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Arkko 6 Expires: July 26, 2016 Ericsson Research NomadicLab 7 January 23, 2016 9 Host Mobility with the Host Identity Protocol 10 draft-ietf-hip-rfc5206-bis-10 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 July 26, 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 . . . . . . . . . . . . . . . . . 12 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 . . . . . . . . . . . . . . . . . . 14 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 . . . . . . . . . . . . 17 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 . . . . . . . . . . . . . . . 23 98 5.6.1. Handling Payload Packets . . . . . . . . . . . . . . 24 99 5.6.2. Credit Aging . . . . . . . . . . . . . . . . . . . . 25 100 6. Security Considerations . . . . . . . . . . . . . . . . . . . 26 101 6.1. Impersonation Attacks . . . . . . . . . . . . . . . . . . 27 102 6.2. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 28 103 6.2.1. Flooding Attacks . . . . . . . . . . . . . . . . . . 28 104 6.2.2. Memory/Computational-Exhaustion DoS Attacks . . . . . 28 105 6.3. Mixed Deployment Environment . . . . . . . . . . . . . . 29 106 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 107 8. Authors and Acknowledgments . . . . . . . . . . . . . . . . . 30 108 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 109 9.1. Normative references . . . . . . . . . . . . . . . . . . 30 110 9.2. Informative references . . . . . . . . . . . . . . . . . 31 111 Appendix A. Document Revision History . . . . . . . . . . . . . 32 112 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 114 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. However, elements of procedure to recover from 302 simultaneous movement of both hosts are not specified herein. In 303 addition, internal notification of transport layer protocols of the 304 path change (e.g. to reset congestion control variables), and 305 elements of procedure for traversing middleboxes including network 306 address translators are not covered by this document. 308 3.1.1. Locator 310 This document defines a generalization of an address called a 311 "locator". A locator specifies a point-of-attachment to the network 312 but may also include additional end-to-end tunneling or per-host 313 demultiplexing context that affects how packets are handled below the 314 logical HIP sublayer of the stack. This generalization is useful 315 because IP addresses alone may not be sufficient to describe how 316 packets should be handled below HIP. For example, in a host 317 multihoming context, certain IP addresses may need to be associated 318 with certain ESP SPIs to avoid violating the ESP anti-replay window. 319 Addresses may also be affiliated with transport ports in certain 320 tunneling scenarios. Locators may simply be traditional network 321 addresses. The format of the locator fields in the LOCATOR_SET 322 parameter is defined in Section 4. 324 3.1.2. Mobility Overview 326 When a host moves to another address, it notifies its peer of the new 327 address by sending a HIP UPDATE packet containing a LOCATOR_SET 328 parameter. This UPDATE packet is acknowledged by the peer. For 329 reliability in the presence of packet loss, the UPDATE packet is 330 retransmitted as defined in the HIP protocol specification [RFC7401]. 331 The peer can authenticate the contents of the UPDATE packet based on 332 the signature and keyed hash of the packet. 334 When using ESP Transport Format [RFC7402], the host may at the same 335 time decide to rekey its security association and possibly generate a 336 new Diffie-Hellman key; all of these actions are triggered by 337 including additional parameters in the UPDATE packet, as defined in 338 the base protocol specification [RFC7401] and ESP extension 339 [RFC7402]. 341 When using ESP (and possibly other transport modes in the future), 342 the host is able to receive packets that are protected using a HIP 343 created ESP SA from any address. Thus, a host can change its IP 344 address and continue to send packets to its peers without necessarily 345 rekeying. However, the peers are not able to send packets to these 346 new addresses before they can reliably and securely update the set of 347 addresses that they associate with the sending host. Furthermore, 348 mobility may change the path characteristics in such a manner that 349 reordering occurs and packets fall outside the ESP anti-replay window 350 for the SA, thereby requiring rekeying. 352 3.2. Protocol Overview 354 In this section, we briefly introduce a number of usage scenarios for 355 HIP host mobility. These scenarios assume that HIP is being used 356 with the ESP transform [RFC7402], although other scenarios may be 357 defined in the future. To understand these usage scenarios, the 358 reader should be at least minimally familiar with the HIP protocol 359 specification [RFC7401]. However, for the (relatively) uninitiated 360 reader, it is most important to keep in mind that in HIP the actual 361 payload traffic is protected with ESP, and that the ESP SPI acts as 362 an index to the right host-to-host context. More specification 363 details are found later in Section 4 and Section 5. 365 The scenarios below assume that the two hosts have completed a single 366 HIP base exchange with each other. Both of the hosts therefore have 367 one incoming and one outgoing SA. Further, each SA uses the same 368 pair of IP addresses, which are the ones used in the base exchange. 370 The readdressing protocol is an asymmetric protocol where a mobile 371 host informs a peer host about changes of IP addresses on affected 372 SPIs. The readdressing exchange is designed to be piggybacked on 373 existing HIP exchanges. The majority of the packets on which the 374 LOCATOR_SET parameters are expected to be carried are UPDATE packets. 376 The scenarios below at times describe addresses as being in either an 377 ACTIVE, UNVERIFIED, or DEPRECATED state. From the perspective of a 378 host, newly-learned addresses of the peer must be verified before put 379 into active service, and addresses removed by the peer are put into a 380 deprecated state. Under limited conditions described below 381 (Section 5.6), an UNVERIFIED address may be used. The addressing 382 states are defined more formally in Section 5.1. 384 Hosts that use link-local addresses as source addresses in their HIP 385 handshakes may not be reachable by a mobile peer. Such hosts SHOULD 386 provide a globally routable address either in the initial handshake 387 or via the LOCATOR_SET parameter. 389 3.2.1. Mobility with a Single SA Pair (No Rekeying) 391 A mobile host must sometimes change an IP address bound to an 392 interface. The change of an IP address might be needed due to a 393 change in the advertised IPv6 prefixes on the link, a reconnected PPP 394 link, a new DHCP lease, or an actual movement to another subnet. In 395 order to maintain its communication context, the host must inform its 396 peers about the new IP address. This first example considers the 397 case in which the mobile host has only one interface, one IP address 398 in use within the HIP session, a single pair of SAs (one inbound, one 399 outbound), and no rekeying occurs on the SAs. We also assume that 400 the new IP addresses are within the same address family (IPv4 or 401 IPv6) as the first address. This is the simplest scenario, depicted 402 in Figure 3. 404 Mobile Host Peer Host 406 UPDATE(ESP_INFO, LOCATOR_SET, SEQ) 407 -----------------------------------> 408 UPDATE(ESP_INFO, SEQ, ACK, ECHO_REQUEST) 409 <----------------------------------- 410 UPDATE(ACK, ECHO_RESPONSE) 411 -----------------------------------> 413 Figure 3: Readdress without Rekeying, but with Address Check 415 The steps of the packet processing are as follows: 417 1. The mobile host may be disconnected from the peer host for a 418 brief period of time while it switches from one IP address to 419 another; this case is sometimes referred to in the literature as 420 a "break-before-make" case. The host may also obtain its new IP 421 address before loosing the old one ("make-before-break" case). 422 In either case, upon obtaining a new IP address, the mobile host 423 sends a LOCATOR_SET parameter to the peer host in an UPDATE 424 message. The UPDATE message also contains an ESP_INFO parameter 425 containing the values of the old and new SPIs for a security 426 association. In this case, the OLD SPI and NEW SPI parameters 427 both are set to the value of the preexisting incoming SPI; this 428 ESP_INFO does not trigger a rekeying event but is instead 429 included for possible parameter-inspecting middleboxes on the 430 path. The LOCATOR_SET parameter contains the new IP address 431 (Locator Type of "1", defined below) and a locator lifetime. The 432 mobile host waits for this UPDATE to be acknowledged, and 433 retransmits if necessary, as specified in the base specification 434 [RFC7401]. 436 2. The peer host receives the UPDATE, validates it, and updates any 437 local bindings between the HIP association and the mobile host's 438 destination address. The peer host MUST perform an address 439 verification by placing a nonce in the ECHO_REQUEST parameter of 440 the UPDATE message sent back to the mobile host. It also 441 includes an ESP_INFO parameter with the OLD SPI and NEW SPI 442 parameters both set to the value of the preexisting incoming SPI, 443 and sends this UPDATE (with piggybacked acknowledgment) to the 444 mobile host at its new address. The peer MAY use the new address 445 immediately, but it MUST limit the amount of data it sends to the 446 address until address verification completes. 448 3. The mobile host completes the readdress by processing the UPDATE 449 ACK and echoing the nonce in an ECHO_RESPONSE. Once the peer 450 host receives this ECHO_RESPONSE, it considers the new address to 451 be verified and can put the address into full use. 453 While the peer host is verifying the new address, the new address is 454 marked as UNVERIFIED in the interim, and the old address is 455 DEPRECATED. Once the peer host has received a correct reply to its 456 UPDATE challenge, it marks the new address as ACTIVE and removes the 457 old address. 459 3.2.2. Mobility with a Single SA Pair (Mobile-Initiated Rekey) 461 The mobile host may decide to rekey the SAs at the same time that it 462 notifies the peer of the new address. In this case, the above 463 procedure described in Figure 3 is slightly modified. The UPDATE 464 message sent from the mobile host includes an ESP_INFO with the OLD 465 SPI set to the previous SPI, the NEW SPI set to the desired new SPI 466 value for the incoming SA, and the KEYMAT Index desired. Optionally, 467 the host may include a DIFFIE_HELLMAN parameter for a new Diffie- 468 Hellman key. The peer completes the request for a rekey as is 469 normally done for HIP rekeying, except that the new address is kept 470 as UNVERIFIED until the UPDATE nonce challenge is received as 471 described above. Figure 4 illustrates this scenario. 473 Mobile Host Peer Host 475 UPDATE(ESP_INFO, LOCATOR_SET, SEQ, [DIFFIE_HELLMAN]) 476 -----------------------------------> 477 UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) 478 <----------------------------------- 479 UPDATE(ACK, ECHO_RESPONSE) 480 -----------------------------------> 482 Figure 4: Readdress with Mobile-Initiated Rekey 484 3.2.3. Mobility messaging through rendezvous server 486 Section 6.11 of [RFC7401] specifies procedures for sending HIP UPDATE 487 packets. The UPDATE packets are protected by a timer subject to 488 exponential backoff and resent UPDATE_RETRY_MAX times. It may be, 489 however, that the peer is itself in the process of moving when the 490 local host is trying to update the IP address bindings of the HIP 491 association. This is sometimes called the "double-jump" mobility 492 problem; each host's UPDATE packets are simultaneously sent to a 493 stale address of the peer, and the hosts are no longer reachable from 494 one another. 496 The HIP Rendezvous Extension [I-D.ietf-hip-rfc5204-bis] specifies a 497 rendezvous service that permits the I1 packet from the base exchange 498 to be relayed from a stable or well-known public IP address location 499 to the current IP address of the host. It is possible to support 500 double-jump mobility with this rendezvous service if the following 501 extensions to the specifications of [I-D.ietf-hip-rfc5204-bis] and 502 [RFC7401] are followed. 504 1. The mobile host sending an UPDATE to the peer, and not receiving 505 an ACK, MAY resend the UPDATE to a rendezvous server (RVS) of the 506 peer, if such a server is known. The host may try the RVS of the 507 peer up to UPDATE_RETRY_MAX times as specified in [RFC7401]. The 508 host may try to use the peer's RVS before it has tried 509 UPDATE_RETRY_MAX times to the last working address (i.e. the RVS 510 may be tried in parallel with retries to the last working 511 address). 513 2. A rendezvous server supporting the UPDATE forwarding extensions 514 specified herein MUST modify the UPDATE in the same manner as it 515 modifies the I1 packet before forwarding. Specifically, it MUST 516 rewrite the IP header source and destination addresses, recompute 517 the IP header checksum, and include the FROM and RVS_HMAC 518 parameters. 520 3. A host receiving an UPDATE packet MUST be prepared to process the 521 FROM and RVS_HMAC parameters, and MUST include a VIA_RVS 522 parameter in the UPDATE reply that contains the ACK of the UPDATE 523 SEQ. 525 4. This scenario requires that hosts using rendezvous servers also 526 take steps to update their current address bindings with their 527 rendezvous server upon a mobility event. 528 [I-D.ietf-hip-rfc5204-bis] does not specify how to update the 529 rendezvous server with a client host's new address. 530 [I-D.ietf-hip-rfc5203-bis] Section 3.2 describes how a host may 531 send a REG_REQUEST in either an I2 packet (if there is no active 532 association) or an UPDATE packet (if such association exists). 533 The procedures described in [I-D.ietf-hip-rfc5203-bis] for 534 sending a REG_REQUEST and REG_RESPONSE to the rendezvous server 535 apply also to this mobility scenario. 537 3.2.4. Network Renumbering 539 It is expected that IPv6 networks will be renumbered much more often 540 than most IPv4 networks. From an end-host point of view, network 541 renumbering is similar to mobility. 543 3.3. Other Considerations 545 3.3.1. Address Verification 547 When a HIP host receives a set of locators from another HIP host in a 548 LOCATOR_SET, it does not necessarily know whether the other host is 549 actually reachable at the claimed addresses. In fact, a malicious 550 peer host may be intentionally giving bogus addresses in order to 551 cause a packet flood towards the target addresses [RFC4225]. 552 Therefore, the HIP host must first check that the peer is reachable 553 at the new address. 555 An additional potential benefit of performing address verification is 556 to allow middleboxes in the network along the new path to obtain the 557 peer host's inbound SPI. 559 Address verification is implemented by the challenger sending some 560 piece of unguessable information to the new address, and waiting for 561 some acknowledgment from the Responder that indicates reception of 562 the information at the new address. This may include the exchange of 563 a nonce, or the generation of a new SPI and observation of data 564 arriving on the new SPI. 566 3.3.2. Credit-Based Authorization 568 Credit-Based Authorization (CBA) allows a host to securely use a new 569 locator even though the peer's reachability at the address embedded 570 in the locator has not yet been verified. This is accomplished based 571 on the following three hypotheses: 573 1. A flooding attacker typically seeks to somehow multiply the 574 packets it generates for the purpose of its attack because 575 bandwidth is an ample resource for many victims. 577 2. An attacker can often cause unamplified flooding by sending 578 packets to its victim, either by directly addressing the victim 579 in the packets, or by guiding the packets along a specific path 580 by means of an IPv6 Routing header, if Routing headers are not 581 filtered by firewalls. 583 3. Consequently, the additional effort required to set up a 584 redirection-based flooding attack (without CBA and return 585 routability checks) would pay off for the attacker only if 586 amplification could be obtained this way. 588 On this basis, rather than eliminating malicious packet redirection 589 in the first place, Credit-Based Authorization prevents 590 amplifications. This is accomplished by limiting the data a host can 591 send to an unverified address of a peer by the data recently received 592 from that peer. Redirection-based flooding attacks thus become less 593 attractive than, for example, pure direct flooding, where the 594 attacker itself sends bogus packets to the victim. 596 Figure 5 illustrates Credit-Based Authorization: Host B measures the 597 amount of data recently received from peer A and, when A readdresses, 598 sends packets to A's new, unverified address as long as the sum of 599 the packet sizes does not exceed the measured, received data volume. 600 When insufficient credit is left, B stops sending further packets to 601 A until A's address becomes ACTIVE. The address changes may be due 602 to mobility, multihoming, or any other reason. Not shown in Figure 5 603 are the results of credit aging (Section 5.6.2), a mechanism used to 604 dampen possible time-shifting attacks. 606 +-------+ +-------+ 607 | A | | B | 608 +-------+ +-------+ 609 | | 610 address |------------------------------->| credit += size(packet) 611 ACTIVE | | 612 |------------------------------->| credit += size(packet) 613 |<-------------------------------| do not change credit 614 | | 615 + address change | 616 + address verification starts | 617 address |<-------------------------------| credit -= size(packet) 618 UNVERIFIED |------------------------------->| credit += size(packet) 619 |<-------------------------------| credit -= size(packet) 620 | | 621 |<-------------------------------| credit -= size(packet) 622 | X credit < size(packet) 623 | | => do not send packet! 624 + address verification concludes | 625 address | | 626 ACTIVE |<-------------------------------| do not change credit 627 | | 629 Figure 5: Readdressing Scenario 631 3.3.3. Preferred Locator 633 When a host has multiple locators, the peer host must decide which to 634 use for outbound packets. It may be that a host would prefer to 635 receive data on a particular inbound interface. HIP allows a 636 particular locator to be designated as a Preferred locator and 637 communicated to the peer (see Section 4). 639 4. LOCATOR_SET Parameter Format 641 The LOCATOR_SET parameter is a critical parameter as defined by 642 [RFC7401]. It consists of the standard HIP parameter Type and Length 643 fields, plus zero or more Locator sub-parameters. Each Locator sub- 644 parameter contains a Traffic Type, Locator Type, Locator Length, 645 Preferred locator bit, Locator Lifetime, and a Locator encoding. A 646 LOCATOR_SET containing zero Locator fields is permitted but has the 647 effect of deprecating all addresses. 649 0 1 2 3 650 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 1 651 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 652 | Type | Length | 653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 654 | Traffic Type | Locator Type | Locator Length | Reserved |P| 655 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 656 | Locator Lifetime | 657 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 658 | Locator | 659 | | 660 | | 661 | | 662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 663 . . 664 . . 665 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 666 | Traffic Type | Locator Type | Locator Length | Reserved |P| 667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 668 | Locator Lifetime | 669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 670 | Locator | 671 | | 672 | | 673 | | 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 676 Figure 6: LOCATOR_SET Parameter Format 678 Type: 193 680 Length: Length in octets, excluding Type and Length fields, and 681 excluding padding. 683 Traffic Type: Defines whether the locator pertains to HIP signaling, 684 user data, or both. 686 Locator Type: Defines the semantics of the Locator field. 688 Locator Length: Defines the length of the Locator field, in units of 689 4-byte words (Locators up to a maximum of 4*255 octets are 690 supported). 692 Reserved: Zero when sent, ignored when received. 694 P: Preferred locator. Set to one if the locator is preferred for 695 that Traffic Type; otherwise, set to zero. 697 Locator Lifetime: Locator lifetime, in seconds. 699 Locator: The locator whose semantics and encoding are indicated by 700 the Locator Type field. All Locator sub-fields are integral 701 multiples of four octets in length. 703 The Locator Lifetime indicates how long the following locator is 704 expected to be valid. The lifetime is expressed in seconds. Each 705 locator MUST have a non-zero lifetime. The address is expected to 706 become deprecated when the specified number of seconds has passed 707 since the reception of the message. A deprecated address SHOULD NOT 708 be used as a destination address if an alternate (non-deprecated) is 709 available and has sufficient scope. 711 4.1. Traffic Type and Preferred Locator 713 The following Traffic Type values are defined: 715 0: Both signaling (HIP control packets) and user data. 717 1: Signaling packets only. 719 2: Data packets only. 721 The "P" bit, when set, has scope over the corresponding Traffic Type. 722 That is, when a "P" bit is set for Traffic Type "2", for example, it 723 means that the locator is preferred for data packets. If there is a 724 conflict (for example, if the "P" bit is set for an address of Type 725 "0" and a different address of Type "2"), the more specific Traffic 726 Type rule applies (in this case, "2"). By default, the IP addresses 727 used in the base exchange are Preferred locators for both signaling 728 and user data, unless a new Preferred locator supersedes them. If no 729 locators are indicated as preferred for a given Traffic Type, the 730 implementation may use an arbitrary destination locator from the set 731 of active locators. 733 4.2. Locator Type and Locator 735 The following Locator Type values are defined, along with the 736 associated semantics of the Locator field: 738 0: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [RFC4291] 739 (128 bits long). This locator type is defined primarily for non- 740 ESP-based usage. 742 1: The concatenation of an ESP SPI (first 32 bits) followed by an 743 IPv6 address or an IPv4-in-IPv6 format IPv4 address (an additional 744 128 bits). This IP address is defined primarily for ESP-based 745 usage. 747 4.3. UPDATE Packet with Included LOCATOR_SET 749 A number of combinations of parameters in an UPDATE packet are 750 possible (e.g., see Section 3.2). In this document, procedures are 751 defined only for the case in which one LOCATOR_SET and one ESP_INFO 752 parameter is used in any HIP packet. Furthermore, the LOCATOR_SET 753 SHOULD list all of the locators that are active on the HIP 754 association (including those on SAs not covered by the ESP_INFO 755 parameter). Any UPDATE packet that includes a LOCATOR_SET parameter 756 SHOULD include both an HMAC and a HIP_SIGNATURE parameter. The 757 UPDATE MAY also include a HOST_ID parameter (which may be useful for 758 middleboxes inspecting the HIP messages for the first time). If the 759 UPDATE includes the HOST_ID parameter, the receiving host MUST verify 760 that the HOST_ID corresponds to the HOST_ID that was used to 761 establish the HIP association, and the HIP_SIGNATURE must verify with 762 the public key assodiated with this HOST_ID parameter. The 763 relationship between the announced Locators and any ESP_INFO 764 parameters present in the packet is defined in Section 5.2. This 765 draft does not support any elements of procedure for sending more 766 than one LOCATOR_SET or ESP_INFO parameter in a single UPDATE. 768 5. Processing Rules 770 This section describes rules for sending and receiving the 771 LOCATOR_SET parameter, testing address reachability, and using 772 Credit-Based Authorization (CBA) on UNVERIFIED locators. 774 5.1. Locator Data Structure and Status 776 In a typical implementation, each locator announced in a LOCATOR_SET 777 parameter is represented by a piece of state that contains the 778 following data: 780 o the actual bit pattern representing the locator, 781 o the lifetime (seconds), 783 o the status (UNVERIFIED, ACTIVE, DEPRECATED), 785 o the Traffic Type scope of the locator, and 787 o whether the locator is preferred for any particular scope. 789 The status is used to track the reachability of the address embedded 790 within the LOCATOR_SET parameter: 792 UNVERIFIED indicates that the reachability of the address has not 793 been verified yet, 795 ACTIVE indicates that the reachability of the address has been 796 verified and the address has not been deprecated, 798 DEPRECATED indicates that the locator lifetime has expired. 800 The following state changes are allowed: 802 UNVERIFIED to ACTIVE The reachability procedure completes 803 successfully. 805 UNVERIFIED to DEPRECATED The locator lifetime expires while the 806 locator is UNVERIFIED. 808 ACTIVE to DEPRECATED The locator lifetime expires while the locator 809 is ACTIVE. 811 ACTIVE to UNVERIFIED There has been no traffic on the address for 812 some time, and the local policy mandates that the address 813 reachability must be verified again before starting to use it 814 again. 816 DEPRECATED to UNVERIFIED The host receives a new lifetime for the 817 locator. 819 A DEPRECATED address MUST NOT be changed to ACTIVE without first 820 verifying its reachability. 822 Note that the state of whether or not a locator is preferred is not 823 necessarily the same as the value of the Preferred bit in the Locator 824 sub-parameter received from the peer. Peers may recommend certain 825 locators to be preferred, but the decision on whether to actually use 826 a locator as a preferred locator is a local decision, possibly 827 influenced by local policy. 829 In addition to state maintained about status and remaining lifetime 830 for each locator learned from the peer, an implementation would 831 typically maintain similar state about its own locators that have 832 been offered to the peer. 834 Finally, the locators used to establish the HIP association are by 835 default assumed to be the initial preferred locators in ACTIVE state, 836 with an unbounded lifetime. 838 5.2. Sending LOCATOR_SETs 840 The decision of when to send LOCATOR_SETs is basically a local policy 841 issue. However, it is RECOMMENDED that a host send a LOCATOR_SET 842 whenever it recognizes a change of its IP addresses in use on an 843 active HIP association, and assumes that the change is going to last 844 at least for a few seconds. Rapidly sending LOCATOR_SETs that force 845 the peer to change the preferred address SHOULD be avoided. 847 We now describe a few cases introduced in Section 3.2. We assume 848 that the Traffic Type for each locator is set to "0" (other values 849 for Traffic Type may be specified in documents that separate the HIP 850 control plane from data plane traffic). Other mobility cases are 851 possible but are left for further study. 853 1. Host mobility with no multihoming and no rekeying. The mobile 854 host creates a single UPDATE containing a single ESP_INFO with a 855 single LOCATOR_SET parameter. The ESP_INFO contains the current 856 value of the SPI in both the OLD SPI and NEW SPI fields. The 857 LOCATOR_SET contains a single Locator with a "Locator Type" of 858 "1"; the SPI must match that of the ESP_INFO. The Preferred bit 859 SHOULD be set and the "Locator Lifetime" is set according to 860 local policy. The UPDATE also contains a SEQ parameter as usual. 861 This packet is retransmitted as defined in the HIP protocol 862 specification [RFC7401]. The UPDATE should be sent to the peer's 863 preferred IP address with an IP source address corresponding to 864 the address in the LOCATOR_SET parameter. 866 2. Host mobility with no multihoming but with rekeying. The mobile 867 host creates a single UPDATE containing a single ESP_INFO with a 868 single LOCATOR_SET parameter (with a single address). The 869 ESP_INFO contains the current value of the SPI in the OLD SPI and 870 the new value of the SPI in the NEW SPI, and a KEYMAT Index as 871 selected by local policy. Optionally, the host may choose to 872 initiate a Diffie Hellman rekey by including a DIFFIE_HELLMAN 873 parameter. The LOCATOR_SET contains a single Locator with 874 "Locator Type" of "1"; the SPI must match that of the NEW SPI in 875 the ESP_INFO. Otherwise, the steps are identical to the case in 876 which no rekeying is initiated. 878 5.3. Handling Received LOCATOR_SETs 880 A host SHOULD be prepared to receive a single LOCATOR_SET parameter 881 in a HIP UPDATE packet. Reception of multiple LOCATOR_SET parameters 882 in a single packet, or in HIP packets other than UPDATE, is outside 883 of the scope of this specification. 885 This document describes sending both ESP_INFO and LOCATOR_SET 886 parameters in an UPDATE. The ESP_INFO parameter is included when 887 there is a need to rekey or key a new SPI, and is otherwise included 888 for the possible benefit of HIP-aware middleboxes. The LOCATOR_SET 889 parameter contains a complete listing of the locators that the host 890 wishes to make or keep active for the HIP association. 892 In general, the processing of a LOCATOR_SET depends upon the packet 893 type in which it is included. Here, we describe only the case in 894 which ESP_INFO is present and a single LOCATOR_SET and ESP_INFO are 895 sent in an UPDATE message; other cases are for further study. The 896 steps below cover each of the cases described in Section 5.2. 898 The processing of ESP_INFO and LOCATOR_SET parameters is intended to 899 be modular and support future generalization to the inclusion of 900 multiple ESP_INFO and/or multiple LOCATOR_SET parameters. A host 901 SHOULD first process the ESP_INFO before the LOCATOR_SET, since the 902 ESP_INFO may contain a new SPI value mapped to an existing SPI, while 903 a Type "1" locator will only contain a reference to the new SPI. 905 When a host receives a validated HIP UPDATE with a LOCATOR_SET and 906 ESP_INFO parameter, it processes the ESP_INFO as follows. The 907 ESP_INFO parameter indicates whether an SA is being rekeyed, created, 908 deprecated, or just identified for the benefit of middleboxes. The 909 host examines the OLD SPI and NEW SPI values in the ESP_INFO 910 parameter: 912 1. (no rekeying) If the OLD SPI is equal to the NEW SPI and both 913 correspond to an existing SPI, the ESP_INFO is gratuitous 914 (provided for middleboxes) and no rekeying is necessary. 916 2. (rekeying) If the OLD SPI indicates an existing SPI and the NEW 917 SPI is a different non-zero value, the existing SA is being 918 rekeyed and the host follows HIP ESP rekeying procedures by 919 creating a new outbound SA with an SPI corresponding to the NEW 920 SPI, with no addresses bound to this SPI. Note that locators in 921 the LOCATOR_SET parameter will reference this new SPI instead of 922 the old SPI. 924 3. (new SA) If the OLD SPI value is zero and the NEW SPI is a new 925 non-zero value, then a new SA is being requested by the peer. 927 This case is also treated like a rekeying event; the receiving 928 host must create a new SA and respond with an UPDATE ACK. 930 4. (deprecating the SA) If the OLD SPI indicates an existing SPI and 931 the NEW SPI is zero, the SA is being deprecated and all locators 932 uniquely bound to the SPI are put into the DEPRECATED state. 934 If none of the above cases apply, a protocol error has occurred and 935 the processing of the UPDATE is stopped. 937 Next, the locators in the LOCATOR_SET parameter are processed. For 938 each locator listed in the LOCATOR_SET parameter, check that the 939 address therein is a legal unicast or anycast address. That is, the 940 address MUST NOT be a broadcast or multicast address. Note that some 941 implementations MAY accept addresses that indicate the local host, 942 since it may be allowed that the host runs HIP with itself. 944 The below assumes that all locators are of Type "1" with a Traffic 945 Type of "0"; other cases are for further study. 947 For each Type "1" address listed in the LOCATOR_SET parameter, the 948 host checks whether the address is already bound to the SPI 949 indicated. If the address is already bound, its lifetime is updated. 950 If the status of the address is DEPRECATED, the status is changed to 951 UNVERIFIED. If the address is not already bound, the address is 952 added, and its status is set to UNVERIFIED. Mark all addresses 953 corresponding to the SPI that were NOT listed in the LOCATOR_SET 954 parameter as DEPRECATED. 956 As a result, at the end of processing, the addresses listed in the 957 LOCATOR_SET parameter have either a state of UNVERIFIED or ACTIVE, 958 and any old addresses on the old SA not listed in the LOCATOR_SET 959 parameter have a state of DEPRECATED. 961 Once the host has processed the locators, if the LOCATOR_SET 962 parameter contains a new Preferred locator, the host SHOULD initiate 963 a change of the Preferred locator. This requires that the host first 964 verifies reachability of the associated address, and only then 965 changes the Preferred locator; see Section 5.5. 967 If a host receives a locator with an unsupported Locator Type, and 968 when such a locator is also declared to be the Preferred locator for 969 the peer, the host SHOULD send a NOTIFY error with a Notify Message 970 Type of LOCATOR_TYPE_UNSUPPORTED, with the Notification Data field 971 containing the locator(s) that the receiver failed to process. 972 Otherwise, a host MAY send a NOTIFY error if a (non-preferred) 973 locator with an unsupported Locator Type is received in a LOCATOR_SET 974 parameter. 976 A host MAY add the source IP address of a received HIP packet as a 977 candidate locator for the peer even if it is not listed in the peer's 978 LOCATOR_SET, but it SHOULD prefer locators explicitly listed in the 979 LOCATOR_SET. 981 5.4. Verifying Address Reachability 983 A host MUST verify the reachability of an UNVERIFIED address. The 984 status of a newly learned address MUST initially be set to UNVERIFIED 985 unless the new address is advertised in a R1 packet as a new 986 Preferred locator. A host MAY also want to verify the reachability 987 of an ACTIVE address again after some time, in which case it would 988 set the status of the address to UNVERIFIED and reinitiate address 989 verification. 991 A host typically starts the address-verification procedure by sending 992 a nonce to the new address. For example, when the host is changing 993 its SPI and sending an ESP_INFO to the peer, the NEW SPI value SHOULD 994 be random and the value MAY be copied into an ECHO_REQUEST sent in 995 the rekeying UPDATE. However, if the host is not changing its SPI, 996 it MAY still use the ECHO_REQUEST parameter in an UPDATE message sent 997 to the new address. A host MAY also use other message exchanges as 998 confirmation of the address reachability. 1000 In some cases, it MAY be sufficient to use the arrival of data on a 1001 newly advertised SA as implicit address reachability verification as 1002 depicted in Figure 7, instead of waiting for the confirmation via a 1003 HIP packet. In this case, a host advertising a new SPI as part of 1004 its address reachability check SHOULD be prepared to receive traffic 1005 on the new SA. 1007 Mobile host Peer host 1009 prepare incoming SA 1010 NEW SPI in ESP_INFO (UPDATE) 1011 <----------------------------------- 1012 switch to new outgoing SA 1013 data on new SA 1014 -----------------------------------> 1015 mark address ACTIVE 1017 Figure 7: Address Activation Via Use of a New SA 1019 When address verification is in progress for a new Preferred locator, 1020 the host SHOULD select a different locator listed as ACTIVE, if one 1021 such locator is available, to continue communications until address 1022 verification completes. Alternatively, the host MAY use the new 1023 Preferred locator while in UNVERIFIED status to the extent Credit- 1024 Based Authorization permits. Credit-Based Authorization is explained 1025 in Section 5.6. Once address verification succeeds, the status of 1026 the new Preferred locator changes to ACTIVE. 1028 5.5. Changing the Preferred Locator 1030 A host MAY want to change the Preferred outgoing locator for 1031 different reasons, e.g., because traffic information or ICMP error 1032 messages indicate that the currently used preferred address may have 1033 become unreachable. Another reason may be due to receiving a 1034 LOCATOR_SET parameter that has the "P" bit set. 1036 To change the Preferred locator, the host initiates the following 1037 procedure: 1039 1. If the new Preferred locator has ACTIVE status, the Preferred 1040 locator is changed and the procedure succeeds. 1042 2. If the new Preferred locator has UNVERIFIED status, the host 1043 starts to verify its reachability. The host SHOULD use a 1044 different locator listed as ACTIVE until address verification 1045 completes if one such locator is available. Alternatively, the 1046 host MAY use the new Preferred locator, even though in UNVERIFIED 1047 status, to the extent Credit-Based Authorization permits. Once 1048 address verification succeeds, the status of the new Preferred 1049 locator changes to ACTIVE and its use is no longer governed by 1050 Credit-Based Authorization. 1052 3. If the peer host has not indicated a preference for any address, 1053 then the host picks one of the peer's ACTIVE addresses randomly 1054 or according to policy. This case may arise if, for example, 1055 ICMP error messages that deprecate the Preferred locator arrive, 1056 but the peer has not yet indicated a new Preferred locator. 1058 4. If the new Preferred locator has DEPRECATED status and there is 1059 at least one non-deprecated address, the host selects one of the 1060 non-deprecated addresses as a new Preferred locator and 1061 continues. If the selected address is UNVERIFIED, the address 1062 verification procedure described above will apply. 1064 5.6. Credit-Based Authorization 1066 To prevent redirection-based flooding attacks, the use of a Credit- 1067 Based Authorization (CBA) approach is mandatory when a host sends 1068 data to an UNVERIFIED locator. The following algorithm meets the 1069 security considerations for prevention of amplification and time- 1070 shifting attacks. Other forms of credit aging, and other values for 1071 the CreditAgingFactor and CreditAgingInterval parameters in 1072 particular, are for further study, and so are the advanced CBA 1073 techniques specified in [CBA-MIPv6]. 1075 5.6.1. Handling Payload Packets 1077 A host maintains a "credit counter" for each of its peers. Whenever 1078 a packet arrives from a peer, the host SHOULD increase that peer's 1079 credit counter by the size of the received packet. When the host has 1080 a packet to be sent to the peer, and when the peer's Preferred 1081 locator is listed as UNVERIFIED and no alternative locator with 1082 status ACTIVE is available, the host checks whether it can send the 1083 packet to the UNVERIFIED locator. The packet SHOULD be sent if the 1084 value of the credit counter is higher than the size of the outbound 1085 packet. If the credit counter is too low, the packet MUST be 1086 discarded or buffered until address verification succeeds. When a 1087 packet is sent to a peer at an UNVERIFIED locator, the peer's credit 1088 counter MUST be reduced by the size of the packet. The peer's credit 1089 counter is not affected by packets that the host sends to an ACTIVE 1090 locator of that peer. 1092 Figure 8 depicts the actions taken by the host when a packet is 1093 received. Figure 9 shows the decision chain in the event a packet is 1094 sent. 1096 Inbound 1097 packet 1098 | 1099 | +----------------+ +---------------+ 1100 | | Increase | | Deliver | 1101 +-----> | credit counter |-------------> | packet to | 1102 | by packet size | | application | 1103 +----------------+ +---------------+ 1105 Figure 8: Receiving Packets with Credit-Based Authorization 1107 Outbound 1108 packet 1109 | _________________ 1110 | / \ +---------------+ 1111 | / Is the preferred \ No | Send packet | 1112 +-----> | destination address |-------------> | to preferred | 1113 \ UNVERIFIED? / | address | 1114 \_________________/ +---------------+ 1115 | 1116 | Yes 1117 | 1118 v 1119 _________________ 1120 / \ +---------------+ 1121 / Does an ACTIVE \ Yes | Send packet | 1122 | destination address |-------------> | to ACTIVE | 1123 \ exist? / | address | 1124 \_________________/ +---------------+ 1125 | 1126 | No 1127 | 1128 v 1129 _________________ 1130 / \ +---------------+ 1131 / Credit counter \ No | | 1132 | >= |-------------> | Drop packet | 1133 \ packet size? / | | 1134 \_________________/ +---------------+ 1135 | 1136 | Yes 1137 | 1138 v 1139 +---------------+ +---------------+ 1140 | Reduce credit | | Send packet | 1141 | counter by |----------------> | to preferred | 1142 | packet size | | address | 1143 +---------------+ +---------------+ 1145 Figure 9: Sending Packets with Credit-Based Authorization 1147 5.6.2. Credit Aging 1149 A host ensures that the credit counters it maintains for its peers 1150 gradually decrease over time. Such "credit aging" prevents a 1151 malicious peer from building up credit at a very slow speed and using 1152 this, all at once, for a severe burst of redirected packets. 1154 Credit aging may be implemented by multiplying credit counters with a 1155 factor, CreditAgingFactor (a fractional value less than one), in 1156 fixed time intervals of CreditAgingInterval length. Choosing 1157 appropriate values for CreditAgingFactor and CreditAgingInterval is 1158 important to ensure that a host can send packets to an address in 1159 state UNVERIFIED even when the peer sends at a lower rate than the 1160 host itself. When CreditAgingFactor or CreditAgingInterval are too 1161 small, the peer's credit counter might be too low to continue sending 1162 packets until address verification concludes. 1164 The parameter values proposed in this document are as follows: 1166 CreditAgingFactor 7/8 1167 CreditAgingInterval 5 seconds 1169 These parameter values work well when the host transfers a file to 1170 the peer via a TCP connection and the end-to-end round-trip time does 1171 not exceed 500 milliseconds. Alternative credit-aging algorithms may 1172 use other parameter values or different parameters, which may even be 1173 dynamically established. 1175 6. Security Considerations 1177 The HIP mobility mechanism provides a secure means of updating a 1178 host's IP address via HIP UPDATE packets. Upon receipt, a HIP host 1179 cryptographically verifies the sender of an UPDATE, so forging or 1180 replaying a HIP UPDATE packet is very difficult (see [RFC7401]). 1181 Therefore, security issues reside in other attack domains. The two 1182 we consider are malicious redirection of legitimate connections as 1183 well as redirection-based flooding attacks using this protocol. This 1184 can be broken down into the following: 1186 Impersonation attacks 1188 - direct conversation with the misled victim 1190 - man-in-the-middle attack 1192 DoS attacks 1194 - flooding attacks (== bandwidth-exhaustion attacks) 1196 * tool 1: direct flooding 1198 * tool 2: flooding by zombies 1200 * tool 3: redirection-based flooding 1202 - memory-exhaustion attacks 1204 - computational-exhaustion attacks 1206 We consider these in more detail in the following sections. 1208 In Section 6.1 and Section 6.2, we assume that all users are using 1209 HIP. In Section 6.3 we consider the security ramifications when we 1210 have both HIP and non-HIP users. Security considerations for Credit- 1211 Based Authorization are discussed in [SIMPLE-CBA]. 1213 6.1. Impersonation Attacks 1215 An attacker wishing to impersonate another host will try to mislead 1216 its victim into directly communicating with them, or carry out a man- 1217 in-the-middle (MitM) attack between the victim and the victim's 1218 desired communication peer. Without mobility support, both attack 1219 types are possible only if the attacker resides on the routing path 1220 between its victim and the victim's desired communication peer, or if 1221 the attacker tricks its victim into initiating the connection over an 1222 incorrect routing path (e.g., by acting as a router or using spoofed 1223 DNS entries). 1225 The HIP extensions defined in this specification change the situation 1226 in that they introduce an ability to redirect a connection (like 1227 IPv6), both before and after establishment. If no precautionary 1228 measures are taken, an attacker could misuse the redirection feature 1229 to impersonate a victim's peer from any arbitrary location. The 1230 authentication and authorization mechanisms of the HIP base exchange 1231 [RFC7401] and the signatures in the UPDATE message prevent this 1232 attack. Furthermore, ownership of a HIP association is securely 1233 linked to a HIP HI/HIT. If an attacker somehow uses a bug in the 1234 implementation or weakness in some protocol to redirect a HIP 1235 connection, the original owner can always reclaim their connection 1236 (they can always prove ownership of the private key associated with 1237 their public HI). 1239 MitM attacks are always possible if the attacker is present during 1240 the initial HIP base exchange and if the hosts do not authenticate 1241 each other's identities. However, once the opportunistic base 1242 exchange has taken place, even a MitM cannot steal the HIP connection 1243 anymore because it is very difficult for an attacker to create an 1244 UPDATE packet (or any HIP packet) that will be accepted as a 1245 legitimate update. UPDATE packets use HMAC and are signed. Even 1246 when an attacker can snoop packets to obtain the SPI and HIT/HI, they 1247 still cannot forge an UPDATE packet without knowledge of the secret 1248 keys. 1250 6.2. Denial-of-Service Attacks 1252 6.2.1. Flooding Attacks 1254 The purpose of a denial-of-service attack is to exhaust some resource 1255 of the victim such that the victim ceases to operate correctly. A 1256 denial-of-service attack can aim at the victim's network attachment 1257 (flooding attack), its memory, or its processing capacity. In a 1258 flooding attack, the attacker causes an excessive number of bogus or 1259 unwanted packets to be sent to the victim, which fills their 1260 available bandwidth. Note that the victim does not necessarily need 1261 to be a node; it can also be an entire network. The attack basically 1262 functions the same way in either case. 1264 An effective DoS strategy is distributed denial of service (DDoS). 1265 Here, the attacker conventionally distributes some viral software to 1266 as many nodes as possible. Under the control of the attacker, the 1267 infected nodes, or "zombies", jointly send packets to the victim. 1268 With such an 'army', an attacker can take down even very high 1269 bandwidth networks/victims. 1271 With the ability to redirect connections, an attacker could realize a 1272 DDoS attack without having to distribute viral code. Here, the 1273 attacker initiates a large download from a server, and subsequently 1274 redirects this download to its victim. The attacker can repeat this 1275 with multiple servers. This threat is mitigated through reachability 1276 checks and credit-based authorization. Both strategies do not 1277 eliminate flooding attacks per se, but they preclude: (i) their use 1278 from a location off the path towards the flooded victim; and (ii) any 1279 amplification in the number and size of the redirected packets. As a 1280 result, the combination of a reachability check and credit-based 1281 authorization lowers a HIP redirection-based flooding attack to the 1282 level of a direct flooding attack in which the attacker itself sends 1283 the flooding traffic to the victim. 1285 6.2.2. Memory/Computational-Exhaustion DoS Attacks 1287 We now consider whether or not the proposed extensions to HIP add any 1288 new DoS attacks (consideration of DoS attacks using the base HIP 1289 exchange and updates is discussed in [RFC7401]). A simple attack is 1290 to send many UPDATE packets containing many IP addresses that are not 1291 flagged as preferred. The attacker continues to send such packets 1292 until the number of IP addresses associated with the attacker's HI 1293 crashes the system. Therefore, there SHOULD be a limit to the number 1294 of IP addresses that can be associated with any HI. Other forms of 1295 memory/computationally exhausting attacks via the HIP UPDATE packet 1296 are handled in the base HIP document [RFC7401]. 1298 A central server that has to deal with a large number of mobile 1299 clients may consider increasing the SA lifetimes to try to slow down 1300 the rate of rekeying UPDATEs or increasing the cookie difficulty to 1301 slow down the rate of attack-oriented connections. 1303 6.3. Mixed Deployment Environment 1305 We now assume an environment with both HIP and non-HIP aware hosts. 1306 Four cases exist. 1308 1. A HIP host redirects its connection onto a non-HIP host. The 1309 non-HIP host will drop the reachability packet, so this is not a 1310 threat unless the HIP host is a MitM that could somehow respond 1311 successfully to the reachability check. 1313 2. A non-HIP host attempts to redirect their connection onto a HIP 1314 host. This falls into IPv4 and IPv6 security concerns, which are 1315 outside the scope of this document. 1317 3. A non-HIP host attempts to steal a HIP host's session (assume 1318 that Secure Neighbor Discovery is not active for the following). 1319 The non-HIP host contacts the service that a HIP host has a 1320 connection with and then attempts to change its IP address to 1321 steal the HIP host's connection. What will happen in this case 1322 is implementation dependent but such a request should fail by 1323 being ignored or dropped. Even if the attack were successful, 1324 the HIP host could reclaim its connection via HIP. 1326 4. A HIP host attempts to steal a non-HIP host's session. A HIP 1327 host could spoof the non-HIP host's IP address during the base 1328 exchange or set the non-HIP host's IP address as its preferred 1329 address via an UPDATE. Other possibilities exist, but a simple 1330 solution is to prevent the use of HIP address check information 1331 to influence non-HIP sessions. 1333 7. IANA Considerations 1335 The following changes to the "Host Identity Protocol (HIP) 1336 Parameters" registries are requested. 1338 The existing Parameter Type of 'LOCATOR' (value 193) should be 1339 renamed to 'LOCATOR_SET' and the reference should be updated from 1340 RFC5206 to this specification. 1342 The existing Notify Message Type of 'LOCATOR_TYPE_UNSUPPORTED' (value 1343 46) should have its reference updated from RFC5206 to this 1344 specification. 1346 8. Authors and Acknowledgments 1348 Pekka Nikander and Jari Arkko originated this document, and Christian 1349 Vogt and Thomas Henderson (editor) later joined as co-authors. Greg 1350 Perkins contributed the initial draft of the security section. Petri 1351 Jokela was a co-author of the initial individual submission. 1353 The authors thank Jeff Ahrenholz, Baris Boyvat, Rene Hummen, Miika 1354 Komu, Mika Kousa, Jan Melen, and Samu Varjonen for improvements to 1355 the document. 1357 9. References 1359 9.1. Normative references 1361 [I-D.ietf-hip-rfc5203-bis] 1362 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1363 Registration Extension", draft-ietf-hip-rfc5203-bis-09 1364 (work in progress), June 2015. 1366 [I-D.ietf-hip-rfc5204-bis] 1367 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1368 Rendezvous Extension", draft-ietf-hip-rfc5204-bis-07 (work 1369 in progress), December 2015. 1371 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1372 Requirement Levels", BCP 14, RFC 2119, 1373 DOI 10.17487/RFC2119, March 1997, 1374 . 1376 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1377 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1378 2006, . 1380 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 1381 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 1382 RFC 7401, DOI 10.17487/RFC7401, April 2015, 1383 . 1385 [RFC7402] Jokela, P., Moskowitz, R., and J. Melen, "Using the 1386 Encapsulating Security Payload (ESP) Transport Format with 1387 the Host Identity Protocol (HIP)", RFC 7402, 1388 DOI 10.17487/RFC7402, April 2015, 1389 . 1391 9.2. Informative references 1393 [CBA-MIPv6] 1394 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1395 Mobile IPv6 Early Binding Updates", February 2005. 1397 [RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. 1398 Nordmark, "Mobile IP Version 6 Route Optimization Security 1399 Design Background", RFC 4225, DOI 10.17487/RFC4225, 1400 December 2005, . 1402 [SIMPLE-CBA] 1403 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1404 Concurrent Reachability Verification", February 2006. 1406 Appendix A. Document Revision History 1408 To be removed upon publication 1410 +----------+--------------------------------------------------------+ 1411 | Revision | Comments | 1412 +----------+--------------------------------------------------------+ 1413 | draft-00 | Initial version from RFC5206 xml (unchanged). | 1414 | | | 1415 | draft-01 | Remove multihoming-specific text; no other changes. | 1416 | | | 1417 | draft-02 | Update references to point to -bis drafts; no other | 1418 | | changes. | 1419 | | | 1420 | draft-03 | issue 4: add make before break use case | 1421 | | | 1422 | | issue 6: peer locator exposure policies | 1423 | | | 1424 | | issue 10: rename LOCATOR to LOCATOR_SET | 1425 | | | 1426 | | issue 14: use of UPDATE packet's IP address | 1427 | | | 1428 | draft-04 | Document refresh; no other changes. | 1429 | | | 1430 | draft-05 | Document refresh; no other changes. | 1431 | | | 1432 | draft-06 | Document refresh; no other changes. | 1433 | | | 1434 | draft-07 | Document refresh; IANA considerations updated. | 1435 | | | 1436 | draft-08 | Remove sending LOCATOR_SET in R1, I2, and NOTIFY | 1437 | | (multihoming) | 1438 | | | 1439 | | State that only one LOCATOR_SET parameter may be sent | 1440 | | in an UPDATE packet (according to this draft) | 1441 | | (multihoming) | 1442 | | | 1443 | | Remove text about cross-family handovers (multihoming) | 1444 | | | 1445 | draft-09 | Add specification text regarding double-jump mobility | 1446 | | procedures. | 1447 | | | 1448 | draft-10 | issue 21: clarified that HI MAY be included in UPDATE | 1449 | | for benefit of middleboxes | 1450 | | | 1451 | | changed one informative reference from RFC 4423-bis to | 1452 | | RFC 7401 | 1453 | | | 1454 | | removed discussion about possible multiple LOCATOR_SET | 1455 | | and ESP_INFO parameters in an UPDATE (per previous | 1456 | | mailing list discussion) | 1457 | | | 1458 | | removed discussion about handling LOCATOR_SET | 1459 | | parameters in packets other than UPDATE (per previous | 1460 | | mailing list discussion) | 1461 +----------+--------------------------------------------------------+ 1463 Authors' Addresses 1465 Thomas R. Henderson (editor) 1466 University of Washington 1467 Campus Box 352500 1468 Seattle, WA 1469 USA 1471 EMail: tomhend@u.washington.edu 1473 Christian Vogt 1474 Ericsson Research NomadicLab 1475 Hirsalantie 11 1476 JORVAS FIN-02420 1477 FINLAND 1479 EMail: christian.vogt@ericsson.com 1481 Jari Arkko 1482 Ericsson Research NomadicLab 1483 JORVAS FIN-02420 1484 FINLAND 1486 Phone: +358 40 5079256 1487 EMail: jari.arkko@ericsson.com