- A
The router does not have NAT hairpinning enabled, so internal traffic to the public IP is not translated.
Correct because by default, Cisco routers do not perform NAT for traffic that enters and leaves the same interface (inside-to-inside). This requires the ip nat enable route-map or similar configuration.
- B
The static NAT entry is missing the extendable keyword.
Why wrong: Incorrect because the extendable keyword is used when multiple static NAT entries share the same public IP; it is not related to hairpinning.
- C
The internal hosts have a route to the public IP via the router's outside interface.
Why wrong: Incorrect because even with a route, the NAT translation would not occur for inside-to-inside traffic without hairpinning.
- D
The access list used for NAT is blocking internal traffic.
Why wrong: Incorrect because the static NAT entry does not use an access list; it is a direct mapping.
Quick Answer
The answer is that the router lacks NAT hairpinning, also known as NAT reflection, which is required when internal hosts attempt to access an internal server using its public IP address. The core issue is that the router’s NAT rule translates traffic arriving on the outside interface, but traffic originating from an internal host and destined for the public IP never leaves the internal network—it hits the router’s inside interface, and without hairpinning support, the router does not apply the translation or loop the traffic back. On the ENCOR 350-401 exam, this scenario tests your understanding of NAT behavior in asymmetric routing contexts; a common trap is assuming that a static NAT rule works for all traffic flows, when in fact it only applies to inbound traffic from the external interface. A helpful memory tip is “Hairpin for Home”—if internal users need to reach a server via its public IP, you must enable hairpinning so the router “turns the traffic around” like a hairpin bending back on itself.
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 configuring NAT on a Cisco router to allow internal hosts to access the internet. The engineer uses the command ip nat inside source static tcp 192.168.1.10 80 203.0.113.1 80. After testing, external users can access the internal web server using the public IP. However, internal hosts cannot access the web server using the public IP. 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.
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 does not have NAT hairpinning enabled, so internal traffic to the public IP is not translated.
This is a classic NAT hairpinning issue. When an internal host tries to reach the public IP of the server, the router may not support or be configured for NAT reflection (hairpinning), so the packet is not translated correctly.
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 does not have NAT hairpinning enabled, so internal traffic to the public IP is not translated.
Why this is correct
Correct because by default, Cisco routers do not perform NAT for traffic that enters and leaves the same interface (inside-to-inside). This requires the ip nat enable route-map or similar configuration.
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 static NAT entry is missing the extendable keyword.
Why it's wrong here
Incorrect because the extendable keyword is used when multiple static NAT entries share the same public IP; it is not related to hairpinning.
- ✗
The internal hosts have a route to the public IP via the router's outside interface.
Why it's wrong here
Incorrect because even with a route, the NAT translation would not occur for inside-to-inside traffic without hairpinning.
- ✗
The access list used for NAT is blocking internal traffic.
Why it's wrong here
Incorrect because the static NAT entry does not use an access list; it is a direct mapping.
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.
Trap categories for this question
Keyword trap
Incorrect because the extendable keyword is used when multiple static NAT entries share the same public IP; it is not related to hairpinning.
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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NAT and DHCP — study guide chapter
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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 does not have NAT hairpinning enabled, so internal traffic to the public IP is not translated. — This is a classic NAT hairpinning issue. When an internal host tries to reach the public IP of the server, the router may not support or be configured for NAT reflection (hairpinning), so the packet is not translated correctly.
What should I do if I get this 350-401 question wrong?
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.
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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Last reviewed: Jun 18, 2026
This 350-401 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 350-401 exam.
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