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286 lines
11 KiB
XML
286 lines
11 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>2004-07-15</pubdate>
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<copyright>
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<year>2001 - 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>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. The packet is
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accepted and cannot 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 also cannot be logged.</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 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 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 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 url="Documentation.htm#Policy">/etc/shorewall/policy</ulink>.
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These may be logged by specifying a syslog level in the LOG LEVEL
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column of the policy's entry (e.g., <quote>loc net ACCEPT
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<emphasis 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 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 <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> (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 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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</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 it's own log
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destination then that destination will also receive all kernel
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messages of 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 available from <ulink
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url="http://www.gnumonks.org/projects/ulogd">http://www.gnumonks.org/projects/ulogd</ulink>
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and can be configured to log all Shorewall message 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 role="underline">completely
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separate</emphasis> from syslog. Once you switch to ULOG, the settings
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in /etc/syslog.conf have absolutely no effect on your Shorewall
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logging (except for Shorewall status messages which still go to
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syslog).</para>
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</note>
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<para>You will need to have the kernel source available to compile
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ulogd.</para>
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<para>Download the ulog tar file and:</para>
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<orderedlist>
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<listitem>
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<para>Be sure that /usr/src/linux is linked to your kernel source
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tree</para>
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</listitem>
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<listitem>
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<para>cd /usr/local/src (or whereever you do your builds)</para>
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</listitem>
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<listitem>
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<para>tar -zxf <emphasis>source-tarball-that-you-downloaded</emphasis></para>
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</listitem>
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<listitem>
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<para>cd ulod-<emphasis>version</emphasis></para>
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</listitem>
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<listitem>
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<para>./configure</para>
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</listitem>
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<listitem>
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<para>make</para>
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</listitem>
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<listitem>
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<para>make install</para>
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</listitem>
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</orderedlist>
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<para>If you are like me and don't have a development environment on
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your firewall, you can do the first six steps on another system then
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either NFS mount your /usr/local/src directory or tar up the
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/usr/local/src/ulogd-<emphasis>version</emphasis> directory and move it
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to your firewall system.</para>
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<para>Now on the firewall system, edit /usr/local/etc/ulogd.conf and
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set:</para>
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<orderedlist>
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<listitem>
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<para>syslogfile <<emphasis>the file that you wish to log to</emphasis>></para>
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</listitem>
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<listitem>
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<para>syslogsync 1</para>
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</listitem>
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</orderedlist>
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<para>Also on the firewall system:</para>
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<simplelist>
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<member>touch <<emphasis>the file that you wish to log to</emphasis>></member>
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</simplelist>
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<para>I also copied the file /usr/local/src/ulogd-<emphasis>version</emphasis>/ulogd.init
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to /etc/init.d/ulogd. I had to edit the line that read <quote>daemon
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/usr/local/sbin/ulogd</quote> to read <quote>daemon
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/usr/local/sbin/ulogd -d</quote>. On a RedHat system, a simple
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<quote>chkconfig --level 3 ulogd on</quote> starts ulogd during boot up.
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Your init system may need something else done to activate the script.</para>
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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 configuration files to <quote>ULOG</quote>
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- this includes entries in the policy, rules and shorewall.conf files.
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Here's what I have:</para>
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<programlisting> [root@gateway shorewall]# grep ULOG *
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policy:loc fw REJECT ULOG
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policy:net all DROP ULOG 10/sec:40
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policy:all all REJECT ULOG
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rules:REJECT:ULOG loc net tcp 6667
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shorewall.conf:TCP_FLAGS_LOG_LEVEL=ULOG
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shorewall.conf:RFC1918_LOG_LEVEL=ULOG
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[root@gateway shorewall]#</programlisting>
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<para>Finally edit /etc/shorewall/shorewall.conf and set LOGFILE=<<emphasis>file
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that you wish to log to</emphasis>>. This tells the /sbin/shorewall
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program where to look for the log when processing its <quote>show log</quote>,
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<quote>logwatch</quote> and <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 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 url="FAQ.htm#faq17">FAQ
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#17</ulink>.</para>
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</section>
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</article> |