easyMultiple Choice
200-201 A security analyst reviews the firewall log Practice Question
Network Topology
A security analyst reviews the firewall log. What is the most likely reason for the denied connection?
⚠ Common exam trap
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.
Answer choices
Why each option matters
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.
Answer analysis
Option-by-option breakdown
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
A default-deny rule on that port would explain the denial only if the log shows the port is unlisted rather than explicitly blocked; the stem gives no port detail. It tempts because firewalls do ship with default-deny policies, making this the right answer when a service runs on a non-standard port with no permit rule.
- ✗
The source IP address is an external threat
Why it's wrong here
Firewall logs record the five-tuple and rule matched, not threat reputation; an external source address alone does not cause a deny unless a rule blocks it. Source reputation feeds threat intelligence platforms, which would be the right tool for judging an address's maliciousness.
- ✗
The destination IP is a known malicious host
Why it's wrong here
A deny entry reflects a policy or rule match, not the destination's reputation; firewalls do not inherently block hosts merely because they are known malicious. Blocklists belong in threat intelligence or DNS filtering, which is the correct control when the requirement is blocking known-bad destinations.
- ✓
The access control list does not permit the traffic
Why this is correct
Firewall logs record denied connections when a rule or access control list evaluates the traffic and drops it. The most likely cause is that no ACL entry permits the flow, so the implicit deny terminates the session before it reaches the destination.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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