Optix
Before I get into my problem, here's the basic setup that I'm attempting to use:
- Server is Serv-U v5.1, running XP firewall only with a true external IP. Server is configured to accept PASV transfers with implicit SSL. Control connection port is non-standard (25201), and a narrow port range for PASV data port connections has been specified in server & forwarded in XP firewall.
- Client is SmartFTP v1.5.989, running behind (presumed) NAT firewall. Client is configured to PASV mode, using AUTH mode SSL, and all data connection modes are set to Private (Secure). Keep Alive feature is enabled.
Basically, my situation involves some sort of forced connection close that happens in the middle of transfers. The client connects to the server on 25201, negotiates a TLS session successfully, and logs on normally. PASV mode is then initiated, and the client successfully connects securely on a port from the server's specified data port range. A large file transfer (download) is begun, and the data transfers normally until . . . exactly 1 or 2 hours later to the minute, the connection is unexpectedly aborted. Checking my Serv-U logs shows multiple FD_CLOSE messages, initiated seemingly by the client although I suspect they may actually be coming from the NAT.
The only reasoning I can come up with is that the control connection port is being perceived by the NAT as idle since the connection is secure and therefore the NOOP's can't be unencrypted. However, one would expect the NAT to refuse to open the data port at all because it can't unencrypt the PASV data port request coming from the server in the first place, right? Yet somehow it allows the data port connection, at least for those couple of hours.
I haven't tried connecting without the SSL, but I would rather work out a method for maintaining privacy and working successfully with the NAT if possible. I've also tried setting the client option for Control Connection Mode to Clear, but that setting causes a 500 Command Not Understood error from the server and an immediate disconnect.
Sorry about the length of this, but I'm getting a bit desperate, so any suggestions would be very much appreciated. TIA!
- Server is Serv-U v5.1, running XP firewall only with a true external IP. Server is configured to accept PASV transfers with implicit SSL. Control connection port is non-standard (25201), and a narrow port range for PASV data port connections has been specified in server & forwarded in XP firewall.
- Client is SmartFTP v1.5.989, running behind (presumed) NAT firewall. Client is configured to PASV mode, using AUTH mode SSL, and all data connection modes are set to Private (Secure). Keep Alive feature is enabled.
Basically, my situation involves some sort of forced connection close that happens in the middle of transfers. The client connects to the server on 25201, negotiates a TLS session successfully, and logs on normally. PASV mode is then initiated, and the client successfully connects securely on a port from the server's specified data port range. A large file transfer (download) is begun, and the data transfers normally until . . . exactly 1 or 2 hours later to the minute, the connection is unexpectedly aborted. Checking my Serv-U logs shows multiple FD_CLOSE messages, initiated seemingly by the client although I suspect they may actually be coming from the NAT.
The only reasoning I can come up with is that the control connection port is being perceived by the NAT as idle since the connection is secure and therefore the NOOP's can't be unencrypted. However, one would expect the NAT to refuse to open the data port at all because it can't unencrypt the PASV data port request coming from the server in the first place, right? Yet somehow it allows the data port connection, at least for those couple of hours.
I haven't tried connecting without the SSL, but I would rather work out a method for maintaining privacy and working successfully with the NAT if possible. I've also tried setting the client option for Control Connection Mode to Clear, but that setting causes a 500 Command Not Understood error from the server and an immediate disconnect.
Sorry about the length of this, but I'm getting a bit desperate, so any suggestions would be very much appreciated. TIA!