draft-ietf-grow-wkc-behavior-04.txt		draft-ietf-grow-wkc-behavior-05.txt
	Network Working Group J. Borkenhagen		Network Working Group J. Borkenhagen
	Internet-Draft AT&T		Internet-Draft AT&T
	Intended status: Best Current Practice R. Bush		Updates: 1997 (if approved) R. Bush
	Expires: November 17, 2019 Internet Initiative Japan		Intended status: Standards Track Internet Initiative Japan
	R. Bonica		Expires: December 1, 2019 R. Bonica
	Juniper Networks		Juniper Networks
	S. Bayraktar		S. Bayraktar
	Cisco Systems		Cisco Systems
	May 16, 2019		May 30, 2019
	Well-Known Community Policy Behavior		Well-Known Community Policy Behavior
	draft-ietf-grow-wkc-behavior-04		draft-ietf-grow-wkc-behavior-05
	Abstract		Abstract
	Popular BGP implementations manipulate Well-known Communities		Well-Known BGP Communities are manipulated differently across various
	differently from one another. This results in difficulties for		current implementations; resulting in difficulties for operators.
	operators. Network operators are encouraged to deploy consistent		Network operators should deploy consistent community handling across
	community handling across their networks, taking the inconsistent		their networks while taking the inconsistent behaviors from the
	behaviors from the various BGP implementations they operate into		various BGP implementations into consideration.. This document
	consideration. This document recommends specific action items to		recommends specific actions to limit future inconsistency, namely BGP
	limit future inconsistency, namely BGP implementors are expected to		implementors must not create further inconsistencies from this point
	not create any further inconsistencies from this point forward.		forward.
			Requirements Language
			The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
			"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
			be interpreted as described in RFC 2119 [RFC2119] only when they
			appear in all upper case. They may also appear in lower or mixed
			case as English words, without normative meaning.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	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 December 1, 2019.
	This Internet-Draft will expire on November 17, 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
	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
	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. Requirements Language . . . . . . . . . . . . . . . . . . . . 3		2. Manipulation of Communities by Policy . . . . . . . . . . . . 3
	3. Manipulation of Communities by Policy . . . . . . . . . . . . 3		3. Community Manipulation Policy Differences . . . . . . . . . . 3
	4. Community Manipulation Policy Differences . . . . . . . . . . 3		4. Documentation of Vendor Implementations . . . . . . . . . . . 3
	5. Documentation of Vendor Implementations . . . . . . . . . . . 4		4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4
	5.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 5		5. Note for Those Writing RFCs for New Community-Like Attributes 5
	6. Note for Those Writing RFCs for New Community-Like Attributes 5		6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5
	7. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5		7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 6		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
	10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6		10. Normative References . . . . . . . . . . . . . . . . . . . . 6
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
	11.1. Normative References . . . . . . . . . . . . . . . . . . 6
	11.2. Informative References . . . . . . . . . . . . . . . . . 6
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
	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 action items to limit future		This document recommends specific actions to limit future
	inconsistency.		inconsistency, namely BGP implementors MUST NOT create further
			inconsistencies from this point forward.
	2. 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.
	3. 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 attribute
	may modify this attribute according to the local policy."		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 received set. The focus of this document is		communities to the set. The focus of this document is another common
	another common operational need, to replace all communities with a		operational need, to replace all communities with a new set. To
	new set. To simplify this second case, most BGP policy		simplify this second case, most BGP policy implementations provide
	implementations provide syntax to "set" community that operators use		syntax to "set" community that operators use to mean "remove any/all
	to mean "remove any/all communities present on the route, and apply		communities present on the route, and apply this set of communities
	this set of communities instead."		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 using "set;" i.e. using a "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 received communities. The same community		attempt to replace all communities. The same community manipulation
	manipulation policy differences described in the following section		policy differences described in the following section exist in both
	exist in both "set" and "delete community *:*" syntax. For		"set" and "delete community *:*" syntax. For simplicity, the
	simplicity, the remainder of this document refers only to the "set"		remainder of this document refers only to the "set" behaviors, which
	behaviors, which we refer to collectively as each implementation's		we refer to collectively as each implementation's '"set" directive.'
	'"set" directive.'
	4. 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, while others replace all non-Well-Known Communities but do
	not modify any Well-Known Communities that are present.		not 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.
	5. 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.		"set" directive in several popular BGP implementations to illustrate
			the severity of the problem operators face.
	In Juniper Networks' Junos OS, "community set" removes all received		In Juniper Networks' Junos OS, "community set" removes all
	communities, Well-Known or otherwise.		communities, Well-Known or otherwise.
	In Cisco Systems' IOS XR, "set community" removes all received		In Cisco IOS XR, "set community" removes all communities except for
	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		Communities not removed by Cisco IOS XR
	Table 1		Table 1
	IOS XR does allow Well-Known communities to be removed by explicitly		Cisco IOS XR does allow Well-Known communities to be removed only by
	enumerating each one, not in the aggregate; for example, "delete		explicitly enumerating one at a time, not in the aggregate; for
	community accept-own". Operators are advised to consult IOS XR		example, "delete community accept-own". Operators are advised to
	documentation and/or Cisco Systems support for full details.		consult Cisco IOS XR documentation and/or Cisco support for full
			details.
	On Extreme networks' Brocade NetIron: "set community X" removes all		On Extreme networks' Brocade NetIron: "set community X" removes all
	received communities and sets X.		communities and sets X.
	In Huawei's VRP product, "community set" removes all received		In Huawei's VRP product, "community set" removes all communities,
	communities, well-Known or otherwise.		Well-Known or otherwise.
	In OpenBSD's OpenBGPD, "set community" does not remove any		In OpenBGPD, "set community" does not remove any communities, Well-
	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 received communities, Well-Known or otherwise, with the specified		all communities, Well-Known or otherwise, with the specified
	communities.		communities.
	5.1. Note on an Inconsistency		4.1. Note on an Inconsistency
	In IOS XR, "set community" will not overwrite some well-known		The IANA publishes a list of Well-Known Communities [IANA-WKC].
	communities. However, it will overwrite other well-known
	communities. Conversely, In IOS XR, "set community" will not		Cisco IOS XR's set of Well-Known communities that "set community"
	overwrite some communities that are not well-known (e.g., (internet		will not overwrite diverges from the IANA's list of Well-Known
	== 0:0).		communities. Quite a few Well-Known communities from IANA's list do
			not receive special treatment in Cisco IOS XR, and at least one
			specific community on Cisco IOS XR's special treatment list (internet
			== 0:0) is not really on IANA's list -- it's 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 entire IANA list from "set community."		the entire IANA list from "set community."
	6. 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 [RFC1997]-like attributes (large communities,
	wide communities, etc.), RFC authors should state how the new		wide communities, etc.), RFC authors should state explicitly how the
	community attribute is to be handled.		> new attribute is to be handled.
	7. 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 the readability of their		directive (within reason), to improve consistency across platforms.
	configurations and hopefully to achieve behavioral 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 SHOULD clearly document the behavior of "set" directive in		Vendors SHOULD clearly document the behavior of "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
	skipping to change at page 6, line 5 ¶		skipping to change at page 5, line 42 ¶
	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. I.e.,
	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.
	8. 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.
	Also see Appendix A of [RFC5706].		8. IANA Considerations
	9. IANA Considerations
	This document has no IANA Considerations.		This document has no IANA Considerations; though the IANA may wish to
			refer to this document, if/when published, in [IANA-WKC].
	10. Acknowledgments		9. Acknowledgments
	The authors thank Martijn Schmidt, Qin Wu for the Huawei data point,		The authors thank Martijn Schmidt, Qin Wu for the Huawei data point,
	Greg Hankins, Job Snijders, David Farmer, John Heasley, and Jakob		Greg Hankins, Job Snijders, David Farmer, John Heasley, and Jakob
	Heitz.		Heitz.
	11. References		10. Normative References
	11.1. Normative References		[IANA-WKC]
			IANA, "Border Gateway Protocol (BGP) Well-Known
			Communities", <https://www.iana.org/assignments/
			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,
	<https://www.rfc-editor.org/info/rfc1997>.		<http://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,
	<https://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	11.2. Informative References
	[RFC5706] Harrington, D., "Guidelines for Considering Operations and
	Management of New Protocols and Protocol Extensions",
	RFC 5706, DOI 10.17487/RFC5706, November 2009,
	<https://www.rfc-editor.org/info/rfc5706>.
	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
	Internet Initiative Japan		Internet Initiative Japan
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