Simple firewall in linux

Just try this.

To use it:

1. Create a file named /etc/init.d/firewall
2. Copy and paste the script into it and save
3. Edit the ALLOWED variable with port numbers you want to allow, default is ports 22 (SSH) and 80 (HTTP)
4. Execute:

   touch /usr/local/etc/whitelist.txt && touch /usr/local/etc/blacklist.txt

5. Edit the whitelist/blacklist files if you want
6. Execute:

   chmod 755 /etc/init.d/firewall

7. Execute:

   chkconfig --add firewall && chkconfig firewall on

The script:

#!/bin/bash
# chkconfig: 345 30 99
# description: Starts and stops iptables based firewall

## List Locations
#

WHITELIST=/usr/local/etc/whitelist.txt
BLACKLIST=/usr/local/etc/blacklist.txt

#
## Specify ports you wish to use.
#

ALLOWED="22 80 25"

#
## Specify where IP Tables is located
#

IPTABLES=/sbin/iptables

##
#DO NOT EDIT BELOW THIS LINE
###
RETVAL=0

# To start the firewall
start() {
  echo "Setting up firewall rules..."

	echo 'Allowing Localhost'
	#Allow localhost.
	$IPTABLES -A INPUT -t filter -s 127.0.0.1 -j ACCEPT

	#
	## Whitelist
	#

	for x in `grep -v ^# $WHITELIST | awk '{print $1}'`; do
	        echo "Permitting $x..."
	        $IPTABLES -A INPUT -t filter -s $x -j ACCEPT
	done

	#
	## Blacklist
	#

	for x in `grep -v ^# $BLACKLIST | awk '{print $1}'`; do
	        echo "Denying $x..."
	        $IPTABLES -A INPUT -t filter -s $x -j DROP
	done

	#
	## Permitted Ports
	#

	for port in $ALLOWED; do
	        echo "Accepting port TCP $port..."
	        $IPTABLES -A INPUT -t filter -p tcp --dport $port -j ACCEPT
	done

	for port in $ALLOWED; do
	        echo "Accepting port UDP $port..."
	        $IPTABLES -A INPUT -t filter -p udp --dport $port -j ACCEPT
	done

	$IPTABLES -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
	$IPTABLES -A INPUT -p udp -j DROP
	$IPTABLES -A INPUT -p tcp --syn -j DROP

  RETVAL=0
}

# To stop the firewall
stop() {
  echo "Removing all iptables rules..."
  /sbin/iptables -F
  /sbin/iptables -X
  /sbin/iptables -Z
  RETVAL=0
}

case $1 in
  start)
		stop
    start
    ;;
  stop)
    stop
    ;;
  restart)
    stop
    start
    ;;
  status)
    /sbin/iptables -L
    /sbin/iptables -t nat -L
    RETVAL=0
    ;;
  *)
    echo "Usage: firewall {start|stop|restart|status}"
    RETVAL=1
esac

exit $RETVAL

Tags: centos firewall, firewall, iptables