CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 192.168.1.10 203.0.113.5
access-list 100 permit ip 192.168.2.0 0.0.0.255 any
!
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip nat outside
!
interface GigabitEthernet0/1
ip address 203.0.113.1 255.255.255.0
ip nat inside
!
You are connected to R1. Configure PAT (NAT overload) so that hosts on the 192.168.1.0/24 inside network can reach the Internet through the outside interface GigabitEthernet0/1 using the IP address 203.0.113.1. Additionally, configure static NAT to map internal server 192.168.1.10 to public IP 203.0.113.5. The current configuration has several errors. Identify and correct them.
R1# show running-config | section ip nat
ip nat inside source list 100 interface GigabitEthernet0/1
ip nat inside source static 192.168.1.10 203.0.113.5
access-list 100 permit ip 192.168.2.0 0.0.0.255 any
!
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip nat outside
!
interface GigabitEthernet0/1
ip address 203.0.113.1 255.255.255.0
ip nat inside
!
A
Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.
This option correctly identifies all three errors: swapped interface NAT directions, missing 'overload' keyword, and incorrect ACL subnet. Fixing these enables PAT for the inside network and static NAT for the server.
B
Change the NAT interface directions: G0/0 as outside, G0/1 as inside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.
Why wrong: This is incorrect because the interface directions are reversed: G0/0 should be inside (connected to internal network) and G0/1 should be outside (connected to Internet).
C
Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Keep ACL 100 as is because it already permits the correct subnet.
Why wrong: This is incorrect because ACL 100 currently permits 192.168.2.0/24, not 192.168.1.0/24. The ACL must be updated to match the correct inside network.
D
Change the NAT interface directions: G0/0 as outside, G0/1 as inside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.
Why wrong: This is incorrect because it combines two errors: reversed interface directions and an incorrect ACL change (though the ACL change is correct, the interface directions are wrong).
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.
The configuration had three issues: (1) Inside and outside interfaces were swapped — G0/0 (inside) was marked 'ip nat outside' and G0/1 (outside) was 'ip nat inside'. (2) The PAT command was missing the 'overload' keyword. (3) ACL 100 matched the wrong subnet (192.168.2.0 instead of 192.168.1.0). To fix: correct interface NAT directions, add 'overload', and update ACL to permit 192.168.1.0/24.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.
Why this is correct
This option correctly identifies all three errors: swapped interface NAT directions, missing 'overload' keyword, and incorrect ACL subnet. Fixing these enables PAT for the inside network and static NAT for the server.
Change the NAT interface directions: G0/0 as outside, G0/1 as inside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.
Why it's wrong here
This is incorrect because the interface directions are reversed: G0/0 should be inside (connected to internal network) and G0/1 should be outside (connected to Internet).
✗
Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Keep ACL 100 as is because it already permits the correct subnet.
Why it's wrong here
This is incorrect because ACL 100 currently permits 192.168.2.0/24, not 192.168.1.0/24. The ACL must be updated to match the correct inside network.
✗
Change the NAT interface directions: G0/0 as outside, G0/1 as inside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.
Why it's wrong here
This is incorrect because it combines two errors: reversed interface directions and an incorrect ACL change (though the ACL change is correct, the interface directions are wrong).
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.
✓Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.Correct answer▾
Why this is correct
This option correctly identifies all three errors: swapped interface NAT directions, missing 'overload' keyword, and incorrect ACL subnet. Fixing these enables PAT for the inside network and static NAT for the server.
✗Change the NAT interface directions: G0/0 as outside, G0/1 as inside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the inside and outside interfaces are swapped; G0/0 is the internal interface and must be 'ip nat inside'.
Why candidates choose this
Candidates might confuse which interface is inside/outside, especially if they misread the topology or think the external interface should be marked inside.
✗Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Keep ACL 100 as is because it already permits the correct subnet.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the ACL permits the wrong subnet (192.168.2.0 instead of 192.168.1.0).
Why candidates choose this
Candidates may overlook the ACL error if they assume the existing ACL is correct, or they may misread the subnet in the question.
✗Change the NAT interface directions: G0/0 as outside, G0/1 as inside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that both the interface directions are swapped and the ACL is changed, but the interface directions must be correct for NAT to work.
Why candidates choose this
Candidates might think that changing the ACL is the only fix and ignore the interface direction issue, or they may incorrectly assume that the outside interface should be marked inside.
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: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
Network Services and Security — This question tests Network Services and Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Correct the NAT interface directions: G0/0 as inside, G0/1 as outside. Add 'overload' to the PAT command. Change ACL 100 to permit 192.168.1.0 0.0.0.255. — The configuration had three issues: (1) Inside and outside interfaces were swapped — G0/0 (inside) was marked 'ip nat outside' and G0/1 (outside) was 'ip nat inside'. (2) The PAT command was missing the 'overload' keyword. (3) ACL 100 matched the wrong subnet (192.168.2.0 instead of 192.168.1.0). To fix: correct interface NAT directions, add 'overload', and update ACL to permit 192.168.1.0/24.
What should I do if I get this 200-301 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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