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Old 02-14-2003, 01:34 PM   #1
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Registered: Jan 2002
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Windows FTP clients through Linux Firewall

I was hopping that somebody could help me with what looks like a firewall issue on the clients side.

We run an FTP server in house and it works for most all people trying to connect

The clients having trouble are ones running Linux (specifically redhat 7.x and above) and using windows boxes to connect with ftp clients to our server.

If the clients uses passive mode they connect OK but can't do things like create directories or upload files. Change directory seems to work OK.

If they use active mode they can't connect at all or have great troubles doing it.

I have ip_conntrack_ftp module running on their end so that can't be it. We even opened them up the ports quite a lot and still no go.

If I run an FTP session from that Linux box it connects perfect so I am assuming it has something to do with either the client OR IPTABLES.

However here is the wierd part. IE doesn't work, Command line doesn't work, BUT WS-FTP LE works awesome. Not sure what it does special but it works. Problem is that people won't just use that. They want their stuff to work.
Old 02-14-2003, 07:13 PM   #2
Registered: Apr 2002
Location: Melbourne, Australia
Distribution: Gentoo
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active ftp is a bit of a bugger. It uses port 21 to send commands etc and port 20 to send data. You have the conntrack module loaded so you need to configure the states to make this work. For passive FTP an ESTABLISHED connection is suffiecient but because active FTP uses a different port for the data you need to use the REALTED state. Check out for a good description of this, down the bottom of the document there is a description of the state youneed to set for active (and passive) ftp to work.

Old 02-14-2003, 09:42 PM   #3
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Thanx for that info. That is acutally something that will help elsewhere.

I should add that I WANT the clients using Passive but that doesn't work either. They are able to log in, change directories and that is about it.
Old 02-15-2003, 11:59 PM   #4
Registered: Apr 2002
Location: Melbourne, Australia
Distribution: Gentoo
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does LIST work? or can they only change directories if they know where the directory is. In other words do they log in send LIST and get the list of files? If they do then maybe it is a permission thing, although if WS FTP works then maybe not.

nothing in the logs that sheds any light? does it work on a machine on the local network (may prove whether it is iptables or something in the ftp setup, assuming that your local rules are fairly open) I guess you could log a session with tcpdump and run it though ethereal to see what might be going on.

Do you log dumped packets with iptables? If you don't that may also be worth trying see if after they connect packets start getting dumped. Just a the -LOG command before the final DROP

Old 02-16-2003, 02:51 AM   #5
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do not forget the passive port range ... if you can define a port range in your ftp server then define it in the firewall also ...


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