The answer is that the ACL is blocking more traffic than intended because it uses the 'deny ip' statement, which blocks all IP traffic to the server instead of only HTTPS. This is a classic ACL misconfiguration where the entry is too broad, as 'deny ip' matches any protocol, while blocking only HTTPS requires matching TCP port 443 with a command like 'deny tcp any host [server-ip] eq 443'. On the CCNA 200-301 v2 exam, this tests your understanding of extended ACL syntax and the critical difference between protocol-specific and protocol-generic entries. A common trap is assuming 'deny ip' is sufficient for blocking a single application, but it inadvertently blocks everything, including necessary services like DNS or ICMP. Remember the memory tip: "IP is all, TCP is specific"—when filtering by port, always specify the protocol (TCP or UDP) and the port number, never use 'ip' unless you intend to block all traffic to that destination.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS.. 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
Requirement:
- Block HTTPS from 10.20.20.0/24 to 172.16.5.10
- Allow all other traffic
Configured entry:
deny ip 10.20.20.0 0.0.0.255 host 172.16.5.10
Based on the exhibit, why is the ACL not meeting the requirement to block only HTTPS traffic to the server?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Because the ACL entry is too broad and blocks all IP traffic to the host.
The ACL fails because it uses 'deny ip' which blocks all IP traffic to the server, not just HTTPS. To block only HTTPS, the ACL should match TCP port 443 with 'deny tcp eq 443'. Option B is wrong because HTTPS uses TCP, not UDP. Option C is wrong because extended ACLs (not standard) are required to filter by port. Option D is wrong because a host destination is perfectly valid in extended ACLs; a wildcard subnet is not required.
Key principle: Extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Because the ACL entry is too broad and blocks all IP traffic to the host.
Why this is correct
This is correct because `deny ip` blocks far more than only HTTPS.
Related concept
Extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS.
In a different question scenario where the focus is on protocols and their transport layers, if the question asked about blocking traffic for a protocol that indeed uses UDP, such as QUIC (which is used for HTTP/3), then this option could be correct.
✗
Because standard ACLs are required for HTTPS filtering.
Why it's wrong here
This is wrong because filtering by protocol and port requires extended ACL behavior.
When this WOULD be correct
In a different exam scenario where the question states that only standard ACLs can be used for filtering traffic types, and the focus is on the limitations of standard ACLs in filtering specific protocols, this option could be correct. For example, if the question specified that only standard ACLs are allowed for traffic filtering, it would imply that advanced filtering for HTTPS is not possible.
✗
Because the destination must always be a wildcarded subnet, not a host.
Why it's wrong here
This is wrong because host-specific matches are valid and common.
When this WOULD be correct
In a different exam scenario where the question specifically states that only wildcarded subnets can be used for ACL entries, option D would be correct. For instance, if the question asked about a requirement to block traffic to a range of IP addresses rather than a single host, this option would apply.
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.
✓Because the ACL entry is too broad and blocks all IP traffic to the host.Correct answer▾
Why this is correct
This is correct because `deny ip` blocks far more than only HTTPS.
✗Because HTTPS uses UDP, not TCP.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because HTTPS operates over TCP, not UDP. Therefore, the statement that HTTPS uses UDP is fundamentally flawed and does not address the ACL's blocking behavior.
★ When this WOULD be the correct answer
In a different question scenario where the focus is on protocols and their transport layers, if the question asked about blocking traffic for a protocol that indeed uses UDP, such as QUIC (which is used for HTTP/3), then this option could be correct.
Why candidates choose this
Candidates may be misled by the association of HTTPS with secure communication and mistakenly recall that it could use UDP, leading them to select this option without fully understanding the transport layer details.
✗Because standard ACLs are required for HTTPS filtering.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because HTTPS operates over TCP, not UDP. Therefore, standard ACLs can be used to filter HTTPS traffic based on TCP port 443.
★ When this WOULD be the correct answer
In a different exam scenario where the question states that only standard ACLs can be used for filtering traffic types, and the focus is on the limitations of standard ACLs in filtering specific protocols, this option could be correct. For example, if the question specified that only standard ACLs are allowed for traffic filtering, it would imply that advanced filtering for HTTPS is not possible.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of the transport layer protocols, confusing HTTPS with other protocols that do use UDP, such as DNS or certain streaming services.
✗Because the destination must always be a wildcarded subnet, not a host.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because HTTPS operates over TCP, not UDP. Therefore, the issue of blocking HTTPS traffic cannot be attributed to the protocol type being used.
★ When this WOULD be the correct answer
In a different exam scenario where the question specifically states that only wildcarded subnets can be used for ACL entries, option D would be correct. For instance, if the question asked about a requirement to block traffic to a range of IP addresses rather than a single host, this option would apply.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of ACL configurations, believing that specific destination types (wildcarded subnets) are universally required for all types of traffic filtering, including HTTPS.
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: answer the scenario, not the keyword
Ensure you understand the difference between blocking specific ports and blocking all traffic. Misconfiguring an ACL by using 'deny ip' instead of 'deny tcp eq 443' is a common mistake.
Detailed technical explanation
How to think about this question
Access Control Lists (ACLs) are fundamental tools in Cisco networking used to filter traffic based on defined criteria such as protocol, source and destination IP addresses, 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 protocol-specific filtering like HTTPS. HTTPS traffic specifically uses TCP port 443, so an ACL intended to block only HTTPS must explicitly deny TCP traffic on port 443 while permitting other traffic.
When designing an ACL to block only HTTPS traffic to a server, the rule must precisely match TCP protocol and destination port 443. Using a broad statement like "deny ip" blocks all IP traffic regardless of protocol or port, which is overly restrictive and does not meet the requirement. The decision process involves selecting an extended ACL with a deny statement for TCP destination port 443 followed by a permit statement for other traffic, ensuring only HTTPS is blocked and all other services remain accessible.
A common exam trap is confusing broad IP denies with protocol-specific denies. Using "deny ip" in an ACL blocks all IP traffic, not just HTTPS, which can cause unintended network outages or service disruptions. Practically, this means legitimate traffic such as HTTP, DNS, or ICMP is also blocked. Understanding the difference between standard and extended ACLs and the importance of specifying protocol and port numbers is critical to avoid this mistake and to implement precise security policies in Cisco environments.
KKey Concepts to Remember
Extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS.
A deny statement with protocol TCP and destination port 443 specifically blocks HTTPS traffic without affecting other IP traffic.
Using a deny ip statement in an ACL blocks all IP traffic between specified endpoints, which is broader than just blocking HTTPS.
Standard ACLs filter only by source IP address and cannot filter traffic based on protocol or port numbers, making them unsuitable for HTTPS filtering.
Host-specific ACL entries using the 'host' keyword are valid and commonly used to target individual devices precisely.
ACLs are processed top-down, and the first matching rule determines the action, so precise ordering and specificity are essential.
Failing to specify the correct protocol and port in an ACL can lead to unintended traffic blocking, causing network connectivity issues.
Cisco devices implicitly deny all traffic not explicitly permitted by ACL entries, so permit statements are necessary to allow desired traffic.
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.
Key takeaway
Extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS.
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 extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — Extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS..
What is the correct answer to this question?
The correct answer is: Because the ACL entry is too broad and blocks all IP traffic to the host. — The ACL fails because it uses 'deny ip' which blocks all IP traffic to the server, not just HTTPS. To block only HTTPS, the ACL should match TCP port 443 with 'deny tcp eq 443'. Option B is wrong because HTTPS uses TCP, not UDP. Option C is wrong because extended ACLs (not standard) are required to filter by port. Option D is wrong because a host destination is perfectly valid in extended ACLs; a wildcard subnet is not required.
What should I do if I get this 200-301 question wrong?
Review extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Extended ACLs allow filtering based on Layer 3 IP addresses and Layer 4 protocol ports, enabling precise control over specific traffic types like HTTPS.
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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. Based on the exhibit, why is the ACL blocking more traffic than intended?
hard
✓ A.Because the ACL denies all TCP traffic to the server instead of only Telnet.
B.Because Telnet uses UDP, not TCP.
C.Because the ACL should be a standard ACL, not an extended ACL.
D.Because the host keyword can never be used with TCP statements.
Why A: The ACL is blocking more traffic than intended because it uses a broad deny against all TCP traffic to the server instead of only the one service that should be denied. In practical terms, the requirement is narrow, but the configured entry is much wider. As a result, multiple TCP-based applications to that server are blocked, not just the intended one.
This is a classic precision problem in ACL design. It tests whether you can compare what the business requirement says against what the ACL actually matches.
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Question Discussion
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