- A
PAT is working correctly, translating multiple inside hosts to one outside IP.
Each inside host gets a unique source port on the outside IP.
- B
NAT is failing because the outside address is the same for all.
Why wrong: That is expected in PAT.
- C
The translations are static.
Why wrong: Static translations would not show port changes.
- D
The inside hosts are using the same port numbers.
Why wrong: They are using different ports (1234, 1235, 80).
Question 437 of 2,152
Debug IP NAT Overload
This 300-410 practice question tests your understanding of nat and pat. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 to debug NAT with overload:
R1# debug ip nat overload
NAT: overload: s=10.1.1.1:1234->203.0.113.1:5678, d=192.168.1.1:80 [50] NAT: overload: s=10.1.1.1:1235->203.0.113.1:5679, d=192.168.1.1:80 [51] NAT: overload: s=10.1.1.2:80->203.0.113.1:5680, d=192.168.1.1:1024 [52]
What does this output indicate?
Quick Answer
The answer is that PAT is working correctly, translating multiple inside hosts to a single outside IP address. This is evident because the debug ip nat overload output shows three different inside local addresses—10.1.1.1 and 10.1.1.2—each with unique source ports, all being mapped to the same outside global address 203.0.113.1 but with distinct port numbers (5678, 5679, 5680). This is the core behavior of NAT overload, also known as Port Address Translation (PAT), where the router uses layer 4 port information to multiplex many private hosts behind one public IP. On the Cisco CCNP ENARSI 300-410 exam, this command tests your ability to verify PAT operation and distinguish it from static or dynamic NAT; a common trap is misreading the output as an error when you see multiple translations, but the different ports confirm normal PAT. Remember the memory tip: “Same IP, different port—PAT is doing its job.”
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 working correctly, translating multiple inside hosts to one outside IP.
The debug output shows PAT (Port Address Translation) functioning correctly: three distinct inside local addresses (10.1.1.1:1234, 10.1.1.1:1235, 10.1.1.2:80) are being translated to the same outside global address (203.0.113.1) but with unique port numbers (5678, 5679, 5680). This is the essence of NAT with overload, where multiple inside hosts share a single public IP by multiplexing on Layer 4 ports.
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 working correctly, translating multiple inside hosts to one outside IP.
Why this is correct
Each inside host gets a unique source port on the outside IP.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
NAT is failing because the outside address is the same for all.
Why it's wrong here
That is expected in PAT.
- ✗
The translations are static.
Why it's wrong here
Static translations would not show port changes.
- ✗
The inside hosts are using the same port numbers.
Why it's wrong here
They are using different ports (1234, 1235, 80).
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that NAT with overload is 'failing' when multiple inside hosts share the same outside IP, leading candidates to incorrectly select Option B, when in fact this is the intended behavior of PAT.
Trap categories for this question
Command / output trap
Static translations would not show port changes.
Detailed technical explanation
How to think about this question
PAT (NAT overload) relies on the TCP/UDP port space (0–65535) to differentiate sessions, allowing up to ~65,000 concurrent translations per public IP. The debug output uses the format 's=original→translated, d=destination' with a sequence number in brackets; the fact that all three translations use the same destination IP (192.168.1.1) but different source ports demonstrates how PAT maintains session uniqueness. In real-world deployments, PAT is critical for conserving IPv4 addresses, but it can break protocols that embed IP addresses in the payload (e.g., FTP, SIP) unless ALG support is configured.
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
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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 working correctly, translating multiple inside hosts to one outside IP. — The debug output shows PAT (Port Address Translation) functioning correctly: three distinct inside local addresses (10.1.1.1:1234, 10.1.1.1:1235, 10.1.1.2:80) are being translated to the same outside global address (203.0.113.1) but with unique port numbers (5678, 5679, 5680). This is the essence of NAT with overload, where multiple inside hosts share a single public IP by multiplexing on Layer 4 ports.
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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