What do OSPF Hello and Dead intervals represent?

• A. Hello interval is how often routers send Hello packets; Dead interval is the time to wait without Hello before declaring the neighbor down.
• B. Hello interval is the time to wait before declaring neighbor down; Dead interval is how often Hello packets are sent.
• C. Hello interval defines the MTU; Dead interval defines the maximum hop count.
• D. Hello interval sets LSA aging interval; Dead interval sets SPF timer.

Answer: (A)

OSPF uses Hello and Dead timers to manage neighbor relationships. The Hello interval is how often Hello packets are sent on an interface to discover neighbors and keep the adjacency alive. The Dead interval is the time the router will wait without receiving a Hello before declaring the neighbor down and removing the adjacency. These timers must match on both sides for an adjacency to form, otherwise discovery and maintenance fail. In practice, Dead is often four times the Hello interval, though both can be tuned for the network design. This description precisely captures how these timers function. Other options describe concepts from different aspects of OSPF or networking (such as MTU, maximum hop count, LSA aging, or SPF timing) and do not define how neighbor maintenance works.