CompTIA: Advanced Security Practitioner (CASP) Exam Prep

Answer: A - Routers can be configured to act as packet-filtering firewalls. When configured so, they can prevent unauthorized ports from being opened.

Key Takeaway: A packet-filtering router makes a permit or deny decision for each packet that it receives. The router examines each datagram to determine whether it matches one of its packet-filtering rules. The filtering rules are based on the packet header information that is made available to the IP forwarding process. If a match is found and the rule permits the packet, the packet is forwarded according to the information in the routing table. If a match is found and the rule denies the packet, the packet is discarded. If there is no matching rule, a user-configurable default parameter determines whether the packet is forwarded or discarded.