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  <articleinfo>
    <title>Shorewall on a Laptop</title>

    <authorgroup>
      <author>
        <firstname>Tom</firstname>

        <surname>Eastep</surname>
      </author>
    </authorgroup>

    <pubdate><?dbtimestamp format="Y/m/d"?></pubdate>

    <copyright>
      <year>2009</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>Overview</title>

    <para>Laptop computers generally have several network interfaces, one of
    which will be used at a time.</para>

    <orderedlist>
      <listitem>
        <para>Ethernet interface ‒ Used when the computer is on the desktop at
        home or at work.</para>
      </listitem>

      <listitem>
        <para>Wireless interface ‒ Used when the laptop is being used in a
        cafe, train or airline terminal.</para>
      </listitem>

      <listitem>
        <para>Point-to-point (PPP) interface ‒ Used when neither wired nor
        wireless service are available.</para>
      </listitem>
    </orderedlist>

    <para>Shorewall can be configured to treat these interfaces the same and
    to be able to switch between them without having to reconfigure.</para>
  </section>

  <section>
    <title>Configuration</title>

    <para>The key to configuring Shorewall on a laptop is to define multiple
    optional interfaces for the 'net' zone in
    <filename>/etc/shorewall/interfaces</filename>.</para>

    <programlisting>#ZONE          INTERFACE      BROADCAST           OPTIONS
net            eth0           detect              optional,…
net            wlan0          detect              optional,…
net            ppp0           -                   optional,…</programlisting>

    <para>With this configuration, access to the 'net' zone is possible
    regardless of which of the interfaces is being used.</para>
  </section>
</article>
