forked from extern/shorewall_code
16906234c8
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@535 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
1030 lines
42 KiB
HTML
1030 lines
42 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
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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 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
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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,
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Frame Relay, 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><b>If you are running Shorewall under Mandrake 9.0 or later, you can easily
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configure the above setup using the Mandrake "Internet Connection Sharing"
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applet. From the Mandrake Control Center, select "Network & Internet"
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then "Connection Sharing".<br>
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</b></p>
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<p><b>Note however, that the Shorewall configuration produced by Mandrake
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Internet Connection Sharing is strange and is apt to confuse you if you use
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the rest of this documentation (it has two local zones; "loc" and "masq"
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where "loc" is empty; this conflicts with this documentation which assumes
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a single local zone "loc"). We therefore recommend that once you have set
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up this sharing that you uninstall the Mandrake Shorewall RPM and install
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the one from the <a href="download.htm">download page</a> then follow the
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instructions in this Guide.</b><br>
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</p>
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<p>Shorewall requires 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
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tell if this package is installed by the presence of an <b>ip</b> program
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on your firewall system. As root, you can use the 'which' command
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to check for this program:</p>
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<pre> [root@gateway root]# which ip<br> /sbin/ip<br> [root@gateway root]#</pre>
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<p>I recommend that you first read through the guide to familiarize yourself
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with what's involved then go back through it again making your configuration
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changes. Points at which configuration changes are recommended are
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flagged with <img border="0" src="images/BD21298_.gif" width="13"
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height="13">
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. Configuration notes that are unique to LEAF/Bering are
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marked with<74><img src="images/leaflogo.gif" alt="(LEAF Logo)" width="49"
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height="36">
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</p>
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<p><img border="0" src="images/j0213519.gif" width="60" height="60">
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<20><><EFBFBD> If you edit your configuration files on a Windows system,
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you must save them as Unix files if your editor supports that option
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or you must run them through dos2unix before trying to use them. Similarly,
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if you copy a configuration file from your Windows hard drive to a
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floppy disk, you must run dos2unix against the copy before using it with
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Shorewall.</p>
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<ul>
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<li><a
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href="http://www.simtel.net/pub/pd/51438.html">Windows Version of
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dos2unix</a></li>
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<li><a
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href="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux Version of
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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
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directory /etc/shorewall -- for simple setups, you will only need to
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deal with a few of these as described in this guide. After you have <a
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href="Install.htm">installed Shorewall</a>, <b>download the <a
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href="http://www.shorewall.net/pub/shorewall/LATEST.samples/two-interfaces.tgz">two-interface
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sample</a>, un-tar it (tar -zxvf two-interfaces.tgz) and and copy
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the files to /etc/shorewall (these files will replace files with
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the same name).</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
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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 a
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set of <i>zones.</i> In the two-interface sample configuration, the
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following zone names are used:</p>
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<table border="0" style="border-collapse: collapse;" cellpadding="3"
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cellspacing="0" id="AutoNumber2">
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<tbody>
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<tr>
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<td><u><b>Name</b></u></td>
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<td><u><b>Description</b></u></td>
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</tr>
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<tr>
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<td><b>net</b></td>
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<td><b>The Internet</b></td>
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</tr>
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<tr>
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<td><b>loc</b></td>
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<td><b>Your Local Network</b></td>
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</tr>
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</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
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one zone to another zone in the<a
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href="Documentation.htm#Policy"> /etc/shorewall/policy </a>file.</li>
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<li>You define exceptions to those default policies in
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the <a href="Documentation.htm#Rules">/etc/shorewall/rules </a>file.</li>
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</ul>
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<p>For each connection request entering the firewall, the request is first
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checked against the /etc/shorewall/rules file. If no rule in that
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file 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
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DROP<4F> the request is first checked against the rules in /etc/shorewall/common
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(the samples provide that file for you).</p>
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<p>The /etc/shorewall/policy file included with the 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
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on the internet, uncomment that line.</p>
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<table border="1" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber3">
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<tbody>
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<tr>
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<td><u><b>Source Zone</b></u></td>
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<td><u><b>Destination Zone</b></u></td>
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<td><u><b>Policy</b></u></td>
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<td><u><b>Log Level</b></u></td>
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<td><u><b>Limit:Burst</b></u></td>
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</tr>
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<tr>
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<td>fw</td>
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<td>net</td>
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<td>ACCEPT</td>
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<td><EFBFBD></td>
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<td><EFBFBD></td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<p>The above policy will:</p>
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<ol>
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<li>allow all connection requests from your local network
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to the internet</li>
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<li>drop (ignore) all connection requests from the internet
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to your firewall or local network</li>
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<li>optionally accept all connection requests from the
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firewall to the internet (if you uncomment the additional policy)</li>
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<li>reject all other connection requests.</li>
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</ol>
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<p><img border="0" src="images/BD21298_.gif" width="13" height="13">
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<20><><EFBFBD> At this point, edit your /etc/shorewall/policy and make
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any changes that you wish.</p>
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<h2 align="left">Network Interfaces</h2>
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||
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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
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||
<u>T</u>unneling <u>P</u>rotocol </i>(PPTP) in which case the External
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Interface will be a ppp interface (e.g., <b>ppp0</b>). If you connect
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via a regular modem, your External Interface will also be <b>ppp0</b>.
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||
If you connect via ISDN, 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>
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then you will want to set CLAMPMSS=yes in <a
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href="Documentation.htm#Conf"> /etc/shorewall/shorewall.conf.</a></p>
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<p align="left">Your <i>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
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computers will be connected to the same hub/switch (note: If you have
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||
only a single internal system, you can connect the firewall directly
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||
to the computer using a <i>cross-over </i> cable).</p>
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||
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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
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||
to the same hub or switch (even for testing). It won't work the way
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||
that you think that it will and you will end up confused and believing
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||
that Shorewall doesn't work at all.</p>
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||
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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
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that the external interface is <b>eth0</b> and the internal interface
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is <b>eth1</b>. If your configuration is different, you will have to
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modify the sample <a href="Documentation.htm#Interfaces">/etc/shorewall/interfaces</a>
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file accordingly. While you are there, you may wish to review the
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list of options 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 "-".
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</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
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the option list. </p>
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</li>
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</ul>
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<h2 align="left">IP Addresses</h2>
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<p align="left">Before going further, we should say a few words about Internet
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Protocol (IP) <i>addresses</i>. Normally, your ISP will assign you
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a single <i> Public</i> IP address. This address may be assigned via
|
||
the<i> Dynamic Host Configuration Protocol</i> (DHCP) or as part of
|
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establishing your connection when you dial in (standard modem) or establish
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||
your PPP connection. In rare cases, your ISP may assign you a<i> static</i>
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||
IP address; that means that you configure your firewall's external interface
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||
to use that address permanently.<i> </i>However your external address
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||
is assigned, it will be shared by all of your systems when you access the
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Internet. You will have to assign your own addresses in your internal
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network (the Internal Interface on your firewall plus your other computers).
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RFC 1918 reserves 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
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IP address of your external interface and if it is one of the above
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ranges, you should remove the 'norfc1918' option from the external
|
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interface's entry in /etc/shorewall/interfaces.</p>
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||
</div>
|
||
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<div align="left">
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<p align="left">You will want to assign your 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 will have a <i>Subnet Mask </i>of 255.255.255.0. The address
|
||
x.y.z.0 is reserved as the <i>Subnet Address</i> and x.y.z.255 is
|
||
reserved as the <i>Subnet Broadcast</i> <i>Address</i>. In Shorewall,
|
||
a subnet is described using<6E><a
|
||
href="shorewall_setup_guide.htm#Subnets"><i>Classless InterDomain Routing
|
||
</i>(CIDR) notation</a> with consists of the subnet address followed
|
||
by "/24". The "24" refers to the number of consecutive leading "1"
|
||
bits from the left of the subnet mask. </p>
|
||
</div>
|
||
|
||
<div align="left">
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<p align="left">Example sub-network:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" style="border-collapse: collapse;" id="AutoNumber1"
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||
cellpadding="2">
|
||
<tbody>
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||
<tr>
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||
<td><b>Range:</b></td>
|
||
<td>10.10.10.0 - 10.10.10.255</td>
|
||
</tr>
|
||
<tr>
|
||
<td><b>Subnet Address:</b></td>
|
||
<td>10.10.10.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td><b>Broadcast Address:</b></td>
|
||
<td>10.10.10.255</td>
|
||
</tr>
|
||
<tr>
|
||
<td><b>CIDR<EFBFBD>Notation:</b></td>
|
||
<td>10.10.10.0/24</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">It is conventional to assign the internal interface either
|
||
the first usable address in the subnet (10.10.10.1 in the above
|
||
example) or the last usable address (10.10.10.254).</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">One of the purposes of subnetting is to allow all computers
|
||
in the subnet to understand which other computers can be communicated
|
||
with directly. To communicate with systems outside of the subnetwork,
|
||
systems send packets through a<i><EFBFBD> gateway</i><EFBFBD> (router).</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> Your local computers (computer 1 and computer 2 in
|
||
the above diagram) should be configured with their<i> default gateway</i>
|
||
to be the IP address of the firewall's internal interface.<i><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
</i> </p>
|
||
</div>
|
||
|
||
<p align="left">The foregoing short discussion barely scratches the surface
|
||
regarding subnetting and routing. If you are interested in learning
|
||
more about IP addressing and routing, I highly recommend <i>"IP Fundamentals:
|
||
What Everyone Needs to Know about Addressing & Routing",</i>
|
||
Thomas A. Maufer, Prentice-Hall, 1999, ISBN 0-13-975483-0.</p>
|
||
|
||
<p align="left">The remainder of this quide will assume that you have configured
|
||
your network as shown here:</p>
|
||
|
||
<p align="center"> <img border="0" src="images/basics1.png" width="444"
|
||
height="635">
|
||
</p>
|
||
|
||
<p align="left">The default gateway for computer's 1 & 2 would be 10.10.10.254.<br>
|
||
</p>
|
||
|
||
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
|
||
height="13" alt="">
|
||
<20><><EFBFBD> <font color="#ff0000"><b>WARNING: </b></font><b>Your ISP might assign
|
||
your external interface an RFC 1918 address. If that address is in the 10.10.10.0/24
|
||
subnet then you will need to select a DIFFERENT RFC 1918 subnet for your
|
||
local network.</b><br>
|
||
</p>
|
||
|
||
<h2 align="left">IP Masquerading (SNAT)</h2>
|
||
|
||
<p align="left">The addresses reserved by RFC 1918 are sometimes referred
|
||
to as <i>non-routable</i> because the Internet backbone routers don't
|
||
forward packets which have an RFC-1918 destination address. When one
|
||
of your local systems (let's assume computer 1) sends a connection
|
||
request to an internet host, the firewall must perform <i>Network Address
|
||
Translation </i>(NAT). The firewall rewrites the source address in
|
||
the packet to be the address of the firewall's external interface; in
|
||
other words, the firewall makes it look as if the firewall itself is
|
||
initiating the connection.<2E> This is necessary so that the destination
|
||
host will be able to route return packets back to the firewall (remember
|
||
that packets whose destination address is reserved by RFC 1918 can't
|
||
be routed across the internet so the remote host can't address its response
|
||
to computer 1). When the firewall receives a return packet, it rewrites
|
||
the destination address back to 10.10.10.1 and forwards the packet on
|
||
to computer 1. </p>
|
||
|
||
<p align="left">On Linux systems, the above process is often referred to as<i>
|
||
IP Masquerading</i> but you will also see the term <i>Source Network Address
|
||
Translation </i>(SNAT) used. Shorewall follows the convention used with
|
||
Netfilter:</p>
|
||
|
||
<ul>
|
||
<li>
|
||
<p align="left"><i>Masquerade</i> describes the case where you let your
|
||
firewall system automatically detect the external interface address.
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p align="left"><i>SNAT</i> refers to the case when you explicitly specify
|
||
the source address that you want outbound packets from your local
|
||
network to use. </p>
|
||
</li>
|
||
|
||
</ul>
|
||
|
||
<p align="left">In Shorewall, both Masquerading and SNAT are configured with
|
||
entries in the /etc/shorewall/masq file. You will normally use Masquerading
|
||
if your external IP is dynamic and SNAT if the IP is static.</p>
|
||
|
||
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> If your external firewall interface is <b>eth0</b>,
|
||
you do not need to modify the file provided with the sample. Otherwise,
|
||
edit /etc/shorewall/masq 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.<br>
|
||
<br>
|
||
<img border="0" src="images/BD21298_.gif" width="13"
|
||
height="13" alt="">
|
||
<20><><EFBFBD> If you are using the Debian package, please check your shorewall.conf
|
||
file to ensure that the following are set correctly; if they are not,
|
||
change them appropriately:<br>
|
||
</p>
|
||
|
||
<ul>
|
||
<li>NAT_ENABLED=Yes</li>
|
||
<li>IP_FORWARDING=On<br>
|
||
</li>
|
||
|
||
</ul>
|
||
|
||
<h2 align="left">Port Forwarding (DNAT)</h2>
|
||
|
||
<p align="left">One of your goals 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 src="images/leaflogo.gif" alt="(LEAF Logo)"
|
||
width="49" height="36">
|
||
<20><><EFBFBD> Bering users will want to add the following two rules to be compatible
|
||
with Jacques's Shorewall configuration.</p>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber4">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>ACTION</b></u></td>
|
||
<td><u><b>SOURCE</b></u></td>
|
||
<td><u><b>DESTINATION</b></u></td>
|
||
<td><u><b>PROTOCOL</b></u></td>
|
||
<td><u><b>PORT</b></u></td>
|
||
<td><u><b>SOURCE PORT</b></u></td>
|
||
<td><u><b>ORIGINAL ADDRESS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc<br>
|
||
</td>
|
||
<td>fw</td>
|
||
<td>udp<br>
|
||
</td>
|
||
<td>53<br>
|
||
</td>
|
||
<td>#Allow DNS Cache to</td>
|
||
<td>work<br>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>fw</td>
|
||
<td>tcp</td>
|
||
<td>80</td>
|
||
<td>#Allow weblet to work</td>
|
||
<td><br>
|
||
</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<p align="left"><br>
|
||
<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 2/21/2003 - <a
|
||
href="support.htm">Tom Eastep</a></font></p>
|
||
|
||
<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002, 2003
|
||
Thomas M. Eastep</font></a><br>
|
||
</p>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
</body>
|
||
</html>
|