NetCallback is a Java application permitting the export of TCP and UDP ports behind a firewall to hosts outside the firewall. This may be useful in some special cases, for example, centralized control of test (demo) networks, or connection to applets running in browsers. NetCallback consists of a public and a private server. The public server executes on a host outside the firewall and is responsible for receiving port forwarding requests. The private server is run on a host behind the firewall and is responsible for contacting the public server and connecting the protected TCP and/or UDP service to the public server clients. The connection between public and private servers may optionally be encrypted using SSL.