forked from extern/shorewall_code
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git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@385 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
1145 lines
47 KiB
HTML
1145 lines
47 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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<table border="0" cellpadding="0" cellspacing="0"
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style="border-collapse: collapse;" bordercolor="#111111" width="100%"
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id="AutoNumber5" bgcolor="#400169" height="90">
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<tbody>
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<tr>
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<td width="100%">
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<h1 align="center"><font color="#ffffff">Three-Interface Firewall</font></h1>
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</td>
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</tr>
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</tbody>
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</table>
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<h2 align="center">Version 2.0.1</h2>
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<p align="left">Setting up a Linux system as a firewall for a small network
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with DMZ is a fairly straight-forward task if you understand the basics
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and follow the documentation.</p>
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<p>This guide doesn't attempt to acquaint you with all of the features of
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Shorewall. It rather focuses on what is required to configure Shorewall
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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
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network.</li>
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<li>Single public IP address.</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,
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dial-up, ...</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">
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</p>
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<p>This guide assumes that you have the iproute/iproute2 package installed
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(on RedHat, the package is called <i>iproute</i>)<i>. </i>You can tell
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if this package is installed by the presence of an <b>ip</b> program
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on your firewall system. As root, you can use the 'which' command to
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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 yourself
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with what's involved then go back through it again making your configuration
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changes. Points at which configuration changes are recommended are
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flagged with <img border="0" src="images/BD21298_.gif" width="13"
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height="13">
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</p>
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<p><img border="0" src="images/j0213519.gif" width="60" height="60">
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<20><><EFBFBD> If you edit your configuration files on a Windows system,
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you must save them as Unix files if your editor supports that option
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or you must run them through dos2unix before trying to use them. Similarly,
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if you copy a configuration file from your Windows hard drive to a floppy
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disk, you must run dos2unix against the 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
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Version of dos2unix</a></li>
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<li><a
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href="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux Version
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of dos2unix</a></li>
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</ul>
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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="">
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<20><><EFBFBD> The configuration files for Shorewall are contained in the directory
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/etc/shorewall -- for simple setups, you will only need to deal with a
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few of these as described in this guide. After you have <a
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href="Install.htm">installed Shorewall</a>, <b>download the <a
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href="/pub/shorewall/LATEST.samples/three-interfaces.tgz">three-interface
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sample</a>, un-tar it (tar -zxvf three-interfaces.tgz) and and copy
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the 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 installed)</b>.</p>
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<p>As each file is introduced, I suggest that you look through the actual
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file on your system -- each file contains detailed configuration instructions
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and default entries.</p>
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<p>Shorewall views the network where it is running as being composed of a
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set of <i>zones.</i> In the three-interface sample configuration, the
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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"> /etc/shorewall/zones</a>.</p>
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<p>Shorewall also recognizes the firewall system as its own zone - by default,
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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 expressed
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in terms of zones.</p>
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<ul>
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<li>You express your default policy for connections from one
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zone to another zone in the<a href="Documentation.htm#Policy"> /etc/shorewall/policy
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</a>file.</li>
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<li>You define exceptions to those default policies in the
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<a 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 first
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checked against the /etc/shorewall/rules file. If no rule in that file
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matches the connection request then the first policy in /etc/shorewall/policy
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that matches the request is applied. If that policy is REJECT or DROP<4F>
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the request is first checked against the rules in /etc/shorewall/common
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(the samples provide that file for you).</p>
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<p>The /etc/shorewall/policy file included with the three-interface sample
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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><EFBFBD></td>
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<td><EFBFBD></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><EFBFBD></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><EFBFBD></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 commented
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out. If you want your firewall system to have full access to servers
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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><EFBFBD></td>
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<td><EFBFBD></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 network to
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the internet</li>
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<li>drop (ignore) all connection requests from the internet
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to your firewall or local network</li>
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<li>optionally accept all connection requests from the firewall
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to 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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<20><><EFBFBD> At this point, edit your /etc/shorewall/policy file and make
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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">
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</p>
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<p align="left">The firewall has three network interfaces. Where Internet
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connectivity is through a cable or DSL "Modem", the <i>External Interface</i>
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will be the ethernet adapter that is connected to that "Modem" (e.g.,
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<b>eth0</b>)<29> <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 External
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Interface will be a ppp interface (e.g., <b>ppp0</b>). If you connect via
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a regular modem, your External Interface will also be <b>ppp0</b>. If you
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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">
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<20><><EFBFBD> If your external interface is <b>ppp0</b> or <b>ippp0 </b>then
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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 adapter (eth0,
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eth1 or eth2) and will be connected to a hub or switch. Your local
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computers will be connected to the same switch (note: If you have only
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a single local system, you can connect the firewall directly to the
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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 adapter
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(eth0, eth1 or eth2) and will be connected to a hub or switch. Your
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DMZ computers will be connected to the same switch (note: If you have
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only a single DMZ system, you can connect the firewall directly to the
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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">
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</b></u>Do not connect more than one interface to the same hub
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or switch (even for testing). It won't work the way that you expect it
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to and you will end up confused and believing that Shorewall doesn't
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work at all.</p>
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<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
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height="13">
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<20><><EFBFBD> The Shorewall three-interface sample configuration assumes
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that the external interface is <b>eth0, </b>the local interface is <b>eth1
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</b>and the DMZ interface is <b> eth2</b>. If your configuration is different,
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you will have to modify the sample /etc/shorewall/interfaces file accordingly.
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While you are there, you may wish to review the list of options that
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are specified for the 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 Internet
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Protocol (IP) <i>addresses</i>. Normally, your ISP will assign you
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a single <i> Public</i> IP address. This address may be assigned via
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the<i> Dynamic Host Configuration Protocol</i> (DHCP) or as part of
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establishing your connection when you dial in (standard modem) or establish
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your PPP connection. In rare cases, your ISP may assign you a<i> static</i>
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IP address; that means that you configure your firewall's external interface
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to use that address permanently.<i> </i>Regardless of how the address is
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assigned, it will be shared by all of your systems when you access the
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Internet. You will have to assign your own addresses for your internal
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network (the local and DMZ Interfaces on your firewall plus your other
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computers). RFC 1918 reserves several <i>Private </i>IP address ranges for
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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">
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<20><><EFBFBD> Before starting Shorewall, you should look at the IP address
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of your external interface and if it is one of the above ranges, you
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should remove the 'norfc1918' option from the external interface's
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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 another
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subnet. For our purposes, we can consider a subnet to consists of a
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range of addresses x.y.z.0 - x.y.z.255. Such a subnet will have a <i>Subnet
|
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Mask </i>of 255.255.255.0. The address x.y.z.0 is reserved as the <i>Subnet
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Address</i> and x.y.z.255 is reserved as the <i>Subnet Broadcast</i>
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<i>Address</i>. In Shorewall, a subnet is described using<6E><a
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href="shorewall_setup_guide.htm#Subnets"><i>Classless InterDomain Routing
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</i>(CIDR)</a> notation with consists of the subnet address followed
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by "/24". The "24" refers to the number of consecutive "1" bits from
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the left of the subnet mask. </p>
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</div>
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||
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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<EFBFBD>Notation:</b></td>
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<td>10.10.10.0/24</td>
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</tr>
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||
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||
</tbody>
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||
</table>
|
||
</blockquote>
|
||
</div>
|
||
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<div align="left">
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<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>
|
||
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||
<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><EFBFBD> gateway</i><EFBFBD> (router).</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> Your local computers (Local Computers 1 & 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 & 2) should be configured with their default gateway
|
||
set to the IP address of the firewall's DMZ interface.<2E><> </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 & 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.</p>
|
||
|
||
<h2 align="left">IP Masquerading (SNAT)</h2>
|
||
|
||
<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.<2E> 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">
|
||
<20><><EFBFBD> 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">
|
||
<20><><EFBFBD> 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="">
|
||
<20><><EFBFBD> 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</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><EFBFBD></td>
|
||
<td><EFBFBD></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><EFBFBD></td>
|
||
<td><EFBFBD></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>
|
||
<20></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">
|
||
<20><><EFBFBD> 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">
|
||
<20><><EFBFBD> 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><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>fw</td>
|
||
<td>udp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz</td>
|
||
<td>fw</td>
|
||
<td>tcp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz</td>
|
||
<td>fw</td>
|
||
<td>udp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></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><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:10.10.11.1</td>
|
||
<td>udp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:10.10.10.1</td>
|
||
<td>tcp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:10.10.10.1</td>
|
||
<td>udp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></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><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>net</td>
|
||
<td>tcp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></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><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz</td>
|
||
<td>tcp</td>
|
||
<td>22</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></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><EFBFBD></td>
|
||
<td><EFBFBD></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>tcp</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><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> 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">
|
||
<20><><EFBFBD> The <a href="Install.htm">installation procedure </a> configures
|
||
your system to start Shorewall at system boot<6F> 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">
|
||
<20><><EFBFBD> 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>.</p>
|
||
</div>
|
||
|
||
<p align="left"><font size="2">Last updated 12/20/2002 - <a
|
||
href="support.htm">Tom Eastep</a></font></p>
|
||
|
||
<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002 Thomas
|
||
M. Eastep</font></a></p>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
</body>
|
||
</html>
|