< draft-ietf-ospf-link-overload-11.txt		draft-ietf-ospf-link-overload-12.txt >
	Open Shortest Path First IGP S. Hegde		Open Shortest Path First IGP S. Hegde
	Internet-Draft Juniper Networks, Inc.		Internet-Draft Juniper Networks, Inc.
	Intended status: Standards Track P. Sarkar		Intended status: Standards Track P. Sarkar
	Expires: July 5, 2018 H. Gredler		Expires: July 20, 2018 H. Gredler
	Individual		Individual
	M. Nanduri		M. Nanduri
	ebay Corporation		ebay Corporation
	L. Jalil		L. Jalil
	Verizon		Verizon
	January 1, 2018		January 16, 2018
	OSPF Link Overload		OSPF Graceful Link shutdown
	draft-ietf-ospf-link-overload-11		draft-ietf-ospf-link-overload-12
	Abstract		Abstract
	When a link is being prepared to be taken out of service, the traffic		When a link is being prepared to be taken out of service, the traffic
	needs to be diverted from both ends of the link. Increasing the		needs to be diverted from both ends of the link. Increasing the
	metric to the highest metric on one side of the link is not		metric to the highest value on one side of the link is not sufficient
	sufficient to divert the traffic flowing in the other direction.		to divert the traffic flowing in the other direction.
	It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be		It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be
	able to advertise a link as being in an overload state to indicate		able to advertise a link as being in a graceful-shutdown state to
	impending maintenance activity on the link. This information can be		indicate impending maintenance activity on the link. This
	used by the network devices to re-route the traffic effectively.		information can be used by the network devices to re-route the
			traffic effectively.
	This document describes the protocol extensions to disseminate link-		This document describes the protocol extensions to disseminate
	overload information in OSPFv2 and OSPFv3.		graceful-link-shutdown information in OSPFv2 and OSPFv3.
	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" 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 2119 [RFC2119].
	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
	skipping to change at page 2, line 7 ¶		skipping to change at page 2, line 10 ¶
	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 5, 2018.		This Internet-Draft will expire on July 20, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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 29 ¶		skipping to change at page 2, line 32 ¶
	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 . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4		3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4
	4. Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4		4. Graceful-Link-Shutdown sub-TLV . . . . . . . . . . . . . . . 4
	4.1. OSPFv2 Link-overload sub-TLV . . . . . . . . . . . . . . 4		4.1. OSPFv2 graceful-link-shutdown sub-TLV . . . . . . . . . . 4
	4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 4		4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 5
	4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5		4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5
	4.4. OSPFv3 Link-Overload sub-TLV . . . . . . . . . . . . . . 6		4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV . . . . . . . . . . 6
	4.5. BGP-LS Link-overload TLV . . . . . . . . . . . . . . . . 6		4.5. BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . . 6
	4.6. Distinguishing parallel links . . . . . . . . . . . . . . 7		4.6. Distinguishing parallel links . . . . . . . . . . . . . . 7
	5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 8		5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 8
	5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 8		5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 8
	5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 8		5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 9
	5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 9		5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 9
	5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 9		5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 9
	5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 9		5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 10
	6. Backward compatibility . . . . . . . . . . . . . . . . . . . 10		6. Backward compatibility . . . . . . . . . . . . . . . . . . . 10
	7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 10		7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 10
	7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 10		7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 10
	7.2. Controller based Traffic Engineering Deployments . . . . 11		7.2. Controller based Traffic Engineering Deployments . . . . 11
	7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 12		7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 12
	7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 13		7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 13
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 13		8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
	11.1. Normative References . . . . . . . . . . . . . . . . . . 14		11.1. Normative References . . . . . . . . . . . . . . . . . . 14
	11.2. Informative References . . . . . . . . . . . . . . . . . 14		11.2. Informative References . . . . . . . . . . . . . . . . . 14
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
	1. Introduction		1. Introduction
	When a node is being prepared for a planned maintenance or upgrade,		When a node is being prepared for a planned maintenance or upgrade,
	[RFC6987] provides mechanisms to advertise the node being in an		[RFC6987] provides mechanisms to advertise the node being in a
	overload state by setting all outgoing link costs to MaxLinkMetric		graceful-shutdown state by setting all outgoing link costs to
	(0xffff). These procedures are specific to the maintenance activity		MaxLinkMetric (0xffff). These procedures are specific to the
	on a node and cannot be used when a single link on the node requires		maintenance activity on a node and cannot be used when a single link
	maintenance.		on the node requires maintenance.
	In traffic-engineering deployments, LSPs need to be diverted from the		In traffic-engineering deployments, LSPs need to be diverted from the
	link without disrupting the services. [RFC5817] describes		link without disrupting the services. [RFC5817] describes
	requirements and procedures for graceful shutdown of MPLS links. It		requirements and procedures for graceful shutdown of MPLS links. It
	is useful to be able to advertise the impending maintenance activity		is useful to be able to advertise the impending maintenance activity
	on the link and to have LSP re-routing policies at the ingress to		on the link and to have LSP re-routing policies at the ingress to
	route the LSPs away from the link.		route the LSPs away from the link.
	Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned		Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned
	by means of pseudo-wires or L2-circuits. Prior to devices in the		by means of pseudo-wires or L2-circuits. Prior to devices in the
	underlying network going offline for maintenance, it is useful to		underlying network going offline for maintenance, it is useful to
	divert the traffic away from the node before the maintenance is		divert the traffic away from the node before the maintenance is
	actually performed. Since the nodes in the underlying network are		actually performed. Since the nodes in the underlying network are
	not visible to OSPF, the existing stub router mechanism described in		not visible to OSPF, the existing stub router mechanism described in
	[RFC6987] cannot be used. An application specific to this use case		[RFC6987] cannot be used. An application specific to this use case
	is described in Section 7.1.		is described in Section 7.1.
	This document provides mechanisms to advertise link-overload state in		The procedures described in this draft may be used to divert the
	the flexible encodings provided by OSPFv2 Prefix/Link Attribute		traffic away from the link in other scenarios and is not restricted
	Advertisement [RFC7684]. Throughout this document, OSPF is used when		to link-shutdown or link-replacement activity.
	the text applies to both OSPFv2 and OSPFv3. OSPFv2 or OSPFv3 is used
	when the text is specific to one version of the OSPF protocol.		This document provides mechanisms to advertise graceful-link-shutdown
			state in the flexible encodings provided by OSPFv2 Prefix/Link
			Attribute Advertisement [RFC7684]. Throughout this document, OSPF is
			used when the text applies to both OSPFv2 and OSPFv3. OSPFv2 or
			OSPFv3 is used when the text is specific to one version of the OSPF
			protocol.
	2. Motivation		2. Motivation
	The motivation of this document is to reduce manual intervention		The motivation of this document is to reduce manual intervention
	during maintenance activities. The following objectives help to		during maintenance activities. The following objectives help to
	accomplish this in a range of deployment scenarios.		accomplish this in a range of deployment scenarios.
	1. Advertise impending maintenance activity so that traffic from		1. Advertise impending maintenance activity so that traffic from
	both directions can be diverted away from the link.		both directions can be diverted away from the link.
	2. Allow the solution to be backward compatible so that nodes that		2. Allow the solution to be backward compatible so that nodes that
	do not understand the new advertisement do not cause routing		do not understand the new advertisement do not cause routing
	loops.		loops.
	3. Advertise the maintenance activity to other nodes in the network		3. Advertise the maintenance activity to other nodes in the network
	so that LSP ingress routers/controllers can learn of the		so that LSP ingress routers/controllers can learn about the
	impending maintenance activity and apply specific policies to re-		impending maintenance activity and apply specific policies to re-
	route the LSPs for traffic-engineering based deployments.		route the LSPs for traffic-engineering based deployments.
	4. Allow the link to be used as last resort link to prevent traffic		4. Allow the link to be used as last resort link to prevent traffic
	disruption when alternate paths are not available.		disruption when alternate paths are not available.
	3. Flooding Scope		3. Flooding Scope
	The link-overload information is flooded in area-scoped Extended Link		The graceful-link-shutdown information is flooded in area-scoped
	Opaque LSA [RFC7684]. The Link-Overload sub-TLV MAY be processed by		Extended Link Opaque LSA [RFC7684]. The Graceful-Link-Shutdown sub-
	the head-end nodes or the controller as described in the Section 7.		TLV MAY be processed by the head-end nodes or the controller as
	The procedures for processing the Link-Overload sub-TLV are described		described in the Section 7. The procedures for processing the
	in Section 5.		Graceful-Link-Shutdown sub-TLV are described in Section 5.
	4. Link-Overload sub-TLV		4. Graceful-Link-Shutdown sub-TLV
	4.1. OSPFv2 Link-overload sub-TLV		4.1. OSPFv2 graceful-link-shutdown sub-TLV
	The Link-Overload sub-TLV identifies the link as being in overload		The Graceful-Link-Shutdown sub-TLV identifies the link as being
	state.It is advertised in extended Link TLV of the Extended Link		gracefully shutdown. It is advertised in extended Link TLV of the
	Opaque LSA as defined in [RFC7684].		Extended Link Opaque LSA as defined in [RFC7684].
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length |		| Type | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Figure 1: Link-Overload sub-TLV for OSPFv2		Figure 1: Graceful-Link-Shutdown sub-TLV for OSPFv2
	Type : TBA (suggested value 7)		Type : TBA (suggested value 7)
	Length: 0		Length: 0
	4.2. Remote IPv4 Address Sub-TLV		4.2. Remote IPv4 Address Sub-TLV
	This sub-TLV specifies the IPv4 address of remote endpoint on the		This sub-TLV specifies the IPv4 address of remote endpoint on the
	link. It is advertised in the Extended Link TLV as defined in		link. It is advertised in the Extended Link TLV as defined in
	[RFC7684]. This sub-TLV is optional and MAY be advertised in area-		[RFC7684]. This sub-TLV is optional and MAY be advertised in area-
	skipping to change at page 6, line 24 ¶		skipping to change at page 6, line 24 ¶
	Figure 3: Local/Remote Interface ID Sub-TLV		Figure 3: Local/Remote Interface ID Sub-TLV
	Type : TBA (suggested value 9)		Type : TBA (suggested value 9)
	Length: 8		Length: 8
	Value: 4 octets of Local Interface ID followed by 4 octets of Remote		Value: 4 octets of Local Interface ID followed by 4 octets of Remote
	interface ID.		interface ID.
	4.4. OSPFv3 Link-Overload sub-TLV		4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV
	The Link Overload sub-TLV is carried in the Router-Link TLV as		The Graceful-Link-Shutdown sub-TLV is carried in the Router-Link TLV
	defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The		as defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The
	Router-Link TLV contains the neighbour interface-id and can uniquely		Router-Link TLV contains the neighbour interface-id and can uniquely
	identify the link on the remote node.		identify the link on the remote node.
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length |		| Type | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Figure 4: Link-Overload sub-TLV for OSPFv3		Figure 4: Graceful-Link-Shutdown sub-TLV for OSPFv3
	Type : TBA (Suggested value 7)		Type : TBA (Suggested value 7)
	Length: 0		Length: 0
	4.5. BGP-LS Link-overload TLV		4.5. BGP-LS Graceful-Link-Shutdown TLV
	BGP-LS as defined in [RFC7752] is a mechanism to distribute network		BGP-LS as defined in [RFC7752] is a mechanism to distribute network
	information to external entities using BGP routing protocol. link-		information to external entities using BGP routing protocol.
	overload is an imporatant link information that the external entities		Graceful-link-shutdown is an imporatant link information that the
	can use for various usecases as defined in Section 7. BGP Link NLRI		external entities can use for various use cases as defined in
	is used to carry the link information. a new TLV called Link-		Section 7. BGP Link NLRI is used to carry the link information. A
	Overload is defined to describe the link attribute corresponding to		new TLV called Graceful-Link-Shutdown is defined to describe the link
	link-overload state.		attribute corresponding to graceful-link-shutdown state.
	4.6. Distinguishing parallel links		4.6. Distinguishing parallel links
	++++++++++I.w I.y +++++++++		++++++++++I.w I.y +++++++++
	|Router A|------------------|Router B |		|Router A|------------------|Router B |
	| |------------------| |		| |------------------| |
	++++++++++I.x I.z++++++++++		++++++++++I.x I.z++++++++++
	Figure 5: Parallel Linkls		Figure 5: Parallel Linkls
	skipping to change at page 7, line 35 ¶		skipping to change at page 7, line 35 ¶
	Link-ID: Router-ID B		Link-ID: Router-ID B
	Link-Data = I.w		Link-Data = I.w
	A third node (controller or head-end) in the network cannot		A third node (controller or head-end) in the network cannot
	distinguish the Interface on router B which is connected to this		distinguish the Interface on router B which is connected to this
	particular Interface with the above information. Interface with		particular Interface with the above information. Interface with
	address I.y or I.z could be chosen due to this ambiguity. In such		address I.y or I.z could be chosen due to this ambiguity. In such
	cases Remote-IPv4 Address sub-TLV should be originated and added to		cases Remote-IPv4 Address sub-TLV should be originated and added to
	the extended link-TLV. The usecases as described in Section 7		the extended link-TLV. The use cases as described in Section 7
	require controller or head-end nodes to interpret the link-overload		require controller or head-end nodes to interpret the graceful-link-
	information and hence the need for the RemoteIPv4 address sub-TLV.		shutdown information and hence the need for the RemoteIPv4 address
	I.y is carried in the extended-link-TLV which unambiguously		sub-TLV. I.y is carried in the extended-link-TLV which unambiguously
	identifies the interface on the remote side. OSPFv3 Router-link-TLV		identifies the interface on the remote side. OSPFv3 Router-link-TLV
	as described in [I-D.ietf-ospf-ospfv3-lsa-extend] contains Interface		as described in [I-D.ietf-ospf-ospfv3-lsa-extend] contains Interface
	ID and neighbor's Interface-ID which can uniquely identify connecting		ID and neighbor's Interface-ID which can uniquely identify connecting
	interface on the remote side and hence OSPFv3 does not require		interface on the remote side and hence OSPFv3 does not require
	seperate Remote-IPv6 address to be advertised along with OSPFv2-link-		seperate Remote-IPv6 address to be advertised along with OSPFv3-
	overload-sub-TLV.		Graceful-Link-Shutdown sub-TLV.
	5. Elements of procedure		5. Elements of procedure
	As defined in [RFC7684] every link on the node will have a separate		As defined in [RFC7684] every link on the node will have a separate
	Extended Link Opaque LSA. The node that has the link to be taken out		Extended Link Opaque LSA. The node that has the link to be taken out
	of service SHOULD advertise the Link-Overload sub-TLV in the Extended		of service SHOULD advertise the Graceful-Link-Shutdown sub-TLV in the
	Link TLV of the Extended Link Opaque LSA as defined in [RFC7684] for		Extended Link TLV of the Extended Link Opaque LSA as defined in
	OSPFv2. The Link-Overload sub-TLV indicates that the link identified		[RFC7684] for OSPFv2. The Graceful-Link-Shutdown sub-TLV indicates
	by the sub-TLV is overloaded. The Link-Overload information is		that the link identified by the sub-TLV is subjected to maintenance.
	advertised as a property of the link and is flooded across the area.		The Graceful-Link-Shutdown information is advertised as a property of
	This information can be used by ingress routers or controllers to		the link and is flooded across the area. This information can be
	take special actions. An application specific to this use case is		used by ingress routers or controllers to take special actions. An
	described in Section 7.2.		application specific to this use case is described in Section 7.2.
	The precise action taken by the remote node at the other end of the		The precise action taken by the remote node at the other end of the
	link identified as overloaded depends on the link type.		link identified for graceful-shutdown depends on the link type.
	5.1. Point-to-point links		5.1. Point-to-point links
	The node that has the link to be taken out of service MUST set metric		The node that has the link to be taken out of service MUST set metric
	of the link to MaxLinkMetric (0xffff) and re-originate its router-		of the link to MaxLinkMetric (0xffff) and re-originate its router-
	LSA. The TE metric SHOULD be set to MAX-TE-METRIC (0xfffffffe) and		LSA. MAX-TE-METRIC is a constant defined by this draft and set to
	the node SHOULD re-originate the corresponding TE Link Opaque LSAs.		0xfffffffe. The TE metric SHOULD be set to MAX-TE-METRIC
	When a Link-Overload sub-TLV is received for a point-to-point link,		(0xfffffffe) and the node SHOULD re-originate the corresponding TE
	the remote node MUST identify the local link which corresponds to the		Link Opaque LSAs. When a Graceful-Link-Shutdown sub-TLV is received
	overloaded link and set the metric to MaxLinkMetric (0xffff)and the		for a point-to-point link, the remote node MUST identify the local
	remote node MUST re-originate its router-LSA with the changed metric.		link which corresponds to the graceful-shutdown link and set the
	The TE metric SHOULD be set to MAX-TE-METRIC (0xfffffffe) and the TE		metric to MaxLinkMetric (0xffff) and the remote node MUST re-
	opaque LSA for the link SHOULD be re-originated with new value.		originate its router-LSA with the changed metric. The TE metric
			SHOULD be set to MAX-TE-METRIC (0xfffffffe) and the TE opaque LSA for
			the link SHOULD be re-originated with new value.
	The Extended link opaque LSAs and the Extended link TLV are not		The Extended link opaque LSAs and the Extended link TLV are not
	scoped for multi-topology [RFC4915]. In multi-topology deployments		scoped for multi-topology [RFC4915]. In multi-topology deployments
	[RFC4915], the Link-Overload sub-TLV advertised in an Extended Link		[RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an
	opaque LSA corresponds to all the topologies which include the link.		Extended Link opaque LSA corresponds to all the topologies which
	The receiver node SHOULD change the metric in the reverse direction		include the link. The receiver node SHOULD change the metric in the
	for all the topologies which include the remote link and re-originate		reverse direction for all the topologies which include the remote
	the router-LSA as defined in [RFC4915].		link and re-originate the router-LSA as defined in [RFC4915].
	When the originator of the Link-Overload sub-TLV purges the Extended		When the originator of the Graceful-Link-Shutdown sub-TLV purges the
	Link Opaque LSA or re-originates it without the Link-Overload sub-		Extended Link Opaque LSA or re-originates it without the Graceful-
	TLV, the remote node must re-originate the appropriate LSAs with the		Link-Shutdown sub-TLV, the remote node must re-originate the
	metric and TE metric values set to their original values.		appropriate LSAs with the metric and TE metric values set to their
			original values.
	5.2. Broadcast/NBMA links		5.2. Broadcast/NBMA links
	Broadcast or NBMA networks in OSPF are represented by a star topology		Broadcast or NBMA networks in OSPF are represented by a star topology
	where the Designated Router (DR) is the central point to which all		where the Designated Router (DR) is the central point to which all
	other routers on the broadcast or NBMA network logically connect. As		other routers on the broadcast or NBMA network logically connect. As
	a result, routers on the broadcast or NBMA network advertise only		a result, routers on the broadcast or NBMA network advertise only
	their adjacency to the DR. Routers that do not act as DR do not form		their adjacency to the DR. Routers that do not act as DR do not form
	or advertise adjacencies with each other. For the Broadcast links,		or advertise adjacencies with each other. For the Broadcast links,
	the MaxLinkMetric on the remote link cannot be changed since all the		the MaxLinkMetric on the remote link cannot be changed since all the
	neighbors are on same link. Setting the link cost to MaxLinkMetric		neighbors are on same link. Setting the link cost to MaxLinkMetric
	would impact paths going via all neighbors.		would impact paths going via all neighbors.
	The node that has the link to be taken out of service MUST set metric		The node that has the link to be taken out of service MUST set metric
	of the link to MaxLinkMetric (0xffff) and re-originate the Router-		of the link to MaxLinkMetric (0xffff) and re-originate the Router-
	LSA. The TE metric SHOULD be set to MAX-TE-METRIC( 0xfffffffe) and		LSA. The TE metric SHOULD be set to MAX-TE-METRIC( 0xfffffffe) and
	the node SHOULD re-originate the corresponding TE Link Opaque LSAs.		the node SHOULD re-originate the corresponding TE Link Opaque LSAs.
	For a broadcast link, the two part metric as described in [RFC8042]		For a broadcast link, the two part metric as described in [RFC8042]
	is used. The node originating the Link-Overload sub-TLV MUST set the		is used. The node originating the Graceful-Link-Shutdown sub-TLV
	metric in the Network-to-Router Metric sub-TLV to MaxLinkMetric		MUST set the metric in the Network-to-Router Metric sub-TLV to
	(0xffff) for OSPFv2 and OSPFv3 and re-originate the corresponding		MaxLinkMetric (0xffff) for OSPFv2 and OSPFv3 and re-originate the
	LSAs. The nodes that receive the two-part metric should follow the		corresponding LSAs. The nodes that receive the two-part metric
	procedures described in [RFC8042]. The backward compatibility		should follow the procedures described in [RFC8042]. The backward
	procedures described in [RFC8042] should be followed to ensure loop		compatibility procedures described in [RFC8042] should be followed to
	free routing.		ensure loop free routing.
	5.3. Point-to-multipoint links		5.3. Point-to-multipoint links
	Operation for the point-to-multipoint links is similar to the point-		Operation for the point-to-multipoint links is similar to the point-
	to-point links. When a Link-Overload sub-TLV is received for a		to-point links. When a Graceful-Link-Shutdown sub-TLV is received
	point-to-multipoint link the remote node MUST identify the neighbour		for a point-to-multipoint link the remote node MUST identify the
	which corresponds to the overloaded link and set the metric to		neighbour which corresponds to the graceful-shutdown link and set the
	MaxLinkMetric (0xffff). The remote node MUST re-originate the		metric to MaxLinkMetric (0xffff). The remote node MUST re-originate
	router-LSA with the changed metric for the correponding neighbor.		the router-LSA with the changed metric for the correponding neighbor.
	5.4. Unnumbered interfaces		5.4. Unnumbered interfaces
	Unnumbered interface do not have a unique IP address and borrow their		Unnumbered interface do not have a unique IP address and borrow their
	address from other interfaces. [RFC2328] describes procedures to		address from other interfaces. [RFC2328] describes procedures to
	handle unnumbered interfaces in the context of the router-LSA. We		handle unnumbered interfaces in the context of the router-LSA. We
	apply a similar procedure to the Extended Link TLV advertising the		apply a similar procedure to the Extended Link TLV advertising the
	Link-Overload sub-TLV in order to handle unnumbered interfaces. The		Graceful-Link-Shutdown sub-TLV in order to handle unnumbered
	link-data field in the Extended Link TLV includes the Local		interfaces. The link-data field in the Extended Link TLV includes
	interface-id instead of the IP address. The Local/Remote Interface		the Local interface-id instead of the IP address. The Local/Remote
	ID sub-TLV MUST be advertised when there are multiple parallel		Interface ID sub-TLV MUST be advertised when there are multiple
	unnumbered interfaces between two nodes. One of the mechanisms to		parallel unnumbered interfaces between two nodes. One of the
	obtain the interface-id of the remote side are defined in [RFC4203].		mechanisms to obtain the interface-id of the remote side are defined
			in [RFC4203].
	5.5. Hybrid Broadcast and P2MP interfaces		5.5. Hybrid Broadcast and P2MP interfaces
	Hybrid Broadcast and P2MP interfaces represent a broadcast network		Hybrid Broadcast and P2MP interfaces represent a broadcast network
	modeled as P2MP interfaces. [RFC6845] describes procedures to handle		modeled as P2MP interfaces. [RFC6845] describes procedures to handle
	these interfaces. Operation for the Hybrid interfaces is similar to		these interfaces. Operation for the Hybrid interfaces is similar to
	the P2MP interfaces. When a Link-Overload sub-TLV is received for a		the P2MP interfaces. When a Graceful-Link-Shutdown sub-TLV is
	hybrid link, the remote node MUST identify the neighbor which		received for a hybrid link, the remote node MUST identify the
	corresponds to the overloaded link and set the metric to		neighbor which corresponds to the graceful-shutdown link and set the
	MaxLinkMetric (0xffff). All the remote nodes connected to originator		metric to MaxLinkMetric (0xffff). All the remote nodes connected to
	MUST re-originate the router-LSA with the changed metric for the		originator MUST re-originate the router-LSA with the changed metric
	neighbor.		for the neighbor.
	6. Backward compatibility		6. Backward compatibility
	The mechanisms described in the document are fully backward		The mechanisms described in the document are fully backward
	compatible. It is required that the node adverting the Link-Overload		compatible. It is required that the node adverting the Graceful-
	sub-TLV as well as the node at the remote end of the overloaded link		Link-Shutdown sub-TLV as well as the node at the remote end of the
	support the extensions described herein for the traffic to diverted		graceful-shutdown link support the extensions described herein for
	from the overloaded link. If the remote node doesn't support the		the traffic to diverted from the graceful-shutdown link. If the
	capability, it will still use the overloaded link but there are no		remote node doesn't support the capability, it will still use the
	other adverse effects. In the case of broadcast links using two-part		graceful-shutdown link but there are no other adverse effects. In
	metrics, the backward compatibility procedures as described in		the case of broadcast links using two-part metrics, the backward
	[RFC8042] are applicable.		compatibility procedures as described in [RFC8042] are applicable.
	7. Applications		7. Applications
	7.1. Pseudowire Services		7.1. Pseudowire Services
	Many service providers offer pseudo-wire services to customers using		Many service providers offer pseudo-wire services to customers using
	L2 circuits. The IGP protocol that runs in the customer network		L2 circuits. The IGP protocol that runs in the customer network
	would also run over the pseudo-wire to create a seamless private		would also run over the pseudo-wire to create a seamless private
	network for the customer. Service providers want to offer overload		network for the customer. Service providers want to offer graceful-
	functionality when the PE device is taken-out for maintenance. The		shutdown functionality when the PE device is taken-out for
	provider should guarantee that the PE is taken out for maintenance		maintenance. The provider should guarantee that the PE is taken out
	only after the service is successfully diverted on an alternate path.		for maintenance only after the service is successfully diverted on an
	There can be large number of customers attached to a PE node and the		alternate path. There can be large number of customers attached to a
	remote end-points for these pseudo-wires are spread across the		PE node and the remote end-points for these pseudo-wires are spread
	service provider's network. It is a tedious and error-prone process		across the service provider's network. It is a tedious and error-
	to change the metric for all pseudo-wires in both directions. The		prone process to change the metric for all pseudo-wires in both
	link-overload feature simplifies the process by increasing the metric		directions. The graceful-link-shutdown feature simplifies the
	on the link in the reverse direction as well so that traffic in both		process by increasing the metric on the link in the reverse direction
	directions is diverted away from the PE undergoing maintenance. The		as well so that traffic in both directions is diverted away from the
	Link-Overload feature allows the link to be used as a last resort		PE undergoing maintenance. The Graceful-Link-Shutdown feature allows
	link so that traffic is not disrupted when alternative paths are not		the link to be used as a last resort link so that traffic is not
	available.		disrupted when alternative paths are not available.
	Private VLAN		Private VLAN
	=======================================		=======================================
	| |		| |
	| |		| |
	| ------PE3---------------PE4------CE3		| ------PE3---------------PE4------CE3
	| / \		| / \
	| / \		| / \
	CE1---------PE1----------PE2---------CE2		CE1---------PE1----------PE2---------CE2
	| \		| \
	skipping to change at page 11, line 25 ¶		skipping to change at page 11, line 25 ¶
	| ------CE4		| ------CE4
	| |		| |
	| |		| |
	| |		| |
	=================================		=================================
	Private VLAN		Private VLAN
	Figure 6: Pseudowire Services		Figure 6: Pseudowire Services
	In the example shown in Figure 6, when the PE1 node is going out of		In the example shown in Figure 6, when the PE1 node is going out of
	service for maintenance, service providers set the PE1 to overload		service for maintenance, service providers set the PE1 to graceful-
	state. The PE1 going in to overload state triggers all the CEs		link-shutdown state. The PE1 going in to maintenance state triggers
	connected to the PE (CE1 in this case) to set their pseudowire links		all the CEs connected to the PE (CE1 in this case) to set their
	passing via PE1 to link-overload state. The mechanisms used to		pseudowire links passing via PE1 to graceful-link-shutdown state.
	communicate between PE1 and CE1 is outside the scope of this		The mechanisms used to communicate between PE1 and CE1 is outside the
	document. CE1 sets the link-overload state on its private VLAN		scope of this document. CE1 sets the graceful-link-shutdown state on
	connecting CE3, CE2 and CE4 and changes the metric to MAX_METRIC and		its private VLAN connecting CE3, CE2 and CE4 and changes the metric
	re-originates the corresponding LSA. The remote end of the link at		to MAX_METRIC and re-originates the corresponding LSA. The remote
	CE3, CE2, and CE4 also set the metric on the link to MaxLinkMetric		end of the link at CE3, CE2, and CE4 also set the metric on the link
	and the traffic from both directions gets diverted away from the		to MaxLinkMetric and the traffic from both directions gets diverted
	pseudowires.		away from the pseudowires.
	7.2. Controller based Traffic Engineering Deployments		7.2. Controller based Traffic Engineering Deployments
	In controller-based deployments where the controller participates in		In controller-based deployments where the controller participates in
	the IGP protocol, the controller can also receive the link-overload		the IGP protocol, the controller can also receive the graceful-link-
	information as a warning that link maintenance is imminent. Using		shutdown information as a warning that link maintenance is imminent.
	this information, the controller can find alternate paths for traffic		Using this information, the controller can find alternate paths for
	which uses the affected link. The controller can apply various		traffic which uses the affected link. The controller can apply
	policies and re-route the LSPs away from the link undergoing		various policies and re-route the LSPs away from the link undergoing
	maintenance. If there are no alternate paths satisfying the traffic		maintenance. If there are no alternate paths satisfying the traffic
	engineering constraints, the controller might temporarily relax those		engineering constraints, the controller might temporarily relax those
	constraints and put the service on a different path. Increasing the		constraints and put the service on a different path. Increasing the
	link metric alone does not specify the maintenance activity as the		link metric alone does not specify the maintenance activity as the
	metric could increase in events such as LDP-IGP synchronisation. An		metric could increase in events such as LDP-IGP synchronisation. An
	explicit indication from the router using the link-overload sub-TLV		explicit indication from the router using the graceful-link-shutdown
	is needed to inform the Controller or head-end routers.		sub-TLV is needed to inform the Controller or head-end routers.
	_____________		_____________
	| |		| |
	-------------| Controller |--------------		-------------| Controller |--------------
	| |____________ | |		| |____________ | |
	| |		| |
	|--------- Primary Path ------------------|		|--------- Primary Path ------------------|
	PE1---------P1----------------P2---------PE2		PE1---------P1----------------P2---------PE2
	| |		| |
	| |		| |
	|________P3________|		|________P3________|
	Alternate Path		Alternate Path
	Figure 7: Controller based Traffic Engineering		Figure 7: Controller based Traffic Engineering
	In the above example, PE1->PE2 LSP is set-up to satisfy a constraint		In the above example, PE1->PE2 LSP is set-up to satisfy a constraint
	of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have		of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have
	only 1 Gbps capacity and there is no alternate path satisfying the		only 1 Gbps capacity and there is no alternate path satisfying the
	bandwidth constraint of 10Gbps. When P1->P2 link is being prepared		bandwidth constraint of 10Gbps. When P1->P2 link is being prepared
	for maintenance, the controller receives the link-overload		for maintenance, the controller receives the graceful-link-shutdown
	information, as there is no alternate path available which satisfies		information, as there is no alternate path available which satisfies
	the constraints, the controller chooses a path that is less optimal		the constraints, the controller chooses a path that is less optimal
	and temporarily sets up an alternate path via P1->P3->P2. Once the		and temporarily sets up an alternate path via P1->P3->P2. Once the
	traffic is diverted, the P1->P2 link can be taken out of service for		traffic is diverted, the P1->P2 link can be taken out of service for
	maintenance/upgrade.		maintenance/upgrade.
	7.3. L3VPN Services and sham-links		7.3. L3VPN Services and sham-links
	Many service providers offer L3VPN services to customers and CE-PE		Many service providers offer L3VPN services to customers and CE-PE
	links run OSPF [RFC4577]. When PE is taken out of service for		links run OSPF [RFC4577]. When PE is taken out of service for
	maintenance, all the links on the PE can be set to link-overload		maintenance, all the links on the PE can be set to graceful-link-
	state which will gurantee that the traffic to/from dual-homed CEs		shutdown state which will gurantee that the traffic to/from dual-
	gets diverted. The interaction between OSPF and BGP is outside the		homed CEs gets diverted. The interaction between OSPF and BGP is
	scope of this document. [RFC6987] based mechanism with summaries and		outside the scope of this document. [RFC6987] based mechanism with
	externals advertised with high metrics could also be used to achieve		summaries and externals advertised with high metrics could also be
	the same functionality when implementations support high metrics		used to achieve the same functionality when implementations support
	advertisement for summaries and externals.		high metrics advertisement for summaries and externals.
	Another useful usecase is when ISPs provide sham-link services to		Another useful usecase is when ISPs provide sham-link services to
	customers [RFC4577]. When PE goes out of service for maintenance,		customers [RFC4577]. When PE goes out of service for maintenance,
	all sham-links on the PE can be set to link-overload state and		all sham-links on the PE can be set to graceful-link-shutdown state
	traffic can be divered from both ends without having to touch the		and traffic can be divered from both ends without having to touch the
	configurations on the remote end of the sham-links.		configurations on the remote end of the sham-links.
	7.4. Hub and spoke deployment		7.4. Hub and spoke deployment
	OSPF is largely deployed in Hub and Spoke deployments with a large		OSPF is largely deployed in Hub and Spoke deployments with a large
	number of spokes connecting to the Hub. It is a general practice to		number of spokes connecting to the Hub. It is a general practice to
	deploy multiple Hubs with all spokes connecting to these Hubs to		deploy multiple Hubs with all spokes connecting to these Hubs to
	achieve redundancy. The [RFC6987] mechanism can be used to divert		achieve redundancy. The [RFC6987] mechanism can be used to divert
	the spoke-to-spoke traffic from the overloaded hub router. The		the spoke-to-spoke traffic from the overloaded hub router. The
	traffic that flows from spokes via the hub into an external network		traffic that flows from spokes via the hub into an external network
	may not be diverted in certain scenarios.When a Hub node goes down		may not be diverted in certain scenarios.When a Hub node goes down
	for maintenance, all links on the Hub can be set to link-overload		for maintenance, all links on the Hub can be set to graceful-link-
	state and traffic gets divered from the spoke sites as well without		shutdown state and traffic gets divered from the spoke sites as well
	having to make configuration changes on the spokes.		without having to make configuration changes on the spokes.
	8. Security Considerations		8. Security Considerations
	This document does not introduce any further security issues other		This document does not introduce any further security issues other
	than those discussed in [RFC2328] and [RFC5340].		than those discussed in [RFC2328] and [RFC5340].
	9. IANA Considerations		9. IANA Considerations
	This specification updates one OSPF registry:		This specification updates one OSPF registry:
	OSPFv2 Extended Link TLV Sub-TLVs		OSPFv2 Extended Link TLV Sub-TLVs
	i) Link-Overload Sub-TLV - Suggested value 7		i) Graceful-Link-Shutdown Sub-TLV - Suggested value 7
	ii) Remote IPv4 Address Sub-TLV - Suggested value 8		ii) Remote IPv4 Address Sub-TLV - Suggested value 8
	iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9		iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9
	OSPFv3 Extended-LSA sub-TLV Registry		OSPFv3 Extended-LSA sub-TLV Registry
	i) Link-Overload sub-TLV - suggested value 7		i) Graceful-Link-Shutdown sub-TLV - suggested value 7
	BGP-LS Link NLRI Registry [RFC7752]		BGP-LS Link NLRI Registry [RFC7752]
	i)Link-Overload TLV - Suggested 1101		i)Graceful-Link-Shutdown TLV - Suggested 1101
	10. Acknowledgements		10. Acknowledgements
	Thanks to Chris Bowers for valuable inputs and edits to the document.		Thanks to Chris Bowers for valuable inputs and edits to the document.
	Thanks to Jeffrey Zhang, Acee Lindem and Ketan Talaulikar for inputs.		Thanks to Jeffrey Zhang, Acee Lindem and Ketan Talaulikar for inputs.
	Thanks to Karsten Thomann for careful review and inputs on the		Thanks to Karsten Thomann for careful review and inputs on the
	applications where link-overload is useful.		applications where graceful-link-shutdown is useful.
	11. References		11. References
	11.1. Normative References		11.1. Normative References
	[I-D.ietf-ospf-ospfv3-lsa-extend]		[I-D.ietf-ospf-ospfv3-lsa-extend]
	Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3		Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
	LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-10		LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-10
	(work in progress), May 2016.		(work in progress), May 2016.
End of changes. 48 change blocks.
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