The correct answer is that the OSPF dead interval is automatically set to 20 seconds. This happens because when you manually configure the hello interval using the `ip ospf hello-interval` command, Cisco IOS automatically adjusts the dead interval to four times the hello interval to maintain the standard ratio, unless the dead interval is also explicitly configured. In this case, setting the hello interval to 5 seconds triggers the router to calculate a dead interval of 20 seconds (4 × 5). On the ENCOR 350-401 exam, this tests your understanding of OSPF timer behavior on broadcast networks, where the default hello interval is 10 seconds and dead interval is 40 seconds. A common trap is assuming the dead interval remains at the default 40 seconds after changing the hello interval, or forgetting that the automatic adjustment only applies when the dead interval is not manually set. Remember the 4-to-1 ratio: the dead interval is always four times the hello interval by default, so if you change one without the other, the router recalculates to keep that relationship.
350-401 OSPF Practice Question
This 350-401 practice question tests your understanding of ospf. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Consider the following OSPF configuration on router R2:
interface GigabitEthernet0/0
ip address 192.168.1.2 255.255.255.0
ip ospf 1 area 0
ip ospf hello-interval 5
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The OSPF dead interval is automatically set to 20 seconds.
The correct answer is A because the OSPF dead interval is automatically set to four times the hello interval when the hello interval is manually configured. By default, OSPF uses a hello interval of 10 seconds and a dead interval of 40 seconds on broadcast networks. However, when you explicitly set the hello interval to 5 seconds using the 'ip ospf hello-interval 5' command, the router automatically adjusts the dead interval to 20 seconds (4 × 5 seconds) to maintain the standard ratio, unless the dead interval is also manually configured.
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.
✓
The OSPF dead interval is automatically set to 20 seconds.
Why this is correct
By default, the dead interval is 4 times the hello interval, so with hello 5, dead becomes 20 seconds.
Related concept
Read the scenario before looking for a memorised answer.
✗
The OSPF dead interval remains at the default of 40 seconds.
Why it's wrong here
The dead interval is automatically adjusted to 4 times the hello interval unless explicitly set.
✗
This configuration will cause OSPF to use MD5 authentication.
Why it's wrong here
No authentication is configured; hello-interval does not affect authentication.
✗
The OSPF network type changes to point-to-point.
Why it's wrong here
The network type is not changed; it remains broadcast by default on Ethernet.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the automatic relationship between the OSPF hello and dead intervals, and the trap here is that candidates assume the dead interval remains at the default value (40 seconds) even after changing the hello interval, rather than understanding it scales proportionally to 4× the new hello interval.
Detailed technical explanation
How to think about this question
Under the hood, OSPF uses the dead interval to determine when a neighbor is considered unreachable; if no Hello packets are received within the dead interval, the neighbor is declared down. The default dead interval is four times the hello interval (RFC 2328, Section 10.5), and this ratio is preserved when only the hello interval is modified. In real-world scenarios, adjusting the hello and dead intervals can speed up convergence on lossy links, but it also increases OSPF control plane overhead, so it must be balanced carefully.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
OSPF — This question tests OSPF — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The OSPF dead interval is automatically set to 20 seconds. — The correct answer is A because the OSPF dead interval is automatically set to four times the hello interval when the hello interval is manually configured. By default, OSPF uses a hello interval of 10 seconds and a dead interval of 40 seconds on broadcast networks. However, when you explicitly set the hello interval to 5 seconds using the 'ip ospf hello-interval 5' command, the router automatically adjusts the dead interval to 20 seconds (4 × 5 seconds) to maintain the standard ratio, unless the dead interval is also manually configured.
What should I do if I get this 350-401 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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Question Discussion
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