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330 lines
12 KiB
XML
330 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article id="Multiple_Zones">
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<!--$Id$-->
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<articleinfo>
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<title>Routing on One Interface</title>
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<authorgroup>
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<author>
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<firstname>Tom</firstname>
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<surname>Eastep</surname>
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</author>
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</authorgroup>
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<pubdate>2004-02-07</pubdate>
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<copyright>
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<year>2003</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled
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<quote><ulink url="GnuCopyright.htm">GNU Free Documentation License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<section>
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<title>Introduction</title>
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<para>While most configurations can be handled with each of the
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firewall's network interfaces assigned to a single zone, there are
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cases where you will want to divide the hosts accessed through an
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interface between two or more zones.</para>
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<itemizedlist>
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<listitem>
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<para>The interface has multiple addresses on multiple subnetworks.
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This case is covered in the <ulink
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url="Shorewall_and_Aliased_Interfaces.html">Aliased Interface
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documentation</ulink>.</para>
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</listitem>
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<listitem>
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<para>You are using some form of NAT and want to access a server by
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its external IP address from the same LAN segment. This is covered in
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<ulink url="FAQ.htm#faq2">FAQs 2 and 2a</ulink>.</para>
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</listitem>
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<listitem>
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<para>There are routers accessible through the interface and you want
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to treat the networks accessed through that router as a separate zone.</para>
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</listitem>
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<listitem>
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<para>Some of the hosts accessed through an interface have
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significantly different firewalling requirements from the others so
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you want to assign them to a different zone.</para>
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</listitem>
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</itemizedlist>
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<para>The key points to keep in mind when setting up multiple zones per
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interface are:</para>
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<itemizedlist>
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<listitem>
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<para>Shorewall generates rules for zones in the order that the zone
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declarations appear in /etc/shorewall/zones.</para>
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</listitem>
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<listitem>
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<para>The order of entries in /etc/shorewall/hosts is immaterial as
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far as the generated ruleset is concerned.</para>
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</listitem>
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</itemizedlist>
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<para><emphasis role="bold">These examples use the local zone but the same
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technique works for any zone.</emphasis> Remember that Shorewall
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doesn't have any conceptual knowledge of <quote>Internet</quote>,
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<quote>Local</quote>, or <quote>DMZ</quote> so all zones except the
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firewall itself ($FW) are the same as far as Shorewall is concerned. Also,
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the examples use private (RFC 1918) addresses but public IP addresses can
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be used in exactly the same way.</para>
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</section>
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<section>
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<title>Router in the Local Zone</title>
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<para>Here is an example of a router in the local zone.</para>
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<note>
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<para>the <emphasis role="bold">box called <quote>Router</quote> could
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be a VPN server</emphasis> or other such device; from the point of view
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of this discussion, it makes no difference.</para>
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</note>
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<graphic fileref="images/MultiZone1.png" />
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<section>
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<title>Can You Use the Standard Configuration?</title>
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<para>In many cases, the <ulink url="two-interface.htm">standard
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two-interface Shorewall setup</ulink> will work fine in this
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configuration. It will work if:</para>
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<itemizedlist>
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<listitem>
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<para>The firewall requirements to/from the internet are the same
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for 192.168.1.0/24 and 192.168.2.0/24.</para>
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</listitem>
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<listitem>
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<para>The hosts in 192.168.1.0/24 know that the route to
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192.168.2.0/24 is through the <emphasis role="bold">router</emphasis>.</para>
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</listitem>
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</itemizedlist>
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<para>All you have to do on the firewall is add a route to
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192.168.2.0/24 through the <emphasis role="bold">router</emphasis> and
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restart Shorewall.</para>
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</section>
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<section>
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<title>Will One Zone be Enough?</title>
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<para>If the firewalling requirements for the two local networks is the
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same but the hosts in 192.168.1.0/24 don't know how to route to
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192.168.2.0/24 then you need to configure the firewall slightly
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differently. This type of configuration is rather stupid from an IP
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networking point of view but it is sometimes necessary because you
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simply don't want to have to reconfigure all of the hosts in
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192.168.1.0/24 to add a persistent route to 192.168.2.0/24. On the
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firewall:</para>
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<orderedlist>
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<listitem>
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<para>Add a route to 192.168.2.0/24 through the <emphasis
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role="bold">Router</emphasis>.</para>
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</listitem>
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<listitem>
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<para>Set the <quote>routeback</quote> and <quote>newnotsyn</quote>
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options for eth1 (the local firewall interface) in
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/etc/shorewall/interfaces.</para>
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</listitem>
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<listitem>
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<para>Restart Shorewall.</para>
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</listitem>
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</orderedlist>
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</section>
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<section>
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<title>I Need Separate Zones</title>
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<para>If you need to make 192.168.2.0/24 into it's own zone, you can
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do it one of two ways; Nested Zones or Parallel Zones.</para>
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<section>
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<title>Nested Zones</title>
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<para>You can define one zone (called it <quote>loc</quote>) as being
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all hosts connectied to eth1 and a second zone <quote>loc1</quote>
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(192.168.2.0/24) as a sub-zone.</para>
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<graphic fileref="images/MultiZone1A.png" />
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<para>The advantage of this approach is that the zone <quote>loc1</quote>
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can use CONTINUE policies such that if a connection request
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doesn't match a <quote>loc1</quote> rule, it will be matched
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against the <quote>loc</quote> rules. For example, if your
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loc1->net policy is CONTINUE then if a connection request from
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loc1 to the internet doesn't match any rules for loc1->net
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then it will be checked against the loc->net rules.</para>
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<para><filename>/etc/shorewall/zones</filename></para>
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<programlisting>#ZONE DISPLAY COMMENTS
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loc1 Local1 Hosts accessed through internal router
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loc Local All hosts accessed via eth1</programlisting>
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<note>
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<para>the sub-zone (loc1) is defined first!</para>
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</note>
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<para><filename>/etc/shorewall/interfaces</filename></para>
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<programlisting>#ZONE INTERFACE BROADCAST
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loc eth1 192.168.1.255</programlisting>
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<para><filename>/etc/shorewall/hosts</filename></para>
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<programlisting>#ZONE HOSTS
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loc1 eth1:192.168.2.0/24</programlisting>
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<para>If you don't need Shorewall to set up infrastructure to
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route traffic between <quote>loc</quote> and <quote>loc1</quote>, add
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these two policies.</para>
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<para>/etc/shorewall/policy</para>
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<programlisting>#SOURCE DEST POLICY
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loc loc1 NONE
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loc1 loc NONE</programlisting>
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</section>
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<section>
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<title>Parallel Zones</title>
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<para>You define both zones in the /etc/shorewall/hosts file to create
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two disjoint zones.</para>
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<graphic fileref="images/MultiZone1B.png" />
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<para><filename>/etc/shorewall/zones</filename></para>
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<programlisting>#ZONE DISPLAY COMMENTS
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loc1 Local1 Hosts accessed Directly from Firewall
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loc2 Local2 Hosts accessed via the internal Router</programlisting>
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<note>
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<para>Here it doesn't matter which zone is defined first.</para>
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</note>
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<para><filename>/etc/shorewall/interfaces</filename></para>
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<programlisting>#ZONE INTERFACE BROADCAST
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- eth1 192.168.1.255</programlisting>
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<para><filename>/etc/shorewall/hosts</filename></para>
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<programlisting>#ZONE HOSTS
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loc1 eth1:192.168.1.0/24
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loc2 eth1:192.168.2.0/24</programlisting>
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<para>You don't need Shorewall to set up infrastructure to route
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traffic between <quote>loc</quote> and <quote>loc1</quote>, so add
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these two policies:</para>
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<programlisting>#SOURCE DEST POLICY
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loc1 loc2 NONE
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loc2 loc1 NONE</programlisting>
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</section>
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</section>
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</section>
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<section>
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<title>Some Hosts have Special Firewalling Requirements</title>
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<para>There are cases where a subset of the addresses associated with an
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interface need special handling. Here's an example.</para>
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<graphic fileref="images/MultiZone2.png" />
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<para>In this example, addresses 192.168.1.8 - 192.168.1.15
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(192.168.1.8/29) are to be treated as their own zone (loc1).</para>
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<para><filename>/etc/shorewall/zones</filename></para>
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<programlisting>#ZONE DISPLAY COMMENTS
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loc1 Local1 192.168.1.8-192.168.1.15
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loc Local All hosts accessed via eth1</programlisting>
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<note>
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<para>the sub-zone (loc1) is defined first!</para>
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</note>
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<para><filename>/etc/shorewall/interfaces</filename></para>
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<programlisting>#ZONE INTERFACE BROADCAST
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loc eth1 192.168.1.255</programlisting>
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<para><filename>/etc/shorewall/hosts</filename><programlisting>#ZONE HOSTS
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loc1 eth1:192.168.1.8/29</programlisting></para>
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<para>You probably don't want Shorewall to set up infrastructure to
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route traffic between <quote>loc</quote> and <quote>loc1</quote> so you
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should add these two policies.</para>
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<para><filename>/etc/shorewall/policy</filename></para>
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<programlisting>#SOURCE DEST POLICY
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loc loc1 NONE
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loc1 loc NONE</programlisting>
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</section>
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<section id="OneArmed">
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<title>One-armed Router</title>
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<para>Nested zones may also be used to configure a <quote>one-armed</quote>
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router (I don't call it a <quote>firewall</quote> because it is very
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insecure. For example, if you connect to the internet via cable modem,
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your next door neighbor has full access to your local systems as does
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everyone else connected to the same cable modem head-end controller). Here
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eth0 is configured with both a public IP address and an RFC 1918 address
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(More on that topic may be found <ulink
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url="Shorewall_and_Aliased_Interfaces.html">here</ulink>). Hosts in the
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<quote>loc</quote> zone are configured with their default gateway set to
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the Shorewall router's RFC1918 address.<graphic
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fileref="images/MultiZone3.png" /></para>
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<para><filename>/etc/shorewall/zones</filename></para>
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<programlisting>#ZONE DISPLAY COMMENTS
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loc Local Local Zone
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net Internet The big bad Internet</programlisting>
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<note>
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<para>the sub-zone (loc) is defined first!</para>
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</note>
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<para><filename>/etc/shorewall/interfaces</filename></para>
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<programlisting>#ZONE INTERFACE BROADCAST
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net eth0 detect</programlisting>
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<para><filename>/etc/shorewall/hosts</filename></para>
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<programlisting>#ZONE HOSTS
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loc eth0:192.168.1.0/24</programlisting>
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</section>
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</article> |