Hi!
I have an Linux server hosting 1 internetconnection to some other computers in an internal network
Everything is working fine and everyone can use the internet.

This is what i have used in my script.

# Generated by iptables-save v1.2.1a on Sun Jan 6 00:53:38 2002
*nat
:PREROUTING ACCEPT [228:17791]
:POSTROUTING ACCEPT [12:708]
:OUTPUT ACCEPT [13:841]

-A PREROUTING -d "my external ip" -p tcp -m tcp --dport 20000 -j DNAT --to-destination 192.168.10.6:21

-A POSTROUTING -o eth0 -j MASQUERADE
COMMIT
# Completed on Sun Jan 6 00:53:38 2002
# Generated by iptables-save v1.2.1a on Sun Jan 6 00:53:38 2002
*filter
:INPUT ACCEPT [20:2848]
:FORWARD ACCEPT [42364:42333238]
:OUTPUT ACCEPT [5:240]
-A FORWARD -i eth1 -o eth0 -j ACCEPT
COMMIT
# Completed on Sun Jan 6 00:53:38 2002

It´s a very simple script.
The problem is this:
I have a ftp server on the internal network that i want to connect to from the outside. But when i try to connect i always get connection refused!!!
Have i closed that port or what?????
I realy hope that someone outthere can help me!!

You may have to enable support for connection tracking of FTP.

/sbin/modprobe ip_conntrack_ftp

This will track all ftp connections made as part of IPtables "statefullness".