LSVR                                                            K. Patel
Internet-Draft                                              Arrcus, Inc.
Intended status: Informational                                 A. Lindem
Expires: September 6, 2018                                 Cisco Systems
                                                                S. Zandi
                                                                G. Dawra
                                                                Linkedin
                                                           March 5, 2018


  Usage and Applicability of Link State Vector Routing in Data Centers
                draft-keyupate-lsvr-applicability-00.txt

Abstract

   This document discusses the usage and applicability of Link State
   Vector Routing (LSVR) extensions in the CLOS architecture of Data
   Center Networks.  The document is intended to provide a simplified
   guide for the deployment of LSVR extensions.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on September 6, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  Recommended Reading . . . . . . . . . . . . . . . . . . . . .   2
   4.  Common Deployment Scenario  . . . . . . . . . . . . . . . . .   3
   5.  Justification for BGP modifications . . . . . . . . . . . . .   3
   6.  LSVR Applicability to CLOS Networks . . . . . . . . . . . . .   4
     6.1.  Usage of LSVR SAFI  . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This document complements [I-D.keyupate-lsvr-bgp-spf] by discussing
   the applicability of the technology in a simple and fairly common
   deployment scenario, which is described in Section 4.

   After describing the deployment scenario, Section 5 will describe the
   reasons for BGP modifications for such deployments.

   Once the control plane routing protocol requirements are described,
   Section 6 will cover the LSVR protocol enhancements to BGP to meet
   these requirements and their applicability to Data Center CLOS
   networks.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] only when
   they appear in all upper case.  They may also appear in lower or
   mixed case as English words, without any normative meaning.

3.  Recommended Reading

   This document assumes knowledge of existing data center networks and
   data center network topologies [CLOS].  This document also assumes
   knowledge of data center routing protocols like BGP [RFC4271], BGP-



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   SPF [I-D.keyupate-lsvr-bgp-spf], OSPF [RFC2328], as well as, data
   center OAM protocols like LLDP [RFC4957] and BFD [RFC5580].

4.  Common Deployment Scenario

   Within a Data Center, a common network design to interconnect servers
   is done using the CLOS topology [CLOS].  The CLOS topology is fully
   non-blocking and the topology is realized using Equal Cost Multipath
   (ECMP).  In a CLOS topology, the minimum number of parallel paths
   between two servers is determined by the width of a tier-1 stage as
   shown in the figure 1.

   The following example illustrates multistage CLOS topology.


                                      Tier-1
                                     +-----+
                                     |NODE |
                                  +->| 12  |--+
                                  |  +-----+  |
                          Tier-2  |           |   Tier-2
                         +-----+  |  +-----+  |  +-----+
           +------------>|NODE |--+->|NODE |--+--|NODE |-------------+
           |       +-----|  9  |--+  | 10  |  +--| 11  |-----+       |
           |       |     +-----+     +-----+     +-----+     |       |
           |       |                                         |       |
           |       |     +-----+     +-----+     +-----+     |       |
           | +-----+---->|NODE |--+  |NODE |  +--|NODE |-----+-----+ |
           | |     | +---|  6  |--+->|  7  |--+--|  8  |---+ |     | |
           | |     | |   +-----+  |  +-----+  |  +-----+   | |     | |
           | |     | |            |           |            | |     | |
         +-----+ +-----+          |  +-----+  |          +-----+ +-----+
         |NODE | |NODE | Tier-3   +->|NODE |--+   Tier-3 |NODE | |NODE |
         |  1  | |  2  |             |  3  |             |  4  | |  5  |
         +-----+ +-----+             +-----+             +-----+ +-----+
           | |     | |                                     | |     | |
           A O     B O            <- Servers ->            Z O     O O


                 Figure 1: Illustration of the basic CLOS

5.  Justification for BGP modifications

   Many data centers use BGP as a routing protocol to create an overlay
   as well as an underlay network for their CLOS Topologies to simplify
   layer-3 routing and operations [RFC7938].  However, BGP is a path-
   vector routing protocol.  Since it does not have a way for creating a
   topology, it uses hop-by-hop EBGP peering to facilitate hop-by-hop



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   routing for creating underlay network and for resolving any overlay
   next hops.  The hop-by-hop BGP peering paradigm imposes several
   restrictions within a CLOS.  It severely prohibits a deployment of
   Route Reflectors/Route Controllers as the EBGP peerings are inline
   with the data path.  The BGP best path algorithm is prefix based and
   it prevents announcements of prefixes to other BGP speakers until the
   best path decision process is performed for the prefix at each hop.
   These restrictions significantly delay the overall convergence of the
   underlay network within a CLOS.

   The LSVR SPF modifications allow BGP to overcome these limitations.
   Furthermore, using the BGP-LS NLRI format [RFC7752] allows the LSVR
   data to be advertised for nodes, links, and prefixes in the BGP
   routing domain and used for SPF computations.

6.  LSVR Applicability to CLOS Networks

   With the BGP SPF extensions [I-D.keyupate-lsvr-bgp-spf], the BGP best
   path computation and route computation are replaced with OSPF-like
   algorithms [RFC2328] both to determine whether an BGP-LS NLRI has
   changed and needs to be re-advertised and to compute the routing
   table.  These modifications will significantly improve convergence of
   the underlay while affording the operational benefits of a single
   routing protocol [RFC7938].

   Since every router in the BGP SPF domain will have a complete view of
   the topology, BGP sessions are not required on every link in the data
   center fabric as with the hop-by-hop peering model described in
   [RFC7938].  Rather, protocols such as BFD [RFC5580] can be used to
   determine the availability links and switches as opposed to requiring
   a single-hop BGP session on every link in the data centric fabric.
   Consequently, the BGP session topology can be much sparser than the
   data center fabric topology itself and can utilize a BGP route
   reflector hierarchy with the desired level of redundancy.

   Data center controllers typically require visibility to the BGP
   topology to compute traffic-engineered paths.  These controllers
   learn the topology and other relevant information via the BGP-LS
   address family [RFC7752] which is totally independent of the underlay
   address families (usually IPv4/IPv6 unicast).  Furthermore, in
   traditional BGP underlays, all the BGP routers will need to advertise
   their BGP-LS information independently.  With the BGP SPF extensions,
   controllers can learn the topology using the same BGP advertisements
   used to compute the underlay routes.  Furthermore, these data center
   controllers can avail the convergence advantages of the BGP SPF
   extensions.  The placement of controllers can be outside of the
   forwarding path or within the forwarding path.




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   Alternatively, as each and every router in the BGP SPF domain will
   have a complete view of the topology, the operator can also choose to
   configure BGP sessions in hop-by-hop peering model described in
   [RFC7938] along with BFD [RFC5580].  In doing so, while the hop-by-
   hop peering model lacks inherent benefits of the controller-based
   model, BGP updates need not be serialized by BGP best path algorithm
   in either of these models.  This helps overall network convergence.

6.1.  Usage of LSVR SAFI

   The BGP SPF extensions [I-D.keyupate-lsvr-bgp-spf] define a new BGP-
   LS SAFI for announcement of BGP SPF link-state.  The NLRI format and
   its associated attributes follow the format of BGP-LS for node, link,
   and prefix announcements.  Whether the peering model within a CLOS
   follows hop-by-hop peering described in [RFC7938] or any controller-
   based or route-reflector peering, an operator can exchange BGP SPF
   SAFI routes over the BGP peering by simply configuring BGP SPF SAFI
   between the necessary BGP speakers.

   The BGP-LS SPF SAFI can also co-exist with BGP IP Unicast SAFI which
   could exchange overlapping IP routes.  The routes received by these
   SAFIs are evaluated, stored, and announced separately according to
   the rules of [RFC4760].  The tie-breaking of route installation is a
   matter of the local policies and preferences of the network operator.

   Finally, as the BGP SPF peering is done following the procedures
   described in [RFC4271], all the existing transport security
   mechanisms including [RFC5925] are available for the BGP-LS SPF SAFI.

7.  IANA Considerations

   No IANA updates are requested by this document.

8.  Security Considerations

   This document introduces no new security considerations above and
   beyond those already specified in the [RFC4271] and
   [I-D.keyupate-lsvr-bgp-spf].

9.  Acknowledgements

   The authors would like to thank Alvaro Retana and Yan Filyurin for
   the review and comments.








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10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
              editor.org/info/rfc2119>.

10.2.  Informative References

   [CLOS]     "A Study of Non-Blocking Switching Networks",  The Bell
              System Technical Journal, Vol. 32(2), DOI
              10.1002/j.1538-7305.1953.tb01433.x, March 1953.

   [I-D.keyupate-lsvr-bgp-spf]
              Patel, K., Lindem, A., Zandi, S., and W. Henderickx,
              "Shortest Path Routing Extensions for BGP Protocol",
              draft-keyupate-lsvr-bgp-spf-00 (work in progress), March
              2018.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998, <https://www.rfc-
              editor.org/info/rfc2328>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006, <https://www.rfc-
              editor.org/info/rfc4271>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007, <https://www.rfc-
              editor.org/info/rfc4760>.

   [RFC4957]  Krishnan, S., Ed., Montavont, N., Njedjou, E., Veerepalli,
              S., and A. Yegin, Ed., "Link-Layer Event Notifications for
              Detecting Network Attachments", RFC 4957,
              DOI 10.17487/RFC4957, August 2007, <https://www.rfc-
              editor.org/info/rfc4957>.

   [RFC5580]  Tschofenig, H., Ed., Adrangi, F., Jones, M., Lior, A., and
              B. Aboba, "Carrying Location Objects in RADIUS and
              Diameter", RFC 5580, DOI 10.17487/RFC5580, August 2009,
              <https://www.rfc-editor.org/info/rfc5580>.






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   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016, <https://www.rfc-
              editor.org/info/rfc7752>.

   [RFC7938]  Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
              BGP for Routing in Large-Scale Data Centers", RFC 7938,
              DOI 10.17487/RFC7938, August 2016, <https://www.rfc-
              editor.org/info/rfc7938>.

Authors' Addresses

   Keyur Patel
   Arrcus, Inc.
   2077 Gateway Pl
   San Jose, CA  95110
   USA

   Email: keyur@arrcus.com


   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   Cary, NC  95110
   USA

   Email: acee@cisco.com


   Shawn Zandi
   Linkedin
   222 2nd Street
   San Francisco, CA  94105
   USA

   Email: szandi@linkedin.com









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   Gaurav Dawra
   Linkedin
   222 2nd Street
   San Francisco, CA  94105
   USA

   Email: gdawra@linkedin.com












































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