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shorewall_code/Shorewall-docsN/Accounting.xml
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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>2004-04-19</pubdate>
<copyright>
<year>2003-2004</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>
<para>Shorewall Traffic Accounting support was added in Shorewall release
1.4.7.</para>
<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 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&#39;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&#39;t attempt to match any
following accounting rules.</para>
</listitem>
<listitem>
<para><emphasis>&#60;chain&#62;</emphasis> - The name of a chain to
jump to. Shorewall will create the chain automatically. If the name
of the chain is followed by <quote>:COUNT</quote> then a COUNT rule
matching this rule will automatically be added to &#60;chain&#62;.
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 man also contain embedded dashes (<quote>-</quote>) and
are not required to start with a letter.</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.</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>) or a protocol number.</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).</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>
</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> 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> 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
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&#39;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&#39;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>
</article>