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2540 lines
113 KiB
HTML
2540 lines
113 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>Shorewall Setup Guide</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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<h1 align="center">Shorewall Setup Guide</h1>
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<p><a href="#Introduction">1.0 Introduction</a><br>
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<a href="#Concepts">2.0 Shorewall Concepts</a><br>
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<a href="#Interfaces">3.0 Network Interfaces</a><br>
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<a href="#Addressing">4.0 Addressing, Subnets and Routing</a></p>
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<blockquote>
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<p><a href="#Addresses">4.1 IP Addresses</a><br>
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<a href="#Subnets">4.2 Subnets</a><br>
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<a href="#Routing">4.3 Routing</a><br>
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<a href="#ARP">4.4 Address Resolution Protocol</a><br>
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<a href="#RFC1918">4.5 RFC 1918</a></p>
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</blockquote>
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<p><a href="#Options">5.0 Setting up your Network</a></p>
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<blockquote>
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<p><a href="#Routed">5.1 Routed</a><br>
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<a href="#NonRouted">5.2 Non-routed</a></p>
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<blockquote>
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<p><a href="#SNAT">5.2.1 SNAT</a><br>
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<a href="#DNAT">5.2.2 DNAT</a><br>
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<a href="#ProxyARP">5.2.3 Proxy ARP</a><br>
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<a href="#NAT">5.2.4 Static NAT</a></p>
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</blockquote>
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<p><a href="#Rules">5.3 Rules</a><br>
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<a href="#OddsAndEnds">5.4 Odds and Ends</a></p>
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</blockquote>
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<p><a href="#DNS">6.0 DNS</a><br>
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<a href="#StartingAndStopping">7.0 Starting and Stopping the Firewall</a></p>
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<h2><a name="Introduction"></a>1.0 Introduction</h2>
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<p>This guide is intended for users who are setting up Shorewall in an environment
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where a set of public IP addresses must be managed or who want to know
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more about Shorewall than is contained in the <a
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href="shorewall_quickstart_guide.htm">single-address guides</a>. Because
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the range of possible applications is so broad, the Guide will give you
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general guidelines and will point you to other resources as necessary.</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 run LEAF Bering, your Shorewall configuration is NOT
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what I release -- I suggest that you consider installing a stock Shorewall
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lrp from the shorewall.net site before you proceed.</p>
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<p>Shorewall requires that the iproute/iproute2 package be installed (on
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RedHat, the package is called <i>iproute</i>)<i>. </i>You can tell if
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this package is installed by the presence of an <b>ip</b> program on your
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firewall system. As root, you can use the 'which' command to check for
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this program:</p>
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<pre> [root@gateway root]# which ip<br> /sbin/ip<br> [root@gateway root]#</pre>
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<p>I recommend that you first read through the guide to familiarize yourself
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with what's involved then go back through it again making your configuration
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changes. Points at which configuration changes are recommended are flagged
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with <img border="0" src="images/BD21298_.gif" width="13"
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height="13">
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.</p>
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<p><img border="0" src="images/j0213519.gif" width="60" height="60">
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<20><><EFBFBD> If you edit your configuration files on a Windows system, you
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must save them as Unix files if your editor supports that option or you
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must run them through dos2unix before trying to use them with Shorewall.
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Similarly, if you copy a configuration file from your Windows hard drive
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to a floppy disk, you must run dos2unix against the copy before using
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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
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Version of dos2unix</a></li>
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<li><a
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href="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux Version
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of dos2unix</a></li>
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</ul>
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<h2 align="left"><a name="Concepts"></a>2.0 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 most setups, you will only need to deal with a few
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of these as described in this guide. Skeleton files are created during the
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<a href="Install.htm">Shorewall Installation Process</a>.</p>
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<p>As each file is introduced, I suggest that you look through the actual
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file on your system -- each file contains detailed configuration instructions
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and some contain 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 default installation, the following zone
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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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<tr>
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<td><b>dmz</b></td>
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<td><b>Demilitarized Zone</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> but that may be changed in
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the <a href="Documentation.htm#Configs">/etc/shorewall/shorewall.conf</a>
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file. In this guide, the default name (<b>fw</b>) will be used.</p>
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<p>With the exception of <b>fw</b>, Shorewall attaches absolutely no meaning
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to zone names. Zones are entirely what YOU make of them. That means that
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you should not expect Shorewall to do something special "because this
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is the internet zone" or "because that is the DMZ".</p>
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<p><img border="0" src="images/BD21298_.gif" width="13" height="13">
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<20><><EFBFBD> Edit the /etc/shorewall/zones file and make any changes necessary.</p>
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<p>Rules about what traffic to allow and what traffic to deny are expressed
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in terms of zones.</p>
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<ul>
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<li>You express your default policy for connections from one
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zone to another zone in the<a href="Documentation.htm#Policy"> /etc/shorewall/policy
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</a>file.</li>
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<li>You define exceptions to those default policies in the
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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> Shorewall is built on top of the <a href="http://www.netfilter.org">Netfilter</a>
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kernel facility. Netfilter implements a <a
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href="http://www.cs.princeton.edu/%7Ejns/security/iptables/iptables_conntrack.html">connection
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tracking function</a> that allows what is often referred to as <i>stateful
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inspection</i> of packets. This stateful property allows firewall rules
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to be defined in terms of <i>connections</i> rather than in terms of
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packets. With Shorewall, you:</p>
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<ol>
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<li> Identify the source zone.</li>
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<li> Identify the destination zone.</li>
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<li> If the POLICY from the client's zone to the server's
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zone is what you want for this client/server pair, you need do
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nothing further.</li>
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<li> If the POLICY is not what you want, then you must
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add a rule. That rule is expressed in terms of the client's zone
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and the server's zone.</li>
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</ol>
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<p> Just because connections of a particular type are allowed from zone A
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to the firewall and are also allowed from the firewall to zone B <font
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color="#ff6633"><b><u> DOES NOT mean that these connections are allowed
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from zone A to zone B</u></b></font>. It rather means that you can
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have a proxy running on the firewall that accepts a connection from zone
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A and then establishes its own separate connection from the firewall to
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zone B.</p>
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<p>For each connection request entering the firewall, the request is first
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checked against the /etc/shorewall/rules file. If no rule in that file
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matches the connection request then the first policy in /etc/shorewall/policy
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that matches the request is applied. If that policy is REJECT or DROP<4F>
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the request is first checked against the rules in /etc/shorewall/common.def.</p>
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<p>The default /etc/shorewall/policy file 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>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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<p>The above policy will:</p>
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<ol>
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<li>allow all connection requests from your local network to
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the internet</li>
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<li>drop (ignore) all connection requests from the internet to
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your firewall or local network and log a message at the <i>info</i>
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level (<a href="shorewall_logging.html">here</a> is a description of log
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levels).</li>
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<li>reject all other connection requests and log a message at
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the <i>info</i> level. When a request is rejected, the firewall
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will return an RST (if the protocol is TCP) or an ICMP port-unreachable
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packet for other protocols.</li>
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</ol>
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<p><img border="0" src="images/BD21298_.gif" width="13" height="13">
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<20><><EFBFBD> At this point, edit your /etc/shorewall/policy and make any
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changes that you wish.</p>
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<h2 align="left"><a name="Interfaces"></a>3.0 Network Interfaces</h2>
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<p align="left">For the remainder of this guide, we'll refer to the following
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diagram. While it may not look like your own network, it can be used
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to illustrate the important aspects of Shorewall configuration.</p>
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<p align="left">In this diagram:</p>
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<ul>
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<li>The DMZ Zone consists of systems DMZ 1 and DMZ 2. A DMZ is
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used to isolate your internet-accessible servers from your local systems
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so that if one of those servers is compromised, you still have the firewall
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between the compromised system and your local systems. </li>
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<li>The Local Zone consists of systems Local 1, Local 2 and Local
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3. </li>
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<li>All systems from the ISP outward comprise the Internet Zone.
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</li>
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</ul>
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<p align="center"> <img border="0" src="images/dmz3.png" width="692"
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height="635">
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</p>
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<p align="left">The simplest way to define zones is to simply associate the
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zone name (previously defined in /etc/shorewall/zones) with a network
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interface. This is done in the <a
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href="Documentation.htm#Interfaces">/etc/shorewall/interfaces</a> file.</p>
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<p align="left">The firewall illustrated above has three network interfaces.
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Where Internet connectivity is through a cable or DSL "Modem", the <i>External
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Interface</i> will be the Ethernet adapter that is connected to that
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"Modem" (e.g., <b>eth0</b>)<29> <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 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 using ISDN, you 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>then
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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>Local Interface</i> will be an Ethernet adapter (eth0,
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eth1 or eth2) and will be connected to a hub or switch. Your local computers
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will be connected to the same switch (note: If you have only a single
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local system, you can connect the firewall directly to the computer using
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a <i>cross-over </i> cable).</p>
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<p align="left">Your <i>DMZ Interface</i> will also be an Ethernet adapter
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(eth0, eth1 or eth2) and will be connected to a hub or switch. Your DMZ
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computers will be connected to the same switch (note: If you have only
|
||
a single DMZ system, you can connect the firewall directly to the computer
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using a <i>cross-over </i> cable).</p>
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<p align="left"><u><b> <img border="0" src="images/j0213519.gif"
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width="60" height="60">
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</b></u>Do not connect more than one interface to the same hub
|
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or switch (even for testing). It won't work the way that you expect
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it to and you will end up confused and believing that Linux networking
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doesn't work at all.</p>
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<p align="left">For the remainder of this Guide, we will assume that:</p>
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<ul>
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<li>
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<p align="left">The external interface is <b>eth0</b>.</p>
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</li>
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<li>
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<p align="left">The Local interface is <b>eth1</b>.</p>
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</li>
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<li>
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<p align="left">The DMZ interface is <b>eth2</b>.</p>
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</li>
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</ul>
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<p align="left">The Shorewall default configuration does not define the contents
|
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of any zone. To define the above configuration using the /etc/shorewall/interfaces
|
||
file, that file would might contain:</p>
|
||
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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>Zone</b></u></td>
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<td><u><b>Interface</b></u></td>
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<td><u><b>Broadcast</b></u></td>
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<td><u><b>Options</b></u></td>
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</tr>
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<tr>
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<td>net</td>
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<td>eth0</td>
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<td>detect</td>
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<td>norfc1918</td>
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||
</tr>
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<tr>
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||
<td>loc</td>
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||
<td>eth1</td>
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||
<td>detect</td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>dmz</td>
|
||
<td>eth2</td>
|
||
<td>detect</td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> Edit the /etc/shorewall/interfaces file and define the network
|
||
interfaces on your firewall and associate each interface with a zone.
|
||
If you have a zone that is interfaced through more than one interface,
|
||
simply include one entry for each interface and repeat the zone name as
|
||
many times as necessary.</p>
|
||
|
||
<p align="left">Example:</p>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber4">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>Zone</b></u></td>
|
||
<td><u><b>Interface</b></u></td>
|
||
<td><u><b>Broadcast</b></u></td>
|
||
<td><u><b>Options</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>net</td>
|
||
<td>eth0</td>
|
||
<td>detect</td>
|
||
<td>norfc1918</td>
|
||
</tr>
|
||
<tr>
|
||
<td>loc</td>
|
||
<td>eth1</td>
|
||
<td>detect</td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>loc</td>
|
||
<td>eth2</td>
|
||
<td>detect</td>
|
||
<td>dhcp</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<div align="left">
|
||
<p align="left">When you have more than one interface to a zone, you will
|
||
usually want a policy that permits intra-zone traffic:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber3">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>Source Zone</b></u></td>
|
||
<td><u><b>Destination Zone</b></u></td>
|
||
<td><u><b>Policy</b></u></td>
|
||
<td><u><b>Log Level</b></u></td>
|
||
<td><u><b>Limit:Burst</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>loc</td>
|
||
<td>loc</td>
|
||
<td>ACCEPT</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> You may define more complicated zones using the <a
|
||
href="Documentation.htm#Hosts">/etc/shorewall/hosts</a> file but in most
|
||
cases, that isn't necessary.</p>
|
||
|
||
<h2 align="left"><a name="Addressing"></a>4.0 Addressing, Subnets and Routing</h2>
|
||
|
||
<p align="left">Normally, your ISP will assign you a set of <i> Public</i>
|
||
IP addresses. You will configure your firewall's external interface to
|
||
use one of those addresses permanently and you will then have to decide
|
||
how you are going to use the rest of your addresses. Before we tackle that
|
||
question though, some background is in order.</p>
|
||
|
||
<p align="left">If you are thoroughly familiar with IP addressing and routing,
|
||
you may <a href="#Options">go to the next section</a>.</p>
|
||
|
||
<p align="left">The following discussion barely scratches the surface of addressing
|
||
and routing. If you are interested in learning more about this subject,
|
||
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>
|
||
|
||
<h3 align="left"><a name="Addresses"></a>4.1 IP Addresses</h3>
|
||
|
||
<p align="left">IP version 4 (<i>IPv4) </i>addresses are 32-bit numbers.
|
||
The notation w.x.y.z refers to an address where the high-order byte has
|
||
value "w", the next byte has value "x", etc. If we take the address 192.0.2.14
|
||
and express it in hexadecimal, we get:</p>
|
||
|
||
<blockquote>
|
||
<p align="left">C0.00.02.0E</p>
|
||
</blockquote>
|
||
|
||
<p align="left">or looking at it as a 32-bit integer</p>
|
||
|
||
<blockquote>
|
||
<p align="left">C000020E</p>
|
||
</blockquote>
|
||
|
||
<h3 align="left"><a name="Subnets"></a>4.2 Subnets</h3>
|
||
|
||
<p align="left">You will still hear the terms "Class A network", "Class B
|
||
network" and "Class C network". In the early days of IP, networks only
|
||
came in three sizes (there were also Class D networks but they were used
|
||
differently):</p>
|
||
|
||
<blockquote>
|
||
<p align="left">Class A - netmask 255.0.0.0, size = 2 ** 24</p>
|
||
|
||
<p align="left">Class B - netmask 255.255.0.0, size = 2 ** 16</p>
|
||
|
||
<p align="left">Class C - netmask 255.255.255.0, size = 256</p>
|
||
</blockquote>
|
||
|
||
<p align="left">The class of a network was uniquely determined by the value
|
||
of the high order byte of its address so you could look at an IP address
|
||
and immediately determine the associated <i>netmask</i>. The netmask
|
||
is a number that when logically ANDed with an address isolates the <i>network
|
||
number</i>; the remainder of the address is the <i>host number</i>. For
|
||
example, in the Class C address 192.0.2.14, the network number is hex
|
||
C00002 and the host number is hex 0E.</p>
|
||
|
||
<p align="left">As the internet grew, it became clear that such a gross
|
||
partitioning of the 32-bit address space was going to be very limiting (early
|
||
on, large corporations and universities were assigned their own class A
|
||
network!). After some false starts, the current technique of <i>subnetting</i>
|
||
these networks into smaller <i>subnetworks</i> evolved; that technique is
|
||
referred to as<61><i>Classless InterDomain Routing</i> (CIDR). Today, any system
|
||
that you are likely to work with will understand CIDR and Class-based networking
|
||
is largely a thing of the past.</p>
|
||
|
||
<p align="left">A <i>subnetwork</i> (often referred to as a <i>subnet) </i>is
|
||
a contiguous set of IP addresses such that:</p>
|
||
|
||
<ol>
|
||
<li>
|
||
<p align="left">The number of addresses in the set is a power of 2; and</p>
|
||
</li>
|
||
<li>
|
||
<p align="left">The first address in the set is a multiple of the set
|
||
size.</p>
|
||
</li>
|
||
<li>
|
||
<p align="left">The first address in the subnet is reserved and is referred
|
||
to as the <i> subnet address.</i></p>
|
||
</li>
|
||
<li>
|
||
<p align="left">The last address in the subnet is reserved as the <i>subnet's
|
||
broadcast address.</i></p>
|
||
</li>
|
||
|
||
</ol>
|
||
|
||
<p align="left">As you can see by this definition, in each subnet of size
|
||
<b>n</b> there are (<b>n</b> - 2) usable addresses (addresses that
|
||
can be assigned to hosts). The first and last address in the subnet
|
||
are used for the subnet address and subnet broadcast address respectively.
|
||
Consequently, small subnetworks are more wasteful of IP addresses than
|
||
are large ones. </p>
|
||
|
||
<p align="left">Since <b>n</b> is a power of two, we can easily calculate
|
||
the <i>Natural Logarithm</i> (<b>log2</b>) of <b>n</b>. For the more
|
||
common subnet sizes, the size and its natural logarithm are given in the
|
||
following table:</p>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber5">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>n</b></u></td>
|
||
<td><u><b>log2 n</b></u></td>
|
||
<td><u><b>(32 - log2 n)</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>8</td>
|
||
<td>3</td>
|
||
<td>29</td>
|
||
</tr>
|
||
<tr>
|
||
<td>16</td>
|
||
<td>4</td>
|
||
<td>28</td>
|
||
</tr>
|
||
<tr>
|
||
<td>32</td>
|
||
<td>5</td>
|
||
<td>27</td>
|
||
</tr>
|
||
<tr>
|
||
<td>64</td>
|
||
<td>6</td>
|
||
<td>26</td>
|
||
</tr>
|
||
<tr>
|
||
<td>128</td>
|
||
<td>7</td>
|
||
<td>25</td>
|
||
</tr>
|
||
<tr>
|
||
<td>256</td>
|
||
<td>8</td>
|
||
<td>24</td>
|
||
</tr>
|
||
<tr>
|
||
<td>512</td>
|
||
<td>9</td>
|
||
<td>23</td>
|
||
</tr>
|
||
<tr>
|
||
<td>1024</td>
|
||
<td>10</td>
|
||
<td>22</td>
|
||
</tr>
|
||
<tr>
|
||
<td>2048</td>
|
||
<td>11</td>
|
||
<td>21</td>
|
||
</tr>
|
||
<tr>
|
||
<td>4096</td>
|
||
<td>12</td>
|
||
<td>20</td>
|
||
</tr>
|
||
<tr>
|
||
<td>8192</td>
|
||
<td>13</td>
|
||
<td>19</td>
|
||
</tr>
|
||
<tr>
|
||
<td>16384</td>
|
||
<td>14</td>
|
||
<td>18</td>
|
||
</tr>
|
||
<tr>
|
||
<td>32768</td>
|
||
<td>15</td>
|
||
<td>17</td>
|
||
</tr>
|
||
<tr>
|
||
<td>65536</td>
|
||
<td>16</td>
|
||
<td>16</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p align="left">You will notice that the above table also contains a column
|
||
for (32 - log2 <b>n</b>). That number is the <i>Variable Length Subnet
|
||
Mask</i> for a network of size <b>n</b>. From the above table, we can
|
||
derive the following one which is a little easier to use.</p>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber5">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>Size of Subnet</b></u></td>
|
||
<td><u><b>VLSM</b></u></td>
|
||
<td><u><b>Subnet Mask</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>8</td>
|
||
<td>/29</td>
|
||
<td>255.255.255.248</td>
|
||
</tr>
|
||
<tr>
|
||
<td>16</td>
|
||
<td>/28</td>
|
||
<td>255.255.255.240</td>
|
||
</tr>
|
||
<tr>
|
||
<td>32</td>
|
||
<td>/27</td>
|
||
<td>255.255.255.224</td>
|
||
</tr>
|
||
<tr>
|
||
<td>64</td>
|
||
<td>/26</td>
|
||
<td>255.255.255.192</td>
|
||
</tr>
|
||
<tr>
|
||
<td>128</td>
|
||
<td>/25</td>
|
||
<td>255.255.255.128</td>
|
||
</tr>
|
||
<tr>
|
||
<td>256</td>
|
||
<td>/24</td>
|
||
<td>255.255.255.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>512</td>
|
||
<td>/23</td>
|
||
<td>255.255.254.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>1024</td>
|
||
<td>/22</td>
|
||
<td>255.255.252.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>2048</td>
|
||
<td>/21</td>
|
||
<td>255.255.248.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>4096</td>
|
||
<td>/20</td>
|
||
<td>255.255.240.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>8192</td>
|
||
<td>/19</td>
|
||
<td>255.255.224.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>16384</td>
|
||
<td>/18</td>
|
||
<td>255.255.192.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>32768</td>
|
||
<td>/17</td>
|
||
<td>255.255.128.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>65536</td>
|
||
<td>/16</td>
|
||
<td>255.255.0.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td>2 ** 24</td>
|
||
<td>/8</td>
|
||
<td>255.0.0.0</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p align="left">Notice that the VLSM is written with a slash ("/") -- you
|
||
will often hear a subnet of size 64 referred to as a "slash 26" subnet
|
||
and one of size 8 referred to as a "slash 29".</p>
|
||
|
||
<p align="left">The subnet's mask (also referred to as its <i>netmask) </i>is
|
||
simply a 32-bit number with the first "VLSM" bits set to one and the
|
||
remaining bits set to zero. For example, for a subnet of size 64, the
|
||
subnet mask has 26 leading one bits:</p>
|
||
|
||
<blockquote>
|
||
<p align="left">11111111111111111111111111000000 = FFFFFFC0 = FF.FF.FF.C0
|
||
= 255.255.255.192</p>
|
||
</blockquote>
|
||
|
||
<p align="left">The subnet mask has the property that if you logically AND
|
||
the subnet mask with an address in the subnet, the result is the subnet
|
||
address. Just as important, if you logically AND the subnet mask with
|
||
an address outside the subnet, the result is NOT the subnet address.
|
||
As we will see below, this property of subnet masks is very useful in
|
||
routing.</p>
|
||
|
||
<p align="left">For a subnetwork whose address is <b>a.b.c.d</b> and whose
|
||
Variable Length Subnet Mask is <b>/v</b>, we denote the subnetwork
|
||
as "<b>a.b.c.d/v</b>" using <i>CIDR</i> <i>Notation</i>.<2E> </p>
|
||
|
||
<p align="left">Example:</p>
|
||
|
||
<blockquote>
|
||
<table border="2" style="border-collapse: collapse;" id="AutoNumber1"
|
||
cellpadding="2">
|
||
<tbody>
|
||
<tr>
|
||
<td><b>Subnet:</b></td>
|
||
<td>10.10.10.0 - 10.10.10.127</td>
|
||
</tr>
|
||
<tr>
|
||
<td><b>Subnet Size:</b></td>
|
||
<td>128</td>
|
||
</tr>
|
||
<tr>
|
||
<td><b>Subnet Address:</b></td>
|
||
<td>10.10.10.0</td>
|
||
</tr>
|
||
<tr>
|
||
<td><b>Broadcast Address:</b></td>
|
||
<td>10.10.10.127</td>
|
||
</tr>
|
||
<tr>
|
||
<td><b>CIDR<EFBFBD>Notation:</b></td>
|
||
<td>10.10.10.0/25</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p align="left">There are two degenerate subnets that need mentioning; namely,
|
||
the subnet with one member and the subnet with 2 ** 32 members.</p>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber5">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>Size of Subnetwork</b></u></td>
|
||
<td><u><b>VLSM Length</b></u></td>
|
||
<td><u><b>Subnet Mask</b></u></td>
|
||
<td><u><b>CIDR<EFBFBD>Notation</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>1</td>
|
||
<td>32</td>
|
||
<td>255.255.255.255</td>
|
||
<td>a.b.c.d/32</td>
|
||
</tr>
|
||
<tr>
|
||
<td>2 ** 32</td>
|
||
<td>0</td>
|
||
<td>0.0.0.0</td>
|
||
<td>0.0.0.0/0</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p align="left">So any address <b>a.b.c.d </b>may also be written <b> a.b.c.d/32</b>
|
||
and the set of all possible IP addresses is written <b>0.0.0.0/0</b>.</p>
|
||
|
||
<p align="left">Later in this guide, you will see the notation <b>a.b.c.d/v</b>
|
||
used to describe the ip configuration of a network interface (the 'ip'
|
||
utility also uses this syntax). This simply means that the interface is
|
||
configured with ip address <b>a.b.c.d</b> and with the netmask that corresponds
|
||
to VLSM <b>/v</b>.</p>
|
||
|
||
<p align="left">Example: 192.0.2.65/29</p>
|
||
|
||
<p align="left"><EFBFBD><EFBFBD><EFBFBD> The interface is configured with IP address 192.0.2.65
|
||
and netmask 255.255.255.248.</p>
|
||
|
||
<h3 align="left"><a name="Routing"></a>4.3 Routing</h3>
|
||
|
||
<p align="left">One of the purposes of subnetting is that it forms the basis
|
||
for routing. Here's the routing table on my firewall:</p>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<pre>[root@gateway root]# netstat -nr<br>Kernel IP routing table<br>Destination Gateway Genmask Flags MSS Window irtt Iface<br>192.168.9.1 0.0.0.0 255.255.255.255 UH 40 0 0 texas<br>206.124.146.177 0.0.0.0 255.255.255.255 UH 40 0 0 eth1<br>206.124.146.180 0.0.0.0 255.255.255.255 UH 40 0 0 eth3<br>192.168.3.0 0.0.0.0 255.255.255.0 U 40 0 0 eth3<br>192.168.2.0 0.0.0.0 255.255.255.0 U 40 0 0 eth1<br>192.168.1.0 0.0.0.0 255.255.255.0 U 40 0 0 eth2<br>206.124.146.0 0.0.0.0 255.255.255.0 U 40 0 0 eth0<br>192.168.9.0 192.0.2.223 255.255.255.0 UG 40 0 0 texas<br>127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo<br>0.0.0.0 206.124.146.254 0.0.0.0 UG 40 0 0 eth0<br>[root@gateway root]#</pre>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<p align="left">The device <i>texas</i> is a GRE tunnel to a peer site in
|
||
the Dallas, Texas area.<br>
|
||
<br>
|
||
The first three routes are <i>host routes</i> since they indicate
|
||
how to get to a single host. In the 'netstat' output this can be seen
|
||
by the "Genmask" (Subnet Mask) of 255.255.255.255 and the "H" in the
|
||
Flags column. The remainder are 'net' routes since they tell the kernel
|
||
how to route packets to a subnetwork. The last route is the <i>default
|
||
route</i> and the gateway mentioned in that route is called the <i>default
|
||
gateway</i>.</p>
|
||
|
||
<p align="left">When the kernel is trying to send a packet to IP address <b>A</b>,
|
||
it starts at the top of the routing table and:</p>
|
||
|
||
<ul>
|
||
<li>
|
||
<p align="left"><b>A</b> is logically ANDed with the 'Genmask' value in
|
||
the table entry.</p>
|
||
</li>
|
||
<li>
|
||
<p align="left">The result is compared with the 'Destination' value in
|
||
the table entry.</p>
|
||
</li>
|
||
<li>
|
||
<p align="left">If the result and the 'Destination' value are the same,
|
||
then:</p>
|
||
|
||
<ul>
|
||
<li>
|
||
|
||
<p align="left">If the 'Gateway' column is non-zero, the packet is
|
||
sent to the gateway over the interface named in the 'Iface' column.</p>
|
||
</li>
|
||
<li>
|
||
|
||
<p align="left">Otherwise, the packet is sent directly to <b>A </b>over
|
||
the interface named in the 'iface' column.</p>
|
||
</li>
|
||
|
||
</ul>
|
||
</li>
|
||
<li>
|
||
<p align="left">Otherwise, the above steps are repeated on the next entry
|
||
in the table.</p>
|
||
</li>
|
||
|
||
</ul>
|
||
|
||
<p align="left">Since the default route matches any IP address (<b>A</b> land
|
||
0.0.0.0 = 0.0.0.0), packets that don't match any of the other routing table
|
||
entries are sent to the <i>default gateway</i> which is usually a router
|
||
at your ISP.</p>
|
||
|
||
<p align="left">Lets take an example. Suppose that we want to route a packet
|
||
to 192.168.1.5. That address clearly doesn't match any of the host routes
|
||
in the table but if we logically and that address with 255.255.255.0,
|
||
the result is 192.168.1.0 which matches this routing table entry:</p>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<pre>192.168.1.0 0.0.0.0 255.255.255.0 U 40 0 0 eth2</pre>
|
||
</blockquote>
|
||
|
||
<p>So to route a packet to 192.168.1.5, the packet is sent directly over eth2.</p>
|
||
</div>
|
||
|
||
<p align="left">One more thing needs to be emphasized -- all outgoing packet
|
||
are sent using the routing table and reply packets are not a special
|
||
case. There seems to be a common mis-conception whereby people think that
|
||
request packets are like salmon and contain a genetic code that is magically
|
||
transferred to reply packets so that the replies follow the reverse route
|
||
taken by the request. That isn't the case; the replies may take a totally
|
||
different route back to the client than was taken by the requests -- they
|
||
are totally independent.</p>
|
||
|
||
<h3 align="left"><a name="ARP"></a>4.4 Address Resolution Protocol</h3>
|
||
|
||
<p align="left">When sending packets over Ethernet, IP addresses aren't used.
|
||
Rather Ethernet addressing is based on <i>Media Access Control</i> (MAC)
|
||
addresses. Each Ethernet device has it's own unique<75> MAC address which
|
||
is burned into a PROM on the device during manufacture. You can obtain
|
||
the MAC of an Ethernet device using the 'ip' utility:</p>
|
||
|
||
<blockquote>
|
||
<div align="left">
|
||
<pre>[root@gateway root]# ip addr show eth0<br>2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc htb qlen 100<br>link/ether <u>02:00:08:e3:fa:55</u> brd ff:ff:ff:ff:ff:ff<br>inet 206.124.146.176/24 brd 206.124.146.255 scope global eth0<br>inet 206.124.146.178/24 brd 206.124.146.255 scope global secondary eth0<br>inet 206.124.146.179/24 brd 206.124.146.255 scope global secondary eth0<br>[root@gateway root]#</pre>
|
||
</div>
|
||
</blockquote>
|
||
|
||
<div align="left">
|
||
<p align="left">As you can see from the above output, the MAC is 6 bytes (48
|
||
bits) wide. A card's MAC is usually also printed on a label attached to
|
||
the card itself. </p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Because IP uses IP addresses and Ethernet uses MAC addresses,
|
||
a mechanism is required to translate an IP address into a MAC address;
|
||
that is the purpose of the <i>Address Resolution Protocol</i> (ARP).
|
||
Here is ARP in action:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<div align="left">
|
||
<pre>[root@gateway root]# tcpdump -nei eth2 arp<br>tcpdump: listening on eth2<br>09:56:49.766757 2:0:8:e3:4c:48 0:6:25:aa:8a:f0 arp 42: arp who-has 192.168.1.19 tell 192.168.1.254<br>09:56:49.769372 0:6:25:aa:8a:f0 2:0:8:e3:4c:48 arp 60: arp reply 192.168.1.19 is-at 0:6:25:aa:8a:f0<br><br>2 packets received by filter<br>0 packets dropped by kernel<br>[root@gateway root]#<br></pre>
|
||
</div>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<p align="left">In this exchange, 192.168.1.254 (MAC 2:0:8:e3:4c:48) wants
|
||
to know the MAC of the device with IP address 192.168.1.19. The system
|
||
having that IP address is responding that the MAC address of the device
|
||
with IP address 192.168.1.19 is 0:6:25:aa:8a:f0.</p>
|
||
|
||
<p align="left">In order to avoid having to exchange ARP information each
|
||
time that an IP packet is to be sent, systems maintain an <i>ARP cache</i>
|
||
of IP<->MAC correspondences. You can see the ARP cache on your
|
||
system (including your Windows system) using the 'arp' command:</p>
|
||
|
||
<blockquote>
|
||
<div align="left">
|
||
<pre>[root@gateway root]# arp -na<br>? (206.124.146.177) at 00:A0:C9:15:39:78 [ether] on eth1<br>? (192.168.1.3) at 00:A0:CC:63:66:89 [ether] on eth2<br>? (192.168.1.5) at 00:A0:CC:DB:31:C4 [ether] on eth2<br>? (206.124.146.254) at 00:03:6C:8A:18:38 [ether] on eth0<br>? (192.168.1.19) at 00:06:25:AA:8A:F0 [ether] on eth2</pre>
|
||
</div>
|
||
</blockquote>
|
||
|
||
<p align="left">The leading question marks are a result of my having specified
|
||
the 'n' option (Windows 'arp' doesn't allow that option) which causes
|
||
the 'arp' program to forego IP->DNS name translation. Had I not given
|
||
that option, the question marks would have been replaced with the FQDN
|
||
corresponding to each IP address. Notice that the last entry in the table
|
||
records the information we saw using tcpdump above.</p>
|
||
|
||
<h3 align="left"><a name="RFC1918"></a>4.5 RFC 1918</h3>
|
||
|
||
<p align="left">IP addresses are allocated by the <i> <a
|
||
href="http://www.iana.org">Internet Assigned Number Authority</a> </i>(IANA)
|
||
who delegates allocations on a geographic basis to <i>Regional Internet
|
||
Registries</i> (RIRs). For example, allocation for the Americas and for
|
||
sub-Sahara Africa is delegated to the <i><a
|
||
href="http://www.arin.net">American Registry for Internet Numbers</a>
|
||
</i>(ARIN). These RIRs may in turn delegate to national registries. Most
|
||
of us don't deal with these registrars but rather get our IP addresses
|
||
from our ISP.</p>
|
||
|
||
<p align="left">It's a fact of life that most of us can't afford as many Public
|
||
IP addresses as we have devices to assign them to so we end up making use
|
||
of <i> Private </i>IP addresses. RFC 1918 reserves several IP address ranges
|
||
for this purpose:</p>
|
||
|
||
<div align="left">
|
||
<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>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<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. This is
|
||
understandable given that anyone can select any of these addresses for
|
||
their private use.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">When selecting addresses from these ranges, there's a couple
|
||
of things to keep in mind:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<ul>
|
||
<li>
|
||
<p align="left">As the IPv4 address space becomes depleted, more and more
|
||
organizations (including ISPs) are beginning to use RFC 1918 addresses
|
||
in their infrastructure. </p>
|
||
</li>
|
||
<li>
|
||
<p align="left">You don't want to use addresses that are being used by
|
||
your ISP or by another organization with whom you want to establish
|
||
a VPN relationship. </p>
|
||
</li>
|
||
|
||
</ul>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">So it's a good idea to check with your ISP to see if they
|
||
are using (or are planning to use) private addresses before you decide
|
||
the addresses that you are going to use.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h2 align="left"><a name="Options"></a>5.0 Setting up your Network</h2>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The choice of how to set up your network depends primarily
|
||
on how many Public IP addresses you have vs. how many addressable entities
|
||
you have in your network. Regardless of how many addresses you have,
|
||
your ISP will handle that set of addresses in one of two ways:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<ol>
|
||
<li>
|
||
<p align="left"><b>Routed - </b>Traffic to any of your addresses will
|
||
be routed through a single <i>gateway address</i>. This will generally
|
||
only be done if your ISP has assigned you a complete subnet (/29 or
|
||
larger). In this case, you will assign the gateway address as the IP
|
||
address of your firewall/router's external interface. </p>
|
||
</li>
|
||
<li>
|
||
<p align="left"><b>Non-routed - </b>Your ISP will send traffic to each
|
||
of your addresses directly. </p>
|
||
</li>
|
||
|
||
</ol>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">In the subsections that follow, we'll look at each of these
|
||
separately.<br>
|
||
</p>
|
||
|
||
<p align="left">Before we begin, there is one thing for you to check:</p>
|
||
|
||
<p align="left"><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>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h3 align="left"><a name="Routed"></a>5.1 Routed</h3>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Let's assume that your ISP has assigned you the subnet
|
||
192.0.2.64/28 routed through 192.0.2.65. That means that you have IP addresses
|
||
192.0.2.64 - 192.0.2.79 and that your firewall's external IP address
|
||
is 192.0.2.65. Your ISP has also told you that you should use a netmask
|
||
of 255.255.255.0 (so your /28 is part of a larger /24). With this many
|
||
IP addresses, you are able to subnet your /28 into two /29's and set
|
||
up your network as shown in the following diagram.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="center"> <img border="0" src="images/dmz4.png" width="726"
|
||
height="635">
|
||
</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Here, the DMZ comprises the subnet 192.0.2.64/29 and the Local
|
||
network is 192.0.2.72/29. The default gateway for hosts in the DMZ would
|
||
be configured to 192.0.2.66 and the default gateway for hosts in the local
|
||
network would be 192.0.2.73.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Notice that this arrangement is rather wasteful of public
|
||
IP addresses since it is using 192.0.2.64 and 192.0.2.72 for subnet
|
||
addresses, 192.0.2.71 and 192.0.2.79 for subnet broadcast addresses
|
||
and 192.0.2.66 and 168.0.2.73 for internal addresses on the firewall/router.
|
||
Nevertheless, it shows how subnetting can work and if we were dealing
|
||
with a /24 rather than a /28 network, the use of 6 IP addresses out
|
||
of 256 would be justified because of the simplicity of the setup.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The astute reader may have noticed that the Firewall/Router's
|
||
external interface is actually part of the DMZ subnet (192.0.2.64/29).
|
||
What if DMZ 1 (192.0.2.67) tries to communicate with 192.0.2.65? The
|
||
routing table on DMZ 1 will look like this:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<pre>Kernel IP routing table<br>Destination Gateway Genmask Flags MSS Window irtt Iface<br>192.0.2.64 0.0.0.0 255.255.255.248 U 40 0 0 eth0<br>0.0.0.0 192.0.2.66 0.0.0.0 UG 40 0 0 eth0</pre>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">This means that DMZ 1 will send an ARP "who-has 192.0.2.65"
|
||
request and no device on the DMZ Ethernet segment has that IP address.
|
||
Oddly enough, the firewall will respond to the request with the MAC
|
||
address of its <u>DMZ Interface!!</u> DMZ 1 can then send Ethernet frames
|
||
addressed to that MAC address and the frames will be received (correctly)
|
||
by the firewall/router.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">It is this rather unexpected ARP behavior on the part of the
|
||
Linux Kernel that prompts the warning earlier in this guide regarding the
|
||
connecting of multiple firewall/router interfaces to the same hub or switch.
|
||
When an ARP request for one of the firewall/router's IP addresses is sent
|
||
by another system connected to the hub/switch, all of the firewall's
|
||
interfaces that connect to the hub/switch can respond! It is then a
|
||
race as to which "here-is" response reaches the sender first.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h3 align="left"><a name="NonRouted"></a>5.2 Non-routed</h3>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">If you have the above situation but it is non-routed, you
|
||
can configure your network exactly as described above with one additional
|
||
twist; simply specify the "proxyarp" option on all three firewall interfaces
|
||
in the /etc/shorewall/interfaces file.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Most of us don't have the luxury of having enough public IP
|
||
addresses to set up our networks as shown in the preceding example (even
|
||
if the setup is routed). </p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><b>For the remainder of this section, assume that your ISP
|
||
has assigned you IP addresses 192.0.2.176-180 and has told you to use
|
||
netmask 255.255.255.0 and default gateway 192.0.2.254.</b></p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Clearly, that set of addresses doesn't comprise a subnetwork
|
||
and there aren't enough addresses for all of the network interfaces.
|
||
There are four different techniques that can be used to work around
|
||
this problem.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<ul>
|
||
<li>
|
||
<p align="left"><i>Source Network Address Translation </i>(SNAT).
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p align="left"><i>Destination Network Address Translation </i>(DNAT)
|
||
also known as <i>Port Forwarding.</i> </p>
|
||
</li>
|
||
<li>
|
||
<p align="left"><i>Proxy ARP.</i> </p>
|
||
</li>
|
||
<li>
|
||
<p align="left"><i>Network Address Translation</i> (NAT) also referred
|
||
to as <i>Static NAT</i>. </p>
|
||
</li>
|
||
|
||
</ul>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Often a combination of these techniques is used. Each of these
|
||
will be discussed in the sections that follow.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h4 align="left"><a name="SNAT"></a><EFBFBD>5.2.1 SNAT</h4>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">With SNAT, an internal LAN segment is configured using RFC
|
||
1918 addresses. When a host <b>A </b>on this internal segment initiates
|
||
a connection to host <b>B</b> on the internet, the firewall/router
|
||
rewrites the IP header in the request to use one of your public IP addresses
|
||
as the source address. When <b>B</b> responds and the response is received
|
||
by the firewall, the firewall changes the destination address back
|
||
to the RFC 1918 address of <b>A</b> and forwards the response back to
|
||
<b>A.</b></p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Let's suppose that you decide to use SNAT on your local zone
|
||
and use public address 192.0.2.176 as both your firewall's external
|
||
IP address and the source IP address of internet requests sent from
|
||
that zone.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h2 align="center"> <img border="0" src="images/dmz5.png" width="745"
|
||
height="635">
|
||
</h2>
|
||
</div>
|
||
|
||
<div align="left"> The local zone has been subnetted as 192.168.201.0/29
|
||
(netmask 255.255.255.248).</div>
|
||
|
||
<div align="left"> <20></div>
|
||
|
||
<div align="left"> <img border="0" src="images/BD21298_2.gif"
|
||
width="13" height="13">
|
||
<20><><EFBFBD> The systems in the local zone would be configured with a
|
||
default gateway of 192.168.201.1 (the IP address of the firewall's
|
||
local interface).</div>
|
||
|
||
<div align="left"> <20></div>
|
||
|
||
<div align="left"> <img border="0" src="images/BD21298_2.gif"
|
||
width="13" height="13">
|
||
<20><><EFBFBD> SNAT is configured in Shorewall using the <a
|
||
href="Documentation.htm#Masq"> /etc/shorewall/masq file</a>.</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber6">
|
||
<tbody>
|
||
<tr>
|
||
<td width="33%"><u><b>INTERFACE</b></u></td>
|
||
<td width="33%"><u><b>SUBNET</b></u></td>
|
||
<td width="34%"><u><b>ADDRESS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="33%">eth0</td>
|
||
<td width="33%">192.168.201.0/29</td>
|
||
<td width="34%">192.0.2.176</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">This example used the normal technique of assigning the same
|
||
public IP address for the firewall external interface and for SNAT.
|
||
If you wanted to use a different IP address, you would either have to
|
||
use your distributions network configuration tools to add that IP address
|
||
to the external interface or you could set ADD_SNAT_ALIASES=Yes in
|
||
/etc/shorewall/shorewall.conf and Shorewall will add the address for you.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h4 align="left"><a name="DNAT"></a>5.2.2 DNAT</h4>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">When SNAT is used, it is impossible for hosts on the internet
|
||
to initiate a connection to one of the internal systems since those
|
||
systems do not have a public IP address. DNAT provides a way to allow
|
||
selected connections from the internet.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD><EFBFBD> Suppose that your daughter wants to run a web server on
|
||
her system "Local 3". You could allow connections to the internet
|
||
to her server by adding the following entry in <a
|
||
href="Documentation.htm#Rules">/etc/shorewall/rules</a>:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber7">
|
||
<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 DESTINATION</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>DNAT</td>
|
||
<td>net</td>
|
||
<td>loc:192.168.201.4</td>
|
||
<td>tcp</td>
|
||
<td>www</td>
|
||
<td>-</td>
|
||
<td>192.0.2.176</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">If one of your daughter's friends at address <b>A</b> wants
|
||
to access your daughter's server, she can connect to <a
|
||
href="http://192.0.2.176"> http://192.0.2.176</a> (the firewall's external
|
||
IP address) and the firewall will rewrite the destination IP address
|
||
to 192.168.201.4 (your daughter's system) and forward the request. When
|
||
your daughter's server responds, the firewall will rewrite the source
|
||
address back to 192.0.2.176 and send the response back to <b>A.</b></p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">This example used the firewall's external IP address for DNAT.
|
||
You can use another of your public IP addresses but Shorewall will not
|
||
add that address to the firewall's external interface for you.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h4 align="left"><a name="ProxyARP"></a>5.2.3 Proxy ARP</h4>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The idea behind proxy ARP is that:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<ul>
|
||
<li>
|
||
<p align="left">A host <b>H </b>behind your firewall is assigned one of
|
||
your public IP addresses (<b>A)</b> and is assigned the same netmask
|
||
<b>(M) </b>as the firewall's external interface. </p>
|
||
</li>
|
||
<li>
|
||
<p align="left">The firewall responds to ARP "who has" requests for <b>A.</b>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p align="left">When <b>H</b> issues an ARP "who has" request for an address
|
||
in the subnetwork defined by <b>A</b> and <b>M</b>, the firewall will
|
||
respond (with the MAC if the firewall interface to <b>H</b>). </p>
|
||
</li>
|
||
|
||
</ul>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Let suppose that we decide to use Proxy ARP on the DMZ in
|
||
our example network.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="center"> <img border="0" src="images/dmz6.png" width="745"
|
||
height="635">
|
||
</p>
|
||
</div>
|
||
|
||
<div align="left"> Here, we've assigned the IP addresses 192.0.2.177 to
|
||
system DMZ 1 and 192.0.2.178 to DMZ 2. Notice that we've just assigned
|
||
an arbitrary RFC 1918 IP address and subnet mask to the DMZ interface
|
||
on the firewall. That address and netmask isn't relevant - just be sure
|
||
it doesn't overlap another subnet that you've defined.</div>
|
||
|
||
<div align="left"> <20></div>
|
||
|
||
<div align="left"> <img border="0" src="images/BD21298_2.gif"
|
||
width="13" height="13">
|
||
<20><><EFBFBD> The Shorewall configuration of Proxy ARP is done using the
|
||
<a href="Documentation.htm#ProxyArp">/etc/shorewall/proxyarp</a> file.</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" id="AutoNumber8"
|
||
style="border-collapse: collapse;">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>ADDRESS</b></u></td>
|
||
<td><u><b>INTERFACE</b></u></td>
|
||
<td><u><b>EXTERNAL</b></u></td>
|
||
<td><u><b>HAVE ROUTE</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>192.0.2.177</td>
|
||
<td>eth2</td>
|
||
<td>eth0</td>
|
||
<td>No</td>
|
||
</tr>
|
||
<tr>
|
||
<td>192.0.2.178</td>
|
||
<td>eth2</td>
|
||
<td>eth0</td>
|
||
<td>No</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Because the HAVE ROUTE column contains No, Shorewall will
|
||
add host routes thru eth2 to 192.0.2.177 and 192.0.2.178.<br>
|
||
</p>
|
||
|
||
<p align="left">The ethernet interfaces on DMZ 1 and DMZ 2 should be configured
|
||
to have the IP addresses shown but should have the same default gateway
|
||
as the firewall itself -- namely 192.0.2.254. In other words, they should
|
||
be configured just like they would be if they were parallel to the firewall
|
||
rather than behind it.<br>
|
||
</p>
|
||
|
||
<p><font color="#ff0000"><b>NOTE: Do not add the Proxy ARP'ed address(es)
|
||
(192.0.2.177 and 192.0.2.178 in the above example)<29> to the external interface
|
||
(eth0 in this example) of the firewall.</b></font><br>
|
||
</p>
|
||
<div align="left"> </div>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"></p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<div align="left">
|
||
<p align="left">A word of warning is in order here. ISPs typically configure
|
||
their routers with a long ARP cache timeout. If you move a system from
|
||
parallel to your firewall to behind your firewall with Proxy ARP, it
|
||
will probably be HOURS before that system can communicate with the internet.
|
||
There are a couple of things that you can try:<br>
|
||
</p>
|
||
|
||
<ol>
|
||
<li>(Courtesy of Bradey Honsinger) A reading of Stevens' <i>TCP/IP
|
||
Illustrated, Vol 1</i> reveals that a <br>
|
||
<br>
|
||
"gratuitous" ARP packet should cause the ISP's router to refresh their
|
||
ARP cache (section 4.7). A gratuitous ARP is simply a host requesting
|
||
the MAC address for its own IP; in addition to ensuring that the IP address
|
||
isn't a duplicate,...<br>
|
||
<br>
|
||
"if the host sending the gratuitous ARP has just changed its hardware
|
||
address..., this packet causes any other host...that has an entry in its
|
||
cache for the old hardware address to update its ARP cache entry accordingly."<br>
|
||
<br>
|
||
Which is, of course, exactly what you want to do when you switch a
|
||
host from being exposed to the Internet to behind Shorewall using proxy
|
||
ARP (or static NAT for that matter). Happily enough, recent versions of
|
||
Redhat's iputils package include "arping", whose "-U" flag does just that:<br>
|
||
<br>
|
||
<20><><EFBFBD> <font color="#009900"><b>arping -U -I <net if> <newly
|
||
proxied IP></b></font><br>
|
||
<20><><EFBFBD> <font color="#009900"><b>arping -U -I eth0 66.58.99.83 # for example</b></font><br>
|
||
<br>
|
||
Stevens goes on to mention that not all systems respond correctly
|
||
to gratuitous ARPs, but googling for "arping -U" seems to support the
|
||
idea that it works most of the time.<br>
|
||
<br>
|
||
</li>
|
||
<li>You can call your ISP and ask them to purge the stale ARP
|
||
cache entry but many either can't or won't purge individual entries.</li>
|
||
|
||
</ol>
|
||
You can determine if your ISP's gateway ARP cache is stale using
|
||
ping and tcpdump. Suppose that we suspect that the gateway router has
|
||
a stale ARP cache entry for 130.252.100.19. On the firewall, run tcpdump
|
||
as follows:</div>
|
||
|
||
<div align="left">
|
||
<pre> <font color="#009900"><b>tcpdump -nei eth0 icmp</b></font></pre>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Now from 130.252.100.19, ping the ISP's gateway (which we
|
||
will assume is 130.252.100.254):</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<pre> <b><font color="#009900">ping 130.252.100.254</font></b></pre>
|
||
</div>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">We can now observe the tcpdump output:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<pre> 13:35:12.159321 <u>0:4:e2:20:20:33</u> 0:0:77:95:dd:19 ip 98: 192.0.2.177 > 192.0.2.254: icmp: echo request (DF)<br> 13:35:12.207615 0:0:77:95:dd:19 <u>0:c0:a8:50:b2:57</u> ip 98: 192.0.2.254 > 192.0.2.177 : icmp: echo reply</pre>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Notice that the source MAC address in the echo request is
|
||
different from the destination MAC address in the echo reply!! In this
|
||
case 0:4:e2:20:20:33 was the MAC of the firewall's eth0 NIC while 0:c0:a8:50:b2:57
|
||
was the MAC address of DMZ 1. In other words, the gateway's ARP cache
|
||
still associates 192.0.2.177 with the NIC in DMZ 1 rather than with
|
||
the firewall's eth0.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h4 align="left"><a name="NAT"></a>5.2.4 Static NAT</h4>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">With static NAT, you assign local systems RFC 1918 addresses
|
||
then establish a one-to-one mapping between those addresses and public
|
||
IP addresses. For outgoing connections SNAT (Source Network Address
|
||
Translation) occurs and on incoming connections DNAT (Destination
|
||
Network Address Translation) occurs. Let's go back to our earlier example
|
||
involving your daughter's web server running on system Local 3.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="center"><img border="0" src="images/dmz5.png" width="745"
|
||
height="635">
|
||
</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Recall that in this setup, the local network is using SNAT
|
||
and is sharing the firewall external IP (192.0.2.176) for outbound
|
||
connections. This is done with the following entry in /etc/shorewall/masq:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber6">
|
||
<tbody>
|
||
<tr>
|
||
<td width="33%"><u><b>INTERFACE</b></u></td>
|
||
<td width="33%"><u><b>SUBNET</b></u></td>
|
||
<td width="34%"><u><b>ADDRESS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="33%">eth0</td>
|
||
<td width="33%">192.168.201.0/29</td>
|
||
<td width="34%">192.0.2.176</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> Suppose now that you have decided to give your daughter her
|
||
own IP address (192.0.2.179) for both inbound and outbound connections.
|
||
You would do that by adding an entry in <a
|
||
href="Documentation.htm#NAT">/etc/shorewall/nat</a>.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellspacing="0" cellpadding="2" id="AutoNumber9"
|
||
style="border-collapse: collapse;">
|
||
<tbody>
|
||
<tr>
|
||
<td>EXTERNAL</td>
|
||
<td>INTERFACE</td>
|
||
<td>INTERNAL</td>
|
||
<td>ALL INTERFACES </td>
|
||
<td>LOCAL</td>
|
||
</tr>
|
||
<tr>
|
||
<td>192.0.2.179</td>
|
||
<td>eth0</td>
|
||
<td>192.168.201.4</td>
|
||
<td>No</td>
|
||
<td>No</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">With this entry in place, you daughter has her own IP address
|
||
and the other two local systems share the firewall's IP address.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> Once the relationship between 192.0.2.179 and 192.168.201.4
|
||
is established by the nat file entry above, it is no longer appropriate
|
||
to use a DNAT rule for you daughter's web server -- you would rather
|
||
just use an ACCEPT rule:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber7">
|
||
<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 DESTINATION</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>loc:192.168.201.4</td>
|
||
<td>tcp</td>
|
||
<td>www</td>
|
||
<td><EFBFBD></td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h3 align="left"><a name="Rules"></a>5.3 Rules</h3>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> With the default policies, your local systems (Local 1-3)
|
||
can access any servers on the internet and the DMZ can't access any
|
||
other host (including the firewall). With the exception of <a
|
||
href="#DNAT">DNAT rules</a> which cause address translation and allow
|
||
the translated connection request to pass through the firewall, the
|
||
way to allow connection requests through your firewall is to use ACCEPT
|
||
rules.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><b>NOTE: Since the SOURCE PORT and ORIG. DEST. Columns aren't
|
||
used in this section, they won't be shown</b></p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">You probably want to allow ping between your zones:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber7">
|
||
<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>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>loc</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz</td>
|
||
<td>loc</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Let's suppose that you run mail and pop3 servers on DMZ 2
|
||
and a Web Server on DMZ 1. The rules that you would need are:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber7">
|
||
<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>COMMENTS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail from the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>pop3</td>
|
||
<td># Pop3 from the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail from the Local Network</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>pop3</td>
|
||
<td># Pop3 from the Local Network</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail from the Firewall</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>net</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail to the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>http</td>
|
||
<td># WWW from the Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>https</td>
|
||
<td># Secure HTTP from the Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>https</td>
|
||
<td># Secure HTTP from the Local Net</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">If you run a public DNS server on 192.0.2.177, you would need
|
||
to add the following rules:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber7">
|
||
<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>COMMENTS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS from the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS from the internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS from firewall</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS from firewall</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS from the local Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS from the local Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>net</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS to the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>net</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS to the Internet</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">You probably want some way to communicate with your firewall
|
||
and DMZ systems from the local network -- I recommend SSH which through
|
||
its scp utility can also do publishing and software update distribution.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber7">
|
||
<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>COMMENTS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz</td>
|
||
<td>tcp</td>
|
||
<td>ssh</td>
|
||
<td># SSH to the DMZ</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>fw</td>
|
||
<td>tcp</td>
|
||
<td>ssh</td>
|
||
<td># SSH to the Firewall</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h3 align="left"><a name="OddsAndEnds"></a>5.4 Odds and Ends</h3>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The above discussion reflects my personal preference for using
|
||
Proxy ARP for my servers in my DMZ and SNAT/NAT for my local systems. I
|
||
prefer to use NAT only in cases where a system that is part of an RFC 1918
|
||
subnet needs to have it's own public IP.<2E></p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><img border="0" src="images/BD21298_2.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> If you haven't already, it would be a good idea to browse
|
||
through <a href="Documentation.htm#Conf">/etc/shorewall/shorewall.conf</a>
|
||
just to see if there is anything there that might be of interest. You
|
||
might also want to look at the other configuration files that you
|
||
haven't touched yet just to get a feel for the other things that Shorewall
|
||
can do.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">In case you haven't been keeping score, here's the final set
|
||
of configuration files for our sample network. Only those that were modified
|
||
from the original installation are shown.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">/etc/shorewall/interfaces (The "options" will be very site-specific).</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="0" cellspacing="0"
|
||
style="border-collapse: collapse;" id="AutoNumber4">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>Zone</b></u></td>
|
||
<td><u><b>Interface</b></u></td>
|
||
<td><u><b>Broadcast</b></u></td>
|
||
<td><u><b>Options</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>net</td>
|
||
<td>eth0</td>
|
||
<td>detect</td>
|
||
<td>norfc1918,routefilter </td>
|
||
</tr>
|
||
<tr>
|
||
<td>loc</td>
|
||
<td>eth1</td>
|
||
<td>detect</td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>dmz</td>
|
||
<td>eth2</td>
|
||
<td>detect</td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The setup described here requires that your network interfaces
|
||
be brought up before Shorewall can start. This opens a short window
|
||
during which you have no firewall protection. If you replace 'detect'
|
||
with the actual broadcast addresses in the entries above, you can bring
|
||
up Shorewall before you bring up your network interfaces.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="0" cellspacing="0"
|
||
style="border-collapse: collapse;" id="AutoNumber4">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>Zone</b></u></td>
|
||
<td><u><b>Interface</b></u></td>
|
||
<td><u><b>Broadcast</b></u></td>
|
||
<td><u><b>Options</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>net</td>
|
||
<td>eth0</td>
|
||
<td>192.0.2.255</td>
|
||
<td>norfc1918,routefilter </td>
|
||
</tr>
|
||
<tr>
|
||
<td>loc</td>
|
||
<td>eth1</td>
|
||
<td>192.168.201.7</td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
<tr>
|
||
<td>dmz</td>
|
||
<td>eth2</td>
|
||
<td>192.168.202.7</td>
|
||
<td><EFBFBD></td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">/etc/shorewall/masq - Local subnet</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber6">
|
||
<tbody>
|
||
<tr>
|
||
<td width="33%"><u><b>INTERFACE</b></u></td>
|
||
<td width="33%"><u><b>SUBNET</b></u></td>
|
||
<td width="34%"><u><b>ADDRESS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="33%">eth0</td>
|
||
<td width="33%">192.168.201.0/29</td>
|
||
<td width="34%">192.0.2.176</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">/etc/shorewall/proxyarp - DMZ</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" id="AutoNumber8"
|
||
style="border-collapse: collapse;">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>ADDRESS</b></u></td>
|
||
<td><u><b>INTERFACE</b></u></td>
|
||
<td><u><b>EXTERNAL</b></u></td>
|
||
<td><u><b>HAVE ROUTE</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>192.0.2.177</td>
|
||
<td>eth2</td>
|
||
<td>eth0</td>
|
||
<td>No</td>
|
||
</tr>
|
||
<tr>
|
||
<td>192.0.2.178</td>
|
||
<td>eth2</td>
|
||
<td>eth0</td>
|
||
<td>No</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">/etc/shorewall/nat- Daughter's System</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" id="AutoNumber9"
|
||
style="border-collapse: collapse;">
|
||
<tbody>
|
||
<tr>
|
||
<td>EXTERNAL</td>
|
||
<td>INTERFACE</td>
|
||
<td>INTERNAL</td>
|
||
<td>ALL INTERFACES </td>
|
||
<td>LOCAL</td>
|
||
</tr>
|
||
<tr>
|
||
<td>192.0.2.179</td>
|
||
<td>eth0</td>
|
||
<td>192.168.201.4</td>
|
||
<td>No</td>
|
||
<td>No</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">/etc/shorewall/rules</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber7">
|
||
<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>COMMENTS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail from the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>pop3</td>
|
||
<td># Pop3 from the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail from the Local Network</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>pop3</td>
|
||
<td># Pop3 from the Local Network</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail from the Firewall</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>net</td>
|
||
<td>tcp</td>
|
||
<td>smtp</td>
|
||
<td># Mail to the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>http</td>
|
||
<td># WWW from the Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>https</td>
|
||
<td># Secure HTTP from the Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.178</td>
|
||
<td>tcp</td>
|
||
<td>https</td>
|
||
<td># Secure HTTP from the Local Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS from the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS from the internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS from firewall</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>fw</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS from firewall</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS from the local Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS from the local Net</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>net</td>
|
||
<td>udp</td>
|
||
<td>domain</td>
|
||
<td># UDP DNS to the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz:192.0.2.177</td>
|
||
<td>net</td>
|
||
<td>tcp</td>
|
||
<td>domain</td>
|
||
<td># TCP DNS to the Internet</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>dmz</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
<td># Ping</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>net</td>
|
||
<td>loc</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
<td>#<23> "</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>dmz</td>
|
||
<td>loc</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
<td># "</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz</td>
|
||
<td>icmp</td>
|
||
<td>echo-request</td>
|
||
<td># "</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>dmz</td>
|
||
<td>tcp</td>
|
||
<td>ssh</td>
|
||
<td># SSH to the DMZ</td>
|
||
</tr>
|
||
<tr>
|
||
<td>ACCEPT</td>
|
||
<td>loc</td>
|
||
<td>fw</td>
|
||
<td>tcp</td>
|
||
<td>ssh</td>
|
||
<td># SSH to the Firewall</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h2 align="left"><a name="DNS"></a>6.0 DNS</h2>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Given the collection of RFC 1918 and public addresses in this
|
||
setup, it only makes sense to have separate internal and external DNS
|
||
servers. You can combine the two into a single BIND 9 server using <i>Views.
|
||
</i> If you are not interested in Bind 9 views, you can <a
|
||
href="#StartingAndStopping">go to the next section</a>.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Suppose that your domain is foobar.net and you want the two
|
||
DMZ systems named www.foobar.net and mail.foobar.net and you want the
|
||
three local systems named "winken.foobar.net, blinken.foobar.net and
|
||
nod.foobar.net. You want your firewall to be known as firewall.foobar.net
|
||
externally and it's interface to the local network to be know as gateway.foobar.net
|
||
and its interface to the dmz as dmz.foobar.net. Let's have the DNS server
|
||
on 192.0.2.177 which will also be known by the name ns1.foobar.net.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The /etc/named.conf file would look like this:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<div align="left">
|
||
<pre>options {<br> directory "/var/named";<br> listen-on { 127.0.0.1 ; 192.0.2.177; };<br>};<br><br>logging {<br> channel xfer-log {<br> file "/var/log/named/bind-xfer.log";<br> print-category yes;<br> print-severity yes;<br> print-time yes;<br> severity info;<br> };<br> category xfer-in { xfer-log; };<br> category xfer-out { xfer-log; };<br> category notify { xfer-log; };<br>};</pre>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<pre>#<br># This is the view presented to our internal systems<br>#<br><br>view "internal" {<br> #<br> # These are the clients that see this view<br> #<br> match-clients { 192.168.201.0/29;<br> 192.168.202.0/29;<br> 127.0.0/24;<br> 192.0.2.176/32; <br> 192.0.2.178/32;<br> 192.0.2.179/32;<br> 192.0.2.180/32; };<br> #<br> # If this server can't complete the request, it should use outside<br> # servers to do so<br> #<br> recursion yes;<br><br> zone "." in {<br> type hint;<br> file "int/root.cache";<br> };<br><br> zone "foobar.net" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "int/db.foobar";<br> };<br><br> zone "0.0.127.in-addr.arpa" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "int/db.127.0.0"; <br> };<br><br> zone "201.168.192.in-addr.arpa" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "int/db.192.168.201";<br> };<br><br> zone "202.168.192.in-addr.arpa" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "int/db.192.168.202";<br> };<br><br> zone "176.2.0.192.in-addr.arpa" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "db.192.0.2.176";<br> };<br> (or status NAT for that matter)<br> zone "177.2.0.192.in-addr.arpa" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "db.192.0.2.177";<br> };<br><br> zone "178.2.0.192.in-addr.arpa" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "db.192.0.2.178";<br> };<br><br> zone "179.2.0.192.in-addr.arpa" in {<br> type master;<br> notify no;<br> allow-update { none; };<br> file "db.206.124.146.179";<br> };<br><br>};<br>#<br># This is the view that we present to the outside world<br>#<br>view "external" {<br> match-clients { any; };<br> #<br> # If we can't answer the query, we tell the client so<br> #<br> recursion no;<br><br> zone "foobar.net" in {<br> type master;<br> notify yes;<br> allow-update {none; };<br> allow-transfer { <i><secondary NS IP></i>; };<br> file "ext/db.foobar";<br> };<br><br> zone "176.2.0.192.in-addr.arpa" in {<br> type master;<br> notify yes;<br> allow-update { none; };<br> allow-transfer { <i><secondary NS IP></i>; };<br> file "db.192.0.2.176";<br> };<br><br> zone "177.2.0.192.in-addr.arpa" in {<br> type master;<br> notify yes;<br> allow-update { none; };<br> allow-transfer { <i><secondary NS IP></i>; };<br> file "db.192.0.2.177";<br> };<br><br> zone "178.2.0.192.in-addr.arpa" in {<br> type master;<br> notify yes;<br> allow-update { none; };<br> allow-transfer { <i><secondary NS IP></i>; };<br> file "db.192.0.2.178";<br> };<br><br> zone "179.2.0.192.in-addr.arpa" in {<br> type master;<br> notify yes;<br> allow-update { none; };<br> allow-transfer { <i><secondary NS IP></i>; };<br> file "db.192.0.2.179";<br> };<br>};</pre>
|
||
</div>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Here are the files in /var/named (those not shown are usually
|
||
included in your bind disbribution).</p>
|
||
|
||
<p align="left">db.192.0.2.176 - This is the reverse zone for the firewall's
|
||
external interface</p>
|
||
|
||
<blockquote>
|
||
<pre>; ############################################################<br>; Start of Authority (Inverse Address Arpa) for 192.0.2.176/32<br>; Filename: db.192.0.2.176<br>; ############################################################<br>@ 604800 IN SOA ns1.foobar.net. netadmin.foobar.net. (<br> 2001102303 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ) ; minimum (1 day)<br>;<br>; ############################################################<br>; Specify Name Servers for all Reverse Lookups (IN-ADDR.ARPA)<br>; ############################################################<br>@ 604800 IN NS ns1.foobar.net.<br>@ 604800 IN NS <i><name of secondary ns></i>.<br>;<br>; ############################################################<br>; Iverse Address Arpa Records (PTR's) <br>; ############################################################<br>176.2.0.192.in-addr.arpa. 86400 IN PTR firewall.foobar.net.<br></pre>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<div align="left"> db.192.0.2.177 - This is the reverse zone for the www/DNS
|
||
server
|
||
<blockquote>
|
||
<pre>; ############################################################<br>; Start of Authority (Inverse Address Arpa) for 192.0.2.177/32<br>; Filename: db.192.0.2.177<br>; ############################################################<br>@ 604800 IN SOA ns1.foobar.net. netadmin.foobar.net. (<br> 2001102303 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ) ; minimum (1 day)<br>;<br>; ############################################################<br>; Specify Name Servers for all Reverse Lookups (IN-ADDR.ARPA)<br>; ############################################################<br>@ 604800 IN NS ns1.foobar.net.<br>@ 604800 IN NS <i><name of secondary ns></i>.<br>;<br>; ############################################################<br>; Iverse Address Arpa Records (PTR's) <br>; ############################################################<br>177.2.0.192.in-addr.arpa. 86400 IN PTR www.foobar.net.<br></pre>
|
||
</blockquote>
|
||
</div>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<div align="left"> db.192.0.2.178 - This is the reverse zone for the mail
|
||
server
|
||
<blockquote>
|
||
<pre>; ############################################################<br>; Start of Authority (Inverse Address Arpa) for 192.0.2.178/32<br>; Filename: db.192.0.2.178<br>; ############################################################<br>@ 604800 IN SOA ns1.foobar.net. netadmin.foobar.net. (<br> 2001102303 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ) ; minimum (1 day)<br>;<br>; ############################################################<br>; Specify Name Servers for all Reverse Lookups (IN-ADDR.ARPA)<br>; ############################################################<br>@ 604800 IN NS ns1.foobar.net.<br>@ 604800 IN NS <i><name of secondary ns></i>.<br>;<br>; ############################################################<br>; Iverse Address Arpa Records (PTR's) <br>; ############################################################<br>178.2.0.192.in-addr.arpa. 86400 IN PTR mail.foobar.net.<br></pre>
|
||
</blockquote>
|
||
</div>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<div align="left"> db.192.0.2.179 - This is the reverse zone for daughter's
|
||
web server's public IP
|
||
<blockquote>
|
||
<pre>; ############################################################<br>; Start of Authority (Inverse Address Arpa) for 192.0.2.179/32<br>; Filename: db.192.0.2.179<br>; ############################################################<br>@ 604800 IN SOA ns1.foobar.net. netadmin.foobar.net. (<br> 2001102303 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ) ; minimum (1 day)<br>;<br>; ############################################################<br>; Specify Name Servers for all Reverse Lookups (IN-ADDR.ARPA)<br>; ############################################################<br>@ 604800 IN NS ns1.foobar.net.<br>@ 604800 IN NS <i><name of secondary ns></i>.<br>;<br>; ############################################################<br>; Iverse Address Arpa Records (PTR's) <br>; ############################################################<br>179.2.0.192.in-addr.arpa. 86400 IN PTR nod.foobar.net.<br></pre>
|
||
</blockquote>
|
||
</div>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">int/db.127.0.0 - The reverse zone for localhost</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<pre>; ############################################################<br>; Start of Authority (Inverse Address Arpa) for 127.0.0.0/8<br>; Filename: db.127.0.0<br>; ############################################################<br>@ 604800 IN SOA ns1.foobar.net. netadmin.foobar.net. (<br> 2001092901 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ) ; minimum (1 day)<br>; ############################################################<br>; Specify Name Servers for all Reverse Lookups (IN-ADDR.ARPA)<br>; ############################################################<br>@ 604800 IN NS ns1.foobar.net.<br><br>; ############################################################<br>; Iverse Address Arpa Records (PTR's)<br>; ############################################################<br>1 86400 IN PTR localhost.foobar.net.</pre>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">int/db.192.168.201 - Reverse zone for the local net. This
|
||
is only shown to internal clients</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<pre>; ############################################################<br>; Start of Authority (Inverse Address Arpa) for 192.168.201.0/29<br>; Filename: db.192.168.201<br>; ############################################################<br>@ 604800 IN SOA ns1.foobar.net netadmin.foobar.net. (<br> 2002032501 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ) ; minimum (1 day)<br><br>; ############################################################<br>; Specify Name Servers for all Reverse Lookups (IN-ADDR.ARPA)<br>; ############################################################<br>@ 604800 IN NS ns1.foobar.net.<br><br>; ############################################################<br>; Iverse Address Arpa Records (PTR's)<br>; ############################################################<br>1 86400 IN PTR gateway.foobar.net.<br>2 86400 IN PTR winken.foobar.net.<br>3 86400 IN PTR blinken.foobar.net.<br>4 86400 IN PTR nod.foobar.net.</pre>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">int/db.192.168.202 - Reverse zone for the firewall's DMZ
|
||
interface</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<div align="left">
|
||
<pre>; ############################################################<br>; Start of Authority (Inverse Address Arpa) for 192.168.202.0/29<br>; Filename: db.192.168.202<br>; ############################################################<br>@ 604800 IN SOA ns1.foobar.net netadmin.foobar.net. (<br> 2002032501 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ) ; minimum (1 day)<br><br>; ############################################################<br>; Specify Name Servers for all Reverse Lookups (IN-ADDR.ARPA)<br>; ############################################################<br>@ 604800 IN NS ns1.foobar.net.<br><br>; ############################################################<br>; Iverse Address Arpa Records (PTR's)<br>; ############################################################<br>1 86400 IN PTR dmz.foobar.net.</pre>
|
||
</div>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">int/db.foobar - Forward zone for use by internal clients.</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<pre>;##############################################################<br>; Start of Authority for foobar.net.<br>; Filename: db.foobar<br>;##############################################################<br>@ 604800 IN SOA ns1.foobar.net. netadmin.foobar.net. (<br> 2002071501 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ); minimum (1 day)<br>;############################################################<br>; foobar.net Nameserver Records (NS)<br>;############################################################<br>@ 604800 IN NS ns1.foobar.net.<br><br>;############################################################<br>; Foobar.net Office Records (ADDRESS)<br>;############################################################<br>localhost 86400 IN A 127.0.0.1<br><br>firewall 86400 IN A 192.0.2.176<br>www 86400 IN A 192.0.2.177<br>ns1 86400 IN A 192.0.2.177<br>www 86400 IN A 192.0.2.177<br><br>gateway 86400 IN A 192.168.201.1<br>winken 86400 IN A 192.168.201.2<br>blinken 86400 IN A 192.168.201.3<br>nod 86400 IN A 192.168.201.4</pre>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">ext/db.foobar - Forward zone for external clients</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<div align="left">
|
||
<pre>;##############################################################<br>; Start of Authority for foobar.net.<br>; Filename: db.foobar<br>;##############################################################<br>@ 86400 IN SOA ns1.foobar.net. netadmin.foobar.net. (<br> 2002052901 ; serial<br> 10800 ; refresh (3 hour)<br> 3600 ; retry (1 hour)<br> 604800 ; expire (7 days)<br> 86400 ); minimum (1 day)<br>;############################################################<br>; Foobar.net Nameserver Records (NS)<br>;############################################################<br>@ 86400 IN NS ns1.foobar.net.<br>@ 86400 IN NS <i><secondary NS></i>.<br>;############################################################<br>; Foobar.net Foobar Wa Office Records (ADDRESS)<br>;############################################################<br>localhost 86400 IN A 127.0.0.1<br>;<br>; The firewall itself<br>;<br>firewall 86400 IN A 192.0.2.176<br>;<br>; The DMZ<br>;<br>ns1 86400 IN A 192.0.2.177<br>www 86400 IN A 192.0.2.177<br>mail 86400 IN A 192.0.2.178<br>;<br>; The Local Network<br>;<br>nod 86400 IN A 192.0.2.179<br><br>;############################################################<br>; Current Aliases for foobar.net (CNAME)<br>;############################################################<br><br>;############################################################<br>; foobar.net MX Records (MAIL EXCHANGER)<br>;############################################################<br>foobar.net. 86400 IN A 192.0.2.177<br> 86400 IN MX 0 mail.foobar.net.<br> 86400 IN MX 1 <i><backup MX></i>.</pre>
|
||
</div>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h2 align="left"><a name="StartingAndStopping"></a>7.0 Starting and Stopping
|
||
Your Firewall</h2>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The <a href="Install.htm">installation procedure </a> configures
|
||
your system to start Shorewall at system boot.</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_2.gif" width="13"
|
||
height="13">
|
||
<20><><EFBFBD> Edit the /etc/shorewall/routestopped file and configure those
|
||
systems that you want to be able to access the firewall when it is
|
||
stopped.</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="Documentation.htm#Configs">alternate configuration</a></i>
|
||
and test it using the <a href="Documentation.htm#Starting">"shorewall
|
||
try" command</a>.</p>
|
||
</div>
|
||
|
||
<p align="left"><font size="2">Last updated 3/21/2003 - <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></p>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
</body>
|
||
</html>
|