draft-ietf-isis-segment-routing-msd-15.txt		draft-ietf-isis-segment-routing-msd-16.txt
	IS-IS Working Group J. Tantsura		IS-IS Working Group J. Tantsura
	Internet-Draft Nuage Networks		Internet-Draft Nuage Networks
	Intended status: Standards Track U. Chunduri		Intended status: Standards Track U. Chunduri
	Expires: March 2, 2019 Huawei Technologies		Expires: March 27, 2019 Huawei Technologies
	S. Aldrin		S. Aldrin
	Google, Inc		Google, Inc
	L. Ginsberg		L. Ginsberg
	Cisco Systems		Cisco Systems
	August 29, 2018		September 23, 2018
	Signaling MSD (Maximum SID Depth) using IS-IS		Signaling MSD (Maximum SID Depth) using IS-IS
	draft-ietf-isis-segment-routing-msd-15		draft-ietf-isis-segment-routing-msd-16
	Abstract		Abstract
	This document defines a way for an Intermediate System to		This document defines a way for an Intermediate System to
	Intermediate System (IS-IS) Router to advertise multiple types of		Intermediate System (IS-IS) router to advertise multiple types of
	supported Maximum SID Depths (MSDs) at node and/or link granularity.		supported 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 SID stack can be supported in a given		determine whether a particular SID stack can be supported in a given
	network. This document only defines one type of MSD maximum label		network. This document only defines one type of MSD maximum label
	imposition, but defines an encoding that can support other MSD types.		imposition, but defines an encoding that can support other MSD types.
	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.
	skipping to change at page 1, line 41 ¶		skipping to change at page 1, line 41 ¶
	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 March 2, 2019.		This Internet-Draft will expire on March 27, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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 27 ¶		skipping to change at page 2, line 27 ¶
	2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 3		2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 3
	3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4		3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
	4. Procedures for using Node and Link MSD Advertisements . . . . 5		4. Procedures for using Node and Link MSD Advertisements . . . . 5
	5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6		5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 7		7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7		8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	10.1. Normative References . . . . . . . . . . . . . . . . . . 8		10.1. Normative References . . . . . . . . . . . . . . . . . . 8
	10.2. Informative References . . . . . . . . . . . . . . . . . 8		10.2. Informative References . . . . . . . . . . . . . . . . . 9
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
	1. Introduction		1. Introduction
	When Segment Routing (SR) paths are computed by a centralized		When Segment Routing (SR) paths are computed by a centralized
	controller, it is critical that the controller learns the Maximum SID		controller, it is critical that the controller learns the Maximum SID
	Depth (MSD) that can be imposed at each node/link a given SR path to		Depth (MSD) that can be imposed at each node/link of a given SR path
	insure that the Segment Identifier (SID) stack depth of a computed		to insure that the Segment Identifier (SID) stack depth of a computed
	path doesn't exceed the number of SIDs the node is capable of		path does not exceed the number of SIDs the node is capable of
	imposing.		imposing.
	Path Computation Element Protocol (PCEP) SR extensions draft		[I-D.ietf-pce-segment-routing] defines how to signal MSD in the SR
	[I-D.ietf-pce-segment-routing] signals MSD in SR Path Computation		Path Computation Element (PCE) Capability TLV and in the METRIC
	Element (PCE) Capability TLV and METRIC Object. However, if PCEP is		Object originally defined in [RFC5440]. However, if PCEP is not
	not supported/configured on the head-end of an SR tunnel or a		supported/configured on the head-end of an SR tunnel or a Binding-SID
	Binding-SID anchor node and controller does not participate in IGP		anchor node and controller does not participate in IGP routing, it
	routing, it has no way to learn the MSD of nodes and links. BGP-LS		has no way to learn the MSD of nodes and links. BGP-LS (Distribution
	(Distribution of Link-State and TE Information using Border Gateway		of Link-State and TE Information using Border Gateway Protocol)
	Protocol) [RFC7752] defines a way to expose topology and associated		[RFC7752] defines a way to expose topology and associated attributes
	attributes and capabilities of the nodes in that topology to a		and capabilities of the nodes in that topology to a centralized
	centralized controller. MSD signaling by BGP-LS has been defined in		controller. MSD signaling by BGP-LS has been defined in
	[I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is		[I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is
	configured on a small number of nodes that do not necessarily act as		configured on a small number of nodes that do not necessarily act as
	head-ends. In order for BGP-LS to signal MSD for all the nodes and		head-ends. In order for BGP-LS to signal MSD for all the nodes and
	links in the network MSD is relevant, MSD capabilities should be		links in the network MSD is relevant, MSD capabilities should be
	advertised by every Intermediate System to Intermediate System(IS-IS)		advertised by every Intermediate System to Intermediate System(IS-IS)
	router in the network.		router in the network.
	Other types of MSD are known to be useful. For example,		Other types of MSD are known to be useful. For example,
	[I-D.ietf-isis-mpls-elc] defines Readable Label Depth Capability		[I-D.ietf-isis-mpls-elc] defines 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
	a depth, that could be read by transit nodes.		a depth, that could be read by transit nodes.
	This document defines an extension to IS-IS used to advertise one or		This document defines an extension to IS-IS used to advertise one or
	more types of MSD at node and/or link granularity. It also creates		more types of MSD at node and/or link granularity. It also creates
	an IANA registry for assigning MSD type identifiers. It also defines		an IANA registry for assigning MSD type identifiers. It also defines
	the Base MPLS Imposition MSD type. In the future it is expected,		the Base MPLS Imposition MSD type. In the future it is expected that
	that new MSD types will be defined to signal additional capabilities		new MSD types will be defined to signal additional capabilities e.g.,
	e.g., entropy labels, SIDs that can be imposed through recirculation,		entropy labels, SIDs that can be imposed through recirculation, or
	or SIDs associated with another dataplane e.g., IPv6. Although MSD		SIDs associated with another dataplane e.g., IPv6.
	advertisements are associated with Segment Routing, the
			Although MSD advertisements are associated with Segment Routing, the
	advertisements MAY be present even if Segment Routing itself is not		advertisements MAY be present even if Segment Routing itself is not
	enabled. Note that in a non-SR MPLS network, label depth is what is		enabled. Note that in a non-SR MPLS network, label depth is what is
	defined by the MSD advertisements.		defined by the MSD advertisements.
	1.1. Terminology		1.1. Terminology
	BMI: Base MPLS Imposition is the number of MPLS labels which can be		BMI: Base MPLS Imposition is the number of MPLS labels which can be
	imposed inclusive of all service/transport/special labels		imposed inclusive of all service/transport/special labels
	MSD: Maximum SID Depth - the number of SIDs a node or a link on a		MSD: Maximum SID Depth - the number of SIDs supported by a node or a
	node can support		link on a node
			SID: Segment Identifier as defined in [RFC8402]
	1.2. Requirements Language		1.2. Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here .		capitals, as shown here .
	2. Node MSD Advertisement		2. Node MSD Advertisement
	skipping to change at page 4, line 50 ¶		skipping to change at page 4, line 50 ¶
	If there exist multiple Node MSD advertisements for the same MSD-Type		If there exist multiple Node MSD advertisements for the same MSD-Type
	originated by the same router, the procedures defined in [RFC7981]		originated by the same router, the procedures defined in [RFC7981]
	apply. These procedures may result in different MSD values being		apply. These procedures may result in different MSD values being
	used by (for example) different controllers - but this does not		used by (for example) different controllers - but this does not
	create any interoperability issue.		create any interoperability issue.
	3. Link MSD Advertisement		3. Link MSD Advertisement
	The link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and		The link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and
	223 to carry the MSD of the interface associated with the link. MSD		223 to carry the MSD of the interface associated with the link. MSD
	values may be learned via a hardware API or may be provisioned.		values may be signaled by the forwarding plane or may be provisioned.
	0 1		0 1
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length |		| Type | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| MSD-Type | MSD-Value |		| MSD-Type | MSD-Value |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	// ................... //		// ................... //
	skipping to change at page 5, line 33 ¶		skipping to change at page 5, line 33 ¶
	length of value field.		length of value field.
	Value: consists of one or more pairs of a 1 octet MSD-Type and 1		Value: consists of one or more pairs of a 1 octet MSD-Type and 1
	octet MSD-Value.		octet MSD-Value.
	MSD-Type is a value defined in the MSD Types registry created by the		MSD-Type is a value defined in the MSD Types registry created by the
	IANA Section of this document.		IANA Section of this document.
	MSD-Value is a number in the range of 0-255. For all MSD-Types, 0		MSD-Value is a number in the range of 0-255. For all MSD-Types, 0
	represents lack of the ability to support SID stack of any depth; any		represents lack of the ability to support SID stack of any depth; any
	other value represents that of the link when used as an outgoing		other value represents that of the link.
	link.
	This sub-TLV is optional.		This sub-TLV is optional.
	If multiple Link MSD advertisements for the same MSD-Type and the		If multiple Link MSD advertisements for the same MSD-Type and the
	same link are received, the procedure used to select which copy is		same link are received, the procedure used to select which copy is
	used is undefined.		used is undefined.
	4. Procedures for using Node and Link MSD Advertisements		4. Procedures for using Node and Link MSD Advertisements
	When Link MSD is present for a given MSD type, the value of the Link		When Link MSD is present for a given MSD type, the value of the Link
	MSD MUST take preference over the Node MSD. When a Link MSD type is		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		not signaled but the Node MSD type is, then the Node MSD type value
	MUST be considered as the MSD value for that link.		MUST be considered as the MSD value for that link.
	In order to increase flooding efficiency, it is RECOMMENDED that		In order to increase flooding efficiency, it is RECOMMENDED that
	routers with homogenous link MSD values advertise just the Node MSD		routers with homogenous link MSD values advertise just the Node MSD
	value.		value.
	The meaning of the absence of both Node and Link MSD advertisements		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		for a given MSD type is specific to the MSD type. Generally it can
	only be inferred that the advertising node does not support		only be inferred that the advertising node does not support
	skipping to change at page 7, line 17 ¶		skipping to change at page 7, line 17 ¶
	y y y y y y		y y y y y y
	Figure 5: TLVs where LINK MSD Sub-TLV can be present		Figure 5: TLVs where LINK MSD Sub-TLV can be present
	This document requests creation of an IANA managed registry under the		This document requests creation of an IANA managed registry under the
	category of "Interior Gateway Protocol (IGP) Parameters" IANA		category of "Interior Gateway Protocol (IGP) Parameters" IANA
	registries to identify MSD types as proposed in Section 2 and		registries to identify MSD types as proposed in Section 2 and
	Section 3. The registration procedure is "Expert Review" as defined		Section 3. The registration procedure is "Expert Review" as defined
	in [RFC8126]. Suggested registry name is "IGP MSD Types". Types are		in [RFC8126]. Suggested registry name is "IGP MSD Types". Types are
	an unsigned 8 bit number. The following values are defined by this		an unsigned 8 bit number. The following values are defined by this
	document		document:
	Value Name Reference		Value Name Reference
	----- --------------------- -------------		----- --------------------- -------------
	0 Reserved This document		0 Reserved This document
	1 Base MPLS Imposition MSD This document		1 Base MPLS Imposition MSD This document
	2-250 Unassigned This document		2-250 Unassigned This document
	251-254 Experimental This document		251-254 Experimental This document
	255 Reserved This document		255 Reserved This document
	Figure 6: MSD Types Codepoints Registry		Figure 6: MSD Types Codepoints Registry
	skipping to change at page 7, line 39 ¶		skipping to change at page 7, line 39 ¶
	General guidance for the Designated Experts is as defined in		General guidance for the Designated Experts is as defined in
	[RFC7370]		[RFC7370]
	7. Security Considerations		7. Security Considerations
	Security considerations as specified by [RFC7981] are applicable to		Security considerations as specified by [RFC7981] are applicable to
	this document.		this document.
	Advertisement of the additional information defined in this document		Advertisement of the additional information defined in this document
	that is false, e.g., an MSD that is incorrect, may result in a path		that is false, e.g., an MSD that is incorrect, may result in a path
	computation failing, having a service unavailable, or instantiation		computation failing, having a service unavailable, or calculation of
	of a path that can't be supported by the head-end (the node		a path that cannot be supported by the head-end (the node performing
	performing the imposition).		the imposition).
	The presence of this information also may inform an attacker of how		The presence of this information also may inform an attacker of how
	to induce any of the aforementioned conditions.		to induce any of the aforementioned conditions.
	8. Contributors		8. Contributors
	The following people contributed to this document:		The following people contributed to this document:
	Peter Psenak		Peter Psenak
	Email: ppsenak@cisco.com		Email: ppsenak@cisco.com
	skipping to change at page 8, line 21 ¶		skipping to change at page 8, line 21 ¶
	10. References		10. References
	10.1. 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>.
			[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
			Element (PCE) Communication Protocol (PCEP)", RFC 5440,
			DOI 10.17487/RFC5440, March 2009,
			<https://www.rfc-editor.org/info/rfc5440>.
	[RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints		[RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints
	Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014,		Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014,
	<https://www.rfc-editor.org/info/rfc7370>.		<https://www.rfc-editor.org/info/rfc7370>.
	[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions		[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
	for Advertising Router Information", RFC 7981,		for Advertising Router Information", RFC 7981,
	DOI 10.17487/RFC7981, October 2016,		DOI 10.17487/RFC7981, October 2016,
	<https://www.rfc-editor.org/info/rfc7981>.		<https://www.rfc-editor.org/info/rfc7981>.
	[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for		[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
	Writing an IANA Considerations Section in RFCs", BCP 26,		Writing an IANA Considerations Section in RFCs", BCP 26,
	RFC 8126, DOI 10.17487/RFC8126, June 2017,		RFC 8126, DOI 10.17487/RFC8126, June 2017,
	<https://www.rfc-editor.org/info/rfc8126>.		<https://www.rfc-editor.org/info/rfc8126>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
			[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
			Decraene, B., Litkowski, S., and R. Shakir, "Segment
			Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
			July 2018, <https://www.rfc-editor.org/info/rfc8402>.
	10.2. Informative References		10.2. Informative References
	[I-D.ietf-idr-bgp-ls-segment-routing-msd]		[I-D.ietf-idr-bgp-ls-segment-routing-msd]
	Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,		Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
	"Signaling MSD (Maximum SID Depth) using Border Gateway		"Signaling MSD (Maximum SID Depth) using Border Gateway
	Protocol Link-State", draft-ietf-idr-bgp-ls-segment-		Protocol Link-State", draft-ietf-idr-bgp-ls-segment-
	routing-msd-02 (work in progress), August 2018.		routing-msd-02 (work in progress), August 2018.
	[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.
End of changes. 17 change blocks.
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