idnits 2.17.1 draft-templin-aerolink-50.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == The 'Obsoletes: ' line in the draft header should list only the _numbers_ of the RFCs which will be obsoleted by this document (if approved); it should not include the word 'RFC' in the list. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 810 has weird spacing: '...Version a 4-b...' -- The document date (December 22, 2014) is 3413 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'I-D.taylor-v6ops-fragdrop' is mentioned on line 954, but not defined == Unused Reference: 'RFC0768' is defined on line 2709, but no explicit reference was found in the text == Unused Reference: 'RFC4862' is defined on line 2748, but no explicit reference was found in the text == Unused Reference: 'RFC0879' is defined on line 2780, but no explicit reference was found in the text == Unused Reference: 'RFC4994' is defined on line 2860, but no explicit reference was found in the text == Unused Reference: 'RFC5720' is defined on line 2892, but no explicit reference was found in the text == Unused Reference: 'RFC6146' is defined on line 2907, but no explicit reference was found in the text == Unused Reference: 'RFC6204' is defined on line 2914, but no explicit reference was found in the text == Unused Reference: 'RFC6355' is defined on line 2925, but no explicit reference was found in the text == Unused Reference: 'RFC6691' is defined on line 2933, but no explicit reference was found in the text == Unused Reference: 'RFC6980' is defined on line 2952, but no explicit reference was found in the text == Unused Reference: 'RFC7078' is defined on line 2955, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 3633 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 6434 (Obsoleted by RFC 8504) == Outdated reference: A later version (-21) exists of draft-ietf-dhc-sedhcpv6-05 == Outdated reference: A later version (-09) exists of draft-vandevelde-idr-remote-next-hop-08 -- Obsolete informational reference (is this intentional?): RFC 879 (Obsoleted by RFC 7805, RFC 9293) -- Obsolete informational reference (is this intentional?): RFC 1981 (Obsoleted by RFC 8201) -- Obsolete informational reference (is this intentional?): RFC 5246 (Obsoleted by RFC 8446) -- Obsolete informational reference (is this intentional?): RFC 5996 (Obsoleted by RFC 7296) -- Obsolete informational reference (is this intentional?): RFC 6204 (Obsoleted by RFC 7084) -- Obsolete informational reference (is this intentional?): RFC 6691 (Obsoleted by RFC 9293) Summary: 4 errors (**), 0 flaws (~~), 17 warnings (==), 7 comments (--). 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, December 22, 2014 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: June 25, 2015 10 Transmission of IP Packets over AERO Links 11 draft-templin-aerolink-50.txt 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). Nodes attached 17 to AERO links can exchange packets via trusted intermediate routers 18 that provide forwarding services to reach off-link destinations and 19 redirection services for route optimization. AERO provides an IPv6 20 link-local address format known as the AERO address that supports 21 operation of the IPv6 Neighbor Discovery (ND) protocol and links IPv6 22 ND to IP forwarding. Admission control and provisioning are 23 supported by the Dynamic Host Configuration Protocol for IPv6 24 (DHCPv6), and node mobility is naturally supported through dynamic 25 neighbor cache updates. Although DHCPv6 and IPv6 ND messaging is 26 used in the control plane, both IPv4 and IPv6 are supported in the 27 data plane. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on June 25, 2015. 46 Copyright Notice 48 Copyright (c) 2014 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 6 66 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 6 67 3.2. AERO Link Node Types . . . . . . . . . . . . . . . . . . 7 68 3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 8 69 3.4. AERO Interface Characteristics . . . . . . . . . . . . . 9 70 3.5. AERO Link Registration . . . . . . . . . . . . . . . . . 11 71 3.6. AERO Interface Initialization . . . . . . . . . . . . . . 11 72 3.6.1. AERO Relay Behavior . . . . . . . . . . . . . . . . . 11 73 3.6.2. AERO Server Behavior . . . . . . . . . . . . . . . . 12 74 3.6.3. AERO Client Behavior . . . . . . . . . . . . . . . . 12 75 3.6.4. AERO Forwarding Agent Behavior . . . . . . . . . . . 13 76 3.7. AERO Link Routing System . . . . . . . . . . . . . . . . 13 77 3.8. AERO Interface Neighbor Cache Maintenace . . . . . . . . 14 78 3.9. AERO Interface Sending Algorithm . . . . . . . . . . . . 15 79 3.10. AERO Interface Encapsulation and Re-encapsulation . . . . 17 80 3.11. AERO Interface Decapsulation . . . . . . . . . . . . . . 19 81 3.12. AERO Interface Data Origin Authentication . . . . . . . . 19 82 3.13. AERO Interface MTU and Fragmentation . . . . . . . . . . 20 83 3.13.1. Accommodating Large Control Messages . . . . . . . . 23 84 3.13.2. Integrity . . . . . . . . . . . . . . . . . . . . . 23 85 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 25 86 3.15. AERO Router Discovery, Prefix Delegation and Address 87 Configuration . . . . . . . . . . . . . . . . . . . . . . 29 88 3.15.1. AERO DHCPv6 Service Model . . . . . . . . . . . . . 29 89 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 29 90 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 32 91 3.16. AERO Forwarding Agent Discovery . . . . . . . . . . . . . 34 92 3.17. AERO Intradomain Route Optimization . . . . . . . . . . . 34 93 3.17.1. Reference Operational Scenario . . . . . . . . . . . 35 94 3.17.2. Concept of Operations . . . . . . . . . . . . . . . 36 95 3.17.3. Message Format . . . . . . . . . . . . . . . . . . . 36 96 3.17.4. Sending Predirects . . . . . . . . . . . . . . . . . 37 97 3.17.5. Re-encapsulating and Relaying Predirects . . . . . . 39 98 3.17.6. Processing Predirects and Sending Redirects . . . . 39 99 3.17.7. Re-encapsulating and Relaying Redirects . . . . . . 41 100 3.17.8. Processing Redirects . . . . . . . . . . . . . . . . 42 101 3.17.9. Server-Oriented Redirection . . . . . . . . . . . . 42 102 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 43 103 3.19. Mobility Management . . . . . . . . . . . . . . . . . . . 44 104 3.19.1. Announcing Link-Layer Address Changes . . . . . . . 44 105 3.19.2. Bringing New Links Into Service . . . . . . . . . . 45 106 3.19.3. Removing Existing Links from Service . . . . . . . . 46 107 3.19.4. Moving to a New Server . . . . . . . . . . . . . . . 46 108 3.20. Proxy AERO . . . . . . . . . . . . . . . . . . . . . . . 47 109 3.21. Extending AERO Links Through Security Gateways . . . . . 49 110 3.22. Extending IPv6 AERO Links to the Internet . . . . . . . . 51 111 3.23. Encapsulation Protocol Version Considerations . . . . . . 54 112 3.24. Multicast Considerations . . . . . . . . . . . . . . . . 55 113 3.25. Operation on AERO Links Without DHCPv6 Services . . . . . 55 114 3.26. Operation on Server-less AERO Links . . . . . . . . . . . 55 115 3.27. Manually-Configured AERO Tunnels . . . . . . . . . . . . 55 116 3.28. Intradomain Routing . . . . . . . . . . . . . . . . . . . 56 117 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 56 118 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 56 119 6. Security Considerations . . . . . . . . . . . . . . . . . . . 56 120 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 57 121 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 58 122 8.1. Normative References . . . . . . . . . . . . . . . . . . 58 123 8.2. Informative References . . . . . . . . . . . . . . . . . 59 124 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 63 126 1. Introduction 128 This document specifies the operation of IP over tunnel virtual links 129 using Asymmetric Extended Route Optimization (AERO). The AERO link 130 can be used for tunneling to neighboring nodes over either IPv6 or 131 IPv4 networks, i.e., AERO views the IPv6 and IPv4 networks as 132 equivalent links for tunneling. Nodes attached to AERO links can 133 exchange packets via trusted intermediate routers that provide 134 forwarding services to reach off-link destinations and redirection 135 services for route optimization that addresses the requirements 136 outlined in [RFC5522]. 138 AERO provides an IPv6 link-local address format known as the AERO 139 address that supports operation of the IPv6 Neighbor Discovery (ND) 140 [RFC4861] protocol and links IPv6 ND to IP forwarding. Admission 141 control and provisioning are supported by the Dynamic Host 142 Configuration Protocol for IPv6 (DHCPv6) [RFC3315], and node mobility 143 is naturally supported through dynamic neighbor cache updates. 144 Although DHCPv6 and IPv6 ND message signalling is used in the control 145 plane, both IPv4 and IPv6 can be used in the data plane. The 146 remainder of this document presents the AERO specification. 148 2. Terminology 150 The terminology in the normative references applies; the following 151 terms are defined within the scope of this document: 153 AERO link 154 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 155 configured over a node's attached IPv6 and/or IPv4 networks. All 156 nodes on the AERO link appear as single-hop neighbors from the 157 perspective of the virtual overlay. 159 AERO interface 160 a node's attachment to an AERO link. 162 AERO address 163 an IPv6 link-local address constructed as specified in Section 3.3 164 and assigned to a Client's AERO interface. 166 AERO node 167 a node that is connected to an AERO link and that participates in 168 IPv6 ND and DHCPv6 messaging over the link. 170 AERO Client ("Client") 171 a node that assigns AERO addresses to an AERO interface and 172 receives IP prefixes via a DHCPv6 Prefix Delegation (PD) exchanges 173 with one or more AERO Servers. 175 AERO Server ("Server") 176 a node that configures an AERO interface to provide default 177 forwarding and DHCPv6 services for AERO Clients. The Server 178 assigns the IPv6 link-local subnet router anycast address (fe80::) 179 to the AERO interface and also assigns an administratively 180 assigned IPv6 link-local unicast address used for operation of 181 DHCPv6 and the IPv6 ND protocol. 183 AERO Relay ("Relay") 184 a node that configures an AERO interface to relay IP packets 185 between nodes on the same AERO link and/or forward IP packets 186 between the AERO link and the native Internetwork. The Relay 187 assigns an administratively assigned IPv6 link-local unicast 188 address to the AERO interface the same as for a Server. 190 AERO Forwarding Agent ("Forwarding Agent") 191 a node that performs data plane forwarding services as a companion 192 to other AERO nodes. 194 ingress tunnel endpoint (ITE) 195 an AERO interface endpoint that injects tunneled packets into an 196 AERO link. 198 egress tunnel endpoint (ETE) 199 an AERO interface endpoint that receives tunneled packets from an 200 AERO link. 202 underlying network 203 a connected IPv6 or IPv4 network routing region over which the 204 tunnel virtual overlay is configured. A typical example is an 205 enterprise network. 207 underlying interface 208 an AERO node's interface point of attachment to an underlying 209 network. 211 link-layer address 212 an IP address assigned to an AERO node's underlying interface. 213 When UDP encapsulation is used, the UDP port number is also 214 considered as part of the link-layer address. Link-layer 215 addresses are used as the encapsulation header source and 216 destination addresses. 218 network layer address 219 the source or destination address of the encapsulated IP packet. 221 end user network (EUN) 222 an internal virtual or external edge IP network that an AERO 223 Client connects to the rest of the network via the AERO interface. 225 AERO Service Prefix (ASP) 226 an IP prefix associated with the AERO link and from which AERO 227 Client Prefixes (ACPs) are derived (for example, the IPv6 ACP 228 2001:db8:1:2::/64 is derived from the IPv6 ASP 2001:db8::/32). 230 AERO Client Prefix (ACP) 231 a more-specific IP prefix taken from an ASP and delegated to a 232 Client. 234 Throughout the document, the simple terms "Client", "Server" and 235 "Relay" refer to "AERO Client", "AERO Server" and "AERO Relay", 236 respectively. Capitalization is used to distinguish these terms from 237 DHCPv6 client/server/relay [RFC3315]. 239 The terminology of [RFC4861] (including the names of node variables 240 and protocol constants) applies to this document. Also throughout 241 the document, the term "IP" is used to generically refer to either 242 Internet Protocol version (i.e., IPv4 or IPv6). 244 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 245 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 246 document are to be interpreted as described in [RFC2119]. 248 3. Asymmetric Extended Route Optimization (AERO) 250 The following sections specify the operation of IP over Asymmetric 251 Extended Route Optimization (AERO) links: 253 3.1. AERO Link Reference Model 255 .-(::::::::) 256 .-(:::: IP ::::)-. 257 (:: Internetwork ::) 258 `-(::::::::::::)-' 259 `-(::::::)-' 260 | 261 +--------------+ +--------+-------+ +--------------+ 262 |AERO Server S1| | AERO Relay R1 | |AERO Server S2| 263 | Nbr: C1; R1 | | Nbr: S1; S2 | | Nbr: C2; R1 | 264 | default->R1 | |(H1->S1; H2->S2)| | default->R1 | 265 | H1->C1 | +--------+-------+ | H2->C2 | 266 +-------+------+ | +------+-------+ 267 | | | 268 X---+---+-------------------+------------------+---+---X 269 | AERO Link | 270 +-----+--------+ +--------+-----+ 271 |AERO Client C1| |AERO Client C2| 272 | Nbr: S1 | | Nbr: S2 | 273 | default->S1 | | default->S2 | 274 +--------------+ +--------------+ 275 .-. .-. 276 ,-( _)-. ,-( _)-. 277 .-(_ IP )-. .-(_ IP )-. 278 (__ EUN ) (__ EUN ) 279 `-(______)-' `-(______)-' 280 | | 281 +--------+ +--------+ 282 | Host H1| | Host H2| 283 +--------+ +--------+ 285 Figure 1: AERO Link Reference Model 287 Figure 1 above presents the AERO link reference model. In this 288 model: 290 o Relay R1 acts as a default router for its associated Servers S1 291 and S2, and connects the AERO link to the rest of the IP 292 Internetwork 294 o Servers S1 and S2 associate with Relay R1 and also act as default 295 routers for their associated Clients C1 and C2. 297 o Clients C1 and C2 associate with Servers S1 and S2, respectively 298 and also act as default routers for their associated EUNs 300 o Hosts H1 and H2 attach to the EUNs served by Clients C1 and C2, 301 respectively 303 In common operational practice, there may be many additional Relays, 304 Servers and Clients. (Although not shown in the figure, AERO 305 Forwarding Agents may also be provided for data plane forwarding 306 offload services.) 308 3.2. AERO Link Node Types 310 AERO Relays provide default forwarding services to AERO Servers. 311 Relays forward packets between Servers connected to the same AERO 312 link and also forward packets between the AERO link and the native IP 313 Internetwork. Relays present the AERO link to the native 314 Internetwork as a set of one or more AERO Service Prefixes (ASPs) and 315 serve as a gateway between the AERO link and the Internetwork. AERO 316 Relays maintain an AERO interface neighbor cache entry for each AERO 317 Server, and maintain an IP forwarding table entry for each AERO 318 Client Prefix (ACP). 320 AERO Servers provide default forwarding services to AERO Clients. 321 Each Server also peers with each Relay in a dynamic routing protocol 322 instance to advertise its list of associated ACPs. Servers configure 323 a DHCPv6 server function to facilitate Prefix Delegation (PD) 324 exchanges with Clients. Each delegated prefix becomes an ACP taken 325 from an ASP. Servers forward packets between AERO interface 326 neighbors only, i.e., and not between the AERO link and the native IP 327 Internetwork unless they are also configured as a Relay. AERO 328 Servers maintain an AERO interface neighbor cache entry for each AERO 329 Relay. They also maintain both a neighbor cache entry and an IP 330 forwarding table entry for each of their associated Clients. 332 AERO Clients act as requesting routers to receive ACPs through DHCPv6 333 PD exchanges with AERO Servers over the AERO link and sub-delegate 334 portions of their ACPs to EUN interfaces. (Each Client MAY associate 335 with a single Server or with multiple Servers, e.g., for fault 336 tolerance, load balancing, etc.) Each IPv6 Client receives at least 337 a /64 IPv6 ACP, and may receive even shorter prefixes. Similarly, 338 each IPv4 Client receives at least a /32 IPv4 ACP (i.e., a singleton 339 IPv4 address), and may receive even shorter prefixes. AERO Clients 340 maintain an AERO interface neighbor cache entry for each of their 341 associated Servers as well as for each of their correspondent 342 Clients. 344 AERO Clients that act as hosts typically configure a TUN/TAP 345 interface [TUNTAP] as a point-to-point linkage between the IP layer 346 and the AERO interface. The IP layer therefore sees only the TUN/TAP 347 interface, while the AERO interface provides an intermediate conduit 348 between the TUN/TAP interface and the underlying interfaces. AERO 349 Clients that act as hosts assign one or more IP addresses from their 350 ACPs to the TUN/TAP interface, i.e., and not to the AERO interface. 352 AERO Forwarding Agents provide data plane forwarding services as 353 companions to other AERO nodes. Note that while all Relays, Servers 354 and Clients are required to perform both control and data plane 355 operations on their own behalf, they may optionally enlist the 356 services of special-purpose Forwarding Agents to offload performance- 357 intensive traffic. 359 3.3. AERO Addresses 361 An AERO address is an IPv6 link-local address with an embedded ACP 362 and assigned to a Client's AERO interface. The AERO address is 363 formed as follows: 365 fe80::[ACP] 367 For IPv6, the AERO address begins with the prefix fe80::/64 and 368 includes in its interface identifier the base prefix taken from the 369 Client's IPv6 ACP. The base prefix is determined by masking the ACP 370 with the prefix length. For example, if the AERO Client receives the 371 IPv6 ACP: 373 2001:db8:1000:2000::/56 375 it constructs its AERO address as: 377 fe80::2001:db8:1000:2000 379 For IPv4, the AERO address is formed from the lower 64 bits of an 380 IPv4-mapped IPv6 address [RFC4291] that includes the base prefix 381 taken from the Client's IPv4 ACP. For example, if the AERO Client 382 receives the IPv4 ACP: 384 192.0.2.32/28 386 it constructs its AERO address as: 388 fe80::FFFF:192.0.2.32 390 The AERO address remains stable as the Client moves between 391 topological locations, i.e., even if its link-layer addresses change. 393 NOTE: In some cases, prospective neighbors may not have advanced 394 knowledge of the Client's ACP length and may therefore send initial 395 IPv6 ND messages with an AERO destination address that matches the 396 ACP but does not correspond to the base prefix. In that case, the 397 Client MUST accept the address as equivalent to the base address, but 398 then use the base address as the source address of any IPv6 ND 399 message replies. For example, if the Client receives the IPv6 ACP 400 2001:db8:1000:2000::/56 then subsequently receives an IPv6 ND message 401 with destination address fe80::2001:db8:1000:2001, it accepts the 402 message but uses fe80::2001:db8:1000:2000 as the source address of 403 any IPv6 ND replies. 405 3.4. AERO Interface Characteristics 407 AERO interfaces use encapsulation (see Section 3.10) to exchange 408 packets with neighbors attached to the AERO link. AERO interfaces 409 maintain a neighbor cache, and AERO Clients and Servers use an 410 adaptation of standard unicast IPv6 ND messaging. AERO interfaces 411 use unicast Neighbor Solicitation (NS), Neighbor Advertisement (NA), 412 Router Solicitation (RS) and Router Advertisement (RA) messages the 413 same as for any IPv6 link. AERO interfaces use two redirection 414 message types -- the first known as a Predirect message and the 415 second being the standard Redirect message (see Section 3.17). AERO 416 links further use link-local-only addressing; hence, AERO nodes 417 ignore any Prefix Information Options (PIOs) they may receive in RA 418 messages over an AERO interface. 420 AERO interface ND messages include one or more Source/Target Link- 421 Layer Address Options (S/TLLAOs) formatted as shown in Figure 2: 423 0 1 2 3 424 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 1 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 | Type = 2 | Length = 3 | Reserved | 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | Link ID | Preference | UDP Port Number | 429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 430 | | 431 +-- --+ 432 | | 433 +-- IP Address --+ 434 | | 435 +-- --+ 436 | | 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 Figure 2: AERO Source/Target Link-Layer Address Option (S/TLLAO) 440 Format 442 In this format, Link ID is an integer value between 0 and 255 443 corresponding to an underlying interface of the target node, and 444 Preference is an integer value between 0 and 255 indicating the 445 node's preference for this underlying interface (with 255 being the 446 highest preference, 1 being the lowest, and 0 meaning "link 447 disabled"). UDP Port Number and IP Address are set to the addresses 448 used by the target node when it sends encapsulated packets over the 449 underlying interface. When the encapsulation IP address family is 450 IPv4, IP Address is formed as an IPv4-mapped IPv6 address [RFC4291]. 452 AERO interfaces may be configured over multiple underlying 453 interfaces. For example, common mobile handheld devices have both 454 wireless local area network ("WLAN") and cellular wireless links. 455 These links are typically used "one at a time" with low-cost WLAN 456 preferred and highly-available cellular wireless as a standby. In a 457 more complex example, aircraft frequently have many wireless data 458 link types (e.g. satellite-based, terrestrial, air-to-air 459 directional, etc.) with diverse performance and cost properties. 461 If a Client's multiple underlying interfaces are used "one at a time" 462 (i.e., all other interfaces are in standby mode while one interface 463 is active), then Redirect, Predirect and unsolicited NA messages 464 include only a single TLLAO with Link ID set to a constant value. 466 If the Client has multiple active underlying interfaces, then from 467 the perspective of IPv6 ND it would appear to have a single link- 468 local address with multiple link-layer addresses. In that case, 469 Redirect, Predirect and unsolicited NA messages MAY include multiple 470 TLLAOs -- each with a different Link ID that corresponds to a 471 specific underlying interface of the Client. 473 3.5. AERO Link Registration 475 When an administrative authority first deploys a set of AERO Relays 476 and Servers that comprise an AERO link, they also assign a unique 477 domain name for the link, e.g., "example.com". Next, if 478 administrative policy permits Clients within the domain to serve as 479 correspondent nodes for Internet mobile nodes, the administrative 480 authority adds a Fully Qualified Domain Name (FQDN) for each of the 481 AERO link's ASPs to the Domain Name System (DNS) [RFC1035]. The FQDN 482 is based on the suffix "aero.linkupnetworks.net" with a wildcard- 483 terminated reverse mapping of the ASP [RFC3596][RFC4592], and 484 resolves to a DNS PTR resource record. For example, for the ASP 485 '2001:db8:1::/48' within the domain name "example.com", the DNS 486 database contains: 488 '*.1.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net. PTR example.com' 490 This DNS registration advertises the AERO link's ASPs to prospective 491 mobile nodes. 493 3.6. AERO Interface Initialization 495 3.6.1. AERO Relay Behavior 497 When a Relay enables an AERO interface, it first assigns an 498 administratively-assigned link-local address fe80::ID to the 499 interface. Each fe80::ID address MUST be unique among all Relays and 500 Servers on the link, and MUST NOT collide with any potential AERO 501 addresses. The addresses are typically taken from the range 502 fe80::/96, e.g., as fe80::1, fe80::2, fe80::3, etc. The Relay then 503 engages in a dynamic routing protocol session with all Servers on the 504 link (see: Section 3.7), and advertises the set of ASPs into the 505 native IP Internetwork. 507 Each Relay subsequently maintains an IP forwarding table entry for 508 each Client-Server association, and maintains a neighbor cache entry 509 for each Server on the link. Relays do not require the use of 510 Neighbor Unreachability Detection (NUD) messaging (see: Section 3.18) 511 since the dynamic routing protocol already provides Relay-Server 512 reachability information. At a minimum, however, Relays perform NS/ 513 NA, e.g., to support AERO interface MTU determination (see: 514 Section 3.13). 516 3.6.2. AERO Server Behavior 518 When a Server enables an AERO interface, it assigns the address 519 fe80:: to the interface as a link-local Subnet Router Anycast 520 address, and also assigns an administratively assigned link-local 521 address fe80::ID the same as for Relays. (The Server then accepts 522 DHCPv6 and IPv6 ND control messages destined to either the fe80:: or 523 fe80::ID addresses, but always uses fe80::ID as the source address in 524 the control messages it generates.) The Server further configures a 525 DHCPv6 server function to facilitate DHCPv6 PD exchanges with AERO 526 Clients. The Server maintains a neighbor cache entry for each Relay 527 on the link, and manages per-Client neighbor cache entries and IP 528 forwarding table entries based on control message exchanges. Each 529 Server also engages in a dynamic routing protocol with each Relay on 530 the link (see: Section 3.7). 532 When the Server receives an NS/RS message on the AERO interface it 533 returns an NA/RA message but does not update the neighbor cache. The 534 Server further provides a simple conduit between AERO interface 535 neighbors. Therefore, packets enter the Server's AERO interface from 536 the link layer and are forwarded back out the link layer without ever 537 leaving the AERO interface and therefore without ever disturbing the 538 network layer. 540 3.6.3. AERO Client Behavior 542 When a Client enables an AERO interface, it invokes DHCPv6 PD to 543 receive an ACP from an AERO Server. Next, it assigns the 544 corresponding AERO address to the AERO interface and creates a 545 neighbor cache entry for the Server, i.e., the PD exchange bootstraps 546 the provisioning of a unique link-local address. The Client 547 maintains a neighbor cache entry for each of its Servers and each of 548 its active correspondent Clients. When the Client receives Redirect/ 549 Predirect messages on the AERO interface it updates or creates 550 neighbor cache entries, including link-layer address information. 551 Unsolicited NA messages update the cached link-layer addresses for 552 correspondent Clients (e.g., following a link-layer address change 553 due to node mobility) but do not create new neighbor cache entries. 554 NS/NA messages used for NUD update timers in existing neighbor cache 555 entires but do not update link-layer addresses nor create new 556 neighbor cache entries. 558 Finally, the Client need not maintain any IP forwarding table entries 559 for its Servers or correspondent Clients. Instead, it can set a 560 single "route-to-interface" default route in the IP forwarding table, 561 and all forwarding decisions can be made within the AERO interface 562 based on neighbor cache entries. (On systems in which adding a 563 default route would violate security policy, the default route could 564 instead be installed via a "synthesized RA", e.g., as discussed in 565 Section 3.15.2.) 567 3.6.4. AERO Forwarding Agent Behavior 569 When a Forwarding Agent enables an AERO interface, it assigns the 570 same link-local address(es) as the companion AERO node that manages 571 AERO control messaging services. The Forwarding Agent thereafter 572 provides data plane forwarding services based solely on the 573 forwarding information assigned to it by the companion AERO node. 574 AERO Forwarding Agents perform NS/NA messaging, i.e., the same as for 575 AERO Relays. 577 3.7. AERO Link Routing System 579 Relays require full topology knowledge of all ACP/Server 580 associations, while individual Servers at a minimum only need to know 581 the ACPs for their current set of associated Clients. This is 582 accomplished through the use of an internal instance of the Border 583 Gateway Protocol (BGP) [RFC4271] coordinated between Servers and 584 Relays. This internal BGP instance does not interact with the public 585 Internet BGP instance; therefore, the AERO link is presented to the 586 IP Internetwork as a small set of ASPs as opposed to the full set of 587 individual ACPs. 589 In a reference BGP arrangement, each AERO Server is configured as an 590 Autonomous System Border Router (ASBR) for a stub Autonomous System 591 (AS) (possibly using a private AS Number (ASN) [RFC1930]), and each 592 Server further peers with each Relay but does not peer with other 593 Servers. Similarly, Relays do not peer with each other, since they 594 will reliably receive all updates from all Servers and will therefore 595 have a consistent view of the AERO link ACP delegations. 597 Each Server maintains a working set of associated ACPs, and 598 dynamically announces new ACPs and withdraws departed ACPs in its BGP 599 updates to Relays. Clients are expected to remain associated with 600 their current Servers for extended timeframes, however Servers SHOULD 601 selectively suppress BGP updates for impatient Clients that 602 repeatedly associate and disassociate with them in order to reduce 603 routing churn. 605 In some environments, Relays need not send BGP updates to Servers 606 since Servers can always use Relays as default routers, however this 607 presents a data/control plane performance tradeoff. In environments 608 where sustained packet forwarding over Relays is undesirable, Relays 609 can instead report ACPs to Servers while including a BGP Remote-Next- 610 Hop [I-D.vandevelde-idr-remote-next-hop]. The Server then creates a 611 neighbor cache entry for each ACP with the Remote-Next-Hop as the 612 link-layer address to enable Server-to-Server route optimization. 614 3.8. AERO Interface Neighbor Cache Maintenace 616 Each AERO interface maintains a conceptual neighbor cache that 617 includes an entry for each neighbor it communicates with on the AERO 618 link, the same as for any IPv6 interface [RFC4861]. AERO interface 619 neighbor cache entires are said to be one of "permanent", "static" or 620 "dynamic". 622 Permanent neighbor cache entries are created through explicit 623 administrative action; they have no timeout values and remain in 624 place until explicitly deleted. AERO Relays maintain a permanent 625 neighbor cache entry for each Server on the link, and AERO Servers 626 maintain a permanent neighbor cache entry for each Relay. Each entry 627 maintains the mapping between the neighbor's fe80::ID network-layer 628 address and corresponding link-layer address. 630 Static neighbor cache entries are created though DHCPv6 PD exchanges 631 and remain in place for durations bounded by prefix lifetimes. AERO 632 Servers maintain a static neighbor cache entry for each ACP of each 633 of their associated Clients, and AERO Clients maintain a static 634 neighbor cache for each of their associated Servers. When an AERO 635 Server sends a DHCPv6 Reply message response to a Client's DHCPv6 636 Solicit/Request or Renew message, it creates or updates a static 637 neighbor cache entry based on the AERO address corresponding to the 638 Client's ACP as the network-layer address, the prefix lifetime as the 639 neighbor cache entry lifetime, the Client's encapsulation IP address 640 and UDP port number as the link-layer address and the prefix length 641 as the length to apply to the AERO address. When an AERO Client 642 receives a DHCPv6 Reply message from a Server, it creates or updates 643 a static neighbor cache entry based on the Reply message link-local 644 source address as the network-layer address, the prefix lifetime as 645 the neighbor cache entry lifetime, and the encapsulation IP source 646 address and UDP source port number as the link-layer address. 648 Dynamic neighbor cache entries are created or updated based on 649 receipt of an IPv6 ND message, and are garbage-collected if not used 650 within a short timescale. AERO Clients maintain dynamic neighbor 651 cache entries for each of their active correspondent Client ACPs with 652 lifetimes based on IPv6 ND messaging constants. When an AERO Client 653 receives a valid Predirect message it creates or updates a dynamic 654 neighbor cache entry for the Predirect target network-layer and link- 655 layer addresses plus prefix length. The node then sets an 656 "AcceptTime" variable in the neighbor cache entry to ACCEPT_TIME 657 seconds and uses this value to determine whether packets received 658 from the correspondent can be accepted. When an AERO Client receives 659 a valid Redirect message it creates or updates a dynamic neighbor 660 cache entry for the Redirect target network-layer and link-layer 661 addresses plus prefix length. The Client then sets a "ForwardTime" 662 variable in the neighbor cache entry to FORWARD_TIME seconds and uses 663 this value to determine whether packets can be sent directly to the 664 correspondent. The Client also sets a "MaxRetry" variable to 665 MAX_RETRY to limit the number of keepalives sent when a correspondent 666 may have gone unreachable. 668 For dynamic neighbor cache entries, when an AERO Client receives a 669 valid NS message it (re)sets AcceptTime for the neighbor to 670 ACCEPT_TIME. When an AERO Client receives a valid solicited NA 671 message, it (re)sets ForwardTime for the neighbor to FORWARD_TIME and 672 sets MaxRetry to MAX_RETRY. When an AERO Client receives a valid 673 unsolicited NA message, it updates the correspondent's link-layer 674 addresses but DOES NOT reset AcceptTime, ForwardTime or MaxRetry. 676 It is RECOMMENDED that FORWARD_TIME be set to the default constant 677 value 30 seconds to match the default REACHABLE_TIME value specified 678 for IPv6 ND [RFC4861]. 680 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 681 value 40 seconds to allow a 10 second window so that the AERO 682 redirection procedure can converge before AcceptTime decrements below 683 FORWARD_TIME. 685 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 686 for IPv6 ND address resolution in Section 7.3.3 of [RFC4861]. 688 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 689 administratively set, if necessary, to better match the AERO link's 690 performance characteristics; however, if different values are chosen, 691 all nodes on the link MUST consistently configure the same values. 692 Most importantly, ACCEPT_TIME SHOULD be set to a value that is 693 sufficiently longer than FORWARD_TIME to allow the AERO redirection 694 procedure to converge. 696 3.9. AERO Interface Sending Algorithm 698 IP packets enter a node's AERO interface either from the network 699 layer (i.e., from a local application or the IP forwarding system), 700 or from the link layer (i.e., from the AERO tunnel virtual link). 701 Packets that enter the AERO interface from the network layer are 702 encapsulated and admitted into the AERO link, i.e., they are 703 tunnelled to an AERO interface neighbor. Packets that enter the AERO 704 interface from the link layer are either re-admitted into the AERO 705 link or delivered to the network layer where they are subject to 706 either local delivery or IP forwarding. Since each AERO node may 707 have only partial information about neighbors on the link, AERO 708 interfaces may forward packets with link-local destination addresses 709 at a layer below the network layer. This means that AERO nodes act 710 as both IP routers and sub-IP layer forwarding agents. AERO 711 interface sending considerations for Clients, Servers and Relays are 712 given below. 714 When an IP packet enters a Client's AERO interface from the network 715 layer, if the destination is covered by an ASP the Client searches 716 for a dynamic neighbor cache entry with a non-zero ForwardTime and an 717 AERO address that matches the packet's destination address. (The 718 destination address may be either an address covered by the 719 neighbor's ACP or the (link-local) AERO address itself.) If there is 720 a match, the Client uses a link-layer address in the entry as the 721 link-layer address for encapsulation then admits the packet into the 722 AERO link. If there is no match, the Client instead uses the link- 723 layer address of a neighboring Server as the link-layer address for 724 encapsulation. 726 When an IP packet enters a Server's AERO interface from the link 727 layer, if the destination is covered by an ASP the Server searches 728 for a neighbor cache entry with an AERO address that matches the 729 packet's destination address. (The destination address may be either 730 an address covered by the neighbor's ACP or the AERO address itself.) 731 If there is a match, the Server uses a link-layer address in the 732 entry as the link-layer address for encapsulation and re-admits the 733 packet into the AERO link. If there is no match, the Server instead 734 uses the link-layer address in a permanent neighbor cache entry for a 735 Relay as the link-layer address for encapsulation. 737 When an IP packet enters a Relay's AERO interface from the network 738 layer, the Relay searches its IP forwarding table for an entry that 739 is covered by an ASP and also matches the destination. If there is a 740 match, the Relay uses the link-layer address in a permanent neighbor 741 cache entry for a Server as the link-layer address for encapsulation 742 and admits the packet into the AERO link. When an IP packet enters a 743 Relay's AERO interface from the link-layer, if the destination is not 744 a link-local address and does not match an ASP the Relay removes the 745 packet from the AERO interface and uses IP forwarding to forward the 746 packet to the Internetwork. If the destination address is a link- 747 local address or a non-link-local address that matches an ASP, and 748 there is a more-specific ACP entry in the IP forwarding table, the 749 Relay uses the link-layer address in the corresponding neighbor cache 750 entry as the link-layer address for encapsulation and re-admits the 751 packet into the AERO link. When an IP packet enters a Relay's AERO 752 interface from either the network layer or link-layer, and the 753 packet's destination address matches an ASP but there is no more- 754 specific ACP entry, the Relay drops the packet and returns an ICMP 755 Destination Unreachable message (see: Section 3.14). 757 When an AERO Server receives a packet from a Relay via the AERO 758 interface, the Server MUST NOT forward the packet back to the same or 759 a different Relay. 761 When an AERO Relay receives a packet from a Server via the AERO 762 interface, the Relay MUST NOT forward the packet back to the same 763 Server. 765 When an AERO node re-admits a packet into the AERO link without 766 involving the network layer, the node MUST NOT decrement the network 767 layer TTL/Hop-count. 769 When an AERO node forwards a data packet to the primary link-layer 770 address of a neighbor, it may receive RA messages with one or more 771 SLLAOs that include the link-layer addresses of AERO Forwarding 772 Agents. The AERO node SHOULD record the link-layer addresses in the 773 neighbor cache entry for the neighbor and send subsequent data 774 packets via one of these addresses instead of the neighbor's primary 775 address (see: Section 3.16). 777 3.10. AERO Interface Encapsulation and Re-encapsulation 779 AERO interfaces encapsulate IP packets according to whether they are 780 entering the AERO interface from the network layer or if they are 781 being re-admitted into the same AERO link they arrived on. This 782 latter form of encapsulation is known as "re-encapsulation". 784 The AERO interface encapsulates packets per the base tunneling 785 specifications (e.g., [RFC2003], [RFC2473], [RFC2784], [RFC4213], 786 [RFC4301], [RFC5246], etc.) except that it inserts a UDP header 787 immediately following the IP encapsulation header. If there are no 788 additional encapsulation headers (and no fragmentation, 789 identification, checksum or signature is needed), the AERO interface 790 next encapsulates the IPv4 or IPv6 packet immediately following the 791 UDP header. In that case, the most significant four bits of the 792 encapsulated packet encode the value '4' for IPv4 or '6' for IPv6. 794 For all other encapsulations, the AERO interface MUST insert an AERO 795 Header between the UDP header and the next encapsulation header as 796 shown in Figure 3: 798 0 1 2 3 799 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 1 800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 801 |Version|N|F|C|S| Next Header |Fragment Offset (13 bits)|Res|M| 802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 803 | Identification (32 bits) | 804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 805 | Checksum (16 bits) | Signature (variable length) : 806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 Figure 3: AERO Header 810 Version a 4-bit "Version" field. MUST be 0. 812 N a 1-bit "Next Header" flag. Set to '1' if the "Next Header" field 813 is present; otherwise, set to '0' for "Experimental" per 814 [RFC6706]. "Next Header" encodes the IP protocol number 815 corresponding to the next header in the encapsulation immediately 816 following the AERO header. For example, "Next Header" encodes the 817 value '4' for IPv4, '17' for UDP, '41' for IPv6, '47' for GRE, 818 '50' for ESP, '51' for AH, etc. 820 F a 1-bit "Fragment Header" flag. Set to '1' if the "Fragment 821 Offset", "Res", "M", and "Identification" fields are present and 822 collectively referred to as the "AERO Fragment Header"; otherwise, 823 set to '0'. 825 C a 1-bit "Checksum" flag. Set to '1' if the "Checksum" field is 826 present; otherwise, set to '0'. The Checksum field itself then 827 contains a checksum of the IP/UDP/AERO encapsulation headers prior 828 to the Checksum field. 830 S a 1-bit "Signature" flag. Set to '1' if the "Signature" field is 831 present; otherwise, set to '0'. The Signature field itself then 832 contains a cryptographic signature of the encapsulated packet 833 following the Signature field. The signature is applied prior to 834 any fragmentation; hence' the Signature field only appears in the 835 first fragment of a fragmented packet. 837 During encapsulation, the AERO interface copies the "TTL/Hop Limit", 838 Type of Service/Traffic Class" [RFC2983] and "Congestion Experienced" 839 [RFC3168] values in the packet's IP header into the corresponding 840 fields in the encapsulation IP header. (When IPv6 is used as the 841 encapsulation protocol, the interface also sets the Flow Label value 842 in the encapsulation header per [RFC6438].) For packets undergoing 843 re-encapsulation, the AERO interface instead copies the "TTL/Hop 844 Limit", "Type of Service/Traffic Class", "Flow Label" and "Congestion 845 Experienced" values in the original encapsulation IP header into the 846 corresponding fields in the new encapsulation IP header, i.e., the 847 values are transferred between encapsulation headers and *not* copied 848 from the encapsulated packet's network-layer header. 850 The AERO interface next sets the UDP source port to a constant value 851 that it will use in each successive packet it sends, and sets the UDP 852 length field to the length of the encapsulated packet plus 8 bytes 853 for the UDP header itself, plus the length of the AERO header. For 854 packets sent via a Server, the AERO interface sets the UDP 855 destination port to 8060, i.e., the IANA-registered port number for 856 AERO. For packets sent to a correspondent Client, the AERO interface 857 sets the UDP destination port to the port value stored in the 858 neighbor cache entry for this correspondent. The AERO interface also 859 sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) unless 860 an integrity check is required (see: Section 3.13.2). 862 The AERO interface next sets the IP protocol number in the 863 encapsulation header to 17 (i.e., the IP protocol number for UDP). 864 When IPv4 is used as the encapsulation protocol, the AERO interface 865 sets the DF bit as discussed in Section 3.13. The AERO interface 866 finally sets the AERO header fields as described in Figure 3. 868 3.11. AERO Interface Decapsulation 870 AERO interfaces decapsulate packets destined either to the node 871 itself or to a destination reached via an interface other than the 872 AERO interface the packet was received on. When the AERO interface 873 receives a UDP packet, it examines the first octet of the 874 encapsulated packet. 876 If the most significant four bits of the first octet encode the value 877 '4' (i.e., the IP version number value for IPv4) or the value '6' 878 (i.e., the IP version number value for IPv6), the AERO interface 879 discards the encapsulation headers and accepts the encapsulated 880 packet as an ordinary IPv6 or IPv4 data packet, respectively. If the 881 most significant four bits encode the value '0', however, the AERO 882 interface processes the packet according to the appropriate AERO 883 Header fields as specified in Figure 3. 885 3.12. AERO Interface Data Origin Authentication 887 AERO nodes employ simple data origin authentication procedures for 888 encapsulated packets they receive from other nodes on the AERO link. 889 In particular: 891 o AERO Relays and Servers accept encapsulated packets with a link- 892 layer source address that matches a permanent neighbor cache 893 entry. 895 o AERO Servers accept authentic encapsulated DHCPv6 messages from 896 Clients, and create or update a static neighbor cache entry for 897 the source based on the specific message type. 899 o AERO Servers accept encapsulated packets if there is a neighbor 900 cache entry with an AERO address that matches the packet's 901 network-layer source address and with a link-layer address that 902 matches the packet's link-layer source address. 904 o AERO Clients accept encapsulated packets if there is a static 905 neighbor cache entry with a link-layer source address that matches 906 the packet's link-layer source address. 908 o AERO Clients and Servers accept encapsulated packets if there is a 909 dynamic neighbor cache entry with an AERO address that matches the 910 packet's network-layer source address, with a link-layer address 911 that matches the packet's link-layer source address, and with a 912 non-zero AcceptTime. 914 Note that this simple data origin authentication is effective in 915 environments in which link-layer addresses cannot be spoofed. In 916 other environments, each AERO message must include a signature that 917 the recipient can use to authenticate the message origin. 919 3.13. AERO Interface MTU and Fragmentation 921 The AERO interface is the node's point of attachment to the AERO 922 link. AERO links over IP networks have a maximum link MTU of 64KB 923 minus the encapsulation overhead (termed here "ENCAPS"), since the 924 maximum packet size in the base IP specifications is 64KB 925 [RFC0791][RFC2460] (while IPv6 jumbograms can be up to 4GB, they are 926 considered optional for IPv6 nodes [RFC2675][RFC6434]). 928 IPv6 specifies a minimum link MTU of 1280 bytes [RFC2460]. This is 929 the minimum packet size the AERO interface MUST admit without 930 returning an ICMP Packet Too Big (PTB) message. Although IPv4 931 specifies a smaller minimum link MTU of 68 bytes [RFC0791], AERO 932 interfaces also observe a 1280 byte minimum for IPv4. Additionally, 933 the vast majority of links in the Internet configure an MTU of at 934 least 1500 bytes. Original source hosts have therefore become 935 conditioned to expect that IP packets up to 1500 bytes in length will 936 either be delivered to the final destination or a suitable PTB 937 message returned. However, PTB messages may be lost in the network 939 [RFC2923] resulting in failure of the IP MTU discovery mechanisms 940 [RFC1191][RFC1981]. 942 For these reasons, AERO interfaces admit all packets up to 1500 bytes 943 in length even if some fragmentation is necessary, and admit larger 944 packets without fragmentation in case they are able to traverse the 945 tunnel in one piece. AERO interfaces are therefore considered to 946 have an indefinite MTU, i.e., instead of clamping the MTU to a finite 947 size. 949 For AERO links over IPv4, the IP ID field is only 16 bits in length, 950 meaning that fragmentation at high data rates could result in data 951 corruption due to reassembly misassociations [RFC6864][RFC4963] (see: 952 Section 3.13.2). For AERO links over both IPv4 and IPv6, studies 953 have also shown that IP fragments are dropped unconditionally over 954 some network paths [I-D.taylor-v6ops-fragdrop]. For these reasons, 955 when fragmentation is needed it is performed through insertion of an 956 AERO fragment header (see: Section 3.10) and application of tunnel 957 fragmentation as described in Section 3.1.7 of [RFC2764]. Since the 958 AERO fragment header reduces the room available for packet data, but 959 the original source has no way to control its insertion, the header 960 length MUST be included in the ENCAPS length even for packets in 961 which the header does not appear. 963 The source AERO interface (i.e., the tunnel ingress) therefore sends 964 encapsulated packets to the destination AERO interface (i.e., the 965 tunnel egress) according to the following algorithm: 967 o For IP packets that are no larger than (1280-ENCAPS) bytes, the 968 tunnel ingress encapsulates the packet and admits it into the 969 tunnel without fragmentation. For IPv4 AERO links, the tunnel 970 ingress sets the Don't Fragment (DF) bit to 0 so that these 971 packets will be delivered to the tunnel egress even if there is a 972 restricting link in the path, i.e., unless lost due to congestion 973 or routing errors. 975 o For IP packets that are larger than (1280-ENCAPS) bytes but no 976 larger than 1500 bytes, the tunnel ingress encapsulates the packet 977 and inserts an AERO fragment header. Next, the tunnel ingress 978 uses the fragmentation algorithm in [RFC2460] to break the packet 979 into two non-overlapping fragments where the first fragment 980 (including ENCAPS) is no larger than 1024 bytes and the second is 981 no larger than the first. Each fragment consists of identical 982 UDP/IP encapsulation headers, followed by the AERO header followed 983 by the fragment of the encapsulated packet itself. The tunnel 984 ingress then admits both fragments into the tunnel, and for IPv4 985 sets the DF bit to 0 in the IP encapsulation header. These 986 fragmented encapsulated packets will be delivered to the tunnel 987 egress. When the tunnel egress receives the fragments, it 988 reassembles them into a whole packet per the reassembly algorithm 989 in [RFC2460]. The tunnel egress therefore MUST be capable of 990 reassembling packets up to 1500+ENCAPS bytes in length; hence, it 991 is RECOMMENDED that the tunnel egress be capable of reassembling 992 at least 2KB. 994 o For IPv4 packets that are larger than 1500 bytes and with the DF 995 bit set to 0, the tunnel ingress uses ordinary IPv4 fragmentation 996 to break the unencapsulated packet into a minimum number of non- 997 overlapping fragments where the first fragment is no larger than 998 1024-ENCAPS and all other fragments are no larger than the first 999 fragment. The tunnel ingress then encapsulates each fragment (and 1000 for IPv4 sets the DF bit to 0) then admits them into the tunnel. 1001 These fragments will be delivered to the final destination via the 1002 tunnel egress. 1004 o For all other IP packets, if the packet is too large to enter the 1005 underlying interface following encapsulation, the tunnel ingress 1006 drops the packet and returns a network-layer (L3) PTB message to 1007 the original source with MTU set to the larger of 1500 bytes or 1008 the underlying interface MTU minus ENCAPS. Otherwise, the tunnel 1009 ingress encapsulates the packet and admits it into the tunnel 1010 without fragmentation (and for IPv4 sets the DF bit to 1) and 1011 translates any link-layer (L2) PTB messages it may receive from 1012 the network into corresponding L3 PTB messages to send to the 1013 original source as specified in Section 3.14. Since both L2 and 1014 L3 PTB messages may be either lost or contain insufficient 1015 information, however, it is RECOMMENDED that original sources that 1016 send unfragmentable IP packets larger than 1500 bytes use 1017 Packetization Layer Path MTU Discovery (PLPMTUD) [RFC4821]. 1019 While sending packets according to the above algorithm, the tunnel 1020 ingress MAY also send 1500 byte or larger probe packets to determine 1021 whether they can reach the tunnel egress without fragmentation. If 1022 the probes succeed, the tunnel ingress can discontinue fragmentation 1023 and (for IPv4) set DF to 1. Since the path MTU within the tunnel may 1024 fluctuate due to routing changes, the tunnel ingress SHOULD continue 1025 to send additional probes subject to rate limiting and SHOULD process 1026 any L2 PTB messages as an indication that the path MTU may have 1027 decreased. If the path MTU within the tunnel becomes insufficient, 1028 the source MUST resume fragmentation. 1030 To construct a probe, the tunnel ingress prepares an NS message with 1031 a Nonce option plus trailing NULL padding octets added to the probe 1032 length without including the length of the padding in the IPv6 1033 Payload Length field, but with the length included in the 1034 encapsulating IP header. The tunnel ingress then encapsulates the 1035 padded NS message in the encapsulation headers (and for IPv4 sets DF 1036 to 1) then sends the message to the tunnel egress. If the tunnel 1037 egress returns a solicited NA message with a matching Nonce option, 1038 the tunnel ingress deems the probe successful. Note that in this 1039 process it is essential that probes follow equivalent paths to those 1040 used to convey actual data packets. This means that Equal Cost 1041 MultiPath (ECMP) and Link Aggregation Gateway (LAG) equipment is 1042 assumed to support identical MTUs along all paths. 1044 3.13.1. Accommodating Large Control Messages 1046 Control messages (i.e., IPv6 ND, DHCPv6, etc.) MUST be accommodated 1047 even if some fragmentation is necessary. These packets are therefore 1048 accommodated through a modification of the second rule in the above 1049 algorithm as follows: 1051 o For control messages that are larger than (1280-ENCAPS) bytes, the 1052 tunnel ingress encapsulates the packet and inserts an AERO 1053 fragment header. Next, the tunnel ingress uses the fragmentation 1054 algorithm in [RFC2460] to break the packet into a minimum number 1055 of non-overlapping fragments where the first fragment (including 1056 ENCAPS) is no larger than 1024 bytes and the remaining fragments 1057 are no larger than the first. The tunnel ingress then 1058 encapsulates each fragment (and for IPv4 sets the DF bit to 0) 1059 then admits them into the tunnel. 1061 Control messages that exceed the 2KB minimum reassembly size rarely 1062 occur in the modern era, however the tunnel egress SHOULD be able to 1063 reassemble them if they do. This means that the tunnel egress SHOULD 1064 include a configuration knob allowing the operator to set a larger 1065 reassembly buffer size if large control messages become more common 1066 in the future. 1068 The tunnel ingress can send large control messages without 1069 fragmentation if there is assurance that large packets can traverse 1070 the tunnel without fragmentation. The tunnel ingress MAY send 1500 1071 byte or larger probe packets as specified above to determine a size 1072 for which fragmentation can be avoided. 1074 3.13.2. Integrity 1076 When fragmentation is needed, there must be assurance that reassembly 1077 can be safely conducted without incurring data corruption. Sources 1078 of corruption can include implementation errors, memory errors and 1079 misassociation of fragments from a first datagram with fragments of 1080 another datagram. The first two conditions (implementation and 1081 memory errors) are mitigated by modern systems and implementations 1082 that have demonstrated integrity through decades of operational 1083 practice. The third condition (reassembly misassociations) must be 1084 accounted for by AERO. 1086 The AERO fragmentation procedure described in the above algorithms 1087 reuses standard IPv6 fragmentation and reassembly code. Since the 1088 AERO fragment header includes a 32-bit ID field, there would need to 1089 be 2^32 packets alive in the network before a second packet with a 1090 duplicate ID enters the system with the (remote) possibility for a 1091 reassembly misassociation. For 1280 byte packets, and for a maximum 1092 network lifetime value of 60 seconds[RFC2460], this means that the 1093 tunnel ingress would need to produce ~(7 *10^12) bits/sec in order 1094 for a duplication event to be possible. This exceeds the bandwidth 1095 of data link technologies of the modern era, but not necessarily so 1096 going forward into the future. Although wireless data links commonly 1097 used by AERO Clients support vastly lower data rates, the aggregate 1098 data rates between AERO Servers and Relays may be substantial. 1099 However, high speed data links in the network core are expected to 1100 configure larger MTUs, e.g., 4KB, 8KB or even larger such that 1101 unfragmented packets can be used. Hence, no integrity check is 1102 included to cover the AERO fragmentation and reassembly procedures. 1104 When the tunnel ingress sends an IPv4-encapsulated packet with the DF 1105 bit set to 0 in the above algorithms, there is a chance that the 1106 packet may be fragmented by an IPv4 router somewhere within the 1107 tunnel. Since the largest such packet is only 1280 bytes, however, 1108 it is very likely that the packet will traverse the tunnel without 1109 incurring a restricting link. Even when a link within the tunnel 1110 configures an MTU smaller than 1280 bytes, it is very likely that it 1111 does so due to limited performance characteristics [RFC3819]. This 1112 means that the tunnel would not be able to convey fragmented 1113 IPv4-encapsulated packets fast enough to produce reassembly 1114 misassociations, as discussed above. However, AERO must also account 1115 for the possibility of tunnel paths that include "poorly managed" 1116 IPv4 link MTUs due to misconfigurations. 1118 Since the IPv4 header includes only a 16-bit ID field, there would 1119 only need to be 2^16 packets alive in the network before a second 1120 packet with a duplicate ID enters the system. For 1280 byte packets, 1121 and for a maximum network lifetime value of 120 seconds[RFC0791], 1122 this means that the tunnel ingress would only need to produce ~(5 1123 *10^6) bits/sec in order for a duplication event to be possible - a 1124 value that is well within range for many modern wired and wireless 1125 data link technologies. 1127 Therefore, if there is strong operational assurance that no IPv4 1128 links capable of supporting data rates of 5Mbps or more configure an 1129 MTU smaller than 1280 the tunnel ingress MAY omit an integrity check 1130 for the IPv4 fragmentation and reassembly procedures; otherwise, the 1131 tunnel ingress SHOULD include an integrity check. When an upper 1132 layer encapsulation (e.g., IPsec) already includes an integrity 1133 check, the tunnel ingress need not include an additional check. 1134 Otherwise, the tunnel ingress calculates the UDP checksum over the 1135 encapsulated packet and writes the value into the UDP encapsulation 1136 header, i.e., instead of writing the value 0. The tunnel egress will 1137 then verify the UDP checksum and discard the packet if the checksum 1138 is incorrect. 1140 3.14. AERO Interface Error Handling 1142 When an AERO node admits encapsulated packets into the AERO 1143 interface, it may receive link-layer (L2) or network-layer (L3) error 1144 indications. 1146 An L2 error indication is an ICMP error message generated by a router 1147 on the path to the neighbor or by the neighbor itself. The message 1148 includes an IP header with the address of the node that generated the 1149 error as the source address and with the link-layer address of the 1150 AERO node as the destination address. 1152 The IP header is followed by an ICMP header that includes an error 1153 Type, Code and Checksum. For ICMPv6 [RFC4443], the error Types 1154 include "Destination Unreachable", "Packet Too Big (PTB)", "Time 1155 Exceeded" and "Parameter Problem". For ICMPv4 [RFC0792], the error 1156 Types include "Destination Unreachable", "Fragmentation Needed" (a 1157 Destination Unreachable Code that is analogous to the ICMPv6 PTB), 1158 "Time Exceeded" and "Parameter Problem". 1160 The ICMP header is followed by the leading portion of the packet that 1161 generated the error, also known as the "packet-in-error". For 1162 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1163 much of invoking packet as possible without the ICMPv6 packet 1164 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1165 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1166 "Internet Header + 64 bits of Original Data Datagram", however 1167 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1168 ICMP datagram SHOULD contain as much of the original datagram as 1169 possible without the length of the ICMP datagram exceeding 576 1170 bytes". 1172 The L2 error message format is shown in Figure 4: 1174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1175 ~ ~ 1176 | L2 IP Header of | 1177 | error message | 1178 ~ ~ 1179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1180 | L2 ICMP Header | 1181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1182 ~ ~ P 1183 | IP and other encapsulation | a 1184 | headers of original L3 packet | c 1185 ~ ~ k 1186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1187 ~ ~ t 1188 | IP header of | 1189 | original L3 packet | i 1190 ~ ~ n 1191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1192 ~ ~ e 1193 | Upper layer headers and | r 1194 | leading portion of body | r 1195 | of the original L3 packet | o 1196 ~ ~ r 1197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1199 Figure 4: AERO Interface L2 Error Message Format 1201 The AERO node rules for processing these L2 error messages is as 1202 follows: 1204 o When an AERO node receives an L2 Parameter Problem message, it 1205 processes the message the same as described as for ordinary ICMP 1206 errors in the normative references [RFC0792][RFC4443]. 1208 o When an AERO node receives persistent L2 IPv4 Time Exceeded 1209 messages, the IP ID field may be wrapping before earlier fragments 1210 have been processed. In that case, the node SHOULD begin 1211 including IPv4 integrity checks (see: Section 3.13.2). 1213 o When an AERO Client receives persistent L2 Destination Unreachable 1214 messages in response to tunneled packets that it sends to one of 1215 its dynamic neighbor correspondents, the Client SHOULD test the 1216 path to the correspondent using Neighbor Unreachability Detection 1217 (NUD) (see Section 3.18). If NUD fails, the Client SHOULD set 1218 ForwardTime for the corresponding dynamic neighbor cache entry to 1219 0 and allow future packets destined to the correspondent to flow 1220 through a Server. 1222 o When an AERO Client receives persistent L2 Destination Unreachable 1223 messages in response to tunneled packets that it sends to one of 1224 its static neighbor Servers, the Client SHOULD test the path to 1225 the Server using NUD. If NUD fails, the Client SHOULD delete the 1226 neighbor cache entry and attempt to associate with a new Server. 1228 o When an AERO Server receives persistent L2 Destination Unreachable 1229 messages in response to tunneled packets that it sends to one of 1230 its static neighbor Clients, the Server SHOULD test the path to 1231 the Client using NUD. If NUD fails, the Server SHOULD cancel the 1232 DHCPv6 PD lease for the Client's ACP, withdraw its route for the 1233 ACP from the AERO routing system and delete the neighbor cache 1234 entry (see Section 3.18 and Section 3.19). 1236 o When an AERO Relay or Server receives an L2 Destination 1237 Unreachable message in response to a tunneled packet that it sends 1238 to one of its permanent neighbors, it discards the message since 1239 the routing system is likely in a temporary transitional state 1240 that will soon re-converge. 1242 o When an AERO node receives an L2 PTB message, it translates the 1243 message into an L3 PTB message if possible (*) and forwards the 1244 message toward the original source as described below. 1246 To translate an L2 PTB message to an L3 PTB message, the AERO node 1247 first caches the MTU field value of the L2 ICMP header. The node 1248 next discards the L2 IP and ICMP headers, and also discards the 1249 encapsulation headers of the original L3 packet. Next the node 1250 encapsulates the included segment of the original L3 packet in an L3 1251 IP and ICMP header, and sets the ICMP header Type and Code values to 1252 appropriate values for the L3 IP protocol. In the process, the node 1253 writes the maximum of 1500 bytes and (L2 MTU - ENCAPS) into the MTU 1254 field of the L3 ICMP header. 1256 The node next writes the IP source address of the original L3 packet 1257 as the destination address of the L3 PTB message and determines the 1258 next hop to the destination. If the next hop is reached via the AERO 1259 interface, the node uses the IPv6 address "::" or the IPv4 address 1260 "0.0.0.0" as the IP source address of the L3 PTB message. Otherwise, 1261 the node uses one of its non link-local addresses as the source 1262 address of the L3 PTB message. The node finally calculates the ICMP 1263 checksum over the L3 PTB message and writes the Checksum in the 1264 corresponding field of the L3 ICMP header. The L3 PTB message 1265 therefore is formatted as follows: 1267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1268 ~ ~ 1269 | L3 IP Header of | 1270 | error message | 1271 ~ ~ 1272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1273 | L3 ICMP Header | 1274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1275 ~ ~ p 1276 | IP header of | k 1277 | original L3 packet | t 1278 ~ ~ 1279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i 1280 ~ ~ n 1281 | Upper layer headers and | 1282 | leading portion of body | e 1283 | of the original L3 packet | r 1284 ~ ~ r 1285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1287 Figure 5: AERO Interface L3 Error Message Format 1289 After the node has prepared the L3 PTB message, it either forwards 1290 the message via a link outside of the AERO interface without 1291 encapsulation, or encapsulates and forwards the message to the next 1292 hop via the AERO interface. 1294 When an AERO Relay receives an L3 packet for which the destination 1295 address is covered by an ASP, if there is no more-specific routing 1296 information for the destination the Relay drops the packet and 1297 returns an L3 Destination Unreachable message. The Relay first 1298 writes the IP source address of the original L3 packet as the 1299 destination address of the L3 Destination Unreachable message and 1300 determines the next hop to the destination. If the next hop is 1301 reached via the AERO interface, the Relay uses the IPv6 address "::" 1302 or the IPv4 address "0.0.0.0" as the IP source address of the L3 1303 Destination Unreachable message and forwards the message to the next 1304 hop within the AERO interface. Otherwise, the Relay uses one of its 1305 non link-local addresses as the source address of the L3 Destination 1306 Unreachable message and forwards the message via a link outside the 1307 AERO interface. 1309 When an AERO node receives any L3 error message via the AERO 1310 interface, it examines the destination address in the L3 IP header of 1311 the message. If the next hop toward the destination address of the 1312 error message is via the AERO interface, the node re-encapsulates and 1313 forwards the message to the next hop within the AERO interface. 1314 Otherwise, if the source address in the L3 IP header of the message 1315 is the IPv6 address "::" or the IPv4 address "0.0.0.0", the node 1316 writes one of its non link-local addresses as the source address of 1317 the L3 message and recalculates the IP and/or ICMP checksums. The 1318 node finally forwards the message via a link outside of the AERO 1319 interface. 1321 (*) Note that in some instances the packet-in-error field of an L2 1322 PTB message may not include enough information for translation to an 1323 L3 PTB message. In that case, the AERO interface simply discards the 1324 L2 PTB message. It can therefore be said that translation of L2 PTB 1325 messages to L3 PTB messages can provide a useful optimization when 1326 possible, but is not critical for sources that correctly use PLPMTUD. 1328 3.15. AERO Router Discovery, Prefix Delegation and Address 1329 Configuration 1331 3.15.1. AERO DHCPv6 Service Model 1333 Each AERO Server configures a DHCPv6 server function to facilitate PD 1334 requests from Clients. Each Server is pre-configured with an 1335 identical list of ACP-to-Client ID mappings for all Clients enrolled 1336 in the AERO system, as well as any information necessary to 1337 authenticate Clients. The configuration information is maintained by 1338 a central administrative authority for the AERO link and securely 1339 propagated to all Servers whenever a new Client is enrolled or an 1340 existing Client is withdrawn. 1342 With these identical configurations, each Server can function 1343 independently of all other Servers, including the maintenance of 1344 active leases. Therefore, no Server-to-Server DHCPv6 state 1345 synchronization is necessary, and Clients can optionally hold 1346 separate leases for the same ACP from multiple Servers. 1348 In this way, Clients can easily associate with multiple Servers, and 1349 can receive new leases from new Servers before deprecating leases 1350 held through old Servers. This enables a graceful "make-before- 1351 break" capability. 1353 3.15.2. AERO Client Behavior 1355 AERO Clients discover the link-layer addresses of AERO Servers via 1356 static configuration, or through an automated means such as DNS name 1357 resolution. In the absence of other information, the Client resolves 1358 the FQDN "linkupnetworks.[domainname]" where "linkupnetworks" is a 1359 constant text string and "[domainname]" is the connection-specific 1360 DNS suffix for the Client's underlying network connection (e.g., 1361 "example.com"). After discovering the link-layer addresses, the 1362 Client associates with one or more of the corresponding Servers. 1364 To associate with a Server, the Client acts as a requesting router to 1365 request an ACP through a DHCPv6 PD exchange[RFC3315][RFC3633] in 1366 which the Client's Solicit/Request messages use the IPv6 1367 "unspecified" address (i.e., "::") as the IPv6 source address, 1368 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address 1369 and the link-layer address of the Server as the link-layer 1370 destination address. The Client also includes a Client Identifier 1371 option with a DHCP Unique Identifier (DUID) plus any necessary 1372 authentication options to identify itself to the DHCPv6 server, and 1373 includes a Client Link Layer Address Option (CLLAO) [RFC6939] with 1374 the format shown in Figure 6: 1376 0 1 2 3 1377 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 1378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1379 | OPTION_CLIENT_LINKLAYER_ADDR | option-length | 1380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1381 | link-layer type (16 bits) | Link ID | Preference | 1382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1384 Figure 6: AERO Client Link-Layer Address Option (CLLAO) Format 1386 The Client sets the CLLAO 'option-length' field to 4 and sets the 1387 'link-layer type' field to TBD1 (see: IANA Considerations), then 1388 includes appropriate Link ID and Preference values for the underlying 1389 interface over which the Solicit/Request will be issued (note that 1390 these are the same values that would be included in an S/TLLAO as 1391 shown in Figure 2). If the Client is pre-provisioned with an ACP 1392 associated with the AERO service, it MAY also include the ACP in a 1393 Solicit/Request message Identity Association for Prefix Delegation 1394 (IA_PD) option to indicate its preferred ACP to the DHCPv6 server. 1395 The Client then sends the encapsulated DHCPv6 request via the 1396 underlying interface. 1398 When the Client receives its ACP via a DHCPv6 Reply from the AERO 1399 Server, it creates a static neighbor cache entry with the Server's 1400 link-local address as the network-layer address and the Server's 1401 encapsulation address as the link-layer address. If the Reply 1402 message contains a Vendor-Specific Information Option (see: 1403 Section 3.15.3) the Client also caches each ASP in the option. The 1404 Client then considers the link-layer address of the Server as the 1405 primary default encapsulation address for forwarding packets for 1406 which there is no more-specific forwarding information. 1408 Next, the Client applies the AERO address to the AERO interface and 1409 sub-delegates the ACP to nodes and links within its attached EUNs 1410 (the AERO address thereafter remains stable as the Client moves). 1411 The Client also assigns a default IP route to the AERO interface as a 1412 route-to-interface, i.e., with no explicit next-hop. The next hop 1413 will then be determined after a packet has been submitted to the AERO 1414 interface by inspecting the neighbor cache (see above). 1416 On some platforms (e.g., popular cell phone operating systems), the 1417 act of assigning a default IPv6 route may not be permitted from a 1418 user application due to security policy. Typically, those platforms 1419 include a TUN/TAP interface that acts as a point-to-point conduit 1420 between user applications and the AERO interface. In that case, the 1421 Client can instead generate a "synthesized RA" message. The message 1422 conforms to [RFC4861] and is prepared as follows: 1424 o the IPv6 source address is fe80:: 1426 o the IPv6 destination address is all-nodes multicast 1428 o the Router Lifetime is set to a time that is no longer than the 1429 ACP DHCPv6 lifetime 1431 o the message does not include a Source Link Layer Address Option 1432 (SLLAO) 1434 o the message includes a Prefix Information Option (PIO) with a /64 1435 prefix taken from the ACP as the prefix for autoconfiguration 1437 The Client then sends the synthesized RA message via the TUN/TAP 1438 interface, where the operating system kernel will interpret it as 1439 though it were generated by an actual router. The operating system 1440 will then install a default route and use StateLess Address 1441 AutoConfiguration (SLAAC) to configure an IPv6 address on the TUN/TAP 1442 interface. Methods for similarly installing an IPv4 default route 1443 and IPv4 address on the TUN/TAP interface are based on synthesized 1444 DHCPv4 messages [RFC2131]. Note that in this method, the Client 1445 appears as a mobility proxy for applications that bind to the (point- 1446 to-point) TUN/TAP interface. The arrangement can be likened to a 1447 Proxy AERO scenario in which the mobile node and Client are located 1448 within the same physical platform (see Section 3.20 for further 1449 details on Proxy AERO). 1451 The Client subsequently renews its ACP delegation through each of its 1452 Servers by performing DHCPv6 Renew/Reply exchanges with its AERO 1453 address as the IPv6 source address, 1454 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address, 1455 the link-layer address of a Server as the link-layer destination 1456 address and the same Client identifier, authentication options and 1457 CLLAO option as was used in the initial PD request. Note that if the 1458 Client does not issue a DHCPv6 Renew before the Server has terminated 1459 the lease (e.g., if the Client has been out of touch with the Server 1460 for a considerable amount of time), the Server's Reply will report 1461 NoBinding and the Client must re-initiate the DHCPv6 PD procedure. 1462 If the Client sends synthesized RA and/or DHCPv4 messages (see 1463 above), it also sends a new synthesized message when issuing a DHCPv6 1464 Renew or when re-initiating the DHCPv6 PD procedure. 1466 Since the Client's AERO address is configured from the unique ACP 1467 delegation it receives, there is no need for Duplicate Address 1468 Detection (DAD) on AERO links. Other nodes maliciously attempting to 1469 hijack an authorized Client's AERO address will be denied access to 1470 the network by the DHCPv6 server due to an unacceptable link-layer 1471 address and/or security parameters (see: Security Considerations). 1473 3.15.3. AERO Server Behavior 1475 AERO Servers configure a DHCPv6 server function on their AERO links. 1476 AERO Servers arrange to add their encapsulation layer IP addresses 1477 (i.e., their link-layer addresses) to the DNS resource records for 1478 the FQDN "linkupnetworks.[domainname]" before entering service. 1480 When an AERO Server receives a prospective Client's DHCPv6 PD 1481 Solicit/Request message, it first authenticates the message. If 1482 authentication succeeds, the Server determines the correct ACP to 1483 delegate to the Client by searching an online directory service 1484 (e.g., LDAP) based on a Client identification value. In environments 1485 where spoofing is not considered a threat, the Server MAY use the 1486 Client's DUID as the identification value. Otherwise, the Server 1487 SHOULD use a signed certificate provided by the Client. 1489 The Server then delegates the ACP and creates a static neighbor cache 1490 entry for the Client's AERO address with lifetime set to no more than 1491 the lease lifetime and the Client's link-layer address as the link- 1492 layer address for the Link ID specified in the CLLAO option. The 1493 Server then creates an IP forwarding table entry so that the AERO 1494 routing system will propagate the ACP to all Relays (see: 1495 Section 3.7). Finally, the Server sends a DHCPv6 Reply message to 1496 the Client while using fe80::ID as the IPv6 source address, the 1497 Client's AERO address as the IPv6 destination address, and the 1498 Client's link-layer address as the destination link-layer address. 1499 The Server also includes a Server Unicast option with server-address 1500 set to fe80::ID so that all future Client/Server transactions will be 1501 link-local-only unicast over the AERO link. 1503 When the Server sends the DHCPv6 Reply message, it also includes a 1504 DHCPv6 Vendor-Specific Information Option with 'enterprise-number' 1505 set to "TBD2" (see: IANA Considerations). The option is formatted as 1506 shown in[RFC3315] and with the AERO enterprise-specific format shown 1507 in Figure 7: 1509 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 1510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1511 | OPTION_VENDOR_OPTS | option-len | 1512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1513 | enterprise-number ("TBD2") | 1514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1515 | Reserved | Prefix Length | 1516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1517 | | 1518 + ASP (1) + 1519 | | 1520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1521 | Reserved | Prefix Length | 1522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1523 | | 1524 + ASP (2) + 1525 | | 1526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1527 | Reserved | Prefix Length | 1528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1529 | | 1530 + ASP (3) + 1531 | | 1532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1533 . (etc.) . 1534 . . 1535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1537 Figure 7: AERO Vendor-Specific Information Option 1539 Per Figure 7, the option includes one or more ASP. The ASP field 1540 contains the IP prefix as it would appear in the interface identifier 1541 portion of the corresponding AERO address (see: Section 3.3). For 1542 IPv6, valid values for the Prefix Length field are 0 through 64; for 1543 IPv4, valid values are 0 through 32. 1545 After the initial DHCPv6 PD exchange, the AERO Server maintains the 1546 neighbor cache entry for the Client until the lease lifetime expires. 1547 If the Client issues a Renew/Reply exchange, the Server extends the 1548 lifetime. If the Client issues a Release/Reply, or if the Client 1549 does not issue a Renew/Reply before the lifetime expires, the Server 1550 deletes the neighbor cache entry for the Client and withdraws the IP 1551 route from the AERO routing system. 1553 3.16. AERO Forwarding Agent Discovery 1555 AERO Relays, Servers and Clients MAY associate with one or more 1556 companion AERO Forwarding Agents as platforms for offloading high- 1557 speed data plane traffic. AERO nodes distribute forwarding 1558 information to Forwarding Agents via an out-of-band messaging service 1559 (e.g., NETCONF [RFC6241], etc.). 1561 When an AERO node receives a data packet on an AERO interface with a 1562 network layer destination address for which it has distributed 1563 forwarding information to one or more Forwarding Agents, the node 1564 returns an RA message to the source neighbor (subject to rate 1565 limiting) then forwards the data packet as usual. The RA message 1566 includes one or more SLLAOs with the link-layer addresses of 1567 candidate Forwarding Engines. 1569 If the forwarding information pertains only to a specific ACP, the 1570 AERO node sets the network-layer source address of the RA to the AERO 1571 address corresponding to the ACP, and sets the default router 1572 lifetime to 0. If the forwarding information pertains to all 1573 addresses, the AERO node instead sets the network-layer source 1574 address of the RA to its own link-local address and sets the default 1575 router lifetime to a non-zero value. 1577 When the source neighbor receives the RA message, it SHOULD record 1578 the link-layer addresses in the SLLAOs as the encapsulation addresses 1579 to use for sending subsequent data packets with addresses that match 1580 the information in the RA. However, the source MUST continue to use 1581 the primary link-layer address of the AERO node as the encapsulation 1582 address for sending control messages. 1584 3.17. AERO Intradomain Route Optimization 1586 When a source Client forwards packets to a prospective correspondent 1587 Client within the same AERO link domain (i.e., one for which the 1588 packet's destination address is covered by an ASP), the source Client 1589 initiates an intra-domain AERO route optimization procedure. The 1590 procedure is based on an exchange of IPv6 ND messages using a chain 1591 of AERO Servers and Relays as a trust basis. This procedure is in 1592 contrast to the Return Routability procedure required for route 1593 optimization to a correspondent Client located in the Internet as 1594 described in Section 3.22. The following sections specify the AERO 1595 intradomain route optimization procedure. 1597 3.17.1. Reference Operational Scenario 1599 Figure 8 depicts the AERO intradomain route optimization reference 1600 operational scenario, using IPv6 addressing as the example (while not 1601 shown, a corresponding example for IPv4 addressing can be easily 1602 constructed). The figure shows an AERO Relay ('R1'), two AERO 1603 Servers ('S1', 'S2'), two AERO Clients ('C1', 'C2') and two ordinary 1604 IPv6 hosts ('H1', 'H2'): 1606 +--------------+ +--------------+ +--------------+ 1607 | Server S1 | | Relay R1 | | Server S2 | 1608 +--------------+ +--------------+ +--------------+ 1609 fe80::2 fe80::1 fe80::3 1610 L2(S1) L2(R1) L2(S2) 1611 | | | 1612 X-----+-----+------------------+-----------------+----+----X 1613 | AERO Link | 1614 L2(A) L2(B) 1615 fe80::2001:db8:0:0 fe80::2001:db8:1:0 1616 +--------------+ +--------------+ 1617 |AERO Client C1| |AERO Client C2| 1618 +--------------+ +--------------+ 1619 2001:DB8:0::/48 2001:DB8:1::/48 1620 | | 1621 .-. .-. 1622 ,-( _)-. 2001:db8:0::1 2001:db8:1::1 ,-( _)-. 1623 .-(_ IP )-. +---------+ +---------+ .-(_ IP )-. 1624 (__ EUN )--| Host H1 | | Host H2 |--(__ EUN ) 1625 `-(______)-' +---------+ +---------+ `-(______)-' 1627 Figure 8: AERO Reference Operational Scenario 1629 In Figure 8, Relay ('R1') assigns the address fe80::1 to its AERO 1630 interface with link-layer address L2(R1), Server ('S1') assigns the 1631 address fe80::2 with link-layer address L2(S1),and Server ('S2') 1632 assigns the address fe80::3 with link-layer address L2(S2). Servers 1633 ('S1') and ('S2') next arrange to add their link-layer addresses to a 1634 published list of valid Servers for the AERO link. 1636 AERO Client ('C1') receives the ACP 2001:db8:0::/48 in a DHCPv6 PD 1637 exchange via AERO Server ('S1') then assigns the address 1638 fe80::2001:db8:0:0 to its AERO interface with link-layer address 1639 L2(C1). Client ('C1') configures a default route and neighbor cache 1640 entry via the AERO interface with next-hop address fe80::2 and link- 1641 layer address L2(S1), then sub-delegates the ACP to its attached 1642 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1643 address 2001:db8:0::1. 1645 AERO Client ('C2') receives the ACP 2001:db8:1::/48 in a DHCPv6 PD 1646 exchange via AERO Server ('S2') then assigns the address 1647 fe80::2001:db8:1:0 to its AERO interface with link-layer address 1648 L2(C2). Client ('C2') configures a default route and neighbor cache 1649 entry via the AERO interface with next-hop address fe80::3 and link- 1650 layer address L2(S2), then sub-delegates the ACP to its attached 1651 EUNs. IPv6 host ('H1') connects to the EUN, and configures the 1652 address 2001:db8:1::1. 1654 3.17.2. Concept of Operations 1656 Again, with reference to Figure 8, when source host ('H1') sends a 1657 packet to destination host ('H2'), the packet is first forwarded over 1658 the source host's attached EUN to Client ('C1'). Client ('C1') then 1659 forwards the packet via its AERO interface to Server ('S1') and also 1660 sends a Predirect message toward Client ('C2') via Server ('S1'). 1661 Server ('S1') then re-encapsulates and forwards both the packet and 1662 the Predirect message out the same AERO interface toward Client 1663 ('C2') via Relay ('R1'). 1665 When Relay ('R1') receives the packet and Predirect message, it 1666 consults its forwarding table to discover Server ('S2') as the next 1667 hop toward Client ('C2'). Relay ('R1') then forwards both the packet 1668 and the Predirect message to Server ('S2'), which then forwards them 1669 to Client ('C2'). 1671 After Client ('C2') receives the Predirect message, it process the 1672 message and returns a Redirect message toward Client ('C1') via 1673 Server ('S2'). During the process, Client ('C2') also creates or 1674 updates a dynamic neighbor cache entry for Client ('C1'). 1676 When Server ('S2') receives the Redirect message, it re-encapsulates 1677 the message and forwards it on to Relay ('R1'), which forwards the 1678 message on to Server ('S1') which forwards the message on to Client 1679 ('C1'). After Client ('C1') receives the Redirect message, it 1680 processes the message and creates or updates a dynamic neighbor cache 1681 entry for Client ('C2'). 1683 Following the above Predirect/Redirect message exchange, forwarding 1684 of packets from Client ('C1') to Client ('C2') without involving any 1685 intermediate nodes is enabled. The mechanisms that support this 1686 exchange are specified in the following sections. 1688 3.17.3. Message Format 1690 AERO Redirect/Predirect messages use the same format as for ICMPv6 1691 Redirect messages depicted in Section 4.5 of [RFC4861], but also 1692 include a new "Prefix Length" field taken from the low-order 8 bits 1693 of the Redirect message Reserved field. For IPv6, valid values for 1694 the Prefix Length field are 0 through 64; for IPv4, valid values are 1695 0 through 32. The Redirect/Predirect messages are formatted as shown 1696 in Figure 9: 1698 0 1 2 3 1699 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 1700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1701 | Type (=137) | Code (=0/1) | Checksum | 1702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1703 | Reserved | Prefix Length | 1704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1705 | | 1706 + + 1707 | | 1708 + Target Address + 1709 | | 1710 + + 1711 | | 1712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1713 | | 1714 + + 1715 | | 1716 + Destination Address + 1717 | | 1718 + + 1719 | | 1720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1721 | Options ... 1722 +-+-+-+-+-+-+-+-+-+-+-+- 1724 Figure 9: AERO Redirect/Predirect Message Format 1726 3.17.4. Sending Predirects 1728 When a Client forwards a packet with a source address from one of its 1729 ACPs toward a destination address covered by an ASP (i.e., toward 1730 another AERO Client connected to the same AERO link), the source 1731 Client MAY send a Predirect message forward toward the destination 1732 Client via the Server. 1734 In the reference operational scenario, when Client ('C1') forwards a 1735 packet toward Client ('C2'), it MAY also send a Predirect message 1736 forward toward Client ('C2'), subject to rate limiting (see 1737 Section 8.2 of [RFC4861]). Client ('C1') prepares the Predirect 1738 message as follows: 1740 o the link-layer source address is set to 'L2(C1)' (i.e., the link- 1741 layer address of Client ('C1')). 1743 o the link-layer destination address is set to 'L2(S1)' (i.e., the 1744 link-layer address of Server ('S1')). 1746 o the network-layer source address is set to fe80::2001:db8:0:0 1747 (i.e., the AERO address of Client ('C1')). 1749 o the network-layer destination address is set to fe80::2001:db8:1:0 1750 (i.e., the AERO address of Client ('C2')). 1752 o the Type is set to 137. 1754 o the Code is set to 1 to indicate "Predirect". 1756 o the Prefix Length is set to the length of the prefix to be 1757 assigned to the Target Address. 1759 o the Target Address is set to fe80::2001:db8:0:0 (i.e., the AERO 1760 address of Client ('C1')). 1762 o the Destination Address is set to the source address of the 1763 originating packet that triggered the Predirection event. (If the 1764 originating packet is an IPv4 packet, the address is constructed 1765 in IPv4-compatible IPv6 address format). 1767 o the message includes one or more TLLAOs with Link ID and 1768 Preference set to appropriate values for Client ('C1')'s 1769 underlying interfaces, and with UDP Port Number and IP Address set 1770 to 0'. 1772 o the message SHOULD include a Timestamp option and a Nonce option. 1774 o the message includes a Redirected Header Option (RHO) that 1775 contains the originating packet truncated if necessary to ensure 1776 that at least the network-layer header is included but the size of 1777 the message does not exceed 1280 bytes. 1779 Note that the act of sending Predirect messages is cited as "MAY", 1780 since Client ('C1') may have advanced knowledge that the direct path 1781 to Client ('C2') would be unusable or otherwise undesirable. If the 1782 direct path later becomes unusable after the initial route 1783 optimization, Client ('C1') simply allows packets to again flow 1784 through Server ('S1'). 1786 3.17.5. Re-encapsulating and Relaying Predirects 1788 When Server ('S1') receives a Predirect message from Client ('C1'), 1789 it first verifies that the TLLAOs in the Predirect are a proper 1790 subset of the Link IDs in Client ('C1')'s neighbor cache entry. If 1791 the Client's TLLAOs are not acceptable, Server ('S1') discards the 1792 message. Otherwise, Server ('S1') validates the message according to 1793 the ICMPv6 Redirect message validation rules in Section 8.1 of 1794 [RFC4861], except that the Predirect has Code=1. Server ('S1') also 1795 verifies that Client ('C1') is authorized to use the Prefix Length in 1796 the Predirect when applied to the AERO address in the network-layer 1797 source address by searching for the AERO address in the neighbor 1798 cache. If validation fails, Server ('S1') discards the Predirect; 1799 otherwise, it copies the correct UDP Port numbers and IP Addresses 1800 for Client ('C1')'s links into the (previously empty) TLLAOs. 1802 Server ('S1') then examines the network-layer destination address of 1803 the Predirect to determine the next hop toward Client ('C2') by 1804 searching for the AERO address in the neighbor cache. Since Client 1805 ('C2') is not one of its neighbors, Server ('S1') re-encapsulates the 1806 Predirect and relays it via Relay ('R1') by changing the link-layer 1807 source address of the message to 'L2(S1)' and changing the link-layer 1808 destination address to 'L2(R1)'. Server ('S1') finally forwards the 1809 re-encapsulated message to Relay ('R1') without decrementing the 1810 network-layer TTL/Hop Limit field. 1812 When Relay ('R1') receives the Predirect message from Server ('S1') 1813 it determines that Server ('S2') is the next hop toward Client ('C2') 1814 by consulting its forwarding table. Relay ('R1') then re- 1815 encapsulates the Predirect while changing the link-layer source 1816 address to 'L2(R1)' and changing the link-layer destination address 1817 to 'L2(S2)'. Relay ('R1') then relays the Predirect via Server 1818 ('S2'). 1820 When Server ('S2') receives the Predirect message from Relay ('R1') 1821 it determines that Client ('C2') is a neighbor by consulting its 1822 neighbor cache. Server ('S2') then re-encapsulates the Predirect 1823 while changing the link-layer source address to 'L2(S2)' and changing 1824 the link-layer destination address to 'L2(C2)'. Server ('S2') then 1825 forwards the message to Client ('C2'). 1827 3.17.6. Processing Predirects and Sending Redirects 1829 When Client ('C2') receives the Predirect message, it accepts the 1830 Predirect only if the message has a link-layer source address of one 1831 of its Servers (e.g., L2(S2)). Client ('C2') further accepts the 1832 message only if it is willing to serve as a redirection target. 1833 Next, Client ('C2') validates the message according to the ICMPv6 1834 Redirect message validation rules in Section 8.1 of [RFC4861], except 1835 that it accepts the message even though Code=1 and even though the 1836 network-layer source address is not that of it's current first-hop 1837 router. 1839 In the reference operational scenario, when Client ('C2') receives a 1840 valid Predirect message, it either creates or updates a dynamic 1841 neighbor cache entry that stores the Target Address of the message as 1842 the network-layer address of Client ('C1') , stores the link-layer 1843 addresses found in the TLLAOs as the link-layer addresses of Client 1844 ('C1') and stores the Prefix Length as the length to be applied to 1845 the network-layer address for forwarding purposes. Client ('C2') 1846 then sets AcceptTime for the neighbor cache entry to ACCEPT_TIME. 1848 After processing the message, Client ('C2') prepares a Redirect 1849 message response as follows: 1851 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 1852 layer address of Client ('C2')). 1854 o the link-layer destination address is set to 'L2(S2)' (i.e., the 1855 link-layer address of Server ('S2')). 1857 o the network-layer source address is set to fe80::2001:db8:1:0 1858 (i.e., the AERO address of Client ('C2')). 1860 o the network-layer destination address is set to fe80::2001:db8:0:0 1861 (i.e., the AERO address of Client ('C1')). 1863 o the Type is set to 137. 1865 o the Code is set to 0 to indicate "Redirect". 1867 o the Prefix Length is set to the length of the prefix to be applied 1868 to the Target Address. 1870 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 1871 address of Client ('C2')). 1873 o the Destination Address is set to the destination address of the 1874 originating packet that triggered the Redirection event. (If the 1875 originating packet is an IPv4 packet, the address is constructed 1876 in IPv4-compatible IPv6 address format). 1878 o the message includes one or more TLLAOs with Link ID and 1879 Preference set to appropriate values for Client ('C2')'s 1880 underlying interfaces, and with UDP Port Number and IP Address set 1881 to '0'. 1883 o the message SHOULD include a Timestamp option and MUST echo the 1884 Nonce option received in the Predirect (i.e., if a Nonce option is 1885 included). 1887 o the message includes as much of the RHO copied from the 1888 corresponding AERO Predirect message as possible such that at 1889 least the network-layer header is included but the size of the 1890 message does not exceed 1280 bytes. 1892 After Client ('C2') prepares the Redirect message, it sends the 1893 message to Server ('S2'). 1895 3.17.7. Re-encapsulating and Relaying Redirects 1897 When Server ('S2') receives a Redirect message from Client ('C2'), it 1898 first verifies that the TLLAOs in the Redirect are a proper subset of 1899 the Link IDs in Client ('C2')'s neighbor cache entry. If the 1900 Client's TLLAOs are not acceptable, Server ('S2') discards the 1901 message. Otherwise, Server ('S2') validates the message according to 1902 the ICMPv6 Redirect message validation rules in Section 8.1 of 1903 [RFC4861]. Server ('S2') also verifies that Client ('C2') is 1904 authorized to use the Prefix Length in the Redirect when applied to 1905 the AERO address in the network-layer source address by searching for 1906 the AERO address in the neighbor cache. If validation fails, Server 1907 ('S2') discards the Predirect; otherwise, it copies the correct UDP 1908 Port numbers and IP Addresses for Client ('C2')'s links into the 1909 (previously empty) TLLAOs. 1911 Server ('S2') then examines the network-layer destination address of 1912 the Predirect to determine the next hop toward Client ('C2') by 1913 searching for the AERO address in the neighbor cache. Since Client 1914 ('C2') is not a neighbor, Server ('S2') re-encapsulates the Predirect 1915 and relays it via Relay ('R1') by changing the link-layer source 1916 address of the message to 'L2(S2)' and changing the link-layer 1917 destination address to 'L2(R1)'. Server ('S2') finally forwards the 1918 re-encapsulated message to Relay ('R1') without decrementing the 1919 network-layer TTL/Hop Limit field. 1921 When Relay ('R1') receives the Predirect message from Server ('S2') 1922 it determines that Server ('S1') is the next hop toward Client ('C1') 1923 by consulting its forwarding table. Relay ('R1') then re- 1924 encapsulates the Predirect while changing the link-layer source 1925 address to 'L2(R1)' and changing the link-layer destination address 1926 to 'L2(S1)'. Relay ('R1') then relays the Predirect via Server 1927 ('S1'). 1929 When Server ('S1') receives the Predirect message from Relay ('R1') 1930 it determines that Client ('C1') is a neighbor by consulting its 1931 neighbor cache. Server ('S1') then re-encapsulates the Predirect 1932 while changing the link-layer source address to 'L2(S1)' and changing 1933 the link-layer destination address to 'L2(C1)'. Server ('S1') then 1934 forwards the message to Client ('C1'). 1936 3.17.8. Processing Redirects 1938 When Client ('C1') receives the Redirect message, it accepts the 1939 message only if it has a link-layer source address of one of its 1940 Servers (e.g., ''L2(S1)'). Next, Client ('C1') validates the message 1941 according to the ICMPv6 Redirect message validation rules in 1942 Section 8.1 of [RFC4861], except that it accepts the message even 1943 though the network-layer source address is not that of it's current 1944 first-hop router. Following validation, Client ('C1') then processes 1945 the message as follows. 1947 In the reference operational scenario, when Client ('C1') receives 1948 the Redirect message, it either creates or updates a dynamic neighbor 1949 cache entry that stores the Target Address of the message as the 1950 network-layer address of Client ('C2'), stores the link-layer 1951 addresses found in the TLLAOs as the link-layer addresses of Client 1952 ('C2') and stores the Prefix Length as the length to be applied to 1953 the network-layer address for forwarding purposes. Client ('C1') 1954 then sets ForwardTime for the neighbor cache entry to FORWARD_TIME. 1956 Now, Client ('C1') has a neighbor cache entry with a valid 1957 ForwardTime value, while Client ('C2') has a neighbor cache entry 1958 with a valid AcceptTime value. Thereafter, Client ('C1') may forward 1959 ordinary network-layer data packets directly to Client ('C2') without 1960 involving any intermediate nodes, and Client ('C2') can verify that 1961 the packets came from an acceptable source. (In order for Client 1962 ('C2') to forward packets to Client ('C1'), a corresponding 1963 Predirect/Redirect message exchange is required in the reverse 1964 direction; hence, the mechanism is asymmetric.) 1966 3.17.9. Server-Oriented Redirection 1968 In some environments, the Server nearest the target Client may need 1969 to serve as the redirection target, e.g., if direct Client-to-Client 1970 communications are not possible. In that case, the Server prepares 1971 the Redirect message the same as if it were the destination Client 1972 (see: Section 3.17.6), except that it writes its own link-layer 1973 address in the TLLAO option. The Server must then maintain a dynamic 1974 neighbor cache entry for the redirected source Client. 1976 3.18. Neighbor Unreachability Detection (NUD) 1978 AERO nodes perform Neighbor Unreachability Detection (NUD) by sending 1979 unicast NS messages to elicit solicited NA messages from neighbors 1980 the same as described in [RFC4861]. NUD is performed either 1981 reactively in response to persistent L2 errors (see Section 3.14) or 1982 proactively to refresh existing neighbor cache entries. 1984 When an AERO node sends an NS/NA message, it MUST use its link-local 1985 address as the IPv6 source address and the link-local address of the 1986 neighbor as the IPv6 destination address. When an AERO node receives 1987 an NS message or a solicited NA message, it accepts the message if it 1988 has a neighbor cache entry for the neighbor; otherwise, it ignores 1989 the message. 1991 When a source Client is redirected to a target Client it SHOULD 1992 proactively test the direct path by sending an initial NS message to 1993 elicit a solicited NA response. While testing the path, the source 1994 Client can optionally continue sending packets via the Server, 1995 maintain a small queue of packets until target reachability is 1996 confirmed, or (optimistically) allow packets to flow directly to the 1997 target. The source Client SHOULD thereafter continue to proactively 1998 test the direct path to the target Client (see Section 7.3 of 1999 [RFC4861]) periodically in order to keep dynamic neighbor cache 2000 entries alive. 2002 In particular, while the source Client is actively sending packets to 2003 the target Client it SHOULD also send NS messages separated by 2004 RETRANS_TIMER milliseconds in order to receive solicited NA messages. 2005 If the source Client is unable to elicit a solicited NA response from 2006 the target Client after MAX_RETRY attempts, it SHOULD set ForwardTime 2007 to 0 and resume sending packets via one of its Servers. Otherwise, 2008 the source Client considers the path usable and SHOULD thereafter 2009 process any link-layer errors as a hint that the direct path to the 2010 target Client has either failed or has become intermittent. 2012 When a target Client receives an NS message from a source Client, it 2013 resets AcceptTime to ACCEPT_TIME if a neighbor cache entry exists; 2014 otherwise, it discards the NS message. If ForwardTime is non-zero, 2015 the target Client then sends a solicited NA message to the link-layer 2016 address of the source Client; otherwise, it sends the solicited NA 2017 message to the link-layer address of one of its Servers. 2019 When a source Client receives a solicited NA message from a target 2020 Client, it resets ForwardTime to FORWARD_TIME if a neighbor cache 2021 entry exists; otherwise, it discards the NA message. 2023 When ForwardTime for a dynamic neighbor cache entry expires, the 2024 source Client resumes sending any subsequent packets via a Server and 2025 may (eventually) attempt to re-initiate the AERO redirection process. 2026 When AcceptTime for a dynamic neighbor cache entry expires, the 2027 target Client discards any subsequent packets received directly from 2028 the source Client. When both ForwardTime and AcceptTime for a 2029 dynamic neighbor cache entry expire, the Client deletes the neighbor 2030 cache entry. 2032 3.19. Mobility Management 2034 3.19.1. Announcing Link-Layer Address Changes 2036 When a Client needs to change its link-layer address, e.g., due to a 2037 mobility event, it performs an immediate DHCPv6 Rebind/Reply exchange 2038 via each of its Servers using the new link-layer address as the 2039 source and with a CLLAO that includes the correct Link ID and 2040 Preference values. If authentication succeeds, the Server then 2041 update its neighbor cache and sends a DHCPv6 Reply. Note that if the 2042 Client does not issue a DHCPv6 Rebind before the lease lifetime 2043 expires (e.g., if the Client has been out of touch with the Server 2044 for a considerable amount of time), the Server's Reply will report 2045 NoBinding and the Client must re-initiate the DHCPv6 PD procedure. 2047 Next, the Client sends unsolicited NA messages to each of its 2048 correspondent Client neighbors using the same procedures as specified 2049 in Section 7.2.6 of [RFC4861], except that it sends the messages as 2050 unicast to each neighbor via a Server instead of multicast. In this 2051 process, the Client should send no more than 2052 MAX_NEIGHBOR_ADVERTISEMENT messages separated by no less than 2053 RETRANS_TIMER seconds to each neighbor. 2055 With reference to Figure 8, when Client ('C2') needs to change its 2056 link-layer address it sends unicast unsolicited NA messages to Client 2057 ('C1') via Server ('S2') as follows: 2059 o the link-layer source address is set to 'L2(C2)' (i.e., the link- 2060 layer address of Client ('C2')). 2062 o the link-layer destination address is set to 'L2(S2)' (i.e., the 2063 link-layer address of Server ('S2')). 2065 o the network-layer source address is set to fe80::2001:db8:1:0 2066 (i.e., the AERO address of Client ('C2')). 2068 o the network-layer destination address is set to fe80::2001:db8:0:0 2069 (i.e., the AERO address of Client ('C1')). 2071 o the Type is set to 136. 2073 o the Code is set to 0. 2075 o the Solicited flag is set to 0. 2077 o the Override flag is set to 1. 2079 o the Target Address is set to fe80::2001:db8:1:0 (i.e., the AERO 2080 address of Client ('C2')). 2082 o the message includes one or more TLLAOs with Link ID and 2083 Preference set to appropriate values for Client ('C2')'s 2084 underlying interfaces, and with UDP Port Number and IP Address set 2085 to '0'. 2087 o the message SHOULD include a Timestamp option. 2089 When Server ('S1') receives the NA message, it relays the message in 2090 the same way as described for relaying Redirect messages in 2091 Section 3.17.7. In particular, Server ('S1') copies the correct UDP 2092 port numbers and IP addresses into the TLLAOs, changes the link-layer 2093 source address to its own address, changes the link-layer destination 2094 address to the address of Relay ('R1'), then forwards the NA message 2095 via the relaying chain the same as for a Redirect. 2097 When Client ('C1') receives the NA message, it accepts the message 2098 only if it already has a neighbor cache entry for Client ('C2') then 2099 updates the link-layer addresses for Client ('C2') based on the 2100 addresses in the TLLAOs. Next, Client ('C1') SHOULD initiate the NUD 2101 procedures specified in Section 3.18 to provide Client ('C2') with an 2102 indication that the link-layer source address has been updated, and 2103 to refresh ('C2')'s AcceptTime and ('C1')'s ForwardTime timers. 2105 If Client ('C2') receives an NS message from Client ('C1') indicating 2106 that an unsolicited NA has updated its neighbor cache, Client ('C2') 2107 need not send additional unsolicited NAs. If Client ('C2')'s 2108 unsolicited NA messages are somehow lost, however, Client ('C1') will 2109 soon learn of the mobility event via NUD. 2111 3.19.2. Bringing New Links Into Service 2113 When a Client needs to bring a new underlying interface into service 2114 (e.g., when it activates a new data link), it performs an immediate 2115 Rebind/Reply exchange via each of its Servers using the new link- 2116 layer address as the source address and with a CLLAO that includes 2117 the new Link ID and Preference values. If authentication succeeds, 2118 the Server then updates its neighbor cache and sends a DHCPv6 Reply. 2120 The Client MAY then send unsolicited NA messages to each of its 2121 correspondent Clients to inform them of the new link-layer address as 2122 described in Section 3.19.1. 2124 3.19.3. Removing Existing Links from Service 2126 When a Client needs to remove an existing underlying interface from 2127 service (e.g., when it de-activates an existing data link), it 2128 performs an immediate Rebind/Reply exchange via each of its Servers 2129 over any available link with a CLLAO that includes the deprecated 2130 Link ID and a Preference value of 0. If authentication succeeds, the 2131 Server then updates its neighbor cache and sends a DHCPv6 Reply. The 2132 Client SHOULD then send unsolicited NA messages to each of its 2133 correspondent Clients to inform them of the deprecated link-layer 2134 address as described in Section 3.19.1. 2136 3.19.4. Moving to a New Server 2138 When a Client associates with a new Server, it performs the Client 2139 procedures specified in Section 3.15.2. 2141 When a Client disassociates with an existing Server, it sends a 2142 DHCPv6 Release message via a new Server to the unicast link-local 2143 network layer address of the old Server. The new Server then writes 2144 its own link-layer address in the DHCPv6 release message IP source 2145 address and forwards the message to the old Server. 2147 When the old Server receives the DHCPv6 Release, it first 2148 authenticates the message. The Server then resets the Client's 2149 neighbor cache entry lifetime to 5 seconds, rewrites the link-layer 2150 address in the neighbor cache entry to the address of the new Server, 2151 then returns a DHCPv6 Reply message to the Client via the old Server. 2152 When the lifetime expires, the old Server withdraws the IP route from 2153 the AERO routing system and deletes the neighbor cache entry for the 2154 Client. The Client can then use the Reply message to verify that the 2155 termination signal has been processed, and can delete both the 2156 default route and the neighbor cache entry for the old Server. (Note 2157 that since Release/Reply messages may be lost in the network the 2158 Client MUST retry until it gets Reply indicating that the Release was 2159 successful.) 2161 Clients SHOULD NOT move rapidly between Servers in order to avoid 2162 causing excessive oscillations in the AERO routing system. Such 2163 oscillations could result in intermittent reachability for the Client 2164 itself, while causing little harm to the network. Examples of when a 2165 Client might wish to change to a different Server include a Server 2166 that has gone unreachable, topological movements of significant 2167 distance, etc. 2169 3.20. Proxy AERO 2171 Proxy Mobile IPv6 (PMIPv6) [RFC5213][RFC5844][RFC5949] presents a 2172 localized mobility management scheme for use within an access network 2173 domain. It is typically used in WiFi and cellular wireless access 2174 networks, and allows Mobile Nodes (MNs) to receive and retain an IP 2175 address that remains stable within the access network domain without 2176 needing to implement any special mobility protocols. In the PMIPv6 2177 architecture, access network devices known as Mobility Access 2178 Gateways (MAGs) provide MNs with an access link abstraction and 2179 receive prefixes for the MNs from a Local Mobility Anchor (LMA). 2181 In a proxy AERO domain, a proxy AERO Client (acting as a MAG) can 2182 similarly provide proxy services for MNs that do not participate in 2183 AERO messaging. The proxy Client presents an access link abstraction 2184 to MNs, and performs DHCPv6 PD exchanges over the AERO interface with 2185 an AERO Server (acting as an LMA) to receive ACPs for address 2186 provisioning of new MNs that come onto an access link. This scheme 2187 assumes that proxy Clients act as fixed (non-mobile) infrastructure 2188 elements under the same administrative trust basis as for Relays and 2189 Servers. 2191 When an MN comes onto an access link within a proxy AERO domain for 2192 the first time, the proxy Client authenticates the MN and obtains a 2193 unique identifier that it can use as a DHCPv6 DUID then issues a 2194 DHCPv6 PD Request to its Server. When the Server delegates an ACP, 2195 the proxy Client creates an AERO address for the MN and assigns the 2196 ACP to the MN's access link. The proxy Client then configures itself 2197 as a default router for the MN and provides address autoconfiguration 2198 services (e.g., SLAAC, DHCPv6, DHCPv4, etc.) for provisioning MN 2199 addresses from the ACP over the access link. Since the proxy Client 2200 may serve many such MNs simultaneously, it may receive multiple ACP 2201 prefix delegations and configure multiple AERO addresses, i.e., one 2202 for each MN. 2204 When two MNs are associated with the same proxy Client, the Client 2205 can forward traffic between the MNs without involving a Server since 2206 it configures the AERO addresses of both MNs and therefore also has 2207 the necessary routing information. When two MNs are associated with 2208 different proxy Clients, the source MN's Client can initiate standard 2209 AERO route optimization to discover a direct path to the target MN's 2210 Client through the exchange of Predirect/Redirect messages. 2212 When an MN in a proxy AERO domain leaves an access link provided by 2213 an old proxy Client, the MN issues an access link-specific "leave" 2214 message that informs the old Client of the link-layer address of a 2215 new Client on the planned new access link. This is known as a 2216 "predictive handover". When an MN comes onto an access link provided 2217 by a new proxy Client, the MN issues an access link-specific "join" 2218 message that informs the new Client of the link-layer address of the 2219 old Client on the actual old access link. This is known as a 2220 "reactive handover". 2222 Upon receiving a predictive handover indication, the old proxy Client 2223 sends a DHCPv6 PD Request message directly to the new Client and 2224 queues any arriving data packets addressed to the departed MN. The 2225 Request message includes the MN's ID as the DUID, the ACP in an IA_PD 2226 option, the AERO address derived from the MN's ACP as the network- 2227 layer source address, 'All_DHCP_Relay_Agents_and_Servers' as the 2228 network-layer destination address, the old Client's address as the 2229 link-layer source address and the new Client's address as the link- 2230 layer destination address. When the new Client receives the Request 2231 message, it changes the link-layer source address to its own address, 2232 changes the link-layer destination address to the address of its 2233 Server, and forwards the message to the Server. At the same time, 2234 the new Client creates access link state for the ACP in anticipation 2235 of the MN's arrival (while queuing any data packets until the MN 2236 arrives), creates a neighbor cache entry for the old Client with 2237 AcceptTime set to ACCEPT_TIME, then sends a Redirect message back to 2238 the old Client. When the old Client receives the Redirect message, 2239 it creates a neighbor cache entry for new Client with ForwardTime set 2240 to FORWARD_TIME, then forwards any queued data packets to the new 2241 Client. At the same time, the old Client sends a DHCPv6 PD Release 2242 message to its Server. Finally, the old Client sends unsolicited NA 2243 messages to any of the ACP's correspondents with a TLLAO containing 2244 the link-layer address of the new Client. This follows the procedure 2245 specified in Section 3.19.1, except that it is the old Client and not 2246 the Server that supplies the link-layer address. 2248 Upon receiving a reactive handover indication, the new proxy Client 2249 creates access link state for the MN's ACP, sends a DHCPv6 PD Request 2250 message to its Server, and sends a DHCPv6 PD Release message directly 2251 to the old Client. The Release message includes the MN's ID as the 2252 DUID, the ACP in an IA_PD option, the AERO address derived from the 2253 MN's ACP as the network-layer source address, 2254 'All_DHCP_Relay_Agents_and_Servers' as the network-layer destination 2255 address, the new Client's address as the link-layer source address 2256 and the old Client's address as the link-layer destination address. 2257 When the old Client receives the Release message, it changes the 2258 link-layer source address to its own address, changes the link-layer 2259 destination address to the address of its Server, and forwards the 2260 message to the Server. At the same time, the old Client sends a 2261 Predirect message back to the new Client and queues any arriving data 2262 packets addressed to the departed MN. When the new Client receives 2263 the Predirect, it creates a neighbor cache entry for the old Client 2264 with AcceptTime set to ACCEPT_TIME, then sends a Redirect message 2265 back to the old Client. When the old Client receives the Redirect 2266 message, it creates a neighbor cache entry for the new Client with 2267 ForwardTime set to FORWARD_TIME, then forwards any queued data 2268 packets to the new Client. Finally, the old Client sends unsolicited 2269 NA messages to correspondents the same as for the predictive case. 2271 When a Server processes a DHCPv6 Request message, it creates a 2272 neighbor cache entry for this ACP if none currently exists. If a 2273 neighbor cache entry already exists, however, the Server changes the 2274 link-layer address to the address of the new proxy Client (this 2275 satisfies the case of both the old Client and new Client using the 2276 same Server). 2278 When a Server processes a DHCPv6 Release message, it resets the 2279 neighbor cache entry lifetime for this ACP to 5 seconds if the cached 2280 link-layer address matches the old proxy Client's address. 2281 Otherwise, the Server ignores the Release message (this satisfies the 2282 case of both the old Client and new Client using the same Server). 2284 When a correspondent Client receives an unsolicited NA message, it 2285 changes the link-layer address for the ACP's neighbor cache entry to 2286 the address of the new proxy Client. The correspondent Client then 2287 issues a Predirect/Redirect exchange to establish a new neighbor 2288 cache entry in the new Client. 2290 From an architectural perspective, in addition to the use of DHCPv6 2291 PD and IPv6 ND signaling the AERO approach differs from PMIPv6 in its 2292 use of the NBMA virtual link model instead of point-to-point tunnels. 2293 This provides a more agile interface for Client/Server and Client/ 2294 Client coordinations, and also facilitates simple route optimization. 2295 The AERO routing system is also arranged in such a fashion that 2296 Clients get the same service from any Server they happen to associate 2297 with. This provides a natural fault tolerance and load balancing 2298 capability such as desired for distributed mobility management. 2300 3.21. Extending AERO Links Through Security Gateways 2302 When an enterprise mobile device moves from a campus LAN connection 2303 to a public Internet link, it must re-enter the enterprise via a 2304 security gateway that has both a physical interface connection to the 2305 Internet and a physical interface connection to the enterprise 2306 internetwork. This most often entails the establishment of a Virtual 2307 Private Network (VPN) link over the public Internet from the mobile 2308 device to the security gateway. During this process, the mobile 2309 device supplies the security gateway with its public Internet address 2310 as the link-layer address for the VPN. The mobile device then acts 2311 as an AERO Client to negotiate with the security gateway to obtain 2312 its ACP. 2314 In order to satisfy this need, the security gateway also operates as 2315 an AERO Server with support for AERO Client proxying. In particular, 2316 when a mobile device (i.e., the Client) connects via the security 2317 gateway (i.e., the Server), the Server provides the Client with an 2318 ACP in a DHCPv6 PD exchange the same as if it were attached to an 2319 enterprise campus access link. The Server then replaces the Client's 2320 link-layer source address with the Server's enterprise-facing link- 2321 layer address in all AERO messages the Client sends toward neighbors 2322 on the AERO link. The AERO messages are then delivered to other 2323 devices on the AERO link as if they were originated by the security 2324 gateway instead of by the AERO Client. In the reverse direction, the 2325 AERO messages sourced by devices within the enterprise network can be 2326 forwarded to the security gateway, which then replaces the link-layer 2327 destination address with the Client's link-layer address and replaces 2328 the link-layer source address with its own (Internet-facing) link- 2329 layer address. 2331 After receiving the ACP, the Client can send IP packets that use an 2332 address taken from the ACP as the network layer source address, the 2333 Client's link-layer address as the link-layer source address, and the 2334 Server's Internet-facing link-layer address as the link-layer 2335 destination address. The Server will then rewrite the link-layer 2336 source address with the Server's own enterprise-facing link-layer 2337 address and rewrite the link-layer destination address with the 2338 target AERO node's link-layer address, and the packets will enter the 2339 enterprise network as though they were sourced from a device located 2340 within the enterprise. In the reverse direction, when a packet 2341 sourced by a node within the enterprise network uses a destination 2342 address from the Client's ACP, the packet will be delivered to the 2343 security gateway which then rewrites the link-layer destination 2344 address to the Client's link-layer address and rewrites the link- 2345 layer source address to the Server's Internet-facing link-layer 2346 address. The Server then delivers the packet across the VPN to the 2347 AERO Client. In this way, the AERO virtual link is essentially 2348 extended *through* the security gateway to the point at which the VPN 2349 link and AERO link are effectively grafted together by the link-layer 2350 address rewriting performed by the security gateway. All AERO 2351 messaging services (including route optimization and mobility 2352 signaling) are therefore extended to the Client. 2354 In order to support this virtual link grafting, the security gateway 2355 (acting as an AERO Server) must keep static neighbor cache entries 2356 for all of its associated Clients located on the public Internet. 2357 The neighbor cache entry is keyed by the AERO Client's AERO address 2358 the same as if the Client were located within the enterprise 2359 internetwork. The neighbor cache is then managed in all ways as 2360 though the Client were an ordinary AERO Client. This includes the 2361 AERO IPv6 ND messaging signaling for Route Optimization and Neighbor 2362 Unreachability Detection. 2364 Note that the main difference between a security gateway acting as an 2365 AERO Server and an enterprise-internal AERO Server is that the 2366 security gateway has at least one enterprise-internal physical 2367 interface and at least one public Internet physical interface. 2368 Conversely, the enterprise-internal AERO Server has only enterprise- 2369 internal physical interfaces. For this reason security gateway 2370 proxying is needed to ensure that the public Internet link-layer 2371 addressing space is kept separate from the enterprise-internal link- 2372 layer addressing space. This is afforded through a natural extension 2373 of the security association caching already performed for each VPN 2374 client by the security gateway. 2376 3.22. Extending IPv6 AERO Links to the Internet 2378 When an IPv6 host ('H1') with an address from an ACP owned by AERO 2379 Client ('C1') sends packets to a correspondent IPv6 host ('H2'), the 2380 packets eventually arrive at the IPv6 router that owns ('H2')s 2381 prefix. This IPv6 router may or may not be an AERO Client ('C2') 2382 either within the same home network as ('C1') or in a different home 2383 network. 2385 If Client ('C1') is currently located outside the boundaries of its 2386 home network, it will connect back into the home network via a 2387 security gateway acting as an AERO Server. The packets sent by 2388 ('H1') via ('C1') will then be forwarded through the security gateway 2389 then through the home network and finally to ('C2') where they will 2390 be delivered to ('H2'). This could lead to sub-optimal performance 2391 when ('C2') could instead be reached via a more direct route without 2392 involving the security gateway. 2394 Consider the case when host ('H1') has the IPv6 address 2395 2001:db8:1::1, and Client ('C1') has the ACP 2001:db8:1::/64 with 2396 underlying IPv6 Internet address of 2001:db8:1000::1. Also, host 2397 ('H2') has the IPv6 address 2001:db8:2::1, and Client ('C2') has the 2398 ACP 2001:db8:2::/64 with underlying IPv6 address of 2001:db8:2000::1. 2399 Client ('C1') can determine whether 'C2' is indeed also an AERO 2400 Client willing to serve as a route optimization correspondent by 2401 resolving the AAAA records for the DNS FQDN that matches ('H2')s 2402 prefix, i.e.: 2404 '0.0.0.0.2.0.0.0.8.b.d.0.1.0.0.2.aero.linkupnetworks.net' 2406 If ('C2') is indeed a candidate correspondent, the FQDN lookup will 2407 return a PTR resource record that contains the domain name for the 2408 AERO link that manages ('C2')s ASP. Client ('C1') can then attempt 2409 route optimization using an approach similar to the Return 2410 Routability procedure specified for Mobile IPv6 (MIPv6) [RFC6275]. 2411 In order to support this process, both Clients MUST intercept and 2412 decapsulate packets that have a subnet router anycast address 2413 corresponding to any of the /64 prefixes covered by their respective 2414 ACPs. 2416 To initiate the process, Client ('C1') creates a specially-crafted 2417 encapsulated AERO Predirect message that will be routed through its 2418 home network then through ('C2')s home network and finally to ('C2') 2419 itself. Client ('C1') prepares the initial message in the exchange 2420 as follows: 2422 o The encapsulating IPv6 header source address is set to 2423 2001:db8:1:: (i.e., the IPv6 subnet router anycast address for 2424 ('C1')s ACP) 2426 o The encapsulating IPv6 header destination address is set to 2427 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2428 ('C2')s ACP) 2430 o The encapsulating IPv6 header is followed by a UDP header with 2431 source and destination port set to 8060 2433 o The encapsulated IPv6 header source address is set to 2434 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2436 o The encapsulated IPv6 header destination address is set to 2437 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2439 o The encapsulated AERO Predirect message includes all of the 2440 securing information that would occur in a MIPv6 "Home Test Init" 2441 message (format TBD) 2443 Client ('C1') then further encapsulates the message in the 2444 encapsulating headers necessary to convey the packet to the security 2445 gateway (e.g., through IPsec encapsulation) so that the message now 2446 appears "double-encapsulated". ('C1') then sends the message to the 2447 security gateway, which re-encapsulates and forwards it over the home 2448 network from where it will eventually reach ('C2'). 2450 At the same time, ('C1') creates and sends a second encapsulated AERO 2451 Predirect message that will be routed through the IPv6 Internet 2452 without involving the security gateway. Client ('C1') prepares the 2453 message as follows: 2455 o The encapsulating IPv6 header source address is set to 2456 2001:db8:1000:1 (i.e., the Internet IPv6 address of ('C1')) 2458 o The encapsulating IPv6 header destination address is set to 2459 2001:db8:2:: (i.e., the IPv6 subnet router anycast address for 2460 ('C2')s ACP) 2462 o The encapsulating IPv6 header is followed by a UDP header with 2463 source and destination port set to 8060 2465 o The encapsulated IPv6 header source address is set to 2466 fe80::2001:db8:1:0 (i.e., the AERO address for ('C1')) 2468 o The encapsulated IPv6 header destination address is set to 2469 fe80::2001:db8:2:0 (i.e., the AERO address for ('C2')) 2471 o The encapsulated AERO Predirect message includes all of the 2472 securing information that would occur in a MIPv6 "Care-of Test 2473 Init" message (format TBD) 2475 ('C2') will receive both Predirect messages through its home network 2476 then return a corresponding Redirect for each of the Predirect 2477 messages with the source and destination addresses in the inner and 2478 outer headers reversed. The first message includes all of the 2479 securing information that would occur in a MIPv6 "Home Test" message, 2480 while the second message includes all of the securing information 2481 that would occur in a MIPv6 "Care-of Test" message (formats TBD). 2483 When ('C1') receives the Redirect messages, it performs the necessary 2484 security procedures per the MIPv6 specification. It then prepares an 2485 encapsulated NS message that includes the same source and destination 2486 addresses as for the "Care-of Test Init" Predirect message, and 2487 includes all of the securing information that would occur in a MIPv6 2488 "Binding Update" message (format TBD) and sends the message to 2489 ('C2'). 2491 When ('C2') receives the NS message, if the securing information is 2492 correct it creates or updates a neighbor cache entry for ('C1') with 2493 fe80::2001:db8:1:0 as the network-layer address, 2001:db8:1000::1 as 2494 the link-layer address and with AcceptTime set to ACCEPT_TIME. 2495 ('C2') then sends an encapsulated NA message back to ('C1') that 2496 includes the same source and destination addresses as for the "Care- 2497 of Test" Redirect message, and includes all of the securing 2498 information that would occur in a MIPv6 "Binding Acknowledgement" 2499 message (format TBD) and sends the message to ('C1'). 2501 When ('C1') receives the NA message, it creates or updates a neighbor 2502 cache entry for ('C2') with fe80::2001:db8:2:0 as the network-layer 2503 address and 2001:db8:2:: as the link-layer address and with 2504 ForwardTime set to FORWARD_TIME, thus completing the route 2505 optimization in the forward direction. 2507 ('C1') subsequently forwards encapsulated packets with outer source 2508 address 2001:db8:1000::1, with outer destination address 2509 2001:db8:2::, with inner source address taken from the 2001:db8:1::, 2510 and with inner destination address taken from 2001:db8:2:: due to the 2511 fact that it has a securely-established neighbor cache entry with 2512 non-zero ForwardTime. ('C2') subsequently accepts any such 2513 encapsulated packets due to the fact that it has a securely- 2514 established neighbor cache entry with non-zero AcceptTime. 2516 In order to keep neighbor cache entries alive, ('C1') periodically 2517 sends additional NS messages to ('C2') and receives any NA responses. 2518 If ('C1') moves to a different point of attachment after the initial 2519 route optimization, it sends a new secured NS message to ('C2') as 2520 above to update ('C2')s neighbor cache. 2522 If ('C2') has packets to send to ('C1'), it performs a corresponding 2523 route optimization in the opposite direction following the same 2524 procedures described above. In the process, the already-established 2525 unidirectional neighbor cache entries within ('C1') and ('C2') are 2526 updated to include the now-bidirectional information. In particular, 2527 the AcceptTime and ForwardTime variables for both neighbor cache 2528 entries are updated to non-zero values, and the link-layer address 2529 for ('C1')s neighbor cache entry for ('C2') is reset to 2530 2001:db8:2000::1. 2532 Note that two AERO Clients can use full security protocol messaging 2533 instead of Return Routability, e.g., if strong authentication and/or 2534 confidentiality are desired. In that case, security protocol key 2535 exchanges such as specified for MOBIKE [RFC4555] would be used to 2536 establish security associations and neighbor cache entries between 2537 the AERO clients. Thereafter, AERO NS/NA messaging can be used to 2538 maintain neighbor cache entries, test reachability, and to announce 2539 mobility events. If reachability testing fails, e.g., if both 2540 Clients move at roughly the same time, the Clients can tear down the 2541 security association and neighbor cache entries and again allow 2542 packets to flow through their home network. 2544 3.23. Encapsulation Protocol Version Considerations 2546 A source Client may connect only to an IPvX underlying network, while 2547 the target Client connects only to an IPvY underlying network. In 2548 that case, the target and source Clients have no means for reaching 2549 each other directly (since they connect to underlying networks of 2550 different IP protocol versions) and so must ignore any redirection 2551 messages and continue to send packets via the Server. 2553 3.24. Multicast Considerations 2555 When the underlying network does not support multicast, AERO nodes 2556 map IPv6 link-scoped multicast addresses (including 2557 'All_DHCP_Relay_Agents_and_Servers') to the link-layer address of a 2558 Server. 2560 When the underlying network supports multicast, AERO nodes use the 2561 multicast address mapping specification found in [RFC2529] for IPv4 2562 underlying networks and use a direct multicast mapping for IPv6 2563 underlying networks. (In the latter case, "direct multicast mapping" 2564 means that if the IPv6 multicast destination address of the 2565 encapsulated packet is "M", then the IPv6 multicast destination 2566 address of the encapsulating header is also "M".) 2568 3.25. Operation on AERO Links Without DHCPv6 Services 2570 When Servers on the AERO link do not provide DHCPv6 services, 2571 operation can still be accommodated through administrative 2572 configuration of ACPs on AERO Clients. In that case, administrative 2573 configurations of AERO interface neighbor cache entries on both the 2574 Server and Client are also necessary. However, this may interfere 2575 with the ability for Clients to dynamically change to new Servers, 2576 and can expose the AERO link to misconfigurations unless the 2577 administrative configurations are carefully coordinated. 2579 3.26. Operation on Server-less AERO Links 2581 In some AERO link scenarios, there may be no Servers on the link and/ 2582 or no need for Clients to use a Server as an intermediary trust 2583 anchor. In that case, each Client acts as a Server unto itself to 2584 establish neighbor cache entries by performing direct Client-to- 2585 Client IPv6 ND message exchanges, and some other form of trust basis 2586 must be applied so that each Client can verify that the prospective 2587 neighbor is authorized to use its claimed ACP. 2589 When there is no Server on the link, Clients must arrange to receive 2590 ACPs and publish them via a secure alternate prefix delegation 2591 authority through some means outside the scope of this document. 2593 3.27. Manually-Configured AERO Tunnels 2595 In addition to the dynamic neighbor discovery procedures for AERO 2596 link neighbors described above, AERO encapsulation can be applied to 2597 manually-configured tunnels. In that case, the tunnel endpoints use 2598 an administratively-assigned link-local address and exchange NS/NA 2599 messages the same as for dynamically-established tunnels. 2601 3.28. Intradomain Routing 2603 After a tunnel neighbor relationship has been established, neighbors 2604 can use a traditional dynamic routing protocol over the tunnel to 2605 exchange routing information without having to inject the routes into 2606 the AERO routing system. 2608 4. Implementation Status 2610 An application-layer implementation is in progress. 2612 5. IANA Considerations 2614 IANA is instructed to assign a new 2-octet Hardware Type number 2615 "TBD1" for AERO in the "arp-parameters" registry per Section 2 of 2616 [RFC5494]. The number is assigned from the 2-octet Unassigned range 2617 with Hardware Type "AERO" and with this document as the reference. 2619 IANA is instructed to assign a 4-octet Enterprise Number "TBD2" for 2620 AERO in the "enterprise-numbers" registry per [RFC3315]. 2622 6. Security Considerations 2624 AERO link security considerations are the same as for standard IPv6 2625 Neighbor Discovery [RFC4861] except that AERO improves on some 2626 aspects. In particular, AERO uses a trust basis between Clients and 2627 Servers, where the Clients only engage in the AERO mechanism when it 2628 is facilitated by a trust anchor. Unless there is some other means 2629 of authenticating the Client's identity (e.g., link-layer security), 2630 AERO nodes SHOULD also use DHCPv6 securing services (e.g., DHCPv6 2631 authentication, Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6], etc.) for 2632 Client authentication and network admission control. 2634 AERO Redirect, Predirect and unsolicited NA messages SHOULD include a 2635 Timestamp option (see Section 5.3 of [RFC3971]) that other AERO nodes 2636 can use to verify the message time of origin. AERO Predirect, NS and 2637 RS messages SHOULD include a Nonce option (see Section 5.3 of 2638 [RFC3971]) that recipients echo back in corresponding responses. 2640 AERO links must be protected against link-layer address spoofing 2641 attacks in which an attacker on the link pretends to be a trusted 2642 neighbor. Links that provide link-layer securing mechanisms (e.g., 2643 IEEE 802.1X WLANs) and links that provide physical security (e.g., 2644 enterprise network wired LANs) provide a first line of defense that 2645 is often sufficient. In other instances, additional securing 2646 mechanisms such as Secure Neighbor Discovery (SeND) [RFC3971], IPsec 2647 [RFC4301] or TLS [RFC5246] may be necessary. 2649 AERO Clients MUST ensure that their connectivity is not used by 2650 unauthorized nodes on their EUNs to gain access to a protected 2651 network, i.e., AERO Clients that act as routers MUST NOT provide 2652 routing services for unauthorized nodes. (This concern is no 2653 different than for ordinary hosts that receive an IP address 2654 delegation but then "share" the address with unauthorized nodes via a 2655 NAT function.) 2657 On some AERO links, establishment and maintenance of a direct path 2658 between neighbors requires secured coordination such as through the 2659 Internet Key Exchange (IKEv2) protocol [RFC5996] to establish a 2660 security association. 2662 7. Acknowledgements 2664 Discussions both on IETF lists and in private exchanges helped shape 2665 some of the concepts in this work. Individuals who contributed 2666 insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, 2667 Stewart Bryant, Brian Carpenter, Wojciech Dec, Ralph Droms, Adrian 2668 Farrel, Sri Gundavelli, Brian Haberman, Joel Halpern, Tom Herbert, 2669 Sascha Hlusiak, Lee Howard, Andre Kostur, Ted Lemon, Andy Malis, 2670 Satoru Matsushima, Behcet Saikaya, Joe Touch, Bernie Volz, Ryuji 2671 Wakikawa and Lloyd Wood. Members of the IESG also provided valuable 2672 input during their review process that greatly improved the document. 2673 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 2674 for their shepherding guidance. 2676 This work has further been encouraged and supported by Boeing 2677 colleagues including Keith Bartley, Dave Bernhardt, Cam Brodie, 2678 Balaguruna Chidambaram, Bruce Cornish, Claudiu Danilov, Wen Fang, 2679 Anthony Gregory, Jeff Holland, Ed King, Gen MacLean, Rob Muszkiewicz, 2680 Sean O'Sullivan, Kent Shuey, Brian Skeen, Mike Slane, Brendan 2681 Williams, Julie Wulff, Yueli Yang, and other members of the BR&T and 2682 BIT mobile networking teams. 2684 Earlier works on NBMA tunneling approaches are found in 2685 [RFC2529][RFC5214][RFC5569]. 2687 Many of the constructs presented in this second edition of AERO are 2688 based on the author's earlier works, including: 2690 o The Internet Routing Overlay Network (IRON) 2691 [RFC6179][I-D.templin-ironbis] 2693 o Virtual Enterprise Traversal (VET) 2694 [RFC5558][I-D.templin-intarea-vet] 2696 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2697 [RFC5320][I-D.templin-intarea-seal] 2699 o AERO, First Edition [RFC6706] 2701 Note that these works cite numerous earlier efforts that are not also 2702 cited here due to space limitations. The authors of those earlier 2703 works are acknowledged for their insights. 2705 8. References 2707 8.1. Normative References 2709 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2710 August 1980. 2712 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 2713 1981. 2715 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2716 RFC 792, September 1981. 2718 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 2719 October 1996. 2721 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2722 Requirement Levels", BCP 14, RFC 2119, March 1997. 2724 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2725 (IPv6) Specification", RFC 2460, December 1998. 2727 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2728 IPv6 Specification", RFC 2473, December 1998. 2730 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 2731 and M. Carney, "Dynamic Host Configuration Protocol for 2732 IPv6 (DHCPv6)", RFC 3315, July 2003. 2734 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 2735 Host Configuration Protocol (DHCP) version 6", RFC 3633, 2736 December 2003. 2738 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 2739 Neighbor Discovery (SEND)", RFC 3971, March 2005. 2741 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 2742 for IPv6 Hosts and Routers", RFC 4213, October 2005. 2744 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2745 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2746 September 2007. 2748 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2749 Address Autoconfiguration", RFC 4862, September 2007. 2751 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 2752 Requirements", RFC 6434, December 2011. 2754 8.2. Informative References 2756 [I-D.ietf-dhc-sedhcpv6] 2757 Jiang, S., Shen, S., Zhang, D., and T. Jinmei, "Secure 2758 DHCPv6", draft-ietf-dhc-sedhcpv6-05 (work in progress), 2759 December 2014. 2761 [I-D.templin-intarea-seal] 2762 Templin, F., "The Subnetwork Encapsulation and Adaptation 2763 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 2764 progress), January 2014. 2766 [I-D.templin-intarea-vet] 2767 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 2768 templin-intarea-vet-40 (work in progress), May 2013. 2770 [I-D.templin-ironbis] 2771 Templin, F., "The Interior Routing Overlay Network 2772 (IRON)", draft-templin-ironbis-16 (work in progress), 2773 March 2014. 2775 [I-D.vandevelde-idr-remote-next-hop] 2776 Velde, G., Patel, K., Rao, D., Raszuk, R., and R. Bush, 2777 "BGP Remote-Next-Hop", draft-vandevelde-idr-remote-next- 2778 hop-08 (work in progress), October 2014. 2780 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 2781 RFC 879, November 1983. 2783 [RFC1035] Mockapetris, P., "Domain names - implementation and 2784 specification", STD 13, RFC 1035, November 1987. 2786 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2787 November 1990. 2789 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 2790 1812, June 1995. 2792 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 2793 selection, and registration of an Autonomous System (AS)", 2794 BCP 6, RFC 1930, March 1996. 2796 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 2797 for IP version 6", RFC 1981, August 1996. 2799 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2800 2131, March 1997. 2802 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2803 Domains without Explicit Tunnels", RFC 2529, March 1999. 2805 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 2806 RFC 2675, August 1999. 2808 [RFC2764] Gleeson, B., Heinanen, J., Lin, A., Armitage, G., and A. 2809 Malis, "A Framework for IP Based Virtual Private 2810 Networks", RFC 2764, February 2000. 2812 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 2813 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 2814 March 2000. 2816 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 2817 2923, September 2000. 2819 [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 2820 2983, October 2000. 2822 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 2823 of Explicit Congestion Notification (ECN) to IP", RFC 2824 3168, September 2001. 2826 [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, 2827 "DNS Extensions to Support IP Version 6", RFC 3596, 2828 October 2003. 2830 [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., 2831 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2832 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2833 RFC 3819, July 2004. 2835 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 2836 Protocol 4 (BGP-4)", RFC 4271, January 2006. 2838 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2839 Architecture", RFC 4291, February 2006. 2841 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2842 Internet Protocol", RFC 4301, December 2005. 2844 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 2845 Message Protocol (ICMPv6) for the Internet Protocol 2846 Version 6 (IPv6) Specification", RFC 4443, March 2006. 2848 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 2849 (MOBIKE)", RFC 4555, June 2006. 2851 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name 2852 System", RFC 4592, July 2006. 2854 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2855 Discovery", RFC 4821, March 2007. 2857 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2858 Errors at High Data Rates", RFC 4963, July 2007. 2860 [RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski, 2861 "DHCPv6 Relay Agent Echo Request Option", RFC 4994, 2862 September 2007. 2864 [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., 2865 and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. 2867 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2868 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2869 March 2008. 2871 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 2872 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 2874 [RFC5320] Templin, F., "The Subnetwork Encapsulation and Adaptation 2875 Layer (SEAL)", RFC 5320, February 2010. 2877 [RFC5494] Arkko, J. and C. Pignataro, "IANA Allocation Guidelines 2878 for the Address Resolution Protocol (ARP)", RFC 5494, 2879 April 2009. 2881 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 2882 Route Optimization Requirements for Operational Use in 2883 Aeronautics and Space Exploration Mobile Networks", RFC 2884 5522, October 2009. 2886 [RFC5558] Templin, F., "Virtual Enterprise Traversal (VET)", RFC 2887 5558, February 2010. 2889 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 2890 Infrastructures (6rd)", RFC 5569, January 2010. 2892 [RFC5720] Templin, F., "Routing and Addressing in Networks with 2893 Global Enterprise Recursion (RANGER)", RFC 5720, February 2894 2010. 2896 [RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy 2897 Mobile IPv6", RFC 5844, May 2010. 2899 [RFC5949] Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F. 2900 Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949, 2901 September 2010. 2903 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 2904 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 2905 5996, September 2010. 2907 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 2908 NAT64: Network Address and Protocol Translation from IPv6 2909 Clients to IPv4 Servers", RFC 6146, April 2011. 2911 [RFC6179] Templin, F., "The Internet Routing Overlay Network 2912 (IRON)", RFC 6179, March 2011. 2914 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 2915 Troan, "Basic Requirements for IPv6 Customer Edge 2916 Routers", RFC 6204, April 2011. 2918 [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A. 2919 Bierman, "Network Configuration Protocol (NETCONF)", RFC 2920 6241, June 2011. 2922 [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support 2923 in IPv6", RFC 6275, July 2011. 2925 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2926 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, August 2927 2011. 2929 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 2930 for Equal Cost Multipath Routing and Link Aggregation in 2931 Tunnels", RFC 6438, November 2011. 2933 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 2934 RFC 6691, July 2012. 2936 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 2937 (AERO)", RFC 6706, August 2012. 2939 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 2940 RFC 6864, February 2013. 2942 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 2943 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 2945 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 2946 for the Use of IPv6 UDP Datagrams with Zero Checksums", 2947 RFC 6936, April 2013. 2949 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 2950 Address Option in DHCPv6", RFC 6939, May 2013. 2952 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 2953 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 2955 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 2956 Address Selection Policy Using DHCPv6", RFC 7078, January 2957 2014. 2959 [TUNTAP] Wikipedia, W., "http://en.wikipedia.org/wiki/TUN/TAP", 2960 October 2014. 2962 Author's Address 2964 Fred L. Templin (editor) 2965 Boeing Research & Technology 2966 P.O. Box 3707 2967 Seattle, WA 98124 2968 USA 2970 Email: fltemplin@acm.org