episode-56.xml

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  <title>Flow Translation</title>
  <description>
    <p>
      This is the third in a series of Open vSwitch tech talks that we are
      starting to run internally at VMware every week or two.  This episode is
      about flow translation, the process that OVS follows when a packet
      arrives in the software switch that does not match any already
      established entry in the OVS datapath cache (the megaflow cache).
    </p>

    <p>
      The translation process has two goals.  First, it figures out what to do
      with the particular packet being processed Second, it determines what
      class of packets similar to this packet can be treated the same way.  The
      former determination is generally applied directly to the packet in
      question, and the latter is used to add a new cache entry (megaflow) to
      the datapath.
    </p>

    <p>
      The main source files involved in translation are <a href="https://github.com/openvswitch/ovs/blob/master/ofproto/ofproto-dpif-xlate.c">ofproto-dpif-xlate.c</a> and <a href="https://github.com/openvswitch/ovs/blob/master/ofproto/ofproto-dpif-xlate.h">ofproto-dpif-xlate.h</a>.
    </p>

    <p>
      In addition to the translation process itself, the talk covers some uses
      of relevant tools: <code>ovs-dpctl dump-flows</code> and <code>ovs-appctl
      dpctl/dump-flows</code> for viewing datapath cache entries, and
      <code>ovs-appctl ofproto/trace</code> for understanding how cache entries
      are devised and populated and playing "what-if?" games.  These are
      documented in the <code>ovs-vswitchd</code> and <code>ovs-dpctl</code>
      manpages.
    </p>

    <p>
      The NSDI 2015 paper <a
      href="https://www.usenix.org/conference/nsdi15/technical-sessions/presentation/pfaff">The
      Design and Implementation of Open vSwitch</a> covers in detail how Open
      vSwitch caches translations.
    </p>

    <p class="attribution">
      OVS Orbit is produced by <a href="mailto:blp@ovn.org">Ben Pfaff</a>.  The
      intro music in this episode is <a
      href="http://dig.ccmixter.org/files/AlexBeroza/43098">Drive</a>,
      featuring cdk and DarrylJ, copyright 2013, 2016 by Alex.  The bumper
      music is <a href="http://dig.ccmixter.org/files/speck/42100">Yeah Ant</a>
      featuring Wired Ant and Javolenus, copyright 2013 by Speck.  The outro
      music is <a href="http://dig.ccmixter.org/files/Kirkoid/43005">Space
      Bazooka</a> featuring Doxen Zsigmond, copyright 2013 by Kirkoid.  All
      content is licensed under a Creative Commons <a
      href="http://creativecommons.org/licenses/by/3.0/">Attribution 3.0
      Unported (CC BY 3.0)</a> license.
    </p>
  </description>
  <pubDate>Sun, 29 Apr 2018 15:57:08 GMT</pubDate>
</item>