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Messages SHOULD advertise the BGP E...' RFC 2119 keyword, line 122: '... MAY send Extended Messages to a pee...' (14 more instances...) -- The draft header indicates that this document updates RFC4271, but the abstract doesn't seem to directly say this. It does mention RFC4271 though, so this could be OK. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year (Using the creation date from RFC4271, updated by this document, for RFC5378 checks: 2006-01-13) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. 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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Bush 3 Internet-Draft IIJ & Arrcus 4 Updates: 4271 (if approved) K. Patel 5 Intended status: Standards Track Arrcus, Inc. 6 Expires: January 3, 2020 D. Ward 7 Cisco Systems 8 July 2, 2019 10 Extended Message support for BGP 11 draft-ietf-idr-bgp-extended-messages-32 13 Abstract 15 The BGP specification mandates a maximum BGP message size of 4,096 16 octets. As BGP is extended to support newer AFI/SAFIs and other 17 features, there is a need to extend the maximum message size beyond 18 4,096 octets. This document updates the BGP specification RFC4271 by 19 extending the maximum message size from 4,096 octets to 65,535 octets 20 for all except the OPEN and KEEPALIVE messages. 22 Requirements Language 24 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 25 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 26 "OPTIONAL" in this document are to be interpreted as described in BCP 27 14 [RFC2119] [RFC8174] when, and only when, they appear in all 28 capitals, as shown here. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on January 3, 2020. 47 Copyright Notice 49 Copyright (c) 2019 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 2. BGP Extended Message . . . . . . . . . . . . . . . . . . . . 2 66 3. Extended Message Capability for BGP . . . . . . . . . . . . . 3 67 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 68 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 4 69 6. Changes to RFC4271 . . . . . . . . . . . . . . . . . . . . . 5 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 71 8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 72 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 73 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 74 10.1. Normative References . . . . . . . . . . . . . . . . . . 6 75 10.2. Informative References . . . . . . . . . . . . . . . . . 6 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 78 1. Introduction 80 The BGP specification [RFC4271] mandates a maximum BGP message size 81 of 4,096 octets. As BGP is extended to support newer AFI/SAFIs and 82 newer capabilities (e.g., BGPsec [RFC8205] and BGP-LS [RFC7752]), 83 there is a need to extend the maximum message size beyond 4,096 84 octets. This draft provides an extension to BGP to extend its 85 message size limit from 4,096 octets to 65,535 octets for all except 86 the OPEN and KEEPALIVE messages. 88 2. BGP Extended Message 90 A BGP message over 4,096 octets in length is a BGP Extended Message. 92 BGP Extended Messages have a maximum message size of 65,535 octets. 93 The smallest message that may be sent consists of a BGP KEEPALIVE 94 which consists of 19 octets. 96 3. Extended Message Capability for BGP 98 The BGP Extended Message Capability is a new BGP Capability [RFC5492] 99 defined with Capability code 6 and Capability length 0. 101 To advertise the BGP Extended Message Capability to a peer, a BGP 102 speaker uses BGP Capabilities Advertisement [RFC5492]. By 103 advertising the BGP Extended Message Capability to a peer, a BGP 104 speaker conveys that it is able to send, receive, and properly 105 handle, see Section 4, BGP Extended Messages. 107 A peer which does not advertise this capability MUST NOT send BGP 108 Extended Messages, and BGP Extended Messages MUST NOT be sent to it. 110 Peers that wish to use the BGP Extended Message capability MUST 111 support Error Handling for BGP UPDATE Messages per [RFC7606]. 113 4. Operation 115 The Extended Message Capability applies to all messages except for 116 the OPEN and KEEPALIVE messages. The former exception is to reduce 117 the complexity of providing a backward compatibility. 119 A BGP speaker that is capable of sending and receiving BGP Extended 120 Messages SHOULD advertise the BGP Extended Message Capability to its 121 peers using BGP Capabilities Advertisement [RFC5492]. A BGP speaker 122 MAY send Extended Messages to a peer only if the Extended Message 123 Capability was advertised by both peers. 125 An implementation that advertises the BGP Extended Message capability 126 MUST be capable of receiving a message with a Length up to and 127 including 65,535 octets. 129 Applications generating information which might be encapsulated 130 within BGP messages MUST limit the size of their payload to take the 131 maximum message size into account. 133 If a BGP message with a Length lgreater than 4,096 octets is received 134 by a BGP listener who has not advertised the Extended Message 135 Capability, the listener MUST treat this as a malformed message, and 136 MUST generate a NOTIFICATION with the Error Subcode set to Bad 137 Message Length (see [RFC4271] Sec 6.1). 139 A BGP announcement will (policy, best path, etc., allowing) propagate 140 throughout the BGP speaking Internet; and hence to BGP speakers which 141 may not have the Extended Message capability. Therefore, an 142 announcement in an Extended Message where the size of the attribute 143 set plus the NLRI can not be decomposed to 4,096 octets or less may 144 cause lack of reachability. 146 A BGP UPDATE will typically propagate throughout the BGP speaking 147 Internet; and hence to BGP speakers which may not support Extended 148 Messages. Therefore, a route announcement in an Extended Message 149 where the size of the attribute set plus the NLRI is larger than 150 4,096 octets or less may cause lack of reachability. 152 A BGP speaker with a mixture of peers some of which have advertised 153 the BGP Extended Message capability and some which have not, may 154 receive an UPDATE from one of its capable peers that produces an 155 ongoing announcement that is larger than 4,096 octets. When 156 propagating that UPDATE onward to a neighbor which has not advertised 157 the BGP Extended Message capability, the sender SHOULD try to reduce 158 the outgoing message size by removing attributes eligible under the 159 "attribute discard" approach of [RFC7606]. If the message is still 160 too big, then it MUST NOT be sent to the neighbor ([RFC4271], 161 Section 9.2). Additionally, if the NLRI was previously advertised to 162 that peer, it SHOULD be withdrawn from service ([RFC4271], 163 Section 9.1.3). 165 In an iBGP mesh, if BGP Extended Messages are to be advertized, all 166 peers MUST advertize the BGP Extended Message Capability and 167 [RFC7606]. This is not only for consistent internal routing, but 168 also to give a consistent view to eBGP peers. 170 During the incremental deployment of BGP Extended Messages and 171 [RFC7606] in an iBGP mesh, or with eBGP peers, the operator should 172 monitor any routes dropped as "treat-as-withdraw" and any discarded 173 attributes. 175 It is RECOMMENDED that BGP protocol developers and implementers are 176 conservative in their application and use of Extended Messages. 177 Future protocol specifications MUST describe how to handle peers 178 which can only accommodate 4,096 octet messages. 180 5. Error Handling 182 A BGP speaker that has the ability to use Extended Messages but has 183 not advertised the BGP Extended Messages capability, presumably due 184 to configuration, MUST NOT accept an Extended Message. A speaker 185 MUST NOT implement a more liberal policy accepting BGP Extended 186 Messages. 188 A BGP speaker that does not advertise the BGP Extended Messages 189 capability might also genuinely not support Extended Messages. Such 190 a speaker will follow the error handling procedures of [RFC4271] if 191 it receives an Extended Message. Similarly, any speaker that treats 192 an improper Extended Message as a fatal error, MUST follow the error 193 handling procedures of [RFC4271]. 195 6. Changes to RFC4271 197 [RFC4271] states "The value of the Length field MUST always be at 198 least 19 and no greater than 4,096." This document changes the 199 latter number to 65,535 for all except the OPEN and KEEPALIVE 200 messages. 202 [RFC4271] Sec 6.1, specifies raising an error if the length of a 203 message is over 4,096 octets. For all messages except the OPEN 204 message, if the receiver has advertised the BGP Extended Messages 205 Capability, this document raises that limit to 65,535. 207 7. IANA Considerations 209 The IANA has made an early allocation for this new BGP Extended 210 Message Capability referring to this document. 212 Registry: Capability Codes 214 Value Description Document 215 ----- ----------------------------------- ------------- 216 6 BGP Extended Message [this draft] 218 8. Security Considerations 220 This extension to BGP does not change BGP's underlying security 221 issues; [RFC4272]. 223 Due to increased memory requirements for buffering, there may be 224 increased exposure to resource exhaustion, intentional or 225 unintentional. 227 As this draft requires support for [RFC7606] UPDATE error handling, 228 it inherits the security considerations of [RFC7606]. 230 If a remote attacker is able to craft a large BGP Extended Message to 231 send on a path where one or more peers do not support BGP Extended 232 Messages, peers which support BGP Extended Messages may act to reduce 233 the outgoing message, see Section 4, and in doing so cause a 234 downgrade attack. 236 If a remote attacker is able to craft a large BGP Extended Message to 237 send on a path where one or more peers do not support BGP Extended 238 Messages, peers which support BGP Extended Messages may incur 239 resource load (processing, message resizing, etc.) reformatting the 240 large messages. Worse, [RFC7606] "treat-as-withdraw" may 241 consistently withdraw announcements causing inconsistent routing. 243 9. Acknowledgments 245 The authors thank Alvaro Retana for an amazing review, Enke Chen, 246 Susan Hares, John Scudder, John Levine, and Job Snijders for their 247 input; and Oliver Borchert and Kyehwan Lee for their implementations 248 and testing. 250 10. References 252 10.1. Normative References 254 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 255 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 256 DOI 10.17487/RFC4271, January 2006, 257 . 259 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", 260 RFC 4272, DOI 10.17487/RFC4272, January 2006, 261 . 263 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 264 with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 265 2009, . 267 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 268 Patel, "Revised Error Handling for BGP UPDATE Messages", 269 RFC 7606, DOI 10.17487/RFC7606, August 2015, 270 . 272 10.2. Informative References 274 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 275 S. Ray, "North-Bound Distribution of Link-State and 276 Traffic Engineering (TE) Information Using BGP", RFC 7752, 277 DOI 10.17487/RFC7752, March 2016, 278 . 280 [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol 281 Specification", RFC 8205, DOI 10.17487/RFC8205, September 282 2017, . 284 Authors' Addresses 286 Randy Bush 287 IIJ & Arrcus 288 5147 Crystal Springs 289 Bainbridge Island, Washington 98110 290 US 292 Email: randy@psg.com 294 Keyur Patel 295 Arrcus, Inc. 297 Email: keyur@arrcus.com 299 Dave Ward 300 Cisco Systems 301 170 W. Tasman Drive 302 San Jose, CA 95134 303 US 305 Email: dward@cisco.com