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  <articleinfo>
    <title>Extension Scripts</title>

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

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

    <pubdate>2004-02-01</pubdate>

    <copyright>
      <year>2001-2004</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>

  <para>Extension scripts are user-provided scripts that are invoked at
  various points during firewall start, restart, stop and clear. The scripts
  are placed in /etc/shorewall and are processed using the Bourne shell
  <quote>source</quote> mechanism.</para>

  <caution>
    <orderedlist>
      <listitem>
        <para>Be sure that you actually need to use an extension script to do
        what you want. Shorewall has a wide range of features that cover most
        requirements.</para>
      </listitem>

      <listitem>
        <para>DO NOT SIMPLY COPY RULES THAT YOU FIND ON THE NET INTO AN
        EXTENSION SCRIPT AND EXPECT THEM TO WORK AND TO NOT BREAK SHOREWALL.
        TO USE SHOREWALL EXTENSION SCRIPTS YOU MUST KNOW WHAT YOU ARE DOING
        WITH RESPECT TO iptables/Netfilter</para>
      </listitem>
    </orderedlist>
  </caution>

  <para>The following scripts can be supplied:</para>

  <itemizedlist>
    <listitem>
      <para>init -- invoked early in <quote>shorewall start</quote> and
      <quote>shorewall restart</quote></para>
    </listitem>

    <listitem>
      <para>start -- invoked after the firewall has been started or restarted.</para>
    </listitem>

    <listitem>
      <para>stop -- invoked as a first step when the firewall is being
      stopped.</para>
    </listitem>

    <listitem>
      <para>stopped -- invoked after the firewall has been stopped.</para>
    </listitem>

    <listitem>
      <para>clear -- invoked after the firewall has been cleared.</para>
    </listitem>

    <listitem>
      <para>refresh -- invoked while the firewall is being refreshed but
      before the common and/or blacklst chains have been rebuilt.</para>
    </listitem>

    <listitem>
      <para>newnotsyn (added in version 1.3.6) -- invoked after the
      <quote>newnotsyn</quote> chain has been created but before any rules
      have been added to it.</para>
    </listitem>
  </itemizedlist>

  <para><emphasis role="bold">If your version of Shorewall doesn&#39;t have
  the file that you want to use from the above list, you can simply create the
  file yourself.</emphasis> You can also supply a script with the same name as
  any of the filter chains in the firewall and the script will be invoked
  after the /etc/shorewall/rules file has been processed but before the
  /etc/shorewall/policy file has been processed. The /etc/shorewall/common
  file receives special treatment. If this file is present, the rules that it
  defines will totally replace the default rules in the common chain. These
  default rules are contained in the file /etc/shorewall/common.def which may
  be used as a starting point for making your own customized file. Rather than
  running iptables directly, you should run it using the function
  run_iptables. Similarly, rather than running <quote>ip</quote> directly, you
  should use run_ip. These functions accept the same arguments as the
  underlying command but cause the firewall to be stopped if an error occurs
  during processing of the command. If you decide to create
  /etc/shorewall/common it is a good idea to use the following technique.</para>

  <para>/etc/shorewall/common:</para>

  <programlisting>     &#60;add your rules here&#62;
     . /etc/shorewall/common.def</programlisting>

  <para>Using this technique allows you to add new rules while still getting
  the benefit of the latest common.def file. Remember that
  /etc/shorewall/common defines rules that are only applied if the applicable
  policy is DROP or REJECT. These rules are NOT applied if the policy is
  ACCEPT or CONTINUE</para>
</article>