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87 lines
3.8 KiB
HTML
87 lines
3.8 KiB
HTML
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<html>
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<head>
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<meta http-equiv="Content-Type" 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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<meta name="Microsoft Theme" content="boldstri 011, default">
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</head>
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<body>
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<blockquote>
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<h1 align="center">Static NAT</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 NAT.
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Port forwarding can be accomplished with simple entries in the
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<a href="Documentation.htm#Rules">rules file</a>.</b></font></p>
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<p>Static NAT is a way to make systems behind a
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firewall and configured with private IP addresses (those
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reserved for private use in RFC1918) appear to have public IP
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addresses.</p>
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<p>The following figure represents a static NAT
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environment.</p>
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<p align="center"><strong>
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<img src="images/staticnat.png" width="435" height="397"></strong></p>
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<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 we
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assume that the interface to the upper subnet is eth0, then the following
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/etc/shorewall/NAT file would make the lower left-hand system appear to have
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IP address 130.252.100.18 and the right-hand one to have IP address
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130.252.100.19.</p>
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<table border="2" cellpadding="2" style="border-collapse: collapse">
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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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</table>
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<p>Be sure that the internal system(s) (10.1.1.2 and 10.1.1.3 in the above
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example) is (are) not included in any specification in /etc/shorewall/masq
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or /etc/shorewall/proxyarp.</p>
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<p><a name="AllInterFaces"></a>Note 1: The "ALL INTERFACES" column
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is 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 href="Documentation.htm#Aliases">ADD_IP_ALIASES</a>="no"
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(or "No") in /etc/shorewall/shorewall.conf; If you do not set
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ADD_IP_ALIASES or if you set it to "Yes" or "yes" then you must NOT configure your own alias(es).</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 ADDRESS. If
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this column contains "yes" or "Yes" (and the ALL
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INTERFACES COLUMN also contains "Yes" or "yes") then
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such packets are redirected; otherwise, such packets are not redirected. The
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LOCAL column was added in version 1.1.8.</p>
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</blockquote>
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<blockquote>
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</blockquote>
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<p><font size="2">Last updated 3/27/2002 - </font><font size="2">
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<a href="support.htm">Tom
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Eastep</a></font> </p>
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<font face="Trebuchet MS"><a href="copyright.htm"><font size="2">Copyright</font>
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<EFBFBD> <font size="2">2001, 2002 Thomas M. Eastep.</font></a></font></body></html>
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