iptables masquerading & active ftp connections

PowerMatt · 10-19-2005, 07:09 PM

Whenever I try to actively connect to an FTP server from behind my homemade linux firewall/gateway, for some reason my ftp client (FileZilla) is sending the server my internal IP address and not the external IP address during the PORT command.

Is there anything I can do about this with iptables or am I just going to have to set the external IP address manually in FileZilla?

PowerMatt · 10-20-2005, 04:33 PM

Still looking for an answer on this one... my problem also seems to have spread to Azureus.

I'm beginning to think there's a fundamental flaw somewhere in my configuration, but I'm not sure what it is.

Here's my iptables configuration:

Code:

# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:FORWARD ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -i eth1 -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type echo-request -j DROP
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -d 224.0.0.251 --dport 5353 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
*mangle
:FORWARD ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A PREROUTING -i eth1 -j MARK  --set-mark 0x9
COMMIT
*nat
:PREROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -m mark -j MASQUERADE  --mark 0x9
COMMIT

PowerMatt · 10-20-2005, 05:02 PM

Figured out my problem with Azureus. Now if I could just figure out the FTP thing...

Updated iptables config:

Code:

# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:FORWARD ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -i eth1 -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 50000 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 50000 -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type echo-request -j DROP
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -d 224.0.0.251 --dport 5353 -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
*mangle
:FORWARD ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A PREROUTING -i eth1 -j MARK  --set-mark 0x9
COMMIT
*nat
:OUTPUT ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -m mark -j MASQUERADE  --mark 0x9
-A PREROUTING -p tcp -m tcp --dport 50000 -j DNAT --to-destination 10.0.0.2-10.0.0.2:50000-50000
-A PREROUTING -p udp -m udp --dport 50000 -j DNAT --to-destination 10.0.0.2-10.0.0.2:50000-50000
COMMIT