< draft-ietf-idr-bgp-ls-segment-routing-msd-16.txt		draft-ietf-idr-bgp-ls-segment-routing-msd-17.txt >
	IDR Working Group J. Tantsura		IDR Working Group J. Tantsura
	Internet-Draft Apstra, Inc.		Internet-Draft Apstra, Inc.
	Intended status: Standards Track U. Chunduri		Intended status: Standards Track U. Chunduri
	Expires: October 1, 2020 Futurewei Technologies		Expires: October 28, 2020 Futurewei Technologies
	K. Talaulikar		K. Talaulikar
	Cisco Systems		Cisco Systems
	G. Mirsky		G. Mirsky
	ZTE Corp.		ZTE Corp.
	N. Triantafillis		N. Triantafillis
	Amazon Web Services		Amazon Web Services
	March 30, 2020		April 26, 2020
	Signaling MSD (Maximum SID Depth) using Border Gateway Protocol - Link		Signaling MSD (Maximum SID Depth) using Border Gateway Protocol - Link
	State		State
	draft-ietf-idr-bgp-ls-segment-routing-msd-16		draft-ietf-idr-bgp-ls-segment-routing-msd-17
	Abstract		Abstract
	This document defines a way for a Border Gateway Protocol - Link		This document defines a way for a Border Gateway Protocol - Link
	State (BGP-LS) speaker to advertise multiple types of supported		State (BGP-LS) speaker to advertise multiple types of supported
	Maximum SID Depths (MSDs) at node and/or link granularity.		Maximum SID Depths (MSDs) at node and/or link granularity.
	Such advertisements allow entities (e.g., centralized controllers) to		Such advertisements allow entities (e.g., centralized controllers) to
	determine whether a particular Segment Identifier (SID) stack can be		determine whether a particular Segment Identifier (SID) stack can be
	supported in a given network.		supported in a given network.
	skipping to change at page 1, line 44 ¶		skipping to change at page 1, line 44 ¶
	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 October 1, 2020.		This Internet-Draft will expire on October 28, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2020 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 38 ¶		skipping to change at page 2, line 38 ¶
	4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5		4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5
	5. Procedures for Defining and Using Node and Link MSD		5. Procedures for Defining and Using Node and Link MSD
	Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6		Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	7. Manageability Considerations . . . . . . . . . . . . . . . . 6		7. Manageability Considerations . . . . . . . . . . . . . . . . 6
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 7		8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8		9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	11.1. Normative References . . . . . . . . . . . . . . . . . . 8		11.1. Normative References . . . . . . . . . . . . . . . . . . 8
	11.2. Informative References . . . . . . . . . . . . . . . . . 9		11.2. Informative References . . . . . . . . . . . . . . . . . 8
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
	1. Introduction		1. Introduction
	When Segment Routing (SR) [RFC8402] paths are computed by a		When Segment Routing (SR) [RFC8402] paths are computed by a
	centralized controller, it is critical that the controller learn the		centralized controller, it is critical that the controller learns the
	Maximum SID Depth (MSD) that can be imposed at each node/link on a		Maximum SID Depth (MSD) that can be imposed at each node/link on a
	given SR path. This ensures that the Segment Identifier (SID) stack		given SR path. This ensures that the Segment Identifier (SID) stack
	depth of a computed path doesn't exceed the number of SIDs the node		depth of a computed path doesn't exceed the number of SIDs the node
	is capable of imposing.		is capable of imposing.
	[RFC8664] defines how to signal MSD in the Path Computation Element		[RFC8664] defines how to signal MSD in the Path Computation Element
	Protocol (PCEP). The OSPF and IS-IS extensions for signaling of MSD		Protocol (PCEP). The OSPF and IS-IS extensions for signaling of MSD
	are defined in [RFC8476] and [RFC8491] respectively.		are defined in [RFC8476] and [RFC8491] respectively.
	However, if PCEP is not supported/configured on the head-end of a SR		However, if PCEP is not supported/configured on the head-end of a SR
	tunnel or a Binding-SID anchor node, and controller does not		tunnel or a Binding-SID anchor node, and the controller does not
	participate in IGP routing, it has no way of learning the MSD of		participate in IGP routing, it has no way of learning the MSD of
	nodes and links. BGP-LS [RFC7752] defines a way to expose topology		nodes and links. BGP-LS [RFC7752] defines a way to expose topology
	and associated attributes and capabilities of the nodes in that		and associated attributes and capabilities of the nodes in that
	topology to a centralized controller.		topology to a centralized controller.
	This document defines extensions to BGP-LS to advertise one or more		This document defines extensions to BGP-LS to advertise one or more
	types of MSDs at node and/or link granularity. Other types of MSD		types of MSDs at node and/or link granularity. Other types of MSD
	are known to be useful. For example, [I-D.ietf-ospf-mpls-elc] and		are known to be useful. For example, [I-D.ietf-ospf-mpls-elc] and
	[I-D.ietf-isis-mpls-elc] define Readable Label Depth Capability		[I-D.ietf-isis-mpls-elc] define Readable Label Depth Capability
	(RLDC) that is used by a head-end to insert an Entropy Label (EL) at		(RLDC) that is used by a head-end to insert an Entropy Label (EL) at
	skipping to change at page 3, line 33 ¶		skipping to change at page 3, line 33 ¶
	not enabled. For example, in a non-SR MPLS network, MSD defines the		not enabled. For example, in a non-SR MPLS network, MSD defines the
	maximum label depth.		maximum label depth.
	1.1. Conventions used in this document		1.1. Conventions used in this document
	1.1.1. Terminology		1.1.1. Terminology
	MSD: Maximum SID Depth - the number of SIDs supported by a node or a		MSD: Maximum SID Depth - the number of SIDs supported by a node or a
	link on a node		link on a node
	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 as defined in [RFC8402]		SID: Segment Identifier as defined in [RFC8402]
	SR: Segment Routing		SR: Segment Routing
	Label Imposition: Imposition is the act of modifying and/or adding		Label Imposition: Imposition is the act of modifying and/or adding
	labels to the outgoing label stack associated with a packet. This		labels to the outgoing label stack associated with a packet. This
	skipping to change at page 7, line 29 ¶		skipping to change at page 7, line 24 ¶
	PCE to perform path computations taking into consideration the size		PCE to perform path computations taking into consideration the size
	of SID stack that the specific head-end node may be able to impose.		of SID stack that the specific head-end node may be able to impose.
	Errors in the encoding or decoding of the MSD information may result		Errors in the encoding or decoding of the MSD information may result
	in the unavailability of such information to the SR PCE or incorrect		in the unavailability of such information to the SR PCE or incorrect
	information being made available to it. This may result in the head-		information being made available to it. This may result in the head-
	end node not being able to instantiate the desired SR path in its		end node not being able to instantiate the desired SR path in its
	forwarding and provide the SR based optimization functionality. The		forwarding and provide the SR based optimization functionality. The
	handling of such errors by applications like SR PCE may be		handling of such errors by applications like SR PCE may be
	implementation specific and out of scope of this document.		implementation specific and out of scope of this document.
	The extensions specified in this document, do not specify any new		The extensions specified in this document do not specify any new
	configuration or monitoring aspects in BGP or BGP-LS. The		configuration or monitoring aspects in BGP or BGP-LS. The
	specification of BGP models is an ongoing work based on the		specification of BGP models is an ongoing work based on the
	[I-D.ietf-idr-bgp-model].		[I-D.ietf-idr-bgp-model].
	8. Security Considerations		8. Security Considerations
	The advertisement of an incorrect MSD value may have negative		The advertisement of an incorrect MSD value may have negative
	consequences. If the value is smaller than supported, path		consequences. If the value is smaller than supported, path
	computation may fail to compute a viable path. If the value is		computation may fail to compute a viable path. If the value is
	larger than supported, an attempt to instantiate a path that can't be		larger than supported, an attempt to instantiate a path that can't be
	skipping to change at page 9, line 21 ¶		skipping to change at page 9, line 14 ¶
	[I-D.ietf-isis-mpls-elc]		[I-D.ietf-isis-mpls-elc]
	Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,		Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
	and M. Bocci, "Signaling Entropy Label Capability and		and M. Bocci, "Signaling Entropy Label Capability and
	Entropy Readable Label Depth Using IS-IS", draft-ietf-		Entropy Readable Label Depth Using IS-IS", draft-ietf-
	isis-mpls-elc-11 (work in progress), March 2020.		isis-mpls-elc-11 (work in progress), March 2020.
	[I-D.ietf-ospf-mpls-elc]		[I-D.ietf-ospf-mpls-elc]
	Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,		Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
	and M. Bocci, "Signaling Entropy Label Capability and		and M. Bocci, "Signaling Entropy Label Capability and
	Entropy Readable Label-stack Depth Using OSPF", draft-		Entropy Readable Label Depth Using OSPF", draft-ietf-ospf-
	ietf-ospf-mpls-elc-12 (work in progress), October 2019.		mpls-elc-13 (work in progress), April 2020.
	[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol		[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
	Label Switching Architecture", RFC 3031,		Label Switching Architecture", RFC 3031,
	DOI 10.17487/RFC3031, January 2001,		DOI 10.17487/RFC3031, January 2001,
	<https://www.rfc-editor.org/info/rfc3031>.		<https://www.rfc-editor.org/info/rfc3031>.
	[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A		[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
	Border Gateway Protocol 4 (BGP-4)", RFC 4271,		Border Gateway Protocol 4 (BGP-4)", RFC 4271,
	DOI 10.17487/RFC4271, January 2006,		DOI 10.17487/RFC4271, January 2006,
	<https://www.rfc-editor.org/info/rfc4271>.		<https://www.rfc-editor.org/info/rfc4271>.
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