episode-16.xml

<?xml version="1.0" encoding="utf-8"?>
<item xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd">
  <title>Tunneling and Encapsulation</title>
  <guests>Jesse Gross from VMware</guests>
  <description>
    <p>
      Tunneling and encapsulation, with protocols from GRE to Geneve, have been
      a key part of Open vSwitch since the early days.  Jesse Gross, an early
      employee at Nicira and major contributor to Open vSwitch, and perhaps
      most importantly the maintainer of the Open vSwitch kernel module, joins
      this episode of the podcast to talk about this aspect of OVS.
    </p>

    <p>
      The conversation begins with a discussion of the reasons for L2-in-L3
      tunnels.  Jesse's reasons for such tunnels include adding a layer of
      indirection between physical and virtual networks.  VLANs can provide a
      solution for partitioning networks, but they don't provide the same layer
      of indirection.
    </p>

    <p>
      Jesse describes the motivation for designing and implementing STT
      encapsulation in Open vSwitch.  The biggest reason was performance,
      primarily the cost of losing the network card hardware support for
      various kinds of offloads, such as checksum and TCP segmentation offload
      support.  Most network cards can only implement these for specific
      protocols, so that using an encapsulation not specifically supported by
      the card caused performance degradation.  STT worked around this by using
      (abusing?) TCP as an encapsulation.  Since most network cards can offload
      TCP processing, this allowed STT encapsulation to be very fast on both
      the send and receive sides.  Jesse also describes the challenges in
      implementing STT and his view of STT's future.
    </p>

    <p>
      Whereas STT was designed as a performance hack for existing network
      cards, Geneve, the second encapsulation that Jesse designed and
      implemented in Open vSwitch, addresses the paucity of metadata that the
      existing tunneling protocols supported.  GRE, for example, supports a
      32-bit key, VXLAN supports a 24-bit VNI, STT a 64-bit key, and so on.
      None of them supported a large or flexible amount.  Geneve, on the other
      hand, supports an almost arbitrary number of type-length-value (TLV)
      options, intended to be future-proof.  Geneve has been working its way
      through the IETF for about 3 1/2 years.
    </p>

    <p>
      Jesse talks about NSH (Network Service Header), which is often mentioned
      in conjunction with Geneve.  NSH has some specialization for service
      function changing, whereas Geneve takes a more general-purpose stance.
      NSH does support TLVs, but its primary focus is on a fixed number of
      fixed-size headers that it keeps in the packet, and that is what most
      implementations of Geneve actually implement.  NSH can used inside L2 or
      L3, whereas Geneve as currently runs only inside L3.  Jesse discusses
      pros and cons to each design.
    </p>

    <p>
      Jesse discusses MTU issues in tunneling and encapsulation, which come up
      because they techniques add bytes to each packet, making packets that are
      maximum length before encapsulation exceed the MTU.  Jesse says that the
      solution to MTU problems depends on the use case: for example, in data
      center use cases, a simple solution can be to increase the MTU of the
      physical network.  In the pre-1.10 era, Open vSwitch supported path MTU
      discovery for tunnels, and Jesse describes why it was dropped and what it
      would take to reintroduce it.
    </p>

    <p>
      Jesse describes CAPWAP tunneling, why OVS implemented it, and why OVS
      dropped support.
    </p>

    <p>
      Jesse describes GTP tunneling and the potential for including it in OVS,
      as well as ERSPAN encapsulation.
    </p>

    <p>
      Jesse describes the challenges of encapsulations for IP (as opposed to
      encapsulations for Ethernet).
    </p>

    <p>
      Jesse lays out some thoughts on the future of tunneling in Open vSwitch.
    </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>Mon, 26 Sep 2016 04:10:59 GMT</pubDate>
</item>