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shorewall_code/docs/whitelisting_under_shorewall.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<!-- $Id$ -->
<article id="whitelisting_under_shorewall">
<articleinfo>
<title>Whitelisting Under Shorewall</title>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2002-2005</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<legalnotice>
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version
1.2 or any later version published by the Free Software Foundation; with
no Invariant Sections, with no Front-Cover, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
<quote><ulink type="" url="copyright.htm">GNU Free Documentation
License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<para>White lists are most often used to give special privileges to a set of
hosts within an organization. Let us suppose that we have the following
environment:</para>
<itemizedlist mark="bullet" spacing="compact">
<listitem>
<para>A firewall with three interfaces -- one to the Internet, one to a
local network and one to a <acronym>DMZ</acronym>.</para>
</listitem>
<listitem>
<para>The local network uses <acronym>SNAT</acronym> to the Internet and
is comprised of the Class B network <literal>10.10.0.0/16</literal>
(Note: While this example uses an RFC 1918 local network, the technique
described here in no way depends on that or on <acronym>SNAT</acronym>.
It may be used with Proxy <acronym>ARP</acronym>, Subnet Routing, Static
NAT, etc.).</para>
</listitem>
<listitem>
<para>The network operations staff have workstations with IP addresses
in the Class C network <literal>10.10.10.0/24</literal>.</para>
</listitem>
<listitem>
<para>We want the network operations staff to have full access to all
other hosts.</para>
</listitem>
<listitem>
<para>We want the network operations staff to bypass the transparent
<acronym>HTTP</acronym> proxy running on our firewall.</para>
</listitem>
</itemizedlist>
<para>The basic approach will be that we will place the operations staff's
class C in its own zone called ops. Here are the appropriate configuration
files:</para>
<!-- Zone File -->
<bridgehead renderas="sect4">Zone File</bridgehead>
<programlisting>#ZONE TYPE OPTIONS
fw firewall
net ipv4
ops ipv4
loc ipv4
dmz ipv4</programlisting>
<para>The <literal>ops</literal> zone has been added to the standard 3-zone
zones file -- since <literal>ops</literal> is a sub-zone of
<literal>loc</literal>, we list it <emphasis>BEFORE</emphasis>
<literal>loc</literal>.</para>
<!-- Interfaces File -->
<bridgehead renderas="sect4">Interfaces File</bridgehead>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
net eth0 &lt;whatever&gt; ...
dmz eth1 &lt;whatever&gt; ...
- eth2 10.10.255.255</programlisting>
<para>Because <literal>eth2</literal> interfaces to two zones
(<literal>ops</literal> and <literal>loc</literal>), we don't specify a zone
for it here.</para>
<!-- Hosts File -->
<bridgehead renderas="sect4">Hosts File</bridgehead>
<programlisting>#ZONE HOST(S) OPTIONS
ops eth2:10.10.10.0/24
loc eth2:0.0.0.0/0</programlisting>
<para>Here we define the <literal>ops</literal> and <literal>loc</literal>
zones. When Shorewall is stopped, only the hosts in the
<literal>ops</literal> zone will be allowed to access the firewall and the
<acronym>DMZ</acronym>. I use <literal>0.0.0.0/0</literal> to define the
<literal>loc</literal> zone rather than <literal>10.10.0.0/16</literal> so
that the limited broadcast address (<literal>255.255.255.255</literal>)
falls into that zone. If I used <literal>10.10.0.0/16</literal> then I would
have to have a separate entry for that special address.</para>
<!-- Policy File -->
<bridgehead renderas="sect4">Policy File</bridgehead>
<programlisting>#SOURCE DEST POLICY LOG LEVEL
<emphasis role="bold">ops all ACCEPT
all ops CONTINUE</emphasis>
loc net ACCEPT
net all DROP info
all all REJECT info</programlisting>
<para>Two entries for <literal>ops</literal> (in bold) have been added to
the standard 3-zone policy file.</para>
<!-- Rules File -->
<bridgehead renderas="sect4">Rules File</bridgehead>
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE PORTS(S) ORIGINAL DEST
REDIRECT loc!ops 3128 tcp http</programlisting>
<para>This is the rule that transparently redirects web traffic to the
transparent proxy running on the firewall. The <emphasis
role="bold">SOURCE</emphasis> column explicitly excludes the
<literal>ops</literal> zone from the rule.</para>
<!-- Routestopped File -->
<bridgehead renderas="sect4">Routestopped File</bridgehead>
<programlisting>#INTERFACE HOST(S) OPTIONS
eth1
eth2 10.10.10.0/24</programlisting>
</article>