<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd"> <article id="IPIP"> <!--$Id$--> <articleinfo> <title>Shorewall Logging</title> <authorgroup> <author> <firstname>Tom</firstname> <surname>Eastep</surname> </author> </authorgroup> <pubdate><?dbtimestamp format="Y/m/d"?></pubdate> <copyright> <year>2001 - 2009</year> <holder>Thomas M. Eastep</holder> </copyright> <legalnotice> <para>Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled <quote><ulink url="GnuCopyright.htm">GNU Free Documentation License</ulink></quote>.</para> </legalnotice> </articleinfo> <caution> <para><emphasis role="bold">This article applies to Shorewall 4.3 and later. If you are running a version of Shorewall earlier than Shorewall 4.3.5 then please see the documentation for that release.</emphasis></para> </caution> <section id="Log"> <title>How to Log Traffic Through a Shorewall Firewall</title> <para>The disposition of packets entering a Shorewall firewall is determined by one of a number of Shorewall facilities. Only some of these facilities permit logging.</para> <orderedlist> <listitem> <para>The packet is part of an established connection. While the packet can be logged using LOG rules in the ESTABLISHED section of <ulink url="manpages/shorewall-rules.html">/etc/shorewall/rules</ulink>, that is not recommended because of the large amount of information that may be logged.</para> </listitem> <listitem> <para>The packet represents a connection request that is related to an established connection (such as a <ulink url="FTP.html">data connection associated with an FTP control connection</ulink>). These packets may be logged using LOG rules in the RELATED section of <ulink url="manpages/shorewall-rules.html">/etc/shorewall/rules</ulink>.</para> </listitem> <listitem> <para>The packet is rejected because of an option in <ulink url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink> or <ulink url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink>. These packets can be logged by setting the appropriate logging-related option in <ulink url="manpages/shorewall.conf.html">/etc/shorewall/shorewall.conf</ulink>.</para> </listitem> <listitem> <para>The packet matches a rule in <ulink url="manpages/shorewall-rules.html">/etc/shorewall/rules</ulink>. By including a syslog level (see below) in the ACTION column of a rule (e.g., <quote>ACCEPT<emphasis role="bold">:info</emphasis> net $FW tcp 22</quote>), the connection attempt will be logged at that level.</para> </listitem> <listitem> <para>The packet doesn't match a rule so it is handled by a policy defined in <ulink url="manpages/shorewall-policy.html">/etc/shorewall/policy</ulink>. These may be logged by specifying a syslog level in the LOG LEVEL column of the policy's entry (e.g., <quote>loc net ACCEPT <emphasis role="bold">info</emphasis></quote>).</para> </listitem> </orderedlist> </section> <section id="Where"> <title>Where the Traffic is Logged and How to Change the Destination</title> <para>By default, Shorewall directs Netfilter to log using syslog (8). Syslog classifies log messages by a <emphasis>facility</emphasis> and a <emphasis>priority</emphasis> (using the notation <emphasis>facility.priority</emphasis>).</para> <para>The facilities defined by syslog are <emphasis>auth, authpriv, cron, daemon, kern, lpr, mail, mark, news, syslog, user, uucp</emphasis> and <emphasis>local0</emphasis> through <emphasis>local7.</emphasis></para> <para>Throughout the Shorewall documentation, I will use the term <emphasis>level</emphasis> rather than <emphasis>priority </emphasis>since <emphasis>level</emphasis> is the term used by Netfilter. The syslog documentation uses the term <emphasis>priority</emphasis>.</para> <section id="Levels"> <title>Syslog Levels</title> <para>Syslog levels are a method of describing to syslog (8) the importance of a message. A number of Shorewall parameters have a syslog level as their value.</para> <para>Valid levels are:</para> <simplelist> <member>7 - <emphasis role="bold">debug</emphasis> (Debug-level messages)</member> <member>6 - <emphasis role="bold">info</emphasis> (Informational)</member> <member>5 - <emphasis role="bold">notice</emphasis> (Normal but significant Condition)</member> <member>4 - <emphasis role="bold">warning</emphasis> (Warning Condition)</member> <member>3 - <emphasis role="bold">err</emphasis> (Error Condition)</member> <member>2 - <emphasis role="bold">crit</emphasis> (Critical Conditions)</member> <member>1 - <emphasis role="bold">alert</emphasis> (must be handled immediately)</member> <member>0 - <emphasis role="bold">emerg</emphasis> (System is unusable)</member> </simplelist> <para>For most Shorewall logging, a level of 6 (info) is appropriate. Shorewall log messages are generated by Netfilter and are logged using the <emphasis>kern</emphasis> facility and the level that you specify. If you are unsure of the level to choose, 6 (info) is a safe bet. You may specify levels by name or by number.</para> <para>Syslogd writes log messages to files (typically in <filename class="directory">/var/log/</filename>*) based on their facility and level. The mapping of these facility/level pairs to log files is done in /etc/syslog.conf (5). If you make changes to this file, you must restart syslogd before the changes can take effect.</para> <para>Syslog may also write to your system console. See <ulink url="FAQ.htm#faq16">Shorewall FAQ 16</ulink> for ways to avoid having Shorewall messages written to the console.</para> </section> <section id="ULOG"> <title>Configuring a Separate Log for Shorewall Messages (ulogd)</title> <para>There are a couple of limitations to syslogd-based logging:</para> <orderedlist> <listitem> <para>If you give, for example, kern.info its own log destination then that destination will also receive all kernel messages of levels 5 (notice) through 0 (emerg).</para> </listitem> <listitem> <para>All kernel.info messages will go to that destination and not just those from Netfilter.</para> </listitem> </orderedlist> <para>If your kernel has ULOG target support (and most vendor-supplied kernels do), you may also specify a log level of ULOG (must be all caps). When ULOG is used, Shorewall will direct Netfilter to log the related messages via the ULOG target which will send them to a process called <quote>ulogd</quote>. The ulogd program is included in most distributions and is also available from <ulink url="http://www.netfilter.org/projects/ulogd/index.html">http://www.netfilter.org/projects/ulogd/index.html</ulink>. Ulogd can be configured to log all Shorewall messages to their own log file.</para> <note> <para>The ULOG logging mechanism is <emphasis role="underline">completely separate</emphasis> from syslog. Once you switch to ULOG, the settings in <filename>/etc/syslog.conf</filename> have absolutely no effect on your Shorewall logging (except for Shorewall status messages which still go to syslog).</para> </note> <para>You will need to change all instances of log levels (usually <quote>info</quote>) in your Shorewall configuration files to <quote>ULOG</quote> - this includes entries in the policy, rules and shorewall.conf files. Here's what I had at one time:</para> <programlisting>gateway:/etc/shorewall# grep -v ^\# * | egrep '\$LOG|ULOG|LOGFILE' params:LOG=ULOG policy:loc $FW REJECT $LOG policy:net all DROP $LOG 10/sec:40 policy:all all REJECT $LOG rules:REJECT:$LOG loc net tcp 25 rules:REJECT:$LOG loc net udp 1025:1031 rules:REJECT:$LOG dmz net udp 1025:1031 rules:ACCEPT:$LOG dmz net tcp 1024: 20 rules:REJECT:$LOG $FW net udp 1025:1031 shorewall.conf:LOGFILE=/var/log/shorewall shorewall.conf:LOGUNCLEAN=$LOG shorewall.conf:MACLIST_LOG_LEVEL=$LOG shorewall.conf:TCP_FLAGS_LOG_LEVEL=$LOG shorewall.conf:RFC1918_LOG_LEVEL=$LOG gateway:/etc/shorewall# </programlisting> <para>Finally edit <filename>/etc/shorewall/shorewall.conf</filename> and set LOGFILE=<<emphasis>file that you wish to log to</emphasis>>. This tells the <filename>/sbin/shorewall</filename> program where to look for the log when processing its <quote><command>show log</command></quote>, <quote><command>logwatch</command></quote> and <quote><command>dump</command></quote> commands.</para> <para>The NFLOG target, a successor to ULOG, is supported shorewall. Both ULOG and NFLOG may be followed by a list of up to three numbers in parentheses.</para> <itemizedlist> <listitem> <para>The first number specifies the netlink group (1-32). If omitted (e.g., NFLOG(,0,10)) then a value of 1 is assumed.</para> </listitem> <listitem> <para>The second number specifies the maximum number of bytes to copy. If omitted, 0 (no limit) is assumed.</para> </listitem> <listitem> <para>The third number specifies the number of log messages that should be buffered in the kernel before they are sent to user space. The default is 1.</para> </listitem> </itemizedlist> <para>Examples:</para> <para><filename>/etc/shorewall/shorewall.conf</filename>: <programlisting>MACLIST_LOG_LEVEL=NFLOG(1,0,1)</programlisting></para> <para><filename>/etc/shorewall/rules</filename>:<programlisting>#ACTION SOURCE DEST PROTO DEST # PORT(S) ACCEPT:NFLOG(1,0,1) vpn fw tcp ssh,time,631,8080 </programlisting></para> </section> </section> <section id="Syslog-ng"> <title>Syslog-ng</title> <para><ulink url="http://marc.theaimsgroup.com/?l=gentoo-security&amp;m=106040714910563&amp;w=2">Here</ulink> is a post describing configuring syslog-ng to work with Shorewall. Recent <trademark>SUSE</trademark> releases come preconfigured with syslog-ng with Netfilter messages (including Shorewall's) are written to <filename>/var/log/firewall</filename>.</para> </section> <section id="Contents"> <title>Understanding the Contents of Shorewall Log Messages</title> <para>For general information on the contents of Netfilter log messages, see <ulink url="http://www.net.co.at/doc/howto/docs/iptables_netfilter_howto_de/docs/netfilter_log_format/index.html">http://www.net.co.at/doc/howto/docs/iptables_netfilter_howto_de/docs/netfilter_log_format/index.html</ulink>.</para> <para>For Shorewall-specific information, see <ulink url="FAQ.htm#faq17">FAQ #17</ulink>.</para> </section> </article>