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c2ccd7fd3d
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@800 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
1081 lines
38 KiB
HTML
1081 lines
38 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Language" content="en-us">
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<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
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<meta name="ProgId" content="FrontPage.Editor.Document">
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<meta http-equiv="Content-Type"
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content="text/html; charset=windows-1252">
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<title>Three-Interface Firewall</title>
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</head>
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<body>
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<h1 style="text-align: center;">Three-Interface Firewall<br>
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</h1>
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<p align="left">Setting up a Linux system as a firewall for a small
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network with DMZ is a fairly straight-forward task if you understand
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the basics and follow the documentation.</p>
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<p>This guide doesn't attempt to acquaint you with all of the features
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of Shorewall. It rather focuses on what is required to configure
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Shorewall in one of its more popular configurations:</p>
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<ul>
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<li>Linux system used as a firewall/router for a small local network.</li>
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<li style="font-weight: bold;">Single public IP address. If you have
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more than one public IP address, this is not the guide you want -- see
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the <a href="shorewall_setup_guide.htm">Shorewall Setup Guide</a>
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instead.<br>
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</li>
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<li>DMZ connected to a separate ethernet interface.</li>
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<li>Connection through DSL, Cable Modem, ISDN, Frame Relay, dial-up,
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...</li>
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</ul>
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<p align="left">Here is a schematic of a typical installation.</p>
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<p align="center"> <img border="0" src="images/dmz1.png" width="692"
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height="635"> </p>
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<p>Shorewall requires that you have the iproute/iproute2 package
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installed (on RedHat, the package is called <i>iproute</i>)<i>. </i>You
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can tell if this package is installed by the presence of an <b>ip</b>
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program on your firewall system. As root, you can use the 'which'
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command to check for this program:</p>
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<pre> [root@gateway root]# which ip<br> /sbin/ip<br> [root@gateway root]#</pre>
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<p>I recommend that you first read through the guide to familiarize
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yourself with what's involved then go back through it again making your
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configuration changes. Points at which configuration changes are
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recommended are flagged with <img border="0" src="images/BD21298_.gif"
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width="13" height="13"> . Configuration notes that are unique to
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LEAF/Bering are marked with <img src="images/leaflogo.gif"
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alt="(LEAF Logo)" width="49" height="36"> </p>
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<p><img border="0" src="images/j0213519.gif" width="60" height="60">
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If you edit your configuration files on a Windows
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system, you must save them as Unix files if your editor supports that
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option or you must run them through dos2unix before trying
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to use them. Similarly, if you copy a configuration file from your
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Windows hard drive to a floppy disk, you must run dos2unix against the
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copy before using it with Shorewall.</p>
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<ul>
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<li><a href="http://www.simtel.net/pub/pd/51438.html">Windows Version
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of dos2unix</a></li>
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<li><a href="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux
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Version
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of dos2unix</a></li>
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</ul>
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<h2 align="left">PPTP/ADSL</h2>
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<img style="border: 0px solid ; width: 13px; height: 13px;"
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src="images/BD21298_3.gif" title="" alt=""> If you
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have an ADSL Modem and you use PPTP to communicate with a server in
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that modem, you must make the <a href="PPTP.htm#PPTP_ADSL">changes
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recommended here</a> in addition to those detailed below. ADSL
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with PPTP is most commonly found in Europe, notably in Austria.<br>
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<h2 align="left">Shorewall Concepts</h2>
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<p> <img border="0" src="images/BD21298_.gif" width="13" height="13"
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alt=""> The configuration files for Shorewall are
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contained in the directory /etc/shorewall -- for simple setups, you
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will only need
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to deal with a few of these as described in this guide. After you have
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<a href="Install.htm">installed Shorewall</a>, <b>download the <a
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href="http://www.shorewall.net/pub/shorewall/Samples/">three-interface
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sample</a>, un-tar it (tar -zxvf three-interfaces.tgz) and and copy the
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files to /etc/shorewall (the files will replace files with the same
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names that were placed in /etc/shorewall when Shorewall was
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installed)</b>.</p>
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<p>As each file is introduced, I suggest that you look through the
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actual file on your system -- each file contains detailed configuration
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instructions and default entries.</p>
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<p>Shorewall views the network where it is running as being composed of
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a set of <i>zones.</i> In the three-interface sample configuration,
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the following zone names are used:</p>
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<table border="0" style="border-collapse: collapse;" cellpadding="3"
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cellspacing="0" id="AutoNumber2">
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<tbody>
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<tr>
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<td><u><b>Name</b></u></td>
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<td><u><b>Description</b></u></td>
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</tr>
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<tr>
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<td><b>net</b></td>
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<td><b>The Internet</b></td>
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</tr>
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<tr>
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<td><b>loc</b></td>
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<td><b>Your Local Network</b></td>
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</tr>
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<tr>
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<td><b>dmz</b></td>
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<td><b>Demilitarized Zone</b></td>
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</tr>
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</tbody>
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</table>
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<p>Zone names are defined in <a href="Documentation.htm#Zones">
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/etc/shorewall/zones</a>.</p>
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<p>Shorewall also recognizes the firewall system as its own zone - by
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default, the firewall itself is known as <b>fw</b>.</p>
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<p>Rules about what traffic to allow and what traffic to deny are
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expressed in terms of zones.</p>
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<ul>
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<li>You express your default policy for connections from one zone to
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another zone in the<a href="Documentation.htm#Policy">
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/etc/shorewall/policy </a>file.</li>
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<li>You define exceptions to those default policies in the <a
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href="Documentation.htm#Rules">/etc/shorewall/rules </a>file.</li>
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</ul>
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<p>For each connection request entering the firewall, the request is
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first checked against the /etc/shorewall/rules file. If no rule in that
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file matches the connection request then the first policy in
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/etc/shorewall/policy that matches the request is applied. If that
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policy is REJECT
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or DROP the request is first checked against the rules in
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/etc/shorewall/common if that file exists; otherwise the file
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/etc/shorewall/common.def is checked<br>
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</p>
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<p>The /etc/shorewall/policy file included with the three-interface
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sample has the following policies:</p>
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<blockquote>
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<table border="1" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber3">
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<tbody>
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<tr>
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<td><u><b>Source Zone</b></u></td>
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<td><u><b>Destination Zone</b></u></td>
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<td><u><b>Policy</b></u></td>
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<td><u><b>Log Level</b></u></td>
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<td><u><b>Limit:Burst</b></u></td>
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</tr>
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<tr>
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<td>loc</td>
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<td>net</td>
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<td>ACCEPT</td>
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<td> </td>
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<td> </td>
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</tr>
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<tr>
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<td>net</td>
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<td>all</td>
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<td>DROP</td>
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<td>info</td>
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<td> </td>
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</tr>
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<tr>
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<td>all</td>
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<td>all</td>
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<td>REJECT</td>
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<td>info</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<blockquote>
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<p>In the three-interface sample, the line below is included but
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commented out. If you want your firewall system to have full access to
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servers on the internet, uncomment that line.</p>
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<table border="1" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber3">
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<tbody>
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<tr>
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<td><u><b>Source Zone</b></u></td>
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<td><u><b>Destination Zone</b></u></td>
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<td><u><b>Policy</b></u></td>
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<td><u><b>Log Level</b></u></td>
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<td><u><b>Limit:Burst</b></u></td>
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</tr>
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<tr>
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<td>fw</td>
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<td>net</td>
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<td>ACCEPT</td>
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<td> </td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<p>The above policy will:</p>
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<ol>
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<li>allow all connection requests from your local
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network to the internet</li>
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<li>drop (ignore) all connection requests from the internet to your
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firewall or local network</li>
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<li>optionally accept all connection requests from the firewall to
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the internet (if you uncomment the additional policy)</li>
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<li>reject all other connection requests.</li>
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</ol>
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<p><img border="0" src="images/BD21298_1.gif" width="13" height="13">
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At this point, edit your /etc/shorewall/policy file
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and make any changes that you wish.</p>
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<h2 align="left">Network Interfaces</h2>
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<p align="center"> <img border="0" src="images/dmz1.png" width="692"
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height="635"> </p>
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<p align="left">The firewall has three network interfaces. Where
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Internet connectivity is through a cable or DSL "Modem", the <i>External
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Interface</i> will be the ethernet adapter that is connected to
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that "Modem" (e.g., <b>eth0</b>) <u>unless</u> you connect via <i><u>P</u>oint-to-<u>P</u>oint
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<u>P</u>rotocol over <u>E</u>thernet</i> (PPPoE) or <i><u>P</u>oint-to-<u>P</u>oint
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<u>T</u>unneling <u>P</u>rotocol </i>(PPTP) in which case the
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External Interface will be a ppp interface (e.g., <b>ppp0</b>). If you
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connect via a regular modem, your External Interface will also be <b>ppp0</b>.
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If you connect using ISDN, you external interface will be <b>ippp0.</b></p>
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<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
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height="13"> If your external interface is <b>ppp0</b>
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or <b>ippp0 </b>then you will want to set CLAMPMSS=yes in <a
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href="Documentation.htm#Conf"> /etc/shorewall/shorewall.conf.</a></p>
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<p align="left">Your <i>Local Interface</i> will be an ethernet
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adapter (eth0, eth1 or eth2) and will be connected to a hub or switch.
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Your local computers will be connected to the same switch (note: If you
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have only a single local system, you can connect the firewall directly
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to the computer using a <i>cross-over </i> cable).</p>
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<p align="left">Your <i>DMZ Interface</i> will also be an ethernet
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adapter (eth0, eth1 or eth2) and will be connected to a hub or switch.
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Your DMZ computers will be connected to the same switch (note: If
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you have only a single DMZ system, you can connect the firewall
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directly to the computer using a <i>cross-over </i> cable).</p>
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<p align="left"><u><b> <img border="0" src="images/j0213519.gif"
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width="60" height="60"> </b></u>Do not connect the internal and
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external interface to the same hub or switch except for testing AND you
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are running Shorewall version 1.4.7 or later. When using these
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recent
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versions, you can test using this kind of configuration if you specify
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the <span style="font-weight: bold;">arp_filter</span>
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option in /etc/shorewall/interfaces for all interfaces connected to the
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common hub/switch. Using such a setup with a production firewall is
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strongly recommended against.</p>
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<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
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height="13"> The Shorewall three-interface sample
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configuration assumes that the external interface is <b>eth0, </b>the
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local interface is <b>eth1 </b>and the DMZ interface is <b> eth2</b>.
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If your configuration is different, you will have to modify the sample
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/etc/shorewall/interfaces file accordingly. While you are there, you
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may wish to review the list of options that are specified for the
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interfaces. Some hints:</p>
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<ul>
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<li>
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<p align="left">If your external interface is <b>ppp0</b> or <b>ippp0</b>,
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you can replace the "detect" in the second column with "-". </p>
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</li>
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<li>
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<p align="left">If your external interface is <b>ppp0</b> or <b>ippp0</b>
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or if you have a static IP address, you can remove "dhcp" from the
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option list. </p>
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</li>
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</ul>
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<h2 align="left">IP Addresses</h2>
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<p align="left">Before going further, we should say a few words about
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Internet Protocol (IP) <i>addresses</i>. Normally, your ISP will
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assign
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you a single <i> Public</i> IP address. This address may be assigned
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via the<i> Dynamic Host Configuration Protocol</i> (DHCP) or as part
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of establishing your connection when you dial in (standard modem) or
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establish your PPP connection. In rare cases, your ISP may assign you
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a<i> static</i> IP address; that means that you configure your
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firewall's
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external interface to use that address permanently.<i> </i>Regardless
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of how the address is assigned, it will be shared by all of your
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systems
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when you access the Internet. You will have to assign your own
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addresses for your internal network (the local and DMZ Interfaces on
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your firewall
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plus your other computers). RFC 1918 reserves several <i>Private </i>IP
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address ranges for this purpose:</p>
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<div align="left">
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<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>
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</div>
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<div align="left">
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<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
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height="13"> Before starting Shorewall, you should
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look at
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the IP address of your external interface and if it is one of
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the above ranges, you should remove the 'norfc1918' option from
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the external interface's entry in /etc/shorewall/interfaces.</p>
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</div>
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<div align="left">
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<p align="left">You will want to assign your local addresses from one <i>
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sub-network </i>or <i>subnet</i> and your DMZ addresses from
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another subnet. For our purposes, we can consider a subnet to
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consists of a range of addresses x.y.z.0 - x.y.z.255. Such a subnet
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will have a <i>Subnet Mask </i>of 255.255.255.0. The address x.y.z.0
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is reserved as the <i>Subnet Address</i> and x.y.z.255 is reserved
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as the <i>Subnet Broadcast</i> <i>Address</i>. In Shorewall, a subnet
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is described using <a href="shorewall_setup_guide.htm#Subnets"><i>Classless
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InterDomain Routing </i>(CIDR)</a> notation with consists of the
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subnet address followed by "/24". The "24" refers to the number of
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consecutive "1" bits from the left of the subnet mask. </p>
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</div>
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<div align="left">
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<p align="left">Example sub-network:</p>
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</div>
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<div align="left">
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<blockquote>
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<table border="1" style="border-collapse: collapse;" id="AutoNumber1"
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cellpadding="2">
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<tbody>
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<tr>
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<td><b>Range:</b></td>
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<td>10.10.10.0 - 10.10.10.255</td>
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</tr>
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<tr>
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<td><b>Subnet Address:</b></td>
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<td>10.10.10.0</td>
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</tr>
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<tr>
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<td><b>Broadcast Address:</b></td>
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<td>10.10.10.255</td>
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</tr>
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<tr>
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<td><b>CIDR Notation:</b></td>
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<td>10.10.10.0/24</td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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</div>
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<div align="left">
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<p align="left">It is conventional to assign the internal interface
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either the first usable address in the subnet (10.10.10.1 in the above
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example) or the last usable address (10.10.10.254).</p>
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</div>
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<div align="left">
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<p align="left">One of the purposes of subnetting is to allow all
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computers in the subnet to understand which other computers can be
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communicated with directly. To communicate with systems outside of the
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subnetwork, systems send packets through a<i> gateway</i>
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(router).</p>
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</div>
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<div align="left">
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<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
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height="13"> Your local computers (Local Computers
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1 & 2) should be configured with their<i> default gateway</i> set
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to
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the IP address of the firewall's internal interface and your DMZ
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computers ( DMZ Computers 1 & 2) should be configured with their
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default gateway set to the IP address of the firewall's DMZ
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interface.
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</p>
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</div>
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<p align="left">The foregoing short discussion barely scratches the
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surface regarding subnetting and routing. If you are interested in
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learning more about IP addressing and routing, I highly recommend <i>"IP
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Fundamentals: What Everyone Needs to Know about Addressing &
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Routing",</i> Thomas A. Maufer, Prentice-Hall, 1999, ISBN 0-13-975483-0.</p>
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<p align="left">The remainder of this quide will assume that you have
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configured your network as shown here:</p>
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<p align="center"> <img border="0" src="images/dmz2.png" width="721"
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height="635"> </p>
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<p align="left">The default gateway for the DMZ computers would be
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10.10.11.254 and the default gateway for the Local computers would be
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10.10.10.254.<br>
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</p>
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<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
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height="13" alt=""> <font color="#ff0000"><b>WARNING:
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</b></font><b>Your ISP might assign your external interface an
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RFC 1918 address. If that address is in the 10.10.10.0/24 subnet then
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you will need to select a DIFFERENT RFC 1918 subnet for your local
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network and if it is in the 10.10.11.0/24 subnet then you will need to
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select a different RFC 1918 subnet for your DMZ.</b><br>
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</p>
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<p align="left">IP Masquerading (SNAT)</p>
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<p align="left">The addresses reserved by RFC 1918 are sometimes
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referred to as <i>non-routable</i> because the Internet backbone
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routers
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don't forward packets which have an RFC-1918 destination address.
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When one of your local systems (let's assume local computer 1) sends
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a connection request to an internet host, the firewall must perform
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<i>Network Address Translation </i>(NAT). The firewall rewrites the
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source address in the packet to be the address of the firewall's
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external
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interface; in other words, the firewall makes it look as if the
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firewall itself is initiating the connection. This is necessary
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so that the destination host will be able to route return packets back
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to the firewall (remember that packets whose destination address is
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reserved by RFC
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1918 can't be routed accross the internet). When the firewall receives
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a return packet, it rewrites the destination address back to 10.10.10.1
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and forwards the packet on to local computer 1. </p>
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<p align="left">On Linux systems, the above process is often referred
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to
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as<i> IP Masquerading</i> and you will also see the term <i>Source
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|
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"> 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"> 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=""> 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><server local ip address> </i>[:<i><server
|
|
port></i>]</td>
|
|
<td><i><protocol></i></td>
|
|
<td><i><port></i></td>
|
|
<td> </td>
|
|
<td> </td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
</blockquote>
|
|
<p>If you don't specify the <i><server port></i>, it is assumed
|
|
to
|
|
be the same as <i><port></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> </td>
|
|
<td> </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->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><external IP></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>
|
|
</li>
|
|
<li>Make your loc->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">
|
|
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"> 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> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>loc</td>
|
|
<td>fw</td>
|
|
<td>udp</td>
|
|
<td>53</td>
|
|
<td> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>dmz</td>
|
|
<td>fw</td>
|
|
<td>tcp</td>
|
|
<td>53</td>
|
|
<td> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>dmz</td>
|
|
<td>fw</td>
|
|
<td>udp</td>
|
|
<td>53</td>
|
|
<td> </td>
|
|
<td> </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> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>loc</td>
|
|
<td>dmz:10.10.11.1</td>
|
|
<td>udp</td>
|
|
<td>53</td>
|
|
<td> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>fw</td>
|
|
<td>dmz:10.10.10.1</td>
|
|
<td>tcp</td>
|
|
<td>53</td>
|
|
<td> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>fw</td>
|
|
<td>dmz:10.10.10.1</td>
|
|
<td>udp</td>
|
|
<td>53</td>
|
|
<td> </td>
|
|
<td> </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> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>fw</td>
|
|
<td>net</td>
|
|
<td>tcp</td>
|
|
<td>53</td>
|
|
<td> </td>
|
|
<td> </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> </td>
|
|
<td> </td>
|
|
</tr>
|
|
<tr>
|
|
<td>ACCEPT</td>
|
|
<td>loc</td>
|
|
<td>dmz</td>
|
|
<td>tcp</td>
|
|
<td>22</td>
|
|
<td> </td>
|
|
<td> </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><source zone></i></td>
|
|
<td><i><destination zone></i></td>
|
|
<td><i><protocol></i></td>
|
|
<td><i><port></i></td>
|
|
<td> </td>
|
|
<td> </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> </td>
|
|
<td> </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"> 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"> 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"> The <a href="Install.htm">installation
|
|
procedure </a> configures your system to start Shorewall at system
|
|
boot 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"> 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>
|