RMI transport layer usually opens direct sockets to the server. Several Intranets have firewalls that do not accept this. To get through the firewall an RMI call may be embedded within the firewall-trusted HTTP protocol. To get across firewalls, RMI builds use of HTTP tunneling by encapsulating RMI calls within an HTTP POST request.
The firewall proxy server will supply the request to a HTTP server listening on port 80, and a CGI script will be implemented to forward the call to the target RMI server port on the similar machine.