Question 1,366 of 2,152

NAT and PAT →mediumMultiple ChoiceObjective-mapped

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.

A network engineer is troubleshooting connectivity from a host inside a corporate network to a public web server. The host has IP 10.1.1.10/24, and the router's outside interface is 203.0.113.1/24. The engineer configured a dynamic NAT pool (203.0.113.10-203.0.113.20) and an access list permitting 10.1.1.0/24. However, traffic from the host fails. A 'show ip nat translations' reveals no translations. 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.

A
The NAT pool is exhausted.
Why wrong: Incorrect because the pool has 11 addresses, and only one host is trying to translate; no translations appear at all, not a pool exhaustion issue.
B
The 'ip nat inside' and 'ip nat outside' commands are misapplied on the interfaces.
Why wrong: Incorrect because if the interfaces are not correctly designated, translations might still appear but traffic would not flow; however, no translations at all suggests the ACL is the issue.
C
The access list used in the NAT configuration does not match the source IP of the host.
Correct because dynamic NAT requires the ACL to match the source; if the ACL is misconfigured (e.g., denies the subnet), no translations are created.
D
The host's default gateway is not the router's inside interface.
Why wrong: Incorrect because even if the gateway is wrong, the router would still see the traffic and attempt NAT if the ACL matches; no translations indicate a different issue.

Full breakdown with real-world context →

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 access list used in the NAT configuration does not match the source IP of the host.

While the ACL appears to permit the source IP range (10.1.1.0/24), the most likely cause is that the ACL is not correctly applied to the NAT process. The `ip nat inside source list` command must reference the specific ACL number or name. If misreferenced or omitted, NAT will not see any traffic to translate, hence no translations appear in the table. Other options are less likely because the pool has available addresses (A), interface commands might be correct but not the cause (B), and default gateway issues would not prevent translations but cause routing failures (D).

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 NAT pool is exhausted.
Why it's wrong here
Incorrect because the pool has 11 addresses, and only one host is trying to translate; no translations appear at all, not a pool exhaustion issue.
✗
The 'ip nat inside' and 'ip nat outside' commands are misapplied on the interfaces.
Why it's wrong here
Incorrect because if the interfaces are not correctly designated, translations might still appear but traffic would not flow; however, no translations at all suggests the ACL is the issue.
✓
The access list used in the NAT configuration does not match the source IP of the host.
Why this is correct
Correct because dynamic NAT requires the ACL to match the source; if the ACL is misconfigured (e.g., denies the subnet), no translations are created.
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 host's default gateway is not the router's inside interface.
Why it's wrong here
Incorrect because even if the gateway is wrong, the router would still see the traffic and attempt NAT if the ACL matches; no translations indicate a different issue.

Common exam traps

Common exam trap: answer the scenario, not the keyword

A common trap in Cisco NAT questions is that candidates see 'no translations' and immediately blame interface configuration or pool exhaustion, without verifying that the access list used in the NAT command actually matches the source traffic. Even when the ACL appears to permit the correct subnet, a small typo or incorrect wildcard mask can cause the match to fail.

Detailed technical explanation

How to think about this question

Dynamic NAT uses an access list to identify which source IPs are eligible for translation; if the access list does not permit the host's source IP, the router will not create a NAT entry. Under the hood, the router checks the access list during the first packet of a flow; if the source IP is denied, the packet is forwarded without translation. In real-world scenarios, engineers often forget to include the correct wildcard mask or accidentally use a standard access list with a reversed permit statement, leading to silent failure.

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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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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: The access list used in the NAT configuration does not match the source IP of the host. — While the ACL appears to permit the source IP range (10.1.1.0/24), the most likely cause is that the ACL is not correctly applied to the NAT process. The `ip nat inside source list` command must reference the specific ACL number or name. If misreferenced or omitted, NAT will not see any traffic to translate, hence no translations appear in the table. Other options are less likely because the pool has available addresses (A), interface commands might be correct but not the cause (B), and default gateway issues would not prevent translations but cause routing failures (D).

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.

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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