When an IS-IS router restarts, neighbors time out adjacencies and the network converges around it. IS-IS restart support, with the help of restart helper neighbors, can prevent this. A restarting router can send a restart request to indicate to its neighbors that it is restarting. Neighbors—provided they are helpers—send the restarting router a CSNP so that it can reconstruct its LSDB by tracking which LSPs it has and has not received. Neighbors can still time out the adjacency, so this might not work in environments with low hold timers.
IS-IS restart can be configured for planned and unplanned events. Planned events are user-initiated process restarts and user-initiated failovers. Unplanned events are process restarts or failovers that are not administratively initiated.
For information on configuring IS-IS restart, see Configuring the Graceful Restart Feature.
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