Configuring IS-IS GR
GR ensures forwarding continuity when a routing protocol restarts or an active/standby switchover occurs.
Two routers are required to complete a GR process. The following are router roles in a GR process.
GR restarter—Graceful restarting router. It must have GR capability.
GR helper—A neighbor of the GR restarter. It assists the GR restarter to complete the GR process. By default, the device acts as the GR helper.
Configure IS-IS GR on the GR restarter.
GR restarter uses the following timers:
T1 timer—Specifies the times that GR restarter can send a Restart TLV with the RR bit set. When rebooted, the GR restarter sends a Restart TLV with the RR bit set to its neighbor. If the GR restarter receives a Restart TLV with the RA set from its neighbor before the T1 timer expires, the GR process starts. Otherwise, the GR process fails.
T2 timer—Specifies the LSDB synchronization interval. Each LSDB has a T2 timer. The Level-1-2 router has a Level-1 timer and a Level-2 timer. If the LSDBs have not synchronized before the two timers expire, the GR process fails.
T3 timer—Specifies the GR interval. The GR interval is set as the holdtime in hello PDUs. Within the interval, the neighbors maintain their adjacency with the GR restarter. If the GR process has not completed within the holdtime, the neighbors tear down the neighbor relationship and the GR process fails.
![[IMPORTANT: ]](images/important.png) | IMPORTANT: IS-IS GR and IS-IS NSR are mutually exclusive. Do not configure them at the same time. | |
To configure GR on the GR restarter:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enable IS-IS and enter IS-IS view. | isis [ process-id ] [ vpn-instance vpn-instance-name ] | N/A |
3. Enable IS-IS GR. | graceful-restart | By default, the GR capability for IS-IS is disabled. |
4. (Optional.) Suppress the SA bit during restart. | graceful-restart suppress-sa | By default, the SA bit is not suppressed. By enabling the GR restarter to suppress the Suppress-Advertisement (SA) bit in the hello PDUs, the neighbors will still advertise their adjacency with the GR restarter. |
5. (Optional.) Configure the T1 timer. | graceful-restart t1 seconds count count | By default, the T1 timer is 3 seconds and can expire 10 times. |
6. (Optional.) Configure the T2 timer. | graceful-restart t2 seconds | By default, the T2 timer is 60 seconds. |
7. (Optional.) Configure the T3 timer. | graceful-restart t3 seconds | By default, the T2 timer is 300 seconds. |