A Framework for Loop-Free Convergence
RFC 5715
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RFC - Informational
(January 2010; No errata)
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2015-10-14
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draft-bryant-shand-lf-conv-frmwk
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IETF
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plain text
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RFC 5715 (Informational)
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Ross Callon
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Internet Engineering Task Force (IETF) M. Shand
Request for Comments: 5715 S. Bryant
Category: Informational Cisco Systems
ISSN: 2070-1721 January 2010
A Framework for Loop-Free Convergence
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.
This framework provides a summary of the causes and consequences of
micro-loops and enables the reader to form a judgement on whether
micro-looping is an issue that needs to be addressed in specific
networks. It also provides a survey of the currently proposed
mechanisms that may be used to prevent or to suppress the formation
of micro-loops when an IP or MPLS network undergoes topology change
due to failure, repair, or management action. When sufficiently fast
convergence is not available and the topology is susceptible to
micro-loops, use of one or more of these mechanisms may be desirable.
Status 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/rfc5715.
Shand & Bryant Informational [Page 1]
RFC 5715 A Framework for Loop-Free Convergence January 2010
Copyright Notice
Copyright (c) 2010 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
(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
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 ....................................................3
2. The Nature of Micro-Loops .......................................4
3. Applicability ...................................................5
4. Micro-Loop Control Strategies ...................................6
5. Loop Mitigation .................................................8
5.1. Fast Convergence ...........................................8
5.2. PLSN .......................................................8
6. Micro-Loop Prevention ..........................................10
6.1. Incremental Cost Advertisement ............................10
6.2. Nearside Tunneling ........................................12
6.3. Farside Tunnels ...........................................13
6.4. Distributed Tunnels .......................................14
6.5. Packet Marking ............................................14
6.6. MPLS New Labels ...........................................15
6.7. Ordered FIB Update ........................................16
6.8. Synchronised FIB Update ...................................18
7. Using PLSN in Conjunction with Other Methods ...................18
8. Loop Suppression ...............................................19
9. Compatibility Issues ...........................................20
10. Comparison of Loop-Free Convergence Methods ...................20
11. Security Considerations .......................................21
12. Acknowledgments ...............................................21
13. Informative References ........................................21
Shand & Bryant Informational [Page 2]
RFC 5715 A Framework for Loop-Free Convergence January 2010
1. Introduction
When there is a change to the network topology (due to the failure or
restoration of a link or router, or as a result of management
action), the routers need to converge on a common view of the new
topology and the paths to be used for forwarding traffic to each
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