idnits 2.17.1 draft-ietf-seamoby-ctp-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** It looks like you're using RFC 3978 boilerplate. You should update this to the boilerplate described in the IETF Trust License Policy document (see https://trustee.ietf.org/license-info), which is required now. -- Found old boilerplate from RFC 3667, Section 5.1 on line 15. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 1411. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 1424. ** Found boilerplate matching RFC 3978, Section 5.4, paragraph 1 (on line 1392), which is fine, but *also* found old RFC 2026, Section 10.4C, paragraph 1 text on line 35. ** The document seems to lack an RFC 3978 Section 5.1 IPR Disclosure Acknowledgement -- however, there's a paragraph with a matching beginning. Boilerplate error? ** This document has an original RFC 3978 Section 5.4 Copyright Line, instead of the newer IETF Trust Copyright according to RFC 4748. ** The document seems to lack an RFC 3978 Section 5.5 (updated by RFC 4748) Disclaimer -- however, there's a paragraph with a matching beginning. Boilerplate error? ** The document seems to lack an RFC 3979 Section 5, para. 2 IPR Disclosure Acknowledgement -- however, there's a paragraph with a matching beginning. Boilerplate error? ** The document uses RFC 3667 boilerplate or RFC 3978-like boilerplate instead of verbatim RFC 3978 boilerplate. After 6 May 2005, submission of drafts without verbatim RFC 3978 boilerplate is not accepted. The following non-3978 patterns matched text found in the document. That text should be removed or replaced: By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- ** The document is more than 15 pages and seems to lack a Table of Contents. == The page length should not exceed 58 lines per page, but there was 30 longer pages, the longest (page 8) being 61 lines == It seems as if not all pages are separated by form feeds - found 0 form feeds but 31 pages Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 28 instances of too long lines in the document, the longest one being 4 characters in excess of 72. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (April 14, 2004) is 7316 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Missing Reference: 'FMIPV6' is mentioned on line 188, but not defined == Missing Reference: 'RFC 791' is mentioned on line 689, but not defined == Missing Reference: 'RFC 2373' is mentioned on line 691, but not defined ** Obsolete undefined reference: RFC 2373 (Obsoleted by RFC 3513) == Missing Reference: 'PerkCal04' is mentioned on line 1062, but not defined == Unused Reference: 'RFC2026' is defined on line 1125, but no explicit reference was found in the text == Unused Reference: 'RFC2434' is defined on line 1131, but no explicit reference was found in the text == Unused Reference: 'CARD' is defined on line 1147, but no explicit reference was found in the text == Unused Reference: 'CTHC' is defined on line 1156, but no explicit reference was found in the text == Unused Reference: 'RFC2401' is defined on line 1170, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2434 (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 2409 (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2406 (ref. 'ESP') (Obsoleted by RFC 4303, RFC 4305) ** Obsolete normative reference: RFC 2960 (ref. 'SCTP') (Obsoleted by RFC 4960) -- Obsolete informational reference (is this intentional?): RFC 2401 (Obsoleted by RFC 4301) -- Obsolete informational reference (is this intentional?): RFC 2461 (Obsoleted by RFC 4861) -- Obsolete informational reference (is this intentional?): RFC 2462 (Obsoleted by RFC 4862) Summary: 14 errors (**), 0 flaws (~~), 12 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Seamoby WG J. Loughney (editor) 3 Internet Draft M. Nakhjiri 4 Category: Experimental C. Perkins 5 R. Koodli 6 Expires: October 13, 2004 April 14, 2004 8 Context Transfer Protocol 10 Status of this Memo 12 By submitting this Internet-Draft, I certify that any applicable 13 patent or other IPR claims of which I am aware have been disclosed, 14 and any of which I become aware will be disclosed, in accordance with 15 RFC 3668. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 Copyright Notice 35 Copyright (C) The Internet Society 2004. All Rights Reserved. 37 Abstract 39 This document presents a context transfer protocol that enables 40 authorized context transfers. Context transfers allow better support 41 for node based mobility so that the applications running on mobile 42 nodes can operate with minimal disruption. Key objectives are to 43 reduce latency, packet losses and avoiding re-initiation of signaling 44 to and from the mobile node. 46 Table of Contents 48 1. Introduction 49 1.1 The Problem 50 1.2 Conventions Used in This Document 51 1.3 Abbreviations Used in the Document 52 2. Protocol Overview 53 2.1 Context Transfer Scenarios 54 2.2 Context Transfer Message Format 55 2.3 Context Types 56 2.4 Context Data Block (CTB) 57 2.5 Messages 58 3. Transport 59 3.1 Inter-Router Transport 60 3.2 MN-AR Transport 61 4. Error Codes and Constants 62 5. Examples and Signaling Flows 63 5.1 Network controlled, Initiated by pAR, Predictive 64 5.2 Network controlled, Initiated by nAR, Reactive 65 5.3 Mobile controlled, Predictive New L2 up/old L2 down 66 6. Security Considerations 67 6.1 Threats 68 6.2 Access Router Considerations 69 6.3 Mobile Node Considerations 70 7. IANA Considerations 71 8. Acknowledgements & Contributors 72 9. References 73 9.1 Normative References 74 9.2 Non-Normative References 75 Appendix A. Timing and Trigger Considerations 76 Appendix B. Multicast Listener Context Transfer 77 Authors' Addresses 78 Full Copyright Statement 79 Intellectual Property 80 Acknowledgement 82 1. Introduction 84 This document describes the Context Transfer Protocol overview, which 85 provides: 87 * Representation for feature contexts. 88 * Messages to initiate and authorize context transfer, and notify 89 a mobile node of the status of the transfer. 90 * Messages for transferring contexts prior to, during and after 91 handovers. 93 The proposed protocol is designed to work in conjunction with other 94 protocols in order to provide seamless mobility. The protocol 95 supports both IPv4 and IPv6, though support for IPv4 private 96 addresses is for future study. 98 1.1 The Problem 100 "Problem Description: Reasons For Performing Context Transfers 101 between Nodes in an IP Access Network" [RFC3374] defines the 102 following main reasons why Context Transfer procedures may be useful 103 in IP networks. 105 1) The primary motivation, as mentioned in the introduction, is the 106 need to quickly re-establish context transfer-candidate services 107 without requiring the mobile host to explicitly perform all 108 protocol flows for those services from scratch. An example of a 109 service is included in Appendix B. 111 2) An additional motivation is to provide an interoperable solution 112 that supports various Layer 2 radio access technologies. 114 1.2 Conventions Used in This Document 116 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 117 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 118 document are to be interpreted as described in RFC 2119 [RFC2119]. 120 1.3 Abbreviations Used in the Document 122 Mobility Related Terminology [TERM] defines basic mobility 123 terminology. In addition to the material in that document, we use 124 the following terms and abbreviation in this document. 126 CTP Context Transfer Protocol 128 DoS Denial-of-Service 129 FPT Feature Profile Types 131 PCTD Predictive Context Transfer Data 133 2. Protocol Overview 135 This section provides a protocol overview. A context transfer can be 136 either started by a request from the mobile node ("mobile 137 controlled") or at the initiative of either the new or the previous 138 access router ("network controlled"). 140 * The mobile node (MN) sends the CT Activate Request to its current 141 access router (AR) immediately prior to handover whenever possible 142 to initiate predictive context transfer. In any case, the MN 143 always sends the CTAR message to new AR (nAR). If the contexts are 144 already present, nAR verifies the authorization token present in 145 CTAR with its own computation using the parameters supplied by the 146 previous access router (pAR), and subsequently activates those 147 contexts. If the contexts are not present, nAR requests pAR to 148 supply them using the Context Transfer Request message, in which 149 it supplies the authorization token present in CTAR. 151 * Either nAR or pAR may request or start (respectively) context 152 transfer based on internal or network triggers (see Appendix A). 154 The Context Transfer protocol typically operates between a source 155 node and a target node. In the future, there may be multiple target 156 nodes involved; the protocol described here would work with multiple 157 target nodes. For simplicity, we describe the protocol assuming a 158 single receiver or target node. 160 Typically, the source node is a MN's pAR and the target node is MN's 161 nAR. Context Transfer takes place when an event, such as a handover, 162 takes place. We call such an event a Context Transfer Trigger. In 163 response to such a trigger, the pAR may transfer the contexts; the 164 nAR may request contexts; and the MN may send a message to the 165 routers to transfer contexts. Such a trigger must be capable of 166 providing the necessary information (such as the MN's IP address) by 167 which the contexts are identified, the IP addresses of the access 168 routers, and authorization to transfer context. 170 Context transfer protocol messages use Feature Profile Types (FPTs) 171 that identify the way that data is organized for the particular 172 feature contexts. The FPTs are registered in a number space (with 173 IANA Type Numbers) that allows a node to unambiguously determine the 174 type of context and the context parameters present in the protocol 175 messages. Contexts are transferred by laying out the appropriate 176 feature data within Context Data Blocks according to the format in 177 Section 2.3, as well as any IP addresses necessary to associate the 178 contexts to a particular MN. The context transfer initiation messages 179 contain parameters that identify the source and target nodes, the 180 desired list of feature contexts and IP addresses to identify the 181 contexts. The messages that request transfer of context data also 182 contain an appropriate token to authorize the context transfer. 184 Performing context transfer in advance of the MN attaching to nAR can 185 increase handover performance. For this to take place, certain 186 conditions must be met. For example, pAR must have sufficient time 187 and knowledge about the impending handover. This is feasible, for 188 instance, in Mobile IP fast handovers [LLMIP][FMIPV6]. Additionally, 189 many cellular networks have mechanisms to detect handovers in 190 advance. However, when the advance knowledge of impending handover is 191 not available, or if a mechanism such as fast handover fails, 192 retrieving feature contexts after the MN attaches to nAR is the only 193 available means for context transfer. Performing context transfer 194 after handover might still be better than having to re-establish all 195 the contexts from scratch. Finally, some contexts may simply need to 196 be transferred during handover signaling. For instance, any context 197 that gets updated on a per-packet basis must clearly be transferred 198 only after packet forwarding to the MN on its previous link is 199 terminated. 201 2.1 Context Transfer Scenarios 203 The Previous Access Router transfers feature contexts under two 204 general scenarios. 206 2.1.1 Scenario 1 208 The pAR receives a Context Transfer Activate Request (CTAR) message 209 from the MN whose feature contexts are to be transferred, or it 210 receives an internally generated trigger (e.g., a link-layer trigger 211 on the interface to which the MN is connected). The CTAR message, 212 described in Section 2.5, provides the IP address of nAR, the IP 213 address of MN on pAR, the list of feature contexts to be transferred 214 (by default requesting all contexts to be transferred), and a token 215 authorizing the transfer. In response to a CT-Activate Request 216 message or to the CT trigger, pAR predictively transmits a Context 217 Transfer Data (CTD) message that contains feature contexts. This 218 message, described in Section 2.5, contains the MN's previous IP 219 address. It also contains parameters for nAR to compute an 220 authorization token to verify the MN's token present in CTAR message. 221 Recall that the MN always sends CTAR message to nAR regardless of 222 whether it sent the CTAR message to pAR. The reason for this is that 223 there is no means for the MN to ascertain that context transfer 224 reliably took place. By always sending the CTAR message to nAR, the 225 Context Transfer Request (see below) can be sent to pAR if necessary. 227 When context transfer takes place without the nAR requesting it, nAR 228 requires MN to present its authorization token. Doing this locally at 229 nAR when the MN attaches to it improves performance and increases 230 security, since the contexts are highly likely to be present already. 231 Token verification takes place at the router possessing the contexts. 233 2.1.2 Scenario 2 235 In the second scenario, pAR receives a Context Transfer Request (CT- 236 Req), described in Section 2.5, message from nAR. The nAR itself 237 generates the CT-Req message as a result of receiving the CTAR 238 message, or, alternatively, from receiving a context transfer 239 trigger. In the CT-Req message, nAR supplies the MN's previous IP 240 address, the FPTs for the feature contexts to be transferred, the 241 sequence number from the CTAR, and the authorization token from the 242 CTAR. In response to CT-Req message, pAR transmits a Context Transfer 243 Data (CTD) message that includes the MN's previous IP address and 244 feature contexts. When it receives a corresponding CTD message, nAR 245 may generate a CTD Reply (CTDR) message to report the status of 246 processing the received contexts. The nAR installs the contexts once 247 it has received them from the pAR. 249 2.2 Context Transfer Message Format 251 A CTP message consists of a message-specific header and one or more 252 data blocks. Data blocks may be bundled together in order to ensure 253 a more efficient transfer. On the inter-AR interface, SCTP is used 254 so fragmentation should not be a problem. On the MN-AR interface, the 255 total packet size, including transport protocol and IP protocol 256 headers SHOULD be less than the path MTU, in order to avoid packet 257 fragmentation. Each message contains a three bit version number field 258 in the low order octet, along with the 5 bit message type code. This 259 specification only applies to Version 1 of the protocol, and the 260 therefore version number field MUST be set to 0x1. If future 261 revisions of the protocol make binary incompatible changes, the 262 version number number MUST be incremented. 264 2.3 Context Types 266 Contexts are identified by FPT code, which is a 16-bit unsigned 267 integer. The meaning of each context type is determined by a 268 specification document and the context type numbers are to be 269 tabulated in a registry maintained by IANA [IANA], and handled 270 according to the message specifications in this document. The 271 instantiation of each context by nAR is determined by the messages in 272 this document along with the specification associated with the 273 particular context type. The following diagram illustrates the 274 general format for CTP messages: 276 +----------------------+ 277 | Message Header | 278 +----------------------+ 279 | CTP Data 1 | 280 +----------------------+ 281 | CTP Data 2 | 282 +----------------------+ 283 | ... | 285 Each context type specification contains the following details: 286 - Number, size (in bits), and ordering of data fields in the 287 state variable vector which embodies the context. 288 - Default values (if any) for each individual datum of the 289 context state vector. 290 - Procedures and requirements for creating a context at a new 291 access router, given the data transferred from a previous 292 access router, and formatted according to the ordering rules 293 and date field sizes presented in the specification. 294 - If possible, status codes for success or failure related to the 295 context transfer. For instance, a QoS context transfer might 296 have different status codes depending on which elements of the 297 context data failed to be instantiated at nAR. 299 2.4 Context Data Block (CTB) 301 The Context Data Block (CTB) is used both for request and response 302 operation. When a request is constructed, only the first 4 bytes are 303 typically necessary (See CTAR below). When used for transferring the 304 actual feature context itself, the context data is present, and 305 sometimes the presence vector is present. 307 0 1 2 3 308 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 1 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | Feature Profile Type (FTP) | Length |P| Reserved | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | Presence Vector (if P = 1) | 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 314 ~ Data ~ 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 317 Feature Profile Type 318 16 bit integer, assigned by IANA, 319 indicating the type of data 320 included in the Data field 322 Length Message length in units of 8 octet 323 words. 325 'P' bit 0 = No presence vector 326 1 = Presence vector present. 328 Reserved Reserved for future use. Set to 329 zero by the sender. 331 Data Context type-dependent data, whose 332 length is defined by the Length 333 Field. If the data is not 64-bit 334 aligned, the data field is 335 padded with zeros. 337 The Feature Profile Type (FPT) code indicates the type of data in the 338 data field. Typically, this will be context data but it might be an 339 error indication. The 'P' bit, which is the high order bit in the 340 Length field, specifies whether or not the "presence vector" is used. 341 When the presence vector is in use, the Presence Vector is 342 interpreted to indicate whether particular data fields are present 343 (and containing non-default values). The ordering of the bits in the 344 presence vector is the same as the ordering of the data fields 345 according to the context type specification, one bit per data field 346 regardless of the size of the data field. The Length field indicates 347 the size of the CTB in 8 octet words including the first 4 bytes 348 starting from FPT. 350 Notice that the length of the context data block is defined by the 351 sum of lengths of each data field specified by the context type 352 specification, plus 4 bytes if the 'P' bit is set, minus the 353 accumulated size of all the context data that is implicitly given as 354 a default value. 356 2.5 Messages 358 In this section, the CTP messages are defined. The MN for which 359 context transfer protocol operations are undertaken is always 360 identified by its previous IP access address. At any time, only one 361 context transfer operation per MN may be in progress so that the CTDR 362 message unambiguously identifies which CTD message is acknowledged 363 simply by including the MN's identifying previous IP address. The 'V' 364 flag indicates whether the IP addresses are IPv4 or IPv6. 366 2.5.1 Context Transfer Activate Request (CTAR) Message 368 This message is always sent by MN to nAR to request context transfer. 369 Even when the MN does not know if contexts need to be transferred, 370 the MN sends the CTAR message. If an acknowledgement for this message 371 is needed, the MN sets the 'A' flag to 1; otherwise the MN does not 372 expect an acknowledgement. This message may include a list of FPTs 373 that require transfer. 375 The MN may also send this message to pAR while still connected to 376 pAR. In such a case, the MN includes the nAR's IP address; otherwise, 377 if the message is sent to nAR, the pAR address is sent. The MN MUST 378 set the sequence number to the same value for the message sent on 379 both pAR and nAR so pAR can determine whether to use a cached 380 message. 382 0 1 2 3 383 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 1 384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 385 |Vers.| Type |V|A| Reserved | Length | 386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 387 ~ MN's Previous IP Address ~ 388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 389 ~ Previous (New) AR IP Address ~ 390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 391 | Sequence Number | 392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 393 | MN Authorization Token | 394 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 395 | Requested Context Data Block (if present) | 396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 397 | Next Requested Context Data Block (if present) | 398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 399 | ........ | 400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 402 Vers. Version number of CTP protocol = 0x1 404 Type CTAR = 0x1 406 'V' flag When set to '0', IPv6 addresses. 407 When set to '1', IPv4 addresses. 409 'A' bit If set, the MN requests an 410 acknowledgement. 412 Reserved Set to zero by the sender, ignored by 413 the receiver. 415 Length Message length in units of bytes. 417 MN's Previous IP Address Field contains either: 418 IPv4 Address as defined in [RFC 791], 419 4 octets. 420 IPv6 Address as defined in [RFC 2373], 421 16 octets. 423 nAR / pAR IP Address Field contains either: 424 IPv4 Address as defined in [RFC 791], 425 4 octets. 426 IPv6 Address as defined in [RFC 2373], 427 16 octets. 429 Sequence Number A value used to identify requests and 430 acknowledgements (see Section 3.2). 432 Authorization Token An unforgeable value calculated as 433 discussed below. This authorizes the 434 receiver of CTAR to perform context 435 transfer. 437 Context Block Variable length field defined in 438 Section 2.4. 440 If no context types are specified, all contexts for the MN are 441 requested. 443 The Authorization Token is calculated as: 445 First (32, HMAC_SHA1 446 (Key, (Previous IP address | Sequence Number| CTBs))) 448 where Key is a shared secret between the MN and pAR, and CTBs is a 449 concatenation of all the Context Data Blocks specifying the contexts 450 to be transfered which are included in the CTAR message. 452 2.5.2 Context Transfer Activate Acknowledge (CTAA) Message 454 This is an informative message sent by the receiver of CTAR to the MN 455 to acknowledge a CTAR message. Acknowledgement is optional, depending 456 on whether the MN requested it. This message may include a list of 457 FPTs that were not transferred successfully. 459 0 1 2 3 460 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 1 461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 462 |Vers.| Type |V| Reserved | Length | 463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 464 ~ Mobile Node's Previous IP address ~ 465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 466 | FPT (if present) | Status code | Reserved | 467 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 468 | ........ | 469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 Vers. Version number of CTP protocol = 0x1 473 Type CTAA = 0x2 475 'V' flag When set to '0', IPv6 addresses. 476 When set to '1', IPv4 addresses. 478 Reserved Set to zero by the sender and ignored by 479 the receiver. 481 Length Message length in units of bytes. 483 MN's Previous IP Address Field contains either: 484 IPv4 Address as defined in [RFC 791], 485 4 octets. 486 IPv6 Address as defined in [RFC 2373], 487 16 octets. 489 FPT 16 bit unsigned integer, listing the FTP 490 that was not successfully transferred. 492 Status Code An octet, containing failure reason. 494 2.5.3 Context Transfer Data (CTD) Message 496 Sent by pAR to nAR, and includes feature data (CTP data). This 497 message handles predictive as well as normal CT. An acknowledgement 498 flag, 'A', included in this message indicates whether a reply is 499 required by pAR. 501 0 1 2 3 502 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 1 503 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 504 |Vers.| Type |V|A| Reserved | Length | 505 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 506 | Elapsed Time (in milliseconds) | 507 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 508 ~ Mobile Node's Previous Care-of Address ~ 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ^ 510 | Algorithm | Key Length | 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ PCTD 512 | Key | only 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ V 514 ~ First Context Data Block ~ 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 516 ~ Next Context Data Block ~ 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 518 ~ ........ ~ 519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 Vers. Version number of CTP protocol = 0x1 523 Type CTD = 0x3 (Context Transfer Data) 524 PCTD = 0x4 (Predictive Context Transfer 525 Data) 527 'V' flag When set to '0', IPv6 addresses. 528 When set to '1', IPv4 addresses. 530 'A' bit When set, the pAR requests an 531 acknowledgement. 533 Length Message length in units of bytes. 535 Elapsed Time The number of milliseconds since the 536 transmission of the first CTD message for 537 this MN. 539 MN's Previous IP Address Field contains either: 540 IPv4 Address as defined in [RFC 791], 541 4 octets. 542 IPv6 Address as defined in [RFC 2373], 543 16 octets. 545 Algorithm Algorithm for carrying out the computation 546 of the MN Authorization Token. Currently 547 only 1 algorithm is defined, HMAC_SHA1 = 1. 549 Key Length Length of key, in octets. 551 Key Shared key between MN and AR for CTP. 553 Context Data Block The Context Data Block (see Section 2.4). 555 When CTD is sent predictively, the supplied parameters including the 556 algorithm, key length and the key itself, allowing nAR to compute a 557 token locally and verify against the token present in the CTAR 558 message. This material is also sent if the pAR receives a CTD 559 message with a null Authorization Token, indicating that the CT-Req 560 message has been sent before the nAR received the CTAR message. CTD 561 MUST be protected by IPsec, see Section 6. 563 As described previously, the algorithm for carrying out the 564 computation of the MN Authorization Token is HMAC_SHA1. The token 565 authentication calculation algorithm is described in Section 2.5.1. 567 For predictive handover, the pAR SHOULD keep track of the CTAR 568 sequence number and cache the CTD message until receiving either a 569 CTDR message for the MN's previous IP address from the pAR, 570 indicating that the context transfer was successful, or until 571 CT_MAX_HANDOVER_TIME expires. The nAR MAY send a CT-Req message 572 containing the same sequence number if the predictive CTD message 573 failed to arrive or the context was corrupted, In that case, the nAR 574 sends a CT-Req message with a matching sequence number and pAR can 575 resend the context. 577 2.5.4 Context Transfer Data Reply (CTDR) Message 579 This message is sent by nAR to pAR depending on the value of the 'A' 580 flag in CTD. Indicates success or failure. 582 0 1 2 3 583 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 1 584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 585 |Vers.| Type |V|S| Reserved | Length | 586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 587 ~ Mobile Node's Previous IP Address ~ 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 589 | FPT (if present) | Status code | Reserved | 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 ~ ....... ~ 592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 594 Vers. Version number of CTP protocol = 0x1 596 Type CTDR = 0x5 (Context Transfer Data) 597 'V' flag When set to '0', IPv6 addresses. 598 When set to '1', IPv4 addresses. 600 'S' bit When set to one, this bit indicates 601 that all feature contexts sent in CTD 602 or PCTD were received successfully. 604 Reserved Set to zero by the sender and ignored by 605 the receiver. 607 Length Message length in units of bytes. 609 MN's Previous IP Address Field contains either: 610 IPv4 Address as defined in [RFC 791], 611 4 octets. 612 IPv6 Address as defined in [RFC 2373], 613 16 octets. 615 Status Code A context-specific return value, 616 zero for success, nonzero when 'S' is 617 not set to one. 619 FPT 16 bit unsigned integer, listing the FTP 620 that is being acknowledged. 622 2.5.5 Context Transfer Cancel (CTC) Message 624 If transferring a context cannot be completed in a timely fashion, 625 then nAR may send CTC to pAR to cancel an ongoing CT process. 627 0 1 2 3 628 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 1 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 |Vers.| Type |V| Reserved | Length | 631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 632 ~ Mobile Node's Previous IP Address ~ 633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 635 Vers. Version number of CTP protocol = 0x1 637 Type CTC = 0x6 (Context Transfer Cancel) 639 Length Message length in units of bytes. 641 'V' flag When set to '0', IPv6 addresses. 642 When set to '1', IPv4 addresses. 644 Reserved Set to zero by the sender and ignored by 645 the receiver. 647 MN's Previous IP Address Field contains either: 648 IPv4 Address as defined in [RFC 791], 649 4 octets. 650 IPv6 Address as defined in [RFC 2373], 651 16 octets. 653 2.5.6 Context Transfer Request (CT-Req) Message 655 Sent by nAR to pAR to request start of context transfer. This message 656 is sent as a response to CTAR message from the MN. The fields 657 following the Previous IP address of the MN are included verbatim 658 from the CTAR message. 660 0 1 2 3 661 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 1 662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 663 |Vers.| Type |V| Reserved | Length | 664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 665 ~ Mobile Node's Previous IP Address ~ 666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 667 | Sequence Number | 668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 669 | MN Authorization Token | 670 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 671 ~ Next Requested Context Data Block (if present) ~ 672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 673 ~ ........ ~ 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 676 Vers. Version number of CTP protocol = 0x1 678 Type CTREQ = 0x7 (Context Transfer Request) 680 'V' flag When set to '0', IPv6 addresses. 681 When set to '1', IPv4 addresses. 683 Reserved Set to zero by the sender and ignored 684 by the receiver. 686 Length Message length in units of bytes. 688 MN's Previous IP Address Field contains either: 689 IPv4 Address as defined in [RFC 791], 690 4 octets. 691 IPv6 Address as defined in [RFC 2373], 692 16 octets. 694 Sequence Number Copied from the CTAR message, allows the 695 pAR to distinguish requests for previously 696 sent context. 698 MN's Authorization Token 699 An unforgeable value calculated as 700 discussed in Section 2.5.1. This 701 authorizes the receiver of CTAR to 702 perform context transfer. Copied from 703 CTAR. 705 Context Data Request Block 706 A request block for context data, see 707 Section 2.4. 709 The sequence number is used by pAR to correlate a request for 710 previously transmitted context. In predictive transfer, if the MN 711 sends CTAR prior to handover, pAR pushes context to nAR using CTD. If 712 the CTD fails, the nAR will send CT-Req with the same sequence 713 number, allowing the pAR to distinguish which context to resend. pAR 714 drops the context after CTP_MAX_TRANSFER_TIME. The sequence number is 715 not used in reactive transfer. 717 For predictive transfer the pAR sends the keying material and other 718 information necessary to calculate the Authorization Token, with no 719 CT-Req message necessary. For reactive transfer, if the nAR receives 720 a context transfer trigger but has not yet received the CTAR message 721 with the authorization token, the Authorization Token field in CT-Req 722 is set to zero. The pAR interprets this as an indication to include 723 the keying material and other information necessary to calculate the 724 Authorization Token, and includes this material into the CTD message 725 as if the message were being sent due to predictive transfer. This 726 provides nAR with the information it needs to calculate the 727 authorization token when the MN sends CTAR. 729 3. Transport 731 3.1 Inter-Router Transport 733 Since the types of access networks in which CTP might be useful are 734 not today deployed or, if they have been deployed, have not been 735 extensively measured, it is difficult to know whether congestion will 736 be a problem for CTP. Part of the research task in preparing CTP for 737 consideration as a candidate for possible standardization is to 738 quantify this issue. However, in order to avoid potential 739 interference with production applications should a prototype CTP 740 deployment involve running over the public Internet, it seems prudent 741 to recommend a default transport protocol that accommodates 742 congestion. In addition, since the feature context information has a 743 definite lifetime, the transport protocol must accommodate flexible 744 retransmission, so stale contexts that are held up by congestion are 745 dropped. Finally, because the amount of context data can be 746 arbitrarily large, the transport protocol should not be limited to a 747 single packet, or require implementing a custom fragmentation 748 protocol. 750 These considerations argue that implementations of CTP MUST support 751 and prototype deployments of CTP SHOULD use Stream Control Transport 752 Protocol (SCTP) [SCTP] for the transport protocol on the inter-router 753 interface, especially if deployment over the public Internet is 754 contemplated. SCTP supports congestion control, fragmentation, and 755 partial retransmission based on a programmable retransmission timer. 756 SCTP also supports many advanced and complex features, such as 757 multiple streams and multiple IP addresses for failover, that are not 758 necessary for experimental implementation and prototype deployment of 759 CTP. In this specification, the use of such SCTP features is not 760 recommended at this time. 762 The SCTP Payload Data Chunk carries the context transfer protocol 763 messages. The User Data part of each SCTP message contains an 764 appropriate context transfer protocol message defined in this 765 document. The messages sent using SCTP are CTD (Section 2.5.3), CTDR 766 (Section 2.5.4), CTC (Section 2.5.5) and CT-Req (Section 2.5.6). In 767 general, each SCTP message can carry feature contexts belonging to 768 any MN. If the SCTP checksum calculation fails, the nAR returns the 769 BAD_CHECKSUM error code in a CTDR message. 771 A single stream is used for context transfer without in-sequence 772 delivery of SCTP messages. Each message, unless fragmented, 773 corresponds to a single MN's feature context collection. A single 774 stream provides simplicity. Use of multiple streams to prevent head- 775 of-line blocking is for future study. Having unordered delivery 776 allows the receiver to not block for in-sequence delivery of messages 777 that belong to different MNs. The Payload Protocol Identifier in the 778 SCTP header is 'CTP'. Inter-router CTP uses the Seamoby SCTP port 779 [IANA]. 781 Timeliness of the context transfer information SHOULD be accommodated 782 by setting the SCTP maximum retransmission value to 783 CT_MAX_TRANSFER_TIME in order to accommodate the maximum acceptable 784 handover delay time, and the AR SHOULD be configured with 785 CT_MAX_TRANSFER_TIME to accommodate the particular wireless link 786 technology and local wireless propagation conditions. SCTP message 787 bundling SHOULD be turned off in order to reduce any extra delay in 788 sending messages. Within CTP, the nAR SHOULD estimate the retransmit 789 timer from the receipt of the first fragment of a CTP message and 790 avoid processing any IP traffic from the MN until either context 791 transfer is complete or the estimated retransmit timer expires. If 792 both routers support PR-SCTP [PR-SCTP], then PR-SCTP SHOULD be used. 793 PR-SCTP modifies the lifetime parameter of the Send() operation 794 defined in Section 10.1 E in [SCTP] so that it applies to retransmits 795 as well as transmits; that is, in PR-SCTP if the lifetime expires and 796 the data chunk has not been acknowledged, the transmitter stops 797 retransmitting, whereas in the base protocol the data would be 798 retransmitted until acknowledged or the connection timed out. 800 The format of Payload Data Chunk taken from [SCTP] is shown in the 801 following diagram. 803 0 1 2 3 804 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 1 805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 806 | Type = 0 | Reserved|U|B|E| Length | 807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 | TSN | 809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 810 | Stream Identifier S | Stream Sequence Number n | 811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 812 | Payload Protocol Identifier | 813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 814 ~ User Data (seq n of Stream S) ~ 815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 817 'U' bit The Unordered bit. MUST be set to 1 (one). 818 'B' bit The Beginning fragment bit. See [SCTP]. 820 'E' bit The Ending fragment bit. See [SCTP]. 822 TSN Transmission Sequence Number. See [SCTP]. 824 Stream Identifier S 825 Identifies the context transfer protocol stream. 827 Stream Sequence Number n 828 Since the 'U' bit is set to one, the 829 receiver ignores this number. See [SCTP]. 831 Payload Protocol Identifier 832 Set to 'CTP' (see [IANA]). 834 User Data Contains the context transfer protocol messages. 836 If a CTP deployment will never run over the public Internet, and it 837 is known that congestion is not a problem in the access network, 838 alternative transport protocols MAY be appropriate vehicles for 839 experimentation. An example is piggybacking CTP messages on top of 840 handover signaling for routing, such as provided by FMIPv6 in ICMP 841 [FMIPv6]. Implementations of CTP MAY support ICMP for such purposes. 842 If such piggybacking is used, an experimental message extension for 843 the protocol on which CTP is piggybacking MUST be designed. Direct 844 deployment on top of a transport protocol for experimental purposes 845 is also possible, in that case, the researcher MUST be careful to 846 accommodate good Internet transport protocol engineering practices, 847 including using retransmits with exponential backoff. 849 3.2 MN-AR Transport 851 The MN-AR interface MUST implement and SHOULD use ICMP for transport 852 of the CTAR and CTAA messages. Because ICMP contains no provisions 853 for retransmitting packets if signaling is lost, the CTP protocol 854 incorporates provisions for improving transport performance on the 855 MN-AR interface. The MN and AR SHOULD limit the number of context 856 data block identifiers included in the CTAR and CTAA messages so that 857 the message will fit into a single packet, since ICMP has no 858 provision for fragmentation above the IP level. The ICMP message 859 format for CTP messages is as follows: 861 0 1 2 3 862 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 1 863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 864 | Type | Code | Checksum | 865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 866 | Reserved | 867 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 868 | Message... 869 +-+-+-+-+-+-+-+-+-+-+-+- - - - 871 IP Fields: 873 Source Address An IP address assigned to the sending 874 interface. 876 Destination Address 877 An IP address assigned to the receiving 878 interface. 880 Hop Limit 255 882 ICMP Fields: 884 Type Seamoby Type (To be assigned by IANA, 885 for IPv4 and IPv6, see [IANA]) 887 Code 1 889 Checksum The ICMP checksum. 891 Reserved Set to zero by the sender and ignored by 892 the receiver. 894 Message The body of the CTAR or CTAA message. 896 CTAR messages for which a response is requested but which fail to 897 elicit a response are retransmitted. The initial retransmission 898 occurs after a CTP_REQUEST_RETRY wait period. Retransmissions MUST 899 be made with exponentially increasing wait intervals (doubling the 900 wait each time). CTAR messages should be retransmitted until 901 either a response (which might be an error) has been obtained, or 902 until CTP_RETRY_MAX seconds after the initial transmission. 904 MNs SHOULD generate the sequence number in the CTAR message 905 randomly, and, for predictive transfer, MUST use the same sequence 906 number in a CTAR to the nAR as for the pAR. An AR MUST ignore the 907 CTAR if it has already received one with the same sequence number 908 and MN IP address. 910 Implementations MAY, for research purposes, try other transport 911 protocols. Examples are the definition of a Mobile IPv6 Mobility 912 Header [MIPv6] for use with the FMIPv6 Fast Binding Update 913 [FMIPv6] to allow bundling of both routing change and context 914 transfer signaling from the MN to AR, or definition of a UDP 915 protocol instead of ICMP. If such implementations are done, they 916 should abide carefully by good Internet transport engineering 917 practices and be used for prototype and demonstration purposes 918 only. Deployment on large scale networks should be avoided until 919 the transport characteristics are well understood. 921 4. Error Codes and Constants 923 Error Code Section Value Meaning 924 ------------------------------------------------------------ 925 BAD_CHECKSUM 3.1 0x01 Error code if the 926 SCTP checksum fails. 928 Constant Section Default Value Meaning 929 -------------------------------------------------------------------- 931 CT_REQUEST_RATE 6.3 10 requests/ Maximum number of 932 sec. CTAR messages before 933 AR institutes rate 934 limiting. 936 CT_MAX_TRANSFER_TIME 3.1 200 ms Maximum amount of time 937 pAR should wait before 938 aborting the transfer. 940 CT_REQUEST_RETRY 3.2 2 seconds Wait interval before 941 initial retransmit 942 on MN-AR interface. 944 CT_RETRY_MAX 3.2 15 seconds Give up retrying 945 on MN-AR interface. 947 5. Examples and Signaling Flows 949 5.1 Network controlled, Initiated by pAR, Predictive 951 MN nAR pAR 952 | | | 953 T | | CT trigger 954 I | | | 955 M | |<------- CTD ----------| 956 E |--------CTAR--------->| | 957 : | | | 958 | | |-------- CTDR -------->| 959 V | | | 960 | | | 962 in 0 5.2 Network controlled, initiated by nAR, Reactive 964 MN nAR pAR 965 | | | 966 T | CT trigger | 967 I | | | 968 M | |--------- CT-Req ----->| 969 E | | | 970 : | |<------- CTD ----------| 971 | | | | 972 V |--------CTAR--------->| | 973 | |----- CTDR (opt) ----->| 974 | | | 976 5.3 Mobile controlled, Predictive New L2 up/old L2 down 978 CTAR request to nAR 980 MN nAR pAR 981 | | | 982 new L2 link up | | 983 | | | 984 CT trigger | | 985 | | | 986 T |--------CTAR ------->| | 987 I | |-------- CT-Req ------>| 988 M | | | 989 E | |<-------- CTD ---------| 990 : | | | 991 | | | | 992 V | | | 993 | | | 995 It is for future study whether the nAR sends the MN a CTAR reject if 996 CT is not supported. 998 6. Security Considerations 1000 At this time, the threats to IP handover in general and context 1001 transfer in particular are incompletely understood, particularly on 1002 the MN to AR link, and mechanisms for countering them are not well 1003 defined. Part of the experimental task in preparing CTP for eventual 1004 standards track will be to better characterize threats to context 1005 transfer and design specific mechanisms to counter them. This section 1006 provides some general guidelines about security based on discussions 1007 among the Design Team and Working Group members. 1009 6.1. Threats 1011 The Context Transfer Protocol transfers state between access routers. 1012 If the MNs are not authenticated and authorized before moving on the 1013 network, there is a potential for DoS attacks to shift state between 1014 ARs, causing network disruptions. 1016 Additionally, DoS attacks can be launched from MNs towards the access 1017 routers by requesting multiple context transfers and then 1018 disappearing. Finally, a rogue access router could flood mobile 1019 nodes with packets, attempting DoS attacks, and issue bogus context 1020 transfer requests to surrounding routers. 1022 6.2. Access Router Considerations 1023 The CTP interrouter interface relies on IETF standardized security 1024 mechanisms for protecting traffic between access routers, as opposed 1025 to creating application security mechanisms. IPsec MUST be supported 1026 between access routers. 1028 In order to avoid the introduction of additional latency due to the 1029 need for establishment of a secure channel between the context 1030 transfer peers (ARs), the two ARs SHOULD establish such a secure 1031 channel in advance. The two access routers need to engage in a key 1032 exchange mechanisms such as IKE [RFC2409], establish IPSec SAs, 1033 defining the keys, algorithms and IPSec protocols (such as ESP) in 1034 anticipation for any upcoming context transfer. This will save time 1035 during handovers that require secure transfer. Such SAs can be 1036 maintained and used for all upcoming context transfers between the 1037 two ARs. Security should be negotiated prior to the sending of 1038 context. 1040 Access Routers MUST implement IPsec ESP [ESP] in transport mode with 1041 non-null encryption and authentication algorithms to provide per- 1042 packet authentication, integrity protection and confidentiality, and 1043 MUST implement the replay protection mechanisms of IPsec. In those 1044 scenarios where IP layer protection is needed, ESP in tunnel mode 1045 SHOULD be used. Non-null encryption should be used when using IPSec 1046 ESP. Strong security on the inter-router interface is required to 1047 protect against attacks by rogue routers, and to ensure 1048 confidentiality on the context transfer authorization key in 1049 predicative transfer. 1051 6.3 Mobile Node Considerations 1053 The CTAR message requires the MN and AR to possess a shared secret 1054 key in order to calculate the authorization token. Validation of this 1055 token MUST precede context transfer or installation of context for 1056 the MN, removing the risk that an attacker could cause an 1057 unauthorized transfer. How the shared key is established is out of 1058 scope of the current specification. If both the MN and AR know 1059 certified public keys of the other party, Diffie-Helman can be used 1060 to generate a shared secret [RFC2631]. If an AAA protocol of some 1061 sort is run for network entry, the shared key can be established 1062 using that protocol [PerkCal04]. 1064 If predictive context transfer is used, the shared key for 1065 calculating the authorization token is transferred between ARs. A 1066 transfer of confidential material of this sort poses certain security 1067 risks, even if the actual transfer itself is confidential and 1068 authenticated, as is the case for inter-router CTP. The more entities 1069 know the key, the more likely a compromise may occur. In order to 1070 mitigate this risk, nAR MUST discard the key immediately after using 1071 it to validate the authorization token. The MN MUST establish a new 1072 key with the AR for future CTP transactions. The MN and AR SHOULD 1073 exercise care in using a key established for other purposes for also 1074 authorizing context transfer. It is RECOMMENDED that a separate key 1075 be established for context transfer authorization. 1077 Replay protection on the MN-AR protocol is provided by limiting the 1078 time period in which context is maintained. For predictive transfer, 1079 the pAR receives a CTAR message with a sequence number, transfers the 1080 context, then drops the context immediately upon completion of the 1081 transfer, along with the authorization token key. For reactive 1082 transfer, the nAR receives the CTAR, requests the context along with 1083 the sequence number and authorization token, allowing the pAR to 1084 check whether the transfer is authorized. The pAR drops the context 1085 and authorization token key after the transfer has been completed. 1086 The pAR and nAR ignore any requests containing the same MN IP address 1087 during the transfer process. After the key has been dropped, any 1088 attempt at replay will fail because the authorization token fails to 1089 validate. The AR MUST NOT reuse the key for other MNs. 1091 DoS attacks on the MN-AR interface can be limited by having the AR 1092 rate limit the number of CTAR messages it processes. The AR SHOULD 1093 limit the number of CTAR messages to CT_REQUEST_RATE. If the request 1094 exceeds this rate, the AR SHOULD randomly drop messages until the 1095 rate is established. The actual rate SHOULD be configured on the AR 1096 to match the maximum number of handovers that the access network is 1097 expected to support. 1099 7. IANA Considerations 1101 Instructions for IANA allocations are included in [IANA]. 1103 8. Acknowledgements & Contributors 1105 This document is the result of a design team formed by the Working 1106 Group chairs of the SeaMoby working group. The team included John 1107 Loughney, Madjid Nakhjiri, Rajeev Koodli and Charles Perkins. 1109 Contributors to the Context Transfer Protocol review are Basavaraj 1110 Patil, Pekka Savola, and Antti Tuominen. 1112 The working group chairs are Pat Calhoun and James Kempf, whose 1113 comments have been very helpful during the creation of this 1114 specification. 1116 The authors would also like to thank Julien Bournelle, Vijay 1117 Devarapalli, Dan Forsberg, Xiaoming Fu, Michael Georgiades, Yusuf 1118 Motiwala, Phil Neumiller, Hesham Soliman and Lucian Suciu for their 1119 help and suggestions with this document. 1121 9. References 1123 9.1 Normative References 1125 [RFC2026] S. Bradner, "The Internet Standards Process -- Revision 3", 1126 BCP 9, RFC 2026, October 1996. 1128 [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate 1129 Requirement Levels", BCP 14, RFC 2119, March 1997. 1131 [RFC2434] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA 1132 Considerations Section in RFCs", BCP 26, RFC 2434, October 1133 1998. 1135 [RFC2409] D. Harkins, D. Carrel, "The Internet Key Exchange (IKE)", 1136 RFC 2409, November 1998. 1138 [ESP] Kent, S. and R. Atkinson, "IP Encapsulating Security 1139 Payload (ESP)", RFC 2406, November 1998. 1141 [SCTP] Stewert, R., et. al., "Stream Control Transmission 1142 Protocol", RFC 2960, October, 2000. 1144 [PR-SCTP] Stewert, R., et. al., "SCTP Partial Reliability Extension", 1145 Internet Engineering Task Force. Work in Progress. 1147 [CARD] Liebisch, M., and Singh, A., editors, et. al., "Candidate 1148 Access Router Discovery", Internet Engineering Task Force. 1149 Work in Progress. 1151 [IANA] Kempf, J., "Instructions for Seamoby Experimental Protocol 1152 IANA Allocations", Internet Engineering Task Force. Work in 1153 Progress. 1155 9.2 Non-Normative References 1156 [CTHC] R. Koodli et al., "Context Relocation for Seamless Header 1157 Compression in IP Networks", Internet Draft, Internet 1158 Engineering Task Force, Work in Progress. 1160 [FMIPv6] R. Koodli (Ed), "Fast Handovers for Mobile IPv6", Internet 1161 Engineering Task Force. Work in Progress. 1163 [LLMIP] K. El Malki et. al, "Low Latency Handoffs in Mobile IPv4", 1164 Internet Engineering Task Force. Work in Progress. 1166 [RFC3374] J. Kempf et al., "Problem Description: Reasons For Performing 1167 Context Transfers Between Nodes in an IP Access Network", RFC 1168 3374, May 2001. 1170 [RFC2401] S. Kent, R. Atkinson, "Security Architecture for the Internet 1171 Protocol", RFC 2401, November 1998. 1173 [TERM] J. Manner, M. Kojo, "Mobility Related Terminology", Internet 1174 Engineering Task Force, Work in Progress. 1176 [RFC2631] E. Rescorla, "Diffie-Hellman Key Agreement Method", RFC 2631, 1177 June, 1999. 1179 [PerkCal04]C. Perkins and P. Calhoun, "AAA Registration Keys for Mobile 1180 IPv4", Internet Engineering Task Force, Work in Progress. 1182 [MIPv6] D. Johnson, C. Perkins, and J. Arkko, "Mobility Support in 1183 IPv6", Internet Engineering Task Force, Work in Progress. 1185 [RFC2710] S. Deering, W. Fenner, and B. Haberman, " Multicast Listener 1186 Discovery (MLD) for IPv6," RFC 2710, October, 1999. 1188 [RFC2461] T. Narten, E. Nordmark, and W. Simpson, "Neighbor Discovery 1189 for IP Version 6 (IPv6)," RFC 2461, December, 1998. 1191 [RFC2462] S. Thompson, and T. Narten, "IPv6 Address Autoconfiguration," 1192 RFC 2462, December, 1998. 1194 [RFC3095] C. Borman, ed., "RObust Header Compression (ROHC)", RFC 3095, 1195 July, 2001. 1197 [BT] IEEE, "IEEE Standard for information technology - Telecommuni- 1198 cation and information exchange between systems - LAN/MAN - 1199 Part 15.1: Wireless Medium Access Control (MAC) and Physical 1200 Layer (PHY) specifications for Wireless Personal Area Networks 1201 (WPANs)", IEEE Standard 802.15.1, 2002. 1203 Appendix A. Timing and Trigger Considerations 1205 Basic Mobile IP handover signaling can introduce disruptions to the 1206 services running on top of Mobile IP, which may introduce unwanted 1207 latencies that practically prohibit its use for certain types of 1208 services. Mobile IP latency and packet loss is being optimized through 1209 several alternative procedures, such as Fast Mobile IP [FMIPv6] and 1210 Low Latency Mobile IP [LLMIP]. 1212 Feature re-establishment through context transfer should contribute 1213 zero (optimally) or minimal extra disruption of services in 1214 conjunction to handovers. This means that the timing of context 1215 transfer SHOULD be carefully aligned with basic Mobile IP handover 1216 events, and with optimized Mobile IP handover signaling mechanisms, 1217 as those protocols become available. 1219 Furthermore, some of those optimized mobile IP handover mechanisms 1220 may provide more flexibility in choosing the timing and order for 1221 transfer of various context information. 1223 Appendix B. Multicast Listener Context Transfer 1225 In the past, credible proposals have been made in the Seamoby Working 1226 Group and elsewhere for using context transfer to speed handover of 1227 authentication, authorization, and accounting context, distributed 1228 firewall context, PPP context, and header compression context. 1229 Because the Working Group was not chartered to develop context 1230 profile definitions for specific applications, none of the drafts 1231 submitted to Seamoby were accepted as Working Group items. At this 1232 time, work continues to develop a context profile definition for RFC 1233 3095 header compression context [RFC3095] and to characterize the 1234 performance gains obtainable by using header compression, but the 1235 work is not yet complete. In addition, there are several commercial 1236 wireless products that reportedly use non-standard, non-interoperable 1237 context transfer protocols, though none is as yet widely deployed. 1239 As a consequence, it is difficult at this time to point to a solid 1240 example of how context transfer could result in a commercially 1241 viable, widely deployable, interoperable benefit for wireless 1242 networks. This is one reason why CTP is being proposed as an 1243 Experimental protocol, rather than Standards Track. However, it 1244 nevertheless seems valuable to have a simple example that shows 1245 how handover could benefit from using CTP. The example we consider 1246 here is transferring IPv6 MLD state [RFC2710]. MLD state is a 1247 particularly good example because every IPv6 node must perform at 1248 least one MLD messaging sequence on the wireless link to establish 1249 itself as an MLD listener prior to performing router discovery 1250 [RFC2461] or duplicate address detection [RFC2462] or before 1251 sending/receiving any application-specific traffic (including Mobile 1252 IP handover signaling, if any). The node must subscribe to the 1253 Solicited Node Multicast Address as soon as it comes up on the link. 1254 Any application-specific multicast addresses must be re-established 1255 as well. Context transfer can significantly speed up re-establishing 1256 multicast state by allowing the nAR to initialize MLD for a node that 1257 just completed handover without any MLD signaling on the new 1258 wireless link. The same approach could be used for transferring 1259 multicast context in IPv4. 1261 An approximate quantitative estimate for the amount of savings in 1262 handover time can be obtained as follows. MLD messages are 24 bytes, 1263 to which the headers must be added, because there is no header 1264 compression on the new link, with IPv6 header being 40 bytes, and a 1265 required Router Alert Hop-by-Hop option being 8 bytes including pad- 1266 ding. The total MLD message size is 72 bytes per subscribed multicast 1267 address. RFC 2710 recommends that nodes send 2 to 3 MLD Report 1268 messages per address subscription, since the Report message is 1269 unacknowledged. Assuming 2 MLD messages sent for a subscribed address, 1270 the MN would need to send 144 bytes per address subscription. If MLD 1271 messages are sent for both the All Nodes Multicast address and the 1272 Solicited Node Multicast address for the node's link local address, a 1273 total of 288 bytes are required when the node hands over to the new 1274 link. Note that some implementations of IPv6 optimize by not sending 1275 an MLD message for the All Nodes Multicast Address, since the router 1276 can infer that at least one node is on the link (itself) when it 1277 comes up and always will be, but for purposes of this calculation, we 1278 assume that the IPv6 implementation is conformant and that the 1279 message is sent. The amount of time required for MLD signaling will, 1280 of course, depend on the per node available wireless link bandwidth, 1281 but some representative numbers can be obtained by assuming bandwidths 1282 of 20 kbps or 100 kbps. With these two bit rates, the savings from not 1283 having to perform the pre-router discovery messages are 115 msec. and 1284 23 msec., respectively. If any application-specific multicast 1285 addresses are subscribed, the amount of time saved could be 1286 substantially more. 1288 This example might seem a bit contrived because MLD isn't used in the 1289 3G cellular protocols and wireless local area network protocols 1290 typically have enough bandwidth, if radio propagation conditions are 1291 optimal, so sending a single MLD message might not be viewed as such 1292 a performance burden. An example of a wireless protocol where MLD 1293 context transfer might be useful is IEEE 802.15.1 (Bluetooth)[BT]. 1294 IEEE 802.15.1 has two IP "profiles": one with and one without PPP. 1295 The profile without PPP would use MLD. The 802.15.1 protocol has a 1296 maximum bandwidth of about 800 kbps, shared between all nodes on the 1297 link, so a host on a moderately loaded 802.15.1 access point could 1298 experience the kind of bandwidth described in the previous paragraph. 1299 In addition 802.15.1 handover times typically run upwards of a second 1300 or more because the host must resynchronize its frequency hopping 1301 pattern with the access point, so anything the IP layer could do to 1302 alleviate further delay would be beneficial. 1304 The context-specific data field for MLD context transfer included in 1305 the CTP Context Data Block message for a single IPv6 multicast 1306 address has the following format: 1308 0 1 2 3 1309 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 1310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1311 | | 1312 + Subnet Prefix on nAR Wireless Interface + 1313 | | 1314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1315 | | 1316 + + 1317 | | 1318 + Subscribed IPv6 Multicast Address + 1319 | | 1320 + + 1321 | | 1322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1324 The Subnet Prefix on nAR Wireless Interface field contains a subnet 1325 prefix that identifies the interface on which multicast routing 1326 should be established. The Subscribed IPv6 Multicast Address field 1327 contains the multicast address for which multicast routing should be 1328 established. 1330 The pAR sends one MLD context block per subscribed IPv6 multicast 1331 address. 1333 No changes are required in the MLD state machine. 1335 Upon receipt of a CTP Context Data Block for MLD, the state machine 1336 takes the following actions: 1338 - If the router is in the No Listeners present state on the wireless 1339 interface on which the Subnet Prefix field in the Context Data 1340 Block is advertised, it transitions into the Listeners Present 1341 state for the Subscribed IPv6 Multicast Address field in the 1342 Context Data Block. This transition is exactly the same as if the 1343 router had received a Report message. 1345 - If the router is in the Listeners present state on that interface, 1346 it remains in that state but restarts the timer, as if it had 1347 received a Report message. 1349 If more than one MLD router is on the link, a router receiving an MLD 1350 Context Data Block SHOULD send the block to the other routers on the 1351 link. If wireless bandwidth is not an issue, the router MAY instead 1352 send a proxy MLD Report message on the wireless interface that 1353 advertises the Subnet Prefix field from the Context Data Block. Since 1354 MLD routers do not keep track of which nodes are listening to munticast 1355 addresses, only whether a particular multicast address is being 1356 listened to, proxying the subscription should cause no difficulty. 1358 Authors' Addresses 1360 Rajeev Koodli 1361 Nokia Research Center 1362 313 Fairchild Drive 1363 Mountain View, California 94043 1364 USA 1365 Rajeev.koodli@nokia.com 1367 John Loughney 1368 Nokia 1369 Itdmerenkatu 11-13 1370 00180 Espoo 1371 Finland 1372 john.loughney@nokia.com 1374 Madjid F. Nakhjiri 1375 Motorola Labs 1376 1031 East Algonquin Rd., Room 2240 1377 Schaumburg, IL, 60196 1378 USA 1379 madjid.nakhjiri@motorola.com 1381 Charles E. Perkins 1382 Nokia Research Center 1383 313 Fairchild Drive 1384 Mountain View, California 94043 1385 USA 1386 charliep@iprg.nokia.com 1388 Full Copyright Statement 1390 Copyright (C) The Internet Society (2004). This document is subject 1391 to the rights, licenses and restrictions contained in BCP 78, and 1392 except as set forth therein, the authors retain all their rights. 1394 This document and the information contained herein are provided on an 1395 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1396 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 1397 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 1398 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFOR- 1399 MATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES 1400 OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1402 Intellectual Property 1404 The IETF takes no position regarding the validity or scope of any 1405 Intellectual Property Rights or other rights that might be claimed to 1406 pertain to the implementation or use of the technology described in 1407 this document or the extent to which any license under such rights 1408 might or might not be available; nor does it represent that it has 1409 made any independent effort to identify any such rights. Information 1410 on the procedures with respect to rights in RFC documents can be 1411 found in BCP 78 and BCP 79. 1413 Copies of IPR disclosures made to the IETF Secretariat and any 1414 assurances of licenses to be made available, or the result of an 1415 attempt made to obtain a general license or permission for the use of 1416 such proprietary rights by implementers or users of this specifica- 1417 tion can be obtained from the IETF on-line IPR repository at 1418 http://www.ietf.org/ipr. 1420 The IETF invites any interested party to bring to its attention any 1421 copyrights, patents or patent applications, or other proprietary 1422 rights that may cover technology that may be required to implement 1423 this standard. Please address the information to the IETF at ietf- 1424 ipr@ietf.org. 1426 Acknowledgement 1428 Funding for the RFC Editor function is currently provided by the 1429 Internet Society.