PASV mode & ftp server - Information needed.

[slewis1972]

Having a few problems setting up a ftp server and it seems the problem could be with PASV mode.

Anyway, what I want to know is that I know on setting up an ftp server as standard port 21 needs to be open. BUT with PASV does another port need to be open, as on Zonealarm Pro it asks for a port for outgoing TCP connections.

Any ideas,

Scott

[Dave22]

Normal mode FTP:

Client source port is > 1023 with a destination of port 21. This opens the command channel. Then the SERVER initiates a connection sourced from port 20 with a destination of > 1023 (the client tells the server which port to connect to via the PORT command). Note that this is "strange" because the SERVER initiates a connection.

Passive mode:

Client opens the command channel (source > 1023, destination = 21). Then the CLIENT opens the data channel using the PASV command (source > 1023, destination also > 1023) Notice that the CLIENT does all the requesting and that in passive mode, port 20 is NOT used.