A database stores information about known hosts, the applications or services they host, and the ports (known as confirmed ports) used by the applications/services. A static traffic analyzer analyzes traffic data and identifies packets communicating with (either sent to or received from) confirmed ports on hosts. A dynamic traffic analyzer analyzes the traffic data and identifies packets communicating with unconfirmed ports on hosts. A host identifier uses the resulting static and dynamic traffic to identify hosts for which firewall rules should be generated.