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254 lines
10 KiB
XML
254 lines
10 KiB
XML
<?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 id="IPIP">
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<!--$Id$-->
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<articleinfo>
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<title>Shorewall Logging</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>2001 - 2005</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 3.0 and
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later. If you are running a version of Shorewall earlier than Shorewall
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3.0.0 then please see the documentation for that
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release.</emphasis></para>
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</caution>
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<section>
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<title>How to Log Traffic Through a Shorewall Firewall</title>
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<para>The disposition of packets entering a Shorewall firewall is
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determined by one of a number of Shorewall facilities. Only some of these
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facilities permit logging.</para>
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<orderedlist>
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<listitem>
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<para>The packet is part of an established connecection. While the
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packet can be logged using LOG rules in the ESTABLISHED section of
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<ulink url="Documentation.htm#Rules">/etc/shorewall/rules</ulink>,
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that is not recommended because of the large amount of information
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that may be logged.</para>
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</listitem>
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<listitem>
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<para>The packet represents a connection request that is related to an
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established connection (such as a <ulink url="FTP.html">data
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connection associated with an FTP control connection</ulink>). These
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packets may be logged using LOG rules in the RELATED section of <ulink
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url="Documentation.htm#Rules">/etc/shorewall/rules</ulink>.</para>
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</listitem>
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<listitem>
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<para>The packet is rejected because of an option in <ulink
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url="Documentation.htm#Conf">/etc/shorewall/shorewall.conf</ulink> or
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<ulink
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url="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink>.
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These packets can be logged by setting the appropriate logging-related
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option in <ulink
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url="Documentation.htm#Conf">/etc/shorewall/shorewall.conf</ulink>.</para>
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</listitem>
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<listitem>
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<para>The packet matches a rule in <ulink
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url="Documentation.htm#Rules">/etc/shorewall/rules</ulink>. By
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including a syslog level (see below) in the ACTION column of a rule
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(e.g., <quote>ACCEPT<emphasis role="bold">:info</emphasis> net $FW tcp
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22</quote>), the connection attempt will be logged at that
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level.</para>
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</listitem>
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<listitem>
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<para>The packet doesn't match a rule so it is handled by a policy
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defined in <ulink
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url="Documentation.htm#Policy">/etc/shorewall/policy</ulink>. These
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may be logged by specifying a syslog level in the LOG LEVEL column of
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the policy's entry (e.g., <quote>loc net ACCEPT <emphasis
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role="bold">info</emphasis></quote>).</para>
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</listitem>
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</orderedlist>
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</section>
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<section>
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<title>Where the Traffic is Logged and How to Change the
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Destination</title>
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<para>By default, Shorewall directs NetFilter to log using syslog (8).
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Syslog classifies log messages by a <emphasis>facility</emphasis> and a
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<emphasis>priority</emphasis> (using the notation
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<emphasis>facility.priority</emphasis>).</para>
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<para>The facilities defined by syslog are <emphasis>auth, authpriv, cron,
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daemon, kern, lpr, mail, mark, news, syslog, user, uucp</emphasis> and
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<emphasis>local0</emphasis> through <emphasis>local7.</emphasis></para>
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<para>Throughout the Shorewall documentation, I will use the term
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<emphasis>level</emphasis> rather than <emphasis>priority </emphasis>since
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<emphasis>level</emphasis> is the term used by NetFilter. The syslog
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documentation uses the term <emphasis>priority</emphasis>.</para>
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<section>
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<title>Syslog Levels</title>
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<para>Syslog levels are a method of describing to syslog (8) the
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importance of a message. A number of Shorewall parameters have a syslog
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level as their value.</para>
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<para>Valid levels are:</para>
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<simplelist>
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<member>7 - <emphasis role="bold">debug</emphasis> (Debug-level
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messages)</member>
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<member>6 - <emphasis role="bold">info</emphasis>
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(Informational)</member>
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<member>5 - <emphasis role="bold">notice</emphasis> (Normal but
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significant Condition)</member>
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<member>4 - <emphasis role="bold">warning</emphasis> (Warning
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Condition)</member>
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<member>3 - <emphasis role="bold">err</emphasis> (Error
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Condition)</member>
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<member>2 - <emphasis role="bold">crit</emphasis> (Critical
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Conditions)</member>
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<member>1 - <emphasis role="bold">alert</emphasis> (must be handled
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immediately)</member>
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<member>0 - <emphasis role="bold">emerg</emphasis> (System is
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unusable)</member>
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</simplelist>
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<para>For most Shorewall logging, a level of 6 (info) is appropriate.
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Shorewall log messages are generated by NetFilter and are logged using
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the <emphasis>kern</emphasis> facility and the level that you specify.
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If you are unsure of the level to choose, 6 (info) is a safe bet. You
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may specify levels by name or by number.</para>
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<para>Syslogd writes log messages to files (typically in /var/log/*)
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based on their facility and level. The mapping of these facility/level
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pairs to log files is done in /etc/syslog.conf (5). If you make changes
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to this file, you must restart syslogd before the changes can take
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effect.</para>
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<para>Syslog may also write to your system console. See <ulink
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url="FAQ.htm#faq16">Shorewall FAQ 16</ulink> for ways to avoid having
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Shorewall messages written to the console.</para>
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</section>
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<section>
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<title>Configuring a Separate Log for Shorewall Messages (ulogd)</title>
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<para>There are a couple of limitations to syslogd-based logging:</para>
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<orderedlist>
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<listitem>
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<para>If you give, for example, kern.info its own log destination
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then that destination will also receive all kernel messages of
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levels 5 (notice) through 0 (emerg).</para>
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</listitem>
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<listitem>
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<para>All kernel.info messages will go to that destination and not
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just those from NetFilter.</para>
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</listitem>
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</orderedlist>
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<para>Beginning with Shorewall version 1.3.12, if your kernel has ULOG
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target support (and most vendor-supplied kernels do), you may also
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specify a log level of ULOG (must be all caps). When ULOG is used,
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Shorewall will direct netfilter to log the related messages via the ULOG
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target which will send them to a process called <quote>ulogd</quote>.
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The ulogd program is included in most distributions and is also
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available from <ulink
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url="http://www.netfilter.org/projects/ulogd/index.html">http://www.netfilter.org/projects/ulogd/index.html</ulink>.
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Ulogd can be configured to log all Shorewall messages to their own log
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file.</para>
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<note>
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<para>The ULOG logging mechanism is <emphasis
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role="underline">completely separate</emphasis> from syslog. Once you
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switch to ULOG, the settings in /etc/syslog.conf have absolutely no
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effect on your Shorewall logging (except for Shorewall status messages
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which still go to syslog).</para>
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</note>
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<para>You will need to change all instances of log levels (usually
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<quote>info</quote>) in your Shorewall configuration files to
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<quote>ULOG</quote> - this includes entries in the policy, rules and
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shorewall.conf files. Here's what I had at one time:</para>
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<programlisting>gateway:/etc/shorewall# grep -v ^\# * | egrep '\$LOG|ULOG|LOGFILE'
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params:LOG=ULOG
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policy:loc $FW REJECT $LOG
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policy:net all DROP $LOG 10/sec:40
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policy:all all REJECT $LOG
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rules:REJECT:$LOG loc net tcp 25
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rules:REJECT:$LOG loc net udp 1025:1031
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rules:REJECT:$LOG dmz net udp 1025:1031
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rules:ACCEPT:$LOG dmz net tcp 1024: 20
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rules:REJECT:$LOG $FW net udp 1025:1031
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shorewall.conf:LOGFILE=/var/log/shorewall
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shorewall.conf:LOGUNCLEAN=$LOG
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shorewall.conf:MACLIST_LOG_LEVEL=$LOG
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shorewall.conf:TCP_FLAGS_LOG_LEVEL=$LOG
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shorewall.conf:RFC1918_LOG_LEVEL=$LOG
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gateway:/etc/shorewall# </programlisting>
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<para>Finally edit /etc/shorewall/shorewall.conf and set
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LOGFILE=<<emphasis>file that you wish to log to</emphasis>>. This
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tells the /sbin/shorewall program where to look for the log when
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processing its <quote>show log</quote>, <quote>logwatch</quote> and
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<quote>monitor</quote> commands.</para>
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</section>
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</section>
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<section>
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<title>Syslog-ng</title>
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<para><ulink
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url="http://marc.theaimsgroup.com/?l=gentoo-security&amp;m=106040714910563&amp;w=2">Here</ulink>
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is a post describing configuring syslog-ng to work with Shorewall.</para>
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</section>
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<section>
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<title>Understanding the Contents of Shorewall Log Messages</title>
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<para>For general information on the contents of Netfilter log messages,
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see <ulink
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url="http://logi.cc/linux/netfilter-log-format.php3">http://logi.cc/linux/netfilter-log-format.php3</ulink>.</para>
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<para>For Shorewall-specific information, see <ulink
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url="FAQ.htm#faq17">FAQ #17</ulink>.</para>
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</section>
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</article>
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