draft-ietf-idr-bgp-ls-segment-routing-msd-17.txt		draft-ietf-idr-bgp-ls-segment-routing-msd-18.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 28, 2020 Futurewei Technologies		Expires: November 9, 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
	April 26, 2020		May 8, 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-17		draft-ietf-idr-bgp-ls-segment-routing-msd-18
	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 28, 2020.		This Internet-Draft will expire on November 9, 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 29 ¶		skipping to change at page 2, line 29 ¶
	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. Procedures for Defining and Using Node and Link MSD		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6		6. Manageability Considerations . . . . . . . . . . . . . . . . 6
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	7. Manageability Considerations . . . . . . . . . . . . . . . . 6		8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 7		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
	9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8		10.1. Normative References . . . . . . . . . . . . . . . . . . 8
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8		10.2. Informative References . . . . . . . . . . . . . . . . . 8
	11.1. Normative References . . . . . . . . . . . . . . . . . . 8
	11.2. Informative References . . . . . . . . . . . . . . . . . 8
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9		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 5 ¶		skipping to change at page 6, line 5 ¶
	1-octet MSD-Value.		1-octet MSD-Value.
	* MSD-Type : MSD-Type : one of the values defined in the "IGP		* MSD-Type : MSD-Type : one of the values defined in the "IGP
	MSD-Types" registry defined in [RFC8491].		MSD-Types" registry defined in [RFC8491].
	* MSD-Value : a number in the range of 0-255. For all MSD-Types,		* MSD-Value : a number in the range of 0-255. For all MSD-Types,
	0 represents the lack of ability to impose an MSD stack of any		0 represents the lack of ability to impose an MSD stack of any
	depth; any other value represents that of the link when used as		depth; any other value represents that of the link when used as
	an outgoing interface.		an outgoing interface.
	5. Procedures for Defining and Using Node and Link MSD Advertisements		5. IANA Considerations
	When Link MSD is present for a given MSD-type, the value of the Link
	MSD MUST take precedence over the Node MSD. When a Link MSD-type is
	not signaled but the Node MSD-type is, then the Node MSD-type value
	MUST be considered as the MSD value for that link.
	In order to increase flooding efficiency, it is RECOMMENDED that
	routers with homogenous link MSD values advertise just the Node MSD
	value.
	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 in [RFC8491].
	6. IANA Considerations
	This document requests assigning code-points from the registry "BGP-		This document requests assigning code-points from the registry "BGP-
	LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute		LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
	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 | Reference |		| Code Point | Description | IS-IS TLV/Sub-TLV | Reference |
	+------------+-----------------+---------------------------+-------------------+		+------------+-----------------+---------------------------+-------------------+
	| 266 | Node MSD | 242/23 | This document |		| 266 | Node MSD | 242/23 | This document |
	| 267 | Link MSD | (22,23,25,141,222,223)/15 | This document |		| 267 | Link MSD | (22,23,25,141,222,223)/15 | This document |
	+------------+-----------------+---------------------------+-------------------+		+------------+-----------------+---------------------------+-------------------+
	7. Manageability Considerations		6. Manageability Considerations
	The new protocol extensions introduced in this document augment the		The new protocol extensions introduced in this document augment the
	existing IGP topology information that is distributed via [RFC7752].		existing IGP topology information that is distributed via [RFC7752].
	Procedures and protocol extensions defined in this document do not		Procedures and protocol extensions defined in this document do not
	affect the BGP protocol operations and management other than as		affect the BGP protocol operations and management other than as
	discussed in the Manageability Considerations section of [RFC7752].		discussed in the Manageability Considerations section of [RFC7752].
	Specifically, the malformed attribute tests for syntactic checks in		Specifically, the malformed attribute tests for syntactic checks in
	the Fault Management section of [RFC7752] now encompass the new BGP-		the Fault Management section of [RFC7752] now encompass the new BGP-
	LS Attribute TLVs defined in this document. The semantic or content		LS Attribute TLVs defined in this document. The semantic or content
	checking for the TLVs specified in this document and their		checking for the TLVs specified in this document and their
	skipping to change at page 7, line 12 ¶		skipping to change at page 6, line 41 ¶
	left to the consumer of the BGP-LS information (e.g. an application		left to the consumer of the BGP-LS information (e.g. an application
	or a controller) and not the BGP protocol.		or a controller) and not the BGP protocol.
	A consumer of the BGP-LS information retrieves this information over		A consumer of the BGP-LS information retrieves this information over
	a BGP-LS session (refer Section 1 and 2 of [RFC7752]).		a BGP-LS session (refer Section 1 and 2 of [RFC7752]).
	This document only introduces new Attribute TLVs and any syntactic		This document only introduces new Attribute TLVs and any syntactic
	error in them would result in the BGP-LS Attribute being discarded		error in them would result in the BGP-LS Attribute being discarded
	[RFC7752]. The MSD information introduced in BGP-LS by this		[RFC7752]. The MSD information introduced in BGP-LS by this
	specification, may be used by BGP-LS consumer applications like a SR		specification, may be used by BGP-LS consumer applications like a SR
	path computation engine (PCE) to learn the SR SID stack handling		PCE to learn the SR SID stack handling capabilities of the nodes in
	capabilities of the nodes in the topology. This can enable the SR		the topology. This can enable the SR PCE to perform path
	PCE to perform path computations taking into consideration the size		computations taking into consideration the size of SID stack that the
	of SID stack that the specific head-end node may be able to impose.		specific head-end node may be able to impose. Errors in the encoding
	Errors in the encoding or decoding of the MSD information may result		or decoding of the MSD information may result in the unavailability
	in the unavailability of such information to the SR PCE or incorrect		of such information to the SR PCE or incorrect information being made
	information being made available to it. This may result in the head-		available to it. This may result in the head-end node not being able
	end node not being able to instantiate the desired SR path in its		to instantiate the desired SR path in its forwarding and provide the
	forwarding and provide the SR based optimization functionality. The		SR based optimization functionality. The handling of such errors by
	handling of such errors by applications like SR PCE may be		applications like SR PCE may be implementation specific and out of
	implementation specific and out of scope of this document.		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		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.
	The procedures and protocol extensions defined in this document do		The procedures and protocol extensions defined in this document do
	skipping to change at page 7, line 51 ¶		skipping to change at page 7, line 32 ¶
	section of [RFC4271] for a discussion of BGP security. Also, refer		section of [RFC4271] for a discussion of BGP security. Also, refer
	to [RFC4272] and [RFC6952] for analyses of security issues for BGP.		to [RFC4272] and [RFC6952] for analyses of security issues for BGP.
	Security considerations for acquiring and distributing BGP-LS		Security considerations for acquiring and distributing BGP-LS
	information are discussed in [RFC7752]. The TLVs introduced in this		information are discussed in [RFC7752]. The TLVs introduced in this
	document are used to propagate the MSD IGP extensions defined in		document are used to propagate the MSD IGP extensions defined in
	[RFC8476] [RFC8491]. It is assumed that the IGP instances		[RFC8476] [RFC8491]. It is assumed that the IGP instances
	originating these TLVs will support all the required security (as		originating these TLVs will support all the required security (as
	described in [RFC8476] [RFC8491]) in order to prevent any security		described in [RFC8476] [RFC8491]) in order to prevent any security
	issues when propagating the TLVs into BGP-LS. The advertisement of		issues when propagating the TLVs into BGP-LS. The advertisement of
	the node and link attribute information defined in this document		the node and link attribute information defined in this document
	presents no additional risk beyond that associated with the existing		presents no significant additional risk beyond that associated with
	node and link attribute information already supported in [RFC7752].		the existing node and link attribute information already supported in
			[RFC7752].
	9. Contributors		8. Contributors
	Siva Sivabalan		Siva Sivabalan
	Cisco Systems Inc.		Cisco Systems Inc.
	Canada		Canada
	Email: msiva@cisco.com		Email: msiva@cisco.com
	10. Acknowledgements		9. Acknowledgements
	We like to thank Acee Lindem, Stephane Litkowski, Bruno Decraene and		We like to thank Acee Lindem, Stephane Litkowski, Bruno Decraene and
	Alvaro Retana for their reviews and valuable comments.		Alvaro Retana for their reviews and valuable comments.
	11. References		10. References
	11.1. 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 8, line 47 ¶		skipping to change at page 8, line 34 ¶
	[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>.
	11.2. Informative References		10.2. Informative References
	[I-D.ietf-idr-bgp-model]		[I-D.ietf-idr-bgp-model]
	Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP		Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
	YANG Model for Service Provider Networks", draft-ietf-idr-		YANG Model for Service Provider Networks", draft-ietf-idr-
	bgp-model-08 (work in progress), February 2020.		bgp-model-08 (work in progress), February 2020.
	[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-
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