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
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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
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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.
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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.
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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.
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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 +-+-+-+-++ ++-+-+-+-+ +-+-+-+-++
+------+ | | | | | | | | | | | +------+ | | | | | | | | | | |
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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
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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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