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Arkko 6 Expires: November 6, 2016 Ericsson Research NomadicLab 7 May 5, 2016 9 Host Mobility with the Host Identity Protocol 10 draft-ietf-hip-rfc5206-bis-11 12 Abstract 14 This document defines mobility extensions to the Host Identity 15 Protocol (HIP). Specifically, this document defines a general 16 "LOCATOR_SET" parameter for HIP messages that allows for a HIP host 17 to notify peers about alternate addresses at which it may be reached. 18 This document also defines elements of procedure for mobility of a 19 HIP host -- the process by which a host dynamically changes the 20 primary locator that it uses to receive packets. While the same 21 LOCATOR_SET parameter can also be used to support end-host 22 multihoming, detailed procedures are out of scope for this document. 23 This document obsoletes RFC 5206. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on November 6, 2016. 42 Copyright Notice 44 Copyright (c) 2016 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 This document may contain material from IETF Documents or IETF 58 Contributions published or made publicly available before November 59 10, 2008. The person(s) controlling the copyright in some of this 60 material may not have granted the IETF Trust the right to allow 61 modifications of such material outside the IETF Standards Process. 62 Without obtaining an adequate license from the person(s) controlling 63 the copyright in such materials, this document may not be modified 64 outside the IETF Standards Process, and derivative works of it may 65 not be created outside the IETF Standards Process, except to format 66 it for publication as an RFC or to translate it into languages other 67 than English. 69 Table of Contents 71 1. Introduction and Scope . . . . . . . . . . . . . . . . . . . 3 72 2. Terminology and Conventions . . . . . . . . . . . . . . . . . 4 73 3. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . 5 74 3.1. Operating Environment . . . . . . . . . . . . . . . . . . 5 75 3.1.1. Locator . . . . . . . . . . . . . . . . . . . . . . . 8 76 3.1.2. Mobility Overview . . . . . . . . . . . . . . . . . . 8 77 3.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 9 78 3.2.1. Mobility with a Single SA Pair (No Rekeying) . . . . 9 79 3.2.2. Mobility with a Single SA Pair (Mobile-Initiated 80 Rekey) . . . . . . . . . . . . . . . . . . . . . . . 11 81 3.2.3. Mobility messaging through rendezvous server . . . . 11 82 3.2.4. Network Renumbering . . . . . . . . . . . . . . . . . 13 83 3.3. Other Considerations . . . . . . . . . . . . . . . . . . 13 84 3.3.1. Address Verification . . . . . . . . . . . . . . . . 13 85 3.3.2. Credit-Based Authorization . . . . . . . . . . . . . 13 86 3.3.3. Preferred Locator . . . . . . . . . . . . . . . . . . 15 87 4. LOCATOR_SET Parameter Format . . . . . . . . . . . . . . . . 15 88 4.1. Traffic Type and Preferred Locator . . . . . . . . . . . 16 89 4.2. Locator Type and Locator . . . . . . . . . . . . . . . . 17 90 4.3. UPDATE Packet with Included LOCATOR_SET . . . . . . . . . 17 91 5. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 17 92 5.1. Locator Data Structure and Status . . . . . . . . . . . . 18 93 5.2. Sending LOCATOR_SETs . . . . . . . . . . . . . . . . . . 19 94 5.3. Handling Received LOCATOR_SETs . . . . . . . . . . . . . 20 95 5.4. Verifying Address Reachability . . . . . . . . . . . . . 22 96 5.5. Changing the Preferred Locator . . . . . . . . . . . . . 23 97 5.6. Credit-Based Authorization . . . . . . . . . . . . . . . 24 98 5.6.1. Handling Payload Packets . . . . . . . . . . . . . . 24 99 5.6.2. Credit Aging . . . . . . . . . . . . . . . . . . . . 26 100 6. Security Considerations . . . . . . . . . . . . . . . . . . . 27 101 6.1. Impersonation Attacks . . . . . . . . . . . . . . . . . . 28 102 6.2. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 29 103 6.2.1. Flooding Attacks . . . . . . . . . . . . . . . . . . 29 104 6.2.2. Memory/Computational-Exhaustion DoS Attacks . . . . . 29 105 6.3. Mixed Deployment Environment . . . . . . . . . . . . . . 30 106 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 107 8. Authors and Acknowledgments . . . . . . . . . . . . . . . . . 31 108 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 109 9.1. Normative references . . . . . . . . . . . . . . . . . . 31 110 9.2. Informative references . . . . . . . . . . . . . . . . . 32 111 Appendix A. Document Revision History . . . . . . . . . . . . . 33 112 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 114 1. Introduction and Scope 116 The Host Identity Protocol [RFC7401] (HIP) supports an architecture 117 that decouples the transport layer (TCP, UDP, etc.) from the 118 internetworking layer (IPv4 and IPv6) by using public/private key 119 pairs, instead of IP addresses, as host identities. When a host uses 120 HIP, the overlying protocol sublayers (e.g., transport layer sockets 121 and Encapsulating Security Payload (ESP) Security Associations (SAs)) 122 are instead bound to representations of these host identities, and 123 the IP addresses are only used for packet forwarding. However, each 124 host must also know at least one IP address at which its peers are 125 reachable. Initially, these IP addresses are the ones used during 126 the HIP base exchange. 128 One consequence of such a decoupling is that new solutions to 129 network-layer mobility and host multihoming are possible. There are 130 potentially many variations of mobility and multihoming possible. 131 The scope of this document encompasses messaging and elements of 132 procedure for basic network-level host mobility, leaving more 133 complicated mobility scenarios, multihoming, and other variations for 134 further study. More specifically: 136 This document defines a generalized LOCATOR_SET parameter for use 137 in HIP messages. The LOCATOR_SET parameter allows a HIP host to 138 notify a peer about alternate locators at which it is reachable. 139 The locators may be merely IP addresses, or they may have 140 additional multiplexing and demultiplexing context to aid with the 141 packet handling in the lower layers. For instance, an IP address 142 may need to be paired with an ESP Security Parameter Index (SPI) 143 so that packets are sent on the correct SA for a given address. 145 This document also specifies the messaging and elements of 146 procedure for end-host mobility of a HIP host -- the sequential 147 change in the preferred IP address used to reach a host. In 148 particular, message flows to enable successful host mobility, 149 including address verification methods, are defined herein. 151 However, while the same LOCATOR_SET parameter is intended to 152 support host multihoming (simultaneous use of a number of 153 addresses), detailed elements of procedure for host multihoming 154 are out of scope. 156 While HIP can potentially be used with transports other than the ESP 157 transport format [RFC7402], this document largely assumes the use of 158 ESP and leaves other transport formats for further study. 160 There are a number of situations where the simple end-to-end 161 readdressing functionality is not sufficient. These include the 162 initial reachability of a mobile host, location privacy, simultaneous 163 mobility of both hosts, and some modes of NAT traversal. In these 164 situations, there is a need for some helper functionality in the 165 network, such as a HIP rendezvous server [I-D.ietf-hip-rfc5204-bis]. 166 Use of the HIP rendezvous server to manage the simultaneous mobility 167 of both hosts is specified herein, but other such scenarios are out 168 of scope for this document. We also do not consider localized 169 mobility management extensions (i.e., mobility management techniques 170 that do not involve directly signaling the correspondent node); this 171 document is concerned with end-to-end mobility. Making underlying IP 172 mobility transparent to the transport layer has implications on the 173 proper response of transport congestion control, path MTU selection, 174 and Quality of Service (QoS). Transport-layer mobility triggers, and 175 the proper transport response to a HIP mobility or multihoming 176 address change, are outside the scope of this document. 178 2. Terminology and Conventions 180 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 181 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 182 document are to be interpreted as described in RFC 2119 [RFC2119]. 184 LOCATOR_SET. The name of a HIP parameter containing zero or more 185 Locator fields. 187 Locator. A name that controls how the packet is routed through the 188 network and demultiplexed by the end host. It may include a 189 concatenation of traditional network addresses such as an IPv6 190 address and end-to-end identifiers such as an ESP SPI. It may 191 also include transport port numbers or IPv6 Flow Labels as 192 demultiplexing context, or it may simply be a network address. 194 Address. A name that denotes a point-of-attachment to the network. 195 The two most common examples are an IPv4 address and an IPv6 196 address. The set of possible addresses is a subset of the set of 197 possible locators. 199 Preferred locator. A locator on which a host prefers to receive 200 data. With respect to a given peer, a host always has one active 201 Preferred locator, unless there are no active locators. By 202 default, the locators used in the HIP base exchange are the 203 Preferred locators. 205 Credit Based Authorization. A host must verify a peer host's 206 reachability at a new locator. Credit-Based Authorization 207 authorizes the peer to receive a certain amount of data at the new 208 locator before the result of such verification is known. 210 3. Protocol Model 212 This section is an overview; more detailed specification follows this 213 section. 215 3.1. Operating Environment 217 The Host Identity Protocol (HIP) [RFC7401] is a key establishment and 218 parameter negotiation protocol. Its primary applications are for 219 authenticating host messages based on host identities, and 220 establishing security associations (SAs) for the ESP transport format 221 [RFC7402] and possibly other protocols in the future. 223 +--------------------+ +--------------------+ 224 | | | | 225 | +------------+ | | +------------+ | 226 | | Key | | HIP | | Key | | 227 | | Management | <-+-----------------------+-> | Management | | 228 | | Process | | | | Process | | 229 | +------------+ | | +------------+ | 230 | ^ | | ^ | 231 | | | | | | 232 | v | | v | 233 | +------------+ | | +------------+ | 234 | | IPsec | | ESP | | IPsec | | 235 | | Stack | <-+-----------------------+-> | Stack | | 236 | | | | | | | | 237 | +------------+ | | +------------+ | 238 | | | | 239 | | | | 240 | Initiator | | Responder | 241 +--------------------+ +--------------------+ 243 Figure 1: HIP Deployment Model 245 The general deployment model for HIP is shown above, assuming 246 operation in an end-to-end fashion. This document specifies 247 extensions to the HIP protocol to enable end-host mobility and 248 multihoming. In summary, these extensions to the HIP base protocol 249 enable the signaling of new addressing information to the peer in HIP 250 messages. The messages are authenticated via a signature or keyed 251 hash message authentication code (HMAC) based on its Host Identity. 252 This document specifies the format of this new addressing 253 (LOCATOR_SET) parameter, the procedures for sending and processing 254 this parameter to enable basic host mobility, and procedures for a 255 concurrent address verification mechanism. 257 --------- 258 | TCP | (sockets bound to HITs) 259 --------- 260 | 261 --------- 262 ----> | ESP | {HIT_s, HIT_d} <-> SPI 263 | --------- 264 | | 265 ---- --------- 266 | MH |-> | HIP | {HIT_s, HIT_d, SPI} <-> {IP_s, IP_d, SPI} 267 ---- --------- 268 | 269 --------- 270 | IP | 271 --------- 273 Figure 2: Architecture for HIP Host Mobility (MH) 275 Figure 2 depicts a layered architectural view of a HIP-enabled stack 276 using the ESP transport format. In HIP, upper-layer protocols 277 (including TCP and ESP in this figure) are bound to Host Identity 278 Tags (HITs) and not IP addresses. The HIP sublayer is responsible 279 for maintaining the binding between HITs and IP addresses. The SPI 280 is used to associate an incoming packet with the right HITs. The 281 block labeled "MH" is introduced below. 283 Consider first the case in which there is no mobility or multihoming, 284 as specified in the base protocol specification [RFC7401]. The HIP 285 base exchange establishes the HITs in use between the hosts, the SPIs 286 to use for ESP, and the IP addresses (used in both the HIP signaling 287 packets and ESP data packets). Note that there can only be one such 288 set of bindings in the outbound direction for any given packet, and 289 the only fields used for the binding at the HIP layer are the fields 290 exposed by ESP (the SPI and HITs). For the inbound direction, the 291 SPI is all that is required to find the right host context. ESP 292 rekeying events change the mapping between the HIT pair and SPI, but 293 do not change the IP addresses. 295 Consider next a mobility event, in which a host moves to another IP 296 address. Two things must occur in this case. First, the peer must 297 be notified of the address change using a HIP UPDATE message. 298 Second, each host must change its local bindings at the HIP sublayer 299 (new IP addresses). It may be that both the SPIs and IP addresses 300 are changed simultaneously in a single UPDATE; the protocol described 301 herein supports this. Although internal notification of transport 302 layer protocols regarding the path change (e.g. to reset congestion 303 control variables) may be desired, this specification does not 304 address such internal notification. In addition, elements of 305 procedure for traversing middleboxes, including network address 306 translators, may complicate the above basic scenario and are not 307 covered by this document. 309 3.1.1. Locator 311 This document defines a generalization of an address called a 312 "locator". A locator specifies a point-of-attachment to the network 313 but may also include additional end-to-end tunneling or per-host 314 demultiplexing context that affects how packets are handled below the 315 logical HIP sublayer of the stack. This generalization is useful 316 because IP addresses alone may not be sufficient to describe how 317 packets should be handled below HIP. For example, in a host 318 multihoming context, certain IP addresses may need to be associated 319 with certain ESP SPIs to avoid violating the ESP anti-replay window. 320 Addresses may also be affiliated with transport ports in certain 321 tunneling scenarios. Locators may simply be traditional network 322 addresses. The format of the locator fields in the LOCATOR_SET 323 parameter is defined in Section 4. 325 3.1.2. Mobility Overview 327 When a host moves to another address, it notifies its peer of the new 328 address by sending a HIP UPDATE packet containing a LOCATOR_SET 329 parameter. This UPDATE packet is acknowledged by the peer. For 330 reliability in the presence of packet loss, the UPDATE packet is 331 retransmitted as defined in the HIP protocol specification [RFC7401]. 332 The peer can authenticate the contents of the UPDATE packet based on 333 the signature and keyed hash of the packet. 335 When using ESP Transport Format [RFC7402], the host may at the same 336 time decide to rekey its security association and possibly generate a 337 new Diffie-Hellman key; all of these actions are triggered by 338 including additional parameters in the UPDATE packet, as defined in 339 the base protocol specification [RFC7401] and ESP extension 340 [RFC7402]. 342 When using ESP (and possibly other transport modes in the future), 343 the host is able to receive packets that are protected using a HIP 344 created ESP SA from any address. Thus, a host can change its IP 345 address and continue to send packets to its peers without necessarily 346 rekeying. However, the peers are not able to send packets to these 347 new addresses before they can reliably and securely update the set of 348 addresses that they associate with the sending host. Furthermore, 349 mobility may change the path characteristics in such a manner that 350 reordering occurs and packets fall outside the ESP anti-replay window 351 for the SA, thereby requiring rekeying. 353 3.2. Protocol Overview 355 In this section, we briefly introduce a number of usage scenarios for 356 HIP host mobility. These scenarios assume that HIP is being used 357 with the ESP transform [RFC7402], although other scenarios may be 358 defined in the future. To understand these usage scenarios, the 359 reader should be at least minimally familiar with the HIP protocol 360 specification [RFC7401]. However, for the (relatively) uninitiated 361 reader, it is most important to keep in mind that in HIP the actual 362 payload traffic is protected with ESP, and that the ESP SPI acts as 363 an index to the right host-to-host context. More specification 364 details are found later in Section 4 and Section 5. 366 The scenarios below assume that the two hosts have completed a single 367 HIP base exchange with each other. Both of the hosts therefore have 368 one incoming and one outgoing SA. Further, each SA uses the same 369 pair of IP addresses, which are the ones used in the base exchange. 371 The readdressing protocol is an asymmetric protocol where a mobile 372 host informs a peer host about changes of IP addresses on affected 373 SPIs. The readdressing exchange is designed to be piggybacked on 374 existing HIP exchanges. The majority of the packets on which the 375 LOCATOR_SET parameters are expected to be carried are UPDATE packets. 377 The scenarios below at times describe addresses as being in either an 378 ACTIVE, UNVERIFIED, or DEPRECATED state. From the perspective of a 379 host, newly-learned addresses of the peer must be verified before put 380 into active service, and addresses removed by the peer are put into a 381 deprecated state. Under limited conditions described below 382 (Section 5.6), an UNVERIFIED address may be used. The addressing 383 states are defined more formally in Section 5.1. 385 Hosts that use link-local addresses as source addresses in their HIP 386 handshakes may not be reachable by a mobile peer. Such hosts SHOULD 387 provide a globally routable address either in the initial handshake 388 or via the LOCATOR_SET parameter. 390 3.2.1. Mobility with a Single SA Pair (No Rekeying) 392 A mobile host must sometimes change an IP address bound to an 393 interface. The change of an IP address might be needed due to a 394 change in the advertised IPv6 prefixes on the link, a reconnected PPP 395 link, a new DHCP lease, or an actual movement to another subnet. In 396 order to maintain its communication context, the host must inform its 397 peers about the new IP address. This first example considers the 398 case in which the mobile host has only one interface, one IP address 399 in use within the HIP session, a single pair of SAs (one inbound, one 400 outbound), and no rekeying occurs on the SAs. We also assume that 401 the new IP addresses are within the same address family (IPv4 or 402 IPv6) as the first address. This is the simplest scenario, depicted 403 in Figure 3. 405 Mobile Host Peer Host 407 UPDATE(ESP_INFO, LOCATOR_SET, SEQ) 408 -----------------------------------> 409 UPDATE(ESP_INFO, SEQ, ACK, ECHO_REQUEST) 410 <----------------------------------- 411 UPDATE(ACK, ECHO_RESPONSE) 412 -----------------------------------> 414 Figure 3: Readdress without Rekeying, but with Address Check 416 The steps of the packet processing are as follows: 418 1. The mobile host may be disconnected from the peer host for a 419 brief period of time while it switches from one IP address to 420 another; this case is sometimes referred to in the literature as 421 a "break-before-make" case. The host may also obtain its new IP 422 address before loosing the old one ("make-before-break" case). 423 In either case, upon obtaining a new IP address, the mobile host 424 sends a LOCATOR_SET parameter to the peer host in an UPDATE 425 message. The UPDATE message also contains an ESP_INFO parameter 426 containing the values of the old and new SPIs for a security 427 association. In this case, the OLD SPI and NEW SPI parameters 428 both are set to the value of the preexisting incoming SPI; this 429 ESP_INFO does not trigger a rekeying event but is instead 430 included for possible parameter-inspecting middleboxes on the 431 path. The LOCATOR_SET parameter contains the new IP address 432 (Locator Type of "1", defined below) and a locator lifetime. The 433 mobile host waits for this UPDATE to be acknowledged, and 434 retransmits if necessary, as specified in the base specification 435 [RFC7401]. 437 2. The peer host receives the UPDATE, validates it, and updates any 438 local bindings between the HIP association and the mobile host's 439 destination address. The peer host MUST perform an address 440 verification by placing a nonce in the ECHO_REQUEST parameter of 441 the UPDATE message sent back to the mobile host. It also 442 includes an ESP_INFO parameter with the OLD SPI and NEW SPI 443 parameters both set to the value of the preexisting incoming SPI, 444 and sends this UPDATE (with piggybacked acknowledgment) to the 445 mobile host at its new address. The peer MAY use the new address 446 immediately, but it MUST limit the amount of data it sends to the 447 address until address verification completes. 449 3. The mobile host completes the readdress by processing the UPDATE 450 ACK and echoing the nonce in an ECHO_RESPONSE. Once the peer 451 host receives this ECHO_RESPONSE, it considers the new address to 452 be verified and can put the address into full use. 454 While the peer host is verifying the new address, the new address is 455 marked as UNVERIFIED in the interim, and the old address is 456 DEPRECATED. Once the peer host has received a correct reply to its 457 UPDATE challenge, it marks the new address as ACTIVE and removes the 458 old address. 460 3.2.2. Mobility with a Single SA Pair (Mobile-Initiated Rekey) 462 The mobile host may decide to rekey the SAs at the same time that it 463 notifies the peer of the new address. In this case, the above 464 procedure described in Figure 3 is slightly modified. The UPDATE 465 message sent from the mobile host includes an ESP_INFO with the OLD 466 SPI set to the previous SPI, the NEW SPI set to the desired new SPI 467 value for the incoming SA, and the KEYMAT Index desired. Optionally, 468 the host may include a DIFFIE_HELLMAN parameter for a new Diffie- 469 Hellman key. The peer completes the request for a rekey as is 470 normally done for HIP rekeying, except that the new address is kept 471 as UNVERIFIED until the UPDATE nonce challenge is received as 472 described above. Figure 4 illustrates this scenario. 474 Mobile Host Peer Host 476 UPDATE(ESP_INFO, LOCATOR_SET, SEQ, [DIFFIE_HELLMAN]) 477 -----------------------------------> 478 UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) 479 <----------------------------------- 480 UPDATE(ACK, ECHO_RESPONSE) 481 -----------------------------------> 483 Figure 4: Readdress with Mobile-Initiated Rekey 485 3.2.3. Mobility messaging through rendezvous server 487 Section 6.11 of [RFC7401] specifies procedures for sending HIP UPDATE 488 packets. The UPDATE packets are protected by a timer subject to 489 exponential backoff and resent UPDATE_RETRY_MAX times. It may be, 490 however, that the peer is itself in the process of moving when the 491 local host is trying to update the IP address bindings of the HIP 492 association. This is sometimes called the "double-jump" mobility 493 problem; each host's UPDATE packets are simultaneously sent to a 494 stale address of the peer, and the hosts are no longer reachable from 495 one another. 497 The HIP Rendezvous Extension [I-D.ietf-hip-rfc5204-bis] specifies a 498 rendezvous service that permits the I1 packet from the base exchange 499 to be relayed from a stable or well-known public IP address location 500 to the current IP address of the host. It is possible to support 501 double-jump mobility with this rendezvous service if the following 502 extensions to the specifications of [I-D.ietf-hip-rfc5204-bis] and 503 [RFC7401] are followed. 505 1. The mobile host sending an UPDATE to the peer, and not receiving 506 an ACK, MAY resend the UPDATE to a rendezvous server (RVS) of the 507 peer, if such a server is known. The host may try the RVS of the 508 peer up to UPDATE_RETRY_MAX times as specified in [RFC7401]. The 509 host may try to use the peer's RVS before it has tried 510 UPDATE_RETRY_MAX times to the last working address (i.e. the RVS 511 may be tried in parallel with retries to the last working 512 address). 514 2. A rendezvous server supporting the UPDATE forwarding extensions 515 specified herein MUST modify the UPDATE in the same manner as it 516 modifies the I1 packet before forwarding. Specifically, it MUST 517 rewrite the IP header source and destination addresses, recompute 518 the IP header checksum, and include the FROM and RVS_HMAC 519 parameters. 521 3. A host receiving an UPDATE packet MUST be prepared to process the 522 FROM and RVS_HMAC parameters, and MUST include a VIA_RVS 523 parameter in the UPDATE reply that contains the ACK of the UPDATE 524 SEQ. 526 4. An initiator receiving a VIA_RVS in the UPDATE reply should 527 initiate address reachability tests (described later in this 528 document) towards the end host's address and not towards the 529 address included in the VIA_RVS. 531 This scenario requires that hosts using rendezvous servers also take 532 steps to update their current address bindings with their rendezvous 533 server upon a mobility event. [I-D.ietf-hip-rfc5204-bis] does not 534 specify how to update the rendezvous server with a client host's new 535 address. [I-D.ietf-hip-rfc5203-bis] Section 3.2 describes how a host 536 may send a REG_REQUEST in either an I2 packet (if there is no active 537 association) or an UPDATE packet (if such association exists). 538 According to procedures described in [I-D.ietf-hip-rfc5203-bis], if a 539 mobile host has an active registration, it may use mobility updates 540 specified herein, within the context of that association, to 541 readdress the association. 543 3.2.4. Network Renumbering 545 It is expected that IPv6 networks will be renumbered much more often 546 than most IPv4 networks. From an end-host point of view, network 547 renumbering is similar to mobility, and procedures described herein 548 also apply to notify a peer of a changed address. 550 3.3. Other Considerations 552 3.3.1. Address Verification 554 When a HIP host receives a set of locators from another HIP host in a 555 LOCATOR_SET, it does not necessarily know whether the other host is 556 actually reachable at the claimed addresses. In fact, a malicious 557 peer host may be intentionally giving bogus addresses in order to 558 cause a packet flood towards the target addresses [RFC4225]. 559 Therefore, the HIP host must first check that the peer is reachable 560 at the new address. 562 Address verification is implemented by the challenger sending some 563 piece of unguessable information to the new address, and waiting for 564 some acknowledgment from the Responder that indicates reception of 565 the information at the new address. This may include the exchange of 566 a nonce, or the generation of a new SPI and observation of data 567 arriving on the new SPI. 569 An additional potential benefit of performing address verification is 570 to allow middleboxes in the network along the new path to obtain the 571 peer host's inbound SPI. 573 3.3.2. Credit-Based Authorization 575 Credit-Based Authorization (CBA) allows a host to securely use a new 576 locator even though the peer's reachability at the address embedded 577 in the locator has not yet been verified. This is accomplished based 578 on the following three hypotheses: 580 1. A flooding attacker typically seeks to somehow multiply the 581 packets it generates for the purpose of its attack because 582 bandwidth is an ample resource for many victims. 584 2. An attacker can often cause unamplified flooding by sending 585 packets to its victim, either by directly addressing the victim 586 in the packets, or by guiding the packets along a specific path 587 by means of an IPv6 Routing header, if Routing headers are not 588 filtered by firewalls. 590 3. Consequently, the additional effort required to set up a 591 redirection-based flooding attack (without CBA and return 592 routability checks) would pay off for the attacker only if 593 amplification could be obtained this way. 595 On this basis, rather than eliminating malicious packet redirection 596 in the first place, Credit-Based Authorization prevents 597 amplifications. This is accomplished by limiting the data a host can 598 send to an unverified address of a peer by the data recently received 599 from that peer. Redirection-based flooding attacks thus become less 600 attractive than, for example, pure direct flooding, where the 601 attacker itself sends bogus packets to the victim. 603 Figure 5 illustrates Credit-Based Authorization: Host B measures the 604 amount of data recently received from peer A and, when A readdresses, 605 sends packets to A's new, unverified address as long as the sum of 606 the packet sizes does not exceed the measured, received data volume. 607 When insufficient credit is left, B stops sending further packets to 608 A until A's address becomes ACTIVE. The address changes may be due 609 to mobility, multihoming, or any other reason. Not shown in Figure 5 610 are the results of credit aging (Section 5.6.2), a mechanism used to 611 dampen possible time-shifting attacks. 613 +-------+ +-------+ 614 | A | | B | 615 +-------+ +-------+ 616 | | 617 address |------------------------------->| credit += size(packet) 618 ACTIVE | | 619 |------------------------------->| credit += size(packet) 620 |<-------------------------------| do not change credit 621 | | 622 + address change | 623 + address verification starts | 624 address |<-------------------------------| credit -= size(packet) 625 UNVERIFIED |------------------------------->| credit += size(packet) 626 |<-------------------------------| credit -= size(packet) 627 | | 628 |<-------------------------------| credit -= size(packet) 629 | X credit < size(packet) 630 | | => do not send packet! 631 + address verification concludes | 632 address | | 633 ACTIVE |<-------------------------------| do not change credit 634 | | 636 Figure 5: Readdressing Scenario 638 3.3.3. Preferred Locator 640 When a host has multiple locators, the peer host must decide which to 641 use for outbound packets. It may be that a host would prefer to 642 receive data on a particular inbound interface. HIP allows a 643 particular locator to be designated as a Preferred locator and 644 communicated to the peer (see Section 4). 646 4. LOCATOR_SET Parameter Format 648 The LOCATOR_SET parameter is a critical parameter as defined by 649 [RFC7401]. It consists of the standard HIP parameter Type and Length 650 fields, plus zero or more Locator sub-parameters. Each Locator sub- 651 parameter contains a Traffic Type, Locator Type, Locator Length, 652 Preferred locator bit, Locator Lifetime, and a Locator encoding. A 653 LOCATOR_SET containing zero Locator fields is permitted but has the 654 effect of deprecating all addresses. 656 0 1 2 3 657 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 658 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 659 | Type | Length | 660 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 661 | Traffic Type | Locator Type | Locator Length | Reserved |P| 662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 663 | Locator Lifetime | 664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 665 | Locator | 666 | | 667 | | 668 | | 669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 670 . . 671 . . 672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 673 | Traffic Type | Locator Type | Locator Length | Reserved |P| 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 675 | Locator Lifetime | 676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 677 | Locator | 678 | | 679 | | 680 | | 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 Figure 6: LOCATOR_SET Parameter Format 685 Type: 193 687 Length: Length in octets, excluding Type and Length fields, and 688 excluding padding. 690 Traffic Type: Defines whether the locator pertains to HIP signaling, 691 user data, or both. 693 Locator Type: Defines the semantics of the Locator field. 695 Locator Length: Defines the length of the Locator field, in units of 696 4-byte words (Locators up to a maximum of 4*255 octets are 697 supported). 699 Reserved: Zero when sent, ignored when received. 701 P: Preferred locator. Set to one if the locator is preferred for 702 that Traffic Type; otherwise, set to zero. 704 Locator Lifetime: Locator lifetime, in seconds. 706 Locator: The locator whose semantics and encoding are indicated by 707 the Locator Type field. All Locator sub-fields are integral 708 multiples of four octets in length. 710 The Locator Lifetime indicates how long the following locator is 711 expected to be valid. The lifetime is expressed in seconds. Each 712 locator MUST have a non-zero lifetime. The address is expected to 713 become deprecated when the specified number of seconds has passed 714 since the reception of the message. A deprecated address SHOULD NOT 715 be used as a destination address if an alternate (non-deprecated) is 716 available and has sufficient scope. 718 4.1. Traffic Type and Preferred Locator 720 The following Traffic Type values are defined: 722 0: Both signaling (HIP control packets) and user data. 724 1: Signaling packets only. 726 2: Data packets only. 728 The "P" bit, when set, has scope over the corresponding Traffic Type. 729 That is, when a "P" bit is set for Traffic Type "2", for example, it 730 means that the locator is preferred for data packets. If there is a 731 conflict (for example, if the "P" bit is set for an address of Type 732 "0" and a different address of Type "2"), the more specific Traffic 733 Type rule applies (in this case, "2"). By default, the IP addresses 734 used in the base exchange are Preferred locators for both signaling 735 and user data, unless a new Preferred locator supersedes them. If no 736 locators are indicated as preferred for a given Traffic Type, the 737 implementation may use an arbitrary destination locator from the set 738 of active locators. 740 4.2. Locator Type and Locator 742 The following Locator Type values are defined, along with the 743 associated semantics of the Locator field: 745 0: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [RFC4291] 746 (128 bits long). This locator type is defined primarily for non- 747 ESP-based usage. 749 1: The concatenation of an ESP SPI (first 32 bits) followed by an 750 IPv6 address or an IPv4-in-IPv6 format IPv4 address (an additional 751 128 bits). This IP address is defined primarily for ESP-based 752 usage. 754 4.3. UPDATE Packet with Included LOCATOR_SET 756 A number of combinations of parameters in an UPDATE packet are 757 possible (e.g., see Section 3.2). In this document, procedures are 758 defined only for the case in which one LOCATOR_SET and one ESP_INFO 759 parameter is used in any HIP packet. Any UPDATE packet that includes 760 a LOCATOR_SET parameter SHOULD include both an HMAC and a 761 HIP_SIGNATURE parameter. 763 The UPDATE MAY also include a HOST_ID parameter (which may be useful 764 for middleboxes inspecting the HIP messages for the first time). If 765 the UPDATE includes the HOST_ID parameter, the receiving host MUST 766 verify that the HOST_ID corresponds to the HOST_ID that was used to 767 establish the HIP association, and the HIP_SIGNATURE must verify with 768 the public key associated with this HOST_ID parameter. 770 The relationship between the announced Locators and any ESP_INFO 771 parameters present in the packet is defined in Section 5.2. This 772 document does not support any elements of procedure for sending more 773 than one LOCATOR_SET or ESP_INFO parameter in a single UPDATE. 775 5. Processing Rules 777 This section describes rules for sending and receiving the 778 LOCATOR_SET parameter, testing address reachability, and using 779 Credit-Based Authorization (CBA) on UNVERIFIED locators. 781 5.1. Locator Data Structure and Status 783 In a typical implementation, each locator announced in a LOCATOR_SET 784 parameter is represented by a piece of state that contains the 785 following data: 787 o the actual bit pattern representing the locator, 789 o the lifetime (seconds), 791 o the status (UNVERIFIED, ACTIVE, DEPRECATED), 793 o the Traffic Type scope of the locator, and 795 o whether the locator is preferred for any particular scope. 797 The status is used to track the reachability of the address embedded 798 within the LOCATOR_SET parameter: 800 UNVERIFIED indicates that the reachability of the address has not 801 been verified yet, 803 ACTIVE indicates that the reachability of the address has been 804 verified and the address has not been deprecated, 806 DEPRECATED indicates that the locator lifetime has expired. 808 The following state changes are allowed: 810 UNVERIFIED to ACTIVE The reachability procedure completes 811 successfully. 813 UNVERIFIED to DEPRECATED The locator lifetime expires while the 814 locator is UNVERIFIED. 816 ACTIVE to DEPRECATED The locator lifetime expires while the locator 817 is ACTIVE. 819 ACTIVE to UNVERIFIED There has been no traffic on the address for 820 some time, and the local policy mandates that the address 821 reachability must be verified again before starting to use it 822 again. 824 DEPRECATED to UNVERIFIED The host receives a new lifetime for the 825 locator. 827 A DEPRECATED address MUST NOT be changed to ACTIVE without first 828 verifying its reachability. 830 Note that the state of whether or not a locator is preferred is not 831 necessarily the same as the value of the Preferred bit in the Locator 832 sub-parameter received from the peer. Peers may recommend certain 833 locators to be preferred, but the decision on whether to actually use 834 a locator as a preferred locator is a local decision, possibly 835 influenced by local policy. 837 In addition to state maintained about status and remaining lifetime 838 for each locator learned from the peer, an implementation would 839 typically maintain similar state about its own locators that have 840 been offered to the peer. 842 Finally, the locators used to establish the HIP association are by 843 default assumed to be the initial preferred locators in ACTIVE state, 844 with an unbounded lifetime. 846 5.2. Sending LOCATOR_SETs 848 The decision of when to send LOCATOR_SETs is basically a local policy 849 issue. However, it is RECOMMENDED that a host send a LOCATOR_SET 850 whenever it recognizes a change of its IP addresses in use on an 851 active HIP association, and assumes that the change is going to last 852 at least for a few seconds. Rapidly sending LOCATOR_SETs that force 853 the peer to change the preferred address SHOULD be avoided. 855 We now describe a few cases introduced in Section 3.2. We assume 856 that the Traffic Type for each locator is set to "0" (other values 857 for Traffic Type may be specified in documents that separate the HIP 858 control plane from data plane traffic). Other mobility cases are 859 possible but are left for further study. 861 1. Host mobility with no multihoming and no rekeying. The mobile 862 host creates a single UPDATE containing a single ESP_INFO with a 863 single LOCATOR_SET parameter. The ESP_INFO contains the current 864 value of the SPI in both the OLD SPI and NEW SPI fields. The 865 LOCATOR_SET contains a single Locator with a "Locator Type" of 866 "1"; the SPI must match that of the ESP_INFO. The Preferred bit 867 SHOULD be set and the "Locator Lifetime" is set according to 868 local policy. The UPDATE also contains a SEQ parameter as usual. 869 This packet is retransmitted as defined in the HIP protocol 870 specification [RFC7401]. The UPDATE should be sent to the peer's 871 preferred IP address with an IP source address corresponding to 872 the address in the LOCATOR_SET parameter. 874 2. Host mobility with no multihoming but with rekeying. The mobile 875 host creates a single UPDATE containing a single ESP_INFO with a 876 single LOCATOR_SET parameter (with a single address). The 877 ESP_INFO contains the current value of the SPI in the OLD SPI and 878 the new value of the SPI in the NEW SPI, and a KEYMAT Index as 879 selected by local policy. Optionally, the host may choose to 880 initiate a Diffie Hellman rekey by including a DIFFIE_HELLMAN 881 parameter. The LOCATOR_SET contains a single Locator with 882 "Locator Type" of "1"; the SPI must match that of the NEW SPI in 883 the ESP_INFO. Otherwise, the steps are identical to the case in 884 which no rekeying is initiated. 886 5.3. Handling Received LOCATOR_SETs 888 A host SHOULD be prepared to receive a single LOCATOR_SET parameter 889 in a HIP UPDATE packet. Reception of multiple LOCATOR_SET parameters 890 in a single packet, or in HIP packets other than UPDATE, is outside 891 of the scope of this specification. 893 This document describes sending both ESP_INFO and LOCATOR_SET 894 parameters in an UPDATE. The ESP_INFO parameter is included when 895 there is a need to rekey or key a new SPI, and is otherwise included 896 for the possible benefit of HIP-aware middleboxes. The LOCATOR_SET 897 parameter contains a complete listing of the locators that the host 898 wishes to make or keep active for the HIP association. 900 In general, the processing of a LOCATOR_SET depends upon the packet 901 type in which it is included. Here, we describe only the case in 902 which ESP_INFO is present and a single LOCATOR_SET and ESP_INFO are 903 sent in an UPDATE message; other cases are for further study. The 904 steps below cover each of the cases described in Section 5.2. 906 The processing of ESP_INFO and LOCATOR_SET parameters is intended to 907 be modular and support future generalization to the inclusion of 908 multiple ESP_INFO and/or multiple LOCATOR_SET parameters. A host 909 SHOULD first process the ESP_INFO before the LOCATOR_SET, since the 910 ESP_INFO may contain a new SPI value mapped to an existing SPI, while 911 a Type "1" locator will only contain a reference to the new SPI. 913 When a host receives a validated HIP UPDATE with a LOCATOR_SET and 914 ESP_INFO parameter, it processes the ESP_INFO as follows. The 915 ESP_INFO parameter indicates whether an SA is being rekeyed, created, 916 deprecated, or just identified for the benefit of middleboxes. The 917 host examines the OLD SPI and NEW SPI values in the ESP_INFO 918 parameter: 920 1. (no rekeying) If the OLD SPI is equal to the NEW SPI and both 921 correspond to an existing SPI, the ESP_INFO is gratuitous 922 (provided for middleboxes) and no rekeying is necessary. 924 2. (rekeying) If the OLD SPI indicates an existing SPI and the NEW 925 SPI is a different non-zero value, the existing SA is being 926 rekeyed and the host follows HIP ESP rekeying procedures by 927 creating a new outbound SA with an SPI corresponding to the NEW 928 SPI, with no addresses bound to this SPI. Note that locators in 929 the LOCATOR_SET parameter will reference this new SPI instead of 930 the old SPI. 932 3. (new SA) If the OLD SPI value is zero and the NEW SPI is a new 933 non-zero value, then a new SA is being requested by the peer. 934 This case is also treated like a rekeying event; the receiving 935 host must create a new SA and respond with an UPDATE ACK. 937 4. (deprecating the SA) If the OLD SPI indicates an existing SPI and 938 the NEW SPI is zero, the SA is being deprecated and all locators 939 uniquely bound to the SPI are put into the DEPRECATED state. 941 If none of the above cases apply, a protocol error has occurred and 942 the processing of the UPDATE is stopped. 944 Next, the locators in the LOCATOR_SET parameter are processed. For 945 each locator listed in the LOCATOR_SET parameter, check that the 946 address therein is a legal unicast or anycast address. That is, the 947 address MUST NOT be a broadcast or multicast address. Note that some 948 implementations MAY accept addresses that indicate the local host, 949 since it may be allowed that the host runs HIP with itself. 951 The below assumes that all locators are of Type "1" with a Traffic 952 Type of "0"; other cases are for further study. 954 For each Type "1" address listed in the LOCATOR_SET parameter, the 955 host checks whether the address is already bound to the SPI 956 indicated. If the address is already bound, its lifetime is updated. 957 If the status of the address is DEPRECATED, the status is changed to 958 UNVERIFIED. If the address is not already bound, the address is 959 added, and its status is set to UNVERIFIED. Mark all addresses 960 corresponding to the SPI that were NOT listed in the LOCATOR_SET 961 parameter as DEPRECATED. 963 As a result, at the end of processing, the addresses listed in the 964 LOCATOR_SET parameter have either a state of UNVERIFIED or ACTIVE, 965 and any old addresses on the old SA not listed in the LOCATOR_SET 966 parameter have a state of DEPRECATED. 968 Once the host has processed the locators, if the LOCATOR_SET 969 parameter contains a new Preferred locator, the host SHOULD initiate 970 a change of the Preferred locator. This requires that the host first 971 verifies reachability of the associated address, and only then 972 changes the Preferred locator; see Section 5.5. 974 If a host receives a locator with an unsupported Locator Type, and 975 when such a locator is also declared to be the Preferred locator for 976 the peer, the host SHOULD send a NOTIFY error with a Notify Message 977 Type of LOCATOR_TYPE_UNSUPPORTED, with the Notification Data field 978 containing the locator(s) that the receiver failed to process. 979 Otherwise, a host MAY send a NOTIFY error if a (non-preferred) 980 locator with an unsupported Locator Type is received in a LOCATOR_SET 981 parameter. 983 A host MAY add the source IP address of a received HIP packet as a 984 candidate locator for the peer even if it is not listed in the peer's 985 LOCATOR_SET, but it SHOULD prefer locators explicitly listed in the 986 LOCATOR_SET. 988 5.4. Verifying Address Reachability 990 A host MUST verify the reachability of an UNVERIFIED address. The 991 status of a newly learned address MUST initially be set to UNVERIFIED 992 unless the new address is advertised in a R1 packet as a new 993 Preferred locator. A host MAY also want to verify the reachability 994 of an ACTIVE address again after some time, in which case it would 995 set the status of the address to UNVERIFIED and reinitiate address 996 verification. 998 A host typically starts the address-verification procedure by sending 999 a nonce to the new address. A host MAY choose from different message 1000 exchanges or different nonce values so long as it establishes that 1001 the peer has received and replied to the nonce at the new address. 1002 For example, when the host is changing its SPI and sending an 1003 ESP_INFO to the peer, the NEW SPI value SHOULD be random and the 1004 random value MAY be copied into an ECHO_REQUEST sent in the rekeying 1005 UPDATE. However, if the host is not changing its SPI, it MAY still 1006 use the ECHO_REQUEST parameter for verification but with some other 1007 random value. A host MAY also use other message exchanges as 1008 confirmation of the address reachability. 1010 In some cases, it MAY be sufficient to use the arrival of data on a 1011 newly advertised SA as implicit address reachability verification as 1012 depicted in Figure 7, instead of waiting for the confirmation via a 1013 HIP packet. In this case, a host advertising a new SPI as part of 1014 its address reachability check SHOULD be prepared to receive traffic 1015 on the new SA. 1017 Mobile host Peer host 1019 prepare incoming SA 1020 NEW SPI in ESP_INFO (UPDATE) 1021 <----------------------------------- 1022 switch to new outgoing SA 1023 data on new SA 1024 -----------------------------------> 1025 mark address ACTIVE 1027 Figure 7: Address Activation Via Use of a New SA 1029 When address verification is in progress for a new Preferred locator, 1030 the host SHOULD select a different locator listed as ACTIVE, if one 1031 such locator is available, to continue communications until address 1032 verification completes. Alternatively, the host MAY use the new 1033 Preferred locator while in UNVERIFIED status to the extent Credit- 1034 Based Authorization permits. Credit-Based Authorization is explained 1035 in Section 5.6. Once address verification succeeds, the status of 1036 the new Preferred locator changes to ACTIVE. 1038 5.5. Changing the Preferred Locator 1040 A host MAY want to change the Preferred outgoing locator for 1041 different reasons, e.g., because traffic information or ICMP error 1042 messages indicate that the currently used preferred address may have 1043 become unreachable. Another reason may be due to receiving a 1044 LOCATOR_SET parameter that has the "P" bit set. 1046 To change the Preferred locator, the host initiates the following 1047 procedure: 1049 1. If the new Preferred locator has ACTIVE status, the Preferred 1050 locator is changed and the procedure succeeds. 1052 2. If the new Preferred locator has UNVERIFIED status, the host 1053 starts to verify its reachability. The host SHOULD use a 1054 different locator listed as ACTIVE until address verification 1055 completes if one such locator is available. Alternatively, the 1056 host MAY use the new Preferred locator, even though in UNVERIFIED 1057 status, to the extent Credit-Based Authorization permits. Once 1058 address verification succeeds, the status of the new Preferred 1059 locator changes to ACTIVE and its use is no longer governed by 1060 Credit-Based Authorization. 1062 3. If the peer host has not indicated a preference for any address, 1063 then the host picks one of the peer's ACTIVE addresses randomly 1064 or according to local policy. This case may arise if, for 1065 example, ICMP error messages that deprecate the Preferred locator 1066 arrive, but the peer has not yet indicated a new Preferred 1067 locator. 1069 4. If the new Preferred locator has DEPRECATED status and there is 1070 at least one non-deprecated address, the host selects one of the 1071 non-deprecated addresses as a new Preferred locator and 1072 continues. If the selected address is UNVERIFIED, the address 1073 verification procedure described above will apply. 1075 5.6. Credit-Based Authorization 1077 To prevent redirection-based flooding attacks, the use of a Credit- 1078 Based Authorization (CBA) approach MUST be used when a host sends 1079 data to an UNVERIFIED locator. The following algorithm meets the 1080 security considerations for prevention of amplification and time- 1081 shifting attacks. Other forms of credit aging, and other values for 1082 the CreditAgingFactor and CreditAgingInterval parameters in 1083 particular, are for further study, and so are the advanced CBA 1084 techniques specified in [CBA-MIPv6]. 1086 5.6.1. Handling Payload Packets 1088 A host maintains a "credit counter" for each of its peers. Whenever 1089 a packet arrives from a peer, the host SHOULD increase that peer's 1090 credit counter by the size of the received packet. When the host has 1091 a packet to be sent to the peer, and when the peer's Preferred 1092 locator is listed as UNVERIFIED and no alternative locator with 1093 status ACTIVE is available, the host checks whether it can send the 1094 packet to the UNVERIFIED locator. The packet SHOULD be sent if the 1095 value of the credit counter is higher than the size of the outbound 1096 packet. If the credit counter is too low, the packet MUST be 1097 discarded or buffered until address verification succeeds. When a 1098 packet is sent to a peer at an UNVERIFIED locator, the peer's credit 1099 counter MUST be reduced by the size of the packet. The peer's credit 1100 counter is not affected by packets that the host sends to an ACTIVE 1101 locator of that peer. 1103 Figure 8 depicts the actions taken by the host when a packet is 1104 received. Figure 9 shows the decision chain in the event a packet is 1105 sent. 1107 Inbound 1108 packet 1109 | 1110 | +----------------+ +---------------+ 1111 | | Increase | | Deliver | 1112 +-----> | credit counter |-------------> | packet to | 1113 | by packet size | | application | 1114 +----------------+ +---------------+ 1116 Figure 8: Receiving Packets with Credit-Based Authorization 1118 Outbound 1119 packet 1120 | _________________ 1121 | / \ +---------------+ 1122 | / Is the preferred \ No | Send packet | 1123 +-----> | destination address |-------------> | to preferred | 1124 \ UNVERIFIED? / | address | 1125 \_________________/ +---------------+ 1126 | 1127 | Yes 1128 | 1129 v 1130 _________________ 1131 / \ +---------------+ 1132 / Does an ACTIVE \ Yes | Send packet | 1133 | destination address |-------------> | to ACTIVE | 1134 \ exist? / | address | 1135 \_________________/ +---------------+ 1136 | 1137 | No 1138 | 1139 v 1140 _________________ 1141 / \ +---------------+ 1142 / Credit counter \ No | | 1143 | >= |-------------> | Drop or | 1144 \ packet size? / | buffer packet | 1145 \_________________/ +---------------+ 1146 | 1147 | Yes 1148 | 1149 v 1150 +---------------+ +---------------+ 1151 | Reduce credit | | Send packet | 1152 | counter by |----------------> | to preferred | 1153 | packet size | | address | 1154 +---------------+ +---------------+ 1156 Figure 9: Sending Packets with Credit-Based Authorization 1158 5.6.2. Credit Aging 1160 A host ensures that the credit counters it maintains for its peers 1161 gradually decrease over time. Such "credit aging" prevents a 1162 malicious peer from building up credit at a very slow speed and using 1163 this, all at once, for a severe burst of redirected packets. 1165 Credit aging may be implemented by multiplying credit counters with a 1166 factor, CreditAgingFactor (a fractional value less than one), in 1167 fixed time intervals of CreditAgingInterval length. Choosing 1168 appropriate values for CreditAgingFactor and CreditAgingInterval is 1169 important to ensure that a host can send packets to an address in 1170 state UNVERIFIED even when the peer sends at a lower rate than the 1171 host itself. When CreditAgingFactor or CreditAgingInterval are too 1172 small, the peer's credit counter might be too low to continue sending 1173 packets until address verification concludes. 1175 The parameter values proposed in this document are as follows: 1177 CreditAgingFactor 7/8 1178 CreditAgingInterval 5 seconds 1180 These parameter values work well when the host transfers a file to 1181 the peer via a TCP connection and the end-to-end round-trip time does 1182 not exceed 500 milliseconds. Alternative credit-aging algorithms may 1183 use other parameter values or different parameters, which may even be 1184 dynamically established. 1186 6. Security Considerations 1188 The HIP mobility mechanism provides a secure means of updating a 1189 host's IP address via HIP UPDATE packets. Upon receipt, a HIP host 1190 cryptographically verifies the sender of an UPDATE, so forging or 1191 replaying a HIP UPDATE packet is very difficult (see [RFC7401]). 1192 Therefore, security issues reside in other attack domains. The two 1193 we consider are malicious redirection of legitimate connections as 1194 well as redirection-based flooding attacks using this protocol. This 1195 can be broken down into the following: 1197 Impersonation attacks 1199 - direct conversation with the misled victim 1201 - man-in-the-middle attack 1203 DoS attacks 1205 - flooding attacks (== bandwidth-exhaustion attacks) 1207 * tool 1: direct flooding 1209 * tool 2: flooding by botnets 1211 * tool 3: redirection-based flooding 1213 - memory-exhaustion attacks 1215 - computational-exhaustion attacks 1217 We consider these in more detail in the following sections. 1219 In Section 6.1 and Section 6.2, we assume that all users are using 1220 HIP. In Section 6.3 we consider the security ramifications when we 1221 have both HIP and non-HIP hosts. Security considerations for Credit- 1222 Based Authorization are discussed in [SIMPLE-CBA]. 1224 6.1. Impersonation Attacks 1226 An attacker wishing to impersonate another host will try to mislead 1227 its victim into directly communicating with them, or carry out a man- 1228 in-the-middle (MitM) attack between the victim and the victim's 1229 desired communication peer. Without mobility support, such attacks 1230 are possible only if the attacker resides on the routing path between 1231 its victim and the victim's desired communication peer, or if the 1232 attacker tricks its victim into initiating the connection over an 1233 incorrect routing path (e.g., by acting as a router or using spoofed 1234 DNS entries). 1236 The HIP extensions defined in this specification change the situation 1237 in that they introduce an ability to redirect a connection, both 1238 before and after establishment. If no precautionary measures are 1239 taken, an attacker could potentially misuse the redirection feature 1240 to impersonate a victim's peer from any arbitrary location. However, 1241 the authentication and authorization mechanisms of the HIP base 1242 exchange [RFC7401] and the signatures in the UPDATE message prevent 1243 this attack. Furthermore, ownership of a HIP association is securely 1244 linked to a HIP HI/HIT. If an attacker somehow uses a bug in the 1245 implementation to redirect a HIP connection, the original owner can 1246 always reclaim their connection (they can always prove ownership of 1247 the private key associated with their public HI). 1249 MitM attacks are possible if an on-path attacker is present during 1250 the initial HIP base exchange and if the hosts do not authenticate 1251 each other's identities. However, once such an opportunistic base 1252 exchange has taken place, a MitM attacker that comes later to the 1253 path cannot steal the HIP connection because it is very difficult for 1254 an attacker to create an UPDATE packet (or any HIP packet) that will 1255 be accepted as a legitimate update. UPDATE packets use HMAC and are 1256 signed. Even when an attacker can snoop packets to obtain the SPI 1257 and HIT/HI, they still cannot forge an UPDATE packet without 1258 knowledge of the secret keys. Also, replay attacks on the UPDATE 1259 packet are prevented as described in [RFC7401]. 1261 6.2. Denial-of-Service Attacks 1263 6.2.1. Flooding Attacks 1265 The purpose of a denial-of-service attack is to exhaust some resource 1266 of the victim such that the victim ceases to operate correctly. A 1267 denial-of-service attack can aim at the victim's network attachment 1268 (flooding attack), its memory, or its processing capacity. In a 1269 flooding attack, the attacker causes an excessive number of bogus or 1270 unwanted packets to be sent to the victim, which fills their 1271 available bandwidth. Note that the victim does not necessarily need 1272 to be a node; it can also be an entire network. The attack basically 1273 functions the same way in either case. 1275 An effective DoS strategy is distributed denial of service (DDoS). 1276 Here, the attacker conventionally distributes some viral software to 1277 as many nodes as possible. Under the control of the attacker, the 1278 infected nodes (e.g. nodes in a botnet), jointly send packets to the 1279 victim. With such an 'army', an attacker can take down even very 1280 high bandwidth networks/victims. 1282 With the ability to redirect connections, an attacker could realize a 1283 DDoS attack without having to distribute viral code. Here, the 1284 attacker initiates a large download from a server, and subsequently 1285 uses the HIP mobility mechanism to redirect this download to its 1286 victim. The attacker can repeat this with multiple servers. This 1287 threat is mitigated through reachability checks and credit-based 1288 authorization. Both strategies do not eliminate flooding attacks per 1289 se, but they preclude: (i) their use from a location off the path 1290 towards the flooded victim; and (ii) any amplification in the number 1291 and size of the redirected packets. As a result, the combination of 1292 a reachability check and credit-based authorization lowers a HIP 1293 redirection-based flooding attack to the level of a direct flooding 1294 attack in which the attacker itself sends the flooding traffic to the 1295 victim. 1297 6.2.2. Memory/Computational-Exhaustion DoS Attacks 1299 We now consider whether or not the proposed extensions to HIP add any 1300 new DoS attacks (consideration of DoS attacks using the base HIP 1301 exchange and updates is discussed in [RFC7401]). A simple attack is 1302 to send many UPDATE packets containing many IP addresses that are not 1303 flagged as preferred. The attacker continues to send such packets 1304 until the number of IP addresses associated with the attacker's HI 1305 crashes the system. Therefore, a HIP association SHOULD limit the 1306 number of IP addresses that can be associated with any HI. Other 1307 forms of memory/computationally exhausting attacks via the HIP UPDATE 1308 packet are handled in the base HIP document [RFC7401]. 1310 A central server that has to deal with a large number of mobile 1311 clients MAY consider increasing the SA lifetimes to try to slow down 1312 the rate of rekeying UPDATEs or increasing the cookie difficulty to 1313 slow down the rate of attack-oriented connections. 1315 6.3. Mixed Deployment Environment 1317 We now assume an environment with both HIP and non-HIP aware hosts. 1318 Four cases exist. 1320 1. A HIP host redirects its connection onto a non-HIP host. The 1321 non-HIP host will drop the reachability packet, so this is not a 1322 threat unless the HIP host is a MitM that could somehow respond 1323 successfully to the reachability check. 1325 2. A non-HIP host attempts to redirect their connection onto a HIP 1326 host. This falls into IPv4 and IPv6 security concerns, which are 1327 outside the scope of this document. 1329 3. A non-HIP host attempts to steal a HIP host's session (assume 1330 that Secure Neighbor Discovery is not active for the following). 1331 The non-HIP host contacts the service that a HIP host has a 1332 connection with and then attempts to change its IP address to 1333 steal the HIP host's connection. What will happen in this case 1334 is implementation dependent but such a request should fail by 1335 being ignored or dropped. Even if the attack were successful, 1336 the HIP host could reclaim its connection via HIP. 1338 4. A HIP host attempts to steal a non-HIP host's session. A HIP 1339 host could spoof the non-HIP host's IP address during the base 1340 exchange or set the non-HIP host's IP address as its preferred 1341 address via an UPDATE. Other possibilities exist, but a solution 1342 is to prevent the local redirection of sessions that were 1343 previously using an unverified address, but outside of the 1344 existing HIP context, into the HIP SAs until the address change 1345 can be verified. 1347 7. IANA Considerations 1349 The following changes to the "Host Identity Protocol (HIP) 1350 Parameters" registries are requested. 1352 The existing Parameter Type of 'LOCATOR' (value 193) should be 1353 renamed to 'LOCATOR_SET' and the reference should be updated from 1354 RFC5206 to this specification. 1356 The existing Notify Message Type of 'LOCATOR_TYPE_UNSUPPORTED' (value 1357 46) should have its reference updated from RFC5206 to this 1358 specification. 1360 8. Authors and Acknowledgments 1362 Pekka Nikander and Jari Arkko originated this document, and Christian 1363 Vogt and Thomas Henderson (editor) later joined as co-authors. Greg 1364 Perkins contributed the initial draft of the security section. Petri 1365 Jokela was a co-author of the initial individual submission. 1367 The authors thank Jeff Ahrenholz, Baris Boyvat, Rene Hummen, Miika 1368 Komu, Mika Kousa, Jan Melen, and Samu Varjonen for improvements to 1369 the document. 1371 9. References 1373 9.1. Normative references 1375 [I-D.ietf-hip-rfc5203-bis] 1376 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1377 Registration Extension", draft-ietf-hip-rfc5203-bis-10 1378 (work in progress), January 2016. 1380 [I-D.ietf-hip-rfc5204-bis] 1381 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1382 Rendezvous Extension", draft-ietf-hip-rfc5204-bis-07 (work 1383 in progress), December 2015. 1385 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1386 Requirement Levels", BCP 14, RFC 2119, 1387 DOI 10.17487/RFC2119, March 1997, 1388 . 1390 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1391 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1392 2006, . 1394 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 1395 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 1396 RFC 7401, DOI 10.17487/RFC7401, April 2015, 1397 . 1399 [RFC7402] Jokela, P., Moskowitz, R., and J. Melen, "Using the 1400 Encapsulating Security Payload (ESP) Transport Format with 1401 the Host Identity Protocol (HIP)", RFC 7402, 1402 DOI 10.17487/RFC7402, April 2015, 1403 . 1405 9.2. Informative references 1407 [CBA-MIPv6] 1408 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1409 Mobile IPv6 Early Binding Updates", February 2005. 1411 [RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. 1412 Nordmark, "Mobile IP Version 6 Route Optimization Security 1413 Design Background", RFC 4225, DOI 10.17487/RFC4225, 1414 December 2005, . 1416 [SIMPLE-CBA] 1417 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1418 Concurrent Reachability Verification", February 2006. 1420 Appendix A. Document Revision History 1422 To be removed upon publication 1424 +----------+--------------------------------------------------------+ 1425 | Revision | Comments | 1426 +----------+--------------------------------------------------------+ 1427 | draft-00 | Initial version from RFC5206 xml (unchanged). | 1428 | | | 1429 | draft-01 | Remove multihoming-specific text; no other changes. | 1430 | | | 1431 | draft-02 | Update references to point to -bis drafts; no other | 1432 | | changes. | 1433 | | | 1434 | draft-03 | issue 4: add make before break use case | 1435 | | | 1436 | | issue 6: peer locator exposure policies | 1437 | | | 1438 | | issue 10: rename LOCATOR to LOCATOR_SET | 1439 | | | 1440 | | issue 14: use of UPDATE packet's IP address | 1441 | | | 1442 | draft-04 | Document refresh; no other changes. | 1443 | | | 1444 | draft-05 | Document refresh; no other changes. | 1445 | | | 1446 | draft-06 | Document refresh; no other changes. | 1447 | | | 1448 | draft-07 | Document refresh; IANA considerations updated. | 1449 | | | 1450 | draft-08 | Remove sending LOCATOR_SET in R1, I2, and NOTIFY | 1451 | | (multihoming) | 1452 | | | 1453 | | State that only one LOCATOR_SET parameter may be sent | 1454 | | in an UPDATE packet (according to this draft) | 1455 | | (multihoming) | 1456 | | | 1457 | | Remove text about cross-family handovers (multihoming) | 1458 | | | 1459 | draft-09 | Add specification text regarding double-jump mobility | 1460 | | procedures. | 1461 | | | 1462 | draft-10 | issue 21: clarified that HI MAY be included in UPDATE | 1463 | | for benefit of middleboxes | 1464 | | | 1465 | | changed one informative reference from RFC 4423-bis to | 1466 | | RFC 7401 | 1467 | | | 1468 | | removed discussion about possible multiple LOCATOR_SET | 1469 | | and ESP_INFO parameters in an UPDATE (per previous | 1470 | | mailing list discussion) | 1471 | | | 1472 | | removed discussion about handling LOCATOR_SET | 1473 | | parameters in packets other than UPDATE (per previous | 1474 | | mailing list discussion) | 1475 | | | 1476 | draft-11 | Editorial improvements from WGLC | 1477 +----------+--------------------------------------------------------+ 1479 Authors' Addresses 1481 Thomas R. Henderson (editor) 1482 University of Washington 1483 Campus Box 352500 1484 Seattle, WA 1485 USA 1487 EMail: tomhend@u.washington.edu 1489 Christian Vogt 1490 Ericsson Research NomadicLab 1491 Hirsalantie 11 1492 JORVAS FIN-02420 1493 FINLAND 1495 EMail: christian.vogt@ericsson.com 1497 Jari Arkko 1498 Ericsson Research NomadicLab 1499 JORVAS FIN-02420 1500 FINLAND 1502 Phone: +358 40 5079256 1503 EMail: jari.arkko@ericsson.com