Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
Requirement: - Block HTTPS from 10.44.44.0/24 to 172.16.8.20 Configured ACL entry: deny tcp 10.44.44.0 0.0.0.255 host 172.16.8.20 eq 80
Based on the exhibit, why does the ACL still allow HTTPS traffic from the branch subnet to the server?
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
The ACL blocks TCP port 80 instead of TCP port 443.
This is correct because HTTPS normally uses TCP port 443, not port 80.
B
Distractor review
HTTPS uses UDP port 443, so TCP matching can never work.
This is wrong because HTTPS normally uses TCP, not UDP.
C
Distractor review
The ACL must deny all IP traffic to the server to stop HTTPS.
This is wrong because a narrow service-specific deny is sufficient and preferable.
D
Distractor review
ACLs cannot filter by destination port when a host keyword is used.
This is wrong because host-based matches and port filters are both valid in extended ACL logic.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is assuming that blocking TCP port 80 also blocks HTTPS traffic. Candidates may see a deny statement for port 80 and mistakenly conclude that all web traffic is blocked. However, HTTPS uses TCP port 443, so if the ACL does not explicitly deny port 443, HTTPS traffic will still be allowed. This trap tests attention to detail and understanding of port assignments for common services. Overlooking the exact port number leads to incorrect conclusions about ACL effectiveness and network security.
Technical deep dive
How to think about this question
Access Control Lists (ACLs) are fundamental security tools in Cisco networking that filter traffic based on defined criteria such as source/destination IP addresses, protocols, and port numbers. Extended ACLs specifically allow filtering by protocol and port numbers, enabling precise control over traffic types like HTTP or HTTPS. HTTPS traffic typically uses TCP port 443, while HTTP uses TCP port 80, so ACLs must match the correct port to effectively permit or deny traffic. When configuring ACLs to block or allow traffic, the exact port number is critical. A deny statement targeting TCP port 80 will block HTTP but not HTTPS traffic, which uses port 443. Cisco devices evaluate ACL entries sequentially, so if the ACL only denies port 80 and permits other traffic, HTTPS traffic will pass through. This behavior underscores the importance of matching the correct port in ACL rules to enforce intended security policies. The exam trap arises when candidates assume blocking HTTP (port 80) also blocks HTTPS (port 443), which is incorrect. Practically, this means encrypted web traffic remains allowed if the ACL does not explicitly deny port 443. Understanding this distinction is vital for both exam success and real-world network security, as misconfigured ACLs can leave sensitive traffic unfiltered and vulnerable.
KKey Concepts to Remember
- An extended ACL in Cisco IOS can filter traffic based on protocol type and specific TCP or UDP port numbers to control network access precisely.
- HTTPS traffic uses TCP port 443 by default, so ACL rules must explicitly reference port 443 to block or permit HTTPS connections.
- Denying TCP port 80 in an ACL only blocks HTTP traffic and does not affect HTTPS traffic, which uses a different port.
- Cisco ACLs process entries in sequential order and stop at the first match, so the order and specificity of rules impact traffic filtering.
- Using the 'host' keyword in ACLs allows matching a specific IP address, and this can be combined with port filtering for granular control.
- Misconfiguring ACLs by targeting incorrect ports is a common mistake that results in unintended traffic being allowed or blocked.
- ACLs do not implicitly block traffic unless a deny statement matches; traffic not explicitly denied is permitted by default or by an implicit deny at the end.
- Understanding the difference between TCP and UDP ports is essential when writing ACLs to ensure correct protocol filtering.
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 in Cisco IOS can filter traffic based on protocol type and specific TCP or UDP port numbers to control network access precisely.
What is the correct answer to this question?
The correct answer is: The ACL blocks TCP port 80 instead of TCP port 443. — The ACL still allows the HTTPS traffic because the deny statement is matching TCP port 80, not TCP port 443. In practical terms, the entry blocks HTTP, not HTTPS. Since the requirement is specifically to block encrypted web traffic on TCP 443, the current line is aimed at the wrong service. This is a good precision question because it tests whether the candidate pays attention to the exact destination port rather than just seeing a generic web-related deny.
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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