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git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@339 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
924 lines
36 KiB
HTML
924 lines
36 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>Two-Interface Firewall</title>
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<meta name="Microsoft Theme" content="none">
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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;" width="100%" id="AutoNumber5"
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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">Basic Two-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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<p align="left">Setting up a Linux system as a firewall for a small network
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is a fairly straight-forward task if you understand the basics and follow
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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 its most common configuration:</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>Single public IP address.</li>
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<li>Internet connection through cable modem, DSL, 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/basics.png" width="444"
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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 on
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your firewall system. As root, you can use the 'which' command to check
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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 flagged
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with <img border="0" src="images/BD21298_.gif" width="13" 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, you must
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save them as Unix files if your editor supports that option or you must
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run them through dos2unix before trying to use them. Similarly, if you
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copy a configuration file from your Windows hard drive to a floppy disk,
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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 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 of dos2unix</a></li>
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</ul>
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<h2 align="left">Shorewall Concepts</h2>
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<p>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 few
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of these as described in this guide. After you have <a
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href="Install.htm">installed Shorewall</a>, download the <a
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href="/pub/shorewall/LATEST.samples/two-interfaces.tgz">two-interface sample</a>,
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un-tar it (tar -zxvf two-interfaces.tgz) and and copy the files to /etc/shorewall
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(these files will replace files with the same name).</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 two-interface sample configuration, the following
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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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</tbody>
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</table>
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<p>Zones are defined in the <a href="Documentation.htm#Zones"> /etc/shorewall/zones</a>
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file.</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 zone
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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 <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 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 (the
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samples provide that file for you).</p>
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<p>The /etc/shorewall/policy file included with the two-interface sample has
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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 two-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 on
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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 the
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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_.gif" width="13" height="13">
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<20><><EFBFBD> At this point, edit your /etc/shorewall/policy and make any changes
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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/basics.png" width="444"
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height="635">
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</p>
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<p align="left">The firewall has two 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., <b>eth0</b>)<29>
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<u>unless</u> you connect via <i><u>P</u>oint-to-<u>P</u>oint <u>P</u>rotocol
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over <u>E</u>thernet</i> (PPPoE) or <i><u>P</u>oint-to-<u>P</u>oint <u>T</u>unneling
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<u>P</u>rotocol </i>(PPTP) in which case the External Interface will be
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a ppp interface (e.g., <b>ppp0</b>). If you connect via a regular modem,
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your External Interface will also be <b>ppp0</b>. If you connect via ISDN,
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your 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><EFBFBD> then
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you will want to set CLAMPMSS=yes in <a href="Documentation.htm#Conf">
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/etc/shorewall/shorewall.conf.</a></p>
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<p align="left">Your <i>Internal Interface</i> will be an ethernet adapter
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(eth1 or eth0) and will be connected to a hub or switch. Your other computers
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will be connected to the same hub/switch (note: If you have only a single
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internal system, you can connect the firewall directly to the computer
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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 the internal and external interface to the same
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hub or switch (even for testing). It won't work the way that you think
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that it will and you will end up confused and believing that Shorewall
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doesn't work at all.</p>
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<p align="left"><img border="0" src="images/BD21298_.gif" align="left"
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width="13" height="13">
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<20><><EFBFBD> The Shorewall two-interface sample configuration assumes that the
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external interface is <b>eth0</b> and the internal interface is <b>eth1</b>.
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If your configuration is different, you will have to modify the sample
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<a href="Documentation.htm#Interfaces">/etc/shorewall/interfaces</a> file
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accordingly. While you are there, you may wish to review the list of options
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that 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 option
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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 a single
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<i> Public</i> IP address. This address may be assigned via the<i> Dynamic
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Host Configuration Protocol</i> (DHCP) or as part of establishing your
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connection when you dial in (standard modem) or establish your PPP connection.
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In rare cases, your ISP may assign you a<i> static</i> IP address; that
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means that you configure your firewall's external interface to use that
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address permanently.<i> </i>However your external address is assigned, it
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will be shared by all of your systems when you access the Internet. You will
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have to assign your own addresses in your internal network (the Internal
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Interface on your firewall plus your other computers). RFC 1918 reserves
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several <i>Private </i>IP 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">
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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 entry
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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 addresses from the same <i>
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sub-network </i>(<i>subnet)</i>.<2E> For our purposes, we can consider a subnet
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to 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 as
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the <i>Subnet Broadcast</i> <i>Address</i>. In Shorewall, a subnet is described
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using<6E><a href="subnet_masks.htm"><i>Classless InterDomain Routing </i>(CIDR)
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notation</a> with consists of the subnet address followed by "/24". The
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"24" refers to the number of consecutive leading "1" bits from the left
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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<EFBFBD>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 either
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the first usable address in the subnet (10.10.10.1 in the above example)
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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 computers
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in the subnet to understand which other computers can be communicated
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with directly. To communicate with systems outside of the subnetwork,
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systems send packets through a<i><EFBFBD> gateway</i><EFBFBD> (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">
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<20><><EFBFBD> Your local computers (computer 1 and computer 2 in the above
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diagram) should be configured with their<i> default gateway</i> to be
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the IP address of the firewall's internal interface.<i><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> </i> </p>
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</div>
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<p align="left">The foregoing short discussion barely scratches the surface
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regarding subnetting and routing. If you are interested in learning more
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about IP addressing and routing, I highly recommend <i>"IP Fundamentals:
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What Everyone Needs to Know about Addressing & Routing",</i> Thomas
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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 configured
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your network as shown here:</p>
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<p align="center"> <img border="0" src="images/basics1.png" width="444"
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height="635">
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</p>
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<p align="left">The default gateway for computer's 1 & 2 would be 10.10.10.254.</p>
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<h2 align="left">IP Masquerading (SNAT)</h2>
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<p align="left">The addresses reserved by RFC 1918 are sometimes referred
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to as <i>non-routable</i> because the Internet backbone routers don't forward
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packets which have an RFC-1918 destination address. When one of your local
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systems (let's assume computer 1) sends a connection request to an internet
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host, the firewall must perform <i>Network Address Translation </i>(NAT).
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The firewall rewrites the source address in the packet to be the address
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of the firewall's external interface; in other words, the firewall makes
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it look as if the firewall itself is initiating the connection.<2E> This is
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necessary so that the destination host will be able to route return packets
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back to the firewall (remember that packets whose destination address
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is reserved by RFC 1918 can't be routed across the internet so the remote
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host can't address its response to computer 1). 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 computer 1. </p>
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<p align="left">On Linux systems, the above process is often referred to as<i>
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IP Masquerading</i> but you will also see the term <i>Source Network Address
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Translation </i>(SNAT) used. Shorewall follows the convention used with
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Netfilter:</p>
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<ul>
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<li>
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<p align="left"><i>Masquerade</i> describes the case where you let your
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firewall system automatically detect the external interface address.
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</p>
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</li>
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<li>
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<p align="left"><i>SNAT</i> refers to the case when you explicitly specify
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the source address that you want outbound packets from your local network
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to use. </p>
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</li>
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</ul>
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<p align="left">In Shorewall, both Masquerading and SNAT are configured with
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entries in the /etc/shorewall/masq file. You will normally use Masquerading
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if your external IP is dynamic and SNAT if the IP is static.</p>
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|
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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> If your external firewall interface is <b>eth0</b>, you do not
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need to modify the file provided with the sample. Otherwise, edit /etc/shorewall/masq
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and change the first column to the name of your external interface and
|
||
the second column to the name of your internal interface.</p>
|
||
|
||
<p align="left"><img border="0" src="images/BD21298_.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 processing outgoing packets a little more efficient. </p>
|
||
|
||
<h2 align="left">Port Forwarding (DNAT)</h2>
|
||
|
||
<p align="left">One of your goals may be to run one or more servers on your
|
||
local 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 the 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>loc:<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>Example - you run a Web Server on computer 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>loc:10.10.10.2</td>
|
||
<td>tcp</td>
|
||
<td>80</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p>A couple of important points to keep in mind:</p>
|
||
|
||
<ul>
|
||
<li>You must test the above rule from a client outside of your local
|
||
network (i.e., don't test from a browser running on computers 1 or 2
|
||
or on the firewall). If you want to be able to access your web server
|
||
using the IP address of your external interface, see <a
|
||
href="FAQ.htm#faq2">Shorewall FAQ #2</a>.</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.</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>loc:10.10.10.2:80</td>
|
||
<td>tcp</td>
|
||
<td>5000</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p> <img border="0" src="images/BD21298_.gif" width="13" height="13">
|
||
<20><><EFBFBD> At this point, modify /etc/shorewall/rules to add any DNAT rules
|
||
that you require.</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. Regardless of how DNS gets configured
|
||
on your firewall, 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_.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> You can configure a<i> Caching Name Server </i>on your firewall.<i>
|
||
</i>Red Hat has an RPM for a caching name server (the RPM 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 firewall
|
||
itself 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. 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 firewall; you do that by adding the following rules in /etc/shorewall/rules.
|
||
</p>
|
||
</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>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>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<div align="left">
|
||
<h2 align="left">Other Connections</h2>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The two-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>tcp</td>
|
||
<td>53</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></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>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Those rules allow DNS access from your firewall and may be
|
||
removed if you uncommented 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>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">That rule allows you to run an SSH server on your firewall
|
||
and connect to that server from your local systems.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">If you wish to enable other connections between your firewall
|
||
and other 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 Web 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>80</td>
|
||
<td>#Allow web access</td>
|
||
<td>from the internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>fw</td>
|
||
<td>tcp</td>
|
||
<td>80</td>
|
||
<td>#Allow web access</td>
|
||
<td>from the local network</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 "You can configure a Caching 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_.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> Now edit your /etc/shorewall/rules file to add or delete 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_.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> The two-interface sample assumes that you want to enable routing
|
||
to/from <b>eth1 </b>(the local network) when Shorewall is stopped. If
|
||
your local network isn't connected to <b>eth1</b> or if you wish to enable
|
||
access to/from other hosts, change /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 11/21/2002 - <a
|
||
href="support.htm">Tom Eastep</a></font></p>
|
||
|
||
<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002 Thomas
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M. Eastep</font></a></p>
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