CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Network Topology
You are connected to R1. The network uses a single router with two subnets: 192.168.1.0/24 (connected to GigabitEthernet0/0) and 10.0.0.0/30 (connected to GigabitEthernet0/1). Configure an extended named ACL called 'FILTER_HTTP' that permits HTTP traffic (TCP port 80) from the 192.168.1.0/24 subnet to any destination, and includes an explicit deny statement to deny all other IP traffic. Apply the ACL inbound on GigabitEthernet0/0. Then verify that HTTP traffic is allowed and all other traffic is blocked.
R1# show running-config | section interface
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
duplex auto
speed auto
!
interface GigabitEthernet0/1
ip address 10.0.0.1 255.255.255.252
duplex auto
speed auto
!
R1# show access-lists
(no output – no ACLs configured)
A
ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/0
ip access-group FILTER_HTTP in
This sequence correctly creates an extended named ACL that permits HTTP (TCP port 80) from the 192.168.1.0/24 subnet to any destination, explicitly denies all other IP traffic, and applies the ACL inbound on GigabitEthernet0/0. The explicit deny ip any any ensures that the intent is clear and that all non-HTTP traffic is blocked.
B
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 80
access-list 100 deny ip any any
interface GigabitEthernet0/0
ip access-group 100 in
Why wrong: This is incorrect because the question specifies an extended named ACL called 'FILTER_HTTP', not a numbered ACL. Using a numbered ACL (100) does not meet the requirement for a named ACL.
C
ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
interface GigabitEthernet0/0
ip access-group FILTER_HTTP in
Why wrong: This is incorrect because it omits the explicit deny ip any any statement. While the implicit deny at the end of the ACL will block all other traffic, the question explicitly states 'denies all other IP traffic', so an explicit deny is required to make the intent clear.
D
ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/1
ip access-group FILTER_HTTP in
Why wrong: This is incorrect because the ACL is applied inbound on GigabitEthernet0/1 instead of GigabitEthernet0/0. The requirement states to apply the ACL inbound on GigabitEthernet0/0, which is the interface connected to the 192.168.1.0/24 subnet.
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 extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/0
ip access-group FILTER_HTTP in
The task requires creating an extended named ACL 'FILTER_HTTP' that permits TCP port 80 from source 192.168.1.0/24 to any destination, and then denies all other IP traffic (the implicit deny will block everything else, but you must explicitly add a deny ip any any statement to make the intent clear). The ACL must be applied inbound on GigabitEthernet0/0. The solution uses the commands: ip access-list extended FILTER_HTTP, permit tcp 192.168.1.0 0.0.0.255 any eq 80, deny ip any any, and interface GigabitEthernet0/0, ip access-group FILTER_HTTP in. Verification with show access-lists and show ip interface GigabitEthernet0/0 confirms the ACL and its application.
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 extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/0
ip access-group FILTER_HTTP in
Why this is correct
This sequence correctly creates an extended named ACL that permits HTTP (TCP port 80) from the 192.168.1.0/24 subnet to any destination, explicitly denies all other IP traffic, and applies the ACL inbound on GigabitEthernet0/0. The explicit deny ip any any ensures that the intent is clear and that all non-HTTP traffic is blocked.
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 80
access-list 100 deny ip any any
interface GigabitEthernet0/0
ip access-group 100 in
Why it's wrong here
This is incorrect because the question specifies an extended named ACL called 'FILTER_HTTP', not a numbered ACL. Using a numbered ACL (100) does not meet the requirement for a named ACL.
✗
ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
interface GigabitEthernet0/0
ip access-group FILTER_HTTP in
Why it's wrong here
This is incorrect because it omits the explicit deny ip any any statement. While the implicit deny at the end of the ACL will block all other traffic, the question explicitly states 'denies all other IP traffic', so an explicit deny is required to make the intent clear.
✗
ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/1
ip access-group FILTER_HTTP in
Why it's wrong here
This is incorrect because the ACL is applied inbound on GigabitEthernet0/1 instead of GigabitEthernet0/0. The requirement states to apply the ACL inbound on GigabitEthernet0/0, which is the interface connected to the 192.168.1.0/24 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.
✓ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/0
ip access-group FILTER_HTTP inCorrect answer▾
Why this is correct
This sequence correctly creates an extended named ACL that permits HTTP (TCP port 80) from the 192.168.1.0/24 subnet to any destination, explicitly denies all other IP traffic, and applies the ACL inbound on GigabitEthernet0/0. The explicit deny ip any any ensures that the intent is clear and that all non-HTTP traffic is blocked.
✗access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 80
access-list 100 deny ip any any
interface GigabitEthernet0/0
ip access-group 100 inWrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the ACL must be named 'FILTER_HTTP', but this option uses a numbered ACL (100).
Why candidates choose this
Candidates might pick this because they know that extended ACLs can be numbered (100-199) and the permit/deny statements are correct, but they overlook the requirement for a named ACL.
✗ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
interface GigabitEthernet0/0
ip access-group FILTER_HTTP inWrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the ACL does not include an explicit deny ip any any, which is needed to satisfy the requirement of denying all other IP traffic.
Why candidates choose this
Candidates might pick this because they know that ACLs have an implicit deny, so they think an explicit deny is unnecessary. However, the question explicitly requires a deny statement.
✗ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/1
ip access-group FILTER_HTTP inWrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the ACL is applied to the wrong interface (GigabitEthernet0/1 instead of GigabitEthernet0/0).
Why candidates choose this
Candidates might pick this because they confuse the two interfaces or think that applying the ACL on the other interface might also work, but the direction and interface must match the requirement.
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: ip access-list extended FILTER_HTTP
permit tcp 192.168.1.0 0.0.0.255 any eq 80
deny ip any any
interface GigabitEthernet0/0
ip access-group FILTER_HTTP in — The task requires creating an extended named ACL 'FILTER_HTTP' that permits TCP port 80 from source 192.168.1.0/24 to any destination, and then denies all other IP traffic (the implicit deny will block everything else, but you must explicitly add a deny ip any any statement to make the intent clear). The ACL must be applied inbound on GigabitEthernet0/0. The solution uses the commands: ip access-list extended FILTER_HTTP, permit tcp 192.168.1.0 0.0.0.255 any eq 80, deny ip any any, and interface GigabitEthernet0/0, ip access-group FILTER_HTTP in. Verification with show access-lists and show ip interface GigabitEthernet0/0 confirms the ACL and its application.
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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