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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (February 6, 2010) is 5193 days in the past. Is this intentional? 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 3107 (Obsoleted by RFC 8277) Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). 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 Intended Status: Standards Track E. Chen 5 Expiration Date: August 2010 Cisco Systems 6 J. Scudder 7 Juniper Networks 8 February 6, 2010 10 Advertisement of Multiple Paths in BGP 12 draft-ietf-idr-add-paths-03.txt 14 Status of this Memo 16 This Internet-Draft is submitted to IETF in full conformance with the 17 provisions of BCP 78 and BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/1id-abstracts.html 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html 35 This Internet-Draft will expire on August 6, 2010. 37 Copyright Notice 39 Copyright (c) 2010 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Abstract 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 1. Introduction 62 The BGP specification [RFC4271] defines an "Update-Send Process" to 63 advertise the routes chosen by the Decision Process to other BGP 64 speakers. No provisions are made to allow the advertisement of 65 multiple paths for the same address prefix, or Network Layer 66 Reachability Information (NLRI). In fact, a route with the same NLRI 67 as a previously advertised route implicitly replaces the previous 68 advertisement. 70 In this document we propose a BGP extension that allows the 71 advertisement of multiple paths for the same address prefix without 72 the new paths implicitly replacing any previous ones. The essence of 73 the extension is that each path is identified by a path identifier in 74 addition to the address prefix. 76 1.1. Specification of Requirements 78 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 79 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 80 document are to be interpreted as described in [RFC2119]. 82 2. How to Identify a Path 84 As defined in [RFC4271], a path refers to the information reported in 85 the path attribute field of an UPDATE message. As the procedures 86 specified in [RFC4271] allow only the advertisement of one path for a 87 particular address prefix, a path for an address prefix from a BGP 88 peer can be keyed on the address prefix. 90 In order for a BGP speaker to advertise multiple paths for the same 91 address prefix, a new identifier (termed "Path Identifier" hereafter) 92 needs to be introduced so that a particular path for an address 93 prefix can be identified by the combination of the address prefix and 94 the Path Identifier. 96 The assignment of the Path Identifier for a path by a BGP speaker is 97 purely a local matter. However, the Path Identifier MUST be assigned 98 in such a way that the BGP speaker is able to use the (prefix, path 99 identifier) to uniquely identify a path advertised to a neighbor. A 100 BGP speaker that re-advertises a route MUST generate its own Path 101 Identifier to be associated with the re-advertised route. A BGP 102 speaker that receives a route SHOULD NOT assume that the identifier 103 carries any particular semantics; it SHOULD be treated as an opaque 104 value. 106 3. Extended NLRI Encodings 108 In order to carry the Path Identifier in an UPDATE message, the 109 existing NLRI encodings are extended by prepending the Path 110 Identifier field, which is of four-octets. 112 For example, the NLRI encodings specified in [RFC4271, RFC4760] are 113 extended as the following: 115 +--------------------------------+ 116 | Path Identifier (4 octets) | 117 +--------------------------------+ 118 | Length (1 octet) | 119 +--------------------------------+ 120 | Prefix (variable) | 121 +--------------------------------+ 123 and the NLRI encoding specified in [RFC3107] is extended as the 124 following: 126 +--------------------------------+ 127 | Path Identifier (4 octets) | 128 +--------------------------------+ 129 | Length (1 octet) | 130 +--------------------------------+ 131 | Label (3 octets) | 132 +--------------------------------+ 133 | ... | 134 +--------------------------------+ 135 | Prefix (variable) | 136 +--------------------------------+ 138 The usage of the extended NLRI encodings is specified in the 139 Operation section. 141 4. ADD-PATH Capability 143 The ADD-PATH Capability is a new BGP capability [RFC5492]. The 144 Capability Code for this capability is specified in the IANA 145 Considerations section of this document. The Capability Length field 146 of this capability is variable. The Capability Value field consists 147 of one or more of the following tuples: 149 +------------------------------------------------+ 150 | Address Family Identifier (2 octets) | 151 +------------------------------------------------+ 152 | Subsequent Address Family Identifier (1 octet) | 153 +------------------------------------------------+ 154 | Send/Receive (1 octet) | 155 +------------------------------------------------+ 157 The meaning and use of the fields are as follows: 159 Address Family Identifier (AFI): 161 This field is the same as the one used in [RFC4760]. 163 Subsequent Address Family Identifier (SAFI): 165 This field is the same as the one used in [RFC4760]. 167 Send/Receive: 169 This field indicates whether the sender is (a) willing to 170 receive multiple paths from its peer (value 1), (b) would 171 like to send multiple paths to its peer (value 2), or (c) 172 both (value 3) for the . 174 5. Operation 176 The Path Identifier specified in the previous section can be used to 177 advertise multiple paths for the same address prefix without 178 subsequent advertisements replacing the previous ones. Apart from 179 the fact that this is now possible, the route advertisement rules of 180 [RFC4271] are not changed. In particular, a new advertisement for a 181 given address prefix and a given path identifier replaces a previous 182 advertisement for the given address prefix and the given path 183 identifier. 185 A BGP speaker that is willing to receive multiple paths from its 186 peer, or would like to send multiple paths to its peer, SHOULD 187 advertise the ADD-PATH Capability to the peer using BGP Capabilities 188 advertisement [RFC5492]. 190 A BGP speaker MUST follow the existing procedures in generating an 191 UPDATE message for a particular to a peer unless the BGP 192 speaker advertises the ADD-PATH Capability to the peer indicating its 193 desire to send multiple paths for the , and also receives 194 the ADD-PATH Capability from the peer indicating its willingness to 195 receive multiple paths for the , in which case the speaker 196 MUST generate a route update for the based on the 197 combination of the address prefix and the Path Identifier, and use 198 the extended NLRI encodings specified in this document. The peer 199 SHALL act accordingly in processing an UPDATE message related to a 200 particular . 202 As the Path Identifiers are locally assigned, and may or may not be 203 persistent across a control plane restart of a BGP speaker, an 204 implementation SHOULD take special care so that the underlying 205 forwarding plane of a "Receiving Speaker" as described in [RFC4724] 206 is not affected during the graceful restart of a BGP session. 208 6. Applications 210 The BGP extension specified in this document can be used by a BGP 211 speaker to advertise multiple paths in certain applications. The 212 availability of the additional paths can help reduce or eliminate 213 persistent route oscillations [RFC3345]. It can also help with 214 optimal routing and routing convergence in a network. The 215 applications are detailed in separate documents. 217 7. Deployment Considerations 219 The extension proposed in this document provides a mechanism for a 220 BGP speaker to advertise multiple paths over a BGP session. Care 221 needs to be taken in its deployment to ensure consistent routing and 222 forwarding in a network, the details of which will be described in 223 separate application documents. 225 8. IANA Considerations 227 IANA has assigned capability number 69 for the ADD-PATH Capability 228 described in this document. This registration is in the BGP 229 Capability Codes registry. 231 9. Security Considerations 233 This document introduces no new security concerns to BGP or other 234 specifications referenced in this document. 236 10. Acknowledgments 238 We would like to thank David Cook and Naiming Shen for their 239 contributions to the design and development of the extension. 241 Many people have made valuable comments and suggestions, including 242 Rex Fernando, Eugene Kim, Danny McPherson, Dave Meyer, Pradosh 243 Mohapatra, Keyur Patel, Robert Raszuk, Eric Rosen, Srihari Sangli, 244 Dan Tappan, and Mark Turner. 246 11. References 248 11.1. Normative References 250 [RFC4271] Rekhter, Y., T. Li, and S. Hares, "A Border Gateway 251 Protocol 4 (BGP-4)," RFC 4271, January 2006. 253 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 254 with BGP-4", RFC 5492, February 2009. 256 [RFC4760] Bates, T., Chandra, R., Rekhter, Y., and D. Katz, 257 "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007. 259 [RFC3107] Rekhter, R. and E. Rosen, "Carrying Label Information in 260 BGP-4," RFC 3107, May 2001. 262 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 263 Requirement Levels," RFC 2119, BCP 14, March 1997. 265 [RFC4724] Sangli, S., E. Chen, R. Fernando, J. Scudder, and Y. 266 Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, January 267 2007. 269 11.2. Informative References 271 [RFC3345] McPherson, D., V. Gill, D. Walton, and A. Retana, "Border 272 Gateway Protocol (BGP) Persistent Route Oscillation Condition", RFC 273 3345, August 2002. 275 12. Authors' Addresses 277 Daniel Walton 278 Cisco Systems, Inc. 279 7025 Kit Creek Rd. 280 Research Triangle Park, NC 27709 282 Email: dwalton@cisco.com 284 Alvaro Retana 285 Cisco Systems, Inc. 286 7025 Kit Creek Rd. 287 Research Triangle Park, NC 27709 289 Email: aretana@cisco.com 290 Enke Chen 291 Cisco Systems, Inc. 292 170 W. Tasman Dr. 293 San Jose, CA 95134 295 Email: enkechen@cisco.com 297 John Scudder 298 Juniper Networks 300 Email: jgs@juniper.net