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Network Working Group                                            H. Chen
Internet-Draft                                                 Futurewei
Intended status: Standards Track                                D. Cheng
Expires: January 30, 2020                                     Individual
                                                                  M. Toy
                                                                 Verizon
                                                                 Y. Yang
                                                                     IBM
                                                                 A. Wang
                                                           China Telecom
                                                                  X. Liu
                                                          Volta Networks
                                                                  Y. Fan
                                                            Casa Systems
                                                                  L. Liu
                                                                 Fujitsu
                                                           July 29, 2019


                Flooding Topology Computation Algorithm
                   draft-cc-lsr-flooding-reduction-05

Abstract

   This document proposes an algorithm for a node to compute a flooding
   topology, which is a subgraph of the complete topology per underline
   physical network.  When every node in an area automatically
   calculates a flooding topology by using a same algorithm and floods
   the link states using the flooding topology, the amount of flooding
   traffic in the network is greatly reduced.  This would reduce
   convergence time with a more stable and optimized routing
   environment.

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].

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.



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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on January 30, 2020.

Copyright Notice

   Copyright (c) 2019 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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Flooding Topology . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Flooding Topology Construction  . . . . . . . . . . . . .   3
   4.  Algorithms to Compute Flooding Topology . . . . . . . . . . .   4
     4.1.  Algorithm with Considering Degree . . . . . . . . . . . .   5
     4.2.  Algorithm with Considering Others . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   For some networks such as dense Data Center (DC) networks, the
   existing Link State (LS) flooding mechanism is not efficient and may
   have some issues.  The extra LS flooding consumes network bandwidth.
   Processing the extra LS flooding, including receiving, buffering and
   decoding the extra LSs, wastes memory space and processor time.  This
   may cause scalability issues and affect the network convergence
   negatively.



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   This document proposes an algorithm for a node to compute a flooding
   topology, which is a subgraph of the complete topology per underline
   physical network.  When every node in an area automatically
   calculates a flooding topology by using a same algorithm and floods
   the link states using the flooding topology, the amount of flooding
   traffic in the network is greatly reduced.  This would reduce
   convergence time with a more stable and optimized routing
   environment.

   There may be multiple algorithms for computing a flooding topology.
   Users can select one they prefer, and smoothly switch from one to
   another.

2.  Terminology

   LSA:  A Link State Advertisement in OSPF.

   LSP:  A Link State Protocol Data Unit (PDU) in IS-IS.

   LS: A Link Sate, which is an LSA or LSP.

   FT: Flooding Topology.

   FTC:  Flooding Topology Computation.

3.  Flooding Topology

   For a given network topology, a flooding topology is a sub-graph or
   sub-network of the given network topology that has the same
   reachability to every node as the given network topology.  Thus all
   the nodes in the given network topology MUST be in the flooding
   topology.  All the nodes MUST be inter-connected directly or
   indirectly.  As a result, LS flooding will in most cases occur only
   on the flooding topology, that includes all nodes but a subset of
   links.  Note even though the flooding topology is a sub-graph of the
   original topology, any single LS MUST still be disseminated in the
   entire network.

3.1.  Flooding Topology Construction

   Many different flooding topologies can be constructed for a given
   network topology.  For example, a chain connecting all the nodes in
   the given network topology is a flooding topology.  A circle
   connecting all the nodes is another flooding topology.  A tree
   connecting all the nodes is a flooding topology.  In addition, the
   tree plus the connections between some leaves of the tree and branch
   nodes of the tree is a flooding topology.




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   The following parameters need to be considered for constructing a
   flooding topology:

   o  Degree: The degree of the flooding topology is the maximum degree
      among the degrees of the nodes on the flooding topology.  The
      degree of a node on the flooding topology is the number of
      connections on the flooding topology it has to other nodes.

   o  Number of links: The number of links on the flooding topology is a
      key factor for reducing the amount of LS flooding.  In general,
      the smaller the number of links, the less the amount of LS
      flooding.

   o  Diameter: The diameter of the flooding topology is the shortest
      distance between the two most distant nodes on the flooding
      topology.  It is a key factor for reducing the network convergence
      time.  The smaller the diameter, the less the convergence time.

   o  Redundancy: The redundancy of the flooding topology means a
      tolerance to the failures of some links and nodes on the flooding
      topology.  If the flooding topology is split by some failures, it
      is not tolerant to these failures.  In general, the larger the
      number of links on the flooding topology is, the more tolerant the
      flooding topology to failures.

   Note that the flooding topology constructed by a node is dynamic in
   nature, that means when the base topology (the entire topology graph)
   changes, the flooding topology (the sub-graph) MUST be re-computed/
   re-constructed to ensure that any node that is reachable on the base
   topology MUST also be reachable on the flooding topology.

4.  Algorithms to Compute Flooding Topology

   There are many algorithms to compute a flooding topology.  A simple
   and efficient one is briefed below.

   o  Select a node R0 according to a rule such as the node with the
      smallest node ID;

   o  Build a tree using R0 as root of the tree; and then

   o  Connect each node whose degree is one to the tree to have a
      flooding topology.








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4.1.  Algorithm with Considering Degree

   The algorithm starts from node R0 as root with a given maximum degree
   MaxD such as MaxD = 3, a candidate queue Cq = {(R0, D = 0, PHs = {
   })}, and an empty flooding topology FT = { }.  Cq contains one
   element (R0, D = 0, PHs = { }), where node R0 is the root, D = 0
   indicates that the Degree (D for short) of R0 is 0 (i.e., the number
   of links on the flooding topology connected to R0 is 0), PHs = { }
   indicates that the Previous Hops (PHs for short) of R0 is empty.

   1.  Finding and removing the first element with node A in Cq that is
       not on FT and one PH's D in PHs < MaxD.

       If A is root R0, then add the element into FT

       otherwise  (i.e., A != R0 with one PH's D in PHs < MaxD.  Assume
          that PH is the first one in PHs whose D < MaxD), PH's D++, and
          add A with D = 1 and PHs = {PH} into FT.

       Note:  if there is no element in Cq satisfying the conditions,
          then algorithm may be restarted from R0, ++MaxD, Cq =
          {(R0,D=0,PHs = { })}, FT = { };

   2.  If all the nodes are on the FT, then goto step 4;

   3.  Suppose that node Xi (i = 1, 2,..., n) is connected to node A and
       not on FT, and X1, X2,..., Xn are in an increasing order by their
       IDs (i.e., X1's ID < X2's ID < ... < Xn's ID).  If Xi is not in
       Cq, then add it into the end of Cq with D = 0 and PHs = {A};
       otherwise (i.e., Xi is in Cq), add A into the end of Xi's PHs;
       Goto step 1.

   4.  For each node B in FT whose D is one (from minimum to maximum
       node ID), find a link L attached to B such that L's remote node R
       has minimum D and ID, add link L between B and R into FT and
       increase B's D and R's D by one.  Return FT.

4.2.  Algorithm with Considering Others

   There may be some contraints on some nodes in a network.  For
   example, in a spine-and-leaf network, there may be a constraint on
   the degree of every leaf node on the flooding topology, which is that
   the degree of every leaf node is not greater than a given number
   ConMaxD such as ConMaxD = 2.  For each of the other nodes such as the
   spine nodes, there is no such constraint, that is that ConMaxD is a
   huge number for each of these nodes.





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   Step 1 of the algorithm described above is updated below to consider
   this constraint.  In addition to checking constraint PH's D < MaxD,
   step 1 checks another constraint PH's D < PH's ConMaxD.

   1.  Finding and removing the first element with node A in Cq that is
       not on FT and one PH's D in PHs < MaxD and PH's D < PH's ConMaxD.

       If A is root R0, then add the element into FT

       otherwise  (i.e., A != R0 with one PH's D in PHs < MaxD and PH's
          D < PH's ConMaxD.  Assume that PH is the first one in PHs
          whose D < MaxD and PH's D < PH's ConMaxD), PH's D++, and add A
          with D = 1 and PHs = {PH} into FT.

       Note:  if there is no element with a node in Cq satisfying the
          conditions, then algorithm may be restarted from R0, ++MaxD,
          Cq = {(R0,D=0,PHs = { })}, FT = { };

5.  Security Considerations

   This document does not introduce any new security issue.

6.  IANA Considerations

   Under Registry Name: "IGP Algorithm Type For Computing Flooding
   Topology" under an existing "Interior Gateway Protocol (IGP)
   Parameters" IANA registries (refer to Section 7.3.  IGP
   [I-D.ietf-lsr-dynamic-flooding]), IANA is requested to assign one
   value of IGP Algorithm Type For Computing Flooding Topology as
   follows:

   +==========+========================================+=============+
   |Type Value|               Type Name                | reference   |
   +==========+========================================+=============+
   |    1     | Breadth First Minimum Degree Algorithm |This document|
   +----------+----------------------------------------+-------------+

7.  Acknowledgements

   The authors would like to thank Acee Lindem, Zhibo Hu, Robin Li,
   Stephane Litkowski and Alvaro Retana for their valuable suggestions
   and comments on this draft.

8.  References







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8.1.  Normative References

   [I-D.ietf-lsr-dynamic-flooding]
              Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,
              T., Cooper, D., Jalil, L., and S. Dontula, "Dynamic
              Flooding on Dense Graphs", draft-ietf-lsr-dynamic-
              flooding-03 (work in progress), June 2019.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <https://www.rfc-editor.org/info/rfc1195>.

   [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>.

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

8.2.  Informative References

   [I-D.ietf-rtgwg-spf-uloop-pb-statement]
              Litkowski, S., Decraene, B., and M. Horneffer, "Link State
              protocols SPF trigger and delay algorithm impact on IGP
              micro-loops", draft-ietf-rtgwg-spf-uloop-pb-statement-10
              (work in progress), January 2019.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Authors' Addresses

   Huaimo Chen
   Futurewei
   Boston
   USA

   Email: huaimo.chen@futurewei.com









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   Dean Cheng
   Individual
   Santa Clara
   USA

   Email: deanccheng@gmail.com


   Mehmet Toy
   Verizon
   USA

   Email: mehmet.toy@verizon.com


   Yi Yang
   IBM
   Cary, NC
   United States of America

   Email: yyietf@gmail.com


   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing  102209
   China

   Email: wangaj.bri@chinatelecom.cn


   Xufeng Liu
   Volta Networks
   McLean, VA
   USA

   Email: xufeng.liu.ietf@gmail.com


   Yanhe Fan
   Casa Systems
   USA

   Email: yfan@casa-systems.com






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   Lei Liu
   Fujitsu
   USA

   Email: liulei.kddi@gmail.com














































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