Quick Answer
The answer is that the access control list does not permit the traffic. When a firewall log shows a denied connection, the most likely reason is that no ACL rule explicitly allowed the packet based on its source and destination IP, port, or protocol, triggering the implicit deny rule at the end of every ACL. This is the default behavior for stateful firewalls, and understanding this concept is critical for the Cisco CyberOps Associate 200-201 exam, where you must interpret log entries to identify policy violations rather than misconfigurations or attacks. A common trap is assuming a denied connection indicates a security threat, but in most cases it simply means the traffic was not permitted by the ACL. For the exam, remember that firewalls are “deny by default, allow by exception,” so a denied log entry almost always points back to the ACL. Memory tip: “Implicit deny ends the party—if it’s not allowed, it’s denied.”
This 200-201 practice question tests your understanding of security policies and procedures. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A security analyst reviews the firewall log. What is the most likely reason for the denied connection?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The destination port is blocked by default
Why wrong: Port 80 is not blocked by default.
The source IP address is an external threat
Why wrong: Source IP is internal.
The destination IP is a known malicious host
Why wrong: No evidence of malicious destination.
The access control list does not permit the traffic
Denied by access-group indicates ACL blocking.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The access control list does not permit the traffic
The firewall log shows a denied connection, and the most likely reason is that the access control list (ACL) does not permit the traffic. Firewalls enforce security policies by evaluating traffic against ACL rules; if no rule explicitly allows the packet (based on source/destination IP, port, and protocol), the implicit deny at the end of the ACL drops the connection. This is the default behavior for stateful firewalls and is the most common cause of denied connections in logs.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The destination port is blocked by default
Why it's wrong here
Port 80 is not blocked by default.
The source IP address is an external threat
Why it's wrong here
Source IP is internal.
The destination IP is a known malicious host
Why it's wrong here
No evidence of malicious destination.
The access control list does not permit the traffic
Why this is correct
Denied by access-group indicates ACL blocking.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Cisco often tests the concept that the implicit deny at the end of an ACL is the most common reason for denied traffic, tempting candidates to overthink with threat-based answers like external IPs or malicious hosts.
Detailed technical explanation
Cisco firewalls (e.g., ASA, FTD) use ACLs that are evaluated in sequential order; the first matching permit or deny rule is applied, and if no match occurs, the implicit deny at the end drops the packet. In firewall logs, a denied connection with no specific rule name often corresponds to this implicit deny, which is a fundamental security principle (default-deny stance). Real-world scenarios include misconfigured ACLs where a required permit statement is missing, such as allowing outbound HTTP traffic but forgetting to permit the return traffic for stateful inspection.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
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FAQ
Security Policies and Procedures — This question tests Security Policies and Procedures — Read the scenario before looking for a memorised answer..
The correct answer is: The access control list does not permit the traffic — The firewall log shows a denied connection, and the most likely reason is that the access control list (ACL) does not permit the traffic. Firewalls enforce security policies by evaluating traffic against ACL rules; if no rule explicitly allows the packet (based on source/destination IP, port, and protocol), the implicit deny at the end of the ACL drops the connection. This is the default behavior for stateful firewalls and is the most common cause of denied connections in logs.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
This 200-201 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-201 exam.
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