forked from extern/shorewall_code
313 lines
13 KiB
HTML
313 lines
13 KiB
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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" content="text/html; charset=windows-1252">
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<title>Standalone Firewall</title>
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<meta name="Microsoft Theme" content="boldstri 011, default">
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</head>
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<body>
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<h1 align="center">Standalone Firewall</h1>
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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 easy if you understand the basics and follow the
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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 in one
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of its
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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 (on
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RedHat, the package is called <i>iproute</i>)<i>. </i>You can tell if this
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package is installed by the presence of an <b>ip</b> program on your firewall
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system. As root, you can use the 'which' command to check for this program:</p>
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<pre> [root@gateway root]# which ip
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/sbin/ip
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[root@gateway root]#</pre><p>I recommend that you read through the guide
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first to familiarize yourself with what's involved then go back through it again
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making your configuration changes. Points at which configuration changes
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are recommended are flagged with <img border="0" src="images/BD21298_.gif" width="13" 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 system, you must save them as
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Unix files if your editor supports that option or you must run them through
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dos2unix before trying to use them. Similarly, if you copy a configuration file
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from your Windows hard drive to a floppy disk, you must run dos2unix against the
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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 of
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dos2unix</a></li>
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<li><a href="http://www.megaloman.com/~hany/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>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 href="Install.htm">installed Shorewall</a>,
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download the <a href="/pub/shorewall/LATEST.samples/one-interface.tgz">one-interface sample</a>, un-tar it
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(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).</p>
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<p>As each file is introduced, I suggest that you
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look through the actual file on your system -- each file contains detailed
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configuration instructions and default entries.</p>
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<p>Shorewall views the network where it is running as being composed of a set of
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<i>zones.</i> In the one-interface sample configuration, only one zone is
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defined:</p>
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<table border="0" style="border-collapse: collapse" cellpadding="3" cellspacing="0" id="AutoNumber2">
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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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</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 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 in
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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 another
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zone in the<a href="Documentation.htm#Policy"> /etc/shorewall/policy </a>file.</li>
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<li>You define exceptions to those default policies in the
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<a href="Documentation.htm#Rules">/etc/shorewall/rules </a>file.</li>
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</ul>
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<p>For each connection request entering the firewall, the request is first checked against the
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/etc/shorewall/rules file. If no rule in that file matches the connection
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request then the first policy in /etc/shorewall/policy that matches the
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request is applied. If that policy is REJECT or DROP the request is first
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checked against the rules in /etc/shorewall/common (the samples provide that
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file for you).</p>
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<p>The /etc/shorewall/policy file included with the one-interface sample has the
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following policies:</p>
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<blockquote>
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<table border="1" cellpadding="2" style="border-collapse: collapse" bordercolor="#111111" id="AutoNumber3">
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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>net</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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</table>
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</blockquote>
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<pre> fw net ACCEPT
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net all DROP info
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all all REJECT info</pre>
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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 firewall</li>
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<li>reject all other connection requests (Shorewall requires this catchall
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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 you
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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"
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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 a <b>ppp0</b>. If you connect via a regular modem, your External
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Interface will also be <b>ppp0</b>. If you connect using ISDN, your external
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interface will be<b> ippp0.</b></p>
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<p align="left"><img border="0" src="images/BD21298_3.gif" width="13" height="13"> The Shorewall one-interface sample configuration assumes that
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the external interface is <b>eth0</b>.
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If 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 may wish to
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review the list of options that are 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>, you can replace the
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"detect" in the second column with "-".</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> or if you have a static IP
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address, you can remove "dhcp" from the option list.</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 for
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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
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172.16.0.0 - 172.31.255.255
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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 are
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assigning these addresses then using <i>Network Address Translation </i>to
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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" width="13" height="13">
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Before starting Shorewall, you should look at the IP address of your external
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interface and if it is one of the above ranges, you should remove the
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'norfc1918' option from the entry in /etc/shorewall/interfaces.</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 firewall, the general format is:</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" bordercolor="#111111" id="AutoNumber4">
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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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</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 your firewall
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system:</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" bordercolor="#111111" id="AutoNumber5">
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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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</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>.</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 shell
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access to your firewall from the internet, use SSH:</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" bordercolor="#111111" id="AutoNumber4">
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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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</table>
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</blockquote>
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</div>
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<div align="left">
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<pre> ACCEPT net fw tcp 22</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_3.gif" width="13" height="13"> At this point, edit
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/etc/shorewall/rules to add other connections as desired.</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">The <a href="Install.htm">installation procedure </a>
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configures your system to start Shorewall at system boot.</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 is
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enabled on those hosts that have an entry in
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<a href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>. A
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running firewall may be restarted using the "shorewall restart" command. If
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you want to totally remove any trace of Shorewall from your Netfilter
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configuration, use "shorewall clear".</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 the
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internet, do not issue a "shorewall stop" command unless you have added an
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entry for the IP address that you are connected from to
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<a 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 an
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<i><a href="Documentation.htm#Configs">alternate configuration</a></i> and
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test it using the <a href="Documentation.htm#Starting">"shorewall try" command</a>.</div>
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<p align="left"><font size="2">Last updated
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7/23/2002 - <a href="support.htm">Tom
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Eastep</a></font></p>
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<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002 Thomas M. Eastep</font></a></p>
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</body>
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