draft-ietf-grow-wkc-behavior-02.txt		draft-ietf-grow-wkc-behavior-03.txt
	Network Working Group J. Borkenhagen		Network Working Group J. Borkenhagen
	Internet-Draft AT&T		Internet-Draft AT&T
	Intended status: Standards Track R. Bush		Intended status: Standards Track R. Bush
	Expires: July 26, 2019 Internet Initiative Japan		Expires: September 11, 2019 Internet Initiative Japan
	R. Bonica		R. Bonica
	Juniper Networks		Juniper Networks
	S. Bayraktar		S. Bayraktar
	Cisco Systems		Cisco Systems
	January 22, 2019		March 10, 2019
	Well-Known Community Policy Behavior		Well-Known Community Policy Behavior
	draft-ietf-grow-wkc-behavior-02		draft-ietf-grow-wkc-behavior-03
	Abstract		Abstract
	Well-Known BGP Communities are manipulated inconsistently by current		Well-Known BGP Communities are manipulated inconsistently by current
	implementations. This results in difficulties for operators.		implementations. This results in difficulties for operators.
	Network operators are encouraged to deploy consistent community		Network operators are encouraged to deploy consistent community
	handling across their networks, taking the inconsistent behaviors		handling across their networks, taking the inconsistent behaviors
	from the various bgp implementations they operate into consideration.		from the various BGP implementations they operate into consideration.
	Also, bgp implementors are expected to not create any further		Also, BGP implementors are expected to not create any further
	inconsistencies from this point forward.		inconsistencies from this point forward.
	Requirements Language		Requirements Language
	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" are to		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
	be interpreted as described in RFC 2119 [RFC2119] only when they		be interpreted as described in RFC 2119 [RFC2119] only when they
	appear in all upper case. They may also appear in lower or mixed		appear in all upper case. They may also appear in lower or mixed
	case as English words, without normative meaning.		case as English words, without normative meaning.
	skipping to change at page 1, line 49 ¶		skipping to change at page 1, line 49 ¶
	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 July 26, 2019.		This Internet-Draft will expire on September 11, 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 27 ¶		skipping to change at page 2, line 27 ¶
	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 . . . . . . . . . . . 3
	4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4		4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4
	5. Note for Those Writing RFCs for New Community-Like		5. Note for Those Writing RFCs for New Community-Like Attributes 5
	Attributes . . . . . . . . . . . . . . . . . . . . . . . . . 4
	6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5		6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 5		7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5		9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
	10. Normative References . . . . . . . . . . . . . . . . . . . . 5		10. Normative 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
	skipping to change at page 3, line 12 ¶		skipping to change at page 3, line 12 ¶
	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.
	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 attribute
	may modify this attribute according to the local policy."		may modify this attribute according to the local policy."
	A basic operational need is to add or remove one or more communities		One basic operational need is to add or remove one or more
	to the received set. Another common need is to replace all received		communities to the received set. The focus of this document is
	communities with a new set. To simplify the second case, most BGP		another common operational need, to replace all communities with a
	policy implementations provide syntax to "set" community that		new set. To simplify this second case, most BGP policy
	operators use to mean "remove any/all communities present on the		implementations provide syntax to "set" community that operators use
	update received from the neighbor, and apply this set of communities		to mean "remove any/all communities present on the route, and apply
	instead."		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 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 received communities. The same community
	manipulation policy differences described in the following section		manipulation policy differences described in the following section
	exist in both "set" and "delete community *:*" syntax. For		exist in both "set" and "delete community *:*" syntax. For
	simplicity, the remainder of this document refers only to the "set"		simplicity, the remainder of this document refers only to the "set"
	behaviors.		behaviors, 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, 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.
	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.		"set" directive in several popular BGP implementations.
	In Juniper Networks' JunOS, "community set" removes all received		In Juniper Networks' Junos OS, "community set" removes all received
	communities, Well-Known or otherwise.		communities, Well-Known or otherwise.
	In Cisco Systems' IOS-XR, "set community" removes all received		In Cisco Systems' IOS XR, "set community" removes all received
	communities except for the following:		communities except for 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 one at a time		IOS XR does allow Well-Known communities to be removed one at a time
	by explicit policy; for example, "delete community accept-own".		by explicit policy; for example, "delete community accept-own".
	Operators are advised to consult IOS-XR documentation and/or Cisco		Operators are advised to consult IOS XR documentation and/or Cisco
	Systems support for full details.		Systems support for full details.
	On Brocade NetIron: "set community X" removes all communities and		On Extreme networks' Brocade NetIron: "set community X" removes all
	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 received
	communities, well-Known or otherwise.		communities, well-Known or otherwise.
	In OpenBSD's OpenBGPD, "set community" does not remove any		In OpenBSD's OpenBGPD, "set community" does not remove any
	communities, Well-Known or otherwise.		communities, Well-Known or otherwise.
			Nokia's SR OS has several directives that operate on communities.
			Its "set" directive is called using the "replace" keyword, replacing
			all communities, Well-Known or otherwise, with the specified
			communities.
	4.1. Note on an Inconsistency		4.1. Note on an Inconsistency
	The IANA publishes a list of Well-Known Communities [IANA-WKS].		The IANA publishes a list of Well-Known Communities [IANA-WKS].
	IOS-XR's set of well-known communities that "set community" will not		IOS XR's set of well-known communities that "set community" will not
	overwrite diverges from IANA's list. Quite a few well-known		overwrite diverges from IANA's list. Quite a few well-known
	communities from IANA's list do not receive special treatment in IOS-		communities from IANA's list do not receive special treatment in IOS
	XR, and at least one specific community on IOS-XR's special treatment		XR, and at least one specific community on IOS XR's special treatment
	list (internet == 0:0) is not really on IANA's list -- it's taken		list (internet == 0:0) is not really on IANA's list -- it's taken
	from the "Reserved" range [0x00000000-0x0000FFFF].		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."
	5. Note for Those Writing RFCs for New Community-Like Attributes		5. Note for Those Writing RFCs for New Community-Like Attributes
	Care should be taken when establishing new [RFC1997]-like attributes		Care should be taken when establishing new [RFC1997]-like attributes
	(large communities, wide communities, etc) to avoid repeating this		(large communities, wide communities, etc) to avoid repeating this
	mistake.		mistake.
	6. Action Items		6. Action Items
	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 any Well-Known Communities specified after		Vendors MUST ensure that their implementations' "set" directive
	this document's publication are removed by their "set" directive.		treatment of any specific community does not change if/when that
			community becomes a new Well-Known Community through future
			standardization. For most implementations, this means that the "set"
			directive MUST continue to remove the community; for those
			implementations where the "set" directive removes no communities,
			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.
	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 the readability of their
	configurations and hopefully to achieve behavioral consistency across		configurations and hopefully to achieve behavioral consistency across
	platforms.		platforms.
	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
	This document has no IANA Considerations other than to be aware that		This document has no IANA Considerations other than to be aware that
	any future Well-Known Communities will be subject to the policy		any future Well-Known Communities will be subject to the policy
	treatment described here.		treatment described here.
	9. Acknowledgements		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,
	Job Snijders, David Farmer,John Heasley, and Jakob Heitz.		Greg Hankins, Job Snijders, David Farmer, John Heasley, and Jakob
			Heitz.
	10. Normative References		10. Normative References
	[IANA-WKS]		[IANA-WKS]
	"IANA Well-Known Comunities",		"IANA Well-Known Communities",
	<https://www.iana.org/assignments/bgp-well-known-		<https://www.iana.org/assignments/bgp-well-known-
	communities/bgp-well-known-communities.xhtml>.		communities/bgp-well-known-communities.xhtml>.
	[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>.		<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,
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