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600 lines
22 KiB
XML
600 lines
22 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article>
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<!--$Id: template.xml 4194 2006-07-07 01:04:16Z judas_iscariote $-->
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<articleinfo>
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<title>Shorewall-perl</title>
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<authorgroup>
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<author>
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<firstname>Tom</firstname>
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<surname>Eastep</surname>
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</author>
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</authorgroup>
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<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2007</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled
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<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<section id="What">
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<title>Shorewall-perl - What is it?</title>
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<para>Shorewall-perl is a companion product to Shorewall.</para>
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<para>Shorewall-perl contains a re-implementation of the Shorewall
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compiler written in Perl. The advantages of using Shorewall-perl over
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Shorewall-shell (the shell-based compiler included in earlier Shorewall
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3.x releases) are:</para>
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<itemizedlist>
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<listitem>
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<para>The Shorewall-perl compiler is much faster.</para>
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</listitem>
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<listitem>
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<para>The script generated by the compiler uses
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<command>iptables-restore</command> to instantiate the Netfilter
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configuration. So it runs much faster than the script generated by the
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Shorewall-shell compiler.</para>
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</listitem>
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<listitem>
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<para>The Shorewall-perl compiler does more thorough checking of the
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configuration than the Shorewall-shell compiler does.</para>
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</listitem>
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<listitem>
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<para>The error messages produced by the compiler are better, more
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consistent and always include the file name and line number where the
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error was detected.</para>
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</listitem>
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<listitem>
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<para>Going forward, the Shorewall-perl compiler will get all
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enhancements; the Shorewall-shell compiler will only get those
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enhancements that are easy to retrofit.</para>
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</listitem>
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</itemizedlist>
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</section>
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<section id="DownSide">
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<title>Shorewall-perl - The down side</title>
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<para>While there are advantages to using Shorewall-perl, there are also
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disadvantages.</para>
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<section id="Incompatibilities">
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<title>Incompatibilities</title>
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<para>There are a number of incompatibilities between the Shorewall-perl
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compiler and the earlier one.</para>
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<orderedlist>
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<listitem>
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<para>The Perl-based compiler requires the following capabilities in
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your kernel and iptables.</para>
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<itemizedlist>
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<listitem>
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<para>addrtype match (Restriction relaxed in Shorewall-perl
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4.0.1)</para>
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</listitem>
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<listitem>
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<para>multiport match (will not be relaxed)</para>
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</listitem>
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</itemizedlist>
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<para>These capabilities are in current distributions.</para>
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</listitem>
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<listitem>
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<para>Now that Netfilter has features to deal reasonably with port
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lists, I see no reason to duplicate those features in Shorewall. The
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Shorewall-shell compiler goes to great pain (in some cases) to break
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very long port lists ( > 15 where port ranges in lists count as
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two ports) into individual rules. In the new compiler, I'm avoiding
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the ugliness required to do that. The new compiler just generates an
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error if your list is too long. It will also produce an error if you
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insert a port range into a port list and you don't have extended
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multiport support.</para>
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</listitem>
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<listitem>
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<para>BRIDGING=Yes is not supported. The kernel code necessary to
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support this option was removed in Linux kernel 2.6.20. <ulink
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url="bridge-Shorewall-perl.html">Alternative bridge support</ulink>
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is provided by Shorewall-perl.</para>
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</listitem>
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<listitem>
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<para>The BROADCAST column in the interfaces file is essentially
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unused; if you enter anything in this column but '-' or 'detect',
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you will receive a warning. This will be relaxed if and when the
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addrtype match requirement is relaxed.</para>
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</listitem>
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<listitem>
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<para>The 'refresh' command is now similar to restart with the
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exceptios that:</para>
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<itemizedlist>
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<listitem>
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<para>The command fails if Shorewall is not running.</para>
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</listitem>
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<listitem>
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<para>A directory name cannot be specified in the
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command.</para>
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</listitem>
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<listitem>
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<para>The refresh command does not alter the Netfilter
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configuration except for the static blacklist.</para>
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</listitem>
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</itemizedlist>
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</listitem>
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<listitem>
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<para>With the shell-based compiler, extension scripts were copied
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into the compiled script and executed at run-time. In many cases,
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this approach doesn't work with Shorewall Perl because (almost) the
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entire ruleset is built by the compiler. As a result, Shorewall-perl
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runs many extension scripts at compile-time rather than at run-time.
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Because the compiler is written in Perl, your extension scripts from
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earlier versions will no longer work.</para>
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<para>The following table summarizes when the various extension
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scripts are run:<informaltable frame="all">
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<tgroup cols="3">
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<tbody>
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<row>
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<entry><emphasis
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role="bold">Compile-time</emphasis></entry>
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<entry><emphasis role="bold">Run-time</emphasis></entry>
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<entry><emphasis role="bold">Eliminated</emphasis></entry>
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</row>
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<row>
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<entry>initdone</entry>
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<entry>clear</entry>
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<entry>continue</entry>
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</row>
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<row>
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<entry>maclog</entry>
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<entry>initdone</entry>
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<entry></entry>
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</row>
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<row>
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<entry>Per-chain (including those associated with
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actions)</entry>
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<entry>start</entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry>started</entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry>stop</entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry>stopped</entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry>tcclear</entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable></para>
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<para>Compile-time extension scripts are executed using the Perl
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'eval `cat <file>`' mechanism. Be sure that each script
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returns a 'true' value; otherwise, the compiler will assume that the
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script failed and will abort the compilation.</para>
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<para>When a script is invoked, the <emphasis
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role="bold">$chainref</emphasis> scalar variable will hold a
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reference to a chain table entry.</para>
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<simplelist>
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<member><emphasis role="bold">$chainref->{name}</emphasis>
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contains the name of the chain</member>
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<member><emphasis role="bold">$chainref->{table}</emphasis>
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holds the table name</member>
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</simplelist>
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<para>To add a rule to the chain:</para>
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<simplelist>
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<member>add_rule $chainref, <<replaceable>the
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rule</replaceable>></member>
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</simplelist>
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<para>Where</para>
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<simplelist>
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<member><<replaceable>the rule</replaceable>> is a scalar
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argument holding the rule text. Do not include "-A
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<<replaceable>chain name</replaceable>>"</member>
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</simplelist>
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<para>Example:</para>
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<simplelist>
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<member>add_rule $chainref, '-j ACCEPT';</member>
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</simplelist>
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<para>To insert a rule into the chain:</para>
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<simplelist>
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<member>insert_rule $chainref,
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<<replaceable>rulenum</replaceable>>, <<replaceable>the
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rule</replaceable>></member>
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</simplelist>
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<para>The log_rule_limit function works like it does in the shell
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compiler with two exceptions:</para>
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<itemizedlist>
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<listitem>
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<para>You pass the chain reference rather than the name of the
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chain.</para>
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</listitem>
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<listitem>
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<para>The commands are 'add' and 'insert' rather than '-A' and
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'-I'.</para>
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</listitem>
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<listitem>
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<para>There is only a single "pass as-is to iptables" argument
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(so you must quote that part</para>
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</listitem>
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</itemizedlist>
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<para>Example:</para>
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<programlisting> log_rule_limit
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'info' ,
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$chainref ,
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$chainref->{name},
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'DROP' ,
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'', #Limit
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'' , #Log tag
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'add'
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'-p tcp '; </programlisting>
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<para>Here is an example of an actual initdone script used with
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Shorewall 3.4:<programlisting>run_iptables -t mangle -I PREROUTING -p esp -j MARK --set-mark 0x50
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run_iptables -t filter -I INPUT -p udp --dport 1701 -m mark --mark 0x50 -j ACCEPT
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run_iptables -t filter -I OUTPUT -p udp --sport 1701 -j ACCEPT
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</programlisting></para>
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<para>Here is the corresponding script used with
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Shorewall-perl:<programlisting>use Shorewall::Chains;
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insert_rule $mangle_table->{PREROUTING}, 1, "-p esp -j MARK --set-mark 0x50";
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insert_rule $filter_table->{INPUT}, 1, "-p udp --dport 1701 -m mark --mark 0x50 -j ACCEPT";
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insert_rule $filter_table->{OUTPUT}, 1, "-p udp --sport 1701 -j ACCEPT";
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1;</programlisting></para>
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<para>The initdone script is unique because the $chainref variable
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is not set before the script is called. The above script illustrates
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how the $mangle_table, $filter_table, and $nat_table references can
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be used to add or insert rules in arbitrary chains.</para>
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</listitem>
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<listitem>
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<para>The <filename>/etc/shorewall/tos</filename> file now has
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zone-independent SOURCE and DEST columns as do all other files
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except the rules and policy files.</para>
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<para>The SOURCE column may be one of the following:</para>
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<simplelist>
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<member>[<command>all</command>:]<<replaceable>address</replaceable>>[,...]</member>
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<member>[<command>all</command>:]<<replaceable>interface</replaceable>>[:<<replaceable>address</replaceable>>[,...]]</member>
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<member><command>$FW</command>[:<<replaceable>address</replaceable>>[,...]]</member>
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</simplelist>
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<para>The DEST column may be one of the following:</para>
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<simplelist>
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<member>[<command>all</command>:]<<replaceable>address</replaceable>>[,...]</member>
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<member>[<command>all</command>:]<<replaceable>interface</replaceable>>[:<<replaceable>address</replaceable>>[,...]]</member>
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</simplelist>
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<para>This is a permanent change. The old zone-based rules have
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never worked right and this is a good time to replace them. I've
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tried to make the new syntax cover the most common cases without
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requiring change to existing files. In particular, it will handle
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the tos file released with Shorewall 1.4 and earlier.</para>
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</listitem>
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<listitem>
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<para>Shorewall-perl insists that ipset names begin with a letter
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and be composed of alphanumeric characters and underscores (_). When
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used in a Shorewall configuration file, the name must be preceded by
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a plus sign (+) as with the shell-based compiler.</para>
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<para>Shorewall is now out of the ipset load/reload business. With
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scripts generated by the Perl-based Compiler, the Netfilter ruleset
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is never cleared. That means that there is no opportunity for
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Shorewall to load/reload your ipsets since that cannot be done while
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there are any current rules using ipsets.</para>
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<para>So:</para>
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<orderedlist numeration="upperroman">
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<listitem>
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<para>Your ipsets must be loaded before Shorewall starts. You
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are free to try to do that with the following code in
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<filename>/etc/shorewall/start</filename>:</para>
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<programlisting>if [ "$COMMAND" = start ]; then
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ipset -U :all: :all:
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ipset -F
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ipset -X
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ipset -R < /etc/shorewall/ipsets
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fi</programlisting>
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<para>The file <filename>/etc/shorewall/ipsets</filename> will
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normally be produced using the <command>ipset -S</command>
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command.</para>
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<para>The above will work most of the time but will fail in a
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<command>shorewall stop</command> - <command>shorewall
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start</command> sequence if you use ipsets in your routestopped
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file (see below).</para>
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</listitem>
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<listitem>
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<para>Your ipsets may not be reloaded until Shorewall is stopped
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or cleared.</para>
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</listitem>
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<listitem>
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<para>If you specify ipsets in your routestopped file then
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Shorewall must be cleared in order to reload your ipsets.</para>
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</listitem>
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</orderedlist>
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<para>As a consequence, scripts generated by the Perl-based compiler
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will ignore <filename>/etc/shorewall/ipsets</filename> and will
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issue a warning if you set SAVE_IPSETS=Yes in
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<filename>shorewall.conf</filename>.</para>
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</listitem>
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<listitem>
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<para>Because the configuration files (with the exception of
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<filename>/etc/shorewall/params</filename>) are now processed by the
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Shorewall-perl compiler rather than by the shell, only the basic
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forms of Shell expansion ($variable and ${variable}) are supported.
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The more exotic forms such as ${variable:=default} are not
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supported. Both variables defined in /etc/shorewall/params and
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environmental variables (exported by the shell) can be used in
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configuration files.</para>
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</listitem>
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<listitem>
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<para>USE_ACTIONS=No is not supported. That option is intended to
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minimize Shorewall's footprint in embedded applications. As a
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consequence, Default Macros are not supported.</para>
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</listitem>
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<listitem>
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<para>DELAYBLACKLISTLOAD=Yes is not supported. The entire ruleset is
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atomically loaded with one execution of
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<command>iptables-restore</command>.</para>
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</listitem>
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<listitem>
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<para>MAPOLDACTIONS=Yes is not supported. People should have
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converted to using macros by now.</para>
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</listitem>
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<listitem>
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<para>The pre Shorewall-3.0 format of the zones file is not
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supported; neither is the <filename>/etc/shorewall/ipsec</filename>
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file.</para>
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</listitem>
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<listitem>
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<para>BLACKLISTNEWONLY=No is not permitted with FASTACCEPT=Yes. This
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combination doesn't work in previous versions of Shorewall so the
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Perl-based compiler simply rejects it.</para>
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</listitem>
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<listitem>
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<para>Shorewall-perl has a single rule generator that is used for
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all rule-oriented files. So it is important that the syntax is
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consistent between files.</para>
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<para>With shorewall-shell, there is a special syntax in the SOURCE
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column of /etc/shorewall/masq to designate "all traffic entering the
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firewall on this interface except...".</para>
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<para>Example:<programlisting>#INTERFACE SOURCE ADDRESSES
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eth0 eth1!192.168.4.9 ...</programlisting>Shorewall-perl
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uses syntax that is consistent with the rest of
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Shorewall:<programlisting>#INTERFACE SOURCE ADDRESSES
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eth0 eth1:!192.168.4.9 ...</programlisting></para>
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</listitem>
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<listitem>
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<para>The 'allowoutUPnP' built-in action is no longer supported. In
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kernel 2.6.14, the Netfilter team have removed support for '-m owner
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--owner-cmd' which that action depended on.</para>
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</listitem>
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<listitem>
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<para>The PKTTYPE option is ignored by Shorewall-perl.
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Shorewall-perl 4.0.0 requires Address type match. Shorewall-perl
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versions 4.0.1 and later will use Address type match if it is
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available; otherwise, they will behave as if PKTTYPE=No had been
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specified.</para>
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</listitem>
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<listitem>
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<para>Shorewall-perl detects dead policy file entries that result
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when an entry is masked by an earlier more general entry.</para>
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<para>Example:</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL
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all all REJECT info
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loc net ACCEPT</programlisting>
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</listitem>
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</orderedlist>
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</section>
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<section id="PerlDep">
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<title>Dependence on Perl</title>
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|
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<para>Shorewall-perl is dependent on Perl (see the next section) which
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has a large disk footprint. This makes Shorewall-perl less desirable in
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an embedded environment.</para>
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</section>
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</section>
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|
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<section id="Prerequisites">
|
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<title>Shorewall-perl - Prerequisites</title>
|
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|
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<itemizedlist>
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<listitem>
|
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<para>Perl (I use Perl 5.8.8 but other 5.8 or later versions should
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work fine)</para>
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</listitem>
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<listitem>
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<para>Perl Cwd Module</para>
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</listitem>
|
|
|
|
<listitem>
|
|
<para>Perl File::Basename Module</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Perl File::Temp Module</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Perl Getopt::Long Module</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Perl Carp Module</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Perl FindBin Module (Shorewall 4.0.3 and later)</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<section id="Install">
|
|
<title>Shorewall-perl - Installation</title>
|
|
|
|
<para>Either</para>
|
|
|
|
<programlisting><command>tar -jxf shorewall-perl-4.0.x.tar.bz2</command>
|
|
<command>cd shorewall-perl-4.0.x</command>
|
|
<command>./install.sh</command></programlisting>
|
|
|
|
<para>or</para>
|
|
|
|
<programlisting><command>rpm -ivh shorewall-perl-4.0.x.noarch.rpm</command></programlisting>
|
|
</section>
|
|
|
|
<section id="Using">
|
|
<title>Using Shorewall-perl</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
|
|
depends on the SHOREWALL_COMPILER setting in
|
|
<filename>shorewall.conf</filename>. The value of this 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>You may also 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 twice, the second time using
|
|
the <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> |