#!/bin/sh
#
# firewall		This script sets up firewall rules.
#
# chkconfig: 2345 09 91
# description: Sets up or removes firewall rules.
#
# Firewall rules for a firewall between a private internal network and the
# Internet.
#
# Copyright (C) 2000 Roaring Penguin Software Inc.  This software may
# be distributed under the terms of the GNU General Public License, version
# 2 or any later version.

# Interface to Internet
EXTIF=ppp0

# Internal network address.  For stand-alone machines, delete this and
# all the "forward" rules.
INTERNAL=192.168.2.0/24

# Wildcard address
ANY=0.0.0.0/0

# Source function library.  THIS WORKS ONLY ON RED HAT-LIKE SYSTEMS.

. /etc/rc.d/init.d/functions

### For details, see the man page ipchains(1) and
### /usr/share/doc/HOWTO/IPCHAINS-HOWTO -- David.

case "$1" in
    start)
	echo -n "Setting up firewall rules"

	# Turn on forwarding to silence warnings...
	echo 1 > /proc/sys/net/ipv4/ip_forward

	# Set default policies; clear all rules
	ipchains -P input ACCEPT
	ipchains -P output ACCEPT
	ipchains -P forward DENY

	ipchains -F forward
	ipchains -F input
	ipchains -F output

	### Spoof protection: Drop obviously suspect packets ###

	# Drop packets claiming to be from unroutable addresses
	ipchains -A input -l -s 10.0.0.0/8     -i $EXTIF -j DENY
	ipchains -A input -l -s 172.16.0.0/12  -i $EXTIF -j DENY
	ipchains -A input -l -s 192.168.0.0/16 -i $EXTIF -j DENY

	# Drop packets wanting to go to unroutable addresses
	ipchains -A input -l -d 10.0.0.0/8     -i $EXTIF -j DENY
	ipchains -A input -l -d 172.16.0.0/12  -i $EXTIF -j DENY
	ipchains -A input -l -d 192.168.0.0/16 -i $EXTIF -j DENY

	### External access to services on this machine ###

	# Reject identd packets without logging
	ipchains -A input -i $EXTIF -p tcp -d $ANY 113 -j REJECT

	# Allow access to sendmail -- log connection attempts
	#ipchains -A input -l -i $EXTIF -p tcp -d $ANY 25 -y -j ACCEPT
	#ipchains -A input  -i $EXTIF -p tcp -d $ANY 25 -j ACCEPT

	# Allow access to ssh -- we run ssh on port 23 because of
	# a stupid client firewall at one place we work.
	#ipchains -A input -l -i $EXTIF -p tcp -d $ANY 23 -y -j ACCEPT
	#ipchains -A input -i $EXTIF -p tcp -d $ANY 23 -j ACCEPT

	# Deny all other TCP connection attempts on the external interface
	ipchains -A input -l -i $EXTIF -p tcp -y -j DENY

	# Deny TCP and UDP packets to privileged ports
	ipchains -A input -l -i $EXTIF -d $ANY 0:1023 -p udp -j DENY
	ipchains -A input -l -i $EXTIF -d $ANY 0:1023 -p tcp -j DENY

	### FORWARD rules only apply if you have an internal LAN gatewaying
	### through this computer.
	# Allow DNS queries
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 53 -p udp -j MASQ

	# Allow internal users to browse web (http and https)
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 80  -p tcp -b -j MASQ
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 443  -p tcp -b -j MASQ

	# Allow internal users to read news
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 119  -p tcp -b -j MASQ

	# Allow internal users to access POP and IMAP services on mail server
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 25 -p tcp -b -j MASQ
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 110 -p tcp -b -j MASQ
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 143 -p tcp -b -j MASQ

	# Allow internal users to access external FTP servers
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 21  -p tcp -b -j MASQ

	# Allow internal users to access external Telnet and SSH servers
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 22  -p tcp -b -j MASQ
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 23  -p tcp -b -j MASQ

	# Allow unprivileged ports --> unprivileged ports for passive FTP
	ipchains -A forward -s $INTERNAL 1024: -d $ANY 1024: -p tcp -b -j MASQ

	# A catch-all rule for logging purposes
	ipchains -A forward -s $ANY            -d $ANY -l            -j DENY

	# Turn on forwarding
	echo 1 > /proc/sys/net/ipv4/ip_forward

	echo_success
	echo ""
	;;

    stop)
	echo -n "Shutting down firewall rules"
	# Turn off forwarding
	echo 0 > /proc/sys/net/ipv4/ip_forward

	# Set default policies; clear all rules
	ipchains -P input ACCEPT
	ipchains -P output ACCEPT
	ipchains -P forward DENY

	ipchains -F forward
	ipchains -F input
	ipchains -F output
	echo_success
	echo ""
        ;;

    *)
	echo "Usage: firewall {start|stop}"
	exit 1
esac

exit 0