The FTP protocol is relatively easy to proxy; the firewall decides, for example, whether an outsider should be able to access a particular directory in the file system and issues a corresponding...

The FTP protocol is relatively easy to proxy; the firewall decides, for example, whether an outsider should be able to access a particular directory in the file system and issues a corresponding command to the inside file manager or responds negatively to the outsider. Other protocols are not feasible to proxy. List three protocols that it would be prohibitively difficult or impossible to proxy