< draft-ietf-ospf-segment-routing-msd-08.txt		draft-ietf-ospf-segment-routing-msd-09.txt >
	OSPF Working Group J. Tantsura		OSPF Working Group J. Tantsura
	Internet-Draft Individual		Internet-Draft Nuage Networks
	Intended status: Standards Track U. Chunduri		Intended status: Standards Track U. Chunduri
	Expires: June 17, 2018 Huawei Technologies		Expires: August 30, 2018 Huawei Technologies
	S. Aldrin		S. Aldrin
	Google, Inc		Google, Inc
	P. Psenak		P. Psenak
	Cisco Systems		Cisco Systems
	December 14, 2017		February 26, 2018
	Signaling MSD (Maximum SID Depth) using OSPF		Signaling MSD (Maximum SID Depth) using OSPF
	draft-ietf-ospf-segment-routing-msd-08		draft-ietf-ospf-segment-routing-msd-09
	Abstract		Abstract
	This document proposes a way to signal Maximum SID Depth (MSD)		This document defines a way for an OSPF Router to advertise multiple
	supported by a node at node and/or link granularity by an OSPF		types of supported Maximum SID Depths (MSDs) at node and/or link
	Router. In a Segment Routing (SR) enabled network a centralized		granularity. Such advertisements allow entities (e.g., centralized
	controller that programs SR tunnels needs to know the MSD supported		controllers) to determine whether a particular SID stack is
	by the head-end at node and/or link granularity to impose the SID		supportable in a given network. This document only defines one type
	stack of an appropriate depth. MSD is relevant to the head-end of a		of MSD (maximum label imposition) - but defines an encoding which can
	SR tunnel or Binding-SID anchor node where Binding-SID expansions		support other MSD types. Here the term OSPF means both OSPFv2 and
	might result in creation of a new SID stack. Here the term OSPF		OSPFv3.
	means both OSPFv2 and OSPFv3.
	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
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	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 June 17, 2018.		This Internet-Draft will expire on August 30, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2017 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.
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	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
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	skipping to change at page 2, line 24 ¶		skipping to change at page 2, line 24 ¶
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Conventions used in this document . . . . . . . . . . . . 3		1.1. Conventions used in this document . . . . . . . . . . . . 3
	1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3		1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
	1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3		1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4		3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
	4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5		4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5
	5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5		5. Using Node and Link MSD Advertisements . . . . . . . . . . . 5
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		6. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 6		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6		8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6		9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
	10.1. Normative References . . . . . . . . . . . . . . . . . . 7		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	10.2. Informative References . . . . . . . . . . . . . . . . . 7		11.1. Normative References . . . . . . . . . . . . . . . . . . 7
			11.2. Informative References . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	When Segment Routing tunnels are computed by a centralized		When Segment Routing(SR) paths are computed by a centralized
	controller, it is critical that the controller learns the MSD		controller, it is critical that the controller learns the Maximum SID
	"Maximum SID Depth" of the node or link SR tunnel exits over, so the		Depth(MSD) which can be imposed at the node/link a given SR path is
	SID stack depth of a path computed doesn't exceed the number of SIDs		applied so as to insure that the SID stack depth of a computed path
	the node is capable of imposing. This document describes how to use		doesn't exceed the number of SIDs the node is capable of imposing.
	OSPF to signal the MSD of a node or link to a centralized controller.
	PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD		PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD
	in SR PCE Capability TLV and METRIC Object. However, if PCEP is not		in SR PCE Capability TLV and METRIC Object. However, if PCEP is not
	supported/configured on the head-end of a SR tunnel or a Binding-SID		supported/configured on the head-end of a SR tunnel or a Binding-SID
	anchor node and controller does not participate in IGP routing, it		anchor node and controller does not participate in IGP routing, it
	has no way to learn the MSD of nodes and links which has been		has no way to learn the MSD of nodes and links which has been
	configured. BGP-LS [RFC7752] defines a way to expose topology and		configured. BGP-LS [RFC7752] defines a way to expose topology and
	associated attributes and capabilities of the nodes in that topology		associated attributes and capabilities of the nodes in that topology
	to a centralized controller. MSD signaling by BGP-LS has been		to a centralized controller. MSD signaling by BGP-LS has been
	defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically,		defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically,
	BGP-LS is configured on a small number of nodes, that do not		BGP-LS is configured on a small number of nodes, that do not
	necessarily act as head-ends. In order, for BGP-LS to signal MSD for		necessarily act as head-ends. In order, for BGP-LS to signal MSD for
	the all nodes and links in the network MSD is relevant, MSD		all the nodes and links in the network MSD is relevant, MSD
	capabilites SHOULD be distributed to every OSPF router in the		capabilites should be advertised to every OSPF router in the network.
	network.
			Other types of MSD are known to be useful. For example,
	[I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability		[I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability
	(RLDC) that is used by a head-end to insert Entropy Label (EL) at		(RLDC) that is used by a head-end to insert Entropy Label (EL) at
	appropriate depth, so it could be read by transit nodes. MSD in		appropriate depth, so it could be read by transit nodes.
	contrary signals ability to impose SID's stack of a particular depth.
	MSD of type 1 (IANA Registry), called Base MSD is used to signal the		This document defines an extension to OSPF used to advertise one or
	total number of SIDs a node is capable of imposing, to be used by a		more types of MSD at node and/or link granularity. It also creates
	path computation element/controller. In case, there are additional		an IANA registry for assigning MSD type identifiers. It also defines
	SIDs (e.g. service) that are to be imposed to the stack - this would		one MSD type called Base MPLS Imposition MSD. In the future it is
	be signaled with an another MSD type (TBD), no adjustment to the Base		expected that new MSD types will be defined to signal additional
	MSD should be made. In the future, new MSD types could be defined to		capabilities e.g., entropy labels, SIDs that can be imposed through
	signal additional capabilities: entropy labels, SIDs that can be		recirculation, or SIDs associated with another dataplane e.g., IPv6.
	imposed thru recirculation, or another dataplane e.g. IPv6.
	1.1. Conventions used in this document		1.1. Conventions used in this document
	1.1.1. Terminology		1.1.1. Terminology
	BGP-LS: Distribution of Link-State and TE Information using Border		BGP-LS: Distribution of Link-State and TE Information using Border
	Gateway Protocol		Gateway Protocol
			BMI: Base MPLS Imposition is the number of MPLS labels which can be
			imposed inclusive of any service/transport labels
	OSPF: Open Shortest Path First		OSPF: Open Shortest Path First
	MSD: Maximum SID Depth		MSD: Maximum SID Depth - the number of SIDs a node or a link on a
			node can support
	PCC: Path Computation Client		PCC: Path Computation Client
	PCE: Path Computation Element		PCE: Path Computation Element
	PCEP: Path Computation Element Protocol		PCEP: Path Computation Element Protocol
	SID: Segment Identifier		SID: Segment Identifier
	SR: Segment routing		SR: Segment Routing
	1.2. Requirements Language		1.2. 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].
	2. Terminology		2. Terminology
	This memo makes use of the terms defined in [RFC4970].		This memo makes use of the terms defined in [RFC4970].
	skipping to change at page 5, line 46 ¶		skipping to change at page 5, line 46 ¶
	Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD		Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
	of the router originating the corresponding LSA as specified for		of the router originating the corresponding LSA as specified for
	OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0		OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0
	represents lack of the ability to impose MSD stack of any depth; any		represents lack of the ability to impose MSD stack of any depth; any
	other value represents that of the particular link MSD value.		other value represents that of the particular link MSD value.
	Other Sub-types other than defined above are reserved for future		Other Sub-types other than defined above are reserved for future
	extensions.		extensions.
	5. Node MSD vs Link MSD conflict resolution		5. Using Node and Link MSD Advertisements
	When both Node MSD and Link MSD are present, the value in the Link		When Link MSD is present for a given MSD type, the value of the Link
	MSD MUST be used.		MSD MUST be used in preference to the Node MSD.
	6. IANA Considerations		The meaning of the absence of both Node and Link MSD advertisements
			for a given MSD type is specific to the MSD type. Generally it can
			only be inferred that the advertising node does not support
			advertisement of that MSD type. However, in some cases the lack of
			advertisement might imply that the functionality associated with the
			MSD type is not supported. The correct interpretation MUST be
			specified when an MSD type is defined.
			6. Base MPLS Imposition MSD
			Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
			labels a node is capable of imposing, including any service/transport
			labels.
			Absence of BMI-MSD advertisements indicates only that the advertising
			node does not support advertisement of this capability.
			7. IANA Considerations
	This document includes a request to IANA to allocate TLV type codes		This document includes a request to IANA to allocate TLV type codes
	for the new TLV proposed in Section 3 of this document from OSPF		for the new TLV proposed in Section 3 of this document from OSPF
	Router Information (RI) TLVs Registry as defined by [RFC4970]. For		Router Information (RI) TLVs Registry as defined by [RFC4970]. For
	the link MSD, we request IANA to allocate new sub-TLV codes as		the link MSD, we request IANA to allocate new sub-TLV codes as
	proposed in Section 4 from OSPFv2 Extended Link TLV Sub-TLVs registry		proposed in Section 4 from OSPFv2 Extended Link TLV Sub-TLVs registry
	and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV		and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV
	registry.		registry.
	This document also requests IANA to create a new Sub-type registry as		This document requests creation of a new IANA managed registry under
	proposed in Section 3, Section 4.		a new category of "Interior Gateway Protocol (IGP) Parameters" IANA
			registries to identify MSD types as proposed in Section 3, Section 4.
			The registration procedure is "Expert Review" as defined in
			[RFC8126]. Suggested registry name is "MSD types". Types are an
			unsigned 8 bit number. The following values are defined by this
			document
	Value Name Reference		Value Name Reference
	----- --------------------- -------------		----- --------------------- -------------
	0 Reserved This document		0 Reserved This document
	1 Base MSD This document		1 Base MPLS Imposition MSD This document
	2-250 Unassigned This document		2-250 Unassigned This document
	251-254 Experimental This document		251-254 Experimental This document
	255 Reserved This document		255 Reserved This document
	Figure 3: MSD Sub-type Codepoints Registry		Figure 3: MSD Types Codepoints Registry
	7. Security Considerations		8. Security Considerations
	This document describes a mechanism to signal Segment Routing MSD		Security considerations, as specified by [RFC7770] are applicable to
	supported at node and/or link granularity through OSPF LSA's and does		this document
	not introduce any new security issues.
	8. Contributors		9. Contributors
	The following people contributed to this document:		The following people contributed to this document:
	Les Ginsberg		Les Ginsberg
	Email: ginsberg@cisco.com		Email: ginsberg@cisco.com
	9. Acknowledgements		10. Acknowledgements
	The authors would like to thank Stephane Litkowski and Bruno Decraene		The authors would like to thank Stephane Litkowski and Bruno Decraene
	for their reviews and valuable comments.		for their reviews and valuable comments.
	10. References		11. References
	10.1. Normative References
			11.1. Normative References
	[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>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and		[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
	S. Shaffer, "Extensions to OSPF for Advertising Optional		S. Shaffer, "Extensions to OSPF for Advertising Optional
	Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July		Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
	2007, <https://www.rfc-editor.org/info/rfc4970>.		2007, <https://www.rfc-editor.org/info/rfc4970>.
	10.2. Informative References		[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
			S. Shaffer, "Extensions to OSPF for Advertising Optional
			Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
			February 2016, <https://www.rfc-editor.org/info/rfc7770>.
			11.2. Informative References
	[I-D.ietf-idr-bgp-ls-segment-routing-msd]		[I-D.ietf-idr-bgp-ls-segment-routing-msd]
	Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,		Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
	"Signaling Maximum SID Depth using Border Gateway Protocol		"Signaling Maximum SID Depth using Border Gateway Protocol
	Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01		Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
	(work in progress), October 2017.		(work in progress), October 2017.
	[I-D.ietf-ospf-mpls-elc]		[I-D.ietf-ospf-mpls-elc]
	Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.		Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
	Litkowski, "Signaling Entropy Label Capability Using		Litkowski, "Signaling Entropy Label Capability and
	OSPF", draft-ietf-ospf-mpls-elc-04 (work in progress),		Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
	November 2016.		mpls-elc-05 (work in progress), January 2018.
	[I-D.ietf-ospf-ospfv3-lsa-extend]		[I-D.ietf-ospf-ospfv3-lsa-extend]
	Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.		Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
	Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-		Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
	lsa-extend-18 (work in progress), November 2017.		lsa-extend-23 (work in progress), January 2018.
	[I-D.ietf-pce-segment-routing]		[I-D.ietf-pce-segment-routing]
	Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,		Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
	and J. Hardwick, "PCEP Extensions for Segment Routing",		and J. Hardwick, "PCEP Extensions for Segment Routing",
	draft-ietf-pce-segment-routing-11 (work in progress),		draft-ietf-pce-segment-routing-11 (work in progress),
	November 2017.		November 2017.
	[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and		[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
	R. Aggarwal, "Support of Address Families in OSPFv3",		R. Aggarwal, "Support of Address Families in OSPFv3",
	RFC 5838, DOI 10.17487/RFC5838, April 2010,		RFC 5838, DOI 10.17487/RFC5838, April 2010,
	skipping to change at page 8, line 11 ¶		skipping to change at page 8, line 38 ¶
	Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute		Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
	Advertisement", RFC 7684, DOI 10.17487/RFC7684, November		Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
	2015, <https://www.rfc-editor.org/info/rfc7684>.		2015, <https://www.rfc-editor.org/info/rfc7684>.
	[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and		[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
	S. Ray, "North-Bound Distribution of Link-State and		S. Ray, "North-Bound Distribution of Link-State and
	Traffic Engineering (TE) Information Using BGP", RFC 7752,		Traffic Engineering (TE) Information Using BGP", RFC 7752,
	DOI 10.17487/RFC7752, March 2016,		DOI 10.17487/RFC7752, March 2016,
	<https://www.rfc-editor.org/info/rfc7752>.		<https://www.rfc-editor.org/info/rfc7752>.
			[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
			Writing an IANA Considerations Section in RFCs", BCP 26,
			RFC 8126, DOI 10.17487/RFC8126, June 2017,
			<https://www.rfc-editor.org/info/rfc8126>.
	Authors' Addresses		Authors' Addresses
	Jeff Tantsura		Jeff Tantsura
	Individual		Nuage Networks
	Email: jefftant.ietf@gmail.com		Email: jefftant.ietf@gmail.com
	Uma Chunduri		Uma Chunduri
	Huawei Technologies		Huawei Technologies
	Email: uma.chunduri@huawei.com		Email: uma.chunduri@huawei.com
	Sam Aldrin		Sam Aldrin
	Google, Inc		Google, Inc
	Email: aldrin.ietf@gmail.com		Email: aldrin.ietf@gmail.com
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