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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Obsoletes: rfc6706 (if approved) March 27, 2014 5 Intended status: Standards Track 6 Expires: September 28, 2014 8 Transmission of IPv6 Packets over AERO Links 9 draft-templin-aerolink-10.txt 11 Abstract 13 This document specifies the operation of IPv6 over tunnel virtual 14 Non-Broadcast, Multiple Access (NBMA) links using Asymmetric Extended 15 Route Optimization (AERO). Nodes attached to AERO links can exchange 16 packets via trusted intermediate routers on the link that provide 17 forwarding services to reach off-link destinations and/or redirection 18 services to inform the node of an on-link neighbor that is closer to 19 the final destination. Operation of the IPv6 Neighbor Discovery (ND) 20 protocol over AERO links is based on an IPv6 link local address 21 format known as the AERO address. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on September 28, 2014. 40 Copyright Notice 42 Copyright (c) 2014 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 6 60 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 6 61 3.2. AERO Interface Characteristics . . . . . . . . . . . . . . 7 62 3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . . 9 63 3.4. AERO Interface Data Origin Authentication . . . . . . . . 9 64 3.5. AERO Interface Conceptual Data Structures and Protocol 65 Constants . . . . . . . . . . . . . . . . . . . . . . . . 9 66 3.6. AERO Interface MTU Considerations . . . . . . . . . . . . 11 67 3.7. AERO Interface Encapsulation, Re-encapsulation and 68 Decapsulation . . . . . . . . . . . . . . . . . . . . . . 12 69 3.8. AERO Reference Operational Scenario . . . . . . . . . . . 13 70 3.9. AERO Router Discovery and Prefix Delegation . . . . . . . 15 71 3.9.1. AERO Client Behavior . . . . . . . . . . . . . . . . . 15 72 3.9.2. AERO Server Behavior . . . . . . . . . . . . . . . . . 16 73 3.10. AERO Neighbor Solicitation and Advertisement . . . . . . . 16 74 3.11. AERO Redirection . . . . . . . . . . . . . . . . . . . . . 18 75 3.11.1. Classical Redirection Approaches . . . . . . . . . . . 18 76 3.11.2. AERO Redirection Concept of Operations . . . . . . . . 19 77 3.11.3. AERO Redirection Message Format . . . . . . . . . . . 19 78 3.11.4. Sending Predirects . . . . . . . . . . . . . . . . . . 20 79 3.11.5. Processing Predirects and Sending Redirects . . . . . 21 80 3.11.6. Re-encapsulating and Relaying Redirects . . . . . . . 22 81 3.11.7. Processing Redirects . . . . . . . . . . . . . . . . . 23 82 3.12. Neighbor Reachability Maintenance . . . . . . . . . . . . 23 83 3.13. Mobility and Link-Layer Address Change Considerations . . 24 84 3.14. Underlying Protocol Version Considerations . . . . . . . . 25 85 3.15. Multicast Considerations . . . . . . . . . . . . . . . . . 25 86 3.16. Operation on Server-less AERO Links . . . . . . . . . . . 25 87 3.17. Other Considerations . . . . . . . . . . . . . . . . . . . 26 88 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 26 89 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 90 6. Security Considerations . . . . . . . . . . . . . . . . . . . 26 91 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27 92 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 93 8.1. Normative References . . . . . . . . . . . . . . . . . . . 27 94 8.2. Informative References . . . . . . . . . . . . . . . . . . 28 95 Appendix A. AERO Server and Relay Interworking . . . . . . . . . 30 96 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 31 98 1. Introduction 100 This document specifies the operation of IPv6 over tunnel virtual 101 Non-Broadcast, Multiple Access (NBMA) links using Asymmetric Extended 102 Route Optimization (AERO). Nodes attached to AERO links can exchange 103 packets via trusted intermediate routers on the link that provide 104 forwarding services to reach off-link destinations and/or redirection 105 services to inform the node of an on-link neighbor that is closer to 106 the final destination. 108 Nodes on AERO links use an IPv6 link-local address format known as 109 the AERO Address. This address type has properties that statelessly 110 link IPv6 Neighbor Discovery (ND) to IPv6 routing. The AERO link can 111 be used for tunneling to neighboring nodes on either IPv6 or IPv4 112 networks, i.e., AERO views the IPv6 and IPv4 networks as equivalent 113 links for tunneling. The remainder of this document presents the 114 AERO specification. 116 2. Terminology 118 The terminology in the normative references applies; the following 119 terms are defined within the scope of this document: 121 AERO link 122 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 123 configured over a node's attached IPv6 and/or IPv4 networks. All 124 nodes on the AERO link appear as single-hop neighbors from the 125 perspective of IPv6. 127 AERO interface 128 a node's attachment to an AERO link. The AERO interface MTU is 129 less than or equal to the AERO link MTU. 131 AERO address 132 an IPv6 link-local address assigned to an AERO interface and 133 constructed as specified in Section 3.6. 135 AERO node 136 a node that is connected to an AERO link and that participates in 137 IPv6 Neighbor Discovery over the link. 139 AERO Client ("client") 140 a node that configures either a host interface or a router 141 interface on an AERO link. 143 AERO Server ("server") 144 a node that configures a router interface on an AERO link over 145 which it can provide default forwarding and redirection services 146 for other AERO nodes. 148 AERO Relay ("relay") 149 a node that relays IPv6 packets between Servers on the same AERO 150 link, and/or that forwards IPv6 packets between the AERO link and 151 the IPv6 Internet. An AERO Relay may or may not also be 152 configured as an AERO Server. 154 ingress tunnel endpoint (ITE) 155 an AERO interface endpoint that injects tunneled packets into an 156 AERO link. 158 egress tunnel endpoint (ETE) 159 an AERO interface endpoint that receives tunneled packets from an 160 AERO link. 162 underlying network 163 a connected IPv6 or IPv4 network routing region over which AERO 164 nodes tunnel IPv6 packets. 166 underlying interface 167 an AERO node's interface point of attachment to an underlying 168 network. 170 underlying address 171 an IPv6 or IPv4 address assigned to an AERO node's underlying 172 interface. When UDP encapsulation is used, the UDP port number is 173 also considered as part of the underlying address. Underlying 174 addresses are used as the source and destination addresses of the 175 AERO encapsulation header. 177 link-layer address 178 the same as defined for "underlying address" above. 180 network layer address 181 an IPv6 address used as the source or destination address of the 182 inner IPv6 packet header. 184 end user network (EUN) 185 an IPv6 network attached to a downstream interface of an AERO 186 Client (where the AERO interface is seen as the upstream 187 interface). 189 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 190 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 191 document are to be interpreted as described in [RFC2119]. 193 3. Asymmetric Extended Route Optimization (AERO) 195 The following sections specify the operation of IPv6 over Asymmetric 196 Extended Route Optimization (AERO) links: 198 3.1. AERO Node Types 200 AERO Relays relay packets between nodes connected to the same AERO 201 link and also forward packets between the AERO link and the native 202 IPv6 network. The relaying process entails re-encapsulation of IPv6 203 packets that were received from a first AERO node and are to be 204 forwarded without modification to a second AERO node. 206 AERO Servers configure their AERO interfaces as router interfaces, 207 and provide default routing services to AERO Clients. AERO Servers 208 configure a DHCPv6 Relay or Server function and facilitate DHCPv6 209 Prefix Delegation (PD) exchanges. An AERO Server may also act as an 210 AERO Relay. 212 AERO Clients act as requesting routers to receive IPv6 prefixes 213 through a DHCPv6 PD exchange via an AERO Server over the AERO link. 214 Each AERO Client receives at least a /64 prefix delegation, and may 215 receive even shorter prefixes. 217 AERO Clients that act as routers configure their AERO interfaces as 218 router interfaces, i.e., even if the AERO Client otherwise displays 219 the outward characteristics of an ordinary host (for example, the 220 Client may internally configure both an AERO interface and (internal 221 virtual) End User Network (EUN) interfaces). AERO Clients that act 222 as routers sub-delegate portions of their received prefix delegations 223 to links on EUNs. 225 AERO Clients that act as ordinary hosts configure their AERO 226 interfaces as host interfaces and assign one or more IPv6 addresses 227 taken from their received prefix delegations to the AERO interface 228 but DO NOT assign the delegated prefix itself to the AERO interface. 229 Instead, the host assigns the delegated prefix to a "black hole" 230 route so that unused portions of the prefix are nullified. 232 End system applications on AERO hosts bind directly to the AERO 233 interface, while applications on AERO routers (or IPv6 hosts served 234 by an AERO router) bind to EUN interfaces. 236 3.2. AERO Interface Characteristics 238 AERO interfaces use IPv6-in-IPv6 encapsulation [RFC2473] to exchange 239 tunneled packets with AERO neighbors attached to an underlying IPv6 240 network, and use IPv6-in-IPv4 encapsulation [RFC4213] to exchange 241 tunneled packets with AERO neighbors attached to an underlying IPv4 242 network. AERO interfaces can also use IPsec encapsulation [RFC4301] 243 (either IPv6-in-IPsec-in-IPv6 or IPv6-in-IPsec-in-IPv4) in 244 environments where strong authentication and confidentiality are 245 required. When NAT traversal and/or filtering middlebox traversal is 246 necessary, a UDP header is further inserted between the outer IP 247 encapsulation header and the inner packet. 249 AERO interfaces assign a topology-relative link-local address of the 250 form 'fe80::[ID]' that is derived from their current link-layer 251 topology. For IPv6-in-IPv4 encapsulation, 'ID' is the IPv4 address 252 of the node's underlying IPv4 interface preceded by zeros per Section 253 3.7 of [RFC4213]. For IPv6-in-IPv6 encapsulation, 'ID' is the CRC64 254 calculation of the node's underlying interface IPv6 address, 255 beginning with the most significant bit. 257 AERO interfaces maintain a neighbor cache and use a variation of 258 standard unicast IPv6 ND messaging. AERO interfaces use Neighbor 259 Solicitation (NS), Neighbor Advertisement (NA) and Redirect messages 260 the same as for any IPv6 link. They do not use Router Solicitation 261 (RS) and Router Advertisement (RA) messages for several reasons. 262 First, default router discovery is supported through other means more 263 appropriate for AERO links as described below. Second, discovery of 264 more-specific routes is through the receipt of Redirect messages. 265 Finally, AERO nodes register their delegated IPv6 prefixes using 266 DHCPv6 PD; hence, there is no need for RA-based prefix discovery. 268 AERO Neighbor Solicitation (NS) and Neighbor Advertisement (NA) 269 messages do not include Source/Target Link Layer Address Options 270 (S/TLLAO). Instead, AERO nodes determine the link-layer addresses of 271 neighbors by examining the encapsulation IP source address and UDP 272 port number (when UDP encapsulation is used) of any NS/NA messages 273 they receive and ignore any S/TLLAOs included in these messages. 274 This is vital to the operation of AERO links for which neighbors are 275 separated by Network Address Translators (NATs) - either IPv4 or 276 IPv6. 278 AERO Redirect messages include a TLLAO the same as for any IPv6 link. 279 The TLLAO includes the link-layer address of the target node, 280 including both the IP address and the UDP source port number used by 281 the target when it sends UDP-encapsulated packets over the AERO 282 interface (the TLLAO instead encodes the value 0 when the target does 283 not use UDP encapsulation). TLLAOs for target nodes that use an IPv6 284 underlying address include the full 16 bytes of the IPv6 address as 285 shown in Figure 1, while TLLAOs for target nodes that use an IPv4 286 underlying address include only the 4 bytes of the IPv4 address as 287 shown in Figure 2. 289 0 1 2 3 290 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 1 291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 | Type = 2 | Length = 3 | UDP Source Port (or 0) | 293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 294 | Reserved | 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | | 297 +-- --+ 298 | | 299 +-- IPv6 Address --+ 300 | | 301 +-- --+ 302 | | 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 Figure 1: AERO TLLAO Format for IPv6 307 0 1 2 3 308 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 1 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | Type = 2 | Length = 1 | UDP Source Port (or 0) | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | IPv4 Address | 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 Figure 2: AERO TLLAO Format for IPv4 317 Finally, AERO interface NS/NA messages only update existing neighbor 318 cache entires and do not create new neighbor cache entries, whereas 319 Redirect messages both update and create neighbor cache entries. 320 This represents a departure from the normal operation of IPv6 ND over 321 common link types, but is consistent with the spirit of IPv6 over 322 NBMA links as discussed in [RFC4861]. Note however that this 323 restriction may be relaxed and/or redefined on AERO links that 324 participate in a fully distributed mobility management model 325 coordinated in a manner outside the scope of this document. 327 3.3. AERO Addresses 329 An AERO address is an IPv6 link-local address assigned to an AERO 330 interface and with an IPv6 prefix embedded within the interface 331 identifier. The AERO address is formatted as: 333 fe80::[IPv6 prefix] 335 Each AERO Client configures an AERO address based on the delegated 336 prefix it has received from the AERO link prefix delegation 337 authority. The address begins with the prefix fe80::/64 and includes 338 in its interface identifier the base /64 prefix taken from the 339 Client's delegated IPv6 prefix. The base prefix is determined by 340 masking the delegated prefix with the prefix length. For example, if 341 an AERO Client has received the prefix delegation: 343 2001:db8:1000:2000::/56 345 it would construct its AERO address as: 347 fe80::2001:db8:1000:2000 349 Unlike the node's topology-relative link local address (i.e., 350 fe80::[ID]), the AERO address remains stable as the Client moves 351 between topological locations. 353 3.4. AERO Interface Data Origin Authentication 355 Nodes on AERO interfaces use a simple data origin authentication for 356 encapsulated packets they receive from other nodes. In particular, 357 AERO Clients accept encapsulated packets with a link-layer source 358 address belonging to their current AERO Server. AERO nodes also 359 accept encapsulated packets with a link-layer source address that is 360 correct for the network-layer source address. 362 The AERO node considers the link-layer source address correct for the 363 network-layer source address if there is an IPv6 route that matches 364 the network-layer source address as well as a neighbor cache entry 365 corresponding to the next hop that includes the link-layer address. 366 An exception is that NS, NA and Redirect messages may include a 367 different link-layer address than the one currently in the neighbor 368 cache, and the new link-layer address updates the neighbor cache 369 entry. 371 3.5. AERO Interface Conceptual Data Structures and Protocol Constants 373 Each AERO node maintains a per-AERO interface conceptual neighbor 374 cache that includes an entry for each neighbor it communicates with 375 on the AERO link, the same as for any IPv6 interface (see [RFC4861]). 376 Neighbor cache entries are either static or dynamic. Static neighbor 377 cache entries (including a Client's neighbor cache entry for a Server 378 or a Server's neighbor cache entry for a Client) do not have timeout 379 values and are retained until explicitly deleted. Dynamic neighbor 380 cache entries are created and maintained by the AERO redirection 381 procedures describe in the following sections. 383 When an AERO node receives a valid Predirect message (See Section 384 3.11.5) it creates or updates a dynamic neighbor cache entry for the 385 Predirect target L3 and L2 addresses, and also creates an IPv6 route 386 for the Predirected (source) prefix. The node then sets an ACCEPT 387 timer and uses this timer to validate any messages received from the 388 Predirected neighbor. 390 When an AERO node receives a valid Redirect message (see Section 391 3.11.7) it creates or updates a dynamic neighbor cache entry for the 392 Redirect target L3 and L2 addresses, and also creates an IPv6 route 393 for the Redirected (destination) prefix. The node then sets a 394 FORWARD timer and uses this timer to determine whether packets can be 395 sent directly to the Redirected neighbor. The node also maintains a 396 constant value MAX_RETRY to limit the number of keepalives sent when 397 a neighbor has gone unreachable. 399 It is RECOMMENDED that FORWARD_TIME be set to the default constant 400 value 30 seconds to match the default REACHABLE_TIME value specified 401 for IPv6 neighbor discovery [RFC4861]. 403 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 404 value 40 seconds to allow a 10 second window so that the AERO 405 redirection procedure can converge before the ACCEPT_TIME timer 406 decrements below FORWARD_TIME. 408 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 409 for IPv6 neighbor discovery address resolution in Section 7.3.3 of 410 [RFC4861]. 412 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 413 administratively set, if necessary, to better match the AERO link's 414 performance characteristics; however, if different values are chosen, 415 all nodes on the link MUST consistently configure the same values. 416 ACCEPT_TIME SHOULD further be set to a value that is sufficiently 417 longer than FORWARD_TIME to allow the AERO redirection procedure to 418 converge. 420 3.6. AERO Interface MTU Considerations 422 The AERO link Maximum Transmission Unit (MTU) is 64KB minus the 423 encapsulation overhead for IPv4 [RFC0791] and 4GB minus the 424 encapsulation overhead for IPv6 [RFC2675]. This is the most that 425 IPv4 and IPv6 (respectively) can convey within the constraints of 426 protocol constants, but actual sizes available for tunneling will 427 frequently be much smaller. 429 The base tunneling specifications for IPv4 and IPv6 typically set a 430 static MTU on the tunnel interface to 1500 bytes minus the 431 encapsulation overhead or smaller still if the tunnel is likely to 432 incur additional encapsulations such as IPsec on the path. This can 433 result in path MTU related black holes when packets that are too 434 large to be accommodated over the AERO link are dropped, but the 435 resulting ICMP Packet Too Big (PTB) messages are lost on the return 436 path. As a result, AERO nodes use the following MTU mitigations to 437 accommodate larger packets. 439 AERO nodes set their AERO interface MTU to the larger of 1500 bytes 440 and the underlying interface MTU minus the encapsulation overhead. 441 AERO nodes optionally cache other per-neighbor MTU values in the 442 underlying IP path MTU discovery cache initialized to the underlying 443 interface MTU. 445 AERO nodes admit packets that are no larger than 1280 bytes minus the 446 encapsulation overhead (*) as well as packets that are larger than 447 1500 bytes into the tunnel without fragmentation, i.e., as long as 448 they are no larger than the AERO interface MTU before encapsulation 449 and also no larger than the cached per-neighbor MTU following 450 encapsulation. For IPv4, the node sets the "Don't Fragment" (DF) bit 451 to 0 for packets no larger than 1280 bytes minus the encapsulation 452 overhead (*) and sets the DF bit to 1 for packets larger than 1500 453 bytes. If a large packet is lost in the path, the node may 454 optionally cache the MTU reported in the resulting PTB message or may 455 ignore the message, e.g., if there is a possibility that the message 456 is spurious. 458 For packets destined to an AERO node that are larger than 1280 bytes 459 minus the encapsulation overhead (*) but no larger than 1500 bytes, 460 the node uses outer IP fragmentation to fragment the packet into two 461 pieces (where the first fragment contains 1024 bytes of the 462 fragmented inner packet) then admits the fragments into the tunnel. 463 If the outer protocol is IPv4, the node admits the packet into the 464 tunnel with DF set to 0 and subject to rate limiting to avoid 465 reassembly errors [RFC4963][RFC6864]. For both IPv4 and IPv6, the 466 node also sends a 1500 byte probe message (**) to the neighbor, 467 subject to rate limiting. To construct a probe, the node prepares an 468 ICMPv6 Neighbor Solicitation (NS) message with trailing padding 469 octets added to a length of 1500 bytes but does not include the 470 length of the padding in the IPv6 Payload Length field. The node 471 then encapsulates the NS in the outer encapsulation headers (while 472 including the length of the padding in the outer length fields), sets 473 DF to 1 (for IPv4) and sends the padded NS message to the neighbor. 474 If the neighbor returns an NA message, the node may then send whole 475 packets within this size range and (for IPv4) relax the rate limiting 476 requirement. 478 AERO nodes MUST be capable of reassembling packets up to 1500 bytes 479 plus the encapsulation overhead length. It is therefore RECOMMENDED 480 that AERO nodes be capable of reassembling at least 2KB. 482 (*) Note that if it is known that the minimum Path MTU to an AERO 483 node is MINMTU bytes (where 1280 < MINMTU < 1500) then MINMTU can be 484 used instead of 1280 in the fragmentation threshold considerations 485 listed above. 487 (**) It is RECOMMENDED that no probes smaller than 1500 bytes be used 488 for MTU probing purposes, since smaller probes may be fragmented if 489 there is a nested tunnel somewhere on the path to the neighbor. 491 3.7. AERO Interface Encapsulation, Re-encapsulation and Decapsulation 493 AERO interfaces encapsulate IPv6 packets according to whether they 494 are entering the AERO interface for the first time or if they are 495 being forwarded out the same AERO interface that they arrived on. 496 This latter form of encapsulation is known as "re-encapsulation". 498 AERO interfaces encapsulate packets per the specifications in , 499 [RFC2473], [RFC4213] except that the interface copies the "TTL/Hop 500 Limit", "Type of Service/Traffic Class" and "Congestion Experienced" 501 values in the inner network layer header into the corresponding 502 fields in the outer IP header. For packets undergoing re- 503 encapsulation, the AERO interface instead copies the "TTL/Hop Limit", 504 "Type of Service/Traffic Class" and "Congestion Experienced" values 505 in the original outer IP header into the corresponding fields in the 506 new outer IP header (i.e., the values are transferred between outer 507 headers and *not* copied from the inner network layer header). 509 When UDP encapsulation is used, the AERO interface inserts a UDP 510 header between the inner packet and outer IP header. If the outer 511 header is IPv6 and is followed by an IPv6 Fragment header, the AERO 512 interface inserts the UDP header between the outer IPv6 header and 513 IPv6 Fragment header. The AERO interface sets the UDP source port to 514 a constant value that it will use in each successive packet it sends, 515 sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) and 516 sets the UDP length field to the length of the inner packet plus 8 517 bytes for the UDP header itself. For packets sent via a Server, the 518 AERO interface sets the UDP destination port to 8060 (i.e., the IANA- 519 registerd port number for AERO). For packets sent to a neighboring 520 Client, the AERO interface sets the UDP destination port to the port 521 value stored in the neighbor cache entry for this neighbor. 523 The AERO interface next sets the outer IP protocol number to the 524 appropriate value for the first protocol layer within the 525 encapsulation (e.g., IPv6, IPv6 Fragment Header, UDP, etc.). When 526 IPv6 is used as the outer IP protocol, the ITE then sets the flow 527 label value in the outer IPv6 header the same as described in 528 [RFC6438]. When IPv4 is used as the outer IP protocol, the AERO 529 interface sets the DF bit as discussed in Section 3.2. 531 AERO interfaces decapsulate packets destined either to the node 532 itself or to a destination reached via an interface other than the 533 receiving AERO interface per the specifications in , [RFC2473], 534 [RFC4213]. When the encapsulated packet includes a UDP header, the 535 AERO interface examines the first octet of data following the UDP 536 header to determine the inner header type. If the most significant 537 four bits of the first octet encode the value '0110', the inner 538 header is an IPv6 header. Otherwise, the interface considers the 539 first octet as an IP protocol type that encodes the value '44' for 540 IPv6 fragment header, the value '50' for Encapsulating Security 541 Payload, the value '51' for Authentication Header etc. (If the first 542 octet encodes the value '0', the interface instead discards the 543 packet, since this is the value reserved for experimentation under , 544 [RFC6706]). During the decapsulation, the AERO interface records the 545 UDP source port in the neighbor cache entry for this neighbor then 546 discards the UDP header. 548 3.8. AERO Reference Operational Scenario 550 Figure 3 depicts the AERO reference operational scenario. The figure 551 shows an AERO Server('A'), two AERO Clients ('B', 'D') and three 552 ordinary IPv6 hosts ('C', 'E', 'F'): 554 .-(::::::::) 555 .-(::: IPv6 :::)-. +-------------+ 556 (:::: Internet ::::)--| Host F | 557 `-(::::::::::::)-' +-------------+ 558 `-(::::::)-' 2001:db8:3::1 559 | 560 +--------------+ 561 | AERO Server A| 562 | (C->B; E->D) | 563 +--------------+ 564 fe80::[ID] 565 L2(A) 566 | 567 X-----+-----------+-----------+--------X 568 | AERO Link | 569 L2(B) L2(D) 570 fe80::2001:db8:0:0 fe80::2001:db8:1:0 .-. 571 +--------------+ +--------------+ ,-( _)-. 572 | AERO Client B| | AERO Client D| .-(_ IPv6 )-. 573 | (default->A) | | (default->A) |--(__ EUN ) 574 +--------------+ +--------------+ `-(______)-' 575 2001:DB8:0::/48 2001:DB8:1::/48 | 576 | 2001:db8:1::1 577 .-. +-------------+ 578 ,-( _)-. 2001:db8:0::1 | Host E | 579 .-(_ IPv6 )-. +-------------+ +-------------+ 580 (__ EUN )--| Host C | 581 `-(______)-' +-------------+ 583 Figure 3: AERO Reference Operational Scenario 585 In Figure 3, AERO Server ('A') connects to the AERO link and connects 586 to the IPv6 Internet, either directly or via an AERO Relay (not 587 shown). Server ('A') assigns the address fe80::[ID] to its AERO 588 interface with link-layer address L2(A). Server ('A') next arranges 589 to add L2(A) to a published list of valid Servers for the AERO link. 591 AERO Client ('B') registers the IPv6 prefix 2001:db8:0::/48 in a 592 DHCPv6 PD exchange via Server ('A') then assigns the address fe80:: 593 2001:db8:0:0 to its AERO interface with link-layer address L2(B). 594 Client ('B') configures a default route via the AERO interface with 595 next-hop address fe80::[ID] and link-layer address L2(A), then sub- 596 delegates the prefix 2001:db8:0::/48 to its attached EUNs. IPv6 host 597 ('C') connects to the EUN, and configures the address 2001:db8:0::1. 599 AERO Client ('D') registers the IPv6 prefix 2001:db8:1::/48 in a 600 DHCPv6 PD exchange via Server ('A') then assigns the address fe80:: 601 2001:db8:1:0 to its AERO interface with link-layer address L2(D). 603 Client ('D') configures a default route via the AERO interface with 604 next-hop address fe80::[ID] and link-layer address L2(A), then sub- 605 delegates the prefix 2001:db8:1::/48 to its attached EUNs. IPv6 host 606 ('E') connects to the EUN, and configures the address 2001:db8:1::1. 608 Finally, IPv6 host ('F') connects to an IPv6 network outside of the 609 AERO link domain. Host ('F') configures its IPv6 interface in a 610 manner specific to its attached IPv6 link, and assigns the address 611 2001:db8:3::1 to its IPv6 link interface. 613 3.9. AERO Router Discovery and Prefix Delegation 615 3.9.1. AERO Client Behavior 617 AERO Clients observe the IPv6 router requirements defined in 618 [RFC6434]. AERO Clients first discover the link-layer address of an 619 AERO Server via static configuration, or through an automated means 620 such as DNS name resolution. In the absence of other information, 621 the Client resolves the Fully-Qualified Domain Name (FQDN) 622 "linkupnetworks.domainname", where "domainname" is the DNS domain 623 appropriate for the Client's attached underlying network. The Client 624 then creates a static neighbor cache entry with the Server's IPv6 625 link-local address and the discovered link-layer address as the link- 626 layer address. The Client further creates a static default IPv6 627 route with the Server's link-local address as the next hop. 629 Next, the Client acts as a requesting router to register its IPv6 630 prefix through DHCPv6 PD [RFC3633] via the Server using its current 631 topology-relative link-local address as the IPv6 source address. 632 After the Client registers its prefixes, it assigns the link-local 633 AERO address taken from its delegated prefix to the AERO interface 634 (see: Section 3.3) and sub-delegates the prefix to nodes and links 635 within its attached EUNs. The AERO link-local address therefore 636 becomes an additional link-local address on the interface that 637 remains stable as the Client moves. 639 After configuring a default route and registering its prefix, the 640 Client sends periodic NS messages to the Server to obtain new NAs in 641 order to refresh any network state. The Client can also forward IPv6 642 packets destined to networks beyond its local EUNs via the Server as 643 an IPv6 default router. The Server may in turn return a Redirect 644 message informing the Client of a neighbor on the AERO link that is 645 topologically closer to the final destination as specified in 646 Section 3.11. 648 3.9.2. AERO Server Behavior 650 AERO Servers observe the IPv6 router requirements defined in 651 [RFC6434]. They further configure a DHCPv6 relay/server function on 652 their AERO links. When the Server facilitates prefix delegation, it 653 also creates a static neighbor cache entry for the Client's AERO 654 address (see: Section 3.3) and a static IPv6 forwarding table entry 655 that lists the Client's AERO address as the next hop toward the 656 delegated IPv6 prefix . 658 Servers respond to NS messages from Clients on their AERO interfaces 659 by returning an NA message. When the Server receives an NS message, 660 it updates the neighbor cache entry using the network layer source 661 address as the neighbor's network layer address and using the link- 662 layer source address of the NS message as the neighbor's link-layer 663 address. 665 When the Server forwards a packet via the same AERO interface on 666 which it arrived, it initiates an AERO route optimization procedure 667 as specified in Section 3.11. 669 3.10. AERO Neighbor Solicitation and Advertisement 671 Each AERO node uses its delegated prefix to create an AERO address 672 (see: Section 3.3). It can then send NS messages to elicit NA 673 messages from other AERO nodes. When the AERO node sends NS/NA 674 messages, however, it must also include the length of the prefix 675 corresponding to the AERO address. AERO NS/NA messages therefore 676 include an 8-bit "Prefix Length" field take from the low-order 8 bits 677 of the Reserved field as shown in Figure 4 and Figure 5. 679 0 1 2 3 680 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 1 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | Type (=135) | Code | Checksum | 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 | Reserved | Prefix Length | 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 686 | | 687 + + 688 | | 689 + Target Address + 690 | | 691 + + 692 | | 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 694 | Options ... 695 +-+-+-+-+-+-+-+-+-+-+-+- 697 Figure 4: AERO Neighbor Solicitation (NS) Message Format 699 0 1 2 3 700 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 1 701 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 702 | Type (=136) | Code | Checksum | 703 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 704 | R|S|O| Reserved | Prefix Length | 705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 | | 707 + + 708 | | 709 + Target Address + 710 | | 711 + + 712 | | 713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 714 | Options ... 715 +-+-+-+-+-+-+-+-+-+-+-+- 717 Figure 5: AERO Neighbor Advertisement (NA) Message Format 719 When an AERO node sends an NS/NA message, it MUST use its AERO 720 address as the IPv6 source address and the AERO address of the 721 neighbor as the IPv6 destination address. It MUST also include its 722 AERO address prefix length in the Prefix Length field. 724 When an AERO node receives an NS/NA message, it accepts the message 725 if the Prefix Length applied to the source address is correct for the 726 neighbor; otherwise, it ignores the message. 728 3.11. AERO Redirection 730 Section 3.8 describes the AERO reference operational scenario. We 731 now discuss the operation and protocol details of AERO Redirection 732 with respect to this reference scenario. 734 3.11.1. Classical Redirection Approaches 736 With reference to Figure 3, when the IPv6 source host ('C') sends a 737 packet to an IPv6 destination host ('E'), the packet is first 738 forwarded via the EUN to AERO Client ('B'). Client ('B') then 739 forwards the packet over its AERO interface to AERO Server ('A'), 740 which then re-encapsulates and forwards the packet to AERO Client 741 ('D'), where the packet is finally forwarded to the IPv6 destination 742 host ('E'). When Server ('A') re-encapsulates and forwards the 743 packet back out on its advertising AERO interface, it must arrange to 744 redirect Client ('B') toward Client ('D') as a better next-hop node 745 on the AERO link that is closer to the final destination. However, 746 this redirection process applied to AERO interfaces must be more 747 carefully orchestrated than on ordinary links since the parties may 748 be separated by potentially many underlying network routing hops. 750 Consider a first alternative in which Server ('A') informs Client 751 ('B') only and does not inform Client ('D') (i.e., "classical 752 redirection"). In that case, Client ('D') has no way of knowing that 753 Client ('B') is authorized to forward packets from the claimed source 754 address, and it may simply elect to drop the packets. Also, Client 755 ('B') has no way of knowing whether Client ('D') is performing some 756 form of source address filtering that would reject packets arriving 757 from a node other than a trusted default router, nor whether Client 758 ('D') is even reachable via a direct path that does not involve 759 Server ('A'). 761 Consider a second alternative in which Server ('A') informs both 762 Client ('B') and Client ('D') separately, via independent redirection 763 control messages (i.e., "augmented redirection"). In that case, if 764 Client ('B') receives the redirection control message but Client 765 ('D') does not, subsequent packets sent by Client ('B') could be 766 dropped due to filtering since Client ('D') would not have a route to 767 verify the claimed source address. Also, if Client ('D') receives 768 the redirection control message but Client ('B') does not, subsequent 769 packets sent in the reverse direction by Client ('D') would be lost. 771 Since both of these alternatives have shortcomings, a new redirection 772 technique (i.e., "AERO redirection") is needed. 774 3.11.2. AERO Redirection Concept of Operations 776 Again, with reference to Figure 3, when source host ('C') sends a 777 packet to destination host ('E'), the packet is first forwarded over 778 the source host's attached EUN to Client ('B'), which then forwards 779 the packet via its AERO interface to Server ('A'). 781 Server ('A') then re-encapsulates and forwards the packet out the 782 same AERO interface toward Client ('D') and also sends an AERO 783 "Predirect" message forward to Client ('D') as specified in 784 Section 3.11.4. The Predirect message includes Client ('B')'s 785 network- and link-layer addresses as well as information that Client 786 ('D') can use to determine the IPv6 prefix used by Client ('B') . 787 After Client ('D') receives the Predirect message, it process the 788 message and returns an AERO Redirect message destined for Client 789 ('B') via Server ('A') as specified in Section 3.11.5. During the 790 process, Client ('D') also creates or updates a dynamic neighbor 791 cache entry for Client ('B'), and creates an IPv6 route for Client 792 ('B')'s IPv6 prefix. 794 When Server ('A') receives the Redirect message, it re-encapsulates 795 the message and forwards it on to Client ('B') as specified in 796 Section 3.11.6. The message includes Client ('D')'s network- and 797 link-layer addresses as well as information that Client ('B') can use 798 to determine the IPv6 prefix used by Client ('D'). After Client 799 ('B') receives the Redirect message, it processes the message as 800 specified in Section 3.11.7. During the process, Client ('B') also 801 creates or updates a dynamic neighbor cache entry for Client ('D'), 802 and creates an IPv6 route for Client ('D')'s IPv6 prefix. 804 Following the above Predirect/Redirect message exchange, forwarding 805 of packets from Client ('B') to Client ('D') without involving Server 806 ('A) as an intermediary is enabled. The mechanisms that support this 807 exchange are specified in the following sections. 809 3.11.3. AERO Redirection Message Format 811 AERO Redirect/Predirect messages use the same format as for ICMPv6 812 Redirect messages depicted in Section 4.5 of [RFC4861], but also 813 include a new "Prefix Length" field taken from the low-order 8 bits 814 of the Redirect message Reserved field. The Redirect/Predirect 815 messages are formatted as shown in Figure 6: 817 0 1 2 3 818 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 1 819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 820 | Type (=137) | Code (=0/1) | Checksum | 821 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 822 | Reserved | Prefix Length | 823 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 824 | | 825 + + 826 | | 827 + Target Address + 828 | | 829 + + 830 | | 831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 832 | | 833 + + 834 | | 835 + Destination Address + 836 | | 837 + + 838 | | 839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 840 | Options ... 841 +-+-+-+-+-+-+-+-+-+-+-+- 843 Figure 6: AERO Redirect/Predirect Message Format 845 3.11.4. Sending Predirects 847 When an AERO Server forwards a packet out the same AERO interface 848 that it arrived on, the Server sends a Predirect message forward 849 toward the AERO Client nearest the destination instead of sending a 850 Redirect message back to AERO Client nearest the source. 852 In the reference operational scenario, when Server ('A') forwards a 853 packet sent by Client ('B') toward Client ('D'), it also sends a 854 Predirect message forward toward Client ('D'), subject to rate 855 limiting (see Section 8.2 of [RFC4861]). Server ('A') prepares the 856 Predirect message as follows: 858 o the link-layer source address is set to 'L2(A)' (i.e., the 859 underlying address of Server ('A')). 861 o the link-layer destination address is set to 'L2(D)' (i.e., the 862 underlying address of Client ('D')). 864 o the network-layer source address is set to fe80::[ID] (i.e., the 865 link-local address of Server ('A')). 867 o the network-layer destination address is set to fe80::2001:db8:1:0 868 (i.e., the AERO address of Client ('D')). 870 o the Type is set to 137. 872 o the Code is set to 1 to indicate "Predirect". 874 o the Prefix Length is set to the length of the prefix to be applied 875 to Target address. 877 o the Target Address is set to fe80::2001:db8:0::0 (i.e., the AERO 878 address of Client ('B')). 880 o the Destination Address is set to the IPv6 source address of the 881 packet that triggered the Predirection event. 883 o the message includes a TLLAO set to 'L2(B)' (i.e., the underlying 884 address of Client ('B')). 886 o the message includes a Redirected Header Option (RHO) that 887 contains the originating packet truncated to ensure that at least 888 the network-layer header is included but the size of the message 889 does not exceed 1280 bytes. 891 Server ('A') then sends the message forward to Client ('D'). 893 3.11.5. Processing Predirects and Sending Redirects 895 When Client ('D') receives a Predirect message, it accepts the 896 message only if it has a link-layer source address of the Server, 897 i.e. 'L2(A)'. Client ('D') further accepts the message only if it 898 is willing to serve as a redirection target. Next, Client ('D') 899 validates the message according to the ICMPv6 Redirect message 900 validation rules in Section 8.1 of [RFC4861]. 902 In the reference operational scenario, when the Client ('D') receives 903 a valid Predirect message, it either creates or updates a dynamic 904 neighbor cache entry that stores the Target Address of the message as 905 the network-layer address of Client ('B') and stores the link-layer 906 address found in the TLLAO as the link-layer address of Client ('B'). 907 Client ('D') then applies the Prefix Length to the Interface 908 Identifier portion of the Target Address and records the resulting 909 IPv6 prefix in its IPv6 forwarding table. 911 After processing the message, Client ('D') prepares a Redirect 912 message response as follows: 914 o the link-layer source address is set to 'L2(D)' (i.e., the link- 915 layer address of Client ('D')). 917 o the link-layer destination address is set to 'L2(A)' (i.e., the 918 link-layer address of Server ('A')). 920 o the network-layer source address is set to 'L3(D)' (i.e., the AERO 921 address of Client ('D')). 923 o the network-layer destination address is set to 'L3(B)' (i.e., the 924 AERO address of Client ('B')). 926 o the Type is set to 137. 928 o the Code is set to 0 to indicate "Redirect". 930 o the Prefix Length is set to the length of the prefix to be applied 931 to the Target and Destination address. 933 o the Target Address is set to fe80::2001:db8:1::1 (i.e., the AERO 934 address of Client ('D')). 936 o the Destination Address is set to the IPv6 destination address of 937 the packet that triggered the Redirection event. 939 o the message includes a TLLAO set to 'L2(D)' (i.e., the underlying 940 address of Client ('D')). 942 o the message includes as much of the RHO copied from the 943 corresponding AERO Predirect message as possible such that at 944 least the network-layer header is included but the size of the 945 message does not exceed 1280 bytes. 947 After Client ('D') prepares the Redirect message, it sends the 948 message to Server ('A'). 950 3.11.6. Re-encapsulating and Relaying Redirects 952 When Server ('A') receives a Redirect message, it accepts the message 953 only if it has a neighbor cache entry that associates the message's 954 link-layer source address with the network-layer source address. 955 Next, Server ('A') validates the message according to the ICMPv6 956 Redirect message validation rules in Section 8.1 of [RFC4861]. 957 Following validation, Server ('A') re-encapsulates the Redirect then 958 relays the re-encapsulated Redirect on to Client ('B') as follows. 960 In the reference operational scenario, Server ('A') receives the 961 Redirect message from Client ('D') and prepares to re-encapsulate and 962 forward the message to Client ('B'). Server ('A') first verifies 963 that Client ('D') is authorized to use the Prefix Length in the 964 Redirect message when applied to the AERO address in the network- 965 layer source of the Redirect message, and discards the message if 966 verification fails. Otherwise, Server ('A') re-encapsulates the 967 message by changing the link-layer source address of the message to 968 'L2(A)', changing the network-layer source address of the message to 969 fe80::[ID], and changing the link-layer destination address to 970 'L2(B)' . Server ('A') finally relays the re-encapsulated message to 971 the ingress node ('B') without decrementing the network-layer IPv6 972 header Hop Limit field. 974 While not shown in Figure 3, AERO Relays relay Redirect and Predirect 975 messages in exactly this same fashion described above. See Figure 7 976 in Appendix A for an extension of the reference operational scenario 977 that includes Relays. 979 3.11.7. Processing Redirects 981 When Client ('B') receives the Redirect message, it accepts the 982 message only if it has a link-layer source address of the Server, 983 i.e. 'L2(A)'. Next, Client ('B') validates the message according to 984 the ICMPv6 Redirect message validation rules in Section 8.1 of 985 [RFC4861]. Following validation, Client ('B') then processes the 986 message as follows. 988 In the reference operational scenario, when Client ('B') receives the 989 Redirect message, it either cre ates or updates a dynamic neighbor 990 cache entry that stores the Target Address of the message as the 991 network-layer address of Client ('D') and stores the link-layer 992 address found in the TLLAO as the link-layer address of Client ('D'). 993 Client ('B') then applies the Prefix Length to the Interface 994 Identifier portion of the Target Address and records the resulting 995 IPv6 prefix in its IPv6 forwarding table. 997 Now, Client ('B') has an IPv6 forwarding table entry for 998 Client('D')'s prefix, and Client ('D') has an IPv6 forwarding table 999 entry for Client ('B')'s prefix. Thereafter, the clients may 1000 exchange ordinary network-layer data packets directly without 1001 forwarding through Server ('A'). 1003 3.12. Neighbor Reachability Maintenance 1005 When a source Client is redirected to a target Client it MUST test 1006 the direct path to the target by sending an initial NS message to 1007 elicit a solicited NA response. While testing the path, the source 1008 Client SHOULD continue sending packets via the Server until target 1009 Client reachability has been confirmed. The source Client MUST 1010 thereafter continue to test the direct path to the target Client 1011 using Neighbor Unreachability Detection (NUD) (see Section 7.3 of 1012 [RFC4861]) in order to keep dynamic neighbor cache entries alive. In 1013 particular, the source Client sends NS messages to the target Client 1014 subject to rate limiting in order to receive solicited NA messages. 1015 If at any time the direct path appears to be failing, the source 1016 Client can resume sending packets via the Server which may or may not 1017 result in a new redirection event. 1019 When a target Client receives an NS message from a source Client, it 1020 resets the ACCEPT_TIME timer if a neighbor cache entry exists; 1021 otherwise, it discards the NS message. 1023 When a source Client receives a solicited NA message form a target 1024 Client, it resets the FORWARD_TIME timer if a neighbor cache entry 1025 exists; otherwise, it discards the NA message. 1027 When both the FORWARD_TIME and ACCEPT_TIME timers on a dynamic 1028 neighbor cache entry expire, the Client deletes both the neighbor 1029 cache entry and the corresponding IPv6 route. 1031 If the source Client is unable to elicit an NA response from the 1032 target Client after MAX_RETRY attempts, it SHOULD consider the direct 1033 path unusable for forwarding purposes. Otherwise, the source Client 1034 may continue to send packets directly to the target Client and SHOULD 1035 thereafter process any link-layer errors as a hint that the direct 1036 path to the target Client has either failed or has become 1037 intermittent. 1039 3.13. Mobility and Link-Layer Address Change Considerations 1041 When a Client needs to change its link-layer address (e.g., due to a 1042 mobility event, due to a change in underlying network interface, 1043 etc.), it sends an immediate NS message forward to any of its 1044 correspondents (including the Server and any other Clients) which 1045 then discover the new link-layer address. 1047 If two Clients change their link-layer addresses simultaneously, the 1048 NS/NA messages may be lost. In that case, the Clients SHOULD delete 1049 their respective dynamic neighbor cache entries and IPv6 routes, and 1050 allow packets to again flow through their Server(s) which MAY result 1051 in a new AERO redirection exchange. 1053 When a Client needs to change to a new Server, it performs a DHCPv6 1054 "Release" message exchange with the delegating router via the old 1055 Server then sends a DHCPv6 "Request" message to the delegating router 1056 via the new Server. During this process, the Client and old Server 1057 both delete their respective static neighbor cache entries while the 1058 Client and new Server both create new respective static neighbor 1059 cache entries. Note that this may result in a temporary service 1060 outage during Server "handovers". 1062 3.14. Underlying Protocol Version Considerations 1064 A source Client may connect only to an IPvX underlying network, while 1065 the target Client connects only to an IPvY underlying network. In 1066 that case, the source Client has no means for reaching the target 1067 directly (since they connect to underlying networks of different IP 1068 protocol versions) and so must ignore any Redirects and continue to 1069 send packets via the Server. 1071 3.15. Multicast Considerations 1073 When the underlying network does not support multicast, AERO nodes 1074 map IPv6 link-scoped multicast addresses (including 1075 "All_DHCP_Relay_Agents_and_Servers") to the underlying IP address of 1076 the AERO Server. 1078 When the underlying network supports multicast, AERO nodes use the 1079 multicast address mapping specification found in [RFC2529] for IPv4 1080 underlying networks and use a direct multicast mapping for IPv6 1081 underlying networks. (In the latter case, "direct multicast mapping" 1082 means that if the IPv6 multicast destination address of the inner 1083 packet is "M", then the IPv6 multicast destination address of the 1084 encapsulating header is also "M".) 1086 3.16. Operation on Server-less AERO Links 1088 In some AERO link scenarios, there may be no Server on the link 1089 and/or no need for Clients to use a Server as an intermediary trust 1090 anchor. In that case, Clients can establish dynamic neighbor cache 1091 entries and IPv6 routes by performing direct Client-to-Client 1092 exchanges, and some other form of trust basis must be applied so that 1093 each Client can verify that the prospective neighbor is authorized to 1094 use its claimed prefix. 1096 When there is no Server on the link, Clients must arrange to receive 1097 prefix delegations and publish the delegations via a secure prefix 1098 discovery service through some means outside the scope of this 1099 document. 1101 3.17. Other Considerations 1103 IPv6 hosts serviced by an AERO Client can reach IPv4-only services 1104 via a NAT64 gateway [RFC6146] within the IPv6 network. 1106 AERO nodes can use the Default Address Selection Policy with DHCPv6 1107 option [RFC7078] the same as on any IPv6 link. 1109 All other (non-multicast) functions that operate over ordinary IPv6 1110 links operate in the same fashion over AERO links. 1112 4. Implementation Status 1114 An early implementation is available at: 1115 http://linkupnetworks.com/aero/aerov2-0.1.tgz. 1117 5. IANA Considerations 1119 This document uses the UDP Service Port Number 8060 reserved by IANA 1120 for AERO in [RFC6706]. Therefore, there are no new IANA actions 1121 required for this document. 1123 6. Security Considerations 1125 AERO link security considerations are the same as for standard IPv6 1126 Neighbor Discovery [RFC4861] except that AERO improves on some 1127 aspects. In particular, AERO is dependent on a trust basis between 1128 AERO Clients and Servers, where the Clients only engage in the AERO 1129 mechanism when it is facilitated by a trust anchor. 1131 AERO links must be protected against link-layer address spoofing 1132 attacks in which an attacker on the link pretends to be a trusted 1133 neighbor. Links that provide link-layer securing mechanisms (e.g., 1134 WiFi networks) and links that provide physical security (e.g., 1135 enterprise network LANs) provide a first line of defense that is 1136 often sufficient. In other instances, securing mechanisms such as 1137 Secure Neighbor Discovery (SeND) [RFC3971] or IPsec [RFC4301] may be 1138 necessary. 1140 AERO Clients MUST ensure that their connectivity is not used by 1141 unauthorized nodes to gain access to a protected network. (This 1142 concern is no different than for ordinary hosts that receive an IP 1143 address delegation but then "share" the address with unauthorized 1144 nodes via an IPv6/IPv6 NAT function.) 1145 On some AERO links, establishment and maintenance of a direct path 1146 between neighbors requires secured coordination such as through the 1147 Internet Key Exchange (IKEv2) protocol [RFC5996]. 1149 7. Acknowledgements 1151 Discussions both on the v6ops list and in private exchanges helped 1152 shape some of the concepts in this work. Individuals who contributed 1153 insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant, 1154 Brian Carpenter, Brian Haberman, Joel Halpern, Sascha Hlusiak, Lee 1155 Howard and Joe Touch. Members of the IESG also provided valuable 1156 input during their review process that greatly improved the document. 1157 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 1158 for their shepherding guidance. 1160 This work has further been encouraged and supported by Boeing 1161 colleagues including Keith Bartley, Balaguruna Chidambaram, Jeff 1162 Holland, Cam Brodie, Yueli Yang, Wen Fang, Ed King, Mike Slane, Kent 1163 Shuey, Gen MacLean, and other members of the BR&T and BIT mobile 1164 networking teams. 1166 Earlier works on NBMA tunneling approaches are found in 1167 [RFC2529][RFC5214][RFC5569]. 1169 8. References 1171 8.1. Normative References 1173 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1174 August 1980. 1176 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1177 September 1981. 1179 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 1180 RFC 792, September 1981. 1182 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1183 Requirement Levels", BCP 14, RFC 2119, March 1997. 1185 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1186 (IPv6) Specification", RFC 2460, December 1998. 1188 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1189 IPv6 Specification", RFC 2473, December 1998. 1191 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 1192 Host Configuration Protocol (DHCP) version 6", RFC 3633, 1193 December 2003. 1195 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 1196 for IPv6 Hosts and Routers", RFC 4213, October 2005. 1198 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1199 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1200 September 2007. 1202 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1203 Address Autoconfiguration", RFC 4862, September 2007. 1205 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 1206 Requirements", RFC 6434, December 2011. 1208 8.2. Informative References 1210 [IRON] Templin, F., "The Internet Routing Overlay Network 1211 (IRON)", Work in Progress, June 2012. 1213 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 1214 RFC 879, November 1983. 1216 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 1217 Domains without Explicit Tunnels", RFC 2529, March 1999. 1219 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 1220 RFC 2675, August 1999. 1222 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 1223 and M. Carney, "Dynamic Host Configuration Protocol for 1224 IPv6 (DHCPv6)", RFC 3315, July 2003. 1226 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 1227 Neighbor Discovery (SEND)", RFC 3971, March 2005. 1229 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1230 Internet Protocol", RFC 4301, December 2005. 1232 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 1233 Discovery", RFC 4821, March 2007. 1235 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 1236 Errors at High Data Rates", RFC 4963, July 2007. 1238 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1239 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1240 March 2008. 1242 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 1243 Infrastructures (6rd)", RFC 5569, January 2010. 1245 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 1246 "Internet Key Exchange Protocol Version 2 (IKEv2)", 1247 RFC 5996, September 2010. 1249 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 1250 NAT64: Network Address and Protocol Translation from IPv6 1251 Clients to IPv4 Servers", RFC 6146, April 2011. 1253 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 1254 Troan, "Basic Requirements for IPv6 Customer Edge 1255 Routers", RFC 6204, April 2011. 1257 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 1258 for Equal Cost Multipath Routing and Link Aggregation in 1259 Tunnels", RFC 6438, November 2011. 1261 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 1262 RFC 6691, July 2012. 1264 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 1265 (AERO)", RFC 6706, August 2012. 1267 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 1268 RFC 6864, February 2013. 1270 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 1271 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 1273 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1274 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1275 RFC 6936, April 2013. 1277 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 1278 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 1280 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 1281 Address Selection Policy Using DHCPv6", RFC 7078, 1282 January 2014. 1284 Appendix A. AERO Server and Relay Interworking 1286 Figure 3 depicts a reference AERO operational scenario with a single 1287 Server on the AERO link. In order to support scaling to larger 1288 numbers of nodes, the AERO link can deploy multiple Servers and 1289 Relays, e.g., as shown in Figure 7. 1291 .-(::::::::) 1292 .-(::: IPv6 :::)-. 1293 (:: Internetwork ::) 1294 `-(::::::::::::)-' 1295 `-(::::::)-' 1296 | 1297 +--------------+ +------+-------+ +--------------+ 1298 |AERO Server C | | AERO Relay D | |AERO Server E | 1299 | (default->D) | | (A->C; G->E) | | (default->D) | 1300 | (A->B) | +-------+------+ | (G->F) | 1301 +-------+------+ | +------+-------+ 1302 | | | 1303 X---+---+-------------------+------------------+---+---X 1304 | AERO Link | 1305 +-----+--------+ +--------+-----+ 1306 |AERO Client B | |AERO Client F | 1307 | (default->C) | | (default->E) | 1308 +--------------+ +--------------+ 1309 .-. .-. 1310 ,-( _)-. ,-( _)-. 1311 .-(_ IPv6 )-. .-(_ IPv6 )-. 1312 (__ EUN ) (__ EUN ) 1313 `-(______)-' `-(______)-' 1314 | | 1315 +--------+ +--------+ 1316 | Host A | | Host G | 1317 +--------+ +--------+ 1319 Figure 7: AERO Server/Relay Interworking 1321 In this example, AERO Client ('B') associates with AERO Server ('C'), 1322 while AERO Client ('F') associates with AERO Server ('E'). 1323 Furthermore, AERO Servers ('C') and ('E') do not associate with each 1324 other directly, but rather have an association with AERO Relay ('D') 1325 (i.e., a router that has full topology information concerning its 1326 associated Servers and their Clients). Relay ('D') connects to the 1327 AERO link, and also connects to the native IPv6 Internetwork. 1329 When host ('A') sends a packet toward destination host ('G'), IPv6 1330 forwarding directs the packet through the EUN to Client ('B'), which 1331 forwards the packet to Server ('C') in absence of more-specific 1332 forwarding information. Server ('C') forwards the packet, and it 1333 also generates an AERO Predirect message that is then forwarded 1334 through Relay ('D') to Server ('E'). When Server ('E') receives the 1335 message, it forwards the message to Client ('F'). 1337 After processing the AERO Predirect message, Client ('F') sends an 1338 AERO Redirect message to Server ('E'). Server ('E'), in turn, 1339 forwards the message through Relay ('D') to Server ('C'). When 1340 Server ('C') receives the message, it forwards the message to Client 1341 ('B') informing it that host 'G's EUN can be reached via Client 1342 ('F'), thus completing the AERO redirection. 1344 The network layer routing information shared between Servers and 1345 Relays must be carefully coordinated in a manner outside the scope of 1346 this document. In particular, Relays require full topology 1347 information, while individual Servers only require partial topology 1348 information (i.e., they only need to know the EUN prefixes associated 1349 with their current set of Clients). See [IRON] for an architectural 1350 discussion of routing coordination between Relays and Servers. 1352 Author's Address 1354 Fred L. Templin (editor) 1355 Boeing Research & Technology 1356 P.O. Box 3707 1357 Seattle, WA 98124 1358 USA 1360 Email: fltemplin@acm.org