Passive FTP problem with a change of IP address

Frédéric Massot <[email protected]> Fri, 15 Nov 2013 13:03:19 +0100
Newsgroups gmane.linux.debian.devel.firewall
Organization JULIANA Multimédia
Message-ID <[email protected]>
Hi,

I have a firewall with iptables rules (kernel 3.10), until now I have 
always been able to connect to FTP server in passive or active mode.

Here are the rules I use:

iptables -A FORWARD -p tcp -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A FORWARD -p tcp -i $INTERNAL_INTERFACE -o $EXTERNAL_INTERFACE 
-s $INTERNAL_LAN --sport $UNPRIVPORTS --dport 21 -m state --state NEW -j 
ACCEPT


I have a problem with the FTP server of one hoster. I connect well, but 
the data do not go into passive mode.

I looked at the packets that pass through the firewall with iptraf and I 
noticed that the ftp-data connection that was on a different IP address.

Connect to the FTP server (yy.yy.10.2) :
192.168.11.66:59577 --> yy.yy.10.2:21

ftp-data transmission on another IP address (yy.yy.10.10) :
192.168.11.66:32777 --> yy.yy.10.10:30527

ftp-data transmission on the other IP address is blocked by my firewall, 
it is not considered as RELATED.


- Is it lack any thing in my rules?

- Does the nf_conntrack_ftp module take care of the IP address change?


Regards.
-- 
==============================================
|              FRÉDÉRIC MASSOT               |
|     http://www.juliana-multimedia.com      |
|   mailto:[email protected]   |
| +33.(0)2.97.54.77.94  +33.(0)6.67.19.95.69 |
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