< draft-ietf-ospf-segment-routing-msd-11.txt		draft-ietf-ospf-segment-routing-msd-12.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: November 8, 2018 Huawei Technologies		Expires: November 10, 2018 Huawei Technologies
	S. Aldrin		S. Aldrin
	Google, Inc		Google, Inc
	P. Psenak		P. Psenak
	Cisco Systems		Cisco Systems
	May 07, 2018		May 09, 2018
	Signaling MSD (Maximum SID Depth) using OSPF		Signaling MSD (Maximum SID Depth) using OSPF
	draft-ietf-ospf-segment-routing-msd-11		draft-ietf-ospf-segment-routing-msd-12
	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 can be		controllers) to determine whether a particular SID stack can be
	supported in a given network. This document defines only one type of		supported in a given network. This document defines only one type of
	MSD, but defines an encoding that can support other MSD types. Here		MSD, but defines an encoding that can support other MSD types. Here
	the term OSPF means both OSPFv2 and OSPFv3.		the term OSPF means both OSPFv2 and OSPFv3.
	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 November 8, 2018.		This Internet-Draft will expire on November 10, 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 22 ¶		skipping to change at page 2, line 22 ¶
	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
	1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4		1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
	2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4		2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
	3. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5		3. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5
	4. Using Node and Link MSD Advertisements . . . . . . . . . . . 6		4. Using Node and Link MSD Advertisements . . . . . . . . . . . 6
	5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6		5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 7		7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7		8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	10.1. Normative References . . . . . . . . . . . . . . . . . . 7		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 on a given SR path		Depth(MSD) that can be imposed at each node/link on a given SR path
	to insure that the SID stack depth of a computed path doesn't exceed		to insure that the SID stack depth of a computed path doesn't exceed
	the number of SIDs the node is capable of imposing.		the number of SIDs the node is capable of imposing.
	skipping to change at page 4, line 37 ¶		skipping to change at page 4, line 37 ¶
	| MSD Type and Value ...		| MSD Type and Value ...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
	Figure 1: Node MSD TLV		Figure 1: Node MSD TLV
	The Type: TBD1		The Type: TBD1
	Length: variable (minimum of 2, multiple of 2 octets) and represents		Length: variable (minimum of 2, multiple of 2 octets) and represents
	the total length of value field.		the total length of value field.
	Value: consists of one or more pairs of a 1 octet sub-type (IANA		Value: consists of one or more pairs of a 1 octet type (IANA
	Registry) and 1 octet value.		Registry) and 1 octet value.
	MSD Type 1 (IANA Section), MSD and the Value field contains the MSD		MSD Type 1 (IANA Section), MSD and the Value field contains the MSD
	of the originating router. Node MSD is a number in the range of		of the originating router. Node MSD is a number in the range of
	0-255. 0 represents lack of the ability to impose MSD stack of any		0-255. 0 represents lack of the ability to impose MSD stack of any
	depth; any other value represents that of the node. This value		depth; any other value represents that of the node. This value
	SHOULD represent the minimum value supported by a node.		SHOULD represent the minimum value supported by a node.
	Other MSD Types are reserved for future extensions.		Other MSD Types are reserved for future 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.
			When multiple Node MSD TLVs are received from a given router, the
			receiver MUST use the first occurrence of the TLV in the Router
			Information LSA. If the Node MSD TLV appears in multiple Router
			Information LSAs that have different flooding scopes, the Node MSD
			TLV in the Router Information LSA with the area-scoped flooding scope
			MUST be used. If the Node MSD TLV appears in multiple Router
			Information LSAs that have the same flooding scope, the Node MSD TLV
			in the Router Information (RI) LSA with the numerically smallest
			Instance ID MUST be used and subsequent instances of the Node MSD TLV
			MUST be ignored. The RI LSA can be advertised at any of the defined
			opaque flooding scopes (link, area, or Autonomous System (AS)). For
			the purpose of Node MSD TLV advertisement, area-scoped flooding is
			REQUIRED.
	3. Link MSD sub-TLV		3. Link MSD sub-TLV
	The link sub-TLV is defined to carry the MSD of the interface		The link sub-TLV is defined to carry the MSD of the interface
	associated with the link. MSD values may be learned via a hardware		associated with the link. MSD values may be learned via a hardware
	API or may be provisioned.		API or may be provisioned.
	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
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	skipping to change at page 5, line 45 ¶		skipping to change at page 6, line 13 ¶
	Registry) and 1 octet value.		Registry) and 1 octet value.
	MSD Type 1 (IANA Section), MSD and the Value field contains Link MSD		MSD 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 0-255. 0		OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-255. 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 MSD Types are reserved for future extensions.		Other MSD Types are reserved for future extensions.
	If these TLVs are advertised multiple times, only the first instance		If this TLV is advertised multiple times in the same OSPFv2 Extended
	of the TLV is used by receiving OSPF routers. This situation SHOULD		Link Opaque LSA, only the first instance of the TLV is used by
	be logged as an error.		receiving OSPFv2 routers. This situation SHOULD be logged as an
			error.
	If these TLV is advertised multiple times for the same link in		If this TLV is advertised multiple times for the same link in
	different LSAs originated by the same OSPF router, the TLV with the		different OSPFv2 Extended Link Opaque LSAs originated by the same
	smallest Opaque ID/Link State ID is used by receiving OSPF routers.		OSPFv2 router, the OSPFv2 Extended Link TLV in the OSPFv2 Extended
	This situation MAY be logged as a warning.		Link Opaque LSA with the smallest Opaque ID is used by receiving
			OSPFv2 routers. This situation may be logged as a warning.
	4. Using Node and Link MSD Advertisements		4. 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 preference over the Node MSD. When a Link MSD type is
	not signalled but the Node MSD type is, then the value of that Link		not signalled but the Node MSD type is, then the value of that Link
	MSD type MUST be considered as the corresponding Node MSD type value.		MSD type MUST be considered as the corresponding Node MSD type value.
	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.
	skipping to change at page 6, line 28 ¶		skipping to change at page 6, line 45 ¶
	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.
	5. Base MPLS Imposition MSD		5. Base MPLS Imposition MSD
	The Base MPLS Imposition MSD (BMI-MSD) signals the total number of		The Base MPLS Imposition MSD (BMI-MSD) signals the total number of
	MPLS labels a node is capable of imposing, including any service/		MPLS labels a node is capable of imposing, including all
	transport labels.		service/transport/special labels.
	Absence of BMI-MSD advertisements indicates solely that the		Absence of BMI-MSD advertisements indicates solely that the
	advertising node does not support advertisement of this capability.		advertising node does not support advertisement of this capability.
	6. IANA Considerations		6. IANA Considerations
	This document requests IANA to allocate TLV type (TBD1) from the OSPF		This document requests IANA to allocate TLV type (TBD1) from the OSPF
	Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA		Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA
	has allocated the value 12 through the early assignment process.		has allocated the value 12 through the early assignment process.
	Also, this document requests IANA to allocate a sub-TLV type (TBD2)		Also, this document requests IANA to allocate a sub-TLV type (TBD2)
	skipping to change at page 7, line 17 ¶		skipping to change at page 7, line 36 ¶
	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
	7. Security Considerations		7. Security Considerations
	Security concerns for OSPF are addressed in [RFC7474] and [RFC5310].		Security concerns for OSPF are addressed in [RFC7474]. Further
	Further security analysis for OSPF protocol is done in [RFC6853]		security analysis for OSPF protocol is done in [RFC6863] including
	including analysis of both the above documents. Security		analysis of both the above documents. Security considerations, as
	considerations, as specified by [RFC7770] are applicable to this		specified by [RFC7770], [RFC7684] and [RFC8362] are applicable to
	document.		this document.
	Advertisement of the additional information defined in this document		Advertisement of an incorrect MSD value may result: in a path
	that is false, e.g. MSD that is incorrect may result: in a path
	computation failing and the service unavailable or instantiation of a		computation failing and the service unavailable or instantiation of a
	path that can't be supported by the head-end (the node performing the		path that can't be supported by the head-end (the node performing the
	imposition).		imposition).
	8. Contributors		8. 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
	9. Acknowledgements		9. Acknowledgements
	The authors would like to thank Acee Lindem, Stephane Litkowski and		The authors would like to thank Acee Lindem, Ketan Talaulikar,
	Bruno Decraene for their reviews and valuable comments.		Stephane Litkowski and Bruno Decraene for their reviews and valuable
			comments.
	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>.
	[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>.
			[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
			"Security Extension for OSPFv2 When Using Manual Key
			Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
			<https://www.rfc-editor.org/info/rfc7474>.
			[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
			Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
			Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
			2015, <https://www.rfc-editor.org/info/rfc7684>.
	[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		[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>.
	[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and		[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
	skipping to change at page 8, line 49 ¶		skipping to change at page 9, line 30 ¶
	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-11 (work in progress),		draft-ietf-pce-segment-routing-11 (work in progress),
	November 2017.		November 2017.
	[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and		[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
	R. Aggarwal, "Support of Address Families in OSPFv3",		R. Aggarwal, "Support of Address Families in OSPFv3",
	RFC 5838, DOI 10.17487/RFC5838, April 2010,		RFC 5838, DOI 10.17487/RFC5838, April 2010,
	<https://www.rfc-editor.org/info/rfc5838>.		<https://www.rfc-editor.org/info/rfc5838>.
	[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,		[RFC6863] Hartman, S. and D. Zhang, "Analysis of OSPF Security
	Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute		According to the Keying and Authentication for Routing
	Advertisement", RFC 7684, DOI 10.17487/RFC7684, November		Protocols (KARP) Design Guide", RFC 6863,
	2015, <https://www.rfc-editor.org/info/rfc7684>.		DOI 10.17487/RFC6863, March 2013,
			<https://www.rfc-editor.org/info/rfc6863>.
	[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,
	<https://www.rfc-editor.org/info/rfc7752>.		<https://www.rfc-editor.org/info/rfc7752>.
	[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,
End of changes. 17 change blocks.
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