< draft-ietf-isis-segment-routing-msd-00.txt		draft-ietf-isis-segment-routing-msd-01.txt >
	IS-IS Working Group J. Tantsura		IS-IS 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 2, 2017 Huawei
			S. Aldrin
			Google, Inc
			L. Ginsberg
			Cisco Systems
			March 1, 2017
	Signaling MSD (Maximum SID Depth) using IS-IS		Signaling MSD (Maximum SID Depth) using IS-IS
	draft-ietf-isis-segment-routing-msd-00		draft-ietf-isis-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 ISIS Router. In		supported by a node at node and/or link granularity by an ISIS
	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.		of an appropriate depth. MSD is relevent to the head-end of a SR
			tunnel or Binding-SID anchor node where Binding-SID expansions migth
			result in creation of a new SID stack.
	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.
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	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
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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 . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 3		3. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
	4. LINK MSD Advertisement . . . . . . . . . . . . . . . . . . . 4		4. LINK MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
	5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 4		5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 4		7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4		8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
	9.1. Normative References . . . . . . . . . . . . . . . . . . 4		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
	9.2. Informative References . . . . . . . . . . . . . . . . . 5		10.1. Normative References . . . . . . . . . . . . . . . . . . 6
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6		10.2. Informative References . . . . . . . . . . . . . . . . . 7
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
	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 that the node is
	or link used is capable of imposing. This document describes how to		capable of imposing. This document describes how to use IS-IS to
	use IS-IS to expose the MSD of the node or link to a centralized		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 MSD 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-idr-bgp-ls-segment-routing-msd]. For		to a centralized controller. MSD signaling by BGP-LS has been
	this information to be advertised by BGP for the all nodes and links		defined in [I-D.tantsura-idr-bgp-ls-segment-routing-msd]. Tipicaly,
	of the network, where this is provisioned, IS-IS module should have		BGP-LS is configured on a small number of nodes, that do not
	this 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 IS-IS router in the
			network.
	[I-D.ietf-isis-mpls-elc] defines, RLSDC which indicates how many		[I-D.ietf-isis-mpls-elc] defines Readable Label Deepth Capability
	labels a node can read to take a decision to insert an Entropy Label		(RLDC) that is used by a head-end to insert Entropy Label (EL) at
	(EL) and is different than how many labels a node can push as defined		appropriate depth, so it coud be read by transit nodes. MSD in
	by MSD in this draft.		contrary signals ability to push SID's stack of a particular depth.
			MSD of type 1 (IANA Registry) is used to signal number of SID 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, etc.
	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
	ISIS: Intermediate System to Intermediate System		ISIS: Intermediate System to Intermediate System
	MSD: Maximum SID Depth		MSD: Maximum SID Depth
	PCC: Path Computation Client		PCC: Path Computation Client
	PCE: Path Computation Element		PCE: Path Computation Element
	skipping to change at page 3, line 39 ¶		skipping to change at page 4, line 12 ¶
	"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 [RFC4971].		This memo makes use of the terms defined in [RFC4971].
	3. Node MSD Advertisement		3. Node MSD Advertisement
	A new sub-TLV within the body of IS-IS Router Capability TLV		A new sub-TLV within the body of IS-IS Router Capability TLV
	[RFC4971], called Node MSD sub-TLV is defined to carry the		[RFC4971], Node MSD sub-TLV is defined to carry the provisioned MSD
	provisioned SID depth of the router originating the Router Capability		of the router originating the Router Capability TLV. Node MSD is the
	TLV. Node MSD is the lowest MSD supported by the node and can be		lowest MSD supported by the node and can be provisioned in IS-IS
	provisioned in IS-IS instance.		instance.
	The Type (1 byte) of this sub-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 1 bytes, and		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Type | Length | Sub-Type and Value |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	the Value field contains MSD of the router originating the Router		Figure 1: Node MSD Sub-TLV
	Capability 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 node. This value SHOULD represent the
	lowest value supported by node.
	This TLV is optional. The scope of the advertisement is specific to		The Type (1 byte) of this sub-TLV is TBD (IANA).
	the deployment.
			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 Router Capability TLV. 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 optional. The scope of the advertisement is
			specific to the deployment.
	4. LINK MSD Advertisement		4. LINK MSD Advertisement
	A new sub-TLV called Link MSD sub-TLV is defined to carry the		A new sub-TLV - Link MSD sub-TLV is defined to carry the provisioned
	provisioned SID depth of the interface associated with the link.		MSD of the interface associated with the link.
	The Type (1 byte) of this sub- 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 1 byte, 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 TLV's 22, 23, 141, 222, and 223. Link MSD is a number
	in the range of 0-254. 0 represents lack of the ability to push MSD		The Type (1 byte) of this sub-TLV is TBD (IANA).
	of any depth; any other value represents that of the particular link
	MSD value.		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 TLV's 22, 23, 141, 222,
			and 223. 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.
	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. IANA Considerations		6. IANA Considerations
	This document includes a request to IANA to allocate sub-TLV type		This document includes a request to IANA to allocate sub-TLV type
	codes for the new TLV proposed in Section 3 of this document from IS-		codes for the new sub TLV proposed in Section 3 of this document from
	IS Router Capability TLV Registry as defined by [RFC4971]. Also for		IS-IS Router Capability TLV Registry as defined by [RFC4971]. Also
	link MSD, we request IANA to allocate new sub-TLV codes as defined in		for link MSD, we request IANA to allocate new sub-TLV codes as
	Section 4 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223 registry.		defined in Section 4 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223
			registry.
			This document also request IANA to create a new Sub-type registry as
			proposed in Section 3, Section 4.
			Value Name Reference
			----- --------------------- -------------
			0 Reserved This document
			1 MSD This document
			2-250 Unassigned This document
			251-254 Experimental This document
			255 Reserved This document
			Figure 3: MSD Sub-type Codepoints Registry
	7. Security Considerations		7. Security Considerations
	This document describes a mechanism for advertising Segment Routing		This document describes a mechanism to signal Segment Routing MSD
	SID depth supported at node and link level information through IS-IS		supported at node and/or link granularity through IS-IS LSPs and does
	LSPs and does not introduce any new security issues.		not introduce any new security issues.
	8. Acknowledgements		8. Contributors
	TBD		The following people contributed to this document:
	9. References		Peter Psenak
	9.1. Normative References		Email: ppsenak@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>.
	[RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,		[RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
	"Intermediate System to Intermediate System (IS-IS)		"Intermediate System to Intermediate System (IS-IS)
	Extensions for Advertising Router Information", RFC 4971,		Extensions for Advertising Router Information", RFC 4971,
	DOI 10.17487/RFC4971, July 2007,		DOI 10.17487/RFC4971, July 2007,
	<http://www.rfc-editor.org/info/rfc4971>.		<http://www.rfc-editor.org/info/rfc4971>.
	[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic		[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
	Engineering", RFC 5305, DOI 10.17487/RFC5305, October		Engineering", RFC 5305, DOI 10.17487/RFC5305, October
	2008, <http://www.rfc-editor.org/info/rfc5305>.		2008, <http://www.rfc-editor.org/info/rfc5305>.
	9.2. Informative References		10.2. Informative References
	[I-D.ietf-isis-mpls-elc]		[I-D.ietf-isis-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 IS-		Litkowski, "Signaling Entropy Label Capability Using IS-
	IS", draft-ietf-isis-mpls-elc-02 (work in progress),		IS", draft-ietf-isis-mpls-elc-02 (work in progress),
	October 2016.		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-idr-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-idr-bgp-ls-segment-routing-		Link-State", draft-tantsura-idr-bgp-ls-segment-routing-
	msd-01 (work in progress), July 2016.		msd-02 (work in progress), January 2017.
	[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and		[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
	dual environments", RFC 1195, DOI 10.17487/RFC1195,		dual environments", RFC 1195, DOI 10.17487/RFC1195,
	December 1990, <http://www.rfc-editor.org/info/rfc1195>.		December 1990, <http://www.rfc-editor.org/info/rfc1195>.
	[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi		[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
	Topology (MT) Routing in Intermediate System to		Topology (MT) Routing in Intermediate System to
	Intermediate Systems (IS-ISs)", RFC 5120,		Intermediate Systems (IS-ISs)", RFC 5120,
	DOI 10.17487/RFC5120, February 2008,		DOI 10.17487/RFC5120, February 2008,
	<http://www.rfc-editor.org/info/rfc5120>.		<http://www.rfc-editor.org/info/rfc5120>.
	skipping to change at page 6, line 17 ¶		skipping to change at page 8, line 4 ¶
	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,
	<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
	Email: uma.chunduri@gmail.com		Email: uma.chunduri@huawei.com
			Sam Aldrin
			Google, Inc
			Email: aldrin.ietf@gmail.com
			Les Ginsberg
			Cisco Systems
			Email: ginsberg@cisco.com
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