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.
Router R1 is configured with ip nat inside source list 100 interface Loopback0 overload. Internal hosts at 192.168.1.0/24 can access the internet, but external hosts cannot initiate connections to an internal server at 10.1.1.10 that is also behind NAT. The server is supposed to be reachable via static NAT. Configuration: ip nat inside source static tcp 10.1.1.10 80 interface Loopback0 80. Router R1 shows: show ip nat translations: Pro Inside global Inside local Outside local Outside global tcp 10.1.1.10:80 10.1.1.10:80 --- ---. External users get connection timeouts. What is the root cause?
The static NAT should use a specific global IP address instead of the interface; configure ip nat inside source static tcp 10.1.1.10 80 203.0.113.10 80.
Using the interface IP for static NAT is not supported; a specific global IP must be defined.
B
The access-list 100 is blocking inbound traffic.
Why wrong: ACL 100 is for dynamic NAT, not static NAT, and inbound traffic is not matched by it.
C
The Loopback0 interface is not in the routing table.
Why wrong: Loopback0 is a virtual interface and is always up, but it is not the correct interface for NAT.
D
The static NAT entry is missing the 'add-route' option.
Why wrong: The 'add-route' option is for route maps, not required for static NAT.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The static NAT should use a specific global IP address instead of the interface; configure ip nat inside source static tcp 10.1.1.10 80 203.0.113.10 80.
The static NAT entry is correctly configured, but the issue is that the Loopback0 interface is used as the inside global interface. For static NAT to work for inbound connections, the outside interface must be the one facing the external network. The Loopback0 is likely not the correct egress interface; the static NAT should be applied to the actual outside interface (e.g., GigabitEthernet0/1). Additionally, the 'interface' keyword in the static NAT command is incorrect; it should use 'ip nat inside source static tcp 10.1.1.10 80 203.0.113.10 80' with a specific global IP.
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 static NAT should use a specific global IP address instead of the interface; configure ip nat inside source static tcp 10.1.1.10 80 203.0.113.10 80.
Why this is correct
Using the interface IP for static NAT is not supported; a specific global IP must be defined.
Related concept
Static NAT maps one inside address to one outside address.
✗
The access-list 100 is blocking inbound traffic.
Why it's wrong here
ACL 100 is for dynamic NAT, not static NAT, and inbound traffic is not matched by it.
✗
The Loopback0 interface is not in the routing table.
Why it's wrong here
Loopback0 is a virtual interface and is always up, but it is not the correct interface for NAT.
✗
The static NAT entry is missing the 'add-route' option.
Why it's wrong here
The 'add-route' option is for route maps, not required for static NAT.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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 300-410 NAT questions on configuration and troubleshooting.
NAT and PAT — This question tests NAT and PAT — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The static NAT should use a specific global IP address instead of the interface; configure ip nat inside source static tcp 10.1.1.10 80 203.0.113.10 80. — The static NAT entry is correctly configured, but the issue is that the Loopback0 interface is used as the inside global interface. For static NAT to work for inbound connections, the outside interface must be the one facing the external network. The Loopback0 is likely not the correct egress interface; the static NAT should be applied to the actual outside interface (e.g., GigabitEthernet0/1). Additionally, the 'interface' keyword in the static NAT command is incorrect; it should use 'ip nat inside source static tcp 10.1.1.10 80 203.0.113.10 80' with a specific global IP.
What should I do if I get this 300-410 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 300-410 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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