Spot the OSPF mistake: the silent neighbor
Same subnet. Same area. No adjacency. One timer has other plans.
The scenario
Two routers share a broadcast Ethernet segment. Both interfaces are up, OSPF is enabled, addressing is compatible and authentication matches.
R1: Area 0 · Hello 10 seconds · Dead 40 seconds.
R2: Area 0 · Hello 5 seconds · Dead 20 seconds.
A colleague says: “Let’s reboot both routers.” What should you compare first, and why?
Show answer & explanation
The Hello and Dead intervals do not match. Align them intentionally on both ends and verify that compatible Hellos are accepted. Rebooting does not resolve a persistent configuration mismatch.
This scenario supplies the other prerequisites; in a real network, verify them rather than assuming.
Protocol reference: RFC 2328 (OSPFv2). NSSA reference: RFC 3101.
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