The Need for Fast Reroute
Network administrators have been dealing with link and node failures for as long as there have been networks. It has traditionally fallen to the Interior Gateway Protocol (IGP) to quickly route around failures, converging on the remaining topology. However, there are a few things the IGP doesn't do that well when it comes to convergence:
In a large network, your IGP can take quite a few seconds to converge; until the entire network is converged, there is packet loss. It's not uncommon to see 5 to 10 seconds of packet loss when a core link flaps in a large network.
A link failure can lead to congestion in some parts of the network while leaving other parts free of congestion.
Configuring the IGP to converge quickly can ...
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