# Simple firewall

This is a very simple firewall I was once taught by my friend Fabio.
Just copy these lines in a blank file, make it executable, and have it
executed some time during your init process. My favorite way is to add
this in /etc/network/interfaces:

    auto eth1iface eth1 inet staticaddress 192.168.0.1netmask 255.255.255.0post-up /etc/network/if-up.d/firewall.sh

This is the firewall script:

    #!/bin/sh# Cleans the iptablesiptables -F# Enables internet connection sharingmodprobe iptable_natiptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADEecho 1 > /proc/sys/net/ipv4/ip_forward# Opens some ports (22=SSH, 1080=Socks)iptables -A INPUT -p tcp --destination-port 22 -j ACCEPTiptables -A INPUT -p tcp --destination-port 1080 -j ACCEPT# Allows localhost everywhere                                                              iptables -A INPUT -s 127.0.0.1 -j ACCEPTiptables -A OUTPUT -s 127.0.0.1 -j ACCEPT# Opens local networkiptables -A INPUT -p tcp --syn -s 192.168.0.0/255.255.255.0 -j ACCEPT# Closes everything elseiptables -A INPUT -p tcp --syn -j DROP