[Bug 1957817] Re: Multicast traffic is broken between VMs on different hypervisors using provider networks

[Frode Nordahl]

Control test:
With basis in the OVN package currently in the Focal Main archive, I added only the functional test part of debian/patches/lp-1957817-ovn-northd-Add-localnet-ports-to-Multicast_Groups-cr.patch

## ----------------------- ##
## ovn 20.03.2 test suite. ##
## ----------------------- ##

OVN end-to-end tests

117: ovn -- IGMP snoop/querier/relay                 FAILED (ovs-macros.at:222)
118: ovn -- MLD snoop/querier/relay                  FAILED (ovs-macros.at:222)

## ------------- ##
## Test results. ##
## ------------- ##

ERROR: All 2 tests were run,
2 failed unexpectedly.

Now instead download source of the proposed package and build it:
## ----------------------- ##
## ovn 20.03.2 test suite. ##
## ----------------------- ##

...

117: ovn -- IGMP snoop/querier/relay                 ok
118: ovn -- MLD snoop/querier/relay                  ok

...
## ------------- ##
## Test results. ##
## ------------- ##

All 242 tests were successful.


** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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https://bugs.launchpad.net/bugs/1957817

Title:
  Multicast traffic is broken between VMs on different hypervisors using
  provider networks

Status in Ubuntu Cloud Archive:
  Fix Released
Status in Ubuntu Cloud Archive ussuri series:
  New
Status in ovn package in Ubuntu:
  Fix Released
Status in ovn source package in Focal:
  Fix Committed

Bug description:
  [Impact]
  In an OpenStack Ussuri (both Focal and Bionic) cloud we discovered that multicast traffic would fail between VMs on different hypervisors and when using provider networks.

  [Test Plan]
  The upstream fix also contains an addition to the OVN testsuite confirming the correct behavior. We cat utilize this test case to perform both a control test on a unmodified package as well as confirming that a updated package fixes the problem.

  [Regression Potential]
  The fix touches a code path that is executed only when OVN is configured to enable handling of Multicast traffic. The fix has also been available for several upstream releases without any reported issues.

  [Original Bug Description]
  In an OpenStack Ussuri (both Focal and Bionic) cloud we discovered that multicast traffic would fail between VMs on different hypervisors and when using provider networks.  The following table reflects what we found works/didn't work:

   https://paste.ubuntu.com/p/QZZBjrTSFQ/

  Based on this, I went looking at relevant changes upstream and found
  that this appears to have been fixed upstream, but not backported to
  OVN 20.03:

  https://github.com/ovn-
  org/ovn/commit/97778ab3e422ac071faa67f9f477fd54977e9c04

  I backported this patch to the version of OVN in Ussuri here:

    https://launchpad.net/~elmo/+archive/ubuntu/sf322809

  These patched packages have been tested on a customer site and
  confirmed to fix the problem.

  I've attached the patch from the PPA for convenience.

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