forked from extern/shorewall_code
656 lines
26 KiB
XML
656 lines
26 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</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>2005</year>
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<year>2007</year>
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<year>2008</year>
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<year>2009</year>
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<year>2010</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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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 4.3 and
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later. If you are running a version of Shorewall earlier than Shorewall
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4.3.5 then please see the documentation for that
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release.</emphasis></para>
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</caution>
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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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file entry, in which case the traffic matching that rules file entry will
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be 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. As an example, here is
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the definition of the <firstterm>AllowSMB</firstterm> standard action
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from Shorewall version 2.2.</para>
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<programlisting>#
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# Shorewall 2.2 /usr/share/shorewall/action.AllowSMB
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#
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# Allow Microsoft SMB traffic. You need to invoke this action in
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# both directions.
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#
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######################################################################################
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#TARGET SOURCE DEST PROTO DEST SOURCE RATE USER/
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# PORT PORT(S) LIMIT GROUP
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ACCEPT - - udp 135,445
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ACCEPT - - udp 137:139
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ACCEPT - - udp 1024: 137
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ACCEPT - - tcp 135,139,445
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#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
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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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<para>Standard Actions have been largely replaced by <ulink
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url="Macros.html">macros</ulink> .</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 (Formerly Common 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 and REJECT policies. Default actions provide
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a way to invoke a set of common rules just before the policy is enforced.
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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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<warning>
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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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</warning>
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</section>
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<section id="Defining">
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<title>Defining your own Actions</title>
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<para>Before defining a new action, you should evaluate whether your goal
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can be best accomplished using an action or a
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<firstterm>macro</firstterm>. See <ulink url="Macros.html">this
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article</ulink> for details.</para>
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<para>To define a new action:</para>
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<orderedlist>
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<listitem>
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<para>Add a line to <filename>/etc/shorewall/actions</filename> that
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names your new action. Action names must be valid shell variable names
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(must begin with a letter and be composed of letters, digits and
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underscore characters) as well as valid Netfilter chain names. If you
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intend to log from the action, the name must have a maximum of 11
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characters. It is recommended that the name you select for a new
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action begins with a capital letter; that way, the name won't conflict
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with a Shorewall-defined chain name.</para>
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<para>Shorewall includes pre-defined actions for DROP and REJECT --
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see above.</para>
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</listitem>
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<listitem>
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<para>Once you have defined your new action name (ActionName), then
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copy <filename>/usr/share/shorewall/action.template</filename> to
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<filename>/etc/shorewall/action.ActionName</filename> (for example, if
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your new action name is <quote>Foo</quote> then copy
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<filename>/usr/share/shorewall/action.template</filename> to
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<filename>/etc/shorewall/action.Foo</filename>).</para>
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</listitem>
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<listitem>
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<para>Now modify the new file to define the new action.</para>
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</listitem>
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</orderedlist>
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<para>Columns in the <filename>action.template</filename> file are as
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follows:</para>
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<itemizedlist>
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<listitem>
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<para>TARGET - Must be ACCEPT, DROP, REJECT, LOG, CONTINUE, QUEUE or
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<<emphasis>action</emphasis>> where
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<<emphasis>action</emphasis>> is a previously-defined action
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(that is, it must precede the action being defined in this file in
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your <filename>/etc/shorewall/actions</filename> file). These actions
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have the same meaning as they do in the
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<filename>/etc/shorewall/rules</filename> file (CONTINUE terminates
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processing of the current action and returns to the point where that
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action was invoked). The TARGET may optionally be followed by a colon
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(<quote>:</quote>) and a syslog log level (e.g, REJECT:info or
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ACCEPT:debugging). This causes the packet to be logged at the
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specified level. You may also specify ULOG (must be in upper case) as
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a log level. This will log to the ULOG target for routing to a
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separate log through use of ulogd (<ulink
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url="http://www.netfilter.org/projects/ulogd/index.html">http://www.netfilter.org/projects/ulogd/index.html</ulink>).</para>
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<para>You may also use a <ulink url="Macros.html">macro</ulink> in
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your action provided that the macro's expansion only results in the
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ACTIONs ACCEPT, DROP, REJECT, LOG, CONTINUE, or QUEUE. See
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<filename>/usr/share/shorewall/action.Drop</filename> for an example
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of an action that users macros extensively.</para>
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</listitem>
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<listitem>
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<para>SOURCE - Source hosts to which the rule applies. A
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comma-separated list of subnets and/or hosts. Hosts may be specified
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by IP or MAC address; MAC addresses must begin with <quote>~</quote>
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and must use <quote>-</quote> as a separator.</para>
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<para>Alternatively, clients may be specified by interface name. For
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example, eth1 specifies a client that communicates with the firewall
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system through eth1. This may be optionally followed by another colon
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(<quote>:</quote>) and an IP/MAC/subnet address as described above
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(e.g., eth1:192.168.1.5).</para>
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</listitem>
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<listitem>
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<para>DEST - Location of Server. Same as above with the exception that
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MAC addresses are not allowed.</para>
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<para>Unlike in the SOURCE column, you may specify a range of up to
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256 IP addresses using the syntax <<emphasis>first
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ip</emphasis>>-<<emphasis>last ip</emphasis>>.</para>
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</listitem>
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<listitem>
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<para>PROTO - Protocol - Must be <quote>tcp</quote>,
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<quote>udp</quote>, <quote>icmp</quote>, a protocol number, or
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<quote>all</quote>.</para>
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</listitem>
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<listitem>
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<para>DEST PORT(S) - Destination Ports. A comma-separated list of Port
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names (from <filename>/etc/services</filename>), port numbers or port
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ranges; if the protocol is <quote>icmp</quote>, this column is
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interpreted as the destination icmp-type(s).</para>
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<para>A port range is expressed as <<emphasis>low
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port</emphasis>>:<<emphasis>high port</emphasis>>.</para>
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<para>This column is ignored if PROTO = <quote>all</quote>, but must
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be entered if any of the following fields are supplied. In that case,
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it is suggested that this field contain <quote>-</quote>.</para>
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<para>If your kernel contains multi-port match support, then only a
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single Netfilter rule will be generated if in this list and in the
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CLIENT PORT(S) list below:</para>
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<orderedlist>
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<listitem>
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<para>There are 15 or less ports listed.</para>
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</listitem>
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<listitem>
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<para>No port ranges are included.</para>
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</listitem>
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</orderedlist>
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<para>Otherwise, a separate rule will be generated for each
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port.</para>
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</listitem>
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<listitem>
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<para>SOURCE PORT(S) - Port(s) used by the client. If omitted, any
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source port is acceptable. Specified as a comma-separated list of port
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names, port numbers or port ranges.</para>
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<para>If you don't want to restrict client ports but need to specify
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any of the subsequent fields, then place <quote>-</quote> in this
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column.</para>
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<para>If your kernel contains multi-port match support, then only a
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single Netfilter rule will be generated if in this list and in the
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DEST PORT(S) list above:</para>
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<orderedlist>
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<listitem>
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<para>There are 15 or less ports listed.</para>
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</listitem>
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<listitem>
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<para>No port ranges are included.</para>
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</listitem>
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</orderedlist>
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<para>Otherwise, a separate rule will be generated for each
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port.</para>
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</listitem>
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<listitem>
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<para>RATE LIMIT - You may rate-limit the rule by placing a value in
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this column:</para>
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<para><programlisting> <<emphasis>rate</emphasis>>/<<emphasis>interval</emphasis>>[:<<emphasis>burst</emphasis>>]</programlisting>where
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<<emphasis>rate</emphasis>> is the number of connections per
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<<emphasis>interval</emphasis>> (<quote>sec</quote> or
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<quote>min</quote>) and <<emphasis>burst</emphasis>> is the
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largest burst permitted. If no <<emphasis>burst</emphasis>> is
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given, a value of 5 is assumed. There may be no whitespace embedded in
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the specification.</para>
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<para><programlisting> Example: 10/sec:20</programlisting></para>
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</listitem>
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<listitem>
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<para>USER/GROUP - For output rules (those with the firewall as their
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source), you may control connections based on the effective UID and/or
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GID of the process requesting the connection. This column can contain
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any of the following:</para>
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<simplelist>
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<member>[!]<<emphasis>user number</emphasis>>[:]</member>
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<member>[!]<<emphasis>user name</emphasis>>[:]</member>
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<member>[!]:<<emphasis>group number</emphasis>></member>
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<member>[!]:<<emphasis>group name</emphasis>></member>
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<member>[!]<<emphasis>user
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number</emphasis>>:<<emphasis>group
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number</emphasis>></member>
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<member>[!]<<emphasis>user
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name</emphasis>>:<<emphasis>group
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number</emphasis>></member>
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<member>[!]<<emphasis>user
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inumber</emphasis>>:<<emphasis>group
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name</emphasis>></member>
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<member>[!]<<emphasis>user
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name</emphasis>>:<<emphasis>group name</emphasis>></member>
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<member>[!]+<<emphasis>program name</emphasis>> (Note: support
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for this form was removed from Netfilter in kernel version
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2.6.14).</member>
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</simplelist>
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</listitem>
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<listitem>
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<para>MARK</para>
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<para><simplelist>
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<member>[!]<<emphasis>value</emphasis>>[/<<emphasis>mask</emphasis>>][:C]</member>
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</simplelist></para>
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<para>Defines a test on the existing packet or connection mark. The
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rule will match only if the test returns true.</para>
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<para>If you don’t want to define a test but need to specify anything
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in the subsequent columns, place a <quote>-</quote> in this
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field.<simplelist>
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<member>! — Inverts the test (not equal)</member>
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<member><<emphasis>value</emphasis>> — Value of the packet
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or connection mark.</member>
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<member><<emphasis>mask</emphasis>> —A mask to be applied to
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the mark before testing.</member>
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<member>:C — Designates a connection mark. If omitted, the packet
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mark’s value is tested. This option is only supported by
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Shorewall-perl</member>
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</simplelist></para>
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</listitem>
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</itemizedlist>
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<para>Omitted column entries should be entered using a dash
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(<quote>-</quote>).</para>
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<para>Example:</para>
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||
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<para><filename>/etc/shorewall/actions</filename>:</para>
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<para><programlisting> #ACTION COMMENT (place '# ' below the 'C' in comment followed by
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# v a comment describing the action)
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LogAndAccept # LOG and ACCEPT a connection</programlisting><emphasis
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role="bold">Note:</emphasis> If your
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<filename>/etc/shorewall/actions</filename> file doesn't have an
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indication where to place the comment, put the <quote>#</quote> in column
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21.</para>
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<para><phrase><filename>/etc/shorewall/action.LogAndAccept</filename></phrase><programlisting> LOG:info
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ACCEPT</programlisting></para>
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<para>Placing a comment on the line causes the comment to appear in the
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output of the <command>shorewall show actions</command> command.</para>
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<para>To use your action, in <filename>/etc/shorewall/rules</filename> you
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might do something like:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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LogAndAccept loc $FW tcp 22</programlisting>
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</section>
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<section id="Logging">
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<title>Actions and Logging</title>
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<para>Specifying a log level in a rule that specifies a user-defined or
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Shorewall-defined action will cause each rule in the action to be logged
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with the specified level (and tag).</para>
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|
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<para>The extent to which logging of action rules occur is governed by the
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following:</para>
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|
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<orderedlist>
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||
<listitem>
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<para>When you invoke an action and specify a log level, only those
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rules in the action that have no log level will be changed to log at
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the level specified at the action invocation.</para>
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<para>Example:</para>
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<para>/etc/shorewall/action.foo</para>
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<programlisting>#TARGET SOURCE DEST PROTO DEST PORT(S)
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ACCEPT - - tcp 22
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bar:info</programlisting>
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<para>/etc/shorewall/rules:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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foo:debug $FW net</programlisting>
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|
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<para>Logging in the invoke <quote>foo</quote> action will be as if
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foo had been defined as:</para>
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<programlisting>#TARGET SOURCE DEST PROTO DEST PORT(S)
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ACCEPT:debug - - tcp 22
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bar:info</programlisting>
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</listitem>
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<listitem>
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||
<para>If you follow the log level with <quote>!</quote> then logging
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will be set at that level for all rules recursively invoked by the
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action.</para>
|
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|
||
<para>Example:</para>
|
||
|
||
<para>/etc/shorewall/action.foo</para>
|
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|
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<programlisting>#TARGET SOURCE DEST PROTO DEST PORT(S)
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ACCEPT - - tcp 22
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bar:info</programlisting>
|
||
|
||
<para>/etc/shorewall/rules:</para>
|
||
|
||
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
||
foo:debug! $FW net</programlisting>
|
||
|
||
<para>Logging in the invoke <quote>foo</quote> action will be as if
|
||
foo had been defined as:</para>
|
||
|
||
<programlisting>#TARGET SOURCE DEST PROTO DEST PORT(S)
|
||
ACCEPT:debug - - tcp 22
|
||
bar:debug</programlisting>
|
||
</listitem>
|
||
</orderedlist>
|
||
</section>
|
||
|
||
<section id="Extension">
|
||
<title>Creating an Action using an Extension Script</title>
|
||
|
||
<para>There may be cases where you wish to create a chain with rules that
|
||
can't be constructed using the tools defined in the
|
||
<filename>action.template</filename>. In that case, you can use an <ulink
|
||
url="shorewall_extension_scripts.htm">extension script</ulink>.<note>
|
||
<para>If you actually need an action to drop broadcast packets, use
|
||
the <command>dropBcast</command> standard action rather than create
|
||
one like this.</para>
|
||
</note></para>
|
||
|
||
<example id="Example">
|
||
<title>An action to drop all broadcast packets</title>
|
||
|
||
<para>If you define an action <quote>acton</quote> and you have an
|
||
<filename>/etc/shorewall/acton</filename> script, the rules compiler
|
||
sets lexical variables as follows:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem>
|
||
<para><emphasis role="bold">$chainref</emphasis> is a reference to
|
||
the chain-table entry for the chain where your rules are to be
|
||
placed.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para><emphasis role="bold">$level</emphasis> is the log level. If
|
||
false, no logging was specified.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para><emphasis role="bold">$tag</emphasis> is the log tag.</para>
|
||
</listitem>
|
||
</itemizedlist>
|
||
|
||
<para>Example:</para>
|
||
|
||
<para>/etc/shorewall/actions<programlisting>DropBcasts</programlisting></para>
|
||
|
||
<para>/etc/shorewall/action.DropBcasts<programlisting># This file is empty</programlisting>/etc/shorewall/DropBcasts<programlisting>use Shorewall::Chains;
|
||
|
||
log_rule_limit( $level, $chainref, 'DropBcasts', 'DROP', '', $tag, 'add', '' ) if $level ne '';
|
||
add_rule( $chainref, '-m pkttype --pkttype broadcast -j DROP' );
|
||
|
||
1;</programlisting></para>
|
||
</example>
|
||
|
||
<para>For a richer example, see the next section.</para>
|
||
</section>
|
||
|
||
<section id="Limit">
|
||
<title>Limiting Per-IP Connection Rate using the Limit Action</title>
|
||
|
||
<para>Shorewall supports a <quote>Limit</quote> built-in action. Limit is
|
||
invoked with a comma-separated list in place of a logging tag. The list
|
||
has three elements:</para>
|
||
|
||
<orderedlist>
|
||
<listitem>
|
||
<para>The name of a <quote>recent</quote> list. You select the list
|
||
name which must conform to the rules for a valid chain name. Different
|
||
rules that specify the same list name will use the same set of
|
||
counters.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The number of connections permitted in a specified time
|
||
period.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The time period, expressed in seconds.</para>
|
||
</listitem>
|
||
</orderedlist>
|
||
|
||
<para>Connections that exceed the specified rate are dropped.</para>
|
||
|
||
<para>For example, to use a recent list name of <emphasis
|
||
role="bold">SSHA</emphasis>, and to limit SSH connections to 3 per minute,
|
||
use this entry in <filename>/etc/shorewall/rules</filename>:</para>
|
||
|
||
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
||
Limit:none:SSHA,3,60 net $FW tcp 22</programlisting>
|
||
|
||
<para>If you want dropped connections to be logged at the info level, use
|
||
this rule instead:</para>
|
||
|
||
<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
|
||
Limit:info:SSHA,3,60 net $FW tcp 22</programlisting>
|
||
|
||
<para>To summarize, you pass four pieces of information to the Limit
|
||
action:</para>
|
||
|
||
<itemizedlist>
|
||
<listitem>
|
||
<para>The log level. If you don't want to log, specify
|
||
<quote>none</quote>.</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The name of the recent list that you want to use
|
||
(<quote>SSHA</quote> in this example).</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The maximum number of connections to accept (3 in this
|
||
example).</para>
|
||
</listitem>
|
||
|
||
<listitem>
|
||
<para>The number of seconds over which you are willing to accept that
|
||
many connections (60 in this example).</para>
|
||
</listitem>
|
||
</itemizedlist>
|
||
|
||
<section id="LimitImp">
|
||
<title>How Limit is Implemented</title>
|
||
|
||
<para>For those who are curious, the Limit action is implemented as
|
||
follows:</para>
|
||
|
||
<programlisting>use Shorewall::Chains;
|
||
|
||
my @tag = split /,/, $tag;
|
||
|
||
fatal_error 'Limit rules must include <list name>,<max connections>,<interval> as the log tag (' . join( ':', 'Limit', $level eq '' ? 'none' : $level , $tag ) . ')'
|
||
unless @tag == 3;
|
||
|
||
my $list = $tag[0];
|
||
|
||
for ( @tag[1,2] ) {
|
||
fatal_error 'Max connections and interval in Limit rules must be numeric (' . join( ':', 'Limit', $level eq '' ? 'none' : $level, $tag ) . ')' unless /^\d+$/
|
||
}
|
||
|
||
my $count = $tag[1] + 1;
|
||
|
||
add_rule $chainref, "-m recent --name $list --set";
|
||
|
||
if ( $level ) {
|
||
my $xchainref = new_chain 'filter' , "$chainref->{name}%";
|
||
log_rule_limit $level, $xchainref, $tag[0], 'DROP', '', '', 'add', '';
|
||
add_rule $xchainref, '-j DROP';
|
||
add_rule $chainref, "-m recent --name $list --update --seconds $tag[2] --hitcount $count -j $xchainref->{name}";
|
||
} else {
|
||
add_rule $chainref, "-m recent --update --name $list --seconds $tag[2] --hitcount $count -j DROP";
|
||
}
|
||
|
||
add_rule $chainref, '-j ACCEPT';
|
||
|
||
1; </programlisting>
|
||
</section>
|
||
</section>
|
||
</article>
|