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Computer Networks
Volume 52, Issue 3, 22 February 2008, Pages 593-609
 
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doi:10.1016/j.comnet.2007.10.012    How to Cite or Link Using DOI (Opens New Window)
Copyright © 2007 Elsevier B.V. All rights reserved.

Mitigating transient loops through interface-specific forwarding

Srihari Nelakuditia, Corresponding Author Contact Information, E-mail The Corresponding Author, Zifei Zhonga, Junling Wanga, Ram Keralapurab and Chen-Nee Chuahb

aDepartment of Computer Science and Engineering, University of South Carolina, Columbia, SC 29208, United States bDepartment of Electrical and Computer Engineering, University of California at Davis, Davis, CA 95616, United States

Received 20 February 2007; 
revised 1 August 2007; 
accepted 24 October 2007. 
Responsible Editor: I.F. Akyildiz. 
Available online 7 November 2007.

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Abstract

Under link-state routing protocols such as OSPF and IS–IS, when there is a change in the topology, propagation of link-state advertisements, path recomputation, and updating of forwarding tables (FIBs) will all incur some delay before traffic forwarding can resume on alternate paths. During this convergence period, routers may have inconsistent views of the network, resulting in transient forwarding loops. Previous remedies proposed to address this issue enforce a certain order among the nodes in which they update their FIBs. While such approaches succeed in avoiding transient loops, they incur additional message overhead and/or increased convergence delay. We explore an alternative approach, loopless interface-specific forwarding (LISF), that mitigates transient loops by forwarding a packet based on both its incoming interface and destination address. LISF needs to compute and update interface-specific instead of interface-independent forwarding tables. But it requires neither the synchronization of FIB updates at different nodes nor the modification of the existing link-state routing mechanisms. LISF is easily deployable with current routers if they already maintain a FIB at each interface for lookup efficiency. This paper presents the LISF approach, illustrates its strengths and limitations, discusses four alternative implementations of it and evaluates their performance.

Keywords: Link state routing; Transient forwarding loops; Interface-specific forwarding

Article Outline

1. Introduction
2. Transient looping problem and existing approaches
3. Our approach
3.1. Interface-specific forwarding
3.2. Loopless interface-specific forwarding
3.2.1. Discard if PIng-POng (PIPO)
3.2.2. Discard if CYCLe (CYCL)
3.2.3. Discard if NO Forward Progress (NOFP)
3.2.4. Discard if UNusual Incoming Interface (UNIN)
3.2.5. Differences between LISF methods
4. Proof of loop-free property of LISF
4.1. Change in the state of a single link
4.2. Change in the state of a single node
5. Limitations of LISF methods
5.1. Single link failure with asymmetric links
5.2. Multiple failures with symmetric links
6. Performance evaluation
6.1. Single link failures in a Tier-1 ISP
6.2. Single and multiple link failures in Abilene and Rocketfuel topologies
6.3. Multiple failures in a Tier-1 ISP
7. Conclusions
Acknowledgements
References
Vitae











Computer Networks
Volume 52, Issue 3, 22 February 2008, Pages 593-609
 
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