Which is a primary purpose of implementing an Access Control List on a router?

• A. To filter traffic and enforce security policies between networks.
• B. To improve wireless coverage in a subnet.
• C. To automatically adapt routing protocols to topology changes.
• D. To assign IP addresses to clients.

Answer: (A)

Access Control Lists on a router are used to filter traffic and enforce security policies between networks. By listing criteria such as source and destination IP addresses, protocols, and sometimes ports, an ACL determines which packets are permitted to pass across an interface and which should be blocked. This boundary control is the primary way routers enforce access restrictions, protect sensitive segments, and control who can reach what resources across network boundaries. For instance, you can block traffic from a guest subnet to the internal network while still allowing essential services to pass.

The other options don’t fit because wireless coverage is about signal reach and quality, not packet filtering. Automatically adapting routing protocols to topology changes is about dynamic routing behavior, not access control. Assigning IP addresses to clients falls under DHCP or manual addressing, not ACLs.