- A
PAT is not assigning unique source ports; both translations use port 80, which will cause conflicts.
In PAT, the router should change the source port to a unique value. Both translations showing the same inside global port 80 indicates a problem.
- B
The NAT pool is misconfigured because it uses the interface address.
Why wrong: Using the interface address for PAT is valid.
- C
The inside and outside interfaces are swapped.
Why wrong: The statistics show correct interface assignment.
- D
Static NAT is interfering with dynamic NAT.
Why wrong: No static translations are present.
Question 1,476 of 2,152
How to Identify and Fix PAT Port Conflicts in NAT Translations
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.
A network engineer runs the following command on Router R1:
R1# show ip nat translations
Pro Inside global Inside local Outside local Outside global tcp 192.0.2.10:80 10.0.0.10:80 203.0.113.5:12345 203.0.113.5:12345 tcp 192.0.2.10:80 10.0.0.11:80 203.0.113.5:67890 203.0.113.5:67890
R1# show ip nat statistics
Total active translations: 2 (0 static, 2 dynamic; 2 extended) Outside interfaces: GigabitEthernet0/1 Inside interfaces: GigabitEthernet0/0 Hits: 50 Misses: 0 CEF Translated packets: 50, CEF Punted packets: 0 Expired translations: 0 Dynamic mappings: -- Inside Source
[Id] ip nat inside source list ACL1 interface GigabitEthernet0/1 overload
refcount 2
Based on this output, what is the problem?
Quick Answer
The answer is that PAT is failing to assign unique source ports, creating a port conflict that will break connectivity. When troubleshooting PAT port conflict in show ip nat translations, the key issue is that both inside hosts (10.0.0.10 and 10.0.0.11) share the same inside global address 192.0.2.10 and the same port 80, which violates how Port Address Translation operates. PAT must translate the source port to a unique high-numbered port for each session to distinguish between multiple internal hosts using the same global IP; identical ports mean the router cannot correctly return traffic to the correct internal host. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of NAT overload behavior and the importance of unique port allocation—a common trap is assuming two identical translations are fine because they show different outside ports. Remember the memory tip: "PAT needs a unique port per host, or return traffic gets lost."
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
✓
PAT is not assigning unique source ports; both translations use port 80, which will cause conflicts.
The output shows two dynamic NAT translations mapping different inside local hosts (10.0.0.10 and 10.0.0.11) to the same inside global IP address (192.0.2.10) and the same source port (80). PAT (Port Address Translation) should assign unique source ports to differentiate the sessions, but here both translations use port 80, which will cause conflicts when return traffic arrives because the router cannot determine which inside host should receive the packet. This indicates a misconfiguration or a bug where PAT is not performing port overload correctly.
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.
- ✓
PAT is not assigning unique source ports; both translations use port 80, which will cause conflicts.
Why this is correct
In PAT, the router should change the source port to a unique value. Both translations showing the same inside global port 80 indicates a problem.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The NAT pool is misconfigured because it uses the interface address.
Why it's wrong here
Using the interface address for PAT is valid.
- ✗
The inside and outside interfaces are swapped.
Why it's wrong here
The statistics show correct interface assignment.
- ✗
Static NAT is interfering with dynamic NAT.
Why it's wrong here
No static translations are present.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that PAT always works automatically without verifying unique port assignments, leading candidates to overlook the duplicate port issue in the translation output.
Trap categories for this question
Command / output trap
The statistics show correct interface assignment.
Detailed technical explanation
How to think about this question
PAT relies on the transport-layer port number (TCP or UDP) to multiplex multiple inside hosts to a single public IP address. According to RFC 2663, the NAT device must translate the source port to a unique value for each session, typically from a high port range (e.g., 1024-65535). In this scenario, both translations show the same source port 80, which violates PAT behavior; this could occur if the ACL matches only the IP address and not the port, or if the router's PAT feature is not enabled properly. In a real-world scenario, this would cause asymmetric routing and session failures for HTTP traffic.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
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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 — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: PAT is not assigning unique source ports; both translations use port 80, which will cause conflicts. — The output shows two dynamic NAT translations mapping different inside local hosts (10.0.0.10 and 10.0.0.11) to the same inside global IP address (192.0.2.10) and the same source port (80). PAT (Port Address Translation) should assign unique source ports to differentiate the sessions, but here both translations use port 80, which will cause conflicts when return traffic arrives because the router cannot determine which inside host should receive the packet. This indicates a misconfiguration or a bug where PAT is not performing port overload correctly.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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