draft-ietf-grow-wkc-behavior-08.txt		rfc8642.txt
	Network Working Group J. Borkenhagen		Internet Engineering Task Force (IETF) J. Borkenhagen
	Internet-Draft AT&T		Request for Comments: 8642 AT&T
	Updates: 1997 (if approved) R. Bush		Updates: 1997 R. Bush
	Intended status: Standards Track IIJ & Arrcus		Category: Standards Track IIJ & Arrcus
	Expires: December 15, 2019 R. Bonica		ISSN: 2070-1721 R. Bonica
	Juniper Networks		Juniper Networks
	S. Bayraktar		S. Bayraktar
	Cisco Systems		Cisco Systems
	June 13, 2019		August 2019
	Well-Known Community Policy Behavior		Policy Behavior for Well-Known BGP Communities
	draft-ietf-grow-wkc-behavior-08
	Abstract		Abstract
	Well-Known BGP Communities are manipulated differently across various		Well-known BGP communities are manipulated differently across various
	current implementations; resulting in difficulties for operators.		current implementations, resulting in difficulties for operators.
	Network operators should deploy consistent community handling across		Network operators should deploy consistent community handling across
	their networks while taking the inconsistent behaviors from the		their networks while taking the inconsistent behaviors from the
	various BGP implementations into consideration.. This document		various BGP implementations into consideration. This document
	recommends specific actions to limit future inconsistency, namely BGP		recommends specific actions to limit future inconsistency: namely,
	implementors must not create further inconsistencies from this point		BGP implementors must not create further inconsistencies from this
	forward.		point forward. These behavioral changes, though subtle, actually
			update RFC 1997.
	Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This is an Internet Standards Track document.
	provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		This document is a product of the Internet Engineering Task Force
	Task Force (IETF). Note that other groups may also distribute		(IETF). It represents the consensus of the IETF community. It has
	working documents as Internet-Drafts. The list of current Internet-		received public review and has been approved for publication by the
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Internet Engineering Steering Group (IESG). Further information on
			Internet Standards is available in Section 2 of RFC 7841.
	Internet-Drafts are draft documents valid for a maximum of six months		Information about the current status of this document, any errata,
	and may be updated, replaced, or obsoleted by other documents at any		and how to provide feedback on it may be obtained at
	time. It is inappropriate to use Internet-Drafts as reference		https://www.rfc-editor.org/info/rfc8642.
	material or to cite them other than as "work in progress."
	This Internet-Draft will expire on December 15, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 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
	skipping to change at page 2, line 26 ¶		skipping to change at page 2, line 25 ¶
	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
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Manipulation of Communities by Policy . . . . . . . . . . . . 3		2. Manipulation of Communities by Policy . . . . . . . . . . . . 3
	3. Community Manipulation Policy Differences . . . . . . . . . . 3		3. Community Manipulation Policy Differences . . . . . . . . . . 3
	4. Documentation of Vendor Implementations . . . . . . . . . . . 3		4. Documentation of Vendor Implementations . . . . . . . . . . . 4
	4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4		4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 5
	5. Note for Those Writing RFCs for New Community-Like Attributes 5		5. Note for Those Writing RFCs for New Community-Like Attributes 5
	6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5		6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 5		7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6		9. Normative References . . . . . . . . . . . . . . . . . . . . 6
	10. Normative References . . . . . . . . . . . . . . . . . . . . 6		Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 6
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
	1. Introduction		1. Introduction
	The BGP Communities Attribute was specified in [RFC1997] which		The BGP Communities attribute was specified in [RFC1997], which
	introduced the concept of Well-Known Communities. In hindsight,		introduced the concept of well-known communities. In hindsight,
	[RFC1997] did not prescribe as fully as it should have how Well-Known		[RFC1997] did not prescribe as fully as it should have how well-known
	Communities may be manipulated by policies applied by operators.		communities may be manipulated by policies applied by operators.
	Currently, implementations differ in this regard, and these		Currently, implementations differ in this regard, and these
	differences can result in inconsistent behaviors that operators find		differences can result in inconsistent behaviors that operators find
	difficult to identify and resolve.		difficult to identify and resolve.
	This document describes the current behavioral differences in order		This document describes the current behavioral differences in order
	to assist operators in generating consistent community-manipulation		to assist operators in generating consistent community-manipulation
	policies in a multi-vendor environment, and to prevent the		policies in a multi-vendor environment and to prevent the
	introduction of additional divergence in implementations.		introduction of additional divergence in implementations.
	This document recommends specific actions to limit future		This document recommends specific actions to limit future
	inconsistency, namely BGP implementors MUST NOT create further		inconsistency: namely, BGP implementors MUST NOT create further
	inconsistencies from this point forward.		inconsistencies from this point forward.
			The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
			"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
			"OPTIONAL" in this document are to be interpreted as described in
			BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
			capitals, as shown here.
	2. Manipulation of Communities by Policy		2. Manipulation of Communities by Policy
	[RFC1997] says:		[RFC1997] says:
	"A BGP speaker receiving a route with the COMMUNITIES path attribute		A BGP speaker receiving a route with the COMMUNITIES path
	may modify this attribute according to the local policy."		attribute may modify this attribute according to the local policy.
	One basic operational need is to add or remove one or more		One basic operational need is to add or remove one or more
	communities to the set. The focus of this document is another common		communities to or from the set. The focus of this document is
	operational need, to replace all communities with a new set. To		another common operational need: to replace all communities with a
	simplify this second case, most BGP policy implementations provide		new set. To simplify this second case, most BGP policy
	syntax to "set" community that operators use to mean "remove any/all		implementations provide a syntax to "set" a community that operators
	communities present on the route, and apply this set of communities		use to mean "remove any/all communities present on the route and
	instead."		apply this set of communities instead".
	Some operators prefer to write explicit policy to delete unwanted		Some operators prefer to write explicit policy to delete unwanted
	communities rather than using "set;" i.e. using a "delete community		communities rather than use "set", i.e., using "delete community *:*"
	*:*" and then "add community x:y ..." configuration statements in an		and then "add community x:y ..." configuration statements in an
	attempt to replace all communities. The same community manipulation		attempt to replace all communities. The same community-manipulation
	policy differences described in the following section exist in both		policy differences described in the following section exist in the
	"set" and "delete community *:*" syntax. For simplicity, the		syntax for both "set" and "delete community *:*". For simplicity,
	remainder of this document refers only to the "set" behaviors, which		the remainder of this document refers only to the "set" behaviors,
	we refer to collectively as each implementation's '"set" directive.'		which we refer to collectively as each implementation's '"set"
			directive'.
	3. Community Manipulation Policy Differences		3. Community Manipulation Policy Differences
	Vendor implementations differ in the treatment of certain Well-Known		Vendor implementations differ in the treatment of certain well-known
	communities when modified using the syntax to "set" the community.		communities when modified using the syntax to "set" the community.
	Some replace all communities including the Well-Known ones with the		Some replace all communities, including the well-known ones, with the
	new set, while others replace all non-Well-Known Communities but do		new set; others replace all non-well-known communities but do not
	not modify any Well-Known Communities that are present.		modify any well-known communities that are present.
	These differences result in what would appear to be identical policy		These differences result in what would appear to be identical policy
	configurations having very different results on different platforms.		configurations having very different results on different platforms.
	4. Documentation of Vendor Implementations		4. Documentation of Vendor Implementations
	In this section we document the syntax and observed behavior of the		In this section, we document the syntax and observed behavior of the
	"set" directive in several popular BGP implementations to illustrate		"set" directive in several popular BGP implementations to illustrate
	the severity of the problem operators face.		the severity of the problem operators face.
	In Juniper Networks' Junos OS, "community set" removes all		In Juniper Networks' Junos OS, "community set" removes all
	communities, Well-Known or otherwise.		communities, well-known or otherwise.
	In Cisco IOS XR, "set community" removes all communities except for		In Cisco IOS XR, "set community" removes all communities except for
	the following:		the following:
	+-------------+-----------------------------------+		+-------------+-----------------------------------+
	| Numeric | Common Name |		| Numeric | Common Name |
	+-------------+-----------------------------------+		+-------------+-----------------------------------+
	| 0:0 | internet |		| 0:0 | internet |
	| 65535:0 | graceful-shutdown |		| 65535:0 | graceful-shutdown |
	| 65535:1 | accept-own rfc7611 |		| 65535:1 | accept-own rfc7611 |
	| 65535:65281 | NO_EXPORT |		| 65535:65281 | NO_EXPORT |
	| 65535:65282 | NO_ADVERTISE |		| 65535:65282 | NO_ADVERTISE |
	| 65535:65283 | NO_EXPORT_SUBCONFED (or local-AS) |		| 65535:65283 | NO_EXPORT_SUBCONFED (or local-AS) |
	+-------------+-----------------------------------+		+-------------+-----------------------------------+
	Communities not removed by Cisco IOS XR		Table 1: Communities Not Removed by Cisco's IOS XR
	Table 1
	Cisco IOS XR does allow Well-Known communities to be removed only by		Cisco IOS XR allows well-known communities to be removed only by
	explicitly enumerating one at a time, not in the aggregate; for		explicitly enumerating one at a time and not in the aggregate -- for
	example, "delete community accept-own". Operators are advised to		example, "delete community accept-own". Operators are advised to
	consult Cisco IOS XR documentation and/or Cisco support for full		consult Cisco IOS XR documentation and/or Cisco support for full
	details.		details.
	On Extreme networks' Brocade NetIron: "set community X" removes all		On Extreme networks' Brocade NetIron, "set community X" removes all
	communities and sets X.		communities and sets X.
	In Huawei's VRP product, "community set" removes all communities,		In Huawei's VRP product, "community set" removes all communities,
	Well-Known or otherwise.		well-known or otherwise.
	In OpenBGPD, "set community" does not remove any communities, Well-		In OpenBGPD, "set community" does not remove any communities, well-
	Known or otherwise.		known or otherwise.
	Nokia's SR OS has several directives that operate on communities.		Nokia's SR OS has several directives that operate on communities.
	Its "set" directive is called using the "replace" keyword, replacing		Its "set" directive is called using the "replace" keyword, replacing
	all communities, Well-Known or otherwise, with the specified		all communities, well-known or otherwise, with the specified
	communities.		communities.
	4.1. Note on an Inconsistency		4.1. Note on an Inconsistency
	The IANA publishes a list of Well-Known Communities [IANA-WKC].		IANA publishes a list of well-known communities [IANA-WKC].
	Cisco IOS XR's set of Well-Known communities that "set community"		Cisco IOS XR's set of well-known communities that "set community"
	will not overwrite diverges from the IANA's list of Well-Known		will not overwrite diverges from the IANA's list of well-known
	communities. Quite a few Well-Known communities from IANA's list do		communities. Quite a few well-known communities from IANA's list do
	not receive special treatment in Cisco IOS XR, and at least one		not receive special treatment in Cisco IOS XR, and at least one
	community on Cisco IOS XR's special treatment list, internet == 0:0,		community on Cisco IOS XR's special treatment list, internet == 0:0,
	is not formally a Well-Known Community as it is not in [IANA-WKC];		is not formally a well-known community as it is not in [IANA-WKC] (it
	but taken from the Reserved range [0x00000000-0x0000FFFF].		is taken from the Reserved range [0x00000000-0x0000FFFF]).
	This merely notes an inconsistency. It is not a plea to 'protect'		This merely notes an inconsistency. It is not a plea to protect the
	the entire IANA list from "set community."		entire IANA list from "set community".
	5. Note for Those Writing RFCs for New Community-Like Attributes		5. Note for Those Writing RFCs for New Community-Like Attributes
	When establishing new [RFC1997]-like attributes (large communities,		When establishing new attributes similar to those in [RFC1997] (large
	wide communities, etc.), RFC authors should state explicitly how the		communities, wide communities, etc.), RFC authors should state
	new attribute is to be handled.		explicitly how the new attribute is to be handled.
	6. Action Items		6. Action Items
	Network operators are encouraged to limit their use of the "set"		Network operators are encouraged to limit their use of the "set"
	directive (within reason), to improve consistency across platforms.		directive (within reason) to improve consistency across platforms.
	Unfortunately, it would be operationally disruptive for vendors to		Unfortunately, it would be operationally disruptive for vendors to
	change their current implementations.		change their current implementations.
	Vendors MUST clearly document the behavior of "set" directive in		Vendors MUST clearly document the behavior of the "set" directive in
	their implementations.		their implementations.
	Vendors MUST ensure that their implementations' "set" directive		Vendors MUST ensure that their implementations' "set" directive
	treatment of any specific community does not change if/when that		treatment of any specific community does not change if/when that
	community becomes a new Well-Known Community through future		community becomes a new well-known community through future
	standardization. For most implementations, this means that the "set"		standardization. For most implementations, this means that the "set"
	directive MUST continue to remove the community; for those		directive MUST continue to remove the community; for those
	implementations where the "set" directive removes no communities,		implementations where the "set" directive removes no communities,
	that behavior MUST continue.		that behavior MUST continue.
	Given the implementation inconsistencies described in this document,		Given the implementation inconsistencies described in this document,
	network operators are urged never to rely on any implicit		network operators are urged never to rely on any implicit
	understanding of a neighbor ASN's BGP community handling. I.e.,		understanding of a neighbor ASN's BGP community handling. That is,
	before announcing prefixes with NO_EXPORT or any other community to a		before announcing prefixes with NO_EXPORT or any other community to a
	neighbor ASN, the operator should confirm with that neighbor how the		neighbor ASN, the operator should confirm with that neighbor how the
	community will be treated.		community will be treated.
	7. Security Considerations		7. Security Considerations
	Surprising defaults and/or undocumented behaviors are not good for		Surprising defaults and/or undocumented behaviors are not good for
	security. This document attempts to remedy that.		security. This document attempts to remedy that.
	8. IANA Considerations		8. IANA Considerations
	The IANA is requested to list this document as an additional		The IANA has listed this document as an additional reference for the
	reference for the [IANA-WKC] registry.		[IANA-WKC] registry.
	9. Acknowledgments
	The authors thank Martijn Schmidt, Qin Wu for the Huawei data point,
	Greg Hankins, Job Snijders, David Farmer, John Heasley, and Jakob
	Heitz.
	10. Normative References		9. Normative References
	[IANA-WKC]		[IANA-WKC] IANA, "Border Gateway Protocol (BGP) Well-known
	IANA, "Border Gateway Protocol (BGP) Well-Known
	Communities", <https://www.iana.org/assignments/		Communities", <https://www.iana.org/assignments/
	bgp-well-known-communities>.		bgp-well-known-communities>.
	[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities		[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
	Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,		Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
	<http://www.rfc-editor.org/info/rfc1997>.		<https://www.rfc-editor.org/info/rfc1997>.
	[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,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<http://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <http://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
			Acknowledgments
			The authors thank Martijn Schmidt and Qin Wu for the Huawei data
			point as well as Greg Hankins, Job Snijders, David Farmer, John
			Heasley, and Jakob Heitz.
	Authors' Addresses		Authors' Addresses
	Jay Borkenhagen		Jay Borkenhagen
	AT&T		AT&T
	200 Laurel Avenue South		200 Laurel Avenue South
	Middletown, NJ 07748		Middletown, NJ 07748
	United States of America		United States of America
	Email: jayb@att.com		Email: jayb@att.com
	Randy Bush		Randy Bush
	IIJ & Arrcus		IIJ & Arrcus
	5147 Crystal Springs		5147 Crystal Springs
	Bainbridge Island, WA 98110		Bainbridge Island, WA 98110
	US		United States of America
	Email: randy@psg.com		Email: randy@psg.com
	Ron Bonica		Ron Bonica
	Juniper Networks		Juniper Networks
	2251 Corporate Park Drive		2251 Corporate Park Drive
	Herndon, VA 20171		Herndon, VA 20171
	US		United States of America
	Email: rbonica@juniper.net		Email: rbonica@juniper.net
	Serpil Bayraktar		Serpil Bayraktar
	Cisco Systems		Cisco Systems
	170 W. Tasman Drive		170 W. Tasman Drive
	San Jose, CA 95134		San Jose, CA 95134
	United States of America		United States of America
	Email: serpil@cisco.com		Email: serpil@cisco.com
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