isis priority number-value [level-1 | level-2]
no isis priority [number-value] [level-1 | level-2]
number-value Sets the priority of a router and is a number from 0 to 127. The default value is 64. level-1 (Optional) Sets the priority for Level 1 independently. level-2 (Optional) Sets the priority for Level 2 independently.
To configure the priority of designated routers, use the isis priority command in interface configuration mode. To reset the default priority, use the no form of this command.
Priority of 64
Level 1 and Level 2
Priorities can be configured for Level 1 and Level 2 independently. Specifying the level-1 or level-2 keyword resets priority only for Level 1 or Level 2 routing, respectively.
The priority is used to determine which router on a LAN will be the designated router or Designated Intermediate System (DIS). The priorities are advertised in the hello packets. The router with the highest priority will become the DIS.
In IS-IS, there is no backup designated router. Setting the priority to 0 lowers the chance of this system becoming the DIS, but does not prevent it. If a router with a higher priority comes on line, it will take over the role from the current DIS. In the case of equal priorities, the highest MAC address breaks the tie.
The following example shows Level 1 routing given priority by setting the priority level to 80. This router is now more likely to become the DIS.Router(config)# interface ethernet 0 Router(config-if)# isis priority 80 level-1
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