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Arkko 6 Expires: July 16, 2015 Ericsson Research NomadicLab 7 January 12, 2015 9 Host Mobility with the Host Identity Protocol 10 draft-ietf-hip-rfc5206-bis-08 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 16, 2015. 42 Copyright Notice 44 Copyright (c) 2015 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. Network Renumbering . . . . . . . . . . . . . . . . . 11 82 3.3. Other Considerations . . . . . . . . . . . . . . . . . . 11 83 3.3.1. Address Verification . . . . . . . . . . . . . . . . 12 84 3.3.2. Credit-Based Authorization . . . . . . . . . . . . . 12 85 3.3.3. Preferred Locator . . . . . . . . . . . . . . . . . . 13 86 4. LOCATOR_SET Parameter Format . . . . . . . . . . . . . . . . 14 87 4.1. Traffic Type and Preferred Locator . . . . . . . . . . . 15 88 4.2. Locator Type and Locator . . . . . . . . . . . . . . . . 16 89 4.3. UPDATE Packet with Included LOCATOR_SET . . . . . . . . . 16 90 5. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 16 91 5.1. Locator Data Structure and Status . . . . . . . . . . . . 16 92 5.2. Sending LOCATOR_SETs . . . . . . . . . . . . . . . . . . 18 93 5.3. Handling Received LOCATOR_SETs . . . . . . . . . . . . . 19 94 5.4. Verifying Address Reachability . . . . . . . . . . . . . 21 95 5.5. Changing the Preferred Locator . . . . . . . . . . . . . 22 96 5.6. Credit-Based Authorization . . . . . . . . . . . . . . . 23 97 5.6.1. Handling Payload Packets . . . . . . . . . . . . . . 23 98 5.6.2. Credit Aging . . . . . . . . . . . . . . . . . . . . 25 99 6. Security Considerations . . . . . . . . . . . . . . . . . . . 26 100 6.1. Impersonation Attacks . . . . . . . . . . . . . . . . . . 27 101 6.2. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 28 102 6.2.1. Flooding Attacks . . . . . . . . . . . . . . . . . . 28 103 6.2.2. Memory/Computational-Exhaustion DoS Attacks . . . . . 28 104 6.3. Mixed Deployment Environment . . . . . . . . . . . . . . 29 105 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 106 8. Authors and Acknowledgments . . . . . . . . . . . . . . . . . 30 107 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 108 9.1. Normative references . . . . . . . . . . . . . . . . . . 30 109 9.2. Informative references . . . . . . . . . . . . . . . . . 30 110 Appendix A. Document Revision History . . . . . . . . . . . . . 32 112 1. Introduction and Scope 114 The Host Identity Protocol [I-D.ietf-hip-rfc4423-bis] (HIP) supports 115 an architecture that decouples the transport layer (TCP, UDP, etc.) 116 from the internetworking layer (IPv4 and IPv6) by using public/ 117 private key pairs, instead of IP addresses, as host identities. When 118 a host uses HIP, the overlying protocol sublayers (e.g., transport 119 layer sockets and Encapsulating Security Payload (ESP) Security 120 Associations (SAs)) are instead bound to representations of these 121 host identities, and the IP addresses are only used for packet 122 forwarding. However, each host must also know at least one IP 123 address at which its peers are reachable. Initially, these IP 124 addresses are the ones used during the HIP base exchange 125 [I-D.ietf-hip-rfc5201-bis]. 127 One consequence of such a decoupling is that new solutions to 128 network-layer mobility and host multihoming are possible. There are 129 potentially many variations of mobility and multihoming possible. 130 The scope of this document encompasses messaging and elements of 131 procedure for basic network-level host mobility, leaving more 132 complicated mobility scenarios, multihoming, and other variations for 133 further study. More specifically: 135 This document defines a generalized LOCATOR_SET parameter for use 136 in HIP messages. The LOCATOR_SET parameter allows a HIP host to 137 notify a peer about alternate locators at which it is reachable. 138 The locators may be merely IP addresses, or they may have 139 additional multiplexing and demultiplexing context to aid with the 140 packet handling in the lower layers. For instance, an IP address 141 may need to be paired with an ESP Security Parameter Index (SPI) 142 so that packets are sent on the correct SA for a given address. 144 This document also specifies the messaging and elements of 145 procedure for end-host mobility of a HIP host -- the sequential 146 change in the preferred IP address used to reach a host. In 147 particular, message flows to enable successful host mobility, 148 including address verification methods, are defined herein. 150 However, while the same LOCATOR_SET parameter is intended to 151 support host multihoming (simultaneous use of a number of 152 addresses), detailed elements of procedure for host multihoming 153 are out of scope. 155 While HIP can potentially be used with transports other than the ESP 156 transport format [I-D.ietf-hip-rfc5202-bis], this document largely 157 assumes the use of ESP and leaves other transport formats for further 158 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 Such functionality is out of the scope of this document. We also do 167 not consider localized mobility management extensions (i.e., mobility 168 management techniques that do not involve directly signaling the 169 correspondent node); this document is concerned with end-to-end 170 mobility. Making underlying IP mobility transparent to the transport 171 layer has implications on the proper response of transport congestion 172 control, path MTU selection, and Quality of Service (QoS). 173 Transport-layer mobility triggers, and the proper transport response 174 to a HIP mobility or multihoming address change, are outside the 175 scope of this document. 177 2. Terminology and Conventions 179 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 180 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 181 document are to be interpreted as described in RFC 2119 [RFC2119]. 183 LOCATOR_SET. The name of a HIP parameter containing zero or more 184 Locator fields. 186 Locator. A name that controls how the packet is routed through the 187 network and demultiplexed by the end host. It may include a 188 concatenation of traditional network addresses such as an IPv6 189 address and end-to-end identifiers such as an ESP SPI. It may 190 also include transport port numbers or IPv6 Flow Labels as 191 demultiplexing context, or it may simply be a network address. 193 Address. A name that denotes a point-of-attachment to the network. 194 The two most common examples are an IPv4 address and an IPv6 195 address. The set of possible addresses is a subset of the set of 196 possible locators. 198 Preferred locator. A locator on which a host prefers to receive 199 data. With respect to a given peer, a host always has one active 200 Preferred locator, unless there are no active locators. By 201 default, the locators used in the HIP base exchange are the 202 Preferred locators. 204 Credit Based Authorization. A host must verify a peer host's 205 reachability at a new locator. Credit-Based Authorization 206 authorizes the peer to receive a certain amount of data at the new 207 locator before the result of such verification is known. 209 3. Protocol Model 211 This section is an overview; more detailed specification follows this 212 section. 214 3.1. Operating Environment 216 The Host Identity Protocol (HIP) [I-D.ietf-hip-rfc5201-bis] is a key 217 establishment and parameter negotiation protocol. Its primary 218 applications are for authenticating host messages based on host 219 identities, and establishing security associations (SAs) for the ESP 220 transport format [I-D.ietf-hip-rfc5202-bis] and possibly other 221 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 285 [I-D.ietf-hip-rfc5201-bis]. The HIP base exchange establishes the 286 HITs in use between the hosts, the SPIs to use for ESP, and the IP 287 addresses (used in both the HIP signaling packets and ESP data 288 packets). Note that there can only be one such set of bindings in 289 the outbound direction for any given packet, and the only fields used 290 for the binding at the HIP layer are the fields exposed by ESP (the 291 SPI and HITs). For the inbound direction, the SPI is all that is 292 required to find the right host context. ESP rekeying events change 293 the mapping between the HIT pair and SPI, but do not change the IP 294 addresses. 296 Consider next a mobility event, in which a host moves to another IP 297 address. Two things must occur in this case. First, the peer must 298 be notified of the address change using a HIP UPDATE message. 299 Second, each host must change its local bindings at the HIP sublayer 300 (new IP addresses). It may be that both the SPIs and IP addresses 301 are changed simultaneously in a single UPDATE; the protocol described 302 herein supports this. However, simultaneous movement of both hosts, 303 notification of transport layer protocols of the path change, and 304 procedures for possibly traversing middleboxes are not covered by 305 this document. 307 3.1.1. Locator 309 This document defines a generalization of an address called a 310 "locator". A locator specifies a point-of-attachment to the network 311 but may also include additional end-to-end tunneling or per-host 312 demultiplexing context that affects how packets are handled below the 313 logical HIP sublayer of the stack. This generalization is useful 314 because IP addresses alone may not be sufficient to describe how 315 packets should be handled below HIP. For example, in a host 316 multihoming context, certain IP addresses may need to be associated 317 with certain ESP SPIs to avoid violating the ESP anti-replay window. 318 Addresses may also be affiliated with transport ports in certain 319 tunneling scenarios. Locators may simply be traditional network 320 addresses. The format of the locator fields in the LOCATOR_SET 321 parameter is defined in Section 4. 323 3.1.2. Mobility Overview 325 When a host moves to another address, it notifies its peer of the new 326 address by sending a HIP UPDATE packet containing a LOCATOR_SET 327 parameter. This UPDATE packet is acknowledged by the peer. For 328 reliability in the presence of packet loss, the UPDATE packet is 329 retransmitted as defined in the HIP protocol specification 330 [I-D.ietf-hip-rfc5201-bis]. The peer can authenticate the contents 331 of the UPDATE packet based on the signature and keyed hash of the 332 packet. 334 When using ESP Transport Format [I-D.ietf-hip-rfc5202-bis], the host 335 may at the same time decide to rekey its security association and 336 possibly generate a new Diffie-Hellman key; all of these actions are 337 triggered by including additional parameters in the UPDATE packet, as 338 defined in the base protocol specification [I-D.ietf-hip-rfc5201-bis] 339 and ESP extension [I-D.ietf-hip-rfc5202-bis]. 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 [I-D.ietf-hip-rfc5202-bis], although other 357 scenarios may be defined in the future. To understand these usage 358 scenarios, the reader should be at least minimally familiar with the 359 HIP protocol specification [I-D.ietf-hip-rfc5201-bis]. However, for 360 the (relatively) uninitiated reader, it is most important to keep in 361 mind that in HIP the actual payload traffic is protected with ESP, 362 and that the ESP SPI acts as an index to the right host-to-host 363 context. More specification details are found later in Section 4 and 364 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 [I-D.ietf-hip-rfc5201-bis]. 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. Network Renumbering 487 It is expected that IPv6 networks will be renumbered much more often 488 than most IPv4 networks. From an end-host point of view, network 489 renumbering is similar to mobility. 491 3.3. Other Considerations 492 3.3.1. Address Verification 494 When a HIP host receives a set of locators from another HIP host in a 495 LOCATOR_SET, it does not necessarily know whether the other host is 496 actually reachable at the claimed addresses. In fact, a malicious 497 peer host may be intentionally giving bogus addresses in order to 498 cause a packet flood towards the target addresses [RFC4225]. 499 Therefore, the HIP host must first check that the peer is reachable 500 at the new address. 502 An additional potential benefit of performing address verification is 503 to allow middleboxes in the network along the new path to obtain the 504 peer host's inbound SPI. 506 Address verification is implemented by the challenger sending some 507 piece of unguessable information to the new address, and waiting for 508 some acknowledgment from the Responder that indicates reception of 509 the information at the new address. This may include the exchange of 510 a nonce, or the generation of a new SPI and observation of data 511 arriving on the new SPI. 513 3.3.2. Credit-Based Authorization 515 Credit-Based Authorization (CBA) allows a host to securely use a new 516 locator even though the peer's reachability at the address embedded 517 in the locator has not yet been verified. This is accomplished based 518 on the following three hypotheses: 520 1. A flooding attacker typically seeks to somehow multiply the 521 packets it generates for the purpose of its attack because 522 bandwidth is an ample resource for many victims. 524 2. An attacker can often cause unamplified flooding by sending 525 packets to its victim, either by directly addressing the victim 526 in the packets, or by guiding the packets along a specific path 527 by means of an IPv6 Routing header, if Routing headers are not 528 filtered by firewalls. 530 3. Consequently, the additional effort required to set up a 531 redirection-based flooding attack (without CBA and return 532 routability checks) would pay off for the attacker only if 533 amplification could be obtained this way. 535 On this basis, rather than eliminating malicious packet redirection 536 in the first place, Credit-Based Authorization prevents 537 amplifications. This is accomplished by limiting the data a host can 538 send to an unverified address of a peer by the data recently received 539 from that peer. Redirection-based flooding attacks thus become less 540 attractive than, for example, pure direct flooding, where the 541 attacker itself sends bogus packets to the victim. 543 Figure 5 illustrates Credit-Based Authorization: Host B measures the 544 amount of data recently received from peer A and, when A readdresses, 545 sends packets to A's new, unverified address as long as the sum of 546 the packet sizes does not exceed the measured, received data volume. 547 When insufficient credit is left, B stops sending further packets to 548 A until A's address becomes ACTIVE. The address changes may be due 549 to mobility, multihoming, or any other reason. Not shown in Figure 5 550 are the results of credit aging (Section 5.6.2), a mechanism used to 551 dampen possible time-shifting attacks. 553 +-------+ +-------+ 554 | A | | B | 555 +-------+ +-------+ 556 | | 557 address |------------------------------->| credit += size(packet) 558 ACTIVE | | 559 |------------------------------->| credit += size(packet) 560 |<-------------------------------| do not change credit 561 | | 562 + address change | 563 + address verification starts | 564 address |<-------------------------------| credit -= size(packet) 565 UNVERIFIED |------------------------------->| credit += size(packet) 566 |<-------------------------------| credit -= size(packet) 567 | | 568 |<-------------------------------| credit -= size(packet) 569 | X credit < size(packet) 570 | | => do not send packet! 571 + address verification concludes | 572 address | | 573 ACTIVE |<-------------------------------| do not change credit 574 | | 576 Figure 5: Readdressing Scenario 578 3.3.3. Preferred Locator 580 When a host has multiple locators, the peer host must decide which to 581 use for outbound packets. It may be that a host would prefer to 582 receive data on a particular inbound interface. HIP allows a 583 particular locator to be designated as a Preferred locator and 584 communicated to the peer (see Section 4). 586 4. LOCATOR_SET Parameter Format 588 The LOCATOR_SET parameter is a critical parameter as defined by 589 [I-D.ietf-hip-rfc5201-bis]. It consists of the standard HIP 590 parameter Type and Length fields, plus zero or more Locator sub- 591 parameters. Each Locator sub-parameter contains a Traffic Type, 592 Locator Type, Locator Length, Preferred locator bit, Locator 593 Lifetime, and a Locator encoding. A LOCATOR_SET containing zero 594 Locator fields is permitted but has the effect of deprecating all 595 addresses. 597 0 1 2 3 598 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 1 599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 | Type | Length | 601 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 602 | Traffic Type | Locator Type | Locator Length | Reserved |P| 603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 | Locator Lifetime | 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 | Locator | 607 | | 608 | | 609 | | 610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 611 . . 612 . . 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 614 | Traffic Type | Locator Type | Locator Length | Reserved |P| 615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 616 | Locator Lifetime | 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | Locator | 619 | | 620 | | 621 | | 622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 624 Figure 6: LOCATOR_SET Parameter Format 626 Type: 193 628 Length: Length in octets, excluding Type and Length fields, and 629 excluding padding. 631 Traffic Type: Defines whether the locator pertains to HIP signaling, 632 user data, or both. 634 Locator Type: Defines the semantics of the Locator field. 636 Locator Length: Defines the length of the Locator field, in units of 637 4-byte words (Locators up to a maximum of 4*255 octets are 638 supported). 640 Reserved: Zero when sent, ignored when received. 642 P: Preferred locator. Set to one if the locator is preferred for 643 that Traffic Type; otherwise, set to zero. 645 Locator Lifetime: Locator lifetime, in seconds. 647 Locator: The locator whose semantics and encoding are indicated by 648 the Locator Type field. All Locator sub-fields are integral 649 multiples of four octets in length. 651 The Locator Lifetime indicates how long the following locator is 652 expected to be valid. The lifetime is expressed in seconds. Each 653 locator MUST have a non-zero lifetime. The address is expected to 654 become deprecated when the specified number of seconds has passed 655 since the reception of the message. A deprecated address SHOULD NOT 656 be used as a destination address if an alternate (non-deprecated) is 657 available and has sufficient scope. 659 4.1. Traffic Type and Preferred Locator 661 The following Traffic Type values are defined: 663 0: Both signaling (HIP control packets) and user data. 665 1: Signaling packets only. 667 2: Data packets only. 669 The "P" bit, when set, has scope over the corresponding Traffic Type. 670 That is, when a "P" bit is set for Traffic Type "2", for example, it 671 means that the locator is preferred for data packets. If there is a 672 conflict (for example, if the "P" bit is set for an address of Type 673 "0" and a different address of Type "2"), the more specific Traffic 674 Type rule applies (in this case, "2"). By default, the IP addresses 675 used in the base exchange are Preferred locators for both signaling 676 and user data, unless a new Preferred locator supersedes them. If no 677 locators are indicated as preferred for a given Traffic Type, the 678 implementation may use an arbitrary locator from the set of active 679 locators. 681 4.2. Locator Type and Locator 683 The following Locator Type values are defined, along with the 684 associated semantics of the Locator field: 686 0: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [RFC4291] 687 (128 bits long). This locator type is defined primarily for non- 688 ESP-based usage. 690 1: The concatenation of an ESP SPI (first 32 bits) followed by an 691 IPv6 address or an IPv4-in-IPv6 format IPv4 address (an additional 692 128 bits). This IP address is defined primarily for ESP-based 693 usage. 695 4.3. UPDATE Packet with Included LOCATOR_SET 697 A number of combinations of parameters in an UPDATE packet are 698 possible (e.g., see Section 3.2). In this document, procedures are 699 defined only for the case in which one LOCATOR_SET and one ESP_INFO 700 parameter is used in any HIP packet. Furthermore, the LOCATOR_SET 701 SHOULD list all of the locators that are active on the HIP 702 association (including those on SAs not covered by the ESP_INFO 703 parameter). Any UPDATE packet that includes a LOCATOR_SET parameter 704 SHOULD include both an HMAC and a HIP_SIGNATURE parameter. The 705 relationship between the announced Locators and any ESP_INFO 706 parameters present in the packet is defined in Section 5.2. The 707 sending of multiple LOCATOR_SET and/or ESP_INFO parameters is for 708 further study; receivers may wish to experiment with supporting such 709 a possibility. 711 5. Processing Rules 713 This section describes rules for sending and receiving the 714 LOCATOR_SET parameter, testing address reachability, and using 715 Credit-Based Authorization (CBA) on UNVERIFIED locators. 717 5.1. Locator Data Structure and Status 719 In a typical implementation, each locator announced in a LOCATOR_SET 720 parameter is represented by a piece of state that contains the 721 following data: 723 o the actual bit pattern representing the locator, 725 o the lifetime (seconds), 727 o the status (UNVERIFIED, ACTIVE, DEPRECATED), 728 o the Traffic Type scope of the locator, and 730 o whether the locator is preferred for any particular scope. 732 The status is used to track the reachability of the address embedded 733 within the LOCATOR_SET parameter: 735 UNVERIFIED indicates that the reachability of the address has not 736 been verified yet, 738 ACTIVE indicates that the reachability of the address has been 739 verified and the address has not been deprecated, 741 DEPRECATED indicates that the locator lifetime has expired. 743 The following state changes are allowed: 745 UNVERIFIED to ACTIVE The reachability procedure completes 746 successfully. 748 UNVERIFIED to DEPRECATED The locator lifetime expires while the 749 locator is UNVERIFIED. 751 ACTIVE to DEPRECATED The locator lifetime expires while the locator 752 is ACTIVE. 754 ACTIVE to UNVERIFIED There has been no traffic on the address for 755 some time, and the local policy mandates that the address 756 reachability must be verified again before starting to use it 757 again. 759 DEPRECATED to UNVERIFIED The host receives a new lifetime for the 760 locator. 762 A DEPRECATED address MUST NOT be changed to ACTIVE without first 763 verifying its reachability. 765 Note that the state of whether or not a locator is preferred is not 766 necessarily the same as the value of the Preferred bit in the Locator 767 sub-parameter received from the peer. Peers may recommend certain 768 locators to be preferred, but the decision on whether to actually use 769 a locator as a preferred locator is a local decision, possibly 770 influenced by local policy. 772 In addition to state maintained about status and remaining lifetime 773 for each locator learned from the peer, an implementation would 774 typically maintain similar state about its own locators that have 775 been offered to the peer. 777 Finally, the locators used to establish the HIP association are by 778 default assumed to be the initial preferred locators in ACTIVE state, 779 with an unbounded lifetime. 781 5.2. Sending LOCATOR_SETs 783 The decision of when to send LOCATOR_SETs is basically a local policy 784 issue. However, it is RECOMMENDED that a host send a LOCATOR_SET 785 whenever it recognizes a change of its IP addresses in use on an 786 active HIP association, and assumes that the change is going to last 787 at least for a few seconds. Rapidly sending LOCATOR_SETs that force 788 the peer to change the preferred address SHOULD be avoided. 790 We now describe a few cases introduced in Section 3.2. We assume 791 that the Traffic Type for each locator is set to "0" (other values 792 for Traffic Type may be specified in documents that separate the HIP 793 control plane from data plane traffic). Other mobility cases are 794 possible but are left for further study. 796 1. Host mobility with no multihoming and no rekeying. The mobile 797 host creates a single UPDATE containing a single ESP_INFO with a 798 single LOCATOR_SET parameter. The ESP_INFO contains the current 799 value of the SPI in both the OLD SPI and NEW SPI fields. The 800 LOCATOR_SET contains a single Locator with a "Locator Type" of 801 "1"; the SPI must match that of the ESP_INFO. The Preferred bit 802 SHOULD be set and the "Locator Lifetime" is set according to 803 local policy. The UPDATE also contains a SEQ parameter as usual. 804 This packet is retransmitted as defined in the HIP protocol 805 specification [I-D.ietf-hip-rfc5201-bis]. The UPDATE should be 806 sent to the peer's preferred IP address with an IP source address 807 corresponding to the address in the LOCATOR_SET parameter. 809 2. Host mobility with no multihoming but with rekeying. The mobile 810 host creates a single UPDATE containing a single ESP_INFO with a 811 single LOCATOR_SET parameter (with a single address). The 812 ESP_INFO contains the current value of the SPI in the OLD SPI and 813 the new value of the SPI in the NEW SPI, and a KEYMAT Index as 814 selected by local policy. Optionally, the host may choose to 815 initiate a Diffie Hellman rekey by including a DIFFIE_HELLMAN 816 parameter. The LOCATOR_SET contains a single Locator with 817 "Locator Type" of "1"; the SPI must match that of the NEW SPI in 818 the ESP_INFO. Otherwise, the steps are identical to the case in 819 which no rekeying is initiated. 821 5.3. Handling Received LOCATOR_SETs 823 A host SHOULD be prepared to receive a single LOCATOR_SET parameter 824 in a HIP UPDATE packet. Reception of multiple LOCATOR_SET parameters 825 in a single packet, or in HIP packets other than UPDATE, is outside 826 of the scope of this specification. 828 This document describes sending both ESP_INFO and LOCATOR_SET 829 parameters in an UPDATE. The ESP_INFO parameter is included when 830 there is a need to rekey or key a new SPI, and is otherwise included 831 for the possible benefit of HIP-aware middleboxes. The LOCATOR_SET 832 parameter contains a complete listing of the locators that the host 833 wishes to make or keep active for the HIP association. 835 In general, the processing of a LOCATOR_SET depends upon the packet 836 type in which it is included. Here, we describe only the case in 837 which ESP_INFO is present and a single LOCATOR_SET and ESP_INFO are 838 sent in an UPDATE message; other cases are for further study. The 839 steps below cover each of the cases described in Section 5.2. 841 The processing of ESP_INFO and LOCATOR_SET parameters is intended to 842 be modular and support future generalization to the inclusion of 843 multiple ESP_INFO and/or multiple LOCATOR_SET parameters. A host 844 SHOULD first process the ESP_INFO before the LOCATOR_SET, since the 845 ESP_INFO may contain a new SPI value mapped to an existing SPI, while 846 a Type "1" locator will only contain a reference to the new SPI. 848 When a host receives a validated HIP UPDATE with a LOCATOR_SET and 849 ESP_INFO parameter, it processes the ESP_INFO as follows. The 850 ESP_INFO parameter indicates whether an SA is being rekeyed, created, 851 deprecated, or just identified for the benefit of middleboxes. The 852 host examines the OLD SPI and NEW SPI values in the ESP_INFO 853 parameter: 855 1. (no rekeying) If the OLD SPI is equal to the NEW SPI and both 856 correspond to an existing SPI, the ESP_INFO is gratuitous 857 (provided for middleboxes) and no rekeying is necessary. 859 2. (rekeying) If the OLD SPI indicates an existing SPI and the NEW 860 SPI is a different non-zero value, the existing SA is being 861 rekeyed and the host follows HIP ESP rekeying procedures by 862 creating a new outbound SA with an SPI corresponding to the NEW 863 SPI, with no addresses bound to this SPI. Note that locators in 864 the LOCATOR_SET parameter will reference this new SPI instead of 865 the old SPI. 867 3. (new SA) If the OLD SPI value is zero and the NEW SPI is a new 868 non-zero value, then a new SA is being requested by the peer. 870 This case is also treated like a rekeying event; the receiving 871 host must create a new SA and respond with an UPDATE ACK. 873 4. (deprecating the SA) If the OLD SPI indicates an existing SPI and 874 the NEW SPI is zero, the SA is being deprecated and all locators 875 uniquely bound to the SPI are put into the DEPRECATED state. 877 If none of the above cases apply, a protocol error has occurred and 878 the processing of the UPDATE is stopped. 880 Next, the locators in the LOCATOR_SET parameter are processed. For 881 each locator listed in the LOCATOR_SET parameter, check that the 882 address therein is a legal unicast or anycast address. That is, the 883 address MUST NOT be a broadcast or multicast address. Note that some 884 implementations MAY accept addresses that indicate the local host, 885 since it may be allowed that the host runs HIP with itself. 887 The below assumes that all locators are of Type "1" with a Traffic 888 Type of "0"; other cases are for further study. 890 For each Type "1" address listed in the LOCATOR_SET parameter, the 891 host checks whether the address is already bound to the SPI 892 indicated. If the address is already bound, its lifetime is updated. 893 If the status of the address is DEPRECATED, the status is changed to 894 UNVERIFIED. If the address is not already bound, the address is 895 added, and its status is set to UNVERIFIED. Mark all addresses 896 corresponding to the SPI that were NOT listed in the LOCATOR_SET 897 parameter as DEPRECATED. 899 As a result, at the end of processing, the addresses listed in the 900 LOCATOR_SET parameter have either a state of UNVERIFIED or ACTIVE, 901 and any old addresses on the old SA not listed in the LOCATOR_SET 902 parameter have a state of DEPRECATED. 904 Once the host has processed the locators, if the LOCATOR_SET 905 parameter contains a new Preferred locator, the host SHOULD initiate 906 a change of the Preferred locator. This requires that the host first 907 verifies reachability of the associated address, and only then 908 changes the Preferred locator; see Section 5.5. 910 If a host receives a locator with an unsupported Locator Type, and 911 when such a locator is also declared to be the Preferred locator for 912 the peer, the host SHOULD send a NOTIFY error with a Notify Message 913 Type of LOCATOR_TYPE_UNSUPPORTED, with the Notification Data field 914 containing the locator(s) that the receiver failed to process. 915 Otherwise, a host MAY send a NOTIFY error if a (non-preferred) 916 locator with an unsupported Locator Type is received in a LOCATOR_SET 917 parameter. 919 A host MAY add the source IP address of a received HIP packet as a 920 candidate locator for the peer even if it is not listed in the peer's 921 LOCATOR_SET, but it SHOULD prefer locators explicitly listed in the 922 LOCATOR_SET. 924 5.4. Verifying Address Reachability 926 A host MUST verify the reachability of an UNVERIFIED address. The 927 status of a newly learned address MUST initially be set to UNVERIFIED 928 unless the new address is advertised in a R1 packet as a new 929 Preferred locator. A host MAY also want to verify the reachability 930 of an ACTIVE address again after some time, in which case it would 931 set the status of the address to UNVERIFIED and reinitiate address 932 verification. 934 A host typically starts the address-verification procedure by sending 935 a nonce to the new address. For example, when the host is changing 936 its SPI and sending an ESP_INFO to the peer, the NEW SPI value SHOULD 937 be random and the value MAY be copied into an ECHO_REQUEST sent in 938 the rekeying UPDATE. However, if the host is not changing its SPI, 939 it MAY still use the ECHO_REQUEST parameter in an UPDATE message sent 940 to the new address. A host MAY also use other message exchanges as 941 confirmation of the address reachability. 943 Note that in the case of receiving a LOCATOR_SET in an R1 and 944 replying with an I2 to the new address in the LOCATOR_SET, receiving 945 the corresponding R2 is sufficient proof of reachability for the 946 Responder's preferred address. Since further address verification of 947 such an address can impede the HIP-base exchange, a host MUST NOT 948 separately verify reachability of a new Preferred locator that was 949 received on an R1. 951 In some cases, it MAY be sufficient to use the arrival of data on a 952 newly advertised SA as implicit address reachability verification as 953 depicted in Figure 7, instead of waiting for the confirmation via a 954 HIP packet. In this case, a host advertising a new SPI as part of 955 its address reachability check SHOULD be prepared to receive traffic 956 on the new SA. 958 Mobile host Peer host 960 prepare incoming SA 961 NEW SPI in ESP_INFO (UPDATE) 962 <----------------------------------- 963 switch to new outgoing SA 964 data on new SA 965 -----------------------------------> 966 mark address ACTIVE 968 Figure 7: Address Activation Via Use of a New SA 970 When address verification is in progress for a new Preferred locator, 971 the host SHOULD select a different locator listed as ACTIVE, if one 972 such locator is available, to continue communications until address 973 verification completes. Alternatively, the host MAY use the new 974 Preferred locator while in UNVERIFIED status to the extent Credit- 975 Based Authorization permits. Credit-Based Authorization is explained 976 in Section 5.6. Once address verification succeeds, the status of 977 the new Preferred locator changes to ACTIVE. 979 5.5. Changing the Preferred Locator 981 A host MAY want to change the Preferred outgoing locator for 982 different reasons, e.g., because traffic information or ICMP error 983 messages indicate that the currently used preferred address may have 984 become unreachable. Another reason may be due to receiving a 985 LOCATOR_SET parameter that has the "P" bit set. 987 To change the Preferred locator, the host initiates the following 988 procedure: 990 1. If the new Preferred locator has ACTIVE status, the Preferred 991 locator is changed and the procedure succeeds. 993 2. If the new Preferred locator has UNVERIFIED status, the host 994 starts to verify its reachability. The host SHOULD use a 995 different locator listed as ACTIVE until address verification 996 completes if one such locator is available. Alternatively, the 997 host MAY use the new Preferred locator, even though in UNVERIFIED 998 status, to the extent Credit-Based Authorization permits. Once 999 address verification succeeds, the status of the new Preferred 1000 locator changes to ACTIVE and its use is no longer governed by 1001 Credit-Based Authorization. 1003 3. If the peer host has not indicated a preference for any address, 1004 then the host picks one of the peer's ACTIVE addresses randomly 1005 or according to policy. This case may arise if, for example, 1006 ICMP error messages that deprecate the Preferred locator arrive, 1007 but the peer has not yet indicated a new Preferred locator. 1009 4. If the new Preferred locator has DEPRECATED status and there is 1010 at least one non-deprecated address, the host selects one of the 1011 non-deprecated addresses as a new Preferred locator and 1012 continues. If the selected address is UNVERIFIED, the address 1013 verification procedure described above will apply. 1015 5.6. Credit-Based Authorization 1017 To prevent redirection-based flooding attacks, the use of a Credit- 1018 Based Authorization (CBA) approach is mandatory when a host sends 1019 data to an UNVERIFIED locator. The following algorithm meets the 1020 security considerations for prevention of amplification and time- 1021 shifting attacks. Other forms of credit aging, and other values for 1022 the CreditAgingFactor and CreditAgingInterval parameters in 1023 particular, are for further study, and so are the advanced CBA 1024 techniques specified in [CBA-MIPv6]. 1026 5.6.1. Handling Payload Packets 1028 A host maintains a "credit counter" for each of its peers. Whenever 1029 a packet arrives from a peer, the host SHOULD increase that peer's 1030 credit counter by the size of the received packet. When the host has 1031 a packet to be sent to the peer, and when the peer's Preferred 1032 locator is listed as UNVERIFIED and no alternative locator with 1033 status ACTIVE is available, the host checks whether it can send the 1034 packet to the UNVERIFIED locator. The packet SHOULD be sent if the 1035 value of the credit counter is higher than the size of the outbound 1036 packet. If the credit counter is too low, the packet MUST be 1037 discarded or buffered until address verification succeeds. When a 1038 packet is sent to a peer at an UNVERIFIED locator, the peer's credit 1039 counter MUST be reduced by the size of the packet. The peer's credit 1040 counter is not affected by packets that the host sends to an ACTIVE 1041 locator of that peer. 1043 Figure 8 depicts the actions taken by the host when a packet is 1044 received. Figure 9 shows the decision chain in the event a packet is 1045 sent. 1047 Inbound 1048 packet 1049 | 1050 | +----------------+ +---------------+ 1051 | | Increase | | Deliver | 1052 +-----> | credit counter |-------------> | packet to | 1053 | by packet size | | application | 1054 +----------------+ +---------------+ 1056 Figure 8: Receiving Packets with Credit-Based Authorization 1058 Outbound 1059 packet 1060 | _________________ 1061 | / \ +---------------+ 1062 | / Is the preferred \ No | Send packet | 1063 +-----> | destination address |-------------> | to preferred | 1064 \ UNVERIFIED? / | address | 1065 \_________________/ +---------------+ 1066 | 1067 | Yes 1068 | 1069 v 1070 _________________ 1071 / \ +---------------+ 1072 / Does an ACTIVE \ Yes | Send packet | 1073 | destination address |-------------> | to ACTIVE | 1074 \ exist? / | address | 1075 \_________________/ +---------------+ 1076 | 1077 | No 1078 | 1079 v 1080 _________________ 1081 / \ +---------------+ 1082 / Credit counter \ No | | 1083 | >= |-------------> | Drop packet | 1084 \ packet size? / | | 1085 \_________________/ +---------------+ 1086 | 1087 | Yes 1088 | 1089 v 1090 +---------------+ +---------------+ 1091 | Reduce credit | | Send packet | 1092 | counter by |----------------> | to preferred | 1093 | packet size | | address | 1094 +---------------+ +---------------+ 1096 Figure 9: Sending Packets with Credit-Based Authorization 1098 5.6.2. Credit Aging 1100 A host ensures that the credit counters it maintains for its peers 1101 gradually decrease over time. Such "credit aging" prevents a 1102 malicious peer from building up credit at a very slow speed and using 1103 this, all at once, for a severe burst of redirected packets. 1105 Credit aging may be implemented by multiplying credit counters with a 1106 factor, CreditAgingFactor (a fractional value less than one), in 1107 fixed time intervals of CreditAgingInterval length. Choosing 1108 appropriate values for CreditAgingFactor and CreditAgingInterval is 1109 important to ensure that a host can send packets to an address in 1110 state UNVERIFIED even when the peer sends at a lower rate than the 1111 host itself. When CreditAgingFactor or CreditAgingInterval are too 1112 small, the peer's credit counter might be too low to continue sending 1113 packets until address verification concludes. 1115 The parameter values proposed in this document are as follows: 1117 CreditAgingFactor 7/8 1118 CreditAgingInterval 5 seconds 1120 These parameter values work well when the host transfers a file to 1121 the peer via a TCP connection and the end-to-end round-trip time does 1122 not exceed 500 milliseconds. Alternative credit-aging algorithms may 1123 use other parameter values or different parameters, which may even be 1124 dynamically established. 1126 6. Security Considerations 1128 The HIP mobility mechanism provides a secure means of updating a 1129 host's IP address via HIP UPDATE packets. Upon receipt, a HIP host 1130 cryptographically verifies the sender of an UPDATE, so forging or 1131 replaying a HIP UPDATE packet is very difficult (see 1132 [I-D.ietf-hip-rfc5201-bis]). Therefore, security issues reside in 1133 other attack domains. The two we consider are malicious redirection 1134 of legitimate connections as well as redirection-based flooding 1135 attacks using this protocol. This can be broken down into the 1136 following: 1138 Impersonation attacks 1140 - direct conversation with the misled victim 1142 - man-in-the-middle attack 1144 DoS attacks 1146 - flooding attacks (== bandwidth-exhaustion attacks) 1148 * tool 1: direct flooding 1150 * tool 2: flooding by zombies 1152 * tool 3: redirection-based flooding 1154 - memory-exhaustion attacks 1156 - computational-exhaustion attacks 1158 We consider these in more detail in the following sections. 1160 In Section 6.1 and Section 6.2, we assume that all users are using 1161 HIP. In Section 6.3 we consider the security ramifications when we 1162 have both HIP and non-HIP users. Security considerations for Credit- 1163 Based Authorization are discussed in [SIMPLE-CBA]. 1165 6.1. Impersonation Attacks 1167 An attacker wishing to impersonate another host will try to mislead 1168 its victim into directly communicating with them, or carry out a man- 1169 in-the-middle (MitM) attack between the victim and the victim's 1170 desired communication peer. Without mobility support, both attack 1171 types are possible only if the attacker resides on the routing path 1172 between its victim and the victim's desired communication peer, or if 1173 the attacker tricks its victim into initiating the connection over an 1174 incorrect routing path (e.g., by acting as a router or using spoofed 1175 DNS entries). 1177 The HIP extensions defined in this specification change the situation 1178 in that they introduce an ability to redirect a connection (like 1179 IPv6), both before and after establishment. If no precautionary 1180 measures are taken, an attacker could misuse the redirection feature 1181 to impersonate a victim's peer from any arbitrary location. The 1182 authentication and authorization mechanisms of the HIP base exchange 1183 [I-D.ietf-hip-rfc5201-bis] and the signatures in the UPDATE message 1184 prevent this attack. Furthermore, ownership of a HIP association is 1185 securely linked to a HIP HI/HIT. If an attacker somehow uses a bug 1186 in the implementation or weakness in some protocol to redirect a HIP 1187 connection, the original owner can always reclaim their connection 1188 (they can always prove ownership of the private key associated with 1189 their public HI). 1191 MitM attacks are always possible if the attacker is present during 1192 the initial HIP base exchange and if the hosts do not authenticate 1193 each other's identities. However, once the opportunistic base 1194 exchange has taken place, even a MitM cannot steal the HIP connection 1195 anymore because it is very difficult for an attacker to create an 1196 UPDATE packet (or any HIP packet) that will be accepted as a 1197 legitimate update. UPDATE packets use HMAC and are signed. Even 1198 when an attacker can snoop packets to obtain the SPI and HIT/HI, they 1199 still cannot forge an UPDATE packet without knowledge of the secret 1200 keys. 1202 6.2. Denial-of-Service Attacks 1204 6.2.1. Flooding Attacks 1206 The purpose of a denial-of-service attack is to exhaust some resource 1207 of the victim such that the victim ceases to operate correctly. A 1208 denial-of-service attack can aim at the victim's network attachment 1209 (flooding attack), its memory, or its processing capacity. In a 1210 flooding attack, the attacker causes an excessive number of bogus or 1211 unwanted packets to be sent to the victim, which fills their 1212 available bandwidth. Note that the victim does not necessarily need 1213 to be a node; it can also be an entire network. The attack basically 1214 functions the same way in either case. 1216 An effective DoS strategy is distributed denial of service (DDoS). 1217 Here, the attacker conventionally distributes some viral software to 1218 as many nodes as possible. Under the control of the attacker, the 1219 infected nodes, or "zombies", jointly send packets to the victim. 1220 With such an 'army', an attacker can take down even very high 1221 bandwidth networks/victims. 1223 With the ability to redirect connections, an attacker could realize a 1224 DDoS attack without having to distribute viral code. Here, the 1225 attacker initiates a large download from a server, and subsequently 1226 redirects this download to its victim. The attacker can repeat this 1227 with multiple servers. This threat is mitigated through reachability 1228 checks and credit-based authorization. Both strategies do not 1229 eliminate flooding attacks per se, but they preclude: (i) their use 1230 from a location off the path towards the flooded victim; and (ii) any 1231 amplification in the number and size of the redirected packets. As a 1232 result, the combination of a reachability check and credit-based 1233 authorization lowers a HIP redirection-based flooding attack to the 1234 level of a direct flooding attack in which the attacker itself sends 1235 the flooding traffic to the victim. 1237 6.2.2. Memory/Computational-Exhaustion DoS Attacks 1239 We now consider whether or not the proposed extensions to HIP add any 1240 new DoS attacks (consideration of DoS attacks using the base HIP 1241 exchange and updates is discussed in [I-D.ietf-hip-rfc5201-bis]). A 1242 simple attack is to send many UPDATE packets containing many IP 1243 addresses that are not flagged as preferred. The attacker continues 1244 to send such packets until the number of IP addresses associated with 1245 the attacker's HI crashes the system. Therefore, there SHOULD be a 1246 limit to the number of IP addresses that can be associated with any 1247 HI. Other forms of memory/computationally exhausting attacks via the 1248 HIP UPDATE packet are handled in the base HIP document 1249 [I-D.ietf-hip-rfc5201-bis]. 1251 A central server that has to deal with a large number of mobile 1252 clients may consider increasing the SA lifetimes to try to slow down 1253 the rate of rekeying UPDATEs or increasing the cookie difficulty to 1254 slow down the rate of attack-oriented connections. 1256 6.3. Mixed Deployment Environment 1258 We now assume an environment with both HIP and non-HIP aware hosts. 1259 Four cases exist. 1261 1. A HIP host redirects its connection onto a non-HIP host. The 1262 non-HIP host will drop the reachability packet, so this is not a 1263 threat unless the HIP host is a MitM that could somehow respond 1264 successfully to the reachability check. 1266 2. A non-HIP host attempts to redirect their connection onto a HIP 1267 host. This falls into IPv4 and IPv6 security concerns, which are 1268 outside the scope of this document. 1270 3. A non-HIP host attempts to steal a HIP host's session (assume 1271 that Secure Neighbor Discovery is not active for the following). 1272 The non-HIP host contacts the service that a HIP host has a 1273 connection with and then attempts to change its IP address to 1274 steal the HIP host's connection. What will happen in this case 1275 is implementation dependent but such a request should fail by 1276 being ignored or dropped. Even if the attack were successful, 1277 the HIP host could reclaim its connection via HIP. 1279 4. A HIP host attempts to steal a non-HIP host's session. A HIP 1280 host could spoof the non-HIP host's IP address during the base 1281 exchange or set the non-HIP host's IP address as its preferred 1282 address via an UPDATE. Other possibilities exist, but a simple 1283 solution is to prevent the use of HIP address check information 1284 to influence non-HIP sessions. 1286 7. IANA Considerations 1288 The following changes to the "Host Identity Protocol (HIP) 1289 Parameters" registries are requested. 1291 The existing Parameter Type of 'LOCATOR' (value 193) should be 1292 renamed to 'LOCATOR_SET' and the reference should be updated from 1293 RFC5206 to this specification. 1295 The existing Notify Message Type of 'LOCATOR_TYPE_UNSUPPORTED' (value 1296 46) should have its reference updated from RFC5206 to this 1297 specification. 1299 8. Authors and Acknowledgments 1301 Pekka Nikander and Jari Arkko originated this document, and Christian 1302 Vogt and Thomas Henderson (editor) later joined as co-authors. Greg 1303 Perkins contributed the initial draft of the security section. Petri 1304 Jokela was a co-author of the initial individual submission. 1306 The authors thank Jeff Ahrenholz, Baris Boyvat, Rene Hummen, Miika 1307 Komu, Mika Kousa, Jan Melen, and Samu Varjonen for improvements to 1308 the document. 1310 9. References 1312 9.1. Normative references 1314 [I-D.ietf-hip-rfc5201-bis] 1315 Moskowitz, R., Heer, T., Jokela, P., and T. Henderson, 1316 "Host Identity Protocol Version 2 (HIPv2)", draft-ietf- 1317 hip-rfc5201-bis-20 (work in progress), October 2014. 1319 [I-D.ietf-hip-rfc5202-bis] 1320 Jokela, P., Moskowitz, R., and J. Melen, "Using the 1321 Encapsulating Security Payload (ESP) Transport Format with 1322 the Host Identity Protocol (HIP)", draft-ietf-hip- 1323 rfc5202-bis-07 (work in progress), September 2014. 1325 [I-D.ietf-hip-rfc5204-bis] 1326 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1327 Rendezvous Extension", draft-ietf-hip-rfc5204-bis-05 (work 1328 in progress), December 2014. 1330 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1331 Requirement Levels", BCP 14, RFC 2119, March 1997. 1333 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1334 Architecture", RFC 4291, February 2006. 1336 9.2. Informative references 1338 [CBA-MIPv6] 1339 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1340 Mobile IPv6 Early Binding Updates", February 2005. 1342 [I-D.ietf-hip-rfc4423-bis] 1343 Moskowitz, R. and M. Komu, "Host Identity Protocol 1344 Architecture", draft-ietf-hip-rfc4423-bis-09 (work in 1345 progress), October 2014. 1347 [RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. 1348 Nordmark, "Mobile IP Version 6 Route Optimization Security 1349 Design Background", RFC 4225, December 2005. 1351 [SIMPLE-CBA] 1352 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1353 Concurrent Reachability Verification", February 2006. 1355 Appendix A. Document Revision History 1357 To be removed upon publication 1359 +----------+--------------------------------------------------------+ 1360 | Revision | Comments | 1361 +----------+--------------------------------------------------------+ 1362 | draft-00 | Initial version from RFC5206 xml (unchanged). | 1363 | | | 1364 | draft-01 | Remove multihoming-specific text; no other changes. | 1365 | | | 1366 | draft-02 | Update references to point to -bis drafts; no other | 1367 | | changes. | 1368 | | | 1369 | draft-03 | issue 4: add make before break use case | 1370 | | | 1371 | | issue 6: peer locator exposure policies | 1372 | | | 1373 | | issue 10: rename LOCATOR to LOCATOR_SET | 1374 | | | 1375 | | issue 14: use of UPDATE packet's IP address | 1376 | | | 1377 | draft-04 | Document refresh; no other changes. | 1378 | | | 1379 | draft-05 | Document refresh; no other changes. | 1380 | | | 1381 | draft-06 | Document refresh; no other changes. | 1382 | | | 1383 | draft-07 | Document refresh; IANA considerations updated. | 1384 | | | 1385 | draft-08 | Remove sending LOCATOR_SET in R1, I2, and NOTIFY | 1386 | | (multihoming) | 1387 | | | 1388 | | State that only one LOCATOR_SET parameter may be sent | 1389 | | in an UPDATE packet (according to this draft) | 1390 | | (multihoming) | 1391 | | | 1392 | | Remove text about cross-family handovers (multihoming) | 1393 +----------+--------------------------------------------------------+ 1395 Authors' Addresses 1396 Thomas R. Henderson (editor) 1397 University of Washington 1398 Campus Box 352500 1399 Seattle, WA 1400 USA 1402 EMail: tomhend@u.washington.edu 1404 Christian Vogt 1405 Ericsson Research NomadicLab 1406 Hirsalantie 11 1407 JORVAS FIN-02420 1408 FINLAND 1410 EMail: christian.vogt@ericsson.com 1412 Jari Arkko 1413 Ericsson Research NomadicLab 1414 JORVAS FIN-02420 1415 FINLAND 1417 Phone: +358 40 5079256 1418 EMail: jari.arkko@ericsson.com