Mine

#!/bin/sh
EXTIF="eth0"
#INTIF1="eth1"
#INTIF2="wlan0"

EXTIP="`/sbin/ifconfig $EXTIF | grep 'inet addr' | awk '{print $2}' | sed -e 's/.*://'`"

#EXTIP="192.168.0.231"

# For users who wish to use STATIC IP addresses:
#
#  # out the EXTIP line above and un-# out the EXTIP line below
#
#EXTIP="your.static.PPP.address"

# Assign the internal TCP/IP network and IP address
INTNET1="192.168.2.0/24"
#INTIP="192.168.0.106/24"

INTNET2="192.168.9.0/24"

IPTABLES=/sbin/iptables
#IPTABLES=/usr/local/sbin/iptables
LSMOD=/sbin/lsmod
GREP=/bin/grep
AWK=/bin/awk


UNIVERSE="0.0.0.0/0"

echo 1 > /proc/sys/net/ipv4/ip_forward

#tc qdisc del dev ppp0 root

$IPTABLES -P INPUT ACCEPT
$IPTABLES -F INPUT 
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -F OUTPUT 
$IPTABLES -P FORWARD ACCEPT 
$IPTABLES -F FORWARD 
$IPTABLES -F -t nat

$IPTABLES -A FORWARD -s $UNIVERSE -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -s $INTNET1 -j ACCEPT
$IPTABLES -A FORWARD -s $INTNET2 -j ACCEPT

#$IPTABLES -A FORWARD -j drop-and-log-it


echo "     - NAT: Enabling SNAT (MASQUERADE) functionality on $EXTIF"
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE
$IPTABLES -t nat -A POSTROUTING -s $INTNET1 -j MASQUERADE
$IPTABLES -t nat -A POSTROUTING -s $INTNET2 -j MASQUERADE

echo -e "\nDone.\n"