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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Obsoletes: rfc5320, rfc5558, rfc5720, June 1, 2015 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: December 3, 2015 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-aerolink-54.txt 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). Nodes attached 17 to AERO links can exchange packets via trusted intermediate routers 18 that provide forwarding services to reach off-link destinations and 19 redirection services for route optimization. AERO provides an IPv6 20 link-local address format known as the AERO address that supports 21 operation of the IPv6 Neighbor Discovery (ND) protocol and links IPv6 22 ND to IP forwarding. Admission control and provisioning are 23 supported by the Dynamic Host Configuration Protocol for IPv6 24 (DHCPv6), and node mobility is naturally supported through dynamic 25 neighbor cache updates. Although DHCPv6 and IPv6 ND messaging are 26 used in the control plane, both IPv4 and IPv6 are supported in the 27 data plane. AERO is a widely-applicable tunneling solution using 28 standard control messaging exchanges as described in this document. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on December 3, 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 Behavior . . . . . . . . . . . . . 37 94 3.17. AERO Intradomain Route Optimization . . . . . . . . . . . 38 95 3.17.1. Reference Operational Scenario . . . . . . . . . . . 38 96 3.17.2. Concept of Operations . . . . . . . . . . . . . . . 40 97 3.17.3. Message Format . . . . . . . . . . . . . . . . . . . 40 98 3.17.4. Sending Predirects . . . . . . . . . . . . . . . . . 41 99 3.17.5. Re-encapsulating and Relaying Predirects . . . . . . 42 100 3.17.6. Processing Predirects and Sending Redirects . . . . 43 101 3.17.7. Re-encapsulating and Relaying Redirects . . . . . . 45 102 3.17.8. Processing Redirects . . . . . . . . . . . . . . . . 46 103 3.17.9. Server-Oriented Redirection . . . . . . . . . . . . 46 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 46 105 3.19. Mobility Management . . . . . . . . . . . . . . . . . . . 48 106 3.19.1. Announcing Link-Layer Address Changes . . . . . . . 48 107 3.19.2. Bringing New Links Into Service . . . . . . . . . . 49 108 3.19.3. Removing Existing Links from Service . . . . . . . . 49 109 3.19.4. Moving to a New Server . . . . . . . . . . . . . . . 50 110 3.20. Proxy AERO . . . . . . . . . . . . . . . . . . . . . . . 50 111 3.21. Extending AERO Links Through Security Gateways . . . . . 53 112 3.22. Extending IPv6 AERO Links to the Internet . . . . . . . . 55 113 3.23. Encapsulation Protocol Version Considerations . . . . . . 58 114 3.24. Multicast Considerations . . . . . . . . . . . . . . . . 58 115 3.25. Operation on AERO Links Without DHCPv6 Services . . . . . 59 116 3.26. Operation on Server-less AERO Links . . . . . . . . . . . 59 117 3.27. Manually-Configured AERO Tunnels . . . . . . . . . . . . 59 118 3.28. Intradomain Routing . . . . . . . . . . . . . . . . . . . 59 119 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 59 120 5. Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . 60 121 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60 122 7. Security Considerations . . . . . . . . . . . . . . . . . . . 60 123 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 61 124 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 62 125 9.1. Normative References . . . . . . . . . . . . . . . . . . 62 126 9.2. Informative References . . . . . . . . . . . . . . . . . 63 127 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 68 129 1. Introduction 131 This document specifies the operation of IP over tunnel virtual links 132 using Asymmetric Extended Route Optimization (AERO). The AERO link 133 can be used for tunneling to neighboring nodes over either IPv6 or 134 IPv4 networks, i.e., AERO views the IPv6 and IPv4 networks as 135 equivalent links for tunneling. Nodes attached to AERO links can 136 exchange packets via trusted intermediate routers that provide 137 forwarding services to reach off-link destinations and redirection 138 services for route optimization that addresses the requirements 139 outlined in [RFC5522]. 141 AERO provides an IPv6 link-local address format known as the AERO 142 address that supports operation of the IPv6 Neighbor Discovery (ND) 144 [RFC4861] protocol and links IPv6 ND to IP forwarding. Admission 145 control and provisioning are supported by the Dynamic Host 146 Configuration Protocol for IPv6 (DHCPv6) [RFC3315], and node mobility 147 is naturally supported through dynamic neighbor cache updates. 148 Although DHCPv6 and IPv6 ND messaging are used in the control plane, 149 both IPv4 and IPv6 can be used in the data plane. AERO is a widely- 150 applicable tunneling solution using standard control messaging 151 exchanges as described in this document. The remainder of this 152 document presents the AERO specification. 154 2. Terminology 156 The terminology in the normative references applies; the following 157 terms are defined within the scope of this document: 159 AERO link 160 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 161 configured over a node's attached IPv6 and/or IPv4 networks. All 162 nodes on the AERO link appear as single-hop neighbors from the 163 perspective of the virtual overlay. 165 AERO interface 166 a node's attachment to an AERO link. Nodes typically have a 167 single AERO interface; support for multiple AERO interfaces is 168 also possible but out of scope for this document. 170 AERO address 171 an IPv6 link-local address constructed as specified in Section 3.3 172 and assigned to a Client's AERO interface. 174 AERO node 175 a node that is connected to an AERO link and that participates in 176 IPv6 ND and DHCPv6 messaging over the link. 178 AERO Client ("Client") 179 a node that issues DHCPv6 messages using the special IPv6 link- 180 local address 'fe80::ffff:ffff:ffff:ffff' to receive IP Prefix 181 Delegations (PD) from one or more AERO Servers. Following PD, the 182 Client assigns an AERO address to the AERO interface which it uses 183 in IPv6 ND messaging to coordinate with other AERO nodes. 185 AERO Server ("Server") 186 a node that configures an AERO interface to provide default 187 forwarding and DHCPv6 services for AERO Clients. The Server 188 assigns an administratively provisioned IPv6 link-local unicast 189 address to support the operation of DHCPv6 and the IPv6 ND 190 protocol. An AERO Server can also act as an AERO Relay. 192 AERO Relay ("Relay") 193 a node that configures an AERO interface to relay IP packets 194 between nodes on the same AERO link and/or forward IP packets 195 between the AERO link and the native Internetwork. The Relay 196 assigns an administratively provisioned IPv6 link-local unicast 197 address to the AERO interface the same as for a Server. An AERO 198 Relay can also act as an AERO Server. 200 AERO Forwarding Agent ("Forwarding Agent") 201 a node that performs data plane forwarding services as a companion 202 to an AERO Server. 204 ingress tunnel endpoint (ITE) 205 an AERO interface endpoint that injects tunneled packets into an 206 AERO link. 208 egress tunnel endpoint (ETE) 209 an AERO interface endpoint that receives tunneled packets from an 210 AERO link. 212 underlying network 213 a connected IPv6 or IPv4 network routing region over which the 214 tunnel virtual overlay is configured. A typical example is an 215 enterprise network. 217 underlying interface 218 an AERO node's interface point of attachment to an underlying 219 network. 221 link-layer address 222 an IP address assigned to an AERO node's underlying interface. 223 When UDP encapsulation is used, the UDP port number is also 224 considered as part of the link-layer address. Link-layer 225 addresses are used as the encapsulation header source and 226 destination addresses. 228 network layer address 229 the source or destination address of the encapsulated IP packet. 231 end user network (EUN) 232 an internal virtual or external edge IP network that an AERO 233 Client connects to the rest of the network via the AERO interface. 235 AERO Service Prefix (ASP) 236 an IP prefix associated with the AERO link and from which AERO 237 Client Prefixes (ACPs) are derived (for example, the IPv6 ACP 238 2001:db8:1:2::/64 is derived from the IPv6 ASP 2001:db8::/32). 240 AERO Client Prefix (ACP) 241 a more-specific IP prefix taken from an ASP and delegated to a 242 Client. 244 Throughout the document, the simple terms "Client", "Server" and 245 "Relay" refer to "AERO Client", "AERO Server" and "AERO Relay", 246 respectively. Capitalization is used to distinguish these terms from 247 DHCPv6 client/server/relay [RFC3315]. 249 The terminology of [RFC4861] (including the names of node variables 250 and protocol constants) applies to this document. Also throughout 251 the document, the term "IP" is used to generically refer to either 252 Internet Protocol version (i.e., IPv4 or IPv6). 254 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 255 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 256 document are to be interpreted as described in [RFC2119]. Lower case 257 uses of these words are not to be interpreted as carrying RFC2119 258 significance. 260 3. Asymmetric Extended Route Optimization (AERO) 262 The following sections specify the operation of IP over Asymmetric 263 Extended Route Optimization (AERO) links: 265 3.1. AERO Link Reference Model 266 .-(::::::::) 267 .-(:::: IP ::::)-. 268 (:: Internetwork ::) 269 `-(::::::::::::)-' 270 `-(::::::)-' 271 | 272 +--------------+ +--------+-------+ +--------------+ 273 |AERO Server S1| | AERO Relay R1 | |AERO Server S2| 274 | Nbr: C1; R1 | | Nbr: S1; S2 | | Nbr: C2; R1 | 275 | default->R1 | |(H1->S1; H2->S2)| | default->R1 | 276 | H1->C1 | +--------+-------+ | H2->C2 | 277 +-------+------+ | +------+-------+ 278 | | | 279 X---+---+-------------------+------------------+---+---X 280 | AERO Link | 281 +-----+--------+ +--------+-----+ 282 |AERO Client C1| |AERO Client C2| 283 | Nbr: S1 | | Nbr: S2 | 284 | default->S1 | | default->S2 | 285 +--------------+ +--------------+ 286 .-. .-. 287 ,-( _)-. ,-( _)-. 288 .-(_ IP )-. .-(_ IP )-. 289 (__ EUN ) (__ EUN ) 290 `-(______)-' `-(______)-' 291 | | 292 +--------+ +--------+ 293 | Host H1| | Host H2| 294 +--------+ +--------+ 296 Figure 1: AERO Link Reference Model 298 Figure 1 presents the AERO link reference model. In this model: 300 o Relay R1 acts as a default router for its associated Servers S1 301 and S2, and connects the AERO link to the rest of the IP 302 Internetwork 304 o Servers S1 and S2 associate with Relay R1 and also act as default 305 routers for their associated Clients C1 and C2. 307 o Clients C1 and C2 associate with Servers S1 and S2, respectively 308 and also act as default routers for their associated EUNs 310 o Hosts H1 and H2 attach to the EUNs served by Clients C1 and C2, 311 respectively 313 Each node maintains a neighbor cache and IP forwarding table. (For 314 example, AERO Relay R1 in the diagram has neighbor cache entries for 315 Servers S1 and S2 and IP forwarding table entries for ACPs H1 and 316 H2.) In common operational practice, there may be many additional 317 Relays, Servers and Clients. (Although not shown in the figure, AERO 318 Forwarding Agents may also be provided for data plane forwarding 319 offload services.) 321 3.2. AERO Link Node Types 323 AERO Relays provide default forwarding services to AERO Servers. 324 Relays forward packets between Servers connected to the same AERO 325 link and also forward packets between the AERO link and the native IP 326 Internetwork. Relays present the AERO link to the native 327 Internetwork as a set of one or more AERO Service Prefixes (ASPs) and 328 serve as a gateway between the AERO link and the Internetwork. AERO 329 Relays maintain an AERO interface neighbor cache entry for each AERO 330 Server, and maintain an IP forwarding table entry for each AERO 331 Client Prefix (ACP). AERO Relays can also be configured to act as 332 AERO Servers. (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 AERO Servers. Note that while Servers are required to 372 perform both control and data plane operations on their own behalf, 373 they may optionally enlist the services of special-purpose Forwarding 374 Agents to offload performance-intensive traffic. 376 3.3. AERO Addresses 378 An AERO address is an IPv6 link-local address with an embedded ACP 379 and assigned to a Client's AERO interface. The AERO address is 380 formed as follows: 382 fe80::[ACP] 384 For IPv6, the AERO address begins with the prefix fe80::/64 and 385 includes in its interface identifier the base prefix taken from the 386 Client's IPv6 ACP. The base prefix is determined by masking the ACP 387 with the prefix length. For example, if the AERO Client receives the 388 IPv6 ACP: 390 2001:db8:1000:2000::/56 392 it constructs its AERO address as: 394 fe80::2001:db8:1000:2000 396 For IPv4, the AERO address is formed from the lower 64 bits of an 397 IPv4-mapped IPv6 address [RFC4291] that includes the base prefix 398 taken from the Client's IPv4 ACP. For example, if the AERO Client 399 receives the IPv4 ACP: 401 192.0.2.32/28 403 it constructs its AERO address as: 405 fe80::FFFF:192.0.2.32 407 The AERO address remains stable as the Client moves between 408 topological locations, i.e., even if its link-layer addresses change. 410 NOTE: In some cases, prospective neighbors may not have advanced 411 knowledge of the Client's ACP length and may therefore send initial 412 IPv6 ND messages with an AERO destination address that matches the 413 ACP but does not correspond to the base prefix. In that case, the 414 Client MUST accept the address as equivalent to the base address, but 415 then use the base address as the source address of any IPv6 ND 416 message replies. For example, if the Client receives the IPv6 ACP 417 2001:db8:1000:2000::/56 then subsequently receives an IPv6 ND message 418 with destination address fe80::2001:db8:1000:2001, it accepts the 419 message but uses fe80::2001:db8:1000:2000 as the source address of 420 any IPv6 ND replies. 422 3.4. AERO Interface Characteristics 424 AERO interfaces use encapsulation (see Section 3.10) to exchange 425 packets with neighbors attached to the AERO link. AERO interfaces 426 maintain a neighbor cache, and AERO Clients and Servers use unicast 427 IPv6 ND messaging. AERO interfaces use unicast Neighbor Solicitation 428 (NS), Neighbor Advertisement (NA), Router Solicitation (RS) and 429 Router Advertisement (RA) messages the same as for any IPv6 link. 430 AERO interfaces use two redirection message types -- the first known 431 as a Predirect message and the second being the standard Redirect 432 message (see Section 3.17). AERO links further use link-local-only 433 addressing; hence, AERO nodes ignore any Prefix Information Options 434 (PIOs) they may receive in RA messages over an AERO interface. 436 AERO interface ND messages include one or more Source/Target Link- 437 Layer Address Options (S/TLLAOs) formatted as shown in Figure 2: 439 0 1 2 3 440 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 1 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 442 | Type = 2 | Length = 3 | Reserved | 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | Link ID | NDSCPs | DSCP #1 |Prf| DSCP #2 |Prf| 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 | DSCP #3 |Prf| DSCP #4 |Prf| .... 447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 448 | UDP Port Number | | 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 450 | | 451 + + 452 | IP Address | 453 + + 454 | | 455 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 456 | | 457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 459 Figure 2: AERO Source/Target Link-Layer Address Option (S/TLLAO) 460 Format 462 In this format, Link ID is an integer value between 0 and 255 463 corresponding to an underlying interface of the target node, NDSCPs 464 encodes an integer value between 1 and 64 indicating the number of 465 Differentiated Services Code Point (DSCP) octets that follow. Each 466 DSCP octet is a 6-bit integer DSCP value followed by a 2-bit 467 Preference ("Prf") value. Each DSCP value encodes an integer between 468 0 and 63 associated with this Link ID, where the value 0 means 469 "default" and other values are interpreted as specified in [RFC2474]. 470 The 'Prf' qualifier for each DSCP value is set to the value 0 471 ("deprecated'), 1 ("low"), 2 ("medium"), or 3 ("high") to indicate a 472 preference level for packet forwarding purposes. UDP Port Number and 473 IP Address are set to the addresses used by the target node when it 474 sends encapsulated packets over the underlying interface. When the 475 encapsulation IP address family is IPv4, IP Address is formed as an 476 IPv4-mapped IPv6 address [RFC4291]. 478 AERO interfaces may be configured over multiple underlying 479 interfaces. For example, common mobile handheld devices have both 480 wireless local area network ("WLAN") and cellular wireless links. 481 These links are typically used "one at a time" with low-cost WLAN 482 preferred and highly-available cellular wireless as a standby. In a 483 more complex example, aircraft frequently have many wireless data 484 link types (e.g. satellite-based, terrestrial, air-to-air 485 directional, etc.) with diverse performance and cost properties. 487 If a Client's multiple underlying interfaces are used "one at a time" 488 (i.e., all other interfaces are in standby mode while one interface 489 is active), then Redirect, Predirect and unsolicited NA messages 490 include only a single TLLAO with Link ID set to a constant value. 492 If the Client has multiple active underlying interfaces, then from 493 the perspective of IPv6 ND it would appear to have a single link- 494 local address with multiple link-layer addresses. In that case, 495 Redirect, Predirect and unsolicited NA messages MAY include multiple 496 TLLAOs -- each with a different Link ID that corresponds to a 497 specific underlying interface of the Client. 499 3.5. AERO Link Registration 501 When an administrative authority first deploys a set of AERO Relays 502 and Servers that comprise an AERO link, they also assign a unique 503 domain name for the link, e.g., "linkupnetworks.example.com". Next, 504 if administrative policy permits Clients within the domain to serve 505 as correspondent nodes for Internet mobile nodes, the administrative 506 authority adds a Fully Qualified Domain Name (FQDN) for each of the 507 AERO link's ASPs to the Domain Name System (DNS) [RFC1035]. The FQDN 508 is based on the suffix "aero.linkupnetworks.net" with a prefix formed 509 from the wildcard-terminated reverse mapping of the ASP 510 [RFC3596][RFC4592], and resolves to a DNS PTR resource record. For 511 example, for the ASP '2001:db8:1::/48' within the domain name 512 "linkupnetworks.example.com", the DNS database contains: 514 '*.1.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net. PTR 515 linkupnetworks.example.com' 517 This DNS registration advertises the AERO link's ASPs to prospective 518 mobile nodes. 520 3.6. AERO Interface Initialization 522 3.6.1. AERO Relay Behavior 524 When a Relay enables an AERO interface, it first assigns an 525 administratively provisioned link-local address fe80::ID to the 526 interface. Each fe80::ID address MUST be unique among all AERO nodes 527 on the link, and MUST NOT collide with any potential AERO addresses 528 nor the special addresses fe80:: and fe80::ffff:ffff:ffff:ffff. (The 529 fe80::ID addresses are typically taken from the available range 530 fe80::/96, e.g., as fe80::1, fe80::2, fe80::3, etc.) The Relay then 531 engages in a dynamic routing protocol session with all Servers on the 532 link (see: Section 3.7), and advertises the set of ASPs into the 533 native IP Internetwork. 535 Each Relay subsequently maintains an IP forwarding table entry for 536 each Client-Server association, and maintains a neighbor cache entry 537 for each Server on the link. Relays exchange NS/NA messages with 538 AERO link neighbors the same as for any AERO node, however they 539 typically do not perform explicit Neighbor Unreachability Detection 540 (NUD) (see: Section 3.18) since the dynamic routing protocol already 541 provides reachability confirmation. 543 3.6.2. AERO Server Behavior 545 When a Server enables an AERO interface, it assigns an 546 administratively provisioned link-local address fe80::ID the same as 547 for Relays. The Server further configures a DHCPv6 server function 548 to facilitate DHCPv6 PD exchanges with AERO Clients. The Server 549 maintains a neighbor cache entry for each Relay on the link, and 550 manages per-Client neighbor cache entries and IP forwarding table 551 entries based on control message exchanges. Each Server also engages 552 in a dynamic routing protocol with each Relay on the link (see: 553 Section 3.7). 555 When the Server receives an NS/RS message on the AERO interface it 556 returns an NA/RA message but does not update the neighbor cache. The 557 Server further provides a simple conduit between AERO interface 558 neighbors. Therefore, packets enter the Server's AERO interface from 559 the link layer and are forwarded back out the link layer without ever 560 leaving the AERO interface and therefore without ever disturbing the 561 network layer. 563 3.6.3. AERO Client Behavior 565 When a Client enables an AERO interface, it uses the special address 566 fe80::ffff:ffff:ffff:ffff to obtain an ACP from an AERO Server via 567 DHCPv6 PD. Next, it assigns the corresponding AERO address to the 568 AERO interface and creates a neighbor cache entry for the Server, 569 i.e., the PD exchange bootstraps autoconfiguration of a unique link- 570 local address. The Client maintains a neighbor cache entry for each 571 of its Servers and each of its active correspondent Clients. When 572 the Client receives Redirect/Predirect messages on the AERO interface 573 it updates or creates neighbor cache entries, including link-layer 574 address information. Unsolicited NA messages update the cached link- 575 layer addresses for correspondent Clients (e.g., following a link- 576 layer address change due to node mobility) but do not create new 577 neighbor cache entries. NS/NA messages used for NUD update timers in 578 existing neighbor cache entires but do not update link-layer 579 addresses nor create new neighbor cache entries. 581 Finally, the Client need not maintain any IP forwarding table entries 582 for its Servers or correspondent Clients. Instead, it can set a 583 single "route-to-interface" default route in the IP forwarding table, 584 and all forwarding decisions can be made within the AERO interface 585 based on neighbor cache entries. (On systems in which adding a 586 default route would violate security policy, the default route could 587 instead be installed via a "synthesized RA", e.g., as discussed in 588 Section 3.15.2.) 590 3.6.4. AERO Forwarding Agent Behavior 592 When a Forwarding Agent enables an AERO interface, it assigns the 593 same link-local address(es) as the companion AERO Server. The 594 Forwarding Agent thereafter provides data plane forwarding services 595 based solely on the forwarding information assigned to it by the 596 companion AERO Server. AERO Forwarding Agents perform NS/NA 597 messaging, i.e., the same as for any AERO node. 599 3.7. AERO Link Routing System 601 Relays require full topology knowledge of all ACP/Server 602 associations, while individual Servers at a minimum only need to know 603 the ACPs for their current set of associated Clients. This is 604 accomplished through the use of an internal instance of the Border 605 Gateway Protocol (BGP) [RFC4271] coordinated between Servers and 606 Relays. This internal BGP instance does not interact with the public 607 Internet BGP instance; therefore, the AERO link is presented to the 608 IP Internetwork as a small set of ASPs as opposed to the full set of 609 individual ACPs. 611 In a reference BGP arrangement, each AERO Server is configured as an 612 Autonomous System Border Router (ASBR) for a stub Autonomous System 613 (AS) using an AS Number (ASN) that is unique within the BGP instance, 614 and each Server further peers with each Relay but does not peer with 615 other Servers. Similarly, Relays do not peer with each other, since 616 they will reliably receive all updates from all Servers and will 617 therefore have a consistent view of the AERO link ACP delegations. 619 Each Server maintains a working set of associated ACPs, and 620 dynamically announces new ACPs and withdraws departed ACPs in its BGP 621 updates to Relays. Clients are expected to remain associated with 622 their current Servers for extended timeframes, however Servers SHOULD 623 selectively suppress BGP updates for impatient Clients that 624 repeatedly associate and disassociate with them in order to dampen 625 routing churn. 627 In some environments, Relays need not send BGP updates to Servers 628 since Servers can always use Relays as default routers, however this 629 presents a data/control plane performance tradeoff. In environments 630 where sustained packet forwarding over Relays is undesirable, Relays 631 can instead report ACPs to Servers while including a BGP Remote-Next- 632 Hop [I-D.vandevelde-idr-remote-next-hop]. The Server then creates a 633 neighbor cache entry for each ACP with the Remote-Next-Hop as the 634 link-layer address to enable Server-to-Server route optimization. 636 3.8. AERO Interface Neighbor Cache Maintenace 638 Each AERO interface maintains a conceptual neighbor cache that 639 includes an entry for each neighbor it communicates with on the AERO 640 link, the same as for any IPv6 interface [RFC4861]. AERO interface 641 neighbor cache entires are said to be one of "permanent", "static" or 642 "dynamic". 644 Permanent neighbor cache entries are created through explicit 645 administrative action; they have no timeout values and remain in 646 place until explicitly deleted. AERO Relays maintain a permanent 647 neighbor cache entry for each Server on the link, and AERO Servers 648 maintain a permanent neighbor cache entry for each Relay. Each entry 649 maintains the mapping between the neighbor's fe80::ID network-layer 650 address and corresponding link-layer address. 652 Static neighbor cache entries are created though DHCPv6 PD exchanges 653 and remain in place for durations bounded by prefix lifetimes. AERO 654 Servers maintain static neighbor cache entries for the ACPs of each 655 of their associated Clients, and AERO Clients maintain a static 656 neighbor cache entry for each of their associated Servers. When an 657 AERO Server sends a DHCPv6 Reply message response to a Client's 658 DHCPv6 Solicit/Request, Rebind or Renew message, it creates or 659 updates a static neighbor cache entry based on the AERO address 660 corresponding to the Client's ACP as the network-layer address, the 661 prefix lifetime as the neighbor cache entry lifetime, the Client's 662 encapsulation IP address and UDP port number as the link-layer 663 address and the prefix length as the length to apply to the AERO 664 address. When an AERO Client receives a DHCPv6 Reply message from a 665 Server, it creates or updates a static neighbor cache entry based on 666 the Reply message link-local source address as the network-layer 667 address, the prefix lifetime as the neighbor cache entry lifetime, 668 and the encapsulation IP source address and UDP source port number as 669 the link-layer address. 671 Dynamic neighbor cache entries are created or updated based on 672 receipt of an IPv6 ND message, and are garbage-collected if not used 673 within a bounded timescale. AERO Clients maintain dynamic neighbor 674 cache entries for each of their active correspondent Client ACPs with 675 lifetimes based on IPv6 ND messaging constants. When an AERO Client 676 receives a valid Predirect message it creates or updates a dynamic 677 neighbor cache entry for the Predirect target network-layer and link- 678 layer addresses plus prefix length. The node then sets an 679 "AcceptTime" variable in the neighbor cache entry to ACCEPT_TIME 680 seconds and uses this value to determine whether packets received 681 from the correspondent can be accepted. When an AERO Client receives 682 a valid Redirect message it creates or updates a dynamic neighbor 683 cache entry for the Redirect target network-layer and link-layer 684 addresses plus prefix length. The Client then sets a "ForwardTime" 685 variable in the neighbor cache entry to FORWARD_TIME seconds and uses 686 this value to determine whether packets can be sent directly to the 687 correspondent. The Client also sets a "MaxRetry" variable to 688 MAX_RETRY to limit the number of keepalives sent when a correspondent 689 may have gone unreachable. 691 For dynamic neighbor cache entries, when an AERO Client receives a 692 valid NS message it (re)sets AcceptTime for the neighbor to 693 ACCEPT_TIME. When an AERO Client receives a valid solicited NA 694 message, it (re)sets ForwardTime for the neighbor to FORWARD_TIME and 695 sets MaxRetry to MAX_RETRY. When an AERO Client receives a valid 696 unsolicited NA message, it updates the correspondent's link-layer 697 addresses but DOES NOT reset AcceptTime, ForwardTime or MaxRetry. 699 It is RECOMMENDED that FORWARD_TIME be set to the default constant 700 value 30 seconds to match the default REACHABLE_TIME value specified 701 for IPv6 ND [RFC4861]. 703 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 704 value 40 seconds to allow a 10 second window so that the AERO 705 redirection procedure can converge before AcceptTime decrements below 706 FORWARD_TIME. 708 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 709 for IPv6 ND address resolution in Section 7.3.3 of [RFC4861]. 711 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 712 administratively set, if necessary, to better match the AERO link's 713 performance characteristics; however, if different values are chosen, 714 all nodes on the link MUST consistently configure the same values. 715 Most importantly, ACCEPT_TIME SHOULD be set to a value that is 716 sufficiently longer than FORWARD_TIME to allow the AERO redirection 717 procedure to converge. 719 3.9. AERO Interface Sending Algorithm 721 IP packets enter a node's AERO interface either from the network 722 layer (i.e., from a local application or the IP forwarding system), 723 or from the link layer (i.e., from the AERO tunnel virtual link). 724 Packets that enter the AERO interface from the network layer are 725 encapsulated and admitted into the AERO link, i.e., they are 726 tunnelled to an AERO interface neighbor. Packets that enter the AERO 727 interface from the link layer are either re-admitted into the AERO 728 link or delivered to the network layer where they are subject to 729 either local delivery or IP forwarding. Since each AERO node may 730 have only partial information about neighbors on the link, AERO 731 interfaces may forward packets with link-local destination addresses 732 at a layer below the network layer. This means that AERO nodes act 733 as both IP routers and sub-IP layer forwarding agents. AERO 734 interface sending considerations for Clients, Servers and Relays are 735 given below. 737 When an IP packet enters a Client's AERO interface from the network 738 layer, if the destination is covered by an ASP the Client searches 739 for a dynamic neighbor cache entry with a non-zero ForwardTime and an 740 AERO address that matches the packet's destination address. (The 741 destination address may be either an address covered by the 742 neighbor's ACP or the (link-local) AERO address itself.) If there is 743 a match, the Client uses a link-layer address in the entry as the 744 link-layer address for encapsulation then admits the packet into the 745 AERO link. If there is no match, the Client instead uses the link- 746 layer address of a neighboring Server as the link-layer address for 747 encapsulation. 749 When an IP packet enters a Server's AERO interface from the link 750 layer, if the destination is covered by an ASP the Server searches 751 for a neighbor cache entry with an AERO address that matches the 752 packet's destination address. (The destination address may be either 753 an address covered by the neighbor's ACP or the AERO address itself.) 754 If there is a match, the Server uses a link-layer address in the 755 entry as the link-layer address for encapsulation and re-admits the 756 packet into the AERO link. If there is no match, the Server instead 757 uses the link-layer address in a permanent neighbor cache entry for a 758 Relay as the link-layer address for encapsulation. 760 When an IP packet enters a Relay's AERO interface from the network 761 layer, the Relay searches its IP forwarding table for an entry that 762 is covered by an ASP and also matches the destination. If there is a 763 match, the Relay uses the link-layer address in a permanent neighbor 764 cache entry for a Server as the link-layer address for encapsulation 765 and admits the packet into the AERO link. When an IP packet enters a 766 Relay's AERO interface from the link-layer, if the destination is not 767 a link-local address and does not match an ASP the Relay removes the 768 packet from the AERO interface and uses IP forwarding to forward the 769 packet to the Internetwork. If the destination address is a link- 770 local address or a non-link-local address that matches an ASP, and 771 there is a more-specific ACP entry in the IP forwarding table, the 772 Relay uses the link-layer address in the corresponding neighbor cache 773 entry as the link-layer address for encapsulation and re-admits the 774 packet into the AERO link. When an IP packet enters a Relay's AERO 775 interface from either the network layer or link-layer, and the 776 packet's destination address matches an ASP but there is no more- 777 specific ACP entry, the Relay drops the packet and returns an ICMP 778 Destination Unreachable message (see: Section 3.14). 780 When an AERO Server receives a packet from a Relay via the AERO 781 interface, the Server MUST NOT forward the packet back to the same or 782 a different Relay. 784 When an AERO Relay receives a packet from a Server via the AERO 785 interface, the Relay MUST NOT forward the packet back to the same 786 Server. 788 When an AERO node re-admits a packet into the AERO link without 789 involving the network layer, the node MUST NOT decrement the network 790 layer TTL/Hop-count. 792 When an AERO node forwards a data packet to the primary link-layer 793 address of a Server, it may receive Redirect messages with an SLLAO 794 that include the link-layer address of an AERO Forwarding Agent. The 795 AERO node SHOULD record the link-layer address in the neighbor cache 796 entry for the neighbor and send subsequent data packets via this 797 address instead of the Server's primary address (see: Section 3.16). 799 3.10. AERO Interface Encapsulation and Re-encapsulation 801 AERO interfaces encapsulate IP packets according to whether they are 802 entering the AERO interface from the network layer or if they are 803 being re-admitted into the same AERO link they arrived on. This 804 latter form of encapsulation is known as "re-encapsulation". 806 The AERO interface encapsulates packets per the base tunneling 807 specifications (e.g., [RFC2003], [RFC2473], [RFC2784], [RFC4213], 808 [RFC4301], [RFC5246], etc.) except that it inserts a UDP header 809 immediately following the IP encapsulation header. If there are no 810 additional encapsulation headers (and no fragmentation, 811 identification, checksum or signature is needed), the AERO interface 812 next encapsulates the IPv4 or IPv6 packet immediately following the 813 UDP header. In that case, the most significant four bits of the 814 encapsulated packet encode the value '4' for IPv4 or '6' for IPv6. 816 For all other encapsulations, the AERO interface MUST insert an AERO 817 Header between the UDP header and the next encapsulation header as 818 shown in Figure 3: 820 0 1 2 3 821 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 1 822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 823 |Version|N|F|C|S| Next Header |Fragment Offset (13 bits)|Res|M| 824 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 825 | Identification (32 bits) | 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 827 | Checksum (16 bits) | Signature (variable length) : 828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 830 Figure 3: AERO Header 832 Version a 4-bit "Version" field. MUST be 0 for the purpose of this 833 specification. 835 N a 1-bit "Next Header" flag. MUST be 1 for the purpose of this 836 specification to indicate that "Next Header" field is present. 837 "Next Header" encodes the IP protocol number corresponding to the 838 next header in the encapsulation immediately following the AERO 839 header. For example, "Next Header" encodes the value '4' for 840 IPv4, '17' for UDP, '41' for IPv6, '47' for GRE, '50' for ESP, 841 '51' for AH, etc. 843 F a 1-bit "Fragment Header" flag. Set to '1' if the "Fragment 844 Offset", "Res", "M", and "Identification" fields are present and 845 collectively referred to as the "AERO Fragment Header"; otherwise, 846 set to '0'. 848 C a 1-bit "Checksum" flag. Set to '1' if the "Checksum" field is 849 present; otherwise, set to '0'. When present, the Checksum field 850 contains a checksum of the IP/UDP/AERO encapsulation headers prior 851 to the Checksum field. 853 S a 1-bit "Signature" flag. Set to '1' if the "Signature" field is 854 present; otherwise, set to '0'. When present, the Signature field 855 contains a cryptographic signature of the encapsulated packet 856 following the Signature field. The signature is applied prior to 857 any fragmentation; hence' the Signature field only appears in the 858 first fragment of a fragmented packet. 860 (Note: [RFC6706] defines an experimental use in which the bits 861 corresponding to (Version, N, F, C, S) are all zero, which can be 862 unambiguously distinguished from the values permitted by this 863 specification.) 865 During encapsulation, the AERO interface copies the "TTL/Hop Limit", 866 "Type of Service/Traffic Class" [RFC2983] and "Congestion 867 Experienced" [RFC3168] values in the packet's IP header into the 868 corresponding fields in the encapsulation IP header. (When IPv6 is 869 used as the encapsulation protocol, the interface also sets the Flow 870 Label value in the encapsulation header per [RFC6438].) For packets 871 undergoing re-encapsulation, the AERO interface instead copies the 872 "TTL/Hop Limit", "Type of Service/Traffic Class", "Flow Label" and 873 "Congestion Experienced" values in the original encapsulation IP 874 header into the corresponding fields in the new encapsulation IP 875 header, i.e., the values are transferred between encapsulation 876 headers and *not* copied from the encapsulated packet's network-layer 877 header. 879 The AERO interface next sets the UDP source port to a constant value 880 that it will use in each successive packet it sends, and sets the UDP 881 length field to the length of the encapsulated packet plus 8 bytes 882 for the UDP header itself, plus the length of the AERO header. For 883 packets sent via a Server, the AERO interface sets the UDP 884 destination port to 8060, i.e., the IANA-registered port number for 885 AERO. For packets sent to a correspondent Client, the AERO interface 886 sets the UDP destination port to the port value stored in the 887 neighbor cache entry for this correspondent. The AERO interface also 888 sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) unless 889 an integrity check is required (see: Section 3.13.2). 891 The AERO interface next sets the IP protocol number in the 892 encapsulation header to 17 (i.e., the IP protocol number for UDP). 893 When IPv4 is used as the encapsulation protocol, the AERO interface 894 sets the DF bit as discussed in Section 3.13. The AERO interface 895 finally sets the AERO header fields as described in Figure 3. 897 3.11. AERO Interface Decapsulation 899 AERO interfaces decapsulate packets destined either to the node 900 itself or to a destination reached via an interface other than the 901 AERO interface the packet was received on. When the AERO interface 902 receives a UDP packet, it examines the first octet of the 903 encapsulated packet. 905 If the most significant four bits of the first octet encode the value 906 '4' (i.e., the IP version number value for IPv4) or the value '6' 907 (i.e., the IP version number value for IPv6), the AERO interface 908 discards the encapsulation headers and accepts the encapsulated 909 packet as an ordinary IPv6 or IPv4 data packet, respectively. If the 910 most significant four bits encode the value '0', however, the AERO 911 interface processes the packet according to the appropriate AERO 912 Header fields as specified in Figure 3. 914 3.12. AERO Interface Data Origin Authentication 916 AERO nodes employ simple data origin authentication procedures for 917 encapsulated packets they receive from other nodes on the AERO link. 918 In particular: 920 o AERO Relays and Servers accept encapsulated packets with a link- 921 layer source address that matches a permanent neighbor cache 922 entry. 924 o AERO Servers accept authentic encapsulated DHCPv6 messages from 925 Clients, and create or update a static neighbor cache entry for 926 the source based on the specific message type. 928 o AERO Servers accept encapsulated packets if there is a neighbor 929 cache entry with an AERO address that matches the packet's 930 network-layer source address and with a link-layer address that 931 matches the packet's link-layer source address. 933 o AERO Clients accept encapsulated packets if there is a static 934 neighbor cache entry with a link-layer source address that matches 935 the packet's link-layer source address. 937 o AERO Clients and Servers accept encapsulated packets if there is a 938 dynamic neighbor cache entry with an AERO address that matches the 939 packet's network-layer source address, with a link-layer address 940 that matches the packet's link-layer source address, and with a 941 non-zero AcceptTime. 943 Note that this simple data origin authentication is effective in 944 environments in which link-layer addresses cannot be spoofed. In 945 other environments, each AERO message must include a signature that 946 the recipient can use to authenticate the message origin. 948 3.13. AERO Interface MTU and Fragmentation 950 The AERO interface is the node's point of attachment to the AERO 951 link. AERO links over IP networks have a maximum link MTU of 64KB 952 minus the encapsulation overhead (termed here "ENCAPS"), since the 953 maximum packet size in the base IP specifications is 64KB 954 [RFC0791][RFC2460] (while IPv6 jumbograms can be up to 4GB, they are 955 considered optional for IPv6 nodes [RFC2675][RFC6434]). 957 IPv6 specifies a minimum link MTU of 1280 bytes [RFC2460]. This is 958 the minimum packet size the AERO interface MUST admit without 959 returning an ICMP Packet Too Big (PTB) message. Although IPv4 960 specifies a smaller minimum link MTU of 68 bytes [RFC0791], AERO 961 interfaces also observe a 1280 byte minimum for IPv4. Additionally, 962 the vast majority of links in the Internet configure an MTU of at 963 least 1500 bytes. Original source hosts have therefore become 964 conditioned to expect that IP packets up to 1500 bytes in length will 965 either be delivered to the final destination or a suitable PTB 966 message returned. However, PTB messages may be lost in the network 967 [RFC2923] resulting in failure of the IP Path MTU Discovery (PMTUD) 968 mechanisms [RFC1191][RFC1981]. 970 For these reasons, the source AERO interface (i.e., the tunnel 971 ingress)admit packets into the tunnel subject to their reasonable 972 expectation that PMTUD will convey the correct information to the 973 original source in the event that the packet is too large. In 974 particular, if the original source is within the same well-managed 975 administrative domain as the tunnel ingress, the ingress drops the 976 packet and sends a PTB message back to the original source if the 977 packet is too large to traverse the tunnel in one piece. Similarly, 978 if the tunnel ingress is within the same well-managed administrative 979 domain as the to the destination AERO interface (i.e., the tunnel 980 egress), the ingress can cache MTU values reported in PTB messages 981 received from a router on the path to the egress. 983 In all other cases, AERO interfaces admit all packets up to 1500 984 bytes in length even if some fragmentation is necessary, and admit 985 larger packets without fragmentation in case they are able to 986 traverse the tunnel in one piece. AERO interfaces are therefore 987 considered to have an indefinite MTU, i.e., instead of clamping the 988 MTU to a finite size. 990 For AERO links over IPv4, the IP ID field is only 16 bits in length, 991 meaning that fragmentation at high data rates could result in data 992 corruption due to reassembly misassociations [RFC6864][RFC4963] (see: 993 Section 3.13.2). For AERO links over both IPv4 and IPv6, studies 994 have also shown that IP fragments are dropped unconditionally over 995 some network paths [I-D.taylor-v6ops-fragdrop]. For these reasons, 996 when fragmentation is needed it is performed through insertion of an 997 AERO fragment header (see: Section 3.10) and application of tunnel 998 fragmentation as described in Section 3.1.7 of [RFC2764]. Since the 999 AERO fragment header reduces the room available for packet data, but 1000 the original source has no way to control its insertion, the header 1001 length MUST be included in the ENCAPS length even for packets in 1002 which the header does not appear. 1004 The tunnel ingress therefore sends encapsulated packets to the tunnel 1005 egress according to the following algorithm: 1007 o For IP packets that are no larger than (1280-ENCAPS) bytes, the 1008 tunnel ingress encapsulates the packet and admits it into the 1009 tunnel without fragmentation. For IPv4 AERO links, the tunnel 1010 ingress sets the Don't Fragment (DF) bit to 0 so that these 1011 packets will be delivered to the tunnel egress even if there is a 1012 restricting link in the path, i.e., unless lost due to congestion 1013 or routing errors. 1015 o For IP packets that are larger than (1280-ENCAPS) bytes but no 1016 larger than 1500 bytes, the tunnel ingress encapsulates the packet 1017 and inserts an AERO fragment header. Next, the tunnel ingress 1018 uses the fragmentation algorithm in [RFC2460] to break the packet 1019 into two non-overlapping fragments where the first fragment 1020 (including ENCAPS) is no larger than 1024 bytes and the second is 1021 no larger than the first. Each fragment consists of identical 1022 UDP/IP encapsulation headers, followed by the AERO header followed 1023 by the fragment of the encapsulated packet itself. The tunnel 1024 ingress then admits both fragments into the tunnel, and for IPv4 1025 sets the DF bit to 0 in the IP encapsulation header. These 1026 fragmented encapsulated packets will be delivered to the tunnel 1027 egress. When the tunnel egress receives the fragments, it 1028 reassembles them into a whole packet per the reassembly algorithm 1029 in [RFC2460]. The tunnel egress therefore MUST be capable of 1030 reassembling packets up to 1500+ENCAPS bytes in length; hence, it 1031 is RECOMMENDED that the tunnel egress be capable of reassembling 1032 at least 2KB. 1034 o For IPv4 packets that are larger than 1500 bytes and with the DF 1035 bit set to 0, the tunnel ingress uses ordinary IPv4 fragmentation 1036 to break the unencapsulated packet into a minimum number of non- 1037 overlapping fragments where the first fragment is no larger than 1038 1024-ENCAPS and all other fragments are no larger than the first 1039 fragment. The tunnel ingress then encapsulates each fragment (and 1040 for IPv4 sets the DF bit to 0) then admits them into the tunnel. 1041 These fragments will be delivered to the final destination via the 1042 tunnel egress. 1044 o For all other IP packets, if the packet is too large to enter the 1045 underlying interface following encapsulation, the tunnel ingress 1046 drops the packet and returns a network-layer (L3) PTB message to 1047 the original source with MTU set to the larger of 1500 bytes or 1048 the underlying interface MTU minus ENCAPS. Otherwise, the tunnel 1049 ingress encapsulates the packet and admits it into the tunnel 1050 without fragmentation (and for IPv4 sets the DF bit to 1) and 1051 translates any link-layer (L2) PTB messages it may receive from 1052 the network into corresponding L3 PTB messages to send to the 1053 original source as specified in Section 3.14. Since both L2 and 1054 L3 PTB messages may be either lost or contain insufficient 1055 information, however, it is RECOMMENDED that original sources that 1056 send unfragmentable IP packets larger than 1500 bytes use 1057 Packetization Layer Path MTU Discovery (PLPMTUD) [RFC4821]. 1059 While sending packets according to the above algorithm, the tunnel 1060 ingress MAY also send 1500 byte or larger probe packets to determine 1061 whether they can reach the tunnel egress without fragmentation. If 1062 the probes succeed, the tunnel ingress can discontinue fragmentation 1063 and (for IPv4) set DF to 1. Since the path MTU within the tunnel may 1064 fluctuate due to routing changes, the tunnel ingress SHOULD continue 1065 to send additional probes subject to rate limiting and SHOULD process 1066 any L2 PTB messages as an indication that the path MTU may have 1067 decreased. If the path MTU within the tunnel becomes insufficient, 1068 the source MUST resume fragmentation. 1070 To construct a probe, the tunnel ingress prepares an NS message with 1071 a Nonce option plus trailing NULL padding octets added to the probe 1072 length without including the length of the padding in the IPv6 1073 Payload Length field, but with the length included in the 1074 encapsulating IP header. The tunnel ingress then encapsulates the 1075 padded NS message in the encapsulation headers (and for IPv4 sets DF 1076 to 1) then sends the message to the tunnel egress. If the tunnel 1077 egress returns a solicited NA message with a matching Nonce option, 1078 the tunnel ingress deems the probe successful. Note that in this 1079 process it is essential that probes follow equivalent paths to those 1080 used to convey actual data packets. This means that Equal Cost 1081 MultiPath (ECMP) and Link Aggregation Gateway (LAG) equipment in the 1082 path would need to ensure that probes and data packets follow the 1083 same path, which is outside the scope of this specification. 1085 3.13.1. Accommodating Large Control Messages 1087 Control messages (i.e., IPv6 ND, DHCPv6, etc.) MUST be accommodated 1088 even if some fragmentation is necessary. These packets are therefore 1089 accommodated through a modification of the second rule in the above 1090 algorithm as follows: 1092 o For control messages that are larger than (1280-ENCAPS) bytes, the 1093 tunnel ingress encapsulates the packet and inserts an AERO 1094 fragment header. Next, the tunnel ingress uses the fragmentation 1095 algorithm in [RFC2460] to break the packet into a minimum number 1096 of non-overlapping fragments where the first fragment (including 1097 ENCAPS) is no larger than 1024 bytes and the remaining fragments 1098 are no larger than the first. The tunnel ingress then 1099 encapsulates each fragment (and for IPv4 sets the DF bit to 0) 1100 then admits them into the tunnel. 1102 Control messages that exceed the 2KB minimum reassembly size rarely 1103 occur in the modern era, however the tunnel egress SHOULD be able to 1104 reassemble them if they do. This means that the tunnel egress SHOULD 1105 include a configuration knob allowing the operator to set a larger 1106 reassembly buffer size if large control messages become more common 1107 in the future. 1109 The tunnel ingress can send large control messages without 1110 fragmentation if there is assurance that large packets can traverse 1111 the tunnel without fragmentation. The tunnel ingress MAY send 1500 1112 byte or larger probe packets as specified above to determine a size 1113 for which fragmentation can be avoided. 1115 3.13.2. Integrity 1117 When fragmentation is needed, there must be assurance that reassembly 1118 can be safely conducted without incurring data corruption. Sources 1119 of corruption can include implementation errors, memory errors and 1120 misassociation of fragments from a first datagram with fragments of 1121 another datagram. The first two conditions (implementation and 1122 memory errors) are mitigated by modern systems and implementations 1123 that have demonstrated integrity through decades of operational 1124 practice. The third condition (reassembly misassociations) must be 1125 accounted for by AERO. 1127 The AERO fragmentation procedure described in the above algorithms 1128 reuses standard IPv6 fragmentation and reassembly code. Since the 1129 AERO fragment header includes a 32-bit ID field, there would need to 1130 be 2^32 packets alive in the network before a second packet with a 1131 duplicate ID enters the system with the (remote) possibility for a 1132 reassembly misassociation. For 1280 byte packets, and for a maximum 1133 network lifetime value of 60 seconds[RFC2460], this means that the 1134 tunnel ingress would need to produce ~(7 *10^12) bits/sec in order 1135 for a duplication event to be possible. This exceeds the bandwidth 1136 of data link technologies of the modern era, but not necessarily so 1137 going forward into the future. Although wireless data links commonly 1138 used by AERO Clients support vastly lower data rates, the aggregate 1139 data rates between AERO Servers and Relays may be substantial. 1140 However, high speed data links in the network core are expected to 1141 configure larger MTUs, e.g., 4KB, 8KB or even larger such that 1142 unfragmented packets can be used. Hence, no integrity check is 1143 included to cover the AERO fragmentation and reassembly procedures. 1145 When the tunnel ingress sends an IPv4-encapsulated packet with the DF 1146 bit set to 0 in the above algorithms, there is a chance that the 1147 packet may be fragmented by an IPv4 router somewhere within the 1148 tunnel. Since the largest such packet is only 1280 bytes, however, 1149 it is very likely that the packet will traverse the tunnel without 1150 incurring a restricting link. Even when a link within the tunnel 1151 configures an MTU smaller than 1280 bytes, it is very likely that it 1152 does so due to limited performance characteristics [RFC3819]. This 1153 means that the tunnel would not be able to convey fragmented 1154 IPv4-encapsulated packets fast enough to produce reassembly 1155 misassociations, as discussed above. However, AERO must also account 1156 for the possibility of tunnel paths that include "poorly managed" 1157 IPv4 link MTUs due to misconfigurations. 1159 Since the IPv4 header includes only a 16-bit ID field, there would 1160 only need to be 2^16 packets alive in the network before a second 1161 packet with a duplicate ID enters the system. For 1280 byte packets, 1162 and for a maximum network lifetime value of 120 seconds[RFC0791], 1163 this means that the tunnel ingress would only need to produce ~(5 1164 *10^6) bits/sec in order for a duplication event to be possible - a 1165 value that is well within range for many modern wired and wireless 1166 data link technologies. 1168 Therefore, if there is strong operational assurance that no IPv4 1169 links capable of supporting data rates of 5Mbps or more configure an 1170 MTU smaller than 1280 the tunnel ingress MAY omit an integrity check 1171 for the IPv4 fragmentation and reassembly procedures; otherwise, the 1172 tunnel ingress SHOULD include an integrity check. When an upper 1173 layer encapsulation (e.g., IPsec) already includes an integrity 1174 check, the tunnel ingress need not include an additional check. 1175 Otherwise, the tunnel ingress calculates the UDP checksum over the 1176 encapsulated packet and writes the value into the UDP encapsulation 1177 header, i.e., instead of writing the value 0. The tunnel egress will 1178 then verify the UDP checksum and discard the packet if the checksum 1179 is incorrect. 1181 3.14. AERO Interface Error Handling 1183 When an AERO node admits encapsulated packets into the AERO 1184 interface, it may receive link-layer (L2) or network-layer (L3) error 1185 indications. 1187 An L2 error indication is an ICMP error message generated by a router 1188 on the path to the neighbor or by the neighbor itself. The message 1189 includes an IP header with the address of the node that generated the 1190 error as the source address and with the link-layer address of the 1191 AERO node as the destination address. 1193 The IP header is followed by an ICMP header that includes an error 1194 Type, Code and Checksum. For ICMPv6 [RFC4443], the error Types 1195 include "Destination Unreachable", "Packet Too Big (PTB)", "Time 1196 Exceeded" and "Parameter Problem". For ICMPv4 [RFC0792], the error 1197 Types include "Destination Unreachable", "Fragmentation Needed" (a 1198 Destination Unreachable Code that is analogous to the ICMPv6 PTB), 1199 "Time Exceeded" and "Parameter Problem". 1201 The ICMP header is followed by the leading portion of the packet that 1202 generated the error, also known as the "packet-in-error". For 1203 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1204 much of invoking packet as possible without the ICMPv6 packet 1205 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1206 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1207 "Internet Header + 64 bits of Original Data Datagram", however 1208 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1209 ICMP datagram SHOULD contain as much of the original datagram as 1210 possible without the length of the ICMP datagram exceeding 576 1211 bytes". 1213 The L2 error message format is shown in Figure 4: 1215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1216 ~ ~ 1217 | L2 IP Header of | 1218 | error message | 1219 ~ ~ 1220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1221 | L2 ICMP Header | 1222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1223 ~ ~ P 1224 | IP and other encapsulation | a 1225 | headers of original L3 packet | c 1226 ~ ~ k 1227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1228 ~ ~ t 1229 | IP header of | 1230 | original L3 packet | i 1231 ~ ~ n 1232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1233 ~ ~ e 1234 | Upper layer headers and | r 1235 | leading portion of body | r 1236 | of the original L3 packet | o 1237 ~ ~ r 1238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1240 Figure 4: AERO Interface L2 Error Message Format 1242 The AERO node rules for processing these L2 error messages is as 1243 follows: 1245 o When an AERO node receives an L2 Parameter Problem message, it 1246 processes the message the same as described as for ordinary ICMP 1247 errors in the normative references [RFC0792][RFC4443]. 1249 o When an AERO node receives persistent L2 IPv4 Time Exceeded 1250 messages, the IP ID field may be wrapping before earlier fragments 1251 have been processed. In that case, the node SHOULD begin 1252 including IPv4 integrity checks (see: Section 3.13.2). 1254 o When an AERO Client receives persistent L2 Destination Unreachable 1255 messages in response to tunneled packets that it sends to one of 1256 its dynamic neighbor correspondents, the Client SHOULD test the 1257 path to the correspondent using Neighbor Unreachability Detection 1258 (NUD) (see Section 3.18). If NUD fails, the Client SHOULD set 1259 ForwardTime for the corresponding dynamic neighbor cache entry to 1260 0 and allow future packets destined to the correspondent to flow 1261 through a Server. 1263 o When an AERO Client receives persistent L2 Destination Unreachable 1264 messages in response to tunneled packets that it sends to one of 1265 its static neighbor Servers, the Client SHOULD test the path to 1266 the Server using NUD. If NUD fails, the Client SHOULD delete the 1267 neighbor cache entry and attempt to associate with a new Server. 1269 o When an AERO Server receives persistent L2 Destination Unreachable 1270 messages in response to tunneled packets that it sends to one of 1271 its static neighbor Clients, the Server SHOULD test the path to 1272 the Client using NUD. If NUD fails, the Server SHOULD cancel the 1273 DHCPv6 PD for the Client's ACP, withdraw its route for the ACP 1274 from the AERO routing system and delete the neighbor cache entry 1275 (see Section 3.18 and Section 3.19). 1277 o When an AERO Relay or Server receives an L2 Destination 1278 Unreachable message in response to a tunneled packet that it sends 1279 to one of its permanent neighbors, it discards the message since 1280 the routing system is likely in a temporary transitional state 1281 that will soon re-converge. 1283 o When an AERO node receives an L2 PTB message, it translates the 1284 message into an L3 PTB message if possible (*) and forwards the 1285 message toward the original source as described below. 1287 To translate an L2 PTB message to an L3 PTB message, the AERO node 1288 first caches the MTU field value of the L2 ICMP header. The node 1289 next discards the L2 IP and ICMP headers, and also discards the 1290 encapsulation headers of the original L3 packet. Next the node 1291 encapsulates the included segment of the original L3 packet in an L3 1292 IP and ICMP header, and sets the ICMP header Type and Code values to 1293 appropriate values for the L3 IP protocol. In the process, the node 1294 writes the maximum of 1500 bytes and (L2 MTU - ENCAPS) into the MTU 1295 field of the L3 ICMP header. 1297 The node next writes the IP source address of the original L3 packet 1298 as the destination address of the L3 PTB message and determines the 1299 next hop to the destination. If the next hop is reached via the AERO 1300 interface, the node uses the IPv6 address "::" or the IPv4 address 1301 "0.0.0.0" as the IP source address of the L3 PTB message. Otherwise, 1302 the node uses one of its non link-local addresses as the source 1303 address of the L3 PTB message. The node finally calculates the ICMP 1304 checksum over the L3 PTB message and writes the Checksum in the 1305 corresponding field of the L3 ICMP header. The L3 PTB message 1306 therefore is formatted as follows: 1308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1309 ~ ~ 1310 | L3 IP Header of | 1311 | error message | 1312 ~ ~ 1313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1314 | L3 ICMP Header | 1315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1316 ~ ~ p 1317 | IP header of | k 1318 | original L3 packet | t 1319 ~ ~ 1320 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i 1321 ~ ~ n 1322 | Upper layer headers and | 1323 | leading portion of body | e 1324 | of the original L3 packet | r 1325 ~ ~ r 1326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1328 Figure 5: AERO Interface L3 Error Message Format 1330 After the node has prepared the L3 PTB message, it either forwards 1331 the message via a link outside of the AERO interface without 1332 encapsulation, or encapsulates and forwards the message to the next 1333 hop via the AERO interface. 1335 When an AERO Relay receives an L3 packet for which the destination 1336 address is covered by an ASP, if there is no more-specific routing 1337 information for the destination the Relay drops the packet and 1338 returns an L3 Destination Unreachable message. The Relay first 1339 writes the IP source address of the original L3 packet as the 1340 destination address of the L3 Destination Unreachable message and 1341 determines the next hop to the destination. If the next hop is 1342 reached via the AERO interface, the Relay uses the IPv6 address "::" 1343 or the IPv4 address "0.0.0.0" as the IP source address of the L3 1344 Destination Unreachable message and forwards the message to the next 1345 hop within the AERO interface. Otherwise, the Relay uses one of its 1346 non link-local addresses as the source address of the L3 Destination 1347 Unreachable message and forwards the message via a link outside the 1348 AERO interface. 1350 When an AERO node receives any L3 error message via the AERO 1351 interface, it examines the destination address in the L3 IP header of 1352 the message. If the next hop toward the destination address of the 1353 error message is via the AERO interface, the node re-encapsulates and 1354 forwards the message to the next hop within the AERO interface. 1355 Otherwise, if the source address in the L3 IP header of the message 1356 is the IPv6 address "::" or the IPv4 address "0.0.0.0", the node 1357 writes one of its non link-local addresses as the source address of 1358 the L3 message and recalculates the IP and/or ICMP checksums. The 1359 node finally forwards the message via a link outside of the AERO 1360 interface. 1362 (*) Note that in some instances the packet-in-error field of an L2 1363 PTB message may not include enough information for translation to an 1364 L3 PTB message. In that case, the AERO interface simply discards the 1365 L2 PTB message. It can therefore be said that translation of L2 PTB 1366 messages to L3 PTB messages can provide a useful optimization when 1367 possible, but is not critical for sources that correctly use PLPMTUD. 1369 3.15. AERO Router Discovery, Prefix Delegation and Address 1370 Configuration 1372 3.15.1. AERO DHCPv6 Service Model 1374 Each AERO Server configures a DHCPv6 server function to facilitate PD 1375 requests from Clients. Each Server is provisioned with a database of 1376 ACP-to-Client ID mappings for all Clients enrolled in the AERO 1377 system, as well as any information necessary to authenticate each 1378 Client. The Client database is maintained by a central 1379 administrative authority for the AERO link and securely distributed 1380 to all Servers, e.g., via the Lightweight Directory Access Protocol 1381 (LDAP) [RFC4511] or a similar distributed database service. 1383 Therefore, no Server-to-Server DHCPv6 PD delegation state 1384 synchronization is necessary, and Clients can optionally hold 1385 separate delegations for the same ACP from multiple Servers. In this 1386 way, Clients can associate with multiple Servers, and can receive new 1387 delegations from new Servers before deprecating delegations received 1388 from existing Servers. 1390 AERO Clients and Servers exchange Client link-layer address 1391 information using an option format similar to the Client Link Layer 1392 Address Option (CLLAO) defined in [RFC6939]. Due to practical 1393 limitations of CLLAO, however, AERO interfaces instead use Vendor- 1394 Specific Information Options as described in the following sections. 1396 3.15.2. AERO Client Behavior 1398 AERO Clients discover the link-layer addresses of AERO Servers via 1399 static configuration, or through an automated means such as DNS name 1400 resolution. In the absence of other information, the Client resolves 1401 the FQDN "linkupnetworks.[domainname]" where "linkupnetworks" is a 1402 constant text string and "[domainname]" is the connection-specific 1403 DNS suffix for the Client's underlying network connection (e.g., 1404 "example.com"). After discovering the link-layer addresses, the 1405 Client associates with one or more of the corresponding Servers. 1407 To associate with a Server, the Client acts as a requesting router to 1408 request an ACP through a two-message (i.e., Request/Reply) DHCPv6 PD 1409 exchange [RFC3315][RFC3633]. The Client's Request message includes 1410 fe80::ffff:ffff:ffff:ffff as the IPv6 source address, 1411 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address 1412 and the link-layer address of the Server as the link-layer 1413 destination address. The Request message also includes a Client 1414 Identifier option with a DHCP Unique Identifier (DUID) and an 1415 Identity Association for Prefix Delegation (IA_PD) option. If the 1416 Client is pre-provisioned with an ACP associated with the AERO 1417 service, it MAY also include the ACP in the IA_PD to indicate its 1418 preference to the DHCPv6 server. 1420 The Client also SHOULD include an AERO Link-registration Request 1421 (ALREQ) option to register one or more links with the Server. The 1422 Server will include an AERO Link-registration Reply (ALREP) option in 1423 the corresponding DHCPv6 Reply message as specified in 1424 Section 3.15.3. (The Client MAY omit the ALREQ option, in which case 1425 the Server will still include an ALREP option in its Reply with "Link 1426 ID" set to 0, "DSCP" set to 0, and "Prf" set to 3.) 1428 The format for the ALREQ option is shown in Figure 6: 1430 0 1 2 3 1431 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 1432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1433 | OPTION_VENDOR_OPTS | option-len (1) | 1434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1435 | enterprise-number = 45282 | 1436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1437 | opt-code = OPTION_ALREQ (0) | option-len (2) | 1438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1439 | Link ID | DSCP #1 |Prf| DSCP #2 |Prf| ... 1440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1442 Figure 6: AERO Link-registration Request (ALREQ) Option 1444 In the above format, the Client sets 'option-code' to 1445 OPTION_VENDOR_OPTS, sets 'option-len (1)' to the length of the option 1446 following this field, sets 'enterprise-number' to 45282 (see: "IANA 1447 Considerations"), sets opt-code to the value 0 ("OPTION_ALREQ") and 1448 sets 'option-len (2)' to the length of the remainder of the option. 1449 The Client includes appropriate 'Link ID, 'DSCP' and 'Prf' values for 1450 the underlying interface over which the DHCPv6 PD Request will be 1451 issued the same as specified for an S/TLLAO Section 3.4. The Client 1452 MAY include multiple (DSCP, Prf) values with this Link ID, with the 1453 number of values indicated by option-len (2). The Server will 1454 register each value with the Link ID in the Client's neighbor cache 1455 entry. The Client finally includes any necessary authentication 1456 options to identify itself to the DHCPv6 server, and sends the 1457 encapsulated DHCPv6 PD Request via the underlying interface 1458 corresponding to Link ID. (Note that this implies that the Client 1459 must perform additional Renew/Reply DHCPv6 exchanges with the server 1460 following the initial Request/Reply using different underlying 1461 interfaces and their corresponding Link IDs if it wishes to register 1462 additional link-layer addresses and their associated DSCPs.) 1464 When the Client receives its ACP via a DHCPv6 Reply from the AERO 1465 Server, it creates a static neighbor cache entry with the Server's 1466 link-local address as the network-layer address and the Server's 1467 encapsulation address as the link-layer address. The Client then 1468 considers the link-layer address of the Server as the primary default 1469 encapsulation address for forwarding packets for which no more- 1470 specific forwarding information is available. The Client further 1471 caches any ASPs included in the ALREP option as ASPs to apply to the 1472 AERO link. 1474 Next, the Client autoconfigures an AERO address from the delegated 1475 ACP, assigns the AERO address to the AERO interface and sub-delegates 1476 the ACP to its attached EUNs and/or the Client's own internal virtual 1477 interfaces. The Client also assigns a default IP route to the AERO 1478 interface as a route-to-interface, i.e., with no explicit next-hop. 1479 The Client can then determine the correct next hops for packets 1480 submitted to the AERO interface by inspecting the neighbor cache. 1482 The Client subsequently renews its ACP delegation through each of its 1483 Servers by performing DHCPv6 Renew/Reply exchanges with the link- 1484 layer address of a Server as the link-layer destination address and 1485 the same options that were used in the initial PD request. Note that 1486 if the Client does not issue a DHCPv6 Renew before the delegation 1487 expires (e.g., if the Client has been out of touch with the Server 1488 for a considerable amount of time) it must re-initiate the DHCPv6 PD 1489 procedure. 1491 Since the Client's AERO address is obtained from the unique ACP 1492 delegation it receives, there is no need for Duplicate Address 1493 Detection (DAD) on AERO links. Other nodes maliciously attempting to 1494 hijack an authorized Client's AERO address will be denied access to 1495 the network by the DHCPv6 server due to an unacceptable link-layer 1496 address and/or security parameters (see: Security Considerations). 1498 3.15.2.1. Autoconfiguration for Constrained Platforms 1500 On some platforms (e.g., popular cell phone operating systems), the 1501 act of assigning a default IPv6 route and/or assigning an address to 1502 an interface may not be permitted from a user application due to 1503 security policy. Typically, those platforms include a TUN/TAP 1504 interface that acts as a point-to-point conduit between user 1505 applications and the AERO interface. In that case, the Client can 1506 instead generate a "synthesized RA" message. The message conforms to 1507 [RFC4861] and is prepared as follows: 1509 o the IPv6 source address is the Client's AERO address 1511 o the IPv6 destination address is all-nodes multicast 1513 o the Router Lifetime is set to a time that is no longer than the 1514 ACP DHCPv6 lifetime 1516 o the message does not include a Source Link Layer Address Option 1517 (SLLAO) 1519 o the message includes a Prefix Information Option (PIO) with a /64 1520 prefix taken from the ACP as the prefix for autoconfiguration 1522 The Client then sends the synthesized RA message via the TUN/TAP 1523 interface, where the operating system kernel will interpret it as 1524 though it were generated by an actual router. The operating system 1525 will then install a default route and use StateLess Address 1526 AutoConfiguration (SLAAC) to configure an IPv6 address on the TUN/TAP 1527 interface. Methods for similarly installing an IPv4 default route 1528 and IPv4 address on the TUN/TAP interface are based on synthesized 1529 DHCPv4 messages [RFC2131]. 1531 3.15.2.2. Client DHCPv6 Message Source Address 1533 In the initial DHCPv6 PD message exchanges, AERO Clients use the 1534 special IPv6 source address 'fe80::ffff:ffff:ffff:ffff' since their 1535 AERO addresses are not yet configured. After AERO address 1536 autoconfiguration, however, AERO Clients can either continue to use 1537 'fe80::ffff:ffff:ffff:ffff' as the source address for further DHCPv6 1538 messaging or begin using their AERO address as the source address. 1540 3.15.3. AERO Server Behavior 1542 AERO Servers configure a DHCPv6 server function on their AERO links. 1543 AERO Servers arrange to add their encapsulation layer IP addresses 1544 (i.e., their link-layer addresses) to the DNS resource records for 1545 the FQDN "linkupnetworks.[domainname]" before entering service. 1547 When an AERO Server receives a prospective Client's DHCPv6 PD Request 1548 on its AERO interface, it first authenticates the message. If 1549 authentication succeeds, the Server determines the correct ACP to 1550 delegate to the Client by searching the Client database. In 1551 environments where spoofing is not considered a threat, the Server 1552 MAY use the Client's DUID as the identification value. Otherwise, 1553 the Server SHOULD use a signed certificate provided by the Client. 1555 When the Server delegates the ACP, it also creates an IP forwarding 1556 table entry so that the AERO routing system will propagate the ACP to 1557 all Relays (see: Section 3.7). Next, the Server prepares a DHCPv6 1558 Reply message to send to the Client while using fe80::ID as the IPv6 1559 source address, the link-local address taken from the Client's 1560 Request as the IPv6 destination address, the Server's link-layer 1561 address as the source link-layer address, and the Client's link-layer 1562 address as the destination link-layer address. The server also 1563 includes an IA_PD option with the delegated ACP. 1565 The Server also includes an ALREP option that includes the UDP Port 1566 Number and IP Address values it observed when it received the ALREQ 1567 in the Client's original DHCPv6 message (if present) followed by the 1568 ASP(s) for the AERO link. The ALREP option is formatted as shown in 1569 Figure 7: 1571 0 1 2 3 1572 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 1573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1574 | OPTION_VENDOR_OPTS | option-len (1) | 1575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1576 | enterprise-number = 45282 | 1577 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1578 | opt-code = OPTION_ALREP (1) | option-len (2) | 1579 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1580 | Link ID | Reserved | UDP Port Number | 1581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1582 | | 1583 + + 1584 | | 1585 + IP Address + 1586 | | 1587 + + 1588 | | 1589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1590 | | 1591 + AERO Service Prefix (ASP) #1 +-+-+-+-+-+-+-+-+ 1592 | | Prefix Len | 1593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1594 | | 1595 + AERO Service Prefix (ASP) #2 +-+-+-+-+-+-+-+-+ 1596 | | Prefix Len | 1597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1598 ~ ~ 1599 ~ ~ 1601 Figure 7: AERO Link-registration Reply (ALREP) Option 1603 In the ALREP, the Server sets 'option-code' to OPTION_VENDOR_OPTS, 1604 sets 'option-length (1)' to the length of the option, sets 1605 'enterprise-number' to 45282 (see: "IANA Considerations"), sets opt- 1606 code to OPTION_ALREP (1), and sets 'option-len (2)' to the length of 1607 the remainder of the option. Next, the Server sets 'Link ID' to the 1608 same value that appeared in the ALREQ, sets Reserved to 0 and sets 1609 'UDP Port Number' and 'IP address' to the Client's link-layer 1610 address. The Server next includes one or more ASP with the IP prefix 1611 as it would appear in the interface identifier portion of the 1612 corresponding AERO address (see: Section 3.3), except that the low- 1613 order 8 bits of the ASP field encode the prefix length instead of the 1614 low-order 8 bits of the prefix. The longest prefix that can 1615 therefore appear as an ASP is /56 for IPv6 or /24 for IPv4. (Note 1616 that if the Client did not include an ALREQ option in its DHCPv6 1617 message, the Server MUST still include an ALREP option in the 1618 corresponding reply with 'Link ID' set to 0.) 1620 When the Server admits the DHCPv6 Reply message into the AERO 1621 interface, it creates a static neighbor cache entry for the Client's 1622 AERO address with lifetime set to no more than the delegation 1623 lifetime and the Client's link-layer address as the link-layer 1624 address for the Link ID specified in the ALREQ. The Server then uses 1625 the Client link-layer address information in the ALREQ option as the 1626 link-layer address for encapsulation based on the (DSCP, Prf) 1627 information. 1629 After the initial DHCPv6 PD exchange, the AERO Server maintains the 1630 neighbor cache entry for the Client until the delegation lifetime 1631 expires. If the Client issues a Renew/Reply exchange, the Server 1632 extends the lifetime. If the Client issues a Release/Reply, or if 1633 the Client does not issue a Renew/Reply before the lifetime expires, 1634 the Server deletes the neighbor cache entry for the Client and 1635 withdraws the IP route from the AERO routing system. 1637 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1639 AERO Clients and Servers are always on the same link (i.e., the AERO 1640 link) from the perspective of DHCPv6. However, in some 1641 implementations the DHCPv6 server and AERO interface driver may be 1642 located in separate modules. In that case, the Server's AERO 1643 interface driver module acts as a Lightweight DHCPv6 Relay Agent 1644 (LDRA)[RFC6221] to relay DHCPv6 messages to and from the DHCPv6 1645 server module. 1647 When the LDRA receives a DHCPv6 message from a client, it prepares an 1648 ALREP option the same as described above then wraps the option in a 1649 Relay-Supplied DHCP Option option (RSOO) [RFC6422]. The LDRA then 1650 incorporates the option into the Relay-Forward message and forwards 1651 the message to the DHCPv6 server. 1653 When the DHCPv6 server receives the Relay-Forward message, it caches 1654 the ALREP option and authenticates the encapsulated DHCPv6 message. 1655 The DHCPv6 server subsequently ignores the ALREQ option itself, since 1656 the relay has already included the ALREP option. 1658 When the DHCPv6 server prepares a Reply message, it then includes the 1659 ALREP option in the body of the message along with any other options, 1660 then wraps the message in a Relay-Reply message. The DHCPv6 server 1661 then delivers the Relay-Reply message to the LDRA, which discards the 1662 Relay-Reply wrapper and delivers the DHCPv6 message to the Client. 1664 3.15.4. Deleting Link Registrations 1666 After an AERO Client registers its Link IDs and their associated 1667 (DSCP,Prf) values with the AERO Server, the Client may wish to delete 1668 one or more Link registrations, e.g., if an underlying link becomes 1669 unavailable. To do so, the Client prepares a DHCPv6 Renew message 1670 that includes an AERO Link-registration Delete (ALDEL) option and 1671 sends the Renew message to the Server over any available underlying 1672 link. The ALDEL option is formatted as shown in Figure 8: 1674 0 1 2 3 1675 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 1676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1677 | OPTION_VENDOR_OPTS | option-len (1) | 1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1679 | enterprise-number = 45282 | 1680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1681 | opt-code = OPTION_ALDEL (2) | option-len (2) | 1682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1683 | Link ID #1 | Link ID #2 | Link ID #3 | ... 1684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1686 Figure 8: AERO Link-registration Delete (ALDEL) Option 1688 In the ALDEL, the Client sets 'option-code' to OPTION_VENDOR_OPTS, 1689 sets 'option-length (1)' to the length of the option, sets 1690 'enterprise-number' to 45282 (see: "IANA Considerations"), sets 1691 optcode to OPTION_ALDEL (2), and sets 'option-len (2)' to the length 1692 of the remainder of the option. Next, the Server includes each 'Link 1693 ID' value that it wishes to delete. 1695 If the Client wishes to discontinue use of a Server and thereby 1696 delete all of its Link ID associations, it must use a DHCPv6 Release/ 1697 Reply exchange to delete the entire neighbor cache entry, i.e., 1698 instead of using a DHCPv6 Renew/Reply exchange with one or more ALDEL 1699 options. 1701 3.16. AERO Forwarding Agent Behavior 1703 AERO Servers MAY associate with one or more companion AERO Forwarding 1704 Agents as platforms for offloading high-speed data plane traffic. 1705 When an AERO Server receives a Client's DHCPv6 Request/Renew/Rebind/ 1706 Release message, it services the message then forwards the 1707 corresponding Reply message to the Forwarding Agent. When the 1708 Forwarding Agent receives the Reply message, it creates or updates a 1709 neighbor cache entry with the Client's AERO address and link-layer 1710 information included in the Reply message. The Forwarding Agent then 1711 forwards the Reply message back to the AERO Server, which forwards 1712 the message to the Client. In this way, Forwarding Agent state is 1713 managed in conjunction with Server state, with the Client responsible 1714 for reliability. If the Client subsequently disappears without 1715 issuing a Release, the Server is responsible for purging the 1716 Forwarding Agent state by sending synthesized Reply messages. 1718 When an AERO Server receives a data packet on an AERO interface with 1719 a network layer destination address for which it has distributed 1720 forwarding information to a Forwarding Agent, the Server returns a 1721 Redirect message to the source neighbor (subject to rate limiting) 1722 then forwards the data packet as usual. The Redirect message 1723 includes a TLLAO with the link-layer address of the Forwarding 1724 Engine. 1726 When the source neighbor receives the Redirect message, it SHOULD 1727 record the link-layer address in the TLLAO as the encapsulation 1728 addresses to use for sending subsequent data packets. However, the 1729 source MUST continue to use the primary link-layer address of the 1730 Server as the encapsulation address for sending control messages. 1732 3.17. AERO Intradomain Route Optimization 1734 When a source Client forwards packets to a prospective correspondent 1735 Client within the same AERO link domain (i.e., one for which the 1736 packet's destination address is covered by an ASP), the source Client 1737 initiates an intra-domain AERO route optimization procedure. The 1738 procedure is based on an exchange of IPv6 ND messages using a chain 1739 of AERO Servers and Relays as a trust basis. This procedure is in 1740 contrast to the Return Routability procedure required for route 1741 optimization to a correspondent Client located in the Internet as 1742 described in Section 3.22. The following sections specify the AERO 1743 intradomain route optimization procedure. 1745 3.17.1. Reference Operational Scenario 1747 Figure 9 depicts the AERO intradomain route optimization reference 1748 operational scenario, using IPv6 addressing as the example (while not 1749 shown, a corresponding example for IPv4 addressing can be easily 1750 constructed). The figure shows an AERO Relay ('R1'), two AERO 1751 Servers ('S1', 'S2'), two AERO Clients ('C1', 'C2') and two ordinary 1752 IPv6 hosts ('H1', 'H2'): 1754 +--------------+ +--------------+ +--------------+ 1755 | Server S1 | | Relay R1 | | Server S2 | 1756 +--------------+ +--------------+ +--------------+ 1757 fe80::2 fe80::1 fe80::3 1758 L2(S1) L2(R1) L2(S2) 1759 | | | 1760 X-----+-----+------------------+-----------------+----+----X 1761 | AERO Link | 1762 L2(A) L2(B) 1763 fe80::2001:db8:0:0 fe80::2001:db8:1:0 1764 +--------------+ +--------------+ 1765 |AERO Client C1| |AERO Client C2| 1766 +--------------+ +--------------+ 1767 2001:DB8:0::/48 2001:DB8:1::/48 1768 | | 1769 .-. .-. 1770 ,-( _)-. 2001:db8:0::1 2001:db8:1::1 ,-( _)-. 1771 .-(_ IP )-. +---------+ +---------+ .-(_ IP )-. 1772 (__ EUN )--| Host H1 | | Host H2 |--(__ EUN ) 1773 `-(______)-' +---------+ +---------+ `-(______)-' 1775 Figure 9: AERO Reference Operational Scenario 1777 In Figure 9, Relay ('R1') assigns the address fe80::1 to its AERO 1778 interface with link-layer address L2(R1), Server ('S1') assigns the 1779 address fe80::2 with link-layer address L2(S1),and Server ('S2') 1780 assigns the address fe80::3 with link-layer address L2(S2). Servers 1781 ('S1') and ('S2') next arrange to add their link-layer addresses to a 1782 published list of valid Servers for the AERO link. 1784 AERO Client ('C1') receives the ACP 2001:db8:0::/48 in a DHCPv6 PD 1785 exchange via AERO Server ('S1') then assigns the address 1786 fe80::2001:db8:0:0 to its AERO interface with link-layer address 1787 L2(C1). Client ('C1') configures a default route and neighbor cache 1788 entry via the AERO interface with next-hop address fe80::2 and link- 1789 layer address L2(S1), then sub-delegates the ACP to its attached 1790 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1791 address 2001:db8:0::1. 1793 AERO Client ('C2') receives the ACP 2001:db8:1::/48 in a DHCPv6 PD 1794 exchange via AERO Server ('S2') then assigns the address 1795 fe80::2001:db8:1:0 to its AERO interface with link-layer address 1796 L2(C2). Client ('C2') configures a default route and neighbor cache 1797 entry via the AERO interface with next-hop address fe80::3 and link- 1798 layer address L2(S2), then sub-delegates the ACP to its attached 1799 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1800 address 2001:db8:1::1. 1802 3.17.2. Concept of Operations 1804 Again, with reference to Figure 9, when source host ('H1') sends a 1805 packet to destination host ('H2'), the packet is first forwarded over 1806 the source host's attached EUN to Client ('C1'). Client ('C1') then 1807 forwards the packet via its AERO interface to Server ('S1') and also 1808 sends a Predirect message toward Client ('C2') via Server ('S1'). 1809 Server ('S1') then re-encapsulates and forwards both the packet and 1810 the Predirect message out the same AERO interface toward Client 1811 ('C2') via Relay ('R1'). 1813 When Relay ('R1') receives the packet and Predirect message, it 1814 consults its forwarding table to discover Server ('S2') as the next 1815 hop toward Client ('C2'). Relay ('R1') then forwards both the packet 1816 and the Predirect message to Server ('S2'), which then forwards them 1817 to Client ('C2'). 1819 After Client ('C2') receives the Predirect message, it process the 1820 message and returns a Redirect message toward Client ('C1') via 1821 Server ('S2'). During the process, Client ('C2') also creates or 1822 updates a dynamic neighbor cache entry for Client ('C1'). 1824 When Server ('S2') receives the Redirect message, it re-encapsulates 1825 the message and forwards it on to Relay ('R1'), which forwards the 1826 message on to Server ('S1') which forwards the message on to Client 1827 ('C1'). After Client ('C1') receives the Redirect message, it 1828 processes the message and creates or updates a dynamic neighbor cache 1829 entry for Client ('C2'). 1831 Following the above Predirect/Redirect message exchange, forwarding 1832 of packets from Client ('C1') to Client ('C2') without involving any 1833 intermediate nodes is enabled. The mechanisms that support this 1834 exchange are specified in the following sections. 1836 3.17.3. Message Format 1838 AERO Redirect/Predirect messages use the same format as for ICMPv6 1839 Redirect messages depicted in Section 4.5 of [RFC4861], but also 1840 include a new "Prefix Length" field taken from the low-order 8 bits 1841 of the Redirect message Reserved field. For IPv6, valid values for 1842 the Prefix Length field are 0 through 64; for IPv4, valid values are 1843 0 through 32. The Redirect/Predirect messages are formatted as shown 1844 in Figure 10: 1846 0 1 2 3 1847 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 1848 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1849 | Type (=137) | Code (=0/1) | Checksum | 1850 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1851 | Reserved | Prefix Length | 1852 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1853 | | 1854 + + 1855 | | 1856 + Target Address + 1857 | | 1858 + + 1859 | | 1860 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1861 | | 1862 + + 1863 | | 1864 + Destination Address + 1865 | | 1866 + + 1867 | | 1868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1869 | Options ... 1870 +-+-+-+-+-+-+-+-+-+-+-+- 1872 Figure 10: AERO Redirect/Predirect Message Format 1874 3.17.4. Sending Predirects 1876 When a Client forwards a packet with a source address from one of its 1877 ACPs toward a destination address covered by an ASP (i.e., toward 1878 another AERO Client connected to the same AERO link), the source 1879 Client MAY send a Predirect message forward toward the destination 1880 Client via the Server. 1882 In the reference operational scenario, when Client ('C1') forwards a 1883 packet toward Client ('C2'), it MAY also send a Predirect message 1884 forward toward Client ('C2'), subject to rate limiting (see 1885 Section 8.2 of [RFC4861]). Client ('C1') prepares the Predirect 1886 message as follows: 1888 o the link-layer source address is set to 'L2(C1)' (i.e., the link- 1889 layer address of Client ('C1')). 1891 o the link-layer destination address is set to 'L2(S1)' (i.e., the 1892 link-layer address of Server ('S1')). 1894 o the network-layer source address is set to fe80::2001:db8:0:0 1895 (i.e., the AERO address of Client ('C1')). 1897 o the network-layer destination address is set to fe80::2001:db8:1:0 1898 (i.e., the AERO address of Client ('C2')). 1900 o the Type is set to 137. 1902 o the Code is set to 1 to indicate "Predirect". 1904 o the Prefix Length is set to the length of the prefix to be 1905 assigned to the Target Address. 1907 o the Target Address is set to fe80::2001:db8:0:0 (i.e., the AERO 1908 address of Client ('C1')). 1910 o the Destination Address is set to the source address of the 1911 originating packet that triggered the Predirection event. (If the 1912 originating packet is an IPv4 packet, the address is constructed 1913 in IPv4-compatible IPv6 address format). 1915 o the message includes one or more TLLAOs with Link ID and DSCPs set 1916 to appropriate values for Client ('C1')'s underlying interfaces, 1917 and with UDP Port Number and IP Address set to 0'. 1919 o the message SHOULD include a Timestamp option and a Nonce option. 1921 o the message includes a Redirected Header Option (RHO) that 1922 contains the originating packet truncated if necessary to ensure 1923 that at least the network-layer header is included but the size of 1924 the message does not exceed 1280 bytes. 1926 Note that the act of sending Predirect messages is cited as "MAY", 1927 since Client ('C1') may have advanced knowledge that the direct path 1928 to Client ('C2') would be unusable or otherwise undesirable. If the 1929 direct path later becomes unusable after the initial route 1930 optimization, Client ('C1') simply allows packets to again flow 1931 through Server ('S1'). 1933 3.17.5. Re-encapsulating and Relaying Predirects 1935 When Server ('S1') receives a Predirect message from Client ('C1'), 1936 it first verifies that the TLLAOs in the Predirect are a proper 1937 subset of the Link IDs in Client ('C1')'s neighbor cache entry. If 1938 the Client's TLLAOs are not acceptable, Server ('S1') discards the 1939 message. Otherwise, Server ('S1') validates the message according to 1940 the ICMPv6 Redirect message validation rules in Section 8.1 of 1941 [RFC4861], except that the Predirect has Code=1. Server ('S1') also 1942 verifies that Client ('C1') is authorized to use the Prefix Length in 1943 the Predirect when applied to the AERO address in the network-layer 1944 source address by searching for the AERO address in the neighbor 1945 cache. If validation fails, Server ('S1') discards the Predirect; 1946 otherwise, it copies the correct UDP Port numbers and IP Addresses 1947 for Client ('C1')'s links into the (previously empty) TLLAOs. 1949 Server ('S1') then examines the network-layer destination address of 1950 the Predirect to determine the next hop toward Client ('C2') by 1951 searching for the AERO address in the neighbor cache. Since Client 1952 ('C2') is not one of its neighbors, Server ('S1') re-encapsulates the 1953 Predirect and relays it via Relay ('R1') by changing the link-layer 1954 source address of the message to 'L2(S1)' and changing the link-layer 1955 destination address to 'L2(R1)'. Server ('S1') finally forwards the 1956 re-encapsulated message to Relay ('R1') without decrementing the 1957 network-layer TTL/Hop Limit field. 1959 When Relay ('R1') receives the Predirect message from Server ('S1') 1960 it determines that Server ('S2') is the next hop toward Client ('C2') 1961 by consulting its forwarding table. Relay ('R1') then re- 1962 encapsulates the Predirect while changing the link-layer source 1963 address to 'L2(R1)' and changing the link-layer destination address 1964 to 'L2(S2)'. Relay ('R1') then relays the Predirect via Server 1965 ('S2'). 1967 When Server ('S2') receives the Predirect message from Relay ('R1') 1968 it determines that Client ('C2') is a neighbor by consulting its 1969 neighbor cache. Server ('S2') then re-encapsulates the Predirect 1970 while changing the link-layer source address to 'L2(S2)' and changing 1971 the link-layer destination address to 'L2(C2)'. Server ('S2') then 1972 forwards the message to Client ('C2'). 1974 3.17.6. Processing Predirects and Sending Redirects 1976 When Client ('C2') receives the Predirect message, it accepts the 1977 Predirect only if the message has a link-layer source address of one 1978 of its Servers (e.g., L2(S2)). Client ('C2') further accepts the 1979 message only if it is willing to serve as a redirection target. 1980 Next, Client ('C2') validates the message according to the ICMPv6 1981 Redirect message validation rules in Section 8.1 of [RFC4861], except 1982 that it accepts the message even though Code=1 and even though the 1983 network-layer source address is not that of it's current first-hop 1984 router. 1986 In the reference operational scenario, when Client ('C2') receives a 1987 valid Predirect message, it either creates or updates a dynamic 1988 neighbor cache entry that stores the Target Address of the message as 1989 the network-layer address of Client ('C1') , stores the link-layer 1990 addresses found in the TLLAOs as the link-layer addresses of Client 1991 ('C1') and stores the Prefix Length as the length to be applied to 1992 the network-layer address for forwarding purposes. Client ('C2') 1993 then sets AcceptTime for the neighbor cache entry to ACCEPT_TIME. 1995 After processing the message, Client ('C2') prepares a Redirect 1996 message response as follows: 1998 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 1999 layer address of Client ('C2')). 2001 o the link-layer destination address is set to 'L2(S2)' (i.e., the 2002 link-layer address of Server ('S2')). 2004 o the network-layer source address is set to fe80::2001:db8:1:0 2005 (i.e., the AERO address of Client ('C2')). 2007 o the network-layer destination address is set to fe80::2001:db8:0:0 2008 (i.e., the AERO address of Client ('C1')). 2010 o the Type is set to 137. 2012 o the Code is set to 0 to indicate "Redirect". 2014 o the Prefix Length is set to the length of the prefix to be applied 2015 to the Target Address. 2017 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 2018 address of Client ('C2')). 2020 o the Destination Address is set to the destination address of the 2021 originating packet that triggered the Redirection event. (If the 2022 originating packet is an IPv4 packet, the address is constructed 2023 in IPv4-compatible IPv6 address format). 2025 o the message includes one or more TLLAOs with Link ID and DSCPs set 2026 to appropriate values for Client ('C2')'s underlying interfaces, 2027 and with UDP Port Number and IP Address set to '0'. 2029 o the message SHOULD include a Timestamp option and MUST echo the 2030 Nonce option received in the Predirect (i.e., if a Nonce option is 2031 included). 2033 o the message includes as much of the RHO copied from the 2034 corresponding AERO Predirect message as possible such that at 2035 least the network-layer header is included but the size of the 2036 message does not exceed 1280 bytes. 2038 After Client ('C2') prepares the Redirect message, it sends the 2039 message to Server ('S2'). 2041 3.17.7. Re-encapsulating and Relaying Redirects 2043 When Server ('S2') receives a Redirect message from Client ('C2'), it 2044 first verifies that the TLLAOs in the Redirect are a proper subset of 2045 the Link IDs in Client ('C2')'s neighbor cache entry. If the 2046 Client's TLLAOs are not acceptable, Server ('S2') discards the 2047 message. Otherwise, Server ('S2') validates the message according to 2048 the ICMPv6 Redirect message validation rules in Section 8.1 of 2049 [RFC4861]. Server ('S2') also verifies that Client ('C2') is 2050 authorized to use the Prefix Length in the Redirect when applied to 2051 the AERO address in the network-layer source address by searching for 2052 the AERO address in the neighbor cache. If validation fails, Server 2053 ('S2') discards the Predirect; otherwise, it copies the correct UDP 2054 Port numbers and IP Addresses for Client ('C2')'s links into the 2055 (previously empty) TLLAOs. 2057 Server ('S2') then examines the network-layer destination address of 2058 the Predirect to determine the next hop toward Client ('C2') by 2059 searching for the AERO address in the neighbor cache. Since Client 2060 ('C2') is not a neighbor, Server ('S2') re-encapsulates the Predirect 2061 and relays it via Relay ('R1') by changing the link-layer source 2062 address of the message to 'L2(S2)' and changing the link-layer 2063 destination address to 'L2(R1)'. Server ('S2') finally forwards the 2064 re-encapsulated message to Relay ('R1') without decrementing the 2065 network-layer TTL/Hop Limit field. 2067 When Relay ('R1') receives the Predirect message from Server ('S2') 2068 it determines that Server ('S1') is the next hop toward Client ('C1') 2069 by consulting its forwarding table. Relay ('R1') then re- 2070 encapsulates the Predirect while changing the link-layer source 2071 address to 'L2(R1)' and changing the link-layer destination address 2072 to 'L2(S1)'. Relay ('R1') then relays the Predirect via Server 2073 ('S1'). 2075 When Server ('S1') receives the Predirect message from Relay ('R1') 2076 it determines that Client ('C1') is a neighbor by consulting its 2077 neighbor cache. Server ('S1') then re-encapsulates the Predirect 2078 while changing the link-layer source address to 'L2(S1)' and changing 2079 the link-layer destination address to 'L2(C1)'. Server ('S1') then 2080 forwards the message to Client ('C1'). 2082 3.17.8. Processing Redirects 2084 When Client ('C1') receives the Redirect message, it accepts the 2085 message only if it has a link-layer source address of one of its 2086 Servers (e.g., ''L2(S1)'). Next, Client ('C1') validates the message 2087 according to the ICMPv6 Redirect message validation rules in 2088 Section 8.1 of [RFC4861], except that it accepts the message even 2089 though the network-layer source address is not that of it's current 2090 first-hop router. Following validation, Client ('C1') then processes 2091 the message as follows. 2093 In the reference operational scenario, when Client ('C1') receives 2094 the Redirect message, it either creates or updates a dynamic neighbor 2095 cache entry that stores the Target Address of the message as the 2096 network-layer address of Client ('C2'), stores the link-layer 2097 addresses found in the TLLAOs as the link-layer addresses of Client 2098 ('C2') and stores the Prefix Length as the length to be applied to 2099 the network-layer address for forwarding purposes. Client ('C1') 2100 then sets ForwardTime for the neighbor cache entry to FORWARD_TIME. 2102 Now, Client ('C1') has a neighbor cache entry with a valid 2103 ForwardTime value, while Client ('C2') has a neighbor cache entry 2104 with a valid AcceptTime value. Thereafter, Client ('C1') may forward 2105 ordinary network-layer data packets directly to Client ('C2') without 2106 involving any intermediate nodes, and Client ('C2') can verify that 2107 the packets came from an acceptable source. (In order for Client 2108 ('C2') to forward packets to Client ('C1'), a corresponding 2109 Predirect/Redirect message exchange is required in the reverse 2110 direction; hence, the mechanism is asymmetric.) 2112 3.17.9. Server-Oriented Redirection 2114 In some environments, the Server nearest the target Client may need 2115 to serve as the redirection target, e.g., if direct Client-to-Client 2116 communications are not possible. In that case, the Server prepares 2117 the Redirect message the same as if it were the destination Client 2118 (see: Section 3.17.6), except that it writes its own link-layer 2119 address in the TLLAO option. The Server must then maintain a dynamic 2120 neighbor cache entry for the redirected source Client. 2122 3.18. Neighbor Unreachability Detection (NUD) 2124 AERO nodes perform Neighbor Unreachability Detection (NUD) by sending 2125 unicast NS messages to elicit solicited NA messages from neighbors 2126 the same as described in [RFC4861]. NUD is performed either 2127 reactively in response to persistent L2 errors (see Section 3.14) or 2128 proactively to refresh existing neighbor cache entries. 2130 When an AERO node sends an NS/NA message, it MUST use its link-local 2131 address as the IPv6 source address and the link-local address of the 2132 neighbor as the IPv6 destination address. When an AERO node receives 2133 an NS message or a solicited NA message, it accepts the message if it 2134 has a neighbor cache entry for the neighbor; otherwise, it ignores 2135 the message. 2137 When a source Client is redirected to a target Client it SHOULD 2138 proactively test the direct path by sending an initial NS message to 2139 elicit a solicited NA response. While testing the path, the source 2140 Client can optionally continue sending packets via the Server, 2141 maintain a small queue of packets until target reachability is 2142 confirmed, or (optimistically) allow packets to flow directly to the 2143 target. The source Client SHOULD thereafter continue to proactively 2144 test the direct path to the target Client (see Section 7.3 of 2145 [RFC4861]) periodically in order to keep dynamic neighbor cache 2146 entries alive. 2148 In particular, while the source Client is actively sending packets to 2149 the target Client it SHOULD also send NS messages separated by 2150 RETRANS_TIMER milliseconds in order to receive solicited NA messages. 2151 If the source Client is unable to elicit a solicited NA response from 2152 the target Client after MAX_RETRY attempts, it SHOULD set ForwardTime 2153 to 0 and resume sending packets via one of its Servers. Otherwise, 2154 the source Client considers the path usable and SHOULD thereafter 2155 process any link-layer errors as a hint that the direct path to the 2156 target Client has either failed or has become intermittent. 2158 When a target Client receives an NS message from a source Client, it 2159 resets AcceptTime to ACCEPT_TIME if a neighbor cache entry exists; 2160 otherwise, it discards the NS message. If ForwardTime is non-zero, 2161 the target Client then sends a solicited NA message to the link-layer 2162 address of the source Client; otherwise, it sends the solicited NA 2163 message to the link-layer address of one of its Servers. 2165 When a source Client receives a solicited NA message from a target 2166 Client, it resets ForwardTime to FORWARD_TIME if a neighbor cache 2167 entry exists; otherwise, it discards the NA message. 2169 When ForwardTime for a dynamic neighbor cache entry expires, the 2170 source Client resumes sending any subsequent packets via a Server and 2171 may (eventually) attempt to re-initiate the AERO redirection process. 2172 When AcceptTime for a dynamic neighbor cache entry expires, the 2173 target Client discards any subsequent packets received directly from 2174 the source Client. When both ForwardTime and AcceptTime for a 2175 dynamic neighbor cache entry expire, the Client deletes the neighbor 2176 cache entry. 2178 3.19. Mobility Management 2180 3.19.1. Announcing Link-Layer Address Changes 2182 When a Client needs to change its link-layer address, e.g., due to a 2183 mobility event, it performs an immediate DHCPv6 Rebind/Reply exchange 2184 via each of its Servers using the new link-layer address as the 2185 source address and with an ALREQ that includes the correct Link ID 2186 and DSCP values. If authentication succeeds, the Server then update 2187 its neighbor cache and sends a DHCPv6 Reply. Note that if the Client 2188 does not issue a DHCPv6 Rebind before the prefix delegation lifetime 2189 expires (e.g., if the Client has been out of touch with the Server 2190 for a considerable amount of time), the Server's Reply will report 2191 NoBinding and the Client must re-initiate the DHCPv6 PD procedure. 2193 Next, the Client sends unsolicited NA messages to each of its 2194 correspondent Client neighbors using the same procedures as specified 2195 in Section 7.2.6 of [RFC4861], except that it sends the messages as 2196 unicast to each neighbor via a Server instead of multicast. In this 2197 process, the Client should send no more than 2198 MAX_NEIGHBOR_ADVERTISEMENT messages separated by no less than 2199 RETRANS_TIMER seconds to each neighbor. 2201 With reference to Figure 9, when Client ('C2') needs to change its 2202 link-layer address it sends unicast unsolicited NA messages to Client 2203 ('C1') via Server ('S2') as follows: 2205 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 2206 layer address of Client ('C2')). 2208 o the link-layer destination address is set to 'L2(S2)' (i.e., the 2209 link-layer address of Server ('S2')). 2211 o the network-layer source address is set to fe80::2001:db8:1:0 2212 (i.e., the AERO address of Client ('C2')). 2214 o the network-layer destination address is set to fe80::2001:db8:0:0 2215 (i.e., the AERO address of Client ('C1')). 2217 o the Type is set to 136. 2219 o the Code is set to 0. 2221 o the Solicited flag is set to 0. 2223 o the Override flag is set to 1. 2225 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 2226 address of Client ('C2')). 2228 o the message includes one or more TLLAOs with Link ID and DSCPs set 2229 to appropriate values for Client ('C2')'s underlying interfaces, 2230 and with UDP Port Number and IP Address set to '0'. 2232 o the message SHOULD include a Timestamp option. 2234 When Server ('S1') receives the NA message, it relays the message in 2235 the same way as described for relaying Redirect messages in 2236 Section 3.17.7. In particular, Server ('S1') copies the correct UDP 2237 port numbers and IP addresses into the TLLAOs, changes the link-layer 2238 source address to its own address, changes the link-layer destination 2239 address to the address of Relay ('R1'), then forwards the NA message 2240 via the relaying chain the same as for a Redirect. 2242 When Client ('C1') receives the NA message, it accepts the message 2243 only if it already has a neighbor cache entry for Client ('C2') then 2244 updates the link-layer addresses for Client ('C2') based on the 2245 addresses in the TLLAOs. Next, Client ('C1') SHOULD initiate the NUD 2246 procedures specified in Section 3.18 to provide Client ('C2') with an 2247 indication that the link-layer source address has been updated, and 2248 to refresh ('C2')'s AcceptTime and ('C1')'s ForwardTime timers. 2250 If Client ('C2') receives an NS message from Client ('C1') indicating 2251 that an unsolicited NA has updated its neighbor cache, Client ('C2') 2252 need not send additional unsolicited NAs. If Client ('C2')'s 2253 unsolicited NA messages are somehow lost, however, Client ('C1') will 2254 soon learn of the mobility event via NUD. 2256 3.19.2. Bringing New Links Into Service 2258 When a Client needs to bring a new underlying interface into service 2259 (e.g., when it activates a new data link), it performs an immediate 2260 Renew/Reply exchange via each of its Servers using the new link-layer 2261 address as the source address and with an ALREQ that includes the new 2262 Link ID and DSCP values. If authentication succeeds, the Server then 2263 updates its neighbor cache and sends a DHCPv6 Reply. The Client MAY 2264 then send unsolicited NA messages to each of its correspondent 2265 Clients to inform them of the new link-layer address as described in 2266 Section 3.19.1. 2268 3.19.3. Removing Existing Links from Service 2270 When a Client needs to remove an existing underlying interface from 2271 service (e.g., when it de-activates an existing data link), it 2272 performs an immediate Renew/Reply exchange via each of its Servers 2273 over any available link with an ALDEL that includes the deprecated 2274 Link ID. If authentication succeeds, the Server then updates its 2275 neighbor cache and sends a DHCPv6 Reply. The Client SHOULD then send 2276 unsolicited NA messages to each of its correspondent Clients to 2277 inform them of the deprecated link-layer address as described in 2278 Section 3.19.1. 2280 3.19.4. Moving to a New Server 2282 When a Client associates with a new Server, it performs the Client 2283 procedures specified in Section 3.15.2. 2285 When a Client disassociates with an existing Server, it sends a 2286 DHCPv6 Release message via a new Server to the unicast link-local 2287 network layer address of the old Server. The new Server then writes 2288 its own link-layer address in the DHCPv6 Release message IP source 2289 address and forwards the message to the old Server. 2291 When the old Server receives the DHCPv6 Release, it first 2292 authenticates the message. The Server then resets the Client's 2293 neighbor cache entry lifetime to 5 seconds, rewrites the link-layer 2294 address in the neighbor cache entry to the address of the new Server, 2295 then returns a DHCPv6 Reply message to the Client via the old Server. 2296 When the lifetime expires, the old Server withdraws the IP route from 2297 the AERO routing system and deletes the neighbor cache entry for the 2298 Client. The Client can then use the Reply message to verify that the 2299 termination signal has been processed, and can delete both the 2300 default route and the neighbor cache entry for the old Server. (Note 2301 that since Release/Reply messages may be lost in the network the 2302 Client MUST retry until it gets Reply indicating that the Release was 2303 successful.) 2305 Clients SHOULD NOT move rapidly between Servers in order to avoid 2306 causing excessive oscillations in the AERO routing system. Such 2307 oscillations could result in intermittent reachability for the Client 2308 itself, while causing little harm to the network. Examples of when a 2309 Client might wish to change to a different Server include a Server 2310 that has gone unreachable, topological movements of significant 2311 distance, etc. 2313 3.20. Proxy AERO 2315 Proxy Mobile IPv6 (PMIPv6) [RFC5213][RFC5844][RFC5949] presents a 2316 localized mobility management scheme for use within an access network 2317 domain. It is typically used in WiFi and cellular wireless access 2318 networks, and allows Mobile Nodes (MNs) to receive and retain an IP 2319 address that remains stable within the access network domain without 2320 needing to implement any special mobility protocols. In the PMIPv6 2321 architecture, access network devices known as Mobility Access 2322 Gateways (MAGs) provide MNs with an access link abstraction and 2323 receive prefixes for the MNs from a Local Mobility Anchor (LMA). 2325 In a proxy AERO domain, a proxy AERO Client (acting as a MAG) can 2326 similarly provide proxy services for MNs that do not participate in 2327 AERO messaging. The proxy Client presents an access link abstraction 2328 to MNs, and performs DHCPv6 PD exchanges over the AERO interface with 2329 an AERO Server (acting as an LMA) to receive ACPs for address 2330 provisioning of new MNs that come onto an access link. This scheme 2331 assumes that proxy Clients act as fixed (non-mobile) infrastructure 2332 elements under the same administrative trust basis as for Relays and 2333 Servers. 2335 When an MN comes onto an access link within a proxy AERO domain for 2336 the first time, the proxy Client authenticates the MN and obtains a 2337 unique identifier that it can use as a DHCPv6 DUID then issues a 2338 DHCPv6 PD Request to its Server. When the Server delegates an ACP, 2339 the proxy Client creates an AERO address for the MN and assigns the 2340 ACP to the MN's access link. The proxy Client then configures itself 2341 as a default router for the MN and provides address autoconfiguration 2342 services (e.g., SLAAC, DHCPv6, DHCPv4, etc.) for provisioning MN 2343 addresses from the ACP over the access link. Since the proxy Client 2344 may serve many such MNs simultaneously, it may receive multiple ACP 2345 prefix delegations and configure multiple AERO addresses, i.e., one 2346 for each MN. 2348 When two MNs are associated with the same proxy Client, the Client 2349 can forward traffic between the MNs without involving a Server since 2350 it configures the AERO addresses of both MNs and therefore also has 2351 the necessary routing information. When two MNs are associated with 2352 different proxy Clients, the source MN's Client can initiate standard 2353 AERO route optimization to discover a direct path to the target MN's 2354 Client through the exchange of Predirect/Redirect messages. 2356 When an MN in a proxy AERO domain leaves an access link provided by 2357 an old proxy Client, the MN issues an access link-specific "leave" 2358 message that informs the old Client of the link-layer address of a 2359 new Client on the planned new access link. This is known as a 2360 "predictive handover". When an MN comes onto an access link provided 2361 by a new proxy Client, the MN issues an access link-specific "join" 2362 message that informs the new Client of the link-layer address of the 2363 old Client on the actual old access link. This is known as a 2364 "reactive handover". 2366 Upon receiving a predictive handover indication, the old proxy Client 2367 sends a DHCPv6 PD Request message directly to the new Client and 2368 queues any arriving data packets addressed to the departed MN. The 2369 Request message includes the MN's ID as the DUID, the ACP in an IA_PD 2370 option, the old Client's address as the link-layer source address and 2371 the new Client's address as the link-layer destination address. When 2372 the new Client receives the Request message, it changes the link- 2373 layer source address to its own address, changes the link-layer 2374 destination address to the address of its Server, and forwards the 2375 message to the Server. At the same time, the new Client creates 2376 access link state for the ACP in anticipation of the MN's arrival 2377 (while queuing any data packets until the MN arrives), creates a 2378 neighbor cache entry for the old Client with AcceptTime set to 2379 ACCEPT_TIME, then sends a Redirect message back to the old Client. 2380 When the old Client receives the Redirect message, it creates a 2381 neighbor cache entry for the new Client with ForwardTime set to 2382 FORWARD_TIME, then forwards any queued data packets to the new 2383 Client. At the same time, the old Client sends a DHCPv6 PD Release 2384 message to its Server. Finally, the old Client sends unsolicited NA 2385 messages to any of the ACP's correspondents with a TLLAO containing 2386 the link-layer address of the new Client. This follows the procedure 2387 specified in Section 3.19.1, except that it is the old Client and not 2388 the Server that supplies the link-layer address. 2390 Upon receiving a reactive handover indication, the new proxy Client 2391 creates access link state for the MN's ACP, sends a DHCPv6 PD Request 2392 message to its Server, and sends a DHCPv6 PD Release message directly 2393 to the old Client. The Release message includes the MN's ID as the 2394 DUID, the ACP in an IA_PD option, the new Client's address as the 2395 link-layer source address and the old Client's address as the link- 2396 layer destination address. When the old Client receives the Release 2397 message, it changes the link-layer source address to its own address, 2398 changes the link-layer destination address to the address of its 2399 Server, and forwards the message to the Server. At the same time, 2400 the old Client sends a Predirect message back to the new Client and 2401 queues any arriving data packets addressed to the departed MN. When 2402 the new Client receives the Predirect, it creates a neighbor cache 2403 entry for the old Client with AcceptTime set to ACCEPT_TIME, then 2404 sends a Redirect message back to the old Client. When the old Client 2405 receives the Redirect message, it creates a neighbor cache entry for 2406 the new Client with ForwardTime set to FORWARD_TIME, then forwards 2407 any queued data packets to the new Client. Finally, the old Client 2408 sends unsolicited NA messages to correspondents the same as for the 2409 predictive case. 2411 When a Server processes a DHCPv6 Request message, it creates a 2412 neighbor cache entry for this ACP if none currently exists. If a 2413 neighbor cache entry already exists, however, the Server changes the 2414 link-layer address to the address of the new proxy Client (this 2415 satisfies the case of both the old Client and new Client using the 2416 same Server). 2418 When a Server processes a DHCPv6 Release message, it resets the 2419 neighbor cache entry lifetime for this ACP to 5 seconds if the cached 2420 link-layer address matches the old proxy Client's address. 2421 Otherwise, the Server ignores the Release message (this satisfies the 2422 case of both the old Client and new Client using the same Server). 2424 When a correspondent Client receives an unsolicited NA message, it 2425 changes the link-layer address for the ACP's neighbor cache entry to 2426 the address of the new proxy Client. The correspondent Client then 2427 issues a Predirect/Redirect exchange to establish a new neighbor 2428 cache entry in the new Client. 2430 From an architectural perspective, in addition to the use of DHCPv6 2431 PD and IPv6 ND signaling the AERO approach differs from PMIPv6 in its 2432 use of the NBMA virtual link model instead of point-to-point tunnels. 2433 This provides a more agile interface for Client/Server and Client/ 2434 Client coordinations, and also facilitates simple route optimization. 2435 The AERO routing system is also arranged in such a fashion that 2436 Clients get the same service from any Server they happen to associate 2437 with. This provides a natural fault tolerance and load balancing 2438 capability such as desired for distributed mobility management. 2440 3.21. Extending AERO Links Through Security Gateways 2442 When an enterprise mobile device moves from a campus LAN connection 2443 to a public Internet link, it must re-enter the enterprise via a 2444 security gateway that has both a physical interface connection to the 2445 Internet and a physical interface connection to the enterprise 2446 internetwork. This most often entails the establishment of a Virtual 2447 Private Network (VPN) link over the public Internet from the mobile 2448 device to the security gateway. During this process, the mobile 2449 device supplies the security gateway with its public Internet address 2450 as the link-layer address for the VPN. The mobile device then acts 2451 as an AERO Client to negotiate with the security gateway to obtain 2452 its ACP. 2454 In order to satisfy this need, the security gateway also operates as 2455 an AERO Server with support for AERO Client proxying. In particular, 2456 when a mobile device (i.e., the Client) connects via the security 2457 gateway (i.e., the Server), the Server provides the Client with an 2458 ACP in a DHCPv6 PD exchange the same as if it were attached to an 2459 enterprise campus access link. The Server then replaces the Client's 2460 link-layer source address with the Server's enterprise-facing link- 2461 layer address in all AERO messages the Client sends toward neighbors 2462 on the AERO link. The AERO messages are then delivered to other 2463 devices on the AERO link as if they were originated by the security 2464 gateway instead of by the AERO Client. In the reverse direction, the 2465 AERO messages sourced by devices within the enterprise network can be 2466 forwarded to the security gateway, which then replaces the link-layer 2467 destination address with the Client's link-layer address and replaces 2468 the link-layer source address with its own (Internet-facing) link- 2469 layer address. 2471 After receiving the ACP, the Client can send IP packets that use an 2472 address taken from the ACP as the network layer source address, the 2473 Client's link-layer address as the link-layer source address, and the 2474 Server's Internet-facing link-layer address as the link-layer 2475 destination address. The Server will then rewrite the link-layer 2476 source address with the Server's own enterprise-facing link-layer 2477 address and rewrite the link-layer destination address with the 2478 target AERO node's link-layer address, and the packets will enter the 2479 enterprise network as though they were sourced from a device located 2480 within the enterprise. In the reverse direction, when a packet 2481 sourced by a node within the enterprise network uses a destination 2482 address from the Client's ACP, the packet will be delivered to the 2483 security gateway which then rewrites the link-layer destination 2484 address to the Client's link-layer address and rewrites the link- 2485 layer source address to the Server's Internet-facing link-layer 2486 address. The Server then delivers the packet across the VPN to the 2487 AERO Client. In this way, the AERO virtual link is essentially 2488 extended *through* the security gateway to the point at which the VPN 2489 link and AERO link are effectively grafted together by the link-layer 2490 address rewriting performed by the security gateway. All AERO 2491 messaging services (including route optimization and mobility 2492 signaling) are therefore extended to the Client. 2494 In order to support this virtual link grafting, the security gateway 2495 (acting as an AERO Server) must keep static neighbor cache entries 2496 for all of its associated Clients located on the public Internet. 2497 The neighbor cache entry is keyed by the AERO Client's AERO address 2498 the same as if the Client were located within the enterprise 2499 internetwork. The neighbor cache is then managed in all ways as 2500 though the Client were an ordinary AERO Client. This includes the 2501 AERO IPv6 ND messaging signaling for Route Optimization and Neighbor 2502 Unreachability Detection. 2504 Note that the main difference between a security gateway acting as an 2505 AERO Server and an enterprise-internal AERO Server is that the 2506 security gateway has at least one enterprise-internal physical 2507 interface and at least one public Internet physical interface. 2508 Conversely, the enterprise-internal AERO Server has only enterprise- 2509 internal physical interfaces. For this reason security gateway 2510 proxying is needed to ensure that the public Internet link-layer 2511 addressing space is kept separate from the enterprise-internal link- 2512 layer addressing space. This is afforded through a natural extension 2513 of the security association caching already performed for each VPN 2514 client by the security gateway. 2516 3.22. Extending IPv6 AERO Links to the Internet 2518 When an IPv6 host ('H1') with an address from an ACP owned by AERO 2519 Client ('C1') sends packets to a correspondent IPv6 host ('H2'), the 2520 packets eventually arrive at the IPv6 router that owns ('H2')s 2521 prefix. This IPv6 router may or may not be an AERO Client ('C2') 2522 either within the same home network as ('C1') or in a different home 2523 network. 2525 If Client ('C1') is currently located outside the boundaries of its 2526 home network, it will connect back into the home network via a 2527 security gateway acting as an AERO Server. The packets sent by 2528 ('H1') via ('C1') will then be forwarded through the security gateway 2529 then through the home network and finally to ('C2') where they will 2530 be delivered to ('H2'). This could lead to sub-optimal performance 2531 when ('C2') could instead be reached via a more direct route without 2532 involving the security gateway. 2534 Consider the case when host ('H1') has the IPv6 address 2535 2001:db8:1::1, and Client ('C1') has the ACP 2001:db8:1::/64 with 2536 underlying IPv6 Internet address of 2001:db8:1000::1. Also, host 2537 ('H2') has the IPv6 address 2001:db8:2::1, and Client ('C2') has the 2538 ACP 2001:db8:2::/64 with underlying IPv6 address of 2001:db8:2000::1. 2539 Client ('C1') can determine whether 'C2' is indeed also an AERO 2540 Client willing to serve as a route optimization correspondent by 2541 resolving the AAAA records for the DNS FQDN that matches ('H2')s 2542 prefix, i.e.: 2544 '0.0.0.0.2.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net' 2546 If ('C2') is indeed a candidate correspondent, the FQDN lookup will 2547 return a PTR resource record that contains the domain name for the 2548 AERO link that manages ('C2')s ASP. Client ('C1') can then attempt 2549 route optimization using an approach similar to the Return 2550 Routability procedure specified for Mobile IPv6 (MIPv6) [RFC6275]. 2551 In order to support this process, both Clients MUST intercept and 2552 decapsulate packets that have a subnet router anycast address 2553 corresponding to any of the /64 prefixes covered by their respective 2554 ACPs. 2556 To initiate the process, Client ('C1') creates a specially-crafted 2557 encapsulated AERO Predirect message that will be routed through its 2558 home network then through ('C2')s home network and finally to ('C2') 2559 itself. Client ('C1') prepares the initial message in the exchange 2560 as follows: 2562 o The encapsulating IPv6 header source address is set to 2563 2001:db8:1:: (i.e., the IPv6 subnet router anycast address for 2564 ('C1')s ACP) 2566 o The encapsulating IPv6 header destination address is set to 2567 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2568 ('C2')s ACP) 2570 o The encapsulating IPv6 header is followed by a UDP header with 2571 source and destination port set to 8060 2573 o The encapsulated IPv6 header source address is set to 2574 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2576 o The encapsulated IPv6 header destination address is set to 2577 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2579 o The encapsulated AERO Predirect message includes all of the 2580 securing information that would occur in a MIPv6 "Home Test Init" 2581 message (format TBD) 2583 Client ('C1') then further encapsulates the message in the 2584 encapsulating headers necessary to convey the packet to the security 2585 gateway (e.g., through IPsec encapsulation) so that the message now 2586 appears "double-encapsulated". ('C1') then sends the message to the 2587 security gateway, which re-encapsulates and forwards it over the home 2588 network from where it will eventually reach ('C2'). 2590 At the same time, ('C1') creates and sends a second encapsulated AERO 2591 Predirect message that will be routed through the IPv6 Internet 2592 without involving the security gateway. Client ('C1') prepares the 2593 message as follows: 2595 o The encapsulating IPv6 header source address is set to 2596 2001:db8:1000:1 (i.e., the Internet IPv6 address of ('C1')) 2598 o The encapsulating IPv6 header destination address is set to 2599 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2600 ('C2')s ACP) 2602 o The encapsulating IPv6 header is followed by a UDP header with 2603 source and destination port set to 8060 2605 o The encapsulated IPv6 header source address is set to 2606 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2608 o The encapsulated IPv6 header destination address is set to 2609 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2611 o The encapsulated AERO Predirect message includes all of the 2612 securing information that would occur in a MIPv6 "Care-of Test 2613 Init" message (format TBD) 2615 ('C2') will receive both Predirect messages through its home network 2616 then return a corresponding Redirect for each of the Predirect 2617 messages with the source and destination addresses in the inner and 2618 outer headers reversed. The first message includes all of the 2619 securing information that would occur in a MIPv6 "Home Test" message, 2620 while the second message includes all of the securing information 2621 that would occur in a MIPv6 "Care-of Test" message (formats TBD). 2623 When ('C1') receives the Redirect messages, it performs the necessary 2624 security procedures per the MIPv6 specification. It then prepares an 2625 encapsulated NS message that includes the same source and destination 2626 addresses as for the "Care-of Test Init" Predirect message, and 2627 includes all of the securing information that would occur in a MIPv6 2628 "Binding Update" message (format TBD) and sends the message to 2629 ('C2'). 2631 When ('C2') receives the NS message, if the securing information is 2632 correct it creates or updates a neighbor cache entry for ('C1') with 2633 fe80::2001:db8:1:0 as the network-layer address, 2001:db8:1000::1 as 2634 the link-layer address and with AcceptTime set to ACCEPT_TIME. 2635 ('C2') then sends an encapsulated NA message back to ('C1') that 2636 includes the same source and destination addresses as for the "Care- 2637 of Test" Redirect message, and includes all of the securing 2638 information that would occur in a MIPv6 "Binding Acknowledgement" 2639 message (format TBD) and sends the message to ('C1'). 2641 When ('C1') receives the NA message, it creates or updates a neighbor 2642 cache entry for ('C2') with fe80::2001:db8:2:0 as the network-layer 2643 address and 2001:db8:2:: as the link-layer address and with 2644 ForwardTime set to FORWARD_TIME, thus completing the route 2645 optimization in the forward direction. 2647 ('C1') subsequently forwards encapsulated packets with outer source 2648 address 2001:db8:1000::1, with outer destination address 2649 2001:db8:2::, with inner source address taken from the 2001:db8:1::, 2650 and with inner destination address taken from 2001:db8:2:: due to the 2651 fact that it has a securely-established neighbor cache entry with 2652 non-zero ForwardTime. ('C2') subsequently accepts any such 2653 encapsulated packets due to the fact that it has a securely- 2654 established neighbor cache entry with non-zero AcceptTime. 2656 In order to keep neighbor cache entries alive, ('C1') periodically 2657 sends additional NS messages to ('C2') and receives any NA responses. 2658 If ('C1') moves to a different point of attachment after the initial 2659 route optimization, it sends a new secured NS message to ('C2') as 2660 above to update ('C2')s neighbor cache. 2662 If ('C2') has packets to send to ('C1'), it performs a corresponding 2663 route optimization in the opposite direction following the same 2664 procedures described above. In the process, the already-established 2665 unidirectional neighbor cache entries within ('C1') and ('C2') are 2666 updated to include the now-bidirectional information. In particular, 2667 the AcceptTime and ForwardTime variables for both neighbor cache 2668 entries are updated to non-zero values, and the link-layer address 2669 for ('C1')s neighbor cache entry for ('C2') is reset to 2670 2001:db8:2000::1. 2672 Note that two AERO Clients can use full security protocol messaging 2673 instead of Return Routability, e.g., if strong authentication and/or 2674 confidentiality are desired. In that case, security protocol key 2675 exchanges such as specified for MOBIKE [RFC4555] would be used to 2676 establish security associations and neighbor cache entries between 2677 the AERO clients. Thereafter, AERO NS/NA messaging can be used to 2678 maintain neighbor cache entries, test reachability, and to announce 2679 mobility events. If reachability testing fails, e.g., if both 2680 Clients move at roughly the same time, the Clients can tear down the 2681 security association and neighbor cache entries and again allow 2682 packets to flow through their home network. 2684 3.23. Encapsulation Protocol Version Considerations 2686 A source Client may connect only to an IPvX underlying network, while 2687 the target Client connects only to an IPvY underlying network. In 2688 that case, the target and source Clients have no means for reaching 2689 each other directly (since they connect to underlying networks of 2690 different IP protocol versions) and so must ignore any redirection 2691 messages and continue to send packets via the Server. 2693 3.24. Multicast Considerations 2695 When the underlying network does not support multicast, AERO nodes 2696 map IPv6 link-scoped multicast addresses (including 2697 'All_DHCP_Relay_Agents_and_Servers') to the link-layer address of a 2698 Server. 2700 When the underlying network supports multicast, AERO nodes use the 2701 multicast address mapping specification found in [RFC2529] for IPv4 2702 underlying networks and use a direct multicast mapping for IPv6 2703 underlying networks. (In the latter case, "direct multicast mapping" 2704 means that if the IPv6 multicast destination address of the 2705 encapsulated packet is "M", then the IPv6 multicast destination 2706 address of the encapsulating header is also "M".) 2708 3.25. Operation on AERO Links Without DHCPv6 Services 2710 When Servers on the AERO link do not provide DHCPv6 services, 2711 operation can still be accommodated through administrative 2712 configuration of ACPs on AERO Clients. In that case, administrative 2713 configurations of AERO interface neighbor cache entries on both the 2714 Server and Client are also necessary. However, this may interfere 2715 with the ability for Clients to dynamically change to new Servers, 2716 and can expose the AERO link to misconfigurations unless the 2717 administrative configurations are carefully coordinated. 2719 3.26. Operation on Server-less AERO Links 2721 In some AERO link scenarios, there may be no Servers on the link and/ 2722 or no need for Clients to use a Server as an intermediary trust 2723 anchor. In that case, each Client acts as a Server unto itself to 2724 establish neighbor cache entries by performing direct Client-to- 2725 Client IPv6 ND message exchanges, and some other form of trust basis 2726 must be applied so that each Client can verify that the prospective 2727 neighbor is authorized to use its claimed ACP. 2729 When there is no Server on the link, Clients must arrange to receive 2730 ACPs and publish them via a secure alternate prefix delegation 2731 authority through some means outside the scope of this document. 2733 3.27. Manually-Configured AERO Tunnels 2735 In addition to the dynamic neighbor discovery procedures for AERO 2736 link neighbors described above, AERO encapsulation can be applied to 2737 manually-configured tunnels. In that case, the tunnel endpoints use 2738 an administratively-assigned link-local address and exchange NS/NA 2739 messages the same as for dynamically-established tunnels. 2741 3.28. Intradomain Routing 2743 After a tunnel neighbor relationship has been established, neighbors 2744 can use a traditional dynamic routing protocol over the tunnel to 2745 exchange routing information without having to inject the routes into 2746 the AERO routing system. 2748 4. Implementation Status 2750 User-level and kernel-level AERO implementations have been developed 2751 and are undergoing internal testing within Boeing. 2753 5. Next Steps 2755 A new Generic UDP Encapsulation (GUE) format has been specified in 2756 [I-D.herbert-gue-fragmentation] [I-D.ietf-nvo3-gue]. The GUE 2757 encapsulation format will eventually supplant the native AERO UDP 2758 encapsulation format. 2760 Future versions of the spec will explore the subject of DSCP marking 2761 in more detail. 2763 6. IANA Considerations 2765 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2766 AERO in the "enterprise-numbers" registry. 2768 The IANA has assigned the UDP port number "8060" for an earlier 2769 experimental version of AERO [RFC6706]. This document obsoletes 2770 [RFC6706] and claims the UDP port number "8060" for all future use. 2772 No further IANA actions are required. 2774 7. Security Considerations 2776 AERO link security considerations are the same as for standard IPv6 2777 Neighbor Discovery [RFC4861] except that AERO improves on some 2778 aspects. In particular, AERO uses a trust basis between Clients and 2779 Servers, where the Clients only engage in the AERO mechanism when it 2780 is facilitated by a trust anchor. Unless there is some other means 2781 of authenticating the Client's identity (e.g., link-layer security), 2782 AERO nodes SHOULD also use DHCPv6 securing services (e.g., DHCPv6 2783 authentication, Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6], etc.) for 2784 Client authentication and network admission control. 2786 AERO Redirect, Predirect and unsolicited NA messages SHOULD include a 2787 Timestamp option (see Section 5.3 of [RFC3971]) that other AERO nodes 2788 can use to verify the message time of origin. AERO Predirect, NS and 2789 RS messages SHOULD include a Nonce option (see Section 5.3 of 2790 [RFC3971]) that recipients echo back in corresponding responses. 2792 AERO links must be protected against link-layer address spoofing 2793 attacks in which an attacker on the link pretends to be a trusted 2794 neighbor. Links that provide link-layer securing mechanisms (e.g., 2795 IEEE 802.1X WLANs) and links that provide physical security (e.g., 2796 enterprise network wired LANs) provide a first line of defense that 2797 is often sufficient. In other instances, additional securing 2798 mechanisms such as Secure Neighbor Discovery (SeND) [RFC3971], IPsec 2799 [RFC4301] or TLS [RFC5246] may be necessary. 2801 AERO Clients MUST ensure that their connectivity is not used by 2802 unauthorized nodes on their EUNs to gain access to a protected 2803 network, i.e., AERO Clients that act as routers MUST NOT provide 2804 routing services for unauthorized nodes. (This concern is no 2805 different than for ordinary hosts that receive an IP address 2806 delegation but then "share" the address with unauthorized nodes via a 2807 NAT function.) 2809 On some AERO links, establishment and maintenance of a direct path 2810 between neighbors requires secured coordination such as through the 2811 Internet Key Exchange (IKEv2) protocol [RFC5996] to establish a 2812 security association. 2814 An AERO Client's link-layer address could be rewritten by a link- 2815 layer switching element on the path from the Client to the Server and 2816 not detected by the DHCPv6 security mechanism. However, such a 2817 condition would only be a matter of concern on unmanaged/unsecured 2818 links where the link-layer switching elements themselves present a 2819 man-in-the-middle attack threat. For this reason, IP security MUST 2820 be used when AERO is employed over unmanaged/unsecured links. 2822 8. Acknowledgements 2824 Discussions both on IETF lists and in private exchanges helped shape 2825 some of the concepts in this work. Individuals who contributed 2826 insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, 2827 Stewart Bryant, Brian Carpenter, Wojciech Dec, Ralph Droms, Adrian 2828 Farrel, Sri Gundavelli, Brian Haberman, Joel Halpern, Tom Herbert, 2829 Sascha Hlusiak, Lee Howard, Andre Kostur, Ted Lemon, Andy Malis, 2830 Satoru Matsushima, Tomek Mrugalski, Behcet Saikaya, Joe Touch, Bernie 2831 Volz, Ryuji Wakikawa and Lloyd Wood. Members of the IESG also 2832 provided valuable input during their review process that greatly 2833 improved the document. Special thanks go to Stewart Bryant, Joel 2834 Halpern and Brian Haberman for their shepherding guidance. 2836 This work has further been encouraged and supported by Boeing 2837 colleagues including Dave Bernhardt, Cam Brodie, Balaguruna 2838 Chidambaram, Bruce Cornish, Claudiu Danilov, Wen Fang, Anthony 2839 Gregory, Jeff Holland, Ed King, Gen MacLean, Rob Muszkiewicz, Sean 2840 O'Sullivan, Kent Shuey, Brian Skeen, Mike Slane, Brendan Williams, 2841 Julie Wulff, Yueli Yang, and other members of the BR&T and BIT mobile 2842 networking teams. 2844 Earlier works on NBMA tunneling approaches are found in 2845 [RFC2529][RFC5214][RFC5569]. 2847 Many of the constructs presented in this second edition of AERO are 2848 based on the author's earlier works, including: 2850 o The Internet Routing Overlay Network (IRON) 2851 [RFC6179][I-D.templin-ironbis] 2853 o Virtual Enterprise Traversal (VET) 2854 [RFC5558][I-D.templin-intarea-vet] 2856 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2857 [RFC5320][I-D.templin-intarea-seal] 2859 o AERO, First Edition [RFC6706] 2861 Note that these works cite numerous earlier efforts that are not also 2862 cited here due to space limitations. The authors of those earlier 2863 works are acknowledged for their insights. 2865 9. References 2867 9.1. Normative References 2869 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2870 August 1980. 2872 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 2873 1981. 2875 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2876 RFC 792, September 1981. 2878 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 2879 October 1996. 2881 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2882 Requirement Levels", BCP 14, RFC 2119, March 1997. 2884 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2885 (IPv6) Specification", RFC 2460, December 1998. 2887 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2888 IPv6 Specification", RFC 2473, December 1998. 2890 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2891 "Definition of the Differentiated Services Field (DS 2892 Field) in the IPv4 and IPv6 Headers", RFC 2474, December 2893 1998. 2895 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2896 and M. Carney, "Dynamic Host Configuration Protocol for 2897 IPv6 (DHCPv6)", RFC 3315, July 2003. 2899 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2900 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2901 December 2003. 2903 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2904 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2906 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 2907 for IPv6 Hosts and Routers", RFC 4213, October 2005. 2909 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2910 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2911 September 2007. 2913 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2914 Address Autoconfiguration", RFC 4862, September 2007. 2916 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 2917 Requirements", RFC 6434, December 2011. 2919 9.2. Informative References 2921 [I-D.herbert-gue-fragmentation] 2922 Herbert, T. and F. Templin, "Fragmentation option for 2923 Generic UDP Encapsulation", draft-herbert-gue- 2924 fragmentation-00 (work in progress), March 2015. 2926 [I-D.ietf-dhc-sedhcpv6] 2927 Jiang, S., Shen, S., Zhang, D., and T. Jinmei, "Secure 2928 DHCPv6", draft-ietf-dhc-sedhcpv6-07 (work in progress), 2929 March 2015. 2931 [I-D.ietf-nvo3-gue] 2932 Herbert, T., Yong, L., and O. Zia, "Generic UDP 2933 Encapsulation", draft-ietf-nvo3-gue-00 (work in progress), 2934 April 2015. 2936 [I-D.templin-intarea-seal] 2937 Templin, F., "The Subnetwork Encapsulation and Adaptation 2938 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 2939 progress), January 2014. 2941 [I-D.templin-intarea-vet] 2942 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 2943 templin-intarea-vet-40 (work in progress), May 2013. 2945 [I-D.templin-ironbis] 2946 Templin, F., "The Interior Routing Overlay Network 2947 (IRON)", draft-templin-ironbis-16 (work in progress), 2948 March 2014. 2950 [I-D.vandevelde-idr-remote-next-hop] 2951 Velde, G., Patel, K., Rao, D., Raszuk, R., and R. Bush, 2952 "BGP Remote-Next-Hop", draft-vandevelde-idr-remote-next- 2953 hop-09 (work in progress), March 2015. 2955 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 2956 RFC 879, November 1983. 2958 [RFC1035] Mockapetris, P., "Domain names - implementation and 2959 specification", STD 13, RFC 1035, November 1987. 2961 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2962 November 1990. 2964 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 2965 1812, June 1995. 2967 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 2968 selection, and registration of an Autonomous System (AS)", 2969 BCP 6, RFC 1930, March 1996. 2971 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 2972 for IP version 6", RFC 1981, August 1996. 2974 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2975 2131, March 1997. 2977 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2978 Domains without Explicit Tunnels", RFC 2529, March 1999. 2980 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 2981 RFC 2675, August 1999. 2983 [RFC2764] Gleeson, B., Heinanen, J., Lin, A., Armitage, G., and A. 2984 Malis, "A Framework for IP Based Virtual Private 2985 Networks", RFC 2764, February 2000. 2987 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 2988 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 2989 March 2000. 2991 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 2992 2923, September 2000. 2994 [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 2995 2983, October 2000. 2997 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 2998 of Explicit Congestion Notification (ECN) to IP", RFC 2999 3168, September 2001. 3001 [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, 3002 "DNS Extensions to Support IP Version 6", RFC 3596, 3003 October 2003. 3005 [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., 3006 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3007 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3008 RFC 3819, July 2004. 3010 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 3011 Protocol 4 (BGP-4)", RFC 4271, January 2006. 3013 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3014 Architecture", RFC 4291, February 2006. 3016 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3017 Internet Protocol", RFC 4301, December 2005. 3019 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 3020 Message Protocol (ICMPv6) for the Internet Protocol 3021 Version 6 (IPv6) Specification", RFC 4443, March 2006. 3023 [RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol 3024 (LDAP): The Protocol", RFC 4511, June 2006. 3026 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 3027 (MOBIKE)", RFC 4555, June 2006. 3029 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 3030 System", RFC 4592, July 2006. 3032 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 3033 Discovery", RFC 4821, March 2007. 3035 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3036 Errors at High Data Rates", RFC 4963, July 2007. 3038 [RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski, 3039 "DHCPv6 Relay Agent Echo Request Option", RFC 4994, 3040 September 2007. 3042 [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., 3043 and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. 3045 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3046 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3047 March 2008. 3049 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3050 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 3052 [RFC5320] Templin, F., "The Subnetwork Encapsulation and Adaptation 3053 Layer (SEAL)", RFC 5320, February 2010. 3055 [RFC5494] Arkko, J. and C. Pignataro, "IANA Allocation Guidelines 3056 for the Address Resolution Protocol (ARP)", RFC 5494, 3057 April 2009. 3059 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3060 Route Optimization Requirements for Operational Use in 3061 Aeronautics and Space Exploration Mobile Networks", RFC 3062 5522, October 2009. 3064 [RFC5558] Templin, F., "Virtual Enterprise Traversal (VET)", RFC 3065 5558, February 2010. 3067 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3068 Infrastructures (6rd)", RFC 5569, January 2010. 3070 [RFC5720] Templin, F., "Routing and Addressing in Networks with 3071 Global Enterprise Recursion (RANGER)", RFC 5720, February 3072 2010. 3074 [RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy 3075 Mobile IPv6", RFC 5844, May 2010. 3077 [RFC5949] Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F. 3078 Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949, 3079 September 2010. 3081 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 3082 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 3083 5996, September 2010. 3085 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3086 NAT64: Network Address and Protocol Translation from IPv6 3087 Clients to IPv4 Servers", RFC 6146, April 2011. 3089 [RFC6179] Templin, F., "The Internet Routing Overlay Network 3090 (IRON)", RFC 6179, March 2011. 3092 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 3093 Troan, "Basic Requirements for IPv6 Customer Edge 3094 Routers", RFC 6204, April 2011. 3096 [RFC6221] Miles, D., Ooghe, S., Dec, W., Krishnan, S., and A. 3097 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, May 3098 2011. 3100 [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A. 3101 Bierman, "Network Configuration Protocol (NETCONF)", RFC 3102 6241, June 2011. 3104 [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support 3105 in IPv6", RFC 6275, July 2011. 3107 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3108 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, August 3109 2011. 3111 [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", RFC 3112 6422, December 2011. 3114 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3115 for Equal Cost Multipath Routing and Link Aggregation in 3116 Tunnels", RFC 6438, November 2011. 3118 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 3119 RFC 6691, July 2012. 3121 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 3122 (AERO)", RFC 6706, August 2012. 3124 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3125 RFC 6864, February 2013. 3127 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3128 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 3130 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3131 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3132 RFC 6936, April 2013. 3134 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 3135 Address Option in DHCPv6", RFC 6939, May 2013. 3137 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 3138 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 3140 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 3141 Address Selection Policy Using DHCPv6", RFC 7078, January 3142 2014. 3144 [TUNTAP] Wikipedia, W., "http://en.wikipedia.org/wiki/TUN/TAP", 3145 October 2014. 3147 Author's Address 3149 Fred L. Templin (editor) 3150 Boeing Research & Technology 3151 P.O. Box 3707 3152 Seattle, WA 98124 3153 USA 3155 Email: fltemplin@acm.org