A database administrator contacts a security administrator to request firewall changes for a connection to a new internal application. The security administrator notices that the new application…

Explicit deny is a specific type of ACL rule entry (a written deny statement), not the broader practice of reviewing and enforcing port-based policies described in the scenario.

Port security is a Layer 2 switch feature that limits network access by MAC address on physical ports, and is unrelated to firewall rule management or application port assignment.

Access control lists enable administrators to define explicit permit and deny rules based on port numbers and protocols. By denying the firewall request for a port associated with known malware and directing the team to use an alternative, the administrator is enforcing a port-based ACL policy. This is a proactive use of ACLs to reduce exposure to known threat vectors by controlling which ports traverse the network boundary.

Implicit deny is the default drop-all behavior at the end of an ACL when no rule matches; the administrator here is making an active, deliberate policy decision rather than relying on a default fallback.