#!/bin/bash

IPTABLES="/sbin/iptables"
SERVER_IPS=`/sbin/ifconfig | grep inet | cut -d : -f 2 | cut -d \  -f 1 | grep -v 127.0.0.1`

FWIN="${IPTABLES} -A INPUT"
FWOUT="${IPTABLES} -A OUTPUT"
OK="-j ACCEPT"
NO="-j DROP"


# Flush tables and change default policy to DROP
function initialize() {
        local TABLE="${1}"
        ${IPTABLES} -F ${TABLE}
        ${IPTABLES} -P ${TABLE} DROP
}

# Flush tables and change default policy to ACCEPT
function stop() {
        local TABLE="${1}"
        ${IPTABLES} -F ${TABLE}
        ${IPTABLES} -P ${TABLE} ACCEPT
}

# Verify call switch
case "$1" in
start|restart)

        initialize INPUT
        initialize OUTPUT
        initialize FORWARD
        
         # INPUT
         # 1) loopback
         ${FWIN} -i lo ${OK}
         ${FWIN} -d 127.0.0.0/8 ${NO}
         
         # 2) We allow incoming SSH connections and answers to
         # our own SSH connections:
         for OURIP in ${SERVER_IPS}; do
            ${FWIN} -p tcp -d ${OURIP} --dport 22 ${OK}
            ${FWIN} -p tcp --sport 22 -d ${OURIP} --dport 1024: "!" --syn ${OK}
         done
         
         # 3) We allow incoming DNS queries as well as answers to our
         # DNS queries.
         for OURIP in ${SERVER_IPS}; do
            ${FWIN} -p tcp -d ${OURIP} --dport 53 ${OK}
            ${FWIN} -p udp -d ${OURIP} --dport 53 ${OK}
            ${FWIN} -p tcp --sport 53 -d ${OURIP} --dport 1024: "!" --syn ${OK}
            ${FWIN} -p udp --sport 53 -d ${OURIP} --dport 1024: ${OK}
         done
         
         # 4) We allow access to our SMTP server, as well as answers
         # to our SMTP connections and, temporarily, identd stuff:
         for OURIP in ${SERVER_IPS}; do
            ${FWIN} -p tcp -d ${OURIP} --dport 25 ${OK}
            ${FWIN} -p tcp --sport 25 -d ${OURIP} --dport 1024: "!" --syn ${OK}
            ${FWIN} -p tcp --sport 1024: -d ${OURIP} --dport 113 ${OK}
            #${FWIN} -p udp --sport 1024: -d ${OURIP} --dport 113 ${OK}
            ${FWIN} -p tcp --sport 113 -d ${OURIP} --dport 1024: "!" --syn ${OK}
            #${FWIN} -p udp --sport 113 -d ${OURIP} --dport 1024: ${OK}
         done
         
         # 5) We also allow access to our POP/sPOP server.
         for OURIP in ${SERVER_IPS}; do
           ${FWIN} -p tcp -d ${OURIP} --dport 110 ${OK}
           ${FWIN} -p tcp -d ${OURIP} --dport 995 ${OK}
         done
         
         # 6) and to IMAP/IMAPs
         for OURIP in ${SERVER_IPS}; do
            ${FWIN} -p tcp -d ${OURIP} --dport 143 ${OK}
            ${FWIN} -p tcp -d ${OURIP} --dport 993 ${OK}
         done
         
         # 7) we would like to be able to use lynx ;)
         for OURIP in ${SERVER_IPS}; do
         ${FWIN} -p tcp --sport 80 -d ${OURIP} --dport 1024: "!" --syn ${OK}
         done
         
         # 8) We allow incoming echo replies/requests from everywhere:
         for OURIP in ${SERVER_IPS}; do
            ${FWIN} -p icmp -d ${OURIP} --icmp-type 0 ${OK}
            ${FWIN} -p icmp -d ${OURIP} --icmp-type 3 ${OK}
            ${FWIN} -p icmp -d ${OURIP} --icmp-type 8 ${OK}
            ${FWIN} -p icmp -d ${OURIP} --icmp-type 11 ${OK}
         done
         
         # 9) We also would like to allow access to our web server:
         for OURIP in ${SERVER_IPS}; do
            ${FWIN} -p tcp -d ${OURIP} --dport 80 ${OK}
            ${FWIN} -p tcp -d ${OURIP} --dport 443 ${OK}
         done

         
          10) people are still crazy enough to use ftp
         for OURIP in ${SERVER_IPS}; do
           for PORT in 20 21; do
            ${FWIN} -p tcp -d ${OURIP} --dport ${PORT} ${OK}
            ${FWIN} -p tcp --sport  ${PORT} -d ${OURIP} --dport 1024: "!" --syn ${OK}
            ${FWIN} -p udp -d ${OURIP} --dport ${PORT} ${OK}
            ${FWIN} -p udp --sport ${PORT} -d ${OURIP} --dport 1024: ${OK}
           done
         done
         
    

         # allow answers on high ports
         ${FWIN} -p tcp -m tcp --dport 1024:65535 ! --tcp-flags SYN,RST,ACK SYN ${OK}
         ${FWIN} -p udp -m udp --dport 1024:65535 ${OK}


         # Everything else is denied by default - policy is DROP.
         
         # OUTPUT
         # 1) Loopback packets.
         ${FWOUT} -o lo ${OK}
         ${FWOUT} -s 127.0.0.0/8 ${NO}
         
         # 2) We allow all outgoing traffic:
         for OURIP in ${SERVER_IPS}; do
            ${FWOUT} -s ${OURIP} ${OK} 
         done
        
        ;;

stop)
        # turn off the firewall, flush all rules
        echo "Flushing rulesets.."

        stop INPUT
        stop OUTPUT
        stop FORWARD

        ;;

status)
        # display the current status - both firewall rules and masquerading
        # connections

        # list rules. -n avoids DNS lookups
        $IPTABLES -nL 

        ;;

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

exit 0