Operation Manual – IP Routing-GR OverviewH3C S5500-EI Series Ethernet Switches Chapter 2 GR Overview2-1Chapter 2 GR OverviewGo to these sections for information you are interested in:z Introduction to Graceful Restartz Basic Concepts in Graceful Restartz Graceful Restart Communication Procedurez Graceful Restart Mechanism for Several Commonly Used ProtocolsNote:Throughout this chapter, the term router and the router icon refers to a router in ageneric sense or a Layer 3 switch running routing protocols.2.1 Introduction to Graceful RestartGraceful Restart ensures the continuity of packet forwarding when a routing protocolrestarts.The mechanism of Graceful Restart works as follows: after the routing protocol on aGraceful Restart capable device has restarted, the device will notify its neighbors totemporarily preserve its adjacency with them and the routing information. Theneighbors will help the restarting device to update its routing information and to restoreit to the state prior to the restart in minimal time. The routing and forwarding remainhighly stable across the restart, the packet forwarding path remains the same, and thewhole system can forward IP packets continuously. Hence, it is called “GracefulRestart”.2.2 Basic Concepts in Graceful RestartA router with the Graceful Restart feature enabled is called a Graceful Restart capablerouter. It can perform a Graceful Restart when its routing protocol restarts. Routers thatare not Graceful Restart capable will follow the normal restart procedures after arouting protocol restart.z GR Restarter: Graceful restarting router, the router whose routing protocol hasrestarted due to administrator instructions or network failure. It must be GracefulRestart capable.z GR Helper: The neighbor of the GR Restarter, which helps the GR Restarter toretain the routing information. It must be Graceful Restart capable.
