shorewall_code/docs/Accounting.xml

<?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 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
            &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 don’t 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
            mark’s 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>