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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Quaizar Vohra 3 Internet Draft Juniper Networks 4 Expiration Date: January 2006 Enke Chen 5 Cisco Systems 7 BGP support for four-octet AS number space 9 draft-ietf-idr-as4bytes-10.txt 11 1. Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 2. Abstract 36 Currently the Autonomous System number is encoded in BGP [BGP] as a 37 two-octets field. This document describes extensions to BGP to carry 38 the Autonomous System number as a four-octets field. 40 3. Specification of Requirements 42 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 43 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 44 document are to be interpreted as described in [RFC2119]. 46 4. Protocol Extensions 48 For the purpose of this document lets define a BGP speaker which 49 doesn���t support the new 4-octets AS number extensions as an OLD BGP 50 speaker, and a BGP speaker which supports the new 4-octets AS number 51 extensions as a NEW BGP speaker. 53 BGP carries the Autonomous System number in the My Autonomous System 54 field of the OPEN message, in the AS_PATH attribute of the UPDATE 55 message, and in the AGGREGATOR attribute of the UPDATE message. BGP 56 also carries the Autonomous System number in the BGP Communities 57 attribute. 59 A NEW BGP speaker uses BGP Capability Advertisements [RFC2842] to 60 advertise to its neighbors (either internal or external) that it 61 supports 4-octets AS number extensions, as specified in this 62 document. 64 The Capability that is used by a BGP speaker to convey to its BGP 65 peer the 4-octets Autonomous System number capability, also carries 66 the 4-octets Autonomous System number of the speaker in the 67 Capability Value field of the Capability Optional Parameter. The 68 Capability Length field of the Capability is set to 4. 70 NEW BGP speakers carry AS path information expressed in terms of 71 4-octets Autonomous Systems numbers by using the existing AS_PATH 72 attribute, except that each AS number in this attribute is encoded 73 not as a 2-octets, but as a 4-octets entity. The same applies to the 74 AGGREGATOR attribute - NEW BGP speakers use the same attribute, 75 except that the AS carried in this attribute is encoded as a 4-octets 76 entity. 78 To preserve AS path information with 4-octets AS numbers across OLD 79 BGP speakers, this document defines a new AS path attribute, called 80 NEW_AS_PATH. This attribute is optional transitive and contains the 81 AS path encoded with 4-octets AS numbers. The NEW_AS_PATH attribute 82 has the same semantics as the AS_PATH attribute, except that it is 83 optional transitive, and it carries 4-octets AS numbers. 85 To prevent the possible propagation of confederation path segments 86 outside of a confederation, the path segment types AS_CONFED_SEQUENCE 87 and AS_CONFED_SET [RFC3065] are declared invalid for the NEW_AS_PATH 88 attribute. 90 Similarly, this document defines a new aggregator attribute called 91 NEW_AGGREGATOR, which is optional transitive. The NEW_AGGREGATOR 92 attribute has the same semantics as the AGGREGATOR attribute, except 93 that it carries 4-octets AS numbers. 95 Currently assigned 2-octets Autonomous System numbers are converted 96 into 4-octets Autonomous System numbers by setting the high-order 2 97 octets of the 4-octets field to zero. Such a 4-octets AS number is 98 said to be mappable to a 2-octets AS number. 100 To represent 4-octets AS numbers (which are not mapped from 2-octets) 101 as 2-octets AS numbers in the AS path information encoded with 102 2-octets AS numbers, this document reserves a 2-octets AS number. 103 Lets denote this special AS number as AS_TRANS for ease of 104 description in the rest of this specification. This AS number is also 105 placed in the My Autonomous System field of the OPEN message 106 originated by a NEW BGP speaker if the speaker doesn���t have a 107 (globally unique) 2-octets AS number. 109 5. Operations 111 5.1. Interaction between NEW BGP speakers 113 A BGP speaker that supports 4-octets Autonomous System numbers may 114 advertise this to its peers using the BGP Capability Advertisements. 115 A BGP speaker that advertises such capability to a particular peer, 116 and receives from that peer the advertisement of such capability MUST 117 encode Autonomous System numbers as 4-octets entities in both the 118 AS_PATH and the AGGREGATOR attributes in the updates it sends to the 119 peer, and MUST assume that these attributes in the updates received 120 from the peer encode Autonomous System numbers as 4-octets entities. 122 The new attributes, NEW_AS_PATH and NEW_AGGREGATOR should not be 123 carried in the UPDATE messages between NEW BGP peers. A NEW BGP 124 speaker that receives the NEW_AS_PATH and NEW_AGGREGATOR path 125 attributes in an UPDATE message from a NEW BGP speaker should discard 126 these path attributes and continue processing the UPDATE message. 128 5.2. Interaction between NEW and OLD BGP speaker 130 5.2.1. BGP Peering 132 Note that peering between a NEW BGP speaker and an OLD one is 133 possible only if the NEW BGP speaker has a 2-octets AS number. 134 However, this document doesn���t assume that an Autonomous System with 135 NEW speakers has to have a globally unique 2-octets AS number - 136 AS_TRANS could be used instead (even if multiple Autonomous System 137 would use it). 139 5.2.2. Generating Updates 141 When communicating with an OLD BGP speaker, a NEW speaker MUST send 142 the AS path information in the AS_PATH attribute encoded with 143 2-octets AS numbers. The NEW speaker also MUST send the AS path 144 information in the NEW_AS_PATH attribute (encoded with 4-octets AS 145 numbers), except for the case where the entire AS path information is 146 composed of 2-octets AS numbers only. In this case the NEW speaker 147 should not send the NEW_AS_PATH attribute. 149 In the AS_PATH attribute encoded with 2-octets AS numbers, non- 150 mappable 4-octets AS numbers are represented by the well known 151 2-octets AS number, AS_TRANS. This will preserve the path length 152 property of the AS path information; and will also help in updating 153 the AS path information received on a NEW BGP speaker from an OLD 154 speaker, as explained in the next section. 156 The NEW speaker constructs the NEW_AS_PATH attribute from the 157 information carried in the AS_PATH attribute. In the case where the 158 AS_PATH attribute contains either AS_CONFED_SEQUENCE or AS_CONFED_SET 159 path segments, the NEW speaker, when constructing the NEW_AS_PATH 160 attribute from the AS_PATH attribute, must exclude such path 161 segments. The NEW_AS_PATH attribute will be carried across a series 162 of OLD BGP speakers without modification and will help preserve the 163 truely 4-octets AS numbers in the AS path information. 165 Similarly, if the NEW speaker has to send the AGGREGATOR attribute, 166 and if the aggregating Autonomous System���s AS number is truely 167 4-octets, the speaker constructs the NEW_AGGREGATOR attributes by 168 taking the attribute length and attribute value from the AGGREGATOR 169 attribute and placing them into the attribute length and attribute 170 value of the NEW_AGGREGATOR attribute, and sets the AS number field 171 in the existing AGGREGATOR attribute to the reserved AS number, 172 AS_TRANS. Note that if the AS number is 2-octets only, then the 173 NEW_AGGREGATE attribute should not be sent. 175 5.2.3. Processing Received Updates 177 When a NEW BGP speaker receives an update from an OLD one, it should 178 be prepared to receive the NEW_AS_PATH attribute along with the 179 existing AS_PATH attribute. If NEW_AS_PATH attribute is also 180 received, both the attributes will be used to construct the exact AS 181 path information, and therefore the information carried by both the 182 attributes will be considered for AS path loop detection. 184 Note that a route may have traversed a series of autonomous systems 185 with 2-octets AS numbers and OLD BGP speakers only. In that case, if 186 the route carries a NEW_AS_PATH attribute, this attribute may not 187 have been updated since the route left the last NEW BGP speaker. The 188 trailing AS path information (representing autonomous systems with 189 2-octets AS numbers and OLD BGP speakers only) is contained only in 190 the current AS_PATH attribute (encoded in the leading part of the 191 AS_PATH attribute). This AS path information should be prepended to 192 the NEW_AS_PATH attribute to construct the exact AS path information. 194 Similarly, a NEW BGP speaker should be prepared to receive the 195 NEW_AGGREGATOR attribute from an OLD BGP speaker. In that case, the 196 AGGREGATOR attribute is ignored and the NEW_AGGREGATOR contains the 197 exact information about the aggregating node. 199 5.3. Interaction between OLD BGP speakers 201 In all other cases the speaker MUST encode Autonomous System numbers 202 as 2-octets entities in both the AS_PATH and the AGGREGATOR attribute 203 in the updates it sends to the peer, and MUST assume that these 204 attributes in the updates received from the peer encoded Autonomous 205 System numbers as 2-octets entities. 207 6. Handling BGP Communities 209 As specified in [RFC1997], when the high-order two-octets of the 210 community attribute is neither 0x0000 nor 0xffff, these two octets 211 encode the Autonomous System number. Quite clearly this would not 212 work for routers that use 4-octets Autonomous System numbers. Such 213 routers should use the Extended Communities [EXT-COMM] attribute 214 instead. 216 7. Transition 218 The scheme described in this document allows a gradual transition 219 from 2-octets AS numbers to 4-octets AS numbers. One can upgrade one 220 Autonomous system or one router at a time. 222 To simplify transition this document assumes that an Autonomous 223 System could start using 4-octets AS number only after all the BGP 224 speakers within that Autonomous System have been upgraded to support 225 4-octets AS numbers. 227 An OLD BGP speaker should not use AS_TRANS as its Autonomous System 228 number. 230 A non-mappable 4-octets AS number can not be used as a "Member AS 231 Number" of a BGP Confederation until all the BGP speakers within the 232 Confederation transitioned to support 4-octets AS numbers. 234 In an environment where an Autonomous System that has OLD BGP 235 speakers peers with two or more Autonomous Systems that have NEW BGP 236 speakers and use AS_TRANS (rather than having a globally unique AS 237 number), use of Multi-Exit Discriminators by the Autonomous System 238 with the OLD speakers may result in a situation where Multi-Exit 239 Discriminator will influence route selection among the routes that 240 were received from different neighboring Autonomous Systems. 242 Under certain conditions it may not be possible to reconstruct the 243 entire AS path information from the AS_PATH and the NEW_AS_PATH 244 attributes of a route. This occurs when two or more routes that carry 245 the NEW_AS_PATH attribute are aggregated by an OLD BGP speaker, and 246 the NEW_AS_PATH attribute of at least one of these routes carries at 247 least one 4-octets AS number (as oppose to a 2-octets AS number that 248 is encoded in 4 octets). When such aggregation results in creating a 249 route that is less specific than any of the component routes, (route 250 whose NLRI covers NLRI of all the component routes), loss of the AS 251 path information does not create a risk of a routing loop. In all 252 other cases loss of the AS path information does create a risk of a 253 routing loop. 255 8. IANA Consideration 257 This document uses a BGP Capability code to indicate that a BGP 258 speaker supports the 4-octets AS numbers. The Capability code has 259 been assigned by IANA per RFC 2842. 261 In addition, this document introduces two new BGP optional transitive 262 attributes. The first is the NEW_AS_PATH attribute, which preserves 263 the AS path information with 4-octet AS numbers across old BGP 264 speakers. The second is the NEW_AGGREGATOR attribute, which is 265 similar in use to the current AGGREGATOR attribute but it carries 266 4-octet AS numbers. The Type Codes for these attributes has been 267 assigned by IANA. 269 Finally, this document introduces a reserved 2-octets AS number - 270 AS_TRANS. The AS number for AS_TRANS has been assigned by the IANA. 272 9. Security Considerations 274 Security issues are not discussed in this document. 276 10. Acknowledgments 278 The authors would like to thank Yakov Rekhter, Chaitanya Kodeboyina, 279 and Jeffrey Haas for the numerous discussions which went into the 280 making of this draft. 282 11. References 284 [BGP] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway Protocol 285 4 (BGP-4)", draft-ietf-idr-bgp4-26.txt, October 2004. 287 [EXT-COM] Ramachandra, S., Tappan, D., and Rekter Y. "BGP Extended 288 Communities Attribute", draft-ramachandra-bgp-ext-communities-09.txt, 289 July 2005. 291 [RFC1997] Chandra, R., Traina, P. and T. Li, "BGP Communities 292 Attribute", RFC 1997, August 1996. 294 [RFC2842] Chandra, R., and Scudder, J., "Capabilities Advertisement 295 with BGP-4", RFC 2842, May 2000. 297 [RFC3065] Traina, P., McPherson, D., Scudder, J., "Autonomous System 298 Confederations for BGP", RFC3065, February 2001. 300 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 301 Requirement Levels", BCP 14, RFC 2119, March 1997. 303 12. Author Information 305 Quaizar Vohra 306 Juniper Networks 307 1194 N.Mathilda Ave 308 Sunnyvale, CA 94089 309 e-mail: qv@juniper.net 311 Enke Chen 312 Cisco Systems, Inc. 313 170 W. Tasman Dr. 314 San Jose, CA 95134 315 e-mail: enkechen@cisco.com 317 13. Intellectual Property Considerations 319 The IETF takes no position regarding the validity or scope of any 320 Intellectual Property Rights or other rights that might be claimed to 321 pertain to the implementation or use of the technology described in 322 this document or the extent to which any license under such rights 323 might or might not be available; nor does it represent that it has 324 made any independent effort to identify any such rights. Information 325 on the procedures with respect to rights in RFC documents can be 326 found in BCP 78 and BCP 79. 328 Copies of IPR disclosures made to the IETF Secretariat and any 329 assurances of licenses to be made available, or the result of an 330 attempt made to obtain a general license or permission for the use of 331 such proprietary rights by implementers or users of this 332 specification can be obtained from the IETF on-line IPR repository at 333 http://www.ietf.org/ipr. 335 The IETF invites any interested party to bring to its attention any 336 copyrights, patents or patent applications, or other proprietary 337 rights that may cover technology that may be required to implement 338 this standard. Please address the information to the IETF at ietf- 339 ipr@ietf.org. 341 14. Full Copyright Notice 343 Copyright (C) The Internet Society (2005). 345 This document is subject to the rights, licenses and restrictions 346 contained in BCP 78, and except as set forth therein, the authors 347 retain all their rights. 349 This document and the information contained herein are provided on an 350 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 351 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 352 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 353 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 354 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 355 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.