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[Bug 1967996] [NEW] [OVN] External subscribers to feed generated in Openstack fails if no internal VM is subscribed to that feed first

To: yahoo-eng-team@xxxxxxxxxxxxxxxxxxx
From: Diko Parvanov <1967996@xxxxxxxxxxxxxxxxxx>
Date: Wed, 06 Apr 2022 07:19:27 -0000
Reply-to: Bug 1967996 <1967996@xxxxxxxxxxxxxxxxxx>
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Public bug reported:

Commit d02fb560aa35c4931d40000e8ca4c0e4105299b7 (1)(2) to Neutron
disabled 'mcast_flood' on localnet ports, in order to avoid multicast
packet duplication.  This introduces a regression because outbound
multicast traffic from VMs is no longer sent to the provider network
unless it is part of a multicast group that OVN has snooped.  This makes
it impossible for something external to OpenStack to subscribe to a
multicast group running on a VM (in OpenStack) unless another VM (in
OpenStack) subscribes to it first (because the multicast traffic never
leaves the OVS).

In my opinion https://review.opendev.org/c/openstack/neutron/+/797418
has to be reverted and a change implemented in ovn itself.

1 https://review.opendev.org/c/openstack/neutron/+/797418
2 https://bugs.launchpad.net/neutron/+bug/1933207

** Affects: neutron
     Importance: Undecided
         Status: New

** Bug watch added: github.com/ovn-org/ovn/issues #125
   https://github.com/ovn-org/ovn/issues/125

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https://bugs.launchpad.net/bugs/1967996

Title:
  [OVN] External subscribers to feed generated in Openstack fails if no
  internal VM is subscribed to that feed first

Status in neutron:
  New

Bug description:
  Commit d02fb560aa35c4931d40000e8ca4c0e4105299b7 (1)(2) to Neutron
  disabled 'mcast_flood' on localnet ports, in order to avoid multicast
  packet duplication.  This introduces a regression because outbound
  multicast traffic from VMs is no longer sent to the provider network
  unless it is part of a multicast group that OVN has snooped.  This
  makes it impossible for something external to OpenStack to subscribe
  to a multicast group running on a VM (in OpenStack) unless another VM
  (in OpenStack) subscribes to it first (because the multicast traffic
  never leaves the OVS).

  In my opinion https://review.opendev.org/c/openstack/neutron/+/797418
  has to be reverted and a change implemented in ovn itself.

  1 https://review.opendev.org/c/openstack/neutron/+/797418
  2 https://bugs.launchpad.net/neutron/+bug/1933207

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