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Network Working Group                                            R. Bush
Internet-Draft                                              Arrcus & IIJ
Intended status: Informational                                  K. Patel
Expires: March 5, 2019                                            Arrcus
                                                       September 1, 2018

                BGP-SPF Topology Discovery Requirements


   For wide scale routing protocols to build their topology and
   reachability databases they need link neighbor discovery, link
   encapsulation data, and layer two liveness.  BGP-LS and its
   enhancements provide an API to present much of these data to BGP
   protocols, but do not actually collect these data.  This document
   explores the needs and criteria for the data needed.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 5, 2019.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Architectural Considerations  . . . . . . . . . . . . . . . .   2
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In a massive scale datacenter or similar environment BGP([RFC4271])
   and BGP-like protocols, e.g.  BGP-SPF (see [I-D.ietf-lsvr-bgp-spf]),
   provide massive scale-out without centralization using a tried and
   tested scalable distributed control plane transport, offering a
   scalable routing solution.  But BGP4 and BGP-SPF need topology
   discovery, link state liveness, and link addressing data from the
   network to build and maintain the routing topology.

   BGP-LS [RFC7752] and its extensions provide an API which BGP4 and
   BGP-SPF can use to get the and distribute topology data.  But BGP-LS
   itself does not gather the data, it merely presents it.  So the
   topology data must be gathered.

   What topology data do BGP-like protocols actually need?  What level
   of freshness is needed?  What are the requirements for scale,
   extensibility, security, etc?

2.  Architectural Considerations

   Massive Data Centers (MDCs) have on the order of 10,000 racks, often
   with two Top Of Rack (TOR) devices per rack.  To provide this level
   of scaling reliably, stably, and securely imposes architectural
   constraints on any discovery protocol.

   o  Simple - If it isn't simple, it will not scale.  Simplicity
      requires restraint in design.  'Union Protocols' which are the sum
      of everyone's desires are complex disasters waiting to happen.
      Often they do not wait.  Prefer 'Intersection Protocols' which
      include only those things which everyone absolutely needs.

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   o  Securable - Security properties should be analysed.  Again,
      simplicity is key; complex protocols increase in complexity over
      time, and security vulnerabilities increase exponentially with
      complexity.  As [RFC5218] 2.2.3 says "The more successful a
      protocol becomes, the more attractive a target it will be."

   o  Extensible - As [RFC5218] Section 2.2.1 said, successful protocols
      are extensible beyond the original expectation.  MDC and similar
      needs are expanding and we are still learning about the space.
      Simplicity and extensibility should go a long way to adaptability;
      complex protocols are hard to extend, especially when they are
      poorly understood.

   o  Implementable - It must be reasonably easy to implement and
      deploy.  Some implications are:

      *  Packet formats should be easy to generate and easily parsable.
         Type/length/Value (TLV) formats are preferred.

      *  The protocols should be free to use and deploy; i.e. not be
         constrained by Intellectual Property Right (IPR) claims.

      *  Again, simpler protocols are simpler to implement, deploy,
         measure, monitor, etc.

      *  Performance Problems arise if the protocol was not designed to

   o  Protocol Control - It is mandatory that the IETF have full control
      over the protocol definition.  This should not preclude
      cooperation with other Standards Development Organisations (SDOs);
      but the final control must rest with the IETF.

3.  Requirements

   The target for the discovery protocol(s) is a massive datacenter
   scale deployment using BGP or similar routing, e.g.  BGP4 or
   [I-D.ietf-lsvr-bgp-spf]; but should be generally usable by other
   routing protocols in other environments.

   The IETF is very good at finding corner cases which expand needs and
   complicate protocols.  This effort should resist this tendency.

   It would be easiest for the BGP-like protocols to consume the data if
   they are presented via the BGP-LS [RFC7752] API as used in
   [I-D.ietf-lsvr-bgp-spf] Section 4.

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   BGP-like protocols will need at least the following information about
   the topology:

   Node Identity:  Each node in the topology must have an identity/
      identifier which must be unique in the topology.

      A node must have one or more links to other nodes or it is, ab
      definito, not in the topology.

   Link Identity:  A link is between two nodes.  Each end of a link is a
      node/device interface.

      Each link in the topology must be uniquely identified and the
      identities of the nodes on the link must be identified.

   L2 Liveness:  Because adjacencies and topology changes must be
      quickly detected, Layer-2 stability of each link should be
      monitored and reported.

   Encapsulations:  The encapsulation(s) (IPv4, IPv6, ...) on each link
      must be known.  One or more of the common AFI/SAFIs must be
      supported on each link, IPv4, IPv6, MPLS, etc.

      It is assumed that the set of encapsulations is the same across
      the entire topology.

   Addresses:  The available addresses on the node interfaces for each
      encapsulation must be known.  More than one address for an
      encapsulation must be supported.

      As BGP-like protocols will be peering between the nodes, there may
      be a preferred encapsulation and address on an link, or a loopback
      interface may be used.

4.  Security Considerations

   While this document has no security considerations per se, it does
   make a plea for securability in protocol design.

   Mis-wires, malicious devices being plugged into ports, and monkey in
   the middle attacks should be considered.

5.  IANA Considerations

   This document has no IANA considerations.

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6.  Acknowledgments

   The authors thank Victor Kuarsingh and Gunter Van De Velde for

7.  References

7.1.  Normative References

              Patel, K., Lindem, A., Zandi, S., and W. Henderickx,
              "Shortest Path Routing Extensions for BGP Protocol",
              draft-ietf-lsvr-bgp-spf-02 (work in progress), August

   [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,

   [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,

7.2.  Informative References

   [RFC5218]  Thaler, D. and B. Aboba, "What Makes for a Successful
              Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,

Authors' Addresses

   Randy Bush
   Arrcus & IIJ
   5147 Crystal Springs
   Bainbridge Island, WA  98110
   United States of America

   Email: randy@psg.com

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   Keyur Patel
   2077 Gateway Place, Suite #250
   San Jose, CA  95119
   United States of America

   Email: keyur@arrcus.com

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