Towards Millisecond IGP Convergence

Cengiz Alaettinoglu, Van Jacobson, Haobo Yu, Packet Design Inc.

"Convergence" times, or the ability to reroute, on currently deployed IP networks is often sighted as one of the key issues in providing new services and larger scale.?It is, however, possible for link-state routing protocols to converge in link propagation time scales, that is in tens of milliseconds. Why then are deployments of ISIS, a link-state routing protocol, not anywhere near this point?

In this talk, we present some analysis about ISIS routing protocol convergence by showing its behavior upon link/router failures and repairs, and its scaling properties to large networks, both in terms of number of nodes and links. We then explore changes needed in the ISIS specification and implementations to reach IGP convergence in milliseconds. Our results are based on experimentation done with ISIS, however, some of the findings may apply to OSPF as well.

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