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git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@427 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
430 lines
16 KiB
HTML
430 lines
16 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>Standalone 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="AutoNumber6" 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">Standalone 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 Shorewall on a standalone Linux system is very
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easy if you understand the basics and follow the documentation.</p>
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<p>This guide doesn't attempt to acquaint you with all of the features of
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Shorewall. It rather focuses on what is required to configure Shorewall
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in one of its most common configurations:</p>
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<ul>
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<li>Linux system</li>
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<li>Single external IP address</li>
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<li>Connection through Cable Modem, DSL, ISDN, Frame Relay, dial-up...</li>
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</ul>
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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 read through the guide first 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.<2E> 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> <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 only need to deal with a few of
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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/one-interface.tgz">one-interface sample</a>,
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un-tar it (tar -zxvf one-interface.tgz) and and copy the files to /etc/shorewall
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(they will replace files with the same names that were placed in /etc/shorewall
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during Shorewall installation)</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 one-interface sample configuration, only one
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zone is defined:</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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</tbody>
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</table>
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<p>Shorewall zones 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 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 one-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>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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<tr>
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<td>net</td>
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<td>all<br>
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</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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<p>The above policy will:</p>
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<ol>
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<li>allow all connection requests from the firewall to the internet</li>
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<li>drop (ignore) all connection requests from the internet to your
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firewall</li>
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<li>reject all other connection requests (Shorewall requires this
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catchall policy).</li>
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</ol>
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<p>At this point, edit your /etc/shorewall/policy and make any changes that
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you wish.</p>
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<h2 align="left">External Interface</h2>
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<p align="left">The firewall has a single network interface. 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 (<b>eth0</b>) that is connected to that "Modem"<22>
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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 <b>ppp0</b>. If you connect via a regular modem, your External Interface
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will also be <b>ppp0</b>. If you connect using ISDN, your external interface
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will be<b> ippp0.</b></p>
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<p align="left"><img border="0" src="images/BD21298_3.gif" width="13"
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height="13">
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<20><><EFBFBD> The Shorewall one-interface sample configuration assumes that the
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external interface is <b>eth0</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 are
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specified for the interface. 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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<div align="left">
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<h2 align="left">IP Addresses</h2>
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</div>
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<div align="left">
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<p align="left">RFC 1918 reserves several <i>Private </i>IP address ranges
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for use in private networks:</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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<p align="left">These addresses are sometimes referred to as <i>non-routable</i>
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because the Internet backbone routers will not forward a packet whose
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destination address is reserved by RFC 1918. In some cases though, ISPs
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are assigning these addresses then using <i>Network Address Translation
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</i>to rewrite packet headers when forwarding to/from the internet.</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><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 should
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remove the 'norfc1918' option from the entry in /etc/shorewall/interfaces.</p>
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</div>
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<div align="left">
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<h2 align="left">Enabling other Connections</h2>
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</div>
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<div align="left">
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<p align="left">If you wish to enable connections from the internet to your
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firewall, the general format is:</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" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber4">
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<tbody>
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<tr>
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<td><u><b>ACTION</b></u></td>
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<td><u><b>SOURCE</b></u></td>
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<td><u><b>DESTINATION</b></u></td>
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<td><u><b>PROTOCOL</b></u></td>
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<td><u><b>PORT</b></u></td>
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<td><u><b>SOURCE PORT</b></u></td>
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<td><u><b>ORIGINAL ADDRESS</b></u></td>
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</tr>
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<tr>
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<td>ACCEPT</td>
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<td>net</td>
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<td>fw</td>
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<td><i><protocol></i></td>
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<td><i><port></i></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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</div>
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<div align="left">
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<p align="left">Example - You want to run a Web Server and a POP3 Server on
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your firewall system:</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" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber5">
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<tbody>
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<tr>
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<td><u><b>ACTION</b></u></td>
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<td><u><b>SOURCE</b></u></td>
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<td><u><b>DESTINATION</b></u></td>
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<td><u><b>PROTOCOL</b></u></td>
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<td><u><b>PORT</b></u></td>
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<td><u><b>SOURCE PORT</b></u></td>
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<td><u><b>ORIGINAL ADDRESS</b></u></td>
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</tr>
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<tr>
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<td>ACCEPT</td>
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<td>net</td>
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<td>fw</td>
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<td>tcp</td>
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<td>80</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>ACCEPT</td>
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<td>net</td>
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<td>fw</td>
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<td>tcp</td>
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<td>110</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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</div>
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<div align="left">
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<p align="left">If you don't know what port and protocol a particular application
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uses, see <a href="ports.htm">here</a>.</p>
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</div>
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<div align="left">
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<p align="left"><b>Important: </b>I don't recommend enabling telnet to/from
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the internet because it uses clear text (even for login!). If you want
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shell access to your firewall from the internet, use SSH:</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" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber4">
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<tbody>
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<tr>
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<td><u><b>ACTION</b></u></td>
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<td><u><b>SOURCE</b></u></td>
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<td><u><b>DESTINATION</b></u></td>
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<td><u><b>PROTOCOL</b></u></td>
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<td><u><b>PORT</b></u></td>
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<td><u><b>SOURCE PORT</b></u></td>
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<td><u><b>ORIGINAL ADDRESS</b></u></td>
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</tr>
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<tr>
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<td>ACCEPT</td>
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<td>net</td>
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<td>fw</td>
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<td>tcp</td>
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<td>22</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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</div>
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<div align="left">
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<p align="left"><img border="0" src="images/BD21298_3.gif" width="13"
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height="13">
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<20><><EFBFBD> At this point, edit /etc/shorewall/rules to add other connections
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as desired.</p>
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</div>
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<div align="left">
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<h2 align="left">Starting and Stopping Your Firewall</h2>
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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_2.gif"
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width="13" height="13" alt="Arrow">
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<20><><EFBFBD> The <a href="Install.htm">installation procedure </a> configures
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your system to start Shorewall at system boot but beginning with Shorewall
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version 1.3.9 startup is disabled so that your system won't try to start
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Shorewall before configuration is complete. Once you have completed configuration
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of your firewall, you can enable Shorewall startup by removing the file
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/etc/shorewall/startup_disabled.<br>
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</p>
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<p align="left"><font color="#ff0000"><b>IMPORTANT</b>: Users of the .deb
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package must edit /etc/default/shorewall and set 'startup=1'.</font><br>
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</p>
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</div>
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<div align="left">
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<p align="left">The firewall is started using the "shorewall start" command
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and stopped using "shorewall stop". When the firewall is stopped, routing
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is enabled on those hosts that have an entry in <a
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href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>. A
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running firewall may be restarted using the "shorewall restart" command.
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If you want to totally remove any trace of Shorewall from your Netfilter
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configuration, use "shorewall clear".</p>
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</div>
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<div align="left">
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<p align="left"><b>WARNING: </b>If you are connected to your firewall from
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the internet, do not issue a "shorewall stop" command unless you have
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added an entry for the IP address that you are connected from to <a
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href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>.
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Also, I don't recommend using "shorewall restart"; it is better to create
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an <i><a href="configuration_file_basics.htm#Configs">alternate configuration</a></i>
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and test it using the <a href="starting_and_stopping_shorewall.htm">"shorewall
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try" command</a>.</p>
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</div>
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<p align="left"><font size="2">Last updated 1/26/2003 - <a
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href="support.htm">Tom Eastep</a></font></p>
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<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002, 2003
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Thomas M. Eastep</font></a></p>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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</body>
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</html>
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