Hello:

Sundari KuSumam wrote,
>    I am trying to put IPtables on  a machine conneted to  cablemodem
> It uses debian2.2 potato with 2.4.14 kernel
> 
> here is my script
> #---------BEGIN----------------------------
> #!/bin/sh
> modprobe iptable_nat

Load the connection tracking modules also:

# modprobe ip_conntrack
# modprobe ip_conntrack_ftp
# modprobe ip_conntrack_irc

> echo 1 > /proc/sys/net/ipv4/ip_forward
> 
> iptables -t nat -A POSTROUTING -s 192.168.50.0/24 -j MASQUERADE

Allow ESTB and RELATED connections thru the firewall.

# iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

> I am running squid also. My clients are able to browse But when I try to
> ftp to a sit e from a client machine I get the following
> 
> -------------------- FTP SERVER OUTPUT --------------
> 
> maria@debian:~$ ftp arbornet.org
> Connected to arbornet.org.
> 220-Welcome to M-Net's FTP Server
> 
> 220 ProFTPD 1.2.0 Server (M-Net Ftpd) [m-net.arbornet.org]
> Name (arbornet.org:maria): chathan
> 331 Password required for chathan.
> Password:
> 230 User chathan logged in.
> Remote system type is UNIX.
> Using binary mode to transfer files.
> ftp> ls
> 500 Illegal PORT command.
> ftp: bind: Address already in use
> ftp>
> ------------------------------------------------------
> 
>  However  the same works perfectly on my gateway

FTP is a more complicated protocol which require NAT "helpers" to work
properly. Load the extra connection tracking modules. It should now work
from behind the firewall.

> Somebody please help I would like to build a firewall . I am unable to
> properly understand IPtables . Will some body show how a fire wall
> can be constructed step by step

RTFM at http://people.unix-fu.org/andreasson/

-- Shanu

-- 
Han Solo:
        Wonderful girl! Either I'm going to kill her
        or I'm beginning to like her.

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