He's using http protocol. Just because the hostname has ftp in it, doesn't mean it's the ftp protocol.
Also, yes, I believe sudo only carries over the environment variables explicitly told to do so. Can you download packages with a web browser? Have you tried using the ftp program directly? When you loose connection, can you get to other web sites or is your entire network connection down? Do you have access to the Fitz!Box or whatever to see what it's doing?
