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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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2003-03-18 16:16:33 +01:00
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<meta http-equiv="Content-Type"
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content="text/html; charset=windows-1252">
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<title>GRE/IPIP Tunnels</title>
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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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2002-08-07 16:28:04 +02:00
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</head>
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2003-11-17 22:06:32 +01:00
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<body>
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<h1 style="text-align: center;">GRE and IPIP Tunnels<br>
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</h1>
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<h3><font color="#ff6633">Warning: </font>GRE and IPIP Tunnels are
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insecure when used over the internet; use them at your own risk</h3>
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<p>GRE and IPIP tunneling with Shorewall can be used to bridge two
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masqueraded networks.</p>
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<p>The simple scripts described in the <a href="http://ds9a.nl/lartc">Linux
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Advanced Routing and Shaping HOWTO</a> work fine with Shorewall.
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Shorewall also includes a tunnel script for automating tunnel
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configuration. If you have installed the RPM, the tunnel script may be
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found in the Shorewall documentation directory (usually
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/usr/share/doc/shorewall-<version>/).</p>
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<h2>Bridging two Masqueraded Networks</h2>
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<p>Suppose that we have the following situation:</p>
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<p align="center"> <img border="0" src="images/TwoNets1.png"
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width="745" height="427"> </p>
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<p align="left">We want systems in the 192.168.1.0/24 subnetwork to be
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able to communicate with the systems in the 10.0.0.0/8 network. This is
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accomplished through use of the /etc/shorewall/tunnels file, the
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/etc/shorewall/policy file and the /etc/shorewall/tunnel script that is
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included with Shorewall.</p>
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<p align="left">The 'tunnel' script is not installed in /etc/shorewall
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by default -- If you install using the tarball, the script is included
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in the tarball; if you install using the RPM, the file is in your
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Shorewall documentation directory (normally
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/usr/share/doc/shorewall-<version>).</p>
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<p align="left">In the /etc/shorewall/tunnel script, set the
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'tunnel_type' parameter to the type of tunnel that you want to create.</p>
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<p align="left">Example:</p>
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<blockquote>
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<p align="left">tunnel_type=gre</p>
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</blockquote>
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<p align="left">On each firewall, you will need to declare a zone to
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represent the remote subnet. We'll assume that this zone is called
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'vpn' and declare it in /etc/shorewall/zones on both systems as follows.</p>
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<blockquote>
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<table border="2" cellpadding="2" style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><strong>ZONE</strong></td>
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<td><strong>DISPLAY</strong></td>
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<td><strong>COMMENTS</strong></td>
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</tr>
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<tr>
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<td>vpn</td>
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<td>VPN</td>
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<td>Remote Subnet</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 align="left">On system A, the 10.0.0.0/8 will comprise the <b>vpn</b>
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zone.
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In /etc/shorewall/interfaces:</p>
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<blockquote>
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<table border="2" cellpadding="2" style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><b>ZONE</b></td>
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<td><b>INTERFACE</b></td>
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<td><b>BROADCAST</b></td>
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<td><b>OPTIONS</b></td>
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</tr>
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<tr>
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<td>vpn</td>
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<td>tosysb</td>
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<td>10.255.255.255</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<p align="left">In /etc/shorewall/tunnels on system A, we need the
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following:</p>
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<blockquote>
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<table border="2" cellpadding="2" style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><b>TYPE</b></td>
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<td><b>ZONE</b></td>
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<td><b>GATEWAY</b></td>
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<td><b>GATEWAY ZONE</b></td>
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</tr>
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<tr>
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<td>ipip</td>
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<td>net</td>
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<td>134.28.54.2</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<p>This entry in /etc/shorewall/tunnels, opens the firewall so that the
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IP encapsulation protocol (4) will be accepted to/from the remote
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gateway.</p>
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<p>In the tunnel script on system A:</p>
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<blockquote>
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<p>tunnel=tosysb<br>
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myrealip=206.161.148.9 (for GRE tunnel only)<br>
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myip=192.168.1.1<br>
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hisip=10.0.0.1<br>
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gateway=134.28.54.2<br>
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subnet=10.0.0.0/8</p>
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</blockquote>
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<p>Similarly, On system B the 192.168.1.0/24 subnet will comprise the <b>vpn</b>
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zone. In /etc/shorewall/interfaces:</p>
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<blockquote>
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<table border="2" cellpadding="2" style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><b>ZONE</b></td>
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<td><b>INTERFACE</b></td>
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<td><b>BROADCAST</b></td>
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<td><b>OPTIONS</b></td>
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</tr>
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<tr>
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<td>vpn</td>
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<td>tosysa</td>
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<td>192.168.1.255</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<p>In /etc/shorewall/tunnels on system B, we have:</p>
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<blockquote>
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<table border="2" cellpadding="2" style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><b>TYPE</b></td>
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<td><b>ZONE</b></td>
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<td><b>GATEWAY</b></td>
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<td><b>GATEWAY ZONE</b></td>
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</tr>
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<tr>
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<td>ipip</td>
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<td>net</td>
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<td>206.191.148.9</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<p>And in the tunnel script on system B:</p>
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<blockquote>
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<p>tunnel=tosysa<br>
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myrealip=134.28.54.2 (for GRE tunnel only)<br>
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myip=10.0.0.1<br>
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hisip=192.168.1.1<br>
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gateway=206.191.148.9<br>
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subnet=192.168.1.0/24</p>
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</blockquote>
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<p>You can rename the modified tunnel scripts if you like; be sure that
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they are secured so that root can execute them. </p>
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<p align="left"> You will need to allow traffic between the "vpn" zone
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and the "loc" zone on both systems -- if you simply want to admit all
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traffic in both directions, you can use the policy file:</p>
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<blockquote>
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<table border="2" cellpadding="2" style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><strong>SOURCE</strong></td>
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<td><strong>DEST</strong></td>
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<td><strong>POLICY</strong></td>
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<td><strong>LOG LEVEL</strong></td>
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</tr>
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<tr>
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<td>loc</td>
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<td>vpn</td>
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<td>ACCEPT</td>
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<td> </td>
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</tr>
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<tr>
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<td>vpn</td>
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<td>loc</td>
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<td>ACCEPT</td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<p>On both systems, restart Shorewall and run the modified tunnel
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script with
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the "start" argument on each system. The systems in the two masqueraded
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subnetworks
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can now talk to each other</p>
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<p><font size="2">Updated 2/22/2003 - <a href="support.htm">Tom Eastep</a>
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</font></p>
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<p><a href="copyright.htm"><font size="2">Copyright</font> <20> <font
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size="2">2001, 2002, 2003Thomas M. Eastep.</font></a></p>
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<br>
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<br>
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</body>
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</html>
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