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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: April 9, 2012 U.S. NIST 6 October 07, 2011 8 Recommendation for Not Using AS_SET and AS_CONFED_SET in BGP 9 draft-ietf-idr-deprecate-as-sets-06 11 Abstract 13 This document recommends against the use of the AS_SET and 14 AS_CONFED_SET types of the AS_PATH in BGPv4. This is done to 15 simplify the design and implementation of the BGP protocol and to 16 make the semantics of the originator of a route more clear. This 17 will also simplify the design, implementation and deployment of 18 ongoing work in the Secure 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 April 9, 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 . . . . . . . . . . . . . . . . . . . . . 4 56 3. Recommendation to Network Operators . . . . . . . . . . . . . . 4 57 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 58 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 59 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 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 77 route. Said aggregation can therefore cause operational issues such 78 as not being able to authenticate a route origin for the aggregate 79 prefix in new BGP security technologies (such as those that take 80 advantage of the "X.509 Extensions for IP Addresses and AS 81 Identifiers" [RFC3779]). This in turn would result in reachability 82 problems for aggregated prefix and its components (i.e., more 83 specifics). Said aggregation also creates traffic engineering issues 84 because the precise path information for the component prefixes is 85 not preserved. 87 From analysis of past Internet routing data it is apparent that 88 aggregation that involves AS_SETs is very seldom used in practice on 89 the public network [analysis] and, when it is used, it is usually 90 used incorrectly -- reserved AS numbers ([RFC1930]) and / or only a 91 single AS in the AS_SET are by far the most common case. Because the 92 aggregation involving AS_SETs is very rarely used, the reduction in 93 table size provided by said aggregation is extremely small, and any 94 advantage thereof is outweighed by additional complexity in the BGP 95 protocol. As noted above, said aggregation also poses impediments to 96 implementation of said new BGP security technologies. 98 In the past, AS_SET had been used in a few rare cases to allow route 99 aggregation where two or more providers could form the same prefix, 100 using the exact match of the other's prefix in some advertisement and 101 configuring the aggregation differently elsewhere. The key to 102 configuring this correctly was to form the aggregate at the border in 103 the outbound BGP policy and omit prefixes from the AS that the 104 aggregate was being advertised to. The AS_SET therefore allowed this 105 practice without the loss of BGP's AS_PATH loop protection. This use 106 of AS_SET served a purpose which fell in line with the original 107 intended use. Without use of AS_SET, aggregates must always contain 108 only less specific prefixes (not less than or equal to), and must 109 never aggregate an exact match. 111 2. Requirements notation 113 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 114 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 115 document are to be interpreted as described in [RFC2119]. 117 3. Recommendation to Network Operators 119 It is RECOMMENDED that operators not generate any new announcements 120 containing AS_SETs or AS_CONFED_SETs. If they have already announced 121 routes with AS_SETs or AS_CONFED_SETs in them, then they SHOULD 122 withdraw those routes and re-announce routes for the component 123 prefixes (i.e., the more specifics of the previously aggregated 124 prefix) without AS_SETs in the updates. This involves undoing the 125 aggregation that was previously performed (with AS_SETs), and 126 announcing more specifics (without AS_SETs). Route aggregation that 127 was previously performed by proxy aggregation (i.e., without the use 128 of AS_SETs) is still possible under some conditions. As with any 129 change, the operator should understand the full implications of the 130 change. 132 It is worth noting that new technologies (such as those that take 133 advantage of the "X.509 Extensions for IP Addresses and AS 134 Identifiers" [RFC3779]) might not support routes with AS_SETs / 135 AS_CONFED_SETs in them, and may treat as infeasible routes containing 136 them. Future BGP implementations may also do the same. It is 137 expected that, even before the deployment of these new or future 138 technologies, operators may filter routes with AS_SETs / 139 AS_CONFED_SETs in them. Other than making that observation, this 140 document is not intended to make any recommendation for how an 141 operator should behave when receiving a route with AS_SET or 142 AS_CONFED_SET in it. This document's focus is entirely on the sender 143 side as discussed in the preceding paragraph. 145 4. IANA Considerations 147 This document requires no IANA actions. 149 5. Security Considerations 151 This document discourages the use of aggregation techniques that 152 create AS_SETs. Future work may update the protocol to remove 153 support for the AS_SET path segment type of the AS_PATH attribute. 154 This will remove complexity and code that is not exercised very 155 often, which decreases the attack surface. This will also simplify 156 the design and implementation of the RPKI and systems that will rely 157 on it. 159 6. Acknowledgements 161 The authors would like to thank Tony Li, Randy Bush, John Scudder, 162 Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, Ilya 163 Varlashkin as well as Douglas Montgomery, Enke Chen, Florian Weimer, 164 Jakob Heitz, John Leslie, Keyur Patel, Paul Jakma, Rob Austein, Russ 165 Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett, 166 Alfred Hones, Alvaro Retana, everyone in IDR and everyone else who 167 provided input 169 Apologies to those who we may have missed, it was not intentional. 171 7. Informative References 173 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 174 selection, and registration of an Autonomous System (AS)", 175 BCP 6, RFC 1930, March 1996. 177 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 178 Requirement Levels", BCP 14, RFC 2119, March 1997. 180 [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP 181 Addresses and AS Identifiers", RFC 3779, June 2004. 183 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 184 Protocol 4 (BGP-4)", RFC 4271, January 2006. 186 [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous 187 System Confederations for BGP", RFC 5065, August 2007. 189 [analysis] 190 Sriram, K., "Measurement Data on AS_SET and AGGREGATOR, 191 SIDR WG presentation, IETF-78", July 2010, < http:// 192 www.antd.nist.gov/~ksriram/AS_SET_Aggregator_Stats.pdf>. 194 Authors' Addresses 196 Warren Kumari 197 Google, Inc. 198 1600 Amphitheatre Parkway 199 Mountain View, CA 94043 200 US 202 Phone: +1 571 748 4373 203 Email: warren@kumari.net 205 Kotikalapudi Sriram 206 U.S. NIST 207 100 Bureau Drive 208 Gaithersburg, MD 20899 209 US 211 Phone: +1 301 975 3973 212 Email: ksriram@nist.gov