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shorewall_code/Shorewall-docs2/ping.xml
teastep a44e4a46f8 Initial revision
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@1143 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
2004-02-14 18:06:39 +00:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article>
<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;= 2.0.0</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
<filename>/etc/shoreall/rules</filename> of the form:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
AllowPing z1 z2</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)
AllowPing loc fw</programlisting>
</example>
<para>If you would like to accept <quote>ping</quote> by default even when
the relevant policy is DROP or REJECT, modify /etc/shorewall/action.Drop
or /etc/shorewall/action.Reject respectively and simply add the line:</para>
<programlisting>AllowPing</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)
DropPing z1 z2</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)
DropPing net fw</programlisting>
</example>
<para>Note that the above rule may be used without changing the action
files to prevent your log from being flooded by messages generated from
remote pinging.</para>
</section>
<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
<filename>/etc/shoreall/rules</filename> 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>