Designated Router

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 routers 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 routers. In general, when an interface first becomes functional, it checks whether the network currently has a designated router. If there is one, the router accepts that designated router regardless of its own router priority. Otherwise, if the router has the highest priority on the network, it becomes the designated router. If router priorities tie, the router with the highest router ID (which is typically the router’s IP address) is chosen as the designated router.

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