OSPF Designated Router Overview

Each multiaccess network has a designated router, which performs two main functions:

• Originate network link advertisements on behalf of the network.
• Establish adjacencies with all routing devices on the network, thus participating in the synchronizing of the link-state databases.

The OSPF hello protocol elects a designated router for the network based on the priorities advertised by all the routing devices. In general, when an interface first becomes functional, it checks whether the network currently has a designated router. If there is one, the routing device accepts that designated router regardless of its own router priority. Otherwise, if the routing device has the highest priority on the network, it becomes the designated router. If router priorities tie, the routing device with the highest router ID, which is typically the routing device’s IP address, is chosen as the designated router.