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Versions: 00 01 draft-li-lsr-dynamic-flooding

Internet Engineering Task Force                                    T. Li
Internet-Draft                                           Arista Networks
Intended status: Informational                            March 18, 2018
Expires: September 19, 2018


                       Dynamic Flooding for IS-IS
                   draft-li-dynamic-flooding-isis-01

Abstract

   Routing with link state protocols in dense network topologies can
   result in sub-optimal convergence times due to the overhead
   associated with flooding.  This can be addressed by decreasing the
   flooding topology so that it is less dense.

   This document discusses extensions to the IS-IS routing protocol to
   support a solution to flooding in dense subgraphs.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on September 19, 2018.

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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Area Leader TLV . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Area System IDs TLV . . . . . . . . . . . . . . . . . . . . .   3
   4.  Flooding Path TLV . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   In recent years, there has been increased focused on how to address
   the dynamic routing of networks that have a bipartite (a.k.a. spine-
   leaf), Clos [Clos], or Fat Tree [Leiserson] topology.  Conventional
   Interior Gateway Protocols (IGPs, i.e. IS-IS [ISO10589], OSPF
   [RFC5340]) under-perform, redundantly flooding information throughout
   the dense topology, leading to overloaded control plane inputs and
   thereby creating operational issues.  For practical considerations,
   network architects have resorted to applying unconventional
   techniques to address the problem, applying BGP in the data center
   [RFC7938], however it is very clear that using an Exterior Gateway
   Protocol as an IGP is sub-optimal, if only due to the configuration
   overhead.

   This problem is discussed in more detail in [Architecture], along
   with an architectural solution for the problem.  The remainder of
   this document is focused on describing extensions to the IS-IS
   protocol to implement that architecture.  Three additions appear to
   be necessary.

   1.  A TLV that an IS may inject into its LSP to indicate its
       preference for becoming Area Leader.

   2.  A TLV to carry the list of system IDs that compromise the
       flooding topology for the area.

   3.  A TLV to carry the adjacency matrix for the flooding topology for
       the area.




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1.1.  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 RFC 2119 [RFC2119].

2.  Area Leader TLV

   The Area Leader TLV allows a system to indicate its eligibility and
   priority for becoming Area Leader.  Intermediate Systems (routers)
   not advertising this TLV are not eligible to become Area Leader.

   The Area Leader is the router with the numerically highest Area
   Leader priority in the area.  In the event of ties, the router with
   the numerically highest system ID is the Area Leader.  Due to
   transients during database flooding, different routers may not agree
   on the Area Leader.

   The format of the Area Leader TLV is:

       0                   1                   2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | TLV Type      | TLV Length    | Priority      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      TLV Type: XXX

      TLV Length: 1

      Priority: 0-255, unsigned integer

3.  Area System IDs TLV

   The Area System IDs TLV is used by the Area Leader to enumerate the
   system IDs that it has used in computing the flooding topology.
   Conceptually, the Area Leader creates a list of system IDs for all
   routers in the area, assigning indices to each system, starting with
   index 0.

   Because the space in a single TLV is small, it may require more than
   one TLV to encode all of the system IDs in the area.  This TLV may
   recur in multiple LSP segments so that all system IDs can be
   advertised.

   The format of the Area System IDs TLV is:





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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | TLV Type      | TLV Length    | Starting Index                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Ending Index                  |L| Reserved    | System IDs ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       System IDs continued ....
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      TLV Type: YYY

      TLV Length: 9 + (ID length * N)

      Starting index: The index of the first system ID that appears in
      this TLV.

      Ending index: The index of the last system ID that appears in this
      TLV.

      L (Last): This bit is set if the ending index of this TLV is the
      last index in the full list of system IDs for the area.

      System IDs: A concatenated list of system IDs for the area.

4.  Flooding Path TLV

   The Flooding Path TLV is used to denote a path in the flooding
   topology.  The goal is an efficient encoding of the links of the
   topology.  A single link is a simple case of a path that only covers
   two nodes.  A connected path may be described as a sequence of
   indices: (I1, I2, I3, ...), denoting a link from the system with
   index 1 to the system with index 2, a link from the system with index
   2 to the system with index 3, and so on.

   If a path exceeds the size that can be stored in a single TLV, then
   the path may be distributed across multiple TLVs by the replication
   of a single system index.

   Complex topologies that are not a single path can be described using
   multiple TLVs.

   The Flooding Path TLV contains a list of system indices relative to
   the systems advertised through the Area System IDs TLV.  At least 2
   indices must be included in the TLV.  Due to the lenth restriction of
   TLVs, this TLV can contain at most 126 system indices.

   The Flooding Path TLV has the format:



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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | TLV Type      | TLV Length    | Starting Index                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Index 2                       | Additional indices ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      TLV Type: ZZZ

      TLV Length: 9 + Length of Matrix octet contents

      Starting index: The index of the first system in the path.

      Index 2: The index of the next system in the path.

      Additional indices: A sequence of additional indices to systems
      along the path.

      Matrix: The concatenated rows of the upper right triangular
      portion of the adjacency matrix for the flooding topology, padded
      with 0 bits to an octet boundary.

5.  Acknowledgements

   The author would like to thank Adam Sweeney for his diligent review.

6.  IANA Considerations

   This memo requests that IANA allocate and assign three code points
   from the IS-IS TLV Codepoints registry.  One for each of the
   following TLVs:

   1.  Area Leader TLV

   2.  Area System IDs TLV

   3.  Flooding Path TLV

7.  Security Considerations

   This document introduces no new security issues.  Security of routing
   within a domain is already addressed as part of the routing protocols
   themselves.  This document proposes no changes to those security
   architectures.






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8.  References

8.1.  Normative References

   [ISO10589]
              International Organization for Standardization,
              "Intermediate System to Intermediate System Intra-Domain
              Routing Exchange Protocol for use in Conjunction with the
              Protocol for Providing the Connectionless-mode Network
              Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002.

   [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>.

8.2.  Informative References

   [Architecture]
              Li, T., "An Architecture for Dynamic Flooding on Dense
              Graphs", Internet draft draft-li-dynamic-flooding, Jan.
              2018.

   [Clos]     Clos, C., "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,
              <http://dx.doi.org/10.1002/j.1538-7305.1953.tb01433.x>.

   [Leiserson]
              Leiserson, C., "Fat-Trees: Universal Networks for
              Hardware-Efficient Supercomputing", IEEE Transactions on
              Computers 34(10):892-901, 1985.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [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>.

Author's Address








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   Tony Li
   Arista Networks
   5453 Great America Parkway
   Santa Clara, California  95054
   USA

   Email: tony.li@tony.li












































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