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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: July 2006 Dave Katz (Juniper Networks) 5 Obsoles RFC2858 Yakov Rekhter (Juniper Networks) 7 Multiprotocol Extensions for BGP-4 9 draft-ietf-idr-rfc2858bis-08.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 (c) to allow a given router to report some or all of the 107 Subnetwork Points of Attachment (SNPAs) that exist within the 108 local system 110 The attribute is encoded as shown below: 112 +---------------------------------------------------------+ 113 | Address Family Identifier (2 octets) | 114 +---------------------------------------------------------+ 115 | Subsequent Address Family Identifier (1 octet) | 116 +---------------------------------------------------------+ 117 | Length of Next Hop Network Address (1 octet) | 118 +---------------------------------------------------------+ 119 | Network Address of Next Hop (variable) | 120 +---------------------------------------------------------+ 121 | Number of SNPAs (1 octet) | 122 +---------------------------------------------------------+ 123 | Length of first SNPA(1 octet) | 124 +---------------------------------------------------------+ 125 | First SNPA (variable) | 126 +---------------------------------------------------------+ 127 | Length of second SNPA (1 octet) | 128 +---------------------------------------------------------+ 129 | Second SNPA (variable) | 130 +---------------------------------------------------------+ 131 | ... | 132 +---------------------------------------------------------+ 133 | Length of Last SNPA (1 octet) | 134 +---------------------------------------------------------+ 135 | Last SNPA (variable) | 136 +---------------------------------------------------------+ 137 | Network Layer Reachability Information (variable) | 138 +---------------------------------------------------------+ 140 The use and meaning of these fields are as follows: 142 Address Family Identifier (AFI): 144 This field in combination with the Subsequent Address Family 145 Identifier field identifies the Network Layer protocol 146 associated with the Network Address of Next Hop and the 147 semantics of the Network Layer Reachability Information that 148 follows. 150 Presently defined values for the Address Family Identifier 151 field are specified in RFC1700 (see the Address Family Numbers 152 section). 154 Subsequent Address Family Identifier (SAFI): 156 This field in combination with the Address Family Identifier 157 field identifies the Network Layer protocol associated with the 158 Network Address of the Next Hop and the semantics of the 159 Network Layer Reachability Information that follows. 161 Length of Next Hop Network Address: 163 A 1 octet field whose value expresses the length of the 164 "Network Address of Next Hop" field as measured in octets. 166 Network Address of Next Hop: 168 A variable length field that contains the Network Address of 169 the next router on the path to the destination system. The 170 Network Layer protocol associated with the Network Address of 171 the Next Hop is identified by a combination of 172 carried in the attribute. 174 Number of SNPAs: 176 A 1 octet field which contains the number of distinct SNPAs to 177 be listed in the following fields. The value 0 SHALL be used 178 to indicate that no SNPAs are listed in this attribute. 180 Length of Nth SNPA: 182 A 1 octet field whose value expresses the length of the "Nth 183 SNPA of Next Hop" field as measured in semi-octets 185 Nth SNPA of Next Hop: 187 A variable length field that contains an SNPA of the router 188 whose Network Address is contained in the "Network Address of 189 Next Hop" field. The field length is an integral number of 190 octets in length, namely the rounded-up integer value of one 191 half the SNPA length expressed in semi-octets; if the SNPA 192 contains an odd number of semi-octets, a value in this field 193 MUST be padded with a trailing all-zero semi-octet. 195 Network Layer Reachability Information (NLRI): 197 A variable length field that lists NLRI for the feasible routes 198 that are being advertised in this attribute. The semantics of 199 NLRI is identified by a combination of carried in 200 the attribute. 202 When the Subsequent Address Family Identifier field is set to 203 one of the values defined in this document, each NLRI is 204 encoded as specified in the "NLRI encoding" section of this 205 document. 207 The next hop information carried in the MP_REACH_NLRI path attribute 208 defines the Network Layer address of the router that SHOULD be used 209 as the next hop to the destinations listed in the MP_NLRI attribute 210 in the UPDATE message. 212 The rules for the next hop information are the same as the rules for 213 the information carried in the NEXT_HOP BGP attribute (see Section 214 5.1.3 of [BGP-4]). 216 An UPDATE message that carries the MP_REACH_NLRI MUST also carry the 217 ORIGIN and the AS_PATH attributes (both in EBGP and in IBGP 218 exchanges). Moreover, in IBGP exchanges such a message MUST also 219 carry the LOCAL_PREF attribute. 221 An UPDATE message that carries no NLRI, other than the one encoded in 222 the MP_REACH_NLRI attribute, SHOULD NOT carry the NEXT_HOP attribute. 223 If such a message contains the NEXT_HOP attribute, the BGP speaker 224 that receives the message SHOULD ignore this attribute. 226 An UPDATE message SHOULD NOT include the same address prefix (of the 227 same ) in more than one of the following fields: WITHDRAWN 228 ROUTES field, Network Reachability Information fields, MP_REACH_NLRI 229 field, and MP_UNREACH_NLRI field. The processing of an UPDATE message 230 in this form is un-defined. 232 4. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15): 234 This is an optional non-transitive attribute that can be used for the 235 purpose of withdrawing multiple unfeasible routes from service. 237 The attribute is encoded as shown below: 239 +---------------------------------------------------------+ 240 | Address Family Identifier (2 octets) | 241 +---------------------------------------------------------+ 242 | Subsequent Address Family Identifier (1 octet) | 243 +---------------------------------------------------------+ 244 | Withdrawn Routes (variable) | 245 +---------------------------------------------------------+ 247 The use and the meaning of these fields are as follows: 249 Address Family Identifier (AFI): 251 This field in combination with the Subsequent Address Family 252 Identifier field identifies the semantics associated with the 253 Network Layer Reachability Information (NLRI) that follows. 255 Presently defined values for the Address Family Identifier 256 field are specified in RFC1700 (see the Address Family Numbers 257 section). 259 Subsequent Address Family Identifier (SAFI): 261 This field in combination with the Address Family Identifier 262 field identifies the semantics associated with the Network 263 Layer Reachability Information (NLRI) that follows. 265 Withdrawn Routes Network Layer Reachability Information: 267 A variable length field that lists NLRI for the routes that are 268 being withdrawn from service. The semantics of NLRI is 269 identified by a combination of carried in the 270 attribute. 272 When the Subsequent Address Family Identifier field is set to 273 one of the values defined in this document, each NLRI is 274 encoded as specified in the "NLRI encoding" section of this 275 document. 277 An UPDATE message that contains the MP_UNREACH_NLRI is not required 278 to carry any other path attributes. 280 5. NLRI encoding 282 The Network Layer Reachability information is encoded as one or more 283 2-tuples of the form , whose fields are described 284 below: 286 +---------------------------+ 287 | Length (1 octet) | 288 +---------------------------+ 289 | Prefix (variable) | 290 +---------------------------+ 292 The use and the meaning of these fields are as follows: 294 a) Length: 296 The Length field indicates the length in bits of the address 297 prefix. A length of zero indicates a prefix that matches all 298 (as specified by the address family) addresses (with prefix, 299 itself, of zero octets). 301 b) Prefix: 303 The Prefix field contains an address prefix followed by enough 304 trailing bits to make the end of the field fall on an octet 305 boundary. Note that the value of trailing bits is irrelevant. 307 6. Subsequent Address Family Identifier 309 This document defines the following values for the Subsequent Address 310 Family Identifier field carried in the MP_REACH_NLRI and 311 MP_UNREACH_NLRI attributes: 313 1 - Network Layer Reachability Information used for unicast 314 forwarding 316 2 - Network Layer Reachability Information used for multicast 317 forwarding 319 An implementation MAY support all, some, or none of the Subsequent 320 Address Family Identifier values defined in this document. 322 7. Error Handling 324 If a BGP speaker receives from a neighbor an Update message that 325 contains the MP_REACH_NLRI or MP_UNREACH_NLRI attribute, and the 326 speaker determines that the attribute is incorrect, the speaker MUST 327 delete all the BGP routes received from that neighbor whose AFI/SAFI 328 is the same as the one carried in the incorrect MP_REACH_NLRI or 329 MP_UNREACH_NLRI attribute. For the duration of the BGP session over 330 which the Update message was received, the speaker then SHOULD ignore 331 all the subsequent routes with that AFI/SAFI received over that 332 session. 334 In addition, the speaker MAY terminate the BGP session over which the 335 Update message was received. The session SHOULD be terminated with 336 the Notification message code/subcode indicating "Update Message 337 Error"/"Optional Attribute Error". 339 8. Use of BGP Capability Advertisement 341 A BGP speaker that uses Multiprotocol Extensions SHOULD use the 342 Capability Advertisment procedures [BGP-CAP] to determine whether the 343 speaker could use Multiprotocol Extensions with a particular peer. 345 The fields in the Capabilities Optional Parameter are set as follows. 346 The Capability Code field is set to 1 (which indicates Multiprotocol 347 Extensions capabilities). The Capability Length field is set to 4. 348 The Capability Value field is defined as: 350 0 7 15 23 31 351 +-------+-------+-------+-------+ 352 | AFI | Res. | SAFI | 353 +-------+-------+-------+-------+ 355 The use and meaning of this field is as follow: 357 AFI - Address Family Identifier (16 bit), encoded the same way 358 as in the Multiprotocol Extensions 360 Res. - Reserved (8 bit) field. SHOULD be set to 0 by the sender 361 and ignored by the receiver. 363 SAFI - Subsequent Address Family Identifier (8 bit), encoded 364 the same way as in the Multiprotocol Extensions. 366 A speaker that supports multiple tuples includes them as 367 multiple Capabilities in the Capabilities Optional Parameter. 369 To have a bi-directional exchange of routing information for a 370 particular between a pair of BGP speakers, each such 371 speaker MUST advertise to the other (via the Capability Advertisement 372 mechanism) the capability to support that particular 373 routes. 375 9. IANA Considerations 377 As specified in this document, the MP_REACH_NLRI and MP_UNREACH_NLRI 378 attributes contain the Subsequence Address Family Identifier (SAFI) 379 field. The SAFI name space is defined in this document. The IANA will 380 maintain and register values for the SAFI namespace as follows: 382 - SAFI values 1 and 2 are assigned in this document. 384 - SAFI value 3 is reserved. It was assigned by RFC 2858 for a use 385 that was never fully implemented, so is deprecated by this 386 document. 388 - SAFI values 5 through 63 are to be assigned by IANA using either 389 the Standards Action process defined in [RFC2434], or the Early 390 IANA Allocation process defined in [RFC4020]. 392 - SAFI values 67 through 127 are to be assigned by IANA, using the 393 "First Come First Served" policy defined in RFC2434. 395 - SAFI values 0 and 255 are reserved. 397 - SAFI values 128 through 240 are part of the previous "private 398 use" range. Of this space, allocations which are currently in use 399 are to be recognized by IANA. Unused values, namely 130, 131, 135 400 through 139, and 141 through 240 should be considered reserved, in 401 order to avoid conflicts. 403 - SAFI values 241 through 254 are for "private use", and values in 404 this range are not to be assigned by IANA. 406 10. Comparison with RFC2858 408 This document makes the use of the next hop information consistent 409 with the information carried in the NEXT_HOP BGP path attribute. 411 This document removes the definition of SAFI 3, and deprecates SAFI 412 3. 414 This document changes partitioning of the SAFI space. Specifically, 415 in RFC2858 SAFI values 128 through 240 were part of the "private use" 416 range. This document specifies that of this range, allocations which 417 are currently in use are to be recognized by IANA, and that unused 418 values, namely 130, 131, 135 through 139, and 141 through 240 should 419 be considered reserved. 421 11. Comparison with RFC2283 423 This document restricts the MP_REACH_NLRI attribute to carry only a 424 single instance of . 426 This document restricts the MP_UNREACH_NLRI attribute to carry only a 427 single instance of . 429 This document clarifies handling of an UPDATE message that carries no 430 NLRI, other than the one encoded in the MP_REACH_NLRI attribute. 432 This document clarifies error handling in the presence of 433 MP_REACH_NLRI or MP_UNREACH_NLRI attributes. 435 This document specifies the use of BGP Capabilities Advertisements in 436 conjunction with Multi-protocol extensions. 438 Finally, this document includes the "IANA Consideration" Section. 440 12. Security Considerations 442 This extension to BGP does not change the underlying security issues 443 inherent in the existing BGP. 445 13. Intellectual Property Considerations 447 This section is taken from Section 5 of RFC 3668. 449 The IETF takes no position regarding the validity or scope of any 450 Intellectual Property Rights or other rights that might be claimed to 451 pertain to the implementation or use of the technology described in 452 this document or the extent to which any license under such rights 453 might or might not be available; nor does it represent that it has 454 made any independent effort to identify any such rights. Information 455 on the procedures with respect to rights in RFC documents can be 456 found in BCP 78 and BCP 79. 458 Copies of IPR disclosures made to the IETF Secretariat and any 459 assurances of licenses to be made available, or the result of an 460 attempt made to obtain a general license or permission for the use of 461 such proprietary rights by implementers or users of this 462 specification can be obtained from the IETF on-line IPR repository at 463 http://www.ietf.org/ipr. 465 The IETF invites any interested party to bring to its attention any 466 copyrights, patents or patent applications, or other proprietary 467 rights that may cover technology that may be required to implement 468 this standard. Please address the information to the IETF at ietf- 469 ipr@ietf.org. 471 14. Copyright Notice 473 Copyright (C) The Internet Society (2006). 475 This document is subject to the rights, licenses and restrictions 476 contained in BCP 78, and except as set forth therein, the authors 477 retain all their rights. 479 This document and the information contained herein are provided on an 480 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 481 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 482 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 483 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 484 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 485 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 487 15. Acknowledgements 489 The authors would like to thank members of the IDR Working Group for 490 their review and comments. 492 16. Normative References 494 [BGP-CAP] "Capabilities Advertisement with BGP-4", R. Chandra, J. 495 Scudder, RFC2842, May 2000 497 [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 498 (BGP-4)", RFC 1771, March 1995. 500 [RFC1700] "Assigned Numbers", J. Reynolds, J. Postel, RFC1700, 501 October 1994 (see also http://www.iana.org/iana/assignments.html) 503 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 504 Requirement Levels", BCP 14, RFC 2119, March 1997. 506 [RFC2434] Narten, T., Alvestrand, H., "Guidelines for Writing an IANA 507 Considerations Section in RFCs", RFC2434, October 1998 509 [RFC4020] "Early IANA Allocation of Standards Track Code Points", K. 510 Kompella, A. Zinin, BCP0100, RFC 4020, February 2005. 512 17. Author Information 514 Tony Bates 515 Cisco Systems, Inc. 516 email: tbates@cisco.com 518 Ravi Chandra 519 Sonoa Systems 520 e-mail: rchandra@sonoasystems.com 522 Dave Katz 523 Juniper Networks, Inc. 524 email: dkatz@juniper.com 526 Yakov Rekhter 527 Juniper Networks, Inc. 528 email: yakov@juniper.com