Link State protocols SPF trigger and delay algorithm impact on IGP micro-loops
draft-ietf-rtgwg-spf-uloop-pb-statement-09
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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: June 24, 2019 Orange
M. Horneffer
Deutsche Telekom
December 21, 2018
Link State protocols SPF trigger and delay algorithm impact on IGP
micro-loops
draft-ietf-rtgwg-spf-uloop-pb-statement-09
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 (Interior Gateway Protocol) implementations
in a single network, with respect to micro-loops. The analysis is
focused on the SPF (Shortest Path First) delay algorithm.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 24, 2019.
Litkowski, et al. Expires June 24, 2019 [Page 1]
Internet-Draft spf-microloop December 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
the Trust Legal Provisions and are provided without warranty as
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 . . . . . . . . . . . . . . . . . . . . 6
4.1. Two steps SPF delay . . . . . . . . . . . . . . . . . . . 6
4.2. Exponential backoff . . . . . . . . . . . . . . . . . . . 7
5. Mixing strategies . . . . . . . . . . . . . . . . . . . . . . 8
6. Benefits of standardized SPF delay behavior . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Link State IGP protocols are based on a topology database on which
the SPF 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 of [RFC1195]) 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 June 24, 2019 [Page 2]
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