IMDEA Networks Institute Publications Repository

Loop-free convergence using oFIB

Shand, Mike and Bryant, Stewart and Previdi, Stefano and Filsfils, Clarence and Francois, Pierre and Bonaventure, Olivier (2012) Loop-free convergence using oFIB. [Standardization Contributions]

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This document describes a mechanism for use in conjunction with link state routing protocols which prevents the transient loops which 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 link or node shutdowns and restarts or link metric changes. It can also be used in conjunction with a fast re-route mechanism which 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 real network topologies and costs, and pathological convergence behaviour.

Item Type: Standardization Contributions
Additional Information: OFIB: With link-state protocols, such as IS-IS and OSPF, each time the network topology changes, some routers need to modify their forwarding information base (FIB) to take into account the new topology. Each topology change causes a convergence phase. During this phase, routers may transiently have inconsistent FIBs, which may lead to packet loops and losses, even if the reachability of the destinations is not compromised after the topology change. Packet losses and transient loops can also occur in the case of a link down event implied by a maintenance operation, even if this operation is predictable and not urgent. The goal of this work is to define a mechanism that sequences the router FIB updates to maintain consistency throughout the network. By correctly setting the FIB change order no looping or packet loss can occur. This mechanism may be applied to the case of managed link-state changes, i.e. link metric change, manual link down/up, manual router down/up, and managed state changes of a set of links attached to one router.
Subjects: Q Science > Q Science (General)
Q Science > QA Mathematics > QA75 Electronic computers. Computer science
T Technology > T Technology (General)
T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Divisions: Faculty of Engineering, Science and Mathematics > School of Electronics and Computer Science
Depositing User: Rebeca De Miguel
Date Deposited: 29 Apr 2013 12:45
Last Modified: 07 Aug 2013 09:11

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