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>2004-02-02</pubdate>

    <copyright>
      <year>2001-2004</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>

  <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>
      <title>Try Searching the Shorewall Site and Mailing List Archives</title>

      <para>The <ulink url="http://lists.shorewall.net/htdig/search.html">Site
      and Mailing List Archives search facility</ulink> can locate documents
      and posts about similar problems.</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><command>shorewall debug start 2&#62; /tmp/trace</command></para>
      </listitem>

      <listitem>
        <para>Look at the <filename>/tmp/trace</filename> 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><command>iptables -A reject -p
      tcp -j REJECT --reject-with tcp-reset</command></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>Some Things to Keep in Mind</title>

    <itemizedlist>
      <listitem>
        <para><emphasis role="bold">You cannot test your firewall from the
        inside</emphasis>. Just because you send requests to your firewall
        external IP address does not mean that the request will be associated
        with the external interface or the <quote>net</quote> zone. Any
        traffic that you generate from the local network will be associated
        with your local interface and will be treated as loc-&#62;fw traffic.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">IP addresses are properties of systems,
        not of interfaces</emphasis>. It is a mistake to believe that your
        firewall is able to forward packets just because you can ping the IP
        address of all of the firewall&#39;s interfaces from the local
        network. The only conclusion you can draw from such pinging success is
        that the link between the local system and the firewall works and that
        you probably have the local system&#39;s default gateway set
        correctly.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">Reply packets do NOT automatically follow
        the reverse path of the one taken by the original request</emphasis>.
        All packets are routed according to the routing table of the host at
        each step of the way. This issue commonly comes up when people install
        a Shorewall firewall parallel to an existing gateway and try to use
        DNAT through Shorewall without changing the default gateway of the
        system receiving the forwarded requests. Requests come in through the
        Shorewall firewall where the destination IP address gets rewritten but
        replies go out unmodified through the old gateway.</para>
      </listitem>

      <listitem>
        <para><emphasis role="bold">Shorewall itself has no notion of inside
        or outside</emphasis>. These concepts are embodied in how Shorewall is
        configured. </para>
      </listitem>
    </itemizedlist>
  </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 <filename><ulink
        url="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink></filename>
        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><command>/sbin/shorewall show log</command></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 <filename><filename>/etc/shorewall/shorewall.conf</filename></filename>:</para>

    <para><programlisting>LOGRATE=
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>#ACTION   SOURCE           DEST                  PROTO   DEST
#                                                        PORT(S)
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>. Here are a couple of tips:</para>

    <itemizedlist>
      <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>#ACTION  SOURCE          DEST                  PROTO   DEST
#                                                      PORT(S)
ACCEPT&#x00A0;&#x00A0; <emphasis>&#60;source zone&#62;</emphasis>&#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 <filename><ulink url="NAT.htm">/etc/shorewall/nat</ulink></filename>:</para>

        <programlisting>#EXTERNAL   INTERFACE  INTERNAL
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>Similarly, since Shorewall gives no special treatment to
        <quote>ping</quote>packets, these packets are subject to logging
        specifications in policies. This allows people pinging your firewall
        to create large number of messages in your log. These messages can be
        eliminated by the following rule:<programlisting>#ACTION   SOURCE           DEST                PROTO   DEST
#                                                      PORT(S)
DROP      net              fw                  icmp    echo-request</programlisting></para>
      </listitem>
    </itemizedlist>
  </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"><filename>/etc/shorewall/hosts</filename></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"><filename>/etc/shorewall/interfaces</filename></ulink>.</para>
          </listitem>
        </orderedlist>
      </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="bold">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 <filename>/etc/shorewall/shorewall.conf</filename>.</para>
      </listitem>
    </itemizedlist>
  </section>

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

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

  <appendix>
    <title>Revision History</title>

    <para><revhistory><revision><revnumber>1.7</revnumber><date>2005-02-02</date><authorinitials>TE</authorinitials><revremark>Add
    hint about testing from inside the firewall.</revremark></revision><revision><revnumber>1.6</revnumber><date>2005-01-06</date><authorinitials>TE</authorinitials><revremark>Add
    pointer to Site and Mailing List Archives Searches.</revremark></revision><revision><revnumber>1.5</revnumber><date>2004-01-01</date><authorinitials>TE</authorinitials><revremark>Added
    information about eliminating ping-generated log messages.</revremark></revision><revision><revnumber>1.4</revnumber><date>2003-12-22</date><authorinitials>TE</authorinitials><revremark>Initial
    Docbook Conversion</revremark></revision></revhistory></para>
  </appendix>
</article>