Avoiding Routing Instability during Graceful Shutdown of OSPF

Many recent router architectures decouple the routing engine from the forwarding engine so that packet forwarding can continue even when the routing software is not active This implies that one can avoid route aps that occur when the routing process goes down provided the forwarding engine remains active during that time period Unfortunately the current de nitions of routing protocols like BGP OSPF and IS IS do not support this behavior In this paper we propose means of extending OSPF by adding a new capability called IBB I ll Be Back Capability to it so that packet forwarding can continue for a certain time period when the OSPF process is down IBB Capability can be used for avoiding route aps that occur when the OSPF process is brought down to facilitate protocol software upgrade operating system upgrade router ID change and AS and interface renumbering We identify the challenges one of which is the inability of the inactive router to adapt to routing changes in making OSPF IBB Capable and propose solutions We then describe a prototype implementation of IBB Capability we have developed using GateD Using the prototype in an experimental setup we demonstrate that the overhead of IBB Capability is modest compared to the bene t it o ers and has good scaling behavior in terms of network that the overhead of IBB Capability is modest compared to the bene t it o ers and has good scaling behavior in terms of network size