- A
The IOS upgrade changed the output of a 'show' command that is used to set a fact, and that fact now contains characters that break YAML syntax.
If a fact contains newlines or special characters, it can cause YAML parsing errors when the playbook tries to process it.
- B
The Jinja2 template now contains syntax errors because the IOS upgrade changed the configuration requirements.
Why wrong: The error message specifically says YAML script error, not a Jinja2 template error.
- C
The ios_config module is incompatible with the new IOS version.
Why wrong: Module incompatibility would cause a different error, such as 'module not found' or 'unable to parse response'.
- D
The playbook file was corrupted during the IOS upgrade process.
Why wrong: The IOS upgrade is performed on the routers, not on the Ansible control node; the playbook file is unaffected.
Quick Answer
The answer is that a dynamic fact derived from a changed IOS show command output now contains characters that break YAML syntax. This is correct because Ansible loads all variables, including facts set via set_fact or gathered from device output, into the playbook’s variable space before parsing the YAML structure; if a fact value includes unescaped colons, curly braces, or newlines, the YAML parser fails with a syntax error even though the Jinja2 template itself is unchanged. On the ENCOR 350-401 exam, this scenario tests your understanding of how Ansible’s variable injection interacts with YAML parsing, often appearing as a trap where candidates blame the template or module instead of the dynamic data source. A key memory tip: when a playbook breaks after a device upgrade but the template remains untouched, suspect the facts, not the files.
350-401 Ansible Automation Practice Question
This 350-401 practice question tests your understanding of ansible 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 company uses Ansible to manage the configuration of 1000 Cisco IOS routers. They have a playbook that uses the ios_config module with the 'src' parameter pointing to a Jinja2 template. The playbook runs successfully for months, but after a recent IOS upgrade on a subset of routers, the playbook fails with 'ERROR! Syntax error while loading YAML script'. The template has not been changed. What is the most likely cause?
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 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
The IOS upgrade changed the output of a 'show' command that is used to set a fact, and that fact now contains characters that break YAML syntax.
The error 'Syntax error while loading YAML script' suggests that the playbook itself has a YAML syntax issue, not the template. However, if the template is included in the playbook via a variable that contains special characters, it could cause a YAML parsing error. But since the template hasn't changed, the most likely cause is that the IOS upgrade changed the output of a command that is used to generate a fact, and that fact is now being passed to the template in a way that breaks YAML. Alternatively, the playbook might be using a 'vars_prompt' or 'set_fact' that now produces invalid YAML.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 IOS upgrade changed the output of a 'show' command that is used to set a fact, and that fact now contains characters that break YAML syntax.
Why this is correct
If a fact contains newlines or special characters, it can cause YAML parsing errors when the playbook tries to process it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
The Jinja2 template now contains syntax errors because the IOS upgrade changed the configuration requirements.
Why it's wrong here
The error message specifically says YAML script error, not a Jinja2 template error.
- ✗
The ios_config module is incompatible with the new IOS version.
Why it's wrong here
Module incompatibility would cause a different error, such as 'module not found' or 'unable to parse response'.
- ✗
The playbook file was corrupted during the IOS upgrade process.
Why it's wrong here
The IOS upgrade is performed on the routers, not on the Ansible control node; the playbook file is unaffected.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this 350-401 question test?
Ansible Automation — This question tests Ansible Automation — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The IOS upgrade changed the output of a 'show' command that is used to set a fact, and that fact now contains characters that break YAML syntax. — The error 'Syntax error while loading YAML script' suggests that the playbook itself has a YAML syntax issue, not the template. However, if the template is included in the playbook via a variable that contains special characters, it could cause a YAML parsing error. But since the template hasn't changed, the most likely cause is that the IOS upgrade changed the output of a command that is used to generate a fact, and that fact is now being passed to the template in a way that breaks YAML. Alternatively, the playbook might be using a 'vars_prompt' or 'set_fact' that now produces invalid YAML.
What should I do if I get this 350-401 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 18, 2026
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