A computer with two or more network interfaces. A dual-homed host can act as a simple firewall on a small network as long as there is no direct IP traffic between the Internet and the internal network. In such a case, all Internet applications are run only on the dual-homed host. See firewall
A Simple Firewall
A dual-homed host can serve as an effective firewall as long as there is no need to connect from users' machines on the private LAN to the Internet. All Internet applications are done in the dual-homed host.