<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
  <meta http-equiv="Content-Language" content="en-us">
  <meta name="GENERATOR" content="Microsoft FrontPage 5.0">
  <meta name="ProgId" content="FrontPage.Editor.Document">
  <meta http-equiv="Content-Type"
 content="text/html; charset=windows-1252">
  <title>Three-Interface Firewall</title>
</head>
<body>
<h1 style="text-align: center;">Three-Interface Firewall<br>
</h1>
<p align="left">Setting up a Linux system as a firewall for a small
network with DMZ is a fairly straight-forward task if you understand
the basics and follow the documentation.</p>
<p>This guide doesn't attempt to acquaint you with all of the features
of Shorewall. It rather focuses on what is required to configure
Shorewall in one of its more popular configurations:</p>
<ul>
  <li>Linux system used as a firewall/router for a small local network.</li>
  <li style="font-weight: bold;">Single public IP address. If you have
more than one public IP address, this is not the guide you want -- see
the <a href="shorewall_setup_guide.htm">Shorewall Setup Guide</a>
instead.<br>
  </li>
  <li>DMZ connected to a separate ethernet interface.</li>
  <li>Connection through DSL, Cable Modem, ISDN, Frame Relay, dial-up,
...</li>
</ul>
<p align="left">Here is a schematic of a typical installation.</p>
<p align="center"> <img border="0" src="images/dmz1.png" width="692"
 height="635"> </p>
<p>Shorewall requires that you have the iproute/iproute2 package
installed (on RedHat, the package is called <i>iproute</i>)<i>. </i>You
can tell if this package is installed by the presence of an <b>ip</b>
program on your firewall system. As root, you can use the 'which'
command to check for this program:</p>
<pre>     [root@gateway root]# which ip<br>     /sbin/ip<br>     [root@gateway root]#</pre>
<p>I recommend that you first read through the guide to familiarize
yourself with what's involved then go back through it again making your
configuration changes. Points at which configuration changes are
recommended are flagged with <img border="0" src="images/BD21298_.gif"
 width="13" height="13"> .&nbsp;Configuration notes that are unique to
LEAF/Bering are marked with&nbsp;<img src="images/leaflogo.gif"
 alt="(LEAF Logo)" width="49" height="36"> </p>
<p><img border="0" src="images/j0213519.gif" width="60" height="60">
&nbsp;&nbsp;&nbsp; If you edit your configuration files on a Windows
system, you must save them as Unix files if your editor supports that
option or you must run them through dos2unix before trying
to use them. Similarly, if you copy a configuration file from your
Windows hard drive to a floppy disk, you must run dos2unix against the
copy before using it with Shorewall.</p>
<ul>
  <li><a href="http://www.simtel.net/pub/pd/51438.html">Windows Version
of dos2unix</a></li>
  <li><a href="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux
Version
of dos2unix</a></li>
</ul>
<h2 align="left">PPTP/ADSL</h2>
<img style="border: 0px solid ; width: 13px; height: 13px;"
 src="images/BD21298_3.gif" title="" alt="">&nbsp;&nbsp;&nbsp; If you
have an ADSL Modem and you use PPTP to communicate with a server in
that modem, you must make the <a href="PPTP.htm#PPTP_ADSL">changes
recommended here</a> in addition to those detailed below.&nbsp; ADSL
with PPTP is most commonly found in Europe, notably in Austria.<br>
<h2 align="left">Shorewall Concepts</h2>
<p> <img border="0" src="images/BD21298_.gif" width="13" height="13"
 alt=""> &nbsp;&nbsp;&nbsp; The configuration files for Shorewall are
contained in the directory /etc/shorewall -- for simple setups, you
will only need
to deal with a few of these as described in this guide. After you have
<a href="Install.htm">installed Shorewall</a>, <b>download the <a
 href="http://www.shorewall.net/pub/shorewall/Samples/">three-interface
sample</a>, un-tar it (tar -zxvf three-interfaces.tgz) and and copy the
files to /etc/shorewall (the files will replace files with the same
names that were placed in /etc/shorewall when Shorewall was
installed)</b>.</p>
<p>As each file is introduced, I suggest that you look through the
actual file on your system -- each file contains detailed configuration
instructions and default entries.</p>
<p>Shorewall views the network where it is running as being composed of
a set of <i>zones.</i> In the three-interface sample configuration,
the following zone names are used:</p>
<table border="0" style="border-collapse: collapse;" cellpadding="3"
 cellspacing="0" id="AutoNumber2">
  <tbody>
    <tr>
      <td><u><b>Name</b></u></td>
      <td><u><b>Description</b></u></td>
    </tr>
    <tr>
      <td><b>net</b></td>
      <td><b>The Internet</b></td>
    </tr>
    <tr>
      <td><b>loc</b></td>
      <td><b>Your Local Network</b></td>
    </tr>
    <tr>
      <td><b>dmz</b></td>
      <td><b>Demilitarized Zone</b></td>
    </tr>
  </tbody>
</table>
<p>Zone names are defined in <a href="Documentation.htm#Zones">
/etc/shorewall/zones</a>.</p>
<p>Shorewall also recognizes the firewall system as its own zone - by
default, the firewall itself is known as <b>fw</b>.</p>
<p>Rules about what traffic to allow and what traffic to deny are
expressed in terms of zones.</p>
<ul>
  <li>You express your default policy for connections from one zone to
another zone in the<a href="Documentation.htm#Policy">
/etc/shorewall/policy </a>file.</li>
  <li>You define exceptions to those default policies in the <a
 href="Documentation.htm#Rules">/etc/shorewall/rules </a>file.</li>
</ul>
<p>For each connection request entering the firewall, the request is
first checked against the /etc/shorewall/rules file. If no rule in that
file matches the connection request then the first policy in
/etc/shorewall/policy that matches the request is applied. If that
policy is REJECT
or DROP&nbsp; the request is first checked against the rules in
/etc/shorewall/common if that file exists; otherwise the file
/etc/shorewall/common.def is checked<br>
</p>
<p>The /etc/shorewall/policy file included with the three-interface
sample has the following policies:</p>
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber3">
    <tbody>
      <tr>
        <td><u><b>Source Zone</b></u></td>
        <td><u><b>Destination Zone</b></u></td>
        <td><u><b>Policy</b></u></td>
        <td><u><b>Log Level</b></u></td>
        <td><u><b>Limit:Burst</b></u></td>
      </tr>
      <tr>
        <td>loc</td>
        <td>net</td>
        <td>ACCEPT</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>net</td>
        <td>all</td>
        <td>DROP</td>
        <td>info</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>all</td>
        <td>all</td>
        <td>REJECT</td>
        <td>info</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
<blockquote>
  <p>In the three-interface sample, the line below is included but
commented out. If you want your firewall system to have full access to
servers on the internet, uncomment that line.</p>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber3">
    <tbody>
      <tr>
        <td><u><b>Source Zone</b></u></td>
        <td><u><b>Destination Zone</b></u></td>
        <td><u><b>Policy</b></u></td>
        <td><u><b>Log Level</b></u></td>
        <td><u><b>Limit:Burst</b></u></td>
      </tr>
      <tr>
        <td>fw</td>
        <td>net</td>
        <td>ACCEPT</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
<p>The above policy will:</p>
<ol>
  <li>allow all connection requests from your local
network to the internet</li>
  <li>drop (ignore) all connection requests from the internet to your
firewall or local network</li>
  <li>optionally accept all connection requests from the firewall to
the internet (if you uncomment the additional policy)</li>
  <li>reject all other connection requests.</li>
</ol>
<p><img border="0" src="images/BD21298_1.gif" width="13" height="13">
&nbsp;&nbsp;&nbsp; At this point, edit your /etc/shorewall/policy file
and make any changes that you wish.</p>
<h2 align="left">Network Interfaces</h2>
<p align="center"> <img border="0" src="images/dmz1.png" width="692"
 height="635"> </p>
<p align="left">The firewall has three network interfaces. Where
Internet connectivity is through a cable or DSL "Modem", the <i>External
Interface</i> will be the ethernet adapter that is connected to
that "Modem" (e.g., <b>eth0</b>)&nbsp; <u>unless</u> you connect via <i><u>P</u>oint-to-<u>P</u>oint
<u>P</u>rotocol over <u>E</u>thernet</i> (PPPoE) or <i><u>P</u>oint-to-<u>P</u>oint
<u>T</u>unneling <u>P</u>rotocol </i>(PPTP) in which case the
External Interface will be a ppp interface (e.g., <b>ppp0</b>). If you
connect via a regular modem, your External Interface will also be <b>ppp0</b>.
If you connect using ISDN, you external interface will be <b>ippp0.</b></p>
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; If your external interface is <b>ppp0</b>
or <b>ippp0 </b>then you will want to set CLAMPMSS=yes in <a
 href="Documentation.htm#Conf"> /etc/shorewall/shorewall.conf.</a></p>
<p align="left">Your <i>Local Interface</i> will be an ethernet
adapter (eth0, eth1 or eth2) and will be connected to a hub or switch.
Your local computers will be connected to the same switch (note: If you
have only a single local system, you can connect the firewall directly
to the computer using a <i>cross-over </i> cable).</p>
<p align="left">Your <i>DMZ Interface</i> will also be an ethernet
adapter (eth0, eth1 or eth2) and will be connected to a hub or switch.
Your DMZ computers will be connected to the same switch (note: If
you have only a single DMZ system, you can connect the firewall
directly to the computer using a <i>cross-over </i> cable).</p>
<p align="left"><u><b> <img border="0" src="images/j0213519.gif"
 width="60" height="60"> </b></u>Do not connect the internal and
external interface to the same hub or switch except for testing AND you
are running Shorewall version 1.4.7 or later.&nbsp; When using these
recent
versions, you can test using this kind of configuration if you specify
the <span style="font-weight: bold;">arp_filter</span>
option in /etc/shorewall/interfaces for all interfaces connected to the
common hub/switch. Using such a setup with a production firewall is
strongly recommended against.</p>
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; The Shorewall three-interface sample
configuration assumes that the external interface is <b>eth0, </b>the
local interface is <b>eth1 </b>and the DMZ interface is <b> eth2</b>.
If your configuration is different, you will have to modify the sample
/etc/shorewall/interfaces file accordingly. While you are there, you
may wish to review the list of options that are specified for the
interfaces. Some hints:</p>
<ul>
  <li>
    <p align="left">If your external interface is <b>ppp0</b> or <b>ippp0</b>,
you can replace the "detect" in the second column with "-". </p>
  </li>
  <li>
    <p align="left">If your external interface is <b>ppp0</b> or <b>ippp0</b>
or if you have a static IP address, you can remove "dhcp" from the
option list. </p>
  </li>
</ul>
<h2 align="left">IP Addresses</h2>
<p align="left">Before going further, we should say a few words about
Internet Protocol (IP) <i>addresses</i>. Normally, your ISP will
assign
you a single <i> Public</i> IP address. This address may be assigned
via the<i> Dynamic Host Configuration Protocol</i> (DHCP) or as part
of establishing your connection when you dial in (standard modem) or
establish your PPP connection. In rare cases, your ISP may assign you
a<i> static</i> IP address; that means that you configure your
firewall's
external interface to use that address permanently.<i> </i>Regardless
of how the address is assigned, it will be shared by all of your
systems
when you access the Internet. You will have to assign your own
addresses for your internal network (the local and DMZ Interfaces on
your firewall
plus your other computers). RFC 1918 reserves several <i>Private </i>IP
address ranges for this purpose:</p>
<div align="left">
<pre>     10.0.0.0    - 10.255.255.255<br>     172.16.0.0  - 172.31.255.255<br>     192.168.0.0 - 192.168.255.255</pre>
</div>
<div align="left">
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; Before starting Shorewall, you should
look at
the IP address of your external interface and if it is one of
the above ranges, you should remove the 'norfc1918' option from
the external interface's entry in /etc/shorewall/interfaces.</p>
</div>
<div align="left">
<p align="left">You will want to assign your local addresses from one <i>
sub-network </i>or <i>subnet</i> and your DMZ addresses from
another subnet. For our purposes, we can consider a subnet to
consists of a range of addresses x.y.z.0 - x.y.z.255. Such a subnet
will have a <i>Subnet Mask </i>of 255.255.255.0. The address x.y.z.0
is reserved as the <i>Subnet Address</i> and x.y.z.255 is reserved
as the <i>Subnet Broadcast</i> <i>Address</i>. In Shorewall, a subnet
is described using&nbsp;<a href="shorewall_setup_guide.htm#Subnets"><i>Classless
InterDomain Routing </i>(CIDR)</a> notation with consists of the
subnet address followed by "/24". The "24" refers to the number of
consecutive "1" bits from the left of the subnet mask. </p>
</div>
<div align="left">
<p align="left">Example sub-network:</p>
</div>
<div align="left">
<blockquote>
  <table border="1" style="border-collapse: collapse;" id="AutoNumber1"
 cellpadding="2">
    <tbody>
      <tr>
        <td><b>Range:</b></td>
        <td>10.10.10.0 - 10.10.10.255</td>
      </tr>
      <tr>
        <td><b>Subnet Address:</b></td>
        <td>10.10.10.0</td>
      </tr>
      <tr>
        <td><b>Broadcast Address:</b></td>
        <td>10.10.10.255</td>
      </tr>
      <tr>
        <td><b>CIDR&nbsp;Notation:</b></td>
        <td>10.10.10.0/24</td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<div align="left">
<p align="left">It is conventional to assign the internal interface
either the first usable address in the subnet (10.10.10.1 in the above
example) or the last usable address (10.10.10.254).</p>
</div>
<div align="left">
<p align="left">One of the purposes of subnetting is to allow all
computers in the subnet to understand which other computers can be
communicated with directly. To communicate with systems outside of the
subnetwork, systems send packets through a<i>&nbsp; gateway</i>&nbsp;
(router).</p>
</div>
<div align="left">
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; Your local computers (Local Computers
1 &amp; 2) should be configured with their<i> default gateway</i> set
to
the IP address of the firewall's internal interface and your DMZ
computers ( DMZ Computers 1 &amp; 2) should be configured with their
default gateway set to the IP address of the firewall's DMZ
interface.&nbsp;&nbsp;
</p>
</div>
<p align="left">The foregoing short discussion barely scratches the
surface regarding subnetting and routing. If you are interested in
learning more about IP addressing and routing, I highly recommend <i>"IP
Fundamentals: What Everyone Needs to Know about Addressing &amp;
Routing",</i> Thomas A. Maufer, Prentice-Hall, 1999, ISBN 0-13-975483-0.</p>
<p align="left">The remainder of this quide will assume that you have
configured your network as shown here:</p>
<p align="center"> <img border="0" src="images/dmz2.png" width="721"
 height="635"> </p>
<p align="left">The default gateway for the DMZ computers would be
10.10.11.254 and the default gateway for the Local computers would be
10.10.10.254.<br>
</p>
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
 height="13" alt=""> &nbsp;&nbsp;&nbsp; <font color="#ff0000"><b>WARNING:
</b></font><b>Your ISP&nbsp; might assign your external interface an
RFC 1918 address. If that address is in the 10.10.10.0/24 subnet then
you will need to select a DIFFERENT RFC 1918 subnet for your local
network and if it is in the 10.10.11.0/24 subnet then you will need to
select a different RFC 1918 subnet for your DMZ.</b><br>
</p>
<p align="left">IP Masquerading (SNAT)</p>
<p align="left">The addresses reserved by RFC 1918 are sometimes
referred to as <i>non-routable</i> because the Internet backbone
routers
don't forward packets which have an RFC-1918 destination address.
When one of your local systems (let's assume local computer 1) sends
a connection request to an internet host, the firewall must perform
<i>Network Address Translation </i>(NAT). The firewall rewrites the
source address in the packet to be the address of the firewall's
external
interface; in other words, the firewall makes it look as if the
firewall itself is initiating the connection.&nbsp; This is necessary
so that the destination host will be able to route return packets back
to the firewall (remember that packets whose destination address is
reserved by RFC
1918 can't be routed accross the internet). When the firewall receives
a return packet, it rewrites the destination address back to 10.10.10.1
and forwards the packet on to local computer 1. </p>
<p align="left">On Linux systems, the above process is often referred
to
as<i> IP Masquerading</i> and you will also see the term <i>Source
Network
Address Translation </i>(SNAT) used. Shorewall follows the convention
used
with Netfilter:</p>
<ul>
  <li>
    <p align="left"><i>Masquerade</i> describes the case where you let
your firewall system automatically detect the external interface
address. </p>
  </li>
  <li>
    <p align="left"><i>SNAT</i> refers to the case when you explicitly
specify the source address that you want outbound packets from your
local network to use. </p>
  </li>
</ul>
<p align="left">In Shorewall, both Masquerading and SNAT are configured
with entries in the /etc/shorewall/masq file.</p>
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; If your external firewall interface is
<b>eth0</b>, your local interface <b>eth1 </b>and your DMZ interface
is <b>eth2</b> then you do not need to modify the file provided with
the sample.
Otherwise, edit /etc/shorewall/masq and change it to match your
configuration.</p>
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; If your external IP is static, you can
enter it
in the third column in the /etc/shorewall/masq entry if you like
although your firewall will work fine if you leave that column empty.
Entering your static IP in column 3 makes <br>
processing outgoing packets a little more efficient.<br>
</p>
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
 height="13" alt=""> &nbsp;&nbsp;&nbsp; If you are using the Debian
package, please check your shorewall.conf file to ensure that the
following are set correctly; if they are not, change them appropriately:<br>
</p>
<ul>
  <li>NAT_ENABLED=Yes (Shorewall versions earlier than 1.4.6)</li>
  <li>IP_FORWARDING=On<br>
  </li>
</ul>
<h2 align="left">Port Forwarding (DNAT)</h2>
<p align="left">One of your goals will be to run one or more servers on
your DMZ computers. Because these computers have RFC-1918 addresses,
it is not possible for clients on the internet to connect directly
to them. It is rather necessary for those clients to address their
connection requests to your firewall who rewrites the destination
address to the address of your server and forwards the packet to that
server. When your server responds, the firewall automatically performs
SNAT to rewrite the source address in the response.</p>
<p align="left">The above process is called<i> Port Forwarding</i> or <i>
Destination Network Address Translation</i> (DNAT). You configure port
forwarding using DNAT rules in the /etc/shorewall/rules file.</p>
<p>The general form of a simple port forwarding rule in
/etc/shorewall/rules is:</p>
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>DNAT</td>
        <td>net</td>
        <td>dmz:<i>&lt;server local ip address&gt; </i>[:<i>&lt;server
port&gt;</i>]</td>
        <td><i>&lt;protocol&gt;</i></td>
        <td><i>&lt;port&gt;</i></td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
<p>If you don't specify the <i>&lt;server port&gt;</i>, it is assumed
to
be the same as <i>&lt;port&gt;</i>.</p>
<p>Example - you run a Web Server on DMZ 2 and you want to forward
incoming TCP port 80 to that system:</p>
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>DNAT</td>
        <td>net</td>
        <td>dmz:10.10.11.2</td>
        <td>tcp</td>
        <td>80</td>
        <td># Forward port 80</td>
        <td>from the internet</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>dmz:10.10.11.2</td>
        <td>tcp</td>
        <td>80</td>
        <td>#Allow connections </td>
        <td>from the local network</td>
      </tr>
    </tbody>
  </table>
</blockquote>
<p>A couple of important points to keep in mind:</p>
<ul>
  <li>When you are connecting to your server from your local systems,
you must use the server's internal IP address (10.10.11.2).</li>
  <li>Many ISPs block incoming connection requests to port 80. If you
have problems connecting to your web server,
try the following rule and try connecting to port 5000 (e.g., connect
to <a href="http://w.x.y.z:5000"> http://w.x.y.z:5000</a> where
w.x.y.z is your external IP).</li>
</ul>
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>DNAT</td>
        <td>net</td>
        <td>dmz:10.10.11.2:80</td>
        <td>tcp</td>
        <td>5000</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
<p>If you want to be able to access your server from the local network
using your external address, then if you have a static external IP you
can replace the loc-&gt;dmz rule above with:</p>
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>DNAT</td>
        <td>net</td>
        <td>dmz:10.10.11.2:80</td>
        <td>tcp</td>
        <td>80</td>
        <td>-</td>
        <td><i>&lt;external IP&gt;</i></td>
      </tr>
    </tbody>
  </table>
</blockquote>
<p>If you have a dynamic ip then you must ensure that your external
interface is up before starting Shorewall and you must take steps as
follows (assume that your external interface is <b>eth0</b>):</p>
<ol>
  <li>Include the following in /etc/shorewall/params:<br>
    <br>
ETH0_IP=`find_interface_address eth0`<br>
&nbsp;</li>
  <li>Make your loc-&gt;dmz rule:</li>
</ol>
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>DNAT</td>
        <td>loc<br>
        </td>
        <td>dmz:10.10.11.2:80</td>
        <td>tcp</td>
        <td>80</td>
        <td>-</td>
        <td>$ETH0_IP</td>
      </tr>
    </tbody>
  </table>
</blockquote>
<p>If you want to access your server from the DMZ using your external
IP address, see <a href="FAQ.htm#faq2a">FAQ 2a</a>.</p>
<p><img border="0" src="images/BD21298_2.gif" width="13" height="13">
&nbsp;&nbsp;&nbsp; At this point, add the DNAT and ACCEPT rules for
your servers. </p>
<h2 align="left">Domain Name Server (DNS)</h2>
<p align="left">Normally, when you connect to your ISP, as part of
getting an IP address your firewall's <i>Domain Name Service </i>(DNS)
resolver will be automatically configured (e.g., the /etc/resolv.conf
file will be written). Alternatively, your ISP may have given you
the IP address of a pair of DNS <i> name servers</i> for you to
manually
configure as your primary and secondary name servers. It is <u>your</u>
responsibility to configure the resolver in your internal systems.
You can take one of two approaches:</p>
<ul>
  <li>
    <p align="left">You can configure your internal systems to use your
ISP's name servers. If you ISP gave you the addresses of their servers
or if those addresses are available on their web site, you can
configure your internal systems to use those addresses. If that
information isn't available, look in /etc/resolv.conf on your firewall
system -- the name servers are given in "nameserver" records in that
file. </p>
  </li>
  <li>
    <p align="left"><img border="0" src="images/BD21298_2.gif"
 width="13" height="13"> &nbsp;&nbsp;&nbsp; You can configure a<i>
Caching Name Server </i>on your firewall or in your DMZ.<i> </i>Red
Hat has an RPM for a caching name server (which also requires the
'bind' RPM) and for Bering users, there is dnscache.lrp. If you take
this approach, you configure your internal systems to use the caching
name server as their primary (and only) name server. You use the
internal IP address of the firewall (10.10.10.254 in the example above)
for the name server address
if you choose to run the name server on your firewall. To allow your
local systems to talk to your caching name server, you must open
port 53 (both UDP and TCP) from the local network to the server; you
do that by adding the rules in /etc/shorewall/rules. </p>
  </li>
</ul>
<blockquote>
  <p align="left">If you run the name server on the firewall:
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>fw</td>
        <td>tcp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>fw</td>
        <td>udp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>dmz</td>
        <td>fw</td>
        <td>tcp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>dmz</td>
        <td>fw</td>
        <td>udp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
  </p>
</blockquote>
<div align="left">
<blockquote>
  <p>Run name server on DMZ computer 1</p>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>dmz:10.10.11.1</td>
        <td>tcp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>dmz:10.10.11.1</td>
        <td>udp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>fw</td>
        <td>dmz:10.10.10.1</td>
        <td>tcp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>fw</td>
        <td>dmz:10.10.10.1</td>
        <td>udp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<div align="left">
<h2 align="left">Other Connections</h2>
</div>
<div align="left">
<p align="left">The three-interface sample includes the following rules:</p>
</div>
<div align="left">
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>fw</td>
        <td>net</td>
        <td>udp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>fw</td>
        <td>net</td>
        <td>tcp</td>
        <td>53</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<div align="left">
<p align="left">Those rules allow DNS access from your firewall and may
be removed if you commented out the line in /etc/shorewall/policy
allowing all connections from the firewall to the internet.</p>
</div>
<div align="left">
<p align="left">The sample also includes:</p>
</div>
<div align="left">
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>fw</td>
        <td>tcp</td>
        <td>22</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>dmz</td>
        <td>tcp</td>
        <td>22</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<div align="left">
<p align="left">That rule allows you to run an SSH server on your
firewall and in each of your DMZ systems and to connect to those
servers from your local systems.</p>
</div>
<div align="left">
<p align="left">If you wish to enable other connections between your
systems, the general format is:</p>
</div>
<div align="left">
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td><i>&lt;source zone&gt;</i></td>
        <td><i>&lt;destination zone&gt;</i></td>
        <td><i>&lt;protocol&gt;</i></td>
        <td><i>&lt;port&gt;</i></td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<div align="left">
<p align="left">Example - You want to run a publicly-available DNS
server on your firewall system:</p>
</div>
<div align="left">
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>net</td>
        <td>fw</td>
        <td>tcp</td>
        <td>53</td>
        <td>#Allow DNS access</td>
        <td>from the internet</td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>net</td>
        <td>fw</td>
        <td>udp<br>
        </td>
        <td>53</td>
        <td>#Allow DNS access</td>
        <td>from the internet</td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<div align="left">
<p align="left">Those two rules would of course be in addition to the
rules listed above under "If you run the name server on your firewall".</p>
</div>
<div align="left">
<p align="left">If you don't know what port and protocol a particular
application uses, look <a href="ports.htm">here</a>.</p>
</div>
<div align="left">
<p align="left"><b>Important: </b>I don't recommend enabling telnet
to/from the internet because it uses clear text (even for login!). If
you want shell access to your firewall from the internet, use
SSH:</p>
</div>
<div align="left">
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>net</td>
        <td>fw</td>
        <td>tcp</td>
        <td>22</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<div align="left">
<p align="left"> </p>
<p align="left"><img src="images/leaflogo.gif" alt="(LEAF Logo)"
 width="49" height="36"> &nbsp;&nbsp;&nbsp; Bering users will want to
add the following two rules to be compatible with Jacques's Shorewall
configuration.<br>
</p>
<div align="left">
<blockquote>
  <table border="1" cellpadding="2" style="border-collapse: collapse;"
 id="AutoNumber4">
    <tbody>
      <tr>
        <td><u><b>ACTION</b></u></td>
        <td><u><b>SOURCE</b></u></td>
        <td><u><b>DESTINATION</b></u></td>
        <td><u><b>PROTOCOL</b></u></td>
        <td><u><b>PORT</b></u></td>
        <td><u><b>SOURCE PORT</b></u></td>
        <td><u><b>ORIGINAL ADDRESS</b></u></td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc<br>
        </td>
        <td>fw</td>
        <td>udp<br>
        </td>
        <td>53<br>
        </td>
        <td>#Allow DNS Cache to</td>
        <td>work<br>
        </td>
      </tr>
      <tr>
        <td>ACCEPT</td>
        <td>loc</td>
        <td>fw</td>
        <td>tcp</td>
        <td>80</td>
        <td>#Allow weblet to work</td>
        <td><br>
        </td>
      </tr>
    </tbody>
  </table>
</blockquote>
</div>
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; Now modify /etc/shorewall/rules to add
or remove other connections as required.</p>
</div>
<div align="left">
<h2 align="left">Starting and Stopping Your Firewall</h2>
</div>
<div align="left">
<p align="left"> <img border="0" src="images/BD21298_2.gif" width="13"
 height="13" alt="Arrow"> &nbsp;&nbsp;&nbsp; The <a href="Install.htm">installation
procedure </a> configures your system to start Shorewall at system
boot&nbsp; but beginning with Shorewall version 1.3.9 startup is
disabled so that your system won't try to start Shorewall before
configuration is complete. Once you have completed configuration of
your firewall, you can enable Shorewall startup by removing the file
/etc/shorewall/startup_disabled.<br>
</p>
<p align="left"><font color="#ff0000"><b>IMPORTANT</b>: </font><font
 color="#ff0000">Users of the .deb package must edit
/etc/default/shorewall and set 'startup=1'.</font><br>
</p>
</div>
<div align="left">
<p align="left">The firewall is started using the "shorewall start"
command and stopped using "shorewall stop". When the firewall is
stopped, routing is enabled on those hosts that have an entry in <a
 href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>.
A running firewall may be restarted using the "shorewall restart"
command. If you want to totally remove any trace of Shorewall
from your Netfilter configuration, use "shorewall clear".</p>
</div>
<div align="left">
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
 height="13"> &nbsp;&nbsp;&nbsp; The three-interface sample assumes
that you want
to enable routing to/from <b>eth1 (</b>your local network) and<b> eth2
</b>(DMZ) when Shorewall is stopped. If these two interfaces don't
connect to your local network and DMZ or if you want to enable a
different set of hosts, modify /etc/shorewall/routestopped accordingly.</p>
</div>
<div align="left">
<p align="left"><b>WARNING: </b>If you are connected to your firewall
from the internet, do not issue a "shorewall stop" command unless
you have added an entry for the IP address that you are connected
from to <a href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>.
Also, I don't recommend using "shorewall restart"; it is better to
create an <i><a href="configuration_file_basics.htm#Configs">alternate
configuration</a></i> and test it using the <a
 href="starting_and_stopping_shorewall.htm">"shorewall try" command</a>.<br>
</p>
<h2>Additional Recommended Reading</h2>
I highly recommend that you review the <a
 href="configuration_file_basics.htm">Common Configuration File
Features page</a> -- it contains helpful tips about Shorewall features
than make administering your firewall easier.
</div>
<p align="left"><font size="2">Last updated 11/15/2003 - <a
 href="support.htm">Tom Eastep</a></font></p>
<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002,
2003 Thomas M. Eastep</font></a><br>
</p>
<br>
<br>
</body>
</html>