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#1 (**permalink**) 01-05-2008, 03:09 AM

Aixers,
I'm not very familiar with FTP but I'm trying to execute a ftp script
to send/receive data over port 20. Will passive ftp serve this
function and if so, will the server or client control this function.

thanks

#2 (**permalink**) 01-05-2008, 03:09 AM

Ken wrote:

> Aixers,
> I'm not very familiar with FTP but I'm trying to execute a ftp script
> to send/receive data over port 20. Will passive ftp serve this
> function and if so, will the server or client control this function.
>
> thanks

FTP uses two ports: A control port and a data port. First, the client
connects to the control port of the server (default is port 21). For data
transfer the client chooses one of the following possibolities:

Port FTP (the traditional version): The client starts a listener at a free
port (>=1024) and tell this port to the server using the control
connection. Than the server acts as a client connect to the FTP client
system using _source port_ 20 and destination port which the FTP client has
transmitted.

Passive FTP: The server starts a listener at a free port (>=1024) and tell
this port to the client using the control connection. The client starts a
new connection to this second server port.

So port 20 is used by port FTP (not passive ftp), but 20 is the source port
of this connection (but on server site), not the destination port. The
client controls which type of connection is used.

Lothar

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