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[Michael Cook <1218959@xxxxxxxxxxxxxxxxxx>]

Thanks for the patch and test instructions.

Should this be tested using U12.04.2 LTS or U12.04.4 LTS as a baseline
and should I apply updates to the installation first?

A few questions:
1)  I don't understand how of the "security update" superceeding this patch affects this problem unless it prevents enabling MC on bridge?  
2) There is reference to an independent kernel update to libvirt has addressed this problem and if so, in which kernel.  The comment #3 mentioned a redhat bug but the comments of that bug say it's not going to be propagated and looks project specific.  Maybe I misread it?
3) I originally applied a udev rule myself, but specific to the single bridged interface I'm using to send multicast over.  Your proposed udev patch applies this to all virbr* interfaces.  Is this ok/sensible?

Personally, I think for U12.04.2LTS back ports, MC traffic should have
simply been left as-is.  Future releases should have adopted proper
handling of MC traffic and required Querier to be enabled.

Appreciate any insight, thanks.

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https://bugs.launchpad.net/bugs/1218959

Title:
  KVM virbr# no longer forwards multicast traffic by default (U12.04)

Status in “libvirt” package in Ubuntu:
  Fix Released
Status in “linux” package in Ubuntu:
  Fix Released
Status in “libvirt” source package in Precise:
  Fix Committed
Status in “linux” source package in Precise:
  Won't Fix

Bug description:
  A recent kernel update (Apr 2013) has made it's way to U12.04.2 LTS
  (approx June-Aug 2013) and has stopped the (default) behaviour of
  automatically forwarding multicast traffic over virbr#.  Some updates
  the bridge subsystem now, by default, disable multicast traffic
  without IGMP Querier being enabled on that bridge.

  The corresponding Fedora/RHEL bug tracks the progress/updates of this specific change in relation to Fedora.  
  https://bugzilla.redhat.com/show_bug.cgi?id=880035

  (I have yet to find a similar bug report in Ubuntu so I have created
  this bug to help the Ubuntu community identify multicast issues that
  may arise since April 2013 in U12.04 LTS and presumably other Ubuntu
  releases as backports are made and break regression testing.)

  Using the latest patches in U12.04.2 LTS this following addition, with some modifications, can be made to the udev rules will enable multicast on virbr# bridge:
  https://bugzilla.redhat.com/show_bug.cgi?id=880035#c38

  While this is an improvement/correction to KVM bridge networking it
  has broken existing functionality in U12.04.2 LTS and broke regressed
  functionality that once worked.

  IMPACT: multicast is broken over libvirt bridges
  FIX: set a (new, introduced by a new kernel) toggle on the bridges
  TEST CASE: cat /sys/devices/virtual/net/virbr0/bridge/multicast_querier - if 0, then forwarding multicast will be broken.
  REGRESSION POTENTIAL: should be none. older kernels do not have the toggle, and failure to set it will be ignored

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