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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 17, 2014 5 Intended status: Standards Track 6 Expires: September 18, 2014 8 Transmission of IPv6 Packets over AERO Links 9 draft-templin-aerolink-07.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 18, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 5 60 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 5 61 3.2. AERO Interface Characteristics . . . . . . . . . . . . . . 6 62 3.3. AERO Interface MTU Considerations . . . . . . . . . . . . 8 63 3.4. AERO Interface Encapsulation, Re-encapsulation and 64 Decapsulation . . . . . . . . . . . . . . . . . . . . . . 9 65 3.5. AERO Addresses . . . . . . . . . . . . . . . . . . . . . . 10 66 3.6. AERO Reference Operational Scenario . . . . . . . . . . . 11 67 3.7. AERO Router Discovery and Prefix Delegation . . . . . . . 13 68 3.7.1. AERO Client Behavior . . . . . . . . . . . . . . . . . 13 69 3.7.2. AERO Server Behavior . . . . . . . . . . . . . . . . . 13 70 3.8. AERO Neighbor Solicitation and Advertisement . . . . . . . 14 71 3.9. AERO Redirection . . . . . . . . . . . . . . . . . . . . . 15 72 3.9.1. Classical Redirection Approaches . . . . . . . . . . . 15 73 3.9.2. AERO Redirection Concept of Operations . . . . . . . . 16 74 3.9.3. AERO Redirection Message Format . . . . . . . . . . . 17 75 3.9.4. Sending Predirects . . . . . . . . . . . . . . . . . . 18 76 3.9.5. Processing Predirects and Sending Redirects . . . . . 19 77 3.9.6. Re-encapsulating and Relaying Redirects . . . . . . . 20 78 3.9.7. Processing Redirects . . . . . . . . . . . . . . . . . 20 79 3.10. Neighbor Reachability Considerations . . . . . . . . . . . 21 80 3.11. Mobility and Link-Layer Address Change Considerations . . 21 81 3.12. Underlying Protocol Version Considerations . . . . . . . . 22 82 3.13. Multicast Considerations . . . . . . . . . . . . . . . . . 22 83 3.14. Operation on Server-less AERO Links . . . . . . . . . . . 22 84 3.15. Other Considerations . . . . . . . . . . . . . . . . . . . 23 85 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 23 86 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 87 6. Security Considerations . . . . . . . . . . . . . . . . . . . 23 88 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24 89 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 90 8.1. Normative References . . . . . . . . . . . . . . . . . . . 24 91 8.2. Informative References . . . . . . . . . . . . . . . . . . 25 92 Appendix A. AERO Server and Relay Interworking . . . . . . . . . 26 93 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 28 95 1. Introduction 97 This document specifies the operation of IPv6 over tunnel virtual 98 Non-Broadcast, Multiple Access (NBMA) links using Asymmetric Extended 99 Route Optimization (AERO). Nodes attached to AERO links can exchange 100 packets via trusted intermediate routers on the link that provide 101 forwarding services to reach off-link destinations and/or redirection 102 services to inform the node of an on-link neighbor that is closer to 103 the final destination. 105 Nodes on AERO links use an IPv6 link-local address format known as 106 the AERO Address. This address type has properties that statelessly 107 link IPv6 Neighbor Discovery (ND) to IPv6 routing. The AERO link can 108 be used for tunneling to neighboring nodes on either IPv6 or IPv4 109 networks, i.e., AERO views the IPv6 and IPv4 networks as equivalent 110 links for tunneling. The remainder of this document presents the 111 AERO specification. 113 2. Terminology 115 The terminology in the normative references applies; the following 116 terms are defined within the scope of this document: 118 AERO link 119 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 120 configured over a node's attached IPv6 and/or IPv4 networks. All 121 nodes on the AERO link appear as single-hop neighbors from the 122 perspective of IPv6. Note that the AERO link Maximum Transmission 123 Unit (MTU) is 64KB minus the encapsulation overhead for IPv4 and 124 4GB minus the encapsulation overhead for IPv6. 126 AERO interface 127 a node's attachment to an AERO link. The AERO interface MTU is 128 less than or equal to the AERO link MTU. 130 AERO address 131 an IPv6 link-local address assigned to an AERO interface and 132 constructed as specified in Section 3.5. 134 AERO node 135 a node that is connected to an AERO link and that participates in 136 IPv6 Neighbor Discovery over the link. 138 AERO Client ("client") 139 a node that configures either a host interface or a router 140 interface on an AERO link. 142 AERO Server ("server") 143 a node that configures a router interface on an AERO link over 144 which it can provide default forwarding and redirection services 145 for other AERO nodes. 147 AERO Relay ("relay") 148 a node that relays IPv6 packets between Servers on the same AERO 149 link, and/or that forwards IPv6 packets between the AERO link and 150 the IPv6 Internet. An AERO Relay may or may not also be 151 configured as an AERO Server. 153 ingress tunnel endpoint (ITE) 154 an AERO interface endpoint that injects tunneled packets into an 155 AERO link. 157 egress tunnel endpoint (ETE) 158 an AERO interface endpoint that receives tunneled packets from an 159 AERO link. 161 underlying network 162 a connected IPv6 or IPv4 network routing region over which AERO 163 nodes tunnel IPv6 packets. 165 underlying interface 166 an AERO node's interface point of attachment to an underlying 167 network. 169 underlying address 170 an IPv6 or IPv4 address assigned to an AERO node's underlying 171 interface. When UDP encapsulation is used, the UDP port number is 172 also considered as part of the underlying address. Underlying 173 addresses are used as the source and destination addresses of the 174 AERO encapsulation header. 176 link-layer address 177 the same as defined for "underlying address" above. 179 network layer address 180 an IPv6 address used as the source or destination address of the 181 inner IPv6 packet header. 183 end user network (EUN) 184 an IPv6 network attached to a downstream interface of an AERO 185 Client (where the AERO interface is seen as the upstream 186 interface). 188 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 189 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 190 document are to be interpreted as described in [RFC2119]. 192 3. Asymmetric Extended Route Optimization (AERO) 194 The following sections specify the operation of IPv6 over Asymmetric 195 Extended Route Optimization (AERO) links: 197 3.1. AERO Node Types 199 AERO Relays relay packets between nodes connected to the same AERO 200 link and also forward packets between the AERO link and the native 201 IPv6 network. The relaying process entails re-encapsulation of IPv6 202 packets that were received from a first AERO node and are to be 203 forwarded without modification to a second AERO node. 205 AERO Servers configure their AERO interfaces as router interfaces, 206 and provide default routing services to AERO Clients. AERO Servers 207 configure a DHCPv6 Relay or Server function and facilitate DHCPv6 208 Prefix Delegation (PD) exchanges. An AERO Server may also act as an 209 AERO Relay. 211 AERO Clients act as requesting routers to receive IPv6 prefixes 212 through a DHCPv6 PD exchange via an AERO Server over the AERO link. 213 Each AERO Client receives at least a /64 prefix delegation, and may 214 receive even shorter prefixes. 216 AERO Clients that act as routers configure their AERO interfaces as 217 router interfaces, i.e., even if the AERO Client otherwise displays 218 the outward characteristics of an ordinary host (for example, the 219 Client may internally configure both an AERO interface and (internal 220 virtual) End User Network (EUN) interfaces). AERO Clients that act 221 as routers sub-delegate portions of their received prefix delegations 222 to links on EUNs. 224 AERO Clients that act as ordinary hosts configure their AERO 225 interfaces as host interfaces and assign one or more IPv6 addresses 226 taken from their received prefix delegations to the AERO interface 227 but DO NOT assign the delegated prefix itself to the AERO interface. 228 Instead, the host assigns the delegated prefix to a "black hole" 229 route so that unused portions of the prefix are nullified. 231 End system applications on AERO hosts bind directly to the AERO 232 interface, while applications on AERO routers (or IPv6 hosts served 233 by an AERO router) bind to EUN interfaces. 235 3.2. AERO Interface Characteristics 237 AERO interfaces use IPv6-in-IPv6 encapsulation [RFC2473] to exchange 238 tunneled packets with AERO neighbors attached to an underlying IPv6 239 network, and use IPv6-in-IPv4 encapsulation [RFC4213] to exchange 240 tunneled packets with AERO neighbors attached to an underlying IPv4 241 network. AERO interfaces can also use IPsec encapsulation [RFC4301] 242 (either IPv6-in-IPsec-in-IPv6 or IPv6-in-IPsec-in-IPv4) in 243 environments where strong authentication and confidentiality are 244 required. When NAT traversal and/or filtering middlebox traversal is 245 necessary, a UDP header is further inserted between the outer IP 246 encapsulation header and the inner packet. 248 AERO interfaces maintain a neighbor cache and use a variation of 249 standard unicast IPv6 ND messaging. AERO interfaces use Neighbor 250 Solicitation (NS), Neighbor Advertisement (NA) and Redirect messages 251 the same as for any IPv6 link. They do not use Router Solicitation 252 (RS) and Router Advertisement (RA) messages for several reasons. 253 First, default router discovery is supported through other means more 254 appropriate for AERO links as described below. Second, discovery of 255 more-specific routes is through the receipt of NS, NA and Redirect 256 messages. Finally, AERO nodes are pre-provisioned with IPv6 prefixes 257 that they register using DHCPv6 PD; hence, there is no need for RA- 258 based prefix discovery. 260 AERO Neighbor Solicitation (NS) and Neighbor Advertisement (NA) 261 messages do not include Source/Target Link Layer Address Options 262 (S/TLLAO). Instead, AERO nodes determine the link-layer addresses of 263 neighbors by examining the encapsulation source address of any NS/NA 264 messages they receive and ignore any S/TLLAOs included in these 265 messages. This is vital to the operation of AERO links for which 266 neighbors are separated by Network Address Translators (NATs) - 267 either IPv4 or IPv6. 269 AERO Redirect messages include a TLLAO the same as for any IPv6 link. 270 The TLLAO includes the link-layer address of the target node, 271 including both the IP address and the UDP source port number used by 272 the target when it sends UDP-encapsulated packets over the AERO 273 interface (the TLLAO instead encodes the value 0 when the target does 274 not use UDP encapsulation). TLLAOs for target nodes that use an IPv6 275 underlying address include the full 16 bytes of the IPv6 address as 276 shown in Figure 1, while TLLAOs for target nodes that use an IPv4 277 underlying address include only the 4 bytes of the IPv4 address as 278 shown in Figure 2. 280 0 1 2 3 281 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 1 282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 283 | Type = 2 | Length = 3 | UDP Source Port (or 0) | 284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 285 | Reserved | 286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 | | 288 +-- --+ 289 | | 290 +-- IPv6 Address --+ 291 | | 292 +-- --+ 293 | | 294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 Figure 1: AERO TLLAO Format for IPv6 298 0 1 2 3 299 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 1 300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 | Type = 2 | Length = 1 | UDP Source Port (or 0) | 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | IPv4 Address | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 Figure 2: AERO TLLAO Format for IPv4 308 Finally, nodes on AERO interfaces use a simple data origin 309 authentication for encapsulated packets they receive from other 310 nodes. In particular, AERO Clients accept encapsulated packets with 311 a link-layer source address belonging to their current AERO Server. 312 AERO nodes also accept encapsulated packets with a link-layer source 313 address that is correct for the network-layer source address. The 314 AERO node considers the link-layer source address correct for the 315 network-layer source address if there is an IPv6 route that matches 316 the network-layer source address as well as a neighbor cache entry 317 corresponding to the next hop that includes the link-layer address. 318 (An exception is that NS, NA and Redirect messages may include a 319 different link-layer address than the one currently in the neighbor 320 cache, and the new link-layer address updates the neighbor cache 321 entry.) 323 3.3. AERO Interface MTU Considerations 325 The base tunneling specifications for IPv4 and IPv6 typically set a 326 static MTU on the tunnel interface to 1500 bytes minus the 327 encapsulation overhead or smaller still if the tunnel is likely to 328 incur additional encapsulations such as IPsec on the path. This can 329 result in path MTU related black holes when packets that are too 330 large to be accommodated over the AERO link are dropped, but the 331 resulting ICMP Packet Too Big (PTB) messages are lost on the return 332 path. As a result, AERO nodes use the following MTU mitigations to 333 accommodate larger packets. 335 AERO nodes set their AERO interface MTU to the larger of 1500 bytes 336 and the underlying interface MTU minus the encapsulation overhead. 337 AERO nodes optionally cache other per-neighbor MTU values in the 338 underlying IP path MTU discovery cache initialized to the underlying 339 interface MTU. 341 AERO nodes admit packets that are no larger than 1280 bytes minus the 342 encapsulation overhead (*) as well as packets that are larger than 343 1500 bytes into the tunnel without fragmentation, i.e., as long as 344 they are no larger than the AERO interface MTU before encapsulation 345 and also no larger than the cached per-neighbor MTU following 346 encapsulation. For IPv4, the node sets the "Don't Fragment" (DF) bit 347 to 0 for packets no larger than 1280 bytes minus the encapsulation 348 overhead (*) and sets the DF bit to 1 for packets larger than 1500 349 bytes. If a large packet is lost in the path, the node may 350 optionally cache the MTU reported in the resulting PTB message or may 351 ignore the message, e.g., if there is a possibility that the message 352 is spurious. 354 For packets destined to an AERO node that are larger than 1280 bytes 355 minus the encapsulation overhead (*) but no larger than 1500 bytes, 356 the node uses outer IP fragmentation to fragment the packet into two 357 pieces (where the first fragment contains 1024 bytes of the 358 fragmented inner packet) then admits the fragments into the tunnel. 359 If the outer protocol is IPv4, the node admits the packet into the 360 tunnel with DF set to 0 and subject to rate limiting to avoid 361 reassembly errors [RFC4963][RFC6864]. For both IPv4 and IPv6, the 362 node also sends a 1500 byte probe message (**) to the neighbor, 363 subject to rate limiting. To construct a probe, the node prepares an 364 ICMPv6 Neighbor Solicitation (NS) message with trailing padding 365 octets added to a length of 1500 bytes but does not include the 366 length of the padding in the IPv6 Payload Length field. The node 367 then encapsulates the NS in the outer encapsulation headers (while 368 including the length of the padding in the outer length fields), sets 369 DF to 1 (for IPv4) and sends the padded NS message to the neighbor. 370 If the neighbor returns an NA message, the node may then send whole 371 packets within this size range and (for IPv4) relax the rate limiting 372 requirement. 374 AERO nodes MUST be capable of reassembling packets up to 1500 bytes 375 plus the encapsulation overhead length. It is therefore RECOMMENDED 376 that AERO nodes be capable of reassembling at least 2KB. 378 (*) Note that if it is known that the minimum Path MTU to an AERO 379 node is MINMTU bytes (where 1280 < MINMTU < 1500) then MINMTU can be 380 used instead of 1280 in the fragmentation threshold considerations 381 listed above. 383 (**) It is RECOMMENDED that no probes smaller than 1500 bytes be used 384 for MTU probing purposes, since smaller probes may be fragmented if 385 there is a nested tunnel somewhere on the path to the neighbor. 387 3.4. AERO Interface Encapsulation, Re-encapsulation and Decapsulation 389 AERO interfaces encapsulate IPv6 packets according to whether they 390 are entering the AERO interface for the first time or if they are 391 being forwarded out the same AERO interface that they arrived on. 392 This latter form of encapsulation is known as "re-encapsulation". 394 AERO interfaces encapsulate packets per the specifications in , 395 [RFC2473], [RFC4213] except that the interface copies the "TTL/Hop 396 Limit", "Type of Service/Traffic Class" and "Congestion Experienced" 397 values in the inner network layer header into the corresponding 398 fields in the outer IP header. For packets undergoing re- 399 encapsulation, the AERO interface instead copies the "TTL/Hop Limit", 400 "Type of Service/Traffic Class" and "Congestion Experienced" values 401 in the original outer IP header into the corresponding fields in the 402 new outer IP header (i.e., the values are transferred between outer 403 headers and *not* copied from the inner network layer header). 405 When UDP encapsulation is used, the AERO interface inserts a UDP 406 header between the inner packet and outer IP header. If the outer 407 header is IPv6 and is followed by an IPv6 Fragment header, the AERO 408 interface inserts the UDP header between the outer IPv6 header and 409 IPv6 Fragment header. The AERO interface sets the UDP source port to 410 a constant value that it will use in each successive packet it sends, 411 sets the UDP destination port to 8060 (i.e., the IANA-registered port 412 number for AERO), sets the UDP checksum field to zero (see: 413 [RFC6935][RFC6936]) and sets the UDP length field to the length of 414 the inner packet plus 8 bytes for the UDP header itself. 416 The AERO interface next sets the outer IP protocol number to the 417 appropriate value for the first protocol layer within the 418 encapsulation (e.g., IPv6, IPv6 Fragment Header, UDP, etc.). When 419 IPv6 is used as the outer IP protocol, the ITE then sets the flow 420 label value in the outer IPv6 header the same as described in 421 [RFC6438]. When IPv4 is used as the outer IP protocol, the AERO 422 interface sets the DF bit as discussed in Section 3.2. 424 AERO interfaces decapsulate packets destined either to the localhost 425 or to a destination reached via an interface other than the receiving 426 AERO interface per the specifications in , [RFC2473], [RFC4213]. 427 When the encapsulated packet includes a UDP header, the AERO 428 interfaces examines the first octet of data following the UDP header 429 to determine the inner header type. If the most significant four 430 bits of the first octet encode the value '0110', the inner header is 431 an IPv6 header. Otherwise, the interface considers the first octet 432 as an IP protocol type that encodes the value '44' for IPv6 fragment 433 header, the value '50' for Encapsulating Security Payload, the value 434 '51' for Authentication Header etc. (If the first octet encodes the 435 value '0', the interface instead discards the packet, since this is 436 the value reserved for experimentation under , [RFC6706]). During 437 the decapsulation, the AERO interface records the UDP source port in 438 the neighbor cache entry for this neighbor then discards the UDP 439 header. 441 3.5. AERO Addresses 443 An AERO address is an IPv6 link-local address assigned to an AERO 444 interface and with an IPv6 prefix embedded within the interface 445 identifier. The AERO address is formatted as: 447 fe80::[IPv6 prefix] 449 Each AERO Client configures an AERO address based on the delegated 450 prefix it has received from the AERO link prefix delegation 451 authority. The address begins with the prefix fe80::/64 and includes 452 in its interface identifier the base /64 prefix taken from the 453 Client's delegated IPv6 prefix. The base prefix is determined by 454 masking the delegated prefix with the prefix length. For example, if 455 an AERO Client has received the prefix delegation: 457 2001:db8:1000:2000::/56 459 it would construct its AERO address as: 461 fe80::2001:db8:1000:2000 463 An AERO Client may have multiple non-contiguous IPv6 prefix 464 delegations, in which case it would configure multiple AERO addresses 465 - one for each prefix. Note that, in order for the DHCPv6 PD 466 function to operate correctly, the AERO Client must already hold a 467 delegated IPv6 prefix so that it can construct an AERO address to use 468 as the source address in the DHCPv6 exchange. This means that the 469 DHCPv6 PD function is really just a registration of a pre-provisioned 470 prefix. 472 Each AERO Server configures the special AERO address fe80::1 to 473 support the operation of IPv6 Neighbor Discovery over the AERO link; 474 the address therefore has the properties of an IPv6 Anycast address. 475 While all Servers configure the same AERO address and therefore 476 cannot be distinguished from one another at the network layer, 477 Clients can still distinguish Servers at the link layer by examining 478 the Servers' link-layer addresses. 480 Nodes that are configured as pure AERO Relays (i.e., and that do not 481 also act as Servers) do not configure an IPv6 address of any kind on 482 their AERO interfaces. The Relay's AERO interface is therefore used 483 purely for transit and does not participate in IPv6 ND message 484 exchanges. 486 3.6. AERO Reference Operational Scenario 488 Figure 3 depicts the AERO reference operational scenario. The figure 489 shows an AERO Server('A'), two AERO Clients ('B', 'D') and three 490 ordinary IPv6 hosts ('C', 'E', 'F'): 492 .-(::::::::) 493 .-(::: IPv6 :::)-. +-------------+ 494 (:::: Internet ::::)--| Host F | 495 `-(::::::::::::)-' +-------------+ 496 `-(::::::)-' 2001:db8:3::1 497 | 498 +--------------+ 499 | AERO Server A| 500 | (C->B; E->D) | 501 +--------------+ 502 fe80::1 503 L2(A) 504 | 505 X-----+-----------+-----------+--------X 506 | AERO Link | 507 L2(B) L2(D) 508 fe80::2001:db8:0:0 fe80::2001:db8:1:0 .-. 509 +--------------+ +--------------+ ,-( _)-. 510 | AERO Client B| | AERO Client D| .-(_ IPv6 )-. 511 | (default->A) | | (default->A) |--(__ EUN ) 512 +--------------+ +--------------+ `-(______)-' 513 2001:DB8:0::/48 2001:DB8:1::/48 | 514 | 2001:db8:1::1 515 .-. +-------------+ 516 ,-( _)-. 2001:db8:0::1 | Host E | 517 .-(_ IPv6 )-. +-------------+ +-------------+ 518 (__ EUN )--| Host C | 519 `-(______)-' +-------------+ 521 Figure 3: AERO Reference Operational Scenario 523 In Figure 3, AERO Server ('A') connects to the AERO link and connects 524 to the IPv6 Internet, either directly or via an AERO Relay (not 525 shown). Server ('A') assigns the address fe80::1 to its AERO 526 interface with link-layer address L2(A). Server ('A') next arranges 527 to add L2(A) to a published list of valid Servers for the AERO link. 529 AERO Client ('B') assigns the address fe80::2001:db8:0:0 to its AERO 530 interface with link-layer address L2(B) and registers the IPv6 prefix 531 2001:db8:0::/48 in a DHCPv6 PD exchange via Server ('A'). Client 532 ('B') configures a default route via the AERO interface with next-hop 533 address fe80::1 and link-layer address L2(A), then sub-delegates the 534 prefix 2001:db8:0::/48 to its attached EUNs. IPv6 host ('C') 535 connects to the EUN, and configures the address 2001:db8:0::1. 537 AERO Client ('D') assigns the address fe80::2001:db8:1:0 to its AERO 538 interface with link-layer address L2(D) and registers the IPv6 prefix 539 2001:db8:1::/48 in a DHCPv6 PD exchange via Server ('A'). Client 540 ('D') configures a default route via the AERO interface with next-hop 541 address fe80::1 and link-layer address L2(A), then sub-delegates the 542 prefix 2001:db8:1::/48 to its attached EUNs. IPv6 host ('E') 543 connects to the EUN, and configures the address 2001:db8:1::1. 545 Finally, IPv6 host ('F') connects to an IPv6 network outside of the 546 AERO link domain. Host ('F') configures its IPv6 interface in a 547 manner specific to its attached IPv6 link, and assigns the address 548 2001:db8:3::1 to its IPv6 link interface. 550 3.7. AERO Router Discovery and Prefix Delegation 552 3.7.1. AERO Client Behavior 554 AERO Clients observe the IPv6 router requirements defined in 555 [RFC6434]. AERO Clients first discover the link-layer address of an 556 AERO Server via static configuration, or through an automated means 557 such as DNS name resolution. In the absence of other information, 558 the Client resolves the Fully-Qualified Domain Name (FQDN) 559 "linkupnetworks.domainname", where "domainname" is the DNS domain 560 appropriate for the Client's attached underlying network. The Client 561 then creates a neighbor cache entry with the IPv6 link-local address 562 fe80::1 and the discovered address as the link-layer address. The 563 Client further creates a default route with the link-local address 564 fe80::1 as the next hop. 566 Next, the Client assigns the link-local AERO address(es) taken from 567 its delegated prefix(es) to the AERO interface (see: Section 3.5). 568 It then acts as a requesting router to register its IPv6 prefixes 569 through DHCPv6 PD [RFC3633] via the Server. After the Client 570 registers its prefixes, it sub-delegates them to nodes and links 571 within its attached EUNs. 573 After configuring a default route and registering its prefixes, the 574 Client sends periodic NS messages to the server to obtain new NAs in 575 order to keep neighbor cache entries alive. The Client can also 576 forward IPv6 packets destined to networks beyond its local EUNs via 577 the Server as an IPv6 default router. The Server may in turn return 578 a Redirect message informing the Client of a neighbor on the AERO 579 link that is topologically closer to the final destination as 580 specified in Section 3.9. 582 3.7.2. AERO Server Behavior 584 AERO Servers observe the IPv6 router requirements defined in 585 [RFC6434]. They further configure a DHCPv6 relay/server function on 586 their AERO links. When the Server delegates prefixes, it also 587 establishes forwarding table and neighbor cache entries that list the 588 AERO address of the Client as the next hop toward the delegated IPv6 589 prefixes (where the AERO address is constructed as specified in 590 Section 3.5). 592 Servers respond to NS messages from Clients on their AERO interfaces 593 by returning an NA message. When the Server receives an NS message, 594 it updates the neighbor cache entry using the network layer source 595 address as the neighbor's network layer address and using the link- 596 layer source address of the NS message as the neighbor's link-layer 597 address. 599 When the Server forwards a packet via the same AERO interface on 600 which it arrived, it initiates an AERO route optimization procedure 601 as specified in Section 3.9. 603 3.8. AERO Neighbor Solicitation and Advertisement 605 After an AERO node has received a prefix delegation, it creates an 606 AERO address as specified in Section 3.5. It can then send NS 607 messages to elicit NA messages from other AERO nodes. When the AERO 608 node sends NS/NA messages, however, it must also include the length 609 of the prefix corresponding to the AERO address. AERO NS/NA messages 610 therefore include an 8-bit "Prefix Length" field take from the low- 611 order 8 bits of the Reserved field as shown in Figure 4 and Figure 5. 613 0 1 2 3 614 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 1 615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 616 | Type (=135) | Code | Checksum | 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | Reserved | Prefix Length | 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 | | 621 + + 622 | | 623 + Target Address + 624 | | 625 + + 626 | | 627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 | Options ... 629 +-+-+-+-+-+-+-+-+-+-+-+- 631 Figure 4: AERO Neighbor Solicitation (NS) Message Format 633 0 1 2 3 634 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 1 635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 636 | Type (=136) | Code | Checksum | 637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 638 | R|S|O| Reserved | Prefix Length | 639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 640 | | 641 + + 642 | | 643 + Target Address + 644 | | 645 + + 646 | | 647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 648 | Options ... 649 +-+-+-+-+-+-+-+-+-+-+-+- 651 Figure 5: AERO Neighbor Advertisement (NA) Message Format 653 When an AERO node sends an NS/NA message, it MUST use its AERO 654 address as the IPv6 source address and MUST include its AERO address 655 prefix length in the Prefix Length field. 657 When an AERO node receives an NS/NA message, it accepts the message 658 if the Prefix Length applied to the source address is correct for the 659 neighbor; otherwise, it ignores the message. 661 3.9. AERO Redirection 663 Section 3.6 describes the AERO reference operational scenario. We 664 now discuss the operation and protocol details of AERO Redirection 665 with respect to this reference scenario. 667 3.9.1. Classical Redirection Approaches 669 With reference to Figure 3, when the IPv6 source host ('C') sends a 670 packet to an IPv6 destination host ('E'), the packet is first 671 forwarded via the EUN to AERO Client ('B'). Client ('B') then 672 forwards the packet over its AERO interface to AERO Server ('A'), 673 which then re-encapsulates and forwards the packet to AERO Client 674 ('D'), where the packet is finally forwarded to the IPv6 destination 675 host ('E'). When Server ('A') re-encapsulates and forwards the 676 packet back out on its advertising AERO interface, it must arrange to 677 redirect Client ('B') toward Client ('D') as a better next-hop node 678 on the AERO link that is closer to the final destination. However, 679 this redirection process applied to AERO interfaces must be more 680 carefully orchestrated than on ordinary links since the parties may 681 be separated by potentially many underlying network routing hops. 683 Consider a first alternative in which Server ('A') informs Client 684 ('B') only and does not inform Client ('D') (i.e., "classical 685 redirection"). In that case, Client ('D') has no way of knowing that 686 Client ('B') is authorized to forward packets from their claimed 687 network-layer source addresses, and it may simply elect to drop the 688 packets. Also, Client ('B') has no way of knowing whether Client 689 ('D') is performing some form of source address filtering that would 690 reject packets arriving from a node other than a trusted default 691 router, nor whether Client ('D') is even reachable via a direct path 692 that does not involve Server ('A'). 694 Consider a second alternative in which Server ('A') informs both 695 Client ('B') and Client ('D') separately, via independent redirection 696 control messages (i.e., "augmented redirection"). In that case, if 697 Client ('B') receives the redirection control message but Client 698 ('D') does not, subsequent packets sent by Client ('B') could be 699 dropped due to filtering since Client ('D') would not have a route to 700 verify their source network-layer addresses. Also, if Client ('D') 701 receives the redirection control message but Client ('B') does not, 702 subsequent packets sent in the reverse direction by Client ('D') 703 would be lost. 705 Since both of these alternatives have shortcomings, a new redirection 706 technique (i.e., "AERO redirection") is needed. 708 3.9.2. AERO Redirection Concept of Operations 710 Again, with reference to Figure 3, when source host ('C') sends a 711 packet to destination host ('E'), the packet is first forwarded over 712 the source host's attached EUN to Client ('B'), which then forwards 713 the packet via its AERO interface to Server ('A'). 715 Server ('A') then re-encapsulates forwards the packet out the same 716 AERO interface toward Client ('D') and also sends an AERO "Predirect" 717 message forward to Client ('D') as specified in Section 3.9.4. The 718 Predirect message includes Client ('B')'s network- and link-layer 719 addresses as well as information that Client ('D') can use to 720 determine the IPv6 prefix used by Client ('B') . After Client ('D') 721 receives the Predirect message, it process the message and returns an 722 AERO Redirect message destined for Client ("B") via Server ('A') as 723 specified in Section 3.9.5. During the process, Client ('D') also 724 creates or updates a neighbor cache entry for Client ('B'), and 725 creates an IPv6 route for Client ('B')'s IPv6 prefix. 727 When Server ('A') receives the Redirect message, it re-encapsulates 728 the message and forwards it on to Client ('B') as specified in 729 Section 3.9.6. The message includes Client ('D')'s network- and 730 link-layer addresses as well as information that Client ('B') can use 731 to determine the IPv6 prefix used by Client ('D'). After Client 732 ('B') receives the Redirect message, it processes the message as 733 specified in Section 3.9.7. During the process, Client ('B') also 734 creates or updates a neighbor cache entry for Client ('D'), and 735 creates an IPv6 route for Client ('D')'s IPv6 prefix. 737 Following the above Predirect/Redirect message exchange, forwarding 738 of packets from Client ('B') to Client ('D') without involving Server 739 ('A) as an intermediary is enabled. The mechanisms that support this 740 exchange are specified in the following sections. 742 3.9.3. AERO Redirection Message Format 744 AERO Redirect/Predirect messages use the same format as for ICMPv6 745 Redirect messages depicted in Section 4.5 of [RFC4861], but also 746 include a new "Prefix Length" field taken from the low-order 8 bits 747 of the Redirect message Reserved field. The Redirect/Predirect 748 messages are formatted as shown in Figure 6: 749 0 1 2 3 750 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 1 751 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 752 | Type (=137) | Code (=0/1) | Checksum | 753 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 754 | Reserved | Prefix Length | 755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 756 | | 757 + + 758 | | 759 + Target Address + 760 | | 761 + + 762 | | 763 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 764 | | 765 + + 766 | | 767 + Destination Address + 768 | | 769 + + 770 | | 771 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 772 | Options ... 773 +-+-+-+-+-+-+-+-+-+-+-+- 775 Figure 6: AERO Redirect/Predirect Message Format 777 3.9.4. Sending Predirects 779 When an AERO Server forwards a packet out the same AERO interface 780 that it arrived on, the Server sends a Predirect message forward 781 toward the AERO Client nearest the destination instead of sending a 782 Redirect message back to AERO Client nearest the source. 784 In the reference operational scenario, when Server ('A') forwards a 785 packet sent by Client ('B') toward Client ('D'), it also sends a 786 Predirect message forward toward Client ('D'), subject to rate 787 limiting (see Section 8.2 of [RFC4861]). Server ('A') prepares the 788 Predirect message as follows: 790 o the link-layer source address is set to 'L2(A)' (i.e., the 791 underlying address of Server ('A')). 793 o the link-layer destination address is set to 'L2(D)' (i.e., the 794 underlying address of Client ('D')). 796 o the network-layer source address is set to fe80::1 (i.e., the AERO 797 address of Server ('A')). 799 o the network-layer destination address is set to fe80::2001:db8:1:0 800 (i.e., the AERO address of Client ('D')). 802 o the Type is set to 137. 804 o the Code is set to 1 to indicate "Predirect". 806 o the Prefix Length is set to the length of the prefix to be applied 807 to Target address. 809 o the Target Address is set to fe80::2001:db8:0::0 (i.e., the AERO 810 address of Client ('B')). 812 o the Destination Address is set to the IPv6 source address of the 813 packet that triggered the Predirection event. 815 o the message includes a TLLAO set to 'L2(B)' (i.e., the underlying 816 address of Client ('B')). 818 o the message includes a Redirected Header Option (RHO) that 819 contains the originating packet truncated to ensure that at least 820 the network-layer header is included but the size of the message 821 does not exceed 1280 bytes. 823 Server ('A') then sends the message forward to Client ('D'). 825 3.9.5. Processing Predirects and Sending Redirects 827 When Client ('D') receives a Predirect message, it accepts the 828 message only if it has a link-layer source address of the Server, 829 i.e. 'L2(A)'. Client ('D') further accepts the message only if it 830 is willing to serve as a redirection target. Next, Client ('D') 831 validates the message according to the ICMPv6 Redirect message 832 validation rules in Section 8.1 of [RFC4861]. 834 In the reference operational scenario, when the Client ('D') receives 835 a valid Predirect message, it either creates or updates a neighbor 836 cache entry that stores the Target Address of the message as the 837 network-layer address of Client ('B') and stores the link-layer 838 address found in the TLLAO as the link-layer address of Client ('B'). 839 Client ('D') then applies the Prefix Length to the Interface 840 Identifier portion of the Target Address and records the resulting 841 IPv6 prefix in its IPv6 forwarding table. 843 After processing the message, Client ('D') prepares a Redirect 844 message response as follows: 846 o the link-layer source address is set to 'L2(D)' (i.e., the link- 847 layer address of Client ('D')). 849 o the link-layer destination address is set to 'L2(A)' (i.e., the 850 link-layer address of Server ('A')). 852 o the network-layer source address is set to 'L3(D)' (i.e., the AERO 853 address of Client ('D')). 855 o the network-layer destination address is set to 'L3(B)' (i.e., the 856 AERO address of Client ('B')). 858 o the Type is set to 137. 860 o the Code is set to 0 to indicate "Redirect". 862 o the Prefix Length is set to the length of the prefix to be applied 863 to the Target and Destination address. 865 o the Target Address is set to fe80::2001:db8:1::1 (i.e., the AERO 866 address of Client ('D')). 868 o the Destination Address is set to the IPv6 destination address of 869 the packet that triggered the Redirection event. 871 o the message includes a TLLAO set to 'L2(D)' (i.e., the underlying 872 address of Client ('D')). 874 o the message includes as much of the RHO copied from the 875 corresponding AERO Predirect message as possible such that at 876 least the network-layer header is included but the size of the 877 message does not exceed 1280 bytes. 879 After Client ('D') prepares the Redirect message, it sends the 880 message to Server ('A'). 882 3.9.6. Re-encapsulating and Relaying Redirects 884 When Server ('A') receives a Redirect message, it accepts the message 885 only if it has a neighbor cache entry that associates the message's 886 link-layer source address with the network-layer source address. 887 Next, Server ('A') validates the message according to the ICMPv6 888 Redirect message validation rules in Section 8.1 of [RFC4861]. 889 Following validation, Server ('A') re-encapsulates the Redirect then 890 relays the re-encapsulated Redirect on to Client ('B') as follows. 892 In the reference operational scenario, Server ('A') receives the 893 Redirect message from Client ('D') and prepares to re-encapsulate and 894 forward the message to Client ('B'). Server ('A') first verifies 895 that Client ('D') is authorized to use the Prefix Length in the 896 Redirect message when applied to the AERO address in the network- 897 layer source of the Redirect message, and discards the message if 898 verification fails. Otherwise, Server ('A') re-encapsulates the 899 message by changing the link-layer source address of the message to 900 'L2(A)', changing the network-layer source address of the message to 901 fe80::1, and changing the link-layer destination address to 'L2(B)' . 902 Server ('A') finally relays the re-encapsulated message to the 903 ingress node ('B') without decrementing the network-layer IPv6 header 904 Hop Limit field. 906 While not shown in Figure 3, AERO Relays relay Redirect and Predirect 907 messages in exactly this same fashion described above. See Figure 7 908 in Appendix A for an extension of the reference operational scenario 909 that includes Relays. 911 3.9.7. Processing Redirects 913 When Client ('B') receives the Redirect message, it accepts the 914 message only if it has a link-layer source address of the Server, 915 i.e. 'L2(A)'. Next, Client ('B') validates the message according to 916 the ICMPv6 Redirect message validation rules in Section 8.1 of 917 [RFC4861]. Following validation, Client ('B') then processes the 918 message as follows. 920 In the reference operational scenario, when Client ('B') receives the 921 Redirect message, it either creates or updates a neighbor cache entry 922 that stores the Target Address of the message as the network-layer 923 address of Client ('D') and stores the link-layer address found in 924 the TLLAO as the link-layer address of Client ('D'). Client ('B') 925 then applies the Prefix Length to the Interface Identifier portion of 926 the Target Address and records the resulting IPv6 prefix in its IPv6 927 forwarding table. 929 Now, Client ('B') has an IPv6 forwarding table entry for 930 Client('D')'s prefix, and Client ('D') has an IPv6 forwarding table 931 entry for Client ('B')'s prefix. Thereafter, the clients may 932 exchange ordinary network-layer data packets directly without 933 forwarding through Server ('A'). 935 3.10. Neighbor Reachability Considerations 937 When a source Client discovers a target neighbor (either through 938 redirection or some other means) it MUST test the direct path to the 939 target, e.g., by sending an initial NS message to elicit a solicited 940 NA response. While testing the path, the Client SHOULD continue 941 sending packets via the Server until target reachability has been 942 confirmed. The Client MUST thereafter follow the Neighbor 943 Unreachability Detection (NUD) procedures in Section 7.3 of 944 [RFC4861], and can resume sending packets via the Server at any time 945 the direct path appears to be failing. 947 If the Client is unable to elicit a NUD response after MAX_RETRY 948 attempts, it SHOULD consider the direct path unusable for forwarding 949 purposes but still viable for ingress filtering purposes. 951 If reachability is confirmed, the Client SHOULD thereafter process 952 any link-layer errors as a hint that the direct path to the target 953 has either failed or has become intermittent. 955 On some AERO links, establishment and maintenance of a direct path 956 between neighbors requires coordination such as through the Internet 957 Key Exchange (IKEv2) protocol [RFC5996]. In those cases, link- 958 specific hints of forward progress can be used instead of NS/NA to 959 test neighbor reachability. 961 3.11. Mobility and Link-Layer Address Change Considerations 963 When a Client needs to change its link-layer address (e.g., due to a 964 mobility event, due to a change in underlying network interface, 965 etc.), it sends an immediate NS message forward to any of its 966 correspondents (including the Server and any other Clients) which 967 then discover the new link-layer address. The Client may instead 968 send an immediate NA message if there is strong assurance that the 969 correspondent would receive the message with no need for an 970 acknowledgement. 972 If two Clients change their link-layer addresses simultaneously, the 973 NS/NA messages may be lost. In that case, the Clients SHOULD delete 974 their respective neighbor cache entries and allow packets to again 975 flow through their Server(s), which MAY result in a new AERO 976 redirection exchange. 978 When a Client needs to change to a new Server, it performs a DHCPv6 979 "Release" message exchange with the delegating router via the old 980 Server then sends a DHCPv6 "Request" message to the delegating router 981 via the new Server. Note that this may result in a temporary service 982 outage during Server "handovers". 984 3.12. Underlying Protocol Version Considerations 986 A source Client may connect only to an IPvX underlying network, while 987 the target Client connects only to an IPvY underlying network. In 988 that case, the source Client has no means for reaching the target 989 directly (since they connect to underlying networks of different IP 990 protocol versions) and so must ignore any Redirects and continue to 991 send packets via the Server. 993 3.13. Multicast Considerations 995 When the underlying network does not support multicast, AERO nodes 996 map IPv6 link-scoped multicast addresses (including 997 "All_DHCP_Relay_Agents_and_Servers") to the underlying IP address of 998 the AERO Server. 1000 When the underlying network supports multicast, AERO nodes use the 1001 multicast address mapping specification found in [RFC2529] for IPv4 1002 underlying networks and use a direct multicast mapping for IPv6 1003 underlying networks. (In the latter case, "direct multicast mapping" 1004 means that if the IPv6 multicast destination address of the inner 1005 packet is "M", then the IPv6 multicast destination address of the 1006 encapsulating header is also "M".) 1008 3.14. Operation on Server-less AERO Links 1010 In some AERO link scenarios, there may be no Server on the link 1011 and/or no need for Clients to use a Server as an intermediary trust 1012 anchor. In that case, Clients can establish neighbor cache entries 1013 and IPv6 routes by performing direct Client-to-Client exchanges, and 1014 some other form of trust basis must be applied so that each Client 1015 can verify that the prospective neighbor is authorized to use its 1016 claimed prefix. 1018 When there is no Server on the link, Clients must arrange to receive 1019 prefix delegations and publish the delegations via a secure prefix 1020 discovery service through some means outside the scope of this 1021 document. 1023 3.15. Other Considerations 1025 IPv6 hosts serviced by an AERO Client can reach IPv4-only services 1026 via a NAT64 gateway [RFC6146] within the IPv6 network. 1028 AERO nodes can use the Default Address Selection Policy with DHCPv6 1029 option [RFC7078] the same as on any IPv6 link. 1031 All other (non-multicast) functions that operate over ordinary IPv6 1032 links operate in the same fashion over AERO links. 1034 4. Implementation Status 1036 An early implementation is available at: 1037 http://linkupnetworks.com/seal/sealv2-1.0.tgz. 1039 5. IANA Considerations 1041 This document uses the UDP Service Port Number 8060 reserved by IANA 1042 for AERO in [RFC6706]. Therefore, there are no new IANA actions 1043 required for this document. 1045 6. Security Considerations 1047 AERO link security considerations are the same as for standard IPv6 1048 Neighbor Discovery [RFC4861] except that AERO improves on some 1049 aspects. In particular, AERO is dependent on a trust basis between 1050 AERO Clients and Servers, where the Clients only engage in the AERO 1051 mechanism when it is facilitated by a trust anchor. 1053 AERO links must be protected against link-layer address spoofing 1054 attacks in which an attacker on the link pretends to be a trusted 1055 neighbor. Links that provide link-layer securing mechanisms (e.g., 1056 WiFi networks) and links that provide physical security (e.g., 1057 enterprise network LANs) provide a first line of defense that is 1058 often sufficient. In other instances, securing mechanisms such as 1059 Secure Neighbor Discovery (SeND) [RFC3971] or IPsec [RFC4301] may be 1060 necessary. 1062 AERO Clients MUST ensure that their connectivity is not used by 1063 unauthorized nodes to gain access to a protected network. (This 1064 concern is no different than for ordinary hosts that receive an IP 1065 address delegation but then "share" the address with unauthorized 1066 nodes via an IPv6/IPv6 NAT function.) 1068 7. Acknowledgements 1070 Discussions both on the v6ops list and in private exchanges helped 1071 shape some of the concepts in this work. Individuals who contributed 1072 insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant, 1073 Brian Carpenter, Brian Haberman, Joel Halpern, Sascha Hlusiak, Lee 1074 Howard and Joe Touch. Members of the IESG also provided valuable 1075 input during their review process that greatly improved the document. 1076 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 1077 for their shepherding guidance. 1079 This work has further been encouraged and supported by Boeing 1080 colleagues including Keith Bartley, Balaguruna Chidambaram, Jeff 1081 Holland, Cam Brodie, Yueli Yang, Wen Fang, Ed King, Mike Slane, Kent 1082 Shuey, Gen MacLean, and other members of the BR&T and BIT mobile 1083 networking teams. 1085 Earlier works on NBMA tunneling approaches are found in 1086 [RFC2529][RFC5214][RFC5569]. 1088 8. References 1090 8.1. Normative References 1092 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1093 August 1980. 1095 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1096 September 1981. 1098 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 1099 RFC 792, September 1981. 1101 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1102 Requirement Levels", BCP 14, RFC 2119, March 1997. 1104 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1105 (IPv6) Specification", RFC 2460, December 1998. 1107 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1108 IPv6 Specification", RFC 2473, December 1998. 1110 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 1111 Host Configuration Protocol (DHCP) version 6", RFC 3633, 1112 December 2003. 1114 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 1115 for IPv6 Hosts and Routers", RFC 4213, October 2005. 1117 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1118 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1119 September 2007. 1121 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1122 Address Autoconfiguration", RFC 4862, September 2007. 1124 [RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node 1125 Requirements", RFC 6434, December 2011. 1127 8.2. Informative References 1129 [IRON] Templin, F., "The Internet Routing Overlay Network 1130 (IRON)", Work in Progress, June 2012. 1132 [RFC0879] Postel, J., "TCP maximum segment size and related topics", 1133 RFC 879, November 1983. 1135 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 1136 Domains without Explicit Tunnels", RFC 2529, March 1999. 1138 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 1139 and M. Carney, "Dynamic Host Configuration Protocol for 1140 IPv6 (DHCPv6)", RFC 3315, July 2003. 1142 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 1143 Neighbor Discovery (SEND)", RFC 3971, March 2005. 1145 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1146 Internet Protocol", RFC 4301, December 2005. 1148 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 1149 Discovery", RFC 4821, March 2007. 1151 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 1152 Errors at High Data Rates", RFC 4963, July 2007. 1154 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1155 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1156 March 2008. 1158 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 1159 Infrastructures (6rd)", RFC 5569, January 2010. 1161 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 1162 "Internet Key Exchange Protocol Version 2 (IKEv2)", 1163 RFC 5996, September 2010. 1165 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 1166 NAT64: Network Address and Protocol Translation from IPv6 1167 Clients to IPv4 Servers", RFC 6146, April 2011. 1169 [RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O. 1170 Troan, "Basic Requirements for IPv6 Customer Edge 1171 Routers", RFC 6204, April 2011. 1173 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 1174 for Equal Cost Multipath Routing and Link Aggregation in 1175 Tunnels", RFC 6438, November 2011. 1177 [RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)", 1178 RFC 6691, July 2012. 1180 [RFC6706] Templin, F., "Asymmetric Extended Route Optimization 1181 (AERO)", RFC 6706, August 2012. 1183 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 1184 RFC 6864, February 2013. 1186 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 1187 UDP Checksums for Tunneled Packets", RFC 6935, April 2013. 1189 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 1190 for the Use of IPv6 UDP Datagrams with Zero Checksums", 1191 RFC 6936, April 2013. 1193 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 1194 with IPv6 Neighbor Discovery", RFC 6980, August 2013. 1196 [RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 1197 Address Selection Policy Using DHCPv6", RFC 7078, 1198 January 2014. 1200 Appendix A. AERO Server and Relay Interworking 1202 Figure 3 depicts a reference AERO operational scenario with a single 1203 Server on the AERO link. In order to support scaling to larger 1204 numbers of nodes, the AERO link can deploy multiple Servers and 1205 Relays, e.g., as shown in Figure 7. 1207 .-(::::::::) 1208 .-(::: IPv6 :::)-. 1209 (:: Internetwork ::) 1210 `-(::::::::::::)-' 1211 `-(::::::)-' 1212 | 1213 +--------------+ +------+-------+ +--------------+ 1214 |AERO Server C | | AERO Relay D | |AERO Server E | 1215 | (default->D) | | (A->C; G->E) | | (default->D) | 1216 | (A->B) | +-------+------+ | (G->F) | 1217 +-------+------+ | +------+-------+ 1218 | | | 1219 X---+---+-------------------+------------------+---+---X 1220 | AERO Link | 1221 +-----+--------+ +--------+-----+ 1222 |AERO Client B | |AERO Client F | 1223 | (default->C) | | (default->E) | 1224 +--------------+ +--------------+ 1225 .-. .-. 1226 ,-( _)-. ,-( _)-. 1227 .-(_ IPv6 )-. .-(_ IPv6 )-. 1228 (__ EUN ) (__ EUN ) 1229 `-(______)-' `-(______)-' 1230 | | 1231 +--------+ +--------+ 1232 | Host A | | Host G | 1233 +--------+ +--------+ 1235 Figure 7: AERO Server/Relay Interworking 1237 In this example, AERO Client ('B') associates with AERO Server ('C'), 1238 while AERO Client ('F') associates with AERO Server ('E'). 1239 Furthermore, AERO Servers ('C') and ('E') do not associate with each 1240 other directly, but rather have an association with AERO Relay ('D') 1241 (i.e., a router that has full topology information concerning its 1242 associated Servers and their Clients). Relay ('D') connects to the 1243 AERO link, and also connects to the native IPv6 Internetwork. 1245 When host ('A') sends a packet toward destination host ('G'), IPv6 1246 forwarding directs the packet through the EUN to Client ('B'), which 1247 forwards the packet to Server ('C') in absence of more-specific 1248 forwarding information. Server ('C') forwards the packet, and it 1249 also generates an AERO Predirect message that is then forwarded 1250 through Relay ('D') to Server ('E'). When Server ('E') receives the 1251 message, it forwards the message to Client ('F'). 1253 After processing the AERO Predirect message, Client ('F') sends an 1254 AERO Redirect message to Server ('E'). Server ('E'), in turn, 1255 forwards the message through Relay ('D') to Server ('C'). When 1256 Server ('C') receives the message, it forwards the message to Client 1257 ('B') informing it that host 'G's EUN can be reached via Client 1258 ('F'), thus completing the AERO redirection. 1260 The network layer routing information shared between Servers and 1261 Relays must be carefully coordinated in a manner outside the scope of 1262 this document. In particular, Relays require full topology 1263 information, while individual Servers only require partial topology 1264 information (i.e., they only need to know the EUN prefixes associated 1265 with their current set of Clients). See [IRON] for an architectural 1266 discussion of routing coordination between Relays and Servers. 1268 Author's Address 1270 Fred L. Templin (editor) 1271 Boeing Research & Technology 1272 P.O. Box 3707 1273 Seattle, WA 98124 1274 USA 1276 Email: fltemplin@acm.org