Introduction To Graceful Restart; Basic Concepts In Graceful Restart; Gr Overview - 3Com S7906E Configuration Manual

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GR Overview

Go to these sections for information you are interested in:

Introduction to Graceful Restart

Basic Concepts in Graceful Restart

Graceful Restart Communication Procedure
Graceful Restart Mechanism for Several Commonly Used Protocols
Throughout this chapter, the term router refers to a router in a generic sense or a Layer 3 switch running
routing protocols or MPLS protocol.
Introduction to Graceful Restart
Graceful Restart ensures the continuity of packet forwarding when a protocol restarts.
The mechanism of Graceful Restart works as follows: When the protocol on a device restarts, the
device will notify its neighbors to temporarily preserve the routing information and adjacency
relationship with the device. After the protocol restarts, the neighbors will help the restarting device to
update information (including various topology, routing and session information maintained by
routing/MPLS related protocols that support Graceful Restart) and to restore it to the state prior to the
restart in minimal time. No route flapping occurs during the restart, the packet forwarding path remains
the same, and the whole system can forward data continuously. Hence, it is called "Graceful Restart".
Basic Concepts in Graceful Restart
A router with the Graceful Restart function enabled is called a Graceful Restart-capable router. It can
perform a Graceful Restart when its routing protocol restarts, ensuring consistent forwarding services.
Routers that are not Graceful Restart capable will follow the normal restart procedures after a routing
protocol restart.
GR Restarter: Graceful restarting router, the router whose routing protocol has restarted due to
administrator instructions or network failure. It must be Graceful Restart capable.
GR Helper: The neighbor of the GR Restarter. It helps the GR Restarter to retain the routing
information. It must be Graceful Restart capable.
GR Session: A Graceful Restart session, which is the negotiation between the GR Restarter and
the GR Helper. A GR session includes restart notification and communications during restart.
Through this session, GR Restarter and GR Helper can know the GR capability of each other.
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