Linux Firewall

My trusty and old firewall script. Simple but effective, deny all incoming connections except SSH and already established connections. It is a good starting point to customize it to your needs.

#!/bin/sh
#

#reject other connections...
/sbin/iptables -P INPUT DROP
/sbin/iptables -P FORWARD DROP

#accept loopback interface
/sbin/iptables -A INPUT -s 127.0.0.1 -d 127.0.0.1 -i lo -j ACCEPT

#accept established connection to pass
/sbin/iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

#enable clients to connect to ssh
/sbin/iptables -A INPUT -m multiport -p tcp --dport ssh  -j ACCEPT

#log activity (uncomment if needed)
#/sbin/iptables -A INPUT -j LOG -m limit