Question 280 of 2,152

NAT and PAT →hardMultiple ChoiceObjective-mapped

Understanding Static NAT Limitations for Outbound Traffic

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 static NAT on a router to map a public IP 203.0.113.5 to an internal server 10.0.0.5. The configuration includes 'ip nat inside source static 10.0.0.5 203.0.113.5'. The server is reachable from the outside, but the server cannot initiate connections to the outside network. 'Show ip nat translations' shows the static entry. 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, the server would not send traffic to the router at all; the issue is that traffic reaches the router but is not translated.
B
The 'ip nat outside' command is missing on the outside interface.
Why wrong: Incorrect because the static entry is for inbound traffic; outbound traffic from the server would need a separate NAT rule (like PAT) to translate the source.
C
Static NAT does not translate the source IP for outbound traffic initiated by the inside host.
Correct because static NAT only translates destination IP for inbound traffic; for outbound, the source remains private unless additional NAT (e.g., overload) is configured for that host.
D
The router's routing table does not have a route back to the server's subnet.
Why wrong: Incorrect because the server is directly connected, so the router has a connected route; the issue is translation, not routing.

Full breakdown with real-world context →

Quick Answer

The answer is that static NAT does not translate the source IP for outbound traffic initiated by the inside host. While the static mapping allows inbound traffic to reach the server at 203.0.113.5, when the server sends packets to the outside network, its source IP remains the private address 10.0.0.5, which is not routable across the internet. This is because the `ip nat inside source static` command creates a one-to-one mapping only for traffic destined to the inside global address; it does not automatically translate the source of outbound packets from the inside host. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that static NAT is unidirectional by default—a common trap is assuming static NAT works like dynamic PAT for outbound traffic. A helpful memory tip: static NAT is like a door that only opens inward; for the server to go out, you need a separate rule or a route-map to enable source translation.

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

✓

Static NAT does not translate the source IP for outbound traffic initiated by the inside host.

Static NAT configured with 'ip nat inside source static' translates the inside local IP to the inside global IP only for inbound traffic. For outbound traffic initiated by the inside host, the source IP is not translated because the static entry is unidirectional by default; it does not create a dynamic translation for outbound sessions. This means the server's source IP remains 10.0.0.5 when it tries to reach the outside, and the return traffic cannot be routed back to the server, breaking outbound connectivity.

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, the server would not send traffic to the router at all; the issue is that traffic reaches the router but is not translated.
✗
The 'ip nat outside' command is missing on the outside interface.
Why it's wrong here
Incorrect because the static entry is for inbound traffic; outbound traffic from the server would need a separate NAT rule (like PAT) to translate the source.
✓
Static NAT does not translate the source IP for outbound traffic initiated by the inside host.
Why this is correct
Correct because static NAT only translates destination IP for inbound traffic; for outbound, the source remains private unless additional NAT (e.g., overload) is configured for that host.
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 router's routing table does not have a route back to the server's subnet.
Why it's wrong here
Incorrect because the server is directly connected, so the router has a connected route; the issue is translation, not routing.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that static NAT is bidirectional by default, leading candidates to overlook the need for separate outbound translation or additional configuration like 'ip nat inside source static ... extendable'.

Detailed technical explanation

How to think about this question

Under the hood, Cisco IOS NAT uses separate translation entries for inside-to-outside and outside-to-inside traffic. A static NAT entry created with 'ip nat inside source static' only installs a unidirectional mapping for inbound traffic; outbound traffic from the inside host uses the original source IP unless a separate 'ip nat inside source static' with the 'extendable' keyword or a PAT overload is configured. In real-world scenarios, this is often overlooked when a server needs to initiate outbound connections (e.g., for software updates or DNS queries), requiring either a dynamic NAT rule or a static NAT with the 'extendable' option to allow bidirectional translation.

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: Static NAT does not translate the source IP for outbound traffic initiated by the inside host. — Static NAT configured with 'ip nat inside source static' translates the inside local IP to the inside global IP only for inbound traffic. For outbound traffic initiated by the inside host, the source IP is not translated because the static entry is unidirectional by default; it does not create a dynamic translation for outbound sessions. This means the server's source IP remains 10.0.0.5 when it tries to reach the outside, and the return traffic cannot be routed back to the server, breaking outbound connectivity.

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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