Link State protocols SPF trigger and delay algorithm impact on IGP micro-loops
draft-ietf-rtgwg-spf-uloop-pb-statement-07

Document Type Active Internet-Draft (rtgwg WG)
Last updated 2018-05-28 (latest revision 2018-05-23)
Replaces draft-litkowski-rtgwg-spf-uloop-pb-statement
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Routing Area Working Group                                  S. Litkowski
Internet-Draft                                   Orange Business Service
Intended status: Informational                               B. Decraene
Expires: November 24, 2018                                        Orange
                                                            M. Horneffer
                                                        Deutsche Telekom
                                                            May 23, 2018

   Link State protocols SPF trigger and delay algorithm impact on IGP
                              micro-loops
               draft-ietf-rtgwg-spf-uloop-pb-statement-07

Abstract

   A micro-loop is a packet forwarding loop that may occur transiently
   among two or more routers in a hop-by-hop packet forwarding paradigm.

   In this document, we are trying to analyze the impact of using
   different Link State IGP implementations in a single network, with
   respect to micro-loops.  The analysis is focused on the SPF delay
   algorithm.

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 24, 2018.

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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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem statement . . . . . . . . . . . . . . . . . . . . . .   4
   3.  SPF trigger strategies  . . . . . . . . . . . . . . . . . . .   5
   4.  SPF delay strategies  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Two steps SPF delay . . . . . . . . . . . . . . . . . . .   6
     4.2.  Exponential backoff . . . . . . . . . . . . . . . . . . .   6
   5.  Mixing strategies . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Benefits of standardized SPF delay behavior . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     10.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Link State IGP protocols are based on a topology database on which
   the SPF (Shortest Path First) algorithm is run to find a consistent
   set of non-looping routing paths.

   Specifications like IS-IS ([RFC1195]) propose some optimizations of
   the route computation (See Appendix C.1) but not all the
   implementations follow those non-mandatory optimizations.

   We will call "SPF triggers", the events that would lead to a new SPF
   computation based on the topology.

   Link State IGP protocols, like OSPF ([RFC2328]) and IS-IS
   ([RFC1195]), are using multiple timers to control the router behavior

Litkowski, et al.       Expires November 24, 2018               [Page 2]
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   in case of churn: SPF delay, PRC delay, LSP generation delay, LSP
   flooding delay, LSP retransmission interval...
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