2002-12-29 19:23:07 +01:00
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<head>
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<title>Shorewall Logging</title>
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<meta http-equiv="content-type"
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content="text/html; charset=ISO-8859-1">
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<meta name="author" content="Tom Eastep">
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</head>
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2003-10-07 00:38:40 +02:00
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<body>
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2003-12-03 00:51:46 +01:00
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<h1 style="text-align: center;">Logging</h1>
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<h2>How to Log Traffic through a Shorewall Firewall</h2>
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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
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these facilities permit logging.<br>
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<ol>
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<li>The packet is part of an established connection. The packet is
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accepted and cannot be logged.</li>
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<li>The packet represents a connection request that is related to an
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established connection (such as a <a href="FTP.html">data connection
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associated with an FTP control connection</a>). These packets
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also cannot be logged.</li>
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<li>The packet is rejected because of an option in <a
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href="Documentation.htm#Conf">/etc/shorewall/shorewall.conf</a> or <a
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href="Documentation.htm#Interfaces">/etc/shorewall/interfaces</a>.
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These packets can be logged by setting the appropriate logging-related
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option in <a href="Documentation.htm#Conf">/etc/shorewall/shorewall.conf.</a></li>
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<li>The packet matches a rule in <a href="Documentation.htm#Rules">/etc/shorewall/rules</a>.
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By including a syslog level (see below) in the ACTION column of a rule
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(e.g., "ACCEPT<span
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style="font-weight: bold; text-decoration: underline;">:info</span>
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net fw tcp 22"), the connection attempt will be logged at that level.</li>
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<li>The packet doesn't match a rule so is handled by a policy defined
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in <a href="Documentation.htm#Policy">/etc/shorewall/policy</a>. 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 entry (e.g., "loc net ACCEPT <span
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style="font-weight: bold; text-decoration: underline;">info</span>"<br>
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</li>
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</ol>
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<h2>Where the Traffic is logged and how to Change the Destination<br>
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</h2>
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2003-10-07 00:38:40 +02:00
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By default, Shorewall directs NetFilter to log using syslog (8). Syslog
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classifies log messages by a <i>facility</i> and a <i>priority</i>
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(using the notation <i>facility.priority</i>). <br>
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<br>
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The facilities defined by syslog are <i>auth, authpriv, cron, daemon,
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kern, lpr, mail, mark, news, syslog, user, uucp</i> and <i>local0</i>
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through <i>local7</i>.<br>
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<br>
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Throughout the Shorewall documentation, I will use the term <i>level</i>
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rather than <i>priority</i> since <i>level</i> is the term used by
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NetFilter. The syslog documentation uses the term <i>priority</i>.<br>
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2002-12-29 19:23:07 +01:00
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<h3>Syslog Levels<br>
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2003-10-07 00:38:40 +02:00
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</h3>
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Syslog levels are a method of describing to syslog (8) the importance
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of a message and a number of Shorewall parameters have a syslog level
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as their value.<br>
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<br>
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Valid levels are:<br>
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<br>
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7 <span style="font-weight: bold;">debug</span>
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(Debug-level messages)<br>
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6 <span style="font-weight: bold;">info</span>
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(Informational)<br>
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5 <span style="font-weight: bold;">notice</span>
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(Normal but significant Condition)<br>
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4 <span style="font-weight: bold;">
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warning</span> (Warning Conditions)<br>
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3 <span style="font-weight: bold;">err</span>
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(Error Conditions)<br>
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2 <span style="font-weight: bold;">crit</span>
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(Critical Conditions)<br>
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1 <span style="font-weight: bold;">alert</span>
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(Must be handled immediately)<br>
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0 <span style="font-weight: bold;">emerg</span>
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(System is unusable)<br>
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<br>
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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 <i>kern</i> facility and the level that you specify. If you are
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unsure of the level to choose, 6 (info) is a safe bet. You may specify
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levels by name or by number.<br>
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<br>
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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.<br>
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2002-12-29 19:23:07 +01:00
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<h3>Configuring a Separate Log for Shorewall Messages</h3>
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There are a couple of limitations to syslogd-based logging:<br>
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<ol>
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<li>If you give, for example, kern.info it's own log destination then
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that destination will also receive all kernel messages of levels 5
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(notice) through 0 (emerg).</li>
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<li>All kernel.info messages will go to that destination and not just
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those from NetFilter.<br>
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</li>
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2003-01-14 18:18:42 +01:00
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</ol>
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2003-10-07 00:38:40 +02:00
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Beginning with Shorewall version 1.3.12, if your kernel has ULOG target
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support (and most vendor-supplied kernels do), you may also specify a
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log level of ULOG (must be all caps). When ULOG is used, Shorewall will
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direct netfilter to log the related messages via the ULOG target which
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will send them to a process called 'ulogd'. The ulogd program is
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available from http://www.gnumonks.org/projects/ulogd and can be
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configured to log all Shorewall message to their own log file.<br>
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<br>
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<b>Note: </b>The ULOG logging mechanism is <u>completely separate</u>
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from syslog. Once you switch to ULOG, the settings in /etc/syslog.conf
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have
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absolutely no effect on your Shorewall logging (except for Shorewall
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status
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messages which still go to syslog).<br>
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<br>
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You will need to have the kernel source available to compile ulogd.<br>
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<br>
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Download the ulod tar file and:<br>
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<ol>
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<li>Be sure that /usr/src/linux is linked to your kernel source tree<br>
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</li>
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<li>cd /usr/local/src (or wherever you do your builds)</li>
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<li>tar -zxf <i>source-tarball-that-you-downloaded</i></li>
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<li>cd ulogd-<i>version</i><br>
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</li>
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<li>./configure</li>
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<li>make</li>
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<li>make install<br>
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</li>
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2002-12-29 19:23:07 +01:00
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</ol>
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2003-10-07 00:38:40 +02:00
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If you are like me and don't have a development environment on your
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firewall, you can do the first six steps on another system then either
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NFS
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mount your /usr/local/src directory or tar up the /usr/local/src/ulogd-<i>version</i>
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directory and move it to your firewall system.<br>
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<br>
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Now on the firewall system, edit /usr/local/etc/ulogd.conf and set:<br>
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<ol>
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<li>syslogfile <i><file that you wish to log to></i></li>
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<li>syslogsync 1</li>
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2002-12-29 19:23:07 +01:00
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</ol>
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2003-08-09 19:14:58 +02:00
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Also on the firewall system:<br>
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<blockquote>touch <<i>file that you wish to log to</i>><br>
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</blockquote>
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2003-10-07 00:38:40 +02:00
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I also copied the file /usr/local/src/ulogd-<i>version</i>/ulogd.init
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to /etc/init.d/ulogd. I had to edit the line that read "daemon
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/usr/local/sbin/ulogd" to read daemon /usr/local/sbin/ulogd -d". On a
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RedHat system, a simple
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"chkconfig --level 3 ulogd on" starts ulogd during boot up. Your init
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system
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may need something else done to activate the script.<br>
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<br>
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You will need to change all instances of log levels (usually 'info') in
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your configuration files to 'ULOG' - this includes entries in the
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policy, rules and shorewall.conf files. Here's what I have:<br>
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2003-01-14 18:18:42 +01:00
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<pre> [root@gateway shorewall]# grep ULOG *<br> policy:loc fw REJECT ULOG<br> policy:net all DROP ULOG 10/sec:40<br> policy:all all REJECT ULOG<br> rules:REJECT:ULOG loc net tcp 6667<br> shorewall.conf:TCP_FLAGS_LOG_LEVEL=ULOG<br> shorewall.conf:RFC1918_LOG_LEVEL=ULOG<br> [root@gateway shorewall]#<br></pre>
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2003-10-07 00:38:40 +02:00
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Finally edit /etc/shorewall/shorewall.conf and set LOGFILE=<i><file
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that you wish to log to></i>. This tells the /sbin/shorewall program
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where to look for the log when processing its "show log", "logwatch"
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and
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"monitor" commands.<br>
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<h2>Syslog-ng</h2>
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<a
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href="http://marc.theaimsgroup.com/?l=gentoo-security&m=106040714910563&w=2">Here</a>
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is a post describing configuring syslog-ng to work with Shorewall.<br>
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2003-12-03 00:51:46 +01:00
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<p><font size="2"> Updated 10/30/2003 - <a href="support.htm">Tom
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Eastep</a>
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2003-10-07 00:38:40 +02:00
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</font></p>
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<p><a href="copyright.htm"><font size="2">Copyright</font> © <font
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size="2">2001, 2002, 2003 Thomas M. Eastep</font></a><br>
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</p>
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<br>
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<br>
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2002-12-29 19:23:07 +01:00
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</body>
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</html>
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