forked from extern/shorewall_code
4f45eeff82
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@1196 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
301 lines
13 KiB
XML
Executable File
301 lines
13 KiB
XML
Executable File
<?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>User-defined 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>2004-03-10</pubdate>
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<copyright>
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<year>2003</year>
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<year>2004</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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<section>
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<title>Creating a New Action</title>
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<para>Prior to Shorewall version 1.4.9, rules in <filename>/etc/shorewall/rules</filename>
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were limited to those defined by Netfilter (ACCEPT, DROP, REJECT, etc.).
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Beginning with Shorewall version 1.4.9, users may use sequences of these
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elementary operations to define more complex actions.</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><filename>/etc/shorewall/actions</filename></filename>
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that names your new action. Action names must be valid shell variable
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names as well as valid Netfilter chain names. It is recommended that
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the name you select for a new action begins with with a capital
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letter; that way, the name won't conflict with a Shorewall-defined
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chain name.</para>
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<para>Beginning with Shorewall-2.0.0-Beta1, the name of the action may
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be optionally followed by a colon (<quote>:</quote>) and ACCEPT, DROP
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or REJECT. When this is done, the named action will become the
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<emphasis>common action </emphasis>for policies of type ACCEPT, DROP
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or REJECT respectively. The common action is applied immediately
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before the policy is enforced (before any logging is done under that
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policy) and is used mainly to suppress logging of uninteresting
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traffic which would otherwise clog your logs. The same policy name can
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appear in multiple actions; the last such action for each policy name
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is the one which Shorewall will use.</para>
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<para>Shorewall includes pre-defined actions for DROP and REJECT --
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see below.</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 /usr/share/shorewall/action.template to <filename>/etc/shorewall/action.ActionName</filename>
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(for example, if 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 action.template file are as 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 <<emphasis>action</emphasis>>
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is a previously-defined action (that is, it must precede the action
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being defined in this file in your <filename>/etc/shorewall/actions</filename>
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file). These actions 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 separate
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log through use of ulogd (<ulink
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url="http://www.gnumonks.org/projects/ulogd">http://www.gnumonks.org/projects/ulogd</ulink>).</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 ip</emphasis>>-<<emphasis>last
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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>, <quote>udp</quote>,
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<quote>icmp</quote>, a number, or <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 port</emphasis>>:<<emphasis>high
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port</emphasis>>.</para>
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<para>This column is ignored if PROTOCOL = all but must be entered if
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any of the following ields are supplied. In that case, it is suggested
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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 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
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specify an ADDRESS in the next column, then place "-" 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 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 number</emphasis>>:<<emphasis>group
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number</emphasis>></member>
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<member>[!]<<emphasis>user name</emphasis>>:<<emphasis>group
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number</emphasis>></member>
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<member>[!]<<emphasis>user inumber</emphasis>>:<<emphasis>group
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name</emphasis>></member>
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<member>[!]<<emphasis>user name</emphasis>>:<<emphasis>group
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name</emphasis>></member>
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</simplelist>
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</listitem>
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</itemizedlist>
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<para>Example:</para>
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<para><filename>/etc/shorewall/actions</filename>:</para>
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<para><programlisting> LogAndAccept</programlisting><phrase><filename>/etc/shorewall/action.LogAndAccept</filename></phrase><programlisting> LOG:info
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ACCEPT</programlisting></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>
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<title>Standard Actions In Shorewall 2.0</title>
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<para>Beginning with Shorewall 2.0.0-Beta1, Shorewall includes a number of
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defined actions. These defined actions are listed in <filename>/usr/share/shorewall/actions.std</filename>.</para>
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<para>The <filename>/usr/share/shorewall/actions.std</filename> file
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includes the common actions <quote>Drop</quote> for DROP policies and
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<quote>Reject</quote> for REJECT policies.</para>
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<example>
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<title>Example of Using a Standard Action</title>
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<para>Suppose that you wish to enable ftp from your local network to
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your firewall. In <filename>/etc/shorewall/rules</filename>:</para>
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<programlisting>#ACTION SOURCE DEST PROTO ...
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AllowFTP loc fw</programlisting>
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</example>
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<para><filename>/usr/share/shorewall/actions.std</filename> is processed
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before <filename>/etc/shorewall/actions</filename> and if you have any
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actions defined with the same name as one in <filename>/usr/share/shorewall/actions.std</filename>,
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your version in <filename class="directory">/etc/shorewall</filename> will
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be the one used. So if you wish to modify a standard action, simply copy
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the associated action file from <filename class="directory">/usr/share/shorewall
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</filename>to <filename class="directory">/etc/shorewall and modify</filename>
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it to suit your needs. The next <command>shorewall restart</command> will
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cause your action to be installed in place of the standard one. In
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particular, if you want to modify the common actions <quote>Drop</quote>
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or <quote>Reject</quote>, simply copy <filename>action.Drop</filename> or
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<filename>Action.Reject</filename> to <filename class="directory">/etc/shorewall</filename>
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and modify that copy as desired.</para>
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</section>
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<section>
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<title>Creating an Action using an Extension Script</title>
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<para>There may be cases where you wish to create a chain with rules that
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can't be constructed using the tools defined in the action.template.
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In that case, you can use an extension script.<note><para>If you actually
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need an action to drop broadcast packets, use the <command>dropBcast</command>
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standard action rather than create one like this.</para></note></para>
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<example>
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<title>An action to drop all broadcast packets</title>
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<para>/etc/shorewall/actions<programlisting>DropBcasts</programlisting></para>
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<para>/etc/shorewall/action.DropBcasts<programlisting># This file is empty</programlisting></para>
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<para>/etc/shorewall/DropBcasts<programlisting>run_iptables -A DropBcasts -m pkttype --pkttype broadcast -j DROP</programlisting></para>
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</example>
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</section>
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</article> |