2003-01-14 21:32:45 +01:00
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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2002-08-07 16:28:04 +02:00
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<meta http-equiv="Content-Type"
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content="text/html; charset=windows-1252">
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<title>Shorewall NAT</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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2003-07-22 00:06:18 +02:00
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<br>
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2003-11-17 22:06:32 +01:00
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<h1 style="text-align: center;">Static NAT<br>
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</h1>
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<p><font color="#ff0000"><b>IMPORTANT: If all you want to do is forward
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ports to servers behind your firewall, you do NOT want to use static
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NAT. Port forwarding can be accomplished with simple entries in the <a
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href="Documentation.htm#Rules">rules file</a>.</b></font></p>
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<blockquote> </blockquote>
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<p>Static NAT is a way to make systems behind a firewall and configured
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with private IP addresses (those reserved for private use in RFC1918)
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appear to have public IP addresses. Before you try to use this
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technique, I strongly recommend that you read the <a
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href="shorewall_setup_guide.htm">Shorewall Setup Guide.</a></p>
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<blockquote> </blockquote>
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<p>The following figure represents a static NAT environment.</p>
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<blockquote>
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<p align="center"><strong> <img src="images/staticnat.png"
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width="435" height="397"> </strong></p>
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<blockquote> </blockquote>
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</blockquote>
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<p align="left">Static NAT can be used to make the systems with the
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10.1.1.* addresses appear to be on the upper (130.252.100.*) subnet. If
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we assume that the interface to the upper subnet is eth0, then the
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following /etc/shorewall/NAT file would make the lower left-hand system
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appear to have IP address 130.252.100.18 and the right-hand one to have
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IP address 130.252.100.19.</p>
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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>EXTERNAL</b></td>
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<td><b>INTERFACE</b></td>
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<td><b>INTERNAL</b></td>
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<td><b>ALL INTERFACES</b></td>
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<td><b>LOCAL</b></td>
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</tr>
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<tr>
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<td>130.252.100.18</td>
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<td>eth0</td>
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<td>10.1.1.2</td>
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<td>yes</td>
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<td>yes</td>
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</tr>
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<tr>
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<td>130.252.100.19</td>
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<td>eth0</td>
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<td>10.1.1.3</td>
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<td>yes</td>
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<td>yes</td>
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</tr>
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</tbody>
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</table>
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<p>Be sure that the internal system(s) (10.1.1.2 and 10.1.1.3 in the
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above example) is (are) not included in any specification in
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/etc/shorewall/masq or /etc/shorewall/proxyarp.</p>
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<p><a name="AllInterFaces"></a>Note 1: The "ALL INTERFACES" column is
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used to specify whether access to the external IP from all firewall
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interfaces should undergo NAT (Yes or yes) or if only access from the
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interface in the INTERFACE column should undergo NAT. If you leave this
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column empty, "Yes" is assumed. The ALL INTERFACES column was
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added in version 1.1.6.</p>
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<p>Note 2: Shorewall will automatically add the external address to the
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specified interface unless you specify <a
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href="Documentation.htm#Aliases">ADD_IP_ALIASES</a>="no" (or "No") in
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/etc/shorewall/shorewall.conf; If you do not set ADD_IP_ALIASES or
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if you set it to "Yes" or "yes" then you must NOT configure your own
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alias(es). <b>RESTRICTION: </b>Shorewall versions earlier than 1.4.6
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can only add external addresses to an interface that is configured with
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a single subnetwork -- if your external interface has addresses in more
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than one subnetwork,
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Shorewall 1.4.5 and earlier can only add addresses to the first one.</p>
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<p><a name="LocalPackets"></a>Note 3: The contents of the "LOCAL"
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column determine whether packets originating on the firewall itself and
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destined for the EXTERNAL address are redirected to the internal
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ADDRESS. If this column contains "yes" or "Yes" (and the ALL INTERFACES
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COLUMN
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also contains "Yes" or "yes") then such packets are redirected;
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otherwise,
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such packets are not redirected. The LOCAL column was added in version
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1.1.8.</p>
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<blockquote> </blockquote>
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<p><font size="2">Last updated 7/6/2003 - </font><font size="2"> <a
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href="support.htm">Tom Eastep</a></font> </p>
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<a href="copyright.htm"><font size="2">Copyright</font> <20> <font
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size="2">2001, 2002, 2003 Thomas M. Eastep.</font></a><br>
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2003-11-17 22:06:32 +01:00
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<br>
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<br>
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2003-01-14 21:32:45 +01:00
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</body>
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</html>
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