The graceful-restart command enables the graceful restart (GR) function for an IS-IS process.
The undo graceful-restart command disables the GR function for an IS-IS process.
By default, the GR function is disabled for an IS-IS process.
Usage Scenario
This command is valid for all topologies in an IS-IS process.
When an IS-IS process on a device is restarted, neighbors delete neighbor relationships with the device and delete LSPs from the device. As a result, routes of neighbors are calculated incorrectly and packets are lost. Consequently, the network is temporarily interrupted.
To solve this problem, you can enable GR of the IS-IS process by running the graceful-restart command.
After the graceful-restart command is run, the device can notify its restart status to neighbors and permit neighbors to maintain neighbor relationships. In this manner, nonstop packet forwarding is implemented.
Configuration Impact
If IS-IS GR is enabled on a router, the holdtimes of this router's neighbors are automatically changed to 60s if they are smaller than 60s, and the holdtimes of this router's neighbors are kept unchanged if they are equal to or greater than 60s. If a router is faulty in non-GR scenarios, its neighbors need to take 60 seconds to detect the fault. A large number of packets may be discarded within the 60 seconds.
To resolve this problem, run the graceful-restart no-impact-holdtime command to configure the holdtimes of the neighbors to remain unchanged after IS-IS GR is enabled.