The correct answer is to configure an extended named ACL called FILTER with three permit statements, then apply it inbound on interface G0/0. This configuration works because extended ACLs evaluate traffic based on source and destination IP addresses, protocols, and port numbers, allowing precise filtering of HTTP and HTTPS from the 192.168.1.0/24 subnet while using a separate permit statement to allow all IP traffic from 192.168.2.0/24 without restriction. On the CCNA 200-301 v2 exam, this task tests your understanding of where to apply an ACL—inbound on the interface where traffic enters the router—and the critical role of the implicit deny, which blocks any traffic not explicitly permitted. A common trap is applying the ACL outbound on G0/0, which would filter traffic leaving the subnet rather than entering, or forgetting that the implicit deny will block the 192.168.2.0/24 traffic if you only permit the two HTTP statements. Remember the memory tip: "Filter inbound, permit the source, and always include a blanket permit for unrestricted subnets before the implicit deny."
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.
Network Topology
You are connected to R1 via console. R1 is a router that connects two internal subnets (192.168.1.0/24 and 192.168.2.0/24) to the internet via a serial link to ISP. Currently, no ACL is applied. Your task is to configure an extended named ACL on R1 that permits only HTTP (TCP/80) and HTTPS (TCP/443) traffic from the 192.168.1.0/24 subnet to the internet, and denies all other traffic from that subnet. Traffic from 192.168.2.0/24 must be permitted without restriction. Apply the ACL inbound on the interface facing the internal subnets. Additionally, verify that the implicit deny is not blocking necessary traffic by ensuring that the ACL correctly handles the traffic.
R1# show running-config | section interface
interface GigabitEthernet0/0
description LAN - 192.168.1.0/24
ip address 192.168.1.1 255.255.255.0
no shutdown
!
interface GigabitEthernet0/1
description LAN - 192.168.2.0/24
ip address 192.168.2.1 255.255.255.0
no shutdown
!
interface Serial0/0/0
description WAN to ISP
ip address 203.0.113.1 255.255.255.252
no shutdown
A
ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER in
This configuration correctly creates a named extended ACL with two permit statements for HTTP and HTTPS from 192.168.1.0/24, followed by a permit all for 192.168.2.0/24. The ACL is applied inbound on G0/0, which is the interface facing the 192.168.1.0/24 subnet, ensuring traffic from that subnet is filtered as required.
B
ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER out
Why wrong: This is incorrect because the ACL is applied outbound on G0/0. Traffic from 192.168.1.0/24 enters R1 through G0/0, so an inbound ACL on G0/0 filters it before routing. An outbound ACL on G0/0 would filter traffic leaving that interface, which is traffic destined to the 192.168.1.0/24 subnet, not traffic from it.
C
ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/1
ip access-group FILTER in
Why wrong: This is incorrect because the ACL is applied inbound on G0/1, which is the interface facing the 192.168.2.0/24 subnet. Traffic from 192.168.1.0/24 enters R1 through G0/0, not G0/1. Applying the ACL on G0/1 would filter traffic from 192.168.2.0/24, which should be permitted without restriction, and would not filter traffic from 192.168.1.0/24 at all.
D
ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER in
interface g0/1
ip access-group FILTER in
Why wrong: This is incorrect because the same ACL is applied inbound on both G0/0 and G0/1. While the ACL permits all traffic from 192.168.2.0/24, applying it on G0/1 is unnecessary and could cause confusion. More importantly, the ACL does not include an explicit deny for traffic from 192.168.1.0/24 other than HTTP/HTTPS; the implicit deny at the end of the ACL will block that traffic, but applying the ACL on G0/1 would also block any traffic from 192.168.2.0/24 that is not IP (though unlikely). The requirement is to apply the ACL only on the interface facing the internal subnets, which is typically one interface per subnet. Applying it on both interfaces is not required and may lead to misconfiguration.
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
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER in
The task required an extended ACL to permit HTTP/HTTPS from 192.168.1.0/24 and all traffic from 192.168.2.0/24. The candidate must create a named ACL (e.g., FILTER), add two permit statements for TCP/80 and TCP/443 from 192.168.1.0 0.0.0.255 to any, then a permit ip from 192.168.2.0 0.0.0.255 to any. The ACL is applied inbound on G0/0 (the interface facing 192.168.1.0/24) because traffic from that subnet enters R1 through G0/0. Applying it outbound on G0/0 would be incorrect, as it would only filter traffic leaving that subnet, not entering. Also, the ACL must be applied on the correct interface to avoid blocking traffic from 192.168.2.0/24, which enters via G0/1.
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
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER in
Why this is correct
This configuration correctly creates a named extended ACL with two permit statements for HTTP and HTTPS from 192.168.1.0/24, followed by a permit all for 192.168.2.0/24. The ACL is applied inbound on G0/0, which is the interface facing the 192.168.1.0/24 subnet, ensuring traffic from that subnet is filtered as required.
ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER out
Why it's wrong here
This is incorrect because the ACL is applied outbound on G0/0. Traffic from 192.168.1.0/24 enters R1 through G0/0, so an inbound ACL on G0/0 filters it before routing. An outbound ACL on G0/0 would filter traffic leaving that interface, which is traffic destined to the 192.168.1.0/24 subnet, not traffic from it.
✗
ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/1
ip access-group FILTER in
Why it's wrong here
This is incorrect because the ACL is applied inbound on G0/1, which is the interface facing the 192.168.2.0/24 subnet. Traffic from 192.168.1.0/24 enters R1 through G0/0, not G0/1. Applying the ACL on G0/1 would filter traffic from 192.168.2.0/24, which should be permitted without restriction, and would not filter traffic from 192.168.1.0/24 at all.
✗
ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER in
interface g0/1
ip access-group FILTER in
Why it's wrong here
This is incorrect because the same ACL is applied inbound on both G0/0 and G0/1. While the ACL permits all traffic from 192.168.2.0/24, applying it on G0/1 is unnecessary and could cause confusion. More importantly, the ACL does not include an explicit deny for traffic from 192.168.1.0/24 other than HTTP/HTTPS; the implicit deny at the end of the ACL will block that traffic, but applying the ACL on G0/1 would also block any traffic from 192.168.2.0/24 that is not IP (though unlikely). The requirement is to apply the ACL only on the interface facing the internal subnets, which is typically one interface per subnet. Applying it on both interfaces is not required and may lead to misconfiguration.
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
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER inCorrect answer▾
Why this is correct
This configuration correctly creates a named extended ACL with two permit statements for HTTP and HTTPS from 192.168.1.0/24, followed by a permit all for 192.168.2.0/24. The ACL is applied inbound on G0/0, which is the interface facing the 192.168.1.0/24 subnet, ensuring traffic from that subnet is filtered as required.
✗ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER outWrong answer — click to see why▾
Why this is wrong here
The ACL is applied in the wrong direction. For traffic originating from 192.168.1.0/24, the ACL must be applied inbound on the interface where that traffic enters the router (G0/0).
Why candidates choose this
Candidates often confuse inbound vs outbound ACL application. They might think 'outbound' filters traffic going out to the internet, but the direction is relative to the interface, not the destination.
✗ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/1
ip access-group FILTER inWrong answer — click to see why▾
Why this is wrong here
The ACL is applied on the wrong interface. The interface facing the restricted subnet (192.168.1.0/24) is G0/0, not G0/1.
Why candidates choose this
Candidates might mistakenly think that because the ACL permits all traffic from 192.168.2.0/24, it should be applied on that interface. However, the ACL must be applied on the interface where the traffic to be filtered enters.
✗ip access-list extended FILTER
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER in
interface g0/1
ip access-group FILTER inWrong answer — click to see why▾
Why this is wrong here
The ACL should only be applied on the interface where the restricted subnet traffic enters (G0/0). Applying it on G0/1 is redundant and could inadvertently filter traffic from 192.168.2.0/24 if the ACL is modified later.
Why candidates choose this
Candidates might think that since the ACL permits traffic from both subnets, it should be applied on both interfaces to be thorough. However, the ACL is designed to restrict traffic from 192.168.1.0/24, so it only needs to be applied where that traffic enters.
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
Similar concept trap
This is incorrect because the same ACL is applied inbound on both G0/0 and G0/1. While the ACL permits all traffic from 192.168.2.0/24, applying it on G0/1 is unnecessary and could cause confusion. More importantly, the ACL does not include an explicit deny for traffic from 192.168.1.0/24 other than HTTP/HTTPS; the implicit deny at the end of the ACL will block that traffic, but applying the ACL on G0/1 would also block any traffic from 192.168.2.0/24 that is not IP (though unlikely). The requirement is to apply the ACL only on the interface facing the internal subnets, which is typically one interface per subnet. Applying it on both interfaces is not required and may lead to misconfiguration.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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
permit tcp 192.168.1.0 0.0.0.255 any eq 80
permit tcp 192.168.1.0 0.0.0.255 any eq 443
permit ip 192.168.2.0 0.0.0.255 any
interface g0/0
ip access-group FILTER in — The task required an extended ACL to permit HTTP/HTTPS from 192.168.1.0/24 and all traffic from 192.168.2.0/24. The candidate must create a named ACL (e.g., FILTER), add two permit statements for TCP/80 and TCP/443 from 192.168.1.0 0.0.0.255 to any, then a permit ip from 192.168.2.0 0.0.0.255 to any. The ACL is applied inbound on G0/0 (the interface facing 192.168.1.0/24) because traffic from that subnet enters R1 through G0/0. Applying it outbound on G0/0 would be incorrect, as it would only filter traffic leaving that subnet, not entering. Also, the ACL must be applied on the correct interface to avoid blocking traffic from 192.168.2.0/24, which enters via G0/1.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to R1 via the console. R1 connects two networks: GigabitEthernet0/0 (192.168.1.1/24) and GigabitEthernet0/1 (192.168.2.1/24). Create an extended ACL named BLOCK_HTTP that denies HTTP traffic (tcp port 80) from the 192.168.1.0/24 network to the 192.168.2.0/24 network, but permits all other IP traffic. Apply this ACL inbound on GigabitEthernet0/0.
medium
✓ A.ip access-list extended BLOCK_HTTP
deny tcp 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 eq 80
permit ip any any
interface GigabitEthernet0/0
ip access-group BLOCK_HTTP in
B.ip access-list extended BLOCK_HTTP
deny tcp 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 eq 80
permit ip any any
interface GigabitEthernet0/1
ip access-group BLOCK_HTTP in
C.ip access-list extended BLOCK_HTTP
deny tcp 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 eq 80
permit ip any any
interface GigabitEthernet0/0
ip access-group BLOCK_HTTP out
D.ip access-list extended BLOCK_HTTP
deny tcp 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 eq 80
permit ip any any
interface GigabitEthernet0/0
ip access-group BLOCK_HTTP in
interface GigabitEthernet0/1
ip access-group BLOCK_HTTP in
Why A: The named extended ACL BLOCK_HTTP denies TCP port 80 from 192.168.1.0/24 to 192.168.2.0/24, then permits all other traffic. Applying it inbound on G0/0 filters traffic from LAN A before routing.
Variation 2. You are connected to R1 via the console. R1 is a router that connects to the internet via GigabitEthernet0/0 (198.51.100.1/30) and to the internal network via GigabitEthernet0/1 (10.1.1.1/24). You need to implement a security policy that permits HTTP traffic (port 80) from the internal network to a web server at 10.1.1.100, and denies all other traffic from internal hosts to the internet. The ACL should be named 'INTERNET-FILTER' and applied inbound on GigabitEthernet0/1.
medium
✓ A.ip access-list extended INTERNET-FILTER
permit tcp 10.1.1.0 0.0.0.255 host 10.1.1.100 eq 80
deny ip 10.1.1.0 0.0.0.255 any
!
interface GigabitEthernet0/1
ip access-group INTERNET-FILTER in
B.ip access-list standard INTERNET-FILTER
permit 10.1.1.0 0.0.0.255
!
interface GigabitEthernet0/1
ip access-group INTERNET-FILTER in
C.ip access-list extended INTERNET-FILTER
permit tcp host 10.1.1.100 10.1.1.0 0.0.0.255 eq 80
deny ip any any
!
interface GigabitEthernet0/1
ip access-group INTERNET-FILTER in
D.ip access-list extended INTERNET-FILTER
permit tcp 10.1.1.0 0.0.0.255 host 10.1.1.100 eq 80
deny ip any any
!
interface GigabitEthernet0/0
ip access-group INTERNET-FILTER in
Why A: The named extended ACL filters traffic based on source, destination, and protocol. The permit allows HTTP from internal to the web server. The deny blocks all other internal-to-internet traffic. Applying it inbound on the internal interface filters traffic as it enters the router.
Variation 3. You are connected to R1. The network currently permits all HTTP traffic from hosts on the 192.168.1.0/24 LAN to reach the web server at 203.0.113.10, but SSH traffic (TCP port 22) from the same LAN is being blocked. Additionally, you must ensure that no other traffic from the LAN reaches the server. Configure an extended ACL on R1 to allow only HTTP and SSH from the LAN to the server, and apply it inbound on the correct interface. Verify your solution.
hard
✓ A.Remove the existing ACL from the interface, delete the ACL, create a new extended ACL that permits tcp from 192.168.1.0/24 to host 203.0.113.10 for ports 80 and 22, and apply it inbound on GigabitEthernet0/0.
B.Modify the existing ACL BLOCK_SSH by adding a permit statement for HTTP and changing the deny SSH to permit SSH, then reapply it inbound on GigabitEthernet0/0.
C.Create a new extended ACL that permits tcp from 192.168.1.0/24 to host 203.0.113.10 for ports 80 and 22, and apply it inbound on GigabitEthernet0/1 (the WAN interface).
D.Create a new extended ACL that permits tcp from 192.168.1.0/24 to host 203.0.113.10 for ports 80 and 22, and apply it outbound on GigabitEthernet0/0.
Why A: The existing ACL BLOCK_SSH is applied inbound on GigabitEthernet0/0 and explicitly denies SSH from the LAN to the server, but permits all other IP traffic (including HTTP). The requirement is to allow only HTTP and SSH, blocking everything else. The solution is to remove the current ACL from the interface, delete the ACL, create a new extended ACL that permits tcp from the LAN to the server for ports 80 (HTTP) and 22 (SSH), and implicitly deny all other traffic, then reapply it inbound on GigabitEthernet0/0.
Last reviewed: Jun 6, 2026
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