- A
The pool has only one IP address, and the router is reusing ports for different hosts.
Why wrong: Incorrect because PAT should assign different ports even with one IP; reusing the same port for different hosts would cause conflicts and is not normal behavior.
- B
The 'ip nat inside source' command is missing the 'overload' keyword.
Why wrong: Incorrect because 'overload' is configured; the issue is not about missing overload.
- C
The router is not performing PAT correctly because the ACL permits more than the pool can handle.
Why wrong: Incorrect because PAT should still assign unique ports; the issue is likely a bug or misconfiguration.
- D
The router has a configuration that uses 'ip nat inside source static' for some hosts, conflicting with the dynamic pool.
Correct because if a static NAT entry maps a host to the same public IP as the pool, and the static entry does not use port translation, it can cause conflicts with dynamic entries.
300-410 NAT and PAT Practice Question
This 300-410 practice question tests your understanding of nat and pat. 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.
An engineer configures NAT on a router with 'ip nat inside source list 1 pool POOL overload' where POOL contains 203.0.113.1-203.0.113.5. The inside hosts are 10.0.0.0/24. Traffic works, but the engineer notices that some hosts are assigned the same public IP and port, causing conflicts. 'Show ip nat translations' shows entries with the same inside global IP and port for different inside local hosts. 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 router has a configuration that uses 'ip nat inside source static' for some hosts, conflicting with the dynamic pool.
PAT with a pool should assign unique ports per session. If two different inside hosts use the same source port and are mapped to the same public IP, the router should still assign a different port. However, if the pool has only one IP or the ports are exhausted, conflicts can occur. The most likely cause is that the pool has only one IP and the port range is exhausted, but the symptom shows the same IP and port, which indicates a misconfiguration.
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 pool has only one IP address, and the router is reusing ports for different hosts.
Why it's wrong here
Incorrect because PAT should assign different ports even with one IP; reusing the same port for different hosts would cause conflicts and is not normal behavior.
- ✗
The 'ip nat inside source' command is missing the 'overload' keyword.
Why it's wrong here
Incorrect because 'overload' is configured; the issue is not about missing overload.
- ✗
The router is not performing PAT correctly because the ACL permits more than the pool can handle.
Why it's wrong here
Incorrect because PAT should still assign unique ports; the issue is likely a bug or misconfiguration.
- ✓
The router has a configuration that uses 'ip nat inside source static' for some hosts, conflicting with the dynamic pool.
Why this is correct
Correct because if a static NAT entry maps a host to the same public IP as the pool, and the static entry does not use port translation, it can cause conflicts with dynamic entries.
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.
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 300-410 NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this 300-410 question test?
NAT and PAT — This question tests NAT and PAT — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The router has a configuration that uses 'ip nat inside source static' for some hosts, conflicting with the dynamic pool. — PAT with a pool should assign unique ports per session. If two different inside hosts use the same source port and are mapped to the same public IP, the router should still assign a different port. However, if the pool has only one IP or the ports are exhausted, conflicts can occur. The most likely cause is that the pool has only one IP and the port range is exhausted, but the symptom shows the same IP and port, which indicates a misconfiguration.
What should I do if I get this 300-410 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 300-410 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 19, 2026
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