Avoiding Instability During Graceful Shutdown of Multiple OSPF Routers

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Executive Summary

Many recent router architectures decouple the routing engine from the forwarding engine, allowing packet forwarding to continue even when the routing process is not active. This opens up the possibility of using the forwarding capability of a router even when its routing process is brought down for software upgrade or maintenance, thus avoiding the route flaps that normally occur when the routing process goes down. Unfortunately, current routing protocols, such as BGP, OSPF and IS-IS do not support such operation. Earlier paper described an enhancement to OSPF, called the IBB (I'll Be Back) capability that enables a router to continue forwarding packets while its routing process is inactive. When the OSPF process in an IBB-capable router is inactive, it cannot adapt its forwarding table to reflect changes in network topology.

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