forked from extern/shorewall_code
368 lines
12 KiB
XML
368 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<article>
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<!--$Id$-->
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<articleinfo>
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<title>Actions in Shorewall 4.5.0 and Later</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><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2012</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
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<section id="Intro">
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<title>What are Shorewall Actions?</title>
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<para>Shorewall actions allow a symbolic name to be associated with a
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series of one or more iptables rules. The symbolic name may appear in the
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ACTION column of an <filename><ulink
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url="manpages/shorewall-rules.html">/etc/shorewall/rules</ulink></filename>
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entry, in a <ulink url="Macros.html">macro</ulink> body and within another
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action, in which case the traffic matching that rules file entry will be
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passed to the series of iptables rules named by the action.</para>
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<para>Actions can be thought of as templates. When an action is invoked in
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an <filename>/etc/shorewall/rules</filename> entry, it may be qualified by
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a logging specification (log level and optionally a log tag). The presence
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of the log level/tag causes a modified series of rules to be generated in
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which each packet/rule match within the action causes a log message to be
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generated.</para>
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<para>For readers familiar with iptables, actions are the way in which you
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can create your own filter-table chains.</para>
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<para>There are three types of Shorewall actions:</para>
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<orderedlist>
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<listitem>
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<para>Built-in Actions. These actions are known by the Shorewall code
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itself. They are listed in the comments at the top of the file
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<filename>/usr/share/shorewall/actions.std</filename>.</para>
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</listitem>
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<listitem>
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<para>Standard Actions. These actions are released as part of
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Shorewall. They are listed in the file
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<filename>/usr/share/shorewall/actions.std</filename> and are defined
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in the corresponding action.* files in <filename
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class="directory">/usr/share/shorewall</filename>. Each
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<filename>action.*</filename> file has a comment at the beginning of
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the file that describes what the action does. Here is an
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example:</para>
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<programlisting>
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# Shorewall version 4 - Drop Action
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#
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# /usr/share/shorewall/action.Drop
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#
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# The default DROP common rules
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#
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# This action is invoked before a DROP policy is enforced. The purpose
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# of the action is:
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#
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# a) Avoid logging lots of useless cruft.
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# b) Ensure that 'auth' requests are rejected, even if the policy is
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# DROP. Otherwise, you may experience problems establishing
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# connections with servers that use auth.
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# c) Ensure that certain ICMP packets that are necessary for successful
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# internet operation are always ACCEPTed.
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#
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# The action accepts five optional parameters:
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#
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# 1 - 'audit' or '-'. Default is '-' which means don't audit in builtin
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# actions.
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# 2 - Action to take with Auth requests. Default is REJECT or A_REJECT,
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# depending on the setting of the first parameter.
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# 3 - Action to take with SMB requests. Default is DROP or A_DROP,
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# depending on the setting of the first parameter.
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# 4 - Action to take with required ICMP packets. Default is ACCEPT or
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# A_ACCEPT depending on the first parameter.
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# 5 - Action to take with late UDP replies (UDP source port 53). Default
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# is DROP or A_DROP depending on the first parameter.
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#
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# IF YOU ARE HAVING CONNECTION PROBLEMS, CHANGING THIS FILE WON'T HELP!!!!!!!!!
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#
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###############################################################################
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FORMAT 2
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#
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# The following magic provides different defaults for $2 thru $5, when $1 is
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# 'audit'.
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#
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?BEGIN PERL;
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use Shorewall::Config;
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my ( $p1, $p2, $p3 , $p4, $p5 ) = get_action_params( 5 );
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if ( defined $p1 ) {
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if ( $p1 eq 'audit' ) {
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set_action_param( 2, 'A_REJECT') unless supplied $p2;
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set_action_param( 3, 'A_DROP') unless supplied $p3;
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set_action_param( 4, 'A_ACCEPT' ) unless supplied $p4;
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set_action_param( 5, 'A_DROP' ) unless supplied $p5;
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} else {
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fatal_error "Invalid value ($p1) for first Drop parameter" if supplied $p1;
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}
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}
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1;
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?END PERL;
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DEFAULTS -,REJECT,DROP,ACCEPT,DROP
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#TARGET SOURCE DEST PROTO DPORT SPORT
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#
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# Count packets that come through here
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#
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COUNT
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#
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# Reject 'auth'
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#
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Auth($2)
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#
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# Don't log broadcasts
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#
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Broadcast(DROP,$1)
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#
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# ACCEPT critical ICMP types
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#
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AllowICMPs($4) - - icmp
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#
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# Drop packets that are in the INVALID state -- these are usually ICMP packets
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# and just confuse people when they appear in the log.
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#
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Invalid(DROP,$1)
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#
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# Drop Microsoft noise so that it doesn't clutter up the log.
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#
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SMB($3)
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DropUPnP($5)
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#
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# Drop 'newnotsyn' traffic so that it doesn't get logged.
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#
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NotSyn(DROP,$1) - - tcp
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#
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# Drop late-arriving DNS replies. These are just a nuisance and clutter up
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# the log.
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#
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DropDNSrep($5)
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</programlisting>
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<para>Most of the standard actions use ?BEGIN PERL...?END PERL to
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perform special processing. See the Using Perl in Action files section
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for additional information.</para>
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<para>If you wish to modify one of the standard actions, do not modify
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the definition in <filename
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class="directory">/usr/share/shorewall</filename>. Rather, copy the
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file to <filename class="directory">/etc/shorewall</filename> (or
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somewhere else on your CONFIG_PATH) and modify the copy.</para>
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</listitem>
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<listitem>
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<para>User-defined Actions. These actions are created by end-users.
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They are listed in the file
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<filename>/etc/shorewall/actions</filename> and are defined in
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<filename>action.*</filename> files in <filename
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class="directory">/etc/shorewall</filename> or in another directory
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listed in your CONFIG_PATH (defined in <filename><ulink
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url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink></filename>).</para>
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</listitem>
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</orderedlist>
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</section>
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<section id="Default">
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<title>Default Actions</title>
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<para>Shorewall allows the association of a <firstterm>default
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action</firstterm> with policies. A separate default action may be
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associated with ACCEPT, DROP, REJECT, QUEUE and NFQUEUE policies. Default
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actions provide a way to invoke a set of common rules just before the
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policy is enforced. Default actions accomplish two goals:</para>
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<orderedlist>
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<listitem>
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<para>Relieve log congestion. Default actions typically include rules
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to silently drop or reject traffic that would otherwise be logged when
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the policy is enforced.</para>
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</listitem>
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<listitem>
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<para>Ensure correct operation. Default actions can also avoid common
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pitfalls like dropping connection requests on port TCP port 113. If
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these connections are dropped (rather than rejected) then you may
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encounter problems connecting to Internet services that utilize the
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AUTH protocol of client authentication<footnote>
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<para>AUTH is actually pretty silly on today's Internet but it's
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amazing how many servers still employ it.</para>
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</footnote>.</para>
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</listitem>
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</orderedlist>
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<para>Shorewall supports default actions for the ACCEPT, REJECT, DROP,
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QUEUE and NFQUEUE policies. These default actions are specified in the
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<filename>/etc/shorewall/shorewall.conf</filename> file using the
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ACCEPT_DEFAULT, REJECT_DEFAULT, DROP_DEFAULT, QUEUE_DEFAULT and
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NFQUEUE_DEFAULT options respectively. Policies whose default is set to a
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value of <quote>none</quote> have no default action.</para>
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<para>In addition, the default specified in
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<filename>/etc/shorewall/shorewall.conf</filename> may be overridden by
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specifying a different action in the POLICY column of <filename><ulink
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url="manpages/shorewall-policy.html">/etc/shorewall/policy</ulink></filename>.</para>
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<important>
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<para>Entries in the DROP and REJECT default actions <emphasis
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role="bold">ARE NOT THE CAUSE OF CONNECTION PROBLEMS</emphasis>.
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Remember — default actions are only invoked immediately before the
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packet is going to be dropped or rejected anyway!!!</para>
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</important>
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<para>The standard Drop (see above) and Reject options are parameterized.
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Each has five parameters as follows:</para>
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<informaltable>
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<tgroup cols="4">
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<tbody>
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<row>
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<entry>ACTION</entry>
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<entry>PARAMETER</entry>
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<entry>VALUE</entry>
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<entry>DEFAULT</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>1</entry>
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<entry>Either '-' or 'audit'. 'audit' causes auditing by the
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builtin actions invoked by Drop</entry>
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<entry>-</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>2</entry>
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<entry>Determines what to do with Auth requests</entry>
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<entry>REJECT or A_REJECT depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>3</entry>
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<entry>Determines what to do with SMB</entry>
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<entry>DROP or A_DROP depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>1</entry>
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<entry>Either '-' or 'audit'. 'audit' causes auditing by the
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builtin actions invoked by Drop</entry>
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<entry>-</entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>2</entry>
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<entry>Determines what to do with Auth requests</entry>
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<entry>REJECT or A_REJECT depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>3</entry>
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<entry>Determines what to do with SMB</entry>
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<entry>REJECT or A_REJECT depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Both</entry>
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<entry>4</entry>
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<entry>Determines what to do with accepted critical ICMP
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packets.</entry>
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<entry>ACCEPT or A_ACCEPT depending on the setting of parameter
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1</entry>
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</row>
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<row>
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<entry>Both</entry>
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<entry>5</entry>
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<entry>Determines what to do with late-arriving DNS replies
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(source port 53) or UPnP (udp port 1900).</entry>
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<entry>DROP or A_DROP depending on the setting of parameter
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1.</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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<para>The parameters may be specified in either shorewall.conf (e.g.,
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DROP_DEFAULT=<emphasis role="bold">Drop(-,DROP)</emphasis> or in the
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POLICY column of <ulink
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url="manpages/shorewall-policy.html">shorewall-policy</ulink>(5) (e.g.,
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DROP:<emphasis role="bold">Drop(audit)</emphasis>:audit).</para>
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</section>
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<section>
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<title>Inline Actions</title>
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<para>Beginning with Shorewall 4.5.10, you may specify the inline option
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in <filename>/etc/shorewall/actions</filename>. As decribed above, </para>
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</section>
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</article>
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