Which statement about OSPF Hello and Dead intervals is true, and what is their effect on neighbor adjacency?

Which statement about OSPF Hello and Dead intervals is true, and what is their effect on neighbor adjacency?

• A. Hello interval sets the router ID; Dead interval sets the LSA refresh rate.
• B. Hello intervals determine how often Hello packets are sent; Dead interval defines how long a neighbour must be unresponsive before adjacency is dropped; they must match on both sides.
• C. Hello interval only applies to ABR routers; Dead interval only to ASBRs.
• D. Hello and Dead intervals are optional and have no impact on adjacency.

Answer: (B)

OSPF uses Hello messages to discover and keep neighbor adjacencies alive. The Hello interval is how often those Hello packets are sent, which sets how often routers check that their neighbor is reachable. The Dead interval defines how long a router will wait without receiving Hello before declaring the neighbor down and tearing down the adjacency. For a stable adjacency, both routers on a link must have the same Hello and Dead intervals; if they differ, the routers cannot form or sustain an adjacency. The Dead interval is not an LSA refresh rate, and these timers apply to all OSPF neighbors, not just ABRs or ASBRs. They are essential timers that determine when a neighbor is considered down and the adjacency is removed (for example, a typical default might be Hello every 10 seconds and Dead after 40 seconds).

OSPF uses Hello messages to discover and keep neighbor adjacencies alive. The Hello interval is how often those Hello packets are sent, which sets how often routers check that their neighbor is reachable. The Dead interval defines how long a router will wait without receiving Hello before declaring the neighbor down and tearing down the adjacency. For a stable adjacency, both routers on a link must have the same Hello and Dead intervals; if they differ, the routers cannot form or sustain an adjacency. The Dead interval is not an LSA refresh rate, and these timers apply to all OSPF neighbors, not just ABRs or ASBRs. They are essential timers that determine when a neighbor is considered down and the adjacency is removed (for example, a typical default might be Hello every 10 seconds and Dead after 40 seconds).