Question 569 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.

An engineer configures NAT on a router with 'ip nat inside source list 1 interface GigabitEthernet0/0 overload'. The inside hosts are 10.0.0.0/24, and the outside interface is 203.0.113.1. Traffic works for most hosts, but one host at 10.0.0.50 cannot access the internet. 'Show ip nat translations' shows no entry for this host. 'Show access-lists' shows ACL 1 permits 10.0.0.0 0.0.0.255. 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 host's IP address is statically assigned and conflicts with another device.
Why wrong: Incorrect because an IP conflict would cause intermittent issues, but the host would still send traffic; the router would see the traffic and attempt NAT.
B
The host has a misconfigured subnet mask or default gateway.
Correct because if the host's default gateway is not the router's inside interface (or subnet mask is wrong), the host will not send traffic to the router, so no NAT translation is attempted.
C
The NAT pool is exhausted.
Why wrong: Incorrect because other hosts work, so ports are available; no translation for this host means its traffic never reaches the NAT process.
D
The router's inside interface is administratively down.
Why wrong: Incorrect because if the interface were down, no hosts would work; the issue is host-specific.

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 host has a misconfigured subnet mask or default gateway.

Option B is correct because the host at 10.0.0.50 is within the ACL 1 permitted range, yet no NAT translation appears, indicating the traffic never reaches the NAT process. A misconfigured subnet mask or default gateway on the host would cause its packets to be sent to the wrong next-hop or be dropped locally, preventing the router from seeing the traffic and creating a translation. Since 'show ip nat translations' shows no entry, the issue is upstream of NAT, pointing to a host-side configuration problem.

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 host's IP address is statically assigned and conflicts with another device.
Why it's wrong here
Incorrect because an IP conflict would cause intermittent issues, but the host would still send traffic; the router would see the traffic and attempt NAT.
✓
The host has a misconfigured subnet mask or default gateway.
Why this is correct
Correct because if the host's default gateway is not the router's inside interface (or subnet mask is wrong), the host will not send traffic to the router, so no NAT translation is attempted.
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 NAT pool is exhausted.
Why it's wrong here
Incorrect because other hosts work, so ports are available; no translation for this host means its traffic never reaches the NAT process.
✗
The router's inside interface is administratively down.
Why it's wrong here
Incorrect because if the interface were down, no hosts would work; the issue is host-specific.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that a missing NAT translation automatically implies a NAT configuration or ACL issue, when in fact the root cause is often a host-side misconfiguration that prevents traffic from reaching the router in the first place.

Detailed technical explanation

How to think about this question

NAT relies on the router receiving packets with a source IP matching the ACL; if the host's default gateway is misconfigured (e.g., pointing to a non-existent or different router), packets never reach the NAT router. Similarly, a wrong subnet mask (e.g., /16 instead of /24) could cause the host to believe the destination is local and attempt an ARP request instead of forwarding to the gateway. In real-world scenarios, this is a common troubleshooting step: verify host IP configuration before investigating NAT issues, as 'show ip nat translations' absence often indicates the traffic never arrived.

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 host has a misconfigured subnet mask or default gateway. — Option B is correct because the host at 10.0.0.50 is within the ACL 1 permitted range, yet no NAT translation appears, indicating the traffic never reaches the NAT process. A misconfigured subnet mask or default gateway on the host would cause its packets to be sent to the wrong next-hop or be dropped locally, preventing the router from seeing the traffic and creating a translation. Since 'show ip nat translations' shows no entry, the issue is upstream of NAT, pointing to a host-side configuration problem.

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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