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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 5226 (Obsoleted by RFC 8126) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force J. Scudder 3 Internet-Draft Juniper Networks 4 Obsoletes: 3392 (if approved) R. Chandra 5 Intended status: Standards Track Sonoa Systems 6 Expires: July 11, 2009 January 7, 2009 8 Capabilities Advertisement with BGP-4 9 draft-ietf-idr-rfc3392bis-05.txt 11 Status of this Memo 13 This Internet-Draft is submitted to IETF in full conformance with the 14 provisions of BCP 78 and BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on July 11, 2009. 34 Copyright Notice 36 Copyright (c) 2009 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. 46 Abstract 48 This document defines an Optional Parameter, called Capabilities, 49 that is expected to facilitate the introduction of new capabilities 50 in the Border Gateway Protocol (BGP) by providing graceful capability 51 advertisement without requiring that BGP peering be terminated. This 52 document obsoletes RFC 3392. 54 1. Introduction 56 The base BGP-4 specification [RFC4271] requires that when a BGP 57 speaker receives an OPEN message with one or more unrecognized 58 Optional Parameters, the speaker must terminate the BGP peering. 59 This complicates the introduction of new capabilities in BGP. 61 This specification defines an Optional Parameter and processing rules 62 that allow BGP speakers to communicate capabilities in an OPEN 63 message. A pair of BGP speakers that support this specification can 64 establish the peering even when presented with unrecognized 65 capabilities, so long as all capabilities required to support the 66 peering are supported. 68 2. Requirements Language 70 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 71 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 72 document are to be interpreted as described in RFC 2119 [RFC2119]. 74 3. Overview of Operations 76 When a BGP speaker [RFC4271] that supports capabilities advertisement 77 sends an OPEN message to its BGP peer, the message MAY include an 78 Optional Parameter, called Capabilities. The parameter lists the 79 capabilities supported by the speaker. 81 A BGP speaker determines the capabilities supported by its peer by 82 examining the list of capabilities present in the Capabilities 83 Optional Parameter carried by the OPEN message that the speaker 84 receives from the peer. 86 A BGP speaker that supports a particular capability may use this 87 capability with its peer after the speaker determines (as described 88 above) that the peer supports this capability. Simply put, a given 89 capability can be used on a peering if that capability has been 90 advertised by both peers. If either peer has not advertised it, the 91 capability cannot be used. 93 A BGP speaker determines that its peer doesn't support capabilities 94 advertisement, if in response to an OPEN message that carries the 95 Capabilities Optional Parameter, the speaker receives a NOTIFICATION 96 message with the Error Subcode set to Unsupported Optional Parameter. 97 (This is a consequence of the base BGP-4 specification [RFC4271] and 98 not a new requirement.) In this case the speaker SHOULD attempt to 99 re-establish a BGP connection with the peer without sending to the 100 peer the Capabilities Optional Parameter. 102 If a BGP speaker that supports a certain capability determines that 103 its peer doesn't support this capability, the speaker MAY send a 104 NOTIFICATION message to the peer and terminate peering (see Section 105 "Extensions to Error Handling" for more details). An example of when 106 this would be done is if the BGP speaker requires that the capability 107 in question be used on a peering, for instance if a BGP speaker is 108 attempting to establish a peering to exchange IPv6 routes but 109 determines that its peer does not support Multiprotocol Extensions 110 for BGP-4 [RFC4760]. The Error Subcode in the NOTIFICATION message 111 is set to Unsupported Capability. The message MUST contain the 112 capability (capabilities) that causes the speaker to send the 113 message. The decision to send the message and terminate the peering 114 is local to the speaker. If terminated, such peering SHOULD NOT be 115 re-established automatically. 117 If a BGP speaker receives from its peer a capability which it does 118 not itself support or recognize, it MUST ignore that capability. In 119 particular, the Unsupported Capability NOTIFICATION message MUST NOT 120 be generated in response to reception of a capability which is not 121 supported by the local speaker. 123 4. Capabilities Optional Parameter (Parameter Type 2): 125 This is an Optional Parameter that is used by a BGP speaker to convey 126 to its BGP peer the list of capabilities supported by the speaker. 127 The encoding of BGP Optional Parameters is specified in Section 4.2 128 of [RFC4271]. The parameter type of the Capabilities Optional 129 Parameter is 2. 131 The parameter contains one or more triples , where each triple is encoded as 133 shown below: 135 +------------------------------+ 136 | Capability Code (1 octet) | 137 +------------------------------+ 138 | Capability Length (1 octet) | 139 +------------------------------+ 140 | Capability Value (variable) | 141 ~ ~ 142 +------------------------------+ 144 The use and meaning of these fields are as follows: 146 Capability Code: 148 Capability Code is a one octet unsigned binary integer that 149 unambiguously identifies individual capabilities. 151 Capability Length: 153 Capability Length is a one octet unsigned binary integer that 154 contains the length of the Capability Value field in octets. 156 Capability Value: 158 Capability Value is a variable length field that is interpreted 159 according to the value of the Capability Code field. 161 BGP speakers SHOULD NOT include more than one instance of a 162 capability with the same Capability Code, Capability Length, and 163 Capability Value. Note however, that processing of multiple 164 instances of such capability does not require special handling, as 165 additional instances do not change the meaning of the announced 166 capability, thus a BGP speaker MUST be prepared to accept such 167 multiple instances. 169 BGP speakers MAY include more than one instance of a capability (as 170 identified by the Capability Code) with non-zero Capability Length 171 field, but with different Capability Value, and either the same or 172 different Capability Length. Processing of these capability 173 instances is specific to the Capability Code and MUST be described in 174 the document introducing the new capability. 176 The Capabilities Optional Parameter (OPEN Optional Parameter Type 2) 177 SHOULD only be included in the OPEN message once. If the BGP speaker 178 wishes to include multiple capabilities in the OPEN message, it 179 SHOULD do so as discussed above, by listing all those capabilities as 180 TLVs within a single Capabilities Optional Parameter. However, for 181 backward compatibility a BGP speaker MUST be prepared to receive an 182 OPEN message which contains multiple Capabilities Optional 183 Parameters, each of which contains one or more capabilities TLVs. 184 The set of capabilities should be processed in the same way in either 185 case, whether it is enumerated within a single Capabilities Optional 186 Parameter of the OPEN message, or split across multiple. 188 5. Extensions to Error Handling 190 This document defines a new Error Subcode, Unsupported Capability. 191 The value of this Subcode is 7. The Data field in the NOTIFICATION 192 message MUST list the set of capabilities that cause the speaker to 193 send the message. Each such capability is encoded in the same way as 194 it would be encoded in the OPEN message. 196 As explained in the Overview of Operations section, the Unsupported 197 Capability NOTIFICATION is a way for a BGP speaker to complain that 198 its peer does not support a required capability, without which the 199 peering cannot proceed. It MUST NOT be used when a BGP speaker 200 receives a capability which it does not understand; such capabilities 201 MUST be ignored. 203 6. IANA Considerations 205 This document defines a Capability Optional Parameter along with a 206 Capability Code field. IANA maintains the registry for Capability 207 Code values. Capability Code value 0 is reserved. Capability Code 208 values 1 through 63 are to be assigned by IANA using the "IETF 209 Consensus" policy defined in [RFC5226]. Capability Code values 64 210 through 127 are to be assigned by IANA, using the "First Come First 211 Served" policy defined in [RFC5226]. Capability Code values 128 212 through 255 are for "Private Use" as defined in [RFC5226]. 214 7. Security Considerations 216 This extension to BGP does not change the underlying security issues 217 inherent in the existing BGP [RFC4272]. 219 8. Acknowledgements 221 The authors would like to thank members of the IDR Working Group and 222 the IESG and its Directorates for their review and comments. 224 9. References 225 9.1. Normative References 227 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 228 Requirement Levels", BCP 14, RFC 2119, March 1997. 230 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 231 Protocol 4 (BGP-4)", RFC 4271, January 2006. 233 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 234 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 235 May 2008. 237 9.2. Informative References 239 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", 240 RFC 4272, January 2006. 242 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 243 "Multiprotocol Extensions for BGP-4", RFC 4760, 244 January 2007. 246 Appendix A. Comparison with RFC 2842 248 In addition to several minor editorial changes, RFC 3392 also 249 clarified how to handle multiple instances of the same capability. 251 Appendix B. Comparison with RFC 3392 253 This document makes minor editorial changes and updated references, 254 clarifies the use of the Unsupported Optional Parameter NOTIFICATION 255 message, clarifies behavior when the Capabilities parameter is 256 included in the OPEN message multiple times, and clarifies 257 requirements by changing a number of SHOULDs to MUSTs. 259 Authors' Addresses 261 John G. Scudder 262 Juniper Networks 264 Email: jgs@juniper.net 265 Ravi Chandra 266 Sonoa Systems 268 Email: rchandra@sonoasystems.com