The graceful-restart command enables GR of the IS-IS process.
The undo graceful-restart command disables GR of the IS-IS process.
By default, IS-IS GR is disabled.
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.