idnits 2.17.1 draft-ietf-hip-multihoming-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to contain a disclaimer for pre-RFC5378 work, but was first submitted on or after 10 November 2008. The disclaimer is usually necessary only for documents that revise or obsolete older RFCs, and that take significant amounts of text from those RFCs. If you can contact all authors of the source material and they are willing to grant the BCP78 rights to the IETF Trust, you can and should remove the disclaimer. Otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (July 15, 2013) is 3935 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-14) exists of draft-ietf-hip-rfc5206-bis-06 ** Obsolete normative reference: RFC 3484 (Obsoleted by RFC 6724) ** Obsolete normative reference: RFC 4423 (Obsoleted by RFC 9063) ** Obsolete normative reference: RFC 5201 (Obsoleted by RFC 7401) ** Obsolete normative reference: RFC 5202 (Obsoleted by RFC 7402) -- Obsolete informational reference (is this intentional?): RFC 5204 (Obsoleted by RFC 8004) Summary: 4 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Henderson, Ed. 3 Internet-Draft The Boeing Company 4 Intended status: Standards Track C. Vogt 5 Expires: January 16, 2014 J. Arkko 6 Ericsson Research NomadicLab 7 July 15, 2013 9 Host Multihoming with the Host Identity Protocol 10 draft-ietf-hip-multihoming-03 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 January 16, 2014. 35 Copyright Notice 37 Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . 3 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 . . . . . . . . . . . . . . 21 92 1. Introduction and Scope 94 The Host Identity Protocol [RFC4423] (HIP) supports an architecture 95 that decouples the transport layer (TCP, UDP, etc.) from the 96 internetworking layer (IPv4 and IPv6) by using public/private key 97 pairs, instead of IP addresses, as host identities. When a host uses 98 HIP, the overlying protocol sublayers (e.g., transport layer sockets 99 and Encapsulating Security Payload (ESP) Security Associations (SAs)) 100 are instead bound to representations of these host identities, and 101 the IP addresses are only used for packet forwarding. However, each 102 host must also know at least one IP address at which its peers are 103 reachable. Initially, these IP addresses are the ones used during 104 the HIP base exchange [RFC5201]. 106 One consequence of such a decoupling is that new solutions to 107 network-layer mobility and host multihoming are possible. Host 108 mobility is defined in [I-D.ietf-hip-rfc5206-bis] and covers the case 109 in which a host has a single address and changes its network point- 110 of-attachment while desiring to preserve the HIP-enabled security 111 association. Host multihoming is somewhat of a dual case to host 112 mobility, in that a host may simultaneously have more than one 113 network point-of-attachment. There are potentially many variations 114 of host multihoming possible. The scope of this document encompasses 115 messaging and elements of procedure for some basic host multihoming 116 scenarios of interest. 118 Another variation of multihoming that has been heavily studied site 119 multihoming. Solutions for site multihoming in IPv6 networks have 120 been specified by the IETF shim6 working group. The shim6 protocol 121 [RFC5533] bears many architectural similarities to HIP but there are 122 differences in the security model and in the protocol. Future 123 versions of this draft will summarize the differences more 124 completely. 126 While HIP can potentially be used with transports other than the ESP 127 transport format [RFC5202], this document largely assumes the use of 128 ESP and leaves other transport formats for further study. 130 There are a number of situations where the simple end-to-end 131 readdressing functionality defined herein is not sufficient. These 132 include the initial reachability of a multihomed host, location 133 privacy, simultaneous mobility of both hosts, and some modes of NAT 134 traversal. In these situations, there is a need for some helper 135 functionality in the network, such as a HIP rendezvous server 136 [RFC5204]. Such functionality is out of the scope of this document. 137 Finally, making underlying IP multihoming transparent to the 138 transport layer has implications on the proper response of transport 139 congestion control, path MTU selection, and Quality of Service (QoS). 141 Transport-layer mobility triggers, and the proper transport response 142 to a HIP multihoming address change, are outside the scope of this 143 document. 145 2. Terminology and Conventions 147 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 148 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 149 document are to be interpreted as described in RFC 2119 [RFC2119]. 151 Terminology is copied from [I-D.ietf-hip-rfc5206-bis]. 153 LOCATOR. The name of a HIP parameter containing zero or more Locator 154 fields. This parameter's name is distinguished from the Locator 155 fields embedded within it by the use of all capital letters. 157 Locator. A name that controls how the packet is routed through the 158 network and demultiplexed by the end host. It may include a 159 concatenation of traditional network addresses such as an IPv6 160 address and end-to-end identifiers such as an ESP SPI. It may 161 also include transport port numbers or IPv6 Flow Labels as 162 demultiplexing context, or it may simply be a network address. 164 Address. A name that denotes a point-of-attachment to the network. 165 The two most common examples are an IPv4 address and an IPv6 166 address. The set of possible addresses is a subset of the set of 167 possible locators. 169 Preferred locator. A locator on which a host prefers to receive 170 data. With respect to a given peer, a host always has one active 171 Preferred locator, unless there are no active locators. By 172 default, the locators used in the HIP base exchange are the 173 Preferred locators. 175 Credit Based Authorization. A host must verify a mobile or 176 multihomed peer's reachability at a new locator. Credit-Based 177 Authorization authorizes the peer to receive a certain amount of 178 data at the new locator before the result of such verification is 179 known. 181 3. Protocol Model 183 This section is an overview; more detailed specification follows this 184 section. 186 The overall protocol model is the same as in Section 3 of 187 [I-D.ietf-hip-rfc5206-bis]; this section only highlights the 188 differences. 190 3.1. Operating Environment 192 The Host Identity Protocol (HIP) [RFC5201] is a key establishment and 193 parameter negotiation protocol. Its primary applications are for 194 authenticating host messages based on host identities, and 195 establishing security associations (SAs) for the ESP transport format 196 [RFC5202] and possibly other protocols in the future. 198 +--------------------+ +--------------------+ 199 | | | | 200 | +------------+ | | +------------+ | 201 | | Key | | HIP | | Key | | 202 | | Management | <-+-----------------------+-> | Management | | 203 | | Process | | | | Process | | 204 | +------------+ | | +------------+ | 205 | ^ | | ^ | 206 | | | | | | 207 | v | | v | 208 | +------------+ | | +------------+ | 209 | | IPsec | | ESP | | IPsec | | 210 | | Stack | <-+-----------------------+-> | Stack | | 211 | | | | | | | | 212 | +------------+ | | +------------+ | 213 | | | | 214 | | | | 215 | Initiator | | Responder | 216 +--------------------+ +--------------------+ 218 Figure 1: HIP Deployment Model 220 The general deployment model for HIP is shown above, assuming 221 operation in an end-to-end fashion. This document specifies 222 extensions to the HIP protocol to enable end-host mobility and basic 223 multihoming. In summary, these extensions to the HIP base protocol 224 enable the signaling of new addressing information to the peer in HIP 225 messages. The messages are authenticated via a signature or keyed 226 hash message authentication code (HMAC) based on its Host Identity. 228 --------- 229 | TCP | (sockets bound to HITs) 230 --------- 231 | 232 --------- 233 ----> | ESP | {HIT_s, HIT_d} <-> SPI 234 | --------- 235 | | 236 ---- --------- 237 | MH |-> | HIP | {HIT_s, HIT_d, SPI} <-> {IP_s, IP_d, SPI} 238 ---- --------- 239 | 240 --------- 241 | IP | 242 --------- 244 Figure 2: Architecture for HIP Multihoming (MH) 246 Figure 2 depicts a layered architectural view of a HIP-enabled stack 247 using the ESP transport format. In HIP, upper-layer protocols 248 (including TCP and ESP in this figure) are bound to Host Identity 249 Tags (HITs) and not IP addresses. The HIP sublayer is responsible 250 for maintaining the binding between HITs and IP addresses. The SPI 251 is used to associate an incoming packet with the right HITs. The 252 block labeled "MH" is introduced below. 254 Consider the case when a host is multihomed (has more than one 255 globally routable address) and has multiple addresses available at 256 the HIP layer as alternative locators for fault tolerance. Examples 257 include the use of (possibly multiple) IPv4 and IPv6 addresses on the 258 same interface, or the use of multiple interfaces attached to 259 different service providers. Such host multihoming generally 260 necessitates that a separate ESP SA is maintained for each interface 261 in order to prevent packets that arrive over different paths from 262 falling outside of the ESP anti-replay window [RFC4303]. Multihoming 263 thus makes it possible that the bindings shown on the right side of 264 Figure 2 are one to many (in the outbound direction, one HIT pair to 265 multiple SPIs, and possibly then to multiple IP addresses). However, 266 only one SPI and address pair can be used for any given packet, so 267 the job of the "MH" block depicted above is to dynamically manipulate 268 these bindings. Beyond locally managing such multiple bindings, the 269 peer-to-peer HIP signaling protocol needs to be flexible enough to 270 define the desired mappings between HITs, SPIs, and addresses, and 271 needs to ensure that UPDATE messages are sent along the right network 272 paths so that any HIP-aware middleboxes can observe the SPIs. This 273 document does not specify the "MH" block, nor does it specify 274 detailed elements of procedure for how to handle various multihoming 275 (perhaps combined with mobility) scenarios. The "MH" block may apply 276 to more general problems outside of HIP. However, this document does 277 describe a basic multihoming case (one host adds one address to its 278 initial address and notifies the peer) and leave more complicated 279 scenarios for experimentation and future documents. 281 3.2. Multihoming Overview 283 In host multihoming, a host has multiple locators simultaneously 284 rather than sequentially, as in the case of mobility. By using the 285 LOCATOR parameter defined in [I-D.ietf-hip-rfc5206-bis], a host can 286 inform its peers of additional (multiple) locators at which it can be 287 reached, and can declare a particular locator as a "preferred" 288 locator. Although this document defines a basic mechanism for 289 multihoming, it does not define detailed policies and procedures, 290 such as which locators to choose when more than one pair is 291 available, the operation of simultaneous mobility and multihoming, 292 source address selection policies (beyond those specified in 293 [RFC3484]), and the implications of multihoming on transport 294 protocols and ESP anti-replay windows. 296 4. Protocol Overview 298 In this section, we briefly introduce a number of usage scenarios for 299 HIP multihoming. These scenarios assume that HIP is being used with 300 the ESP transform [RFC5202], although other scenarios may be defined 301 in the future. To understand these usage scenarios, the reader 302 should be at least minimally familiar with the HIP protocol 303 specification [RFC5201]. However, for the (relatively) uninitiated 304 reader, it is most important to keep in mind that in HIP the actual 305 payload traffic is protected with ESP, and that the ESP SPI acts as 306 an index to the right host-to-host context. 308 The scenarios below assume that the two hosts have completed a single 309 HIP base exchange with each other. Both of the hosts therefore have 310 one incoming and one outgoing SA. Further, each SA uses the same 311 pair of IP addresses, which are the ones used in the base exchange. 313 The readdressing protocol is an asymmetric protocol where a mobile or 314 multihomed host informs a peer host about changes of IP addresses on 315 affected SPIs. The readdressing exchange is designed to be 316 piggybacked on existing HIP exchanges. The majority of the packets 317 on which the LOCATOR parameters are expected to be carried are UPDATE 318 packets. However, some implementations may want to experiment with 319 sending LOCATOR parameters also on other packets, such as R1, I2, and 320 NOTIFY. 322 The scenarios below at times describe addresses as being in either an 323 ACTIVE, VERIFIED, or DEPRECATED state. From the perspective of a 324 host, newly-learned addresses of the peer must be verified before put 325 into active service, and addresses removed by the peer are put into a 326 deprecated state. Under limited conditions described in 327 [I-D.ietf-hip-rfc5206-bis], an UNVERIFIED address may be used. 329 Hosts that use link-local addresses as source addresses in their HIP 330 handshakes may not be reachable by a mobile peer. Such hosts SHOULD 331 provide a globally routable address either in the initial handshake 332 or via the LOCATOR parameter. 334 4.1. Host Multihoming 336 A (mobile or stationary) host may sometimes have more than one 337 interface or global address. The host may notify the peer host of 338 the additional interface or address by using the LOCATOR parameter. 339 To avoid problems with the ESP anti-replay window, a host SHOULD use 340 a different SA for each interface or address used to receive packets 341 from the peer host when multiple locator pairs are being used 342 simultaneously rather than sequentially. 344 When more than one locator is provided to the peer host, the host 345 SHOULD indicate which locator is preferred (the locator on which the 346 host prefers to receive traffic). By default, the addresses used in 347 the base exchange are preferred until indicated otherwise. 349 In the multihoming case, the sender may also have multiple valid 350 locators from which to source traffic. In practice, a HIP 351 association in a multihoming configuration may have both a preferred 352 peer locator and a preferred local locator, although rules for source 353 address selection should ultimately govern the selection of the 354 source locator based on the destination locator. 356 Although the protocol may allow for configurations in which there is 357 an asymmetric number of SAs between the hosts (e.g., one host has two 358 interfaces and two inbound SAs, while the peer has one interface and 359 one inbound SA), it is RECOMMENDED that inbound and outbound SAs be 360 created pairwise between hosts. When an ESP_INFO arrives to rekey a 361 particular outbound SA, the corresponding inbound SA should be also 362 rekeyed at that time. Although asymmetric SA configurations might be 363 experimented with, their usage may constrain interoperability at this 364 time. However, it is recommended that implementations attempt to 365 support peers that prefer to use non-paired SAs. It is expected that 366 this section and behavior will be modified in future revisions of 367 this protocol, once the issue and its implications are better 368 understood. 370 Consider the case between two hosts, one single-homed and one 371 multihomed. The multihomed host may decide to inform the single- 372 homed host about its other address. It is RECOMMENDED that the 373 multihomed host set up a new SA pair for use on this new address. To 374 do this, the multihomed host sends a LOCATOR with an ESP_INFO, 375 indicating the request for a new SA by setting the OLD SPI value to 376 zero, and the NEW SPI value to the newly created incoming SPI. A 377 Locator Type of "1" is used to associate the new address with the new 378 SPI. The LOCATOR parameter also contains a second Type "1" locator, 379 that of the original address and SPI. To simplify parameter 380 processing and avoid explicit protocol extensions to remove locators, 381 each LOCATOR parameter MUST list all locators in use on a connection 382 (a complete listing of inbound locators and SPIs for the host). The 383 multihomed host waits for an ESP_INFO (new outbound SA) from the peer 384 and an ACK of its own UPDATE. As in the mobility case, the peer host 385 must perform an address verification before actively using the new 386 address. Figure 3 illustrates this scenario. 388 Multi-homed Host Peer Host 390 UPDATE(ESP_INFO, LOCATOR, SEQ, [DIFFIE_HELLMAN]) 391 -----------------------------------> 392 UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) 393 <----------------------------------- 394 UPDATE(ACK, ECHO_RESPONSE) 395 -----------------------------------> 397 Figure 3: Basic Multihoming Scenario 399 In multihoming scenarios, it is important that hosts receiving 400 UPDATEs associate them correctly with the destination address used in 401 the packet carrying the UPDATE. When processing inbound LOCATORs 402 that establish new security associations on an interface with 403 multiple addresses, a host uses the destination address of the UPDATE 404 containing the LOCATOR as the local address to which the LOCATOR plus 405 ESP_INFO is targeted. This is because hosts may send UPDATEs with 406 the same (locator) IP address to different peer addresses -- this has 407 the effect of creating multiple inbound SAs implicitly affiliated 408 with different peer source addresses. 410 4.2. Site Multihoming 412 A host may have an interface that has multiple globally routable IP 413 addresses. Such a situation may be a result of the site having 414 multiple upper Internet Service Providers, or just because the site 415 provides all hosts with both IPv4 and IPv6 addresses. The host 416 should stay reachable at all or any subset of the currently available 417 global routable addresses, independent of how they are provided. 419 This case is handled the same as if there were different IP 420 addresses, described above in Section 4.1. Note that a single 421 interface may experience site multihoming while the host itself may 422 have multiple interfaces. 424 Note that a host may be multihomed and mobile simultaneously, and 425 that a multihomed host may want to protect the location of some of 426 its interfaces while revealing the real IP address of some others. 428 This document does not presently specify additional site multihoming 429 extensions to HIP; further alignment with the IETF shim6 working 430 group may be considered in the future. 432 4.3. Dual host multihoming 434 Consider the case in which both hosts would like to add an additional 435 address after the base exchange completes. In Figure 4, consider 436 that host1, which used address addr1a in the base exchange to set up 437 SPI1a and SPI2a, wants to add address addr1b. It would send an 438 UPDATE with LOCATOR (containing the address addr1b) to host2, using 439 destination address addr2a, and a new set of SPIs would be added 440 between hosts 1 and 2 (call them SPI1b and SPI2b -- not shown in the 441 figure). Next, consider host2 deciding to add addr2b to the 442 relationship. Host2 must select one of host1's addresses towards 443 which to initiate an UPDATE. It may choose to initiate an UPDATE to 444 addr1a, addr1b, or both. If it chooses to send to both, then a full 445 mesh (four SA pairs) of SAs would exist between the two hosts. This 446 is the most general case; it often may be the case that hosts 447 primarily establish new SAs only with the peer's Preferred locator. 448 The readdressing protocol is flexible enough to accommodate this 449 choice. 451 -<- SPI1a -- -- SPI2a ->- 452 host1 < > addr1a <---> addr2a < > host2 453 ->- SPI2a -- -- SPI1a -<- 455 addr1b <---> addr2a (second SA pair) 456 addr1a <---> addr2b (third SA pair) 457 addr1b <---> addr2b (fourth SA pair) 459 Figure 4: Dual Multihoming Case in Which Each Host Uses LOCATOR to 460 Add a Second Address 462 4.4. Combined Mobility and Multihoming 464 It looks likely that in the future, many mobile hosts will be 465 simultaneously mobile and multihomed, i.e., have multiple mobile 466 interfaces. Furthermore, if the interfaces use different access 467 technologies, it is fairly likely that one of the interfaces may 468 appear stable (retain its current IP address) while some other(s) may 469 experience mobility (undergo IP address change). 471 The use of LOCATOR plus ESP_INFO should be flexible enough to handle 472 most such scenarios, although more complicated scenarios have not 473 been studied so far. 475 4.5. Initiating the Protocol in R1 or I2 477 A Responder host MAY include a LOCATOR parameter in the R1 packet 478 that it sends to the Initiator. This parameter MUST be protected by 479 the R1 signature. If the R1 packet contains LOCATOR parameters with 480 a new Preferred locator, the Initiator SHOULD directly set the new 481 Preferred locator to status ACTIVE without performing address 482 verification first, and MUST send the I2 packet to the new Preferred 483 locator. The I1 destination address and the new Preferred locator 484 may be identical. All new non-preferred locators must still undergo 485 address verification once the base exchange completes. 487 Initiator Responder 489 R1 with LOCATOR 490 <----------------------------------- 491 record additional addresses 492 change responder address 493 I2 sent to newly indicated preferred address 494 -----------------------------------> 495 (process normally) 496 R2 497 <----------------------------------- 498 (process normally, later verification of non-preferred locators) 500 Figure 5: LOCATOR Inclusion in R1 502 An Initiator MAY include one or more LOCATOR parameters in the I2 503 packet, independent of whether or not there was a LOCATOR parameter 504 in the R1. These parameters MUST be protected by the I2 signature. 505 Even if the I2 packet contains LOCATOR parameters, the Responder MUST 506 still send the R2 packet to the source address of the I2. The new 507 Preferred locator SHOULD be identical to the I2 source address. If 508 the I2 packet contains LOCATOR parameters, all new locators must 509 undergo address verification as usual, and the ESP traffic that 510 subsequently follows should use the Preferred locator. 512 Initiator Responder 514 I2 with LOCATOR 515 -----------------------------------> 516 (process normally) 517 record additional addresses 518 R2 sent to source address of I2 519 <----------------------------------- 520 (process normally) 522 Figure 6: LOCATOR Inclusion in I2 524 The I1 and I2 may be arriving from different source addresses if the 525 LOCATOR parameter is present in R1. In this case, implementations 526 simultaneously using multiple pre-created R1s, indexed by Initiator 527 IP addresses, may inadvertently fail the puzzle solution of I2 528 packets due to a perceived puzzle mismatch. See, for instance, the 529 example in Appendix A of [RFC5201]. As a solution, the Responder's 530 puzzle indexing mechanism must be flexible enough to accommodate the 531 situation when R1 includes a LOCATOR parameter. 533 5. Other Considerations 535 5.1. Address Verification 537 An address verification method is specified in 538 [I-D.ietf-hip-rfc5206-bis]. It is expected that addresses learned in 539 multihoming scenarios also are subject to the same verification 540 rules. 542 5.2. Preferred Locator 544 When a host has multiple locators, the peer host must decide which to 545 use for outbound packets. It may be that a host would prefer to 546 receive data on a particular inbound interface. HIP allows a 547 particular locator to be designated as a Preferred locator and 548 communicated to the peer. 550 In general, when multiple locators are used for a session, there is 551 the question of using multiple locators for failover only or for 552 load-balancing. Due to the implications of load-balancing on the 553 transport layer that still need to be worked out, this document 554 assumes that multiple locators are used primarily for failover. An 555 implementation may use ICMP interactions, reachability checks, or 556 other means to detect the failure of a locator. 558 5.3. Interaction with Security Associations 560 This document uses the HIP LOCATOR protocol parameter, specified in 561 [I-D.ietf-hip-rfc5206-bis]), that allows the hosts to exchange 562 information about their locator(s) and any changes in their 563 locator(s). The logical structure created with LOCATOR parameters 564 has three levels: hosts, Security Associations (SAs) indexed by 565 Security Parameter Indices (SPIs), and addresses. 567 The relation between these levels for an association constructed as 568 defined in the base specification [RFC5201] and ESP transform 569 [RFC5202] is illustrated in Figure 7. 571 -<- SPI1a -- -- SPI2a ->- 572 host1 < > addr1a <---> addr2a < > host2 573 ->- SPI2a -- -- SPI1a -<- 575 Figure 7: Relation between Hosts, SPIs, and Addresses (Base 576 Specification) 578 In Figure 7, host1 and host2 negotiate two unidirectional SAs, and 579 each host selects the SPI value for its inbound SA. The addresses 580 addr1a and addr2a are the source addresses that the hosts use in the 581 base HIP exchange. These are the "preferred" (and only) addresses 582 conveyed to the peer for use on each SA. That is, although packets 583 sent to any of the hosts' interfaces may be accepted on the inbound 584 SA, the peer host in general knows of only the single destination 585 address learned in the base exchange (e.g., for host1, it sends a 586 packet on SPI2a to addr2a to reach host2), unless other mechanisms 587 exist to learn of new addresses. 589 In general, the bindings that exist in an implementation 590 corresponding to this document can be depicted as shown in Figure 8. 591 In this figure, a host can have multiple inbound SPIs (and, not 592 shown, multiple outbound SPIs) associated with another host. 593 Furthermore, each SPI may have multiple addresses associated with it. 594 These addresses that are bound to an SPI are not used to lookup the 595 incoming SA. Rather, the addresses are those that are provided to 596 the peer host, as hints for which addresses to use to reach the host 597 on that SPI. The LOCATOR parameter is used to change the set of 598 addresses that a peer associates with a particular SPI. 600 address11 601 / 602 SPI1 - address12 603 / 604 / address21 605 host -- SPI2 < 606 \ address22 607 \ 608 SPI3 - address31 609 \ 610 address32 612 Figure 8: Relation between Hosts, SPIs, and Addresses (General Case) 614 A host may establish any number of security associations (or SPIs) 615 with a peer. The main purpose of having multiple SPIs with a peer is 616 to group the addresses into collections that are likely to experience 617 fate sharing. For example, if the host needs to change its addresses 618 on SPI2, it is likely that both address21 and address22 will 619 simultaneously become obsolete. In a typical case, such SPIs may 620 correspond with physical interfaces; see below. Note, however, that 621 especially in the case of site multihoming, one of the addresses may 622 become unreachable while the other one still works. In the typical 623 case, however, this does not require the host to inform its peers 624 about the situation, since even the non-working address still 625 logically exists. 627 A basic property of HIP SAs is that the inbound IP address is not 628 used to lookup the incoming SA. Therefore, in Figure 8, it may seem 629 unnecessary for address31, for example, to be associated only with 630 SPI3 -- in practice, a packet may arrive to SPI1 via destination 631 address address31 as well. However, the use of different source and 632 destination addresses typically leads to different paths, with 633 different latencies in the network, and if packets were to arrive via 634 an arbitrary destination IP address (or path) for a given SPI, the 635 reordering due to different latencies may cause some packets to fall 636 outside of the ESP anti-replay window. For this reason, HIP provides 637 a mechanism to affiliate destination addresses with inbound SPIs, 638 when there is a concern that anti-replay windows might be violated. 639 In this sense, we can say that a given inbound SPI has an "affinity" 640 for certain inbound IP addresses, and this affinity is communicated 641 to the peer host. Each physical interface SHOULD have a separate SA, 642 unless the ESP anti-replay window is loose. 644 Moreover, even when the destination addresses used for a particular 645 SPI are held constant, the use of different source interfaces may 646 also cause packets to fall outside of the ESP anti-replay window, 647 since the path traversed is often affected by the source address or 648 interface used. A host has no way to influence the source interface 649 on which a peer sends its packets on a given SPI. A host SHOULD 650 consistently use the same source interface and address when sending 651 to a particular destination IP address and SPI. For this reason, a 652 host may find it useful to change its SPI or at least reset its ESP 653 anti-replay window when the peer host readdresses. 655 An address may appear on more than one SPI. This creates no 656 ambiguity since the receiver will ignore the IP addresses during SA 657 lookup anyway. However, this document does not specify such cases. 659 When the LOCATOR parameter is sent in an UPDATE packet, then the 660 receiver will respond with an UPDATE acknowledgment. When the 661 LOCATOR parameter is sent in an R1 or I2 packet, the base exchange 662 retransmission mechanism will confirm its successful delivery. 663 LOCATORs may experimentally be used in NOTIFY packets; in this case, 664 the recipient MUST consider the LOCATOR as informational and not 665 immediately change the current preferred address, but can test the 666 additional locators when the need arises. The use of the LOCATOR in 667 a NOTIFY message may not be compatible with middleboxes. 669 6. Processing Rules 671 Processing rules are specified in [I-D.ietf-hip-rfc5206-bis]. Future 672 versions of this document will specify multihoming-specific 673 processing rules here. 675 6.1. Sending LOCATORs 677 The decision of when to send LOCATORs is basically a local policy 678 issue. However, it is RECOMMENDED that a host send a LOCATOR 679 whenever it recognizes a change of its IP addresses in use on an 680 active HIP association, and assumes that the change is going to last 681 at least for a few seconds. Rapidly sending LOCATORs that force the 682 peer to change the preferred address SHOULD be avoided. 684 When a host decides to inform its peers about changes in its IP 685 addresses, it has to decide how to group the various addresses with 686 SPIs. The grouping should consider also whether middlebox 687 interaction requires sending the same LOCATOR in separate UPDATEs on 688 different paths. Since each SPI is associated with a different 689 Security Association, the grouping policy may also be based on ESP 690 anti-replay protection considerations. In the typical case, simply 691 basing the grouping on actual kernel level physical and logical 692 interfaces may be the best policy. Grouping policy is outside of the 693 scope of this document. 695 Note that the purpose of announcing IP addresses in a LOCATOR is to 696 provide connectivity between the communicating hosts. In most cases, 697 tunnels or virtual interfaces such as IPsec tunnel interfaces or 698 Mobile IP home addresses provide sub-optimal connectivity. 699 Furthermore, it should be possible to replace most tunnels with HIP 700 based "non-tunneling", therefore making most virtual interfaces 701 fairly unnecessary in the future. Therefore, virtual interfaces 702 SHOULD NOT be announced in general. On the other hand, there are 703 clearly situations where tunnels are used for diagnostic and/or 704 testing purposes. In such and other similar cases announcing the IP 705 addresses of virtual interfaces may be appropriate. 707 Hosts MUST NOT announce broadcast or multicast addresses in LOCATORs. 708 Link-local addresses MAY be announced to peers that are known to be 709 neighbors on the same link, such as when the IP destination address 710 of a peer is also link-local. The announcement of link-local 711 addresses in this case is a policy decision; link-local addresses 712 used as Preferred locators will create reachability problems when the 713 host moves to another link. In any case, link-local addresses MUST 714 NOT be announced to a peer unless that peer is known to be on the 715 same link. 717 Once the host has decided on the groups and assignment of addresses 718 to the SPIs, it creates a LOCATOR parameter that serves as a complete 719 representation of the addresses and affiliated SPIs intended for 720 active use. We now describe a few cases introduced in Section 4. We 721 assume that the Traffic Type for each locator is set to "0" (other 722 values for Traffic Type may be specified in documents that separate 723 the HIP control plane from data plane traffic). Other mobility and 724 multihoming cases are possible but are left for further 725 experimentation. 727 1. Host multihoming (addition of an address). We only describe the 728 simple case of adding an additional address to a (previously) 729 single-homed, non-mobile host. The host SHOULD set up a new SA 730 pair between this new address and the preferred address of the 731 peer host. To do this, the multihomed host creates a new inbound 732 SA and creates a new SPI. For the outgoing UPDATE message, it 733 inserts an ESP_INFO parameter with an OLD SPI field of "0", a NEW 734 SPI field corresponding to the new SPI, and a KEYMAT Index as 735 selected by local policy. The host adds to the UPDATE message a 736 LOCATOR with two Type "1" Locators: the original address and SPI 737 active on the association, and the new address and new SPI being 738 added (with the SPI matching the NEW SPI contained in the 739 ESP_INFO). The Preferred bit SHOULD be set depending on the 740 policy to tell the peer host which of the two locators is 741 preferred. The UPDATE also contains a SEQ parameter and 742 optionally a DIFFIE_HELLMAN parameter, and follows rekeying 743 procedures with respect to this new address. The UPDATE message 744 SHOULD be sent to the peer's Preferred address with a source 745 address corresponding to the new locator. 747 The sending of multiple LOCATORs, locators with Locator Type "0", and 748 multiple ESP_INFO parameters is for further study. Note that the 749 inclusion of LOCATOR in an R1 packet requires the use of Type "0" 750 locators since no SAs are set up at that point. 752 6.2. Handling Received LOCATORs 754 A host SHOULD be prepared to receive a LOCATOR parameter in the 755 following HIP packets: R1, I2, UPDATE, and NOTIFY. 757 This document describes sending both ESP_INFO and LOCATOR parameters 758 in an UPDATE. The ESP_INFO parameter is included when there is a 759 need to rekey or key a new SPI, and is otherwise included for the 760 possible benefit of HIP-aware middleboxes. The LOCATOR parameter 761 contains a complete map of the locators that the host wishes to make 762 or keep active for the HIP association. 764 In general, the processing of a LOCATOR depends upon the packet type 765 in which it is included. Here, we describe only the case in which 766 ESP_INFO is present and a single LOCATOR and ESP_INFO are sent in an 767 UPDATE message; other cases are for further study. The steps below 768 cover each of the cases described in Section 6.1. 770 The processing of ESP_INFO and LOCATOR parameters is intended to be 771 modular and support future generalization to the inclusion of 772 multiple ESP_INFO and/or multiple LOCATOR parameters. A host SHOULD 773 first process the ESP_INFO before the LOCATOR, since the ESP_INFO may 774 contain a new SPI value mapped to an existing SPI, while a Type "1" 775 locator will only contain a reference to the new SPI. 777 When a host receives a validated HIP UPDATE with a LOCATOR and 778 ESP_INFO parameter, it processes the ESP_INFO as follows. The 779 ESP_INFO parameter indicates whether an SA is being rekeyed, created, 780 deprecated, or just identified for the benefit of middleboxes. The 781 host examines the OLD SPI and NEW SPI values in the ESP_INFO 782 parameter: 784 1. (no rekeying) If the OLD SPI is equal to the NEW SPI and both 785 correspond to an existing SPI, the ESP_INFO is gratuitous 786 (provided for middleboxes) and no rekeying is necessary. 788 2. (rekeying) If the OLD SPI indicates an existing SPI and the NEW 789 SPI is a different non-zero value, the existing SA is being 790 rekeyed and the host follows HIP ESP rekeying procedures by 791 creating a new outbound SA with an SPI corresponding to the NEW 792 SPI, with no addresses bound to this SPI. Note that locators in 793 the LOCATOR parameter will reference this new SPI instead of the 794 old SPI. 796 3. (new SA) If the OLD SPI value is zero and the NEW SPI is a new 797 non-zero value, then a new SA is being requested by the peer. 798 This case is also treated like a rekeying event; the receiving 799 host must create a new SA and respond with an UPDATE ACK. 801 4. (deprecating the SA) If the OLD SPI indicates an existing SPI and 802 the NEW SPI is zero, the SA is being deprecated and all locators 803 uniquely bound to the SPI are put into the DEPRECATED state. 805 If none of the above cases apply, a protocol error has occurred and 806 the processing of the UPDATE is stopped. 808 Next, the locators in the LOCATOR parameter are processed. For each 809 locator listed in the LOCATOR parameter, check that the address 810 therein is a legal unicast or anycast address. That is, the address 811 MUST NOT be a broadcast or multicast address. Note that some 812 implementations MAY accept addresses that indicate the local host, 813 since it may be allowed that the host runs HIP with itself. 815 The below assumes that all locators are of Type "1" with a Traffic 816 Type of "0"; other cases are for further study. 818 For each Type "1" address listed in the LOCATOR parameter, the host 819 checks whether the address is already bound to the SPI indicated. If 820 the address is already bound, its lifetime is updated. If the status 821 of the address is DEPRECATED, the status is changed to UNVERIFIED. 822 If the address is not already bound, the address is added, and its 823 status is set to UNVERIFIED. Mark all addresses corresponding to the 824 SPI that were NOT listed in the LOCATOR parameter as DEPRECATED. 826 As a result, at the end of processing, the addresses listed in the 827 LOCATOR parameter have either a state of UNVERIFIED or ACTIVE, and 828 any old addresses on the old SA not listed in the LOCATOR parameter 829 have a state of DEPRECATED. 831 Once the host has processed the locators, if the LOCATOR parameter 832 contains a new Preferred locator, the host SHOULD initiate a change 833 of the Preferred locator. This requires that the host first verifies 834 reachability of the associated address, and only then changes the 835 Preferred locator; see Section 6.4. 837 If a host receives a locator with an unsupported Locator Type, and 838 when such a locator is also declared to be the Preferred locator for 839 the peer, the host SHOULD send a NOTIFY error with a Notify Message 840 Type of LOCATOR_TYPE_UNSUPPORTED, with the Notification Data field 841 containing the locator(s) that the receiver failed to process. 842 Otherwise, a host MAY send a NOTIFY error if a (non-preferred) 843 locator with an unsupported Locator Type is received in a LOCATOR 844 parameter. 846 6.3. Verifying Address Reachability 848 Address verification is defined in [I-D.ietf-hip-rfc5206-bis]. 850 When address verification is in progress for a new Preferred locator, 851 the host SHOULD select a different locator listed as ACTIVE, if one 852 such locator is available, to continue communications until address 853 verification completes. Alternatively, the host MAY use the new 854 Preferred locator while in UNVERIFIED status to the extent Credit- 855 Based Authorization permits. Credit-Based Authorization is explained 856 in [I-D.ietf-hip-rfc5206-bis]. Once address verification succeeds, 857 the status of the new Preferred locator changes to ACTIVE. 859 6.4. Changing the Preferred Locator 861 A host MAY want to change the Preferred outgoing locator for 862 different reasons, e.g., because traffic information or ICMP error 863 messages indicate that the currently used preferred address may have 864 become unreachable. Another reason may be due to receiving a LOCATOR 865 parameter that has the "P" bit set. 867 To change the Preferred locator, the host initiates the following 868 procedure: 870 1. If the new Preferred locator has ACTIVE status, the Preferred 871 locator is changed and the procedure succeeds. 873 2. If the new Preferred locator has UNVERIFIED status, the host 874 starts to verify its reachability. The host SHOULD use a 875 different locator listed as ACTIVE until address verification 876 completes if one such locator is available. Alternatively, the 877 host MAY use the new Preferred locator, even though in UNVERIFIED 878 status, to the extent Credit-Based Authorization permits. Once 879 address verification succeeds, the status of the new Preferred 880 locator changes to ACTIVE and its use is no longer governed by 881 Credit-Based Authorization. 883 3. If the peer host has not indicated a preference for any address, 884 then the host picks one of the peer's ACTIVE addresses randomly 885 or according to policy. This case may arise if, for example, 886 ICMP error messages that deprecate the Preferred locator arrive, 887 but the peer has not yet indicated a new Preferred locator. 889 4. If the new Preferred locator has DEPRECATED status and there is 890 at least one non-deprecated address, the host selects one of the 891 non-deprecated addresses as a new Preferred locator and 892 continues. If the selected address is UNVERIFIED, the address 893 verification procedure described above will apply. 895 7. Security Considerations 897 Security considerations are addressed in [I-D.ietf-hip-rfc5206-bis]. 899 8. IANA Considerations 901 None. 903 9. Authors and Acknowledgments 905 This document contains content that was originally included in 906 RFC5206. Pekka Nikander and Jari Arkko originated RFC5206, and 907 Christian Vogt and Thomas Henderson (editor) later joined as co- 908 authors. Also in RFC5206, Greg Perkins contributed the initial draft 909 of the security section, and Petri Jokela was a co-author of the 910 initial individual submission. 912 The authors thank Miika Komu, Mika Kousa, Jeff Ahrenholz, and Jan 913 Melen for many improvements to the document. 915 10. References 917 10.1. Normative references 919 [I-D.ietf-hip-rfc5206-bis] Henderson, T., Vogt, C., and J. Arkko, 920 "Host Mobility with the Host Identity 921 Protocol", draft-ietf-hip-rfc5206-bis-06 922 (work in progress), July 2013. 924 [RFC2119] Bradner, S., "Key words for use in RFCs 925 to Indicate Requirement Levels", BCP 14, 926 RFC 2119, March 1997. 928 [RFC3484] Draves, R., "Default Address Selection 929 for Internet Protocol version 6 (IPv6)", 930 RFC 3484, February 2003. 932 [RFC4303] Kent, S., "IP Encapsulating Security 933 Payload (ESP)", RFC 4303, December 2005. 935 [RFC4423] Moskowitz, R. and P. Nikander, "Host 936 Identity Protocol (HIP) Architecture", 937 RFC 4423, May 2006. 939 [RFC5201] Moskowitz, R., Nikander, P., Jokela, P., 940 and T. Henderson, "Host Identity 941 Protocol", RFC 5201, April 2008. 943 [RFC5202] Jokela, P., Moskowitz, R., and P. 944 Nikander, "Using the Encapsulating 945 Security Payload (ESP) Transport Format 946 with the Host Identity Protocol (HIP)", 947 RFC 5202, April 2008. 949 10.2. Informative references 951 [RFC5204] Laganier, J. and L. Eggert, "Host 952 Identity Protocol (HIP) Rendezvous 953 Extension", RFC 5204, April 2008. 955 [RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: 956 Level 3 Multihoming Shim Protocol for 957 IPv6", RFC 5533, June 2009. 959 Appendix A. Document Revision History 961 To be removed upon publication 963 +----------+--------------------------------------------------------+ 964 | Revision | Comments | 965 +----------+--------------------------------------------------------+ 966 | draft-00 | Initial version with multihoming text imported from | 967 | | RFC5206. | 968 | draft-01 | Document refresh; no other changes. | 969 | draft-02 | Document refresh; no other changes. | 970 | draft-03 | Document refresh; no other changes. | 971 +----------+--------------------------------------------------------+ 973 Authors' Addresses 975 Thomas R. Henderson (editor) 976 The Boeing Company 977 P.O. Box 3707 978 Seattle, WA 979 USA 981 EMail: thomas.r.henderson@boeing.com 982 Christian Vogt 983 Ericsson Research NomadicLab 984 Hirsalantie 11 985 JORVAS FIN-02420 986 FINLAND 988 Phone: 989 EMail: christian.vogt@ericsson.com 991 Jari Arkko 992 Ericsson Research NomadicLab 993 JORVAS FIN-02420 994 FINLAND 996 Phone: +358 40 5079256 997 EMail: jari.arkko@ericsson.com