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Chandra 5 Intended status: Standards Track Sonoa Systems 6 Expires: July 10, 2009 January 6, 2009 8 Capabilities Advertisement with BGP-4 9 draft-ietf-idr-rfc3392bis-04.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 10, 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 2. Requirements Language 63 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 64 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 65 document are to be interpreted as described in RFC 2119 [RFC2119]. 67 3. Overview of Operations 69 When a BGP speaker [RFC4271] that supports capabilities advertisement 70 sends an OPEN message to its BGP peer, the message MAY include an 71 Optional Parameter, called Capabilities. The parameter lists the 72 capabilities supported by the speaker. 74 A BGP speaker determines the capabilities supported by its peer by 75 examining the list of capabilities present in the Capabilities 76 Optional Parameter carried by the OPEN message that the speaker 77 receives from the peer. 79 A BGP speaker that supports a particular capability may use this 80 capability with its peer after the speaker determines (as described 81 above) that the peer supports this capability. Simply put, a given 82 capability can be used on a peering if that capability has been 83 advertised by both peers. If either peer has not advertised it, the 84 capability cannot be used. 86 A BGP speaker determines that its peer doesn't support capabilities 87 advertisement, if in response to an OPEN message that carries the 88 Capabilities Optional Parameter, the speaker receives a NOTIFICATION 89 message with the Error Subcode set to Unsupported Optional Parameter. 90 (This is a consequence of the base BGP-4 specification [RFC4271] and 91 not a new requirement.) In this case the speaker SHOULD attempt to 92 re-establish a BGP connection with the peer without sending to the 93 peer the Capabilities Optional Parameter. 95 If a BGP speaker that supports a certain capability requires that 96 this capability be used on a peering but determines that its peer 97 doesn't support this capability, the speaker MAY send a NOTIFICATION 98 message to the peer and terminate peering (see Section "Extensions to 99 Error Handling" for more details). The Error Subcode in the message 100 is set to Unsupported Capability. The message SHOULD contain the 101 capability (capabilities) that causes the speaker to send the 102 message. The decision to send the message and terminate the peering 103 is local to the speaker. If terminated, such peering SHOULD NOT be 104 re-established automatically. An example of when this procedure 105 might be followed is if a BGP speaker is attempting to establish an 106 IPv6 peering but determines that its peer does not support 107 Multiprotocol Extensions for BGP-4 [RFC4760]. 109 If a BGP speaker receives from its peer a capability which it does 110 not itself support or recognize, it MUST ignore that capability. In 111 particular, the Unsupported Capability NOTIFICATION message MUST NOT 112 be generated in response to reception of a capability which is not 113 supported by the local speaker. 115 4. Capabilities Optional Parameter (Parameter Type 2): 117 This is an Optional Parameter that is used by a BGP speaker to convey 118 to its BGP peer the list of capabilities supported by the speaker. 119 The encoding of BGP Optional Parameters is specified in Section 4.2 120 of [RFC4271]. The parameter type of the Capabilities Optional 121 Parameter is 2. 123 The parameter contains one or more triples , where each triple is encoded as 125 shown below: 127 +------------------------------+ 128 | Capability Code (1 octet) | 129 +------------------------------+ 130 | Capability Length (1 octet) | 131 +------------------------------+ 132 | Capability Value (variable) | 133 ~ ~ 134 +------------------------------+ 136 The use and meaning of these fields are as follows: 138 Capability Code: 140 Capability Code is a one octet unsigned binary integer that 141 unambiguously identifies individual capabilities. 143 Capability Length: 145 Capability Length is a one octet unsigned binary integer that 146 contains the length of the Capability Value field in octets. 148 Capability Value: 150 Capability Value is a variable length field that is interpreted 151 according to the value of the Capability Code field. 153 BGP speakers SHOULD NOT include more than one instance of a 154 capability with the same Capability Code, Capability Length, and 155 Capability Value. Note however, that processing of multiple 156 instances of such capability does not require special handling, as 157 additional instances do not change the meaning of the announced 158 capability. 160 BGP speakers MAY include more than one instance of a capability (as 161 identified by the Capability Code) with non-zero Capability Length 162 field, but with different Capability Value, and either the same or 163 different Capability Length. Processing of these capability 164 instances is specific to the Capability Code and MUST be described in 165 the document introducing the new capability. 167 The Capabilities Optional Parameter (OPEN Optional Parameter Type 2) 168 SHOULD only be included in the OPEN message once. If the BGP speaker 169 wishes to include multiple capabilities in the OPEN message, it 170 SHOULD do so as discussed above, by listing all those capabilities as 171 TLVs within a single Capabilities Optional Parameter. However, for 172 backward compatibility a BGP speaker MUST be prepared to receive an 173 OPEN message which contains multiple Capabilities Optional 174 Parameters, each of which contains one or more capabilities TLVs. 175 The set of capabilities should be processed in the same way in either 176 case, whether it is enumerated within a single Capabilities Optional 177 Parameter of the OPEN message, or split across multiple. 179 5. Extensions to Error Handling 181 This document defines a new Error Subcode, Unsupported Capability. 182 The value of this Subcode is 7. The Data field in the NOTIFICATION 183 message SHOULD list the set of capabilities that cause the speaker to 184 send the message. Each such capability is encoded in the same way as 185 it would be encoded in the OPEN message. 187 As explained in the Overview of Operations section, the Unsupported 188 Capability NOTIFICATION is a way for a BGP speaker to complain that 189 its peer does not support a required capability, without which the 190 peering cannot proceed. It MUST NOT be used when a BGP speaker 191 receives a capability which it does not understand; such capabilities 192 SHOULD be ignored. 194 6. IANA Considerations 196 This document defines a Capability Optional Parameter along with a 197 Capability Code field. IANA maintains the registry for Capability 198 Code values. Capability Code value 0 is reserved. Capability Code 199 values 1 through 63 are to be assigned by IANA using the "IETF 200 Consensus" policy defined in [RFC5226]. Capability Code values 64 201 through 127 are to be assigned by IANA, using the "First Come First 202 Served" policy defined in [RFC5226]. Capability Code values 128 203 through 255 are for "Private Use" as defined in [RFC5226]. 205 7. Security Considerations 207 This extension to BGP does not change the underlying security issues 208 inherent in the existing BGP [RFC4272]. 210 8. Acknowledgements 212 The authors would like to thank members of the IDR Working Group for 213 their review and comments. 215 9. References 217 9.1. Normative References 219 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 220 Requirement Levels", BCP 14, RFC 2119, March 1997. 222 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 223 Protocol 4 (BGP-4)", RFC 4271, January 2006. 225 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 226 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 227 May 2008. 229 9.2. Informative References 231 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", 232 RFC 4272, January 2006. 234 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 235 "Multiprotocol Extensions for BGP-4", RFC 4760, 236 January 2007. 238 Appendix A. Comparison with RFC 2842 240 In addition to several minor editorial changes, RFC 3392 also 241 clarified how to handle multiple instances of the same capability. 243 Appendix B. Comparison with RFC 3392 245 In addition to minor editorial changes and updated references, this 246 document also clarifies the use of the Unsupported Optional Parameter 247 NOTIFICATION message and clarifies behavior when the Capabilities 248 parameter is included in the OPEN message multiple times. 250 Authors' Addresses 252 John G. Scudder 253 Juniper Networks 255 Email: jgs@juniper.net 257 Ravi Chandra 258 Sonoa Systems 260 Email: rchandra@sonoasystems.com