IP-Masq stronger firewall-2.4

>    Good Luck.

>    FrankM

> > #          An example of a stronger IPTABLES firewall with IP Masquerade
> > #          support for 2.4.x kernels.
> > #
> > # Log:
> > #   0.73s - Added comments in the output section that DHCPd is optional
> > #           and changed the default settings to disabled
> > #   0.72s - Changed the filter from the INTNET to the INTIP to be
> > #           stateful; moved the command VARs to the top and made the
> > #           rest of the script to use them
> > #   0.70s - Added a disabled examples for allowing internal DHCP
> > #           and external WWW access to the server
> > #   0.63s - Added support for the IRC module
> > #   0.62s - Initial version based upon the basic 2.4.x rc.firewall

> > echo -e "\nStronger rc.firewall-2.4 $FWVER done.\n"
> > #Setting the EXTERNAL and INTERNAL interfaces for the network
> > #
> > #  Each IP Masquerade network needs to have at least one
> > #  external and one internal network.  The external network
> > #  is where the natting will occur and the internal network
> > #  should preferably be addressed with a RFC1918 private address
> > #  scheme.
> > #
> > #  For this example, "eth0" is external and "eth1" 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.
> > #
> > EXTIF="ppp0"
> > INTIF="eth0"
> > echo "  External Interface:  $EXTIF"
> > echo "  Internal Interface:  $INTIF"
> > echo "  ---"

> > # 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 calledecho -e "\nStronger 
> > rc.firewall-2.4 $FWVER done.\n" /etc/dhcpc/dhcpcd-eth0.exe
> > #
> > #     NOTE #3:  For Pump users, put the following line in /etc/pump.conf:
> > #
> > #                   script /etc/rc.d/rc.firewall
> > #
> > #   PPP users:
> > #   ----------
> > #   If you aren't already aware, the /etc/ppp/ip-up script is always run when
> > #   a PPP connection comes up.  Because of this, we can make the ruleset go 
> > and
> > #   get the new PPP IP address and update the strong firewall ruleset.
> > #
> > #   If the /etc/ppp/ip-up file already exists, you should edit it and add a 
> > line
> > #   containing "/etc/rc.d/rc.firewall" near the end of the file.
> > #
> > #   If you don't already have a /etc/ppp/ip-up sccript, you need to create the
> > #   following link to run the /etc/rc.d/rc.firewall script.
> > #
> > #       ln -s /etc/rc.d/rc.firewall /etc/ppp/ip-up
> > #
> > #   * You then want to enable the #ed out shell command below *
> > #
> > #
> > # Determine the external IP automatically:
> > # ----------------------------------------
> > #
> > EXTIP="`$IFCONFIG $EXTIF | $GREP 'inet addr' | $AWK '{print $2}' | \
> > $SED -e 's/.*://'`"

> > # Assign the internal TCP/IP network and IP address
> > INTNET="192.168.0.0/24"
> > INTIP="192.168.0.1/24"
> > echo "  Internal Network: $INTNET"
> > echo "  Internal IP:      $INTIP"
> > echo "  ---"

> > 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 - "ip_tables"
> > #  - 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
> >    $INSMOD ip_tables
> > fi

> > #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
> >    $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
> >    $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
> >    $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
> >    $INSMOD iptable_nat
> > fi

> > #Loads the FTP NAT functionality into the core IPTABLES code
> > # Required to support non-PASV FTP.
> > #echo -e "\nStronger rc.firewall-2.4 $FWVER done.\n"
> > # 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
> >    $INSMOD ip_nat_ftp
> > fi

> > # 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
> > #
> > #    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

> > #############################################################################
> > #
> > # Enable Stronger IP forwarding and Masquerading
> > #
> > #  NOTE:  In IPTABLES speak, IP Masquerading is a form of SourceNAT or SNAT.
> > #
> > #  NOTE #2:  The following is an example for an internal LAN address in the
> > #            192.168.1.x network with a 255.255.255.0 or a "24" bit subnet
> > #            mask connecting to the Internet on external interface "eth0".
> > #            This example will MASQ internal traffic out to the Internet
> > #            but not allow non-initiated traffic into your internal network.
> > #
> > #
> > #         ** Please change the above network numbers, subnet mask, and your
> > #         *** Internet connection interface name to match your setup
> > #

> > #Clearing 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.."
> > $IPTABLES -P INPUT DROP
> > $IPTABLES -F INPUT
> > $IPTABLES -P OUTPUT DROP
> > $IPTABLES -F OUTPUT
> > $IPTABLES -P FORWARD DROP
> > $IPTABLES -F FORWARD
> > $IPTABLES -F -t nat

> > #Not needed and it will only load the unneeded kernel module
> > #$IPTABLES -F -t mangle
> > #
> > # Flush the user chain.. if it exists
> > if [ -n "`$IPTABLES -L | $GREP drop-and-log-it`" ]; then
> >    $IPTABLES -F drop-and-log-it
> > fi
> > #
> > # Delete all User-specified chains
> > #
> > # Delete all User-specified chains
> > $IPTABLES -X
> > #
> > # 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

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

> > # HTTPd - Enable the following lines if you run an EXTERNAL WWW server
> > #
> > #echo -e "      - Allowing EXTERNAL access to the WWW server"
> > #$IPTABLES -A INPUT -i $EXTIF -m state --state NEW,ESTABLISHED,RELATED \
> > #-p tcp -s $UNIVERSE -d $EXTIP --dport 80 -j ACCEPT

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

> > echo "     - FWD: Allow all connections OUT and only existing/related IN"
> > $IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED 
> > \
> > -j ACCEPT
> > $IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT

> > echo "     - NAT: Enabling SNAT (MASQUERADE) functionality on $EXTIF"
> > #
> > #More liberal form
> > #$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE
> > #
> > #Stricter form
> > $IPTABLES -t nat -A POSTROUTING -o $EXTIF -j SNAT --to $EXTIP