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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 IPng Working Group Matt Crawford 2 Internet Draft Fermilab 3 Bob Hinden 4 Nokia 5 March 12, 1998 7 Router Renumbering for IPv6 8 10 Status of this Memo 12 This document is an Internet Draft. Internet Drafts are working 13 documents of the Internet Engineering Task Force (IETF), its Areas, 14 and its Working Groups. Note that other groups may also distribute 15 working documents as Internet Drafts. 17 Internet Drafts are draft documents valid for a maximum of six 18 months. Internet Drafts may be updated, replaced, or obsoleted by 19 other documents at any time. It is not appropriate to use Internet 20 Drafts as reference material or to cite them other than as a 21 ``working draft'' or ``work in progress.'' 23 To learn the current status of any Internet-Draft, please check the 24 ``1id-abstracts.txt'' listing contained in the Internet Drafts 25 Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (North 26 Europe), ftp.nis.garr.it (South Europe), ds.internic.net (US East 27 Coast), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). 29 Distribution of this memo is unlimited. 31 1. Abstract 33 IPv6 Neighbor Discovery and Address Autoconfiguration conveniently 34 make initial assignments of address prefixes to hosts. Aside from 35 the problem of connection survival across a renumbering event, these 36 two mechanisms also simplify the reconfiguration of hosts when the 37 set of valid prefixes changes. 39 This document defines a mechanism called Router Renumbering (''RR'') 40 which allows address prefixes on routers to be configured and 41 reconfigured almost as easily as the combination of Neighbor 42 Discovery and Address Autoconfiguration works for hosts. It 43 provides a means for a network manager to make updates to the 44 prefixes used by and advertised by IPv6 routers throughout a site. 46 2. Functional Overview 48 Router Renumbering Command packets contain a sequence of Prefix 49 Control Operations (PCOs). Each PCO specifies an operation, a 50 Match-Prefix, and zero or more Use-Prefixes. A router processes 51 each PCO in sequence, checking each of its interfaces for an address 52 or prefix which matches the Match-Prefix. For every interface on 53 which a match is found, the operation is applied. The operation is 54 one of ADD, CHANGE, or SET-GLOBAL to instruct the router to 55 respectively add the Use-Prefixes to the set of configured prefixes, 56 remove the prefix which matched the Match-Prefix and replace it with 57 the Use-Prefixes, or replace all global-scope prefixes with the 58 Use-Prefixes. If the set of Use-Prefixes in the PCO is empty, the 59 ADD operation does nothing and the other two reduce to deletions. 61 Additional information for each Use-Prefix is included in the Prefix 62 Control Operation: the valid and preferred lifetimes to be included 63 in Router Advertisement Prefix Information Options [ND], and either 64 the L and A flags for the same option, or an indication that they 65 are to be copied from the prefix that matched the Match-Prefix. 67 It is possible to instruct routers to create new prefixes by 68 combining the Use-Prefixes in a PCO with some portion of the 69 existing prefix which matched the Match-Prefix. This simplifies 70 certain operations which are expected to be among the most common. 71 For every Use-Prefix, the PCO specifies a number of bits which 72 should be copied from the existing address or prefix which matched 73 the Match-Prefix and appended to the use-prefix prior to configuring 74 the new prefix on the interface. The copied bits are zero or more 75 bits from the positions immediately after the length of the Use- 76 Prefix. If subnetting information is in the same portion of of the 77 old and new prefixes, this synthesis allows a single Prefix Control 78 Operation to define a new global prefix on every router in a site, 79 while preserving the subnetting structure. 81 Because of the power of the Router Renumbering mechanism, each RR 82 message includes a sequence number and an authenticator to guard 83 against replays. Each elementary RR operation is idempotent and so 84 could be retransmitted for improved reliability, as long as the 85 sequence number is current, without concern about multiple 86 processing. However, non-idempotent combinations of elementary RR 87 operations can easily be constructed and messages containing such 88 combinations could not be safely reprocessed. Therefore, all 89 routers are required to guard against processing an RR message more 90 than once. 92 Possibly a network manager will want to perform more renumbering, or 93 exercise more detailed control, than can be expressed in a single 94 Router Renumbering packet on the available media. The RR mechanism 95 is most powerful when RR packets are multicast, so IP fragmentation 96 is undesirable. For these reasons, each RR packet contains a 97 "Segment Number". All RR packets which have a Sequence Number equal 98 to the highest value seen (for each valid key), and which pass the 99 authentication check, are equally valid and must be processed. 100 However, a router must keep track of the Segment Numbers of RR 101 messages already processed and avoid reprocessing a message whose 102 Sequence Number and Segment Number match a previously processed 103 message. 105 There is a "Test" flag which indicates that all routers should 106 simulate processing of the RR message and not perform any actual 107 reconfiguration. A separate "Report" flag instructs routers to send 108 a Router Renumbering Result message back to the source of the RR 109 Command message indicating the actual or simulated result of the 110 operations in the RR Command message. 112 The effect or simulated effect of an RR Command message may also 113 reported to network management by means outside the scope of this 114 document, regardless of the value of the "Report" flag. 116 3. Definitions 118 3.1. Terminology 120 Address 121 This term always refers to a 128-bit IPv6 address [AARCH]. When 122 referring to bits within an address, they are numbered from 0 to 123 127, with bit 0 being the first bit of the Format Prefix. 125 Prefix 126 A prefix can be understood as an address plus a length, the 127 latter being an integer in the range 0 to 128 indicating how many 128 leading bits are significant. When referring to bits within a 129 prefix, they are numbered in the same way as the bits of an 130 address. For example, the significant bits of a prefix whose 131 length is L are the bits numbered 0 through L-1, inclusive. 133 Match 134 An address A "matches" a prefix P whose length is L if the first 135 L bits of A are identical with the first L bits of P. (Every 136 address matches a prefix of length 0.) A prefix P1 with length 137 L1 matches a prefix P2 of length L2 if L1 >= L2 and the first L2 138 bits of P1 and P2 are identical. 140 Prefix Control Operation, Match-Prefix, Use-Prefix 141 These are defined section 2. 143 Matched Prefix 144 The existing prefix or address which matched a Match-Prefix. 146 New Prefix 147 A prefix constructed from a Use-Prefix, possibly including some 148 of the Matched-Prefix. 150 Recorded Sequence Number 151 The highest sequence number found in a valid, authenticated 152 message with a given key MUST be recorded in non-volatile storage 153 along with that key. 155 Note that "matches" is a transitive relation but not reflexive. If 156 two prefixes match each other, they are identical. 158 3.2. Requirements 160 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 161 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 162 document are to be interpreted as described in [KWORD]. 164 3.3. Authentication Algorithms 166 All implementations MUST support HMAC-MD5 [HMAC] for authentication. 167 Additional algorithms MAY be supported. 169 4. Message Format 171 There are two types of Router Renumbering messages: Commands, which 172 are sent to routers, and Results, which are sent by routers. The 173 two types of messages are distinguished the ICMPv6 "Code" field and 174 differ in the contents of the "Message Body" field. 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | | 178 / IPv6 header, extension headers / 179 | | 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 | | 182 / ICMPv6 & RR Header (16 octets) / 183 | | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | | 186 / RR Message Body / 187 | | 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 | | 190 / Authentication Data (16 octets for HMAC-MD5) / 191 | | 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 Router Renumbering Message Format 196 Router Renumbering messages are carried in ICMPv6 packets with 197 Type = 138. The RR message comprises 199 An RR header, containing the ICMPv6 header, the sequence and 200 segment numbers and information about the authentication key and 201 the location and length of the authentication data within the 202 packet. 204 The RR Message Body, of variable length; 206 The authentication data, with length dependent on the 207 authentication type. The length of HMAC-MD5 authentication data 208 is 16 octets. 210 All fields marked "reserved" or "res" MUST be set to zero on 211 generation of an RR message. During processing of the message they 212 MUST be included in the authentication check, but otherwise ignored. 214 All implementations which generate Router Renumbering Command 215 messages MUST support sending them to the All Routers multicast 216 address with link and site scopes, and to unicast addresses of 217 link-local and site-local formats. All routers MUST be capable of 218 receiving RR messages sent to those multicast addresses and to any 219 of their link local and site local unicast addresses. 220 Implementations SHOULD support sending and receiving RR messages 221 addressed to other unicast addresses. 223 4.1. Router Renumbering Header 225 0 1 2 3 226 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 1 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 228 | Type | Code | Checksum | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | SegmentNumber | Flags | KeyID | 231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 232 | AuthLen | AuthOffset | 233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 234 | SequenceNumber | 235 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 237 Fields: 239 Type 138 (decimal), the ICMPv6 type value assigned to Router 240 Renumbering 242 Code 0 for a Router Renumbering Command 243 1 for a Router Renumbering Result 245 Checksum The ICMPv6 checksum, as specified in [ICMPV6]. The 246 checksum covers the IPv6 pseudo-header and all fields of 247 the RR message from the Type field through the 248 Authentication Data. (For purposes of calculating and 249 verifying the Authentication Data, the ICMPv6 checksum 250 field is considered to be zero.) 252 SegmentNumber 253 An unsigned 8-bit field which enumerates different valid 254 RR messages having the same SequenceNumber and KeyID. 256 Flags A combination of one-bit flags. Six are defined and two 257 bits are reserved. 259 +-+-+-+-+-+-+-+-+ 260 |T|R|A|S|P|E|res| 261 +-+-+-+-+-+-+-+-+ 263 The flags T, R, A and S have defined meanings in an RR 264 Command message. In a Result message they MUST be 265 copied from the corresponding Command. The flags P and 266 E are meaningful only in a Result message and MUST be 267 zero in a Command. 269 T 0 indicates that the router configuration is to be 270 modified; 271 1 indicates a "Test" message: processing is to be 272 simulated and no configuration changes are to be 273 made. 275 R 0 indicates that a Result message MUST NOT be sent 276 (but other forms of logging are not precluded); 277 1 indicates that the router MUST send a Result 278 message upon completion of processing the Command 279 message; 281 A 0 indicates that the Command MUST NOT be applied to 282 interfaces which are administratively shut down; 283 1 indicates that the Command MUST be applied to 284 interfaces regardless of administrative shutdown 285 status. 287 S This flag MUST be ignored unless the router treats 288 interfaces as belonging to different "sites". 289 0 indicates that the Command MUST be applied to 290 interfaces regardless of which site they belong 291 to; 292 1 indicates that the Command MUST be applied only to 293 interfaces which belong to the same site as the 294 interface to which the Command is addressed. If 295 the destination address is appropriate for 296 interfaces belonging to more than one site, then 297 the Command MUST be applied only to interfaces 298 belonging to the same site as the interface on 299 which the Command was received. 301 P 0 indicates that the Result message contains the 302 complete report of processing the Command; 303 1 indicates that the Command message was previously 304 processed (and is not a Test) and the responding 305 router is not processing it again. This Result 306 message MAY have an empty body. 308 E 0 indicates that no error was encountered during 309 processing of the Command; 310 1 indicates that an error was encountered. 312 KeyID An unsigned 16-bit field that identifies the key used to 313 create and verify the Authentication Data for this RR 314 message. If multiple authentication algorithms are 315 supported by the implementation, the choice of algorithm 316 is implicit in the KeyID. If an asymmetric scheme is 317 used, the public key for verification of received 318 messages and the private key for signing transmitted 319 messages are both implied by the KeyID. 321 AuthLen An unsigned 16-bit field giving the length in octets of 322 the Authentication Data. 324 AuthOffset An unsigned 16-bit offset, measured in octets, from the 325 beginning of the RR message (which is the beginning of 326 the ICMPv6 header) to the beginning of the 327 Authentication Data. The smallest valid value for 328 AuthOffset is 16. 330 SequenceNumber 331 An unsigned 32-bit sequence number. The sequence number 332 MUST be non-decreasing for all messages sent with the 333 same KeyID. 335 4.2. Message Body -- Command Message 337 The body of an RR Command message is a sequence of zero or more 338 Prefix Control Operations, each of variable length. The end of the 339 sequence MAY be located by the AuthOffset field in the RR header. 341 4.2.1. Prefix Control Operation 343 A Prefix Control Operation has one Match-Prefix Part of 24 octets, 344 followed by zero or more Use-Prefix Parts of 32 octets each. 346 4.2.1.1. Match-Prefix Part 348 0 1 2 3 349 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 1 350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 | OpCode | OpLength | Ordinal | MatchLen | 352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 353 | reserved | 354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 355 | | 356 +- -+ 357 | | 358 +- MatchPrefix -+ 359 | | 360 +- -+ 361 | | 362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 Fields: 366 OpCode An unsigned 8-bit field specifying the operation to be 367 performed when the associated MatchPrefix matches an 368 interface's prefix or address. Values are: 370 1 the ADD operation 372 2 the CHANGE operation 374 3 the SET-GLOBAL operation 376 OpLength The total length of this Prefix Control Operation, in 377 units of 8 octets. A valid OpLength will always be of 378 the form 4N+3, with N equal to the number of UsePrefix 379 parts (possibly zero). 381 Ordinal An 8-bit field which MUST have a different value in each 382 Prefix Control Operation contained in a given RR Command 383 message. The value is otherwise unconstrained. 385 MatchLen An 8-bit unsigned integer between 0 and 128 inclusive 386 specifying the number of initial bits of MatchPrefix 387 which are significant in matching. 389 MatchPrefix The 128-bit prefix to be compared with each interface's 390 prefix or address. 392 4.2.1.2. Use-Prefix Part 394 0 1 2 3 395 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 1 396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 397 | UseLen | KeepLen | FlagMask | RAFlags | 398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 399 | Valid Lifetime | 400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 401 | Preferred Lifetime | 402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 403 |V|P| reserved | 404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 405 | | 406 +- -+ 407 | | 408 +- UsePrefix -+ 409 | | 410 +- -+ 411 | | 412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 Fields: 416 UseLen An 8-bit unsigned integer less than or equal to 128 417 specifying the number of initial bits of UsePrefix to 418 use in creating a new prefix for an interface. 420 KeepLen An 8-bit unsigned integer less than or equal to (128- 421 UseLen) specifying the number of bits of the prefix or 422 address which matched the associated Match-Prefix which 423 should be retained in the new prefix. The retained bits 424 are those at positions UseLen through (UseLen+KeepLen-1) 425 in the matched address or prefix, and they are copied to 426 the same positions in the New Prefix. 428 FlagMask An 8-bit mask. A 1 bit in any position means that the 429 corresponding flag bit in a Router Advertisement (RA) 430 Prefix Information Option for the New Prefix should be 431 set from the RAFlags field in this Use-Prefix Part. A 0 432 bit in the FlagMask means that the RA flag bit for the 433 New Prefix should be copied from the corresponding RA 434 flag bit of the Matched Prefix. 436 RAFlags An 8 bit field which, under control of the FlagMask 437 field, may be used to initialize the flags in Router 438 Advertisement Prefix Information Options [ND] which 439 advertise the New Prefix. Note that only two flags have 440 defined meanings to date: the L (on-link) and A 441 (autonomous configuration) flags. These flags occupy 442 the two leftmost bit positions in the RAFlags field, 443 corresponding to their position in the Prefix 444 Information Option. 446 Valid Lifetime 447 A 32-bit unsigned integer which is the number of seconds 448 for which the New Prefix will be valid [ND, SAA]. 450 Preferred Lifetime 451 A 32-bit unsigned integer which is the number of seconds 452 for which the New Prefix will be preferred [ND, SAA]. 454 V A 1-bit flag indicating that the valid lifetime of the 455 New Prefix MUST be effectively decremented in real time. 457 P A 1-bit flag indicating that the preferred lifetime of 458 the New Prefix MUST be effectively decremented in real 459 time. 461 UsePrefix The 128-bit Use-prefix which either becomes or is used 462 in forming (if KeepLen is nonzero) the New Prefix. It 463 MUST NOT have the form of a multicast or link-local 464 address [AARCH]. 466 4.3. Message Body -- Result Message 468 The body of an RR Result message is a sequence of zero or more Match 469 Reports of 24 octets. An RR Command message with the "R" flag set 470 will elicit an RR Result message containing one Match Report for 471 each Prefix Control Operation, for each different prefix it matches 472 on each interface. The Match Report has the following format. 474 0 1 2 3 475 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 1 476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 477 | reserved | Ordinal | MatchedLen | 478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 479 | InterfaceIndex | 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 | | 482 +- -+ 483 | | 484 +- MatchedPrefix -+ 485 | | 486 +- -+ 487 | | 488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 490 Fields: 492 Ordinal Copied from the Prefix Control Operation whose 493 MatchPrefix matched the MatchedPrefix on the interface 494 indicated by InterfaceIndex. 496 MatchedLen The length of the existing prefix which was matched by 497 the MatchPrefix. 499 InterfaceIndex 500 The router's numeric designation of the interface on 501 which the MatchedPrefix was configured. This SHOULD be 502 the same designation as is used in the SNMP Interfaces 503 group. 505 It is possible for a Result message to be larger than the Command 506 message which elicited it. Such a Result message may have to be 507 fragmented for transmission. If so, it SHOULD be fragmented to the 508 IPv6 minimum required MTU [IPV6]. 510 4.4. Authentication 512 The authentication covers the following fields, which are to be 513 treated as contiguous data for the purpose of computing and 514 verifying the AuthData. 515 The IPv6 source address, 516 The IPv6 destination address, 517 The ICMPv6 and RR Header, 518 The RR Message Body (which may be empty). 520 4.4.1. HMAC-MD5 522 When the key and algorithm associated with the KeyID indicate that 523 HMAC-MD5 authentication is to be used, the AuthData is generated in 524 accordance with RFC 2104 [HMAC]. 526 Before generating the AuthData, all fields of the RR header and all 527 the PCOs are filled in, except that the ICMPv6 checksum field is set 528 to zero. AuthLen will be 16 and AuthOffset will be equal to the 529 length in octets of the RR message, not including the AuthData, the 530 IPv6 header or any extension headers, but including the ICMPv6 531 header. 533 When checking the AuthData, the ICMPv6 checksum must be effectively 534 set to zero. 536 4.4.2. IPSEC 538 The KeyID value zero is reserved to indicate that no Authentication 539 is done on the Router Renumbering message itself. An RR message 540 with Key ID zero MUST have AuthLen equal to zero and AuthOffset 541 equal to the total length of the ICMPv6/RR header plus the RR 542 message body. Such a message MUST be authenticated at the IP layer 543 [IPSEC]. 545 5. Message Processing 547 Processing of received Router Renumbering Result messages is 548 entirely implementation-defined. 550 Processing of received Router Renumbering Command messages consists 551 of three parts: header check, authentication check, and execution. 553 5.1. Header Check 555 First, the existence and validity of the key indicated by the KeyID 556 are checked. If KeyID and AuthLen are zero and the message was not 557 authenticated by IP layer security, or if KeyID is not zero and does 558 not indicate a valid key, or if the value of AuthLen is not correct 559 for the indicated key, then the message MUST be discarded and SHOULD 560 be logged to network management. 562 Next, if the router is multi-sited, and the S flag is set and the 563 destination address of the Command is appropriate for interfaces 564 belonging to more than one site, but is not appropriate for the 565 interface on which the Command was received, this is an error. If 566 the R flag is set, return a Result message with the E flag set and 567 no Match Reports. The Command message MUST be discarded and SHOULD 568 be logged to network management. 570 Next, the SequenceNumber is compared to the Recorded Sequence Number 571 for the specified key. (If no messages have been received and 572 accepted using this key, the Recorded Sequence Number is zero.) 573 This comparison is done with the two numbers considered as unsigned 574 integers, not as DNS-style serial numbers. If the SequenceNumber is 575 less than the Recorded Sequence Number for the key, the message MUST 576 be discarded and SHOULD be logged to network management. 578 Finally, if the SequenceNumber in the message is greater than the 579 Recorded Sequence Number or the T flag is not set, skip to the 580 Authentication Check. Otherwise the SegmentNumber MUST now be 581 checked. If a correctly authenticated message with the same KeyID, 582 SequenceNumber and SegmentNumber has not already been processed, 583 skip to the Authentication Check. Otherwise, this Command is a 584 duplicate and not a Test Command. If the R flag is not set, the 585 duplicate message MUST be discarded and SHOULD NOT be logged to 586 network management. If R is set, an RR Result message with the P 587 flag set MUST be sent to the source address of the Command. The 588 body of that Result message MUST either be empty or be a saved copy 589 of the Result message body generated by processing of the previous 590 message with the same KeyID, SequenceNumber and SegmentNumber. 591 After sending the Result message, the Command MUST be discarded 592 without further processing. 594 5.2. Authentication Check 596 The authentication check is performed over the RR message, without 597 any IPv6 or extension headers. In the case of HMAC-MD5 it proceeds 598 as described in [HMAC] and [MD5]. If the computed authentication 599 value is not equal to the AuthData in the received packet, the 600 authentication check fails. 602 If the authentication check fails, the message MUST be discarded and 603 SHOULD be logged to network management. 605 If the authentication check passes, and the SequenceNumber is 606 greater than the Recorded Sequence Number for the key, then the list 607 of processed SegmentNumbers, if any, MUST be cleared and the 608 Recorded Sequence Number MUST be updated to the value used in the 609 current message, regardless of subsequent processing errors. 611 At this point, if T is set and R is not set, the message MAY be 612 discarded without further processing. 614 5.3. Execution 616 For each applicable router interface, as determined by the A and S 617 flags, the Prefix Control Operations in an RR Command message must 618 be carried out in order of appearance. The relative order of PCO 619 processing among different interfaces is not specified. 621 If the T flag is set, create a copy of each interface's 622 configuration on which to operate, because the results of processing 623 a PCO may affect the processing of subsequent PCOs. Note that if 624 all operations are performed on one interface before proceeding to 625 another interface, only one interface-configuration copy will be 626 required at a time. 628 If the R flag is set in the RR header, begin constructing an RR 629 Result message. The RR header is completely determined at this time 630 except for the Checksum and AuthOffset. 632 For each interface and for each Prefix Control Operation, each 633 prefix configured on that interface is tested to determine whether 634 it matches (as defined in section 3.1) the MatchPrefix of the PCO. 635 The prefixes are tested in an arbitrary order. Any new prefix 636 configured on an interface by the effect of a given PCO MUST NOT be 637 tested against that PCO, but MUST be tested against any subsequent 638 PCOs in the same RR Command message. 640 Under a certain condition the addresses on an interface are also 641 tested to see whether any of them matches the MatchPrefix. If and 642 only if a configured prefix "P" does not match the MatchPrefix "M" 643 but M does match P (this can happen only if M is longer than P), 644 then those addresses on that interface which match P MUST be tested 645 to determine whether any of them matches M. If any such address 646 does match M, process the PCO as if P matched M, but when forming 647 New Prefixes, if KeepLen is non-zero, bits are copied from the 648 address. This special case allows a PCO to be easily targeted to a 649 single specific interface in a network. 651 If P does not match M, processing is finished for this combination 652 of PCO, interface and prefix. Continue with another prefix on the 653 same interface if there are any more prefixes which have not been 654 tested against this PCO and were not created by the action of this 655 PCO. If no such prefixes remain on the current interface, continue 656 processing with the next PCO on the same interface, or with another 657 interface. 659 If P does match M, either directly or because a configured address 660 which matches P also matches M, then P is the Matched Prefix. 661 Perform the following steps. 663 If the Command has the R flag set, add a Match Report to 664 the Result message being constructed. 666 If the OpCode is CHANGE, mark P for deletion from the 667 current interface. 669 If the OpCode is SET-GLOBAL, mark all global-scope 670 prefixes on the current interface for deletion. 672 If there are any Use-Prefix parts in the current PCO, form 673 the New Prefixes. For each New Prefix which is already 674 configured on the current interface, unmark that prefix 675 for deletion and update the lifetimes and RA flags. For 676 each New Prefix which is not already configured, add the 677 prefix and, if appropriate, configure an address with that 678 prefix. 680 Delete any prefixes which are still marked for deletion, 681 together with any addresses which match those prefixes but 682 do not match any prefix which is not marked for deletion. 684 After processing all the Prefix Control Operations on all the 685 interfaces, an implementation MUST record the SegmentNumber of the 686 packet in a list associated with the KeyID and SequenceNumber. 688 If the Command has the R flag set, compute the AuthData and append 689 it to the Result message, fill in the AuthOffset and Checksum and 690 send the Result message. A copy of the Result message MAY be saved 691 to be retransmitted in response to a duplicate Command. 693 6. Key Management 695 As with all security methods using keys, it is necessary to change 696 the RR Authentication Key on a regular basis. To provide RR 697 functionality during key changes, implementations MUST be able to 698 store and use more than one Authentication Key at the same time. 700 The Authentication Keys SHOULD NOT be stored or transmitted using 701 algorithms or protocols that have known flaws. Implementations MUST 702 support the storage of more than one key at the same time, MUST 703 associate a specific lifetime (start and end times) and a key 704 identifier with each key, and MUST support manual key distribution 705 (e.g., manual entry of the key, key lifetime, and key identifier on 706 the router console). 708 An infinite key lifetime SHOULD NOT be allowed. If infinite 709 lifetimes are allowed, manual deletion of valid keys MUST be 710 supported; otherwise manual deletion SHOULD be supported. The 711 implementation MAY automatically delete expired keys. 713 7. Usage Examples 715 This section sketches some sample applications of Router 716 Renumbering. 718 7.1. Maintaining Global-Scope Prefixes 720 A simple use of the Router Renumbering mechanism, and one which is 721 expected to to be common, is the maintenance of a set of global 722 prefixes with a subnet structure that matches that of the site's 723 site-local address assignments. In the steady state this would 724 serve to keep the Preferred and Valid lifetimes set to their desired 725 values. During a renumbering transition, similar Command messages 726 can add new prefixes and/or delete old ones. An outline of a 727 suitable Command message follows. Fields not listed are presumed 728 set to suitable values. This Command assumes all router interfaces 729 to be maintained already have site-local [AARCH] addresses. 731 IPv6 Header 732 Next Header = 58 (ICMPv6) 733 Source Address = (Management Station) 734 Destination Address = FF05::2 (All Routers, site-local scope) 736 ICMPv6/RR Header 737 Type = 138 (Router Renumbering), Code = 0 (Command) 738 Flags = 60 hex (R, A) 739 AuthOffset = 32 N + 24 (assuming N global prefixes) 741 First (and only) PCO: 743 Match-Prefix Part 744 OpCode = 3 (SET-GLOBAL) 745 OpLength = 4 N + 3 (assuming N global prefixes) 746 Ordinal = 0 (arbitrary) 747 MatchLen = 10 748 MatchPrefix = FEC0::0 750 First Use-Prefix Part 751 UseLen = 48 (Length of TLA ID + RES + NLA ID [AARCH]) 752 KeepLen = 16 (Length of SLA (subnet) ID [AARCH]) 753 FlagMask, RAFlags, Lifetimes, V & P flags -- as desired 754 UsePrefix = First global /48 prefix 756 . . . 758 Nth Use-Prefix Part 759 UseLen = 48 760 KeepLen = 16 761 FlagMask, RAFlags, Lifetimes, V & P flags -- as desired 762 UsePrefix = Last global /48 prefix 764 This will cause N global prefixes to be set (or updated) on each 765 applicable interface. On each interface, the SLA ID (subnet) field 766 of each global prefix will be copied from the existing site-local 767 prefix. 769 7.2. Renumbering a Subnet 771 A subnet can be gracefully renumbered by setting the valid and 772 preferred timers on the old prefix to a short value and having them 773 run down, while concurrently adding adding the new prefix. Later, 774 the expired prefix is deleted. The first step is described by the 775 following RR Command. 777 IPv6 Header 778 Next Header = 58 (ICMPv6) 779 Source Address = (Management Station) 780 Destination Address = FF05::2 (All Routers, site-local scope) 782 ICMPv6/RR Header 783 Type = 138 (Router Renumbering), Code = 0 (Command) 784 Flags = 60 hex (R, A) 785 AuthOffset = 88 787 First (and only) PCO: 789 Match-Prefix Part 790 OpCode = 2 (CHANGE) 791 OpLength = 11 (reflects 2 Use-Prefix Parts) 792 Ordinal = 0 (arbitrary) 793 MatchLen = 64 794 MatchPrefix = Old /64 prefix 796 First Use-Prefix Part 797 UseLen = 0 798 KeepLen = 64 (this retains the old prefix value intact) 799 FlagMask = 0, RAFlags = 0 800 Valid Lifetime = 28800 seconds (8 hours) 801 Preferred Lifetime = 7200 seconds (2 hours) 802 V flag = 1, P flag = 1 803 UsePrefix = 0::0 805 Second Use-Prefix Part 806 UseLen = 64 807 KeepLen = 0 808 FlagMask = 0, RAFlags = 0 809 Lifetimes, V & P flags -- as desired 810 UsePrefix = New /64 prefix 812 The second step, deletion of the old prefix, can be done by an RR 813 Command with the same Match-Prefix Part (except for an OpLength 814 reduced from 11 to 3) and no Use-Prefix Parts. Any temptation to 815 set KeepLen = 64 in the second Use-Prefix Part above should be 816 resisted, as it would instruct the router to sidestep address 817 configuration. 819 7.3. Key Changes 821 Using a new authentication key while a previously used key is still 822 valid can open the possibility of a replay attack. The processing 823 rules as given in section 5 specify that routers keep track of the 824 highest sequence number seen for each key, and that messages with 825 that key and sequence number remain valid until either a higher 826 sequence number is seen or the key expires. The difficulty arises 827 when a new key is used to send a message which supersedes the last 828 message sent with another still-valid key. That older message can 829 still be replayed. 831 This vulnerability can be avoided in practice by sending a "NO-OP" 832 Command message with the old key and a valid new sequence number 833 before using a newer key. This message will then become the only 834 one which can be replayed with the old key. Examples of NO-OP 835 messages are one which contains no Prefix Control Operations, or one 836 with the T flag set. As with any other RR Command, the NO-OP SHOULD 837 be repeated until it is confidently determined that all relevant 838 routers have processed it. 840 Clearly a management station must keep track of the highest sequence 841 number it has used for each authentication key, at least to the 842 extent of being able to generate a larger value when needed. A 843 timestamp may make a good sequence number. 845 8. Security Considerations 847 The Router Renumbering mechanism proposed here is very powerful and 848 prevention of spoofing it is important. Replay of old messages must 849 be prevented, except in the narrow case of idempotent messages which 850 are still valid at the time of replay. We believe the 851 authentication mechanisms included in this specification achieve the 852 necessary protections, so long as authentication keys are not 853 compromised. 855 Authentication keys must be as well protected as is any other access 856 method that allows reconfiguration of a site's routers. 857 Distribution of keys must not expose them or permit alteration, and 858 key lifetimes must be limited. 860 If the messages of several different protocols use the same 861 authentication mechanism then it's possible for one authenticated 862 message body to be grafted onto a different set of headers and cause 863 at least some confusion, and possibly worse. One solution to this 864 problem is never to use the same set of keys for two different 865 protocols. 867 9. Acknowledgments 869 This protocol was designed by Matt Crawford based on an idea of 870 Robert Hinden and Geert Jan de Groot. Several other members of the 871 IPNG Working Group contributed useful comments. Some of the key 872 management text was borrowed from "RIP-2 MD5 Authentication." 874 10. References 876 [AARCH] 877 R. Hinden, S. Deering, "IP Version 6 Addressing Architecture", 878 Currently draft-ietf-ipngwg-addr-arch-v2-06.txt. 880 [HMAC] 881 H. Krawczyk, M. Bellare, R. Canetti, "HMAC: Keyed-Hashing for 882 Message Authentication", RFC 2104. 884 [ICMPV6] 885 A. Conta, S. Deering, "Internet Control Message Protocol 886 (ICMPv6) for the Internet Protocol Version 6 (IPv6)", currently 887 draft-ietf-ipngwg-icmp-v2-00.txt. 889 [IPSEC] 890 S. Kent, R. Atkinson, "Security Architecture for the Internet 891 Protocol", currently draft-ietf-ipsec-arch-sec-03.txt. 893 [IPV6] 894 S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) 895 Specification", currently draft-ietf-ipngwg-ipv6-spec-v2-01.txt. 897 [KWORD] S. Bradner, "Key words for use in RFCs to Indicate 898 Requirement Levels," RFC 2119. 900 [MD5] R. Rivest, "The MD5 Message-Digest Algorithm", RFC 1321. 902 [ND] T. Narten, E. Nordmark, W. Simpson, "Neighbor Discovery for 903 IP Version 6 (IPv6)", currently draft-ietf-ipngwg- 904 discovery-v2-02.txt. 906 [SAA] S. Thomson, T. Narten, "IPv6 Stateless Address 907 Autoconfiguration", draft-ietf-ipngwg-addrconf-v2-02.txt. 909 11. Authors' Addresses 911 Matt Crawford Robert M. Hinden 912 Fermilab MS 368 Nokia 913 PO Box 500 232 Java Drive 914 Batavia, IL 60510 Sunnyvale, CA 94089 915 USA USA 917 Phone: +1 630 840 3461 Phone: +1 408 990 2004 919 Email: crawdad@fnal.gov Email: hinden@ipsilon.com