forked from extern/shorewall_code
Content moved to standalone.xml
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<!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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<h1 style="text-align: center;">Standalone Firewall<br>
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</h1>
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<p align="left">Setting up Shorewall on a standalone Linux system is
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very 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
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of Shorewall. It rather focuses on what is required to configure
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Shorewall 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,
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dial-up...</li>
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</ul>
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<p>Shorewall requires that you have the iproute/iproute2 package
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installed (on RedHat, the package is called <i>iproute</i>)<i>. </i>You
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can tell if this package is installed by the presence of an <b>ip</b>
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program
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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 read through the guide first to familiarize
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yourself with what's involved then go back through it again making your
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configuration changes. Points at which configuration changes are
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recommended are
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flagged with <img border="0" src="images/BD21298_.gif" width="13"
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height="13"> .</p>
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<p><img border="0" src="images/j0213519.gif" width="60" height="60">
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If you edit your configuration files on a Windows
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system,
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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.
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Similarly,
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if you copy a configuration file from your Windows hard drive to a
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floppy disk, you must run dos2unix against the copy before using it
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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">PPTP/ADSL</h2>
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<img style="border: 0px solid ; width: 13px; height: 13px;"
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src="images/BD21298_3.gif" title="" alt=""> If you
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have an ADSL Modem and you use PPTP to communicate with a server in
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that modem, you must make the <a href="PPTP.htm#PPTP_ADSL">changes
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recommended here</a> in addition to those described in the steps below.
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ADSL with PPTP is most commonly found in Europe, notably in Austria.<br>
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<h2 align="left">Shorewall Concepts</h2>
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<p> <img border="0" src="images/BD21298_.gif" width="13" height="13"
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alt=""> The configuration files for Shorewall are
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contained in the directory /etc/shorewall -- for simple setups, you
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only need to deal with a few of these as described in this guide. After
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you have <a href="Install.htm">installed Shorewall</a>, <b>download
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the <a href="http://www1.shorewall.net/pub/shorewall/Samples/">one-interface
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sample</a>, un-tar it (tar -zxvf one-interface.tgz) and and copy the
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files to /etc/shorewall (they will replace files with the same names
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that were placed in /etc/shorewall during Shorewall installation)</b>.</p>
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<p>As each file is introduced, I suggest that you look through the
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actual file on your system -- each file contains detailed configuration
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instructions and default entries.</p>
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<p>Shorewall views the network where it is running as being composed of
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a set of <i>zones.</i> In the one-interface sample configuration, only
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one 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">
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/etc/shorewall/zones</a>.</p>
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<p>Shorewall also recognizes the firewall system as its own zone - by
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default, the firewall itself is known as <b>fw</b>.</p>
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<p>Rules about what traffic to allow and what traffic to deny are
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expressed in terms of zones.</p>
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<ul>
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<li>You express your default policy for connections from one zone to
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another zone in the<a href="Documentation.htm#Policy">
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/etc/shorewall/policy </a>file.</li>
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<li>You define exceptions to those default policies in the <a
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href="Documentation.htm#Rules">/etc/shorewall/rules </a>file.</li>
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</ul>
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<p>For each connection request entering the firewall, the request is
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first checked against the /etc/shorewall/rules file. If no rule in that
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file matches the connection request then the first policy in
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/etc/shorewall/policy that matches the request is applied. If that
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policy is REJECT or DROP the request is first checked against the
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rules in /etc/shorewall/common if that file exists; otherwise the rules
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in /etc/shorewall/common.def are checked.<br>
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</p>
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<p>The /etc/shorewall/policy file included with the one-interface
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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>fw</td>
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<td>net</td>
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<td>ACCEPT</td>
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<td> </td>
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<td> </td>
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</tr>
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<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> </td>
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</tr>
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<tr>
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<td>all</td>
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<td>all</td>
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<td>REJECT</td>
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<td>info</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<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
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to your 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
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that 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
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Internet connectivity is through a cable or DSL "Modem", the <i>External
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Interface</i> will be the ethernet adapter (<b>eth0</b>) that is
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connected to that "Modem" <u>unless</u> you connect via <i><u>P</u>oint-to-<u>P</u>oint
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<u>P</u>rotocol over <u>E</u>thernet</i> (PPPoE) or <i><u>P</u>oint-to-<u>P</u>oint
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<u>T</u>unneling <u>P</u>rotocol </i>(PPTP) in which case the
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External Interface will be a <b>ppp0</b>. If you connect via a regular
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modem, your External Interface will also be <b>ppp0</b>. If you
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connect using ISDN, your external interface 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"> The Shorewall one-interface sample
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configuration assumes that the external interface is <b>eth0</b>. If
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your configuration is different, you will have to modify the sample
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/etc/shorewall/interfaces file accordingly. While you are there, you
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may wish to review the list of options that are specified for the
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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
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option list.<br>
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</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
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ranges 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,
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ISPs are assigning these addresses then using <i>Network Address
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Translation </i>to rewrite packet headers when forwarding to/from the
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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"> Before starting
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Shorewall, you should look at the IP address of your external interface
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and if it is one of the above ranges, you should remove the 'norfc1918'
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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
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your 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> </td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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</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
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Server
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on 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> </td>
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<td> </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> </td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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||||||
</blockquote>
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||||||
</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
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application uses, see <a href="ports.htm">here</a>.</p>
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||||||
</div>
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<div align="left">
|
|
||||||
<p align="left"><b>Important: </b>I don't recommend enabling telnet
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||||||
to/from the internet because it uses clear text (even for login!). If
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|
||||||
you
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|
||||||
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;"
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id="AutoNumber4">
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|
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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> </td>
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<td> </td>
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</tr>
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</tbody>
|
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</table>
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||||||
</blockquote>
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|
||||||
</div>
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|
||||||
<div align="left">
|
|
||||||
<p align="left"><img border="0" src="images/BD21298_3.gif" width="13"
|
|
||||||
height="13"> At this point, edit
|
|
||||||
/etc/shorewall/rules to add other connections as desired.</p>
|
|
||||||
</div>
|
|
||||||
<div align="left">
|
|
||||||
<h2 align="left">Starting and Stopping Your Firewall</h2>
|
|
||||||
</div>
|
|
||||||
<div align="left">
|
|
||||||
<p align="left"> <img border="0" src="images/BD21298_2.gif" width="13"
|
|
||||||
height="13" alt="Arrow"> The <a href="Install.htm">installation
|
|
||||||
procedure </a> configures your system to start Shorewall at system
|
|
||||||
boot but beginning with Shorewall version 1.3.9 startup is disabled so
|
|
||||||
that your system won't try to start Shorewall before configuration is
|
|
||||||
complete. Once you have completed configuration of your firewall, you
|
|
||||||
can enable Shorewall startup by removing the file
|
|
||||||
/etc/shorewall/startup_disabled.<br>
|
|
||||||
</p>
|
|
||||||
<p align="left"><font color="#ff0000"><b>IMPORTANT</b>: 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"><b>WARNING: </b>If you are connected to your firewall
|
|
||||||
from the internet, do not issue a "shorewall stop" command unless you
|
|
||||||
have added an entry for the IP address that you are connected from
|
|
||||||
to <a href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>.
|
|
||||||
Also, I don't recommend using "shorewall restart"; it is better to
|
|
||||||
create an <i><a href="configuration_file_basics.htm#Configs">alternate
|
|
||||||
configuration</a></i> and test it using the <a
|
|
||||||
href="starting_and_stopping_shorewall.htm">"shorewall try" command</a>.<br>
|
|
||||||
</p>
|
|
||||||
<h2>Additional Recommended Reading</h2>
|
|
||||||
I highly recommend that you review the <a
|
|
||||||
href="configuration_file_basics.htm">Common Configuration File
|
|
||||||
Features page</a> -- it contains helpful tips about Shorewall features
|
|
||||||
than make administering your firewall easier.<br>
|
|
||||||
</div>
|
|
||||||
<p align="left"><font size="2">Last updated 11/15/2003 - <a
|
|
||||||
href="support.htm">Tom Eastep</a></font></p>
|
|
||||||
<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002,
|
|
||||||
2003 Thomas M. Eastep</font></a></p>
|
|
||||||
</body>
|
|
||||||
</html>
|
|
||||||
Loading…
Reference in New Issue
Block a user