< draft-chunduri-lsr-isis-mt-deployment-cons-00.txt		draft-chunduri-lsr-isis-mt-deployment-cons-01.txt >
	LSR Working Group U. Chunduri		LSR Working Group U. Chunduri
	Internet-Draft Huawei USA		Internet-Draft Huawei USA
	Intended status: Informational J. Tantsura		Intended status: Standards Track J. Tantsura
	Expires: October 26, 2018 Nuage Networks		Expires: April 25, 2019 Apstra, Inc.
	April 24, 2018		October 22, 2018
	IS-IS Multi Topology Deployment Considerations		IS-IS Multi Topology Deployment Considerations
	draft-chunduri-lsr-isis-mt-deployment-cons-00		draft-chunduri-lsr-isis-mt-deployment-cons-01
	Abstract		Abstract
	This document analyzes IS-IS Multi Topology (MT) considerations in		This document analyzes IS-IS Multi Topology (MT) considerations in
	various deployments (Core/Mobile Backhaul/Data Center underlay).		various deployments (Core/Mobile Backhaul/Data Center underlays).
	This document explores nuances around various IS-IS address families,		This document explores the nuances around the terminology and usage
	topologies and considerations while choosing the right combination		of various IS-IS address families, topologies and considerations,
	for a specific DC/mobile backhaul deployment.		while choosing the right combination for a specific deployment
			scenario.
			This document also discusses various ways one can deploy IPv6 only
			IS-IS topology.
	Requirements Language		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", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC2119 [RFC2119].		document are to be interpreted as described in RFC2119 [RFC2119].
	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
	skipping to change at page 1, line 41 ¶		skipping to change at page 1, line 45 ¶
	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 26, 2018.		This Internet-Draft will expire on April 25, 2019.
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 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 17 ¶		skipping to change at page 2, line 27 ¶
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Need for MT in IS-IS networks . . . . . . . . . . . . . . . . 3		2. Need for MT in IS-IS networks . . . . . . . . . . . . . . . . 3
	3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 3		3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	4. Topologies and Address Families . . . . . . . . . . . . . . . 3		4. Topologies and Address Families . . . . . . . . . . . . . . . 4
	4.1. Single Topology Mode and Multiple Address Families . . . 4		4.1. Single Topology Mode and Multiple Address Families . . . 4
	4.2. Multiple Topology Mode and Multiple Address Families . . 5		4.2. Multiple Topology Mode and Multiple Address Families . . 5
	4.2.1. Transition Mode . . . . . . . . . . . . . . . . . . . 5		4.2.1. Transition Mode . . . . . . . . . . . . . . . . . . . 6
	4.3. IPv6 Only Topology . . . . . . . . . . . . . . . . . . . 6		4.3. IPv6 Only Topology . . . . . . . . . . . . . . . . . . . 6
	5. IS-IS MT and LFA . . . . . . . . . . . . . . . . . . . . . . 6		5. IS-IS MT and LFA . . . . . . . . . . . . . . . . . . . . . . 6
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 6		8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	9.1. Normative References . . . . . . . . . . . . . . . . . . 7		9.1. Normative References . . . . . . . . . . . . . . . . . . 7
	9.2. Informative References . . . . . . . . . . . . . . . . . 7		9.2. Informative References . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	ISIS originally developed for OSI [ISO10589], extensions have been		ISIS originally developed for OSI [ISO10589], extensions have been
	made available to support IPv4 [RFC1195]. A method for exchanging		made available to support IPv4 [RFC1195]. A method for exchanging
	IPv6 routing information using the IS-IS routing protocol is		IPv6 routing information using the IS-IS routing protocol is
	specified in [RFC5308]. How to run a set of independent IP		specified in [RFC5308]. How to run a set of independent IP
	topologies with topology specific adjacencies, within a single IS-IS		topologies with topology specific adjacencies, within a single IS-IS
	domain has been defined in IS-IS MT [RFC5120].		domain has been defined in IS-IS MT [RFC5120].
	Multiple mobile backhaul network user plane proposals like		Multiple mobile backhaul network user plane proposals like
	[I-D.ietf-dmm-srv6-mobile-uplane] and [I-D.herbert-ila-mobile] use		[I-D.ietf-dmm-srv6-mobile-uplane] and [I-D.herbert-ila-mobile] use
	IPv6 only solution using source routing, address transformation		IPv6 only solution using source routing, address transformation
	respectively. It is possible to conceive, various parts of the		respectively. It is possible to conceive, various parts of the
	backhaul networks use IPv4 and appropriate migration strategy needed		backhaul networks use IPv4 and appropriate migration strategy needed
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 2018
	before eventually moving towards IPv6 only network. While any IGP		before eventually moving towards IPv6 only network. While any IGP
	can be used in these networks, this document covers only IS-IS		can be used in these networks, this document covers only IS-IS
	protocol aspects.		protocol aspects.
	Various layer-3 DC fabric routing options (refs: openfabric, spine-		Various layer-3 DC fabric routing options (refs: openfabric, spine-
	leaf, controller-based) by changing or optimizing some aspects w.r.t		leaf, controller-based) by changing or optimizing some aspects w.r.t
	adjacency formation, flooding optimizations, or/and mechanisms to		adjacency formation, flooding optimizations, or/and mechanisms to
	automatically compute the location of the node in the fat tree		automatically compute the location of the node in the fat tree
	topology are proposed recently and this document brings some of the		topology are proposed recently and this document brings some of the
	multi topology deployment aspects relevant to these networks. Please		multi topology deployment aspects relevant to these networks. Please
	note part of the discussion around IS-IS MT is not specific to DC or		note, part of the discussion around IS-IS MT is not specific to DC or
	CLOS fabrics and generally applicable to any IS-IS deployment but		CLOS fabrics and generally applicable to any IS-IS deployment but
	discussed here because of multiple proposals to use various forms of		discussed here because of multiple proposals to use various forms of
	IS-IS in this context.		IS-IS in this context.
	2. Need for MT in IS-IS networks		2. Need for MT in IS-IS networks
	For mobile transport backhaul networks seeking only IPv6 network or		For mobile transport backhaul networks seeking only IPv6 network or
	transitioning from parts of the network with only IPv4, IS-IS MT is		transitioning from parts of the network with only IPv4, IS-IS MT is
	needed. For DC fabric underlay, which provide reachability, only one		needed. For layer-3 DC fabric underlay, which provide reachability,
	address family (either IPv4 or IPv6) SHOULD be sufficient. However		only one address family (either IPv4 or IPv6) SHOULD be sufficient.
	if either only IPv6 address family is needed in the underlay or		However if either only IPv6 address family is needed in the underlay
	deploying both IPv4 and IPv6 address families are desired discussion		or deploying both IPv4 and IPv6 address families are desired
	in Section 4 is relevant.		discussion in Section 4 is relevant.
	It is an unlikely requirement, where DC fabric to be partitioned		It is an unlikely requirement, where DC fabric to be partitioned
	logically to have different topologies in the underlay. If one does		logically to have different topologies in the underlay. If one does
	to meet a particular requirement, this does introduce manageability		the same to meet a particular requirement, it introduces a
	complexity of these logical topologies. IS-IS MT [RFC 5120] also		manageability complexity of these logical topologies. IS-IS MT
	designed to address the above need and discussion in Section 4.2 is		[RFC5120] also designed to address the above need and discussion in
	relevant. It is worth noting, majority of the IS-IS deployments (non		Section 4.2 is relevant. It is worth noting, majority of the IS-IS
	DC) use MT primarily to have a separate logical topology for IPv6		deployments use MT primarily to have a separate logical topology for
	address family.		IPv6 address family.
	3. Acronyms		3. Acronyms
	IIH : IS-IS Hello Protocol Data Unit		IIH : IS-IS Hello Protocol Data Unit
	LSP : Link State PDU		LSP : Link State PDU
	MT : Multi Topology		MT : Multi Topology
	SPF : Shortest Path First		SPF : Shortest Path First
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 2018
	4. Topologies and Address Families		4. Topologies and Address Families
	Terminology around IS-IS topologies and address families is somewhat		Terminology around IS-IS topologies and address families is somewhat
	confusing at best. Just to give an example, MT ID #2 defined in [RFC		confusing at best. Just to give an example, MT ID #2 defined in [RFC
	5120] says, it is "Reserved for IPv6 routing topology". While		5120] says, it is "Reserved for IPv6 routing topology". While
	multiple MT ID's can be deployed in a network with IPv6 topologies,		multiple MT ID's can be deployed in a network with IPv6 topologies,
	MT ID #2, perhaps referring to a first such topology with IPv6 only		MT ID #2, perhaps referring to a first such topology with IPv6 only
	address family. This section details various topology and address		address family. This section details various topology and address
	family options possible with currently available IS-IS specifications		family options possible with currently available IS-IS specifications
	with respective defined TLVs.		with respective defined TLVs.
	skipping to change at page 4, line 31 ¶		skipping to change at page 5, line 5 ¶
	However, for the above to work effectively, both IPv4 and IPv6		However, for the above to work effectively, both IPv4 and IPv6
	address families MUST share a common network topology. That is to		address families MUST share a common network topology. That is to
	use IS-IS for IPv4 and IPv6 routing, any interface configured for		use IS-IS for IPv4 and IPv6 routing, any interface configured for
	IPv4 IS-IS MUST also be configured for IPv6 IS-IS, and vice versa.		IPv4 IS-IS MUST also be configured for IPv6 IS-IS, and vice versa.
	All routers within an IS-IS area (Level 1 routing) or domain (Level 2		All routers within an IS-IS area (Level 1 routing) or domain (Level 2
	routing) MUST also support the same set of address families: IPv4		routing) MUST also support the same set of address families: IPv4
	only, IPv6 only, or both IPv4 and IPv6. Any discrepancy in the		only, IPv6 only, or both IPv4 and IPv6. Any discrepancy in the
	configuration w.r.t above can cause routing black holes and one such		configuration w.r.t above can cause routing black holes and one such
	scenario is discussed below.		scenario is discussed below.
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 2018
	| / \|		| / \|
	...Rx Ry...		...Rx Ry...
	| \ /		| \ /
	| \ / |		| \ / |
	| \ / |		| \ / |
	| /\ |		| /\ |
	| / \ |		| / \ |
	| / \|		| / \|
	... R1 R2...		... R1 R2...
	| \ / |		| \ / |
	skipping to change at page 5, line 8 ¶		skipping to change at page 5, line 30 ¶
	As shown, in the above diagram all routers in the network enabled		As shown, in the above diagram all routers in the network enabled
	with both IPv4 and IPv6 unicast address families at the IS level and		with both IPv4 and IPv6 unicast address families at the IS level and
	single topology would be built. However, at a link level all but		single topology would be built. However, at a link level all but
	except one link, say if IPv6 is not configured on the link between		except one link, say if IPv6 is not configured on the link between
	the routers Rx and R2; due to a single IS-IS topology, the shortest		the routers Rx and R2; due to a single IS-IS topology, the shortest
	path between Rx and R2 is the direct link and since IPv6 is not		path between Rx and R2 is the direct link and since IPv6 is not
	enabled on that link, Rx and R2 cannot exchange IPv6 data traffic		enabled on that link, Rx and R2 cannot exchange IPv6 data traffic
	even though there's an alternate path between them in the topology		even though there's an alternate path between them in the topology
	through Rx, R1, Ry and R2.		through Rx, R1, Ry and R2.
	Hence to summarize the restrictions, as laid out above: all routers		Hence to summarize the restrictions: all routers in the topology MUST
	in the topology MUST support only IPv4, only IPv6 or both IPv4 and		support only IPv4, only IPv6 or both IPv4 and IPv6 address families
	IPv6 address families on all links and node. In other words, network		on all links and node. In other words, network MUST be congruent.
	MUST be congruent. While this model is to simpler to operate, might		While this model is to simpler to operate, might not be flexible
	not be flexible enough for some IS-IS deployments.		enough for some IS-IS deployments.
	4.2. Multiple Topology Mode and Multiple Address Families		4.2. Multiple Topology Mode and Multiple Address Families
	Multi-topology IS-IS uses multiple SPFs to compute routes and removes		Multi-topology IS-IS uses multiple SPFs to compute routes and removes
	the restriction that all interfaces MUST support all configured		the restriction that all interfaces MUST support all configured
	address families and that all routers in an IS-IS area or domain MUST		address families and that all routers in an IS-IS area or domain MUST
	support the same set of address families. This introduces the		support the same set of address families. This introduces the
	concept of topology specific adjacency with MT IS Reachability TLV		concept of topology specific adjacency with MT IS Reachability TLV
	222 and MT capable IPv4 Reachability with TLV 235 and MT capable IPv6		222 and MT capable IPv4 Reachability with TLV 235 and MT capable IPv6
	Reachability with TLV 237.		Reachability with TLV 237.
	When MT IS-IS is enabled with IPv4 and IPv6 address families, the		When MT IS-IS is enabled with IPv4 and IPv6 address families, the
	routers build two topologies, one for each address family (IPv4 and		routers build two topologies, one for each address family (IPv4 and
	IPv6) and can find the optimum path for each address family even when		IPv6) and can find the optimum path for each address family even when
	some links in the network support only one of them. IS-IS MT [RFC		some links in the network support only one of them. IS-IS MT [RFC
	5120] defines MT ID #0 for backward compatibility, as the "standard"		5120] defines MT ID #0 for backward compatibility, as the "standard"
	topology and this essentially operate as IS-IS single topology mode		topology and this essentially operate as IS-IS single topology mode
	as specified in Section 4.1 and supports both IPv4 and IPv6 address		as specified in Section 4.1 and supports both IPv4 and IPv6 address
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 2018
	families. MT ID #2 [RFC 5120] is defined for IPv6 address family in		families. MT ID #2 [RFC 5120] is defined for IPv6 address family in
	MT mode.		MT mode.
	4.2.1. Transition Mode		4.2.1. Transition Mode
	Most of the vendors supported MT transition feature (though some		Most of the vendors supported MT transition feature (though some
	vendors disabled to avoid confusion around this) in the IS-IS		vendors disabled to avoid confusion around this) in the IS-IS
	networks to facilitate MT deployments without disrupting the single		networks to facilitate MT deployments without disrupting the single
	topology mode. The MT transition mode allows a network operating in		topology mode. The MT transition mode allows a network operating in
	single topology IS-IS IPv6 [RFC 5308] to continue to work while		single topology IS-IS IPv6 [RFC 5308] to continue to work while
	skipping to change at page 6, line 20 ¶		skipping to change at page 6, line 43 ¶
	4.3. IPv6 Only Topology		4.3. IPv6 Only Topology
	Though it is theoretically possible to build IPv6 only underlay (with		Though it is theoretically possible to build IPv6 only underlay (with
	TLV 236 for IPv6 reachability prefixes) in single topology mode as		TLV 236 for IPv6 reachability prefixes) in single topology mode as
	discussed in Section 4.1, lot of legacy implementations require IPv4		discussed in Section 4.1, lot of legacy implementations require IPv4
	address families too be configured in single topology mode (ingrained		address families too be configured in single topology mode (ingrained
	code structures for IPv4 address family). IPv6 only DC underlay		code structures for IPv4 address family). IPv6 only DC underlay
	network can be built with multi topology adjacencies (TLV 222) and		network can be built with multi topology adjacencies (TLV 222) and
	reachability prefixes (TLV 237) with MT ID #2 as discussed above in		reachability prefixes (TLV 237) with MT ID #2 as discussed above in
	Section 4.2. With this any other address family can be introduced		Section 4.2. With this, any other address family can be introduced
	including "standard" topology MT ID #0 (Single topology mode with		including "standard" topology MT ID #0 (Single topology mode with
	both address families) and there are no restrictions on which address		both address families) and there are no restrictions on which address
	family has to enable on which link as specified in Section 4.1.		family has to enable on which link as specified in Section 4.1.
	5. IS-IS MT and LFA		5. IS-IS MT and LFA
	IP Fast Reroute (FRR) or Loop Free Alternative (LFA) computation in		IP Fast Reroute (FRR) or Loop Free Alternative (LFA) computation in
	MT mode are described in detail in Section 5.2 of		MT mode are described in detail in Section 5.2 of
	[I-D.ietf-rtgwg-multihomed-prefix-lfa].		[I-D.ietf-rtgwg-multihomed-prefix-lfa].
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 2018
	6. Acknowledgements		6. Acknowledgements
	Thanks to .. TBD.		Thanks to .. TBD.
	7. IANA Considerations		7. IANA Considerations
	This document has no actions for IANA.		This document has no actions for IANA.
	8. Security Considerations		8. Security Considerations
	skipping to change at page 7, line 29 ¶		skipping to change at page 7, line 49 ¶
	[I-D.herbert-ila-mobile]		[I-D.herbert-ila-mobile]
	Herbert, T. and K. Bogineni, "Identifier Locator		Herbert, T. and K. Bogineni, "Identifier Locator
	Addressing for Mobile User-Plane", draft-herbert-ila-		Addressing for Mobile User-Plane", draft-herbert-ila-
	mobile-01 (work in progress), March 2018.		mobile-01 (work in progress), March 2018.
	[I-D.ietf-dmm-srv6-mobile-uplane]		[I-D.ietf-dmm-srv6-mobile-uplane]
	Matsushima, S., Filsfils, C., Kohno, M., Camarillo, P.,		Matsushima, S., Filsfils, C., Kohno, M., Camarillo, P.,
	daniel.voyer@bell.ca, d., and C. Perkins, "Segment Routing		daniel.voyer@bell.ca, d., and C. Perkins, "Segment Routing
	IPv6 for Mobile User Plane", draft-ietf-dmm-srv6-mobile-		IPv6 for Mobile User Plane", draft-ietf-dmm-srv6-mobile-
	uplane-01 (work in progress), March 2018.		uplane-03 (work in progress), October 2018.
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 2018
	[I-D.ietf-rtgwg-multihomed-prefix-lfa]		[I-D.ietf-rtgwg-multihomed-prefix-lfa]
	Sarkar, P., Hegde, S., Chunduri, U., Tantsura, J., and H.		Sarkar, P., Chunduri, U., Hegde, S., Tantsura, J., and H.
	Gredler, "LFA selection for Multi-Homed Prefixes", draft-		Gredler, "LFA selection for Multi-Homed Prefixes", draft-
	ietf-rtgwg-multihomed-prefix-lfa-06 (work in progress),		ietf-rtgwg-multihomed-prefix-lfa-08 (work in progress),
	February 2018.		October 2018.
	[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi		[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
	Topology (MT) Routing in Intermediate System to		Topology (MT) Routing in Intermediate System to
	Intermediate Systems (IS-ISs)", RFC 5120,		Intermediate Systems (IS-ISs)", RFC 5120,
	DOI 10.17487/RFC5120, February 2008,		DOI 10.17487/RFC5120, February 2008,
	<https://www.rfc-editor.org/info/rfc5120>.		<https://www.rfc-editor.org/info/rfc5120>.
	[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic		[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
	Authentication", RFC 5304, DOI 10.17487/RFC5304, October		Authentication", RFC 5304, DOI 10.17487/RFC5304, October
	2008, <https://www.rfc-editor.org/info/rfc5304>.		2008, <https://www.rfc-editor.org/info/rfc5304>.
	skipping to change at page 8, line 29 ¶		skipping to change at page 9, line 5 ¶
	Authors' Addresses		Authors' Addresses
	Uma Chunduri		Uma Chunduri
	Huawei USA		Huawei USA
	2330 Central Expressway		2330 Central Expressway
	Santa Clara, CA 95050		Santa Clara, CA 95050
	USA		USA
	Email: uma.chunduri@huawei.com		Email: uma.chunduri@huawei.com
			Internet-DrafIS-IS Multi Topology Deployment Considerations October 2018
	Jeff Tantsura		Jeff Tantsura
	Nuage Networks		Apstra, Inc.
	755 Ravendale Drive
	Mountain View, CA 94043
	USA
	Email: jefftant.ietf@gmail.com		Email: jefftant.ietf@gmail.com
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