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  <articleinfo>
    <title>ICMP Echo-request (Ping)</title>

    <authorgroup>
      <author>
        <firstname>Tom</firstname>

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

    <pubdate>2004-01-03</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 url="GnuCopyright.htm">GNU Free Documentation License</ulink></quote>.</para>
    </legalnotice>
  </articleinfo>

  <note>
    <para>Shorewall <quote>Ping</quote> management has evolved over time with
    the latest change coming in Shorewall version 1.4.0. To find out which
    version of Shorewall you are running, at a shell prompt type
    <quote><command>/sbin/shorewall version</command></quote>. If that command
    gives you an error, it&#39;s time to upgrade since you have a very old
    version of Shorewall installed (1.2.4 or earlier).</para>
  </note>

  <note>
    <para>Enabling <quote>ping</quote> will also enable ICMP-based
    <emphasis>traceroute</emphasis>. For UDP-based traceroute, see the <ulink
    url="ports.htm">port information page</ulink>.</para>
  </note>

  <section>
    <title>Shorewall Versions &#62;= 1.4.0</title>

    <para>In Shoreall 1.4.0 and later version, ICMP echo-request&#39;s are
    treated just like any other connection request.</para>

    <para>In order to accept ping requests from zone z1 to zone z2 where the
    policy for z1 to z2 is not ACCEPT, you need a rule in /etc/shoreall/rules
    of the form:</para>

    <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
ACCEPT    z1        z2       icmp     8</programlisting>

    <example>
      <title>Ping from local zone to firewall</title>

      <para>To permit ping from the local zone to the firewall:</para>

      <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
ACCEPT    loc       fw       icmp     8</programlisting>
    </example>

    <para>If you would like to accept <quote>ping</quote> by default even when
    the relevant policy is DROP or REJECT, create /etc/shorewall/icmpdef if it
    doesn&#39;t already exist and in that file place the following command:</para>

    <programlisting>run_iptables -A icmpdef -p icmp --icmp-type 8 -j ACCEPT</programlisting>

    <para>With that rule in place, if you want to ignore <quote>ping</quote>
    from z1 to z2 then you need a rule of the form:</para>

    <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
DROP      z1        z2       icmp     8</programlisting>

    <example>
      <title>Silently drop pings from the Internet</title>

      <para>To drop ping from the internet, you would need this rule in
      /etc/shorewall/rules:</para>

      <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
DROP      net       fw       icmp     8</programlisting>
    </example>

    <para>Note that the above rule may be used without any additions to
    /etc/shorewall/icmpdef to prevent your log from being flooded by messages
    generated from remote pinging.</para>
  </section>

  <section>
    <title>Shorewall Versions &#62;= 1.3.14 and &#60; 1.4.0 with
    OLD_PING_HANDLING=No in /etc/shorewall/shorewall.conf</title>

    <para>In 1.3.14, Ping handling was put under control of the rules and
    policies just like any other connection request. In order to accept ping
    requests from zone z1 to zone z2 where the policy for z1 to z2 is not
    ACCEPT, you need a rule in /etc/shoreall/rules of the form:</para>

    <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
ACCEPT    z1        z2       icmp     8</programlisting>

    <example>
      <title>Ping from local zone to firewall</title>

      <para>To permit ping from the local zone to the firewall:</para>

      <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
ACCEPT    loc       fw       icmp     8</programlisting>
    </example>

    <para>If you would like to accept <quote>ping</quote> by default even when
    the relevant policy is DROP or REJECT, create /etc/shorewall/icmpdef if it
    doesn&#39;t already exist and in that file place the following command:</para>

    <programlisting>run_iptables -A icmpdef -p icmp --icmp-type 8 -j ACCEPT</programlisting>

    <para>With that rule in place, if you want to ignore <quote>ping</quote>
    from z1 to z2 then you need a rule of the form:</para>

    <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
DROP      z1        z2       icmp     8</programlisting>

    <example>
      <title>Silently drop pings from the Internet</title>

      <para>To drop ping from the internet, you would need this rule in
      /etc/shorewall/rules:</para>

      <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
DROP      net       fw       icmp     8</programlisting>
    </example>

    <para>The above rule may be used without any additions to
    /etc/shorewall/icmpdef to prevent your log from being flooded by messages
    generated from remote pinging.</para>

    <note>
      <para>There is one exception to the above description. In 1.3.14 and
      1.3.14a, ping from the firewall itself is enabled unconditionally. This
      suprising <quote>feature</quote> was removed in version 1.4.0.</para>
    </note>
  </section>

  <section>
    <title>Shorewall Versions &#60; 1.3.14 or with OLD_PING_HANDLING=Yes in
    /etc/shorewall/shorewall.conf</title>

    <para>There are several aspects to the old Shorewall Ping management:</para>

    <orderedlist>
      <listitem>
        <para>The <emphasis role="bold">noping</emphasis> and <emphasis
        role="bold">filterping</emphasis> interface options in <ulink
        url="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink>.</para>
      </listitem>

      <listitem>
        <para>The <emphasis role="bold">FORWARDPING</emphasis> option in
        <ulink url="Documentation.htm#Config">/etc/shorewall/shorewall.conf</ulink>.</para>
      </listitem>

      <listitem>
        <para>Explicit rules in <ulink url="Documentation.htm#rules">/etc/shorewall/rules</ulink>.</para>
      </listitem>
    </orderedlist>

    <para>There are two cases to consider:</para>

    <orderedlist>
      <listitem>
        <para>Ping requests addressed to the firewall itself; and</para>
      </listitem>

      <listitem>
        <para>Ping requests being forwarded to another system. Included here
        are all cases of packet forwarding including NAT, DNAT rule, Proxy ARP
        and simple routing.</para>
      </listitem>
    </orderedlist>

    <para>These cases will be covered separately.</para>

    <section>
      <title>Ping Requests Addressed to the Firewall Itself</title>

      <para>For ping requests addressed to the firewall, the sequence is as
      follows:</para>

      <orderedlist>
        <listitem>
          <para>If neither <emphasis role="bold">noping</emphasis> nor
          <emphasis role="bold">filterping</emphasis> are specified for the
          interface that receives the ping request then the request will be
          responded to with an ICMP echo-reply.</para>
        </listitem>

        <listitem>
          <para>If <emphasis role="bold">noping</emphasis> is specified for
          the interface that receives the ping request then the request is
          ignored.</para>
        </listitem>

        <listitem>
          <para>If <emphasis role="bold">filterping</emphasis> is specified
          for the interface then the request is passed to the rules/policy
          evaluation.</para>
        </listitem>
      </orderedlist>
    </section>

    <section>
      <title>Ping Requests Forwarded by the Firewall</title>

      <para>These requests are always passed to rules/policy evaluation.</para>

      <section>
        <title>Rules Evaluation</title>

        <para>Ping requests are ICMP type 8. So the general rule format is:</para>

        <programlisting>#ACTION   SOURCE    DEST          PROTO    DEST PORT(S)
<emphasis>&#60;action&#62;</emphasis>  <emphasis>&#60;source&#62;</emphasis>  <emphasis>&#60;destination&#62;</emphasis>          icmp     8</programlisting>

        <example>
          <title>Allow ping from DMZ to Net</title>

          <para>Example 1. Accept pings from the dmz to the net:</para>

          <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
ACCEPT    dmz       net      icmp     8</programlisting>
        </example>

        <example>
          <title>Silently drop pings from the Net</title>

          <para>Drop pings from the net to the firewall:</para>

          <programlisting>#ACTION   SOURCE    DEST     PROTO    DEST PORT(S)
DROP      net       fw       icmp     8</programlisting>
        </example>
      </section>

      <section>
        <title>Policy Evaluation</title>

        <para>If no applicable rule is found, then the policy for the source
        to the destination is applied.</para>

        <orderedlist>
          <listitem>
            <para>If the relevant policy is ACCEPT then the request is
            responded to with an ICMP echo-reply.</para>
          </listitem>

          <listitem>
            <para>If <emphasis role="bold">FORWARDPING</emphasis> is set to
            Yes in /etc/shorewall/shorewall.conf then the request is responded
            to with an ICMP echo-reply.</para>
          </listitem>

          <listitem>
            <para>Otherwise, the relevant REJECT or DROP policy is used and
            the request is either rejected or simply ignored.</para>
          </listitem>
        </orderedlist>
      </section>
    </section>
  </section>

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

    <para><revhistory><revision><revnumber>1.2</revnumber><date>2004-01-03</date><authorinitials>TE</authorinitials><revremark>Add
    traceroute reference</revremark></revision><revision><revnumber>1.1</revnumber><date>2003-08-23</date><authorinitials>TE</authorinitials><revremark>Initial
    version converted to Docbook XML</revremark></revision></revhistory></para>
  </appendix>
</article>