forked from extern/shorewall_code
681 lines
18 KiB
XML
681 lines
18 KiB
XML
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<?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>ICMP Echo-request (Ping)</title>
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<authorgroup>
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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>2003-08-23</pubdate>
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<copyright>
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<year>2001-2003</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 License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<note>
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<para>Shorewall 'Ping' management has evolved over time with the
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latest change coming in Shorewall version 1.4.0. To find out which version
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of Shorewall you are running, at a shell prompt type "/sbin/shorewall
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version". If that command gives you an error, it's time to upgrade
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since you have a very old version of Shorewall installed (1.2.4 or
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earlier).</para>
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</note>
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<section>
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<title>Shorewall Versions >= 1.4.0</title>
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<para>In Shoreall 1.4.0 and later version, ICMP echo-request's are
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treated just like any other connection request.</para>
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<para>In order to accept ping requests from zone z1 to zone z2 where the
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policy for z1 to z2 is not ACCEPT, you need a rule in /etc/shoreall/rules
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of the form:</para>
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<informaltable>
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<tgroup cols="7">
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<thead>
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>ACCEPT</entry>
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<entry>z1</entry>
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<entry>z2</entry>
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<entry>icmp</entry>
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<entry>8</entry>
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<entry></entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<example>
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<title>Ping from local zone to firewall</title>
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<para>To permit ping from the local zone to the firewall:</para>
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<informaltable>
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<tgroup cols="7">
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<thead>
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>ACCEPT</entry>
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<entry>loc</entry>
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<entry>fw</entry>
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<entry>icmp</entry>
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<entry>8</entry>
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<entry></entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</example>
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<para>If you would like to accept 'ping' by default even when the
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relevant policy is DROP or REJECT, create /etc/shorewall/icmpdef if it
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doesn't already exist and in that file place the following command:</para>
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<programlisting> run_iptables -A icmpdef -p icmp --icmp-type 8 -j ACCEPT</programlisting>
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<para>With that rule in place, if you want to ignore 'ping' from
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z1 to z2 then you need a rule of the form:</para>
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<informaltable>
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<tgroup cols="7">
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<thead>
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>DROP</entry>
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<entry>z1</entry>
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<entry>z2</entry>
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<entry>icmp</entry>
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<entry>8</entry>
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<entry></entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<example>
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<title>Silently drop pings from the Internet</title>
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<para>To drop ping from the internet, you would need this rule in
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/etc/shorewall/rules:</para>
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<informaltable>
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<tgroup cols="7">
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<thead>
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>DROP</entry>
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<entry>net</entry>
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<entry>fw</entry>
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<entry>icmp</entry>
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<entry>8</entry>
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<entry></entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</example>
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<para>Note that the above rule may be used without any additions to
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/etc/shorewall/icmpdef to prevent your log from being flooded by messages
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generated from remote pinging.</para>
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</section>
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<section>
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<title>Shorewall Versions >= 1.3.14 and < 1.4.0 with
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OLD_PING_HANDLING=No in /etc/shorewall/shorewall.conf</title>
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<para>In 1.3.14, Ping handling was put under control of the rules and
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policies just like any other connection request. In order to accept ping
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requests from zone z1 to zone z2 where the policy for z1 to z2 is not
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ACCEPT, you need a rule in /etc/shoreall/rules of the form:</para>
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<informaltable>
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<tgroup cols="7">
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<thead>
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>ACCEPT</entry>
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<entry>z1</entry>
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<entry>z2</entry>
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<entry>icmp</entry>
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<entry>8</entry>
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<entry></entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<example>
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<title>Ping from local zone to firewall</title>
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<para>To permit ping from the local zone to the firewall:</para>
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<informaltable>
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<tgroup cols="7">
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<thead>
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>ACCEPT</entry>
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<entry>loc</entry>
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<entry>fw</entry>
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<entry>icmp</entry>
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<entry>8</entry>
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<entry></entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</example>
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<para>If you would like to accept 'ping' by default even when the
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|
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relevant policy is DROP or REJECT, create /etc/shorewall/icmpdef if it
|
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|
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doesn't already exist and in that file place the following command:</para>
|
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|
|
|
||
|
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<programlisting> run_iptables -A icmpdef -p icmp --icmp-type 8 -j ACCEPT</programlisting>
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|
|
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<para>With that rule in place, if you want to ignore 'ping' from
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|
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z1 to z2 then you need a rule of the form:</para>
|
||
|
|
|
||
|
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<informaltable>
|
||
|
|
<tgroup cols="7">
|
||
|
|
<thead>
|
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|
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>DROP</entry>
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<entry>z1</entry>
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<entry>z2</entry>
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<entry>icmp</entry>
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<entry>8</entry>
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<entry></entry>
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<entry></entry>
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</row>
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</tbody>
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</tgroup>
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||
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</informaltable>
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||
|
|
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<example>
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<title>Silently drop pings from the Internet</title>
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||
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<para>To drop ping from the internet, you would need this rule in
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/etc/shorewall/rules:</para>
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||
|
|
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||
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<informaltable>
|
||
|
|
<tgroup cols="7">
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||
|
|
<thead>
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||
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|
<row>
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||
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<entry align="center">ACTION</entry>
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||
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DEST</entry>
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</row>
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||
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</thead>
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<tbody>
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<row>
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<entry>DROP</entry>
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<entry>net</entry>
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<entry>fw</entry>
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|
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<entry>icmp</entry>
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||
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<entry>8</entry>
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||
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|
||
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<entry></entry>
|
||
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||
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<entry></entry>
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||
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</row>
|
||
|
|
</tbody>
|
||
|
|
</tgroup>
|
||
|
|
</informaltable>
|
||
|
|
</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 "feature" was removed in version 1.4.0.</para>
|
||
|
|
</note>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section>
|
||
|
|
<title>Shorewall Versions < 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>
|
||
|
|
|
||
|
|
<informaltable>
|
||
|
|
<tgroup cols="7">
|
||
|
|
<thead>
|
||
|
|
<row>
|
||
|
|
<entry align="center">ACTION</entry>
|
||
|
|
|
||
|
|
<entry align="center">SOURCE</entry>
|
||
|
|
|
||
|
|
<entry align="center">DESTINATION</entry>
|
||
|
|
|
||
|
|
<entry align="center">PROTOCOL</entry>
|
||
|
|
|
||
|
|
<entry align="center">PORT(S)</entry>
|
||
|
|
|
||
|
|
<entry align="center">SOURCE PORT(S)</entry>
|
||
|
|
|
||
|
|
<entry align="center">ORIGINAL DEST</entry>
|
||
|
|
</row>
|
||
|
|
</thead>
|
||
|
|
|
||
|
|
<tbody>
|
||
|
|
<row>
|
||
|
|
<entry><<emphasis>action</emphasis>></entry>
|
||
|
|
|
||
|
|
<entry><<emphasis>source</emphasis>></entry>
|
||
|
|
|
||
|
|
<entry><<emphasis>destination</emphasis>></entry>
|
||
|
|
|
||
|
|
<entry>icmp</entry>
|
||
|
|
|
||
|
|
<entry>8</entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
</row>
|
||
|
|
</tbody>
|
||
|
|
</tgroup>
|
||
|
|
</informaltable>
|
||
|
|
|
||
|
|
<example>
|
||
|
|
<title>Allow ping from DMZ to Net</title>
|
||
|
|
|
||
|
|
<para>Example 1. Accept pings from the net to the dmz (pings are
|
||
|
|
responded to with an ICMP echo-reply):</para>
|
||
|
|
|
||
|
|
<informaltable>
|
||
|
|
<tgroup cols="7">
|
||
|
|
<thead>
|
||
|
|
<row>
|
||
|
|
<entry align="center">ACTION</entry>
|
||
|
|
|
||
|
|
<entry align="center">SOURCE</entry>
|
||
|
|
|
||
|
|
<entry align="center">DESTINATION</entry>
|
||
|
|
|
||
|
|
<entry align="center">PROTOCOL</entry>
|
||
|
|
|
||
|
|
<entry align="center">PORT(S)</entry>
|
||
|
|
|
||
|
|
<entry align="center">SOURCE PORT(S)</entry>
|
||
|
|
|
||
|
|
<entry align="center">ORIGINAL DEST</entry>
|
||
|
|
</row>
|
||
|
|
</thead>
|
||
|
|
|
||
|
|
<tbody>
|
||
|
|
<row>
|
||
|
|
<entry>ACCEPT</entry>
|
||
|
|
|
||
|
|
<entry>dmz</entry>
|
||
|
|
|
||
|
|
<entry>net</entry>
|
||
|
|
|
||
|
|
<entry>icmp</entry>
|
||
|
|
|
||
|
|
<entry>8</entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
</row>
|
||
|
|
</tbody>
|
||
|
|
</tgroup>
|
||
|
|
</informaltable>
|
||
|
|
</example>
|
||
|
|
|
||
|
|
<example>
|
||
|
|
<title>Silently drop pings from the Net</title>
|
||
|
|
|
||
|
|
<para>Drop pings from the net to the firewall:</para>
|
||
|
|
|
||
|
|
<informaltable>
|
||
|
|
<tgroup cols="7">
|
||
|
|
<thead>
|
||
|
|
<row>
|
||
|
|
<entry align="center">ACTION</entry>
|
||
|
|
|
||
|
|
<entry align="center">SOURCE</entry>
|
||
|
|
|
||
|
|
<entry align="center">DESTINATION</entry>
|
||
|
|
|
||
|
|
<entry align="center">PROTOCOL</entry>
|
||
|
|
|
||
|
|
<entry align="center">PORT(S)</entry>
|
||
|
|
|
||
|
|
<entry align="center">SOURCE PORT(S)</entry>
|
||
|
|
|
||
|
|
<entry align="center">ORIGINAL DEST</entry>
|
||
|
|
</row>
|
||
|
|
</thead>
|
||
|
|
|
||
|
|
<tbody>
|
||
|
|
<row>
|
||
|
|
<entry>DROP</entry>
|
||
|
|
|
||
|
|
<entry>net</entry>
|
||
|
|
|
||
|
|
<entry>fw</entry>
|
||
|
|
|
||
|
|
<entry>icmp</entry>
|
||
|
|
|
||
|
|
<entry>8</entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
</row>
|
||
|
|
</tbody>
|
||
|
|
</tgroup>
|
||
|
|
</informaltable>
|
||
|
|
</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>
|
||
|
|
</article>
|