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353 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<article>
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<!--$Id$-->
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<articleinfo>
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<title>Universal Configuration</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>2010</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>
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<title>Configuring Shorewall</title>
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<para>Once you have installed the Shorewall software, you must configure
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it. The easiest way to do that is to use one of Shorewall's
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<firstterm>Sample Configurations</firstterm>. The Universal Configuration
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is one of those samples.</para>
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</section>
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<section>
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<title>What the Universal Configuration does</title>
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<para>The Universal Shorewall configuration requires that you simply copy
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the configuration to <filename class="directory">/etc/shorewall</filename>
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and start Shorewall. This sample configuation:</para>
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<itemizedlist>
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<listitem>
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<para>Allows all outgoing traffic.</para>
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</listitem>
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<listitem>
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<para>Blocks all incoming connections except:</para>
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<itemizedlist>
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<listitem>
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<para>Secure Shell</para>
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</listitem>
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<listitem>
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<para>Ping</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>Allows forwarding of traffic, provided that the system has more
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than one interface or is set up to route between networks on a single
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interface.</para>
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</listitem>
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</itemizedlist>
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</section>
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<section>
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<title>How to Install it</title>
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<para>The location of the sample configuration files is dependent on your
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distribution and <ulink url="Install.htm">how you installed
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Shorewall</ulink>.</para>
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<orderedlist>
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<listitem>
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<para>If you installed using an <acronym>RPM</acronym>, the samples
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will be in the <filename
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class="directory">Samples/Universal</filename> subdirectory of the
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Shorewall documentation directory. If you don't know where the
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Shorewall documentation directory is, you can find the samples using
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this command:</para>
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<programlisting>~# rpm -ql shorewall-common | fgrep Universal
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/usr/share/doc/packages/shorewall/Samples/Universal
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/usr/share/doc/packages/shorewall/Samples/Universal/interfaces
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/usr/share/doc/packages/shorewall/Samples/Universal/policy
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/usr/share/doc/packages/shorewall/Samples/Universal/rules
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/usr/share/doc/packages/shorewall/Samples/Universal/zones
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~#</programlisting>
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</listitem>
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<listitem>
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<para>If you installed using the tarball, the samples are in the
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<filename class="directory">Samples/Universal</filename> directory in
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the tarball.</para>
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</listitem>
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<listitem>
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<para>If you installed using a Shorewall 4.x .deb, the samples are in
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<filename
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class="directory">/usr/share/doc/shorewall-common/examples/Universal</filename>..
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You do not need the shorewall-doc package to have access to the
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samples.</para>
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</listitem>
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</orderedlist>
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<para>Simple copy the files from the Universal directory to
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/etc/shorewall.</para>
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</section>
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<section>
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<title>How to Start the firewall</title>
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<para>Before starting Shorewall for the first time, it's a good idea to
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stop your existing firewall. On Redhat/CentOS/Fedora, at a root prompt
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type:</para>
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<blockquote>
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<para><command>service iptables stop</command></para>
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</blockquote>
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<para>If you are running SuSE, use Yast or Yast2 to stop
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SuSEFirewall.</para>
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<para>Once you have Shorewall running to your satisfaction, you should
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totally disable your existing firewall. On /Redhat/CentOS/Fedora:</para>
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<blockquote>
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<para><command>chkconfig --del iptables</command></para>
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</blockquote>
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<para>At a root prompt, type:</para>
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<blockquote>
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<para><command>/sbin/shorewall start</command></para>
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</blockquote>
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<para>That's it. Shorewall will automatically start again when you
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reboot.</para>
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</section>
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<section>
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<title>Now that it is running, ...</title>
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<section>
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<title>How do I stop the firewall?</title>
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<para>At a root prompt, type:</para>
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<blockquote>
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<para><command>/sbin/shorewall clear</command></para>
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</blockquote>
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<para>The system is now 'wide open'.</para>
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</section>
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<section>
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<title>How do I prevent it from responding to ping?</title>
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<para>Edit <filename>/etc/shorewall/rules</filename> and remove the line
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that reads:</para>
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<blockquote>
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<para>Ping(ACCEPT) net $FW</para>
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</blockquote>
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<para>and at a root prompt, type:</para>
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<blockquote>
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<para><command>/sbin/shorewall restart</command></para>
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</blockquote>
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</section>
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<section>
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<title>How do I allow other kinds of incoming connections?</title>
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<para>Shorewall includes a collection of <firstterm>macros</firstterm>
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that can be used to quickly allow or deny services. You can find a list
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of the macros included in your version of Shorewall using the command
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<command>ls <filename>/usr/share/shorewall/macro.*</filename></command>
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or at a shell prompt type:</para>
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<blockquote>
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<para><command>/sbin/shorewall show macros</command></para>
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</blockquote>
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<para>If you wish to enable connections from the Internet to your
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firewall and you find an appropriate macro in
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<filename>/etc/shorewall/macro.*</filename>, the general format of a
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rule in <filename>/etc/shorewall/rules</filename> is:</para>
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<programlisting>#ACTION SOURCE DESTINATION PROTO DPORT
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<<emphasis>macro</emphasis>>(ACCEPT) net $FW</programlisting>
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<important>
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<para>Be sure to add your rules after the line that reads <emphasis
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role="bold">SECTION NEW.</emphasis></para>
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</important>
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<example id="Example1">
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<title>You want to run a Web Server and a IMAP Server on your firewall
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system:</title>
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<programlisting>#ACTION SOURCE DESTINATION PROTO DPORT
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Web(ACCEPT) net $FW
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IMAP(ACCEPT)net $FW</programlisting>
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</example>
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<para>You may also choose to code your rules directly without using the
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pre-defined macros. This will be necessary in the event that there is
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not a pre-defined macro that meets your requirements. In that case the
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general format of a rule in <filename>/etc/shorewall/rules</filename>
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is:</para>
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<programlisting>#ACTION SOURCE DESTINATION PROTO DPORT
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ACCEPT net $FW <emphasis><protocol></emphasis> <emphasis><port></emphasis></programlisting>
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<example id="Example2">
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<title>You want to run a Web Server and a IMAP Server on your firewall
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system:</title>
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<para><programlisting>#ACTION SOURCE DESTINATION PROTO DPORT
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ACCEPT net $FW tcp 80
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ACCEPT net $FW tcp 143</programlisting></para>
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</example>
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<para>If you don't know what port and protocol a particular application
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uses, see <ulink url="ports.htm">here</ulink>.</para>
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</section>
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<section>
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<title>How do I make the firewall log a message when it disallows an
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incoming connection?</title>
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<para>Shorewall does not maintain a log itself but rather relies on your
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<ulink url="shorewall_logging.html">system's logging
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configuration</ulink>. The following <ulink
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url="manpages/shorewall.html">commands</ulink> rely on knowing where
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Netfilter messages are logged:</para>
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<itemizedlist>
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<listitem>
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<para><command>shorewall show log</command> (Displays the last 20
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Netfilter log messages)</para>
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</listitem>
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<listitem>
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<para><command>shorewall logwatch</command> (Polls the log at a
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settable interval</para>
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</listitem>
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<listitem>
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<para><command>shorewall dump</command> (Produces an extensive
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report for inclusion in Shorewall problem reports)</para>
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</listitem>
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</itemizedlist>
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<para>It is important that these commands work properly because when you
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encounter connection problems when Shorewall is running, the first thing
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that you should do is to look at the Netfilter log; with the help of
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<ulink url="FAQ.htm#faq17">Shorewall FAQ 17</ulink>, you can usually
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resolve the problem quickly.</para>
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<para>The Netfilter log location is distribution-dependent:</para>
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<itemizedlist>
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<listitem>
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<para>Debian and its derivatives log Netfilter messages to
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<filename>/var/log/kern.log</filename>.</para>
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</listitem>
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<listitem>
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<para>Recent <trademark>SuSE/OpenSuSE</trademark> releases come
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preconfigured with syslog-ng and log netfilter messages to
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<filename>/var/log/firewall</filename>.</para>
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</listitem>
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<listitem>
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<para>For other distributions, Netfilter messages are most commonly
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logged to <filename>/var/log/messages</filename>.</para>
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</listitem>
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</itemizedlist>
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<para>Modify the LOGFILE setting in
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<filename>/etc/shorewall/shorewall.conf</filename> to specify the name
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of your log.</para>
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<important>
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<para>The LOGFILE setting does not control where the Netfilter log is
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maintained -- it simply tells the /sbin/<filename>shorewall</filename>
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utility where to find the log.</para>
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</important>
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<para>Now, edit <filename>/etc/shorewall/policy</filename> and modify
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the line that reads:</para>
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<blockquote>
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<para>net all DROP</para>
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</blockquote>
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<para>to</para>
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<blockquote>
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<para>net all DROP <emphasis role="bold">info</emphasis></para>
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</blockquote>
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<para>Then at a root prompt, type:</para>
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<blockquote>
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<para><command>/sbin/shorewall reload</command></para>
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</blockquote>
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</section>
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<section>
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<title>How do I prevent the firewall from forwarding connection
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requests?</title>
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<para>Edit /etc/shorewall/interfaces, and remove the routeback option
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from the interface. e.g., change the line that reads:</para>
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<blockquote>
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<para>net all - dhcp,physical=+<emphasis
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role="bold">,routeback</emphasis>,optional</para>
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</blockquote>
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<para>to</para>
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<blockquote>
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<para>net all - dhcp,physical=+,optional</para>
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</blockquote>
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<para>Then at a root prompt, type:</para>
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<blockquote>
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<para><command>/sbin/shorewall reload</command></para>
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</blockquote>
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</section>
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</section>
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</article>
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