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
hostname R1
!
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
no shutdown
!
interface GigabitEthernet0/1
ip address 203.0.113.1 255.255.255.0
no shutdown
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1
!
You are connected to R1. The network has a web server at 203.0.113.10 and a DNS server at 203.0.113.20. Hosts in the 192.168.1.0/24 subnet should be able to access HTTP to the web server and DNS queries to the DNS server, but all other traffic from that subnet to the servers must be blocked. Configure an extended ACL on R1 to achieve this, and apply it inbound on the correct interface. The current configuration is shown below.
This ACL permits HTTP to the web server and DNS to the DNS server, then denies all other IP traffic from the 192.168.1.0/24 subnet to the 203.0.113.0/24 network. It is applied inbound on GigabitEthernet0/0, which is the interface facing the 192.168.1.0/24 subnet, ensuring traffic is filtered as it enters R1.
B
access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 203.0.113.10 eq 80
access-list 100 permit udp 192.168.1.0 0.0.0.255 host 203.0.113.20 eq 53
access-list 100 deny ip any any
interface GigabitEthernet0/1
ip access-group 100 in
Why wrong: This ACL denies all IP traffic from any source, which would block the permitted traffic as well. Additionally, it is applied inbound on GigabitEthernet0/1, which is likely the interface facing the servers, not the subnet. The deny ip any any at the end would block everything, making the permit statements ineffective.
Why wrong: This ACL is applied outbound on GigabitEthernet0/0, which means it filters traffic leaving R1 through that interface. However, the traffic from the 192.168.1.0/24 subnet destined to the servers would exit via GigabitEthernet0/1 (or another interface), not GigabitEthernet0/0. Applying it outbound on the wrong interface would not filter the traffic as intended.
Why wrong: This ACL is applied inbound on GigabitEthernet0/1, which is the interface facing the servers. Inbound ACLs filter traffic entering the router through that interface. Traffic from the 192.168.1.0/24 subnet arrives via GigabitEthernet0/0, not GigabitEthernet0/1, so this ACL would not filter that traffic.
The required ACL must permit HTTP (tcp dst eq 80) and DNS (udp dst eq 53) from 192.168.1.0/24 to the servers, then deny all other IP traffic from that subnet. The ACL is applied inbound on GigabitEthernet0/0 to filter traffic as it enters R1 from the 192.168.1.0/24 subnet. The commands sequence creates the ACL with the correct permit statements, an explicit deny ip any any (optional but shown for clarity), and applies it to the interface.
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.
This ACL permits HTTP to the web server and DNS to the DNS server, then denies all other IP traffic from the 192.168.1.0/24 subnet to the 203.0.113.0/24 network. It is applied inbound on GigabitEthernet0/0, which is the interface facing the 192.168.1.0/24 subnet, ensuring traffic is filtered as it enters R1.
access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 203.0.113.10 eq 80
access-list 100 permit udp 192.168.1.0 0.0.0.255 host 203.0.113.20 eq 53
access-list 100 deny ip any any
interface GigabitEthernet0/1
ip access-group 100 in
Why it's wrong here
This ACL denies all IP traffic from any source, which would block the permitted traffic as well. Additionally, it is applied inbound on GigabitEthernet0/1, which is likely the interface facing the servers, not the subnet. The deny ip any any at the end would block everything, making the permit statements ineffective.
This ACL is applied outbound on GigabitEthernet0/0, which means it filters traffic leaving R1 through that interface. However, the traffic from the 192.168.1.0/24 subnet destined to the servers would exit via GigabitEthernet0/1 (or another interface), not GigabitEthernet0/0. Applying it outbound on the wrong interface would not filter the traffic as intended.
This ACL is applied inbound on GigabitEthernet0/1, which is the interface facing the servers. Inbound ACLs filter traffic entering the router through that interface. Traffic from the 192.168.1.0/24 subnet arrives via GigabitEthernet0/0, not GigabitEthernet0/1, so this ACL would not filter that traffic.
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.
This ACL permits HTTP to the web server and DNS to the DNS server, then denies all other IP traffic from the 192.168.1.0/24 subnet to the 203.0.113.0/24 network. It is applied inbound on GigabitEthernet0/0, which is the interface facing the 192.168.1.0/24 subnet, ensuring traffic is filtered as it enters R1.
✗access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 203.0.113.10 eq 80
access-list 100 permit udp 192.168.1.0 0.0.0.255 host 203.0.113.20 eq 53
access-list 100 deny ip any any
interface GigabitEthernet0/1
ip access-group 100 inWrong answer — click to see why▾
Why this is wrong here
The deny ip any any statement overrides the permit statements because ACLs are processed sequentially; any packet matching the deny is dropped. Also, applying the ACL inbound on the server-facing interface would filter traffic coming from the servers, not from the 192.168.1.0/24 subnet.
Why candidates choose this
Candidates might think that a deny ip any any is needed to block all other traffic, but they forget that the implicit deny any already exists. They may also confuse which interface to apply the ACL inbound.
✗access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 203.0.113.10 eq 80
access-list 100 permit udp 192.168.1.0 0.0.0.255 host 203.0.113.20 eq 53
access-list 100 deny ip 192.168.1.0 0.0.0.255 203.0.113.0 0.0.0.255
interface GigabitEthernet0/0
ip access-group 100 outWrong answer — click to see why▾
Why this is wrong here
The ACL should be applied inbound on the interface receiving traffic from the 192.168.1.0/24 subnet (GigabitEthernet0/0) to filter before routing. Applying it outbound on the same interface would only filter traffic leaving that interface, which is not the traffic path from the subnet to the servers.
Why candidates choose this
Candidates may confuse inbound vs outbound ACL application. They might think outbound is correct because the traffic is going out to the servers, but the ACL must be placed where the traffic enters the router from the source subnet.
✗access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 203.0.113.10 eq 80
access-list 100 permit udp 192.168.1.0 0.0.0.255 host 203.0.113.20 eq 53
access-list 100 deny ip 192.168.1.0 0.0.0.255 203.0.113.0 0.0.0.255
interface GigabitEthernet0/1
ip access-group 100 inWrong answer — click to see why▾
Why this is wrong here
The ACL must be applied on the interface closest to the source of the traffic to be filtered. Since the traffic originates from the 192.168.1.0/24 subnet, the ACL should be applied inbound on GigabitEthernet0/0, not on the server-facing interface.
Why candidates choose this
Candidates might think that applying the ACL inbound on the server-facing interface will protect the servers, but inbound ACLs filter traffic coming into the router from that interface, which would be traffic from the servers, not from the subnet.
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 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: access-list 100 permit tcp 192.168.1.0 0.0.0.255 host 203.0.113.10 eq 80
access-list 100 permit udp 192.168.1.0 0.0.0.255 host 203.0.113.20 eq 53
access-list 100 deny ip 192.168.1.0 0.0.0.255 203.0.113.0 0.0.0.255
interface GigabitEthernet0/0
ip access-group 100 in — The required ACL must permit HTTP (tcp dst eq 80) and DNS (udp dst eq 53) from 192.168.1.0/24 to the servers, then deny all other IP traffic from that subnet. The ACL is applied inbound on GigabitEthernet0/0 to filter traffic as it enters R1 from the 192.168.1.0/24 subnet. The commands sequence creates the ACL with the correct permit statements, an explicit deny ip any any (optional but shown for clarity), and applies it to the interface.
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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