I am behind the firewall and I have a problem in establishing data connection from my Windows PC(which is behind firewall)with many FTP servers(I tried Agrosoft,Bison etc,,)
I understood in ACTIVE mode, data connection is started by the ftp server from local
data port which is 20. But Bison and other FTP server is not always using local data port
as 20 and hence Firewall is dropping the packet. We could see from the logs that
the packet dropped has server's local port as an unpriviledged port (> 1024).
What will be the solution for this issue other than using passive mode??has anybody faced this similar type of issue and your firewall is allowing this??(understanding that this is only response to the control connection which is already open and not a new request from outside eventhough FTP server uses other than port 20 for data connection)
Re: Problem In FTP Data Connection with Active Mode
Passive mode is the only way out that I know of. If you disable the FTP fixup with the no fixup protocol ftp command, outbound users can start connection in the passive mode only. This should solve the problem of the server using a non-standard port for the data channel since in the passive mode, the data channel is opened by the client on a non-standard port specified by the server. A little bit of background: In the active/normal mode, the server does a passive open on the control channel (ie it starts listening on the port) while the client does a passive open on the data channel. Next, the client opens the control channel (active open) . It then requests the server to open a data channel to the client using the PORT command on a port specified in the command. The server now opens a data channel to the client. To open a data channel in the passive mode, the client sends a PASV command. In response to this command, the server chooses a random port on which it does a passive open, ie starts listening on that port for a data channel. Ths port is communicated to the client which does an active open to the server for the data channel. Thus both the control and the data channels are initiated by the client and the data channel is opened on a port specified by the server.
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