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CAS-004 Practice Question: A network administrator is configuring a firewall…
A network administrator is configuring a firewall to block traffic from a specific IP address range. The firewall uses ACLs. Which ACL entry would deny traffic from 192.168.1.0/24?
⚠ Common exam trap
It's easy for candidates to confuse subnet masks with wildcard masks, selecting option D (255.255.255.0) instead of the correct wildcard mask 0.0.0.255.
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
✓
deny ip 192.168.1.0 0.0.0.255 any
In Cisco ACL syntax, the wildcard mask 0.0.0.255 matches all addresses in the 192.168.1.0/24 network. The 'deny ip 192.168.1.0 0.0.0.255 any' entry blocks any IP traffic from the source subnet 192.168.1.0 through 192.168.1.255 to any destination.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
deny ip 192.168.1.0 0.0.0.255 any
Why this is correct
Wildcard 0.0.0.255 matches the entire /24 subnet.
- ✗
deny ip 192.168.1.0 0.0.0.0 any
Why it's wrong here
Wildcard 0.0.0.0 matches only the specific host 192.168.1.0.
- ✗
deny ip 192.168.1.0 0.0.0.127 any
Why it's wrong here
Wildcard 0.0.0.127 matches a /25 subnet, not /24.
- ✗
deny ip 192.168.1.0 255.255.255.0 any
Why it's wrong here
ACLs use wildcard masks, not subnet masks.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 practice question is part of Courseiva's free CompTIA 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 CAS-005 exam.