Which of the following is a common feature of firewalls?

A common feature of firewalls is the use of an Access Control List (ACL). ACLs are crucial for determining which traffic is allowed or denied access through the firewall. They consist of a set of rules that specify the conditions under which network traffic can pass, based on criteria like IP addresses, protocols, ports, and other attributes.

This functionality is essential for safeguarding a network from unauthorized access and potential security threats. By meticulously defining what is permissible and what is not, ACLs help in creating a fortified barrier that only permits authenticated and approved traffic, thereby enhancing the overall security posture of a network.

In contrast, data retrieval is not a firewall function; rather, it pertains more to database management or data storage systems. File sharing typically relates to software or services designed to facilitate document transfer between users, which is separate from a firewall's primary purpose. System monitoring, while important for maintaining security, usually refers to tracking system performance and activities rather than controlling access to a network.