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<article id="Multiple_Zones">
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<articleinfo>
<title>Routing on One Interface</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate>2004-03-15</pubdate>
<copyright>
<year>2003</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 url="GnuCopyright.htm">GNU Free Documentation License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<section>
<title>Introduction</title>
<para>While most configurations can be handled with each of the
firewall's network interfaces assigned to a single zone, there are
cases where you will want to divide the hosts accessed through an
interface between two or more zones.</para>
<itemizedlist>
<listitem>
<para>The interface has multiple addresses on multiple subnetworks.
This case is covered in the <ulink
url="Shorewall_and_Aliased_Interfaces.html">Aliased Interface
documentation</ulink>.</para>
</listitem>
<listitem>
<para>You are using some form of NAT and want to access a server by
its external IP address from the same LAN segment. This is covered in
<ulink url="FAQ.htm#faq2">FAQs 2 and 2a</ulink>.</para>
</listitem>
<listitem>
<para>There are routers accessible through the interface and you want
to treat the networks accessed through that router as a separate zone.</para>
</listitem>
<listitem>
<para>Some of the hosts accessed through an interface have
significantly different firewalling requirements from the others so
you want to assign them to a different zone.</para>
</listitem>
</itemizedlist>
<para>The key points to keep in mind when setting up multiple zones per
interface are:</para>
<itemizedlist>
<listitem>
<para>Shorewall generates rules for zones in the order that the zone
declarations appear in /etc/shorewall/zones.</para>
</listitem>
<listitem>
<para>The order of entries in /etc/shorewall/hosts is immaterial as
far as the generated ruleset is concerned.</para>
</listitem>
</itemizedlist>
<para><emphasis role="bold">These examples use the local zone but the same
technique works for any zone.</emphasis> Remember that Shorewall
doesn't have any conceptual knowledge of <quote>Internet</quote>,
<quote>Local</quote>, or <quote>DMZ</quote> so all zones except the
firewall itself ($FW) are the same as far as Shorewall is concerned. Also,
the examples use private (RFC 1918) addresses but public IP addresses can
be used in exactly the same way.</para>
</section>
<section>
<title>Router in the Local Zone</title>
<para>Here is an example of a router in the local zone.</para>
<note>
<para>the <emphasis role="bold">box called <quote>Router</quote> could
be a VPN server</emphasis> or other such device; from the point of view
of this discussion, it makes no difference.</para>
</note>
<graphic fileref="images/MultiZone1.png" />
<section>
<title>Can You Use the Standard Configuration?</title>
<para>In many cases, the <ulink url="two-interface.htm">standard
two-interface Shorewall setup</ulink> will work fine in this
configuration. It will work if:</para>
<itemizedlist>
<listitem>
<para>The firewall requirements to/from the internet are the same
for 192.168.1.0/24 and 192.168.2.0/24.</para>
</listitem>
<listitem>
<para>The hosts in 192.168.1.0/24 know that the route to
192.168.2.0/24 is through the <emphasis role="bold">router</emphasis>.</para>
</listitem>
</itemizedlist>
<para>All you have to do on the firewall is add a route to
192.168.2.0/24 through the <emphasis role="bold">router</emphasis> and
restart Shorewall.</para>
</section>
<section>
<title>Will One Zone be Enough?</title>
<para>If the firewalling requirements for the two local networks is the
same but the hosts in 192.168.1.0/24 don't know how to route to
192.168.2.0/24 then you need to configure the firewall slightly
differently. This type of configuration is rather stupid from an IP
networking point of view but it is sometimes necessary because you
simply don't want to have to reconfigure all of the hosts in
192.168.1.0/24 to add a persistent route to 192.168.2.0/24. On the
firewall:</para>
<orderedlist>
<listitem>
<para>Add a route to 192.168.2.0/24 through the <emphasis
role="bold">Router</emphasis>.</para>
</listitem>
<listitem>
<para>Set the <quote>routeback</quote> and <quote>newnotsyn</quote>
options for eth1 (the local firewall interface) in
/etc/shorewall/interfaces.</para>
</listitem>
<listitem>
<para>Restart Shorewall.</para>
</listitem>
</orderedlist>
</section>
<section>
<title>I Need Separate Zones</title>
<para>If you need to make 192.168.2.0/24 into it's own zone, you can
do it one of two ways; Nested Zones or Parallel Zones.</para>
<section>
<title>Nested Zones</title>
<para>You can define one zone (called it <quote>loc</quote>) as being
all hosts connectied to eth1 and a second zone <quote>loc1</quote>
(192.168.2.0/24) as a sub-zone.</para>
<graphic fileref="images/MultiZone1A.png" />
<para>The advantage of this approach is that the zone <quote>loc1</quote>
can use CONTINUE policies such that if a connection request
doesn't match a <quote>loc1</quote> rule, it will be matched
against the <quote>loc</quote> rules. For example, if your
loc1->net policy is CONTINUE then if a connection request from
loc1 to the internet doesn't match any rules for loc1->net
then it will be checked against the loc->net rules.</para>
<para><filename>/etc/shorewall/zones</filename></para>
<programlisting>#ZONE DISPLAY COMMENTS
loc1 Local1 Hosts accessed through internal router
loc Local All hosts accessed via eth1</programlisting>
<note>
<para>the sub-zone (loc1) is defined first!</para>
</note>
<para><filename>/etc/shorewall/interfaces</filename></para>
<programlisting>#ZONE INTERFACE BROADCAST
loc eth1 192.168.1.255</programlisting>
<para><filename>/etc/shorewall/hosts</filename></para>
<programlisting>#ZONE HOSTS
loc1 eth1:192.168.2.0/24</programlisting>
<para>If you don't need Shorewall to set up infrastructure to
route traffic between <quote>loc</quote> and <quote>loc1</quote>, add
these two policies.</para>
<para>/etc/shorewall/policy</para>
<programlisting>#SOURCE DEST POLICY
loc loc1 NONE
loc1 loc NONE</programlisting>
</section>
<section>
<title>Parallel Zones</title>
<para>You define both zones in the /etc/shorewall/hosts file to create
two disjoint zones.</para>
<graphic fileref="images/MultiZone1B.png" />
<para><filename>/etc/shorewall/zones</filename></para>
<programlisting>#ZONE DISPLAY COMMENTS
loc1 Local1 Hosts accessed Directly from Firewall
loc2 Local2 Hosts accessed via the internal Router</programlisting>
<note>
<para>Here it doesn't matter which zone is defined first.</para>
</note>
<para><filename>/etc/shorewall/interfaces</filename></para>
<programlisting>#ZONE INTERFACE BROADCAST
- eth1 192.168.1.255</programlisting>
<para><filename>/etc/shorewall/hosts</filename></para>
<programlisting>#ZONE HOSTS
loc1 eth1:192.168.1.0/24
loc2 eth1:192.168.2.0/24</programlisting>
<para>You don't need Shorewall to set up infrastructure to route
traffic between <quote>loc</quote> and <quote>loc1</quote>, so add
these two policies:</para>
<programlisting>#SOURCE DEST POLICY
loc1 loc2 NONE
loc2 loc1 NONE</programlisting>
</section>
</section>
</section>
<section>
<title>Some Hosts have Special Firewalling Requirements</title>
<para>There are cases where a subset of the addresses associated with an
interface need special handling. Here's an example.</para>
<graphic fileref="images/MultiZone2.png" />
<para>In this example, addresses 192.168.1.8 - 192.168.1.15
(192.168.1.8/29) are to be treated as their own zone (loc1).</para>
<para><filename>/etc/shorewall/zones</filename></para>
<programlisting>#ZONE DISPLAY COMMENTS
loc1 Local1 192.168.1.8-192.168.1.15
loc Local All hosts accessed via eth1</programlisting>
<note>
<para>the sub-zone (loc1) is defined first!</para>
</note>
<para><filename>/etc/shorewall/interfaces</filename></para>
<programlisting>#ZONE INTERFACE BROADCAST
loc eth1 192.168.1.255</programlisting>
<para><filename>/etc/shorewall/hosts</filename><programlisting>#ZONE HOSTS
loc1 eth1:192.168.1.8/29</programlisting></para>
<para>You probably don't want Shorewall to set up infrastructure to
route traffic between <quote>loc</quote> and <quote>loc1</quote> so you
should add these two policies.</para>
<para><filename>/etc/shorewall/policy</filename></para>
<programlisting>#SOURCE DEST POLICY
loc loc1 NONE
loc1 loc NONE</programlisting>
</section>
<section id="OneArmed">
<title>One-armed Router</title>
<para>Nested zones may also be used to configure a <quote>one-armed</quote>
router (I don't call it a <quote>firewall</quote> because it is very
insecure. For example, if you connect to the internet via cable modem,
your next door neighbor has full access to your local systems as does
everyone else connected to the same cable modem head-end controller). Here
eth0 is configured with both a public IP address and an RFC 1918 address
(More on that topic may be found <ulink
url="Shorewall_and_Aliased_Interfaces.html">here</ulink>). Hosts in the
<quote>loc</quote> zone are configured with their default gateway set to
the Shorewall router's RFC1918 address.</para>
<para><graphic fileref="images/MultiZone3.png" /></para>
<para><filename>/etc/shorewall/zones</filename></para>
<programlisting>#ZONE DISPLAY COMMENTS
loc Local Local Zone
net Internet The big bad Internet</programlisting>
<note>
<para>the sub-zone (loc) is defined first!</para>
</note>
<para><filename>/etc/shorewall/interfaces</filename></para>
<programlisting>#ZONE INTERFACE BROADCAST
net eth0 detect</programlisting>
<para><filename>/etc/shorewall/hosts</filename></para>
<programlisting>#ZONE HOSTS OPTIONS
loc eth0:192.168.1.0/24 maclist</programlisting>
<para><filename><filename>/etc/shorewall/masq</filename></filename></para>
<programlisting>#INTERFACE SUBNET ADDRESS
eth0:!192.168.1.0/24 192.168.1.0/24</programlisting>
<para>Note that the maclist option is specified in <filename>/etc/shorewall/interfaces</filename>.
This is to help protect your router from unauthorized access by your
friends and neighbors. Start without maclist then add it and configure
your <ulink url="MAC_Validation.html"><filename>/etc/shorewall/maclist</filename></ulink>
file when everything else is working.</para>
</section>
</article>