#!/bin/sh

INTIF="eth2"
EXTIF="eth1"

INTNET="192.168.0.0/24"
INTIP="192.168.0.254/24"
EXTIP="10.255.26.10"

PROXYSERVER="10.255.26.220"
PROXYPORT="3128"

#EXTIP="`/sbin/ifconfig eth1 | grep 'inet addr' | awk '{print $2}' | sed -e 's/.*://'`"

/sbin/depmod -a
# Force loading and activation of all the NAT and IPTables needed modules
/sbin/modprobe ip_tables
/sbin/modprobe ip_conntrack
/sbin/modprobe ip_conntrack_ftp
/sbin/modprobe ip_conntrack_irc
/sbin/modprobe iptable_nat
/sbin/modprobe ip_nat_ftp
/sbin/modprobe ip_nat_irc

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

UNIVERSE="0.0.0.0/0"

# Clearing any existing rules and setting default policy
iptables -P INPUT ACCEPT
iptables -F INPUT
iptables -P OUTPUT ACCEPT
iptables -F OUTPUT
iptables -P FORWARD DROP
iptables -F FORWARD
iptables -t nat -F

# Flush the user chain.. if it exists
if [ "`iptables -L | grep drop-and-log-it`" ]; then
   iptables -F drop-and-log-it
fi

# Delete all User-specified chains
iptables -X

# Reset all IPTABLES counters
iptables -Z

# Creating a DROP chain
iptables -N drop-and-log-it
iptables -A drop-and-log-it -j LOG --log-level info
iptables -A drop-and-log-it -j REJECT

# ================ INPUT Chain ================
# loopback interfaces are valid.
iptables -A INPUT -i lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT

# local interface, local machines, going anywhere is valid
iptables -A INPUT -i $INTIF -s $INTNET -d $UNIVERSE -j ACCEPT

# remote interface, claiming to be local machines, IP spoofing, get lost
iptables -A INPUT -i $EXTIF -s $INTNET -d $UNIVERSE -j drop-and-log-it

# remote interface, any source, going to permanent PPP address is valid
iptables -A INPUT -i $EXTIF -s $UNIVERSE -d $EXTIP -j ACCEPT

# Allow any related traffic coming back to the MASQ server in
iptables -A INPUT -i $EXTIF -s $UNIVERSE -d $EXTIP -m state --state ESTABLISHED,RELATED -j ACCEPT

# Catch all rule, all other incoming is denied and logged.
iptables -A INPUT -s $UNIVERSE -d $UNIVERSE -j drop-and-log-it

# ================ OUTPUT Chain ================
# loopback interface is valid.
iptables -A OUTPUT -o lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT

# local interfaces, any source going to local net is valid
iptables -A OUTPUT -o $INTIF -s $EXTIP -d $INTNET -j ACCEPT

# local interface, any source going to local net is valid
iptables -A OUTPUT -o $INTIF -s $INTIP -d $INTNET -j ACCEPT

# outgoing to local net on remote interface, stuffed routing, deny
iptables -A OUTPUT -o $EXTIF -s $UNIVERSE -d $INTNET -j drop-and-log-it

# anything else outgoing on remote interface is valid
iptables -A OUTPUT -o $EXTIF -s $EXTIP -d $UNIVERSE -j ACCEPT

# Catch all rule, all other outgoing is denied and logged.
iptables -A OUTPUT -s $UNIVERSE -d $UNIVERSE -j drop-and-log-it

# ================ FORWARD Chain ================
iptables -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT

# Enabling SNAT (MASQUERADE) functionality on $EXTIF
iptables -t nat -A PREROUTING -s $INTNET -p tcp --dport 80 -j REDIRECT --to-ports $PROXYPORT
iptables -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE