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Checking references for intended status: Best Current Practice ---------------------------------------------------------------------------- (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 (==), 1 comment (--). 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 Intended status: BCP K. Sriram 5 Expires: January 28, 2012 U.S. NIST 6 July 27, 2011 8 Deprecation of the use of BGP AS_SET, AS_CONFED_SET. 9 draft-ietf-idr-deprecate-as-sets-05 11 Abstract 13 This document deprecates the use of the AS_SET and AS_CONFED_SET 14 types of the AS_PATH in BGPv4. This is done to simplify the design 15 and implementation of the BGP protocol and to make the semantics of 16 the originator of a route more clear. This will also simplify the 17 design, implementation and deployment of ongoing work in the Secure 18 Inter-Domain Routing Working Group. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on January 28, 2012. 37 Copyright Notice 39 Copyright (c) 2011 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3 56 3. Recommendation to Network Operators . . . . . . . . . . . . . . 4 57 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 58 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 59 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 60 7. Informative References . . . . . . . . . . . . . . . . . . . . 5 61 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 63 1. Introduction 65 The AS_SET path segment type of the AS_PATH attribute ([RFC4271], 66 Section 4.3) is created by a router that is performing route 67 aggregation and contains an unordered set of ASs that the update has 68 traversed. The AS_CONFED_SET path type ([RFC5065]) of the AS_PATH 69 attribute is created by a router that is performing route aggregation 70 and contains an unordered set of Member AS Numbers in the local 71 confederation that the update has traversed. It is very similar to 72 AS_SETs but is used within a confederation. 74 By performing aggregation, a router is, in essence, combining 75 multiple existing routes into a single new route. This type of 76 aggregation blurs the semantics of what it means to originate a route 77 which can cause operational issues that include reachability problems 78 and traffic engineering issues. 80 From analysis of past Internet routing data it is apparent that 81 aggregation that involves AS_SETs is very seldom used in practice on 82 the public network [analysis] and, when it is used, it is usually 83 used incorrectly -- reserved AS numbers ([RFC1930]) and / or only a 84 single AS in the AS_SET are by far the most common case. The 85 reduction in table size provided by the aggregation is outweighed by 86 additional complexity in the BGP protocol and confusion regarding 87 what exactly is meant by originating a route. 89 In the past AS_SET had been used in a few rare cases to allow route 90 aggregation where two or more providers could form the same prefix, 91 using the exact match of the others prefix in some advertisement and 92 configuring the aggregation differently elsewhere. The key to 93 configuring this correctly was to form the aggregate at the border in 94 the outbound BGP policy and omit prefixes from the AS that the 95 aggregate was being advertised to. The AS_SET therefore allowed this 96 practice without the loss of BGP's AS_PATH loop protection. This use 97 of AS_SET served a purpose which fell in line with the original 98 intended use. 100 Without AS_SET aggregates must always contain only less specific 101 prefixes (not less than or equal to), and must never aggregate an 102 exact match. Since this practice is thought to no longer be widely 103 used, it is thought to be safe to deprecate the use of AS_SET. 105 2. Requirements notation 107 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 108 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 109 document are to be interpreted as described in [RFC2119]. 111 3. Recommendation to Network Operators 113 Operators are strongly advised to not generate any new announcements 114 containing AS_SETs or AS_CONFED_SETs. If they have already announced 115 routes with AS_SETs or AS_CONFED_SETs in them, then they should 116 withdraw and re-announce those prefixes without AS_SETs in the 117 updates. This may require undoing the aggregation that was 118 previously performed, and announcing more specifics. Route 119 aggregation that was previously performed by proxy aggregation is 120 still possible under some conditions without the use of AS_SETs. As 121 with any change, the operator should understand the full implications 122 of the change. 124 It is worth noting that new technologies (such as those that take 125 advantage of the "X.509 Extensions for IP Addresses and AS 126 Identifiers" ([RFC3779]) may not support routes with AS_SETs / 127 AS_CONFED_SETs in them, and MAY treat as infeasible routes containing 128 them. Future BGP implementations may also do the same. 130 It is expected that, even before the deployment of these 131 technologies, operators may begin filtering routes that contain 132 AS_SETs or AS_CONFED_SETs. 134 4. IANA Considerations 136 This document requires no IANA actions. 138 5. Security Considerations 140 This document discourages the use of aggregation techniques that 141 create AS_SETs. Future work may update the protocol to remove 142 support for the AS_SET path segment type of the AS_PATH attribute. 143 This will remove complexity and code that is not exercised very 144 often, which decreases the attack surface. This will also simplify 145 the design and implementation of the RPKI and systems that will rely 146 on it. 148 6. Acknowledgements 150 The authors would like to thank Tony Li, Randy Bush, John Scudder, 151 Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, Ilya 152 Varlashkin as well as Douglas Montgomery, Enke Chen, Florian Weimer, 153 Jakob Heitz, John Leslie, Keyur Patel, Paul Jakma, Rob Austein, Russ 154 Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett, 155 Alfred Hones, Alvaro Retana, everyone in IDR and everyone else who 156 provided input 158 Apologies to those who we may have missed, it was not intentional. 160 7. Informative References 162 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 163 selection, and registration of an Autonomous System (AS)", 164 BCP 6, RFC 1930, March 1996. 166 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 167 Requirement Levels", BCP 14, RFC 2119, March 1997. 169 [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP 170 Addresses and AS Identifiers", RFC 3779, June 2004. 172 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 173 Protocol 4 (BGP-4)", RFC 4271, January 2006. 175 [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous 176 System Confederations for BGP", RFC 5065, August 2007. 178 [analysis] 179 Sriram, K., "Measurement Data on AS_SET and AGGREGATOR, 180 SIDR WG presentation, IETF-78", July 2010, < http:// 181 www.antd.nist.gov/~ksriram/AS_SET_Aggregator_Stats.pdf>. 183 Authors' Addresses 185 Warren Kumari 186 Google, Inc. 187 1600 Amphitheatre Parkway 188 Mountain View, CA 94043 189 US 191 Phone: +1 571 748 4373 192 Email: warren@kumari.net 193 Kotikalapudi Sriram 194 U.S. NIST 195 100 Bureau Drive 196 Gaithersburg, MD 20899 197 US 199 Phone: +1 301 975 3973 200 Email: ksriram@nist.gov