< draft-ietf-idr-bgp-ls-segment-routing-msd-05.txt		draft-ietf-idr-bgp-ls-segment-routing-msd-06.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: December 3, 2019 Futurewei Technologies		Expires: March 8, 2020 Futurewei Technologies
	K. Talaulikar		K. Talaulikar
	Cisco Systems		Cisco Systems
	G. Mirsky		G. Mirsky
	ZTE Corp.		ZTE Corp.
	N. Triantafillis		N. Triantafillis
	Apstra, Inc.		Apstra, Inc.
	June 1, 2019		September 5, 2019
	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-05		draft-ietf-idr-bgp-ls-segment-routing-msd-06
	Abstract		Abstract
	This document defines a way for a Border Gateway Protocol Link-State		This document defines a way for a Border Gateway Protocol Link-State
	(BGP-LS) speaker to advertise multiple types of supported Maximum SID		(BGP-LS) speaker to advertise multiple types of supported Maximum SID
	Depths (MSDs) at node and/or link granularity.		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 December 3, 2019.		This Internet-Draft will expire on March 8, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 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 30 ¶		skipping to change at page 2, line 30 ¶
	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
	1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4		1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4
	2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4		2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4
	3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4		3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
	4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5		4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 6		6. Manageability Considerations . . . . . . . . . . . . . . . . 6
	7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6		7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7		8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
	9.1. Normative References . . . . . . . . . . . . . . . . . . 7		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	9.2. Informative References . . . . . . . . . . . . . . . . . 7		10.1. Normative References . . . . . . . . . . . . . . . . . . 8
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8		10.2. Informative References . . . . . . . . . . . . . . . . . 8
			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 learns 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.
	skipping to change at page 6, line 33 ¶		skipping to change at page 6, line 33 ¶
	TLVs" based on table below. Early allocation for these code-points		TLVs" based on table below. Early allocation for these code-points
	have been done by IANA.		have been done by IANA.
	+------------+-----------------+---------------------------+		+------------+-----------------+---------------------------+
	| Code Point | Description | IS-IS TLV/Sub-TLV |		| Code Point | Description | IS-IS TLV/Sub-TLV |
	+------------+-----------------+---------------------------+		+------------+-----------------+---------------------------+
	| 266 | Node MSD | 242/23 |		| 266 | Node MSD | 242/23 |
	| 267 | Link MSD | (22,23,25,141,222,223)/15 |		| 267 | Link MSD | (22,23,25,141,222,223)/15 |
	+------------+-----------------+---------------------------+		+------------+-----------------+---------------------------+
	6. Security Considerations		6. Manageability Considerations
			The new protocol extensions introduced in this document augment the
			existing IGP topology information that is distributed via [RFC7752].
			Procedures and protocol extensions defined in this document do not
			affect the BGP protocol operations and management other than as
			discussed in the Manageability Considerations section of [RFC7752].
			Specifically, the malformed attribute tests for syntactic checks in
			the Fault Management section of [RFC7752] now encompass the new BGP-
			LS Attribute TLVs defined in this document. The semantic or content
			checking for the TLVs specified in this document and their
			association with the BGP-LS NLRI types or their BGP-LS Attribute is
			left to the consumer of the BGP-LS information (e.g. an application
			or a controller) and not the BGP protocol.
			A consumer of the BGP-LS information retrieves this information over
			a BGP-LS session (refer Section 1 and 2 of [RFC7752]). The handling
			of semantic or content errors by the consumer would be dictated by
			the nature of its application usage and hence is beyond the scope of
			this document.
			This document only introduces new Attribute TLVs and any syntactic
			error in them would result in the BGP-LS Attribute being discarded
			with an error log. The MSD information introduced in BGP-LS by this
			specification, may be used by BGP-LS consumer applications like a SR
			path computation engine (PCE) to learn the SR SID-stack handling
			capabilities of the nodes in the topology. This can enable the SR
			PCE to perform path computations taking into consideration the size
			of SID Stack that the specific headend node may be able to impose.
			Errors in the encoding or decoding of the MSD information may result
			in the unavailability of such information to the SR PCE or incorrect
			information being made available to it. This may result in the
			headend node not being able to instantiate the desired SR path in its
			forwarding and provide the SR based optimization functionality. The
			handling of such errors by applications like SR PCE may be
			implementation specific and out of scope of this document.
			The extensions, specified in this document, do not introduce any new
			configuration or monitoring aspects in BGP or BGP-LS other than as
			discussed in [RFC7752]. The manageability aspects of the MSD
			features are covered by [I-D.ietf-spring-sr-yang].
			7. 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
	supported by the head-end (the node performing the SID imposition)		supported by the head-end (the node performing the SID imposition)
	may occur. The presence of this information may also inform an		may occur. The presence of this information may also inform an
	attacker of how to induce any of the aforementioned conditions.		attacker of how to induce any of the aforementioned conditions.
	This document does not introduce security issues beyond those		This document does not introduce security issues beyond those
	discussed in [RFC7752], [RFC8476] and [RFC8491]		discussed in [RFC7752], [RFC8476] and [RFC8491]
	7. Contributors		8. Contributors
	Siva Sivabalan		Siva Sivabalan
	Cisco Systems Inc.		Cisco Systems Inc.
	Canada		Canada
	Email: msiva@cisco.com		Email: msiva@cisco.com
	8. Acknowledgements		9. Acknowledgements
	We like to thank Acee Lindem, Stephane Litkowski and Bruno Decraene		We like to thank Acee Lindem, Stephane Litkowski and Bruno Decraene
	for their reviews and valuable comments.		for their reviews and valuable comments.
	9. References		10. References
	9.1. Normative 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,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[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,
	skipping to change at page 7, line 44 ¶		skipping to change at page 8, line 39 ¶
	[RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,		[RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
	"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,		"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
	DOI 10.17487/RFC8476, December 2018,		DOI 10.17487/RFC8476, December 2018,
	<https://www.rfc-editor.org/info/rfc8476>.		<https://www.rfc-editor.org/info/rfc8476>.
	[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,		[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
	"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,		"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
	DOI 10.17487/RFC8491, November 2018,		DOI 10.17487/RFC8491, November 2018,
	<https://www.rfc-editor.org/info/rfc8491>.		<https://www.rfc-editor.org/info/rfc8491>.
	9.2. Informative References		10.2. Informative References
	[I-D.ietf-isis-mpls-elc]		[I-D.ietf-isis-mpls-elc]
	Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.		Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.
	Litkowski, "Signaling Entropy Label Capability and Entropy		Litkowski, "Signaling Entropy Label Capability and Entropy
	Readable Label Depth Using IS-IS", draft-ietf-isis-mpls-		Readable Label Depth Using IS-IS", draft-ietf-isis-mpls-
	elc-07 (work in progress), May 2019.		elc-08 (work in progress), September 2019.
	[I-D.ietf-ospf-mpls-elc]		[I-D.ietf-ospf-mpls-elc]
	Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.		Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.
	Litkowski, "Signaling Entropy Label Capability and Entropy		Litkowski, "Signaling Entropy Label Capability and Entropy
	Readable Label-stack Depth Using OSPF", draft-ietf-ospf-		Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
	mpls-elc-08 (work in progress), May 2019.		mpls-elc-08 (work in progress), May 2019.
	[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-16 (work in progress),		draft-ietf-pce-segment-routing-16 (work in progress),
	March 2019.		March 2019.
			[I-D.ietf-spring-sr-yang]
			Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J.
			Tantsura, "YANG Data Model for Segment Routing", draft-
			ietf-spring-sr-yang-13 (work in progress), July 2019.
	[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>.
	[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,		[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
	Decraene, B., Litkowski, S., and R. Shakir, "Segment		Decraene, B., Litkowski, S., and R. Shakir, "Segment
	Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,		Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
	July 2018, <https://www.rfc-editor.org/info/rfc8402>.		July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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