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361 lines
14 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/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><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2003-2005</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
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 4.3 and
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later. If you are running a version of Shorewall earlier than Shorewall
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4.3.5 then please see the documentation for that
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release.</emphasis></para>
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</caution>
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<section id="Intro">
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<title>Introduction</title>
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<para>While most configurations can be handled with each of the firewall's
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network interfaces assigned to a single zone, there are cases where you
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will want to divide the hosts accessed through an interface between two or
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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
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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 unless you modify the
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processing order using the explicit
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<emphasis>child-zone</emphasis>:<emphasis>parent-zone</emphasis>
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syntax, in which case the child zone rules are generated first.</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 rule set 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 doesn't
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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 id="Router">
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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 id="Standard">
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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
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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 id="Enough">
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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> option for eth1 (the local
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firewall interface) in /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 id="Separate">
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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 its own zone, you can do
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it one of two ways; Nested Zones or Parallel Zones.</para>
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<section id="Nested">
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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 connected 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><note>
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<para>The Router in the above diagram is assumed to NOT be doing
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SNAT for the hosts in the 192.168.2.0/24 network.</para>
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</note>The advantage of this approach is that the zone
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<quote>loc1</quote> can use CONTINUE policies such that if a
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connection request doesn't match a <quote>loc1</quote> rule, it will
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be matched 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 loc1
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to the Internet doesn't match any rules for loc1->net then it will
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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 TYPE OPTIONS
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loc ipv4
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loc1:loc ipv4</programlisting>
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<note>
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<para>the Parent zone (loc) is defined first then the sub-zone
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(loc1) is defined using the special syntax shown.</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 OPTIONS
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loc eth1 -</programlisting>
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<para><filename>/etc/shorewall/hosts</filename></para>
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<programlisting>#ZONE HOSTS OPTIONS
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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 route
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traffic between <quote>loc</quote> and <quote>loc1</quote>, add these
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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 id="Parallel">
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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><note>
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<para>The Router in the above diagram is assumed to NOT be doing
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SNAT for the hosts in the 192.168.2.0/24 network.</para>
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</note><filename>/etc/shorewall/zones</filename></para>
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<programlisting>#ZONE TYPE OPTIONS
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loc1 ipv4
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loc2 ipv4</programlisting>
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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
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</programlisting>
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<para><filename>/etc/shorewall/hosts</filename></para>
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<programlisting>#ZONE HOSTS OPTIONS
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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 id="Special">
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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 TYPE OPTIONS
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loc ipv4
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loc1:loc ipv4</programlisting>
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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 -</programlisting>
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<para><filename>/etc/shorewall/hosts</filename><programlisting>#ZONE HOSTS OPTIONS
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loc1 eth1:192.168.1.8/29 broadcast</programlisting></para>
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<para>The <option>broadcast</option> option causes limited broadcasts
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(destination IP address 255.255.255.255) to be checked against the loc1
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zone. If that zone allows the packet, then of course it will be seen by
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the mempers of loc that are outside of loc1 as well. If the broadcast is
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not specifically DROPped by the fw->loc1 rules then it will also be
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checked against the fw->loc rules, even if there is a DROP or REJECT
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fw->loc1 policy.</para>
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<para>You probably don't want Shorewall to set up infrastructure to route
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traffic between <quote>loc</quote> and <quote>loc1</quote> so you should
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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
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<quote>one-armed</quote> router (I don't call it a <quote>firewall</quote>
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because it is very insecure. For example, if you connect to the Internet
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via cable modem, your next door neighbor has full access to your local
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systems as does everyone else connected to the same cable modem head-end
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controller). Here eth0 is configured with both a public IP address and an
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RFC 1918 address (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.</para>
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<para><graphic fileref="images/MultiZone3.png" /></para>
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<para><filename>/etc/shorewall/zones</filename></para>
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<programlisting>#ZONE TYPE OPTIONS
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net ipv4
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loc:net ipv4</programlisting>
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<para><filename>/etc/shorewall/interfaces</filename></para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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net eth0 detect routefilter</programlisting>
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<para><filename>/etc/shorewall/hosts</filename></para>
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<programlisting>#ZONE HOSTS OPTIONS
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loc eth0:192.168.1.0/24 maclist</programlisting>
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<para><filename><filename>/etc/shorewall/masq</filename></filename></para>
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<programlisting>#INTERFACE SOURCE ADDRESS
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eth0:!192.168.1.0/24 192.168.1.0/24</programlisting>
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<para>Note that the <emphasis role="bold">maclist</emphasis> option is
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specified in <filename>/etc/shorewall/interfaces</filename>. This is to
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help protect your router from unauthorized access by your friends and
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neighbors. Start without <emphasis role="bold">maclist</emphasis> then add
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it and configure your <ulink
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url="MAC_Validation.html"><filename>/etc/shorewall/maclist</filename></ulink>
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file when everything else is working.</para>
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</section>
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</article>
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