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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>Shorewall Traffic Accounting</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2003-2006</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 4.0 and
later. If you are running a version of Shorewall earlier than Shorewall
4.0.0 then please see the documentation for that
release</emphasis>.</para>
</caution>
<section id="Basics">
<title>Accounting Basics</title>
<para>Shorewall accounting rules are described in the file
/etc/shorewall/accounting. By default, the accounting rules are placed in
a chain called <quote>accounting</quote> and can thus be displayed using
<quote>shorewall[-lite] show accounting</quote>. All traffic passing into,
out of, or through the firewall traverses the accounting chain including
traffic that will later be rejected by interface options such as
<quote>tcpflags</quote> and <quote>maclist</quote>. If your kernel doesn't
support the connection tracking match extension (Kernel 2.4.21) then some
traffic rejected under <quote>norfc1918</quote> will not traverse the
accounting chain.</para>
<para>The columns in the accounting file are as follows:</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">ACTION </emphasis>- What to do when a
match is found. Possible values are:</para>
<itemizedlist>
<listitem>
<para>COUNT- Simply count the match and continue trying to match
the packet with the following accounting rules</para>
</listitem>
<listitem>
<para>DONE- Count the match and don't attempt to match any
following accounting rules.</para>
</listitem>
<listitem>
<para><emphasis>&lt;chain&gt;</emphasis> - The name of a chain;
Shorewall will create the chain automatically if it doesn't
already exist. Causes a jump to this chain will be generated from
the chain specified by the CHAIN column. If the name of the chain
is followed by <quote>:COUNT</quote> then a COUNT rule matching
this entry will automatically be added to &lt;chain&gt;. Chain
names must start with a letter, must be composed of letters and
digits, and may contain underscores (<quote>_</quote>) and periods
(<quote>.</quote>). Beginning with Shorewall version 1.4.8, chain
names may also contain embedded dashes (<quote>-</quote>) and are
not required to start with a letter.</para>
</listitem>
<listitem>
<para>COMMENT - (Shorewall-perl only) - The remainder of the line
is treated as a comment which is <ulink
url="configuration_file_basics.htm#COMMENT">attached to subsequent
rules</ulink> until another COMMENT line is found or until the end
of the file is reached. To stop adding comments to rules, use a
line with only the word COMMENT.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para><emphasis role="bold">CHAIN</emphasis> - The name of the chain
where the accounting rule is to be added. If empty or <quote>-</quote>
then the <quote>accounting</quote> chain is assumed (see <link
linkend="Bridge">below</link> for exceptions).</para>
</listitem>
<listitem>
<para><emphasis role="bold">SOURCE</emphasis> - Packet Source. The
name of an interface, an address (host or net), or an interface name
followed by <quote>:</quote> and a host or net address.</para>
</listitem>
<listitem>
<para><emphasis role="bold">DESTINATION</emphasis> - Packet
Destination Format the same as the SOURCE column.</para>
</listitem>
<listitem>
<para><emphasis role="bold">PROTOCOL</emphasis> - A protocol name
(from <filename>/etc/protocols</filename>), a protocol number or
"ipp2p". For "ipp2p", your kernel and iptables must have ipp2p match
support from <ulink url="http://www.netfilter.org">Netfilter
Patch_o_matic_ng</ulink>.</para>
</listitem>
<listitem>
<para><emphasis role="bold">DEST PORT</emphasis> - Destination Port
number. Service name from <filename>/etc/services</filename> or port
number. May only be specified if the protocol is TCP or UDP (6 or 17).
If the PROTOCOL is "ipp2p", then this column is interpreted as an
ipp2p option without the leading "--" (default "ipp2p"). For a list of
value ipp2p options, as root type <command>iptables -m ipp2p
--help</command>.</para>
</listitem>
<listitem>
<para><emphasis role="bold">SOURCE PORT</emphasis>- Source Port
number. Service name from /etc/services or port number. May only be
specified if the protocol is TCP or UDP (6 or 17).</para>
</listitem>
<listitem>
<para><emphasis role="bold">USER/GROUP</emphasis> - This column may
only be non-empty if the CHAIN is OUTPUT. The column may
contain:</para>
<programlisting> [!][&lt;user name or number&gt;][:&lt;group name or number&gt;][+&lt;program name&gt;]</programlisting>
<para>When this column is non-empty, the rule applies only if the
program generating the output is running under the effective
&lt;user&gt; and/or &lt;group&gt; specified (or is NOT running under
that id if "!" is given).</para>
<para>Examples:</para>
<simplelist>
<member>joe #program must be run by joe</member>
<member>:kids #program must be run by a member of the 'kids'
group.</member>
<member>!:kids #program must not be run by a member of the 'kids'
group</member>
<member>+upnpd #program named upnpd (This feature was removed from
Netfilter in kernel version 2.6.14).</member>
</simplelist>
</listitem>
<listitem>
<para><emphasis role="bold">MARK</emphasis> - Only count packets with
particular mark values.<programlisting>[!]&lt;value&gt;[/&lt;mask&gt;][:C]</programlisting>Defines
a test on the existing packet or connection mark. The rule will match
only if the test returns true.</para>
<para>If you dont want to define a test but need to specify anything
in the following columns, place a "-" in this field.<simplelist>
<member>! — Inverts the test (not equal)</member>
<member>&lt;value&gt; — Value of the packet or connection
mark.</member>
<member>&lt;mask&gt; — A mask to be applied to the mark before
testing.</member>
<member>:C — Designates a connection mark. If omitted, the packet
marks value is tested. This option is only supported by
Shorewall-perl.</member>
</simplelist></para>
</listitem>
</itemizedlist>
<para>In all columns except ACTION and CHAIN, the values
<quote>-</quote>,<quote>any</quote> and <quote>all</quote> are treated as
wild-cards.</para>
<para>The accounting rules are evaluated in the Netfilter
<quote>filter</quote> table. This is the same environment where the
<quote>rules</quote> file rules are evaluated and in this environment,
DNAT has already occurred in inbound packets and SNAT has not yet occurred
on outbound ones.</para>
<para>Accounting rules are not stateful -- each rule only handles traffic
in one direction. For example, if eth0 is your internet interface, and you
have a web server in your DMZ connected to eth1, then to count HTTP
traffic in both directions requires two rules:</para>
<programlisting> #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE
# PORT PORT
DONE - eth0 eth1 tcp 80
DONE - eth1 eth0 tcp - 80</programlisting>
<para>Associating a counter with a chain allows for nice reporting. For
example:</para>
<programlisting> #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE
# PORT PORT
web:COUNT - eth0 eth1 tcp 80
web:COUNT - eth1 eth0 tcp - 80
web:COUNT - eth0 eth1 tcp 443
web:COUNT - eth1 eth0 tcp - 443
DONE web</programlisting>
<para>Now <quote>shorewall show web</quote> (or "shorewall-lite show web"
for Shorewall Lite users) will give you a breakdown of your web
traffic:</para>
<programlisting> [root@gateway shorewall]# shorewall show web
Shorewall-1.4.6-20030821 Chain web at gateway.shorewall.net - Wed Aug 20 09:48:56 PDT 2003
Counters reset Wed Aug 20 09:48:00 PDT 2003
Chain web (4 references)
pkts bytes target prot opt in out source destination
11 1335 tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
18 1962 tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:80
0 0 tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:443
0 0 tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:443
29 3297 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
[root@gateway shorewall]#</programlisting>
<para>Here is a slightly different example:</para>
<programlisting> #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE
# PORT PORT
web - eth0 eth1 tcp 80
web - eth1 eth0 tcp - 80
web - eth0 eth1 tcp 443
web - eth1 eth0 tcp - 443
COUNT web eth0 eth1
COUNT web eth1 eth0</programlisting>
<para>Now <quote>shorewall show web</quote> (or "shorewall-lite show web"
for Shorewall Lite users) simply gives you a breakdown by input and
output:</para>
<programlisting> [root@gateway shorewall]# shorewall show accounting web
Shorewall-1.4.6-20030821 Chains accounting web at gateway.shorewall.net - Wed Aug 20 10:27:21 PDT 2003
Counters reset Wed Aug 20 10:24:33 PDT 2003
Chain accounting (3 references)
pkts bytes target prot opt in out source destination
8767 727K web tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
0 0 web tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:443</programlisting>
<programlisting>
11506 13M web tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:80
0 0 web tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:443
Chain web (4 references)
pkts bytes target prot opt in out source destination
8767 727K all -- eth0 eth1 0.0.0.0/0 0.0.0.0/0
11506 13M all -- eth1 eth0 0.0.0.0/0 0.0.0.0/0
[root@gateway shorewall]#</programlisting>
<para>Here's how the same example would be constructed on an HTTP server
with only one interface (eth0).</para>
<caution>
<para>READ THE ABOVE CAREFULLY -- IT SAYS <emphasis
role="bold">SERVER</emphasis>. If you want to account for web browsing,
you have to reverse the rules below.</para>
</caution>
<programlisting> #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE
# PORT PORT
web - eth0 - tcp 80
web - - eth0 tcp - 80
web - eth0 - tcp 443
web - - eth0 tcp - 443
COUNT web eth0
COUNT web - eth0</programlisting>
<para>Note that with only one interface, only the SOURCE (for input rules)
or the DESTINATION (for output rules) is specified in each rule.</para>
<para>Here's the output:</para>
<programlisting> [root@mail shorewall]# shorewall show accounting web Shorewall-1.4.7
Chains accounting web at mail.shorewall.net - Sun Oct 12 10:27:21 PDT 2003
Counters reset Sat Oct 11 08:12:57 PDT 2003
Chain accounting (3 references)
pkts bytes target prot opt in out source destination
8767 727K web tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
11506 13M web tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:80
0 0 web tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:443
0 0 web tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:443
Chain web (4 references)
pkts bytes target prot opt in out source destination
8767 727K all -- eth0 * 0.0.0.0/0 0.0.0.0/0
11506 13M all -- * eth0 0.0.0.0/0 0.0.0.0/0
[root@mail shorewall]#</programlisting>
<para>For an example of integrating Shorewall Accounting with MRTG, see
<ulink
url="http://www.nightbrawler.com/code/shorewall-stats/">http://www.nightbrawler.com/code/shorewall-stats/</ulink>.</para>
</section>
<section id="Bridge">
<title>Accounting with Bridges</title>
<para>The structure of the accounting rules changes slightly when there
are <ulink url="bridge-Shorewall-perl.html">bridges</ulink> defined in the
Shorewall configuration. Because of the restrictions imposed by Netfilter
in kernel 2.6.21 and later, output accounting rules must be segregated
from forwarding and input rules. To accomplish this separation,
Shorewall-perl creates two accounting chains:</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">accounting</emphasis> - for input and
forwarded traffic.</para>
</listitem>
<listitem>
<para><emphasis role="bold">accountout</emphasis> - for output
traffic.</para>
</listitem>
</itemizedlist>
<para>If the CHAIN column contains '-', then:</para>
<itemizedlist>
<listitem>
<para>If the SOURCE column in a rule includes the name of the firewall
zone (e.g., $FW), then the default chain to insert the rule into is
<emphasis role="bold">accountout</emphasis> only.</para>
</listitem>
<listitem>
<para>Otherwise, if the DEST in the rule is <emphasis
role="bold">any</emphasis> or <emphasis role="bold">all</emphasis> or
0.0.0.0/0, then the rule is added to both <emphasis
role="bold">accounting</emphasis> and <emphasis
role="bold">accountout</emphasis>.</para>
</listitem>
<listitem>
<para>Otherwise, the rule is added to <emphasis
role="bold">accounting</emphasis> only.</para>
</listitem>
</itemizedlist>
</section>
</article>