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.

Question 1mediummultiple choice

Study the full ACL explanation →

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.

If the ACL and NAT configuration are correct, the issue might be that the host's traffic is not reaching the router's inside interface, or the router is not processing the traffic due to a routing or interface issue. However, since other hosts work, the problem is specific to that host.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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
CIDR notation defines the prefix length.
✗
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: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.

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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 — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The host has a misconfigured subnet mask or default gateway. — If the ACL and NAT configuration are correct, the issue might be that the host's traffic is not reaching the router's inside interface, or the router is not processing the traffic due to a routing or interface issue. However, since other hosts work, the problem is specific to that host.

What should I do if I get this 300-410 question wrong?

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?

CIDR notation defines the prefix length.

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