simple firewall

#!/bin/bash
# Internal interface = eth0
# External interface = eth1
# Localnet range = 192.168.0.0/24
# Flushing
iptables -t filter -F
iptables -t filter -X
iptables -t filter -Z

# Drop everything
iptables -t filter -P INPUT DROP
iptables -t filter -P OUTPUT DROP
iptables -t filter -P FORWARD DROP

# Accept local connections
iptables -t filter -A INPUT -i lo -j ACCEPT
iptables -t filter -A OUTPUT -o lo -j ACCEPT

# Accept dns connections
iptables -t filter -A FORWARD -i eth0 -s 192.168.0.0/24 -p udp --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -t filter -A FORWARD -i eth1 -d 192.168.0.0/24 -p udp --sport 53 -m state --state ESTABLISHED -j ACCEPT

# Accept http connections
iptables -t filter -A FORWARD -i eth0 -s 192.168.0.0/24 -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -t filter -A FORWARD -i eth1 -d 192.168.0.0/24 -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT

# ICMP transit
iptables -t filter -A FORWARD -i eth0 -d 192.9.9.3 -p icmp --icmp-type echo-request -j ACCEPT
iptables -t filter -A FORWARD -i eth1 -s 192.9.9.3 -p icmp --icmp-type echo-reply -j ACCEPT