Question 227 of 2,015

NAT and DHCP →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is asymmetric routing causing NAT return traffic failure. This occurs when the outbound packet traverses a router performing NAT, which creates a translation entry for the source IP, but the return traffic from the remote server takes a different physical path that bypasses that same router. Without the return traffic passing through the NAT device, the router cannot reverse the translation, so the destination IP in the response remains the original public address, which the internal host cannot process, leading to a timeout. On the ENCOR 350-401 exam, this scenario tests your understanding that stateful NAT requires symmetric routing—both directions must flow through the same translator. A common trap is assuming a valid outbound translation guarantees a working session; the missing inbound translation is the red flag. Remember the memory tip: “NAT is a two-way street—if return traffic takes a detour, the session is incomplete.”

350-401 NAT and DHCP Practice Question

This 350-401 practice question tests your understanding of nat and dhcp. 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 a NAT issue where an internal host cannot establish an SSH session to a remote server on the internet. The engineer checks the NAT translations on the border router and sees that the translation for the host's source IP is present. However, the SSH session times out. The engineer also notices that the remote server's IP is not in the NAT translation table. 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 1hardmultiple choice

Read the full NAT/PAT explanation →

A
The router is performing NAT only for the source IP, but the return traffic is taking a different path that does not go through the NAT router.
Correct because if the return traffic does not pass through the same NAT router, the router will not create an inbound translation entry, and the packet will not be translated back to the private IP.
B
The SSH server is blocking connections from the public IP address.
Why wrong: Incorrect because the SSH session would still attempt to establish; the timeout indicates a routing/translation issue, not a firewall block.
C
The NAT overload is causing port conflicts for SSH.
Why wrong: Incorrect because SSH uses a specific port (22), and PAT can handle multiple SSH sessions by using different source ports.
D
The access list used for NAT is denying the SSH traffic.
Why wrong: Incorrect because if the access list denied SSH, no translation would be created at all.

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 is performing NAT only for the source IP, but the return traffic is taking a different path that does not go through the NAT router.

For a successful NAT session, both the outbound and inbound translations must be present. If only the outbound translation exists, the return traffic is not being translated back correctly, possibly due to asymmetric routing or a missing route.

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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 router is performing NAT only for the source IP, but the return traffic is taking a different path that does not go through the NAT router.
Why this is correct
Correct because if the return traffic does not pass through the same NAT router, the router will not create an inbound translation entry, and the packet will not be translated back to the private IP.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The SSH server is blocking connections from the public IP address.
Why it's wrong here
Incorrect because the SSH session would still attempt to establish; the timeout indicates a routing/translation issue, not a firewall block.
✗
The NAT overload is causing port conflicts for SSH.
Why it's wrong here
Incorrect because SSH uses a specific port (22), and PAT can handle multiple SSH sessions by using different source ports.
✗
The access list used for NAT is denying the SSH traffic.
Why it's wrong here
Incorrect because if the access list denied SSH, no translation would be created at all.

Common exam traps

Common exam trap: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-401 NAT questions on configuration and troubleshooting.

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FAQ

Questions learners often ask

What does this 350-401 question test?

NAT and DHCP — This question tests NAT and DHCP — Static NAT maps one inside address to one outside address..

What is the correct answer to this question?

The correct answer is: The router is performing NAT only for the source IP, but the return traffic is taking a different path that does not go through the NAT router. — For a successful NAT session, both the outbound and inbound translations must be present. If only the outbound translation exists, the return traffic is not being translated back correctly, possibly due to asymmetric routing or a missing route.

What should I do if I get this 350-401 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?

Static NAT maps one inside address to one outside address.

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