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'BGP-4') (Obsoleted by RFC 4271) ** Obsolete normative reference: RFC 1700 (Obsoleted by RFC 3232) ** Obsolete normative reference: RFC 2434 (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 4020 (Obsoleted by RFC 7120) Summary: 8 errors (**), 0 flaws (~~), 3 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Tony Bates (Cisco Systems) 3 Internet Draft Ravi Chandra (Sonoa Systems) 4 Expiration Date: September 2006 Dave Katz (Juniper Networks) 5 Obsoles RFC2858 Yakov Rekhter (Juniper Networks) 7 Multiprotocol Extensions for BGP-4 9 draft-ietf-idr-rfc2858bis-09.txt 11 Status of this Memo 13 Internet-Drafts are working documents of the Internet Engineering 14 Task Force (IETF), its areas, and its working groups. Note that 15 other groups may also distribute working documents as Internet- 16 Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as "work in progress". 23 The list of current Internet-Drafts can be accessed at 24 http://www.ietf.org/ietf/1id-abstracts.txt 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 IPR Disclosure Acknowledgement 31 By submitting this Internet-Draft, each author represents that any 32 applicable patent or other IPR claims of which he or she is aware 33 have been or will be disclosed, and any of which he or she becomes 34 aware will be disclosed, in accordance with Section 6 of BCP 79. 36 Abstract 38 Currently BGP-4 is capable of carrying routing information only for 39 IPv4. This document defines extensions to BGP-4 to enable it to carry 40 routing information for multiple Network Layer protocols (e.g., IPv6, 41 IPX, etc...). The extensions are backward compatible - a router that 42 supports the extensions can interoperate with a router that doesn't 43 support the extensions. 45 1. Specification of Requirements 47 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 48 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 49 document are to be interpreted as described in RFC 2119 [RFC2119]. 51 2. Overview 53 The only three pieces of information carried by BGP-4 [BGP-4] that 54 are IPv4 specific are (a) the NEXT_HOP attribute (expressed as an 55 IPv4 address), (b) AGGREGATOR (contains an IPv4 address), and (c) 56 NLRI (expressed as IPv4 address prefixes). This document assumes that 57 any BGP speaker (including the one that supports multiprotocol 58 capabilities defined in this document) has to have an IPv4 address 59 (which will be used, among other things, in the AGGREGATOR 60 attribute). Therefore, to enable BGP-4 to support routing for 61 multiple Network Layer protocols the only two things that have to be 62 added to BGP-4 are (a) the ability to associate a particular Network 63 Layer protocol with the next hop information, and (b) the ability to 64 associated a particular Network Layer protocol with NLRI. To 65 identify individual Network Layer protocols associated with the next 66 hop information and semantics of NLRI this document uses a 67 combination of Address Family, as defined in [RFC1700], and 68 Subsequent Address Family (as described in this document). 70 One could further observe that the next hop information (the 71 information provided by the NEXT_HOP attribute) is meaningful (and 72 necessary) only in conjunction with the advertisements of reachable 73 destinations - in conjunction with the advertisements of unreachable 74 destinations (withdrawing routes from service) the next hop 75 information is meaningless. This suggests that the advertisement of 76 reachable destinations should be grouped with the advertisement of 77 the next hop to be used for these destinations, and that the 78 advertisement of reachable destinations should be segregated from the 79 advertisement of unreachable destinations. 81 To provide backward compatibility, as well as to simplify 82 introduction of the multiprotocol capabilities into BGP-4 this 83 document uses two new attributes, Multiprotocol Reachable NLRI 84 (MP_REACH_NLRI), and Multiprotocol Unreachable NLRI 85 (MP_UNREACH_NLRI). The first one (MP_REACH_NLRI) is used to carry the 86 set of reachable destinations together with the next hop information 87 to be used for forwarding to these destinations. The second one 88 (MP_UNREACH_NLRI) is used to carry the set of unreachable 89 destinations. Both of these attributes are optional and non- 90 transitive. This way a BGP speaker that doesn't support the 91 multiprotocol capabilities will just ignore the information carried 92 in these attributes, and will not pass it to other BGP speakers. 94 3. Multiprotocol Reachable NLRI - MP_REACH_NLRI (Type Code 14): 96 This is an optional non-transitive attribute that can be used for the 97 following purposes: 99 (a) to advertise a feasible route to a peer 101 (b) to permit a router to advertise the Network Layer address of 102 the router that should be used as the next hop to the destinations 103 listed in the Network Layer Reachability Information field of the 104 MP_NLRI attribute. 106 The attribute is encoded as shown below: 108 +---------------------------------------------------------+ 109 | Address Family Identifier (2 octets) | 110 +---------------------------------------------------------+ 111 | Subsequent Address Family Identifier (1 octet) | 112 +---------------------------------------------------------+ 113 | Length of Next Hop Network Address (1 octet) | 114 +---------------------------------------------------------+ 115 | Network Address of Next Hop (variable) | 116 +---------------------------------------------------------+ 117 | Reserved (1 octet) | 118 +---------------------------------------------------------+ 119 | Network Layer Reachability Information (variable) | 120 +---------------------------------------------------------+ 122 The use and meaning of these fields are as follows: 124 Address Family Identifier (AFI): 126 This field in combination with the Subsequent Address Family 127 Identifier field identifies the Network Layer protocol 128 associated with the Network Address of Next Hop and the 129 semantics of the Network Layer Reachability Information that 130 follows. 132 Presently defined values for the Address Family Identifier 133 field are specified in RFC1700 (see the Address Family Numbers 134 section). 136 Subsequent Address Family Identifier (SAFI): 138 This field in combination with the Address Family Identifier 139 field identifies the Network Layer protocol associated with the 140 Network Address of the Next Hop and the semantics of the 141 Network Layer Reachability Information that follows. 143 Length of Next Hop Network Address: 145 A 1 octet field whose value expresses the length of the 146 "Network Address of Next Hop" field as measured in octets. 148 Network Address of Next Hop: 150 A variable length field that contains the Network Address of 151 the next router on the path to the destination system. The 152 Network Layer protocol associated with the Network Address of 153 the Next Hop is identified by a combination of 154 carried in the attribute. 156 Reserved: 158 A 1 octet field that SHOULD be set to 0. 160 Network Layer Reachability Information (NLRI): 162 A variable length field that lists NLRI for the feasible routes 163 that are being advertised in this attribute. The semantics of 164 NLRI is identified by a combination of carried in 165 the attribute. 167 When the Subsequent Address Family Identifier field is set to 168 one of the values defined in this document, each NLRI is 169 encoded as specified in the "NLRI encoding" section of this 170 document. 172 The next hop information carried in the MP_REACH_NLRI path attribute 173 defines the Network Layer address of the router that SHOULD be used 174 as the next hop to the destinations listed in the MP_NLRI attribute 175 in the UPDATE message. 177 The rules for the next hop information are the same as the rules for 178 the information carried in the NEXT_HOP BGP attribute (see Section 179 5.1.3 of [BGP-4]). 181 An UPDATE message that carries the MP_REACH_NLRI MUST also carry the 182 ORIGIN and the AS_PATH attributes (both in EBGP and in IBGP 183 exchanges). Moreover, in IBGP exchanges such a message MUST also 184 carry the LOCAL_PREF attribute. 186 An UPDATE message that carries no NLRI, other than the one encoded in 187 the MP_REACH_NLRI attribute, SHOULD NOT carry the NEXT_HOP attribute. 188 If such a message contains the NEXT_HOP attribute, the BGP speaker 189 that receives the message SHOULD ignore this attribute. 191 An UPDATE message SHOULD NOT include the same address prefix (of the 192 same ) in more than one of the following fields: WITHDRAWN 193 ROUTES field, Network Reachability Information fields, MP_REACH_NLRI 194 field, and MP_UNREACH_NLRI field. The processing of an UPDATE message 195 in this form is un-defined. 197 4. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15): 199 This is an optional non-transitive attribute that can be used for the 200 purpose of withdrawing multiple unfeasible routes from service. 202 The attribute is encoded as shown below: 204 +---------------------------------------------------------+ 205 | Address Family Identifier (2 octets) | 206 +---------------------------------------------------------+ 207 | Subsequent Address Family Identifier (1 octet) | 208 +---------------------------------------------------------+ 209 | Withdrawn Routes (variable) | 210 +---------------------------------------------------------+ 212 The use and the meaning of these fields are as follows: 214 Address Family Identifier (AFI): 216 This field in combination with the Subsequent Address Family 217 Identifier field identifies the semantics associated with the 218 Network Layer Reachability Information (NLRI) that follows. 220 Presently defined values for the Address Family Identifier 221 field are specified in RFC1700 (see the Address Family Numbers 222 section). 224 Subsequent Address Family Identifier (SAFI): 226 This field in combination with the Address Family Identifier 227 field identifies the semantics associated with the Network 228 Layer Reachability Information (NLRI) that follows. 230 Withdrawn Routes Network Layer Reachability Information: 232 A variable length field that lists NLRI for the routes that are 233 being withdrawn from service. The semantics of NLRI is 234 identified by a combination of carried in the 235 attribute. 237 When the Subsequent Address Family Identifier field is set to 238 one of the values defined in this document, each NLRI is 239 encoded as specified in the "NLRI encoding" section of this 240 document. 242 An UPDATE message that contains the MP_UNREACH_NLRI is not required 243 to carry any other path attributes. 245 5. NLRI encoding 247 The Network Layer Reachability information is encoded as one or more 248 2-tuples of the form , whose fields are described 249 below: 251 +---------------------------+ 252 | Length (1 octet) | 253 +---------------------------+ 254 | Prefix (variable) | 255 +---------------------------+ 257 The use and the meaning of these fields are as follows: 259 a) Length: 261 The Length field indicates the length in bits of the address 262 prefix. A length of zero indicates a prefix that matches all 263 (as specified by the address family) addresses (with prefix, 264 itself, of zero octets). 266 b) Prefix: 268 The Prefix field contains an address prefix followed by enough 269 trailing bits to make the end of the field fall on an octet 270 boundary. Note that the value of trailing bits is irrelevant. 272 6. Subsequent Address Family Identifier 274 This document defines the following values for the Subsequent Address 275 Family Identifier field carried in the MP_REACH_NLRI and 276 MP_UNREACH_NLRI attributes: 278 1 - Network Layer Reachability Information used for unicast 279 forwarding 281 2 - Network Layer Reachability Information used for multicast 282 forwarding 284 An implementation MAY support all, some, or none of the Subsequent 285 Address Family Identifier values defined in this document. 287 7. Error Handling 289 If a BGP speaker receives from a neighbor an Update message that 290 contains the MP_REACH_NLRI or MP_UNREACH_NLRI attribute, and the 291 speaker determines that the attribute is incorrect, the speaker MUST 292 delete all the BGP routes received from that neighbor whose AFI/SAFI 293 is the same as the one carried in the incorrect MP_REACH_NLRI or 294 MP_UNREACH_NLRI attribute. For the duration of the BGP session over 295 which the Update message was received, the speaker then SHOULD ignore 296 all the subsequent routes with that AFI/SAFI received over that 297 session. 299 In addition, the speaker MAY terminate the BGP session over which the 300 Update message was received. The session SHOULD be terminated with 301 the Notification message code/subcode indicating "Update Message 302 Error"/"Optional Attribute Error". 304 8. Use of BGP Capability Advertisement 306 A BGP speaker that uses Multiprotocol Extensions SHOULD use the 307 Capability Advertisment procedures [BGP-CAP] to determine whether the 308 speaker could use Multiprotocol Extensions with a particular peer. 310 The fields in the Capabilities Optional Parameter are set as follows. 311 The Capability Code field is set to 1 (which indicates Multiprotocol 312 Extensions capabilities). The Capability Length field is set to 4. 313 The Capability Value field is defined as: 315 0 7 15 23 31 316 +-------+-------+-------+-------+ 317 | AFI | Res. | SAFI | 318 +-------+-------+-------+-------+ 320 The use and meaning of this field is as follow: 322 AFI - Address Family Identifier (16 bit), encoded the same way 323 as in the Multiprotocol Extensions 325 Res. - Reserved (8 bit) field. SHOULD be set to 0 by the sender 326 and ignored by the receiver. 328 SAFI - Subsequent Address Family Identifier (8 bit), encoded 329 the same way as in the Multiprotocol Extensions. 331 A speaker that supports multiple tuples includes them as 332 multiple Capabilities in the Capabilities Optional Parameter. 334 To have a bi-directional exchange of routing information for a 335 particular between a pair of BGP speakers, each such 336 speaker MUST advertise to the other (via the Capability Advertisement 337 mechanism) the capability to support that particular 338 routes. 340 9. IANA Considerations 342 As specified in this document, the MP_REACH_NLRI and MP_UNREACH_NLRI 343 attributes contain the Subsequence Address Family Identifier (SAFI) 344 field. The SAFI name space is defined in this document. The IANA will 345 maintain and register values for the SAFI namespace as follows: 347 - SAFI values 1 and 2 are assigned in this document. 349 - SAFI value 3 is reserved. It was assigned by RFC 2858 for a use 350 that was never fully implemented, so is deprecated by this 351 document. 353 - SAFI values 5 through 63 are to be assigned by IANA using either 354 the Standards Action process defined in [RFC2434], or the Early 355 IANA Allocation process defined in [RFC4020]. 357 - SAFI values 67 through 127 are to be assigned by IANA, using the 358 "First Come First Served" policy defined in RFC2434. 360 - SAFI values 0 and 255 are reserved. 362 - SAFI values 128 through 240 are part of the previous "private 363 use" range. Of this space, allocations which are currently in use 364 are to be recognized by IANA. Unused values, namely 130, 131, 135 365 through 139, and 141 through 240 should be considered reserved, in 366 order to avoid conflicts. 368 - SAFI values 241 through 254 are for "private use", and values in 369 this range are not to be assigned by IANA. 371 10. Comparison with RFC2858 373 This document makes the use of the next hop information consistent 374 with the information carried in the NEXT_HOP BGP path attribute. 376 This document removes the definition of SAFI 3, and deprecates SAFI 377 3. 379 This document changes partitioning of the SAFI space. Specifically, 380 in RFC2858 SAFI values 128 through 240 were part of the "private use" 381 range. This document specifies that of this range, allocations which 382 are currently in use are to be recognized by IANA, and that unused 383 values, namely 130, 131, 135 through 139, and 141 through 240 should 384 be considered reserved. 386 This document renames the Number of SNPAs field to Reserved, and 387 removes the rest of the SNPA-related information from the 388 MP_REACH_NLRI attribute. 390 11. Comparison with RFC2283 392 This document restricts the MP_REACH_NLRI attribute to carry only a 393 single instance of . 395 This document restricts the MP_UNREACH_NLRI attribute to carry only a 396 single instance of . 398 This document clarifies handling of an UPDATE message that carries no 399 NLRI, other than the one encoded in the MP_REACH_NLRI attribute. 401 This document clarifies error handling in the presence of 402 MP_REACH_NLRI or MP_UNREACH_NLRI attributes. 404 This document specifies the use of BGP Capabilities Advertisements in 405 conjunction with Multi-protocol extensions. 407 Finally, this document includes the "IANA Consideration" Section. 409 12. Security Considerations 411 This extension to BGP does not change the underlying security issues 412 inherent in the existing BGP. 414 13. Intellectual Property Considerations 416 This section is taken from Section 5 of RFC 3668. 418 The IETF takes no position regarding the validity or scope of any 419 Intellectual Property Rights or other rights that might be claimed to 420 pertain to the implementation or use of the technology described in 421 this document or the extent to which any license under such rights 422 might or might not be available; nor does it represent that it has 423 made any independent effort to identify any such rights. Information 424 on the procedures with respect to rights in RFC documents can be 425 found in BCP 78 and BCP 79. 427 Copies of IPR disclosures made to the IETF Secretariat and any 428 assurances of licenses to be made available, or the result of an 429 attempt made to obtain a general license or permission for the use of 430 such proprietary rights by implementers or users of this 431 specification can be obtained from the IETF on-line IPR repository at 432 http://www.ietf.org/ipr. 434 The IETF invites any interested party to bring to its attention any 435 copyrights, patents or patent applications, or other proprietary 436 rights that may cover technology that may be required to implement 437 this standard. Please address the information to the IETF at ietf- 438 ipr@ietf.org. 440 14. Copyright Notice 442 Copyright (C) The Internet Society (2006). 444 This document is subject to the rights, licenses and restrictions 445 contained in BCP 78, and except as set forth therein, the authors 446 retain all their rights. 448 This document and the information contained herein are provided on an 449 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 450 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 451 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 452 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 453 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 454 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 456 15. Acknowledgements 458 The authors would like to thank members of the IDR Working Group for 459 their review and comments. 461 16. Normative References 463 [BGP-CAP] "Capabilities Advertisement with BGP-4", R. Chandra, J. 464 Scudder, RFC2842, May 2000 466 [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 467 (BGP-4)", RFC 1771, March 1995. 469 [RFC1700] "Assigned Numbers", J. Reynolds, J. Postel, RFC1700, 470 October 1994 (see also http://www.iana.org/iana/assignments.html) 472 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 473 Requirement Levels", BCP 14, RFC 2119, March 1997. 475 [RFC2434] Narten, T., Alvestrand, H., "Guidelines for Writing an IANA 476 Considerations Section in RFCs", RFC2434, October 1998 478 [RFC4020] "Early IANA Allocation of Standards Track Code Points", K. 479 Kompella, A. Zinin, BCP0100, RFC 4020, February 2005. 481 17. Author Information 483 Tony Bates 484 Cisco Systems, Inc. 485 email: tbates@cisco.com 487 Ravi Chandra 488 Sonoa Systems 489 e-mail: rchandra@sonoasystems.com 491 Dave Katz 492 Juniper Networks, Inc. 493 email: dkatz@juniper.com 495 Yakov Rekhter 496 Juniper Networks, Inc. 497 email: yakov@juniper.com