OSPF Discovery, Selection, and Route Maintenance
The best way to understand OSPF discovery, selection, and continuance is to look at OSPF operations in a single-area, broadcast, multi-access scenario. Before anything can happen, OSPF routers must discover one another so they can exchange basic information.
The Hello Protocol
A Hello packet is essentially a multicast packet used by OSPF routers to facilitate neighbor discovery, selection, and maintenance. Neighboring routers can be dynamically discovered with this protocol because Hello leverages the existing broadcast capability of a network. The OSPF designated router (DR), mentioned in the previous bulleted list, is also elected with the Hello protocol. Hello is actually a separate protocol ...