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 10 interface GigabitEthernet0/1 overload
ip nat inside source static tcp 192.168.1.10 80 203.0.113.3 80 extendable
!
access-list 10 permit 10.0.0.0 0.255.255.255
!
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip nat inside
!
interface GigabitEthernet0/1
ip address 203.0.113.2 255.255.255.248
ip nat outside
!
You are connected to R1. The network uses 192.168.1.0/24 for internal hosts and 203.0.113.0/29 for the public IP pool (203.0.113.2 is the outside interface). Configure PAT so that inside hosts can reach the Internet using the pool address 203.0.113.2. Also configure static NAT to map internal server 192.168.1.10 to 203.0.113.3. The initial config has errors; identify and fix them.
R1# show running-config | section ip nat
ip nat inside source list 10 interface GigabitEthernet0/1 overload
ip nat inside source static tcp 192.168.1.10 80 203.0.113.3 80 extendable
!
access-list 10 permit 10.0.0.0 0.255.255.255
!
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip nat inside
!
interface GigabitEthernet0/1
ip address 203.0.113.2 255.255.255.248
ip nat outside
!
A
Change ACL 10 to permit 192.168.1.0 0.0.0.255 and ensure the NAT pool and PAT are correctly configured.
This is correct because the original ACL 10 permits 10.0.0.0/8, which does not match the inside subnet 192.168.1.0/24. By changing the ACL to permit the correct subnet, PAT will work for inside hosts. The static NAT for the server is already correct.
B
Change the NAT pool to use a different public IP address and update the static NAT mapping.
Why wrong: This is incorrect because the NAT pool and static NAT mapping are already correctly configured. The issue is with the ACL, not the pool or static mapping.
C
Remove the static NAT and use PAT for the server as well.
Why wrong: This is incorrect because the requirement explicitly asks for static NAT for the server, and PAT would not provide a fixed public-to-private mapping. Static NAT is needed for inbound access to the server.
D
Change the inside interface IP address to match the ACL.
Why wrong: This is incorrect because changing the inside interface IP would disrupt the internal network. The correct approach is to fix the ACL to match the existing inside subnet.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change ACL 10 to permit 192.168.1.0 0.0.0.255 and ensure the NAT pool and PAT are correctly configured.
The ACL 10 permits 10.0.0.0/8, but inside hosts are on 192.168.1.0/24 — this ACL does not match the inside subnet, so PAT fails. The static NAT is correct. To fix: change ACL 10 to permit 192.168.1.0 0.0.0.255. Also ensure the PAT references the correct ACL; currently it uses list 10, so after fixing the ACL, PAT will work. No other changes needed.
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.
✓
Change ACL 10 to permit 192.168.1.0 0.0.0.255 and ensure the NAT pool and PAT are correctly configured.
Why this is correct
This is correct because the original ACL 10 permits 10.0.0.0/8, which does not match the inside subnet 192.168.1.0/24. By changing the ACL to permit the correct subnet, PAT will work for inside hosts. The static NAT for the server is already correct.
Change the NAT pool to use a different public IP address and update the static NAT mapping.
Why it's wrong here
This is incorrect because the NAT pool and static NAT mapping are already correctly configured. The issue is with the ACL, not the pool or static mapping.
✗
Remove the static NAT and use PAT for the server as well.
Why it's wrong here
This is incorrect because the requirement explicitly asks for static NAT for the server, and PAT would not provide a fixed public-to-private mapping. Static NAT is needed for inbound access to the server.
✗
Change the inside interface IP address to match the ACL.
Why it's wrong here
This is incorrect because changing the inside interface IP would disrupt the internal network. The correct approach is to fix the ACL to match the existing inside subnet.
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.
✓Change ACL 10 to permit 192.168.1.0 0.0.0.255 and ensure the NAT pool and PAT are correctly configured.Correct answer▾
Why this is correct
This is correct because the original ACL 10 permits 10.0.0.0/8, which does not match the inside subnet 192.168.1.0/24. By changing the ACL to permit the correct subnet, PAT will work for inside hosts. The static NAT for the server is already correct.
✗Change the NAT pool to use a different public IP address and update the static NAT mapping.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the pool address 203.0.113.2 and static mapping to 203.0.113.3 are valid and do not need changing.
Why candidates choose this
Candidates might think the pool or static mapping is wrong because they misread the requirements or assume a conflict, but the problem is solely the ACL.
✗Remove the static NAT and use PAT for the server as well.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that PAT does not allow inbound connections initiated from outside; static NAT is required for that purpose.
Why candidates choose this
Candidates might think PAT can handle all traffic, but static NAT is necessary for servers that need to be reachable from the Internet.
✗Change the inside interface IP address to match the ACL.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the inside interface IP is part of the 192.168.1.0/24 network and should not be changed; the ACL should be adjusted instead.
Why candidates choose this
Candidates might think the ACL is correct and the network should be changed to match, but that is not practical and would break connectivity.
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: Change ACL 10 to permit 192.168.1.0 0.0.0.255 and ensure the NAT pool and PAT are correctly configured. — The ACL 10 permits 10.0.0.0/8, but inside hosts are on 192.168.1.0/24 — this ACL does not match the inside subnet, so PAT fails. The static NAT is correct. To fix: change ACL 10 to permit 192.168.1.0 0.0.0.255. Also ensure the PAT references the correct ACL; currently it uses list 10, so after fixing the ACL, PAT will work. No other changes needed.
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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