Internet Engineering Task Force (IETF) M. Shand
Request for Comments: 6976 Individual Contributor
Category: Informational S. Bryant
ISSN: 2070-1721 S. Previdi
C. Filsfils
Cisco Systems
P. Francois
Institute IMDEA Networks
O. Bonaventure
Universite catholique de Louvain
July 2013
Framework for Loop-Free Convergence
Using the Ordered Forwarding Information Base (oFIB) Approach
Abstract
This document describes an illustrative framework of a mechanism for
use in conjunction with link-state routing protocols that prevents
the transient loops that would otherwise occur during topology
changes. It does this by correctly sequencing the forwarding
information base (FIB) updates on the routers.
This mechanism can be used in the case of non-urgent (management
action) link or node shutdowns and restarts or link metric changes.
It can also be used in conjunction with a fast reroute mechanism that
converts a sudden link or node failure into a non-urgent topology
change. This is possible where a complete repair path is provided
for all affected destinations.
After a non-urgent topology change, each router computes a rank that
defines the time at which it can safely update its FIB. A method for
accelerating this loop-free convergence process by the use of
completion messages is also described.
The technology described in this document has been subject to
extensive simulation using pathological convergence behavior and real
network topologies and costs. However, the mechanisms described in
this document are purely illustrative of the general approach and do
not constitute a protocol specification. This document represents a
snapshot of the work of the Routing Area Working Group at the time of
publication and is published as a document of record. Further work
is needed before implementation or deployment.
Shand, et al. Informational [Page 1]RFC 6976 Loop-Free Convergence Using oFIB July 2013Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6976.
Copyright Notice
Copyright (c) 2013 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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described in the Simplified BSD License.
Shand, et al. Informational [Page 2]RFC 6976 Loop-Free Convergence Using oFIB July 2013Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. The Purpose of This Document . . . . . . . . . . . . . . 4
1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
2. The Required FIB Update Order . . . . . . . . . . . . . . . . 6
2.1. Single Link Events . . . . . . . . . . . . . . . . . . . 6
2.1.1. Link Down / Metric Increase . . . . . . . . . . . . . 6
2.1.2. Link Up / Metric Decrease . . . . . . . . . . . . . . 7
2.2. Multi-Link Events . . . . . . . . . . . . . . . . . . . . 8
2.2.1. Router Down Events . . . . . . . . . . . . . . . . . 8
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