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 192.168.10.100 203.0.113.10
!
access-list 100 permit ip host 192.168.10.100 any
!
interface GigabitEthernet0/0
ip address 192.168.10.1 255.255.255.0
ip nat inside
!
interface GigabitEthernet0/1
ip address 203.0.113.2 255.255.255.252
ip nat inside
!
interface GigabitEthernet0/2
ip address 10.0.0.1 255.255.255.252
no ip nat
You are connected to R1. The inside network 192.168.10.0/24 must be able to reach the Internet via PAT (NAT overload) using the outside interface G0/1 with IP 203.0.113.2/30. Additionally, the internal server at 192.168.10.100 must be statically mapped to public IP 203.0.113.10. The current configuration is incomplete and contains errors. Fix the NAT configuration on R1 so that both requirements are met.
R1# show running-config | section ip nat
ip nat inside source list 100 interface GigabitEthernet0/1
ip nat inside source static 192.168.10.100 203.0.113.10
!
access-list 100 permit ip host 192.168.10.100 any
!
interface GigabitEthernet0/0
ip address 192.168.10.1 255.255.255.0
ip nat inside
!
interface GigabitEthernet0/1
ip address 203.0.113.2 255.255.255.252
ip nat inside
!
interface GigabitEthernet0/2
ip address 10.0.0.1 255.255.255.252
no ip nat
A
ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside
This configuration correctly uses an ACL that matches the entire 192.168.10.0/24 subnet, applies PAT with the overload keyword on the outside interface, configures a static NAT for the server, and sets G0/1 as the outside interface.
B
ip access-list standard 100 permit host 192.168.10.100
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside
Why wrong: This is incorrect because ACL 100 only permits the server IP, so only that host can be translated via PAT; the rest of the 192.168.10.0/24 network cannot reach the internet.
C
ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside
Why wrong: This is incorrect because the overload keyword is missing from the PAT command, so only one inside host can be translated at a time, preventing multiple hosts from reaching the internet simultaneously.
D
ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat inside
Why wrong: This is incorrect because G0/1 is configured as ip nat inside, but it should be ip nat outside since it connects to the internet. NAT translations will not work correctly if the outside interface is misconfigured.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside
The correct configuration is a standard ACL matching the entire 192.168.10.0/24 subnet, a PAT statement with the overload keyword, and the outside interface correctly configured as ip nat outside. Option A achieves all three. Option B fails because its ACL only matches the server host, so only 192.168.10.100 can use the PAT translation. Option C omits the overload keyword, meaning only one inside host can translate at a time – PAT is not enabled. Option D configures the external interface as ip nat inside instead of outside, blocking translation of outbound traffic.
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.
✓
ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside
Why this is correct
This configuration correctly uses an ACL that matches the entire 192.168.10.0/24 subnet, applies PAT with the overload keyword on the outside interface, configures a static NAT for the server, and sets G0/1 as the outside interface.
ip access-list standard 100 permit host 192.168.10.100
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside
Why it's wrong here
This is incorrect because ACL 100 only permits the server IP, so only that host can be translated via PAT; the rest of the 192.168.10.0/24 network cannot reach the internet.
✗
ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside
Why it's wrong here
This is incorrect because the overload keyword is missing from the PAT command, so only one inside host can be translated at a time, preventing multiple hosts from reaching the internet simultaneously.
✗
ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat inside
Why it's wrong here
This is incorrect because G0/1 is configured as ip nat inside, but it should be ip nat outside since it connects to the internet. NAT translations will not work correctly if the outside interface is misconfigured.
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.
✓ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outsideCorrect answer▾
Why this is correct
This configuration correctly uses an ACL that matches the entire 192.168.10.0/24 subnet, applies PAT with the overload keyword on the outside interface, configures a static NAT for the server, and sets G0/1 as the outside interface.
✗ip access-list standard 100 permit host 192.168.10.100
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outsideWrong answer — click to see why▾
Why this is wrong here
The ACL must match the entire inside network (192.168.10.0/24), not just the server IP.
Why candidates choose this
Candidates may think the ACL only needs to include the server because the static NAT is separate, but PAT requires the ACL to define which inside addresses are eligible for translation.
✗ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outsideWrong answer — click to see why▾
Why this is wrong here
The overload keyword is required to enable PAT (port address translation) for sharing a single public IP among multiple inside hosts.
Why candidates choose this
Candidates might forget the overload keyword, especially if they are used to configuring dynamic NAT without overload, but PAT is explicitly required for this scenario.
✗ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat insideWrong answer — click to see why▾
Why this is wrong here
The interface facing the internet must be configured as ip nat outside; inside interfaces are those facing the internal network.
Why candidates choose this
Candidates may confuse which interface is inside vs. outside, especially if they think of the router's perspective incorrectly. The outside interface is the one with the public IP.
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.
Trap categories for this question
Keyword trap
This is incorrect because the overload keyword is missing from the PAT command, so only one inside host can be translated at a time, preventing multiple hosts from reaching the internet simultaneously.
Command / output trap
This is incorrect because the overload keyword is missing from the PAT command, so only one inside host can be translated at a time, preventing multiple hosts from reaching the internet simultaneously.
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: ip access-list standard 100 permit 192.168.10.0 0.0.0.255
ip nat inside source list 100 interface GigabitEthernet0/1 overload
ip nat inside source static 192.168.10.100 203.0.113.10
interface GigabitEthernet0/1
ip nat outside — The correct configuration is a standard ACL matching the entire 192.168.10.0/24 subnet, a PAT statement with the overload keyword, and the outside interface correctly configured as ip nat outside. Option A achieves all three. Option B fails because its ACL only matches the server host, so only 192.168.10.100 can use the PAT translation. Option C omits the overload keyword, meaning only one inside host can translate at a time – PAT is not enabled. Option D configures the external interface as ip nat inside instead of outside, blocking translation of outbound traffic.
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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