CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. 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.
Exhibit
R1# show running-config | section ip nat
ip nat inside source list 100 interface GigabitEthernet0/1
ip nat inside source static tcp 192.168.10.100 80 203.0.113.5 80 extendable
!
access-list 100 permit ip 192.168.20.0 0.0.0.255 any
!
interface GigabitEthernet0/0
ip address 192.168.10.1 255.255.255.0
ip nat inside
!
interface GigabitEthernet0/1
ip address 203.0.113.1 255.255.255.0
ip nat outside
!
You are troubleshooting PAT and static NAT on R1. The inside network 192.168.10.0/24 must be translated to the public IP 203.0.113.1 (interface G0/1) using port address translation. Additionally, the server at 192.168.10.100 must be reachable from the outside via static NAT to 203.0.113.5. The current configuration is not working. Identify and correct the errors in the running config on R1.
R1# show running-config | section ip nat
ip nat inside source list 100 interface GigabitEthernet0/1
ip nat inside source static tcp 192.168.10.100 80 203.0.113.5 80 extendable
!
access-list 100 permit ip 192.168.20.0 0.0.0.255 any
!
interface GigabitEthernet0/0
ip address 192.168.10.1 255.255.255.0
ip nat inside
!
interface GigabitEthernet0/1
ip address 203.0.113.1 255.255.255.0
ip nat outside
!
A
The ACL in the NAT configuration incorrectly permits network 192.168.20.0/24 instead of 192.168.10.0/24, and the PAT command is missing the 'overload' keyword.
This is correct because the ACL must match the inside network 192.168.10.0/24 for PAT to translate traffic from that subnet. Additionally, the 'overload' keyword is required to enable port address translation, allowing multiple inside hosts to share the public IP.
B
The static NAT entry uses the wrong inside address; it should be 192.168.10.100 but is configured with 192.168.10.1.
Why wrong: This is incorrect because the static NAT entry is correctly configured with inside address 192.168.10.100 and outside address 203.0.113.5. The problem lies elsewhere.
C
The PAT command is missing the 'overload' keyword, and the static NAT entry maps to the wrong public IP; it should use 203.0.113.1 instead of 203.0.113.5.
Why wrong: This is incorrect because the static NAT entry correctly uses a different public IP (203.0.113.5) for the server, which is necessary to distinguish it from the PAT pool. Using the same IP would cause conflicts.
D
The static NAT entry maps the server to the wrong public IP, 203.0.113.1 instead of 203.0.113.5, and the ACL incorrectly permits network 192.168.20.0/24.
Why wrong: This is incorrect because the static NAT entry is correctly configured with inside address 192.168.10.100 and public IP 203.0.113.5. Using 203.0.113.1 for the server would conflict with PAT translations.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ACL in the NAT configuration incorrectly permits network 192.168.20.0/24 instead of 192.168.10.0/24, and the PAT command is missing the 'overload' keyword.
The running configuration has two errors. First, access-list 100 incorrectly permits the 192.168.20.0/24 network instead of the inside network 192.168.10.0/24, so PAT will not translate any internal hosts. Second, the PAT command is missing the 'overload' keyword, which means only a single translation is possible, breaking connectivity for multiple devices. The static NAT entry for the server is correctly mapping 192.168.10.100 to 203.0.113.5 and does not need correction.
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 ACL in the NAT configuration incorrectly permits network 192.168.20.0/24 instead of 192.168.10.0/24, and the PAT command is missing the 'overload' keyword.
Why this is correct
This is correct because the ACL must match the inside network 192.168.10.0/24 for PAT to translate traffic from that subnet. Additionally, the 'overload' keyword is required to enable port address translation, allowing multiple inside hosts to share the public IP.
Related concept
Static NAT maps one inside address to one outside address.
✗
The static NAT entry uses the wrong inside address; it should be 192.168.10.100 but is configured with 192.168.10.1.
Why it's wrong here
This is incorrect because the static NAT entry is correctly configured with inside address 192.168.10.100 and outside address 203.0.113.5. The problem lies elsewhere.
✗
The PAT command is missing the 'overload' keyword, and the static NAT entry maps to the wrong public IP; it should use 203.0.113.1 instead of 203.0.113.5.
Why it's wrong here
This is incorrect because the static NAT entry correctly uses a different public IP (203.0.113.5) for the server, which is necessary to distinguish it from the PAT pool. Using the same IP would cause conflicts.
✗
The static NAT entry maps the server to the wrong public IP, 203.0.113.1 instead of 203.0.113.5, and the ACL incorrectly permits network 192.168.20.0/24.
Why it's wrong here
This is incorrect because the static NAT entry is correctly configured with inside address 192.168.10.100 and public IP 203.0.113.5. Using 203.0.113.1 for the server would conflict with PAT translations.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The ACL in the NAT configuration incorrectly permits network 192.168.20.0/24 instead of 192.168.10.0/24, and the PAT command is missing the 'overload' keyword.Correct answer▾
Why this is correct
This is correct because the ACL must match the inside network 192.168.10.0/24 for PAT to translate traffic from that subnet. Additionally, the 'overload' keyword is required to enable port address translation, allowing multiple inside hosts to share the public IP.
✗The static NAT entry uses the wrong inside address; it should be 192.168.10.100 but is configured with 192.168.10.1.Wrong answer — click to see why▾
Why this is wrong here
The static NAT entry is correct; the inside address 192.168.10.100 is properly mapped to 203.0.113.5.
Why candidates choose this
Candidates might assume a typo in the static NAT because they focus on the server's IP, but the configuration is actually correct.
✗The PAT command is missing the 'overload' keyword, and the static NAT entry maps to the wrong public IP; it should use 203.0.113.1 instead of 203.0.113.5.Wrong answer — click to see why▾
Why this is wrong here
Static NAT requires a separate public IP to avoid overlapping with PAT translations. The public IP 203.0.113.5 is appropriate.
Why candidates choose this
Candidates may think all translations must use the same public IP, but static NAT often uses a dedicated IP for inbound access.
✗The static NAT entry maps the server to the wrong public IP, 203.0.113.1 instead of 203.0.113.5, and the ACL incorrectly permits network 192.168.20.0/24.Wrong answer — click to see why▾
Why this is wrong here
The static NAT entry is correctly configured with 192.168.10.100 and 203.0.113.5; the error is solely in the ACL and missing overload keyword.
Why candidates choose this
Candidates might think all translations should share the same public IP for simplicity, but that would break inbound access to the server.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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 200-301 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 200-301 NAT questions on configuration and troubleshooting.
Network Services and Security — This question tests Network Services and Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The ACL in the NAT configuration incorrectly permits network 192.168.20.0/24 instead of 192.168.10.0/24, and the PAT command is missing the 'overload' keyword. — The running configuration has two errors. First, access-list 100 incorrectly permits the 192.168.20.0/24 network instead of the inside network 192.168.10.0/24, so PAT will not translate any internal hosts. Second, the PAT command is missing the 'overload' keyword, which means only a single translation is possible, breaking connectivity for multiple devices. The static NAT entry for the server is correctly mapping 192.168.10.100 to 203.0.113.5 and does not need correction.
What should I do if I get this 200-301 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 200-301 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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