2003-01-14 18:18:42 +01:00
|
|
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
2002-08-13 22:45:21 +02:00
|
|
|
|
<html>
|
|
|
|
|
|
<head>
|
2003-01-14 18:18:42 +01:00
|
|
|
|
<meta http-equiv="Content-Type"
|
|
|
|
|
|
content="text/html; charset=windows-1252">
|
|
|
|
|
|
<title>Shorewall NAT</title>
|
|
|
|
|
|
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
|
|
|
|
|
|
<meta name="ProgId" content="FrontPage.Editor.Document">
|
2002-08-13 22:45:21 +02:00
|
|
|
|
</head>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<body>
|
2003-07-16 20:59:33 +02:00
|
|
|
|
<br>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<h1 style="text-align: center;">One-to-one NAT<br>
|
|
|
|
|
|
</h1>
|
|
|
|
|
|
<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
|
|
|
|
|
|
one-to-one 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>One-to-one NAT is a way to make systems behind a firewall and
|
|
|
|
|
|
configured
|
|
|
|
|
|
with private IP addresses (those reserved for private use in RFC 1918)
|
|
|
|
|
|
appear to have public IP addresses. Before you try to use this
|
|
|
|
|
|
technique, I strongly recommend that you read the <a
|
2003-01-14 18:18:42 +01:00
|
|
|
|
href="shorewall_setup_guide.htm">Shorewall Setup Guide.</a></p>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<blockquote> </blockquote>
|
|
|
|
|
|
<p>The following figure represents a one-to-one NAT environment.</p>
|
|
|
|
|
|
<blockquote>
|
|
|
|
|
|
<p align="center"><strong> <img src="images/staticnat.png"
|
|
|
|
|
|
style="width: 456px; height: 397px;" title="" alt=""> </strong></p>
|
|
|
|
|
|
<blockquote> </blockquote>
|
|
|
|
|
|
</blockquote>
|
|
|
|
|
|
<p align="left">One-to-one 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>
|
2003-07-16 20:59:33 +02:00
|
|
|
|
<table border="2" cellpadding="2" style="border-collapse: collapse;">
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<tbody>
|
|
|
|
|
|
<tr>
|
|
|
|
|
|
<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>
|
|
|
|
|
|
</tr>
|
|
|
|
|
|
<tr>
|
|
|
|
|
|
<td>130.252.100.18</td>
|
|
|
|
|
|
<td>eth0</td>
|
|
|
|
|
|
<td>10.1.1.2</td>
|
|
|
|
|
|
<td>yes</td>
|
|
|
|
|
|
<td>yes</td>
|
|
|
|
|
|
</tr>
|
|
|
|
|
|
<tr>
|
|
|
|
|
|
<td>130.252.100.19</td>
|
|
|
|
|
|
<td>eth0</td>
|
|
|
|
|
|
<td>10.1.1.3</td>
|
|
|
|
|
|
<td>yes</td>
|
|
|
|
|
|
<td>yes</td>
|
|
|
|
|
|
</tr>
|
|
|
|
|
|
</tbody>
|
2003-07-16 20:59:33 +02:00
|
|
|
|
</table>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<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. <span style="font-weight: bold;">Specifying
|
|
|
|
|
|
"Yes" in this column will </span><span
|
|
|
|
|
|
style="text-decoration: underline; font-weight: bold;">not</span><span
|
|
|
|
|
|
style="font-weight: bold;"> allow systems on the lower LAN to access
|
|
|
|
|
|
each other using their public IP addresses.</span> For example, the
|
|
|
|
|
|
lower left-hand system (10.1.1.2) cannot connect to 130.252.100.19 and
|
|
|
|
|
|
expect to be connected to the lower right-hand system. <a
|
|
|
|
|
|
href="FAQ.htm#faq2a">See FAQ 2a</a>.<br>
|
|
|
|
|
|
</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,
|
2003-07-07 16:18:52 +02:00
|
|
|
|
Shorewall 1.4.5 and earlier can only add addresses to the first one.</p>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<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
|
2003-07-07 16:18:52 +02:00
|
|
|
|
1.1.8.</p>
|
2003-01-14 18:18:42 +01:00
|
|
|
|
<blockquote> </blockquote>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<p><font size="2">Last updated 11/222003 - </font><font size="2"> <a
|
2003-01-14 18:18:42 +01:00
|
|
|
|
href="support.htm">Tom Eastep</a></font> </p>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<a href="copyright.htm"><font size="2">Copyright</font> <20> <font
|
2003-01-14 18:18:42 +01:00
|
|
|
|
size="2">2001, 2002, 2003 Thomas M. Eastep.</font></a><br>
|
2003-12-03 00:51:46 +01:00
|
|
|
|
<br>
|
|
|
|
|
|
<br>
|
2003-01-14 18:18:42 +01:00
|
|
|
|
</body>
|
|
|
|
|
|
</html>
|
