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347 lines
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347 lines
11 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>AUDIT Target Support</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>2011</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>
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<title>Background</title>
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<para>In early 2011, Thomas Graf submitted a set of patches to the
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Netfilter development list that implemented an AUDIT rule target. This is
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from the initial submittal:</para>
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<blockquote>
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<para>This patch adds a new netfilter target which creates audit records
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for packets traversing a certain chain. It can be used to record packets
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which are rejected administraively as follows:</para>
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<simplelist>
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<member>-N AUDIT_DROP</member>
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<member>-A AUDIT_DROP -j AUDIT --type DROP</member>
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<member>-A AUDIT_DROP -j DROP</member>
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</simplelist>
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<para>A rule which would typically drop or reject a packet would then
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invoke the new chain to record packets before dropping them.</para>
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<simplelist>
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<member>-j AUDIT_DROP</member>
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</simplelist>
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<para>The module is protocol independant and works for iptables,
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ip6tables and ebtables.</para>
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<itemizedlist>
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<listitem>
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<para>netfilter hook</para>
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</listitem>
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<listitem>
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<para>packet length</para>
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</listitem>
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<listitem>
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<para>incoming/outgoing interface</para>
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</listitem>
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<listitem>
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<para>MAC src/dst/proto for ethernet packets</para>
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</listitem>
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<listitem>
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<para>src/dst/protocol address for IPv4/IPv6</para>
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</listitem>
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<listitem>
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<para>src/dst port for TCP/UDP/UDPLITE</para>
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</listitem>
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<listitem>
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<para>icmp type/code</para>
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</listitem>
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</itemizedlist>
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</blockquote>
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<para>The audited packets are sent to a daemon (auditd) that write the
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audit information to a log file.</para>
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<para>In a related post by Eric Paris, the following additional
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information was posted:</para>
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<blockquote>
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<para>AUDIT exists because a very large number of gov't customers (Not
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just USA) have special requirements about how 'relevant' information is
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gathered and stored. They require centralization and standardization and
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require pretty formal documentation describing it's operation. The gov't
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certification authority has recently added a requirement that they be
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able to log 'illegal attempted network connections' via the approved
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audit facility. Thus, this patch.</para>
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</blockquote>
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<para>The AUDIT target was included in Linux kernel 2.6.39.</para>
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</section>
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<section>
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<title>Shorewall Support</title>
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<para>Shorewall support for the AUDIT target was added in 4.4.20.</para>
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<para>The support involves the following:</para>
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<orderedlist numeration="loweralpha">
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<listitem>
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<para>A new "AUDIT Target" capability is added and is required for
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auditing support. To use AUDIT support with a capabilities file, that
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file must be generated using this or a later release.</para>
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<para>Use 'shorewall show capabilities' after installing this release
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to see if your kernel/iptables support the AUDIT target.</para>
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</listitem>
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<listitem>
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<para>In /etc/shorewall/policy's POLICY column, the policy (and
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default action, if any) may be followed by ':audit' to cause
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application of the policy to be audited. Only ACCEPT, DROP and REJECT
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policies may be audited.</para>
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<para>Example:</para>
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<programlisting>#SOURCE DEST POLICY
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net $FW DROP:audit</programlisting>
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<para>It is allowed to also specify a log level on audited policies
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resulting in both auditing and logging.</para>
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</listitem>
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<listitem>
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<para>Three new builtin targets that may be used in the rules file, in
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macros and in other actions.</para>
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<itemizedlist>
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<listitem>
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<para>A_ACCEPT - Audits and accepts the connection request</para>
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</listitem>
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<listitem>
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<para>A_DROP - Audits and drops the connection request</para>
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</listitem>
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<listitem>
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<para>A_REJECT - Audits and rejects</para>
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</listitem>
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</itemizedlist>
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<para>A log level may be supplied with these actions to provide both
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auditing and logging.</para>
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<para>Example:</para>
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<programlisting>#ACTION SOURCE DEST PROTO
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A_ACCEPT:info loc net ...</programlisting>
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</listitem>
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<listitem>
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<para>The BLACKLIST_DISPOSITION, MACLIST_DISPOSITION,
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SMURF_DISPOSITION and TCP_FLAGS_DISPOSITION options may be set as
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follows:</para>
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<informaltable>
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<tgroup cols="2">
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<tbody>
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<row>
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<entry>BLACKLIST_DISPOSITION</entry>
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<entry>A_DROP or A_REJECT</entry>
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</row>
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<row>
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<entry>MACLIST_DISPOSITION</entry>
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<entry>A_DROP, A_REJECT unless MACLIST_TABLE=mangle</entry>
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</row>
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<row>
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<entry>SMURF_DISPOSITION<footnote>
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<para>This option was added in Shorewall 4.4.20</para>
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</footnote></entry>
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<entry>A_DROP</entry>
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</row>
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<row>
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<entry>TCP_FLAGS_DISPOSITION</entry>
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<entry>A_DROP or A_REJECT</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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</listitem>
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<listitem>
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<para>An 'audit' option has been added to the /etc/shorewall/blacklist
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file which causes the packets matching the entryto be audited. 'audit'
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may not be specified together with 'accept'.</para>
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</listitem>
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<listitem>
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<para>The builtin actions (dropBroadcast, rejNonSyn, etc.) now support
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an 'audit' parameter which causes all ACCEPT, DROP and REJECTs
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performed by the action to be audited.</para>
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</listitem>
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<listitem>
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<para>There are audited versions of the standard <ulink
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url="Actions.html#Default">Default Actions</ulink> (A_Drop and
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A_Reject). These actions audit everything they do which is probably
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more than you want; as a consequence, you probably will want to make
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your own copies of these actions and modify them to only audit the
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packets that you are interested in.</para>
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</listitem>
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<listitem>
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<para>In Shorewall 4.4.21, the standard <ulink
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url="Actions.html#Default">Default Actions</ulink> were parameterized,
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accepting three parameters:</para>
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<orderedlist>
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<listitem>
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<para>Pass 'audit' if you want all ACCEPTs, DROPs and REJECTs
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audited. Pass '-' otherwise.</para>
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</listitem>
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<listitem>
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<para>The action to be applied to Auth requests; the default
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depends on the first parameter:</para>
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<informaltable border="">
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<tgroup cols="2">
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<tbody>
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<row>
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<entry><emphasis role="bold">FIRST
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PARAMETER</emphasis></entry>
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<entry><emphasis role="bold">DEFAULT</emphasis></entry>
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</row>
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<row>
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<entry>-</entry>
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<entry>REJECT</entry>
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</row>
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<row>
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<entry>audit</entry>
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<entry>A_REJECT</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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</listitem>
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<listitem>
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<para>The action to be applied to SMB traffic. The default depends
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on the first parameter:</para>
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<informaltable>
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<tgroup cols="3">
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<tbody>
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<row>
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<entry><emphasis role="bold">ACTION</emphasis></entry>
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<entry><emphasis role="bold">FIRST
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PARAMETER</emphasis></entry>
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<entry><emphasis role="bold">DEFAULT</emphasis></entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>-</entry>
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<entry>REJECT</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>-</entry>
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<entry>DROP</entry>
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</row>
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<row>
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<entry>Reject</entry>
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<entry>audit</entry>
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<entry>A_REJECT</entry>
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</row>
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<row>
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<entry>Drop</entry>
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<entry>audit</entry>
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<entry>A_DROP</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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</listitem>
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</orderedlist>
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<para> The parameters can be passed in the POLICY column of the policy
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file. </para>
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<programlisting>#SOURCE DEST POLICY
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net all DROP:Drop(audit):audit #Same as DROP:A_DROP:audit
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</programlisting>
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<programlisting>#SOURCE DEST POLICY
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net all DROP:Drop(-,DROP) #DROP rather than REJECT Auth
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</programlisting>
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<para>The parameters can also be specified in shorewall.conf: </para>
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<programlisting>DROP_DEFAULT=Drop(-,DROP) #DROP Auth rather than REJECT </programlisting>
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</listitem>
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</orderedlist>
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</section>
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</article>
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