Use Passive FTP Transfers

[Steven Barkess]

Hi

On Advanced Network Settings, there is an option to Use Passive FTP Transfers.

For ages I have been unable to load my site in full, I ticked this box and now it has loaded fine.

Whats the function of the Passive part?

Thanks

Steven

[I-CC]

PASSIVE (PASV)

This command requests the server-DTP to "listen" on a data
port (which is not its default data port) and to wait for a
connection rather than initiate one upon receipt of a
transfer command. The response to this command includes the
host and port address this server is listening on.

Is a definitive RFC answer , but basics being:

Normal FTP works on port 21, i.e. you send a request and it leaves you, travels across the internet, into other networks, through numerous firewalls and ends up at the server at the very same port 21....

Using passive FTP, a PASV command is sent instead of a PORT command. Instead of specifying a port that the server can send to, the PASV command asks the server to specify a port it wishes to use for the Data Channel connection. The server replies on the Control Channel with the port number which the client then uses to initiate an exchange on the Data Channel.

[Mike Hughes]

Or, to explain it in a meaningful way (that works for me at least):

With normal (i.e. non passive) ftp the server sometimes has to re-initiate the ftp connection to the PC. Most PC firewalls see this as an incoming connection request (which it is) and block it, thus killing the connection.

Passive ftp tells the server to play a passive role. The ftp client initiates all the connections and the PC firewall sits there happy that the connection is valid and nothing to worry about.

Mike