shorewall_code/Shorewall-docs/troubleshoot.xml

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  <articleinfo>
    <title>Shorewall Troubleshooting Guide</title>

    <author>
      <firstname>Tom</firstname>

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

    <pubdate>2003/12/22</pubdate>

    <copyright>
      <year>2003</year>

      <holder>Thomas M. Eastep</holder>
    </copyright>

    <legalnotice>
      <para>Permission is granted to copy, distribute and/or modify this
      document under the terms of the GNU Free Documentation License, Version
      1.2 or any later version published by the Free Software Foundation; with
      no Invariant Sections, with no Front-Cover, and with no Back-Cover
      Texts. A copy of the license is included in the section entitled
      <quote><ulink type="" url="Copyright.htm">GNU Free Documentation License</ulink></quote>.</para>
    </legalnotice>
  </articleinfo>

  <graphic align="center" fileref="images/obrasinf.gif" />

  <para><emphasis role="bold"><quote>If you think you can you can; if you
  think you can&#39;t you&#39;re right. If you don&#39;t believe that you can,
  why should someone else?</quote> -- Gunnar Tapper</emphasis></para>

  <section>
    <title>First Steps</title>

    <para>Some problems are easily solved by checking one of the resources
    described in the following sections.</para>

    <section>
      <title>Check the FAQs.</title>

      <para>Check the <ulink url="FAQ.htm">FAQs</ulink> for solutions to over
      30 common problems.</para>
    </section>

    <section>
      <title>Check the Errata</title>

      <para>Check the <ulink url="errata.htm">Shorewall Errata</ulink> to be
      sure that there isn&#39;t an update that you are missing for your
      version of the firewall.</para>
    </section>
  </section>

  <section>
    <title><quote>shorewall start</quote> and <quote>shorewall restart</quote>
    Errors</title>

    <para>If you receive an error message when starting or restarting the
    firewall and you can&#39;t determine the cause, then do the following:</para>

    <itemizedlist>
      <listitem>
        <para>Make a note of the error message that you see.</para>
      </listitem>

      <listitem>
        <para>shorewall debug start 2&#62; /tmp/trace</para>
      </listitem>

      <listitem>
        <para>Look at the /tmp/trace file and see if that helps you determine
        what the problem is. Be sure you find the place in the log where the
        error message you saw is generated -- If you are using Shorewall 1.4.0
        or later, you should find the message near the end of the log.</para>
      </listitem>

      <listitem>
        <para>If you still can&#39;t determine what&#39;s wrong then see the
        <ulink url="support.htm">support page</ulink>.</para>
      </listitem>
    </itemizedlist>

    <example>
      <title>Startup Error</title>

      <para>During startup, a user sees the following:</para>

      <programlisting>        Adding Common Rules
        iptables: No chain/target/match by that name
        Terminated</programlisting>

      <para>A search through the trace for <quote>No chain/target/match by
      that name</quote> turned up the following:</para>

      <programlisting>        + echo &#39;Adding Common Rules&#39;
        + add_common_rules
        + run_iptables -A reject -p tcp -j REJECT --reject-with tcp-reset
        ++ echo -A reject -p tcp -j REJECT --reject-with tcp-reset
        ++ sed &#39;s/!/! /g&#39;
        + iptables -A reject -p tcp -j REJECT --reject-with tcp-reset
        iptables: No chain/target/match by that name
</programlisting>

      <para>The command that failed was: <quote>iptables -A reject -p tcp -j
      REJECT --reject-with tcp-reset</quote>. In this case, the user had
      compiled his own kernel and had forgotten to include REJECT target
      support (see <ulink url="kernel.htm">kernel.htm</ulink>)</para>
    </example>
  </section>

  <section>
    <title>Your Network Environment</title>

    <para>Many times when people have problems with Shorewall, the problem is
    actually an ill-conceived network setup. Here are several popular snafus:</para>

    <itemizedlist>
      <listitem>
        <para>Port Forwarding where client and server are in the same subnet.
        See FAQ 2.</para>
      </listitem>

      <listitem>
        <para>Changing the IP address of a local system to be in the external
        subnet, thinking that Shorewall will suddenly believe that the system
        is in the <quote>net</quote> zone.</para>
      </listitem>

      <listitem>
        <para>Multiple interfaces connected to the same HUB or Switch. Given
        the way that the Linux kernel respond to ARP <quote>who-has</quote>
        requests, this type of setup does NOT work the way that you expect it
        to. If you are running Shorewall version 1.4.7 or later, you can test
        using this kind of configuration if you specify the <emphasis
        role="bold">arp_filter</emphasis> option in <ulink
        url="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink>
        for all interfaces connected to the common hub/switch. Using such a
        setup with a production firewall is strongly recommended against.</para>
      </listitem>
    </itemizedlist>
  </section>

  <section>
    <title>Connection Problems</title>

    <para>If the appropriate policy for the connection that you are trying to
    make is ACCEPT, please DO NOT ADD ADDITIONAL ACCEPT RULES TRYING TO MAKE
    IT WORK. Such additional rules will NEVER make it work, they add clutter
    to your rule set and they represent a big security hole in the event that
    you forget to remove them later.</para>

    <para>I also recommend against setting all of your policies to ACCEPT in
    an effort to make something work. That robs you of one of your best
    diagnostic tools - the <quote>Shorewall</quote> messages that Netfilter
    will generate when you try to connect in a way that isn&#39;t permitted by
    your rule set.</para>

    <para>Check your log (<quote>/sbin/shorewall show log</quote>). If you
    don&#39;t see Shorewall messages, then your problem is probably NOT a
    Shorewall problem. If you DO see packet messages, it may be an indication
    that you are missing one or more rules -- see <ulink url="FAQ.htm#faq17">FAQ
    17</ulink>.</para>

    <para>While you are troubleshooting, it is a good idea to clear two
    variables in /etc/shorewall/shorewall.conf:</para>

    <para><programlisting>     LOGRATE=&#34;&#34;
     LOGBURST=&#34;&#34;</programlisting>This way, you will see all of the log
    messages being generated (be sure to restart shorewall after clearing
    these variables).</para>

    <example>
      <title>Log Message</title>

      <programlisting>Jun 27 15:37:56 gateway kernel: Shorewall:all2all:REJECT:IN=eth2 OUT=eth1 SRC=192.168.2.2 DST=192.168.1.3
                                LEN=67 TOS=0x00 PREC=0x00 TTL=63 ID=5805 DF PROTO=UDP SPT=1803 DPT=53 LEN=47</programlisting>

      <para>Let&#39;s look at the important parts of this message:</para>

      <itemizedlist>
        <listitem>
          <para>all2all:REJECT - This packet was REJECTed out of the all2all
          chain -- the packet was rejected under the <quote>all</quote>-&#62;<quote>all</quote>
          REJECT policy (see <ulink url="FAQ.htm#faq17">FAQ 17</ulink>).</para>
        </listitem>

        <listitem>
          <para>IN=eth2 - the packet entered the firewall via eth2</para>
        </listitem>

        <listitem>
          <para>OUT=eth1 - if accepted, the packet would be sent on eth1</para>
        </listitem>

        <listitem>
          <para>SRC=192.168.2.2 - the packet was sent by 192.168.2.2</para>
        </listitem>

        <listitem>
          <para>DST=192.168.1.3 - the packet is destined for 192.168.1.3</para>
        </listitem>

        <listitem>
          <para>PROTO=UDP - UDP Protocol</para>
        </listitem>

        <listitem>
          <para>DPT=53 - DNS</para>
        </listitem>
      </itemizedlist>

      <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>
    <title>Ping Problems</title>

    <para>Either can&#39;t ping when you think you should be able to or are
    able to ping when you think that you shouldn&#39;t be allowed?
    Shorewall&#39;s <quote>Ping</quote> Management is <ulink url="ping.html">described
    here</ulink>.</para>
  </section>

  <section>
    <title>Other Gotchas</title>

    <itemizedlist>
      <listitem>
        <para>Seeing rejected/dropped packets logged out of the INPUT or
        FORWARD chains? This means that:</para>

        <orderedlist>
          <listitem>
            <para>your zone definitions are screwed up and the host that is
            sending the packets or the destination host isn&#39;t in any zone
            (using an <ulink url="Documentation.htm#Hosts">/etc/shorewall/hosts</ulink>
            file are you?); or</para>
          </listitem>

          <listitem>
            <para>the source and destination hosts are both connected to the
            same interface and you don&#39;t have a policy or rule for the
            source zone to or from the destination zone or you haven&#39;t set
            the <emphasis role="bold">routeback</emphasis> option for the
            interface in <ulink url="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink>.</para>
          </listitem>
        </orderedlist>
      </listitem>

      <listitem>
        <para>Remember that Shorewall doesn&#39;t automatically allow ICMP
        type 8 (<quote>ping</quote>) requests to be sent between zones. If you
        want pings to be allowed between zones, you need a rule of the form:</para>

        <programlisting>&#x00A0;&#x00A0;&#x00A0; ACCEPT&#x00A0;&#x00A0;&#x00A0; <emphasis>&#60;source zone&#62;</emphasis>&#x00A0;&#x00A0;&#x00A0; <emphasis>&#60;destination zone&#62;</emphasis>&#x00A0;&#x00A0;&#x00A0; icmp&#x00A0;&#x00A0;&#x00A0; echo-request</programlisting>

        <para>The ramifications of this can be subtle. For example, if you
        have the following in <ulink url="NAT.htm">/etc/shorewall/nat</ulink>:</para>

        <programlisting>&#x00A0;&#x00A0;&#x00A0; 10.1.1.2&#x00A0;&#x00A0;&#x00A0; eth0&#x00A0;&#x00A0;&#x00A0; 130.252.100.18</programlisting>

        <para>and you ping 130.252.100.18, unless you have allowed icmp type 8
        between the zone containing the system you are pinging from and the
        zone containing 10.1.1.2, the ping requests will be dropped.</para>
      </listitem>

      <listitem>
        <para>If you specify <quote>routefilter</quote> for an interface, that
        interface must be up prior to starting the firewall.</para>
      </listitem>

      <listitem>
        <para>Is your routing correct? For example, internal systems usually
        need to be configured with their default gateway set to the IP address
        of their nearest firewall interface. One often overlooked aspect of
        routing is that in order for two hosts to communicate, the routing
        between them must be set up <emphasis role="underline">in both
        directions</emphasis>. So when setting up routing between <emphasis
        role="bold">A</emphasis> and <emphasis role="bold">B</emphasis>, be
        sure to verify that the route from <emphasis role="bold">B</emphasis>
        back to <emphasis role="bold">A</emphasis> is defined.</para>
      </listitem>

      <listitem>
        <para>Some versions of LRP (EigerStein2Beta for example) have a shell
        with broken variable expansion. You can get a corrected shell from the
        <ulink url="ftp://ftp.shorewall.net/pub/shorewall/ash.gz">Shorewall
        Errata download site</ulink>.</para>
      </listitem>

      <listitem>
        <para>Do you have your kernel properly configured? <ulink
        url="kernel.htm">Click here to see my kernel configuration</ulink>.</para>
      </listitem>

      <listitem>
        <para>Shorewall requires the <quote>ip</quote> program. That program
        is generally included in the <quote>iproute</quote> package which
        should be included with your distribution (though many distributions
        don&#39;t install iproute by default). You may also download the
        latest source tarball from <ulink url="ftp://ftp.inr.ac.ru/ip-routing">ftp://ftp.inr.ac.ru/ip-routing</ulink>
        .</para>
      </listitem>

      <listitem>
        <para>Problems with NAT? Be sure that you let Shorewall add all
        external addresses to be use with NAT unless you have set <ulink
        url="Shorewall_and_Aliased_Interfaces.html">ADD_IP_ALIASES</ulink> =No
        in /etc/shorewall/shorewall.conf.</para>
      </listitem>
    </itemizedlist>
  </section>

  <section>
    <title>Still Having Problems?</title>

    <para>See the <ulink url="support.htm">Shorewall Support Page</ulink>.</para>
  </section>
</article>