Setting the Designated Router Priority

You can set the priority for the designated IS-IS router that you have elected to use.

isis priority

Use to set the priority of use for your designated router.
You can configure an individual priority for level 1 and level 2 by choosing a priority level in the range 0–127.
The default priority level is 64.
Specifying the level 1 or level 2 keyword resets the priority only for level 1 or level 2 routing, respectively.
Priorities are used to determine which router in the network is the designated intermediate system (DIS); the router with the highest priority becomes the DIS. Priorities are advertised in hellos.
IS-IS has no backup designated router. Setting the priority to 0 reduces the chance of this router becoming the DIS, but does not prevent it. If a router with a higher priority is identified, it takes over the role from the current DIS. When priorities are equal, the highest MAC address breaks the tie and becomes the DIS.
Example host1(config-if)#isis priority 80 level-1
Use the no version to restore the default value, 64.
See isis priority