Graceful Restart
With standard implementations of routing protocols, any service interruption requires an affected router to recalculate adjacencies with neighboring routers, restore routing table entries, and update other protocol-specific information. As a result, an unprotected restart of a router can result in forwarding delays, route flapping, wait times stemming from protocol reconvergence, and even dropped packets.
In contrast, graceful restart allows a restarting router and its neighbors to continue forwarding packets without disrupting network performance. Because neighboring routers assist in the restart, the restarting router can quickly resume full operation without having to recalculate algorithms from scratch.