< draft-ietf-grow-as-path-prepending-02.txt		draft-ietf-grow-as-path-prepending-03.txt >
	Network Working Group M. McBride		Network Working Group M. McBride
	Internet-Draft Futurewei		Internet-Draft Futurewei
	Intended status: Best Current Practice D. Madory		Intended status: Best Current Practice D. Madory
	Expires: May 5, 2021 Oracle		Expires: August 12, 2021 Kentik
	J. Tantsura		J. Tantsura
	Apstra		Apstra
	R. Raszuk		R. Raszuk
	Bloomberg LP		Bloomberg LP
	H. Li		H. Li
	HPE		HPE
	J. Heitz		J. Heitz
	Cisco		Cisco
	November 1, 2020		February 8, 2021
	AS Path Prepending		AS Path Prepending
	draft-ietf-grow-as-path-prepending-02		draft-ietf-grow-as-path-prepending-03
	Abstract		Abstract
	AS Path Prepending provides a tool to manipulate the BGP AS_Path		AS Path Prepending provides a tool to manipulate the BGP AS_Path
	attribute through prepending multiple entries of an AS. AS Path		attribute through prepending multiple entries of an AS. AS Path
	Prepending is used to deprioritize a route or alternate path. By		Prepending is used to deprioritize a route or alternate path. By
	prepending the local ASN multiple times, ASs can make advertised AS		prepending the local ASN multiple times, ASs can make advertised AS
	paths appear artificially longer. Excessive AS Path Prepending has		paths appear artificially longer. Excessive AS Path Prepending has
	caused routing issues in the internet. This document provides		caused routing issues in the internet. This document provides
	guidance,to the internet community, with how best to utilize AS Path		guidance,to the internet community, with how best to utilize AS Path
	skipping to change at page 1, line 46 ¶		skipping to change at page 1, line 46 ¶
	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 https://datatracker.ietf.org/drafts/current/.		Drafts is at https://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 May 5, 2021.		This Internet-Draft will expire on August 12, 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2021 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
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	skipping to change at page 7, line 30 ¶		skipping to change at page 7, line 30 ¶
	otherwise need to prepend N times) advertises with an INCOMPLETE		otherwise need to prepend N times) advertises with an INCOMPLETE
	origin code.		origin code.
	5. Best Practices		5. Best Practices
	Many of the best practices, or lack thereof, can be illustrated from		Many of the best practices, or lack thereof, can be illustrated from
	the preceeding examples. Here's a summary of the best current		the preceeding examples. Here's a summary of the best current
	practices when using AS Path Prepending:		practices when using AS Path Prepending:
	o Network operators should ensure prepending is absolutely necessary		o Network operators should ensure prepending is absolutely necessary
	as many networks have excessive prepending		as many networks have excessive prepending. It is best to
			innumerate what the routing policies are intended to achieve
			before concluding that prepending is a solution
			o The neighbor you are prepending may have an unconditional
			preference for customer routes and prepending doesn't work. It's
			helpful to check with neighbors to see if they will honor the
			prepend to avoid wasting effort and potentially causing further
			vulnerabilities.
	o There is no need to prepend more than 5 ASs. The following		o There is no need to prepend more than 5 ASs. The following
	diagram shows that, according to Excessive AS Path Prepending [3],		diagram shows that, according to Excessive AS Path Prepending [3],
	90% of AS path lengths are 5 ASNs or fewer in length.		90% of AS path lengths are 5 ASNs or fewer in length.
	+------------------------------------+		+------------------------------------+
	90| |		90| |
	| X |		| X |
	80| X X |		80| X X |
	| X X |		| X X |
	skipping to change at page 10, line 10 ¶		skipping to change at page 10, line 10 ¶
	[3] https://blogs.oracle.com/internetintelligence/excessive-as-path-		[3] https://blogs.oracle.com/internetintelligence/excessive-as-path-
	prepending-is-a-self-inflicted-vulnerability		prepending-is-a-self-inflicted-vulnerability
	Authors' Addresses		Authors' Addresses
	Mike McBride		Mike McBride
	Futurewei		Futurewei
	Email: michael.mcbride@futurewei.com		Email: michael.mcbride@futurewei.com
	Doug Madory		Doug Madory
	Oracle		Kentik
	Email: douglas.madory@oracle.com		Email: dmadory@kentik.com
	Jeff Tantsura		Jeff Tantsura
	Apstra		Apstra
	Email: jefftant.ietf@gmail.com		Email: jefftant.ietf@gmail.com
	Robert Raszuk		Robert Raszuk
	Bloomberg LP		Bloomberg LP
	Email: robert@raszuk.net		Email: robert@raszuk.net
End of changes. 8 change blocks.
	8 lines changed or deleted		16 lines changed or added
This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/