Internet Engineering Task Force (IETF)                         W. Kumari
Request for Comments: 6472                                  Google, Inc.
BCP: 172                                                       K. Sriram
Category: Best Current Practice                                U.S. NIST
ISSN: 2070-1721                                            December 2011
      Recommendation for Not Using AS_SET and AS_CONFED_SET in BGP



This document recommends against the use of the AS_SET and AS_CONFED_SET types of the AS_PATH in BGPv4. This is done to simplify the design and implementation of BGP and to make the semantics of the originator of a route more clear. This will also simplify the design, implementation, and deployment of ongoing work in the Secure Inter-Domain Routing Working Group.


Status of This Memo


This memo documents an Internet Best Current Practice.


This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 5741.

このドキュメントはインターネットエンジニアリングタスクフォース(IETF)の製品です。これは、IETFコミュニティの総意を表しています。これは、公開レビューを受けており、インターネットエンジニアリング運営グループ(IESG)によって公表のために承認されています。 BCPの詳細については、RFC 5741のセクション2で利用可能です。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

著作権(C)2011 IETF信託とドキュメントの作成者として特定の人物。全著作権所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

この文書では、BCP 78と、この文書の発行日に有効なIETFドキュメント(に関連IETFトラストの法律の規定に従うものとします。彼らは、この文書に関してあなたの権利と制限を説明するように、慎重にこれらの文書を確認してください。コードコンポーネントは、トラスト法規定のセクションで説明4.eおよび簡体BSDライセンスで説明したように、保証なしで提供されているよう簡体BSDライセンスのテキストを含める必要があり、この文書から抽出されました。

Table of Contents


   1. Introduction ....................................................2
   2. Requirements Notation ...........................................3
   3. Recommendation to Network Operators .............................3
   4. Security Considerations .........................................4
   5. Acknowledgements ................................................4
   6. References ......................................................4
      6.1. Normative References .......................................4
      6.2. Informative References .....................................4
1. Introduction
1. はじめに

The AS_SET path segment type of the AS_PATH attribute (Sections 4.3 and 5.1.2 of [RFC4271]) is created by a router that is performing route aggregation and contains an unordered set of Autonomous Systems (ASes) that the update has traversed. The AS_CONFED_SET path type ([RFC5065]) of the AS_PATH attribute is created by a router that is performing route aggregation and contains an unordered set of Member AS Numbers in the local confederation that the update has traversed. It is very similar to AS_SETs but is used within a confederation.

AS_PATH属性(セクション4.3と[RFC4271]の5.1.2)のAS_SET経路セグメントタイプは、ルート集約を行い、更新が通過したことを自律システム(のAS)の順不同のセットが含まれているルータによって作成されます。 AS_PATH属性のAS_CONFED_SETパスタイプは、([RFC5065])ルート集約を行い、更新が横断したローカル連合内の数字等の部材の順不同のセットが含まれているルータによって作成されます。それはAS_SETsに非常に似ているが、連合内で使用されます。

By performing aggregation, a router is, in essence, combining multiple existing routes into a single new route. This type of aggregation blurs the semantics of what it means to originate a route. Said aggregation can therefore cause operational issues, such as not being able to authenticate a route origin for the aggregate prefix in new BGP security technologies (such as those that take advantage of the "X.509 Extensions for IP Addresses and AS Identifiers" [RFC3779]). This in turn would result in reachability problems for the aggregated prefix and its components (i.e., more specifics). Said aggregation also creates traffic engineering issues, because the precise path information for the component prefixes is not preserved.


From analysis of past Internet routing data, it is apparent that aggregation that involves AS_SETs is very seldom used in practice on the public network [Analysis] and, when it is used, it is usually used incorrectly -- reserved AS numbers ([RFC1930]) and/or only a single AS in the AS_SET are by far the most common case. Because the aggregation involving AS_SETs is very rarely used, the reduction in table size provided by said aggregation is extremely small, and any advantage thereof is outweighed by additional complexity in BGP. As noted above, said aggregation also poses impediments to implementation of said new BGP security technologies.

過去のインターネットルーティングデータの分析から、それを使用する場合、それは通常、不正に使用され、AS_SETsを伴う凝集はめったにパブリックネットワーク[分析]で実際に使用されていないことは明らかであると - 数字([RFC1930]として予約)、および/またはAS_SETで唯一のシングルとしてはこれまでで最も一般的なケースです。 AS_SETsを含む凝集は非常にまれに使用されているので、が提供するテーブルサイズの縮小は、凝集が極めて小さく、かつ任意の利点は、そのBGPにおけるさらなる複雑で勝っていると述べました。上述したように、凝集はまた、新しいBGPのセキュリティ技術を言ったの実装に障害をもたらすと述べました。

In the past, AS_SET had been used in a few rare cases to allow route aggregation where two or more providers could form the same prefix, using the exact match of the other's prefix in some advertisement and configuring the aggregation differently elsewhere. The key to configuring this correctly was to form the aggregate at the border in the outbound BGP policy and omit prefixes from the AS that the aggregate was being advertised to. The AS_SET therefore allowed this practice without the loss of BGP's AS_PATH loop protection. This use of AS_SET served a purpose that fell in line with the original intended use. Without the use of AS_SET, aggregates must always contain only less specific prefixes (not less than or equal to), and must never aggregate an exact match.

過去には、AS_SETは、二つ以上のプロバイダが、同じプレフィックスを形成し、いくつかの広告での他の接頭辞の完全一致を使用し、他の場所で別々に集約を設定することができ、経路集約を可能にするために、いくつかのまれなケースで使用されていました。これを正しく設定するための鍵は、アウトバウンドBGPポリシーの国境で凝集体を形成し、集計がに宣伝されていたことをASから接頭辞を省略することでした。 AS_SETは、したがって、BGPのASパスループ保護を失うことなく、このような行為を可能にしました。 AS_SETの使用は、元の目的に沿って落ちた目的を務めました。 AS_SETを使用せずに、凝集体は常に(ないよりも小さいか等しい)だけ少ない特定の接頭辞を含まなければならない、と完全一致を集約してはいけません。

2. Requirements Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

この文書のキーワード "MUST"、 "MUST NOT"、 "REQUIRED"、、、、 "べきではない" "べきである" "ないもの" "ものとし"、 "推奨"、 "MAY"、および "OPTIONAL" はあります[RFC2119]に記載されているように解釈されます。

3. Recommendation to Network Operators

It is RECOMMENDED that operators not generate any new announcements containing AS_SETs or AS_CONFED_SETs. If they have already announced routes with AS_SETs or AS_CONFED_SETs in them, then they SHOULD withdraw those routes and re-announce routes for the component prefixes (i.e., the additional specifics of the previously aggregated prefix) without AS_SETs in the updates. This involves undoing the aggregation that was previously performed (with AS_SETs), and announcing more specifics (without AS_SETs). Route aggregation that was previously performed by proxy aggregation (i.e., without the use of AS_SETs) is still possible under some conditions. As with any change, the operator should understand the full implications of the change.


It is worth noting that new technologies (such as those that take advantage of the "X.509 Extensions for IP Addresses and AS Identifiers" [RFC3779]) might not support routes with AS_SETs/ AS_CONFED_SETs in them, and may treat as infeasible routes containing them. Future BGP implementations may also do the same. It is expected that, even before the deployment of these new or future technologies, operators may filter routes with AS_SETs/AS_CONFED_SETs in them. Other than making that observation, this document is not intended to make any recommendation for how an operator should behave when receiving a route with AS_SET or AS_CONFED_SET in it. This document's focus is entirely on the sender side, as discussed in the preceding paragraph.

(例えば、「IPアドレスとAS識別子のためのX.509の拡張機能」[RFC3779]を利用するものなど)の新技術はそれらでAS_SETs / AS_CONFED_SETsとルートをサポートしていない可能性があることは注目に値する、と含むものとして実行不可能なルートを扱うことそれら。将来のBGPの実装も同じことを行うことができます。それも、これらの新しいまたは将来の技術の展開の前に、事業者はその中のAS_SETs / AS_CONFED_SETsとルートをフィルタリングすることができる、ということが予想されます。その観察を行う以外に、この文書は、オペレータがそれにAS_SETやAS_CONFED_SETでルートを受信したときにどのように振る舞うべきかについていかなる勧告を行うことを意図していません。前項で述べたように、この文書の焦点は、完全に、送信者側です。

4. Security Considerations

This document discourages the use of aggregation techniques that create AS_SETs. Future work may update the protocol to remove support for the AS_SET path segment type of the AS_PATH attribute. This future work will remove complexity and code that are not exercised very often, thereby decreasing the attack surface. This future work will also simplify the design and implementation of the Resource Public Key Infrastructure (RPKI) and systems that will rely on it.


5. Acknowledgements

The authors would like to thank Tony Li, Randy Bush, John Scudder, Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, and Ilya Varlashkin, as well as Douglas Montgomery, Enke Chen, Florian Weimer, Jakob Heitz, John Leslie, Keyur Patel, Paul Jakma, Rob Austein, Russ Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett, Alfred Hoenes, Alvaro Retana, everyone in the IDR working group, and everyone else who provided input.


Apologies to those who we may have missed; it was not intentional.


6. References
6.1. Normative References
6.1. 引用規格

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2119]ブラドナーの、S.、 "要件レベルを示すためにRFCsにおける使用のためのキーワード"、BCP 14、RFC 2119、1997年3月。

6.2. Informative References
6.2. 参考文献

[Analysis] Sriram, K. and D. Montgomery, "Measurement Data on AS_SET and AGGREGATOR: Implications for {Prefix, Origin} Validation Algorithms", SIDR WG presentation, IETF 78, July 2010, < AS_SET_Aggregator_Stats.pdf>.

[分析]スリラム、K.およびD.モントゴメリー、 "測定AS_SETのデータアグリゲータ:{プレフィックス、起源}検証アルゴリズムのための含意"、SIDR WGプレゼンテーション、IETF 78、2010年7月、< 〜ksriram / AS_SET_Aggregator_Stats.pdf>。

[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, selection, and registration of an Autonomous System (AS)", BCP 6, RFC 1930, March 1996.

[RFC1930]ホーキンソン、J.およびT.ベイツ、 "作成、選択、および自律システム(AS)の登録のためのガイドライン"、BCP 6、RFC 1930、1996年3月。

[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP Addresses and AS Identifiers", RFC 3779, June 2004.

[RFC3779]リン、C.、ケント、S.、およびK.ソ、 "IPアドレスとAS識別子のためのX.509拡張機能"、RFC 3779、2004年6月。

[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.

[RFC4271] Rekhter、Y.、エド。、李、T.、エド。、およびS.野兎、編、 "ボーダーゲートウェイプロトコル4(BGP-4)"、RFC 4271、2006年1月。

[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous System Confederations for BGP", RFC 5065, August 2007.

[RFC5065] Trainaの、P.、マクファーソン、D.、およびJ.スカダー、 "BGPのための自律システムコンフェデレーション"、RFC 5065、2007年8月。

Authors' Addresses


Warren Kumari Google, Inc. 1600 Amphitheatre Parkway Mountain View, CA 94043 US


Phone: +1 571 748 4373 EMail:

電話:+1 571 748 4373 Eメール

Kotikalapudi Sriram U.S. NIST 100 Bureau Drive Gaithersburg, MD 20899 US

Kotikalapudiスリラム米国NIST 100局ドライブゲーサーズバーグ、MD 20899米国

Phone: +1 301 975 3973 EMail:

電話:+1 301 975 3973 Eメール