shorewall_code/docs/simple_traffic_shaping.xml

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  <articleinfo>
    <title>Simple Traffic Shaping/Control</title>

    <authorgroup>
      <author>
        <firstname>Tom</firstname>

        <surname>Eastep</surname>
      </author>
    </authorgroup>

    <pubdate><?dbtimestamp format="Y/m/d"?></pubdate>

    <copyright>
      <year>2009</year>

      <year>2010</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>

  <section>
    <title>Introduction</title>

    <para>Traffic shaping and control was originally introduced into Shorewall
    in version 2.2.5. That facility was based on Arne Bernin's
    <firstterm>tc4shorewall</firstterm> and is generally felt to be complex
    and difficult to use.</para>

    <para>In Shorewall 4.4.6, a second traffic shaping facility that is simple
    to understand and to configure was introduced. This newer facility is
    described in this document while the original facility is documented in
    <ulink url="traffic_shaping.htm">Complex Traffic
    Shaping/Control</ulink>.</para>
  </section>

  <section>
    <title>Enabling Simple Traffic Shaping</title>

    <para>Simple traffic shaping is enabled by setting TC_ENABLED=Simple in
    <ulink url="manpages/shorewall.conf.html">shorewall.conf</ulink>(5). You
    then add an entry for your external interface to <ulink
    url="manpages/shorewall-tcinterfaces.html">shorewall-tcinterfaces</ulink>(5)
    (<filename>/etc/shorewall/tcinterfaces</filename>).</para>

    <para>Assuming that your external interface is eth0:</para>

    <programlisting>#INTERFACE             TYPE          IN-BANDWIDTH
eth0                   External</programlisting>

    <note>
      <para>If you experience an error such as the following during
      <command>shorewall start</command> or <command>shorewall
      restart</command>, your kernel and iproute do not support the <emphasis
      role="bold">flow</emphasis> classifier. In that case, you must leave the
      TYPE column empty (or specify '-').</para>

      <programlisting>Unknown filter "flow", hence option "hash" is unparsable
   ERROR: Command "tc filter add dev eth0 protocol all prio 1 parent 11: handle 11 flow hash keys nfct-src divisor 1024" Failed</programlisting>

      <para>RHEL5-based systems such as <trademark>CentOS</trademark> 5 and
      <trademark>Foobar</trademark> 5 are known to experience this
      error.</para>

      <para><emphasis role="bold">Update</emphasis>: Beginning with Shorewall
      4.4.7, Shorewall can determine that some environments, such as RHEL5 and
      derivatives, are incapable of using the TYPE parameter and simply ignore
      it.</para>
    </note>

    <para>With this simple configuration, packets to be sent through interface
    eth0 will be assigned to a priority band based on the value of their TOS
    field:</para>

    <programlisting>TOS     Bits  Means                    Linux Priority    BAND
------------------------------------------------------------
0x0     0     Normal Service           0 Best Effort     2
0x2     1     Minimize Monetary Cost   1 Filler          3
0x4     2     Maximize Reliability     0 Best Effort     2
0x6     3     mmc+mr                   0 Best Effort     2
0x8     4     Maximize Throughput      2 Bulk            3
0xa     5     mmc+mt                   2 Bulk            3
0xc     6     mr+mt                    2 Bulk            3
0xe     7     mmc+mr+mt                2 Bulk            3
0x10    8     Minimize Delay           6 Interactive     1
0x12    9     mmc+md                   6 Interactive     1
0x14    10    mr+md                    6 Interactive     1
0x16    11    mmc+mr+md                6 Interactive     1
0x18    12    mt+md                    4 Int. Bulk       2
0x1a    13    mmc+mt+md                4 Int. Bulk       2
0x1c    14    mr+mt+md                 4 Int. Bulk       2
0x1e    15    mmc+mr+mt+md             4 Int. Bulk       2</programlisting>

    <para>When dequeueing, band 1 is tried first and only if it did not
    deliver a packet does the system try band 2, and so onwards. Maximum
    reliability packets should therefore go to band 1, minimum delay to band 2
    and the rest to band 3.</para>

    <note>
      <para>If you run both an IPv4 and an IPv6 firewall on your system, you
      should define each interface in only one of the two
      configurations.</para>
    </note>
  </section>

  <section>
    <title>Customizing Simple Traffic Shaping</title>

    <para>The default mapping of TOS to bands can be changed using the
    TC_PRIOMAP setting in <ulink
    url="manpages/shorewall.conf.html">shorewall.conf</ulink>(5). The default
    setting of this option is:</para>

    <programlisting>TC_PRIOMAP="2 3 3 3 2 3 1 1 2 2 2 2 2 2 2 2"</programlisting>

    <para>These entries map Linux Priority to priority BAND. So only entries
    0, 1, 2, 4 and 6 in the map are relevant to TOS-&gt;BAND mapping.</para>

    <para>Further customizations can be defined in <ulink
    url="manpages/shorewall-tcpri.html">shorewall-tcpri</ulink>(5)
    (<filename>/etc/shorewall/tcpri</filename>). Using that file, you
    can:</para>

    <orderedlist>
      <listitem>
        <para>Assign traffic entering the firewall on a particular interface
        to a specific priority band:</para>

        <programlisting>#BAND         PROTO         PORT(S)         ADDRESS             INTERFACE        HELPER
2               -             -                -                eth1</programlisting>

        <para>In this example, traffic from eth1 will be assigned to priority
        band 2.</para>

        <note>
          <para>When an INTERFACE is specified, the PROTO, PORT(S) and ADDRESS
          column must contain '-'.</para>
        </note>
      </listitem>

      <listitem>
        <para>Assign traffic from a particular IP address to a specific
        priority band:</para>

        <programlisting>#BAND         PROTO         PORT(S)         ADDRESS             INTERFACE        HELPER
1               -             -             192.168.1.44</programlisting>

        <para>In this example, traffic from 192.168.1.44 will be assigned to
        priority band 1.</para>

        <note>
          <para>When an ADDRESS is specified, the PROTO, PORT(S) and INTERFACE
          columns must be empty.</para>
        </note>
      </listitem>

      <listitem>
        <para>Assign traffic to/from a particular application to a specific
        priority band:</para>

        <programlisting>#BAND         PROTO         PORT(S)         ADDRESS             INTERFACE        HELPER
1             udp           1194</programlisting>

        <para>In that example, OpenVPN traffic is assigned to priority band
        1.</para>
      </listitem>

      <listitem>
        <para>Assign traffic that uses a particular Netfilter helper to a
        particular priority band:</para>

        <programlisting>#BAND         PROTO         PORT(S)         ADDRESS             INTERFACE        HELPER
1               -             -             -                   -                sip</programlisting>

        <para>In this example, SIP and associated RTP traffic will be assigned
        to priority band 1 (assuming that the nf_conntrack_sip helper is
        loaded).</para>
      </listitem>
    </orderedlist>

    <para>It is suggested that entries specifying an INTERFACE be placed the
    top of the file. That way, the band assigned to a particular packet will
    be the <emphasis role="bold">last</emphasis> entry matched by the packet.
    Packets which match no entry in <ulink
    url="manpages/shorewall-tcpri.html">shorewall-tcpri</ulink>(5) are
    assigned to priority bands using their TOS field as previously
    described.</para>

    <para>One cause of high latency on interactive traffic can be that queues
    are building up at your ISP's gateway router. If you suspect that is
    happening in your case, you can try to eliminate the problem by using the
    IN-BANDWIDTH setting in <ulink
    url="manpages/shorewall-tcinterfaces.html">shorewall-tcinterfaces</ulink>(5).
    The contents of the column are a <replaceable>rate</replaceable>. For
    defining the rate, use <emphasis role="bold">kbit</emphasis> or <emphasis
    role="bold">kbps</emphasis> (for Kilobytes per second) and make sure there
    is NO space between the number and the unit (it is 100kbit not 100 kbit).
    <emphasis role="bold">mbit</emphasis>, <emphasis
    role="bold">mbps</emphasis> or a raw number (which means bytes) can be
    used, but note that only integer numbers are supported (0.5 is not valid).
    To pick an appropriate setting, we recommend that you start by setting
    IN-BANDWIDTH significantly below your measured download bandwidth (20% or
    so). While downloading, measure the ping response time from the firewall
    to the upstream router as you gradually increase the setting. The optimal
    setting is at the point beyond which the ping time increases sharply as
    you increase the setting.</para>

    <para>Simple Traffic Shaping is only appropriate on interfaces where
    output queuing occurs. As a consequence, you usually only use it on
    extermal interfaces. There are cases where you may need to use it on an
    internal interface (a VPN interface, for example). If so, just add an
    entry to <ulink
    url="manpages/shorewall-tcinterfaces.html">shorewall-tcinterfaces</ulink>(5):</para>

    <programlisting>#INTERFACE             TYPE          IN-BANDWIDTH
tun0                   Internal</programlisting>
  </section>

  <section>
    <title>Additional Reading</title>

    <para>The PRIO(8) (tc-prio) manpage has additional information on the
    facility that Shorewall Simple Traffic Shaping is based on.</para>

    <caution>
      <para>Please note that Shorewall numbers the bands 1-3 whereas PRIO(8)
      refers to them as bands 0-2.</para>
    </caution>
  </section>
</article>