CompTIA CySA+ Practice Test

Blocking traffic to the specified port in the Access Control List (ACL) is the most effective approach for preventing unauthorized access to a specific service. ACLs are used to define which types of traffic are allowed or denied in a network. By specifically configuring an ACL to block traffic on a particular port, you can effectively prevent any unauthorized attempts to connect to the service associated with that port.

This method directly addresses the issue of port access, ensuring that packets destined for the specified port are not processed by the system, thus preventing any potential security threats from accessing that service. This targeted filtering is simple and efficient, making it a preferred tactic in network security practices.

Other options do play roles in security but are not as direct in addressing unauthorized access to a specific service through port blocking. For instance, session limiting can control the number of connections but does not inherently block those connections entirely. Encryption protocols enhance the security of data in transit but do not prevent access to a specific service. Bandwidth throttling manipulates the speed of data transfer and can influence performance but does not restrict access to a specific service. Hence, focusing on ACLs provides the most direct and effective means to secure access to designated services by managing port traffic directly.