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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group W. Kumari 3 Internet-Draft Google, Inc. 4 Obsoletes: 6472 (if approved) K. Sriram 5 Updates: 4271 5065 (if approved) L. Hannachi 6 Intended status: Standards Track USA NIST 7 Expires: May 6, 2020 November 3, 2019 9 Deprecation of AS_SET and AS_CONFED_SET in BGP 10 draft-ietf-idr-deprecate-as-set-confed-set-02 12 Abstract 14 BCP 172 (i.e., RFC 6472) recommends not using AS_SET and 15 AS_CONFED_SET in the Border Gateway Protocol. This document advances 16 this recommendation to a standards requirement in BGP; it proscribes 17 the use of the AS_SET and AS_CONFED_SET types of path segments in the 18 AS_PATH. This is done to simplify the design and implementation of 19 BGP and to make the semantics of the originator of a route clearer. 20 This will also simplify the design, implementation, and deployment of 21 various BGP security mechanisms. This document (if approved) updates 22 RFC 4271 and RFC 5065 by eliminating AS_SET and AS_CONFED_SET types, 23 and obsoletes RFC 6472. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on May 6, 2020. 42 Copyright Notice 44 Copyright (c) 2019 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 61 3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3 62 4. Updates to Existing RFCs . . . . . . . . . . . . . . . . . . 4 63 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 64 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 65 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 66 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 67 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 68 8.2. Informative References . . . . . . . . . . . . . . . . . 5 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 71 1. Introduction 73 BCP 172 [RFC6472] makes a recommendation for not using AS_SET (see 74 [RFC4271]) and AS_CONFED_SET (see [RFC5065]) in the Border Gateway 75 Protocol (BGP). This document advances the BCP recommendation to a 76 standards requirement in BGP; it proscribes the use of the AS_SET and 77 AS_CONFED_SET types of path segments in the AS_PATH. 79 The AS_SET path segment in the AS_PATH attribute (Sections 4.3 and 80 5.1.2 of [RFC4271]) is created by a router that is performing route 81 aggregation and contains an unordered set of Autonomous Systems 82 (ASes) that the update has traversed. The AS_CONFED_SET path segment 83 (see [RFC5065]) in the AS_PATH attribute is created by a router that 84 is performing route aggregation and contains an unordered set of 85 Member AS Numbers in the local confederation that the update has 86 traversed. It is very similar to AS_SETs but is used within a 87 confederation. 89 By performing aggregation, a router is combining multiple existing 90 routes into a single new route. The aggregation together with the 91 use of AS_SET blurs the semantics of origin AS for the prefix being 92 announced. Therefore, the aggregation with AS_SET (or AS_CONFED_SET) 93 can cause operational issues, such as not being able to authenticate 94 a route origin for the aggregate prefix in new BGP security 95 technologies such as those that take advantage of X.509 extensions 96 for IP addresses and AS identifiers [RFC3779] [RFC6480] [RFC6811] 98 [RFC8205]. This in turn could result in reachability problems for 99 the aggregated prefix and its components (i.e., more-specific 100 prefixes). The aggregation as described above could also create 101 traffic engineering issues, because the precise path information for 102 the component prefixes are not preserved. 104 From analysis of past Internet routing data, it is apparent that 105 aggregation that involves AS_SETs is very seldom used in practice on 106 the public Internet [Analysis] and when it is used, it is often used 107 incorrectly -- only a single AS in the AS_SET are by far the most 108 common cases. Also, very often the same AS appears in the 109 AS_SEQUENCE and the AS_SET in the BGP update. The occurrence of 110 reserved AS numbers ([IANA-SP-ASN]) is also somewhat frequent. 111 Because the aggregation involving AS_SETs is very rarely used, the 112 reduction in table size provided by this is extremely small, and any 113 advantage thereof is outweighed by additional complexity in BGP. As 114 noted above, AS_SETs also pose impediments to implementation of new 115 BGP security technologies. 117 2. Requirements Language 119 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 120 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 121 "OPTIONAL" in this document are to be interpreted as described in BCP 122 14 [RFC2119] [RFC8174] when, and only when, they appear in all 123 capitals, as shown here. 125 3. Recommendations 127 BGP speakers conforming to this document (i.e., conformant BGP 128 speakers) MUST NOT locally generate BGP UPDATE messages containing 129 AS_SET or AS_CONFED_SET. Conformant BGP speakers SHOULD NOT send BGP 130 UPDATE messages containing AS_SET or AS_CONFED_SET. Upon receipt of 131 such messages, conformant BGP speakers SHOULD use the "Treat-as- 132 withdraw" error handling behavior as per [RFC7606]. 134 If a network operator wishes to consider BGP UPDATE messages with 135 AS_SET or AS_CONFED_SET (received from an external peer) for path 136 selection, they MAY have a feature (knob) in their BGP speaker to opt 137 to do so on a per peer basis. The operator should understand the 138 full implications of choosing this option. There is no knob 139 concerning locally generated BGP UPDATE messages, i.e., as stated 140 before a conformant BGP speaker must not locally generate BGP UPDATE 141 messages with AS_SET or AS_CONFED_SET. 143 Network operators MUST NOT locally generate any new announcements 144 containing AS_SET or AS_CONFED_SET. If they have announced routes 145 with AS_SET or AS_CONFED_SET in them, then they SHOULD withdraw those 146 routes and re-announce routes for the aggregate or component prefixes 147 (i.e., the more-specific routes subsumed by the previously aggregated 148 route) without AS_SET or AS_CONFED_SET in the updates. 150 It is worth noting that new BGP security technologies (such as those 151 that take advantage of X.509 extensions for IP addresses and AS 152 identifiers [RFC3779] [RFC6480] [RFC6811] [RFC8205]) might not 153 support routes with AS_SET or AS_CONFED_SET in them, and may treat 154 routes containing them as infeasible even before the updated BGP in 155 this document is implemented. 157 4. Updates to Existing RFCs 159 This document deprecates the AS_SET (type 1) AS_PATH segment type 160 from [RFC4271]. BGP speakers conforming to this document (i.e., 161 conformant BGP speakers) MUST NOT locally generate BGP UPDATE 162 messages containing AS_SET. Conformant BGP speakers SHOULD NOT send 163 BGP UPDATE messages containing AS_SET. Upon receipt of such 164 messages, conformant BGP speakers SHOULD use the "Treat-as-withdraw" 165 error handling behavior as per [RFC7606]. 167 This document deprecates the AS_CONFED_SET (type 4) AS_PATH segment 168 type from [RFC5065]. Conformant BGP speakers MUST NOT locally 169 generate BGP UPDATE messages containing AS_CONFED_SET. Conformant 170 BGP speakers SHOULD NOT send BGP UPDATE messages containing 171 AS_CONFED_SET. Upon receipt of such messages, conformant BGP 172 speakers SHOULD use the "Treat-as-withdraw" error handling behavior 173 as per [RFC7606]. 175 Wherever mentions of AS_SET or AS_CONFED_SET occur in [RFC4271] and 176 [RFC5065], appropriate modification or elimination of the text must 177 be made in future RFCs that would replace these RFCs, consistent with 178 the deprecation of AS_SET and AS_CONFED_SET. 180 5. Security Considerations 182 This document obsoletes the use of aggregation techniques that create 183 AS_SETs or AS_CONFED_SETs. Obsoleting these path segment types from 184 BGP and removal of the related code from implementations would 185 potentially decrease the attack surface for BGP. Deployments of new 186 BGP security technologies [RFC6480] [RFC6811] [RFC8205] benefit 187 greatly if AS_SET and AS_CONFED_SET are not used in BGP. 189 6. IANA Considerations 191 This document requires no IANA actions. 193 7. Acknowledgements 195 The authors would like to thank Jeffery Haas, John Heasley, Job 196 Snijders, Jared Mauch, Jakob Heitz, Keyur Patel, Douglas Montgomery, 197 Randy Bush, Susan Hares, John Scudder, Curtis Villamizar, Danny 198 McPherson, Chris Morrow, Tom Petch, Ilya Varlashkin, Enke Chen, Tony 199 Li, Florian Weimer, John Leslie, Paul Jakma, Rob Austein, Russ 200 Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett, 201 Alfred Hoenes, and Alvaro Retana for comments and suggestions. 203 8. References 205 8.1. Normative References 207 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 208 Requirement Levels", BCP 14, RFC 2119, 209 DOI 10.17487/RFC2119, March 1997, 210 . 212 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 213 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 214 DOI 10.17487/RFC4271, January 2006, 215 . 217 [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous 218 System Confederations for BGP", RFC 5065, 219 DOI 10.17487/RFC5065, August 2007, 220 . 222 8.2. Informative References 224 [Analysis] 225 Hannachi, L. and K. Sriram, "Detailed analysis of AS_SETs 226 in BGP updates", NIST Robust Inter-domain Routing Project 227 Website , October 2019, 228 . 231 [IANA-SP-ASN] 232 "Special-Purpose Autonomous System (AS) Numbers", 233 . 236 [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP 237 Addresses and AS Identifiers", RFC 3779, 238 DOI 10.17487/RFC3779, June 2004, 239 . 241 [RFC6472] Kumari, W. and K. Sriram, "Recommendation for Not Using 242 AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472, 243 DOI 10.17487/RFC6472, December 2011, 244 . 246 [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support 247 Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480, 248 February 2012, . 250 [RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R. 251 Austein, "BGP Prefix Origin Validation", RFC 6811, 252 DOI 10.17487/RFC6811, January 2013, 253 . 255 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 256 Patel, "Revised Error Handling for BGP UPDATE Messages", 257 RFC 7606, DOI 10.17487/RFC7606, August 2015, 258 . 260 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 261 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 262 May 2017, . 264 [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol 265 Specification", RFC 8205, DOI 10.17487/RFC8205, September 266 2017, . 268 Authors' Addresses 270 Warren Kumari 271 Google, Inc. 272 1600 Amphitheatre Parkway 273 Mountain View, CA 94043 274 US 276 Phone: +1 571 748 4373 277 Email: warren@kumari.net 279 Kotikalapudi Sriram 280 USA NIST 281 100 Bureau Drive 282 Gaithersburg, MD 20899 283 US 285 Phone: +1 301 975 3973 286 Email: sriram.ietf@gmail.com 287 Lilia Hannachi 288 USA NIST 289 100 Bureau Drive 290 Gaithersburg, MD 20899 291 US 293 Phone: +1 301 975 3259 294 Email: lilia.hannachi@nist.gov