What is the Hello protocol used for in OSPF?

• A. To discover physically connected routing devices running OSPF (and belonging to the same AS)
• B. To encrypt OSPF packets
• C. To rate-limit LSA floods
• D. To reset router adjacencies

Answer: (A)

The Hello protocol in OSPF is the neighbor discovery and adjacency maintenance mechanism. Routers on the same OSPF-enabled link periodically send Hello packets to find directly connected neighbors that belong to the same OSPF domain and to verify they can communicate. These Hello messages carry essential parameters (like Hello and Dead intervals, area and authentication settings) so two routers with matching values can form a neighbor relationship. On multi-access networks, the Hello process also triggers the election of a Designated Router and Backup Designated Router to simplify and optimize flooding. If a neighbor stops sending Hello packets, the adjacency is dropped after the Dead interval. This feature is specifically for discovering and keeping neighbors (and DR/BDR roles) up, not for encrypting OSPF, limiting LSAs, or resetting adjacencies.