As with OSPF, IS-IS selects DRs on multiaccess networks. It does not choose a backup DR, as OSPF does. By default, the priority value is 64. You can change the priority value to a value from 0 to 127. If you set the priority to 0, the router is not eligible to become a DR for that network. IS-IS uses the highest system ID to select the DR if there is a tie with the priorities. On point-to-point networks, the priority is 0 because no DR is elected. In IS-IS, all routers in a multiaccess network establish adjacencies with all others in the subnetwork, and IS-IS neighbors become adjacent upon the discovery of one another. Both of these characteristics are different from OSPF behavior.
