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