easyMultiple Choice
300-410 Practice Question: The default OSPF dead interval on an Ethernet…
What is the default OSPF dead interval on an Ethernet broadcast network?
⚠ Common exam trap
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.
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.
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
The OSPF dead interval on broadcast and point-to-point networks defaults to four times the hello interval, giving 40 seconds, not 10. Ten seconds is tempting because it matches the default hello interval on those network types, which is a separate timer from the dead interval.
- ✗
30 seconds
Why it's wrong here
Thirty seconds is not the OSPF broadcast default; the dead interval is four times the 10-second hello, so 40 seconds. Thirty seconds is tempting because it is the default dead interval on NBMA and point-to-multipoint networks, where the hello timer is 30 seconds.
- ✓
40 seconds
Why this is correct
OSPF derives the dead interval as four times the hello interval. On an Ethernet broadcast network the default hello is 10 seconds, giving a dead interval of 40 seconds, which matches the stem's broadcast media constraint rather than the 120-second non-broadcast default.
- ✗
120 seconds
Why it's wrong here
One hundred and twenty seconds is not the OSPF broadcast default; the dead interval equals four times the 10-second hello, giving 40 seconds. It is tempting because 120 seconds is the default dead interval on NBMA networks configured with a 30-second hello timer.
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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