- A
Configure the OSPF cost on the interface connecting to the preferred ISP to a lower value.
Why wrong: Incorrect because interface cost affects internal routes, not external routes. External routes use the metric set during redistribution.
- B
Use the 'distance ospf external' command to set a higher administrative distance for external routes from the less preferred ISP.
Correct because by setting a higher administrative distance for external routes from one ISP, the router will prefer routes with lower administrative distance from the other ISP.
- C
Use the 'max-metric' command on the router connecting to the less preferred ISP.
Why wrong: Incorrect because the 'max-metric' command is used to advertise a high cost for locally originated routes, not for external routes.
- D
Configure the OSPF network type to point-to-point on both interfaces.
Why wrong: Incorrect because network type does not influence external route path selection.
350-401 OSPF Practice Question
This 350-401 practice question tests your understanding of ospf. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A network engineer is configuring OSPF on a router that connects to two different ISPs. The engineer wants to prefer one ISP for all external routes unless that ISP's link fails, in which case the other ISP should be used. Which OSPF feature should be used to influence the path selection for external routes?
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
Use the 'distance ospf external' command to set a higher administrative distance for external routes from the less preferred ISP.
Option B is correct because the 'distance ospf external' command allows you to set a higher administrative distance for external OSPF routes learned from a specific neighbor or source, making the routes from the less preferred ISP less trustworthy. When the preferred ISP's link fails, those routes are removed, and the router will then use the external routes from the backup ISP due to their lower administrative distance (or default distance if not changed). This directly influences path selection for external routes without altering OSPF metrics or interface costs.
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.
- ✗
Configure the OSPF cost on the interface connecting to the preferred ISP to a lower value.
Why it's wrong here
Incorrect because interface cost affects internal routes, not external routes. External routes use the metric set during redistribution.
- ✓
Use the 'distance ospf external' command to set a higher administrative distance for external routes from the less preferred ISP.
Why this is correct
Correct because by setting a higher administrative distance for external routes from one ISP, the router will prefer routes with lower administrative distance from the other ISP.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use the 'max-metric' command on the router connecting to the less preferred ISP.
Why it's wrong here
Incorrect because the 'max-metric' command is used to advertise a high cost for locally originated routes, not for external routes.
- ✗
Configure the OSPF network type to point-to-point on both interfaces.
Why it's wrong here
Incorrect because network type does not influence external route path selection.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse OSPF cost (metric) with administrative distance, thinking that lowering the interface cost will make external routes from that ISP preferred, but OSPF cost only affects internal path selection, not the preference between different routing sources for external routes.
Trap categories for this question
Command / output trap
Incorrect because the 'max-metric' command is used to advertise a high cost for locally originated routes, not for external routes.
Detailed technical explanation
How to think about this question
Under the hood, OSPF uses administrative distance (default 110 for internal routes, 110 for external routes in Cisco IOS) to compare routes from different routing sources. The 'distance ospf external' command modifies the distance for external routes (type 5 and type 7 LSAs) on a per-neighbor or per-route basis, allowing a router to prefer one ISP's external routes over another's even if both have the same metric. In real-world scenarios, this is critical for multi-homed BGP/OSPF environments where you want to control outbound traffic without manipulating BGP attributes or OSPF metrics.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 350-401 question test?
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: Use the 'distance ospf external' command to set a higher administrative distance for external routes from the less preferred ISP. — Option B is correct because the 'distance ospf external' command allows you to set a higher administrative distance for external OSPF routes learned from a specific neighbor or source, making the routes from the less preferred ISP less trustworthy. When the preferred ISP's link fails, those routes are removed, and the router will then use the external routes from the backup ISP due to their lower administrative distance (or default distance if not changed). This directly influences path selection for external routes without altering OSPF metrics or interface costs.
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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Last reviewed: Jun 24, 2026
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