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[Launchpad Bug Tracker <1894843@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package neutron - 2:17.1.0-0ubuntu3

---------------
neutron (2:17.1.0-0ubuntu3) groovy; urgency=medium

  * d/p/revert-dvr-remove-control-plane-arp-updates.patch: Cherry-picked
    from https://review.opendev.org/c/openstack/neutron/+/777903 to prevent
    permanent arp entries that never get deleted (LP: #1916761).
  * d/p/improve-get-devices-with-ip-performance.patch: Performance of
    get_devices_with_ip is improved to limit the amount of information
    to be sent and reduce the number of syscalls. (LP: #1896734).

neutron (2:17.1.0-0ubuntu2) groovy; urgency=medium

  * Backport fix for dvr-snat missig rfp interfaces (LP: #1894843)
    - d/p/0001-Fix-deletion-of-rfp-interfaces-when-router-is-re-ena.patch

neutron (2:17.1.0-0ubuntu1) groovy; urgency=medium

  * d/watch: Fix typo in watch URL, add trailing slash.
  * New stable point release for OpenStack Victoria (LP: #1915785).
  * d/p/fix-removal-of-dvr-src-mac-flows.patch,
    d/p/ovn-fix-inconsistent-igmp-configuration.patch: Removed after fix landed
    upstream.

 -- Corey Bryant <corey.bryant@xxxxxxxxxxxxx>  Mon, 08 Mar 2021 13:00:21
-0500

** Changed in: neutron (Ubuntu Groovy)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1894843

Title:
  [dvr_snat] Router update deletes rfp interface from qrouter even when
  VM port is present on this host

Status in Ubuntu Cloud Archive:
  Fix Committed
Status in Ubuntu Cloud Archive queens series:
  New
Status in Ubuntu Cloud Archive rocky series:
  New
Status in Ubuntu Cloud Archive stein series:
  New
Status in Ubuntu Cloud Archive train series:
  New
Status in Ubuntu Cloud Archive ussuri series:
  Fix Committed
Status in Ubuntu Cloud Archive victoria series:
  Fix Committed
Status in neutron:
  Fix Released
Status in neutron package in Ubuntu:
  Fix Released
Status in neutron source package in Bionic:
  New
Status in neutron source package in Focal:
  Fix Released
Status in neutron source package in Groovy:
  Fix Released
Status in neutron source package in Hirsute:
  Fix Released

Bug description:
  [Impact]
  When neutron schedules snat namespaces it sometimes deletes the rfp interface from qrouter namespaces which breaks external network (fip) connectivity. The fix prevents this from happening.

  [Test Case]
   * deploy Openstack (Ussuri or above) with dvr_snat enabled in compute hosts.
   * ensure min. 2 compute hosts
   * create one ext network and one private network
   * add private subnet to router and ext as gateway
   * check which compute has the snat ns (ip netns| grep snat)
   * create a vm on each compute host
   * check that qrouter ns on both computes has rfp interface
   * ip netns| grep qrouter; ip netns exec <ns> ip a s| grep rfp
   * disable and re-enable router
   * openstack router set --disable <router>;  openstack router set --enable <router>
   * check again
   * ip netns| grep qrouter; ip netns exec <ns> ip a s| grep rfp

  [Where problems could occur]
  This patch is in fact restoring expected behaviour and is not expected to
  introduce any new regressions.

  -------------------------------------------------------------------------

  Hello,

  In the case of dvr_snat l3 agents are deployed on hypervisors there
  can be race condition. The agent creates snat namespaces on each
  scheduled host and removes them at second step. At this second step
  agent removes the rfp interface from qrouter even when there is VM
  with floating IP on the host.

  When VM is deployed at the time of second step we can lost external
  access to VMs floating IP. The issue can be reproduced by hand:

  1. Create tenant network and router with external gateway
  2. Create VM with floating ip
  3. Ensure that VM on the hypervisor without snat-* namespace
  4. Set the router to disabled state (openstack router set --disable <router>)
  5. Set the router to enabled state (openstack router set --enabled <router>)
  6. The external access to VMs FIP have lost because L3 agent creates the qrouter namespace without rfp interface.

  Environment:

  1. Neutron with ML2 OVS plugin.
  2. L3 agents in dvr_snat mode on each hypervisor
  3. openstack-neutron-common-15.1.1-0.20200611111910.7d97420.el8ost.noarch

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