In a multi access network, an election process will take place to nominate a designated (DR) and backup designated router (BDR). This process will quite happily run its course without human intervention, but like so many other automated processes in networking, there is no real intelligence behind it. The trouble with this unintelligent election process is that the DR and BDR will typically take on extra work to reduce the amount of routing protocol traffic on the segment. In the event a low powered router becomes the DR/BDR, this router may begin to strain under its extra responsibilities.
To mitigate this problem we can influence which routers become the DR and BDR. Ideally we would want these to be the more powerful ones. By assigning a priority to an interface, any DR/BDR elections that take place will first consider the priority of all interfaces in that multi access segment, and whichever has the high value will win. In the event of a tie, then the router id will be used as a tie breaker.
From interface configuration mode, we use the ip ospf priority command to assign a priority of between 0 and 255 to the interface.
Router(config-if)#ip ospf priority <value>