Question:
Whilst attempting to use this control within MS Access, I'm having some
issues and I'm hoping you can point
me in the right direction toward a solution.
Essentially, the windows firewall stops transfers. I've tried clicking
'Unblock', but it makes no difference. In order for the FTP transfer to
occur, the Windows Firewall needs to be disabled.
I've tried creating exceptions for port 21 and the FTP .dll, but to no
avail. Does the ActiveX Control rely on another program or service which
may still be blocked ?
Answer:
The FTP protocol uses a control channel (port 21) for sending and receiving commands and responses. Data transfers however, occur on a separate data connection that is opened and closed with each file transferred.
The Passive mode controls whether the client or server initiates the data connection by selecting a port in a pre-defined range specified by the FTP protocol, and listening on the socket. With a passive connection, the server listens and the client connects. If your firewall has only opened specific port numbers, this is the connection that may be blocked. With an active connection, the client listens on a socket and the server initiates the data connection.
If Windows Firewall is running on the FTP client computer, the data connection may be blocked. In order for FTP to work, at least one side must allow for connection requests for non-privileged ports above 1024.
