Question 2,059 of 2,152

NAT and PAT →hardMultiple 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 runs the following command to troubleshoot PAT exhaustion:

R1# show ip nat statistics

Total active translations: 1024 (0 static, 1024 dynamic; 1024 extended) Outside interfaces: GigabitEthernet0/1 Inside interfaces: GigabitEthernet0/0 Hits: 50000 Misses: 10 CEF Translated packets: 45000, CEF Punted packets: 5000 Expired translations: 2000 Dynamic mappings: -- Inside Source

[Id: 1] access-list NAT permit ip 10.0.0.0 0.255.255.255 any

refcount 1024, pool MyPool pool MyPool: netmask 255.255.255.240 start 203.0.113.1 end 203.0.113.14 type generic, total addresses 14, allocated 14 (100%), misses 0

What is the most likely issue?

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 pool is exhausted; PAT is using all addresses, but port exhaustion may occur.
All 14 addresses are allocated, meaning PAT is using them, but with 1024 translations, ports may be running out.
B
The access list is misconfigured, blocking traffic.
Why wrong: The access list is correct; it matches the inside network.
C
The outside interface is down.
Why wrong: No indication of interface issues.
D
Static translations are missing.
Why wrong: Static translations are not needed here.

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 pool is exhausted; PAT is using all addresses, but port exhaustion may occur.

The output shows that the NAT pool 'MyPool' has 14 addresses, all of which are allocated (100% usage), and there are 1024 active translations. With only 14 public IPs, PAT can theoretically support up to 14 * 65535 = 917,490 ports, but the pool exhaustion indicates that all addresses are in use, and the high number of translations suggests that port exhaustion is imminent or occurring, as each address can only handle a finite number of simultaneous sessions before ports are exhausted.

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 pool is exhausted; PAT is using all addresses, but port exhaustion may occur.
Why this is correct
All 14 addresses are allocated, meaning PAT is using them, but with 1024 translations, ports may be running out.
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 access list is misconfigured, blocking traffic.
Why it's wrong here
The access list is correct; it matches the inside network.
✗
The outside interface is down.
Why it's wrong here
No indication of interface issues.
✗
Static translations are missing.
Why it's wrong here
Static translations are not needed here.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that PAT exhaustion only occurs when the pool has a single address, but here the trap is that even with multiple addresses, all can be fully allocated, leading to port exhaustion per address.

Detailed technical explanation

How to think about this question

PAT (Port Address Translation) uses a single public IP address to map multiple private IPs by differentiating sessions via source port numbers. With 14 addresses in the pool, each can handle up to 65,535 ports (minus reserved ports), but real-world constraints like TCP timestamps or application-specific port limits can reduce this. The 'misses' counter of 10 indicates that some packets failed to find a NAT entry, which could be due to port exhaustion or pool depletion, and the 100% allocation confirms the pool is fully utilized.

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 pool is exhausted; PAT is using all addresses, but port exhaustion may occur. — The output shows that the NAT pool 'MyPool' has 14 addresses, all of which are allocated (100% usage), and there are 1024 active translations. With only 14 public IPs, PAT can theoretically support up to 14 * 65535 = 917,490 ports, but the pool exhaustion indicates that all addresses are in use, and the high number of translations suggests that port exhaustion is imminent or occurring, as each address can only handle a finite number of simultaneous sessions before ports are exhausted.

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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