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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) April 29, 2014 5 Intended status: Standards Track 6 Expires: October 31, 2014 8 Transmission of IPv6 Packets over AERO Links 9 draft-templin-aerolink-16.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 October 31, 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 . . . . . . . . . . . . . . . . . . . . . . . . 10 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 . . . . . . . 17 74 3.11. AERO Redirection . . . . . . . . . . . . . . . . . . . . . 17 75 3.11.1. Classical Redirection Approaches . . . . . . . . . . . 17 76 3.11.2. AERO Redirection Concept of Operations . . . . . . . . 18 77 3.11.3. AERO Redirection Message Format . . . . . . . . . . . 19 78 3.11.4. Sending Predirects . . . . . . . . . . . . . . . . . . 19 79 3.11.5. Processing Predirects and Sending Redirects . . . . . 20 80 3.11.6. Re-encapsulating and Relaying Redirects . . . . . . . 22 81 3.11.7. Processing Redirects . . . . . . . . . . . . . . . . . 22 82 3.12. Neighbor Reachability Maintenance . . . . . . . . . . . . 23 83 3.13. Mobility and Link-Layer Address Change Considerations . . 23 84 3.14. Underlying Protocol Version Considerations . . . . . . . . 24 85 3.15. Multicast Considerations . . . . . . . . . . . . . . . . . 25 86 3.16. Operation on Server-less AERO Links . . . . . . . . . . . 25 87 3.17. Other Considerations . . . . . . . . . . . . . . . . . . . 25 88 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 25 89 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 90 6. Security Considerations . . . . . . . . . . . . . . . . . . . 26 91 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26 92 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 93 8.1. Normative References . . . . . . . . . . . . . . . . . . . 27 94 8.2. Informative References . . . . . . . . . . . . . . . . . . 28 95 Appendix A. AERO Server and Relay Interworking . . . . . . . . . 29 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 Maximum 129 Transmission Unit (MTU) is less than or equal to the AERO link 130 MTU. 132 AERO address 133 an IPv6 link-local address assigned to an AERO interface and 134 constructed as specified in Section 3.6. 136 AERO node 137 a node that is connected to an AERO link and that participates in 138 IPv6 Neighbor Discovery over the link. 140 AERO Client ("client") 141 a node that configures either a host interface or a router 142 interface on an AERO link. 144 AERO Server ("server") 145 a node that configures a router interface on an AERO link over 146 which it can provide default forwarding and redirection services 147 for other AERO nodes. 149 AERO Relay ("relay") 150 a node that relays IPv6 packets between Servers on the same AERO 151 link, and/or that forwards IPv6 packets between the AERO link and 152 the IPv6 Internet. An AERO Relay may or may not also be 153 configured as an AERO Server. 155 ingress tunnel endpoint (ITE) 156 an AERO interface endpoint that injects tunneled packets into an 157 AERO link. 159 egress tunnel endpoint (ETE) 160 an AERO interface endpoint that receives tunneled packets from an 161 AERO link. 163 underlying network 164 a connected IPv6 or IPv4 network routing region over which AERO 165 nodes tunnel IPv6 packets. 167 underlying interface 168 an AERO node's interface point of attachment to an underlying 169 network. 171 underlying address 172 an IPv6 or IPv4 address assigned to an AERO node's underlying 173 interface. When UDP encapsulation is used, the UDP port number is 174 also considered as part of the underlying address. Underlying 175 addresses are used as the source and destination addresses of the 176 AERO encapsulation header. 178 link-layer address 179 the same as defined for "underlying address" above. 181 network layer address 182 an IPv6 address used as the source or destination address of the 183 inner IPv6 packet header. 185 end user network (EUN) 186 an IPv6 network attached to a downstream interface of an AERO 187 Client (where the AERO interface is seen as the upstream 188 interface). 190 Throughout the document, the simple terms "Server" and "Relay" refer 191 to "AERO Server" and "AERO Relay", respectively. Capitalization is 192 used to distinguish these terms from DHCPv6 server and DHCPv6 relay. 193 This is an important distinction, since an AERO Server may be a 194 DHCPv6 relay, and an AERO Relay may be a DHCPv6 server. 196 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 197 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 198 document are to be interpreted as described in [RFC2119]. 200 3. Asymmetric Extended Route Optimization (AERO) 202 The following sections specify the operation of IPv6 over Asymmetric 203 Extended Route Optimization (AERO) links: 205 3.1. AERO Node Types 207 AERO Relays relay packets between nodes connected to the same AERO 208 link and also forward packets between the AERO link and the native 209 IPv6 network. The relaying process entails re-encapsulation of IPv6 210 packets that were received from a first AERO node and are to be 211 forwarded without modification to a second AERO node. 213 AERO Servers configure their AERO interfaces as router interfaces, 214 and provide default routing services to AERO Clients. AERO Servers 215 configure a DHCPv6 relay or server function and facilitate DHCPv6 216 Prefix Delegation (PD) exchanges. An AERO Server may also act as an 217 AERO Relay. 219 AERO Clients act as requesting routers to receive IPv6 prefixes 220 through a DHCPv6 PD exchange via an AERO Server over the AERO link. 221 Each AERO Client receives at least a /64 prefix delegation, and may 222 receive even shorter prefixes. 224 AERO Clients that act as routers configure their AERO interfaces as 225 router interfaces, i.e., even if the AERO Client otherwise displays 226 the outward characteristics of an ordinary host (for example, the 227 Client may internally configure both an AERO interface and (internal 228 virtual) End User Network (EUN) interfaces). AERO Clients that act 229 as routers sub-delegate portions of their received prefix delegations 230 to links on EUNs. 232 AERO Clients that act as ordinary hosts configure their AERO 233 interfaces as host interfaces and assign one or more IPv6 addresses 234 taken from their received prefix delegations to the AERO interface 235 but DO NOT assign the delegated prefix itself to the AERO interface. 236 Instead, the host assigns the delegated prefix to a "black hole" 237 route so that unused portions of the prefix are nullified. 239 End system applications on AERO hosts bind directly to the AERO 240 interface, while applications on AERO routers (or IPv6 hosts served 241 by an AERO router) bind to EUN interfaces. 243 3.2. AERO Interface Characteristics 245 AERO interfaces use IPv6-in-IPv6 encapsulation [RFC2473] to exchange 246 tunneled packets with AERO neighbors attached to an underlying IPv6 247 network, and use IPv6-in-IPv4 encapsulation [RFC4213] to exchange 248 tunneled packets with AERO neighbors attached to an underlying IPv4 249 network. AERO interfaces can also use IPsec encapsulation [RFC4301] 250 (either IPv6-in-IPsec-in-IPv6 or IPv6-in-IPsec-in-IPv4) in 251 environments where strong authentication and confidentiality are 252 required. When NAT traversal and/or filtering middlebox traversal is 253 necessary, a UDP header is further inserted between the outer IP 254 encapsulation header and the inner packet. 256 Servers assign the link-local address 'fe80::0' to their AERO 257 interface; this provides a handle for Clients to insert into a 258 neighbor cache entry for their current Server. Servers also 259 configure administratively-assigned link-local addresses on their 260 AERO interfaces to support the operation of the inter-Server/Relay 261 routing system (see: [IRON]). 263 Clients initially assign no addresses on their AERO interface, but 264 use 'fe80::1' as the IPv6 link-local address in the DHCPv6 PD 265 exchanges used to receive an IPv6 prefix and derive an AERO address. 266 After the Client receives a prefix delegation, it assigns the 267 corresponding AERO address to the AERO interface. 269 AERO interfaces maintain a neighbor cache and use a variation of 270 standard unicast IPv6 ND messaging. AERO interfaces use Neighbor 271 Solicitation (NS), Neighbor Advertisement (NA) and Redirect messages 272 the same as for any IPv6 link. They do not use Router Solicitation 273 (RS) and Router Advertisement (RA) messages for several reasons. 274 First, default router discovery is supported through other means more 275 appropriate for AERO links as described below. Second, discovery of 276 more-specific routes is through the receipt of Redirect messages. 277 Finally, AERO nodes obtain their delegated IPv6 prefixes using DHCPv6 278 PD; hence, there is no need for RA-based prefix discovery. 280 AERO Neighbor Solicitation (NS) and Neighbor Advertisement (NA) 281 messages do not include Source/Target Link Layer Address Options 282 (S/TLLAO). Instead, AERO nodes determine the link-layer addresses of 283 neighbors by examining the encapsulation IP source address and UDP 284 port number (when UDP encapsulation is used) of any NS/NA messages 285 they receive and ignore any S/TLLAOs included in these messages. 286 This is vital to the operation of AERO links for which neighbors are 287 separated by Network Address Translators (NATs) - either IPv4 or 288 IPv6. 290 AERO Redirect messages include a TLLAO the same as for any IPv6 link. 291 The TLLAO includes the link-layer address of the target node, 292 including both the IP address and the UDP source port number used by 293 the target when it sends UDP-encapsulated packets over the AERO 294 interface (the TLLAO instead encodes the value 0 when the target does 295 not use UDP encapsulation). TLLAOs for target nodes that use an IPv6 296 underlying address include the full 16 bytes of the IPv6 address as 297 shown in Figure 1, while TLLAOs for target nodes that use an IPv4 298 underlying address include only the 4 bytes of the IPv4 address as 299 shown in Figure 2. 301 0 1 2 3 302 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 1 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 | Type = 2 | Length = 3 | UDP Source Port (or 0) | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | Reserved | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | | 309 +-- --+ 310 | | 311 +-- IPv6 Address --+ 312 | | 313 +-- --+ 314 | | 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 317 Figure 1: AERO TLLAO Format for IPv6 319 0 1 2 3 320 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 1 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 322 | Type = 2 | Length = 1 | UDP Source Port (or 0) | 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 324 | IPv4 Address | 325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 Figure 2: AERO TLLAO Format for IPv4 329 Finally, AERO interface NS/NA messages only update existing neighbor 330 cache entires and do not create new neighbor cache entries, whereas 331 Redirect messages both update and create neighbor cache entries. 332 This represents a departure from the normal operation of IPv6 ND over 333 common link types, but is consistent with the spirit of IPv6 over 334 NBMA links as discussed in [RFC4861]. Note however that this 335 restriction may be relaxed and/or redefined on AERO links that 336 participate in a fully distributed mobility management model 337 coordinated in a manner outside the scope of this document. 339 3.3. AERO Addresses 341 An AERO address is an IPv6 link-local address assigned to an AERO 342 interface and with an IPv6 prefix embedded within the interface 343 identifier. The AERO address is formatted as: 345 fe80::[IPv6 prefix] 347 Each AERO Client configures an AERO address based on the delegated 348 prefix it has received from the DHCPv6 server. The address begins 349 with the prefix fe80::/64 and includes in its interface identifier 350 the base /64 prefix taken from the Client's delegated IPv6 prefix. 351 The base prefix is determined by masking the delegated prefix with 352 the prefix length. For example, if an AERO Client has received the 353 prefix delegation: 355 2001:db8:1000:2000::/56 357 it would construct its AERO address as: 359 fe80::2001:db8:1000:2000 361 The AERO address remains stable as the Client moves between 362 topological locations, i.e., even if its underlying address changes. 364 3.4. AERO Interface Data Origin Authentication 366 Nodes on AERO interfaces use a simple data origin authentication for 367 encapsulated packets they receive from other nodes. In particular, 368 AERO Clients accept encapsulated packets with a link-layer source 369 address belonging to their current AERO Server. AERO nodes also 370 accept encapsulated packets with a link-layer source address that is 371 correct for the network-layer source address. 373 The AERO node considers the link-layer source address correct for the 374 network-layer source address if there is an IPv6 forwarding table 375 entry that matches the network-layer source address as well as a 376 neighbor cache entry corresponding to the next hop that includes the 377 link-layer address. An exception is that NS, NA and Redirect 378 messages may include a different link-layer address than the one 379 currently in the neighbor cache, and the new link-layer address 380 updates the neighbor cache entry. 382 3.5. AERO Interface Conceptual Data Structures and Protocol Constants 384 Each AERO node maintains a per-AERO interface conceptual neighbor 385 cache that includes an entry for each neighbor it communicates with 386 on the AERO link, the same as for any IPv6 interface (see [RFC4861]). 387 Neighbor cache entries are either static or dynamic. Static neighbor 388 cache entries (including a Client's neighbor cache entry for a Server 389 or a Server's neighbor cache entry for a Client) do not have timeout 390 values and are retained until explicitly deleted. Dynamic neighbor 391 cache entries are created and maintained by the AERO redirection 392 procedures describe in the following sections. 394 When an AERO node receives a valid Predirect message (See Section 395 3.11.5) it creates or updates a dynamic neighbor cache entry for the 396 Predirect target L3 and L2 addresses, and also creates an IPv6 397 forwarding table entry for the Predirected (source) prefix. The node 398 then sets an ACCEPT timer and uses this timer to validate any 399 messages received from the Predirected neighbor. 401 When an AERO node receives a valid Redirect message (see Section 402 3.11.7) it creates or updates a dynamic neighbor cache entry for the 403 Redirect target L3 and L2 addresses, and also creates an IPv6 404 forwarding table entry for the Redirected (destination) prefix. The 405 node then sets a FORWARD timer and uses this timer to determine 406 whether packets can be sent directly to the Redirected neighbor. The 407 node also maintains a constant value MAX_RETRY to limit the number of 408 keepalives sent when a neighbor has gone unreachable. 410 It is RECOMMENDED that FORWARD_TIME be set to the default constant 411 value 30 seconds to match the default REACHABLE_TIME value specified 412 for IPv6 neighbor discovery [RFC4861]. 414 It is RECOMMENDED that ACCEPT_TIME be set to the default constant 415 value 40 seconds to allow a 10 second window so that the AERO 416 redirection procedure can converge before the ACCEPT_TIME timer 417 decrements below FORWARD_TIME. 419 It is RECOMMENDED that MAX_RETRY be set to 3 the same as described 420 for IPv6 neighbor discovery address resolution in Section 7.3.3 of 421 [RFC4861]. 423 Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be 424 administratively set, if necessary, to better match the AERO link's 425 performance characteristics; however, if different values are chosen, 426 all nodes on the link MUST consistently configure the same values. 427 ACCEPT_TIME SHOULD further be set to a value that is sufficiently 428 longer than FORWARD_TIME to allow the AERO redirection procedure to 429 converge. 431 3.6. AERO Interface MTU Considerations 433 The AERO link Maximum Transmission Unit (MTU) is 64KB minus the 434 encapsulation overhead for IPv4 [RFC0791] and 4GB minus the 435 encapsulation overhead for IPv6 [RFC2675]. This is the most that 436 IPv4 and IPv6 (respectively) can convey within the constraints of 437 protocol constants, but actual sizes available for tunneling will 438 frequently be much smaller. 440 The base tunneling specifications for IPv4 and IPv6 typically set a 441 static MTU on the tunnel interface to 1500 bytes minus the 442 encapsulation overhead or smaller still if the tunnel is likely to 443 incur additional encapsulations such as IPsec on the path. This can 444 result in path MTU related black holes when packets that are too 445 large to be accommodated over the AERO link are dropped, but the 446 resulting ICMP Packet Too Big (PTB) messages are lost on the return 447 path. As a result, AERO nodes use the following MTU mitigations to 448 accommodate larger packets. 450 AERO nodes set their AERO interface MTU to the larger of 1500 bytes 451 and the underlying interface MTU minus the encapsulation overhead. 452 AERO nodes optionally cache other per-neighbor MTU values in the 453 underlying IP path MTU discovery cache initialized to the underlying 454 interface MTU. 456 AERO nodes admit packets that are no larger than 1280 bytes minus the 457 encapsulation overhead (*) as well as packets that are larger than 458 1500 bytes into the tunnel without fragmentation, i.e., as long as 459 they are no larger than the AERO interface MTU before encapsulation 460 and also no larger than the cached per-neighbor MTU following 461 encapsulation. For IPv4, the node sets the "Don't Fragment" (DF) bit 462 to 0 for packets no larger than 1280 bytes minus the encapsulation 463 overhead (*) and sets the DF bit to 1 for packets larger than 1500 464 bytes. If a large packet is lost in the path, the node may 465 optionally cache the MTU reported in the resulting PTB message or may 466 ignore the message, e.g., if there is a possibility that the message 467 is spurious. 469 For packets destined to an AERO node that are larger than 1280 bytes 470 minus the encapsulation overhead (*) but no larger than 1500 bytes, 471 the node uses outer IP fragmentation to fragment the packet into two 472 pieces (where the first fragment contains 1024 bytes of the 473 fragmented inner packet) then admits the fragments into the tunnel. 474 If the outer protocol is IPv4, the node admits the packet into the 475 tunnel with DF set to 0 and subject to rate limiting to avoid 476 reassembly errors [RFC4963][RFC6864]. For both IPv4 and IPv6, the 477 node also sends a 1500 byte probe message (**) to the neighbor, 478 subject to rate limiting. To construct a probe, the node prepares an 479 ICMPv6 Neighbor Solicitation (NS) message with trailing padding 480 octets added to a length of 1500 bytes but does not include the 481 length of the padding in the IPv6 Payload Length field. The node 482 then encapsulates the NS in the outer encapsulation headers (while 483 including the length of the padding in the outer length fields), sets 484 DF to 1 (for IPv4) and sends the padded NS message to the neighbor. 485 If the neighbor returns an NA message, the node may then send whole 486 packets within this size range and (for IPv4) relax the rate limiting 487 requirement. 489 AERO nodes MUST be capable of reassembling packets up to 1500 bytes 490 plus the encapsulation overhead length. It is therefore RECOMMENDED 491 that AERO nodes be capable of reassembling at least 2KB. 493 (*) Note that if it is known that the minimum Path MTU to an AERO 494 node is MINMTU bytes (where 1280 < MINMTU < 1500) then MINMTU can be 495 used instead of 1280 in the fragmentation threshold considerations 496 listed above. 498 (**) It is RECOMMENDED that no probes smaller than 1500 bytes be used 499 for MTU probing purposes, since smaller probes may be fragmented if 500 there is a nested tunnel somewhere on the path to the neighbor. 502 3.7. AERO Interface Encapsulation, Re-encapsulation and Decapsulation 504 AERO interfaces encapsulate IPv6 packets according to whether they 505 are entering the AERO interface for the first time or if they are 506 being forwarded out the same AERO interface that they arrived on. 507 This latter form of encapsulation is known as "re-encapsulation". 509 AERO interfaces encapsulate packets per the specifications in , 510 [RFC2473], [RFC4213] except that the interface copies the "TTL/Hop 511 Limit", "Type of Service/Traffic Class" and "Congestion Experienced" 512 values in the inner network layer header into the corresponding 513 fields in the outer IP header. For packets undergoing re- 514 encapsulation, the AERO interface instead copies the "TTL/Hop Limit", 515 "Type of Service/Traffic Class" and "Congestion Experienced" values 516 in the original outer IP header into the corresponding fields in the 517 new outer IP header (i.e., the values are transferred between outer 518 headers and *not* copied from the inner network layer header). 520 When UDP encapsulation is used, the AERO interface inserts a UDP 521 header between the inner packet and outer IP header. If the outer 522 header is IPv6 and is followed by an IPv6 Fragment header, the AERO 523 interface inserts the UDP header between the outer IPv6 header and 524 IPv6 Fragment header. The AERO interface sets the UDP source port to 525 a constant value that it will use in each successive packet it sends, 526 sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) and 527 sets the UDP length field to the length of the inner packet plus 8 528 bytes for the UDP header itself. For packets sent via a Server, the 529 AERO interface sets the UDP destination port to 8060 (i.e., the IANA- 530 registerd port number for AERO). For packets sent to a neighboring 531 Client, the AERO interface sets the UDP destination port to the port 532 value stored in the neighbor cache entry for this neighbor. 534 The AERO interface next sets the outer IP protocol number to the 535 appropriate value for the first protocol layer within the 536 encapsulation (e.g., IPv6, IPv6 Fragment Header, UDP, etc.). When 537 IPv6 is used as the outer IP protocol, the ITE then sets the flow 538 label value in the outer IPv6 header the same as described in 539 [RFC6438]. When IPv4 is used as the outer IP protocol, the AERO 540 interface sets the DF bit as discussed in Section 3.2. 542 AERO interfaces decapsulate packets destined either to the node 543 itself or to a destination reached via an interface other than the 544 receiving AERO interface per the specifications in , [RFC2473], 545 [RFC4213]. When the encapsulated packet includes a UDP header, the 546 AERO interface examines the first octet of data following the UDP 547 header to determine the inner header type. If the most significant 548 four bits of the first octet encode the value '0110', the inner 549 header is an IPv6 header. Otherwise, the interface considers the 550 first octet as an IP protocol type that encodes the value '44' for 551 IPv6 fragment header, the value '50' for Encapsulating Security 552 Payload, the value '51' for Authentication Header etc. (If the first 553 octet encodes the value '0', the interface instead discards the 554 packet, since this is the value reserved for experimentation under , 555 [RFC6706]). During the decapsulation, the AERO interface records the 556 UDP source port in the neighbor cache entry for this neighbor then 557 discards the UDP header. 559 3.8. AERO Reference Operational Scenario 561 Figure 3 depicts the AERO reference operational scenario. The figure 562 shows an AERO Server('A'), two AERO Clients ('B', 'D') and three 563 ordinary IPv6 hosts ('C', 'E', 'F'): 565 .-(::::::::) 566 .-(::: IPv6 :::)-. +-------------+ 567 (:::: Internet ::::)--| Host F | 568 `-(::::::::::::)-' +-------------+ 569 `-(::::::)-' 2001:db8:3::1 570 | 571 +--------------+ 572 | AERO Server A| 573 | (C->B; E->D) | 574 +--------------+ 575 fe80::0 576 L2(A) 577 | 578 X-----+-----------+-----------+--------X 579 | AERO Link | 580 L2(B) L2(D) 581 fe80::2001:db8:0:0 fe80::2001:db8:1:0 .-. 582 +--------------+ +--------------+ ,-( _)-. 583 | AERO Client B| | AERO Client D| .-(_ IPv6 )-. 584 | (default->A) | | (default->A) |--(__ EUN ) 585 +--------------+ +--------------+ `-(______)-' 586 2001:DB8:0::/48 2001:DB8:1::/48 | 587 | 2001:db8:1::1 588 .-. +-------------+ 589 ,-( _)-. 2001:db8:0::1 | Host E | 590 .-(_ IPv6 )-. +-------------+ +-------------+ 591 (__ EUN )--| Host C | 592 `-(______)-' +-------------+ 594 Figure 3: AERO Reference Operational Scenario 596 In Figure 3, AERO Server ('A') connects to the AERO link and connects 597 to the IPv6 Internet, either directly or via an AERO Relay (not 598 shown). Server ('A') assigns the address fe80::0 to its AERO 599 interface with link-layer address L2(A). Server ('A') next arranges 600 to add L2(A) to a published list of valid Servers for the AERO link. 602 AERO Client ('B') registers the IPv6 prefix 2001:db8:0::/48 in a 603 DHCPv6 PD exchange via AERO Server ('A') then assigns the address 604 fe80::2001:db8:0:0 to its AERO interface with link-layer address 605 L2(B). Client ('B') configures a default route via the AERO 606 interface with next-hop address fe80::0 and link-layer address L2(A), 607 then sub-delegates the prefix 2001:db8:0::/48 to its attached EUNs. 608 IPv6 host ('C') connects to the EUN, and configures the address 2001: 609 db8:0::1. 611 AERO Client ('D') registers the IPv6 prefix 2001:db8:1::/48 in a 612 DHCPv6 PD exchange via AERO Server ('A') then assigns the address 613 fe80::2001:db8:1:0 to its AERO interface with link-layer address 614 L2(D). Client ('D') configures a default route via the AERO 615 interface with next-hop address fe80::0 and link-layer address L2(A), 616 then sub-delegates the prefix 2001:db8:1::/48 to its attached EUNs. 617 IPv6 host ('E') connects to the EUN, and configures the address 2001: 618 db8:1::1. 620 Finally, IPv6 host ('F') connects to an IPv6 network outside of the 621 AERO link domain. Host ('F') configures its IPv6 interface in a 622 manner specific to its attached IPv6 link, and assigns the address 623 2001:db8:3::1 to its IPv6 link interface. 625 3.9. AERO Router Discovery and Prefix Delegation 627 3.9.1. AERO Client Behavior 629 AERO Clients observe the IPv6 node requirements defined in [RFC6434]. 630 AERO Clients first discover the link-layer address of an AERO Server 631 via static configuration, or through an automated means such as DNS 632 name resolution. In the absence of other information, the Client 633 resolves the Fully-Qualified Domain Name (FQDN) 634 "linkupnetworks.domainname", where "domainname" is the DNS domain 635 appropriate for the Client's attached underlying network. The Client 636 then creates a static neighbor cache entry with fe80::0 as the 637 network-layer address and the discovered address as the link-layer 638 address. The Client further creates a static default IPv6 forwarding 639 table entry with fe80::0 as the next hop address. 641 Next, the Client acts as a requesting router to request an IPv6 642 prefix through DHCPv6 PD [RFC3633] via the AERO Server using fe80::1 643 as the IPv6 source address and fe80::0 as the IPv6 destination 644 address. The Client further includes a DHCPv6 Unique Identifier 645 (DUID) based on a Universally Unique Identifier (UUID) (also known as 646 DUID-UUID) as described in [RFC6355]. 648 After the Client receives its prefix delegation, it assigns the link- 649 local AERO address taken from the prefix to the AERO interface (see: 650 Section 3.3) and sub-delegates the prefix to nodes and links within 651 its attached EUNs (the AERO link-local address thereafter remains 652 stable as the Client moves). The Client further renews its prefix 653 delegation via standard DHCPv6 procedures by sending DHCPv6 Renew 654 messages with fe80::1 as the IPv6 source address, fe80::0 as the IPv6 655 destination address and the same DUID-UUID value as the DUID. 657 The Client sends periodic NS messages to the Server to obtain new NAs 658 in order to refresh any network state. The Client can also forward 659 IPv6 packets destined to networks beyond its local EUNs via the 660 Server as an IPv6 default router. The Server may in turn return a 661 Redirect message informing the Client of a neighbor on the AERO link 662 that is topologically closer to the final destination as specified in 663 Section 3.11. 665 3.9.2. AERO Server Behavior 667 AERO Servers observe the IPv6 router requirements defined in 668 [RFC6434] and further configure a DHCPv6 relay or server function on 669 their AERO links. When the AERO Server relays a Client's DHCPv6 PD 670 messages to the DHCPv6 server, it wraps each message in a "Relay- 671 forward" message per [RFC3315] and includes a DHCPv6 "Interface-Id" 672 option that encodes a value that identifies the AERO link to the 673 DHCPv6 server. The AERO Server then encodes the Client's link-layer 674 source address and (when UDP encapsulation is used) UDP source port 675 number in the link-address and peer-address fields of the "Relay- 676 forward" message. (Note that the link-address and peer-address 677 fields of the "Relay-forward" message are available for coding since 678 the message includes an "Interface-Id" option (thereby obviating the 679 need for a link-address) and the source address of the DHCPv6 message 680 will always be fe80::1 (thereby obviating the need for a peer- 681 address). Most importantly, encoding the link-layer information in 682 this manner allows the AERO Server to remain stateless while the 683 DHCPv6 server is authoritative for the delegation of IPv6 prefixes to 684 authorized AERO Clients.) 686 When the DHCPv6 server issues the IPv6 prefix delegation in a "Relay- 687 reply" message via the AERO Server (acting as a DHCPv6 relay), the 688 AERO Server creates a static neighbor cache entry for the Client's 689 AERO address (see: Section 3.3) with the coded link-layer address and 690 UDP port number as the link-layer address for the neighbor cache 691 entry. The AERO Server also configures a static IPv6 forwarding 692 table entry that lists the Client's AERO address as the next hop 693 toward the delegated IPv6 prefix .The AERO Server finally injects the 694 Client's prefix as an IPv6 route into the inter-Server/Relay routing 695 system (see: [IRON]) then relays the DHCPv6 message to the Client 696 while using fe80::0 as the IPv6 source address, fe80::1 as the IPv6 697 destination address, and the Client's cached link-layer address as 698 the destination link-layer address. 700 Servers respond to NS messages from Clients on their AERO interfaces 701 by returning an NA message. When the Server receives an NS message, 702 it updates the neighbor cache entry using the network layer source 703 address as the neighbor's network layer address and using the link- 704 layer source address of the NS message as the neighbor's link-layer 705 address. 707 When the Server forwards a packet via the same AERO interface on 708 which it arrived, it initiates an AERO route optimization procedure 709 as specified in Section 3.11. 711 3.10. AERO Neighbor Solicitation and Advertisement 713 Each AERO node uses its delegated prefix to create an AERO address 714 (see: Section 3.3). It can then send unicast NS messages to elicit 715 NA messages from other AERO nodes the same as described for neighbor 716 unreachability detection in[RFC4861] except that the messages do not 717 include S/TLLAOs. 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. The AERO node also 722 includes the AERO address of the neighbor as the NS/NA message Target 723 address with the exception of "terminating NS" messages as described 724 in Section 3.13. 726 When an AERO node receives an NS/NA message, it accepts the message 727 if it has a neighbor cache entry for the neighbor; otherwise, it 728 ignores the message. 730 3.11. AERO Redirection 732 Section 3.8 describes the AERO reference operational scenario. We 733 now discuss the operation and protocol details of AERO Redirection 734 with respect to this reference scenario. 736 3.11.1. Classical Redirection Approaches 738 With reference to Figure 3, when the IPv6 source host ('C') sends a 739 packet to an IPv6 destination host ('E'), the packet is first 740 forwarded via the EUN to AERO Client ('B'). Client ('B') then 741 forwards the packet over its AERO interface to AERO Server ('A'), 742 which then re-encapsulates and forwards the packet to AERO Client 743 ('D'), where the packet is finally forwarded to the IPv6 destination 744 host ('E'). When Server ('A') re-encapsulates and forwards the 745 packet back out on its advertising AERO interface, it must arrange to 746 redirect Client ('B') toward Client ('D') as a better next-hop node 747 on the AERO link that is closer to the final destination. However, 748 this redirection process applied to AERO interfaces must be more 749 carefully orchestrated than on ordinary links since the parties may 750 be separated by potentially many underlying network routing hops. 752 Consider a first alternative in which Server ('A') informs Client 753 ('B') only and does not inform Client ('D') (i.e., "classical 754 redirection"). In that case, Client ('D') has no way of knowing that 755 Client ('B') is authorized to forward packets from the claimed source 756 address, and it may simply elect to drop the packets. Also, Client 757 ('B') has no way of knowing whether Client ('D') is performing some 758 form of source address filtering that would reject packets arriving 759 from a node other than a trusted default router, nor whether Client 760 ('D') is even reachable via a direct path that does not involve 761 Server ('A'). 763 Consider a second alternative in which Server ('A') informs both 764 Client ('B') and Client ('D') separately, via independent redirection 765 control messages (i.e., "augmented redirection"). In that case, if 766 Client ('B') receives the redirection control message but Client 767 ('D') does not, subsequent packets sent by Client ('B') could be 768 dropped due to filtering since Client ('D') would not have a route to 769 verify the claimed source address. Also, if Client ('D') receives 770 the redirection control message but Client ('B') does not, subsequent 771 packets sent in the reverse direction by Client ('D') would be lost. 773 Since both of these alternatives have shortcomings, a new redirection 774 technique (i.e., "AERO redirection") is needed. 776 3.11.2. AERO Redirection Concept of Operations 778 Again, with reference to Figure 3, when source host ('C') sends a 779 packet to destination host ('E'), the packet is first forwarded over 780 the source host's attached EUN to Client ('B'), which then forwards 781 the packet via its AERO interface to Server ('A'). 783 Server ('A') then re-encapsulates and forwards the packet out the 784 same AERO interface toward Client ('D') and also sends an AERO 785 "Predirect" message forward to Client ('D') as specified in 786 Section 3.11.4. The Predirect message includes Client ('B')'s 787 network- and link-layer addresses as well as information that Client 788 ('D') can use to determine the IPv6 prefix used by Client ('B') . 789 After Client ('D') receives the Predirect message, it process the 790 message and returns an AERO Redirect message destined for Client 791 ('B') via Server ('A') as specified in Section 3.11.5. During the 792 process, Client ('D') also creates or updates a dynamic neighbor 793 cache entry for Client ('B'), and creates an IPv6 forwarding table 794 entry for Client ('B')'s IPv6 prefix. 796 When Server ('A') receives the Redirect message, it re-encapsulates 797 the message and forwards it on to Client ('B') as specified in 798 Section 3.11.6. The message includes Client ('D')'s network- and 799 link-layer addresses as well as information that Client ('B') can use 800 to determine the IPv6 prefix used by Client ('D'). After Client 801 ('B') receives the Redirect message, it processes the message as 802 specified in Section 3.11.7. During the process, Client ('B') also 803 creates or updates a dynamic neighbor cache entry for Client ('D'), 804 and creates an IPv6 forwarding table entry for Client ('D')'s IPv6 805 prefix. 807 Following the above Predirect/Redirect message exchange, forwarding 808 of packets from Client ('B') to Client ('D') without involving Server 809 ('A) as an intermediary is enabled. The mechanisms that support this 810 exchange are specified in the following sections. 812 3.11.3. AERO Redirection Message Format 814 AERO Redirect/Predirect messages use the same format as for ICMPv6 815 Redirect messages depicted in Section 4.5 of [RFC4861], but also 816 include a new "Prefix Length" field taken from the low-order 8 bits 817 of the Redirect message Reserved field (valid values for the Prefix 818 Length field are 0 through 64). The Redirect/Predirect messages are 819 formatted as shown in Figure 4: 820 0 1 2 3 821 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 823 | Type (=137) | Code (=0/1) | Checksum | 824 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 825 | Reserved | Prefix Length | 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 827 | | 828 + + 829 | | 830 + Target Address + 831 | | 832 + + 833 | | 834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 835 | | 836 + + 837 | | 838 + Destination Address + 839 | | 840 + + 841 | | 842 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 843 | Options ... 844 +-+-+-+-+-+-+-+-+-+-+-+- 846 Figure 4: AERO Redirect/Predirect Message Format 848 3.11.4. Sending Predirects 850 When an AERO Server forwards a packet out the same AERO interface 851 that it arrived on, the Server sends a Predirect message forward 852 toward the AERO Client nearest the destination instead of sending a 853 Redirect message back to AERO Client nearest the source. 855 In the reference operational scenario, when Server ('A') forwards a 856 packet sent by Client ('B') toward Client ('D'), it also sends a 857 Predirect message forward toward Client ('D'), subject to rate 858 limiting (see Section 8.2 of [RFC4861]). Server ('A') prepares the 859 Predirect message as follows: 861 o the link-layer source address is set to 'L2(A)' (i.e., the 862 underlying address of Server ('A')). 864 o the link-layer destination address is set to 'L2(D)' (i.e., the 865 underlying address of Client ('D')). 867 o the network-layer source address is set to fe80::0 (i.e., the 868 link-local address of Server ('A')). 870 o the network-layer destination address is set to fe80::2001:db8:1:0 871 (i.e., the AERO address of Client ('D')). 873 o the Type is set to 137. 875 o the Code is set to 1 to indicate "Predirect". 877 o the Prefix Length is set to the length of the prefix to be applied 878 to Target address. 880 o the Target Address is set to fe80::2001:db8:0::0 (i.e., the AERO 881 address of Client ('B')). 883 o the Destination Address is set to the IPv6 source address of the 884 packet that triggered the Predirection event. 886 o the message includes a TLLAO set to 'L2(B)' (i.e., the underlying 887 address of Client ('B')). 889 o the message includes a Redirected Header Option (RHO) that 890 contains the originating packet truncated to ensure that at least 891 the network-layer header is included but the size of the message 892 does not exceed 1280 bytes. 894 Server ('A') then sends the message forward to Client ('D'). 896 3.11.5. Processing Predirects and Sending Redirects 898 When Client ('D') receives a Predirect message, it accepts the 899 message only if it has a link-layer source address of the Server, 900 i.e. 'L2(A)'. Client ('D') further accepts the message only if it 901 is willing to serve as a redirection target. Next, Client ('D') 902 validates the message according to the ICMPv6 Redirect message 903 validation rules in Section 8.1 of [RFC4861]. 905 In the reference operational scenario, when the Client ('D') receives 906 a valid Predirect message, it either creates or updates a dynamic 907 neighbor cache entry that stores the Target Address of the message as 908 the network-layer address of Client ('B') and stores the link-layer 909 address found in the TLLAO as the link-layer address of Client ('B'). 910 Client ('D') then applies the Prefix Length to the Interface 911 Identifier portion of the Target Address and records the resulting 912 IPv6 prefix in its IPv6 forwarding table. 914 After processing the message, Client ('D') prepares a Redirect 915 message response as follows: 917 o the link-layer source address is set to 'L2(D)' (i.e., the link- 918 layer address of Client ('D')). 920 o the link-layer destination address is set to 'L2(A)' (i.e., the 921 link-layer address of Server ('A')). 923 o the network-layer source address is set to 'L3(D)' (i.e., the AERO 924 address of Client ('D')). 926 o the network-layer destination address is set to 'L3(B)' (i.e., the 927 AERO address of Client ('B')). 929 o the Type is set to 137. 931 o the Code is set to 0 to indicate "Redirect". 933 o the Prefix Length is set to the length of the prefix to be applied 934 to the Target and Destination address. 936 o the Target Address is set to fe80::2001:db8:1::1 (i.e., the AERO 937 address of Client ('D')). 939 o the Destination Address is set to the IPv6 destination address of 940 the packet that triggered the Redirection event. 942 o the message includes a TLLAO set to 'L2(D)' (i.e., the underlying 943 address of Client ('D')). 945 o the message includes as much of the RHO copied from the 946 corresponding AERO Predirect message as possible such that at 947 least the network-layer header is included but the size of the 948 message does not exceed 1280 bytes. 950 After Client ('D') prepares the Redirect message, it sends the 951 message to Server ('A'). 953 3.11.6. Re-encapsulating and Relaying Redirects 955 When Server ('A') receives a Redirect message, it accepts the message 956 only if it has a neighbor cache entry that associates the message's 957 link-layer source address with the network-layer source address. 958 Next, Server ('A') validates the message according to the ICMPv6 959 Redirect message validation rules in Section 8.1 of [RFC4861]. 960 Following validation, Server ('A') re-encapsulates the Redirect then 961 relays the re-encapsulated Redirect on to Client ('B') as follows. 963 In the reference operational scenario, Server ('A') receives the 964 Redirect message from Client ('D') and prepares to re-encapsulate and 965 forward the message to Client ('B'). Server ('A') first verifies 966 that Client ('D') is authorized to use the Prefix Length in the 967 Redirect message when applied to the AERO address in the network- 968 layer source of the Redirect message, and discards the message if 969 verification fails. Otherwise, Server ('A') re-encapsulates the 970 message by changing the link-layer source address of the message to 971 'L2(A)', changing the network-layer source address of the message to 972 fe80::0, and changing the link-layer destination address to 'L2(B)' . 973 Server ('A') finally relays the re-encapsulated message to the 974 ingress node ('B') without decrementing the network-layer IPv6 header 975 Hop Limit field. 977 While not shown in Figure 3, AERO Relays relay Redirect and Predirect 978 messages in exactly this same fashion described above. See Figure 5 979 in Appendix A for an extension of the reference operational scenario 980 that includes Relays. 982 3.11.7. Processing Redirects 984 When Client ('B') receives the Redirect message, it accepts the 985 message only if it has a link-layer source address of the Server, 986 i.e. 'L2(A)'. Next, Client ('B') validates the message according to 987 the ICMPv6 Redirect message validation rules in Section 8.1 of 988 [RFC4861]. Following validation, Client ('B') then processes the 989 message as follows. 991 In the reference operational scenario, when Client ('B') receives the 992 Redirect message, it either creates or updates a dynamic neighbor 993 cache entry that stores the Target Address of the message as the 994 network-layer address of Client ('D') and stores the link-layer 995 address found in the TLLAO as the link-layer address of Client ('D'). 996 Client ('B') then applies the Prefix Length to the Interface 997 Identifier portion of the Target Address and records the resulting 998 IPv6 prefix in its IPv6 forwarding table. 1000 Now, Client ('B') has an IPv6 forwarding table entry for 1001 Client('D')'s prefix, and Client ('D') has an IPv6 forwarding table 1002 entry for Client ('B')'s prefix. Thereafter, the clients may 1003 exchange ordinary network-layer data packets directly without 1004 forwarding through Server ('A'). 1006 3.12. Neighbor Reachability Maintenance 1008 When a source Client is redirected to a target Client it MUST test 1009 the direct path to the target by sending an initial NS message to 1010 elicit a solicited NA response. While testing the path, the source 1011 Client SHOULD continue sending packets via the Server until target 1012 Client reachability has been confirmed. The source Client MUST 1013 thereafter continue to test the direct path to the target Client (see 1014 Section 7.3 of [RFC4861]) in order to keep dynamic neighbor cache 1015 entries alive. In particular, the source Client sends NS messages to 1016 the target Client subject to rate limiting in order to receive 1017 solicited NA messages. If at any time the direct path appears to be 1018 failing, the source Client can resume sending packets via the Server 1019 which may or may not result in a new redirection event. 1021 When a target Client receives an NS message from a source Client, it 1022 resets the ACCEPT_TIME timer if a neighbor cache entry exists; 1023 otherwise, it discards the NS message. 1025 When a source Client receives a solicited NA message form a target 1026 Client, it resets the FORWARD_TIME timer if a neighbor cache entry 1027 exists; otherwise, it discards the NA message. 1029 When both the FORWARD_TIME and ACCEPT_TIME timers on a dynamic 1030 neighbor cache entry expire, the Client deletes both the neighbor 1031 cache entry and the corresponding IPv6 forwarding table entry. 1033 If the source Client is unable to elicit an NA response from the 1034 target Client after MAX_RETRY attempts, it SHOULD consider the direct 1035 path unusable for forwarding purposes. Otherwise, the source Client 1036 may continue to send packets directly to the target Client and SHOULD 1037 thereafter process any link-layer errors as a hint that the direct 1038 path to the target Client has either failed or has become 1039 intermittent. 1041 3.13. Mobility and Link-Layer Address Change Considerations 1043 When a Client needs to change its link-layer address (e.g., due to a 1044 mobility event, due to a change in underlying network interface, 1045 etc.), it sends an immediate NS message forward to any of its 1046 correspondents (including the Server and any other Clients) which 1047 then discover the new link-layer address. 1049 If two Clients change their link-layer addresses simultaneously, the 1050 NS/NA messages may be lost. In that case, the Clients SHOULD delete 1051 their respective dynamic neighbor cache and IPv6 forwarding table 1052 entries, and allow packets to again flow through their Server(s) 1053 which MAY result in a new AERO redirection exchange. 1055 When a Client needs to change to a new AERO Server, it issues a new 1056 DHCPv6 Request message via the new AERO Server as the DHCPv6 relay. 1057 The new AERO Server then relays the message to the DHCPv6 server and 1058 processes the resulting exchange the same as described in Section 1059 3.9.2. After the Client receives the resulting DHCPv6 Reply message, 1060 it changes the link-layer address of the neighbor cache entry for 1061 fe80::0 to the address of the new AERO Server. 1063 After conducting the above exchange via the new AERO Server, the 1064 Client then sends a "terminating NS" message to the old AERO Server. 1065 The terminating NS message is prepared exactly the same as for an 1066 ordinary NS message, except that the Code field contains the value 1067 '1'. When the old Server receives the terminating NS message, it 1068 withdraws the IPv6 route from the routing system and deletes the 1069 neighbor cache entry and IPv6 forwarding table entry for the Client. 1070 The old Server then returns an NA message which the Client can use to 1071 verify that the termination signal has been processed. (Note that 1072 the old Server can impose a small delay before deleting the neighbor 1073 cache and IPv6 forwarding table entries so that any packets already 1074 in the system can still be delivered to the Client.) 1076 An alternative to sending a "terminating NS" message would be for the 1077 Client to somehow perform a DHCPv6 exchange with the DHCPv6 relay 1078 function on the old AERO Server but without involving the DHCPv6 1079 server. This would be insecure because the Client only has a DHCPv6 1080 security association with the DHCPv6 server and not the DHCPv6 relay. 1081 Conversely, the AERO Client and Server already require an authentic 1082 exchange of IPv6 Neighbor Discovery messages. 1084 3.14. Underlying Protocol Version Considerations 1086 A source Client may connect only to an IPvX underlying network, while 1087 the target Client connects only to an IPvY underlying network. In 1088 that case, the source Client has no means for reaching the target 1089 directly (since they connect to underlying networks of different IP 1090 protocol versions) and so must ignore any Redirects and continue to 1091 send packets via the Server. 1093 3.15. Multicast Considerations 1095 When the underlying network does not support multicast, AERO nodes 1096 map IPv6 link-scoped multicast addresses (including 1097 "All_DHCP_Relay_Agents_and_Servers") to the underlying IP address of 1098 the AERO Server. 1100 When the underlying network supports multicast, AERO nodes use the 1101 multicast address mapping specification found in [RFC2529] for IPv4 1102 underlying networks and use a direct multicast mapping for IPv6 1103 underlying networks. (In the latter case, "direct multicast mapping" 1104 means that if the IPv6 multicast destination address of the inner 1105 packet is "M", then the IPv6 multicast destination address of the 1106 encapsulating header is also "M".) 1108 3.16. Operation on Server-less AERO Links 1110 In some AERO link scenarios, there may be no Server on the link 1111 and/or no need for Clients to use a Server as an intermediary trust 1112 anchor. In that case, Clients can establish dynamic neighbor cache 1113 entries and IPv6 forwarding table entries by performing direct 1114 Client-to-Client Predirect/Redirect exchanges, and some other form of 1115 trust basis must be applied so that each Client can verify that the 1116 prospective neighbor is authorized to use its claimed prefix. 1118 When there is no Server on the link, Clients must arrange to receive 1119 prefix delegations and publish the delegations via a secure prefix 1120 discovery service through some means outside the scope of this 1121 document. 1123 3.17. Other Considerations 1125 IPv6 hosts serviced by an AERO Client can reach IPv4-only services 1126 via a NAT64 gateway [RFC6146] within the IPv6 network. 1128 AERO nodes can use the Default Address Selection Policy with DHCPv6 1129 option [RFC7078] the same as on any IPv6 link. 1131 All other (non-multicast) functions that operate over ordinary IPv6 1132 links operate in the same fashion over AERO links. 1134 4. Implementation Status 1136 An early implementation is available at: 1137 http://linkupnetworks.com/aero/aerov2-0.1.tgz. 1139 5. IANA Considerations 1141 This document uses the UDP Service Port Number 8060 reserved by IANA 1142 for AERO in [RFC6706]. Therefore, there are no new IANA actions 1143 required for this document. 1145 6. Security Considerations 1147 AERO link security considerations are the same as for standard IPv6 1148 Neighbor Discovery [RFC4861] except that AERO improves on some 1149 aspects. In particular, AERO is dependent on a trust basis between 1150 AERO Clients and Servers, where the Clients only engage in the AERO 1151 mechanism when it is facilitated by a trust anchor. 1153 AERO links must be protected against link-layer address spoofing 1154 attacks in which an attacker on the link pretends to be a trusted 1155 neighbor. Links that provide link-layer securing mechanisms (e.g., 1156 WiFi networks) and links that provide physical security (e.g., 1157 enterprise network LANs) provide a first line of defense that is 1158 often sufficient. In other instances, securing mechanisms such as 1159 Secure Neighbor Discovery (SeND) [RFC3971] or IPsec [RFC4301] may be 1160 necessary. 1162 AERO Clients MUST ensure that their connectivity is not used by 1163 unauthorized nodes to gain access to a protected network. (This 1164 concern is no different than for ordinary hosts that receive an IP 1165 address delegation but then "share" the address with unauthorized 1166 nodes via an IPv6/IPv6 NAT function.) 1168 On some AERO links, establishment and maintenance of a direct path 1169 between neighbors requires secured coordination such as through the 1170 Internet Key Exchange (IKEv2) protocol [RFC5996]. 1172 7. Acknowledgements 1174 Discussions both on the v6ops list and in private exchanges helped 1175 shape some of the concepts in this work. Individuals who contributed 1176 insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant, 1177 Brian Carpenter, Brian Haberman, Joel Halpern, Sascha Hlusiak, Lee 1178 Howard and Joe Touch. Members of the IESG also provided valuable 1179 input during their review process that greatly improved the document. 1180 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 1181 for their shepherding guidance. 1183 This work has further been encouraged and supported by Boeing 1184 colleagues including Keith Bartley, Balaguruna Chidambaram, Jeff 1185 Holland, Cam Brodie, Yueli Yang, Wen Fang, Ed King, Mike Slane, Kent 1186 Shuey, Gen MacLean, and other members of the BR&T and BIT mobile 1187 networking teams. 1189 Earlier works on NBMA tunneling approaches are found in 1190 [RFC2529][RFC5214][RFC5569]. 1192 8. References 1194 8.1. Normative References 1196 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1197 August 1980. 1199 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1200 September 1981. 1202 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 1203 RFC 792, September 1981. 1205 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1206 Requirement Levels", BCP 14, RFC 2119, March 1997. 1208 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1209 (IPv6) Specification", RFC 2460, December 1998. 1211 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1212 IPv6 Specification", RFC 2473, December 1998. 1214 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 1215 and M. Carney, "Dynamic Host Configuration Protocol for 1216 IPv6 (DHCPv6)", RFC 3315, July 2003. 1218 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 1219 Host Configuration Protocol (DHCP) version 6", RFC 3633, 1220 December 2003. 1222 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 1223 for IPv6 Hosts and Routers", RFC 4213, October 2005. 1225 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1226 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1227 September 2007. 1229 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1230 Address Autoconfiguration", RFC 4862, September 2007. 1232 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 1233 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 1234 August 2011. 1236 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 1237 Requirements", RFC 6434, December 2011. 1239 8.2. Informative References 1241 [IRON] Templin, F., "The Internet Routing Overlay Network 1242 (IRON)", Work in Progress, June 2012. 1244 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 1245 RFC 879, November 1983. 1247 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 1248 Domains without Explicit Tunnels", RFC 2529, March 1999. 1250 [RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms", 1251 RFC 2675, August 1999. 1253 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 1254 Neighbor Discovery (SEND)", RFC 3971, March 2005. 1256 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1257 Internet Protocol", RFC 4301, December 2005. 1259 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 1260 Discovery", RFC 4821, March 2007. 1262 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 1263 Errors at High Data Rates", RFC 4963, July 2007. 1265 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1266 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1267 March 2008. 1269 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 1270 Infrastructures (6rd)", RFC 5569, January 2010. 1272 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 1273 "Internet Key Exchange Protocol Version 2 (IKEv2)", 1274 RFC 5996, September 2010. 1276 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 1277 NAT64: Network Address and Protocol Translation from IPv6 1278 Clients to IPv4 Servers", RFC 6146, April 2011. 1280 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 1281 Troan, "Basic Requirements for IPv6 Customer Edge 1282 Routers", RFC 6204, April 2011. 1284 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 1285 for Equal Cost Multipath Routing and Link Aggregation in 1286 Tunnels", RFC 6438, November 2011. 1288 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 1289 RFC 6691, July 2012. 1291 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 1292 (AERO)", RFC 6706, August 2012. 1294 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 1295 RFC 6864, February 2013. 1297 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 1298 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 1300 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1301 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1302 RFC 6936, April 2013. 1304 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 1305 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 1307 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 1308 Address Selection Policy Using DHCPv6", RFC 7078, 1309 January 2014. 1311 Appendix A. AERO Server and Relay Interworking 1313 Figure 3 depicts a reference AERO operational scenario with a single 1314 Server on the AERO link. In order to support scaling to larger 1315 numbers of nodes, the AERO link can deploy multiple Servers and 1316 Relays, e.g., as shown in Figure 5. 1318 .-(::::::::) 1319 .-(::: IPv6 :::)-. 1320 (:: Internetwork ::) 1321 `-(::::::::::::)-' 1322 `-(::::::)-' 1323 | 1324 +--------------+ +------+-------+ +--------------+ 1325 |AERO Server C | | AERO Relay D | |AERO Server E | 1326 | (default->D) | | (A->C; G->E) | | (default->D) | 1327 | (A->B) | +-------+------+ | (G->F) | 1328 +-------+------+ | +------+-------+ 1329 | | | 1330 X---+---+-------------------+------------------+---+---X 1331 | AERO Link | 1332 +-----+--------+ +--------+-----+ 1333 |AERO Client B | |AERO Client F | 1334 | (default->C) | | (default->E) | 1335 +--------------+ +--------------+ 1336 .-. .-. 1337 ,-( _)-. ,-( _)-. 1338 .-(_ IPv6 )-. .-(_ IPv6 )-. 1339 (__ EUN ) (__ EUN ) 1340 `-(______)-' `-(______)-' 1341 | | 1342 +--------+ +--------+ 1343 | Host A | | Host G | 1344 +--------+ +--------+ 1346 Figure 5: AERO Server/Relay Interworking 1348 In this example, AERO Client ('B') associates with AERO Server ('C'), 1349 while AERO Client ('F') associates with AERO Server ('E'). 1350 Furthermore, AERO Servers ('C') and ('E') do not associate with each 1351 other directly, but rather have an association with AERO Relay ('D') 1352 (i.e., a router that has full topology information concerning its 1353 associated Servers and their Clients). Relay ('D') connects to the 1354 AERO link, and also connects to the native IPv6 Internetwork. 1356 When host ('A') sends a packet toward destination host ('G'), IPv6 1357 forwarding directs the packet through the EUN to Client ('B'), which 1358 forwards the packet to Server ('C') in absence of more-specific 1359 forwarding information. Server ('C') forwards the packet, and it 1360 also generates an AERO Predirect message that is then forwarded 1361 through Relay ('D') to Server ('E'). When Server ('E') receives the 1362 message, it forwards the message to Client ('F'). 1364 After processing the AERO Predirect message, Client ('F') sends an 1365 AERO Redirect message to Server ('E'). Server ('E'), in turn, 1366 forwards the message through Relay ('D') to Server ('C'). When 1367 Server ('C') receives the message, it forwards the message to Client 1368 ('B') informing it that host 'G's EUN can be reached via Client 1369 ('F'), thus completing the AERO redirection. 1371 The network layer routing information shared between Servers and 1372 Relays must be carefully coordinated in a manner outside the scope of 1373 this document. In particular, Relays require full topology 1374 information, while individual Servers only require partial topology 1375 information (i.e., they only need to know the EUN prefixes associated 1376 with their current set of Clients). See [IRON] for an architectural 1377 discussion of routing coordination between Relays and Servers. 1379 Author's Address 1381 Fred L. Templin (editor) 1382 Boeing Research & Technology 1383 P.O. Box 3707 1384 Seattle, WA 98124 1385 USA 1387 Email: fltemplin@acm.org