... server), you want all external hosts to be able to access the server, so this is not a problem. If you have an FTP server that you only want certain external hosts to access, however, you really ... host. Unfortunately, there is no way to specify which external hosts should be allowed to access the internal resources, so you are forced to allow all external resources access, or allow none ... configuration that most firewalls and routers implement. With port-range forwarding, you enter the starting and ending port that should be permitted, select the appropriate transport protocol (TCP, UDP,...