Simple firewall example
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Public domain
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    #!/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
  
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_BY: Pejman Moghadam_  
_TAG: firewall, iptables, bash-script, bash_  
_DATE: 2007-07-11 21:40:51_