- A
10 seconds
Why wrong: 10 seconds is the default hello interval, not the dead interval.
- B
30 seconds
Why wrong: 30 seconds is not a default OSPF timer for broadcast networks.
- C
40 seconds
The dead interval is 4 times the hello interval (10 seconds) = 40 seconds.
- D
120 seconds
Why wrong: 120 seconds is the default dead interval on non-broadcast networks (hello 30 seconds).
Question 282 of 2,152
Default OSPF Hello Interval and Dead Interval on Broadcast Networks
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?
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."
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
40 seconds
On an Ethernet broadcast network, OSPF defaults to a hello interval of 10 seconds and a dead interval of 40 seconds (four times the hello interval). This is defined in RFC 2328 and is the standard for broadcast multiaccess networks like Ethernet. Option C is correct because the dead interval is explicitly 40 seconds in this scenario.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
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
Read the scenario before looking for a memorised answer.
- ✗
120 seconds
Why it's wrong here
120 seconds is the default dead interval on non-broadcast networks (hello 30 seconds).
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between broadcast and NBMA networks, where candidates mistakenly apply the NBMA dead interval (120 seconds) to Ethernet broadcast networks, or confuse the hello interval (10 seconds) with the dead interval.
Detailed technical explanation
How to think about this question
The OSPF dead interval is calculated as the hello interval multiplied by the dead interval multiplier, which defaults to 4 on broadcast networks. This multiplier is configurable via the 'ip ospf dead-interval' command, but the default ensures that a neighbor is declared down after missing four consecutive hello packets. In real-world scenarios, adjusting the dead interval can speed up convergence in unstable links, but setting it too low may cause flapping due to transient packet loss.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 40 seconds — On an Ethernet broadcast network, OSPF defaults to a hello interval of 10 seconds and a dead interval of 40 seconds (four times the hello interval). This is defined in RFC 2328 and is the standard for broadcast multiaccess networks like Ethernet. Option C is correct because the dead interval is explicitly 40 seconds in this scenario.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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