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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 3392 (Obsoleted by RFC 5492) ** Obsolete normative reference: RFC 3107 (Obsoleted by RFC 8277) Summary: 4 errors (**), 0 flaws (~~), 4 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Walton 3 Internet Draft A. Retana 4 Expiration Date: January 2009 E. Chen 5 Cisco Systems 6 J. Scudder 7 Juniper Networks 9 Advertisement of Multiple Paths in BGP 11 draft-walton-bgp-add-paths-06.txt 13 Status of this Memo 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than a "work in progress." 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/1id-abstracts.html 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html 36 Abstract 38 In this document we propose a BGP extension that allows the 39 advertisement of multiple paths for the same address prefix without 40 the new paths implicitly replacing any previous ones. The essence of 41 the extension is that each path is identified by a path identifier in 42 addition to the address prefix. 44 1. Introduction 46 The BGP specification [RFC4271] defines an "Update-Send Process" to 47 advertise the routes chosen by the Decision Process to other BGP 48 speakers. No provisions are made to allow the advertisement of 49 multiple paths for the same address prefix, or Network Layer 50 Reachability Information (NLRI). In fact, a route with the same NLRI 51 as a previously advertised route implicitly replaces the previous 52 advertisement. 54 In this document we propose a BGP extension that allows the 55 advertisement of multiple paths for the same address prefix without 56 the new paths implicitly replacing any previous ones. The essence of 57 the extension is that each path is identified by a path identifier in 58 addition to the address prefix. 60 2. Specification of Requirements 62 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 63 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 64 document are to be interpreted as described in [RFC2119]. 66 3. How to Identify a Path 68 As defined in [RFC4271], a path refers to the information reported in 69 the path attribute field of an UPDATE message. As the procedures 70 specified in [RFC4271] allow only the advertisement of one path for a 71 particular address prefix, a path for an address prefix from a BGP 72 peer can be keyed on the address prefix. 74 In order for a BGP speaker to advertise multiple paths for the same 75 address prefix, a new identifier (termed "Path Identifier" hereafter) 76 needs to be introduced so that a particular path for an address 77 prefix can be identified by the combination of the address prefix and 78 the Path Identifier. 80 The assignment of the Path Identifier for a path by a BGP speaker is 81 purely a local matter. However, the Path Identifier MUST be assigned 82 in such a way that the BGP speaker is able to use the (prefix, path 83 identifier) to uniquely identify a path advertised to a neighbor. A 84 BGP speaker that re-advertises a route MUST generate its own Path 85 Identifier to be associated with the re-advertised route. A BGP 86 speaker that receives a route SHOULD NOT assume that the identifier 87 carries any particular semantics; it SHOULD be treated as an opaque 88 value. 90 4. Extended NLRI Encodings 92 In order to carry the Path Identifier in an UPDATE message, the 93 existing NLRI encodings are extended by prepending the Path 94 Identifier field, which is of four-octets. 96 For example, the NLRI encodings specified in [RFC4271, RFC4760] are 97 extended as the following: 99 +--------------------------------+ 100 | Path Identifier (4 octets) | 101 +--------------------------------+ 102 | Length (1 octet) | 103 +--------------------------------+ 104 | Prefix (variable) | 105 +--------------------------------+ 107 and the NLRI encoding specified in [RFC3107] is extended as the 108 following: 110 +--------------------------------+ 111 | Path Identifier (4 octets) | 112 +--------------------------------+ 113 | Length (1 octet) | 114 +--------------------------------+ 115 | Label (3 octets) | 116 +--------------------------------+ 117 | ... | 118 +--------------------------------+ 119 | Prefix (variable) | 120 +--------------------------------+ 122 The usage of the extended NLRI encodings is specified in the 123 Operation section. 125 5. ADD-PATH Capability 127 The ADD-PATH Capability is a new BGP capability [RFC3392]. The 128 Capability Code for this capability is specified in the IANA 129 Considerations section of this document. The Capability Length field 130 of this capability is variable. The Capability Value field consists 131 of one or more of the following tuples: 133 +------------------------------------------------+ 134 | Address Family Identifier (2 octets) | 135 +------------------------------------------------+ 136 | Subsequent Address Family Identifier (1 octet) | 137 +------------------------------------------------+ 138 | Send/Receive (1 octet) | 139 +------------------------------------------------+ 141 The meaning and use of the fields are as follows: 143 Address Family Identifier (AFI): 145 This field is the same as the one used in [RFC4760]. 147 Subsequent Address Family Identifier (SAFI): 149 This field is the same as the one used in [RFC4760]. 151 Send/Receive: 153 This field indicates whether the sender is (a) willing to 154 receive multiple paths from its peer (value 1), (b) would 155 like to send multiple paths to its peer (value 2), or (c) 156 both (value 3) for the . 158 6. Operation 160 The Path Identifier specified in the previous section can be used to 161 advertise multiple paths for the same address prefix without 162 subsequent advertisements replacing the previous ones. Apart from 163 the fact that this is now possible, the route advertisement rules of 164 [RFC4271] are not changed. In particular, a new advertisement for a 165 given address prefix and a given path identifier replaces a previous 166 advertisement for the given address prefix and the given path 167 identifier. 169 A BGP speaker that is willing to receive multiple paths from its 170 peer, or would like to send multiple paths to its peer, SHOULD 171 advertise the ADD-PATH Capability to the peer using BGP Capabilities 172 advertisement [RFC3392]. 174 A BGP speaker MUST follow the existing procedures in generating an 175 UPDATE message for a particular to a peer unless the BGP 176 speaker advertises the ADD-PATH Capability to the peer indicating its 177 desire to send multiple paths for the , and also receives 178 the ADD-PATH Capability from the peer indicating its willingness to 179 receive multiple paths for the , in which case the speaker 180 MUST generate a route update for the based on the 181 combination of the address prefix and the Path Identifier, and use 182 the extended NLRI encodings specified in this document. The peer 183 SHALL act accordingly in processing an UPDATE message related to a 184 particular . 186 7. Applications 188 The BGP extension specified in this document can be used by a BGP 189 speaker to advertise multiple paths in certain applications. The 190 availability of the additional paths can help reduce or eliminate 191 persistent route oscillations [RFC3345]. It can also help with 192 optimal routing and routing convergence in a network. The 193 applications are detailed in separate documents. 195 8. Deployment Considerations 197 The extension proposed in this document provides a mechanism for a 198 BGP speaker to advertise multiple paths over a BGP session. Care 199 needs to be taken in its deployment to ensure consistent routing and 200 forwarding in a network, the details of which will be described in 201 separate application documents. 203 9. IANA Considerations 205 IANA needs to assign a capability number for the ADD-PATH Capability 206 described in this document. 208 10. Security Considerations 210 This document introduces no new security concerns to BGP or other 211 specifications referenced in this document. 213 11. Acknowledgments 215 We would like to thank David Cook and Naiming Shen for their 216 contributions to the design and development of the extension, and for 217 co-authoring drafts that lead to the current document. 219 Many people have made valuable comments and suggestions, including 220 Dave Meyer, Srihari Sangli, Eric Rosen, Dan Tappan, Robert Raszuk, 221 Mark Turner, Danny McPherson, Eugene Kim, Pradosh Mohapatra, Rex 222 Fernando, and Keyur Patel. 224 12. Normative References 226 [RFC4271] Rekhter, Y., T. Li, and S. Hares, "A Border Gateway 227 Protocol 4 (BGP-4)," RFC 4271, January 2006. 229 [RFC3392] Chandra, R. and J. Scudder, "Capabilities Advertisement 230 with BGP-4," RFC 3392, November 2002. 232 [RFC4760] Bates, T., Chandra, R., Rekhter, Y., and D. Katz, 233 "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007. 235 [RFC3107] Rekhter, R. and E. Rosen, "Carrying Label Information in 236 BGP-4," RFC 3107, May 2001. 238 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 239 Requirement Levels," RFC 2119, BCP 14, March 1997. 241 13. Informative References 243 [RFC3345] McPherson, D., V. Gill, D. Walton, and A. Retana, "Border 244 Gateway Protocol (BGP) Persistent Route Oscillation Condition", RFC 245 3345, August 2002. 247 14. Authors' Addresses 249 Daniel Walton 250 Cisco Systems, Inc. 251 7025 Kit Creek Rd. 252 Research Triangle Park, NC 27709 254 Email: dwalton@cisco.com 256 Alvaro Retana 257 Cisco Systems, Inc. 258 7025 Kit Creek Rd. 259 Research Triangle Park, NC 27709 261 Email: aretana@cisco.com 263 Enke Chen 264 Cisco Systems, Inc. 265 170 W. Tasman Dr. 266 San Jose, CA 95134 268 Email: enkechen@cisco.com 270 John Scudder 271 Juniper Networks 273 Email: jgs@juniper.net 275 15. Intellectual Property Considerations 277 This section is taken from Section 5 of RFC 3668. 279 The IETF takes no position regarding the validity or scope of any 280 Intellectual Property Rights or other rights that might be claimed to 281 pertain to the implementation or use of the technology described in 282 this document or the extent to which any license under such rights 283 might or might not be available; nor does it represent that it has 284 made any independent effort to identify any such rights. Information 285 on the procedures with respect to rights in RFC documents can be 286 found in BCP 78 and BCP 79. 288 Copies of IPR disclosures made to the IETF Secretariat and any 289 assurances of licenses to be made available, or the result of an 290 attempt made to obtain a general license or permission for the use of 291 such proprietary rights by implementers or users of this 292 specification can be obtained from the IETF on-line IPR repository at 293 http://www.ietf.org/ipr. 295 The IETF invites any interested party to bring to its attention any 296 copyrights, patents or patent applications, or other proprietary 297 rights that may cover technology that may be required to implement 298 this standard. Please address the information to the IETF at ietf- 299 ipr@ietf.org. 301 16. Copyright Notice 303 Copyright (C) The IETF Trust (2008). 305 This document is subject to the rights, licenses and restrictions 306 contained in BCP 78, and except as set forth therein, the authors 307 retain all their rights. 309 This document and the information contained herein are provided on an 310 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 311 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 312 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 313 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 314 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 315 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.