< draft-ietf-ospf-segment-routing-msd-00.txt		draft-ietf-ospf-segment-routing-msd-01.txt >
	OSPF Working Group J. Tantsura		OSPF Working Group J. Tantsura
	Internet-Draft U. Chunduri		Internet-Draft Individual
	Intended status: Standards Track Individual		Intended status: Standards Track U. Chunduri
	Expires: May 20, 2017 November 16, 2016		Expires: September 9, 2017 Huawei Technologies
			S. Aldrin
			Google, Inc
			P. Psenak
			Cisco Systems
			March 8, 2017
	Signaling MSD (Maximum SID Depth) using OSPF		Signaling MSD (Maximum SID Depth) using OSPF
	draft-ietf-ospf-segment-routing-msd-00		draft-ietf-ospf-segment-routing-msd-01
	Abstract		Abstract
	This document proposes a way to expose Maximum SID Depth (MSD)		This document proposes a way to signal Maximum SID Depth (MSD)
	supported by a node at node and/or link level by an OSPF Router. In		supported by a node at node and/or link granularity by an OSPF
	a Segment Routing (SR) enabled network a centralized controller that		Router. In a Segment Routing (SR) enabled network a centralized
	programs SR tunnels at the head-end node needs to know the MSD		controller that programs SR tunnels needs to know the MSD supported
	information at node level and/or link level to push the label stack		by the head-end at node and/or link granularity to push the SID stack
	of an appropriate depth . Here the term OSPF means both OSPFv2 and		of an appropriate depth. MSD is relevant to the head-end of a SR
	OSPFv3.		tunnel or Binding-SID anchor node where Binding-SID expansions might
			result in creation of a new SID stack. Here the term OSPF 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 http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
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	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 May 20, 2017.		This Internet-Draft will expire on September 9, 2017.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 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.
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	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
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	described in the Simplified BSD License.		described in the Simplified BSD License.
	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 . . . . . . . . . . . . . . . . . . 4
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 3		3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
	4. LINK MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 4		4. LINK MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5
	5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 4		5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 6
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 5		8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
	9.1. Normative References . . . . . . . . . . . . . . . . . . 5		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	9.2. Informative References . . . . . . . . . . . . . . . . . 5		10.1. Normative References . . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6		10.2. Informative References . . . . . . . . . . . . . . . . . 7
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	When Segment Routing tunnels are computed by a centralized		When Segment Routing tunnels are computed by a centralized
	controller, it is crucial that the controller knows the MSD "Maximum		controller, it is critical that the controller learns the MSD
	SID Depth" of the node or link SR tunnel exits over, so it doesn't		"Maximum SID Depth" of the node or link SR tunnel exits over, so the
	download a path with SID (label stack) of a depth more than the node		SID stack depth of a path computed doesn't exceed the number of SIDs
	or link used is capable of imposing. This document describes how to		the node is capable of imposing. This document describes how to use
	use OSPF to expose the MSD of the node or link to a centralized		OSPF to signal the MSD of a node or link to a centralized controller.
	controller.
	PCEP SR extensions [I-D.ietf-pce-segment-routing] has defined MSD, to		PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD
	signal in SR PCE Capability TLV, METRIC Object. However, If PCEP is		in SR PCE Capability TLV and METRIC Object. However, if PCEP is not
	not supported by a node (head-end of the SR tunnel) and controller		supported/configured on the head-end of a SR tunnel or a Binding-SID
	does not participate in IGP routing it has no way to learn the MSD of		anchor node and controller does not participate in IGP routing, it
	the node or link configured. BGP-LS [RFC7752] defines a way to		has no way to learn the MSD of nodes and links which has been
	expose topology and associated different attributes, capabilities of		configured. BGP-LS [RFC7752] defines a way to expose topology and
	the nodes in that topology to a centralized controller and MSD has		associated attributes and capabilities of the nodes in that topology
	been defined in [I-D.tantsura-bgp-ls-segment-routing-msd]. For this		to a centralized controller. MSD signaling by BGP-LS has been
	information to be advertised by BGP for the all nodes and links of		defined in [I-D.tantsura-idr-bgp-ls-segment-routing-msd]. Typically,
	the network, where this is provisioned, OSPF module should have this		BGP-LS is configured on a small number of nodes, that do not
	information in the LSDB.		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
			capabilites SHOULD be distributed to every OSPF router in the
			network.
	[I-D.ietf-ospf-mpls-elc] defines, RLSDC which indicates how many		[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
			appropriate depth, so it could be read by transit nodes. MSD in
			contrary signals ability to push SID's stack of a particular depth.
			MSD of type 1 (IANA Registry) is used to signal the number of SIDs a
			node is capable of imposing, to be used by a path computation
			element/controller and is only relevant to the part of the stack
			created as the result of the computation. In case, there are
			additional labels (e.g. service) that are to be pushed to the stack -
			MSD SHOULD be adjusted to reflect that. In the future, new MSD types
			could be defined to signal additional capabilities: entropy labels,
			labels that can be pushed thru recirculation, or another dataplane
			e.g IPv6.
			[I-D.ietf-ospf-mpls-elc] defines, RLDC which indicates how many
	labels a node can read to take a decision to insert an Entropy Label		labels a node can read to take a decision to insert an Entropy Label
	(EL) and is different than how many labels a node can push as defined		(EL) and is different than how many labels a node can push as defined
	by MSD in this draft.		by MSD in this draft.
	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
	skipping to change at page 3, line 43 ¶		skipping to change at page 4, line 22 ¶
	This memo makes use of the terms defined in [RFC4970].		This memo makes use of the terms defined in [RFC4970].
	3. Node MSD TLV		3. Node MSD TLV
	A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD		A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD
	TLV is defined to carry the provisioned SID depth of the router		TLV is defined to carry the provisioned SID depth of the router
	originating the RI LSA. Node MSD is the lowest MSD supported by the		originating the RI LSA. Node MSD is the lowest MSD supported by the
	node.		node.
	The Type (2 bytes) of this TLV is TBD.		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
	Length is 2 bytes, and		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Type | Length |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Sub-Type and Value ...
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
	the Value field contains MSD of the router originating the RI LSA.		Figure 1: Node MSD TLV
	Node MSD is a number in the range of 0-254. 0 represents lack of the
	ability to push MSD of any depth; any other value represents that of		The Type (2 bytes) of this TLV is 12 (Suggested value - to be
	the node. This value SHOULD represent the lowest value supported by		assigned by IANA).
	node.
			Length is variable (minimum of 2, multiple of 2 octets) and
			represents the total length of value field.
			Value field consists of a 1 octet sub-type (IANA Registry) and 1
			octet value.
			Sub-Type 1 (IANA Section), MSD and the Value field contains maximum
			MSD of the router originating the RI LSA. Node Maximum MSD is a
			number in the range of 0-254. 0 represents lack of the ability to
			push MSD of any depth; any other value represents that of the node.
			This value SHOULD represent the lowest value supported by node.
			Other Sub-types other than defined above are reserved for future
			extensions.
	This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is		This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is
	optional. The scope of the advertisement is specific to the		optional. The scope of the advertisement is specific to the
	deployment.		deployment.
	4. LINK MSD sub-TLV		4. LINK MSD sub-TLV
	A new sub-TLV called Link MSD sub-TLV is defined to carry the		A new sub-TLV called Link MSD sub-TLV is defined to carry the
	provisioned SID depth of the interface associated with the link.		provisioned SID depth of the interface associated with the link.
	The Type (2 bytes) of this TLV is TBD.		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
	Length is 2 bytes, and		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Type | Length |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Sub-Type and Value ...
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
	the Value field contains Link MSD of the router originating the		Figure 2: Link MSD Sub-TLV
	corresponding LSA as specified for OSPFv3 and OSPFv3. Link MSD is a
	number in the range of 0-254. 0 represents lack of the ability to		The Type (2 bytes) of this TLV:
	push MSD of any depth; any other value represents that of the
	particular link MSD value.
	For OSPFv2, the Link level MSD value is advertised as an optional		For OSPFv2, the Link level MSD value is advertised as an optional
	Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684].		Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and the
			value is 5 (Suggested value - to be assigned by IANA)
	For OSPFv3, the Link level MSD value is advertised as an optional		For OSPFv3, the Link level MSD value is advertised as an optional
	Sub-TLV of the Router-Link TLV as defined in		Sub-TLV of the Router-Link TLV as defined in
	[I-D.ietf-ospf-ospfv3-lsa-extend].		[I-D.ietf-ospf-ospfv3-lsa-extend], and the value is 3 (Suggested
			value - to be assigned by IANA).
			Length is variable and similar to what is defined in Section 3.
			Value field consists of a 1 octet sub-type (IANA Registry) and 1
			octet value.
			Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
			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
			represents lack of the ability to push MSD of any depth; any other
			value represents that of the particular link MSD value.
			Other Sub-types other than defined above are reserved for future
			extensions.
	5. Node MSD vs Link MSD conflict resolution		5. Node MSD vs Link MSD conflict resolution
	When both Node MSD and Link MSD are present, the value in the Link		When both Node MSD and Link MSD are present, the value in the Link
	MSD MUST be used.		MSD MUST be used.
	6. Acknowledgements		6. IANA Considerations
	TBD
	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]. Also		Router Information (RI) TLVs Registry as defined by [RFC4970]. Also
	for link MSD, we request IANA to allocate new sub-TLV codes as		for link MSD, we request IANA to allocate new sub-TLV codes as
	proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended		proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended
	Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend-		Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend-
	LSA Sub-TLV registry.		LSA Sub-TLV registry.
	8. Security Considerations		This document also request IANA to create a new Sub-type registry as
			proposed in Section 3, Section 4.
	This document describes a mechanism for advertising Segment Routing		Value Name Reference
	SID depth supported at node and link level information through OSPF		----- --------------------- -------------
	LSAs and does not introduce any new security issues.		0 Reserved This document
			1 MSD This document
			2-250 Unassigned This document
			251-254 Experimental This document
			255 Reserved This document
	9. References		Figure 3: MSD Sub-type Codepoints Registry
	9.1. Normative References		7. Security Considerations
			This document describes a mechanism to signal Segment Routing MSD
			supported at node and/or link granularity through OSPF LSA's and does
			not introduce any new security issues.
			8. Contributors
			The following people contributed to this document:
			Les Ginsberg
			Email: ginsberg@cisco.com
			9. Acknowledgements
			The authors would like to thank Stephane Litkowski and Bruno Decraene
			for their reviews and valuable comments.
			10. References
			10.1. 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,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://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, <http://www.rfc-editor.org/info/rfc4970>.		2007, <http://www.rfc-editor.org/info/rfc4970>.
	9.2. Informative References		10.2. Informative References
	[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 Using
	OSPF", draft-ietf-ospf-mpls-elc-03 (work in progress),		OSPF", draft-ietf-ospf-mpls-elc-04 (work in progress),
	October 2016.		November 2016.
	[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-13		LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-13
	(work in progress), October 2016.		(work in progress), October 2016.
	[I-D.ietf-pce-segment-routing]		[I-D.ietf-pce-segment-routing]
	Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,		Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
	Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and		Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and
	J. Hardwick, "PCEP Extensions for Segment Routing", draft-		J. Hardwick, "PCEP Extensions for Segment Routing", draft-
	ietf-pce-segment-routing-08 (work in progress), October		ietf-pce-segment-routing-08 (work in progress), October
	2016.		2016.
	[I-D.tantsura-bgp-ls-segment-routing-msd]		[I-D.tantsura-idr-bgp-ls-segment-routing-msd]
	Tantsura, J., Mirsky, G., Sivabalan, S., and U. Chunduri,		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-tantsura-bgp-ls-segment-routing-msd-02		Link-State", draft-tantsura-idr-bgp-ls-segment-routing-
	(work in progress), January 2016.		msd-02 (work in progress), January 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,
	<http://www.rfc-editor.org/info/rfc5838>.		<http://www.rfc-editor.org/info/rfc5838>.
	[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,		[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
	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, <http://www.rfc-editor.org/info/rfc7684>.		2015, <http://www.rfc-editor.org/info/rfc7684>.
	skipping to change at page 6, line 29 ¶		skipping to change at page 8, line 24 ¶
	<http://www.rfc-editor.org/info/rfc7752>.		<http://www.rfc-editor.org/info/rfc7752>.
	Authors' Addresses		Authors' Addresses
	Jeff Tantsura		Jeff Tantsura
	Individual		Individual
	Email: jefftant.ietf@gmail.com		Email: jefftant.ietf@gmail.com
	Uma Chunduri		Uma Chunduri
	Individual		Huawei Technologies
	Email: uma.chunduri@gmail.com		Email: uma.chunduri@huawei.com
			Sam Aldrin
			Google, Inc
			Email: aldrin.ietf@gmail.com
			Peter Psenak
			Cisco Systems
			Email: ppsenak@cisco.com
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