Which statement best describes the function of an ACL?

• A. Filter traffic based on IP, port, and protocol.
• B. It encrypts traffic between endpoints
• C. Filter traffic based on MAC addresses only
• D. It manages routing protocols

Answer: (A)

An ACL is a tool for controlling which packets can pass by inspecting header information and making a yes/no decision. It primarily filters based on IP addresses, port numbers, and the protocol being used. By specifying which source and destination IPs to allow or deny, along with the applicable transport layer port (like 80 for HTTP or 443 for HTTPS) and the protocol (TCP, UDP, ICMP), you can enforce security policies at a router or switch interface. This is why describing its function as filtering traffic based on IP, port, and protocol best captures what an ACL does. ACLs do not encrypt traffic, and they don’t manage routing protocols. (MAC-based filtering is a different mechanism and less common for typical ACLs.)