Routers utilizing OSPF use which protocol to acquire neighbors and maintain link-state awareness?

• A. HELLO
• B. LSA
• C. SPF
• D. BFD

Answer: (A)

Neighbor discovery and keeping adjacency up in OSPF is handled by the Hello protocol. Routers periodically send Hello packets on each connected interface to find neighbors, verify compatibility (such as area, router ID, authentication, and timer values), and establish or refresh adjacencies. These Hello exchanges also drive roles and elections on multi-access networks, like choosing a designated router, which helps coordinate how topology information is shared.

Once adjacencies are formed, routers exchange Link-State Advertisements to fill the Link-State Database, and the SPF algorithm uses that database to compute routes. Bidirectional Forwarding Detection is a separate mechanism for rapid failure detection, not used to acquire neighbors or maintain the link-state view. LSA messages carry topology information, but they require established adjacencies first, which come from the Hello protocol.