Back-off SPF algorithm for link state IGP
draft-ietf-rtgwg-backoff-algo-00

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Last updated 2015-05-04
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Network Working Group                                        B. Decraene
Internet-Draft                                                    Orange
Intended status: Standards Track                             May 4, 2015
Expires: November 5, 2015

               Back-off SPF algorithm for link state IGP
                    draft-ietf-rtgwg-backoff-algo-00

Abstract

   This document defines a standard algorithm to back-off link-state IGP
   SPF computations.

   Having one standardized algorithm improves interoperability by
   reducing the probability and/or duration of transient forwarding
   loops during the IGP convergence in the area/level when the network
   reacts to multiple consecutive events.

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].

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 November 5, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  High level goals  . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Definitions and parameters  . . . . . . . . . . . . . . . . .   3
   4.  Principle of SPF delay algorithm  . . . . . . . . . . . . . .   4
   5.  Specification of SPF delay algorithm  . . . . . . . . . . . .   4
   6.  Impact on micro-loops . . . . . . . . . . . . . . . . . . . .   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
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Link state IGP, such as IS-IS [ISO10589-Second-Edition] and OSPF
   [RFC2328], performs distributed computation on all nodes of the area/
   level.  In order to have consistent routing tables across the
   network, such distributed computation requires that all routers have
   the same vision of the network (Link State DataBase (LSDB)) and
   perform their computation at the same time.

   In general, when the network is stable, there is a desire to compute
   the new SPF as soon as the failure is known, in order to quickly
   route around the failure.  However, when the network is experiencing
   multiple consecutive failures over a short period of time, there is a
   desire to limit the frequency of SPF computations.  Indeed, this
   allow reducing the control plane resources used by IGP and all
   protocols/sub system reacting on it such as LDP, RSVP-TE, BGP, Fast
   ReRoute computations, FIB updates..., reduce the churn on nodes and
   in the network, in particular reduce side effects such as micro-loops
   which may happen during each IGP convergence.

   To allow for this, some back-off algorithm have been implemented.
   Different implementations choose different algorithms, hence in a

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   multi-vendor network, it's not possible to enforce that all routers
   triggers their SPF computation after the same waiting delay.  This
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