#!/bin/sh
#
#    An example of a IPTABLES firewall with IP Masquerade 
#    requires 2.3.x kernel or greater. 
#
#  save this as /etc/firewall
#  it will be called by /etc/init.d/rc.firewall
#
#  by oldami-AT-cotse-DOT-net
#    created Jan 2004 from rc.firewall-2.4-stronger v0.63s
#    with lots of mods to make it even more restrictive
#


# put your configuration info here
#  For this example, "eth1" is external and "eth0" is internal"
#  NOTE:  If this doesnt EXACTLY fit your configuration, you must 
#         change the EXTIF or INTIF variables above. For example: 
#               EXTIF="ppp0" 
#            if you are a modem user.

# the external interface 
EXTIF="eth1"

# the internal interface
INTIF="eth0"

# internal network and IP - this must be static
INTNET="192.168.1.0/24"
INTIP="192.168.1.2"
INTBRO="192.168.1.255"


# IPs of servers for sending and recieving mail 
# look at your mail client config to get these
# can use DNS names, but IPs are recommended
# multiple entries should be separated by spaces

SMTP_SERVER="123.123.123.123"
POP_SERVER="123.123.123.123 11.22.33.44"

# add each port number you wish to allow out to this variable
OK_PORTS="21 22 23 25 80 443 5190"


# The location of various iptables and other shell programs
#
#   If your Linux distribution came with a copy of iptables, most
#   likely it is located in /sbin.  If you manually compiled 
#   iptables, the default location is in /usr/local/sbin
#
# ** Please use the "which iptables" command to figure out 
# ** where your copy is and change the path below to reflect 
# ** your setup
#
IPTABLES=/sbin/iptables
#IPTABLES=/usr/local/sbin/iptables

# some other executables used by the script
LSMOD=/sbin/lsmod
GREP=/bin/grep
AWK=/usr/bin/awk


echo -e "\nLoading oldami firewall script\n"

logger "===== config firewall using $0 ====="

echo "  External Interface:  $EXTIF"
echo "  Internal Interface:  $INTIF"

# Specify your Static IP address here or let the script take care of it 
# for you.
#
#   If you prefer to use STATIC addresses in your firewalls, un-# out the
#   static example below and # out the dynamic line.  If you don't care,
#   just leave this section alone.
#
#   If you have a DYNAMIC IP address, the ruleset already takes care of
#   this for you.  Please note that the different single and double quote 
#   characters and the script MATTER.
#
#
#   DHCP users:
#   -----------
#   If you get your TCP/IP address via DHCP, **you will need ** to enable the 
#   #ed out command below underneath the PPP section AND replace the word 
#   "eth0" with the name of your EXTERNAL Internet connection (ppp0, ippp0, 
#   etc) on the lines for "ppp-ip" and "extip".  You should also note that the 
#   DHCP server can and will change IP addresses on you.  To deal with this, 
#   users should configure their DHCP client to re-run the rc.firewall ruleset 
#   everytime the DHCP lease is renewed.
#
#     NOTE #1:  Some DHCP clients like the original "pump" (the newer
#               versions have been fixed) did NOT have the ability to run 
#               scripts after a lease-renew.  Because of this, you need to 
#               replace it with something like "dhcpcd" or "dhclient".
#
#     NOTE #2:  The syntax for "dhcpcd" has changed in recent versions.
#
#               Older versions used syntax like:
#                         dhcpcd -c /etc/rc.d/rc.firewall eth0
#
#               Newer versions execute a file called /etc/dhcpc/dhcpcd-eth0.exe
#
#     NOTE #3:  For Pump users, put the following line in /etc/pump.conf:
#
#                   script /etc/rc.d/rc.firewall
#
#   PPP users:
#   ----------
#   If you aren't already aware, the /etc/ppp/ip-up script is always run when 
#   a PPP connection comes up.  Because of this, we can make the ruleset go and 
#   get the new PPP IP address and update the strong firewall ruleset.
#
#   If the /etc/ppp/ip-up file already exists, you should edit it and add a line
#   containing "/etc/rc.d/rc.firewall" near the end of the file.
#
#   If you don't already have a /etc/ppp/ip-up sccript, you need to create the 
#   following link to run the /etc/rc.d/rc.firewall script.
#
#       ln -s /etc/rc.d/rc.firewall /etc/ppp/ip-up
#
#   * You then want to enable the #ed out shell command below *
#
#
# Determine the external IP automatically:
# ----------------------------------------
#
EXTIP="`/sbin/ifconfig $EXTIF | grep 'inet addr' | $AWK '{print $2}' | sed -e 's/.*://'`"

# For users who wish to use STATIC IP addresses:
#  # out the EXTIP line above and un-# out the EXTIP line below
#
#EXTIP="your.static.PPP.address"

echo "  External IP: $EXTIP"
echo "  Internal Network: $INTNET"
echo "  Internal IP:      $INTIP"
echo "  ---"



# Setting a few other local variables
#
UNIVERSE="0.0.0.0/0"

#======================================================================
# Need to verify that all modules have all required dependencies
#
echo "  - Verifying that all kernel modules are ok"
/sbin/depmod -a

echo -en "    Loading kernel modules: "

# With the new IPTABLES code, the core MASQ functionality is now either
# modular or compiled into the kernel.  This HOWTO shows ALL IPTABLES
# options as MODULES.  If your kernel is compiled correctly, there is
# NO need to load the kernel modules manually.  
#
#  NOTE: The following items are listed ONLY for informational reasons.
#        There is no reason to manual load these modules unless your
#        kernel is either mis-configured or you intentionally disabled
#        the kernel module autoloader.
#

# Upon the commands of starting up IP Masq on the server, the
# following kernel modules will be automatically loaded:
#
# NOTE:  Only load the IP MASQ modules you need.  All current IP MASQ 
#        modules are shown below but are commented out from loading.
# ===============================================================

#Load the main body of the IPTABLES module - "iptable"
#  - Loaded automatically when the "iptables" command is invoked
#
#  - Loaded manually to clean up kernel auto-loading timing issues
#
echo -en "ip_tables, "
#
#Verify the module isn't loaded.  If it is, skip it
#
if [ -z "` $LSMOD | $GREP ip_tables | $AWK {'print $1'} `" ]; then
   /sbin/insmod ip_tables
fi


#Load the IPTABLES filtering module - "iptable_filter" 
#
#  - Loaded automatically when filter policies are activated


#Load the stateful connection tracking framework - "ip_conntrack"
#
# The conntrack  module in itself does nothing without other specific 
# conntrack modules being loaded afterwards such as the "ip_conntrack_ftp"
# module
#
#  - This module is loaded automatically when MASQ functionality is 
#    enabled 
#
#  - Loaded manually to clean up kernel auto-loading timing issues
#
echo -en "ip_conntrack, "
#
#Verify the module isn't loaded.  If it is, skip it
#
if [ -z "` $LSMOD | $GREP ip_conntrack | $AWK {'print $1'} `" ]; then
   /sbin/insmod ip_conntrack
fi


#Load the FTP tracking mechanism for full FTP tracking
#
# Enabled by default -- insert a "#" on the next line to deactivate
#
echo -e "ip_conntrack_ftp, "
#
#Verify the module isn't loaded.  If it is, skip it
#
if [ -z "` $LSMOD | $GREP ip_conntrack_ftp | $AWK {'print $1'} `" ]; then
   /sbin/insmod ip_conntrack_ftp
fi


#Load the IRC tracking mechanism for full IRC tracking
#
# Enabled by default -- insert a "#" on the next line to deactivate
#
echo -en "                             ip_conntrack_irc, "
#
#Verify the module isn't loaded.  If it is, skip it
#
if [ -z "` $LSMOD | $GREP ip_conntrack_irc | $AWK {'print $1'} `" ]; then
   /sbin/insmod ip_conntrack_irc
fi


#Load the general IPTABLES NAT code - "iptable_nat"
#  - Loaded automatically when MASQ functionality is turned on
# 
#  - Loaded manually to clean up kernel auto-loading timing issues
#
echo -en "iptable_nat, "
#
#Verify the module isn't loaded.  If it is, skip it
#
if [ -z "` $LSMOD | $GREP iptable_nat | $AWK {'print $1'} `" ]; then
   /sbin/insmod iptable_nat
fi


#Loads the FTP NAT functionality into the core IPTABLES code
# Required to support non-PASV FTP.
#
# Enabled by default -- insert a "#" on the next line to deactivate
#
echo -e "ip_nat_ftp"
#
#Verify the module isn't loaded.  If it is, skip it
#
if [ -z "` $LSMOD | $GREP ip_nat_ftp | $AWK {'print $1'} `" ]; then
   /sbin/insmod ip_nat_ftp
fi

echo "  ---"

# Just to be complete, here is a list of the remaining kernel modules 
# and their function.  Please note that several modules should be only
# loaded by the correct master kernel module for proper operation.
# --------------------------------------------------------------------
#
#    ipt_mark       - this target marks a given packet for future action.
#                     This automatically loads the ipt_MARK module
#
#    ipt_tcpmss     - this target allows to manipulate the TCP MSS
#                     option for braindead remote firewalls.
#                     This automatically loads the ipt_TCPMSS module
#
#    ipt_limit      - this target allows for packets to be limited to
#                     to many hits per sec/min/hr
#
#    ipt_multiport  - this match allows for targets within a range
#                     of port numbers vs. listing each port individually
#
#    ipt_state      - this match allows to catch packets with various
#                     IP and TCP flags set/unset
#
#    ipt_unclean    - this match allows to catch packets that have invalid
#                     IP/TCP flags set
#
#    iptable_filter - this module allows for packets to be DROPped, 
#                     REJECTed, or LOGged.  This module automatically 
#                     loads the following modules:
#
#                     ipt_LOG - this target allows for packets to be 
#                               logged
#
#                     ipt_REJECT - this target DROPs the packet and returns 
#                                  a configurable ICMP packet back to the 
#                                  sender.
# 
#    iptable_mangle - this target allows for packets to be manipulated
#                     for things like the TCPMSS option, etc.


#CRITICAL:  Enable IP forwarding since it is disabled by default since
#
#           Redhat Users:  you may try changing the options in
#                          /etc/sysconfig/network from:
#
#                       FORWARD_IPV4=false
#                             to
#                       FORWARD_IPV4=true
#
echo "  Enabling forwarding.."
echo "1" > /proc/sys/net/ipv4/ip_forward


# Dynamic IP users:
#
#   If you get your IP address dynamically from SLIP, PPP, or DHCP, 
#   enable this following option.  This enables dynamic-address hacking
#   which makes the life with Diald and similar programs much easier.
#
echo "  Enabling DynamicAddr.."
echo "1" > /proc/sys/net/ipv4/ip_dynaddr

echo "  ---"

#=========================================================================
# Clear any previous configuration
#
#  Unless specified, the defaults for INPUT, OUTPUT, and FORWARD to DROP.
#
#    You CANNOT change this to REJECT as it isn't a vaild setting for a
#    policy.  If you want REJECT, you must explictly REJECT at the end
#    of a giving INPUT, OUTPUT, or FORWARD chain
#
echo "  Clearing any existing rules and setting default policy to DROP.."

# flush all chains
$IPTABLES -F 

# delete all user defined chains
$IPTABLES -X

# set default policy to DROP
$IPTABLES -P OUTPUT DROP  
$IPTABLES -P INPUT DROP  
$IPTABLES -P FORWARD DROP  

# Reset all IPTABLES counters
$IPTABLES -Z


#========================================================================
#Configuring specific CHAINS for later use in the ruleset
#
#  NOTE:  Some users prefer to have their firewall silently
#         "DROP" packets while others prefer to use "REJECT"
#         to send ICMP error messages back to the remote 
#         machine.  The default is "REJECT" but feel free to
#         change this below.
#
# NOTE: Without the --log-level set to "info", every single
#       firewall hit will goto ALL vtys.  This is a very big
#       pain.
#
echo "  Creating a DROP chain.."
$IPTABLES -N drop-and-log-it
$IPTABLES -A drop-and-log-it -j LOG --log-level info 
$IPTABLES -A drop-and-log-it -j DROP


#========================================================================
echo "   Enabling SNAT (MASQUERADE) functionality on $EXTIF"
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE


echo -e "\n   - Loading INPUT rulesets"

#######################################################################
# INPUT: Incoming traffic from various interfaces.  All rulesets are 
#        already flushed and set to a default policy of DROP. 
#

# loopback interfaces are valid.
#
$IPTABLES -A INPUT -i lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT

# allow all trafic from inside to the firewall
$IPTABLES -A INPUT -i $INTIF -s $INTNET -d $INTIP -j ACCEPT
$IPTABLES -A INPUT -i $INTIF -s $INTNET -d $INTBRO -j ACCEPT

# remote interface, claiming to be local machines, IP spoofing, get lost
#
$IPTABLES -A INPUT -i $EXTIF -s $INTNET -d $UNIVERSE -j drop-and-log-it

# external interface, from any source, for ICMP traffic is valid
#
#  If you would like your machine to "ping" from the Internet, 
#  enable this next line
#
$IPTABLES -A INPUT -i $EXTIF -p ICMP -s $UNIVERSE -d $EXTIP -j ACCEPT

# Allow any related traffic coming back to the MASQ server in
$IPTABLES -A INPUT -i $EXTIF -s $UNIVERSE -d $EXTIP -m state --state ESTABLISHED,RELATED -j ACCEPT

# DNS - you need this, despite what an MCSE might tell you
$IPTABLES -A INPUT -i $EXTIF -p UDP --sport 53 -j ACCEPT

# Allow DHCP traffic (should restrict this to only the DHCP server)
$IPTABLES -A INPUT -i $EXTIF -p UDP --dport 67:68 -j ACCEPT

# ignore DHCP traffic on inside net
$IPTABLES -A INPUT -i $INTIF -p UDP --dport 67:68 -j DROP

# Allow SSH from outside
$IPTABLES -A INPUT -i $EXTIF -p TCP --dport 22 -j ACCEPT

#### Add other rules here to allow other trafic in

# NetUsage program needs this
$IPTABLES -A INPUT -i $INTIF -p UDP --dport 32123 -j ACCEPT

# Catch all rule, all other incoming is denied and logged. 
$IPTABLES -A INPUT -s $UNIVERSE -d $UNIVERSE -j drop-and-log-it


echo -e "   - Loading OUTPUT rulesets"

#######################################################################
# OUTPUT: Outgoing traffic from various interfaces.  All rulesets are 
#         already flushed and set to a default policy of DROP. 
#
# note: OUTPUT rules are for this box.  For controlling traffic from 
#       other systems on the internal net, add to the FORWARD chain.

# loopback interface is valid.
$IPTABLES -A OUTPUT -o lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT

# local interfaces, any source going to local net is valid
$IPTABLES -A OUTPUT -o $INTIF -s $EXTIP -d $INTNET -j ACCEPT

# anything from this box to internal interface is allowed
$IPTABLES -A OUTPUT -o $INTIF -s $INTIP -d $INTNET -j ACCEPT

# outgoing to local net on remote interface, stuffed routing, deny
$IPTABLES -A OUTPUT -o $EXTIF -s $UNIVERSE -d $INTNET -j drop-and-log-it

$IPTABLES -A OUTPUT -o $EXTIF -m state --state ESTABLISHED,RELATED -j ACCEPT

# DNS - you need this, despite what an MSCE might tell you
$IPTABLES -A OUTPUT -o $EXTIF -p UDP --dport 53 -j ACCEPT

# Allow DHCP requests out
$IPTABLES -A OUTPUT -o $EXTIF -p UDP --dport 67:68 -j ACCEPT

# allow ICMP out
$IPTABLES -A OUTPUT -o $EXTIF -p ICMP -j ACCEPT

# Allow each of the allowed TCP ports to go out
for PORT in $OK_PORTS
do
   $IPTABLES -A OUTPUT -o $EXTIF -p TCP --dport $PORT -j ACCEPT
done 

# NetUsage program needs this
$IPTABLES -A OUTPUT -o $INTIF -p UDP --dport 32123 -j ACCEPT


# Catch all rule, all other outgoing is denied and logged. 
$IPTABLES -A OUTPUT -s $UNIVERSE -d $UNIVERSE -j drop-and-log-it

echo -e "   - Loading FORWARD rulesets"

#######################################################################
# FORWARD: Enable Forwarding and thus IPMASQ
#

$IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED -j ACCEPT

# allow outgoing SMTP to each server in list
for SVR in $SMTP_SERVER
do
   $IPTABLES -A FORWARD -o $EXTIF -p TCP --dport 25 -d $SVR -j ACCEPT
done

# allow POP3 to each server in list
for SVR in $POP_SERVER
do
   $IPTABLES -A FORWARD -o $EXTIF -p TCP --dport 110  -d $SVR -j ACCEPT
done

# Allow each of the TCP ports above 
for PORT in $OK_PORTS
do
   $IPTABLES -A FORWARD -o $EXTIF -p TCP --dport $PORT -j ACCEPT
done 

# drop and log everything else
$IPTABLES -A FORWARD -j drop-and-log-it

#######################################################################

echo -e "\nDone.\n"