Question 1,825 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 is troubleshooting NAT for a web server that is reachable from the internet via a static NAT mapping 203.0.113.20 to 10.0.0.20. The server responds to HTTP requests, but the engineer cannot SSH to the server from the internet. 'Show ip nat translations' shows the static entry. The router's ACL on the outside interface permits TCP port 22 to 203.0.113.20. 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 server's default gateway is not the router's inside interface.
Why wrong: Incorrect because if the gateway were wrong, HTTP would also fail; the issue is protocol-specific.
B
The router's NAT is not translating the return traffic for SSH because the server sends packets with a different source IP.
Correct because if the server has multiple IPs or a different source IP for SSH responses (e.g., from a loopback), the router may not translate that source IP back to 203.0.113.20, breaking the session.
C
The SSH service is not running on the server.
Why wrong: Incorrect because the engineer can test with a different protocol; the issue is likely NAT-related.
D
The router's ACL is blocking SSH traffic despite the permit statement.
Why wrong: Incorrect because the ACL is configured to permit; if it were blocking, HTTP would also be affected if the ACL were misapplied.

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 router's NAT is not translating the return traffic for SSH because the server sends packets with a different source IP.

The static NAT entry maps 203.0.113.20 to 10.0.0.20 only for inbound traffic. When the server responds to SSH, it uses its own IP (10.0.0.20) as the source, not the mapped public IP. The router does not translate the source address of the return packet back to 203.0.113.20 because there is no outbound NAT rule for that traffic. The SSH client on the internet receives a reply from 10.0.0.20 instead of 203.0.113.20 and drops it. HTTP works because the server's HTTP response may be subject to a different NAT rule or the client is tolerant of mismatched source addresses, but typically the same issue would occur unless the server uses the public IP as its source for all traffic. The default gateway is correct since the server can send traffic out. The ACL permits SSH, so that is not the issue. Therefore, the most likely cause is that the router is not translating the return traffic for SSH because the server sends packets with a different source IP.

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 server's default gateway is not the router's inside interface.
Why it's wrong here
Incorrect because if the gateway were wrong, HTTP would also fail; the issue is protocol-specific.
✓
The router's NAT is not translating the return traffic for SSH because the server sends packets with a different source IP.
Why this is correct
Correct because if the server has multiple IPs or a different source IP for SSH responses (e.g., from a loopback), the router may not translate that source IP back to 203.0.113.20, breaking the session.
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 SSH service is not running on the server.
Why it's wrong here
Incorrect because the engineer can test with a different protocol; the issue is likely NAT-related.
✗
The router's ACL is blocking SSH traffic despite the permit statement.
Why it's wrong here
Incorrect because the ACL is configured to permit; if it were blocking, HTTP would also be affected if the ACL were misapplied.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that a static NAT entry automatically handles return traffic for all protocols, when in fact the router only translates packets that match the NAT rule's direction; the trap here is assuming that because HTTP works, SSH must work the same way, ignoring that the server's response source IP must be translated back to the public IP.

Detailed technical explanation

How to think about this question

Static NAT translates inbound packets from the outside IP to the inside IP, but the router does not automatically translate the source IP of return packets unless the inside host sends traffic through the router with a source IP matching the NAT rule. For SSH, the server's reply uses its own IP (10.0.0.20) as the source, so the router sees an untranslated packet and forwards it with the private source IP, which the internet client discards. This is why 'ip nat inside source static' must be paired with proper routing or 'ip nat outside source' for symmetric NAT behavior.

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.

Related 300-410 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Layer 3 Technologies practice questions

Practise 300-410 questions linked to Layer 3 Technologies.

EIGRP Troubleshooting practice questions

Practise 300-410 questions linked to EIGRP Troubleshooting.

OSPF Troubleshooting (v2/v3) practice questions

Practise 300-410 questions linked to OSPF Troubleshooting (v2/v3).

BGP Troubleshooting practice questions

Practise 300-410 questions linked to BGP Troubleshooting.

Route Redistribution practice questions

Practise 300-410 questions linked to Route Redistribution.

Policy-Based Routing (PBR) practice questions

Practise 300-410 questions linked to Policy-Based Routing (PBR).

VRF-Lite practice questions

Practise 300-410 questions linked to VRF-Lite.

Route Maps and Route Filtering practice questions

Practise 300-410 questions linked to Route Maps and Route Filtering.

Administrative Distance practice questions

Practise 300-410 questions linked to Administrative Distance.

Route Summarization practice questions

Practise 300-410 questions linked to Route Summarization.

Bidirectional Forwarding Detection (BFD) practice questions

Practise 300-410 questions linked to Bidirectional Forwarding Detection (BFD).

VPN Technologies practice questions

Practise 300-410 questions linked to VPN Technologies.

Practice this exam

Start a free 300-410 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

300-410 practice-test guide →Study guide →Browse all practice tests

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 router's NAT is not translating the return traffic for SSH because the server sends packets with a different source IP. — The static NAT entry maps 203.0.113.20 to 10.0.0.20 only for inbound traffic. When the server responds to SSH, it uses its own IP (10.0.0.20) as the source, not the mapped public IP. The router does not translate the source address of the return packet back to 203.0.113.20 because there is no outbound NAT rule for that traffic. The SSH client on the internet receives a reply from 10.0.0.20 instead of 203.0.113.20 and drops it. HTTP works because the server's HTTP response may be subject to a different NAT rule or the client is tolerant of mismatched source addresses, but typically the same issue would occur unless the server uses the public IP as its source for all traffic. The default gateway is correct since the server can send traffic out. The ACL permits SSH, so that is not the issue. Therefore, the most likely cause is that the router is not translating the return traffic for SSH because the server sends packets with a different source IP.

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.

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Keep practising

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.