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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 2002 Dave Katz (Juniper Networks) 5 Obsoletes RFC2858 Yakov Rekhter (Juniper Networks) 7 Multiprotocol Extensions for BGP-4 9 draft-ietf-idr-rfc2858bis-02.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 identify 61 individual Network Layer protocols this document uses Address Family, 62 as defined in [RFC1700]. 64 One could further observe that the next hop information (the 65 information provided by the NEXT_HOP attribute) is meaningful (and 66 necessary) only in conjunction with the advertisements of reachable 67 destinations - in conjunction with the advertisements of unreachable 68 destinations (withdrawing routes from service) the next hop 69 information is meaningless. This suggests that the advertisement of 70 reachable destinations should be grouped with the advertisement of 71 the next hop to be used for these destinations, and that the 72 advertisement of reachable destinations should be segregated from the 73 advertisement of unreachable destinations. 75 To provide backward compatibility, as well as to simplify 76 introduction of the multiprotocol capabilities into BGP-4 this 77 document uses two new attributes, Multiprotocol Reachable NLRI 78 (MP_REACH_NLRI), and Multiprotocol Unreachable NLRI 79 (MP_UNREACH_NLRI). The first one (MP_REACH_NLRI) is used to carry the 80 set of reachable destinations together with the next hop information 81 to be used for forwarding to these destinations. The second one 82 (MP_UNREACH_NLRI) is used to carry the set of unreachable 83 destinations. Both of these attributes are optional and non- 84 transitive. This way a BGP speaker that doesn't support the 85 multiprotocol capabilities will just ignore the information carried 86 in these attributes, and will not pass it to other BGP speakers. 88 5. Multiprotocol Reachable NLRI - MP_REACH_NLRI (Type Code 14): 90 This is an optional non-transitive attribute that can be used for the 91 following purposes: 93 (a) to advertise a feasible route to a peer 95 (b) to permit a router to advertise the Network Layer address of 96 the router that should be used as the next hop to the destinations 97 listed in the Network Layer Reachability Information field of the 98 MP_NLRI attribute. 100 (c) to allow a given router to report some or all of the 101 Subnetwork Points of Attachment (SNPAs) that exist within the 102 local system 104 The attribute is encoded as shown below: 106 +---------------------------------------------------------+ 107 | Address Family Identifier (2 octets) | 108 +---------------------------------------------------------+ 109 | Subsequent Address Family Identifier (1 octet) | 110 +---------------------------------------------------------+ 111 | Length of Next Hop Network Address (1 octet) | 112 +---------------------------------------------------------+ 113 | Network Address of Next Hop (variable) | 114 +---------------------------------------------------------+ 115 | Number of SNPAs (1 octet) | 116 +---------------------------------------------------------+ 117 | Length of first SNPA(1 octet) | 118 +---------------------------------------------------------+ 119 | First SNPA (variable) | 120 +---------------------------------------------------------+ 121 | Length of second SNPA (1 octet) | 122 +---------------------------------------------------------+ 123 | Second SNPA (variable) | 124 +---------------------------------------------------------+ 125 | ... | 126 +---------------------------------------------------------+ 127 | Length of Last SNPA (1 octet) | 128 +---------------------------------------------------------+ 129 | Last SNPA (variable) | 130 +---------------------------------------------------------+ 131 | Network Layer Reachability Information (variable) | 132 +---------------------------------------------------------+ 133 The use and meaning of these fields are as follows: 135 Address Family Identifier: 137 This field carries the identity of the Network Layer protocol 138 associated with the Network Address that follows. Presently 139 defined values for this field are specified in RFC1700 (see the 140 Address Family Numbers section). 142 Subsequent Address Family Identifier: 144 This field provides additional information about the type of 145 the Network Layer Reachability Information carried in the 146 attribute. 148 Length of Next Hop Network Address: 150 A 1 octet field whose value expresses the length of the 151 "Network Address of Next Hop" field as measured in octets 153 Network Address of Next Hop: 155 A variable length field that contains the Network Address of 156 the next router on the path to the destination system 158 Number of SNPAs: 160 A 1 octet field which contains the number of distinct SNPAs to 161 be listed in the following fields. The value 0 SHALL be used 162 to indicate that no SNPAs are listed in this attribute. 164 Length of Nth SNPA: 166 A 1 octet field whose value expresses the length of the "Nth 167 SNPA of Next Hop" field as measured in semi-octets 169 Nth SNPA of Next Hop: 171 A variable length field that contains an SNPA of the router 172 whose Network Address is contained in the "Network Address of 173 Next Hop" field. The field length is an integral number of 174 octets in length, namely the rounded-up integer value of one 175 half the SNPA length expressed in semi-octets; if the SNPA 176 contains an odd number of semi-octets, a value in this field 177 will be padded with a trailing all-zero semi-octet. 179 Network Layer Reachability Information: 181 A variable length field that lists NLRI for the feasible routes 182 that are being advertised in this attribute. When the 183 Subsequent Address Family Identifier field is set to one of the 184 values defined in this document, each NLRI is encoded as 185 specified in the "NLRI encoding" section of this document. 187 The next hop information carried in the MP_REACH_NLRI path attribute 188 defines the Network Layer address of the border router that should be 189 used as the next hop to the destinations listed in the MP_NLRI 190 attribute in the UPDATE message. 192 The rules for the next hop information are the same as the rules for 193 the information carried in the NEXT_HOP BGP attribute (see Section 194 5.1.3 of [BGP-4]). 196 An UPDATE message that carries the MP_REACH_NLRI MUST also carry the 197 ORIGIN and the AS_PATH attributes (both in EBGP and in IBGP 198 exchanges). Moreover, in IBGP exchanges such a message MUST also 199 carry the LOCAL_PREF attribute. 201 An UPDATE message that carries no NLRI, other than the one encoded in 202 the MP_REACH_NLRI attribute, SHOULD NOT carry the NEXT_HOP attribute. 203 If such a message contains the NEXT_HOP attribute, the BGP speaker 204 that receives the message SHOULD ignore this attribute. 206 An UPDATE message SHOULD NOT include the same address prefix (of the 207 same ) in more than one of the following fields: WITHDRAWN 208 ROUTES field, Network Reachability Information fields, MP_REACH_NLRI 209 field, and MP_UNREACH_NLRI field. The processing of an UPDATE message 210 in this form is un-defined. 212 6. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15): 214 This is an optional non-transitive attribute that can be used for the 215 purpose of withdrawing multiple unfeasible routes from service. 217 The attribute is encoded as shown below: 219 +---------------------------------------------------------+ 220 | Address Family Identifier (2 octets) | 221 +---------------------------------------------------------+ 222 | Subsequent Address Family Identifier (1 octet) | 223 +---------------------------------------------------------+ 224 | Withdrawn Routes (variable) | 225 +---------------------------------------------------------+ 226 The use and the meaning of these fields are as follows: 228 Address Family Identifier: 230 This field carries the identity of the Network Layer protocol 231 associated with the NLRI that follows. Presently defined values 232 for this field are specified in RFC1700 (see the Address Family 233 Numbers section). 235 Subsequent Address Family Identifier: 237 This field provides additional information about the type of 238 the Network Layer Reachability Information carried in the 239 attribute. 241 Withdrawn Routes: 243 A variable length field that lists NLRI for the routes that are 244 being withdrawn from service. When the Subsequent Address 245 Family Identifier field is set to one of the values defined in 246 this document, each NLRI is encoded as specified in the "NLRI 247 encoding" section of this document. 249 An UPDATE message that contains the MP_UNREACH_NLRI is not required 250 to carry any other path attributes. 252 7. NLRI encoding 254 The Network Layer Reachability information is encoded as one or more 255 2-tuples of the form , whose fields are described 256 below: 258 +---------------------------+ 259 | Length (1 octet) | 260 +---------------------------+ 261 | Prefix (variable) | 262 +---------------------------+ 264 The use and the meaning of these fields are as follows: 266 a) Length: 268 The Length field indicates the length in bits of the address 269 prefix. A length of zero indicates a prefix that matches all 270 (as specified by the address family) addresses (with prefix, 271 itself, of zero octets). 273 b) Prefix: 275 The Prefix field contains an address prefix followed by enough 276 trailing bits to make the end of the field fall on an octet 277 boundary. Note that the value of trailing bits is irrelevant. 279 8. Subsequent Address Family Identifier 281 This document defines the following values for the Subsequent Address 282 Family Identifier field carried in the MP_REACH_NLRI and 283 MP_UNREACH_NLRI attributes: 285 1 - Network Layer Reachability Information used for unicast 286 forwarding 288 2 - Network Layer Reachability Information used for multicast 289 forwarding 291 An implementation MAY support all, some, or none of the Subsequent 292 Address Family Identifier values defined in this document. 294 9. Error Handling 296 If a BGP speaker receives from a neighbor an Update message that 297 contains the MP_REACH_NLRI or MP_UNREACH_NLRI attribute, and the 298 speaker determines that the attribute is incorrect, the speaker MUST 299 delete all the BGP routes received from that neighbor whose AFI/SAFI 300 is the same as the one carried in the incorrect MP_REACH_NLRI or 301 MP_UNREACH_NLRI attribute. For the duration of the BGP session over 302 which the Update message was received, the speaker then SHOULD ignore 303 all the subsequent routes with that AFI/SAFI received over that 304 session. 306 In addition, the speaker MAY terminate the BGP session over which the 307 Update message was received. The session SHOULD be terminated with 308 the Notification message code/subcode indicating "Update Message 309 Error"/"Optional Attribute Error". 311 10. Use of BGP Capability Advertisement 313 A BGP speaker that uses Multiprotocol Extensions SHOULD use the 314 Capability Advertisment procedures [BGP-CAP] to determine whether the 315 speaker could use Multiprotocol Extensions with a particular peer. 317 The fields in the Capabilities Optional Parameter are set as follows. 318 The Capability Code field is set to 1 (which indicates Multiprotocol 319 Extensions capabilities). The Capability Length field is set to 4. 320 The Capability Value field is defined as: 322 0 7 15 23 31 323 +-------+-------+-------+-------+ 324 | AFI | Res. | SAFI | 325 +-------+-------+-------+-------+ 327 The use and meaning of this field is as follow: 329 AFI - Address Family Identifier (16 bit), encoded the same way 330 as in the Multiprotocol Extensions 332 Res. - Reserved (8 bit) field. Should be set to 0 by the sender 333 and ignored by the receiver. 335 SAFI - Subsequent Address Family Identifier (8 bit), encoded 336 the same way as in the Multiprotocol Extensions. 338 A speaker that supports multiple tuples includes them as 339 multiple Capabilities in the Capabilities Optional Parameter. 341 To have a bi-directional exchange of routing information for a 342 particular between a pair of BGP speakers, each such 343 speaker MUST advertise to the other (via the Capability Advertisement 344 mechanism) the capability to support that particular 345 routes. 347 11. IANA Considerations 349 As specified in this document, the MPL_REACH_NLRI and MP_UNREACH_NLRI 350 attributes contain the Subsequence Address Family Identifier (SAFI) 351 field. The SAFI name space is defined in this document. The IANA will 352 maintain and register values for the SAFI namespace as follows. SAFI 353 value 0 is reserved. SAFI values 1 and 2 are assigned in this 354 document. SAFI values 4 through 63 are to be assigned by IANA using 355 the "IETF Consensus" policy defined in RFC2434. SAFI values 64 356 through 127 are to be assigned by IANA, using the "First Come First 357 Served" policy defined in RFC2434. SAFI values 128 through 255 are 358 for "private use", and values in this range are not to be assigned by 359 IANA. 361 12. Comparison with RFC2858 363 This document makes the use of the next hop information consistent 364 with the information carried in the NEXT_HOP BGP path attribute. 366 This document removes the definition of SAFI = 3. 368 13. Comparison with RFC2283 370 This document restricts the MP_REACH_NLRI attribute to carry only a 371 single instance of . 373 This document restricts the MP_UNREACH_NLRI attribute to carry only a 374 single instance of . 376 This document clarifies handling of an UPDATE message that carries no 377 NLRI, other than the one encoded in the MP_REACH_NLRI attribute. 379 This document clarifies error handling in the presence of 380 MP_REACH_NLRI or MP_UNREACH_NLRI attributes. 382 This document specifies the use of BGP Capabilities Advertisements in 383 conjunction with Multi-protocol extensions. 385 Finally, this document includes the "IANA Consideration" Section. 387 14. Security Considerations 389 This extension to BGP does not change the underlying security issues 390 inherent in the existing BGP. 392 15. Acknowledgements 394 The authors would like to thank members of the IDR Working Group for 395 their review and comments. 397 16. References 399 [BGP-CAP] "Capabilities Advertisement with BGP-4", R. Chandra, J. 400 Scudder, RFC2842, May 2000 402 [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 403 (BGP-4)", RFC 1771, March 1995. 405 [RFC1700] "Assigned Numbers", J. Reynolds, J. Postel, RFC1700, 406 October 1994 (see also http://www.iana.org/iana/assignments.html) 408 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 409 Requirement Levels", BCP 14, RFC 2119, March 1997. 411 17. Author Information 413 Tony Bates 414 Cisco Systems, Inc. 415 email: tbates@cisco.com 417 Ravi Chandra 418 Redback Networks 419 e-mail: rchandra@redback.com 421 Dave Katz 422 Juniper Networks, Inc. 423 email: dkatz@juniper.com 425 Yakov Rekhter 426 Juniper Networks, Inc. 427 email: yakov@juniper.com