CCNA Network Services and Security Practice Question
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.
⚠ Common exam trap
Watch out for ACLs that match the wrong subnet in NAT configurations. Also, remember that PAT requires the 'overload' keyword; without it, only one translation is allowed. Static NAT often uses a different public IP than the PAT pool to avoid conflicts.
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 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.
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.
- ✗
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
Although the static entry is alleged to use 192.168.10.1 as the inside address, the running configuration actually contains 'ip nat inside source static 192.168.10.100 203.0.113.5'. That statement correctly maps the internal server to the public IP, so the problem is not in the static translation. If the inside address were 192.168.10.1, it would identify the router's LAN interface or a different host, breaking reachability to the server, but no such misconfiguration appears. The real faults are the ACL matching 192.168.20.0/24 instead of 192.168.10.0/24 and the missing 'overload' keyword.
- ✗
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
The static NAT statement correctly uses public IP 203.0.113.5 for the server; changing it to 203.0.113.1 would create a conflict because 203.0.113.1 is the address used by the PAT configuration for dynamic translations. A Cisco router cannot successfully use the same global address for both a static one-to-one mapping and dynamic PAT overloading without causing unpredictable behavior or denying the server's translation. While the ACL portion of this answer correctly identifies a real fault, the static-NAT portion is false, so the combined answer is wrong. The accurate diagnosis is an ACL permitting the wrong inside subnet and a PAT command lacking 'overload'.
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?”
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Related to this question
Learn chapter
RA Guard — IPv6 First-Hop Security
Key term
Port Address Translation
A networking technique that maps multiple private IP addresses and their ports to a single public IP address using unique port numbers.
Key term
Static NAT
Static Network Address Translation (NAT) is a one-to-one mapping between a private IP address and a public IP address that never changes.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.