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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 (Redback Networks) 4 Expiration Date: October 2004 Dave Katz (Juniper Networks) 5 Obsoles RFC2858 Yakov Rekhter (Juniper Networks) 7 Multiprotocol Extensions for BGP-4 9 draft-ietf-idr-rfc2858bis-04.txt 11 1. Status of this Memo 13 This document is an Internet-Draft and is in full conformance with 14 all provisions of Section 10 of RFC2026. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as ``work in progress.'' 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 2. Abstract 34 Currently BGP-4 is capable of carrying routing information only for 35 IPv4. This document defines extensions to BGP-4 to enable it to carry 36 routing information for multiple Network Layer protocols (e.g., IPv6, 37 IPX, etc...). The extensions are backward compatible - a router that 38 supports the extensions can interoperate with a router that doesn't 39 support the extensions. 41 3. Specification of Requirements 43 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 44 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 45 document are to be interpreted as described in RFC 2119 [RFC2119]. 47 4. Overview 49 The only three pieces of information carried by BGP-4 [BGP-4] that 50 are IPv4 specific are (a) the NEXT_HOP attribute (expressed as an 51 IPv4 address), (b) AGGREGATOR (contains an IPv4 address), and (c) 52 NLRI (expressed as IPv4 address prefixes). This document assumes that 53 any BGP speaker (including the one that supports multiprotocol 54 capabilities defined in this document) has to have an IPv4 address 55 (which will be used, among other things, in the AGGREGATOR 56 attribute). Therefore, to enable BGP-4 to support routing for 57 multiple Network Layer protocols the only two things that have to be 58 added to BGP-4 are (a) the ability to associate a particular Network 59 Layer protocol with the next hop information, and (b) the ability to 60 associated a particular Network Layer protocol with NLRI. To 61 identify individual Network Layer protocols associated with the next 62 hop information and semantics of NLRI this document uses a 63 combination of Address Family, as defined in [RFC1700], and 64 Subsequent Address Family (as described in this document). 66 One could further observe that the next hop information (the 67 information provided by the NEXT_HOP attribute) is meaningful (and 68 necessary) only in conjunction with the advertisements of reachable 69 destinations - in conjunction with the advertisements of unreachable 70 destinations (withdrawing routes from service) the next hop 71 information is meaningless. This suggests that the advertisement of 72 reachable destinations should be grouped with the advertisement of 73 the next hop to be used for these destinations, and that the 74 advertisement of reachable destinations should be segregated from the 75 advertisement of unreachable destinations. 77 To provide backward compatibility, as well as to simplify 78 introduction of the multiprotocol capabilities into BGP-4 this 79 document uses two new attributes, Multiprotocol Reachable NLRI 80 (MP_REACH_NLRI), and Multiprotocol Unreachable NLRI 81 (MP_UNREACH_NLRI). The first one (MP_REACH_NLRI) is used to carry the 82 set of reachable destinations together with the next hop information 83 to be used for forwarding to these destinations. The second one 84 (MP_UNREACH_NLRI) is used to carry the set of unreachable 85 destinations. Both of these attributes are optional and non- 86 transitive. This way a BGP speaker that doesn't support the 87 multiprotocol capabilities will just ignore the information carried 88 in these attributes, and will not pass it to other BGP speakers. 90 5. Multiprotocol Reachable NLRI - MP_REACH_NLRI (Type Code 14): 92 This is an optional non-transitive attribute that can be used for the 93 following purposes: 95 (a) to advertise a feasible route to a peer 97 (b) to permit a router to advertise the Network Layer address of 98 the router that should be used as the next hop to the destinations 99 listed in the Network Layer Reachability Information field of the 100 MP_NLRI attribute. 102 (c) to allow a given router to report some or all of the 103 Subnetwork Points of Attachment (SNPAs) that exist within the 104 local system 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 | Number of SNPAs (1 octet) | 118 +---------------------------------------------------------+ 119 | Length of first SNPA(1 octet) | 120 +---------------------------------------------------------+ 121 | First SNPA (variable) | 122 +---------------------------------------------------------+ 123 | Length of second SNPA (1 octet) | 124 +---------------------------------------------------------+ 125 | Second SNPA (variable) | 126 +---------------------------------------------------------+ 127 | ... | 128 +---------------------------------------------------------+ 129 | Length of Last SNPA (1 octet) | 130 +---------------------------------------------------------+ 131 | Last SNPA (variable) | 132 +---------------------------------------------------------+ 133 | Network Layer Reachability Information (variable) | 134 +---------------------------------------------------------+ 136 The use and meaning of these fields are as follows: 138 Address Family Identifier (AFI): 140 This field in combination with the Subsequent Address Family 141 Identifier field identifies the Network Layer protocol 142 associated with the Network Address of Next Hop and the 143 semantics of the Network Layer Reachability Information that 144 follows. 146 Presently defined values for the Address Family Identifier 147 field are specified in RFC1700 (see the Address Family Numbers 148 section). 150 Subsequent Address Family Identifier (SAFI): 152 This field in combination with the Address Family Identifier 153 field identifies the Network Layer protocol associated with the 154 Network Address of the Next Hop and the semantics of the 155 Network Layer Reachability Information that follows. 157 Length of Next Hop Network Address: 159 A 1 octet field whose value expresses the length of the 160 "Network Address of Next Hop" field as measured in octets. 162 Network Address of Next Hop: 164 A variable length field that contains the Network Address of 165 the next router on the path to the destination system. The 166 Network Layer protocol associated with the Network Address of 167 the Next Hop is identified by a combination of 168 carried in the attribute. 170 Number of SNPAs: 172 A 1 octet field which contains the number of distinct SNPAs to 173 be listed in the following fields. The value 0 SHALL be used 174 to indicate that no SNPAs are listed in this attribute. 176 Length of Nth SNPA: 178 A 1 octet field whose value expresses the length of the "Nth 179 SNPA of Next Hop" field as measured in semi-octets 180 Nth SNPA of Next Hop: 182 A variable length field that contains an SNPA of the router 183 whose Network Address is contained in the "Network Address of 184 Next Hop" field. The field length is an integral number of 185 octets in length, namely the rounded-up integer value of one 186 half the SNPA length expressed in semi-octets; if the SNPA 187 contains an odd number of semi-octets, a value in this field 188 will be padded with a trailing all-zero semi-octet. 190 Network Layer Reachability Information (NLRI): 192 A variable length field that lists NLRI for the feasible routes 193 that are being advertised in this attribute. The semantics of 194 NLRI is identified by a combination of carried in 195 the attribute. 197 When the Subsequent Address Family Identifier field is set to 198 one of the values defined in this document, each NLRI is 199 encoded as specified in the "NLRI encoding" section of this 200 document. 202 The next hop information carried in the MP_REACH_NLRI path attribute 203 defines the Network Layer address of the router that should be used 204 as the next hop to the destinations listed in the MP_NLRI attribute 205 in the UPDATE message. 207 The rules for the next hop information are the same as the rules for 208 the information carried in the NEXT_HOP BGP attribute (see Section 209 5.1.3 of [BGP-4]). 211 An UPDATE message that carries the MP_REACH_NLRI MUST also carry the 212 ORIGIN and the AS_PATH attributes (both in EBGP and in IBGP 213 exchanges). Moreover, in IBGP exchanges such a message MUST also 214 carry the LOCAL_PREF attribute. 216 An UPDATE message that carries no NLRI, other than the one encoded in 217 the MP_REACH_NLRI attribute, SHOULD NOT carry the NEXT_HOP attribute. 218 If such a message contains the NEXT_HOP attribute, the BGP speaker 219 that receives the message SHOULD ignore this attribute. 221 An UPDATE message SHOULD NOT include the same address prefix (of the 222 same ) in more than one of the following fields: WITHDRAWN 223 ROUTES field, Network Reachability Information fields, MP_REACH_NLRI 224 field, and MP_UNREACH_NLRI field. The processing of an UPDATE message 225 in this form is un-defined. 227 6. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15): 229 This is an optional non-transitive attribute that can be used for the 230 purpose of withdrawing multiple unfeasible routes from service. 232 The attribute is encoded as shown below: 234 +---------------------------------------------------------+ 235 | Address Family Identifier (2 octets) | 236 +---------------------------------------------------------+ 237 | Subsequent Address Family Identifier (1 octet) | 238 +---------------------------------------------------------+ 239 | Withdrawn Routes (variable) | 240 +---------------------------------------------------------+ 242 The use and the meaning of these fields are as follows: 244 Address Family Identifier (AFI): 246 This field in combination with the Subsequent Address Family 247 Identifier field identifies the semantics associated with the 248 Network Layer Reachability Information (NLRI) that follows. 250 Presently defined values for the Address Family Identifier 251 field are specified in RFC1700 (see the Address Family Numbers 252 section). 254 Subsequent Address Family Identifier (SAFI): 256 This field in combination with the Address Family Identifier 257 field identifies the semantics associated with the Network 258 Layer Reachability Information (NLRI) that follows. 260 Withdrawn Routes Network Layer Reachability Information: 262 A variable length field that lists NLRI for the routes that are 263 being withdrawn from service. The semantics of NLRI is 264 identified by a combination of carried in the 265 attribute. 267 When the Subsequent Address Family Identifier field is set to 268 one of the values defined in this document, each NLRI is 269 encoded as specified in the "NLRI encoding" section of this 270 document. 272 An UPDATE message that contains the MP_UNREACH_NLRI is not required 273 to carry any other path attributes. 275 7. NLRI encoding 277 The Network Layer Reachability information is encoded as one or more 278 2-tuples of the form , whose fields are described 279 below: 281 +---------------------------+ 282 | Length (1 octet) | 283 +---------------------------+ 284 | Prefix (variable) | 285 +---------------------------+ 287 The use and the meaning of these fields are as follows: 289 a) Length: 291 The Length field indicates the length in bits of the address 292 prefix. A length of zero indicates a prefix that matches all 293 (as specified by the address family) addresses (with prefix, 294 itself, of zero octets). 296 b) Prefix: 298 The Prefix field contains an address prefix followed by enough 299 trailing bits to make the end of the field fall on an octet 300 boundary. Note that the value of trailing bits is irrelevant. 302 8. Subsequent Address Family Identifier 304 This document defines the following values for the Subsequent Address 305 Family Identifier field carried in the MP_REACH_NLRI and 306 MP_UNREACH_NLRI attributes: 308 1 - Network Layer Reachability Information used for unicast 309 forwarding 311 2 - Network Layer Reachability Information used for multicast 312 forwarding 314 An implementation MAY support all, some, or none of the Subsequent 315 Address Family Identifier values defined in this document. 317 9. Error Handling 319 If a BGP speaker receives from a neighbor an Update message that 320 contains the MP_REACH_NLRI or MP_UNREACH_NLRI attribute, and the 321 speaker determines that the attribute is incorrect, the speaker MUST 322 delete all the BGP routes received from that neighbor whose AFI/SAFI 323 is the same as the one carried in the incorrect MP_REACH_NLRI or 324 MP_UNREACH_NLRI attribute. For the duration of the BGP session over 325 which the Update message was received, the speaker then SHOULD ignore 326 all the subsequent routes with that AFI/SAFI received over that 327 session. 329 In addition, the speaker MAY terminate the BGP session over which the 330 Update message was received. The session SHOULD be terminated with 331 the Notification message code/subcode indicating "Update Message 332 Error"/"Optional Attribute Error". 334 10. Use of BGP Capability Advertisement 336 A BGP speaker that uses Multiprotocol Extensions SHOULD use the 337 Capability Advertisment procedures [BGP-CAP] to determine whether the 338 speaker could use Multiprotocol Extensions with a particular peer. 340 The fields in the Capabilities Optional Parameter are set as follows. 341 The Capability Code field is set to 1 (which indicates Multiprotocol 342 Extensions capabilities). The Capability Length field is set to 4. 343 The Capability Value field is defined as: 345 0 7 15 23 31 346 +-------+-------+-------+-------+ 347 | AFI | Res. | SAFI | 348 +-------+-------+-------+-------+ 350 The use and meaning of this field is as follow: 352 AFI - Address Family Identifier (16 bit), encoded the same way 353 as in the Multiprotocol Extensions 355 Res. - Reserved (8 bit) field. Should be set to 0 by the sender 356 and ignored by the receiver. 358 SAFI - Subsequent Address Family Identifier (8 bit), encoded 359 the same way as in the Multiprotocol Extensions. 361 A speaker that supports multiple tuples includes them as 362 multiple Capabilities in the Capabilities Optional Parameter. 364 To have a bi-directional exchange of routing information for a 365 particular between a pair of BGP speakers, each such 366 speaker MUST advertise to the other (via the Capability Advertisement 367 mechanism) the capability to support that particular 368 routes. 370 11. IANA Considerations 372 As specified in this document, the MP_REACH_NLRI and MP_UNREACH_NLRI 373 attributes contain the Subsequence Address Family Identifier (SAFI) 374 field. The SAFI name space is defined in this document. The IANA will 375 maintain and register values for the SAFI namespace as follows. SAFI 376 value 0 is reserved. SAFI values 1 and 2 are assigned in this 377 document. SAFI values 4 through 63 are to be assigned by IANA using 378 the "IETF Consensus" policy defined in RFC2434. SAFI values 64 379 through 127 are to be assigned by IANA, using the "First Come First 380 Served" policy defined in RFC2434. SAFI values 128 through 255 are 381 for "private use", and values in this range are not to be assigned by 382 IANA. 384 12. Comparison with RFC2858 386 This document makes the use of the next hop information consistent 387 with the information carried in the NEXT_HOP BGP path attribute. 389 This document removes the definition of SAFI = 3. 391 13. Comparison with RFC2283 393 This document restricts the MP_REACH_NLRI attribute to carry only a 394 single instance of . 396 This document restricts the MP_UNREACH_NLRI attribute to carry only a 397 single instance of . 399 This document clarifies handling of an UPDATE message that carries no 400 NLRI, other than the one encoded in the MP_REACH_NLRI attribute. 402 This document clarifies error handling in the presence of 403 MP_REACH_NLRI or MP_UNREACH_NLRI attributes. 405 This document specifies the use of BGP Capabilities Advertisements in 406 conjunction with Multi-protocol extensions. 408 Finally, this document includes the "IANA Consideration" Section. 410 14. Security Considerations 412 This extension to BGP does not change the underlying security issues 413 inherent in the existing BGP. 415 15. Acknowledgements 417 The authors would like to thank members of the IDR Working Group for 418 their review and comments. 420 16. References 422 [BGP-CAP] "Capabilities Advertisement with BGP-4", R. Chandra, J. 423 Scudder, RFC2842, May 2000 425 [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 426 (BGP-4)", RFC 1771, March 1995. 428 [RFC1700] "Assigned Numbers", J. Reynolds, J. Postel, RFC1700, 429 October 1994 (see also http://www.iana.org/iana/assignments.html) 431 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 432 Requirement Levels", BCP 14, RFC 2119, March 1997. 434 17. Author Information 436 Tony Bates 437 Cisco Systems, Inc. 438 email: tbates@cisco.com 440 Ravi Chandra 441 Redback Networks 442 e-mail: rchandra@redback.com 444 Dave Katz 445 Juniper Networks, Inc. 446 email: dkatz@juniper.com 447 Yakov Rekhter 448 Juniper Networks, Inc. 449 email: yakov@juniper.com