Efficient Implementation Method for Loop-free Criterion
draft-geng-iac-caba-00

Document Type Active Internet-Draft (individual)
Authors Haijun Geng  , Han Zhang  , Xingang Shi  , Zhiliang Wang  , Xia Yin 
Last updated 2020-05-12
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Internet Engineering Task Force                                Geng, Ed.
Internet-Draft                                              Shanxi Univ.
Intended status: Informational                                     Zhang
Expires: November 13, 2020                                 Beihang Univ.
                                                                     Shi
                                                                    Wang
                                                                     Yin
                                                          Tsinghua Univ.
                                                            May 12, 2020

        Efficient Implementation Method for Loop-free Criterion
                         draft-geng-iac-caba-00

Abstract

   [RFC5286] introduces Loop-Free Criterion (LFC) in detail, which is a
   technology for local fast rerouting when network failures occur.
   With LFC, alternate next hops are stored alongside with the default
   next hops in a routers forwarding table, and can be immediately
   activated to invoke a loop free repair path in face of link failure.
   As long as not introducing routing loops, these alternative next hops
   can also be used for multipath transmission if there are stringent
   demands on bandwidth or load balancing.  However, in such link state
   networks, computing loop free alternates typically requires one or
   more rounds of full shortest path tree computation on a graph, and
   poses a heavy burden to both the processor load and the memory
   consumption of a network equipment.  In this document, we describe an
   efficient Loop-free Criterion (LFC) implementation method which is
   based on incremental shortest path first (i-SPF), which is suitable
   for practical deployment in large scale networks.  The computational
   complexity of the method is independent of the average node degree of
   the network.

Status of This Memo

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Geng, et al.            Expires November 13, 2020               [Page 1]
Internet-Draft                     IAC                          May 2020

   This Internet-Draft will expire on November 13, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Overview of Solution  . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Existing algorithms for computing LFC rely on one or more rounds of
   full shortest path tree computation on a graph, and cannot achieve
   both good coverage of alternates and low computational complexity at
   the same time.  Based on graph properties we newly find, this
   document propose Incremental Alternates Computation IAC, which can
   compute the full set of alternates for a given network topology in a
   highly efficient way.  IAC performs incremental shortest path
   computation on specific link cost update, where the sign of some cost
   is simply reversed.

2.  Terminology

   In this document, we employ OSPF as an example to explain our method.
   Each router in a single routing area maintains an identical network
   map which allows them to compute the shortest path to every other
   router in a routing area.  Then each router construct its FIB table
   employing the above information.  When a packet arrives at a router,
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