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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Henderson, Ed. 3 Internet-Draft University of Washington 4 Intended status: Standards Track C. Vogt 5 Expires: May 16, 2015 J. Arkko 6 Ericsson Research NomadicLab 7 November 12, 2014 9 Host Multihoming with the Host Identity Protocol 10 draft-ietf-hip-multihoming-04 12 Abstract 14 This document defines host multihoming extensions to the Host 15 Identity Protocol (HIP), by leveraging protocol components defined 16 for host mobility. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on May 16, 2015. 35 Copyright Notice 37 Copyright (c) 2014 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 This document may contain material from IETF Documents or IETF 51 Contributions published or made publicly available before November 52 10, 2008. The person(s) controlling the copyright in some of this 53 material may not have granted the IETF Trust the right to allow 54 modifications of such material outside the IETF Standards Process. 55 Without obtaining an adequate license from the person(s) controlling 56 the copyright in such materials, this document may not be modified 57 outside the IETF Standards Process, and derivative works of it may 58 not be created outside the IETF Standards Process, except to format 59 it for publication as an RFC or to translate it into languages other 60 than English. 62 Table of Contents 64 1. Introduction and Scope . . . . . . . . . . . . . . . . . . . 2 65 2. Terminology and Conventions . . . . . . . . . . . . . . . . . 4 66 3. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . 4 67 3.1. Operating Environment . . . . . . . . . . . . . . . . . . 5 68 3.2. Multihoming Overview . . . . . . . . . . . . . . . . . . 7 69 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7 70 4.1. Host Multihoming . . . . . . . . . . . . . . . . . . . . 8 71 4.2. Site Multihoming . . . . . . . . . . . . . . . . . . . . 9 72 4.3. Dual host multihoming . . . . . . . . . . . . . . . . . . 10 73 4.4. Combined Mobility and Multihoming . . . . . . . . . . . . 10 74 4.5. Initiating the Protocol in R1 or I2 . . . . . . . . . . . 11 75 5. Other Considerations . . . . . . . . . . . . . . . . . . . . 12 76 5.1. Address Verification . . . . . . . . . . . . . . . . . . 12 77 5.2. Preferred Locator . . . . . . . . . . . . . . . . . . . . 12 78 5.3. Interaction with Security Associations . . . . . . . . . 13 79 6. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 15 80 6.1. Sending LOCATORs . . . . . . . . . . . . . . . . . . . . 15 81 6.2. Handling Received LOCATORs . . . . . . . . . . . . . . . 17 82 6.3. Verifying Address Reachability . . . . . . . . . . . . . 19 83 6.4. Changing the Preferred Locator . . . . . . . . . . . . . 19 84 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 85 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 86 9. Authors and Acknowledgments . . . . . . . . . . . . . . . . . 20 87 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 88 10.1. Normative references . . . . . . . . . . . . . . . . . . 20 89 10.2. Informative references . . . . . . . . . . . . . . . . . 21 90 Appendix A. Document Revision History . . . . . . . . . . . . . 22 92 1. Introduction and Scope 94 The Host Identity Protocol [I-D.ietf-hip-rfc4423-bis] (HIP) supports 95 an architecture that decouples the transport layer (TCP, UDP, etc.) 96 from the internetworking layer (IPv4 and IPv6) by using public/ 97 private key pairs, instead of IP addresses, as host identities. When 98 a host uses HIP, the overlying protocol sublayers (e.g., transport 99 layer sockets and Encapsulating Security Payload (ESP) Security 100 Associations (SAs)) are instead bound to representations of these 101 host identities, and the IP addresses are only used for packet 102 forwarding. However, each host must also know at least one IP 103 address at which its peers are reachable. Initially, these IP 104 addresses are the ones used during the HIP base exchange 105 [I-D.ietf-hip-rfc5201-bis]. 107 One consequence of such a decoupling is that new solutions to 108 network-layer mobility and host multihoming are possible. Host 109 mobility is defined in [I-D.ietf-hip-rfc5206-bis] and covers the case 110 in which a host has a single address and changes its network point- 111 of-attachment while desiring to preserve the HIP-enabled security 112 association. Host multihoming is somewhat of a dual case to host 113 mobility, in that a host may simultaneously have more than one 114 network point-of-attachment. There are potentially many variations 115 of host multihoming possible. The scope of this document encompasses 116 messaging and elements of procedure for some basic host multihoming 117 scenarios of interest. 119 Another variation of multihoming that has been heavily studied site 120 multihoming. Solutions for site multihoming in IPv6 networks have 121 been specified by the IETF shim6 working group. The shim6 protocol 122 [RFC5533] bears many architectural similarities to HIP but there are 123 differences in the security model and in the protocol. Future 124 versions of this draft will summarize the differences more 125 completely. 127 While HIP can potentially be used with transports other than the ESP 128 transport format [I-D.ietf-hip-rfc5202-bis], this document largely 129 assumes the use of ESP and leaves other transport formats for further 130 study. 132 There are a number of situations where the simple end-to-end 133 readdressing functionality defined herein is not sufficient. These 134 include the initial reachability of a multihomed host, location 135 privacy, simultaneous mobility of both hosts, and some modes of NAT 136 traversal. In these situations, there is a need for some helper 137 functionality in the network, such as a HIP rendezvous server 138 [I-D.ietf-hip-rfc5204-bis]. Such functionality is out of the scope 139 of this document. Finally, making underlying IP multihoming 140 transparent to the transport layer has implications on the proper 141 response of transport congestion control, path MTU selection, and 142 Quality of Service (QoS). Transport-layer mobility triggers, and the 143 proper transport response to a HIP multihoming address change, are 144 outside the scope of this document. 146 2. Terminology and Conventions 148 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 149 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 150 document are to be interpreted as described in RFC 2119 [RFC2119]. 152 Terminology is copied from [I-D.ietf-hip-rfc5206-bis]. 154 LOCATOR. The name of a HIP parameter containing zero or more Locator 155 fields. This parameter's name is distinguished from the Locator 156 fields embedded within it by the use of all capital letters. 158 Locator. A name that controls how the packet is routed through the 159 network and demultiplexed by the end host. It may include a 160 concatenation of traditional network addresses such as an IPv6 161 address and end-to-end identifiers such as an ESP SPI. It may 162 also include transport port numbers or IPv6 Flow Labels as 163 demultiplexing context, or it may simply be a network address. 165 Address. A name that denotes a point-of-attachment to the network. 166 The two most common examples are an IPv4 address and an IPv6 167 address. The set of possible addresses is a subset of the set of 168 possible locators. 170 Preferred locator. A locator on which a host prefers to receive 171 data. With respect to a given peer, a host always has one active 172 Preferred locator, unless there are no active locators. By 173 default, the locators used in the HIP base exchange are the 174 Preferred locators. 176 Credit Based Authorization. A host must verify a mobile or 177 multihomed peer's reachability at a new locator. Credit-Based 178 Authorization authorizes the peer to receive a certain amount of 179 data at the new locator before the result of such verification is 180 known. 182 3. Protocol Model 184 This section is an overview; more detailed specification follows this 185 section. 187 The overall protocol model is the same as in Section 3 of 188 [I-D.ietf-hip-rfc5206-bis]; this section only highlights the 189 differences. 191 3.1. Operating Environment 193 The Host Identity Protocol (HIP) [I-D.ietf-hip-rfc5201-bis] is a key 194 establishment and parameter negotiation protocol. Its primary 195 applications are for authenticating host messages based on host 196 identities, and establishing security associations (SAs) for the ESP 197 transport format [I-D.ietf-hip-rfc5202-bis] and possibly other 198 protocols in the future. 200 +--------------------+ +--------------------+ 201 | | | | 202 | +------------+ | | +------------+ | 203 | | Key | | HIP | | Key | | 204 | | Management | <-+-----------------------+-> | Management | | 205 | | Process | | | | Process | | 206 | +------------+ | | +------------+ | 207 | ^ | | ^ | 208 | | | | | | 209 | v | | v | 210 | +------------+ | | +------------+ | 211 | | IPsec | | ESP | | IPsec | | 212 | | Stack | <-+-----------------------+-> | Stack | | 213 | | | | | | | | 214 | +------------+ | | +------------+ | 215 | | | | 216 | | | | 217 | Initiator | | Responder | 218 +--------------------+ +--------------------+ 220 Figure 1: HIP Deployment Model 222 The general deployment model for HIP is shown above, assuming 223 operation in an end-to-end fashion. This document specifies 224 extensions to the HIP protocol to enable end-host mobility and basic 225 multihoming. In summary, these extensions to the HIP base protocol 226 enable the signaling of new addressing information to the peer in HIP 227 messages. The messages are authenticated via a signature or keyed 228 hash message authentication code (HMAC) based on its Host Identity. 230 --------- 231 | TCP | (sockets bound to HITs) 232 --------- 233 | 234 --------- 235 ----> | ESP | {HIT_s, HIT_d} <-> SPI 236 | --------- 237 | | 238 ---- --------- 239 | MH |-> | HIP | {HIT_s, HIT_d, SPI} <-> {IP_s, IP_d, SPI} 240 ---- --------- 241 | 242 --------- 243 | IP | 244 --------- 246 Figure 2: Architecture for HIP Multihoming (MH) 248 Figure 2 depicts a layered architectural view of a HIP-enabled stack 249 using the ESP transport format. In HIP, upper-layer protocols 250 (including TCP and ESP in this figure) are bound to Host Identity 251 Tags (HITs) and not IP addresses. The HIP sublayer is responsible 252 for maintaining the binding between HITs and IP addresses. The SPI 253 is used to associate an incoming packet with the right HITs. The 254 block labeled "MH" is introduced below. 256 Consider the case when a host is multihomed (has more than one 257 globally routable address) and has multiple addresses available at 258 the HIP layer as alternative locators for fault tolerance. Examples 259 include the use of (possibly multiple) IPv4 and IPv6 addresses on the 260 same interface, or the use of multiple interfaces attached to 261 different service providers. Such host multihoming generally 262 necessitates that a separate ESP SA is maintained for each interface 263 in order to prevent packets that arrive over different paths from 264 falling outside of the ESP anti-replay window [RFC4303]. Multihoming 265 thus makes it possible that the bindings shown on the right side of 266 Figure 2 are one to many (in the outbound direction, one HIT pair to 267 multiple SPIs, and possibly then to multiple IP addresses). However, 268 only one SPI and address pair can be used for any given packet, so 269 the job of the "MH" block depicted above is to dynamically manipulate 270 these bindings. Beyond locally managing such multiple bindings, the 271 peer-to-peer HIP signaling protocol needs to be flexible enough to 272 define the desired mappings between HITs, SPIs, and addresses, and 273 needs to ensure that UPDATE messages are sent along the right network 274 paths so that any HIP-aware middleboxes can observe the SPIs. This 275 document does not specify the "MH" block, nor does it specify 276 detailed elements of procedure for how to handle various multihoming 277 (perhaps combined with mobility) scenarios. The "MH" block may apply 278 to more general problems outside of HIP. However, this document does 279 describe a basic multihoming case (one host adds one address to its 280 initial address and notifies the peer) and leave more complicated 281 scenarios for experimentation and future documents. 283 3.2. Multihoming Overview 285 In host multihoming, a host has multiple locators simultaneously 286 rather than sequentially, as in the case of mobility. By using the 287 LOCATOR parameter defined in [I-D.ietf-hip-rfc5206-bis], a host can 288 inform its peers of additional (multiple) locators at which it can be 289 reached, and can declare a particular locator as a "preferred" 290 locator. Although this document defines a basic mechanism for 291 multihoming, it does not define detailed policies and procedures, 292 such as which locators to choose when more than one pair is 293 available, the operation of simultaneous mobility and multihoming, 294 source address selection policies (beyond those specified in 295 [RFC3484]), and the implications of multihoming on transport 296 protocols and ESP anti-replay windows. 298 4. Protocol Overview 300 In this section, we briefly introduce a number of usage scenarios for 301 HIP multihoming. These scenarios assume that HIP is being used with 302 the ESP transform [I-D.ietf-hip-rfc5202-bis], although other 303 scenarios may be defined in the future. To understand these usage 304 scenarios, the reader should be at least minimally familiar with the 305 HIP protocol specification [I-D.ietf-hip-rfc5201-bis]. However, for 306 the (relatively) uninitiated reader, it is most important to keep in 307 mind that in HIP the actual payload traffic is protected with ESP, 308 and that the ESP SPI acts as an index to the right host-to-host 309 context. 311 The scenarios below assume that the two hosts have completed a single 312 HIP base exchange with each other. Both of the hosts therefore have 313 one incoming and one outgoing SA. Further, each SA uses the same 314 pair of IP addresses, which are the ones used in the base exchange. 316 The readdressing protocol is an asymmetric protocol where a mobile or 317 multihomed host informs a peer host about changes of IP addresses on 318 affected SPIs. The readdressing exchange is designed to be 319 piggybacked on existing HIP exchanges. The majority of the packets 320 on which the LOCATOR parameters are expected to be carried are UPDATE 321 packets. However, some implementations may want to experiment with 322 sending LOCATOR parameters also on other packets, such as R1, I2, and 323 NOTIFY. 325 The scenarios below at times describe addresses as being in either an 326 ACTIVE, VERIFIED, or DEPRECATED state. From the perspective of a 327 host, newly-learned addresses of the peer must be verified before put 328 into active service, and addresses removed by the peer are put into a 329 deprecated state. Under limited conditions described in 330 [I-D.ietf-hip-rfc5206-bis], an UNVERIFIED address may be used. 332 Hosts that use link-local addresses as source addresses in their HIP 333 handshakes may not be reachable by a mobile peer. Such hosts SHOULD 334 provide a globally routable address either in the initial handshake 335 or via the LOCATOR parameter. 337 4.1. Host Multihoming 339 A (mobile or stationary) host may sometimes have more than one 340 interface or global address. The host may notify the peer host of 341 the additional interface or address by using the LOCATOR parameter. 342 To avoid problems with the ESP anti-replay window, a host SHOULD use 343 a different SA for each interface or address used to receive packets 344 from the peer host when multiple locator pairs are being used 345 simultaneously rather than sequentially. 347 When more than one locator is provided to the peer host, the host 348 SHOULD indicate which locator is preferred (the locator on which the 349 host prefers to receive traffic). By default, the addresses used in 350 the base exchange are preferred until indicated otherwise. 352 In the multihoming case, the sender may also have multiple valid 353 locators from which to source traffic. In practice, a HIP 354 association in a multihoming configuration may have both a preferred 355 peer locator and a preferred local locator, although rules for source 356 address selection should ultimately govern the selection of the 357 source locator based on the destination locator. 359 Although the protocol may allow for configurations in which there is 360 an asymmetric number of SAs between the hosts (e.g., one host has two 361 interfaces and two inbound SAs, while the peer has one interface and 362 one inbound SA), it is RECOMMENDED that inbound and outbound SAs be 363 created pairwise between hosts. When an ESP_INFO arrives to rekey a 364 particular outbound SA, the corresponding inbound SA should be also 365 rekeyed at that time. Although asymmetric SA configurations might be 366 experimented with, their usage may constrain interoperability at this 367 time. However, it is recommended that implementations attempt to 368 support peers that prefer to use non-paired SAs. It is expected that 369 this section and behavior will be modified in future revisions of 370 this protocol, once the issue and its implications are better 371 understood. 373 Consider the case between two hosts, one single-homed and one 374 multihomed. The multihomed host may decide to inform the single- 375 homed host about its other address. It is RECOMMENDED that the 376 multihomed host set up a new SA pair for use on this new address. To 377 do this, the multihomed host sends a LOCATOR with an ESP_INFO, 378 indicating the request for a new SA by setting the OLD SPI value to 379 zero, and the NEW SPI value to the newly created incoming SPI. A 380 Locator Type of "1" is used to associate the new address with the new 381 SPI. The LOCATOR parameter also contains a second Type "1" locator, 382 that of the original address and SPI. To simplify parameter 383 processing and avoid explicit protocol extensions to remove locators, 384 each LOCATOR parameter MUST list all locators in use on a connection 385 (a complete listing of inbound locators and SPIs for the host). The 386 multihomed host waits for an ESP_INFO (new outbound SA) from the peer 387 and an ACK of its own UPDATE. As in the mobility case, the peer host 388 must perform an address verification before actively using the new 389 address. Figure 3 illustrates this scenario. 391 Multi-homed Host Peer Host 393 UPDATE(ESP_INFO, LOCATOR, SEQ, [DIFFIE_HELLMAN]) 394 -----------------------------------> 395 UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) 396 <----------------------------------- 397 UPDATE(ACK, ECHO_RESPONSE) 398 -----------------------------------> 400 Figure 3: Basic Multihoming Scenario 402 In multihoming scenarios, it is important that hosts receiving 403 UPDATEs associate them correctly with the destination address used in 404 the packet carrying the UPDATE. When processing inbound LOCATORs 405 that establish new security associations on an interface with 406 multiple addresses, a host uses the destination address of the UPDATE 407 containing the LOCATOR as the local address to which the LOCATOR plus 408 ESP_INFO is targeted. This is because hosts may send UPDATEs with 409 the same (locator) IP address to different peer addresses -- this has 410 the effect of creating multiple inbound SAs implicitly affiliated 411 with different peer source addresses. 413 4.2. Site Multihoming 415 A host may have an interface that has multiple globally routable IP 416 addresses. Such a situation may be a result of the site having 417 multiple upper Internet Service Providers, or just because the site 418 provides all hosts with both IPv4 and IPv6 addresses. The host 419 should stay reachable at all or any subset of the currently available 420 global routable addresses, independent of how they are provided. 422 This case is handled the same as if there were different IP 423 addresses, described above in Section 4.1. Note that a single 424 interface may experience site multihoming while the host itself may 425 have multiple interfaces. 427 Note that a host may be multihomed and mobile simultaneously, and 428 that a multihomed host may want to protect the location of some of 429 its interfaces while revealing the real IP address of some others. 431 This document does not presently specify additional site multihoming 432 extensions to HIP; further alignment with the IETF shim6 working 433 group may be considered in the future. 435 4.3. Dual host multihoming 437 Consider the case in which both hosts would like to add an additional 438 address after the base exchange completes. In Figure 4, consider 439 that host1, which used address addr1a in the base exchange to set up 440 SPI1a and SPI2a, wants to add address addr1b. It would send an 441 UPDATE with LOCATOR (containing the address addr1b) to host2, using 442 destination address addr2a, and a new set of SPIs would be added 443 between hosts 1 and 2 (call them SPI1b and SPI2b -- not shown in the 444 figure). Next, consider host2 deciding to add addr2b to the 445 relationship. Host2 must select one of host1's addresses towards 446 which to initiate an UPDATE. It may choose to initiate an UPDATE to 447 addr1a, addr1b, or both. If it chooses to send to both, then a full 448 mesh (four SA pairs) of SAs would exist between the two hosts. This 449 is the most general case; it often may be the case that hosts 450 primarily establish new SAs only with the peer's Preferred locator. 451 The readdressing protocol is flexible enough to accommodate this 452 choice. 454 -<- SPI1a -- -- SPI2a ->- 455 host1 < > addr1a <---> addr2a < > host2 456 ->- SPI2a -- -- SPI1a -<- 458 addr1b <---> addr2a (second SA pair) 459 addr1a <---> addr2b (third SA pair) 460 addr1b <---> addr2b (fourth SA pair) 462 Figure 4: Dual Multihoming Case in Which Each Host Uses LOCATOR to 463 Add a Second Address 465 4.4. Combined Mobility and Multihoming 467 It looks likely that in the future, many mobile hosts will be 468 simultaneously mobile and multihomed, i.e., have multiple mobile 469 interfaces. Furthermore, if the interfaces use different access 470 technologies, it is fairly likely that one of the interfaces may 471 appear stable (retain its current IP address) while some other(s) may 472 experience mobility (undergo IP address change). 474 The use of LOCATOR plus ESP_INFO should be flexible enough to handle 475 most such scenarios, although more complicated scenarios have not 476 been studied so far. 478 4.5. Initiating the Protocol in R1 or I2 480 A Responder host MAY include a LOCATOR parameter in the R1 packet 481 that it sends to the Initiator. This parameter MUST be protected by 482 the R1 signature. If the R1 packet contains LOCATOR parameters with 483 a new Preferred locator, the Initiator SHOULD directly set the new 484 Preferred locator to status ACTIVE without performing address 485 verification first, and MUST send the I2 packet to the new Preferred 486 locator. The I1 destination address and the new Preferred locator 487 may be identical. All new non-preferred locators must still undergo 488 address verification once the base exchange completes. 490 Initiator Responder 492 R1 with LOCATOR 493 <----------------------------------- 494 record additional addresses 495 change responder address 496 I2 sent to newly indicated preferred address 497 -----------------------------------> 498 (process normally) 499 R2 500 <----------------------------------- 501 (process normally, later verification of non-preferred locators) 503 Figure 5: LOCATOR Inclusion in R1 505 An Initiator MAY include one or more LOCATOR parameters in the I2 506 packet, independent of whether or not there was a LOCATOR parameter 507 in the R1. These parameters MUST be protected by the I2 signature. 508 Even if the I2 packet contains LOCATOR parameters, the Responder MUST 509 still send the R2 packet to the source address of the I2. The new 510 Preferred locator SHOULD be identical to the I2 source address. If 511 the I2 packet contains LOCATOR parameters, all new locators must 512 undergo address verification as usual, and the ESP traffic that 513 subsequently follows should use the Preferred locator. 515 Initiator Responder 517 I2 with LOCATOR 518 -----------------------------------> 519 (process normally) 520 record additional addresses 521 R2 sent to source address of I2 522 <----------------------------------- 523 (process normally) 525 Figure 6: LOCATOR Inclusion in I2 527 The I1 and I2 may be arriving from different source addresses if the 528 LOCATOR parameter is present in R1. In this case, implementations 529 simultaneously using multiple pre-created R1s, indexed by Initiator 530 IP addresses, may inadvertently fail the puzzle solution of I2 531 packets due to a perceived puzzle mismatch. See, for instance, the 532 example in Appendix A of [I-D.ietf-hip-rfc5201-bis]. As a solution, 533 the Responder's puzzle indexing mechanism must be flexible enough to 534 accommodate the situation when R1 includes a LOCATOR parameter. 536 5. Other Considerations 538 5.1. Address Verification 540 An address verification method is specified in 541 [I-D.ietf-hip-rfc5206-bis]. It is expected that addresses learned in 542 multihoming scenarios also are subject to the same verification 543 rules. 545 5.2. Preferred Locator 547 When a host has multiple locators, the peer host must decide which to 548 use for outbound packets. It may be that a host would prefer to 549 receive data on a particular inbound interface. HIP allows a 550 particular locator to be designated as a Preferred locator and 551 communicated to the peer. 553 In general, when multiple locators are used for a session, there is 554 the question of using multiple locators for failover only or for 555 load-balancing. Due to the implications of load-balancing on the 556 transport layer that still need to be worked out, this document 557 assumes that multiple locators are used primarily for failover. An 558 implementation may use ICMP interactions, reachability checks, or 559 other means to detect the failure of a locator. 561 5.3. Interaction with Security Associations 563 This document uses the HIP LOCATOR protocol parameter, specified in 564 [I-D.ietf-hip-rfc5206-bis]), that allows the hosts to exchange 565 information about their locator(s) and any changes in their 566 locator(s). The logical structure created with LOCATOR parameters 567 has three levels: hosts, Security Associations (SAs) indexed by 568 Security Parameter Indices (SPIs), and addresses. 570 The relation between these levels for an association constructed as 571 defined in the base specification [I-D.ietf-hip-rfc5201-bis] and ESP 572 transform [I-D.ietf-hip-rfc5202-bis] is illustrated in Figure 7. 574 -<- SPI1a -- -- SPI2a ->- 575 host1 < > addr1a <---> addr2a < > host2 576 ->- SPI2a -- -- SPI1a -<- 578 Figure 7: Relation between Hosts, SPIs, and Addresses (Base 579 Specification) 581 In Figure 7, host1 and host2 negotiate two unidirectional SAs, and 582 each host selects the SPI value for its inbound SA. The addresses 583 addr1a and addr2a are the source addresses that the hosts use in the 584 base HIP exchange. These are the "preferred" (and only) addresses 585 conveyed to the peer for use on each SA. That is, although packets 586 sent to any of the hosts' interfaces may be accepted on the inbound 587 SA, the peer host in general knows of only the single destination 588 address learned in the base exchange (e.g., for host1, it sends a 589 packet on SPI2a to addr2a to reach host2), unless other mechanisms 590 exist to learn of new addresses. 592 In general, the bindings that exist in an implementation 593 corresponding to this document can be depicted as shown in Figure 8. 594 In this figure, a host can have multiple inbound SPIs (and, not 595 shown, multiple outbound SPIs) associated with another host. 596 Furthermore, each SPI may have multiple addresses associated with it. 597 These addresses that are bound to an SPI are not used to lookup the 598 incoming SA. Rather, the addresses are those that are provided to 599 the peer host, as hints for which addresses to use to reach the host 600 on that SPI. The LOCATOR parameter is used to change the set of 601 addresses that a peer associates with a particular SPI. 603 address11 604 / 605 SPI1 - address12 606 / 607 / address21 608 host -- SPI2 < 609 \ address22 610 \ 611 SPI3 - address31 612 \ 613 address32 615 Figure 8: Relation between Hosts, SPIs, and Addresses (General Case) 617 A host may establish any number of security associations (or SPIs) 618 with a peer. The main purpose of having multiple SPIs with a peer is 619 to group the addresses into collections that are likely to experience 620 fate sharing. For example, if the host needs to change its addresses 621 on SPI2, it is likely that both address21 and address22 will 622 simultaneously become obsolete. In a typical case, such SPIs may 623 correspond with physical interfaces; see below. Note, however, that 624 especially in the case of site multihoming, one of the addresses may 625 become unreachable while the other one still works. In the typical 626 case, however, this does not require the host to inform its peers 627 about the situation, since even the non-working address still 628 logically exists. 630 A basic property of HIP SAs is that the inbound IP address is not 631 used to lookup the incoming SA. Therefore, in Figure 8, it may seem 632 unnecessary for address31, for example, to be associated only with 633 SPI3 -- in practice, a packet may arrive to SPI1 via destination 634 address address31 as well. However, the use of different source and 635 destination addresses typically leads to different paths, with 636 different latencies in the network, and if packets were to arrive via 637 an arbitrary destination IP address (or path) for a given SPI, the 638 reordering due to different latencies may cause some packets to fall 639 outside of the ESP anti-replay window. For this reason, HIP provides 640 a mechanism to affiliate destination addresses with inbound SPIs, 641 when there is a concern that anti-replay windows might be violated. 642 In this sense, we can say that a given inbound SPI has an "affinity" 643 for certain inbound IP addresses, and this affinity is communicated 644 to the peer host. Each physical interface SHOULD have a separate SA, 645 unless the ESP anti-replay window is loose. 647 Moreover, even when the destination addresses used for a particular 648 SPI are held constant, the use of different source interfaces may 649 also cause packets to fall outside of the ESP anti-replay window, 650 since the path traversed is often affected by the source address or 651 interface used. A host has no way to influence the source interface 652 on which a peer sends its packets on a given SPI. A host SHOULD 653 consistently use the same source interface and address when sending 654 to a particular destination IP address and SPI. For this reason, a 655 host may find it useful to change its SPI or at least reset its ESP 656 anti-replay window when the peer host readdresses. 658 An address may appear on more than one SPI. This creates no 659 ambiguity since the receiver will ignore the IP addresses during SA 660 lookup anyway. However, this document does not specify such cases. 662 When the LOCATOR parameter is sent in an UPDATE packet, then the 663 receiver will respond with an UPDATE acknowledgment. When the 664 LOCATOR parameter is sent in an R1 or I2 packet, the base exchange 665 retransmission mechanism will confirm its successful delivery. 666 LOCATORs may experimentally be used in NOTIFY packets; in this case, 667 the recipient MUST consider the LOCATOR as informational and not 668 immediately change the current preferred address, but can test the 669 additional locators when the need arises. The use of the LOCATOR in 670 a NOTIFY message may not be compatible with middleboxes. 672 6. Processing Rules 674 Processing rules are specified in [I-D.ietf-hip-rfc5206-bis]. Future 675 versions of this document will specify multihoming-specific 676 processing rules here. 678 6.1. Sending LOCATORs 680 The decision of when to send LOCATORs is basically a local policy 681 issue. However, it is RECOMMENDED that a host send a LOCATOR 682 whenever it recognizes a change of its IP addresses in use on an 683 active HIP association, and assumes that the change is going to last 684 at least for a few seconds. Rapidly sending LOCATORs that force the 685 peer to change the preferred address SHOULD be avoided. 687 When a host decides to inform its peers about changes in its IP 688 addresses, it has to decide how to group the various addresses with 689 SPIs. The grouping should consider also whether middlebox 690 interaction requires sending the same LOCATOR in separate UPDATEs on 691 different paths. Since each SPI is associated with a different 692 Security Association, the grouping policy may also be based on ESP 693 anti-replay protection considerations. In the typical case, simply 694 basing the grouping on actual kernel level physical and logical 695 interfaces may be the best policy. Grouping policy is outside of the 696 scope of this document. 698 Note that the purpose of announcing IP addresses in a LOCATOR is to 699 provide connectivity between the communicating hosts. In most cases, 700 tunnels or virtual interfaces such as IPsec tunnel interfaces or 701 Mobile IP home addresses provide sub-optimal connectivity. 702 Furthermore, it should be possible to replace most tunnels with HIP 703 based "non-tunneling", therefore making most virtual interfaces 704 fairly unnecessary in the future. Therefore, virtual interfaces 705 SHOULD NOT be announced in general. On the other hand, there are 706 clearly situations where tunnels are used for diagnostic and/or 707 testing purposes. In such and other similar cases announcing the IP 708 addresses of virtual interfaces may be appropriate. 710 Hosts MUST NOT announce broadcast or multicast addresses in LOCATORs. 711 Link-local addresses MAY be announced to peers that are known to be 712 neighbors on the same link, such as when the IP destination address 713 of a peer is also link-local. The announcement of link-local 714 addresses in this case is a policy decision; link-local addresses 715 used as Preferred locators will create reachability problems when the 716 host moves to another link. In any case, link-local addresses MUST 717 NOT be announced to a peer unless that peer is known to be on the 718 same link. 720 Once the host has decided on the groups and assignment of addresses 721 to the SPIs, it creates a LOCATOR parameter that serves as a complete 722 representation of the addresses and affiliated SPIs intended for 723 active use. We now describe a few cases introduced in Section 4. We 724 assume that the Traffic Type for each locator is set to "0" (other 725 values for Traffic Type may be specified in documents that separate 726 the HIP control plane from data plane traffic). Other mobility and 727 multihoming cases are possible but are left for further 728 experimentation. 730 1. Host multihoming (addition of an address). We only describe the 731 simple case of adding an additional address to a (previously) 732 single-homed, non-mobile host. The host SHOULD set up a new SA 733 pair between this new address and the preferred address of the 734 peer host. To do this, the multihomed host creates a new inbound 735 SA and creates a new SPI. For the outgoing UPDATE message, it 736 inserts an ESP_INFO parameter with an OLD SPI field of "0", a NEW 737 SPI field corresponding to the new SPI, and a KEYMAT Index as 738 selected by local policy. The host adds to the UPDATE message a 739 LOCATOR with two Type "1" Locators: the original address and SPI 740 active on the association, and the new address and new SPI being 741 added (with the SPI matching the NEW SPI contained in the 742 ESP_INFO). The Preferred bit SHOULD be set depending on the 743 policy to tell the peer host which of the two locators is 744 preferred. The UPDATE also contains a SEQ parameter and 745 optionally a DIFFIE_HELLMAN parameter, and follows rekeying 746 procedures with respect to this new address. The UPDATE message 747 SHOULD be sent to the peer's Preferred address with a source 748 address corresponding to the new locator. 750 The sending of multiple LOCATORs, locators with Locator Type "0", and 751 multiple ESP_INFO parameters is for further study. Note that the 752 inclusion of LOCATOR in an R1 packet requires the use of Type "0" 753 locators since no SAs are set up at that point. 755 6.2. Handling Received LOCATORs 757 A host SHOULD be prepared to receive a LOCATOR parameter in the 758 following HIP packets: R1, I2, UPDATE, and NOTIFY. 760 This document describes sending both ESP_INFO and LOCATOR parameters 761 in an UPDATE. The ESP_INFO parameter is included when there is a 762 need to rekey or key a new SPI, and is otherwise included for the 763 possible benefit of HIP-aware middleboxes. The LOCATOR parameter 764 contains a complete map of the locators that the host wishes to make 765 or keep active for the HIP association. 767 In general, the processing of a LOCATOR depends upon the packet type 768 in which it is included. Here, we describe only the case in which 769 ESP_INFO is present and a single LOCATOR and ESP_INFO are sent in an 770 UPDATE message; other cases are for further study. The steps below 771 cover each of the cases described in Section 6.1. 773 The processing of ESP_INFO and LOCATOR parameters is intended to be 774 modular and support future generalization to the inclusion of 775 multiple ESP_INFO and/or multiple LOCATOR parameters. A host SHOULD 776 first process the ESP_INFO before the LOCATOR, since the ESP_INFO may 777 contain a new SPI value mapped to an existing SPI, while a Type "1" 778 locator will only contain a reference to the new SPI. 780 When a host receives a validated HIP UPDATE with a LOCATOR and 781 ESP_INFO parameter, it processes the ESP_INFO as follows. The 782 ESP_INFO parameter indicates whether an SA is being rekeyed, created, 783 deprecated, or just identified for the benefit of middleboxes. The 784 host examines the OLD SPI and NEW SPI values in the ESP_INFO 785 parameter: 787 1. (no rekeying) If the OLD SPI is equal to the NEW SPI and both 788 correspond to an existing SPI, the ESP_INFO is gratuitous 789 (provided for middleboxes) and no rekeying is necessary. 791 2. (rekeying) If the OLD SPI indicates an existing SPI and the NEW 792 SPI is a different non-zero value, the existing SA is being 793 rekeyed and the host follows HIP ESP rekeying procedures by 794 creating a new outbound SA with an SPI corresponding to the NEW 795 SPI, with no addresses bound to this SPI. Note that locators in 796 the LOCATOR parameter will reference this new SPI instead of the 797 old SPI. 799 3. (new SA) If the OLD SPI value is zero and the NEW SPI is a new 800 non-zero value, then a new SA is being requested by the peer. 801 This case is also treated like a rekeying event; the receiving 802 host must create a new SA and respond with an UPDATE ACK. 804 4. (deprecating the SA) If the OLD SPI indicates an existing SPI and 805 the NEW SPI is zero, the SA is being deprecated and all locators 806 uniquely bound to the SPI are put into the DEPRECATED state. 808 If none of the above cases apply, a protocol error has occurred and 809 the processing of the UPDATE is stopped. 811 Next, the locators in the LOCATOR parameter are processed. For each 812 locator listed in the LOCATOR parameter, check that the address 813 therein is a legal unicast or anycast address. That is, the address 814 MUST NOT be a broadcast or multicast address. Note that some 815 implementations MAY accept addresses that indicate the local host, 816 since it may be allowed that the host runs HIP with itself. 818 The below assumes that all locators are of Type "1" with a Traffic 819 Type of "0"; other cases are for further study. 821 For each Type "1" address listed in the LOCATOR parameter, the host 822 checks whether the address is already bound to the SPI indicated. If 823 the address is already bound, its lifetime is updated. If the status 824 of the address is DEPRECATED, the status is changed to UNVERIFIED. 825 If the address is not already bound, the address is added, and its 826 status is set to UNVERIFIED. Mark all addresses corresponding to the 827 SPI that were NOT listed in the LOCATOR parameter as DEPRECATED. 829 As a result, at the end of processing, the addresses listed in the 830 LOCATOR parameter have either a state of UNVERIFIED or ACTIVE, and 831 any old addresses on the old SA not listed in the LOCATOR parameter 832 have a state of DEPRECATED. 834 Once the host has processed the locators, if the LOCATOR parameter 835 contains a new Preferred locator, the host SHOULD initiate a change 836 of the Preferred locator. This requires that the host first verifies 837 reachability of the associated address, and only then changes the 838 Preferred locator; see Section 6.4. 840 If a host receives a locator with an unsupported Locator Type, and 841 when such a locator is also declared to be the Preferred locator for 842 the peer, the host SHOULD send a NOTIFY error with a Notify Message 843 Type of LOCATOR_TYPE_UNSUPPORTED, with the Notification Data field 844 containing the locator(s) that the receiver failed to process. 845 Otherwise, a host MAY send a NOTIFY error if a (non-preferred) 846 locator with an unsupported Locator Type is received in a LOCATOR 847 parameter. 849 6.3. Verifying Address Reachability 851 Address verification is defined in [I-D.ietf-hip-rfc5206-bis]. 853 When address verification is in progress for a new Preferred locator, 854 the host SHOULD select a different locator listed as ACTIVE, if one 855 such locator is available, to continue communications until address 856 verification completes. Alternatively, the host MAY use the new 857 Preferred locator while in UNVERIFIED status to the extent Credit- 858 Based Authorization permits. Credit-Based Authorization is explained 859 in [I-D.ietf-hip-rfc5206-bis]. Once address verification succeeds, 860 the status of the new Preferred locator changes to ACTIVE. 862 6.4. Changing the Preferred Locator 864 A host MAY want to change the Preferred outgoing locator for 865 different reasons, e.g., because traffic information or ICMP error 866 messages indicate that the currently used preferred address may have 867 become unreachable. Another reason may be due to receiving a LOCATOR 868 parameter that has the "P" bit set. 870 To change the Preferred locator, the host initiates the following 871 procedure: 873 1. If the new Preferred locator has ACTIVE status, the Preferred 874 locator is changed and the procedure succeeds. 876 2. If the new Preferred locator has UNVERIFIED status, the host 877 starts to verify its reachability. The host SHOULD use a 878 different locator listed as ACTIVE until address verification 879 completes if one such locator is available. Alternatively, the 880 host MAY use the new Preferred locator, even though in UNVERIFIED 881 status, to the extent Credit-Based Authorization permits. Once 882 address verification succeeds, the status of the new Preferred 883 locator changes to ACTIVE and its use is no longer governed by 884 Credit-Based Authorization. 886 3. If the peer host has not indicated a preference for any address, 887 then the host picks one of the peer's ACTIVE addresses randomly 888 or according to policy. This case may arise if, for example, 889 ICMP error messages that deprecate the Preferred locator arrive, 890 but the peer has not yet indicated a new Preferred locator. 892 4. If the new Preferred locator has DEPRECATED status and there is 893 at least one non-deprecated address, the host selects one of the 894 non-deprecated addresses as a new Preferred locator and 895 continues. If the selected address is UNVERIFIED, the address 896 verification procedure described above will apply. 898 7. Security Considerations 900 Security considerations are addressed in [I-D.ietf-hip-rfc5206-bis]. 902 8. IANA Considerations 904 None. 906 9. Authors and Acknowledgments 908 This document contains content that was originally included in 909 RFC5206. Pekka Nikander and Jari Arkko originated RFC5206, and 910 Christian Vogt and Thomas Henderson (editor) later joined as co- 911 authors. Also in RFC5206, Greg Perkins contributed the initial draft 912 of the security section, and Petri Jokela was a co-author of the 913 initial individual submission. 915 The authors thank Miika Komu, Mika Kousa, Jeff Ahrenholz, and Jan 916 Melen for many improvements to the document. 918 10. References 920 10.1. Normative references 922 [I-D.ietf-hip-rfc5201-bis] 923 Moskowitz, R., Heer, T., Jokela, P., and T. Henderson, 924 "Host Identity Protocol Version 2 (HIPv2)", draft-ietf- 925 hip-rfc5201-bis-14 (work in progress), October 2013. 927 [I-D.ietf-hip-rfc5202-bis] 928 Jokela, P., Moskowitz, R., and J. Melen, "Using the 929 Encapsulating Security Payload (ESP) Transport Format with 930 the Host Identity Protocol (HIP)", draft-ietf-hip- 931 rfc5202-bis-05 (work in progress), November 2013. 933 [I-D.ietf-hip-rfc5206-bis] 934 Henderson, T., Vogt, C., and J. Arkko, "Host Mobility with 935 the Host Identity Protocol", draft-ietf-hip-rfc5206-bis-06 936 (work in progress), July 2013. 938 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 939 Requirement Levels", BCP 14, RFC 2119, March 1997. 941 [RFC3484] Draves, R., "Default Address Selection for Internet 942 Protocol version 6 (IPv6)", RFC 3484, February 2003. 944 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 945 4303, December 2005. 947 10.2. Informative references 949 [I-D.ietf-hip-rfc4423-bis] 950 Moskowitz, R. and M. Komu, "Host Identity Protocol 951 Architecture", draft-ietf-hip-rfc4423-bis-08 (work in 952 progress), April 2014. 954 [I-D.ietf-hip-rfc5204-bis] 955 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 956 Rendezvous Extension", draft-ietf-hip-rfc5204-bis-04 (work 957 in progress), June 2014. 959 [RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming 960 Shim Protocol for IPv6", RFC 5533, June 2009. 962 Appendix A. Document Revision History 964 To be removed upon publication 966 +----------+--------------------------------------------------------+ 967 | Revision | Comments | 968 +----------+--------------------------------------------------------+ 969 | draft-00 | Initial version with multihoming text imported from | 970 | | RFC5206. | 971 | | | 972 | draft-01 | Document refresh; no other changes. | 973 | | | 974 | draft-02 | Document refresh; no other changes. | 975 | | | 976 | draft-03 | Document refresh; no other changes. | 977 | | | 978 | draft-04 | Document refresh; no other changes. | 979 +----------+--------------------------------------------------------+ 981 Authors' Addresses 983 Thomas R. Henderson (editor) 984 University of Washington 985 Campus Box 352500 986 Seattle, WA 987 USA 989 EMail: tomhend@u.washington.edu 991 Christian Vogt 992 Ericsson Research NomadicLab 993 Hirsalantie 11 994 JORVAS FIN-02420 995 FINLAND 997 EMail: christian.vogt@ericsson.com 999 Jari Arkko 1000 Ericsson Research NomadicLab 1001 JORVAS FIN-02420 1002 FINLAND 1004 Phone: +358 40 5079256 1005 EMail: jari.arkko@ericsson.com