200-901 Software Development and Design Practice Question
This 200-901 practice question tests your understanding of software development and design. 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 developer is working on a Python application that automates the configuration of multiple Cisco IOS-XE devices using RESTCONF. The application uses the requests library. The developer notices that sometimes the PUT request to update the interface description returns a 409 Conflict error. Upon investigation, the developer finds that the issue occurs when two instances of the application are running concurrently and attempt to update the same interface. The developer wants to implement a strategy to avoid conflicts. Which approach is most effective?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a distributed lock mechanism to ensure exclusive access
A 409 Conflict indicates that the resource was modified by another request. A distributed lock ensures exclusive access, preventing concurrent updates. Option A (retry with backoff) might eventually succeed but does not prevent conflicts and could increase server load. Option C (PATCH) does not solve the underlying concurrency issue. Option D (timestamp force overwrite) is not standard with RESTCONF and could lead to data loss.
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.
✗
Implement a retry mechanism with exponential backoff and random jitter
Why it's wrong here
Retries can reduce collisions but do not prevent them, and may still fail under heavy concurrency.
✓
Use a distributed lock mechanism to ensure exclusive access
Why this is correct
A lock guarantees that only one instance modifies the resource at a time, eliminating conflicts.
Related concept
Static NAT maps one inside address to one outside address.
✗
Change the PUT to PATCH and hope for partial updates
Why it's wrong here
PATCH can also conflict; the method change does not address concurrency.
✗
Use a timestamp in the request to force overwrite
Why it's wrong here
RESTCONF does not typically support last-write-wins; forcing overwrite may cause data inconsistency.
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 200-901 NAT questions on configuration and troubleshooting.
Software Development and Design — This question tests Software Development and Design — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use a distributed lock mechanism to ensure exclusive access — A 409 Conflict indicates that the resource was modified by another request. A distributed lock ensures exclusive access, preventing concurrent updates. Option A (retry with backoff) might eventually succeed but does not prevent conflicts and could increase server load. Option C (PATCH) does not solve the underlying concurrency issue. Option D (timestamp force overwrite) is not standard with RESTCONF and could lead to data loss.
What should I do if I get this 200-901 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 200-901 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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