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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 (September 15, 2011) is 4599 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) -- Possible downref: Non-RFC (?) normative reference: ref. 'FAST-CONV' Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Walton 3 Internet Draft E. Chen 4 Intended Status: Standards Track Cisco Systems 5 Expiration Date: March 16, 2012 A. Retana 6 Hewlett-Packard Co. 7 J. Scudder 8 Juniper Networks 9 September 15, 2011 11 Advertisement of Multiple Paths in BGP 13 draft-ietf-idr-add-paths-06.txt 15 Status of this Memo 17 This Internet-Draft is submitted to IETF in full conformance with the 18 provisions of BCP 78 and 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 as "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 This Internet-Draft will expire on March 16, 2012. 38 Copyright Notice 40 Copyright (c) 2011 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Abstract 55 In this document we propose a BGP extension that allows the 56 advertisement of multiple paths for the same address prefix without 57 the new paths implicitly replacing any previous ones. The essence of 58 the extension is that each path is identified by a path identifier in 59 addition to the address prefix. 61 1. Introduction 63 The BGP specification [RFC4271] defines an "Update-Send Process" to 64 advertise the routes chosen by the Decision Process to other BGP 65 speakers. No provisions are made to allow the advertisement of 66 multiple paths for the same address prefix, or Network Layer 67 Reachability Information (NLRI). In fact, a route with the same NLRI 68 as a previously advertised route implicitly replaces the previous 69 advertisement. 71 In this document we propose a BGP extension that allows the 72 advertisement of multiple paths for the same address prefix without 73 the new paths implicitly replacing any previous ones. The essence of 74 the extension is that each path is identified by a path identifier in 75 addition to the address prefix. 77 1.1. Specification of Requirements 79 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 80 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 81 document are to be interpreted as described in [RFC2119]. 83 2. How to Identify a Path 85 As defined in [RFC4271], a path refers to the information reported in 86 the path attribute field of an UPDATE message. As the procedures 87 specified in [RFC4271] allow only the advertisement of one path for a 88 particular address prefix, a path for an address prefix from a BGP 89 peer can be keyed on the address prefix. 91 In order for a BGP speaker to advertise multiple paths for the same 92 address prefix, a new identifier (termed "Path Identifier" hereafter) 93 needs to be introduced so that a particular path for an address 94 prefix can be identified by the combination of the address prefix and 95 the Path Identifier. 97 The assignment of the Path Identifier for a path by a BGP speaker is 98 purely a local matter. However, the Path Identifier MUST be assigned 99 in such a way that the BGP speaker is able to use the (prefix, path 100 identifier) to uniquely identify a path advertised to a neighbor. A 101 BGP speaker that re-advertises a route MUST generate its own Path 102 Identifier to be associated with the re-advertised route. A BGP 103 speaker that receives a route SHOULD NOT assume that the identifier 104 carries any particular semantics; it SHOULD be treated as an opaque 105 value. 107 3. Extended NLRI Encodings 109 In order to carry the Path Identifier in an UPDATE message, the 110 existing NLRI encodings are extended by prepending the Path 111 Identifier field, which is of four-octets. 113 For example, the NLRI encodings specified in [RFC4271, RFC4760] are 114 extended as the following: 116 +--------------------------------+ 117 | Path Identifier (4 octets) | 118 +--------------------------------+ 119 | Length (1 octet) | 120 +--------------------------------+ 121 | Prefix (variable) | 122 +--------------------------------+ 124 and the NLRI encoding specified in [RFC3107] is extended as the 125 following: 127 +--------------------------------+ 128 | Path Identifier (4 octets) | 129 +--------------------------------+ 130 | Length (1 octet) | 131 +--------------------------------+ 132 | Label (3 octets) | 133 +--------------------------------+ 134 | ... | 135 +--------------------------------+ 136 | Prefix (variable) | 137 +--------------------------------+ 139 The usage of the extended NLRI encodings is specified in the 140 Operation section. 142 4. ADD-PATH Capability 144 The ADD-PATH Capability is a new BGP capability [RFC5492]. The 145 Capability Code for this capability is specified in the IANA 146 Considerations section of this document. The Capability Length field 147 of this capability is variable. The Capability Value field consists 148 of one or more of the following tuples: 150 +------------------------------------------------+ 151 | Address Family Identifier (2 octets) | 152 +------------------------------------------------+ 153 | Subsequent Address Family Identifier (1 octet) | 154 +------------------------------------------------+ 155 | Send/Receive (1 octet) | 156 +------------------------------------------------+ 158 The meaning and use of the fields are as follows: 160 Address Family Identifier (AFI): 162 This field is the same as the one used in [RFC4760]. 164 Subsequent Address Family Identifier (SAFI): 166 This field is the same as the one used in [RFC4760]. 168 Send/Receive: 170 This field indicates whether the sender is (a) willing to 171 receive multiple paths from its peer (value 1), (b) would 172 like to send multiple paths to its peer (value 2), or (c) 173 both (value 3) for the . 175 5. Operation 177 The Path Identifier specified in the previous section can be used to 178 advertise multiple paths for the same address prefix without 179 subsequent advertisements replacing the previous ones. Apart from 180 the fact that this is now possible, the route advertisement rules of 181 [RFC4271] are not changed. In particular, a new advertisement for a 182 given address prefix and a given path identifier replaces a previous 183 advertisement for the given address prefix and the given path 184 identifier. 186 A BGP speaker that is willing to receive multiple paths from its 187 peer, or would like to send multiple paths to its peer, SHOULD 188 advertise the ADD-PATH Capability to the peer using BGP Capabilities 189 advertisement [RFC5492]. 191 A BGP speaker MUST follow the existing procedures in generating an 192 UPDATE message for a particular to a peer unless the BGP 193 speaker advertises the ADD-PATH Capability to the peer indicating its 194 desire to send multiple paths for the , and also receives 195 the ADD-PATH Capability from the peer indicating its willingness to 196 receive multiple paths for the , in which case the speaker 197 MUST generate a route update for the based on the 198 combination of the address prefix and the Path Identifier, and use 199 the extended NLRI encodings specified in this document. The peer 200 SHALL act accordingly in processing an UPDATE message related to a 201 particular . 203 A BGP speaker SHOULD include the bestpath when more than one path are 204 advertised to a neighbor unless the bestpath is a path received from 205 that neighbor. 207 When deployed as a provider edge router or a peering router that 208 interacts with external neighbors, a BGP speaker usually advertises 209 at most one path to the internal neighbors in a network. In the case 210 the speaker is configured to advertise multiple paths to the internal 211 neighbors, it should include the Edge_Discriminator attribute defined 212 in [FAST-CONV] in order to make the route selection consistent inside 213 the network. 215 As the Path Identifiers are locally assigned, and may or may not be 216 persistent across a control plane restart of a BGP speaker, an 217 implementation SHOULD take special care so that the underlying 218 forwarding plane of a "Receiving Speaker" as described in [RFC4724] 219 is not affected during the graceful restart of a BGP session. 221 6. Applications 223 The BGP extension specified in this document can be used by a BGP 224 speaker to advertise multiple paths in certain applications. The 225 availability of the additional paths can help reduce or eliminate 226 persistent route oscillations [RFC3345]. It can also help with 227 optimal routing and routing convergence in a network. The 228 applications are detailed in separate documents. 230 7. Deployment Considerations 232 The extension proposed in this document provides a mechanism for a 233 BGP speaker to advertise multiple paths over a BGP session. Care 234 needs to be taken in its deployment to ensure consistent routing and 235 forwarding in a network, the details of which will be described in 236 separate application documents. 238 8. IANA Considerations 240 IANA has assigned capability number 69 for the ADD-PATH Capability 241 described in this document. This registration is in the BGP 242 Capability Codes registry. 244 9. Security Considerations 246 This document introduces no new security concerns to BGP or other 247 specifications referenced in this document. 249 10. Acknowledgments 251 We would like to thank David Cook and Naiming Shen for their 252 contributions to the design and development of the extension. 254 Many people have made valuable comments and suggestions, including 255 Rex Fernando, Eugene Kim, Danny McPherson, Dave Meyer, Pradosh 256 Mohapatra, Keyur Patel, Robert Raszuk, Eric Rosen, Srihari Sangli, 257 Dan Tappan, and Mark Turner. 259 11. References 261 11.1. Normative References 263 [RFC4271] Rekhter, Y., T. Li, and S. Hares, "A Border Gateway 264 Protocol 4 (BGP-4)," RFC 4271, January 2006. 266 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 267 with BGP-4", RFC 5492, February 2009. 269 [RFC4760] Bates, T., Chandra, R., Rekhter, Y., and D. Katz, 270 "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007. 272 [RFC3107] Rekhter, R. and E. Rosen, "Carrying Label Information in 273 BGP-4," RFC 3107, May 2001. 275 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 276 Requirement Levels," RFC 2119, BCP 14, March 1997. 278 [RFC4724] Sangli, S., E. Chen, R. Fernando, J. Scudder, and Y. 279 Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, January 280 2007. 282 [FAST-CONV] Mohapatra, P., R. Fernando, C. Filsfils, R. Raszuk, "Fast 283 Connectivity Restoration Using BGP Add-path", Work in Progress, March 284 2011. 286 11.2. Informative References 288 [RFC3345] McPherson, D., V. Gill, D. Walton, and A. Retana, "Border 289 Gateway Protocol (BGP) Persistent Route Oscillation Condition", RFC 290 3345, August 2002. 292 12. Authors' Addresses 294 Daniel Walton 295 Cisco Systems, Inc. 296 7025 Kit Creek Rd. 297 Research Triangle Park, NC 27709 299 Email: dwalton@cisco.com 301 Alvaro Retana 302 Hewlett-Packard Co. 304 2610 Wycliff Road 305 Raleigh, NC 27607 307 Email: alvaro.retana@hp.com 309 Enke Chen 310 Cisco Systems, Inc. 311 170 W. Tasman Dr. 312 San Jose, CA 95134 314 Email: enkechen@cisco.com 316 John Scudder 317 Juniper Networks 319 Email: jgs@juniper.net