draft-ietf-lsvr-applicability-00.txt   draft-ietf-lsvr-applicability-01.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: January 26, 2019 Cisco Systems Expires: April 25, 2019 Cisco Systems
S. Zandi S. Zandi
G. Dawra G. Dawra
Linkedin Linkedin
July 25, 2018 October 22, 2018
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-00.txt draft-ietf-lsvr-applicability-01.txt
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 the CLOS architecture of Data Vector Routing (LSVR) extensions in the CLOS architecture of Data
Center Networks. The document is intended to provide a simplified Center Networks. The document is intended to provide a simplified
guide for the deployment of LSVR extensions. 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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 January 26, 2019. This Internet-Draft will expire on April 25, 2019.
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.
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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. Requirements Language . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Recommended Reading . . . . . . . . . . . . . . . . . . . . . 3 3. Recommended Reading . . . . . . . . . . . . . . . . . . . . . 3
4. Common Deployment Scenario . . . . . . . . . . . . . . . . . 3 4. Common Deployment Scenario . . . . . . . . . . . . . . . . . 3
5. Justification for BGP SPF Extension . . . . . . . . . . . . . 4 5. Justification for BGP SPF Extension . . . . . . . . . . . . . 4
6. LSVR Applicability to CLOS Networks . . . . . . . . . . . . . 4 6. LSVR Applicability to CLOS Networks . . . . . . . . . . . . . 5
6.1. Usage of BGP-LS SAFI . . . . . . . . . . . . . . . . . . 5 6.1. Usage of BGP-LS SAFI . . . . . . . . . . . . . . . . . . 5
6.1.1. Relationship to Other BGP AFI/SAFI Tuples . . . . . . 5 6.1.1. Relationship to Other BGP AFI/SAFI Tuples . . . . . . 6
6.2. Peering Models . . . . . . . . . . . . . . . . . . . . . 5 6.2. Peering Models . . . . . . . . . . . . . . . . . . . . . 6
6.2.1. Bi-Connected Graph Heuristic . . . . . . . . . . . . 6 6.2.1. Sparse Peering Model . . . . . . . . . . . . . . . . 6
6.3. BGP Peer Discovery . . . . . . . . . . . . . . . . . . . 6 6.2.2. Bi-Connected Graph Heuristic . . . . . . . . . . . . 7
6.3.1. BGP Peer Discovery Requirements . . . . . . . . . . . 6 6.3. BGP Peer Discovery . . . . . . . . . . . . . . . . . . . 7
6.3.2. BGP Peer Discovery Alternatives . . . . . . . . . . . 7 6.3.1. BGP Peer Discovery Requirements . . . . . . . . . . . 7
6.3.3. Data Center Interconnect (DCI) Applicability . . . . 7 6.3.2. BGP Peer Discovery Alternatives . . . . . . . . . . . 8
6.4. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . 8 6.3.3. Data Center Interconnect (DCI) Applicability . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6.4. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 10.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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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|NODE | |NODE | Tier-3 +->|NODE |--+ Tier-3 |NODE | |NODE | |NODE | |NODE | Tier-3 +->|NODE |--+ Tier-3 |NODE | |NODE |
| 1 | | 2 | | 3 | | 4 | | 5 | | 1 | | 2 | | 3 | | 4 | | 5 |
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
| | | | | | | | | | | | | | | |
A O B O <- Servers -> Z O O O A O B O <- Servers -> Z O O O
Figure 1: Illustration of the basic CLOS Figure 1: Illustration of the basic CLOS
5. Justification for BGP SPF Extension 5. Justification for BGP SPF Extension
Many data centers use BGP as a routing protocol to create an overlay In order to simplify layer-3 routing and operations [RFC7938], many
as well as an underlay network for their CLOS Topologies to simplify data centers use BGP as a routing protocol to create an overlay as
layer-3 routing and operations [RFC7938]. However, BGP is a path- well as an underlay network for their CLOS Topologies. However, BGP
vector routing protocol. Since it does not create a fabric topology, is a path-vector routing protocol. Since it does not create a fabric
it uses hop-by-hop EBGP peering to facilitate hop-by-hop routing to topology, it uses hop-by-hop EBGP peering to facilitate hop-by-hop
create the underlay network and to resolve any overlay next hops. routing to create the underlay network and to resolve any overlay
The hop-by-hop BGP peering paradigm imposes several restrictions next hops. The hop-by-hop BGP peering paradigm imposes several
within a CLOS. It severely prohibits a deployment of Route restrictions within a CLOS. It severely prohibits a deployment of
Reflectors/Route Controllers as the EBGP sessions are inline with the Route Reflectors/Route Controllers as the EBGP sessions are congruent
data path. The BGP best path algorithm is prefix-based and it with the data path. The BGP best path algorithm is prefix-based and
prevents announcements of prefixes to other BGP speakers until the it prevents announcements of prefixes to other BGP speakers until the
best path decision process is performed for the prefix at each best path decision process is performed for the prefix at each
intermediate hop. These restrictions significantly delay the overall intermediate hop. These restrictions significantly delay the overall
convergence of the underlay network within a CLOS. convergence of the underlay network within a CLOS.
The LSVR SPF modifications allow BGP to overcome these limitations. The LSVR SPF modifications allow BGP to overcome these limitations.
Furthermore, using the BGP-LS NLRI format [RFC7752] allows the LSVR Furthermore, using the BGP-LS NLRI format [RFC7752] allows the LSVR
data to be advertised for nodes, links, and prefixes in the BGP data to be advertised for nodes, links, and prefixes in the BGP
routing domain and used for SPF computations. routing domain and used for SPF computations.
6. LSVR Applicability to CLOS Networks 6. LSVR Applicability to CLOS Networks
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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 in the decision process which will converge faster due to changes in the decision process which will
allow NLRI changes to be advertised faster after detecting a change. allow NLRI changes to be advertised faster after detecting a change.
6.2.1. Sparse Peering Model
Alternately, BFD [RFC5580] can be used to swiftly determine the Alternately, BFD [RFC5580] can be used to swiftly determine the
availability of links and the BGP peering model can be significantly availability of links and the BGP peering model can be significantly
sparser than the data center fabric. BGP SPF sessions then only be sparser than the data center fabric. BGP SPF sessions then only be
established with enough peers to provide a bi-connected graph. If established with enough peers to provide a bi-connected graph. If
IEBGP is used, then the BGP routers at tier N-1 will act as route- IEBGP is used, then the BGP routers at tier N-1 will act as route-
reflectors for the routers at tier N. reflectors for the routers at tier N.
6.2.1. Bi-Connected Graph Heuristic The obvious usage of sparse peering is to avoid parallel sessions
between the same two BGP speakers in the data center fabric.
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
topologies. Two more interesting scenarios are described below.
In current Data Center topologies, there is often a very dense mesh
of links between levels, e.g., leaf and spine, providing 32-way,
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
and techniques such as the one described below Section 6.2.2 can be
used establish sessions on some subset of northbound links.
Alternately, controller-based data center topologies are envisioned
where BGP speakers within the data center only establish BGP sessions
with two or more controllers. In these topologies, fabric nodes
below the first tier (using [RFC7938] hierarchy) will establish BGP
multi-hop sessions with the controllers. For the multi-hop sessions,
determining the route to the controllers without depending on BGP
would need to be through some other means beyond the scope of this
document. However, the BGP discovery mechanisms Section 6.3 would be
one possibility.
6.2.2. Bi-Connected Graph Heuristic
With this heuristic, discovery of BGP peers is assumed Section 6.3. With this heuristic, discovery of BGP peers is assumed Section 6.3.
Additionally, it assumed that the direction of the peering can be Additionally, it assumed that the direction of the peering can be
ascertained. In the context of a data center fabric, direction is ascertained. In the context of a data center fabric, direction is
either northbound (toward the spine), southbound (toward the Top-Of- either northbound (toward the spine), southbound (toward the Top-Of-
Rack (TOR) switches) or east-west (same level in hierarchy. The Rack (TOR) switches) or east-west (same level in hierarchy. The
determination of the direction is beyond the scope of this document. determination of the direction is beyond the scope of this document.
However, it would be reasonable to assume a technique where the TOR However, it would be reasonable to assume a technique where the TOR
switches can be identified and the number of hops to the TOR is used switches can be identified and the number of hops to the TOR is used
to determine the direction. to determine the direction.
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authentication, the security capabilities and possibly a key-chain authentication, the security capabilities and possibly a key-chain
[RFC8177] to be used. [RFC8177] to be used.
o Session Policy Identifier - A group number or name used to o Session Policy Identifier - A group number or name used to
associate common session parameters with the peer. For example, associate common session parameters with the peer. For example,
in a data center, BGP sessions with a Top of Rack (ToR) device in a data center, BGP sessions with a Top of Rack (ToR) device
could have parameters than BGP sessions between leaf and spine. could have parameters than BGP sessions between leaf and spine.
In a data center fabric, it is often useful to know whether a peer is In a data center fabric, it is often useful to know whether a peer is
southbound (towards the servers) or northbound (towards the spine or southbound (towards the servers) or northbound (towards the spine or
super-spine) Section 6.2.1. A potential requirement would also be to super-spine) Section 6.2.2. A potential requirement would also be to
determine this dynamically. One mechanism, without specifying all determine this dynamically. One mechanism, without specifying all
the details, might be for the ToRs to be identified when installed the details, might be for the ToRs to be identified when installed
and for the others switches in the fabric to determine their level and for the others switches in the fabric to determine their level
based on the distance from the closest ToR. based on the distance from the closest ToR.
If there are multiple links between BGP speakers or the links between If there are multiple links between BGP speakers or the links between
BGP speakers are unnumbered, it is also useful to be able to BGP speakers are unnumbered, it is also useful to be able to
establish multi-hop sessions using the loopback addresses. This will establish multi-hop sessions using the loopback addresses. This will
often require the discovery protocol to install route(s) toward the often require the discovery protocol to install route(s) toward the
potential peer loopback addresses prior to BGP session establishment. potential peer loopback addresses prior to BGP session establishment.
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While BGP peer discovery is not part of [I-D.ietf-lsvr-bgp-spf], While BGP peer discovery is not part of [I-D.ietf-lsvr-bgp-spf],
there are, at least, three proposals for BGP peer discovery. At there are, at least, three proposals for BGP peer discovery. At
least one of these mechanisms will be adopted and will be applicable least one of these mechanisms will be adopted and will be applicable
to deployments other than the data center. It is strongly to deployments other than the data center. It is strongly
RECOMMENDED that the accepted mechanism be used in conjunction with RECOMMENDED that the accepted mechanism be used in conjunction with
BGP SPF in data centers. The BGP discovery mechanism should BGP SPF in data centers. The BGP discovery mechanism should
discovery both peer addresses and endpoints for BFD discovery. discovery both peer addresses and endpoints for BFD discovery.
Additionally, it would be great if there were a heuristic for Additionally, it would be great if there were a heuristic for
determining whether the peer is at a tier above or below the determining whether the peer is at a tier above or below the
discovering BGP speaker (refer to Section 6.2.1). discovering BGP speaker (refer to Section 6.2.2).
The BGP discovery mechanisms under consideration are The BGP discovery mechanisms under consideration are
[I-D.acee-idr-lldp-peer-discovery], [I-D.acee-idr-lldp-peer-discovery],
[I-D.xu-idr-neighbor-autodiscovery], and [I-D.ymbk-lsvr-lsoe]. [I-D.xu-idr-neighbor-autodiscovery], and [I-D.ymbk-lsvr-lsoe].
6.3.3. Data Center Interconnect (DCI) Applicability 6.3.3. 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.
6.4. Non-CLOS/FAT Tree Topology Applicability 6.4. 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
topologies and avail the inherent convergence improvements. topologies and avail the inherent convergence improvements.
Additionally, sparse peering techniques may be utilized Section 6.2. Additionally, sparse peering techniques may be utilized Section 6.2.
However, determining whether or to establish a BGP session is more However, determining whether or to establish a BGP session is more
complex and the heuristic described in Section 6.2.1 cannot be used. complex and the heuristic described in Section 6.2.2 cannot be used.
In such topologies, other techniques such as those described in In such topologies, other techniques such as those described in
[I-D.li-dynamic-flooding] may be employed. One potential deployment [I-D.li-lsr-dynamic-flooding] may be employed. One potential
would be the underlay for a Service Provider (SP) backbone where deployment would be the underlay for a Service Provider (SP) backbone
usage of a single protocol, i.e., BGP, is desired. where usage of a single protocol, i.e., BGP, is desired.
7. IANA Considerations 7. IANA Considerations
No IANA updates are requested by this document. No IANA updates are requested by this document.
8. Security Considerations 8. Security Considerations
This document introduces no new security considerations above and This document introduces no new security considerations above and
beyond those already specified in the [RFC4271] and beyond those already specified in the [RFC4271] and
[I-D.ietf-lsvr-bgp-spf]. [I-D.ietf-lsvr-bgp-spf].
skipping to change at page 8, line 39 skipping to change at page 9, line 39
The authors would like to thank Alvaro Retana and Yan Filyurin for The authors would like to thank Alvaro Retana and Yan Filyurin for
the review and comments. the review and comments.
10. References 10. References
10.1. Normative References 10.1. 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-01 (work in progress), May 2018. draft-ietf-lsvr-bgp-spf-03 (work in progress), September
2018.
[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, <https://www.rfc- DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>. 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>.
skipping to change at page 9, line 17 skipping to change at page 10, line 17
[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-03 (work in Discovery", draft-acee-idr-lldp-peer-discovery-03 (work in
progress), June 2018. progress), June 2018.
[I-D.li-dynamic-flooding] [I-D.li-lsr-dynamic-flooding]
Li, T. and P. Psenak, "Dynamic Flooding on Dense Graphs", Li, T., Psenak, P., Ginsberg, L., Przygienda, T., and D.
draft-li-dynamic-flooding-05 (work in progress), June Cooper, "Dynamic Flooding on Dense Graphs", draft-li-lsr-
2018. dynamic-flooding-01 (work in progress), October 2018.
[I-D.xu-idr-neighbor-autodiscovery] [I-D.xu-idr-neighbor-autodiscovery]
Xu, X., Bi, K., Tantsura, J., Triantafillis, N., and K. Xu, X., Talaulikar, K., Bi, K., Tantsura, J., and N.
Talaulikar, "BGP Neighbor Autodiscovery", draft-xu-idr- Triantafillis, "BGP Neighbor Discovery", draft-xu-idr-
neighbor-autodiscovery-08 (work in progress), May 2018. neighbor-autodiscovery-10 (work in progress), October
2018.
[I-D.ymbk-lsvr-lsoe] [I-D.ymbk-lsvr-lsoe]
Bush, R. and K. Patel, "Link State Over Ethernet", draft- Bush, R. and K. Patel, "Link State Over Ethernet", draft-
ymbk-lsvr-lsoe-00 (work in progress), March 2018. ymbk-lsvr-lsoe-01 (work in progress), July 2018.
[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, <https://www.rfc- DOI 10.17487/RFC2328, April 1998, <https://www.rfc-
editor.org/info/rfc2328>. editor.org/info/rfc2328>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, <https://www.rfc- DOI 10.17487/RFC4271, January 2006, <https://www.rfc-
editor.org/info/rfc4271>. editor.org/info/rfc4271>.
 End of changes. 18 change blocks. 
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