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2130 lines
83 KiB
XML
2130 lines
83 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article>
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<!--$Id$-->
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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>2004-08-10</pubdate>
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<copyright>
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<year>2001-2004</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled
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<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<section>
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<title>Installing Shorewall</title>
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<section>
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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 empty!!!</title>
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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 empty. This is
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intentional. The released configuration file skeletons may be found on
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your system in the directory <filename
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class="directory">/usr/share/doc/shorewall/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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<para>Note that you must copy <filename
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class="directory">/usr/share/doc/shorewall/default-config/shorewall.conf</filename>
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and <filename>/usr/share/doc/shorewall/default-config/modules</filename>
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to <filename class="directory">/etc/shorewall</filename> even if you do
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not modify those files.</para>
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</section>
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</section>
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<section>
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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 my personal PC with
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IP 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 first example in the
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<ulink url="Documentation.htm#Rules">rules file documentation</ulink>
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shows how to do port forwarding under Shorewall. 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:<l<emphasis>ocal IP address</emphasis>>[:<<emphasis>local port</emphasis>>] <<emphasis>protocol</emphasis>> <<emphasis>port #</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
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internal 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:<l<emphasis>ocal IP address</emphasis>>[:<<emphasis>local port</emphasis>>] <<emphasis>protocol</emphasis>> <<emphasis>port #</emphasis>> - <<emphasis>external IP</emphasis>></programlisting>
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<para>Finally, if you need to forward a range of ports, in the 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) Ok -- 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 should be set to the IP address of your
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firewall's internal interface).</para>
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</listitem>
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<listitem>
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<para>Your ISP is blocking that particular port inbound.</para>
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</listitem>
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<listitem>
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<para>You are running Mandrake Linux and have configured Internet
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Connection Sharing. In that case, the name of your local zone is
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'masq' rather than 'loc' (change all instances of 'loc' to 'masq'
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in your rules). You may want to consider re-installing Shorewall
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in a configuration which matches the Shorewall documentation. See
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the <ulink url="two-interface.htm">two-interface QuickStart
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Guide</ulink> for 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>iptables -t nat
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-Z</command></quote>. This clears the NetFilter counters in the
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nat table.</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
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nat</command></quote></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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</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>In /<filename>etc/shorewall/rules</filename>:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT
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DNAT net loc:192.168.3:22 tcp 1022</programlisting>
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</section>
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</section>
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<section id="faq30">
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<title>(FAQ 30) I'm confused about when to use DNAT rules and when to
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use ACCEPT rules.</title>
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<para>It would be a good idea to review the <ulink
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url="shorewall_quickstart_guide.htm">QuickStart Guide</ulink>
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appropriate for your setup; the guides cover this topic in a tutorial
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fashion. DNAT rules should be used for connections that need to go the
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opposite direction from SNAT/MASQUERADE. So if you masquerade or use
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SNAT from your local network to the internet then you will need to use
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DNAT rules to allow connections from the internet to your local network.
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In all other cases, you use ACCEPT unless you need to hijack connections
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as they go through your firewall and handle them on the firewall box
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itself; in that case, you use a REDIRECT rule.</para>
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</section>
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<section>
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<title>(FAQ 38) Where can I find more information about DNAT?</title>
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<para>Ian Allen has written a <ulink
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url="http://ian.idallen.ca/dnat.txt">Paper about DNAT and
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Linux</ulink>.</para>
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</section>
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</section>
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<section>
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<title>DNS and Port Forwarding/NAT</title>
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<section id="faq2">
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<title>(FAQ 2) I port forward www requests to www.mydomain.com (IP
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130.151.100.69) to system 192.168.1.5 in my local network. External
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clients can browse http://www.mydomain.com but internal clients
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can't.</title>
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<para><emphasis role="bold">Answer:</emphasis> I have two objections to
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this setup.</para>
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<itemizedlist>
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<listitem>
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<para>Having an internet-accessible server in your local network is
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like raising foxes in the corner of your hen house. If the server is
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compromised, there's nothing between that server and your other
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internal systems. For the cost of another NIC and a cross-over
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cable, you can put your server in a DMZ such that it is isolated
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from your local systems - assuming that the Server can be located
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near the Firewall, of course :-)</para>
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</listitem>
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<listitem>
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<para>The accessibility problem is best solved using <ulink
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url="shorewall_setup_guide.htm#DNS">Bind Version 9
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<quote>views</quote></ulink> (or using a separate DNS server for
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local clients) such that www.mydomain.com resolves to 130.141.100.69
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externally and 192.168.1.5 internally. That's what I do here at
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shorewall.net for my local systems that use one-to-one NAT.</para>
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</listitem>
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</itemizedlist>
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<para>If you insist on an IP solution to the accessibility problem
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rather than a DNS solution, then assuming that your external interface
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is eth0 and your internal interface is eth1 and that eth1 has IP address
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192.168.1.254 with subnet 192.168.1.0/24.</para>
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<para>If you are running Shorewall 1.4.0 or earlier see the <ulink
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url="1.3/FAQ.htm#faq2">1.3 FAQ</ulink> for instructions suitable for
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those releases.</para>
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<para>If you are running Shorewall 1.4.1 or Shorewall 1.4.1a, please
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upgrade to Shorewall 1.4.2 or later.</para>
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<para>Otherwise:<warning>
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<para>In this configuration, all loc->loc traffic will look to
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the server as if it came from the firewall rather than from the
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original client!</para>
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</warning></para>
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<itemizedlist>
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<listitem>
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<para>In <filename>/etc/shorewall/interfaces</filename>:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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loc eth1 detect <emphasis role="bold">routeback</emphasis></programlisting>
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</listitem>
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<listitem>
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<para>In <filename>/etc/shorewall/masq</filename>:</para>
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<programlisting>#INTERFACE SUBNET ADDRESS PROTO PORT(S)
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eth1:192.168.1.5 eth1 192.168.1.254 tcp www</programlisting>
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</listitem>
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<listitem>
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<para>In <filename>/etc/shorewall/rules</filename>:</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 loc loc:192.168.1.5 tcp www - 130.151.100.69</programlisting>
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<para>That rule only works of course if you have a static external
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IP address. If you have a dynamic IP address and are running
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Shorewall 1.3.4 or later then include this in
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<filename>/etc/shorewall/init</filename>:</para>
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<programlisting><command>ETH0_IP=`find_interface_address eth0`</command></programlisting>
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<para>and make your DNAT rule:</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 loc loc:192.168.1.5 tcp www - $ETH0_IP</programlisting>
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<para>Using this technique, you will want to configure your
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DHCP/PPPoE client to automatically restart Shorewall each time that
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you get a new IP address.</para>
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</listitem>
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</itemizedlist>
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<section id="faq2a">
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<title>(FAQ 2a) I have a zone <quote>Z</quote> with an RFC1918 subnet
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and I use one-to-one NAT to assign non-RFC1918 addresses to hosts in
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Z. Hosts in Z cannot communicate with each other using their external
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(non-RFC1918 addresses) so they can't access each other using their
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DNS names.</title>
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<note>
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<para>If the ALL INTERFACES column in /etc/shorewall/nat is empty or
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contains <quote>Yes</quote>, you will also see log messages like the
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following when trying to access a host in Z from another host in Z
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using the destination hosts's public address:</para>
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<programlisting>Oct 4 10:26:40 netgw kernel:
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Shorewall:FORWARD:REJECT:IN=eth1 OUT=eth1 SRC=192.168.118.200
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DST=192.168.118.210 LEN=48 TOS=0x00 PREC=0x00 TTL=127 ID=1342 DF
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PROTO=TCP SPT=1494 DPT=1491 WINDOW=17472 RES=0x00 ACK SYN URGP=0</programlisting>
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</note>
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<para><emphasis role="bold">Answer:</emphasis> This is another problem
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that is best solved using Bind Version 9 <quote>views</quote>. It
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allows both external and internal clients to access a NATed host using
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the host's DNS name.</para>
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<para>Another good way to approach this problem is to switch from
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one-to-one NAT to Proxy ARP. That way, the hosts in Z have non-RFC1918
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addresses and can be accessed externally and internally using the same
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address.</para>
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<para>If you don't like those solutions and prefer routing all Z->Z
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traffic through your firewall then:</para>
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<orderedlist>
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<listitem>
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<para>Set the Z->Z policy to ACCEPT.</para>
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</listitem>
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<listitem>
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<para>Masquerade Z to itself.</para>
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</listitem>
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<listitem>
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<para>Set the routeback option on the interface to Z.</para>
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</listitem>
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<listitem>
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<para>Set the ALL INTERFACES column in the nat file to
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<quote>Yes</quote>.</para>
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<warning>
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<para>In this configuration, all Z->Z traffic will look to
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the server as if it came from the firewall rather than from the
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original client! I DO NOT RECOMMEND THIS SETUP.</para>
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</warning>
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</listitem>
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</orderedlist>
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<example>
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<title>Example:</title>
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<literallayout>Zone: dmz Interface: eth2 Subnet: 192.168.2.0/24</literallayout>
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<para>In <filename>/etc/shorewall/interfaces</filename>:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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loc eth2 192.168.2.255 <emphasis role="bold">routeback</emphasis></programlisting>
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<para>In <filename>/etc/shorewall/policy</filename>:</para>
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<programlisting>#SOURCE DESTINATION POLICY LIMIT:BURST
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dmz dmz ACCEPT</programlisting>
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<para>In <filename>/etc/shorewall/masq</filename>:</para>
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<programlisting>#INTERFACE SUBNET ADDRESS
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eth2 192.168.2.0/24</programlisting>
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<para>In <filename>/etc/shorewall/na</filename>t, be sure that you
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have <quote>Yes</quote> in the ALL INTERFACES column.</para>
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</example>
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</section>
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</section>
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</section>
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|
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<section>
|
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<title>Netmeeting/MSN</title>
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|
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<section id="faq3">
|
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<title>(FAQ 3) I want to use Netmeeting or MSN Instant Messenger with
|
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Shorewall. What do I do?</title>
|
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|
|
<para><emphasis role="bold">Answer:</emphasis> There is an <ulink
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url="http://www.kfki.hu/%7Ekadlec/sw/netfilter/newnat-suite/">H.323
|
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connection tracking/NAT module</ulink> that helps with Netmeeting. Note
|
|
however that one of the Netfilter developers recently posted the
|
|
following:</para>
|
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|
|
<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
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|
> contrack module kernel patch with a 2.6 kernel?
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|
> 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.
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|
> Do I have any options besides a gatekeeper app (does not work in my
|
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> network) or a proxy (would prefer to avoid them)?
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|
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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>
|
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</blockquote>
|
|
|
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<para>Look <ulink url="http://linux-igd.sourceforge.net">here</ulink>
|
|
for a solution for MSN IM but be aware that there are significant
|
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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>
|
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|
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<section>
|
|
<title>Open Ports</title>
|
|
|
|
<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> (Shorewall versions prior
|
|
to 2.0.0 only). The common.def included with version 1.3.x always
|
|
rejects connection requests on TCP port 113 rather than dropping them.
|
|
This is necessary to prevent outgoing connection problems to services
|
|
that use the <quote>Auth</quote> mechanism for identifying requesting
|
|
users. Shorewall also rejects TCP ports 135, 137, 139 and 445 as well as
|
|
UDP ports 137-139. These are ports that are used by Windows (Windows
|
|
<emphasis>can</emphasis> be configured to use the DCE cell locator on
|
|
port 135). Rejecting these connection requests rather than dropping them
|
|
cuts down slightly on the amount of Windows chatter on LAN segments
|
|
connected to the Firewall.</para>
|
|
|
|
<para>If you are seeing port 80 being <quote>closed</quote>, that's
|
|
probably your ISP preventing you from running a web server in violation
|
|
of your Service Agreement.</para>
|
|
|
|
<tip>
|
|
<para>You can change the default behavior of Shorewall through use of
|
|
an /etc/shorewall/common file. See the <ulink
|
|
url="shorewall_extension_scripts.htm">Extension Script
|
|
Section</ulink>.</para>
|
|
</tip>
|
|
|
|
<tip>
|
|
<para>Beginning with Shorewall 1.4.9, Shorewall no longer rejects the
|
|
Windows SMB ports (135-139 and 445) by default and silently drops them
|
|
instead.</para>
|
|
</tip>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> (Shorewall versions 2.0.0
|
|
and later). The default Shorewall setup invokes the <emphasis
|
|
role="bold">Drop</emphasis> action prior to enforcing a DROP policy and
|
|
the default policy to all zone from the internet is DROP. The Drop
|
|
action is defined in <filename>/etc/shorewall/action.Drop</filename>
|
|
which in turn invokes the <emphasis role="bold">RejectAuth</emphasis>
|
|
action (defined in
|
|
<filename>/etc/shorewall/action.RejectAuth</filename>). 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 firerwall will block that attempt.</para>
|
|
</section>
|
|
|
|
<section id="faq4c">
|
|
<title>(FAQ 4c) How to I use Shorewall with PortSentry?</title>
|
|
|
|
<para><ulink
|
|
url="http://www.shorewall.net/pub/shorewall/contrib/PortsentryHOWTO.txt">Here's
|
|
a writeup</ulink> on a nice integration of Shorewall and
|
|
PortSentry.</para>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Connection Problems</title>
|
|
|
|
<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 /etc/shorewall/masq
|
|
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 firewall to the internet.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</section>
|
|
|
|
<section id="faq29">
|
|
<title>(FAQ 29) FTP Doesn't Work</title>
|
|
|
|
<para>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 <ulink
|
|
url="Documentation.htm#Conf">/etc/shorewall/shorewall.conf</ulink>.</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 /etc/shorewall/interfaces; the bridged Ethernet
|
|
interfaces are not defined to Shorewall. How do I tell Shorewall to
|
|
allow traffic through the bridge?</title>
|
|
|
|
<para>Answer: Add the <firstterm>routeback</firstterm> option to
|
|
<filename class="devicefile">br0</filename> in <ulink
|
|
url="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<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 <ulink
|
|
url="Documentation.htm#Policy">policies</ulink> and <ulink
|
|
url="Documentation.htm#Rules">rules</ulink>. The destination for
|
|
messaged logged by syslog is controlled by
|
|
<filename>/etc/syslog.conf</filename> (see <quote>man
|
|
syslog.conf</quote>). When you have changed /etc/syslog.conf, be sure to
|
|
restart syslogd (on a RedHat system, <quote>service syslog
|
|
restart</quote>).</para>
|
|
|
|
<para>By default, older versions of Shorewall ratelimited log messages
|
|
through <ulink url="Documentation.htm#Conf">settings</ulink> in
|
|
<filename>/etc/shorewall/shorewall.conf</filename> -- If you want to log
|
|
all messages, set:</para>
|
|
|
|
<programlisting>LOGLIMIT=""
|
|
LOGBURST=""</programlisting>
|
|
|
|
<para>Beginning with Shorewall version 1.3.12, you can <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://www.fireparse.com">http://www.fireparse.com</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>
|
|
<ulink url="http://gege.org/iptables">http://gege.org/iptables</ulink>
|
|
<ulink url="http://home.regit.org/ulogd-php.html">http://home.regit.org/ulogd-php.html</ulink></literallayout>
|
|
|
|
<para>I personally use Logwatch. It emails me a report each day from
|
|
my various systems with each report summarizing the logged activity on
|
|
the corresponding system.</para>
|
|
</section>
|
|
|
|
<section id="faq6b">
|
|
<title>(FAQ 2b) 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>Temporarily add the following rule:</para>
|
|
|
|
<programlisting>DROP net fw udp 10619</programlisting>
|
|
</section>
|
|
|
|
<section id="faq6c">
|
|
<title>(FAQ 6c) All day long I get a steady flow of these DROP
|
|
messages from port 53 to some high numbered port. They get dropped,
|
|
but what the heck are they?</title>
|
|
|
|
<programlisting>Jan 8 15:50:48 norcomix kernel:
|
|
Shorewall:net2all:DROP:IN=eth0 OUT=
|
|
MAC=00:40:c7:2e:09:c0:00:01:64:4a:70:00:08:00 SRC=208.138.130.16
|
|
DST=24.237.22.45 LEN=53 TOS=0x00 PREC=0x00 TTL=251 ID=8288 DF
|
|
PROTO=UDP SPT=53 DPT=40275 LEN=33</programlisting>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> There are two
|
|
possibilities:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>They are late-arriving replies to DNS queries.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>They are corrupted reply packets.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>You can distinguish the difference by setting the <emphasis
|
|
role="bold">logunclean</emphasis> option (<filename><ulink
|
|
url="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink></filename>)
|
|
on your external interface (eth0 in the above example). If they get
|
|
logged twice, they are corrupted. I solve this problem by using an
|
|
/etc/shorewall/common file like this:</para>
|
|
|
|
<programlisting>#
|
|
# Include the standard common.def file
|
|
#
|
|
<command>. /etc/shorewall/common.def</command>
|
|
#
|
|
# The following rule is non-standard and compensates for tardy
|
|
# DNS replies
|
|
#
|
|
<command>run_iptables -A common -p udp --sport 53 -mstate --state NEW -j DROP</command></programlisting>
|
|
|
|
<para>The above file is also include in all of my sample
|
|
configurations available in the <ulink
|
|
url="shorewall_quickstart_guide.htm">Quick Start Guides</ulink> and in
|
|
the common.def file in Shorewall 1.4.0 and later.</para>
|
|
</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>What is labeled as the MAC address in a 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>
|
|
<title>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> If you are running
|
|
Shorewall version 1.4.4 or 1.4.4a then check the <ulink
|
|
url="errata.htm">errata</ulink>. Otherwise:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Find where klogd is being started (it will be from one of the
|
|
files in /etc/init.d -- sysklogd, klogd, ...). Modify that file or
|
|
the appropriate configuration file so that klogd is started with
|
|
<quote>-c <emphasis><n></emphasis></quote> where
|
|
<emphasis><n></emphasis> is a log level of 5 or less;
|
|
or</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>See the <quote>dmesg</quote> man page (<quote>man
|
|
dmesg</quote>). You must add a suitable <quote>dmesg</quote> command
|
|
to your startup scripts or place it in /etc/shorewall/start.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<tip>
|
|
<para>Under RedHat and Mandrake, the max <ulink
|
|
url="shorewall_logging.html">log level</ulink> that is sent to the
|
|
console is specified in /etc/sysconfig/init in the LOGLEVEL variable.
|
|
Set <quote>LOGLEVEL=5</quote> to suppress info (log level 6) messages
|
|
on the console.</para>
|
|
</tip>
|
|
|
|
<tip>
|
|
<para>Under Debian, you can set KLOGD=<quote>-c 5</quote> in
|
|
<filename>/etc/init.d/klogd</filename> to suppress info (log level 6)
|
|
messages on the console.</para>
|
|
</tip>
|
|
|
|
<tip>
|
|
<para>Under SuSE, add <quote>-c 5</quote> to KLOGD_PARAMS in
|
|
/etc/sysconfig/syslog to suppress info (log level 6) messages on the
|
|
console.</para>
|
|
</tip>
|
|
</section>
|
|
|
|
<section id="faq17">
|
|
<title>(FAQ 17) What does this log message mean?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> Logging occurs out of a
|
|
number of chains (as indicated in the log message) in Shorewall:</para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>man1918 or logdrop</term>
|
|
|
|
<listitem>
|
|
<para>The destination address is listed in
|
|
<filename>/usr/share/shorewall/rfc1918</filename> with a <emphasis
|
|
role="bold">logdrop</emphasis> target -- see <filename><ulink
|
|
url="Documentation.htm#rfc1918">/usr/share/shorewall/rfc1918</ulink></filename>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>rfc1918 or logdrop</term>
|
|
|
|
<listitem>
|
|
<para>The source or destination address is listed in
|
|
<filename>/usr/share/shorewall/rfc1918</filename> with a <emphasis
|
|
role="bold">logdrop</emphasis> target -- see <filename><ulink
|
|
url="Documentation.htm#rfc1918">/usr/share/shorewall/rfc1918</ulink></filename>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry id="all2all">
|
|
<term>all2<zone>, <zone>2all or all2all</term>
|
|
|
|
<listitem>
|
|
<para>You have a <ulink
|
|
url="Documentation.htm#Policy">policy</ulink> 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="Documentation.htm#Rules">rule</ulink> to that effect.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><zone1>2<zone2></term>
|
|
|
|
<listitem>
|
|
<para>Either you have a <ulink
|
|
url="Documentation.htm#Policy">policy</ulink> for <emphasis
|
|
role="bold"><zone1></emphasis> to <emphasis
|
|
role="bold"><zone2></emphasis> that specifies a log level
|
|
and this packet is being logged under that policy or this packet
|
|
matches a <ulink url="Documentation.htm#Rules">rule</ulink> that
|
|
includes a log level.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><interface>_mac</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged under the <emphasis
|
|
role="bold">maclist</emphasis> <ulink
|
|
url="Documentation.htm#Interfaces">interface
|
|
option</ulink>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>logpkt</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged under the <emphasis
|
|
role="bold">logunclean</emphasis> <ulink
|
|
url="Documentation.htm#Interfaces">interface
|
|
option</ulink>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>badpkt</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged under the <emphasis
|
|
role="bold">dropunclean</emphasis> <ulink
|
|
url="Documentation.htm#Interfaces">interface option</ulink> as
|
|
specified in the <emphasis role="bold">LOGUNCLEAN</emphasis>
|
|
setting in <ulink
|
|
url="Documentation.htm#Conf"><filename>/etc/shorewall/shorewall.conf</filename></ulink>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>blacklst</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged because the source IP is
|
|
blacklisted in the <filename><ulink
|
|
url="Documentation.htm#Blacklist">/etc/shorewall/blacklist</ulink></filename>
|
|
file.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>newnotsyn</term>
|
|
|
|
<listitem>
|
|
<para>The packet is being logged because it is a TCP packet that
|
|
is not part of any current connection yet it is not a syn packet.
|
|
Options affecting the logging of such packets include <emphasis
|
|
role="bold">NEWNOTSYN</emphasis> and <emphasis
|
|
role="bold">LOGNEWNOTSYN</emphasis> in <ulink
|
|
url="Documentation.htm#Conf"><filename>/etc/shorewall/shorewall.conf</filename></ulink>.</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>shorewall check</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. Also see <xref
|
|
linkend="faq2a" /> for another cause of packets being logged in
|
|
the FORWARD 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="Documentation.htm#Interfaces">interface
|
|
option</ulink>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<example>
|
|
<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 (<xref linkend="all2all" /> 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>
|
|
</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>For additional information about the log message, see <ulink
|
|
url="http://logi.cc/linux/netfilter-log-format.php3">http://logi.cc/linux/netfilter-log-format.php3</ulink>.</para>
|
|
|
|
<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 PROTO=ICMP
|
|
TYPE=3 CODE=3 [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> While most people
|
|
associate the Internet Control Message Protocol (ICMP) with
|
|
<quote>ping</quote>, ICMP is a key piece of the internet. 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 a lot of broken implementations. That is
|
|
what you are seeing with these messages.</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. I have also seen cases where the source IP in the ICMP itself
|
|
isn't set back to the external IP of the remote NAT gateway; that causes
|
|
your firewall to log and drop the packet out of the rfc1918 chain
|
|
because the source IP is reserved by RFC 1918.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<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>Setting this up in Shorewall is easy; setting up the routing is a
|
|
bit harder.</para>
|
|
|
|
<para>Assuming that <filename class="devicefile">eth0</filename> and
|
|
<filename class="devicefile">eth1</filename> are the interfaces to the
|
|
two ISPs then:</para>
|
|
|
|
<para><filename>/etc/shorewall/interfaces</filename>:</para>
|
|
|
|
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
|
|
net eth0 detect
|
|
net eth1 detect</programlisting>
|
|
|
|
<para><filename>/etc/shorewall/policy</filename>:</para>
|
|
|
|
<programlisting>#SOURCE DESTINATION POLICY LIMIT:BURST
|
|
net net DROP</programlisting>
|
|
|
|
<para>If you have masqueraded hosts, be sure to update
|
|
<filename>/etc/shorewall/masq</filename> to masquerade to both ISPs. For
|
|
example, if you masquerade all hosts connected to <filename
|
|
class="devicefile">eth2</filename> then:</para>
|
|
|
|
<programlisting>#INTERFACE SUBNET ADDRESS
|
|
eth0 eth2
|
|
eth1 eth2</programlisting>
|
|
|
|
<para><citetitle>There was an article in SysAdmin covering this topic.
|
|
It may be found at <ulink
|
|
url="http://www.samag.com/documents/s=1824/sam0201h/">http://www.samag.com/documents/s=1824/sam0201h/</ulink></citetitle></para>
|
|
|
|
<para><citetitle>The following information regarding setting up routing
|
|
for this configuration is reproduced from the <ulink
|
|
url="http://www.lartc.org">LARTC HOWTO</ulink> and has not been verified
|
|
by the author. If you have questions or problems with the instructions
|
|
given below, please post to the <ulink
|
|
url="http://www.lartc.org/#mailinglist">LARTC mailing
|
|
list</ulink>.</citetitle></para>
|
|
|
|
<sidebar>
|
|
<para>A common configuration is the following, in which there are two
|
|
providers that connect a local network (or even a single machine) to
|
|
the big Internet.</para>
|
|
|
|
<programlisting> ________
|
|
+------------+ /
|
|
| | |
|
|
+-------------+ Provider 1 +-------
|
|
__ | | | /
|
|
___/ \_ +------+-------+ +------------+ |
|
|
_/ \__ | if1 | /
|
|
/ \ | | |
|
|
| Local network -----+ Linux router | | Internet
|
|
\_ __/ | | |
|
|
\__ __/ | if2 | \
|
|
\___/ +------+-------+ +------------+ |
|
|
| | | \
|
|
+-------------+ Provider 2 +-------
|
|
| | |
|
|
+------------+ \________
|
|
</programlisting>
|
|
|
|
<para>There are usually two questions given this setup.</para>
|
|
|
|
<para><emphasis role="bold">Split access</emphasis></para>
|
|
|
|
<para>The first is how to route answers to packets coming in over a
|
|
particular provider, say Provider 1, back out again over that same
|
|
provider.</para>
|
|
|
|
<para>Let us first set some symbolical names. Let <emphasis
|
|
role="bold">$IF1</emphasis> be the name of the first interface (if1 in
|
|
the picture above) and <emphasis role="bold">$IF2</emphasis> the name
|
|
of the second interface. Then let <emphasis
|
|
role="bold">$IP1</emphasis> be the IP address associated with
|
|
<emphasis role="bold">$IF1</emphasis> and <emphasis
|
|
role="bold">$IP2</emphasis> the IP address associated with <emphasis
|
|
role="bold">$IF2</emphasis>. Next, let <emphasis
|
|
role="bold">$P1</emphasis> be the IP address of the gateway at
|
|
Provider 1, and <emphasis role="bold">$P2</emphasis> the IP address of
|
|
the gateway at provider 2. Finally, let <emphasis
|
|
role="bold">$P1_NET</emphasis> be the IP network <emphasis
|
|
role="bold">$P1</emphasis> is in, and <emphasis
|
|
role="bold">$P2_NET</emphasis> the IP network <emphasis
|
|
role="bold">$P2</emphasis> is in.</para>
|
|
|
|
<para>One creates two additional routing tables, say <emphasis
|
|
role="bold">T1</emphasis> and <emphasis role="bold">T2</emphasis>.
|
|
These are added in /etc/iproute2/rt_tables. Then you set up routing in
|
|
these tables as follows:</para>
|
|
|
|
<programlisting>ip route add $P1_NET dev $IF1 src $IP1 table T1
|
|
ip route add default via $P1 table T1
|
|
ip route add $P2_NET dev $IF2 src $IP2 table T2
|
|
ip route add default via $P2 table T2</programlisting>
|
|
|
|
<para>Nothing spectacular, just build a route to the gateway and build
|
|
a default route via that gateway, as you would do in the case of a
|
|
single upstream provider, but put the routes in a separate table per
|
|
provider. Note that the network route suffices, as it tells you how to
|
|
find any host in that network, which includes the gateway, as
|
|
specified above.</para>
|
|
|
|
<para>Next you set up the main routing table. It is a good idea to
|
|
route things to the direct neighbour through the interface connected
|
|
to that neighbour. Note the `src' arguments, they make sure the right
|
|
outgoing IP address is chosen.</para>
|
|
|
|
<programlisting>ip route add $P1_NET dev $IF1 src $IP1
|
|
ip route add $P2_NET dev $IF2 src $IP2</programlisting>
|
|
|
|
<para>Then, your preference for default route:</para>
|
|
|
|
<programlisting>ip route add default via $P1</programlisting>
|
|
|
|
<para>Next, you set up the routing rules. These actually choose what
|
|
routing table to route with. You want to make sure that you route out
|
|
a given interface if you already have the corresponding source
|
|
address:</para>
|
|
|
|
<programlisting>ip rule add from $IP1 table T1
|
|
ip rule add from $IP2 table T2</programlisting>
|
|
|
|
<para>This set of commands makes sure all answers to traffic coming in
|
|
on a particular interface get answered from that interface.</para>
|
|
|
|
<note>
|
|
<para>'If $P0_NET is the local network and $IF0 is its interface,
|
|
the following additional entries are desirable:</para>
|
|
|
|
<programlisting format="linespecific">ip route add $P0_NET dev $IF0 table T1
|
|
ip route add $P2_NET dev $IF2 table T1
|
|
ip route add 127.0.0.0/8 dev lo table T1
|
|
ip route add $P0_NET dev $IF0 table T2
|
|
ip route add $P1_NET dev $IF1 table T2
|
|
ip route add 127.0.0.0/8 dev lo table T2</programlisting>
|
|
</note>
|
|
|
|
<para>Now, this is just the very basic setup. It will work for all
|
|
processes running on the router itself, and for the local network, if
|
|
it is masqueraded. If it is not, then you either have IP space from
|
|
both providers or you are going to want to masquerade to one of the
|
|
two providers. In both cases you will want to add rules selecting
|
|
which provider to route out from based on the IP address of the
|
|
machine in the local network.</para>
|
|
|
|
<para><emphasis role="bold">Load balancing</emphasis></para>
|
|
|
|
<para>The second question is how to balance traffic going out over the
|
|
two providers. This is actually not hard if you already have set up
|
|
split access as above.</para>
|
|
|
|
<para>Instead of choosing one of the two providers as your default
|
|
route, you now set up the default route to be a multipath route. In
|
|
the default kernel this will balance routes over the two providers. It
|
|
is done as follows (once more building on the example in the section
|
|
on split-access):</para>
|
|
|
|
<programlisting>ip route add default scope global nexthop via $P1 dev $IF1 weight 1 \
|
|
nexthop via $P2 dev $IF2 weight 1</programlisting>
|
|
|
|
<para>This will balance the routes over both providers. The <emphasis
|
|
role="bold">weight</emphasis> parameters can be tweaked to favor one
|
|
provider over the other.</para>
|
|
|
|
<note>
|
|
<para>balancing will not be perfect, as it is route based, and
|
|
routes are cached. This means that routes to often-used sites will
|
|
always be over the same provider.</para>
|
|
</note>
|
|
|
|
<para>Furthermore, if you really want to do this, you probably also
|
|
want to look at Julian Anastasov's patches at <ulink
|
|
url="http://www.ssi.bg/%7Eja/#routes">http://www.ssi.bg/~ja/#routes</ulink>
|
|
, Julian's route patch page. They will make things nicer to work
|
|
with.</para>
|
|
</sidebar>
|
|
|
|
<para>The following was contributed by Martin Brown and is an excerpt
|
|
from <citetitle><ulink
|
|
url="http://www.docum.org/stef.coene/qos/faq/cache/44.html">http://www.docum.org/stef.coene/qos/faq/cache/44.html</ulink></citetitle>.</para>
|
|
|
|
<sidebar>
|
|
<para>There are two issues requiring different handling when dealing
|
|
with multiple Internet providers on a given network. The below assumes
|
|
that the host which has multiple Internet connections is a
|
|
masquerading (or NATting) host and is at the chokepoint between the
|
|
internal and external networks. For the use of multiple inbound
|
|
connections to the same internal server (public IP A from ISP A and
|
|
public IP B from ISP B both get redirected to the same internal
|
|
server), the ideal solution involves using two private IP addresses on
|
|
the internal server. This leads to an end-to-end uniqueness of public
|
|
IP to private IP and can be easily accomplished by following the
|
|
directions here:</para>
|
|
|
|
<para><ulink
|
|
url="http://linux-ip.net/html/adv-multi-internet.html#adv-multi-internet-inbound"><citetitle>http://linux-ip.net/html/adv-multi-internet.html#adv-multi-internet-inbound</citetitle></ulink></para>
|
|
|
|
<para>For the use of multiple outbound links to the Internet, there
|
|
are a number of different techniques. The simplest is identified
|
|
here:</para>
|
|
|
|
<para><citetitle><ulink
|
|
url="http://linux-ip.net/html/adv-multi-internet.html#adv-multi-internet-outbound">http://linux-ip.net/html/adv-multi-internet.html#adv-multi-internet-outbound</ulink></citetitle></para>
|
|
|
|
<para>Better (and more robust) techniques are available after a kernel
|
|
routing patch by Julian Anastasov. See the famous nano-howto.</para>
|
|
|
|
<para><citetitle><ulink
|
|
url="http://www.ssi.bg/~ja/">http://www.ssi.bg/~ja/</ulink></citetitle></para>
|
|
</sidebar>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Starting and Stopping</title>
|
|
|
|
<section id="faq7">
|
|
<title>(FAQ 7) When I stop Shorewall using <quote>shorewall
|
|
stop</quote>, I can't connect to anything. Why doesn't that command
|
|
work?</title>
|
|
|
|
<para>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 clear</command></quote> command.</para>
|
|
</section>
|
|
|
|
<section id="faq8">
|
|
<title>(FAQ 8) When I try to start Shorewall on RedHat, I get messages
|
|
about insmod failing -- what's wrong?</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> The output you will see
|
|
looks something like this:</para>
|
|
|
|
<programlisting>/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: init_module: Device or resource busy
|
|
Hint: insmod errors can be caused by incorrect module parameters, including invalid IO or IRQ parameters
|
|
/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: insmod
|
|
/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o failed
|
|
/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: insmod ip_tables failed
|
|
iptables v1.2.3: can't initialize iptables table `nat': iptables who? (do you need to insmod?)
|
|
Perhaps iptables or your kernel needs to be upgraded.</programlisting>
|
|
|
|
<para>This problem is usually corrected through the following sequence
|
|
of commands</para>
|
|
|
|
<programlisting><command>service ipchains stop
|
|
chkconfig --delete ipchains
|
|
rmmod ipchains</command></programlisting>
|
|
|
|
<para>Also, be sure to check the <ulink url="errata.htm">errata</ulink>
|
|
for problems concerning the version of iptables (v1.2.3) shipped with
|
|
RH7.2.</para>
|
|
|
|
<section id="faq8a">
|
|
<title>(FAQ 8a) When I try to start Shorewall on RedHat I get a
|
|
message referring me to FAQ #8</title>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> This is usually cured
|
|
by the sequence of commands shown above in <xref
|
|
linkend="faq8" />.</para>
|
|
</section>
|
|
</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 start 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 eth0 and the local zone is defined as all hosts
|
|
connected through <filename class="devicefile">eth1</filename>. If you
|
|
are running Shorewall 1.4.10 or later, you can consider setting the
|
|
<ulink url="Documentation.htm#Interfaces"><emphasis
|
|
role="bold">detectnets</emphasis> interface option</ulink> on your local
|
|
interface (<filename class="devicefile">eth1</filename> in the above
|
|
example). That will cause Shorewall to restrict the local zone to only
|
|
those networks routed through that interface.</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>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 to be sure that the
|
|
commands will do what they are 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="faq34">
|
|
<title>(FAQ 34) How can I speed up start (restart)?</title>
|
|
|
|
<para>Using a light-weight shell such as <command>ash</command> can
|
|
dramatically decrease the time required to <emphasis
|
|
role="bold">start</emphasis> or <emphasis role="bold">restart</emphasis>
|
|
Shorewall. See the SHOREWALL_SHELL variable in <filename><ulink
|
|
url="Documentation.htm#Conf">shorewall.conf</ulink></filename>.</para>
|
|
|
|
<para>Beginning with Shorewall version 2.0.2 Beta 1, Shorewall supports
|
|
a fast start capability. To use this capability:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>With Shorewall in the <ulink
|
|
url="starting_and_stopping_shorewall.htm">started state</ulink>, run
|
|
<command>shorewall save</command>. This creates the script
|
|
<filename>/var/lib/shorewall/restore</filename>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Use the <emphasis role="bold">-f </emphasis>option to the
|
|
start command (e.g., <command>shorewall -f start</command>). This
|
|
causes Shorewall to look for the
|
|
<filename>/var/lib/shorewall/restore</filename> script and if that
|
|
script exists, it is run. Running
|
|
<filename>/var/lib/shorewall/restore</filename> takes much less time
|
|
than a full <command>shorewall start</command>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>The <filename>/etc/init.d/shorewall</filename> script that is
|
|
run at boot time uses the <emphasis role="bold">-f</emphasis>
|
|
option.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>The <filename>/var/lib/shorewall/restore</filename> script can
|
|
be run any time to restore the firewall. The script may be run
|
|
directly or it may be run indirectly using the <command>shorewall
|
|
restore</command> command.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>If you change your Shorewall configuration, you must execute a
|
|
<emphasis role="bold">shorewall start</emphasis> (without <emphasis
|
|
role="bold">-f</emphasis>) or <command>shorewall restart</command> prior
|
|
to doing another <command>shorewall save</command>. The
|
|
<command>shorewall save</command> command saves the currently running
|
|
configuration and not the one reflected in your updated configuration
|
|
files.</para>
|
|
|
|
<para>Likewise, if you change your Shorewall configuration then once you
|
|
are satisfied that it is working properly, you must do another
|
|
<command>shorewall save</command>. Otherwise at the next reboot, you
|
|
will revert to the old configuration stored in
|
|
<filename>/var/lib/shorewall/restore</filename>.</para>
|
|
|
|
<section id="faq34a">
|
|
<title>(FAQ 34a) I get errors about a host or network not found when I
|
|
run<filename>/var/lib/shorewall/restore</filename>. The
|
|
<command>shorewall restore</command> and <command>shorewall -f
|
|
start</command> commands gives the same result.</title>
|
|
|
|
<para>Answer: iptables 1.2.9 is broken with respect to iptables-save
|
|
and the connection tracking match extension. You must patch your
|
|
iptables using the patch available from the <ulink
|
|
url="errata.htm">Shorewall errata page</ulink>.</para>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>About Shorewall</title>
|
|
|
|
<section id="faq10">
|
|
<title>(FAQ 10) What Distributions does it work with?</title>
|
|
|
|
<para>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 it 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
|
|
included in Webmin 1.060 and later versions. See <ulink
|
|
url="http://www.webmin.com">http://www.webmin.com</ulink></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 must more commonly used.</para>
|
|
</section>
|
|
|
|
<section id="faq23">
|
|
<title>(FAQ 23) Why do you use such ugly fonts on your web site?</title>
|
|
|
|
<para>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 to I tell which version of Shorewall I am
|
|
running?</title>
|
|
|
|
<para>At the shell prompt, type:</para>
|
|
|
|
<programlisting><command>/sbin/shorewall 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>Answer: Yes.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>Tear Drop: Sending packets that contain overlapping
|
|
fragments?</term>
|
|
|
|
<listitem>
|
|
<para>Answer: 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>Answer: Shorewall can be configured to do that using the
|
|
<ulink url="blacklisting_support.htm">blacklisting</ulink>
|
|
facility. Shorewall versions 2.0.0 and later filter these packets
|
|
under the <firstterm>nosmurfs</firstterm> interface option in
|
|
<ulink
|
|
url="Documentation.htm#Interfaces">/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>Answer: Yes, if the <ulink
|
|
url="Documentation.htm#Interfaces">routefilter interface
|
|
option</ulink> is selected.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>DOS: - SYN Dos - ICMP Dos - Per-host Dos protection</term>
|
|
|
|
<listitem>
|
|
<para>Answer: Shorewall has facilities for limiting SYN and ICMP
|
|
packets. Netfilter as included in standard Linux kernels doesn't
|
|
support per-remote-host limiting except by explicit rule that
|
|
specifies the host IP address; that form of limiting is supported
|
|
by Shorewall.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Given that the Debian Stable Release includes Shorewall 1.2.12,
|
|
how can you not support that version?</title>
|
|
|
|
<para>The first release of Shorewall was in March of 2001. Shorewall
|
|
1.2.12 was released in May of 2002. It is now the year 2004 and
|
|
Shorewall 2.0 is available. Shorewall 1.2.12 is poorly documented and is
|
|
missing many of the features that Shorewall users find essential today
|
|
and it is silly to continue to run it simply because it is bundled with
|
|
an ancient Debian release.</para>
|
|
</section>
|
|
|
|
<section id="faq36">
|
|
<title>(FAQ 36) Does Shorewall Work with the 2.6 Linux Kernel?</title>
|
|
|
|
<para>Shorewall works with the 2.6 Kernels with a couple of
|
|
caveats:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Netfilter/iptables doesn't fully support IPSEC in the 2.6
|
|
Kernels -- there are interim instructions linked from the <ulink
|
|
url="IPSEC.htm">Shorewall IPSEC page</ulink>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>The 2.6 Kernels do not provide support for the logunclean and
|
|
dropunclean options in
|
|
<filename>/etc/shorewall/interfaces</filename>. Note that support
|
|
for those options was also removed from Shorewall in version
|
|
2.0.0.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>RFC 1918</title>
|
|
|
|
<section id="faq14">
|
|
<title>(FAQ 14) I'm connected via a cable modem and it has an internal
|
|
web server that allows me to configure/monitor it but as expected if I
|
|
enable rfc1918 blocking for my eth0 interface (the internet one), it
|
|
also blocks the cable modems web server.</title>
|
|
|
|
<para>Is there any way it can add a rule before the rfc1918 blocking
|
|
that will let all traffic to and from the 192.168.100.1 address of the
|
|
modem in/out but still block all other rfc1918 addresses?</para>
|
|
|
|
<para><emphasis role="bold">Answer:</emphasis> If you are running a
|
|
version of Shorewall earlier than 1.3.1, create /etc/shorewall/start and
|
|
in it, place the following:</para>
|
|
|
|
<programlisting><command>run_iptables -I rfc1918 -s 192.168.100.1 -j ACCEPT</command></programlisting>
|
|
|
|
<para>If you are running version 1.3.1 or later, add the following to
|
|
<ulink url="Documentation.htm#rfc1918">/etc/shorewall/rfc1918</ulink>
|
|
(Note: If you are running Shorewall 2.0.0 or later, you may need to
|
|
first copy <filename>/usr/share/shorewall/rfc1918</filename> to
|
|
<filename>/etc/shorewall/rfc1918</filename>):</para>
|
|
|
|
<para>Be sure that you add the entry ABOVE the entry for
|
|
192.168.0.0/16.</para>
|
|
|
|
<programlisting>#SUBNET TARGET
|
|
192.168.100.1 RETURN</programlisting>
|
|
|
|
<note>
|
|
<para>If you add a second IP address to your external firewall
|
|
interface to correspond to the modem address, you must also make an
|
|
entry in /etc/shorewall/rfc1918 for that address. For example, if you
|
|
configure the address 192.168.100.2 on your firewall, then you would
|
|
add two entries to /etc/shorewall/rfc1918:</para>
|
|
|
|
<programlisting>#SUBNET TARGET
|
|
192.168.100.1 RETURN
|
|
192.168.100.2 RETURN</programlisting>
|
|
</note>
|
|
|
|
<section id="faq14a">
|
|
<title>(FAQ 14a) Even though it assigns public IP addresses, my ISP's
|
|
DHCP server has an RFC 1918 address. If I enable RFC 1918 filtering on
|
|
my external interface, my DHCP client cannot renew its lease.</title>
|
|
|
|
<para>The solution is the same as <xref linkend="faq14" /> above.
|
|
Simply substitute the IP address of your ISPs DHCP server.</para>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<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 rulesets 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>
|
|
|
|
<section>
|
|
<title>Miscellaneous</title>
|
|
|
|
<section id="faq19">
|
|
<title>(FAQ 19) I have added entries to /etc/shorewall/tcrules but they
|
|
don't seem to do anything. Why?</title>
|
|
|
|
<para>You probably haven't set TC_ENABLED=Yes in
|
|
/etc/shorewall/shorewall.conf so the contents of the tcrules file are
|
|
simply being ignored.</para>
|
|
</section>
|
|
|
|
<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>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 conections to let's say the ssh port
|
|
only from specific IP Addresses on the internet?</title>
|
|
|
|
<para>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>
|
|
<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>Edit /etc/shorewall/shorewall.conf and change
|
|
<quote>NEWNOTSYN=No</quote> to <quote>NEWNOTSYN=Yes</quote> then restart
|
|
Shorewall.</para>
|
|
|
|
<section id="faq26a">
|
|
<title>(FAQ 26a) When I try to use the <quote>-O</quote> option of
|
|
nmap from the firewall system, I get <quote>operation not
|
|
permitted</quote>. How do I allow this option?</title>
|
|
|
|
<para>Add this command to your /etc/shorewall/start file:</para>
|
|
|
|
<programlisting><command>run_iptables -D OUTPUT -p ! icmp -m state --state INVALID -j DROP</command></programlisting>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="faq27">
|
|
<title>(FAQ 27) I'm compiling a new kernel for my firewall. What should
|
|
I look out for?</title>
|
|
|
|
<para>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 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>Experimental Shorewall Bridging Firewall support is available —
|
|
<ulink url="bridge.html">check here for details</ulink>.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<appendix>
|
|
<title>Revision History</title>
|
|
|
|
<para><revhistory>
|
|
<revision>
|
|
<revnumber>1.28</revnumber>
|
|
|
|
<date>2004-07-14</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Insert link to Ian Allen's DNAT paper (FAQ
|
|
38)</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.27</revnumber>
|
|
|
|
<date>2004-06-18</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Correct formatting in H323 quote.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.26</revnumber>
|
|
|
|
<date>2004-05-18</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Delete obsolete ping information.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.25</revnumber>
|
|
|
|
<date>2004-05-18</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Empty /etc/shorewall on Debian.</revremark>
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</revision>
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<revision>
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<revnumber>1.25</revnumber>
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<date>2004-05-08</date>
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<authorinitials>TE</authorinitials>
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|
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<revremark>Update for Shorewall 2.0.2</revremark>
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</revision>
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|
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<revision>
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<revnumber>1.24</revnumber>
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<date>2004-04-25</date>
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|
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<authorinitials>TE</authorinitials>
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|
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<revremark>Add MA Brown's notes on multi-ISP routing.</revremark>
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</revision>
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<revision>
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<revnumber>1.23</revnumber>
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<date>2004-04-22</date>
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|
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<authorinitials>TE</authorinitials>
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<revremark>Refined SNAT rule in FAQ #2.</revremark>
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</revision>
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<revision>
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<revnumber>1.22</revnumber>
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<date>2004-04-06</date>
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|
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<authorinitials>TE</authorinitials>
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|
|
<revremark>Added FAQ 36.</revremark>
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</revision>
|
|
|
|
<revision>
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|
<revnumber>1.21</revnumber>
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|
|
|
<date>2004-03-05</date>
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|
|
|
<authorinitials>TE</authorinitials>
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|
|
|
<revremark>Added Bridging link.</revremark>
|
|
</revision>
|
|
|
|
<revision>
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|
<revnumber>1.20</revnumber>
|
|
|
|
<date>2004-02-27</date>
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|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added FAQ 35.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.19</revnumber>
|
|
|
|
<date>2004-02-22</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added mention of nosmurfs option under FAQ
|
|
31.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.18</revnumber>
|
|
|
|
<date>2004-02-15</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added FAQ 34.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.17</revnumber>
|
|
|
|
<date>2004-02-11</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added FAQ 33.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.16</revnumber>
|
|
|
|
<date>2004-02-03</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Updated for Shorewall 2.0.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.15</revnumber>
|
|
|
|
<date>2004-01-25</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Updated FAQ 32 to mention masquerading. Remove
|
|
tables.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.14</revnumber>
|
|
|
|
<date>2004-01-24</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added FAQ 27a regarding kernel/iptables
|
|
incompatibility.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.13</revnumber>
|
|
|
|
<date>2004-01-24</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Add a note about the <emphasis
|
|
role="bold">detectnets</emphasis> interface option in FAQ
|
|
9.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.12</revnumber>
|
|
|
|
<date>2004-01-20</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Improve FAQ 16 answer.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.11</revnumber>
|
|
|
|
<date>2004-01-14</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Corrected broken link</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.10</revnumber>
|
|
|
|
<date>2004-01-09</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added a couple of more legacy FAQ numbers.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.9</revnumber>
|
|
|
|
<date>2004-01-08</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Corrected typo in FAQ 26a. Added warning to FAQ 2
|
|
regarding source address of redirected requests.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.8</revnumber>
|
|
|
|
<date>2003-12-31</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Additions to FAQ 4.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.7</revnumber>
|
|
|
|
<date>2003-12-30</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Remove dead link from FAQ 1.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.6</revnumber>
|
|
|
|
<date>2003.12-18</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Add external link reference to FAQ 17.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.5</revnumber>
|
|
|
|
<date>2003-12-16</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added a link to a Sys Admin article about multiple
|
|
internet interfaces. Added Legal Notice. Moved "abstract" to the
|
|
body of the document. Moved Revision History to this
|
|
Appendix.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.4</revnumber>
|
|
|
|
<date>2003-12-13</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Corrected formatting problems</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.3</revnumber>
|
|
|
|
<date>2003-12-10</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Changed the title of FAQ 17</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.2</revnumber>
|
|
|
|
<date>2003-12-09</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Added Copyright and legacy FAQ numbers</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.1</revnumber>
|
|
|
|
<date>2003-12-04</date>
|
|
|
|
<authorinitials>MN</authorinitials>
|
|
|
|
<revremark>Converted to Simplified DocBook XML</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.0</revnumber>
|
|
|
|
<date>2002-08-13</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Initial revision</revremark>
|
|
</revision>
|
|
</revhistory></para>
|
|
</appendix>
|
|
</article> |