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2624 lines
114 KiB
XML
2624 lines
114 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>Shorewall FAQs</title>
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<authorgroup>
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<corpauthor>Shorewall Community</corpauthor>
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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>2001-2009</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 <quote>
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<ulink url="GnuCopyright.htm">GNU Free Documentation License</ulink>
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</quote>.</para>
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</legalnotice>
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</articleinfo>
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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 4.3 and
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later. If you are running a version of Shorewall earlier than Shorewall
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4.3.0 then please see the documentation for that
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release.</emphasis></para>
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</caution>
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<section id="Install">
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<title>Installing Shorewall</title>
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<section id="Howto">
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<title>Where do I find Step by Step Installation and Configuration
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Instructions?</title>
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<para><emphasis role="bold">Answer:</emphasis> Check out the <ulink
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url="shorewall_quickstart_guide.htm">QuickStart Guides</ulink>.</para>
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</section>
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<section id="faq37">
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<title>(FAQ 37) I just installed Shorewall on Debian and the
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/etc/shorewall directory is almost empty!!!</title>
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<para><emphasis role="bold">Answer:</emphasis></para>
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<important>
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<para>Once you have installed the .deb package and before you attempt
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to configure Shorewall, please heed the advice of Lorenzo Martignoni,
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former Shorewall Debian Maintainer:</para>
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<para><quote>For more information about Shorewall usage on Debian
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system please look at /usr/share/doc/shorewall-common/README.Debian
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provided by [the] shorewall-common Debian package.</quote></para>
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</important>
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<para>If you install using the .deb, you will find that your <filename
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class="directory">/etc/shorewall</filename> directory is almost empty.
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This is intentional. The released configuration file skeletons may be
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found on your system in the directory <filename
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class="directory">/usr/share/doc/shorewall-common/default-config</filename>.
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Simply copy the files you need from that directory to <filename
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class="directory">/etc/shorewall</filename> and modify the
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copies.</para>
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<section id="faq37a">
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<title>(FAQ 37a) I just installed Shorewall on Debian and I can't find
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the sample configurations.</title>
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<para><emphasis role="bold">Answer:</emphasis> Beginning with
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Shorewall 4.0, the samples are in the shorewall-common package and are
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installed in <filename
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class="directory">/usr/share/doc/shorewall-common/examples/</filename>.</para>
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</section>
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</section>
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<section id="faq75">
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<title>(FAQ 75) I can't find the Shorewall 4.0 (or 4.2) shorewall-common
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RPM. Where is it?</title>
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<para><emphasis role="bold">Answer:</emphasis> If you use Simon Matter's
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Redhat/Fedora/CentOS rpms, be aware that Simon calls the
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<emphasis>shorewall-common</emphasis> RPM
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<emphasis>shorewall</emphasis>. So you should download and install the
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appropriate <emphasis>shorewall-4.x.y</emphasis> RPM from his
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site.</para>
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</section>
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<section id="faq14">
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<title>(FAQ 14) I can't find the Shorewall 4.4 shorewall-common,
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shorewall-shell and shorewall-perl packages? Where are they?</title>
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<para><emphasis role="bold">Answer</emphasis>:In Shorewall 4.4, the
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<firstterm>shorewall-shell</firstterm> package was discontinued. The
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<firstterm>shorewall-common</firstterm> and
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<firstterm>shorewall-perl</firstterm> packages were combined to form a
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single <firstterm>shorewall</firstterm> package.</para>
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</section>
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</section>
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<section id="Upgrading">
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<title>Upgrading Shorewall</title>
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<section id="faq66">
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<title>(FAQ 66) I'm trying to upgrade to Shorewall 4.0 (or 4.2); where
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is the 'shorewall' package?</title>
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<para><emphasis role="bold">Answer:</emphasis> Please see the <ulink
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url="upgrade_issues.htm">upgrade issues.</ulink></para>
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<section id="faq66a">
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<title>(FAQ 66a) I'm trying to upgrade to Shorewall 4.0 (or 4.2); do I
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have to uninstall the 'shorewall' package?</title>
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<para><emphasis role="bold">Answer:</emphasis> Please see the <ulink
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url="upgrade_issues.htm">upgrade issues.</ulink></para>
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</section>
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<section id="faq66b">
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<title>(FAQ 66b) I'm trying to upgrade to Shorewall 4.x: which of
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these packages do I need to install?</title>
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<para><emphasis role="bold">Answer:</emphasis> Please see the <ulink
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url="upgrade_issues.htm">upgrade issues.</ulink></para>
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</section>
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</section>
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<section id="faq34">
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<title>(FAQ 34) I am trying to upgrade to Shorewall 4.4 and I can't find
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the shorewall-common, shorewall-shell and shorewall-perl packages? Where
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are they?</title>
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<para><emphasis role="bold">Answer</emphasis>:In Shorewall 4.4, the
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<firstterm>shorewall-shell</firstterm> package was discontinued. The
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<firstterm>shorewall-common</firstterm> and
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<firstterm>shorewall-perl</firstterm> packages were combined to form a
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single <firstterm>shorewall</firstterm> package. For further
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information, please see the <ulink url="upgrade_issues.htm">upgrade
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issues.</ulink>.</para>
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</section>
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<section id="faq34a">
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<title>(FAQ 34a) I am trying to upgrade to Shorewall 4.4 and I'm getting
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errors when I try to start Shorewall. Where can I find information about
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these issues?</title>
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<para><emphasis role="bold">Answer</emphasis>: Please see the <ulink
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url="upgrade_issues.htm">upgrade issues.</ulink></para>
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</section>
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<section id="faq34b">
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<title>(FAQ 34b) I am trying to upgrade to Shorewall 4.4 and I'm seeing
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warning messages when I try to start Shorewall. Where can I find
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information about these issues?</title>
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<para><emphasis role="bold">Answer</emphasis>: Please see the <ulink
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url="upgrade_issues.htm">upgrade issues.</ulink></para>
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</section>
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<section id="faq76">
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<title>(FAQ 76) I just upgraded my Debian (Ubuntu, Kubuntu, ...) system
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and now masquerading doesn't work? What happened?</title>
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<para><emphasis role="bold">Answer:</emphasis> This happens to people
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who ignore <ulink url="Install.htm#Upgrade_Deb">our advice</ulink> and
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allow the installer to replace their working
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<filename>/etc/shorewall/shorewall.conf</filename> with one that has
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default settings. Failure to forward traffic (such as during masqueraded
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net access from a local network) usually means that <filename><ulink
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url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink></filename>
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contains the Debian default setting IP_FORWARDING=Keep; it should be
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IP_FORWARDING=On.</para>
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</section>
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</section>
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<section id="PortForwarding">
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<title>Port Forwarding (Port Redirection)</title>
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<section id="faq1">
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<title>(FAQ 1) I want to forward UDP port 7777 to my personal PC with IP
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address 192.168.1.5. I've looked everywhere and can't find how to do
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it.</title>
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<para><emphasis role="bold">Answer:</emphasis> The format of a
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port-forwarding rule to a local system is as follows:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT
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DNAT net loc:<emphasis>local-IP-address</emphasis>[:<emphasis>local-port</emphasis>] <emphasis>protocol</emphasis> <emphasis>port-number</emphasis></programlisting>
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<para>So to forward UDP port 7777 to internal system 192.168.1.5, the
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rule is:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT
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DNAT net loc:192.168.1.5 udp 7777</programlisting>
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<para>If you want to forward requests directed to a particular address (
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<emphasis>external-IP</emphasis> ) on your firewall to an internal
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system:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
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# PORT DEST.
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DNAT net loc:<emphasis>local-IP-address</emphasis>>[:<emphasis>local-port</emphasis>] <emphasis>protocol</emphasis> <emphasis>port-number</emphasis> - <emphasis>external-IP</emphasis></programlisting>
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<para>If you want to forward requests from a particular Internet address
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( <emphasis>address</emphasis> ):</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
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# PORT DEST.
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DNAT net:<emphasis>address</emphasis> loc:<emphasis>local-IP-address</emphasis>[:<emphasis>local-port</emphasis>] <emphasis> protocol</emphasis> <emphasis>port-number</emphasis> -</programlisting>
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<para>Finally, if you need to forward a range of ports, in the DEST PORT
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column specify the range as
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<emphasis>low-port:high-port</emphasis>.</para>
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<section id="faq1a">
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<title>(FAQ 1a) Okay -- I followed those instructions but it doesn't
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work</title>
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<para><emphasis role="bold">Answer:</emphasis> That is usually the
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result of one of four things:</para>
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<itemizedlist>
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<listitem>
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<para>You are trying to test from inside your firewall (no, that
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won't work -- see <xref linkend="faq2" />).</para>
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</listitem>
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<listitem>
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<para>You have a more basic problem with your local system (the
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one that you are trying to forward to) such as an incorrect
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default gateway (it must be set to the IP address of your
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firewall's internal interface; if that isn't possible for some
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reason, see <link linkend="faq1f">FAQ 1f</link>).</para>
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</listitem>
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<listitem>
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<para>Your ISP is blocking that particular port inbound or, for
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TCP, your ISP is dropping the outbound SYN,ACK response.</para>
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</listitem>
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<listitem>
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<para>You are running Mandriva Linux prior to 10.0 final and have
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configured Internet Connection Sharing. In that case, the name of
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your local zone is 'masq' rather than 'loc' (change all instances
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of 'loc' to 'masq' in your rules). You may want to consider
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re-installing Shorewall in a configuration which matches the
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Shorewall documentation. See the <ulink
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url="two-interface.htm">two-interface QuickStart Guide</ulink> for
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details.</para>
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</listitem>
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</itemizedlist>
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</section>
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<section id="faq1b">
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<title>(FAQ 1b) I'm still having problems with port forwarding</title>
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<para><emphasis role="bold">Answer:</emphasis> To further diagnose
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this problem:</para>
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<itemizedlist>
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<listitem>
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<para>As root, type <quote> <command>shorewall reset</command>
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</quote> ("<command>shorewall-lite reset</command>", if you are
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running Shorewall Lite). This clears all Netfilter
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counters.</para>
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</listitem>
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<listitem>
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<para>Try to connect to the redirected port from an external
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host.</para>
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</listitem>
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<listitem>
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<para>As root type <quote> <command>shorewall show nat</command>
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</quote> ("<command>shorewall-lite show nat</command>", if you are
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running Shorewall Lite).</para>
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</listitem>
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<listitem>
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<para>Locate the appropriate DNAT rule. It will be in a chain
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called <emphasis><source zone></emphasis>_dnat
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(<quote>net_dnat</quote> in the above examples).</para>
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</listitem>
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<listitem>
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<para>Is the packet count in the first column non-zero? If so, the
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connection request is reaching the firewall and is being
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redirected to the server. In this case, the problem is usually a
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missing or incorrect default gateway setting on the local system
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(the system you are trying to forward to -- its default gateway
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should be the IP address of the firewall's interface to that
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system).</para>
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</listitem>
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<listitem>
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<para>If the packet count is zero:</para>
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<itemizedlist>
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<listitem>
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<para>the connection request is not reaching your server
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(possibly it is being blocked by your ISP); or</para>
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</listitem>
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<listitem>
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<para>you are trying to connect to a secondary IP address on
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your firewall and your rule is only redirecting the primary IP
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address (You need to specify the secondary IP address in the
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<quote>ORIG. DEST.</quote> column in your DNAT rule);
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or</para>
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</listitem>
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<listitem>
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<para>your DNAT rule doesn't match the connection request in
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some other way. In that case, you may have to use a packet
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sniffer such as tcpdump or ethereal to further diagnose the
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problem.</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>If the packet count is non-zero, check your log to see if
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the connection is being dropped or rejected. If it is, then you
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may have a zone definition problem such that the server is in a
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different zone than what is specified in the DEST column. At a
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root prompt, type "<command>shorewall show zones</command>"
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("<command>shorewall-lite show zones</command>") then be sure that
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in the DEST column you have specified the <emphasis
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role="bold">first</emphasis> zone in the list that matches
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OUT=<dev> and DEST= <ip>from the REJECT/DROP log
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message.</para>
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</listitem>
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<listitem>
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<para>If everything seems to be correct according to these tests
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but the connection doesn't work, it may be that your ISP is
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blocking SYN,ACK responses. This technique allows your ISP to
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detect when you are running a server (usually in violation of your
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service agreement) and to stop connections to that server from
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being established.</para>
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</listitem>
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</itemizedlist>
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</section>
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<section id="faq1c">
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<title>(FAQ 1c) From the Internet, I want to connect to port 1022 on
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my firewall and have the firewall forward the connection to port 22 on
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local system 192.168.1.3. How do I do that?</title>
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<para><emphasis role="bold">Answer:</emphasis>In
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/<filename>etc/shorewall/rules</filename>:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT
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DNAT net loc:192.168.1.3:22 tcp 1022</programlisting>
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</section>
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<section id="faq1d">
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<title>(FAQ 1d) I have a web server in my DMZ and I use port
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forwarding to make that server accessible from the Internet. That
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works fine but when my local users try to connect to the server using
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the Firewall's external IP address, it doesn't work.</title>
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<para><emphasis role="bold">Answer:</emphasis> See <link
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linkend="faq2b">FAQ 2b</link>.</para>
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</section>
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<section id="faq1e">
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<title>(FAQ 1e) In order to discourage brute force attacks I would
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like to redirect all connections on a non-standard port (4104) to port
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22 on the router/firewall. I notice that setting up a REDIRECT rule
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causes the firewall to open both ports 4104 and 22 to connections from
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the net. Is it possible to only redirect 4104 to the localhost port 22
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and have connection attempts to port 22 from the net dropped?</title>
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<para><emphasis role="bold">Answer </emphasis>courtesy of Ryan: Assume
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that the IP address of your local firewall interface is 192.168.1.1.
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If you configure SSHD to only listen on that interface and add the
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following rule then from the net, you will have 4104 listening, from
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your LAN, port 22.</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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DNAT net fw:192.168.1.1:22 tcp 4104</programlisting>
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</section>
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<section id="faq1f">
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<title>(FAQ 1f) Why must the server that I port forward to have it's
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default gateway set to my Shorewall system's IP address?</title>
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<para><emphasis role="bold">Answer:</emphasis> Let's take an example.
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Suppose that</para>
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<itemizedlist>
|
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<listitem>
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<para>Your Shorewall firewall's external IP address is
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206.124.146.176 (eth0) and its internal IP address is 192.168.1.1
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(eth1).</para>
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</listitem>
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<listitem>
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<para>You have another gateway router with external IP address
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130.252.100.109 and internal IP address 192.168.1.254.</para>
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</listitem>
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<listitem>
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<para>You have an FTP server behind both routers with IP address
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192.168.1.4</para>
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</listitem>
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<listitem>
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<para>The FTP server's default gateway is through the second
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router (192.168.1.254).</para>
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</listitem>
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<listitem>
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<para>You have this rule on the Shorewall system:<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
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# PORT DEST.
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DNAT net loc:192.168.1.4 tcp 21 - 206.124.146.176</programlisting></para>
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</listitem>
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<listitem>
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<para>Internet host 16.105.221.4 issues the command <command>ftp
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206.124.146.176</command></para>
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</listitem>
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</itemizedlist>
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<para>This results in the following set of events:</para>
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<orderedlist>
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<listitem>
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<para>16.105.221.4 sends a TCP SYN packet to 206.124.146.176
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specifying destination port 21.</para>
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</listitem>
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<listitem>
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<para>The Shorewall box rewrites the destination IP address to
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192.168.1.4 and forwards the packet.</para>
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</listitem>
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|
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<listitem>
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<para>The FTP server receives the packet and accepts the
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connection, generating a SYN,ACK packet back to 16.105.221.4.
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Because the server's default gateway is through the second router,
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it sends the packet to that router.</para>
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</listitem>
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</orderedlist>
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<para>At this point, one of two things can happen. Either the second
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router discards or rejects the packet; or, it rewrites the source IP
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address to 130.252.100.109 and forwards the packet back to
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16.105.221.4. Regardless of which happens, the connection is doomed.
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|
Clearly if the packet is rejected or dropped, the connection will not
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|
be successful. But even if the packet reaches 16.105.221.4, that host
|
|
will reject it since it's SOURCE IP address (130.252.100.109) doesn't
|
|
match the DESTINATION IP ADDRESS (206.124.146.176) of the original SYN
|
|
packet.</para>
|
|
|
|
<para>The best way to work around this problem is to change the
|
|
default gateway on the FTP server to the Shorewall system's internal
|
|
IP address (192.168.1.1). But if that isn't possible, you can work
|
|
around the problem with the following ugly hack in
|
|
<filename>/etc/shorewall/masq</filename>:<programlisting>#INTERFACE SOURCE ADDRESS PROTO PORT
|
|
eth1:192.168.1.4 0.0.0.0/0 192.168.1.1 tcp 21</programlisting></para>
|
|
|
|
<para>This rule has the undesirable side effect that it makes all FTP
|
|
connections from the net appear to the FTP server as if they
|
|
originated on the Shorewall system. But it will force the FTP server
|
|
to reply back through the Shorewall system who can then rewrite the
|
|
SOURCE IP address in the responses properly.</para>
|
|
</section>
|
|
|
|
<section id="faq1g">
|
|
<title>(FAQ 1g) I would like to redirect port 80 on my public IP
|
|
address (206.124.146.176) to port 993 on Internet host
|
|
66.249.93.111</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> This requires a vile
|
|
hack similar to the one in <link linkend="faq2">FAQ 2</link>. Assuming
|
|
that your Internet zone is named <emphasis>net</emphasis> and connects
|
|
on interface <filename class="devicefile">eth0</filename>:</para>
|
|
|
|
<para>In <filename>/etc/shorewall/rules</filename>:<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
|
|
# PORT DEST.
|
|
DNAT net net:66.249.93.111:993 tcp 80 - 206.124.146.176</programlisting></para>
|
|
|
|
<para>In <filename>/etc/shorewall/interfaces</filename>, specify the
|
|
<emphasis role="bold">routeback</emphasis> option on
|
|
eth0:<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
|
|
net eth0 detect <emphasis role="bold">routeback</emphasis></programlisting></para>
|
|
|
|
<para>And in <filename>/etc/shorewall/masq</filename>;<programlisting>#INTERFACE SOURCE ADDRESS PROTO PORT
|
|
eth0:66.249.93.111 0.0.0.0/0 206.124.146.176 tcp 993</programlisting></para>
|
|
|
|
<para>Like the hack in FAQ 2, this one results in all forwarded
|
|
connections looking to the server (66.249.93.11) as if they originated
|
|
on your firewall (206.124.146.176).</para>
|
|
</section>
|
|
|
|
<section id="faq1h">
|
|
<title>(FAQ 1h) How do I set shorewall to allow ssh on port 9022 from
|
|
net? SSHD is listening on port 22.</title>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: Use this rule.</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST
|
|
# PORT(S)
|
|
REDIRECT net 22 tcp 9022</programlisting>
|
|
|
|
<para>Note that the above rule will also allow connections from the
|
|
net on TCP port 22. If you don't want that, see <link
|
|
linkend="faq1e">FAQ 1e</link>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="faq30">
|
|
<title>(FAQ 30) I'm confused about when to use DNAT rules and when to
|
|
use ACCEPT rules.</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> It would be a good idea
|
|
to review the <ulink url="shorewall_quickstart_guide.htm">QuickStart
|
|
Guide</ulink> appropriate for your setup; the guides cover this topic in
|
|
a tutorial fashion. DNAT rules should be used for connections that need
|
|
to go the opposite direction from SNAT/MASQUERADE. So if you masquerade
|
|
or use SNAT from your local network to the Internet then you will need
|
|
to use DNAT rules to allow connections from the Internet to your local
|
|
network.<note>
|
|
<para>If you use both 1:1 NAT and SNAT/MASQUERADE, those connections
|
|
that are subject to 1:1 NAT should use ACCEPT rather than DNAT.
|
|
Note, however, that DNAT can be used to override 1:1 NAT so as to
|
|
redirect a connection to a different internal system or port than
|
|
would be the case using 1:1 NAT.</para>
|
|
</note> You also want to use DNAT rules when you intentionally want to
|
|
rewrite the destination IP address or port number. In all other cases,
|
|
you use ACCEPT unless you need to hijack connections as they go through
|
|
your firewall and handle them on the firewall box itself; in that case,
|
|
you use a REDIRECT rule.</para>
|
|
|
|
<note>
|
|
<para>The preceding answer should <emphasis>not</emphasis> be
|
|
interpreted to mean that DNAT can only be used in conjunction with
|
|
SNAT. But in common configurations using private local addresses, that
|
|
is the most common usage.</para>
|
|
</note>
|
|
</section>
|
|
|
|
<section id="faq8">
|
|
<title>(FAQ 8) I have several external IP addresses and use
|
|
/etc/shorewall/nat to associate them with systems in my DMZ. When I add
|
|
a DNAT rule, say for ports 80 and 443, Shorewall redirects connections
|
|
on those ports for all of my addresses. How can I restrict DNAT to only
|
|
a single address?</title>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: Specify the external
|
|
address that you want to redirect in the ORIGINAL DEST column.</para>
|
|
|
|
<para>Example:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
|
|
# PORT DEST.
|
|
DNAT net net:192.168.4.22 tcp 80,443 - <emphasis
|
|
role="bold">206.124.146.178</emphasis></programlisting>
|
|
</section>
|
|
|
|
<section id="faq38">
|
|
<title>(FAQ 38) Where can I find more information about DNAT?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Ian Allen has written a
|
|
<ulink url="http://idallen.com/dnat.txt">Paper about DNAT and
|
|
Linux</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq48">
|
|
<title>(FAQ 48) How do I Set up Transparent HTTP Proxy with
|
|
Shorewall?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> See <ulink
|
|
url="Shorewall_Squid_Usage.html">Shorewall_Squid_Usage.html</ulink>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="DNS-DNAT">
|
|
<title id="DNS">DNS and Port Forwarding/NAT</title>
|
|
|
|
<section id="faq2">
|
|
<title>(FAQ 2) I port forward www requests to www.mydomain.com (IP
|
|
130.151.100.69) to system 192.168.1.5 in my local network. External
|
|
clients can browse http://www.mydomain.com but internal clients
|
|
can't.</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> I have two objections to
|
|
this setup.</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Having an Internet-accessible server in your local network is
|
|
like raising foxes in the corner of your hen house. If the server is
|
|
compromised, there's nothing between that server and your other
|
|
internal systems. For the cost of another NIC and a cross-over
|
|
cable, you can put your server in a DMZ such that it is isolated
|
|
from your local systems - assuming that the Server can be located
|
|
near the Firewall, of course :-)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>The accessibility problem is best solved using
|
|
<firstterm>Split DNS</firstterm> (either <ulink
|
|
url="SplitDNS.html">use a separate DNS server</ulink> for local
|
|
clients or use <ulink url="shorewall_setup_guide.htm#DNS">Bind
|
|
Version 9 <quote>views</quote></ulink> on your main name server)
|
|
such that www.mydomain.com resolves to 130.141.100.69 externally and
|
|
192.168.1.5 internally. That's what I do here at shorewall.net for
|
|
my local systems that use one-to-one NAT.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>So the best and most secure way to solve this problem is to move
|
|
your Internet-accessible server(s) to a separate LAN segment with it's
|
|
own interface to your firewall and follow <link linkend="faq2b">FAQ
|
|
2b</link>. That way, your local systems are still safe if your server
|
|
gets hacked and you don't have to run a split DNS configuration
|
|
(separate server or Bind 9 views).</para>
|
|
|
|
<para>If physical limitations make it impractical to segregate your
|
|
servers on a separate LAN, the next best solution it to use Split DNS.
|
|
Before you complain "It's too hard to set up split DNS!", <ulink
|
|
url="SplitDNS.html"><emphasis role="bold">check
|
|
here</emphasis></ulink>.</para>
|
|
|
|
<para>But if you are the type of person who prefers quick and dirty
|
|
hacks to "doing it right", then proceed as described below.<warning>
|
|
<para>All traffic redirected through use of this hack will look to
|
|
the server as if it originated on the firewall rather than on the
|
|
original client! So the server's access logs will be useless for
|
|
determining which local hosts are accessing the server.</para>
|
|
</warning></para>
|
|
|
|
<para>Assuming that your external interface is eth0 and your internal
|
|
interface is eth1 and that eth1 has IP address 192.168.1.254 with subnet
|
|
192.168.1.0/24, then:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>In <filename>/etc/shorewall/interfaces</filename>:</para>
|
|
|
|
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
|
|
loc eth1 detect <emphasis role="bold">routeback</emphasis> </programlisting>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>In <filename>/etc/shorewall/masq</filename>:</para>
|
|
|
|
<programlisting>#INTERFACE SOURCE ADDRESS PROTO PORT(S)
|
|
<emphasis role="bold">eth1:192.168.1.5 eth1 192.168.1.254 tcp www</emphasis></programlisting>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>In <filename>/etc/shorewall/rules</filename>:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
|
|
# PORT DEST.
|
|
<emphasis role="bold">DNAT loc loc:192.168.1.5 tcp www - 130.151.100.69</emphasis></programlisting>
|
|
|
|
<para>That rule only works of course if you have a static external
|
|
IP address. If you have a dynamic IP address then include this in
|
|
<filename>/etc/shorewall/params</filename> (or your
|
|
<filename><export directory>/init</filename> file if you are
|
|
using Shorewall Lite on the firewall system):</para>
|
|
|
|
<programlisting><command>ETH0_IP=`find_first_interface_address eth0`</command> </programlisting>
|
|
|
|
<para>and make your DNAT rule:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
|
|
# PORT DEST.
|
|
DNAT loc loc:192.168.1.5 tcp www - <emphasis
|
|
role="bold">$ETH0_IP</emphasis></programlisting>
|
|
|
|
<para>Using this technique, you will want to configure your
|
|
DHCP/PPPoE/PPTP/… client to automatically restart Shorewall each
|
|
time that you get a new IP address.</para>
|
|
|
|
<note>
|
|
<para>For optional interfaces, use the function <emphasis
|
|
role="bold">find_first_interface_address_if_any()</emphasis>
|
|
rather than <emphasis
|
|
role="bold">find_first_interface_address()</emphasis>. The former
|
|
will return 0.0.0.0 if the interface has no configured IP address;
|
|
the latter terminates the calling program.</para>
|
|
</note>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<section id="faq2a">
|
|
<title>(FAQ 2a) I have a zone <quote>Z</quote> with an RFC1918 subnet
|
|
and I use one-to-one NAT to assign non-RFC1918 addresses to hosts in
|
|
Z. Hosts in Z cannot communicate with each other using their external
|
|
(non-RFC1918 addresses) so they can't access each other using their
|
|
DNS names.</title>
|
|
|
|
<note>
|
|
<para>If the ALL INTERFACES column in /etc/shorewall/nat is empty or
|
|
contains <quote>Yes</quote>, you will also see log messages like the
|
|
following when trying to access a host in Z from another host in Z
|
|
using the destination host's public address:</para>
|
|
|
|
<programlisting>Oct 4 10:26:40 netgw kernel:
|
|
Shorewall:FORWARD:REJECT:IN=eth1 OUT=eth1 SRC=192.168.118.200
|
|
DST=192.168.118.210 LEN=48 TOS=0x00 PREC=0x00 TTL=127 ID=1342 DF
|
|
PROTO=TCP SPT=1494 DPT=1491 WINDOW=17472 RES=0x00 ACK SYN URGP=0</programlisting>
|
|
</note>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> This is another problem
|
|
that is best solved using split DNS. It allows both external and
|
|
internal clients to access a NATed host using the host's DNS
|
|
name.</para>
|
|
|
|
<para>Another good way to approach this problem is to switch from
|
|
one-to-one NAT to Proxy ARP. That way, the hosts in Z have non-RFC1918
|
|
addresses and can be accessed externally and internally using the same
|
|
address.</para>
|
|
|
|
<para>If you don't like those solutions and prefer, incredibly, to
|
|
route all Z->Z traffic through your firewall then:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>Set the routeback option on the interface to Z.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Set the ALL INTERFACES column in the nat file to
|
|
<quote>Yes</quote>.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<example id="Example1">
|
|
<title>Example:</title>
|
|
|
|
<literallayout>Zone: dmz, Interface: eth2, Subnet: 192.168.2.0/24, Address: 192.168.2.254</literallayout>
|
|
|
|
<para>In <filename>/etc/shorewall/interfaces</filename>:</para>
|
|
|
|
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
|
|
dmz eth2 192.168.2.255 <emphasis role="bold">routeback</emphasis> </programlisting>
|
|
|
|
<para>In <filename>/etc/shorewall/nat</filename>, be sure that you
|
|
have <quote>Yes</quote> in the ALL INTERFACES column.</para>
|
|
|
|
<para>In /etc/shorewall/masq:</para>
|
|
|
|
<programlisting>#INTERFACE SOURCE ADDRESS
|
|
<emphasis role="bold">eth2 eth2 192.168.2.254</emphasis></programlisting>
|
|
|
|
<para>Like the silly hack in FAQ 2 above, this will make all
|
|
dmz->dmz traffic appear to originate on the firewall.</para>
|
|
</example>
|
|
</section>
|
|
|
|
<section id="faq2b">
|
|
<title>(FAQ 2b) I have a web server in my DMZ and I use port
|
|
forwarding to make that server accessible from the Internet as
|
|
www.mydomain.com. That works fine but when my local users try to
|
|
connect to www.mydomain.com, it doesn't work.</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Let's assume the
|
|
following:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>External IP address is 206.124.146.176 on <filename
|
|
class="devicefile">eth0</filename> (www.mydomain.com).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Server's IP address is 192.168.2.4</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>You can enable access to the server from your local network
|
|
using the firewall's external IP address by adding this rule:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL
|
|
# PORT DEST
|
|
<emphasis role="bold">DNAT loc dmz:192.168.2.4 tcp 80 - 206.124.146.176</emphasis></programlisting>
|
|
|
|
<para>If your external IP address is dynamic, then you must do the
|
|
following:</para>
|
|
|
|
<para>In <filename>/etc/shorewall/params</filename> (or in your
|
|
<filename><export directory>/init</filename> file if you are
|
|
using Shorewall Lite on the firewall system):</para>
|
|
|
|
<programlisting><command>ETH0_IP=`find_first_interface_address eth0`</command> </programlisting>
|
|
|
|
<para>and make your DNAT rule:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT SOURCE ORIGINAL
|
|
# PORT DEST.
|
|
DNAT loc dmz:192.168.2.4 tcp 80 - <emphasis
|
|
role="bold">$ETH0_IP</emphasis></programlisting>
|
|
|
|
<warning>
|
|
<para>With dynamic IP addresses, you probably don't want to use
|
|
<ulink
|
|
url="starting_and_stopping_shorewall.htm"><command>shorewall[-lite]
|
|
save</command> and <command>shorewall[-lite]
|
|
restore</command></ulink>.</para>
|
|
</warning>
|
|
|
|
<note>
|
|
<para>For optional interfaces, use the function <emphasis
|
|
role="bold">find_first_interface_address_if_any()</emphasis> rather
|
|
than <emphasis
|
|
role="bold">find_first_interface_address()</emphasis>. The former
|
|
will return 0.0.0.0 if the interface has no configured IP address;
|
|
the latter terminates the calling program.</para>
|
|
</note>
|
|
</section>
|
|
|
|
<section id="faq2c">
|
|
<title>(FAQ 2c) I tried to apply the answer to FAQ 2 to my external
|
|
interface and the net zone and it didn't work. Why?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Did you set <emphasis
|
|
role="bold">IP_FORWARDING=On</emphasis> in
|
|
<filename>shorewall.conf</filename>?</para>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Blacklisting">
|
|
<title>Blacklisting</title>
|
|
|
|
<section id="faq63">
|
|
<title>(FAQ 63) I just blacklisted IP address 206.124.146.176 and I can
|
|
still ping it. What did I do wrong?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Nothing.</para>
|
|
|
|
<para>Blacklisting an IP address blocks incoming traffic from that IP
|
|
address. And if you set BLACKLISTNEWONLY=Yes in
|
|
<filename>shorewall.conf</filename>, then only new connections <emphasis
|
|
role="bold">from</emphasis> that address are disallowed; traffic from
|
|
that address that is part of an established connection (such as ping
|
|
replies) is allowed.</para>
|
|
</section>
|
|
|
|
<section id="faq84">
|
|
<title>(FAQ 84) I put some IPs in the blacklist file in /etc/shorewall
|
|
to block the ips but i'm still getting reports from PSAD from those ips
|
|
saying they're port scanning. Shouldn't being on the blacklist drop all
|
|
packets from those ips?</title>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: You probably forgot to
|
|
specify the <emphasis role="bold">blacklist</emphasis> option for your
|
|
external interface(s) in
|
|
<filename>/etc/shorewall/interfaces</filename>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="MSN">
|
|
<title>Netmeeting/MSN</title>
|
|
|
|
<section id="faq3">
|
|
<title>(FAQ 3) I want to use Netmeeting or MSN Instant Messenger with
|
|
Shorewall. What do I do?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> There is an <ulink
|
|
url="http://www.kfki.hu/~kadlec/sw/netfilter/newnat-suite/">H.323
|
|
connection tracking/NAT module</ulink> that helps with Netmeeting. Note
|
|
however that one of the Netfilter developers recently posted the
|
|
following:</para>
|
|
|
|
<blockquote>
|
|
<para><programlisting>> I know PoM -ng is going to address this issue, but till it is ready, and
|
|
> all the extras are ported to it, is there any way to use the h.323
|
|
> conntrack module kernel patch with a 2.6 kernel?
|
|
> Running 2.6.1 - no 2.4 kernel stuff on the system, so downgrade is not
|
|
> an option... The module is not ported yet to 2.6, sorry.
|
|
> Do I have any options besides a gatekeeper app (does not work in my
|
|
> network) or a proxy (would prefer to avoid them)?
|
|
|
|
I suggest everyone to setup a proxy (gatekeeper) instead: the module is
|
|
really dumb and does not deserve to exist at all. It was an excellent tool
|
|
to debug/develop the newnat interface.</programlisting></para>
|
|
</blockquote>
|
|
|
|
<para>Look <ulink url="UPnP.html">here</ulink> for a solution for MSN IM
|
|
but be aware that there are significant security risks involved with
|
|
this solution. Also check the Netfilter mailing list archives at <ulink
|
|
url="http://www.netfilter.org">http://www.netfilter.org</ulink>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Openports">
|
|
<title>Open Ports</title>
|
|
|
|
<section id="faq51">
|
|
<title>(FAQ 51) How do I Open Ports in Shorewall?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> No one who has installed
|
|
Shorewall using one of the <ulink
|
|
url="shorewall_quickstart_guide.htm">Quick Start Guides</ulink> should
|
|
have to ask this question.</para>
|
|
|
|
<para>Regardless of which guide you used, all outbound communication is
|
|
open by default. So you do not need to 'open ports' for output.</para>
|
|
|
|
<para>For input:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>If you installed using the Standalone Guide, then please
|
|
<ulink url="standalone.htm#Open">re-read this
|
|
section</ulink>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If you installed using the Two-interface Guide, then please
|
|
re-read these sections: <ulink url="two-interface.htm#DNAT">Port
|
|
Forwarding (DNAT)</ulink>, and <ulink
|
|
url="two-interface.htm#Open">Other Connections</ulink></para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If you installed using the Three-interface Guide, then please
|
|
re-read these sections: <ulink url="three-interface.htm#DNAT">Port
|
|
Forwarding (DNAT)</ulink> and <ulink
|
|
url="three-interface.htm#Open">Other Connections</ulink></para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If you installed using the <ulink
|
|
url="shorewall_setup_guide.htm">Shorewall Setup Guide</ulink> then
|
|
you had better read the guide again -- you clearly missed a
|
|
lot.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>Also please see the <link linkend="PortForwarding">Port Forwarding
|
|
section of this FAQ</link>.</para>
|
|
</section>
|
|
|
|
<section id="faq4">
|
|
<title>(FAQ 4) I just used an online port scanner to check my firewall
|
|
and it shows some ports as <quote>closed</quote> rather than
|
|
<quote>blocked</quote>. Why?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> The default Shorewall
|
|
setup invokes the <emphasis role="bold">Drop</emphasis> action prior to
|
|
enforcing a DROP policy and the default policy to all zones from the
|
|
Internet is DROP. The Drop action is defined in
|
|
<filename>/usr/share/shorewall/action.Drop</filename> which in turn
|
|
invokes the <emphasis role="bold">Auth</emphasis> macro (defined in
|
|
<filename>/usr/share/shorewall/macro.Auth</filename>) specifying the
|
|
<emphasis role="bold">REJECT</emphasis> action (i.e., <emphasis
|
|
role="bold">Auth(REJECT)</emphasis>). This is necessary to prevent
|
|
outgoing connection problems to services that use the
|
|
<quote>Auth</quote> mechanism for identifying requesting users. That is
|
|
the only service which the default setup rejects.</para>
|
|
|
|
<para>If you are seeing closed TCP ports other than 113 (auth) then
|
|
either you have added rules to REJECT those ports or a router outside of
|
|
your firewall is responding to connection requests on those
|
|
ports.</para>
|
|
|
|
<section id="faq4a">
|
|
<title>(FAQ 4a) I just ran an nmap UDP scan of my firewall and it
|
|
showed 100s of ports as open!!!!</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Take a deep breath and
|
|
read the nmap man page section about UDP scans. If nmap gets <emphasis
|
|
role="bold">nothing</emphasis> back from your firewall then it reports
|
|
the port as open. If you want to see which UDP ports are really open,
|
|
temporarily change your net->all policy to REJECT, restart
|
|
Shorewall and do the nmap UDP scan again.</para>
|
|
</section>
|
|
|
|
<section id="faq4b">
|
|
<title>(FAQ 4b) I have a port that I can't close no matter how I
|
|
change my rules.</title>
|
|
|
|
<para>I had a rule that allowed telnet from my local network to my
|
|
firewall; I removed that rule and restarted Shorewall but my telnet
|
|
session still works!!!</para>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Rules only govern the
|
|
establishment of new connections. Once a connection is established
|
|
through the firewall it will be usable until disconnected (tcp) or
|
|
until it times out (other protocols). If you stop telnet and try to
|
|
establish a new session your firewall will block that attempt.</para>
|
|
</section>
|
|
|
|
<section id="faq4c">
|
|
<title>(FAQ 4c) How do I use Shorewall with PortSentry?</title>
|
|
|
|
<para><ulink
|
|
url="http://www.shorewall.net/pub/shorewall/contrib/PortsentryHOWTO.txt"><emphasis
|
|
role="bold">Answer:</emphasis> Here's a writeup</ulink> describing a
|
|
nice integration of Shorewall and PortSentry.</para>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Connections">
|
|
<title>Connection Problems</title>
|
|
|
|
<section id="pseudofaq17">
|
|
<title>Why are these packets being Dropped/Rejected? How do I decode
|
|
Shorewall log messages?</title>
|
|
|
|
<para>Please see <link linkend="faq17">FAQ 17</link>.</para>
|
|
</section>
|
|
|
|
<section id="faq5">
|
|
<title>(FAQ 5) I've installed Shorewall and now I can't ping through the
|
|
firewall</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> For a complete
|
|
description of Shorewall <quote>ping</quote> management, see <ulink
|
|
url="ping.html">this page</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq15">
|
|
<title>(FAQ 15) My local systems can't see out to the net</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Every time I read
|
|
<quote>systems can't see out to the net</quote>, I wonder where the
|
|
poster bought computers with eyes and what those computers will
|
|
<quote>see</quote> when things are working properly. That aside, the
|
|
most common causes of this problem are:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>The default gateway on each local system isn't set to the IP
|
|
address of the local firewall interface.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>The entry for the local network in the
|
|
<filename>/etc/shorewall/masq</filename> file is wrong or
|
|
missing.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>The DNS settings on the local systems are wrong or the user is
|
|
running a DNS server on the firewall and hasn't enabled UDP and TCP
|
|
port 53 from the local net to the firewall or from the firewall to
|
|
the Internet.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Forwarding is not enabled (This is often the problem for
|
|
Debian users). Enter this command:</para>
|
|
|
|
<programlisting>cat /proc/sys/net/ipv4/ip_forward</programlisting>
|
|
|
|
<para>If the value displayed is 0 (zero) then set <emphasis
|
|
role="bold">IP_FORWARDING=On</emphasis> in
|
|
<filename>/etc/shorewall/shorewall.conf</filename> and restart
|
|
Shorewall.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</section>
|
|
|
|
<section id="faq29">
|
|
<title>(FAQ 29) FTP Doesn't Work</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> See the <ulink
|
|
url="FTP.html">Shorewall and FTP page</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq33">
|
|
<title>(FAQ 33) From clients behind the firewall, connections to some
|
|
sites fail. Connections to the same sites from the firewall itself work
|
|
fine. What's wrong.</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Most likely, you need to
|
|
set CLAMPMSS=Yes in <filename><ulink
|
|
url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink></filename>.</para>
|
|
</section>
|
|
|
|
<section id="faq35">
|
|
<title>(FAQ 35) I have two Ethernet interfaces to my local network which
|
|
I have bridged. When Shorewall is started, I'm unable to pass traffic
|
|
through the bridge. I have defined the bridge interface (br0) as the
|
|
local interface in <filename>/etc/shorewall/interfaces</filename>; the
|
|
bridged Ethernet interfaces are not defined to Shorewall. How do I tell
|
|
Shorewall to allow traffic through the bridge?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Add the
|
|
<firstterm>routeback</firstterm> option to <filename
|
|
class="devicefile">br0</filename> in <filename><ulink
|
|
url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink></filename>.</para>
|
|
|
|
<para>For more information on this type of configuration, see the <ulink
|
|
url="SimpleBridge.html">Shorewall Simple Bridge
|
|
documentation</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq64">
|
|
<title>(FAQ 64) I just upgraded my kernel to 2.6.20 and my
|
|
bridge/firewall stopped working. What is wrong?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> In kernel 2.6.20, the
|
|
Netfilter <firstterm>physdev match</firstterm> feature was changed such
|
|
that it is no longer capable of matching the output device of
|
|
non-bridged traffic. You will see messages such as the following in your
|
|
log:</para>
|
|
|
|
<programlisting>Apr 20 15:03:50 wookie kernel: [14736.560947] physdev match: using --physdev-out in the OUTPUT, FORWARD and POSTROUTING chains for
|
|
non-bridged traffic is not supported anymore.</programlisting>
|
|
|
|
<para>This kernel change, while necessary, means that Shorewall zones
|
|
may no longer be defined in terms of bridge ports. See the<ulink
|
|
url="bridge-Shorewall-perl.html"> Shorewall-perl bridging
|
|
documentation</ulink> for information about how to configure
|
|
bridge/firewalls.<note>
|
|
<para>Following the instructions in the new bridging documentation
|
|
will not prevent the above message from being issued.</para>
|
|
</note></para>
|
|
</section>
|
|
|
|
<section id="faq85">
|
|
<title>(FAQ 85) Shorewall is rejecting connections from my local lan
|
|
because it thinks they are coming from the 'net' zone.</title>
|
|
|
|
<para>I'm seeing this in my log:</para>
|
|
|
|
<programlisting>Aug 31 16:51:24 fw22 kernel: Shorewall:net2fw:DROP:IN=eth5 OUT= MAC=00:0c:29:74:9c:0c:08:00:20:b2:5f:db:08:00
|
|
SRC=10.1.50.14 DST=10.1.50.7 LEN=57 TOS=0x00 PREC=0x00 TTL=255 ID=32302 DF
|
|
PROTO=UDP SPT=53289 DPT=53 LEN=37</programlisting>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: This occurs when the
|
|
external interface and an internal interface are connected to the same
|
|
switch or hub. See <ulink url="FoolsFirewall.html">this article</ulink>
|
|
for details. The solution is to never connect more than one firewall
|
|
interface to the same hub or switch (an obvious exception is that when
|
|
you have a switch that supports VLAN tagging and the interfaces are
|
|
associated with different VLANs).</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Logging">
|
|
<title>Logging</title>
|
|
|
|
<section id="faq6">
|
|
<title>(FAQ 6) Where are the log messages written and how do I change
|
|
the destination?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> NetFilter uses the
|
|
kernel's equivalent of syslog (see <quote>man syslog</quote>) to log
|
|
messages. It always uses the LOG_KERN (kern) facility (see <quote>man
|
|
openlog</quote>) and you get to choose the log level (again, see
|
|
<quote>man syslog</quote>) in your <filename><ulink
|
|
url="manpages/shorewall-policy.html">policies</ulink></filename> and
|
|
<filename><ulink
|
|
url="manpages/shorewall-rules.html">rules</ulink></filename>. The
|
|
destination for messages logged by syslog is controlled by
|
|
<filename>/etc/syslog.conf</filename> (see <quote>man
|
|
syslog.conf</quote>). When you have changed
|
|
<filename>/etc/syslog.conf</filename>, be sure to restart syslogd (on a
|
|
RedHat system, <quote>service syslog restart</quote>).</para>
|
|
|
|
<para>By default, older versions of Shorewall rate-limited log messages
|
|
through <ulink url="manpages/shorewall.conf.html">settings</ulink> in
|
|
<filename>/etc/shorewall/shorewall.conf</filename> -- If you want to log
|
|
all messages, set:</para>
|
|
|
|
<programlisting>LOGLIMIT=""
|
|
LOGBURST=""</programlisting>
|
|
|
|
<para>It is also possible to <ulink url="shorewall_logging.html">set up
|
|
Shorewall to log all of its messages to a separate file</ulink>.</para>
|
|
|
|
<section id="faq6a">
|
|
<title>(FAQ 6a) Are there any log parsers that work with
|
|
Shorewall?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Here are several links
|
|
that may be helpful:</para>
|
|
|
|
<literallayout>
|
|
<ulink url="http://www.shorewall.net/pub/shorewall/parsefw/">http://www.shorewall.net/pub/shorewall/parsefw/</ulink>
|
|
<ulink url="http://aaron.marasco.com/linux.html">http://aaron.marasco.com/linux.html</ulink>
|
|
<ulink url="http://cert.uni-stuttgart.de/projects/fwlogwatch">http://cert.uni-stuttgart.de/projects/fwlogwatch</ulink>
|
|
<ulink url="http://www.logwatch.org">http://www.logwatch.org</ulink>
|
|
</literallayout>
|
|
|
|
<para>I personally use <ulink
|
|
url="http://www.logwatch.org">Logwatch</ulink>. It emails me a report
|
|
each day from my various systems with each report summarizing the
|
|
logged activity on the corresponding system. I use the brief report
|
|
format; here's a sample:</para>
|
|
|
|
<blockquote>
|
|
<programlisting> --------------------- iptables firewall Begin ------------------------
|
|
|
|
Dropped 111 packets on interface eth0
|
|
From 58.20.162.142 - 5 packets to tcp(1080)
|
|
From 62.163.19.50 - 1 packet to udp(6348)
|
|
From 66.111.45.60 - 9 packets to tcp(192)
|
|
From 69.31.82.50 - 18 packets to tcp(3128)
|
|
From 72.232.183.102 - 2 packets to tcp(3128)
|
|
From 82.96.96.3 - 6 packets to tcp(808,1080,1978,7600,65506)
|
|
From 128.48.51.209 - 5 packets to tcp(143)
|
|
From 164.77.223.150 - 12 packets to tcp(873)
|
|
From 165.233.109.23 - 8 packets to tcp(22)
|
|
From 202.99.172.175 - 4 packets to udp(2,4081)
|
|
From 206.59.41.101 - 2 packets to tcp(5900)
|
|
From 217.91.30.224 - 24 packets to tcp(873)
|
|
From 218.87.47.114 - 6 packets to tcp(3128)
|
|
From 220.110.219.234 - 4 packets to tcp(22)
|
|
From 220.133.116.173 - 5 packets to tcp(3128)
|
|
|
|
---------------------- iptables firewall End -------------------------</programlisting>
|
|
</blockquote>
|
|
</section>
|
|
|
|
<section id="faq6b">
|
|
<title>(FAQ 6b) DROP messages on port 10619 are flooding the logs with
|
|
their connect requests. Can I exclude these error messages for this
|
|
port temporarily from logging in Shorewall?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Temporarily add the
|
|
following rule:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
|
DROP net fw udp 10619</programlisting>
|
|
|
|
<para>Alternatively, if you do not set BLACKLIST_LOGLEVEL and you have
|
|
specifed the 'blacklist' option on your external interface in
|
|
<filename>/etc/shorewall/interfaces</filename>, then you can blacklist
|
|
the port. In <filename>/etc/shorewall/blacklist</filename>:</para>
|
|
|
|
<programlisting>#ADDRESS/SUBNET PROTOCOL PORT
|
|
- udp 10619</programlisting>
|
|
</section>
|
|
|
|
<section id="faq6d">
|
|
<title>(FAQ 6d) Why is the MAC address in Shorewall log messages so
|
|
long? I thought MAC addresses were only 6 bytes in length.</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> What is labeled as the
|
|
MAC address in a Netfilter (Shorewall) log message is actually the
|
|
Ethernet frame header. It contains:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>the destination MAC address (6 bytes)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>the source MAC address (6 bytes)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>the Ethernet frame type (2 bytes)</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para><example id="Example5">
|
|
<title id="Example2">Example</title>
|
|
|
|
<para><programlisting>MAC=00:04:4c:dc:e2:28:00:b0:8e:cf:3c:4c:08:00</programlisting>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Destination MAC address = 00:04:4c:dc:e2:28</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Source MAC address = 00:b0:8e:cf:3c:4c</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Ethernet Frame Type = 08:00 (IP Version 4)</para>
|
|
</listitem>
|
|
</itemizedlist></para>
|
|
</example></para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="faq16">
|
|
<title>(FAQ 16) Shorewall is writing log messages all over my console
|
|
making it unusable!</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis></para>
|
|
|
|
<para>Just to be clear, it is not Shorewall that is writing all over
|
|
your console. Shorewall issues a single log message during each
|
|
<command>start</command>, <command>restart</command>,
|
|
<command>stop</command>, etc. It is rather the klogd daemon that is
|
|
writing messages to your console. Shorewall itself has no control over
|
|
where a particular class of messages are written. See the <ulink
|
|
url="shorewall_logging.html">Shorewall logging
|
|
documentation</ulink>.</para>
|
|
|
|
<para>The max log level to be sent to the console is available in
|
|
/proc/sys/kernel/printk:<programlisting>teastep@ursa:~$ <emphasis
|
|
role="bold">cat /proc/sys/kernel/printk</emphasis>
|
|
6 6 1 7
|
|
teastep@ursa:~$ </programlisting>The first number determines the maximum log
|
|
level (syslog priority) sent to the console. Messages with priority
|
|
<emphasis role="bold">less than</emphasis> this number are sent to the
|
|
console. On the system shown in the example above, priorities 0-5 are
|
|
sent to the console. Since Shorewall defaults to using 'info' (6), the
|
|
Shorewall-generated Netfilter rule set will generate log messages that
|
|
<emphasis role="bold">will not appear on the console.</emphasis></para>
|
|
|
|
<para>The second number is the default log level for kernel printk()
|
|
calls that do not specify a log level.</para>
|
|
|
|
<para>The third number specifies the minimum console log level while the
|
|
fourth gives the default console log level.</para>
|
|
|
|
<para>If, on your system, the first number is 7 or greater, then the
|
|
default Shorewall configurations will cause messages to be written to
|
|
your console. The simplest solution is to add this to your
|
|
<filename>/etc/sysctl.conf</filename> file:<programlisting>kernel.printk = 4 4 1 7</programlisting></para>
|
|
|
|
<para>then<programlisting><command>sysctl -p /etc/sysctl.conf</command></programlisting></para>
|
|
|
|
<section id="faq16a">
|
|
<title>(FAQ 16a) Why can't I see any Shorewall messages in
|
|
/var/log/messages?</title>
|
|
|
|
<para>Some people who ask this question report that the only Shorewall
|
|
messages that they see in <filename>/var/log/messages</filename> are
|
|
'started', 'restarted' and 'stopped' messages.</para>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> First of all, it is
|
|
important to understand that Shorewall itself does not control where
|
|
Netfilter log messages are written. The LOGFILE setting in
|
|
<filename>shorewall.conf</filename> simply tells the
|
|
<filename>/sbin/shorewall[-lite]</filename> program where to look for
|
|
the log. Also, it is important to understand that a log level of
|
|
"debug" will generally cause Netfilter messages to be written to fewer
|
|
files in <filename class="directory">/var/log</filename> than a log
|
|
level of "info". The log level does not control the number of log
|
|
messages or the content of the messages.</para>
|
|
|
|
<para>The actual log file where Netfilter messages are written is not
|
|
standardized and will vary by distribution and distribution version.
|
|
But anytime you see no logging, it's time to look outside the
|
|
Shorewall configuration for the cause. As an example, recent
|
|
<trademark>SUSE</trademark> releases use syslog-ng by default and
|
|
write Shorewall messages to
|
|
<filename>/var/log/firewall</filename>.</para>
|
|
|
|
<para>Please see the <ulink url="shorewall_logging.html">Shorewall
|
|
logging documentation</ulink> for further information.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="faq17">
|
|
<title>(FAQ 17) Why are these packets being Dropped/Rejected? How do I
|
|
decode Shorewall log messages?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Logging of
|
|
dropped/rejected packets occurs out of a number of chains (as indicated
|
|
in the log message) in Shorewall:</para>
|
|
|
|
<variablelist>
|
|
<varlistentry id="all2all">
|
|
<term>all2<emphasis>zone</emphasis>, <emphasis>zone</emphasis>2all
|
|
or all2all</term>
|
|
|
|
<listitem>
|
|
<para>You have a <filename><ulink
|
|
url="manpages/shorewall-policy.html">policy</ulink></filename>
|
|
that specifies a log level and this packet is being logged under
|
|
that policy. If you intend to ACCEPT this traffic then you need a
|
|
<ulink url="manpages/shorewall-rules.html">rule</ulink> to that
|
|
effect.</para>
|
|
|
|
<para>Packets logged out of these chains may have a source and/or
|
|
destination that is not in any defined zone (see the output of
|
|
<command>shorewall[-lite] show zones</command>). Remember that
|
|
zone membership involves both a firewall interface and an ip
|
|
address.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><emphasis>zone</emphasis>12<emphasis>zone2</emphasis></term>
|
|
|
|
<listitem>
|
|
<para>Either you have a <ulink
|
|
url="manpages/shorewall-policy.html">policy</ulink> for
|
|
<emphasis>zone1</emphasis> to <emphasis>zone2</emphasis> that
|
|
specifies a log level and this packet is being logged under that
|
|
policy or this packet matches a <ulink
|
|
url="manpages/shorewall-rules.html">rule</ulink> that includes a
|
|
log level.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>@<emphasis>source</emphasis>2<emphasis>dest</emphasis></term>
|
|
|
|
<listitem>
|
|
<para>You have a policy for traffic from
|
|
<emphasis>source</emphasis> to <emphasis>dest</emphasis> that
|
|
specifies TCP connection rate limiting (value in the LIMIT:BURST
|
|
column). The logged packet exceeds that limit and was dropped.
|
|
Note that these log messages themselves are severely rate-limited
|
|
so that a syn-flood won't generate a secondary DOS because of
|
|
excessive log message. These log messages were added in Shorewall
|
|
2.2.0 Beta 7.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><emphasis>interface</emphasis>_mac or
|
|
<emphasis>interface</emphasis>_rec</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged under the <emphasis
|
|
role="bold">maclist</emphasis> <ulink
|
|
url="manpages/shorewall-interfaces.html">interface
|
|
option</ulink>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>blacklist</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged because the source IP is
|
|
blacklisted in the <filename> <ulink
|
|
url="manpages/shorewall-blacklist.html">/etc/shorewall/blacklist</ulink>
|
|
</filename> file.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>INPUT or FORWARD</term>
|
|
|
|
<listitem>
|
|
<para>The packet has a source IP address that isn't in any of your
|
|
defined zones (<quote><command>shorewall[-lite] show
|
|
zones</command></quote> and look at the printed zone definitions)
|
|
or the chain is FORWARD and the destination IP isn't in any of
|
|
your defined zones. If the chain is FORWARD and the IN and OUT
|
|
interfaces are the same, then you probably need the <emphasis
|
|
role="bold">routeback</emphasis> option on that interface in
|
|
<filename> <ulink
|
|
url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink>
|
|
</filename>, you need the <emphasis
|
|
role="bold">routeback</emphasis> option in the relevant entry in
|
|
<filename> <ulink
|
|
url="manpages/shorewall-hosts.html">/etc/shorewall/hosts</ulink>
|
|
or you've done something silly like define a default route out of
|
|
an internal interface.</filename></para>
|
|
|
|
<para>With OPTIMIZE=1 in <ulink
|
|
url="manpages/shorewall.conf.html">shorewall.conf</ulink>, such
|
|
packets may also be logged out of a <zone>2all chain or the
|
|
all2all chain.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>OUTPUT</term>
|
|
|
|
<listitem>
|
|
<para>The packet has a destination IP address that isn't in any of
|
|
your defined zones(<command>shorewall[-lite] show zones</command>
|
|
and look at the printed zone definitions).</para>
|
|
|
|
<para>With OPTIMIZE=1 in <ulink
|
|
url="manpages/shorewall.conf.html">shorewall.conf</ulink>, such
|
|
packets may also be logged out of the fw2all chain or the all2all
|
|
chain.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>logflags</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged because it failed the checks
|
|
implemented by the <emphasis role="bold">tcpflags</emphasis>
|
|
<ulink url="manpages/shorewall-interfaces.html">interface
|
|
option</ulink>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<example id="Example3">
|
|
<title>Here is an example:</title>
|
|
|
|
<programlisting>Jun 27 15:37:56 gateway kernel:
|
|
Shorewall:<emphasis role="bold">all2all:REJECT</emphasis>:<emphasis
|
|
role="bold">IN=eth2</emphasis>
|
|
<emphasis role="bold">OUT=eth1</emphasis>
|
|
<emphasis role="bold">SRC=192.168.2.2</emphasis>
|
|
<emphasis role="bold">DST=192.168.1.3 </emphasis>LEN=67 TOS=0x00 PREC=0x00 TTL=63 ID=5805 DF <emphasis
|
|
role="bold">PROTO=UDP</emphasis>
|
|
SPT=1803 <emphasis role="bold">DPT=53</emphasis> LEN=47</programlisting>
|
|
|
|
<para>Let's look at the important parts of this message:</para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>all2all:REJECT</term>
|
|
|
|
<listitem>
|
|
<para>This packet was REJECTed out of the <emphasis
|
|
role="bold">all2all</emphasis> chain -- the packet was rejected
|
|
under the <quote>all</quote>-><quote>all</quote> REJECT
|
|
policy (<link linkend="all2all">all2all</link> above).</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>IN=eth2</term>
|
|
|
|
<listitem>
|
|
<para>the packet entered the firewall via eth2. If you see
|
|
<quote>IN=</quote> with no interface name, the packet originated
|
|
on the firewall itself.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>OUT=eth1</term>
|
|
|
|
<listitem>
|
|
<para>if accepted, the packet would be sent on eth1. If you see
|
|
<quote>OUT=</quote> with no interface name, the packet would be
|
|
processed by the firewall itself.</para>
|
|
|
|
<note>
|
|
<para>When a DNAT rule is logged, there will never be an OUT=
|
|
shown because the packet is being logged before it is routed.
|
|
Also, DNAT logging will show the <emphasis>original</emphasis>
|
|
destination IP address and destination port number. When a
|
|
REDIRECT rule is logged, the message will also show the
|
|
original destination IP address and port number.</para>
|
|
</note>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SRC=192.168.2.2</term>
|
|
|
|
<listitem>
|
|
<para>the packet was sent by 192.168.2.2</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>DST=192.168.1.3</term>
|
|
|
|
<listitem>
|
|
<para>the packet is destined for 192.168.1.3</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>PROTO=UDP</term>
|
|
|
|
<listitem>
|
|
<para>UDP Protocol</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>DPT=53</term>
|
|
|
|
<listitem>
|
|
<para>The destination port is 53 (DNS)</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<para>In this case, 192.168.2.2 was in the <quote>dmz</quote> zone and
|
|
192.168.1.3 is in the <quote>loc</quote> zone. I was missing the
|
|
rule:</para>
|
|
|
|
<programlisting>ACCEPT dmz loc udp 53</programlisting>
|
|
</example>
|
|
</section>
|
|
|
|
<section id="faq21">
|
|
<title>(FAQ 21) I see these strange log entries occasionally; what are
|
|
they?</title>
|
|
|
|
<programlisting>Nov 25 18:58:52 linux kernel:
|
|
Shorewall:net2all:DROP:IN=eth1 OUT=
|
|
MAC=00:60:1d:f0:a6:f9:00:60:1d:f6:35:50:08:00 SRC=206.124.146.179
|
|
DST=192.0.2.3 LEN=56 TOS=0x00 PREC=0x00 TTL=110 ID=18558 <emphasis
|
|
role="bold">PROTO=ICMP</emphasis>
|
|
<emphasis role="bold">TYPE=3 CODE=3</emphasis> [SRC=192.0.2.3 DST=172.16.1.10 LEN=128 TOS=0x00 PREC=0x00
|
|
TTL=47 ID=0 DF PROTO=UDP SPT=53 DPT=2857 LEN=108 ]</programlisting>
|
|
|
|
<para>192.0.2.3 is external on my firewall... 172.16.0.0/24 is my
|
|
internal LAN</para>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> First of all, please note
|
|
that the above is a very specific type of log message dealing with ICMP
|
|
port unreachable packets (PROTO=ICMP TYPE=3 CODE=3). Do not read this
|
|
answer and assume that all Shorewall log messages have something to do
|
|
with ICMP (hint -- see <link linkend="faq17">FAQ 17</link>).</para>
|
|
|
|
<para>While most people associate the Internet Control Message Protocol
|
|
(ICMP) with <quote>ping</quote>, ICMP is a key piece of IP. ICMP is used
|
|
to report problems back to the sender of a packet; this is what is
|
|
happening here. Unfortunately, where NAT is involved (including SNAT,
|
|
DNAT and Masquerade), there are many broken implementations. That is
|
|
what you are seeing with these messages. When Netfilter displays these
|
|
messages, the part before the "[" describes the ICMP packet and the part
|
|
between the "[" and "]" describes the packet for which the ICMP is a
|
|
response.</para>
|
|
|
|
<para>Here is my interpretation of what is happening -- to confirm this
|
|
analysis, one would have to have packet sniffers placed a both ends of
|
|
the connection.</para>
|
|
|
|
<para>Host 172.16.1.10 behind NAT gateway 206.124.146.179 sent a UDP DNS
|
|
query to 192.0.2.3 and your DNS server tried to send a response (the
|
|
response information is in the brackets -- note source port 53 which
|
|
marks this as a DNS reply). When the response was returned to to
|
|
206.124.146.179, it rewrote the destination IP TO 172.16.1.10 and
|
|
forwarded the packet to 172.16.1.10 who no longer had a connection on
|
|
UDP port 2857. This causes a port unreachable (type 3, code 3) to be
|
|
generated back to 192.0.2.3. As this packet is sent back through
|
|
206.124.146.179, that box correctly changes the source address in the
|
|
packet to 206.124.146.179 but doesn't reset the DST IP in the original
|
|
DNS response similarly. When the ICMP reaches your firewall (192.0.2.3),
|
|
your firewall has no record of having sent a DNS reply to 172.16.1.10 so
|
|
this ICMP doesn't appear to be related to anything that was sent. The
|
|
final result is that the packet gets logged and dropped in the all2all
|
|
chain.</para>
|
|
</section>
|
|
|
|
<section id="faq52">
|
|
<title>(FAQ 52) When I blacklist an IP address with "shorewall[-lite]
|
|
drop www.xxx.yyy.zzz", why does my log still show REDIRECT and DNAT
|
|
entries from that address?</title>
|
|
|
|
<para>I blacklisted the address 130.252.100.59 using <command>shorewall
|
|
drop 130.252.100.59</command> but I am still seeing these log
|
|
messages:</para>
|
|
|
|
<programlisting>Jan 30 15:38:34 server Shorewall:net_dnat:REDIRECT:IN=eth1 OUT= MAC=00:4f:4e:14:97:8e:00:01:5c:23:24:cc:08:00
|
|
SRC=130.252.100.59 DST=206.124.146.176 LEN=64 TOS=0x00 PREC=0x00 TTL=43 ID=42444 DF
|
|
PROTO=TCP SPT=2215 DPT=139 WINDOW=53760 RES=0x00 SYN URGP=0</programlisting>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Please refer to the
|
|
<ulink url="NetfilterOverview.html">Shorewall Netfilter
|
|
Documentation</ulink>. Logging of REDIRECT and DNAT rules occurs in the
|
|
nat table's PREROUTING chain where the original destination IP address
|
|
is still available. Blacklisting occurs out of the filter table's INPUT
|
|
and FORWARD chains which aren't traversed until later.</para>
|
|
</section>
|
|
|
|
<section id="faq81">
|
|
<title>(FAQ 81) logdrop and logreject don't log.</title>
|
|
|
|
<para>I love the ability to type 'shorewall logdrop ww.xx.yy.zz' and
|
|
>> completely block a particular IP address. However, the log part
|
|
doesn't happen. When I look in the logdrop chain, there is no LOG
|
|
prefix.</para>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: You haven't set a value
|
|
for BLACKLIST_LOGLEVEL in <ulink
|
|
url="manpages/shorewall.conf.html">shorewall.conf</ulink> (5).</para>
|
|
</section>
|
|
|
|
<section id="faq36">
|
|
<title>(FAQ 36) My log is filling up with these BANDWIDTH
|
|
messages!</title>
|
|
|
|
<programlisting>Dec 15 16:47:30 heath-desktop kernel: [17182740.184000] BANDWIDTH_IN:IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:01:5c:23:79:02:08:00 SRC=10.119.248.1 DST=255.255.255.255 LEN=328 TOS=0x00 PREC=0x00 TTL=64 ID=62081 PROTO=UDP SPT=67 DPT=68 LEN=308
|
|
Dec 15 16:47:30 heath-desktop last message repeated 2 times
|
|
Dec 15 16:47:30 heath-desktop kernel: [17182740.188000] BANDWIDTH_IN:IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:01:5c:23:79:02:08:00 SRC=10.112.70.1 DST=255.255.255.255 LEN=328 TOS=0x00 PREC=0x00 TTL=64 ID=62082 PROTO=UDP SPT=67 DPT=68 LEN=308
|
|
Dec 15 16:47:30 heath-desktop last message repeated 2 times</programlisting>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: The Webmin 'bandwidth'
|
|
module adds commands to <filename>/etc/shorewall/start</filename> that
|
|
creates rules to log every packet to/from/through the firewall. DON'T
|
|
START THE BANDWIDTH SERVICE IN WEBMIN!!!!!</para>
|
|
|
|
<para>To correct this situation once it occurs, edit
|
|
<filename>/etc/shorewall/start</filename> and insert 'return 0' prior to
|
|
the BANDWIDTH rules.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Routing">
|
|
<title>Routing</title>
|
|
|
|
<section id="faq32">
|
|
<title>(FAQ 32) My firewall has two connections to the Internet from two
|
|
different ISPs. How do I set this up in Shorewall?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> See <ulink
|
|
url="MultiISP.html">this article about Shorewall and Multiple
|
|
ISPs</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq49">
|
|
<title>(FAQ 49) When I start Shorewall, my routing table gets blown
|
|
away. Why does Shorewall do that?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> This is usually the
|
|
consequence of a one-to-one nat configuration blunder:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>Specifying the primary IP address for an interface in the
|
|
EXTERNAL column of <filename>/etc/shorewall/nat</filename> even
|
|
though the documentation (and the comments in the file) warn you not
|
|
to do that.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Specifying ADD_IP_ALIASES=Yes and RETAIN_ALIASES=No in
|
|
/etc/shorewall/shorewall.conf.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>This combination causes Shorewall to delete the primary IP address
|
|
from the network interface specified in the INTERFACE column which
|
|
usually causes all routes out of that interface to be deleted. The
|
|
solution is to <emphasis role="bold">not specify the primary IP address
|
|
of an interface in the EXTERNAL column</emphasis>.</para>
|
|
</section>
|
|
|
|
<section id="faq82">
|
|
<title>(FAQ 82) When I enable USE_DEFAULT_RT, Shorewall won't
|
|
start</title>
|
|
|
|
<para>I get the following errors:</para>
|
|
|
|
<programlisting>RTNETLINK answers: Numerical result out of range
|
|
ERROR: Command "ip -4 rule add from all table 254 pref 999" Failed</programlisting>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> This is a known kernel
|
|
issue -- see <ulink
|
|
url="http://lkml.org/lkml/2007/3/30/253">http://lkml.org/lkml/2007/3/30/253</ulink>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Start-Stop">
|
|
<title>Starting and Stopping</title>
|
|
|
|
<section id="faq7">
|
|
<title>(FAQ 7) When I stop Shorewall using <quote>shorewall[-lite]
|
|
stop</quote>, I can't connect to anything. Why doesn't that command
|
|
work?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> The <quote>
|
|
<command>stop</command> </quote> command is intended to place your
|
|
firewall into a safe state whereby only those hosts listed in
|
|
<filename>/etc/shorewall/routestopped</filename> are activated. If you
|
|
want to totally open up your firewall, you must use the <quote>
|
|
<command>shorewall[-lite] clear</command> </quote> command.</para>
|
|
</section>
|
|
|
|
<section id="faq9">
|
|
<title>(FAQ 9) Why can't Shorewall detect my interfaces properly at
|
|
startup?</title>
|
|
|
|
<para>I just installed Shorewall and when I issue the
|
|
<command>start</command> command, I see the following:</para>
|
|
|
|
<programlisting>Processing /etc/shorewall/params ...
|
|
Processing /etc/shorewall/shorewall.conf ...
|
|
Starting Shorewall...
|
|
Loading Modules...
|
|
Initializing...
|
|
Determining Zones...
|
|
Zones: net loc
|
|
Validating interfaces file...
|
|
Validating hosts file...
|
|
Determining Hosts in Zones...
|
|
<emphasis role="bold">Net Zone: eth0:0.0.0.0/0
|
|
</emphasis><emphasis role="bold">Local Zone: eth1:0.0.0.0/0</emphasis>
|
|
Deleting user chains...
|
|
Creating input Chains...
|
|
...</programlisting>
|
|
|
|
<para>Why can't Shorewall detect my interfaces properly?</para>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> The above output is
|
|
perfectly normal. The Net zone is defined as all hosts that are
|
|
connected through <filename class="devicefile">eth0</filename> and the
|
|
local zone is defined as all hosts connected through <filename
|
|
class="devicefile">eth1</filename>. You can set the <emphasis
|
|
role="bold">routefilter</emphasis> option on an internal interface if
|
|
you wish to guard against '<firstterm>Martians</firstterm>' (a Martian
|
|
is a packet with a source IP address that is not routed out of the
|
|
interface on which the packet was received). If you do that, it is a
|
|
good idea to also set the <emphasis role="bold">logmartians</emphasis>
|
|
option.</para>
|
|
</section>
|
|
|
|
<section id="faq22">
|
|
<title>(FAQ 22) I have some iptables commands that I want to run when
|
|
Shorewall starts. Which file do I put them in?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis>You can place these
|
|
commands in one of the <ulink
|
|
url="shorewall_extension_scripts.htm">Shorewall Extension
|
|
Scripts</ulink>. Be sure that you look at the contents of the chain(s)
|
|
that you will be modifying with your commands so that the commands will
|
|
do what is intended. Many iptables commands published in HOWTOs and
|
|
other instructional material use the -A command which adds the rules to
|
|
the end of the chain. Most chains that Shorewall constructs end with an
|
|
unconditional DROP, ACCEPT or REJECT rule and any rules that you add
|
|
after that will be ignored. Check <quote>man iptables</quote> and look
|
|
at the -I (--insert) command.</para>
|
|
</section>
|
|
|
|
<section id="faq43">
|
|
<title>(FAQ 43) I just installed the Shorewall RPM and Shorewall doesn't
|
|
start at boot time.</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> When you install using
|
|
the "rpm -U" command, Shorewall doesn't run your distribution's tool for
|
|
configuring Shorewall startup. You will need to run that tool (insserv,
|
|
chkconfig, run-level editor, …) to configure Shorewall to start in the
|
|
the default run-levels of your firewall system.</para>
|
|
</section>
|
|
|
|
<section id="faq45">
|
|
<title>(FAQ 45) Why does "shorewall[-lite] start" fail when trying to
|
|
set up SNAT/Masquerading?</title>
|
|
|
|
<para><command>shorewall start</command> produces the following
|
|
output:</para>
|
|
|
|
<programlisting>…
|
|
Processing /etc/shorewall/policy...
|
|
Policy ACCEPT for fw to net using chain fw2net
|
|
Policy ACCEPT for loc0 to net using chain loc02net
|
|
Policy ACCEPT for loc1 to net using chain loc12net
|
|
Policy ACCEPT for wlan to net using chain wlan2net
|
|
Masqueraded Networks and Hosts:
|
|
iptables: Invalid argument
|
|
ERROR: Command "/sbin/iptables -t nat -A …" Failed</programlisting>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> 99.999% of the time, this
|
|
error is caused by a mismatch between your iptables and kernel.</para>
|
|
|
|
<orderedlist numeration="loweralpha">
|
|
<listitem>
|
|
<para>Your iptables must be compiled against a kernel source tree
|
|
that is Netfilter-compatible with the kernel that you are
|
|
running.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If you rebuild iptables using the defaults and install it, it
|
|
will be installed in /usr/local/sbin/iptables. As shown above, you
|
|
have the IPTABLES variable in shorewall.conf set to
|
|
"/sbin/iptables".</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</section>
|
|
|
|
<section id="faq59">
|
|
<title>(FAQ 59) After I start Shorewall, there are lots of unused
|
|
Netfilter modules loaded. How do I avoid that?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Copy
|
|
<filename>/usr/share/shorewall[-lite]/modules</filename> to
|
|
<filename>/etc/shorewall/modules </filename>and modify the copy to
|
|
include only the modules that you need.</para>
|
|
</section>
|
|
|
|
<section id="faq61">
|
|
<title>(FAQ 61) I just installed the latest Debian kernel and now
|
|
"shorewall start" fails with the message "ipt_policy: matchsize 116 !=
|
|
308". What's wrong?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Your iptables is
|
|
incompatible with your kernel. Either</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>rebuild iptables using the kernel headers that match your new
|
|
kernel; or</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>if you don't need policy match support (you are not using the
|
|
IPSEC implementation builtinto the 2.6 kernel) then you can rename
|
|
<filename>/lib/iptables/libipt_policy.so</filename>.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<note>
|
|
<para>Shorewall does not attempt to use policy match if you have no
|
|
IPSEC zones and you have not specified the <option>ipsec</option>
|
|
option on any entry in <filename>/etc/shorewall/hosts</filename>. The
|
|
subject message will still appear in your kernel log each time that
|
|
Shorewall determines the capabilities of your kernel/iptables.</para>
|
|
</note>
|
|
</section>
|
|
|
|
<section id="faq68">
|
|
<title>(FAQ 68) I have a VM under an OpenVZ system. I can't get rid of
|
|
the following message:</title>
|
|
|
|
<para>ERROR: Command "/sbin/iptables -A FORWARD -m state --state
|
|
ESTABLISHED,RELATED -j ACCEPT" failed.</para>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> See the <ulink
|
|
url="OpenVZ.html">Shorewall OpenVZ article</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq73">
|
|
<title>(FAQ 73) When I stop Shorewall, the firewall is wide open. Isn't
|
|
that a security risk?</title>
|
|
|
|
<para>It is important to understand that the scripts in <filename
|
|
class="directory">/etc/init.d</filename> are generally provided by your
|
|
distribution and not by the Shorewall developers. These scripts must
|
|
meet the requirements of the distribution's packaging system which may
|
|
conflict with the requirements of a tight firewall. So when you say
|
|
"…when I stop Shorewall…" it is necessary to distinguish between the
|
|
commands <command>/sbin/shorewall stop</command> and
|
|
<command>/etc/init.d/shorewall stop</command>.</para>
|
|
|
|
<para><command>/sbin/shorewall stop</command> places the firewall in a
|
|
<firstterm>safe state</firstterm>, the details of which depend on your
|
|
<filename>/etc/shorewall/routestopped</filename> file (<ulink
|
|
url="manpages/shorewall-routestopped.html">shorewall-routestopped</ulink>(5))
|
|
and on the setting of ADMINISABSENTMINDED in
|
|
<filename>/etc/shorewall/shorewall.conf</filename> (<ulink
|
|
url="manpages/shorewall.conf.html">shorewall.conf</ulink>(5)).</para>
|
|
|
|
<para><command>/etc/init.d/shorewall stop</command> may or may not do
|
|
the same thing. In the case of <trademark>Debian</trademark> systems for
|
|
example, that command actually executes <command>/sbin/shorewall
|
|
clear</command> which opens the firewall completely. In other words, in
|
|
the init script, <command>stop</command> reverses the effect of
|
|
<command>start</command>.</para>
|
|
|
|
<para>One way to avoid these differences is to install Shorewall from
|
|
the tarballs available from shorewall.net. This places Shorewall outside
|
|
of the control of the packaging system and provides consistent behavior
|
|
between the init scripts and <filename>/sbin/shorewall</filename> (and
|
|
<filename>/sbin/shorewall-lite</filename>). For more information on the
|
|
factors involved when deciding whether to use the Debian package, see
|
|
<ulink url="http://wiki.shorewall.net/wiki/ShorewallOnDebian">this
|
|
article</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq74">
|
|
<title>(FAQ 74) When I "<command>shorewall start</command>" or
|
|
"<command>shorewall check</command>" on my SuSE 10.0 system, I get FATAL
|
|
ERROR messages and/or the system crashes"</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> These failures result
|
|
from trying to load a particular combination of kernel modules. To work
|
|
around the problem:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>Copy /usr/share/shorewall/modules to
|
|
/etc/shorewall/modules</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Edit /etc/shorewall/modules and remove all entries except for
|
|
those for the helper modules that you need.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</section>
|
|
|
|
<section id="faq78">
|
|
<title>(FAQ 78) After restart and bootup of my Debian firewall, all
|
|
traffic is blocked for hosts behind the firewall trying to connect out
|
|
onto the net or through the vpn (although i can reach the internal
|
|
firewall interface and obtain dumps etc). Once I issue 'shorewall clear'
|
|
followed by 'shorewall start' it then works, despite the config not
|
|
changing</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Set IP_FORWARDING=On in
|
|
<filename><ulink
|
|
url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink></filename>.</para>
|
|
</section>
|
|
|
|
<section id="faq86">
|
|
<title>(FAQ 86) My distribution (Ubuntu) uses NetworkManager to manage
|
|
my interfaces. I want to specify the upnpclient option for my interfaces
|
|
which requires them to be up and configured when Shorewall starts but
|
|
Shorewall is being started before NetworkManager.</title>
|
|
|
|
<para>Answer: I faced a similar problem which I solved as
|
|
follows:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Don't start Shorewall at boot time (Debian and Ubuntu users
|
|
may simply set startup=0 in
|
|
<filename>/etc/default/shorewall</filename>).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>In <filename>/etc/network/ip-up.d</filename>, I added a
|
|
<filename>shorewall</filename> script as follows:</para>
|
|
|
|
<programlisting>#!/bin/sh
|
|
|
|
shorewall status > /dev/null 2>&1 || shorewall start # Start Shorewall if it isn't already running</programlisting>
|
|
|
|
<para>Be sure to secure the script for execute access.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="MultiISP">
|
|
<title>Multiple ISPs</title>
|
|
|
|
<section id="faq57">
|
|
<title>(FAQ 57) I configured two ISPs in Shorewall but when I try to use
|
|
the second one, it doesn't work.</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> The Multi-ISP
|
|
Documentation strongly recommends that you use the <emphasis
|
|
role="bold">balance</emphasis> option on all providers even if you want
|
|
to manually specify which ISP to use. If you don't do that so that your
|
|
main routing table only has one default route, then you must disable
|
|
route filtering. Do not specify the <emphasis
|
|
role="bold">routefilter</emphasis> option on the other interface(s) in
|
|
<filename>/etc/shorewall/interfaces</filename> and disable any
|
|
<emphasis>IP Address Spoofing</emphasis> protection that your
|
|
distribution supplies.</para>
|
|
</section>
|
|
|
|
<section id="faq58">
|
|
<title>(FAQ 58) But if I specify 'balance' then won't Shorewall balance
|
|
the traffic between the interfaces? I don't want that!</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Suppose that you want all
|
|
traffic to go out through ISP1 (mark 1) unless you specify otherwise.
|
|
Then simply add these two rules as the first marking rules in your
|
|
<filename>/etc/shorewall/tcrules</filename> file:</para>
|
|
|
|
<programlisting>#MARK SOURCE DEST
|
|
1:P 0.0.0.0/0
|
|
1 $FW
|
|
<emphasis>other MARK rules</emphasis></programlisting>
|
|
|
|
<para>Now any traffic that isn't marked by one of your other MARK rules
|
|
will have mark = 1 and will be sent via ISP1. That will work whether
|
|
<emphasis role="bold">balance</emphasis> is specified or not!</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Using DNS Names</title>
|
|
|
|
<section id="faq79">
|
|
<title>(FAQ 79) Can I use DNS names in Shorewall configuration file
|
|
entries in place of IP addresses?</title>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: <ulink
|
|
url="configuration_file_basics.htm#dnsnames">Yes</ulink>, but we advise
|
|
strongly against it.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="TC">
|
|
<title>Traffic Shaping</title>
|
|
|
|
<section id="faq67">
|
|
<title>(FAQ 67) I just configured Shorewall's builtin traffic shaping
|
|
and now Shorewall fails to Start.</title>
|
|
|
|
<para>The error I receive is as follows:<programlisting>RTNETLINK answers: No such file or directory
|
|
We have an error talking to the kernel
|
|
ERROR: Command "tc filter add dev eth2 parent ffff: protocol ip prio
|
|
50 u32 match ip src 0.0.0.0/0 police rate 500kbit burst 10k drop flowid
|
|
:1" Failed</programlisting><emphasis
|
|
role="bold">Answer:</emphasis> This message indicates that your kernel
|
|
doesn't have 'traffic policing' support. If your kernel is modularized,
|
|
you may be able to resolve the problem by loading the <emphasis
|
|
role="bold">act_police</emphasis> kernel module. Other kernel modules
|
|
that you will need include:<simplelist>
|
|
<member>cls_fw</member>
|
|
|
|
<member>cls_u32</member>
|
|
|
|
<member>sch_htb</member>
|
|
|
|
<member>sch_ingress</member>
|
|
|
|
<member>sch_sfq</member>
|
|
</simplelist></para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="About">
|
|
<title>About Shorewall</title>
|
|
|
|
<section id="faq10">
|
|
<title>(FAQ 10) What Distributions does Shorewall work with?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Shorewall works with any
|
|
GNU/Linux distribution that includes the <ulink
|
|
url="shorewall_prerequisites.htm">proper prerequisites</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq11">
|
|
<title>(FAQ 11) What Features does Shorewall have?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> See the <ulink
|
|
url="shorewall_features.htm">Shorewall Feature List</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq12">
|
|
<title>(FAQ 12) Is there a GUI?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Yes! Shorewall support is
|
|
available in Webmin. See <ulink
|
|
url="http://www.webmin.com">http://www.webmin.com</ulink>. But beware of
|
|
the issue described in <link linkend="faq36">FAQ 36</link>.</para>
|
|
</section>
|
|
|
|
<section id="faq13">
|
|
<title>(FAQ 13) Why do you call it <quote>Shorewall</quote>?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Shorewall is a
|
|
concatenation of <quote> <emphasis>Shore</emphasis>line</quote> (<ulink
|
|
url="http://www.cityofshoreline.com">the city where I live</ulink>) and
|
|
<quote>Fire<emphasis>wall</emphasis> </quote>. The full name of the
|
|
product is actually <quote>Shoreline Firewall</quote> but
|
|
<quote>Shorewall</quote> is much more commonly used.</para>
|
|
</section>
|
|
|
|
<section id="faq23">
|
|
<title>(FAQ 23) Why do you use such ugly fonts on your web site?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> The Shorewall web site is
|
|
almost font neutral (it doesn't explicitly specify fonts except on a few
|
|
pages) so the fonts you see are largely the default fonts configured in
|
|
your browser. If you don't like them then reconfigure your
|
|
browser.</para>
|
|
</section>
|
|
|
|
<section id="faq25">
|
|
<title>(FAQ 25) How do I tell which version of Shorewall or Shorewall
|
|
Lite I am running?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> At the shell prompt,
|
|
type:</para>
|
|
|
|
<programlisting><command>/sbin/shorewall[-lite] version</command> </programlisting>
|
|
</section>
|
|
|
|
<section id="faq31">
|
|
<title>(FAQ 31) Does Shorewall provide protection against....</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>IP Spoofing: Sending packets over the WAN interface using an
|
|
internal LAP IP address as the source address?</term>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Answer:</emphasis> Yes.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>Tear Drop: Sending packets that contain overlapping
|
|
fragments?</term>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Answer:</emphasis> This is the
|
|
responsibility of the IP stack, not the Netfilter-based firewall
|
|
since fragment reassembly occurs before the stateful packet filter
|
|
ever touches each packet.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>Smurf and Fraggle: Sending packets that use the WAN or LAN
|
|
broadcast address as the source address?</term>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Answer:</emphasis> Shorwall filters
|
|
these packets under the <firstterm>nosmurfs</firstterm> interface
|
|
option in <ulink
|
|
url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>Land Attack: Sending packets that use the same address as the
|
|
source and destination address?</term>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Answer:</emphasis> Yes, if the <ulink
|
|
url="manpages/shorewall-interfaces.html">routefilter interface
|
|
option</ulink> is selected.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>DOS: - SYN Dos - ICMP Dos - Per-host Dos protection</term>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Answer:</emphasis> Yes.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</section>
|
|
|
|
<section id="faq65">
|
|
<title>(FAQ 65) How do I accomplish failover with Shorewall?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> <ulink
|
|
url="http://linuxman.wikispaces.com/Clustering+Shorewall">This article
|
|
by Paul Gear</ulink> should help you get started.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="ALIASES">
|
|
<title>Alias IP Addresses/Virtual Interfaces</title>
|
|
|
|
<section id="faq18">
|
|
<title>(FAQ 18) Is there any way to use aliased ip addresses with
|
|
Shorewall, and maintain separate rule sets for different IPs?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Yes. See <ulink
|
|
url="Shorewall_and_Aliased_Interfaces.html">Shorewall and Aliased
|
|
Interfaces</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq83">
|
|
<title>(FAQ 83) Is there no way to nest the firewall zone or create
|
|
subzones? I've got a system with Linux-VServers, it's one interface
|
|
(eth0) with multiple IPs</title>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: There is no way to create
|
|
sub-zones of the firewall zone. But you can use shell variables to make
|
|
vservers easier to deal with.</para>
|
|
|
|
<para><filename>/etc/shorewall/params</filename>:</para>
|
|
|
|
<programlisting>VS1=fw:192.168.2.12
|
|
VS2=fw:192.168.2.13
|
|
VS3=fw:192.168.2.14</programlisting>
|
|
|
|
<para><filename>/etc/shorewall/rules</filename>:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
|
ACCEPT $VS1 net tcp 25
|
|
DNAT net $VS1 tcp 25
|
|
etc...</programlisting>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Lite">
|
|
<title>Shorewall Lite</title>
|
|
|
|
<section id="faq53">
|
|
<title>(FAQ 53) What is Shorewall Lite?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Shorewall Lite is a
|
|
companion product to Shorewall and is designed to allow you to maintain
|
|
all Shorewall configuration information on a single system within your
|
|
network. See the <ulink url="CompiledPrograms.html#Lite">Compiled
|
|
Firewall script documentation</ulink> for details.</para>
|
|
</section>
|
|
|
|
<section id="faq54">
|
|
<title>(FAQ 54) If I want to use Shorewall Lite, do I also need to
|
|
install Shorewall on the same system?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> No. In fact, we recommend
|
|
that you do <emphasis role="bold">NOT</emphasis> install Shorewall on
|
|
systems where you wish to use Shorewall Lite. You must have Shorewall
|
|
installed on at least one system within your network in order to use
|
|
Shorewall Lite.</para>
|
|
</section>
|
|
|
|
<section id="faq55">
|
|
<title>(FAQ 55) How do I decide which product to use - Shorewall or
|
|
Shorewall Lite?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> If you plan to have only
|
|
a single firewall system, then Shorewall is the logical choice. I also
|
|
think that Shorewall is the appropriate choice for laptop systems that
|
|
may need to have their firewall configuration changed while on the road.
|
|
In the remaining cases, Shorewall Lite will work very well. At
|
|
shorewall.net, the two laptop systems have the full Shorewall product
|
|
installed as does my personal Linux desktop system. All other Linux
|
|
systems that run a firewall use Shorewall Lite and have their
|
|
configuration directories on my desktop system.</para>
|
|
</section>
|
|
|
|
<section id="faq60">
|
|
<title>(FAQ 60) What are the compatibility restrictions between
|
|
Shorewall and Shorewall Lite</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> There are no
|
|
compatibility constraints between Shorewall and Shorewall-lite.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="VOIP">
|
|
<title>VOIP</title>
|
|
|
|
<section id="faq77">
|
|
<title>(FAQ 77) Shorewall is eating my Asterisk egress traffic!</title>
|
|
|
|
<para>Somehow, my firewall config is causing a one-way audio problem in
|
|
Asterisk. If a person calls into the PBX, they cannot hear me speaking,
|
|
but I can hear them. If I plug the Asterisk server directly into the
|
|
router, bypassing the firewall, the problem goes away.</para>
|
|
|
|
<para><emphasis role="bold">Answer (requires Shorewall 4.0.6 or
|
|
later):</emphasis> If your kernel version is 2.6.20 or
|
|
earlier:<programlisting>rmmod ip_nat_sip
|
|
rmmod ip_conntrack_sip</programlisting>Then change the DONT_LOAD specification
|
|
in your shorewall.conf to:<programlisting>DONT_LOAD=ip_nat_sip,ip_conntrack_sip</programlisting>If
|
|
your kernel version is 2.6.21 or later:<programlisting>rmmod nf_nat_sip
|
|
rmmod nf_conntrack_sip</programlisting>Then change the DONT_LOAD specification
|
|
in your shorewall.conf to:<programlisting>DONT_LOAD=nf_nat_sip,nf_conntrack_sip</programlisting>If
|
|
you are running a version of Shorewall earlier than 4.0.6, you can avoid
|
|
loading the sip helper modules by following the suggestions in <link
|
|
linkend="faq59">FAQ 59</link>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="faq40">
|
|
<title>IPv6</title>
|
|
|
|
<section id="faq80">
|
|
<title>(FAQ 80) Does Shorewall support IPV6?</title>
|
|
|
|
<para>Answer: <ulink url="IPv6Support.html">Shorewall IPv6
|
|
support</ulink> is currently available in Shorewall 4.2.4 and
|
|
later.</para>
|
|
|
|
<section id="faq80a">
|
|
<title>(FAQ 80a) Why does Shorewall lPv6 Support Require Kernel 2.6.24
|
|
or later?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Shorewall implements a
|
|
stateful firewall which requires connection tracking be present in
|
|
ip6tables and in the kernel. Linux kernels before 2.6.20 didn't
|
|
support connection tracking for IPv6. So we could not even start to
|
|
develop Shorewall IPv6 support until 2.6.20 and there were significant
|
|
problems with the facility until at least kernel 2.6.23. When
|
|
distributions began offering IPv6 connection tracking support, it was
|
|
with kernel 2.6.25. So that is what we developed IPv6 support on and
|
|
that's all that we initially tested on. Subsequently, we have tested
|
|
Shorewall6 on Ubuntu Hardy with kernel 2.6.24. If you are running
|
|
2.6.20 or later, you can <emphasis role="bold">try</emphasis> to run
|
|
Shorewall6 by hacking<filename>
|
|
/usr/share/shorewall/prog.footer6</filename> and changing the kernel
|
|
version test to check for your kernel version rather than 2.6.24
|
|
(20624). But after that, you are on your own.</para>
|
|
|
|
<programlisting>kernel=$(printf "%2d%02d%02d\n" $(echo $(uname -r) 2> /dev/null | sed 's/-.*//' | tr '.' ' ' ) | head -n1)
|
|
if [ $kernel -lt <emphasis role="bold">20624</emphasis> ]; then
|
|
error_message "ERROR: $PRODUCT requires Linux kernel <emphasis role="bold">2.6.24</emphasis> or later"
|
|
status=2
|
|
else
|
|
</programlisting>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>(FAQ 40) I have an interface that gets its IPv6 configuration
|
|
from radvd. When I start Shorewall6, I immediately loose my default
|
|
route. Why?</title>
|
|
|
|
<para><emphasis role="bold">Answer</emphasis>: You have configured
|
|
forwarding on the interface which disables autoconfiguration of the
|
|
interface. To retain autoconfiguration on the interface when Shorewall6
|
|
starts, specify <emphasis role="bold">forwarding=0</emphasis> in the
|
|
OPTIONS column on the interface's entry in <ulink
|
|
url="manpages6/shorewall6-interfaces.html">shorewall6-interfaces</ulink>
|
|
(5).</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Misc">
|
|
<title>Miscellaneous</title>
|
|
|
|
<section id="faq20">
|
|
<title>(FAQ 20) I have just set up a server. Do I have to change
|
|
Shorewall to allow access to my server from the Internet?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Yes. Consult the <ulink
|
|
url="shorewall_quickstart_guide.htm">QuickStart guide</ulink> that you
|
|
used during your initial setup for information about how to set up rules
|
|
for your server.</para>
|
|
</section>
|
|
|
|
<section id="faq24">
|
|
<title>(FAQ 24) How can I allow connections to, let's say, the ssh port
|
|
only from specific IP Addresses on the Internet?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> In the SOURCE column of
|
|
the rule, follow <quote>net</quote> by a colon and a list of the
|
|
host/subnet addresses as a comma-separated list.</para>
|
|
|
|
<programlisting>net:<ip1>,<ip2>,...</programlisting>
|
|
|
|
<example id="Example4">
|
|
<title>Example:</title>
|
|
|
|
<programlisting>ACCEPT net:192.0.2.16/28,192.0.2.44 fw tcp 22</programlisting>
|
|
</example>
|
|
</section>
|
|
|
|
<section id="faq26">
|
|
<title>(FAQ 26) When I try to use any of the SYN options in nmap on or
|
|
behind the firewall, I get <quote>operation not permitted</quote>. How
|
|
can I use nmap with Shorewall?"</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Temporarily remove and
|
|
rejNotSyn, dropNotSyn and dropInvalid rules from
|
|
<filename>/etc/shorewall/rules</filename> and restart Shorewall.</para>
|
|
</section>
|
|
|
|
<section id="faq27">
|
|
<title>(FAQ 27) I'm compiling a new kernel for my firewall. What should
|
|
I look out for?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> First take a look at the
|
|
<ulink url="kernel.htm">Shorewall kernel configuration page</ulink>. You
|
|
probably also want to be sure that you have selected the <quote>
|
|
<emphasis role="bold">NAT of local connections (READ HELP)</emphasis>
|
|
</quote> on the Netfilter Configuration menu. Otherwise, DNAT rules with
|
|
your firewall as the source zone won't work with your new kernel.</para>
|
|
|
|
<section id="faq27a">
|
|
<title>(FAQ 27a) I just built (or downloaded or otherwise acquired)
|
|
and installed a new kernel and now Shorewall won't start. I know that
|
|
my kernel options are correct.</title>
|
|
|
|
<para>The last few lines of <ulink url="troubleshoot.htm">a startup
|
|
trace</ulink> are these:</para>
|
|
|
|
<programlisting>+ run_iptables2 -t nat -A eth0_masq -s 192.168.2.0/24 -d 0.0.0.0/0 -j
|
|
MASQUERADE
|
|
+ '[' 'x-t nat -A eth0_masq -s 192.168.2.0/24 -d 0.0.0.0/0 -j
|
|
MASQUERADE' = 'x-t nat -A eth0_masq -s 192.168.2.0/24 -d 0.0.0.
|
|
0/0 -j MASQUERADE' ']'
|
|
+ run_iptables -t nat -A eth0_masq -s 192.168.2.0/24 -d 0.0.0.0/0 -j
|
|
MASQUERADE
|
|
+ iptables -t nat -A eth0_masq -s 192.168.2.0/24 -d 0.0.0.0/0 -j
|
|
MASQUERADE
|
|
iptables: Invalid argument
|
|
+ '[' -z '' ']'
|
|
+ stop_firewall
|
|
+ set +x</programlisting>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Your new kernel
|
|
contains headers that are incompatible with the ones used to compile
|
|
your <command>iptables</command> utility. You need to rebuild
|
|
<command>iptables</command> using your new kernel source.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="faq28">
|
|
<title>(FAQ 28) How do I use Shorewall as a Bridging Firewall?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Shorewall Bridging
|
|
Firewall support is available — <ulink
|
|
url="bridge-Shorewall-perl.html">check here for details</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="faq39">
|
|
<title>(FAQ 39) How do I block connections to a particular domain
|
|
name?</title>
|
|
|
|
<para>I tried this rule to block Google's Adsense that you'll find on
|
|
everyone's site. Adsense is a Javascript that people add to their Web
|
|
pages. So I entered the rule:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO
|
|
REJECT fw net:pagead2.googlesyndication.com all</programlisting>
|
|
|
|
<para>However, this also sometimes restricts access to "google.com". Why
|
|
is that? Using dig, I found these IPs for domain
|
|
googlesyndication.com:<programlisting>216.239.37.99
|
|
216.239.39.99</programlisting>And this for google.com:<programlisting>216.239.37.99
|
|
216.239.39.99
|
|
216.239.57.99</programlisting>So my guess is that you are not actually
|
|
blocking the domain, but rather the IP being called. So how in the world
|
|
do you block an actual domain name?</para>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Packet filters like
|
|
Netfilter base their decisions on the contents of the various protocol
|
|
headers at the front of each packet. Stateful packet filters (of which
|
|
Netfilter is an example) use a combination of header contents and state
|
|
created when the packet filter processed earlier packets. Netfilter (and
|
|
Shorewall's use of Netfilter) also consider the network interface(s)
|
|
where each packet entered and/or where the packet will leave the
|
|
firewall/router.</para>
|
|
|
|
<para>When you specify <ulink
|
|
url="configuration_file_basics.htm#dnsnames">a domain name in a
|
|
Shorewall rule</ulink>, the iptables program resolves that name to one
|
|
or more IP addresses and the actual Netfilter rules that are created are
|
|
expressed in terms of those IP addresses. So the rule that you entered
|
|
was equivalent to:</para>
|
|
|
|
<para><programlisting>#ACTION SOURCE DEST PROTO
|
|
REJECT fw net:216.239.37.99 all
|
|
REJECT fw net:216.239.39.99 all</programlisting>Given that
|
|
name-based multiple hosting is a common practice (another example:
|
|
lists.shorewall.net and www1.shorewall.net are both hosted on the same
|
|
system with a single IP address), it is not possible to filter
|
|
connections to a particular name by examination of protocol headers
|
|
alone. While some protocols such as <ulink url="FTP.html">FTP</ulink>
|
|
require the firewall to examine and possibly modify packet payload,
|
|
parsing the payload of individual packets doesn't always work because
|
|
the application-level data stream can be split across packets in
|
|
arbitrary ways. This is one of the weaknesses of the 'string match'
|
|
Netfilter extension available in later Linux kernel releases. The only
|
|
sure way to filter on packet content is to proxy the connections in
|
|
question -- in the case of HTTP, this means running something like
|
|
<ulink url="Shorewall_Squid_Usage.html">Squid</ulink>. Proxying allows
|
|
the proxy process to assemble complete application-level messages which
|
|
can then be accurately parsed and decisions can be made based on the
|
|
result.</para>
|
|
</section>
|
|
|
|
<section id="faq42">
|
|
<title>(FAQ 42) How can I tell which features my kernel and iptables
|
|
support?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Use the
|
|
<command>shorewall[-lite] show capabilities</command> command at a root
|
|
prompt.</para>
|
|
|
|
<programlisting>gateway:~# <command>shorewall show capabilities</command>
|
|
Shorewall has detected the following iptables/netfilter capabilities:
|
|
NAT: Available
|
|
Packet Mangling: Available
|
|
Multi-port Match: Available
|
|
Extended Multi-port Match: Available
|
|
Connection Tracking Match: Available
|
|
Extended Connection Tracking Match Support: Available
|
|
Old Connection Tracking Match Syntax: Not available
|
|
Packet Type Match: Available
|
|
Policy Match: Available
|
|
Physdev Match: Available
|
|
Physdev-is-bridged Support: Available
|
|
Packet length Match: Available
|
|
IP range Match: Available
|
|
Recent Match: Available
|
|
Owner Match: Available
|
|
Ipset Match: Available
|
|
CONNMARK Target: Available
|
|
Extended CONNMARK Target: Available
|
|
Connmark Match: Available
|
|
Extended Connmark Match: Available
|
|
Raw Table: Available
|
|
IPP2P Match: Available
|
|
Old IPP2P Match Syntax: Not available
|
|
CLASSIFY Target: Available
|
|
Extended REJECT: Available
|
|
Repeat match: Available
|
|
MARK Target: Available
|
|
Extended MARK Target: Available
|
|
Mangle FORWARD Chain: Available
|
|
Comments: Available
|
|
Address Type Match: Available
|
|
TCPMSS Match: Available
|
|
Hashlimit Match: Available
|
|
Old Hashlimit Match: Not available
|
|
NFQUEUE Target: Available
|
|
Realm Match: Available
|
|
Helper Match: Available
|
|
Connlimit Match: Available
|
|
Time Match: Available
|
|
Goto Support: Available
|
|
LOGMARK Target: Available
|
|
IPMARK Target: Available
|
|
LOG Target: Available
|
|
Persistent SNAT: Available
|
|
gateway:~# </programlisting>
|
|
</section>
|
|
|
|
<section id="faq19">
|
|
<title>(FAQ 19) How do I open the firewall for all traffic to/from the
|
|
LAN?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Add these two
|
|
policies:</para>
|
|
|
|
<programlisting>#SOURCE DESTINATION POLICY LOG LIMIT:BURST
|
|
# LEVEL
|
|
$FW loc ACCEPT
|
|
loc $FW ACCEPT </programlisting>
|
|
|
|
<para>You should also delete any ACCEPT rules from $FW->loc and
|
|
loc->$FW since those rules are redundant with the above
|
|
policies.</para>
|
|
</section>
|
|
</section>
|
|
</article>
|