301, December 2005. 3021 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 3022 Message Protocol (ICMPv6) for the Internet Protocol 3023 Version 6 (IPv6) Specification", RFC 4443, March 2006. 3025 [RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol 3026 (LDAP): The Protocol", RFC 4511, June 2006. 3028 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 3029 (MOBIKE)", RFC 4555, June 2006. 3031 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 3032 System", RFC 4592, July 2006. 3034 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 3035 Discovery", RFC 4821, March 2007. 3037 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3038 Errors at High Data Rates", RFC 4963, July 2007. 3040 [RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski, 3041 "DHCPv6 Relay Agent Echo Request Option", RFC 4994, 3042 September 2007. 3044 [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., 3045 and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. 3047 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3048 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3049 March 2008. 3051 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3052 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 3054 [RFC5320] Templin, F., "The Subnetwork Encapsulation and Adaptation 3055 Layer (SEAL)", RFC 5320, February 2010. 3057 [RFC5494] Arkko, J. and C. Pignataro, "IANA Allocation Guidelines 3058 for the Address Resolution Protocol (ARP)", RFC 5494, 3059 April 2009. 3061 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3062 Route Optimization Requirements for Operational Use in 3063 Aeronautics and Space Exploration Mobile Networks", RFC 3064 5522, October 2009. 3066 [RFC5558] Templin, F., "Virtual Enterprise Traversal (VET)", RFC 3067 5558, February 2010. 3069 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3070 Infrastructures (6rd)", RFC 5569, January 2010. 3072 [RFC5720] Templin, F., "Routing and Addressing in Networks with 3073 Global Enterprise Recursion (RANGER)", RFC 5720, February 3074 2010. 3076 [RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy 3077 Mobile IPv6", RFC 5844, May 2010. 3079 [RFC5949] Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F. 3080 Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949, 3081 September 2010. 3083 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 3084 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 3085 5996, September 2010. 3087 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3088 NAT64: Network Address and Protocol Translation from IPv6 3089 Clients to IPv4 Servers", RFC 6146, April 2011. 3091 [RFC6179] Templin, F., "The Internet Routing Overlay Network 3092 (IRON)", RFC 6179, March 2011. 3094 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 3095 Troan, "Basic Requirements for IPv6 Customer Edge 3096 Routers", RFC 6204, April 2011. 3098 [RFC6221] Miles, D., Ooghe, S., Dec, W., Krishnan, S., and A. 3099 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, May 3100 2011. 3102 [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A. 3103 Bierman, "Network Configuration Protocol (NETCONF)", RFC 3104 6241, June 2011. 3106 [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support 3107 in IPv6", RFC 6275, July 2011. 3109 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3110 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, August 3111 2011. 3113 [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", RFC 3114 6422, December 2011. 3116 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3117 for Equal Cost Multipath Routing and Link Aggregation in 3118 Tunnels", RFC 6438, November 2011. 3120 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 3121 RFC 6691, July 2012. 3123 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 3124 (AERO)", RFC 6706, August 2012. 3126 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3127 RFC 6864, February 2013. 3129 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3130 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 3132 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3133 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3134 RFC 6936, April 2013. 3136 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 3137 Address Option in DHCPv6", RFC 6939, May 2013. 3139 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 3140 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 3142 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 3143 Address Selection Policy Using DHCPv6", RFC 7078, January 3144 2014. 3146 [TUNTAP] Wikipedia, W., "http://en.wikipedia.org/wiki/TUN/TAP", 3147 October 2014. 3149 Author's Address 3151 Fred L. Templin (editor) 3152 Boeing Research & Technology 3153 P.O. Box 3707 3154 Seattle, WA 98124 3155 USA 3157 Email: fltemplin@acm.org