draft-ietf-grow-bgp-gshut-11.txt		draft-ietf-grow-bgp-gshut-12.txt
	Network Working Group P. Francois, Ed.		Network Working Group P. Francois, Ed.
	Internet-Draft Individual Contributor		Internet-Draft Individual Contributor
	Intended status: Informational B. Decraene, Ed.		Intended status: Informational B. Decraene, Ed.
	Expires: March 24, 2018 Orange		Expires: April 14, 2018 Orange
	C. Pelsser		C. Pelsser
	Strasbourg University		Strasbourg University
	K. Patel		K. Patel
	Arrcus, Inc.		Arrcus, Inc.
	C. Filsfils		C. Filsfils
	Cisco Systems		Cisco Systems
	September 20, 2017		October 11, 2017
	Graceful BGP session shutdown		Graceful BGP session shutdown
	draft-ietf-grow-bgp-gshut-11		draft-ietf-grow-bgp-gshut-12
	Abstract		Abstract
	This draft standardizes a new well-known BGP community		This draft standardizes a new well-known BGP community
	GRACEFUL_SHUTDOWN to signal the graceful shutdown of paths. This		GRACEFUL_SHUTDOWN to signal the graceful shutdown of paths. This
	draft also describes operational procedures which use this community		draft also describes operational procedures which use this community
	to reduce the amount of traffic lost when BGP peering sessions are		to reduce the amount of traffic lost when BGP peering sessions are
	about to be shut down deliberately, e.g. for planned maintenance.		about to be shut down deliberately, e.g. for planned maintenance.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 41 ¶		skipping to change at page 1, line 41 ¶
	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 March 24, 2018.		This Internet-Draft will expire on April 14, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2017 IETF Trust and the persons identified as the		Copyright (c) 2017 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 50 ¶		skipping to change at page 2, line 50 ¶
	Routing changes in BGP can be caused by planned maintenance		Routing changes in BGP can be caused by planned maintenance
	operations. This document defines a well-known community [RFC1997],		operations. This document defines a well-known community [RFC1997],
	called GRACEFUL_SHUTDOWN, for the purpose of reducing the management		called GRACEFUL_SHUTDOWN, for the purpose of reducing the management
	overhead of gracefully shutting down BGP sessions. The well-known		overhead of gracefully shutting down BGP sessions. The well-known
	community allows implementers to provide an automated graceful		community allows implementers to provide an automated graceful
	shutdown mechanism that does not require any router reconfiguration		shutdown mechanism that does not require any router reconfiguration
	at maintenance time.		at maintenance time.
	This document discusses operational procedures to be applied in order		This document discusses operational procedures to be applied in order
	to reduce or eliminate loss of packets during a maintenance. Loss		to reduce or eliminate loss of packets during a maintenance
	comes from transient lack of reachability during BGP convergence		operation. Loss comes from transient lack of reachability during BGP
	which follows the shutdown of an EBGP peering session between two		convergence which follows the shutdown of an EBGP peering session
	Autonomous System Border Routers (ASBR).		between two Autonomous System Border Routers (ASBR).
	This document presents procedures for the cases where the forwarding		This document presents procedures for the cases where the forwarding
	plane is impacted by the maintenance, hence when the use of Graceful		plane is impacted by the maintenance, hence when the use of Graceful
	Restart does not apply.		Restart does not apply.
	The procedures described in this document can be applied to reduce or		The procedures described in this document can be applied to reduce or
	avoid packet loss for outbound and inbound traffic flows initially		avoid packet loss for outbound and inbound traffic flows initially
	forwarded along the peering link to be shut down. These procedures		forwarded along the peering link to be shut down. These procedures
	trigger, in both ASes, rerouting to alternate paths if they exist		trigger, in both Autonomous Sytems (AS), rerouting to alternate paths
	within the AS, while allowing the use of the old path until alternate		if they exist within the AS, while allowing the use of the old path
	ones are learned. This ensures that routers always have a valid		until alternate ones are learned. This ensures that routers always
	route available during the convergence process.		have a valid route available during the convergence process.
	The goal of the document is to meet the requirements described in		The goal of the document is to meet the requirements described in
	[RFC6198] at best, without changing the BGP protocol.		[RFC6198] at best, without changing the BGP protocol.
	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 RFC 2119 [RFC2119].		document are to be interpreted as described in RFC 8174 [RFC8174].
	2. Terminology		2. Terminology
	graceful shutdown initiator: a router on which the session shutdown		graceful shutdown initiator: a router on which the session shutdown
	is performed for the maintenance.		is performed for the maintenance.
	graceful shutdown receiver: a router that has a BGP session, to be		graceful shutdown receiver: a router that has a BGP session, to be
	shutdown, with the graceful shutdown initiator.		shutdown, with the graceful shutdown initiator.
	3. Packet loss upon manual EBGP session shutdown		3. Packet loss upon manual EBGP session shutdown
	skipping to change at page 4, line 14 ¶		skipping to change at page 4, line 14 ¶
	4. EBGP graceful shutdown procedure		4. EBGP graceful shutdown procedure
	This section describes configurations and actions to be performed for		This section describes configurations and actions to be performed for
	the graceful shutdown of EBGP peering links.		the graceful shutdown of EBGP peering links.
	The goal of this procedure is to retain the paths to be shutdown		The goal of this procedure is to retain the paths to be shutdown
	between the peers, but with a lower LOCAL_PREF value, allowing the		between the peers, but with a lower LOCAL_PREF value, allowing the
	paths to remain in use while alternate paths are selected and		paths to remain in use while alternate paths are selected and
	propagated, rather than simply withdrawing the paths. The LOCAL_PREF		propagated, rather than simply withdrawing the paths. The LOCAL_PREF
	value must be lower than the one of the alternate path. 0 being the		value SHOULD be lower than any of the alternative paths. The
	lowest value, it can be used in all cases, except if it already has a		RECOMMENDED value is 0.
	special meaning within the AS.
	4.1. Pre-configuration		4.1. Pre-configuration
	On each ASBR supporting the graceful shutdown receiver procedure, an		On each ASBR supporting the graceful shutdown receiver procedure, an
	inbound BGP route policy is applied on all EBGP sessions of the ASBR,		inbound BGP route policy is applied on all EBGP sessions of the ASBR,
	that:		that:
	o matches the GRACEFUL_SHUTDOWN community.		o matches the GRACEFUL_SHUTDOWN community.
	o sets the LOCAL_PREF attribute of the paths tagged with the		o sets the LOCAL_PREF attribute of the paths tagged with the
	skipping to change at page 4, line 48 ¶		skipping to change at page 4, line 47 ¶
	advertised, and tag them with the GRACEFUL_SHUTDOWN community.		advertised, and tag them with the GRACEFUL_SHUTDOWN community.
	o applies an inbound BGP route policy on the EBGP session to be		o applies an inbound BGP route policy on the EBGP session to be
	shutdown. This policy tags the paths received over the session		shutdown. This policy tags the paths received over the session
	with the GRACEFUL_SHUTDOWN community and sets LOCAL_PREF to a low		with the GRACEFUL_SHUTDOWN community and sets LOCAL_PREF to a low
	value.		value.
	o wait for route readvertisement over the EBGP session, and BGP		o wait for route readvertisement over the EBGP session, and BGP
	routing convergence on both ASBRs.		routing convergence on both ASBRs.
	o shutdown the EBGP session, optionally using		o shutdown the EBGP session, optionally using [RFC8203] to
	[I-D.ietf-idr-shutdown] to communicate the reason of the shutdown.		communicate the reason of the shutdown.
	In the case of a shutdown of the whole router, in addition to the		In the case of a shutdown of the whole router, in addition to the
	graceful shutdown of all EBGP sessions, there is a need to gracefully		graceful shutdown of all EBGP sessions, there is a need to gracefully
	shutdown the routes originated by this router (e.g, BGP aggregates		shutdown the routes originated by this router (e.g, BGP aggregates
	redistributed from other protocols, including static routes). This		redistributed from other protocols, including static routes). This
	can be performed by tagging these routes with the GRACEFUL_SHUTDOWN		can be performed by tagging these routes with the GRACEFUL_SHUTDOWN
	community and setting LOCAL_PREF to a low value.		community and setting LOCAL_PREF to a low value.
	4.3. BGP implementation support for graceful shutdown		4.3. BGP implementation support for graceful shutdown
	skipping to change at page 5, line 40 ¶		skipping to change at page 5, line 39 ¶
	The neighbor could abuse the technique and do inbound traffic		The neighbor could abuse the technique and do inbound traffic
	engineering by declaring some prefixes as undergoing a maintenance so		engineering by declaring some prefixes as undergoing a maintenance so
	as to switch traffic to another peering link.		as to switch traffic to another peering link.
	If this behavior is not tolerated by the ISP, it SHOULD monitor the		If this behavior is not tolerated by the ISP, it SHOULD monitor the
	use of the graceful shutdown community.		use of the graceful shutdown community.
	7. Acknowledgments		7. Acknowledgments
	The authors wish to thank Olivier Bonaventure, Pradosh Mohapatra, Job		The authors wish to thank Olivier Bonaventure, Pradosh Mohapatra, Job
	Snijders John Heasley, and Christopher Morrow for their useful		Snijders, John Heasley, and Christopher Morrow for their useful
	comments.		comments.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[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>.		<https://www.rfc-editor.org/info/rfc1997>.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.
	[RFC6198] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z.,		[RFC6198] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z.,
	Elizondo Armengol, A., and T. Takeda, "Requirements for		Elizondo Armengol, A., and T. Takeda, "Requirements for
	the Graceful Shutdown of BGP Sessions", RFC 6198,		the Graceful Shutdown of BGP Sessions", RFC 6198,
	DOI 10.17487/RFC6198, April 2011,		DOI 10.17487/RFC6198, April 2011,
	<https://www.rfc-editor.org/info/rfc6198>.		<https://www.rfc-editor.org/info/rfc6198>.
			[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>.
	8.2. Informative References		8.2. Informative References
	[I-D.ietf-idr-best-external]		[I-D.ietf-idr-best-external]
	Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H.		Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H.
	Gredler, "Advertisement of the best external route in		Gredler, "Advertisement of the best external route in
	BGP", draft-ietf-idr-best-external-05 (work in progress),		BGP", draft-ietf-idr-best-external-05 (work in progress),
	January 2012.		January 2012.
	[I-D.ietf-idr-shutdown]
	Snijders, J., Heitz, J., and J. Scudder, "BGP
	Administrative Shutdown Communication", draft-ietf-idr-
	shutdown-10 (work in progress), June 2017.
	[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,		[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
	"Advertisement of Multiple Paths in BGP", RFC 7911,		"Advertisement of Multiple Paths in BGP", RFC 7911,
	DOI 10.17487/RFC7911, July 2016,		DOI 10.17487/RFC7911, July 2016,
	<https://www.rfc-editor.org/info/rfc7911>.		<https://www.rfc-editor.org/info/rfc7911>.
			[RFC8203] Snijders, J., Heitz, J., and J. Scudder, "BGP
			Administrative Shutdown Communication", RFC 8203,
			DOI 10.17487/RFC8203, July 2017,
			<https://www.rfc-editor.org/info/rfc8203>.
	Appendix A. Alternative techniques with limited applicability		Appendix A. Alternative techniques with limited applicability
	A few alternative techniques have been considered to provide graceful		A few alternative techniques have been considered to provide graceful
	shutdown capabilities but have been rejected due to their limited		shutdown capabilities but have been rejected due to their limited
	applicability. This section describe them for possible reference.		applicability. This section describes them for possible reference.
	A.1. Multi Exit Discriminator tweaking		A.1. Multi Exit Discriminator tweaking
	The MED attribute of the paths to be avoided can be increased so as		The MED attribute of the paths to be avoided can be increased so as
	to force the routers in the neighboring AS to select other paths.		to force the routers in the neighboring AS to select other paths.
	The solution only works if the alternate paths are as good as the		The solution only works if the alternate paths are as good as the
	initial ones with respect to the Local-Pref value and the AS Path		initial ones with respect to the LOCAL_PREF value and the AS Path
	Length value. In the other cases, increasing the MED value will not		Length value. In the other cases, increasing the MED value will not
	have an impact on the decision process of the routers in the		have an impact on the decision process of the routers in the
	neighboring AS.		neighboring AS.
	A.2. IGP distance Poisoning		A.2. IGP distance Poisoning
	The distance to the BGP NEXT_HOP corresponding to the maintained		The distance to the BGP NEXT_HOP corresponding to the maintained
	session can be increased in the IGP so that the old paths will be		session can be increased in the IGP so that the old paths will be
	less preferred during the application of the IGP distance tie-break		less preferred during the application of the IGP distance tie-break
	rule. However, this solution only works for the paths whose		rule. However, this solution only works for the paths whose
	alternates are as good as the old paths with respect to their Local-		alternates are as good as the old paths with respect to their
	Pref value, their AS Path length, and their MED value.		LOCAL_PREF value, their AS Path length, and their MED value.
	Also, this poisoning cannot be applied when nexthop self is used as		Also, this poisoning cannot be applied when BGP NEXT_HOP self is used
	there is no nexthop specific to the maintained session to poison in		as there is no BGP NEXT_HOP specific to the maintained session to
	the IGP.		poison in the IGP.
	Appendix B. Configuration Examples		Appendix B. Configuration Examples
	This appendix is non-normative.		This appendix is non-normative.
	Example routing policy configurations to honor the GRACEFUL_SHUTDOWN		Example routing policy configurations to honor the GRACEFUL_SHUTDOWN
	well-known BGP community.		well-known BGP community.
	B.1. Cisco IOS XR		B.1. Cisco IOS XR
	skipping to change at page 9, line 13 ¶		skipping to change at page 9, line 13 ¶
	following the injection of new best paths within the IBGP topology.		following the injection of new best paths within the IBGP topology.
	C.2.1. Unreachability local to the ASBR		C.2.1. Unreachability local to the ASBR
	An ASBR that selects as best a path received over a newly established		An ASBR that selects as best a path received over a newly established
	EBGP session may transiently drop traffic. This can typically happen		EBGP session may transiently drop traffic. This can typically happen
	when the NEXT_HOP attribute differs from the IP address of the EBGP		when the NEXT_HOP attribute differs from the IP address of the EBGP
	peer, and the receiving ASBR has not yet resolved the MAC address		peer, and the receiving ASBR has not yet resolved the MAC address
	associated with the IP address of that "third party" NEXT_HOP.		associated with the IP address of that "third party" NEXT_HOP.
	A BGP speaker implementation may avoid such losses by ensuring that		A BGP speaker implementation MAY avoid such losses by ensuring that
	"third party" NEXT_HOPs are resolved before installing paths using		"third party" NEXT_HOPs are resolved before installing paths using
	these in the RIB.		these in the RIB.
	Alternatively, the operator (script) may ping third party NEXT_HOPs		Alternatively, the operator (script) MAY ping third party NEXT_HOPs
	that are expected to be used before establishing the session. By		that are expected to be used before establishing the session. By
	proceeding like this, the MAC addresses associated with these third		proceeding like this, the MAC addresses associated with these third
	party NEXT_HOPs are resolved by the startup initiator.		party NEXT_HOPs are resolved by the startup initiator.
	C.2.2. IBGP convergence		C.2.2. IBGP convergence
	During the establishment of an EBGP session, in some corner cases a		During the establishment of an EBGP session, in some corner cases a
	router may have no path toward an affected prefix, leading to loss of		router may have no path toward an affected prefix, leading to loss of
	connectivity.		connectivity.
	A typical example for such transient unreachability for a given		A typical example for such transient unreachability for a given
	prefix is the following:		prefix is the following:
	Let's consider 3 route reflectors RR1, RR2, RR3. There is a full		Let's consider three Route Reflectors (RR): RR1, RR2, RR3. There is
	mesh of IBGP sessions between them.		a full mesh of IBGP sessions between them.
	1. RR1 is initially advertising the current best path to the		1. RR1 is initially advertising the current best path to the
	members of its IBGP RR full-mesh. It propagated that path within		members of its IBGP RR full-mesh. It propagated that path within
	its RR full-mesh. RR2 knows only that path toward the prefix.		its RR full-mesh. RR2 knows only that path toward the prefix.
	2. RR3 receives a new best path originated by the startup		2. RR3 receives a new best path originated by the startup
	initiator, being one of its RR clients. RR3 selects it as best,		initiator, being one of its RR clients. RR3 selects it as best,
	and propagates an UPDATE within its RR full-mesh, i.e., to RR1 and		and propagates an UPDATE within its RR full-mesh, i.e., to RR1 and
	RR2.		RR2.
End of changes. 21 change blocks.
	40 lines changed or deleted		38 lines changed or added
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