200-901 Application Deployment and Security Practice Question
This 200-901 practice question tests your understanding of application deployment and security. 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 Python script using the Cisco ACI Toolkit (aciToolkit) fails with 'LoginError: unable to login to APIC'. The APIC is reachable via HTTPS. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The script uses an incorrect APIC domain (e.g., 'apic' instead of the FQDN).
The Cisco ACI Toolkit (aciToolkit) requires the APIC domain to be specified as a fully qualified domain name (FQDN) or IP address that matches the APIC's certificate. Using a short name like 'apic' instead of the FQDN (e.g., 'apic.example.com') causes a TLS certificate hostname mismatch, leading to a login failure even though the APIC is reachable. The 'LoginError: unable to login to APIC' error typically indicates an authentication or connectivity issue, and in this scenario, the certificate validation fails because the toolkit verifies the server's hostname against the certificate's Subject Alternative Name (SAN).
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 APIC has reached its maximum session limit.
Why it's wrong here
Session limit would produce a different error (e.g., 'max sessions reached'), and is less common than configuration errors.
✗
The script uses HTTP instead of HTTPS.
Why it's wrong here
The aciToolkit defaults to HTTPS and will raise a different error if HTTP is forced.
✓
The script uses an incorrect APIC domain (e.g., 'apic' instead of the FQDN).
Why this is correct
The aciToolkit's login() requires the correct APIC domain; an incorrect domain prevents proper authentication.
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 APIC is running an unsupported firmware version.
Why it's wrong here
Firmware version is not a direct cause of login failure; the toolkit supports a range of versions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the nuance that a reachable APIC via HTTPS does not guarantee successful login if the hostname in the script does not match the APIC's TLS certificate, leading candidates to overlook certificate validation as the root cause.
Detailed technical explanation
How to think about this question
The aciToolkit uses the Cobra SDK under the hood, which performs a REST API login to the APIC using HTTPS. During the TLS handshake, the toolkit validates the server certificate's CN or SAN against the provided hostname; a mismatch (e.g., using a short name instead of FQDN) triggers a certificate verification failure, raising a LoginError. In real-world deployments, APIC certificates are often issued for the FQDN, so using an IP address or short hostname requires either a matching certificate or disabling certificate verification (not recommended).
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Application Deployment and Security — This question tests Application Deployment and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The script uses an incorrect APIC domain (e.g., 'apic' instead of the FQDN). — The Cisco ACI Toolkit (aciToolkit) requires the APIC domain to be specified as a fully qualified domain name (FQDN) or IP address that matches the APIC's certificate. Using a short name like 'apic' instead of the FQDN (e.g., 'apic.example.com') causes a TLS certificate hostname mismatch, leading to a login failure even though the APIC is reachable. The 'LoginError: unable to login to APIC' error typically indicates an authentication or connectivity issue, and in this scenario, the certificate validation fails because the toolkit verifies the server's hostname against the certificate's Subject Alternative Name (SAN).
What should I do if I get this 200-901 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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