draft-ietf-idr-deprecate-as-sets-03.txt		draft-ietf-idr-deprecate-as-sets-04.txt
	Network Working Group W. Kumari		Network Working Group W. Kumari
	Internet-Draft Google, Inc.		Internet-Draft Google, Inc.
	Intended status: Informational K. Sriram		Intended status: Informational K. Sriram
	Expires: October 24, 2011 U.S. NIST		Expires: November 2, 2011 U.S. NIST
	April 22, 2011		May 1, 2011
	Deprecation of the use of BGP AS_SET, AS_CONFED_SET.		Deprecation of the use of BGP AS_SET, AS_CONFED_SET.
	draft-ietf-idr-deprecate-as-sets-03		draft-ietf-idr-deprecate-as-sets-04
	Abstract		Abstract
	This document deprecates the use of the AS_SET and AS_CONFED_SET		This document deprecates the use of the AS_SET and AS_CONFED_SET
	types of the AS_PATH in BGPv4. This is done to simplify the design		types of the AS_PATH in BGPv4. This is done to simplify the design
	and implementation of the BGP protocol and to make the semantics of		and implementation of the BGP protocol and to make the semantics of
	the originator of a route more clear. This will also simplify the		the originator of a route more clear. This will also simplify the
	design, implementation and deployment of ongoing work in the Secure		design, implementation and deployment of ongoing work in the Secure
	Inter-Domain Routing Working Group.		Inter-Domain Routing Working Group.
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	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on October 24, 2011.		This Internet-Draft will expire on November 2, 2011.
	Copyright Notice		Copyright Notice
	Copyright (c) 2011 IETF Trust and the persons identified as the		Copyright (c) 2011 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 16		skipping to change at page 2, line 16
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3		2. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3
	3. Recommendation to Network Operators . . . . . . . . . . . . . . 4		3. Recommendation to Network Operators . . . . . . . . . . . . . . 4
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
	5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4		5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
	7. Informative References . . . . . . . . . . . . . . . . . . . . 5		7. Informative References . . . . . . . . . . . . . . . . . . . . 5
	Appendix A. Proxy Aggregation without AS_SETs . . . . . . . . . . 5		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
	1. Introduction		1. Introduction
	The AS_SET path segment type of the AS_PATH attribute ([RFC4271],		The AS_SET path segment type of the AS_PATH attribute ([RFC4271],
	Section 4.3) is created by a router that is performing route		Section 4.3) is created by a router that is performing route
	aggregation and contains an unordered set of ASs that the update has		aggregation and contains an unordered set of ASs that the update has
	traversed. The AS_CONFED_SET path type ([RFC5065]) of the AS_PATH		traversed. The AS_CONFED_SET path type ([RFC5065]) of the AS_PATH
	attribute is created by a router that is performing route aggregation		attribute is created by a router that is performing route aggregation
	and contains an unordered set of Member AS Numbers in the local		and contains an unordered set of Member AS Numbers in the local
	confederation that the update has traversed. It is very similar to		confederation that the update has traversed. It is very similar to
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	In the past AS_SET had been used in a few rare cases to allow route		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,		aggregation where two or more providers could form the same prefix,
	using the exact match of the others prefix in some advertisement and		using the exact match of the others prefix in some advertisement and
	configuring the aggregation differently elsewhere. The key to		configuring the aggregation differently elsewhere. The key to
	configuring this correctly was to form the aggregate at the border in		configuring this correctly was to form the aggregate at the border in
	the outbound BGP policy and omit prefixes from the AS that the		the outbound BGP policy and omit prefixes from the AS that the
	aggregate was being advertised to. The AS_SET therefore allowed this		aggregate was being advertised to. The AS_SET therefore allowed this
	practice without the loss of BGP's AS_PATH loop protection. This use		practice without the loss of BGP's AS_PATH loop protection. This use
	of AS_SET served a purpose which fell in line with the original		of AS_SET served a purpose which fell in line with the original
	intended use. Without AS_SET aggregates must always contain only		intended use.
	less specific prefixes (not less than or equal to), and must never
	aggregate an exact match. Since this practice is thought to no		Without AS_SET aggregates must always contain only less specific
	longer be widely used, it is thought to be safe to deprecate the use		prefixes (not less than or equal to), and must never aggregate an
	of AS_SET.		exact match. Since this practice is thought to no longer be widely
			used, it is thought to be safe to deprecate the use of AS_SET.
	2. Requirements notation		2. Requirements notation
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].		document are to be interpreted as described in [RFC2119].
	3. Recommendation to Network Operators		3. Recommendation to Network Operators
	Operators are strongly advised to not generate any new announcements		Operators are strongly advised to not generate any new announcements
	containing AS_SETs or AS_CONFED_SETs. If they have already announced		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		routes with AS_SETs or AS_CONFED_SETs in them, then they should
	withdraw and re-announce those prefixes without AS_SETs in the		withdraw and re-announce those prefixes without AS_SETs in the
	updates. This may require undoing the aggregation that was		updates. This may require undoing the aggregation that was
	previously performed, and announcing more specifics. Route		previously performed, and announcing more specifics. Route
	aggregation is possible under some conditions without the use of		aggregation that was previously performed by proxy aggregation is
	AS_SETs (please see Appendix A for relevant discussion and		still possible under some conditions without the use of AS_SETs. As
	suggestions). As with any change, the operator should understand the		with any change, the operator should understand the full implications
	full implications of the change.		of the change.
	It is worth noting that new technologies (such as those that take		It is worth noting that new technologies (such as those that take
	advantage of the "X.509 Extensions for IP Addresses and AS		advantage of the "X.509 Extensions for IP Addresses and AS
	Identifiers" ([RFC3779]) may not support routes with AS_SETs /		Identifiers" ([RFC3779]) may not support routes with AS_SETs /
	AS_CONFED_SETs in them, and MAY treat as infeasible routes containing		AS_CONFED_SETs in them, and MAY treat as infeasible routes containing
	them. Future BGP implementations may also do the same.		them. Future BGP implementations may also do the same.
	It is expected that, even before the deployment of these		It is expected that, even before the deployment of these
	technologies, operators may begin filtering routes that contain		technologies, operators may begin filtering routes that contain
	AS_SETs or AS_CONFED_SETs.		AS_SETs or AS_CONFED_SETs.
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	on it.		on it.
	6. Acknowledgements		6. Acknowledgements
	The authors would like to thank Tony Li, Randy Bush, John Scudder,		The authors would like to thank Tony Li, Randy Bush, John Scudder,
	Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, Ilya		Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, Ilya
	Varlashkin as well as Douglas Montgomery, Enke Chen, Florian Weimer,		Varlashkin as well as Douglas Montgomery, Enke Chen, Florian Weimer,
	Jakob Heitz, John Leslie, Keyur Patel, Paul Jakma, Rob Austein, Russ		Jakob Heitz, John Leslie, Keyur Patel, Paul Jakma, Rob Austein, Russ
	Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett,		Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett,
	Alfred Hones, Alvaro Retana, everyone in IDR and everyone else who		Alfred Hones, Alvaro Retana, everyone in IDR and everyone else who
	provided input.		provided input
	Apologies to those who I may have missed, it was not intentional.		Apologies to those who we may have missed, it was not intentional.
	7. Informative References		7. Informative References
	[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,		[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
	selection, and registration of an Autonomous System (AS)",		selection, and registration of an Autonomous System (AS)",
	BCP 6, RFC 1930, March 1996.		BCP 6, RFC 1930, March 1996.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP		[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
	Addresses and AS Identifiers", RFC 3779, June 2004.		Addresses and AS Identifiers", RFC 3779, June 2004.
	[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway		[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
	Protocol 4 (BGP-4)", RFC 4271, January 2006.		Protocol 4 (BGP-4)", RFC 4271, January 2006.
	[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous		[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
	System Confederations for BGP", RFC 5065, August 2007.		System Confederations for BGP", RFC 5065, August 2007.
	Appendix A. Proxy Aggregation without AS_SETs
	Using the illustration in Figure 1 below, we attempt to point out how
	an aggregating AS can perform proxy aggregation without using an
	AS_SET in the aggregate announcement.
	In Figure 1, more specific prefixes p0/24, p1/24, p2/24, and p3/24
	are originated by AS-A, AS-B, AS-C, and AS-D, respectively. AS-E and
	AS-F choose not to aggregate; they forward the more specifics to
	AS-G. AS-G aggregates the four more specifics into a single less
	specific prefix p/22, and propagates updates in BGP to its neighbors
	(including AS-E and AS-F) to announce the p/22 prefix. If G were to
	insert the AS_SET [A,B,C,D,E,F] in the update, then AS-E and AS-F
	will be aware of the looping possibility and not install the route
	for p/22. The undesirable consequence here would be that AS-E would
	not have reachability to p2/24 and p3/24, and similarly AS-F would
	not have reachability to p0/24 and p1/24. So there is a hidden
	downside of this nature in proxy aggregation with the use of AS_SET.
	Now consider the case when AS-G performs the same aggregation but
	does not use an AS_SET in the aggregate announcement. The following
	recommendation is in order:
	o An AS should proxy aggregate only prefixes which belong to its
	administrative domain.
	With this recommendation in mind, we attempt to explain here how the
	data-plane looping possibility can still be avoided, and the
	reachability problem identified above is also prevented.
	In Figure 1, please take note of the aggregate announcements (without
	AS_SET) from AS-G to its neighbors. Absent the AS_SET in the
	aggregate announcement, now AS-E and AS-F would install the route for
	p/22 via AS-G in their routing tables. So AS-E will have
	reachability to p2/24 and p3/24, and similarly AS-F will have
	reachability to p0/24 and p1/24. Also, the looping possibility
	between AS-E and AS-G (and likewise between AS-F and AS-G) is avoided
	provided that AS-G observes a slight caution in its aggregation
	decision and packet forwarding. As already stated, AS-G should
	aggregate only those prefixes which belong in its admin domain, and
	secondly if any of those prefixes are withdrawn then AS-G should drop
	the route for that prefix from its FIB even though it still maintains
	the aggregation and continues to announce p/22 to its neighbors. If
	AS-E were to withdraw a prefix (say, p1/24) then AS-G will no longer
	forward packets for that prefix to AS-E. Hence, under said
	circumstance, even though AS-E may forward packets for p1/24 to AS-G,
	those packets will be dropped at AS-G and thus data-plane looping
	would not occur. The other reason for recommending aggregation of
	prefixes from within the same admin domain is that in that case, the
	aggregating AS (AS-G in the example) can create a ROA (in the RPKI
	repository) for the aggregate (p/22) showing itself (AS-G) as the
	origin.
	p0/24--A Update {E,A, p0/24} -->
	\ Update {E,B, p1/24} -->
	E-------------------------------\
	/ <-- Update {G, p/22} \
	p1/24--B (w/o AS_SET) \
	or \
	<-- Update {G,[A,B,C,D,E,F], p/22} \
	(with AS_SET) \
	\
	\
	\
	\
	G---------H
	<-- Update {G, p/22} / --->
	(w/o AS_SET) / same aggregate
	or / update as sent
	p2/24--C <-- Update {G,[A,B,C,D,E,F], p/22} / to E or F
	\ (with AS_SET) /
	F-----------------------------------/
	/ Update {F,C, p2/24} -->
	p3/24--D Update {F,D, p3/24} -->
	Note: p0/24+p1/24+p2/24+p3/24 = p/22
	BGP speaker G has chosen to Aggregate
	Figure 1: Illustration for discussion of loop possibility in data
	forwarding when AS_SET is not used and how it can be mitigated.
	Authors' Addresses		Authors' Addresses
	Warren Kumari		Warren Kumari
	Google, Inc.		Google, Inc.
	1600 Amphitheatre Parkway		1600 Amphitheatre Parkway
	Mountain View, CA 94043		Mountain View, CA 94043
	US		US
	Phone: +1 571 748 4373		Phone: +1 571 748 4373
	Email: warren@kumari.net		Email: warren@kumari.net
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