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[Rodolfo Alonso <1732445@xxxxxxxxxxxxxxxxxx>]

Bug closed due to lack of activity, please feel free to reopen if
needed.

** Changed in: neutron
       Status: Confirmed => Won't Fix

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https://bugs.launchpad.net/bugs/1732445

Title:
  dhcp scheduled to node without l2 segment access

Status in neutron:
  Won't Fix

Bug description:
  In a past release a feature was introduced to make DHCP scheduling
  physical network aware [1].  While that commit addressed the simple
  case of each node only having a single L2 agent running it makes it
  clear in the description that it does not support cases where two L2
  agents (e.g., OVS + SRIOV) exist on the same node.  In such a
  configuration it is possible for the SRIOV mechanism driver to report
  that it has access to a segment while the OVS mechanism driver reports
  that it does not.  Since the ML2 plugin [2] assumes that a host has
  access to a segment as long as one mechanism driver reports that it
  does it will cause the DHCP scheduler to create a binding on a host
  that potentially does not have L2 access to that segment.

  We have run it to this problem in stable/newton but the most recent
  code in master appears to also have this same limitation.

  The configuration to reproduce this is simple.  Create a compute node
  where the OVS agent reports interface mappings to physnet0 and the
  SRIOV agent reports device mappings to physnet1.  Then create a
  network with provider:physical_network=physnet1 with a DHCP enabled
  subnet and the DHCP scheduler will allow scheduling of that network to
  the node when it should not because the OVS agent does not have access
  to physnet1.

  [1] https://git.openstack.org/cgit/openstack/neutron/commit/?id=0267c6a5acdcb68ea7e83ecb980362c4235ed1d7
  [2] neutron.db.agents_db.AgentDbMixin.filter_hosts_with_network_access

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