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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 3107 (Obsoleted by RFC 8277) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 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 Cumulus Networks 4 Intended status: Standards Track A. Retana 5 Expires: April 27, 2015 E. Chen 6 Cisco Systems, Inc. 7 J. Scudder 8 Juniper Networks 9 October 24, 2014 11 Advertisement of Multiple Paths in BGP 12 draft-ietf-idr-add-paths-10 14 Abstract 16 In this document we propose a BGP extension that allows the 17 advertisement of multiple paths for the same address prefix without 18 the new paths implicitly replacing any previous ones. The essence of 19 the extension is that each path is identified by a path identifier in 20 addition to the address prefix. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on April 27, 2015. 39 Copyright Notice 41 Copyright (c) 2014 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Specification of Requirements . . . . . . . . . . . . . . 2 58 2. How to Identify a Path . . . . . . . . . . . . . . . . . . . 3 59 3. Extended NLRI Encodings . . . . . . . . . . . . . . . . . . . 3 60 4. ADD-PATH Capability . . . . . . . . . . . . . . . . . . . . . 4 61 5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 62 6. Applications . . . . . . . . . . . . . . . . . . . . . . . . 5 63 7. Deployment Considerations . . . . . . . . . . . . . . . . . . 6 64 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 65 9. Security Considerations . . . . . . . . . . . . . . . . . . . 6 66 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 67 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 11.1. Normative References . . . . . . . . . . . . . . . . . . 6 69 11.2. Informative References . . . . . . . . . . . . . . . . . 7 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 72 1. Introduction 74 The BGP specification [RFC4271] defines an "Update-Send Process" to 75 advertise the routes chosen by the Decision Process to other BGP 76 speakers. No provisions are made to allow the advertisement of 77 multiple paths for the same address prefix, or Network Layer 78 Reachability Information (NLRI). In fact, a route with the same NLRI 79 as a previously advertised route implicitly replaces the previous 80 advertisement. 82 In this document we propose a BGP extension that allows the 83 advertisement of multiple paths for the same address prefix without 84 the new paths implicitly replacing any previous ones. The essence of 85 the extension is that each path is identified by a path identifier in 86 addition to the address prefix. 88 1.1. Specification of Requirements 90 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 91 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 92 document are to be interpreted as described in [RFC2119]. 94 2. How to Identify a Path 96 As defined in [RFC4271], a path refers to the information reported in 97 the path attribute field of an UPDATE message. As the procedures 98 specified in [RFC4271] allow only the advertisement of one path for a 99 particular address prefix, a path for an address prefix from a BGP 100 peer can be keyed on the address prefix. 102 In order for a BGP speaker to advertise multiple paths for the same 103 address prefix, a new identifier (termed "Path Identifier" hereafter) 104 needs to be introduced so that a particular path for an address 105 prefix can be identified by the combination of the address prefix and 106 the Path Identifier. 108 The assignment of the Path Identifier for a path by a BGP speaker is 109 purely a local matter. However, the Path Identifier MUST be assigned 110 in such a way that the BGP speaker is able to use the (prefix, path 111 identifier) to uniquely identify a path advertised to a neighbor. A 112 BGP speaker that re-advertises a route MUST generate its own Path 113 Identifier to be associated with the re-advertised route. A BGP 114 speaker that receives a route SHOULD NOT assume that the identifier 115 carries any particular semantics; it SHOULD be treated as an opaque 116 value. 118 3. Extended NLRI Encodings 120 In order to carry the Path Identifier in an UPDATE message, the 121 existing NLRI encodings are extended by prepending the Path 122 Identifier field, which is of four-octets. 124 For example, the NLRI encodings specified in [RFC4271] and [RFC4760] 125 are extended as the following: 127 +--------------------------------+ 128 | Path Identifier (4 octets) | 129 +--------------------------------+ 130 | Length (1 octet) | 131 +--------------------------------+ 132 | Prefix (variable) | 133 +--------------------------------+ 135 and the NLRI encoding specified in [RFC3107] is extended as the 136 following: 138 +--------------------------------+ 139 | Path Identifier (4 octets) | 140 +--------------------------------+ 141 | Length (1 octet) | 142 +--------------------------------+ 143 | Label (3 octets) | 144 +--------------------------------+ 145 | ... | 146 +--------------------------------+ 147 | Prefix (variable) | 148 +--------------------------------+ 150 The usage of the extended NLRI encodings is specified in the 151 Operation section. 153 4. ADD-PATH Capability 155 The ADD-PATH Capability is a new BGP capability [RFC5492]. The 156 Capability Code for this capability is specified in the IANA 157 Considerations section of this document. The Capability Length field 158 of this capability is variable. The Capability Value field consists 159 of one or more of the following tuples: 161 +------------------------------------------------+ 162 | Address Family Identifier (2 octets) | 163 +------------------------------------------------+ 164 | Subsequent Address Family Identifier (1 octet) | 165 +------------------------------------------------+ 166 | Send/Receive (1 octet) | 167 +------------------------------------------------+ 169 The meaning and use of the fields are as follows: 171 Address Family Identifier (AFI): 173 This field is the same as the one used in [RFC4760]. 175 Subsequent Address Family Identifier (SAFI): 177 This field is the same as the one used in [RFC4760]. 179 Send/Receive: 181 This field indicates whether the sender is (a) able to receive 182 multiple paths from its peer (value 1), (b) able to send 183 multiple paths to its peer (value 2), or (c) both (value 3) for 184 the . 186 5. Operation 188 The Path Identifier specified in the previous section can be used to 189 advertise multiple paths for the same address prefix without 190 subsequent advertisements replacing the previous ones. Apart from 191 the fact that this is now possible, the route advertisement rules of 192 [RFC4271] are not changed. In particular, a new advertisement for a 193 given address prefix and a given path identifier replaces a previous 194 advertisement for the same address prefix and path identifier. If a 195 BGP speaker receives a message to withdraw a prefix with a path 196 identifier not seen before, it SHOULD silently ignore it. 198 For a BGP speaker to be able to send multiple paths to its peer, that 199 BGP speaker MUST advertise the ADD-PATH capability with the Send/ 200 Receive field set to either 2 or 3, and MUST receive from its peer 201 the ADD-PATH capability with the Send/Receive field set to either 1 202 or 3, for the corresponding . 204 A BGP speaker MUST follow the existing procedures in generating an 205 UPDATE message for a particular to a peer unless the BGP 206 speaker advertises the ADD-PATH Capability to the peer indicating its 207 ability to send multiple paths for the , and also receives 208 the ADD-PATH Capability from the peer indicating its ability to 209 receive multiple paths for the , in which case the speaker 210 MUST generate a route update for the based on the 211 combination of the address prefix and the Path Identifier, and use 212 the extended NLRI encodings specified in this document. The peer 213 SHALL act accordingly in processing an UPDATE message related to a 214 particular . 216 A BGP speaker SHOULD include the bestpath when more than one path are 217 advertised to a neighbor unless the bestpath is a path received from 218 that neighbor. 220 As the Path Identifiers are locally assigned, and may or may not be 221 persistent across a control plane restart of a BGP speaker, an 222 implementation SHOULD take special care so that the underlying 223 forwarding plane of a "Receiving Speaker" as described in [RFC4724] 224 is not affected during the graceful restart of a BGP session. 226 6. Applications 228 The BGP extension specified in this document can be used by a BGP 229 speaker to advertise multiple paths in certain applications. The 230 availability of the additional paths can help reduce or eliminate 231 persistent route oscillations [RFC3345]. It can also help with 232 optimal routing and routing convergence in a network. The 233 applications are detailed in separate documents. 235 7. Deployment Considerations 237 The extension proposed in this document provides a mechanism for a 238 BGP speaker to advertise multiple paths over a BGP session. Care 239 needs to be taken in its deployment to ensure consistent routing and 240 forwarding in a network, the details of which will be described in 241 separate application documents. 243 When deployed as a provider edge router or a peering router that 244 interacts with external neighbors, a BGP speaker usually advertises 245 at most one path to the internal neighbors in a network. In the case 246 the speaker is configured to advertise multiple paths to the internal 247 neighbors, and additional information is needed for the application, 248 the speaker could use attributes such as the Edge_Discriminator 249 attribute [I-D.pmohapat-idr-fast-conn-restore]. The use of that type 250 of additional information is outside the scope of this document. 252 8. IANA Considerations 254 IANA has assigned capability number 69 for the ADD-PATH Capability 255 described in this document. This registration is in the BGP 256 Capability Codes registry. 258 9. Security Considerations 260 This document introduces no new security concerns to BGP or other 261 specifications referenced in this document. 263 10. Acknowledgments 265 We would like to thank David Cook and Naiming Shen for their 266 contributions to the design and development of the extension. 268 Many people have made valuable comments and suggestions, including 269 Rex Fernando, Eugene Kim, Danny McPherson, Dave Meyer, Pradosh 270 Mohapatra, Keyur Patel, Robert Raszuk, Eric Rosen, Srihari Sangli, 271 Dan Tappan, Mark Turner, Jeff Haas and Jay Borkenhagen. 273 11. References 275 11.1. Normative References 277 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 278 Requirement Levels", BCP 14, RFC 2119, March 1997. 280 [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in 281 BGP-4", RFC 3107, May 2001. 283 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 284 Protocol 4 (BGP-4)", RFC 4271, January 2006. 286 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 287 "Multiprotocol Extensions for BGP-4", RFC 4760, January 288 2007. 290 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 291 with BGP-4", RFC 5492, February 2009. 293 11.2. Informative References 295 [I-D.pmohapat-idr-fast-conn-restore] 296 Mohapatra, P., Fernando, R., Filsfils, C., and R. Raszuk, 297 "Fast Connectivity Restoration Using BGP Add-path", draft- 298 pmohapat-idr-fast-conn-restore-03 (work in progress), 299 January 2013. 301 [RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana, 302 "Border Gateway Protocol (BGP) Persistent Route 303 Oscillation Condition", RFC 3345, August 2002. 305 [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. 306 Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, 307 January 2007. 309 Authors' Addresses 311 Daniel Walton 312 Cumulus Networks 313 185 E. Dana Street 314 Mountain View, CA 94041 315 US 317 Email: dwalton@cumulusnetworks.com 319 Alvaro Retana 320 Cisco Systems, Inc. 321 Kit Creek Rd. 322 Research Triangle Park, NC 27709 323 US 325 Email: aretana@cisco.com 326 Enke Chen 327 Cisco Systems, Inc. 328 170 W. Tasman Dr. 329 San Jose, CA 95134 330 US 332 Email: enkechen@cisco.com 334 John Scudder 335 Juniper Networks 336 1194 N. Mathilda Ave 337 Sunnyvale, CA 94089 338 US 340 Email: jgs@juniper.net