This 350-401 practice question tests your understanding of automation. 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 troubleshooting an automated configuration change that caused a routing loop. The change was pushed via an Ansible playbook that modified OSPF cost values on multiple routers simultaneously. What is the most likely reason for the loop?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The changes were applied simultaneously without allowing OSPF to converge between updates
Option C is correct because applying OSPF cost changes simultaneously on multiple routers without allowing convergence between updates can cause transient routing loops. OSPF relies on the SPF algorithm to calculate loop-free paths based on consistent link-state databases across the network. When costs are changed on multiple routers at once, some routers may have outdated LSAs, leading to inconsistent forwarding tables and temporary loops until all routers reconverge.
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.
✗
OSPF does not support changing costs on multiple routers at the same time
Why it's wrong here
OSPF supports changing costs; the issue is the timing of the changes.
✗
OSPF uses hop count as a metric, and the changes caused a count-to-infinity issue
Why it's wrong here
OSPF uses cost, not hop count; count-to-infinity is a distance-vector problem.
✓
The changes were applied simultaneously without allowing OSPF to converge between updates
Why this is correct
Simultaneous changes can create temporary inconsistencies leading to loops.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The OSPF cost values were changed to non-standard values that OSPF cannot process
Why it's wrong here
OSPF accepts any cost value; non-standard values are allowed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that OSPF can handle simultaneous changes without issue, but the trap here is that candidates overlook the need for convergence between updates, confusing protocol capability with operational best practices.
Detailed technical explanation
How to think about this question
Under the hood, OSPF uses the Dijkstra SPF algorithm to compute shortest paths based on the sum of costs along a route. When costs are changed, each router floods a new LSA and recalculates its routing table. If changes are applied too quickly across multiple routers, the network may experience a period where some routers have not yet received or processed the updated LSAs, leading to inconsistent forwarding decisions and temporary routing loops. In real-world automation, this is mitigated by using tools like Ansible's 'serial' keyword or adding delays between configuration pushes to allow OSPF convergence.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Automation — This question tests Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The changes were applied simultaneously without allowing OSPF to converge between updates — Option C is correct because applying OSPF cost changes simultaneously on multiple routers without allowing convergence between updates can cause transient routing loops. OSPF relies on the SPF algorithm to calculate loop-free paths based on consistent link-state databases across the network. When costs are changed on multiple routers at once, some routers may have outdated LSAs, leading to inconsistent forwarding tables and temporary loops until all routers reconverge.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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