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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-12) exists of draft-ietf-hip-multihoming-11 -- Obsolete informational reference (is this intentional?): RFC 5206 (Obsoleted by RFC 8046) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Henderson, Ed. 3 Internet-Draft University of Washington 4 Obsoletes: 5206 (if approved) C. Vogt 5 Intended status: Standards Track Independent 6 Expires: April 13, 2017 J. Arkko 7 Ericsson 8 October 10, 2016 10 Host Mobility with the Host Identity Protocol 11 draft-ietf-hip-rfc5206-bis-14 13 Abstract 15 This document defines a mobility extension to the Host Identity 16 Protocol (HIP). Specifically, this document defines a "LOCATOR_SET" 17 parameter for HIP messages that allows for a HIP host to notify peers 18 about alternate addresses at which it may be reached. This document 19 also defines how the parameter can be used to preserve communications 20 across a change to the IP address used by one or both peer hosts. 21 The same LOCATOR_SET parameter can also be used to support end-host 22 multihoming (specified in RFC[Replace with the RFC number for draft- 23 ietf-hip-multihoming]). 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 April 13, 2017. 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 Table of Contents 59 1. Introduction and Scope . . . . . . . . . . . . . . . . . . . 3 60 2. Terminology and Conventions . . . . . . . . . . . . . . . . . 4 61 3. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . 5 62 3.1. Operating Environment . . . . . . . . . . . . . . . . . . 5 63 3.1.1. Locator . . . . . . . . . . . . . . . . . . . . . . . 7 64 3.1.2. Mobility Overview . . . . . . . . . . . . . . . . . . 7 65 3.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 8 66 3.2.1. Mobility with a Single SA Pair (No Rekeying) . . . . 9 67 3.2.2. Mobility with a Single SA Pair (Mobile-Initiated 68 Rekey) . . . . . . . . . . . . . . . . . . . . . . . 10 69 3.2.3. Mobility messaging through rendezvous server . . . . 11 70 3.2.4. Network Renumbering . . . . . . . . . . . . . . . . . 12 71 3.3. Other Considerations . . . . . . . . . . . . . . . . . . 12 72 3.3.1. Address Verification . . . . . . . . . . . . . . . . 12 73 3.3.2. Credit-Based Authorization . . . . . . . . . . . . . 13 74 3.3.3. Preferred Locator . . . . . . . . . . . . . . . . . . 14 75 4. LOCATOR_SET Parameter Format . . . . . . . . . . . . . . . . 15 76 4.1. Traffic Type and Preferred Locator . . . . . . . . . . . 16 77 4.2. Locator Type and Locator . . . . . . . . . . . . . . . . 17 78 4.3. UPDATE Packet with Included LOCATOR_SET . . . . . . . . . 17 79 5. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 17 80 5.1. Locator Data Structure and Status . . . . . . . . . . . . 18 81 5.2. Sending the LOCATOR_SET . . . . . . . . . . . . . . . . . 19 82 5.3. Handling Received LOCATOR_SETs . . . . . . . . . . . . . 20 83 5.4. Verifying Address Reachability . . . . . . . . . . . . . 22 84 5.5. Changing the Preferred Locator . . . . . . . . . . . . . 23 85 5.6. Credit-Based Authorization . . . . . . . . . . . . . . . 24 86 5.6.1. Handling Payload Packets . . . . . . . . . . . . . . 24 87 5.6.2. Credit Aging . . . . . . . . . . . . . . . . . . . . 26 88 6. Security Considerations . . . . . . . . . . . . . . . . . . . 27 89 6.1. Impersonation Attacks . . . . . . . . . . . . . . . . . . 28 90 6.2. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 29 91 6.2.1. Flooding Attacks . . . . . . . . . . . . . . . . . . 29 92 6.2.2. Memory/Computational-Exhaustion DoS Attacks . . . . . 29 93 6.3. Mixed Deployment Environment . . . . . . . . . . . . . . 30 94 6.4. Privacy Concerns . . . . . . . . . . . . . . . . . . . . 31 95 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 96 8. Differences from RFC 5206 . . . . . . . . . . . . . . . . . . 31 97 9. Authors and Acknowledgments . . . . . . . . . . . . . . . . . 32 98 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 99 10.1. Normative references . . . . . . . . . . . . . . . . . . 33 100 10.2. Informative references . . . . . . . . . . . . . . . . . 34 101 Appendix A. Document Revision History . . . . . . . . . . . . . 35 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36 104 1. Introduction and Scope 106 The Host Identity Protocol [RFC7401] (HIP) supports an architecture 107 that decouples the transport layer (TCP, UDP, etc.) from the 108 internetworking layer (IPv4 and IPv6) by using public/private key 109 pairs, instead of IP addresses, as host identities. When a host uses 110 HIP, the overlying protocol sublayers (e.g., transport layer sockets 111 and Encapsulating Security Payload (ESP) Security Associations (SAs)) 112 are instead bound to representations of these host identities, and 113 the IP addresses are only used for packet forwarding. However, each 114 host needs to also know at least one IP address at which its peers 115 are reachable. Initially, these IP addresses are the ones used 116 during the HIP base exchange. 118 One consequence of such a decoupling is that new solutions to 119 network-layer mobility and host multihoming are possible. There are 120 potentially many variations of mobility and multihoming possible. 121 The scope of this document encompasses messaging and elements of 122 procedure for basic network-level host mobility, leaving more 123 complicated mobility scenarios, multihoming, and other variations for 124 further study. More specifically, the following are in scope: 126 This document defines a LOCATOR_SET parameter for use in HIP 127 messages. The LOCATOR_SET parameter allows a HIP host to notify a 128 peer about alternate locators at which it is reachable. The 129 locators may be merely IP addresses, or they may have additional 130 multiplexing and demultiplexing context to aid with the packet 131 handling in the lower layers. For instance, an IP address may 132 need to be paired with an ESP Security Parameter Index (SPI) so 133 that packets are sent on the correct SA for a given address. 135 This document also specifies the messaging and elements of 136 procedure for end-host mobility of a HIP host. In particular, 137 message flows to enable successful host mobility, including 138 address verification methods, are defined herein. 140 The HIP rendezvous server [I-D.ietf-hip-rfc5204-bis] can be used 141 to manage simultaneous mobility of both hosts, initial 142 reacahability of a mobile host, location privacy, and some modes 143 of NAT traversal. Use of the HIP rendezvous server to manage the 144 simultaneous mobility of both hosts is specified herein. 146 The following topics are out of scope: 148 While the same LOCATOR_SET parameter supports host multihoming 149 (simultaneous use of a number of addresses), procedures for host 150 multihoming are out of scope, and are specified in 151 [I-D.ietf-hip-multihoming]. 153 While HIP can potentially be used with transports other than the 154 ESP transport format [RFC7402], this document largely assumes the 155 use of ESP and leaves other transport formats for further study. 157 We do not consider localized mobility management extensions (i.e., 158 mobility management techniques that do not involve directly 159 signaling the correspondent node); this document is concerned with 160 end-to-end mobility. 162 Finally, making underlying IP mobility transparent to the 163 transport layer has implications on the proper response of 164 transport congestion control, path MTU selection, and Quality of 165 Service (QoS). Transport-layer mobility triggers, and the proper 166 transport response to a HIP mobility or multihoming address 167 change, are outside the scope of this document. 169 The main sections of this document are organized as follows. 170 Section 3 provides a summary overview of operations, scenarios, and 171 other considerations. Section 4 specifies the messaging parameter 172 syntax. Section 5 specifies the processing rules for messages. 173 Section 6 describes security considerations for this specification. 175 2. Terminology and Conventions 177 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 178 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 179 document are to be interpreted as described in RFC 2119 [RFC2119]. 181 LOCATOR_SET. A HIP parameter containing zero or more Locator fields. 183 Locator. A name that controls how the packet is routed through the 184 network and demultiplexed by the end host. It may include a 185 concatenation of traditional network addresses such as an IPv6 186 address and end-to-end identifiers such as an ESP SPI. It may 187 also include transport port numbers or IPv6 Flow Labels as 188 demultiplexing context, or it may simply be a network address. 190 Address. A name that denotes a point-of-attachment to the network. 191 The two most common examples are an IPv4 address and an IPv6 192 address. The set of possible addresses is a subset of the set of 193 possible locators. 195 Preferred locator. A locator on which a host prefers to receive 196 data. Certain locators are labelled as preferred when a host 197 advertises its locator set to its peer. By default, the locators 198 used in the HIP base exchange are the preferred locators. The use 199 of preferred locators, including the scenario where multiple 200 address scopes and families may be in use, is defined more in 201 [I-D.ietf-hip-multihoming] than in this document. 203 Credit Based Authorization. A mechanism allowing a host to send a 204 certain amount of data to a peer's newly announced locator before 205 the result of mandatory address verification is known. 207 3. Protocol Model 209 This section is an overview; more detailed specification follows this 210 section. 212 3.1. Operating Environment 214 The Host Identity Protocol (HIP) [RFC7401] is a key establishment and 215 parameter negotiation protocol. Its primary applications are for 216 authenticating host messages based on host identities, and 217 establishing security associations (SAs) for the ESP transport format 218 [RFC7402] and possibly other protocols in the future. 220 +--------------------+ +--------------------+ 221 | | | | 222 | +------------+ | | +------------+ | 223 | | Key | | HIP | | Key | | 224 | | Management | <-+-----------------------+-> | Management | | 225 | | Process | | | | Process | | 226 | +------------+ | | +------------+ | 227 | ^ | | ^ | 228 | | | | | | 229 | v | | v | 230 | +------------+ | | +------------+ | 231 | | IPsec | | ESP | | IPsec | | 232 | | Stack | <-+-----------------------+-> | Stack | | 233 | | | | | | | | 234 | +------------+ | | +------------+ | 235 | | | | 236 | | | | 237 | Initiator | | Responder | 238 +--------------------+ +--------------------+ 240 Figure 1: HIP Deployment Model 242 The general deployment model for HIP is shown above, assuming 243 operation in an end-to-end fashion. This document specifies an 244 extension to the HIP protocol to enable end-host mobility. In 245 summary, these extensions to the HIP base protocol enable the 246 signaling of new addressing information to the peer in HIP messages. 247 The messages are authenticated via a signature or keyed hash message 248 authentication code (HMAC) based on its Host Identity. This document 249 specifies the format of this new addressing (LOCATOR_SET) parameter, 250 the procedures for sending and processing this parameter to enable 251 basic host mobility, and procedures for a concurrent address 252 verification mechanism. 254 --------- 255 | TCP | (sockets bound to HITs) 256 --------- 257 | 258 --------- 259 ----> | ESP | {HIT_s, HIT_d} <-> SPI 260 | --------- 261 | | 262 ---- --------- 263 | MH |-> | HIP | {HIT_s, HIT_d, SPI} <-> {IP_s, IP_d, SPI} 264 ---- --------- 265 | 266 --------- 267 | IP | 268 --------- 270 Figure 2: Architecture for HIP Host Mobility (MH) 272 Figure 2 depicts a layered architectural view of a HIP-enabled stack 273 using the ESP transport format. In HIP, upper-layer protocols 274 (including TCP and ESP in this figure) are bound to Host Identity 275 Tags (HITs) and not IP addresses. The HIP sublayer is responsible 276 for maintaining the binding between HITs and IP addresses. The SPI 277 is used to associate an incoming packet with the right HITs. The 278 block labeled "MH" is introduced below. 280 Consider first the case in which there is no mobility or multihoming, 281 as specified in the base protocol specification [RFC7401]. The HIP 282 base exchange establishes the HITs in use between the hosts, the SPIs 283 to use for ESP, and the IP addresses (used in both the HIP signaling 284 packets and ESP data packets). Note that there can only be one such 285 set of bindings in the outbound direction for any given packet, and 286 the only fields used for the binding at the HIP layer are the fields 287 exposed by ESP (the SPI and HITs). For the inbound direction, the 288 SPI is all that is required to find the right host context. ESP 289 rekeying events change the mapping between the HIT pair and SPI, but 290 do not change the IP addresses. 292 Consider next a mobility event, in which a host moves to another IP 293 address. Two things need to occur in this case. First, the peer 294 needs to be notified of the address change using a HIP UPDATE 295 message. Second, each host needs to change its local bindings at the 296 HIP sublayer (new IP addresses). It may be that both the SPIs and IP 297 addresses are changed simultaneously in a single UPDATE; the protocol 298 described herein supports this. Although internal notification of 299 transport layer protocols regarding the path change (e.g. to reset 300 congestion control variables) may be desired, this specification does 301 not address such internal notification. In addition, elements of 302 procedure for traversing network address translators (NATs) and 303 firewalls, including NATs and firewalls that may understand the HIP 304 protocol, may complicate the above basic scenario and are not covered 305 by 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 single 327 LOCATOR_SET parameter and a single ESP_INFO parameter. This UPDATE 328 packet is acknowledged by the peer. For reliability in the presence 329 of packet loss, the UPDATE packet is retransmitted as defined in the 330 HIP protocol specification [RFC7401]. The peer can authenticate the 331 contents of the UPDATE packet based on the signature and keyed hash 332 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] and with the use of ESP with HIP [RFC7402]. 360 According to these specifications, the data traffic in a HIP session 361 is protected with ESP, and the ESP SPI acts as an index to the right 362 host-to-host context. More specification details are found later in 363 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. In support of mobility, the LOCATOR_SET 374 parameter is carried in 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 needs to be verified before 379 put into active service, and addresses removed by the peer are put 380 into a 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 sometimes needs to 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 needs to inform 396 its 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 previous address. This is the simplest scenario, 402 depicted in Figure 3. Note that the conventions for message 403 parameter notations in figures (use of parentheses and brackets) is 404 defined in Section 2.2 of [RFC7401]. 406 Mobile Host Peer Host 408 UPDATE(ESP_INFO, LOCATOR_SET, SEQ) 409 -----------------------------------> 410 UPDATE(ESP_INFO, SEQ, ACK, ECHO_REQUEST) 411 <----------------------------------- 412 UPDATE(ACK, ECHO_RESPONSE) 413 -----------------------------------> 415 Figure 3: Readdress without Rekeying, but with Address Check 417 The steps of the packet processing are as follows: 419 1. The mobile host may be disconnected from the peer host for a 420 brief period of time while it switches from one IP address to 421 another; this case is sometimes referred to in the literature as 422 a "break-before-make" case. The host may also obtain its new IP 423 address before loosing the old one ("make-before-break" case). 424 In either case, upon obtaining a new IP address, the mobile host 425 sends a LOCATOR_SET parameter to the peer host in an UPDATE 426 message. The UPDATE message also contains an ESP_INFO parameter 427 containing the values of the old and new SPIs for a security 428 association. In this case, the OLD SPI and NEW SPI parameters 429 both are set to the value of the preexisting incoming SPI; this 430 ESP_INFO does not trigger a rekeying event but is instead 431 included for possible parameter-inspecting firewalls on the path 432 ([RFC5207] specifies some such firewall scenarios in which the 433 HIP-aware firewall may want to associate ESP flows to host 434 identities). The LOCATOR_SET parameter contains the new IP 435 address (Locator Type of "1", defined below) and a locator 436 lifetime. The mobile host waits for this UPDATE to be 437 acknowledged, and retransmits if necessary, as specified in the 438 base specification [RFC7401]. 440 2. The peer host receives the UPDATE, validates it, and updates any 441 local bindings between the HIP association and the mobile host's 442 destination address. The peer host MUST perform an address 443 verification by placing a nonce in the ECHO_REQUEST parameter of 444 the UPDATE message sent back to the mobile host. It also 445 includes an ESP_INFO parameter with the OLD SPI and NEW SPI 446 parameters both set to the value of the preexisting incoming SPI, 447 and sends this UPDATE (with piggybacked acknowledgment) to the 448 mobile host at its new address. This UPDATE also acknowledges 449 the mobile host's UPDATE that triggered the exchange. The peer 450 host waits for its UPDATE to be acknowledged, and retransmits if 451 necessary, as specified in the base specification [RFC7401]. The 452 peer MAY use the new address immediately, but it MUST limit the 453 amount of data it sends to the address until address verification 454 completes. 456 3. The mobile host completes the readdress by processing the UPDATE 457 ACK and echoing the nonce in an ECHO_RESPONSE, containing the ACK 458 of the peer's UPDATE. This UPDATE is not protected by a 459 retransmission timer because it does not contain a SEQ parameter 460 requesting acknowledgment. Once the peer host receives this 461 ECHO_RESPONSE, it considers the new address to be verified and 462 can put the address into full use. 464 While the peer host is verifying the new address, the new address is 465 marked as UNVERIFIED in the interim, and the old address is 466 DEPRECATED. Once the peer host has received a correct reply to its 467 UPDATE challenge, it marks the new address as ACTIVE and removes the 468 old address. 470 3.2.2. Mobility with a Single SA Pair (Mobile-Initiated Rekey) 472 The mobile host may decide to rekey the SAs at the same time that it 473 notifies the peer of the new address. In this case, the above 474 procedure described in Figure 3 is slightly modified. The UPDATE 475 message sent from the mobile host includes an ESP_INFO with the OLD 476 SPI set to the previous SPI, the NEW SPI set to the desired new SPI 477 value for the incoming SA, and the KEYMAT Index desired. Optionally, 478 the host may include a DIFFIE_HELLMAN parameter for a new Diffie- 479 Hellman key. The peer completes the request for a rekey as is 480 normally done for HIP rekeying, except that the new address is kept 481 as UNVERIFIED until the UPDATE nonce challenge is received as 482 described above. Figure 4 illustrates this scenario. 484 Mobile Host Peer Host 486 UPDATE(ESP_INFO, LOCATOR_SET, SEQ, [DIFFIE_HELLMAN]) 487 -----------------------------------> 488 UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) 489 <----------------------------------- 490 UPDATE(ACK, ECHO_RESPONSE) 491 -----------------------------------> 493 Figure 4: Readdress with Mobile-Initiated Rekey 495 3.2.3. Mobility messaging through rendezvous server 497 Section 6.11 of [RFC7401] specifies procedures for sending HIP UPDATE 498 packets. The UPDATE packets are protected by a timer subject to 499 exponential backoff and resent UPDATE_RETRY_MAX times. It may be, 500 however, that the peer is itself in the process of moving when the 501 local host is trying to update the IP address bindings of the HIP 502 association. This is sometimes called the "double-jump" mobility 503 problem; each host's UPDATE packets are simultaneously sent to a 504 stale address of the peer, and the hosts are no longer reachable from 505 one another. 507 The HIP Rendezvous Extension [I-D.ietf-hip-rfc5204-bis] specifies a 508 rendezvous service that permits the I1 packet from the base exchange 509 to be relayed from a stable or well-known public IP address location 510 to the current IP address of the host. It is possible to support 511 double-jump mobility with this rendezvous service if the following 512 extensions to the specifications of [I-D.ietf-hip-rfc5204-bis] and 513 [RFC7401] are followed. 515 1. The mobile host sending an UPDATE to the peer, and not receiving 516 an ACK, MAY resend the UPDATE to a rendezvous server (RVS) of the 517 peer, if such a server is known. The host MAY try the RVS of the 518 peer up to UPDATE_RETRY_MAX times as specified in [RFC7401]. The 519 host MAY try to use the peer's RVS before it has tried 520 UPDATE_RETRY_MAX times to the last working address (i.e. the RVS 521 MAY be tried in parallel with retries to the last working 522 address). The aggressiveness of a host replicating its UPDATEs 523 to multiple destinations, to try candidates in parallel instead 524 of serially, is a policy choice outside of this specification. 526 2. A rendezvous server supporting the UPDATE forwarding extensions 527 specified herein MUST modify the UPDATE in the same manner as it 528 modifies the I1 packet before forwarding. Specifically, it MUST 529 rewrite the IP header source and destination addresses, recompute 530 the IP header checksum, and include the FROM and RVS_HMAC 531 parameters. 533 3. A host receiving an UPDATE packet MUST be prepared to process the 534 FROM and RVS_HMAC parameters, and MUST include a VIA_RVS 535 parameter in the UPDATE reply that contains the ACK of the UPDATE 536 SEQ. 538 4. An initiator receiving a VIA_RVS in the UPDATE reply should 539 initiate address reachability tests (described later in this 540 document) towards the end host's address and not towards the 541 address included in the VIA_RVS. 543 This scenario requires that hosts using rendezvous servers also take 544 steps to update their current address bindings with their rendezvous 545 server upon a mobility event. [I-D.ietf-hip-rfc5204-bis] does not 546 specify how to update the rendezvous server with a client host's new 547 address. [I-D.ietf-hip-rfc5203-bis] Section 3.2 describes how a host 548 may send a REG_REQUEST in either an I2 packet (if there is no active 549 association) or an UPDATE packet (if such association exists). 550 According to procedures described in [I-D.ietf-hip-rfc5203-bis], if a 551 mobile host has an active registration, it may use mobility updates 552 specified herein, within the context of that association, to 553 readdress the association. 555 3.2.4. Network Renumbering 557 It is expected that IPv6 networks will be renumbered much more often 558 than most IPv4 networks. From an end-host point of view, network 559 renumbering is similar to mobility, and procedures described herein 560 also apply to notify a peer of a changed address. 562 3.3. Other Considerations 564 3.3.1. Address Verification 566 When a HIP host receives a set of locators from another HIP host in a 567 LOCATOR_SET, it does not necessarily know whether the other host is 568 actually reachable at the claimed addresses. In fact, a malicious 569 peer host may be intentionally giving bogus addresses in order to 570 cause a packet flood towards the target addresses [RFC4225]. 571 Therefore, the HIP host needs to first check that the peer is 572 reachable at the new address. 574 Address verification is implemented by the challenger sending some 575 piece of unguessable information to the new address, and waiting for 576 some acknowledgment from the Responder that indicates reception of 577 the information at the new address. This may include the exchange of 578 a nonce, or the generation of a new SPI and observation of data 579 arriving on the new SPI. More details are found in Section 5.4 of 580 this document. 582 An additional potential benefit of performing address verification is 583 to allow NATs and firewalls in the network along the new path to 584 obtain the peer host's inbound SPI. 586 3.3.2. Credit-Based Authorization 588 Credit-Based Authorization (CBA) allows a host to securely use a new 589 locator even though the peer's reachability at the address embedded 590 in the locator has not yet been verified. This is accomplished based 591 on the following three hypotheses: 593 1. A flooding attacker typically seeks to somehow multiply the 594 packets it generates for the purpose of its attack because 595 bandwidth is an ample resource for many victims. 597 2. An attacker can often cause unamplified flooding by sending 598 packets to its victim, either by directly addressing the victim 599 in the packets, or by guiding the packets along a specific path 600 by means of an IPv6 Routing header, if Routing headers are not 601 filtered by firewalls. 603 3. Consequently, the additional effort required to set up a 604 redirection-based flooding attack (without CBA and return 605 routability checks) would pay off for the attacker only if 606 amplification could be obtained this way. 608 On this basis, rather than eliminating malicious packet redirection 609 in the first place, Credit-Based Authorization prevents 610 amplifications. This is accomplished by limiting the data a host can 611 send to an unverified address of a peer by the data recently received 612 from that peer. Redirection-based flooding attacks thus become less 613 attractive than, for example, pure direct flooding, where the 614 attacker itself sends bogus packets to the victim. 616 Figure 5 illustrates Credit-Based Authorization: Host B measures the 617 amount of data recently received from peer A and, when A readdresses, 618 sends packets to A's new, unverified address as long as the sum of 619 the packet sizes does not exceed the measured, received data volume. 620 When insufficient credit is left, B stops sending further packets to 621 A until A's address becomes ACTIVE. The address changes may be due 622 to mobility, multihoming, or any other reason. Not shown in Figure 5 623 are the results of credit aging (Section 5.6.2), a mechanism used to 624 dampen possible time-shifting attacks. 626 +-------+ +-------+ 627 | A | | B | 628 +-------+ +-------+ 629 | | 630 address |------------------------------->| credit += size(packet) 631 ACTIVE | | 632 |------------------------------->| credit += size(packet) 633 |<-------------------------------| do not change credit 634 | | 635 + address change | 636 + address verification starts | 637 address |<-------------------------------| credit -= size(packet) 638 UNVERIFIED |------------------------------->| credit += size(packet) 639 |<-------------------------------| credit -= size(packet) 640 | | 641 |<-------------------------------| credit -= size(packet) 642 | X credit < size(packet) 643 | | => do not send packet! 644 + address verification concludes | 645 address | | 646 ACTIVE |<-------------------------------| do not change credit 647 | | 649 Figure 5: Readdressing Scenario 651 This document does not specify how to set the credit limit value, but 652 the goal is to allow data transfers to proceed without much 653 interruption while the new address is verified. A simple heuristic 654 to accomplish this, if the sender knows roughly its round-trip time 655 (RTT) and current sending rate to the host, is to allow enough credit 656 to support maintaining the sending rate for a duration corresponding 657 to two or three RTTs. 659 3.3.3. Preferred Locator 661 When a host has multiple locators, the peer host needs to decide 662 which to use for outbound packets. It may be that a host would 663 prefer to receive data on a particular inbound interface. HIP allows 664 a particular locator to be designated as a Preferred locator and 665 communicated to the peer (see Section 4). 667 4. LOCATOR_SET Parameter Format 669 The LOCATOR_SET parameter has a type number value that is considered 670 to be a 'critical parameter' as per the definition in [RFC7401]; such 671 parameter types MUST be recognized and processed by the recipient. 672 The parameter consists of the standard HIP parameter Type and Length 673 fields, plus zero or more Locator sub-parameters. Each Locator sub- 674 parameter contains a Traffic Type, Locator Type, Locator Length, 675 Preferred locator bit, Locator Lifetime, and a Locator encoding. A 676 LOCATOR_SET containing zero Locator fields is permitted but has the 677 effect of deprecating all addresses. 679 0 1 2 3 680 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 1 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | Type | Length | 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 | Traffic Type | Locator Type | Locator Length | Reserved |P| 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 686 | Locator Lifetime | 687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 688 | Locator | 689 | | 690 | | 691 | | 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 . . 694 . . 695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 | Traffic Type | Locator Type | Locator Length | Reserved |P| 697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 698 | Locator Lifetime | 699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 700 | Locator | 701 | | 702 | | 703 | | 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 Figure 6: LOCATOR_SET Parameter Format 708 Type: 193 710 Length: Length in octets, excluding Type and Length fields, and 711 excluding padding. 713 Traffic Type: Defines whether the locator pertains to HIP signaling, 714 user data, or both. 716 Locator Type: Defines the semantics of the Locator field. 718 Locator Length: Defines the length of the Locator field, in units of 719 4-byte words (Locators up to a maximum of 4*255 octets are 720 supported). 722 Reserved: Zero when sent, ignored when received. 724 P: Preferred locator. Set to one if the locator is preferred for 725 that Traffic Type; otherwise, set to zero. 727 Locator Lifetime: Locator lifetime, in seconds. 729 Locator: The locator whose semantics and encoding are indicated by 730 the Locator Type field. All Locator sub-fields are integral 731 multiples of four octets in length. 733 The Locator Lifetime indicates how long the following locator is 734 expected to be valid. The lifetime is expressed in seconds. Each 735 locator MUST have a non-zero lifetime. The address is expected to 736 become deprecated when the specified number of seconds has passed 737 since the reception of the message. A deprecated address SHOULD NOT 738 be used as a destination address if an alternate (non-deprecated) is 739 available and has sufficient address scope. 741 4.1. Traffic Type and Preferred Locator 743 The following Traffic Type values are defined: 745 0: Both signaling (HIP control packets) and user data. 747 1: Signaling packets only. 749 2: Data packets only. 751 The "P" bit, when set, has scope over the corresponding Traffic Type. 752 That is, when a "P" bit is set for Traffic Type "2", for example, it 753 means that the locator is preferred for data packets. If there is a 754 conflict (for example, if the "P" bit is set for an address of Type 755 "0" and a different address of Type "2"), the more specific Traffic 756 Type rule applies (in this case, "2"). By default, the IP addresses 757 used in the base exchange are Preferred locators for both signaling 758 and user data, unless a new Preferred locator supersedes them. If no 759 locators are indicated as preferred for a given Traffic Type, the 760 implementation may use an arbitrary destination locator from the set 761 of active locators. 763 4.2. Locator Type and Locator 765 The following Locator Type values are defined, along with the 766 associated semantics of the Locator field: 768 0: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [RFC4291] 769 (128 bits long). This locator type is defined primarily for non- 770 ESP-based usage. 772 1: The concatenation of an ESP SPI (first 32 bits) followed by an 773 IPv6 address or an IPv4-in-IPv6 format IPv4 address (an additional 774 128 bits). This IP address is defined primarily for ESP-based 775 usage. 777 4.3. UPDATE Packet with Included LOCATOR_SET 779 A number of combinations of parameters in an UPDATE packet are 780 possible (e.g., see Section 3.2). In this document, procedures are 781 defined only for the case in which one LOCATOR_SET and one ESP_INFO 782 parameter is used in any HIP packet. Any UPDATE packet that includes 783 a LOCATOR_SET parameter SHOULD include both an HMAC and a 784 HIP_SIGNATURE parameter. 786 The UPDATE MAY also include a HOST_ID parameter (which may be useful 787 for HIP-aware firewalls inspecting the HIP messages for the first 788 time). If the UPDATE includes the HOST_ID parameter, the receiving 789 host MUST verify that the HOST_ID corresponds to the HOST_ID that was 790 used to establish the HIP association, and the HIP_SIGNATURE MUST 791 verify with the public key associated with this HOST_ID parameter. 793 The relationship between the announced Locators and any ESP_INFO 794 parameters present in the packet is defined in Section 5.2. This 795 document does not support any elements of procedure for sending more 796 than one LOCATOR_SET or ESP_INFO parameter in a single UPDATE. 798 5. Processing Rules 800 This section describes rules for sending and receiving the 801 LOCATOR_SET parameter, testing address reachability, and using 802 Credit-Based Authorization (CBA) on UNVERIFIED locators. 804 5.1. Locator Data Structure and Status 806 Each locator announced in a LOCATOR_SET parameter is represented by a 807 piece of state that contains the following data: 809 o the actual bit pattern representing the locator, 811 o the lifetime (seconds), 813 o the status (UNVERIFIED, ACTIVE, DEPRECATED), 815 o the Traffic Type scope of the locator, and 817 o whether the locator is preferred for any particular scope. 819 The status is used to track the reachability of the address embedded 820 within the LOCATOR_SET parameter: 822 UNVERIFIED indicates that the reachability of the address has not 823 been verified yet, 825 ACTIVE indicates that the reachability of the address has been 826 verified and the address has not been deprecated, 828 DEPRECATED indicates that the locator lifetime has expired. 830 The following state changes are allowed: 832 UNVERIFIED to ACTIVE The reachability procedure completes 833 successfully. 835 UNVERIFIED to DEPRECATED The locator lifetime expires while the 836 locator is UNVERIFIED. 838 ACTIVE to DEPRECATED The locator lifetime expires while the locator 839 is ACTIVE. 841 ACTIVE to UNVERIFIED There has been no traffic on the address for 842 some time, and the local policy mandates that the address 843 reachability needs to be verified again before starting to use it 844 again. 846 DEPRECATED to UNVERIFIED The host receives a new lifetime for the 847 locator. 849 A DEPRECATED address MUST NOT be changed to ACTIVE without first 850 verifying its reachability. 852 Note that the state of whether or not a locator is preferred is not 853 necessarily the same as the value of the Preferred bit in the Locator 854 sub-parameter received from the peer. Peers may recommend certain 855 locators to be preferred, but the decision on whether to actually use 856 a locator as a preferred locator is a local decision, possibly 857 influenced by local policy. 859 In addition to state maintained about status and remaining lifetime 860 for each locator learned from the peer, an implementation would 861 typically maintain similar state about its own locators that have 862 been offered to the peer. 864 An unbounded locator lifetime can be signified by setting the value 865 of the lifetime field to the maximum (unsigned) value. 867 Finally, the locators used to establish the HIP association are by 868 default assumed to be the initial preferred locators in ACTIVE state, 869 with an unbounded lifetime. 871 5.2. Sending the LOCATOR_SET 873 The decision of when to send the LOCATOR_SET is a local policy issue. 874 However, it is RECOMMENDED that a host send a LOCATOR_SET whenever it 875 recognizes a change of its IP addresses in use on an active HIP 876 association, and assumes that the change is going to last at least 877 for a few seconds. Rapidly sending LOCATOR_SETs that force the peer 878 to change the preferred address SHOULD be avoided. 880 The sending of a new LOCATOR_SET parameter replaces the locator 881 information from any previously sent LOCATOR_SET parameter, and 882 therefore if a host sends a new LOCATOR_SET parameter, it needs to 883 continue to include all active locators. Hosts MUST NOT announce 884 broadcast or multicast addresses in LOCATOR_SETs. 886 We now describe a few cases introduced in Section 3.2. We assume 887 that the Traffic Type for each locator is set to "0" (other values 888 for Traffic Type may be specified in documents that separate the HIP 889 control plane from data plane traffic). Other mobility cases are 890 possible but are left for further study. 892 1. Host mobility with no multihoming and no rekeying. The mobile 893 host creates a single UPDATE containing a single ESP_INFO with a 894 single LOCATOR_SET parameter. The ESP_INFO contains the current 895 value of the SPI in both the OLD SPI and NEW SPI fields. The 896 LOCATOR_SET contains a single Locator with a "Locator Type" of 897 "1"; the SPI MUST match that of the ESP_INFO. The Preferred bit 898 SHOULD be set and the "Locator Lifetime" is set according to 899 local policy. The UPDATE also contains a SEQ parameter as usual. 901 This packet is retransmitted as defined in the HIP protocol 902 specification [RFC7401]. The UPDATE should be sent to the peer's 903 preferred IP address with an IP source address corresponding to 904 the address in the LOCATOR_SET parameter. 906 2. Host mobility with no multihoming but with rekeying. The mobile 907 host creates a single UPDATE containing a single ESP_INFO with a 908 single LOCATOR_SET parameter (with a single address). The 909 ESP_INFO contains the current value of the SPI in the OLD SPI and 910 the new value of the SPI in the NEW SPI, and a KEYMAT Index as 911 selected by local policy. Optionally, the host may choose to 912 initiate a Diffie Hellman rekey by including a DIFFIE_HELLMAN 913 parameter. The LOCATOR_SET contains a single Locator with 914 "Locator Type" of "1"; the SPI MUST match that of the NEW SPI in 915 the ESP_INFO. Otherwise, the steps are identical to the case in 916 which no rekeying is initiated. 918 5.3. Handling Received LOCATOR_SETs 920 A host SHOULD be prepared to receive a single LOCATOR_SET parameter 921 in a HIP UPDATE packet. Reception of multiple LOCATOR_SET parameters 922 in a single packet, or in HIP packets other than UPDATE, is outside 923 of the scope of this specification. 925 Because a host sending the LOCATOR_SET may send the same parameter in 926 different UPDATE messages to different destination addresses, 927 including possibly the rendezvous server of the host, the host 928 receiving the LOCATOR_SET MUST be prepared to handle the possibility 929 of duplicate LOCATOR_SETs sent to more than one of the host's 930 addresses. As a result, the host MUST detect and avoid reprocessing 931 a LOCATOR_SET parameter that is redundant with a LOCATOR_SET 932 parameter that has been recently received and processed. 934 This document describes sending both ESP_INFO and LOCATOR_SET 935 parameters in an UPDATE. The ESP_INFO parameter is included when 936 there is a need to rekey or key a new SPI, and is otherwise included 937 for the possible benefit of HIP-aware NATs and firewalls. The 938 LOCATOR_SET parameter contains a complete listing of the locators 939 that the host wishes to make or keep active for the HIP association. 941 In general, the processing of a LOCATOR_SET depends upon the packet 942 type in which it is included. Here, we describe only the case in 943 which ESP_INFO is present and a single LOCATOR_SET and ESP_INFO are 944 sent in an UPDATE message; other cases are for further study. The 945 steps below cover each of the cases described in Section 5.2. 947 The processing of ESP_INFO and LOCATOR_SET parameters is intended to 948 be modular and support future generalization to the inclusion of 949 multiple ESP_INFO and/or multiple LOCATOR_SET parameters. A host 950 SHOULD first process the ESP_INFO before the LOCATOR_SET, since the 951 ESP_INFO may contain a new SPI value mapped to an existing SPI, while 952 a Type "1" locator will only contain a reference to the new SPI. 954 When a host receives a validated HIP UPDATE with a LOCATOR_SET and 955 ESP_INFO parameter, it processes the ESP_INFO as follows. The 956 ESP_INFO parameter indicates whether an SA is being rekeyed, created, 957 deprecated, or just identified for the benefit of HIP-aware NATs and 958 firewalls. The host examines the OLD SPI and NEW SPI values in the 959 ESP_INFO parameter: 961 1. (no rekeying) If the OLD SPI is equal to the NEW SPI and both 962 correspond to an existing SPI, the ESP_INFO is gratuitous 963 (provided for HIP-aware NATs and firewalls) and no rekeying is 964 necessary. 966 2. (rekeying) If the OLD SPI indicates an existing SPI and the NEW 967 SPI is a different non-zero value, the existing SA is being 968 rekeyed and the host follows HIP ESP rekeying procedures by 969 creating a new outbound SA with an SPI corresponding to the NEW 970 SPI, with no addresses bound to this SPI. Note that locators in 971 the LOCATOR_SET parameter will reference this new SPI instead of 972 the old SPI. 974 3. (new SA) If the OLD SPI value is zero and the NEW SPI is a new 975 non-zero value, then a new SA is being requested by the peer. 976 This case is also treated like a rekeying event; the receiving 977 host MUST create a new SA and respond with an UPDATE ACK. 979 4. (deprecating the SA) If the OLD SPI indicates an existing SPI and 980 the NEW SPI is zero, the SA is being deprecated and all locators 981 uniquely bound to the SPI are put into the DEPRECATED state. 983 If none of the above cases apply, a protocol error has occurred and 984 the processing of the UPDATE is stopped. 986 Next, the locators in the LOCATOR_SET parameter are processed. For 987 each locator listed in the LOCATOR_SET parameter, check that the 988 address therein is a legal unicast or anycast address. That is, the 989 address MUST NOT be a broadcast or multicast address. Note that some 990 implementations MAY accept addresses that indicate the local host, 991 since it may be allowed that the host runs HIP with itself. 993 The below assumes that all locators are of Type "1" with a Traffic 994 Type of "0"; other cases are for further study. 996 For each Type "1" address listed in the LOCATOR_SET parameter, the 997 host checks whether the address is already bound to the SPI 998 indicated. If the address is already bound, its lifetime is updated. 999 If the status of the address is DEPRECATED, the status is changed to 1000 UNVERIFIED. If the address is not already bound, the address is 1001 added, and its status is set to UNVERIFIED. Mark all addresses 1002 corresponding to the SPI that were NOT listed in the LOCATOR_SET 1003 parameter as DEPRECATED. 1005 As a result, at the end of processing, the addresses listed in the 1006 LOCATOR_SET parameter have either a state of UNVERIFIED or ACTIVE, 1007 and any old addresses on the old SA not listed in the LOCATOR_SET 1008 parameter have a state of DEPRECATED. 1010 Once the host has processed the locators, if the LOCATOR_SET 1011 parameter contains a new Preferred locator, the host SHOULD initiate 1012 a change of the Preferred locator. This requires that the host first 1013 verifies reachability of the associated address, and only then 1014 changes the Preferred locator; see Section 5.5. 1016 If a host receives a locator with an unsupported Locator Type, and 1017 when such a locator is also declared to be the Preferred locator for 1018 the peer, the host SHOULD send a NOTIFY error with a Notify Message 1019 Type of LOCATOR_TYPE_UNSUPPORTED, with the Notification Data field 1020 containing the locator(s) that the receiver failed to process. 1021 Otherwise, a host MAY send a NOTIFY error if a (non-preferred) 1022 locator with an unsupported Locator Type is received in a LOCATOR_SET 1023 parameter. 1025 A host MAY add the source IP address of a received HIP packet as a 1026 candidate locator for the peer even if it is not listed in the peer's 1027 LOCATOR_SET, but it SHOULD prefer locators explicitly listed in the 1028 LOCATOR_SET. 1030 5.4. Verifying Address Reachability 1032 A host MUST verify the reachability of an UNVERIFIED address. The 1033 status of a newly learned address MUST initially be set to UNVERIFIED 1034 unless the new address is advertised in a R1 packet as a new 1035 Preferred locator. A host MAY also want to verify the reachability 1036 of an ACTIVE address again after some time, in which case it would 1037 set the status of the address to UNVERIFIED and reinitiate address 1038 verification. A typical verification that is protected by 1039 retransmission timers is to include an ECHO REQUEST within an UPDATE 1040 sent to the new address. 1042 A host typically starts the address-verification procedure by sending 1043 a nonce to the new address. A host MAY choose from different message 1044 exchanges or different nonce values so long as it establishes that 1045 the peer has received and replied to the nonce at the new address. 1046 For example, when the host is changing its SPI and sending an 1047 ESP_INFO to the peer, the NEW SPI value SHOULD be random and the 1048 random value MAY be copied into an ECHO_REQUEST sent in the rekeying 1049 UPDATE. However, if the host is not changing its SPI, it MAY still 1050 use the ECHO_REQUEST parameter for verification but with some other 1051 random value. A host MAY also use other message exchanges as 1052 confirmation of the address reachability. 1054 In some cases, it MAY be sufficient to use the arrival of data on a 1055 newly advertised SA as implicit address reachability verification as 1056 depicted in Figure 7, instead of waiting for the confirmation via a 1057 HIP packet. In this case, a host advertising a new SPI as part of 1058 its address reachability check SHOULD be prepared to receive traffic 1059 on the new SA. 1061 Mobile host Peer host 1063 UPDATE(ESP_INFO, LOCATOR_SET, ...) 1064 ----------------------------------> 1066 prepare incoming SA 1067 UPDATE(ESP_INFO, ...) with new SPI 1068 <----------------------------------- 1069 switch to new outgoing SA 1070 data on new SA 1071 -----------------------------------> 1072 mark address ACTIVE 1073 UPDATE(ACK, ECHO_RESPONSE) later arrives 1074 -----------------------------------> 1076 Figure 7: Address Activation Via Use of a New SA 1078 When address verification is in progress for a new Preferred locator, 1079 the host SHOULD select a different locator listed as ACTIVE, if one 1080 such locator is available, to continue communications until address 1081 verification completes. Alternatively, the host MAY use the new 1082 Preferred locator while in UNVERIFIED status to the extent Credit- 1083 Based Authorization permits. Credit-Based Authorization is explained 1084 in Section 5.6. Once address verification succeeds, the status of 1085 the new Preferred locator changes to ACTIVE. 1087 5.5. Changing the Preferred Locator 1089 A host MAY want to change the Preferred outgoing locator for 1090 different reasons, e.g., because traffic information or ICMP error 1091 messages indicate that the currently used preferred address may have 1092 become unreachable. Another reason may be due to receiving a 1093 LOCATOR_SET parameter that has the "P" bit set. 1095 To change the Preferred locator, the host initiates the following 1096 procedure: 1098 1. If the new Preferred locator has ACTIVE status, the Preferred 1099 locator is changed and the procedure succeeds. 1101 2. If the new Preferred locator has UNVERIFIED status, the host 1102 starts to verify its reachability. The host SHOULD use a 1103 different locator listed as ACTIVE until address verification 1104 completes if one such locator is available. Alternatively, the 1105 host MAY use the new Preferred locator, even though in UNVERIFIED 1106 status, to the extent Credit-Based Authorization permits. Once 1107 address verification succeeds, the status of the new Preferred 1108 locator changes to ACTIVE and its use is no longer governed by 1109 Credit-Based Authorization. 1111 3. If the peer host has not indicated a preference for any address, 1112 then the host picks one of the peer's ACTIVE addresses randomly 1113 or according to local policy. This case may arise if, for 1114 example, ICMP error messages that deprecate the Preferred locator 1115 arrive, but the peer has not yet indicated a new Preferred 1116 locator. 1118 4. If the new Preferred locator has DEPRECATED status and there is 1119 at least one non-deprecated address, the host selects one of the 1120 non-deprecated addresses as a new Preferred locator and 1121 continues. If the selected address is UNVERIFIED, the address 1122 verification procedure described above will apply. 1124 5.6. Credit-Based Authorization 1126 To prevent redirection-based flooding attacks, the use of a Credit- 1127 Based Authorization (CBA) approach MUST be used when a host sends 1128 data to an UNVERIFIED locator. The following algorithm addresses the 1129 security considerations for prevention of amplification and time- 1130 shifting attacks. Other forms of credit aging, and other values for 1131 the CreditAgingFactor and CreditAgingInterval parameters in 1132 particular, are for further study, and so are the advanced CBA 1133 techniques specified in [CBA-MIPv6]. 1135 5.6.1. Handling Payload Packets 1137 A host maintains a "credit counter" for each of its peers. Whenever 1138 a packet arrives from a peer, the host SHOULD increase that peer's 1139 credit counter by the size of the received packet. When the host has 1140 a packet to be sent to the peer, and when the peer's Preferred 1141 locator is listed as UNVERIFIED and no alternative locator with 1142 status ACTIVE is available, the host checks whether it can send the 1143 packet to the UNVERIFIED locator. The packet SHOULD be sent if the 1144 value of the credit counter is higher than the size of the outbound 1145 packet. If the credit counter is too low, the packet MUST be 1146 discarded or buffered until address verification succeeds. When a 1147 packet is sent to a peer at an UNVERIFIED locator, the peer's credit 1148 counter MUST be reduced by the size of the packet. The peer's credit 1149 counter is not affected by packets that the host sends to an ACTIVE 1150 locator of that peer. 1152 Figure 8 depicts the actions taken by the host when a packet is 1153 received. Figure 9 shows the decision chain in the event a packet is 1154 sent. 1156 Inbound 1157 packet 1158 | 1159 | +----------------+ +---------------+ 1160 | | Increase | | Deliver | 1161 +-----> | credit counter |-------------> | packet to | 1162 | by packet size | | application | 1163 +----------------+ +---------------+ 1165 Figure 8: Receiving Packets with Credit-Based Authorization 1167 Outbound 1168 packet 1169 | _________________ 1170 | / \ +---------------+ 1171 | / Is the preferred \ No | Send packet | 1172 +-----> | destination address |-------------> | to preferred | 1173 \ UNVERIFIED? / | address | 1174 \_________________/ +---------------+ 1175 | 1176 | Yes 1177 | 1178 v 1179 _________________ 1180 / \ +---------------+ 1181 / Does an ACTIVE \ Yes | Send packet | 1182 | destination address |-------------> | to ACTIVE | 1183 \ exist? / | address | 1184 \_________________/ +---------------+ 1185 | 1186 | No 1187 | 1188 v 1189 _________________ 1190 / \ +---------------+ 1191 / Credit counter \ No | | 1192 | >= |-------------> | Drop or | 1193 \ packet size? / | buffer packet | 1194 \_________________/ +---------------+ 1195 | 1196 | Yes 1197 | 1198 v 1199 +---------------+ +---------------+ 1200 | Reduce credit | | Send packet | 1201 | counter by |----------------> | to preferred | 1202 | packet size | | address | 1203 +---------------+ +---------------+ 1205 Figure 9: Sending Packets with Credit-Based Authorization 1207 5.6.2. Credit Aging 1209 A host ensures that the credit counters it maintains for its peers 1210 gradually decrease over time. Such "credit aging" prevents a 1211 malicious peer from building up credit at a very slow speed and using 1212 this, all at once, for a severe burst of redirected packets. 1214 Credit aging may be implemented by multiplying credit counters with a 1215 factor, CreditAgingFactor (a fractional value less than one), in 1216 fixed time intervals of CreditAgingInterval length. Choosing 1217 appropriate values for CreditAgingFactor and CreditAgingInterval is 1218 important to ensure that a host can send packets to an address in 1219 state UNVERIFIED even when the peer sends at a lower rate than the 1220 host itself. When CreditAgingFactor or CreditAgingInterval are too 1221 small, the peer's credit counter might be too low to continue sending 1222 packets until address verification concludes. 1224 The parameter values proposed in this document are as follows: 1226 CreditAgingFactor 7/8 1227 CreditAgingInterval 5 seconds 1229 These parameter values work well when the host transfers a file to 1230 the peer via a TCP connection and the end-to-end round-trip time does 1231 not exceed 500 milliseconds. Alternative credit-aging algorithms may 1232 use other parameter values or different parameters, which may even be 1233 dynamically established. 1235 6. Security Considerations 1237 The HIP mobility mechanism provides a secure means of updating a 1238 host's IP address via HIP UPDATE packets. Upon receipt, a HIP host 1239 cryptographically verifies the sender of an UPDATE, so forging or 1240 replaying a HIP UPDATE packet is very difficult (see [RFC7401]). 1241 Therefore, security issues reside in other attack domains. The two 1242 we consider are malicious redirection of legitimate connections as 1243 well as redirection-based flooding attacks using this protocol. This 1244 can be broken down into the following: 1246 1) Impersonation attacks 1248 - direct conversation with the misled victim 1250 - man-in-the-middle attack 1252 2) DoS attacks 1254 - flooding attacks (== bandwidth-exhaustion attacks) 1256 * tool 1: direct flooding 1258 * tool 2: flooding by botnets 1260 * tool 3: redirection-based flooding 1262 - memory-exhaustion attacks 1264 - computational-exhaustion attacks 1266 3) Privacy concerns 1268 We consider these in more detail in the following sections. 1270 In Section 6.1 and Section 6.2, we assume that all users are using 1271 HIP. In Section 6.3 we consider the security ramifications when we 1272 have both HIP and non-HIP hosts. 1274 6.1. Impersonation Attacks 1276 An attacker wishing to impersonate another host will try to mislead 1277 its victim into directly communicating with them, or carry out a man- 1278 in-the-middle (MitM) attack between the victim and the victim's 1279 desired communication peer. Without mobility support, such attacks 1280 are possible only if the attacker resides on the routing path between 1281 its victim and the victim's desired communication peer, or if the 1282 attacker tricks its victim into initiating the connection over an 1283 incorrect routing path (e.g., by acting as a router or using spoofed 1284 DNS entries). 1286 The HIP extensions defined in this specification change the situation 1287 in that they introduce an ability to redirect a connection, both 1288 before and after establishment. If no precautionary measures are 1289 taken, an attacker could potentially misuse the redirection feature 1290 to impersonate a victim's peer from any arbitrary location. However, 1291 the authentication and authorization mechanisms of the HIP base 1292 exchange [RFC7401] and the signatures in the UPDATE message prevent 1293 this attack. Furthermore, ownership of a HIP association is securely 1294 linked to a HIP HI/HIT. If an attacker somehow uses a bug in the 1295 implementation to redirect a HIP connection, the original owner can 1296 always reclaim their connection (they can always prove ownership of 1297 the private key associated with their public HI). 1299 MitM attacks are possible if an on-path attacker is present during 1300 the initial HIP base exchange and if the hosts do not authenticate 1301 each other's identities. However, once such an opportunistic base 1302 exchange has taken place, a MitM attacker that comes later to the 1303 path cannot steal the HIP connection because it is very difficult for 1304 an attacker to create an UPDATE packet (or any HIP packet) that will 1305 be accepted as a legitimate update. UPDATE packets use HMAC and are 1306 signed. Even when an attacker can snoop packets to obtain the SPI 1307 and HIT/HI, they still cannot forge an UPDATE packet without 1308 knowledge of the secret keys. Also, replay attacks on the UPDATE 1309 packet are prevented as described in [RFC7401]. 1311 6.2. Denial-of-Service Attacks 1313 6.2.1. Flooding Attacks 1315 The purpose of a denial-of-service attack is to exhaust some resource 1316 of the victim such that the victim ceases to operate correctly. A 1317 denial-of-service attack can aim at the victim's network attachment 1318 (flooding attack), its memory, or its processing capacity. In a 1319 flooding attack, the attacker causes an excessive number of bogus or 1320 unwanted packets to be sent to the victim, which fills their 1321 available bandwidth. Note that the victim does not necessarily need 1322 to be a node; it can also be an entire network. The attack functions 1323 the same way in either case. 1325 An effective DoS strategy is distributed denial of service (DDoS). 1326 Here, the attacker conventionally distributes some viral software to 1327 as many nodes as possible. Under the control of the attacker, the 1328 infected nodes (e.g. nodes in a botnet), jointly send packets to the 1329 victim. With such an 'army', an attacker can take down even very 1330 high bandwidth networks/victims. 1332 With the ability to redirect connections, an attacker could realize a 1333 DDoS attack without having to distribute viral code. Here, the 1334 attacker initiates a large download from a server, and subsequently 1335 uses the HIP mobility mechanism to redirect this download to its 1336 victim. The attacker can repeat this with multiple servers. This 1337 threat is mitigated through reachability checks and credit-based 1338 authorization. Reachability checks, which when conducted using HIP 1339 can leverage the built-in authentication properties of HIP, can 1340 prevent redirection-based flooding attacks. However, the delay of 1341 such a check can have a noticeable impact on application performance. 1342 To reduce the impact of the delay, credit-based authorization can be 1343 used to send a limited number of packets to the new address while the 1344 validity of the IP address is still in question. Both strategies do 1345 not eliminate flooding attacks per se, but they preclude: (i) their 1346 use from a location off the path towards the flooded victim; and (ii) 1347 any amplification in the number and size of the redirected packets. 1348 As a result, the combination of a reachability check and credit-based 1349 authorization lowers a HIP redirection-based flooding attack to the 1350 level of a direct flooding attack in which the attacker itself sends 1351 the flooding traffic to the victim. 1353 6.2.2. Memory/Computational-Exhaustion DoS Attacks 1355 We now consider whether or not the proposed extensions to HIP add any 1356 new DoS attacks (consideration of DoS attacks using the base HIP 1357 exchange and updates is discussed in [RFC7401]). A simple attack is 1358 to send many UPDATE packets containing many IP addresses that are not 1359 flagged as preferred. The attacker continues to send such packets 1360 until the number of IP addresses associated with the attacker's HI 1361 crashes the system. Therefore, a HIP association SHOULD limit the 1362 number of IP addresses that can be associated with any HI. Other 1363 forms of memory/computationally exhausting attacks via the HIP UPDATE 1364 packet are handled in the base HIP document [RFC7401]. 1366 A central server that has to deal with a large number of mobile 1367 clients MAY consider increasing the SA lifetimes to try to slow down 1368 the rate of rekeying UPDATEs or increasing the cookie difficulty to 1369 slow down the rate of attack-oriented connections. 1371 6.3. Mixed Deployment Environment 1373 We now assume an environment with both HIP and non-HIP aware hosts. 1374 Four cases exist. 1376 1. A HIP host redirects its connection onto a non-HIP host. The 1377 non-HIP host will drop the reachability packet, so this is not a 1378 threat unless the HIP host is a MitM that could somehow respond 1379 successfully to the reachability check. 1381 2. A non-HIP host attempts to redirect their connection onto a HIP 1382 host. This falls into IPv4 and IPv6 security concerns, which are 1383 outside the scope of this document. 1385 3. A non-HIP host attempts to steal a HIP host's session (assume 1386 that Secure Neighbor Discovery is not active for the following). 1387 The non-HIP host contacts the service that a HIP host has a 1388 connection with and then attempts to change its IP address to 1389 steal the HIP host's connection. What will happen in this case 1390 is implementation dependent but such a request should fail by 1391 being ignored or dropped. Even if the attack were successful, 1392 the HIP host could reclaim its connection via HIP. 1394 4. A HIP host attempts to steal a non-HIP host's session. A HIP 1395 host could spoof the non-HIP host's IP address during the base 1396 exchange or set the non-HIP host's IP address as its preferred 1397 address via an UPDATE. Other possibilities exist, but a solution 1398 is to prevent the local redirection of sessions that were 1399 previously using an unverified address, but outside of the 1400 existing HIP context, into the HIP SAs until the address change 1401 can be verified. 1403 6.4. Privacy Concerns 1405 The exposure of a host's IP addresses through HIP mobility extensions 1406 may raise privacy concerns. The administrator of a host may be 1407 trying to hide its location in some context through the use of a VPN 1408 or other virtual interfaces. Similar privacy issues also arise in 1409 other frameworks such as WebRTC and are not specific to HIP. 1410 Implementations SHOULD provide a mechanism to allow the host 1411 administrator to block the exposure of selected addresses or address 1412 ranges. While this issue may be more relevant in a host multihoming 1413 scenario in which multiple IP addresses might be exposed 1414 ([I-D.ietf-hip-multihoming]), it is worth noting also here that 1415 mobility events might cause an implementation to try to inadvertently 1416 use a locator that the adminstrator would rather avoid exposing to 1417 the peer host. 1419 7. IANA Considerations 1421 [RFC5206], obsoleted by this document, specified an allocation for a 1422 LOCATOR parameter in the HIP Parameters registry, with a type value 1423 of 193. This document requests IANA to rename the parameter to 1424 'LOCATOR_SET' and to update the reference from [RFC5206] to this 1425 specification. 1427 [RFC5206], obsoleted by this document, specified an allocation a 1428 LOCATOR_TYPE_UNSUPPORTED type in the Notify Message Type registry, 1429 with a type value of 46. This document requests IANA to update the 1430 reference from [RFC5206] to this specification. 1432 8. Differences from RFC 5206 1434 This section summarizes the technical changes made from [RFC5206]. 1435 This section is informational, intended to help implementors of the 1436 previous protocol version. If any text in this section contradicts 1437 text in other portions of this specification, the text found outside 1438 of this section should be considered normative. 1440 This document specifies extensions to the HIP Version 2 protocol, 1441 while [RFC5206] specifies extensions to the HIP Version 1 protocol. 1442 [RFC7401] documents the differences between these two protocol 1443 versions. 1445 [RFC5206] included procedures for both HIP host mobility and basic 1446 host multihoming. In this document, only host mobility procedures 1447 are included; host multihoming procedures are now specified in 1448 [I-D.ietf-hip-multihoming]. In particular, multihoming-related 1449 procedures related to the exposure of multiple locators in the base 1450 exchange packets, the transmission, reception, and processing of 1451 multiple locators in a single UPDATE packet, handovers across IP 1452 address families, and other multihoming-related specification has 1453 been removed. 1455 The following additional changes have been made: 1457 o The LOCATOR parameter in [RFC5206] has been renamed to 1458 LOCATOR_SET. 1460 o Specification text regarding the handling of mobility when both 1461 hosts change IP addresses at nearly the same time (a 'double-jump' 1462 mobility scenario) has been added. 1464 o Specification text regarding the mobility event in which the host 1465 briefly has an active new locator and old locator at the same time 1466 (a 'make-before-break' mobility scenario) has been added. 1468 o Specification text has been added to note that a host may add the 1469 source IP address of a received HIP packet as a candidate locator 1470 for the peer even if it is not listed in the peer's LOCATOR_SET, 1471 but that it should prefer locators explicitly listed in the 1472 LOCATOR_SET. 1474 o This document clarifies that the HOST_ID parameter may be included 1475 in UPDATE messages containing LOCATOR_SET parameters, for the 1476 possible benefit of HIP-aware firewalls. 1478 o The previous specification mentioned that it may be possible to 1479 include multiple LOCATOR_SET and ESP_INFO parameters in an UPDATE. 1480 This document only specifies the case of a single LOCATOR_SET and 1481 ESP_INFO parameter in an UPDATE. 1483 o The previous specification mentioned that it may be possible to 1484 send LOCATOR_SET parameters in packets other than the UPDATE. 1485 This document only specifies the use of the UPDATE packet. 1487 o This document describes a simple heuristic for setting the credit 1488 value for Credit-Based Authorization. 1490 o This specification mandates that a host must be able to receive 1491 and avoid reprocessing redundant LOCATOR_SET parameters that may 1492 have been sent in parallel to multiple addresses of the host. 1494 9. Authors and Acknowledgments 1496 Pekka Nikander and Jari Arkko originated this document, and Christian 1497 Vogt and Thomas Henderson (editor) later joined as co-authors. Greg 1498 Perkins contributed the initial draft of the security section. Petri 1499 Jokela was a co-author of the initial individual submission. 1501 Credit-Based Authorization was originally introduced in [SIMPLE-CBA], 1502 and portions of this document have been adopted from that earlier 1503 draft. 1505 The authors thank Jeff Ahrenholz, Baris Boyvat, Rene Hummen, Miika 1506 Komu, Mika Kousa, Jan Melen, and Samu Varjonen for improvements to 1507 the document. 1509 10. References 1511 10.1. Normative references 1513 [I-D.ietf-hip-rfc5203-bis] 1514 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1515 Registration Extension", draft-ietf-hip-rfc5203-bis-11 1516 (work in progress), August 2016. 1518 [I-D.ietf-hip-rfc5204-bis] 1519 Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) 1520 Rendezvous Extension", draft-ietf-hip-rfc5204-bis-08 (work 1521 in progress), August 2016. 1523 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1524 Requirement Levels", BCP 14, RFC 2119, 1525 DOI 10.17487/RFC2119, March 1997, 1526 . 1528 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1529 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1530 2006, . 1532 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 1533 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 1534 RFC 7401, DOI 10.17487/RFC7401, April 2015, 1535 . 1537 [RFC7402] Jokela, P., Moskowitz, R., and J. Melen, "Using the 1538 Encapsulating Security Payload (ESP) Transport Format with 1539 the Host Identity Protocol (HIP)", RFC 7402, 1540 DOI 10.17487/RFC7402, April 2015, 1541 . 1543 10.2. Informative references 1545 [CBA-MIPv6] 1546 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1547 Mobile IPv6 Early Binding Updates", February 2005. 1549 [I-D.ietf-hip-multihoming] 1550 Henderson, T., Vogt, C., and J. Arkko, "Host Multihoming 1551 with the Host Identity Protocol", draft-ietf-hip- 1552 multihoming-11 (work in progress), September 2016. 1554 [RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. 1555 Nordmark, "Mobile IP Version 6 Route Optimization Security 1556 Design Background", RFC 4225, DOI 10.17487/RFC4225, 1557 December 2005, . 1559 [RFC5206] Nikander, P., Henderson, T., Ed., Vogt, C., and J. Arkko, 1560 "End-Host Mobility and Multihoming with the Host Identity 1561 Protocol", RFC 5206, DOI 10.17487/RFC5206, April 2008, 1562 . 1564 [RFC5207] Stiemerling, M., Quittek, J., and L. Eggert, "NAT and 1565 Firewall Traversal Issues of Host Identity Protocol (HIP) 1566 Communication", RFC 5207, DOI 10.17487/RFC5207, April 1567 2008, . 1569 [SIMPLE-CBA] 1570 Vogt, C. and J. Arkko, "Credit-Based Authorization for 1571 Concurrent Reachability Verification", February 2006. 1573 Appendix A. Document Revision History 1575 To be removed upon publication 1577 +----------+--------------------------------------------------------+ 1578 | Revision | Comments | 1579 +----------+--------------------------------------------------------+ 1580 | draft-00 | Initial version from RFC5206 xml (unchanged). | 1581 | | | 1582 | draft-01 | Remove multihoming-specific text; no other changes. | 1583 | | | 1584 | draft-02 | Update references to point to -bis drafts; no other | 1585 | | changes. | 1586 | | | 1587 | draft-03 | issue 4: add make before break use case | 1588 | | | 1589 | | issue 6: peer locator exposure policies | 1590 | | | 1591 | | issue 10: rename LOCATOR to LOCATOR_SET | 1592 | | | 1593 | | issue 14: use of UPDATE packet's IP address | 1594 | | | 1595 | draft-04 | Document refresh; no other changes. | 1596 | | | 1597 | draft-05 | Document refresh; no other changes. | 1598 | | | 1599 | draft-06 | Document refresh; no other changes. | 1600 | | | 1601 | draft-07 | Document refresh; IANA considerations updated. | 1602 | | | 1603 | draft-08 | Remove sending LOCATOR_SET in R1, I2, and NOTIFY | 1604 | | (multihoming) | 1605 | | | 1606 | | State that only one LOCATOR_SET parameter may be sent | 1607 | | in an UPDATE packet (according to this draft) | 1608 | | (multihoming) | 1609 | | | 1610 | | Remove text about cross-family handovers (multihoming) | 1611 | | | 1612 | draft-09 | Add specification text regarding double-jump mobility | 1613 | | procedures. | 1614 | | | 1615 | draft-10 | issue 21: clarified that HI MAY be included in UPDATE | 1616 | | for benefit of middleboxes | 1617 | | | 1618 | | changed one informative reference from RFC 4423-bis to | 1619 | | RFC 7401 | 1620 | | | 1621 | | removed discussion about possible multiple LOCATOR_SET | 1622 | | and ESP_INFO parameters in an UPDATE (per previous | 1623 | | mailing list discussion) | 1624 | | | 1625 | | removed discussion about handling LOCATOR_SET | 1626 | | parameters in packets other than UPDATE (per previous | 1627 | | mailing list discussion) | 1628 | | | 1629 | draft-11 | Editorial improvements from WGLC | 1630 | | | 1631 | draft-12 | Update author affiliations and IPR boilerplate to | 1632 | | trust200902 | 1633 | | | 1634 | draft-13 | Editorial improvements to IANA considerations section. | 1635 | | | 1636 | | Moved citation of [SIMPLE-CBA] to Section 9 and | 1637 | | slightly updated text for redirection-based flooding | 1638 | | attacks in the Security Considerations section. | 1639 | | | 1640 | | Editorial improvements based on last call comments. | 1641 | | | 1642 | draft-14 | Added section to summarize changes from RFC5206. | 1643 | | | 1644 | | Replace references to 'middleboxes' with more specific | 1645 | | 'NATs and firewalls'. | 1646 | | | 1647 | | Describe a simple heuristic for setting the credit | 1648 | | value based on sending rate and RTT. | 1649 | | | 1650 | | Add subsection about privacy concerns of locator | 1651 | | exposure to the Security Considerations section. | 1652 | | | 1653 | | Clarify that a host must be able to receive and avoid | 1654 | | reprocessing redundant LOCATOR_SET parameters that may | 1655 | | have been sent in parallel to multiple addresses of | 1656 | | the host. | 1657 | | | 1658 | | Clarify that multicast or broadcast addresses must not | 1659 | | be announced in a LOCATOR_SET. | 1660 | | | 1661 | | Editorial improvements based on last call comments. | 1662 +----------+--------------------------------------------------------+ 1664 Authors' Addresses 1665 Thomas R. Henderson (editor) 1666 University of Washington 1667 Campus Box 352500 1668 Seattle, WA 1669 USA 1671 EMail: tomhend@u.washington.edu 1673 Christian Vogt 1674 Independent 1675 3473 North First Street 1676 San Jose, CA 95134 1677 USA 1679 EMail: mail@christianvogt.net 1681 Jari Arkko 1682 Ericsson 1683 JORVAS FIN-02420 1684 FINLAND 1686 Phone: +358 40 5079256 1687 EMail: jari.arkko@piuha.net