Common firewall config for Linux - bash file

firewall.sh

#!/bin/bash

 # Delete the current firewall setup:
iptables -F

 # Define default rules for all chains:
iptables -P INPUT DROP
iptables -P FORWARD DROP

 # Allow incoming/outgoing localhost frames for tests (e.g.  Webserver, Mailserver):
iptables -A INPUT -d 127.0.0.1 -j ACCEPT
iptables -A OUTPUT -s 127.0.0.1 -j ACCEPT

 # Allow loopback frames for the internal process management:
iptables -A INPUT -i lo -j ACCEPT

 # Allow incoming/outgoing related-established connections:
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

 # Allow incoming PING-Requests:
iptables -A INPUT -p icmp -j ACCEPT

 # Allow incoming SSH connections: 
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

 # Allow incoming HTTP/HTTPS requests:
iptables -A INPUT -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j ACCEPT

 # Allow incoming DNS requests:
iptables -A INPUT -p udp --dport 53 -j ACCEPT
iptables -A INPUT -p tcp --dport 53 -j ACCEPT