< draft-ietf-lsvr-applicability-05.txt		draft-ietf-lsvr-applicability-06.txt >
	LSVR K. Patel		LSVR K. Patel
	Internet-Draft Arrcus, Inc.		Internet-Draft Arrcus, Inc.
	Intended status: Informational A. Lindem		Intended status: Informational A. Lindem
	Expires: September 25, 2020 Cisco Systems		Expires: January 27, 2021 Cisco Systems
	S. Zandi		S. Zandi
	G. Dawra		G. Dawra
	Linkedin		Linkedin
	March 24, 2020		July 26, 2020
	Usage and Applicability of Link State Vector Routing in Data Centers		Usage and Applicability of Link State Vector Routing in Data Centers
	draft-ietf-lsvr-applicability-05		draft-ietf-lsvr-applicability-06
	Abstract		Abstract
	This document discusses the usage and applicability of Link State		This document discusses the usage and applicability of Link State
	Vector Routing (LSVR) extensions in data center networks utilizing		Vector Routing (LSVR) extensions in data center networks utilizing
	CLOS or Fat-Tree topologies. The document is intended to provide a		CLOS or Fat-Tree topologies. The document is intended to provide a
	simplified guide for the deployment of LSVR extensions.		simplified guide for the deployment of LSVR extensions.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 37 ¶		skipping to change at page 1, line 37 ¶
	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 September 25, 2020.		This Internet-Draft will expire on January 27, 2021.
	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 37 ¶		skipping to change at page 2, line 37 ¶
	6.5.4. Data Center Interconnect (DCI) Applicability . . . . 10		6.5.4. Data Center Interconnect (DCI) Applicability . . . . 10
	7. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . . . 10		7. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . . . 10
	8. Non-Transit Node Capability . . . . . . . . . . . . . . . . . 10		8. Non-Transit Node Capability . . . . . . . . . . . . . . . . . 10
	9. BGP Policy Applicability . . . . . . . . . . . . . . . . . . 11		9. BGP Policy Applicability . . . . . . . . . . . . . . . . . . 11
	10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11		10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
	11. Security Considerations . . . . . . . . . . . . . . . . . . . 11		11. Security Considerations . . . . . . . . . . . . . . . . . . . 11
	12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11		12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
	13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
	13.1. Normative References . . . . . . . . . . . . . . . . . . 11		13.1. Normative References . . . . . . . . . . . . . . . . . . 11
	13.2. Informative References . . . . . . . . . . . . . . . . . 12		13.2. Informative References . . . . . . . . . . . . . . . . . 12
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
	1. Introduction		1. Introduction
	This document complements [I-D.ietf-lsvr-bgp-spf] by discussing the		This document complements [I-D.ietf-lsvr-bgp-spf] by discussing the
	applicability of the technology in a simple and fairly common		applicability of the technology in a simple and fairly common
	deployment scenario, which is described in Section 4.		deployment scenario, which is described in Section 4.
	After describing the deployment scenario, Section 5 will describe the		After describing the deployment scenario, Section 5 will describe the
	reasons for BGP modifications for such deployments.		reasons for BGP modifications for such deployments.
	skipping to change at page 6, line 17 ¶		skipping to change at page 6, line 17 ¶
	mechanisms including [RFC5925] are available for the BGP-LS SPF SAFI.		mechanisms including [RFC5925] are available for the BGP-LS SPF SAFI.
	6.1.1. Relationship to Other BGP AFI/SAFI Tuples		6.1.1. Relationship to Other BGP AFI/SAFI Tuples
	Normally, the BGP-LS AFI/SAFI is used solely to compute the underlay		Normally, the BGP-LS AFI/SAFI is used solely to compute the underlay
	and is given preference over other AFI/SAFIs. Other BGP SAFIs, e.g.,		and is given preference over other AFI/SAFIs. Other BGP SAFIs, e.g.,
	IPv6/IPv6 Unicast VPN would use the BGP-SPF computed routes for next		IPv6/IPv6 Unicast VPN would use the BGP-SPF computed routes for next
	hop resolution. However, if BGP-LS NLRI is also being advertised for		hop resolution. However, if BGP-LS NLRI is also being advertised for
	controller consumption, there is no need to replicate the Node, Link,		controller consumption, there is no need to replicate the Node, Link,
	and Prefix NLRI in BGP-NLRI. Rather, additional NLRI attributes can		and Prefix NLRI in BGP-NLRI. Rather, additional NLRI attributes can
	be advertised in the BGP-LS SPF AFI/SAFI as required.		be advertised in the BGP-LS SPF AFI/SAFI as required (e.g., BGP-LS TE
			metric extensions [RFC8571] and BGP-LS segment routing extensions
			[I-D.ietf-idr-bgp-ls-segment-routing-ext]).
	6.2. Peering Models		6.2. Peering Models
	As previously stated, BGP SPF can be deployed using the existing		As previously stated, BGP SPF can be deployed using the existing
	peering model where there is a single-hop BGP session on each and		peering model where there is a single-hop BGP session on each and
	every link in the data center fabric [RFC7938]. This provides for		every link in the data center fabric [RFC7938]. This provides for
	both the advertisement of routes and the determination of link and		both the advertisement of routes and the determination of link and
	neighboring switch availability. With BGP SPF, the underlay will		neighboring switch availability. With BGP SPF, the underlay will
	converge faster due to changes to the decision process that will		converge faster due to changes to the decision process that will
	allow NLRI changes to be advertised faster after detecting a change.		allow NLRI changes to be advertised faster after detecting a change.
	skipping to change at page 6, line 49 ¶		skipping to change at page 6, line 51 ¶
	links between the same two BGP speakers in the data center fabric.		links between the same two BGP speakers in the data center fabric.
	However, this use case is not very useful since parallel layer-3		However, this use case is not very useful since parallel layer-3
	links between the same two BGP routers are rare in CLOS or Fat-Tree		links between the same two BGP routers are rare in CLOS or Fat-Tree
	topologies. Two more interesting scenarios are described below.		topologies. Two more interesting scenarios are described below.
	In current data center topologies, there is often a very dense mesh		In current data center topologies, there is often a very dense mesh
	of links between levels, e.g., leaf and spine, providing 32-way,		of links between levels, e.g., leaf and spine, providing 32-way,
	64-way, or more Equal-Cost Multi-Path (ECMP) paths. In these		64-way, or more Equal-Cost Multi-Path (ECMP) paths. In these
	topologies, it is desirable not to have a BGP session on every link		topologies, it is desirable not to have a BGP session on every link
	and techniques such as the one described in Section 6.2.2 can be used		and techniques such as the one described in Section 6.2.2 can be used
	establish sessions on some subset of northbound links.		establish sessions on some subset of northbound links. For example,
			in a Spine-Leaf topology, each leaf switch would only peer with a
			subset of the spines dependent on the flooding redundancy required to
			be reasonably certain that every node within the BGP-LS SPF routing
			domain has the complete topology.
	Alternately, controller-based data center topologies are envisioned		Alternately, controller-based data center topologies are envisioned
	where BGP speakers within the data center only establish BGP sessions		where BGP speakers within the data center only establish BGP sessions
	with two or more controllers. In these topologies, fabric nodes		with two or more controllers. In these topologies, fabric nodes
	below the first tier (using [RFC7938] hierarchy) will establish BGP		below the first tier (using [RFC7938] hierarchy) will establish BGP
	multi-hop sessions with the controllers. For the multi-hop sessions,		multi-hop sessions with the controllers. For the multi-hop sessions,
	determining the route to the controllers without depending on BGP		determining the route to the controllers without depending on BGP
	would need to be through some other means beyond the scope of this		would need to be through some other means beyond the scope of this
	document. However, the BGP discovery mechanisms described in		document. However, the BGP discovery mechanisms described in
	Section 6.5 would be one possibility.		Section 6.5 would be one possibility.
	skipping to change at page 7, line 36 ¶		skipping to change at page 7, line 42 ¶
	will attempt to maintain two northbound BGP sessions with different		will attempt to maintain two northbound BGP sessions with different
	switches (in data center fabrics there is normally a single layer-3		switches (in data center fabrics there is normally a single layer-3
	connection anyway). For east-west sessions, passive BGP session		connection anyway). For east-west sessions, passive BGP session
	establishment is allowed. However, BGP speaker will never actively		establishment is allowed. However, BGP speaker will never actively
	establish an east-west BGP session unless it cannot establish two		establish an east-west BGP session unless it cannot establish two
	northbound BGP sessions.		northbound BGP sessions.
	6.3. BGP Spine/Leaf Topology Policy		6.3. BGP Spine/Leaf Topology Policy
	One of the advantages of using BGP SPF as the underlay protocol is		One of the advantages of using BGP SPF as the underlay protocol is
	that BGP policy can be applied at any level. In Spine/Leaf		that BGP policy can be applied at any level. For example, depending
	topologies, it is not necessary to advertise BGP-LS NLRI received by		upon the topology, it may be possible to aggregate prefix
	leaves northbound to the spine nodes at the level above. If a common		advertisements using existing BGP policy. In Spine/Leaf topologies,
	AS is used for the spine nodes, this can easily be accomplished with		it is not necessary to advertise BGP-LS NLRI received by leaves
	EBGP and a simple policy to filter advertisements from the leaves to		northbound to the spine nodes at the level above. If a common AS is
	the spine if the first AS in the AS path is the spine AS.		used for the spine nodes, this can easily be accomplished with EBGP
			and a simple policy to filter advertisements from the leaves to the
			spine if the first AS in the AS path is the spine AS.
	In the figure below, the leaves would not advertise any NLRI with AS		In the figure below, the leaves would not advertise any NLRI with AS
	64512 as the first AS in the AS path.		64512 as the first AS in the AS path.
	+--------+ +--------+ +--------+		+--------+ +--------+ +--------+
	AS 64512 | | | | | |		AS 64512 | | | | | |
	for Spine | Spine 1+----+ Spine 2+- ......... -+ Spine N|		for Spine | Spine 1+----+ Spine 2+- ......... -+ Spine N|
	Nodes at | | | | | |		Nodes at | | | | | |
	this Level +-+-+-+-++ ++-+-+-+-+ +-+-+-+-++		this Level +-+-+-+-++ ++-+-+-+-+ +-+-+-+-++
	+------+ | | | | | | | | | | |		+------+ | | | | | | | | | | |
	skipping to change at page 10, line 17 ¶		skipping to change at page 10, line 19 ¶
	6.5.3. BGP-LS SPF Topology Visibility for Management		6.5.3. BGP-LS SPF Topology Visibility for Management
	Irrespective of whether or not BGP-LS SPF is used for route		Irrespective of whether or not BGP-LS SPF is used for route
	calculation, the BGP-LS SPF route advertisements can be used to		calculation, the BGP-LS SPF route advertisements can be used to
	periodically construct the CLOS/FAT Tree topology. This is		periodically construct the CLOS/FAT Tree topology. This is
	especially useful in deployments where an IGP is not used and the		especially useful in deployments where an IGP is not used and the
	base BGP-LS routes [RFC7752] are not available. The resultant		base BGP-LS routes [RFC7752] are not available. The resultant
	topology visibility can then be used for troubleshooting and		topology visibility can then be used for troubleshooting and
	consistency checking. This would normally be done on a central		consistency checking. This would normally be done on a central
	controller but distributed consistency checking is not precluded.		controller or other management tool which could also be used for
	The precise algorithms and heuristics, as well as, the complete set		fabric data path verification. The precise algorithms and
	of management applications is beyond the scope of this document.		heuristics, as well as, the complete set of management applications
			is beyond the scope of this document.
	6.5.4. Data Center Interconnect (DCI) Applicability		6.5.4. Data Center Interconnect (DCI) Applicability
	Since BGP SPF is to be used for the routing underlay and DCI gateway		Since BGP SPF is to be used for the routing underlay and DCI gateway
	boxes typically have direct or very simple connectivity, BGP external		boxes typically have direct or very simple connectivity, BGP external
	sessions would typically not include the BGP SPF SAFI.		sessions would typically not include the BGP SPF SAFI.
	7. Non-CLOS/FAT Tree Topology Applicability		7. Non-CLOS/FAT Tree Topology Applicability
	The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] can be used in other		The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] can be used in other
	skipping to change at page 11, line 44 ¶		skipping to change at page 11, line 46 ¶
	The authors would like to thank Alvaro Retana, Yan Filyurin, and		The authors would like to thank Alvaro Retana, Yan Filyurin, and
	Boris Hassanov for their review and comments.		Boris Hassanov for their review and comments.
	13. References		13. References
	13.1. Normative References		13.1. Normative References
	[I-D.ietf-lsvr-bgp-spf]		[I-D.ietf-lsvr-bgp-spf]
	Patel, K., Lindem, A., Zandi, S., and W. Henderickx,		Patel, K., Lindem, A., Zandi, S., and W. Henderickx,
	"Shortest Path Routing Extensions for BGP Protocol",		"Shortest Path Routing Extensions for BGP Protocol",
	draft-ietf-lsvr-bgp-spf-07 (work in progress), December		draft-ietf-lsvr-bgp-spf-09 (work in progress), May 2020.
	2019.
	[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>.
	[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>.
	13.2. Informative References		13.2. Informative References
	[CLOS] "A Study of Non-Blocking Switching Networks", The Bell		[CLOS] "A Study of Non-Blocking Switching Networks", The Bell
	System Technical Journal, Vol. 32(2), DOI		System Technical Journal, Vol. 32(2), DOI
	10.1002/j.1538-7305.1953.tb01433.x, March 1953.		10.1002/j.1538-7305.1953.tb01433.x, March 1953.
	[I-D.acee-idr-lldp-peer-discovery]		[I-D.acee-idr-lldp-peer-discovery]
	Lindem, A., Patel, K., Zandi, S., Haas, J., and X. Xu,		Lindem, A., Patel, K., Zandi, S., Haas, J., and X. Xu,
	"BGP Logical Link Discovery Protocol (LLDP) Peer		"BGP Logical Link Discovery Protocol (LLDP) Peer
	Discovery", draft-acee-idr-lldp-peer-discovery-06 (work in		Discovery", draft-acee-idr-lldp-peer-discovery-07 (work in
	progress), November 2019.		progress), June 2020.
			[I-D.ietf-idr-bgp-ls-segment-routing-ext]
			Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
			and M. Chen, "BGP Link-State extensions for Segment
			Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
			(work in progress), June 2019.
	[I-D.ietf-lsr-dynamic-flooding]		[I-D.ietf-lsr-dynamic-flooding]
	Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,		Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,
	T., Cooper, D., Jalil, L., and S. Dontula, "Dynamic		T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra,
	Flooding on Dense Graphs", draft-ietf-lsr-dynamic-		"Dynamic Flooding on Dense Graphs", draft-ietf-lsr-
	flooding-04 (work in progress), November 2019.		dynamic-flooding-07 (work in progress), June 2020.
	[I-D.ietf-lsvr-l3dl]		[I-D.ietf-lsvr-l3dl]
	Bush, R., Austein, R., and K. Patel, "Layer 3 Discovery		Bush, R., Austein, R., and K. Patel, "Layer 3 Discovery
	and Liveness", draft-ietf-lsvr-l3dl-03 (work in progress),		and Liveness", draft-ietf-lsvr-l3dl-05 (work in progress),
	November 2019.		May 2020.
	[I-D.xu-idr-neighbor-autodiscovery]		[I-D.xu-idr-neighbor-autodiscovery]
	Xu, X., Talaulikar, K., Bi, K., Tantsura, J., and N.		Xu, X., Talaulikar, K., Bi, K., Tantsura, J., and N.
	Triantafillis, "BGP Neighbor Discovery", draft-xu-idr-		Triantafillis, "BGP Neighbor Discovery", draft-xu-idr-
	neighbor-autodiscovery-12 (work in progress), November		neighbor-autodiscovery-12 (work in progress), November
	2019.		2019.
	[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,		[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
	DOI 10.17487/RFC2328, April 1998,		DOI 10.17487/RFC2328, April 1998,
	<https://www.rfc-editor.org/info/rfc2328>.		<https://www.rfc-editor.org/info/rfc2328>.
	skipping to change at page 13, line 46 ¶		skipping to change at page 14, line 5 ¶
	[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of		[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
	BGP for Routing in Large-Scale Data Centers", RFC 7938,		BGP for Routing in Large-Scale Data Centers", RFC 7938,
	DOI 10.17487/RFC7938, August 2016,		DOI 10.17487/RFC7938, August 2016,
	<https://www.rfc-editor.org/info/rfc7938>.		<https://www.rfc-editor.org/info/rfc7938>.
	[RFC8177] Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.		[RFC8177] Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
	Zhang, "YANG Data Model for Key Chains", RFC 8177,		Zhang, "YANG Data Model for Key Chains", RFC 8177,
	DOI 10.17487/RFC8177, June 2017,		DOI 10.17487/RFC8177, June 2017,
	<https://www.rfc-editor.org/info/rfc8177>.		<https://www.rfc-editor.org/info/rfc8177>.
			[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
			C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
			IGP Traffic Engineering Performance Metric Extensions",
			RFC 8571, DOI 10.17487/RFC8571, March 2019,
			<https://www.rfc-editor.org/info/rfc8571>.
	Authors' Addresses		Authors' Addresses
	Keyur Patel		Keyur Patel
	Arrcus, Inc.		Arrcus, Inc.
	2077 Gateway Pl		2077 Gateway Pl
	San Jose, CA 95110		San Jose, CA 95110
	USA		USA
	Email: keyur@arrcus.com		Email: keyur@arrcus.com
	Acee Lindem		Acee Lindem
	Cisco Systems		Cisco Systems
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