shorewall_code/Shorewall-docs2/shorewall_extension_scripts.xml

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  <articleinfo>
    <title>Extension Scripts and Common Actions</title>

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

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

    <pubdate>2004-02-04</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 AND SHOREWALL.</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.</para>

  <para>Beginning with Shorewall 2.0.0, you can also define a
  <emphasis>common action</emphasis> to be performed immediately before a
  policy of ACCEPT, DROP or REJECT is applied. Separate actions can be
  assigned to each policy type so for example you can have a different common
  action for DROP and REJECT policies. The most common usage of common actions
  is to silently drop traffic that you don&#39;t wish to have logged by the
  policy.</para>

  <para>As released, Shorewall defines a number of actions which are cataloged
  in the <filename>/etc/shorewall/actions.std</filename> file. The default
  <filename>/etc/shorewall/actions</filename> file contains <quote>INCLUDE
  /etc/shorewall/actions.std</quote> so that the Shorewall-defined actions are
  included by default. Among the entries in <filename>/etc/shorewall/actions.std</filename>
  are:</para>

  <programlisting>Drop:DROP
Reject:REJECT</programlisting>

  <para>So the action named <quote>Drop</quote> is performed immediately
  before DROP policies are applied and the action called <quote>Reject</quote>
  is performed before REJECT policies are applied. These actions are defined
  in the files <filename>/etc/shorewall/action.Drop</filename> and
  <filename>/etc/shorewall/action.Reject</filename> respectively.</para>

  <para>You can override these defaults with entries in your
  /etc/shorewall/actions file. For example, if that file were to contain
  <quote>MyDrop:DROP</quote> then the common action for DROP policies would
  become <quote>MyDrop</quote>. For an example, see <ulink url="myfiles.htm">my
  configuration files</ulink>.</para>

  <para>One final note. The chain created to perform an action has the same
  name as the action. You can use an extension script by that name to add
  rules to the action&#39;s chain in the same way as you can any other chain.
  So if you create the new action <quote>Dagger</quote> and define it in
  <filename>/etc/shorewall/action.Dagger</filename>, you can also have an
  extension script named <filename>/etc/shorewall/Dagger</filename> that can
  add rules to the <quote>Dagger</quote> chain that can&#39;t be created using
  <filename>/etc/shorewall/action.Dagger</filename>.</para>
</article>