Quick Answer
The answer is 40 seconds. This is because the default OSPF dead interval on broadcast networks like Ethernet is calculated as four times the hello interval, and the default hello interval on such networks is 10 seconds. The dead interval dictates how long a router waits without receiving a hello packet before declaring a neighbor down, making this 4:1 ratio a fundamental OSPF timing behavior. On the Cisco CCNP ENARSI 300-410 exam, this concept often appears in troubleshooting scenarios where mismatched timers prevent adjacency formation, or in questions testing your recall of default values for different network types. A common trap is confusing the broadcast default with non-broadcast or point-to-point links, where the hello interval is 30 seconds and the dead interval is 120 seconds. To lock it in, remember the mnemonic: "Broadcast beats at ten, dead at forty."
This 300-410 practice question tests your understanding of device management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
What is the default OSPF dead interval on an Ethernet broadcast network?
10 seconds
Why wrong: 10 seconds is the default hello interval, not the dead interval.
30 seconds
Why wrong: 30 seconds is not a default OSPF timer for broadcast networks.
40 seconds
The dead interval is 4 times the hello interval (10 seconds) = 40 seconds.
120 seconds
Why wrong: 120 seconds is the default dead interval on non-broadcast networks (hello 30 seconds).
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
40 seconds
The default OSPF dead interval is 4 times the hello interval. On broadcast networks (like Ethernet), the default hello interval is 10 seconds, so the dead interval is 40 seconds.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
10 seconds
Why it's wrong here
10 seconds is the default hello interval, not the dead interval.
30 seconds
Why it's wrong here
30 seconds is not a default OSPF timer for broadcast networks.
40 seconds
Why this is correct
The dead interval is 4 times the hello interval (10 seconds) = 40 seconds.
Related concept
OSPF neighbours must agree on key parameters.
120 seconds
Why it's wrong here
120 seconds is the default dead interval on non-broadcast networks (hello 30 seconds).
Common exam traps
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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FAQ
Device Management — This question tests Device Management — OSPF neighbours must agree on key parameters..
The correct answer is: 40 seconds — The default OSPF dead interval is 4 times the hello interval. On broadcast networks (like Ethernet), the default hello interval is 10 seconds, so the dead interval is 40 seconds.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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