Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Users in 10.10.10.0/24 must be prevented from reaching the web server at 172.16.1.10 over HTTP, but all other traffic should be allowed. Which ACL entry best matches the requirement?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
deny tcp 10.10.10.0 0.0.0.255 host 172.16.1.10 eq 80
This is correct because it blocks only TCP port 80 traffic from the source subnet to the web server.
B
Distractor review
deny ip 10.10.10.0 0.0.0.255 host 172.16.1.10
This is wrong because it blocks all IP traffic to the server, not just HTTP.
C
Distractor review
deny udp 10.10.10.0 0.0.0.255 host 172.16.1.10 eq 80
This is wrong because normal HTTP uses TCP, not UDP.
D
Distractor review
permit tcp 10.10.10.0 0.0.0.255 host 172.16.1.10 eq 80
This is wrong because it would explicitly allow the traffic that should be blocked.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is selecting a deny statement that blocks all IP traffic (option B) instead of just HTTP traffic. This overblocking disrupts legitimate services beyond HTTP, violating the requirement to allow all other traffic. Another trap is denying UDP port 80 (option C), which is ineffective because HTTP uses TCP, not UDP. Additionally, mistakenly permitting TCP port 80 traffic (option D) contradicts the goal of blocking HTTP access. Understanding the difference between protocol types and the impact of broad versus specific ACL entries is essential to avoid these pitfalls.
Technical deep dive
How to think about this question
Access Control Lists (ACLs) are fundamental Cisco security tools used to filter traffic based on defined criteria such as source IP, destination IP, protocol, and port numbers. Extended ACLs provide granular control by allowing filtering on Layer 3 and Layer 4 parameters, including TCP/UDP ports, which is essential for controlling specific application traffic like HTTP. In this scenario, the goal is to block only HTTP traffic (TCP port 80) from a specific subnet to a particular web server, while permitting all other traffic. The correct ACL entry uses a deny statement targeting TCP traffic from the 10.10.10.0/24 subnet to the host 172.16.1.10 on port 80. This precision ensures that only HTTP traffic is blocked, without affecting other protocols or ports. The use of the wildcard mask 0.0.0.255 correctly matches the entire source subnet, and the 'eq 80' qualifier specifies the HTTP port. This approach follows best practices for ACL design by minimizing unintended traffic disruption. A common exam trap is confusing the protocol or overblocking traffic. For example, denying all IP traffic to the server would block legitimate services beyond HTTP, which is not the requirement. Similarly, denying UDP port 80 is ineffective because HTTP uses TCP. Understanding the protocol and port specificity in ACLs is critical for both exam success and real-world network security. Practically, this ACL entry allows network administrators to enforce precise security policies without impacting overall network functionality.
KKey Concepts to Remember
- An extended ACL can filter traffic based on source IP, destination IP, protocol, and Layer 4 port numbers for precise traffic control.
- The 'deny tcp' statement in an ACL blocks only TCP traffic matching the specified source, destination, and port criteria, allowing other traffic through.
- Using a wildcard mask of 0.0.0.255 in an ACL matches all hosts within the 10.10.10.0/24 subnet as the source address.
- Specifying 'eq 80' in an ACL targets HTTP traffic by matching TCP port 80, which is the standard port for web server communication.
- A broad 'deny ip' ACL entry blocks all IP traffic between source and destination, which can unintentionally disrupt non-HTTP services.
- ACLs process entries in sequential order, so placing a specific deny statement before a permit statement ensures only targeted traffic is blocked.
- HTTP traffic uses TCP, not UDP, so denying UDP port 80 does not block HTTP and is ineffective for this requirement.
- Correct ACL design requires matching the exact protocol and port to avoid overblocking or underblocking traffic, which is critical in Cisco security fundamentals.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
An extended ACL can filter traffic based on source IP, destination IP, protocol, and Layer 4 port numbers for precise traffic control.
What is the correct answer to this question?
The correct answer is: deny tcp 10.10.10.0 0.0.0.255 host 172.16.1.10 eq 80 — The correct ACL entry is an extended ACL deny statement that matches TCP from the source subnet to the destination host on port 80. In practical terms, the requirement is narrow: block HTTP only, from one source network to one server, while allowing everything else. That means using `deny tcp` with the right source, destination, and port is more accurate than using a broad `deny ip`. This is a classic ACL precision question. The exam is testing whether you can match the requirement exactly rather than overblocking.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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