From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Rob Sterenborg" <rob@sterenborg.info>
Subject: RE: ip masqurade
Date: Sun, 8 Jun 2003 23:21:57 +0200
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> computers on my LAN to gateway to the internet via my Linux Modem. My 

You use a modem, so I guess you have aa ppp internet interface and a
dynamic IP address.
That's why we'll be using MASQUERADE. Otherwise use SNAT.

> my lan which will fall in the ip range of 192.168.168.0/24. 

# First disable forwarding so that nothing will happen before your rules
are set.
echo 0 > /proc/sys/net/ipv4/ip_forward

# Forward packets coming from your LAN to internet, DROP everything
else.
# When not specifying a table, the filter table is assumed.
iptables -P FORWARD DROP
iptables -A FORWARD -i <if_lan> -o <if_inet> -s 192.168.168.0/24 -j
ACCEPT
iptables -t nat -A POSTROUTING -o <if_inet> -s 192.168.168.0/24 -j
MASQUERADE 

# Enable forwarding.
echo 1 > /proc/sys/net/ipv4/ip_forward


Gr,
Rob