The graceful restart feature enables a router process to restart with minimal impact on the network. Without graceful restart, every other IS-IS router in the network must update its LSDB when the router goes down, and this generates a lot of traffic, and it introduces delays while new routes are established. With graceful restart, the router process requests restart support from its neighbors, and the neighbors wait for a predefined time before declaring routes dead. If the restart completes before the predefined time ends, the restart causes minimal impact on the network operation. For more information on graceful restart, see IS-IS Restart.
Timers that Control Graceful Restart
| Timer | Configuration Command |
|---|---|
| T1 restart hello interval | configure isis [vlan all | {vlan} vlan_name] timer restart-hello-interval seconds {level [1 | 2]} |
| T2 restart timer | configure isis area area_name timer restart seconds {level [1 | 2]} |
| T3 restart grace period | configure isis restart grace-period seconds |
| Hello interval | configure isis [vlan all | {vlan} vlan_name] timer hello-interval [seconds | minimal] {level [1 | 2]} |
| Hello multiplier | configure isis [vlan all | {vlan} vlan_name] hello-multiplier multiplier {level [1 | 2]} |
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