< draft-ietf-ospf-segment-routing-msd-09.txt		draft-ietf-ospf-segment-routing-msd-10.txt >
	OSPF Working Group J. Tantsura		OSPF 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: August 30, 2018 Huawei Technologies		Expires: October 7, 2018 Huawei Technologies
	S. Aldrin		S. Aldrin
	Google, Inc		Google, Inc
	P. Psenak		P. Psenak
	Cisco Systems		Cisco Systems
	February 26, 2018		April 05, 2018
	Signaling MSD (Maximum SID Depth) using OSPF		Signaling MSD (Maximum SID Depth) using OSPF
	draft-ietf-ospf-segment-routing-msd-09		draft-ietf-ospf-segment-routing-msd-10
	Abstract		Abstract
	This document defines a way for an OSPF Router to advertise multiple		This document defines a way for an OSPF Router to advertise multiple
	types of supported Maximum SID Depths (MSDs) at node and/or link		types of supported Maximum SID Depths (MSDs) at node and/or link
	granularity. Such advertisements allow entities (e.g., centralized		granularity. Such advertisements allow entities (e.g., centralized
	controllers) to determine whether a particular SID stack is		controllers) to determine whether a particular SID stack can be
	supportable in a given network. This document only defines one type		supported in a given network. This document only defines one type of
	of MSD (maximum label imposition) - but defines an encoding which can		MSD maximum label imposition, but defines an encoding which can
	support other MSD types. Here the term OSPF means both OSPFv2 and		support other MSD types. Here the term OSPF means both OSPFv2 and
	OSPFv3.		OSPFv3.
	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.
	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 August 30, 2018.		This Internet-Draft will expire on October 7, 2018.
	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 39 ¶		skipping to change at page 2, line 39 ¶
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	11.1. Normative References . . . . . . . . . . . . . . . . . . 7		11.1. Normative References . . . . . . . . . . . . . . . . . . 7
	11.2. Informative References . . . . . . . . . . . . . . . . . 7		11.2. Informative References . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	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) which can be imposed at the node/link a given SR path is		Depth(MSD) that can be imposed at each node/link a given SR path to
	applied so as to insure that the SID stack depth of a computed path		insure that the SID stack depth of a computed path doesn't exceed the
	doesn't exceed the number of SIDs the node is capable of imposing.		number of SIDs the node is capable of imposing.
	PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD		The PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals
	in SR PCE Capability TLV and METRIC Object. However, if PCEP is not		MSD in SR PCE Capability TLV and METRIC Object. However, if PCEP is
	supported/configured on the head-end of a SR tunnel or a Binding-SID		not supported/configured on the head-end of an SR tunnel or a
	anchor node and controller does not participate in IGP routing, it		Binding-SID anchor node and controller does not participate in IGP
	has no way to learn the MSD of nodes and links which has been		routing, it has no way to learn the MSD of nodes and links which has
	configured. BGP-LS [RFC7752] defines a way to expose topology and		been configured. BGP-LS [RFC7752] defines a way to expose topology
	associated attributes and capabilities of the nodes in that topology		and associated attributes and capabilities of the nodes in that
	to a centralized controller. MSD signaling by BGP-LS has been		topology to a centralized controller. MSD signaling by BGP-LS has
	defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically,		been defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd].
	BGP-LS is configured on a small number of nodes, that do not		Typically, BGP-LS is configured on a small number of nodes that do
	necessarily act as head-ends. In order, for BGP-LS to signal MSD for		not necessarily act as head-ends. In order for BGP-LS to signal MSD
	all the nodes and links in the network MSD is relevant, MSD		for all the nodes and links in the network MSD is relevant, MSD
	capabilites should be advertised to every OSPF router in the network.		capabilites should be advertised to every OSPF 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-ospf-mpls-elc] defines Readable Label Depth Capability		[I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability
	(RLDC) that is used by a head-end to insert Entropy Label (EL) at		(RLDC) that is used by a head-end to insert an Entropy Label (EL) at
	appropriate depth, so it could be read by transit nodes.		a depth that can be read by transit nodes.
	This document defines an extension to OSPF used to advertise one or		This document defines an extension to OSPF 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 laso defines
	one MSD type called Base MPLS Imposition MSD. In the future it is		the Base MPLS Imposition MSD type. In the future it is expected,
	expected that new MSD types will be defined to signal additional		that new MSD types will be defined to signal additional capabilities
	capabilities e.g., entropy labels, SIDs that can be imposed through		e.g., entropy labels, SIDs that can be imposed through recirculation,
	recirculation, or SIDs associated with another dataplane e.g., IPv6.		or SIDs associated with another dataplane e.g., IPv6.
	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
	BMI: Base MPLS Imposition is the number of MPLS labels which can be		BMI: Base MPLS Imposition is the number of MPLS labels that can be
	imposed inclusive of any service/transport labels		imposed inclusive of any service/transport labels
	OSPF: Open Shortest Path First		OSPF: Open Shortest Path First
	MSD: Maximum SID Depth - the number of SIDs a node or a link on a		MSD: Maximum SID Depth - the number of SIDs a node or one of its
	node can support		links can support
	PCC: Path Computation Client		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		SID: Segment Identifier
	SR: Segment Routing		SR: Segment Routing
	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", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	document are to be interpreted as described in RFC 2119 [RFC2119].		"OPTIONAL" in this document are to be interpreted as described in
			BCP14 [RFC2119], [RFC8174] when, and only when they appear in all
			capitals, as shown here .
	2. Terminology		2. Terminology
	This memo makes use of the terms defined in [RFC4970].		This memo makes use of the terms defined in [RFC4970].
	3. Node MSD TLV		3. Node MSD TLV
	A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD		The node MSD TLV within the body of the OSPF RI Opaque LSA is defined
	TLV is defined to carry the provisioned SID depth of the router		to carry the provisioned SID depth of the router originating the RI
	originating the RI LSA. Node MSD is the lowest MSD supported by the		LSA. Node MSD is the minimum MSD supported by the node.
	node.
	0 1 2 3		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		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
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length |		| Type | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Sub-Type and Value ...		| Sub-Type and Value ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
	Figure 1: Node MSD TLV		Figure 1: Node MSD TLV
	The Type (2 bytes) of this TLV has value of 12.		The Type: TBD1
	Length is variable (minimum of 2, multiple of 2 octets) and		Length: variable (minimum of 2, multiple of 2 octets) and represents
	represents the total length of value field.		the total length of value field.
	Value field consists of a 1 octet sub-type (IANA Registry) and 1		Value: consists of a 1 octet sub-type (IANA Registry) and 1 octet
	octet value.		value.
	Sub-Type 1 (IANA Section), MSD and the Value field contains maximum		Sub-Type 1 (IANA Section), MSD and the Value field contains maximum
	MSD of the router originating the RI LSA. Node Maximum MSD is a		MSD of the router originating the RI LSA. Node Maximum MSD is a
	number in the range of 0-254. 0 represents lack of the ability to		number in the range of 0-254. 0 represents lack of the ability to
	impose MSD stack of any depth; any other value represents that of the		impose MSD stack of any depth; any other value represents that of the
	node. This value SHOULD represent the lowest value supported by		node. This value SHOULD represent the minimum value supported by a
	node.		node.
	Other Sub-types other than defined above are reserved for future		Other Sub-types other than defined above are reserved for future
	extensions.		extensions.
	This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is		This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is
	optional. The scope of the advertisement is specific to the		optional. The scope of the advertisement is specific to the
	deployment.		deployment.
	4. Link MSD sub-TLV		4. Link MSD sub-TLV
	skipping to change at page 5, line 21 ¶		skipping to change at page 5, line 21 ¶
	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		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
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length |		| Type | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Sub-Type and Value ...		| Sub-Type and Value ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
	Figure 2: Link MSD Sub-TLV		Figure 2: Link MSD Sub-TLV
	The Type (2 bytes) of this TLV:		Type:
	For OSPFv2, the Link level MSD value is advertised as an optional		For OSPFv2, the Link level MSD value is advertised as an optional
	Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and has		Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and
	value of 6.		has value of TBD2.
	For OSPFv3, the Link level MSD value is advertised as an optional		For OSPFv3, the Link level MSD value is advertised as an optional
	Sub-TLV of the Router-Link TLV as defined in		Sub-TLV of the Router-Link TLV as defined in
	[I-D.ietf-ospf-ospfv3-lsa-extend], and has value of 16 (Suggested		[I-D.ietf-ospf-ospfv3-lsa-extend], and has value of TBD3.
	value - to be assigned by IANA).
	Length is variable and similar to what is defined in Section 3.		Length: variable and similar to what is defined in Section 3.
	Value field consists of a 1 octet sub-type (IANA Registry) and 1		Value: consists of a 1 octet sub-type (IANA Registry) and 1 octet
	octet value.		value.
	Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD		Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
	of the router originating the corresponding LSA as specified for		of the router originating the corresponding LSA as specified for
	OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0		OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0
	represents lack of the ability to impose MSD stack of any depth; any		represents lack of the ability to impose MSD stack of any depth; any
	other value represents that of the particular link MSD value.		other value represents that of the particular link MSD value.
	Other Sub-types other than defined above are reserved for future		Other Sub-types other than defined above are reserved for future
	extensions.		extensions.
	5. Using Node and Link MSD Advertisements		5. 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 be used in preference to the Node MSD.		MSD MUST take preference over the Node MSD.
	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
	advertisement of that MSD type. However, in some cases the lack of		advertisement of that MSD type. However, in some cases the lack of
	advertisement might imply that the functionality associated with the		advertisement might imply that the functionality associated with the
	MSD type is not supported. The correct interpretation MUST be		MSD type is not supported. The correct interpretation MUST be
	specified when an MSD type is defined.		specified when an MSD type is defined.
	6. Base MPLS Imposition MSD		6. Base MPLS Imposition MSD
	Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS		The Base MPLS Imposition MSD (BMI-MSD) signals the total number of
	labels a node is capable of imposing, including any service/transport		MPLS labels a node is capable of imposing, including any service/
	labels.		transport labels.
	Absence of BMI-MSD advertisements indicates only that the advertising		Absence of BMI-MSD advertisements indicates solely that the
	node does not support advertisement of this capability.		advertising node does not support advertisement of this capability.
	7. IANA Considerations		7. IANA Considerations
	This document includes a request to IANA to allocate TLV type codes		This document requests IANA to allocate TLV type (TBD1) from the OSPF
	for the new TLV proposed in Section 3 of this document from OSPF		Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA
	Router Information (RI) TLVs Registry as defined by [RFC4970]. For		has allocated the value 12 through the early assignment process.
	the link MSD, we request IANA to allocate new sub-TLV codes as		Also, this document requests IANA to allocate a sub-TLV type (TBD2)
	proposed in Section 4 from OSPFv2 Extended Link TLV Sub-TLVs registry		from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has
	and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV		allocated the the value 6 through the early assignment process.
	registry.		Finally, this document requests IANA to allocate a sub-TLV type
			(TBD3) from the OSPFv3 Extended-LSA Sub-TLV registry.
	This document requests creation of a new IANA managed registry under		This document requests creation of an IANA managed registry under a
	a new category of "Interior Gateway Protocol (IGP) Parameters" IANA		new category of "Interior Gateway Protocol (IGP) Parameters" IANA
	registries to identify MSD types as proposed in Section 3, Section 4.		registries to identify MSD types as proposed in Section 3, Section 4.
	The registration procedure is "Expert Review" as defined in		The registration procedure is "Expert Review" as defined in
	[RFC8126]. Suggested registry name is "MSD types". Types are an		[RFC8126]. The suggested registry name is "MSD types". Types are an
	unsigned 8 bit number. The following values are defined by this		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 3: MSD Types Codepoints Registry		Figure 3: MSD Types Codepoints Registry
	skipping to change at page 7, line 20 ¶		skipping to change at page 7, line 20 ¶
	9. Contributors		9. Contributors
	The following people contributed to this document:		The following people contributed to this document:
	Les Ginsberg		Les Ginsberg
	Email: ginsberg@cisco.com		Email: ginsberg@cisco.com
	10. Acknowledgements		10. Acknowledgements
	The authors would like to thank Stephane Litkowski and Bruno Decraene		The authors would like to thank Acee Lindem, Stephane Litkowski and
	for their reviews and valuable comments.		Bruno Decraene for their reviews and valuable comments.
	11. References		11. References
	11.1. Normative References		11.1. 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>.
	[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and		[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
	S. Shaffer, "Extensions to OSPF for Advertising Optional		S. Shaffer, "Extensions to OSPF for Advertising Optional
	Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July		Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
	2007, <https://www.rfc-editor.org/info/rfc4970>.		2007, <https://www.rfc-editor.org/info/rfc4970>.
	[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and		[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
	S. Shaffer, "Extensions to OSPF for Advertising Optional		S. Shaffer, "Extensions to OSPF for Advertising Optional
	Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,		Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
	February 2016, <https://www.rfc-editor.org/info/rfc7770>.		February 2016, <https://www.rfc-editor.org/info/rfc7770>.
			[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
			2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
			May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	11.2. Informative References		11.2. 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 Maximum SID Depth using Border Gateway Protocol		"Signaling Maximum SID Depth using Border Gateway Protocol
	Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01		Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
	(work in progress), October 2017.		(work in progress), October 2017.
	[I-D.ietf-ospf-mpls-elc]		[I-D.ietf-ospf-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. 31 change blocks.
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