FTP Port Problem (Active/Passive)???

[rmnewbie]

Hello! I need some FTP help. I'm using the standard Windows FTP Client on NT4sp6 and their FTP server drops my connection as soon as my client tries any data command (DIR, LS, etc). Control commands work fine.

They only accept Active FTP connections- I am almost certain that's what I'm using. no PASV commands executed. I have done a packet capture and the last frame from my client shows...
Request command: PORTRequest arg: 192,x,x,x ,x,x

How can I tell if my client is just saying it's "listening" on Port N+1 or if it's actually issuing a port change command to the server?

I have tried other client (Ws-Ftp_pro, Lexicom) with the same result- I always choose Active FTP.

Please help... Best regards,
Rob McCoy
rmccoy@unionbay.com

 

[jaytco]

A few thoughts. Have you verified the connectivity going the otherway? I have seen in the past where port 21 could be built to the server, but the data connection, port 20 could not be built back. We would receive a timeout after a large amout of time. I would verify the server can connect to your computer, and that port 20/21 are open in the network.

 

[Stijn147]

If your IP-address is 192.168.x.x, you're using a private IP-address and you connect to the internet through a NAT-router.
The problem with private IP-addresses is that you can make connections with servers on the internet, but they can't make connections with you. FTP in active mode opens the data connection (port 20) for the commands DIR,PUT en GET: The client sends a PORT command and listens to that port, then the server opens the connection on that port, wich is impossible.
The solution is to use passive transfers or use a NAT implementation that supports FTP.

 

[bcastner]

Clients that can do PORT mode behind an NAT firewall:
FlashFXP
BPFTP

Also, for the Microsoft clients you need to enable 'Use Folder View' or the client reverts to PASV mode, no matter what what the setting for PASV mode was set to.
See this article:

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q309816

 

[rmnewbie]

Thanks very much! Problem now solved. I was using the wrong rule on our Firewall (I was using the ANY service rule and not an FTP rule). The firewall was killing the 2nd session packets from the FTP server- not asociating them with the original FTP session already working.

Thanks again!

 

[bcastner]

For a very good discussion of PORT FTP problems and cures behind NAT see this link:

http://www.broadbandreports.com/forum/remark,1381832;root=equip,16;mode=flat