The graceful-restart suppress-sa command suppresses the Suppress-Advertisement (SA) bit of the restart TLV.
The undo graceful-restart suppress-sa command disables the suppression of the SA bit.
By default, the SA bit is not suppressed.
Before the graceful-restart interval command is run, the GR of the IS-IS process should be enabled by graceful-restart.
The router that starts for the first time (not including GR) does not maintain the forwarding status. If the router does not start for the first time, the LSPs generated when the router run last time may exist in the LSP database of other routers in the network.
The sequence number of the LSP fragment is reinitialized when the router starts, so the LSPs stored in the LSP database of other routers seem to be newer than the LSPs generated after the router starts. This leads to the black hole in the network, and the black hole lasts until the router regenerates its LSPs and advertises the LSPs with the highest sequence number.
If the neighbor suppresses the advertisement of the adjacency relationship to this router during the router starting until the router advertises the updated LSPs, the preceding case can be avoided.