shorewall_code/docs/Shorewall-4.xml

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  <articleinfo>
    <title>Shorewall Version 4</title>

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

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

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

    <copyright>
      <year>2007</year>

      <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 id="Intro">
    <title>Introduction</title>

    <para>Shorewall version 4 represents a substantial shift in direction for
    Shorewall. Up to now</para>

    <itemizedlist>
      <listitem>
        <para>Shorewall has been written entirely in Bourne Shell.</para>
      </listitem>

      <listitem>
        <para>Shorewall has run the <command>iptables</command> utility to add
        each Netfilter rule.</para>
      </listitem>
    </itemizedlist>

    <para>Shorewall version 4 offers you a choice. You can continue to use the
    existing shell-based implementation or you can use a new implementation of
    the Shorewall compiler written in the Perl programming language. The new
    compiler:</para>

    <itemizedlist>
      <listitem>
        <para>has a small disk footprint</para>
      </listitem>

      <listitem>
        <para>is very fast.</para>
      </listitem>

      <listitem>
        <para>generates a firewall script that uses
        <command>iptables-restore</command>; so the script is very
        fast.</para>
      </listitem>

      <listitem>
        <para>generates better and more consistent error messages.</para>
      </listitem>

      <listitem>
        <para>does a much more thorough job of checking the configuration to
        avoid run-time errors.</para>
      </listitem>

      <listitem>
        <para>supports creating either Ipv4 or Ipv6 firewalls (Shorewall 4.2.4
        and later).</para>
      </listitem>
    </itemizedlist>

    <para>Both compilers may be installed on your system and you can use
    whichever one suits you in a particular case.</para>
  </section>

  <section id="Install">
    <title>Installing Shorewall Version 4</title>

    <para>Shorewall 4 contains six packages:</para>

    <itemizedlist>
      <listitem>
        <para><emphasis role="bold">Shorewall-shell</emphasis> - the old
        shell-based compiler and related components.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">Shorewall-perl</emphasis> - the new
        Perl-based compiler.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">Shorewall-common</emphasis> - the part of
        Shorewall common to both compilers.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">Shorewall-lite</emphasis>- same as the 3.4
        version of Shorewall Lite. Can run scripts generated by either
        Shorewall-perl or Shorewall-shell.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">Shorewall6</emphasis> - The utilities for
        creating and operating an Ipv6 firewall. Requires Shorewall-perl and
        Shorewall-common.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">Shorewall6-lite</emphasis> - Ipv6
        equivalent of Shorewall Lite. Can run scripts generated by
        Shoreall-perl 4.2.4 and later.</para>
      </listitem>
    </itemizedlist>

    <para>If you upgrade to Shorewall Version 4, you must install
    Shorewall-shell and/or Shorewall-perl; in fact, if you are using the
    tarball for your installation, you must install Shorewall-shell and/or
    Shorewall-perl <emphasis role="bold">before</emphasis> you upgrade
    Shorewall. See the <ulink url="upgrade_issues.htm">upgrade issues</ulink>
    for details.</para>
  </section>

  <section id="Prereqs">
    <title>Prerequisites for using the Shorewall Version 4 Perl-based
    Compiler</title>

    <itemizedlist>
      <listitem>
        <para>Perl (I use Perl 5.8.8 but other 5.8 versions should work fine).
        <note>
            <para>If you want to be able to use DNS names in your Shorewall6
            configuration files, then Perl 5.10 is required together with the
            Perl <emphasis role="bold">Socket6</emphasis> module.</para>
          </note></para>
      </listitem>

      <listitem>
        <para>Perl <emphasis role="bold">Cwd</emphasis> Module</para>
      </listitem>

      <listitem>
        <para>Perl <emphasis role="bold">File::Basename</emphasis>
        Module</para>
      </listitem>

      <listitem>
        <para>Perl <emphasis role="bold">File::Temp</emphasis> Module</para>
      </listitem>

      <listitem>
        <para>Perl <emphasis role="bold">Getopt::Long</emphasis> Module</para>
      </listitem>

      <listitem>
        <para>Perl <emphasis role="bold">Carp</emphasis> Module</para>
      </listitem>

      <listitem>
        <para>Perl <emphasis role="bold">FindBin</emphasis> Module (Shorewall
        4.0.3 and later)</para>
      </listitem>

      <listitem>
        <para>Perl <emphasis role="bold">Scalar::Util </emphasis>Module
        (Shorewall 4.0.6 and later)</para>
      </listitem>
    </itemizedlist>
  </section>

  <section id="Incompatibilities">
    <title>Incompatibilities Introduced in the Shorewall Version 4 Perl-based
    Compiler</title>

    <para>The Shorewall-perl compiler is not 100% compatible with the
    Shorewall-shell version. See <ulink url="Shorewall-perl.html">this
    document</ulink> for details.</para>
  </section>

  <section id="CompilerSelection">
    <title>Compiler Selection</title>

    <para>If you only install one compiler, then that compiler will be
    used.</para>

    <para>If you install both compilers, then the compiler actually used for
    IPv4 depends on the SHOREWALL_COMPILER setting in
    <filename>shorewall.conf</filename>.</para>

    <para>The value of this new option can be either 'perl' or 'shell'.</para>

    <para>If you add 'SHOREWALL_COMPILER=perl' to
    <filename>/etc/shorewall/shorewall.conf</filename> then by default, the
    new compiler will be used on the system. If you add it to
    <filename>shorewall.conf</filename> in a separate directory (such as a
    Shorewall-lite export directory) then the new compiler will only be used
    when you compile from that directory.</para>

    <para>If you only install one compiler, it is suggested that you do not
    set SHOREWALL_COMPILER.</para>

    <para>If both compilers are installed, you can select the compiler to use
    on the command line using the 'C option:<simplelist>
        <member>'-C shell' means use the shell compiler</member>

        <member>'-C perl' means use the perl compiler</member>
      </simplelist>The -C option overrides the setting in
    shorewall.conf.</para>

    <para>Example:<programlisting><command>shorewall restart -C perl</command></programlisting></para>

    <para>When the Shorewall-perl compiler has been selected, the
    <filename>params</filename> file is processed using the shell
    <option>-a</option> option which causes all variables set within the file
    to be exported automatically by the shell. The Shorewall-perl compiler
    uses the current environmental variables to perform variable expansion
    within the other Shorewall configuration files.</para>
  </section>
</article>