It also happens with 10 VMs each with one interface.

Note: it happens consistently after a reload of the Nexus switches.

The following tracebacks are logged in screen-q-svc.log:

 from (pid=30887) _edit_config /opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/nexus_network_driver.py:86
2014-12-06 17:09:26.063 ERROR neutron.plugins.ml2.managers [req-d8c65cd0-138f-4397-8d78-86f5196260ca None None] Mechanism driver 'cisco_nexus' failed in update_port_postcommit
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers Traceback (most recent call last):
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 299, in _call_on_drivers
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     getattr(driver.obj, method_name)(context)
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/mech_cisco_nexus.py", line 378, in update_port_postcommit
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     self._configure_nve_member) if vxlan_segment else 0
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/mech_cisco_nexus.py", line 325, in _port_action_vxlan
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     func(vni, device_id, mcast_group, host_id)
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/mech_cisco_nexus.py", line 135, in _configure_nve_member
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     vni, mcast_group)
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/nexus_network_driver.py", line 308, in create_nve_member
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     self._edit_config(nexus_host, config=confstr)
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/nexus_network_driver.py", line 94, in _edit_config
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     raise cexc.NexusConfigFailed(config=config, exc=e)
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers NexusConfigFailed: Failed to configure Nexus: 
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers       <config xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers         <configure>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers           <__XML__MODE__exec_configure>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers <interface>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     <nve>nve1</nve>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     <__XML__MODE_if-nve>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers         <member>member vni 9000 mcast-group 225.1.1.1</member>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers     </__XML__MODE_if-nve>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers </interface>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers 
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers           </__XML__MODE__exec_configure>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers         </configure>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers       </config>
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers . Reason: Unexpected session close
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers IN_BUFFER: `Unexpected session close`.
2014-12-06 17:09:26.063 TRACE neutron.plugins.ml2.managers 
2014-12-06 17:09:26.065 ERROR oslo.messaging.rpc.dispatcher [req-d8c65cd0-138f-4397-8d78-86f5196260ca None None] Exception during message handling: update_port_postcommit failed.
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher Traceback (most recent call last):
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 134, in _dispatch_and_reply
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher     incoming.message))
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 177, in _dispatch
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher     return self._do_dispatch(endpoint, method, ctxt, args)
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 123, in _do_dispatch
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher     result = getattr(endpoint, method)(ctxt, **new_args)
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/rpc.py", line 161, in update_device_up
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher     host)
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/plugin.py", line 1196, in update_port_status
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher     self.mechanism_manager.update_port_postcommit(mech_context)
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 535, in update_port_postcommit
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher     continue_on_failure=True)
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 310, in _call_on_drivers
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher     method=method_name
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher MechanismDriverError: update_port_postcommit failed.
2014-12-06 17:09:26.065 TRACE oslo.messaging.rpc.dispatcher 
2014-12-06 17:09:26.067 ERROR oslo.messaging._drivers.common [req-d8c65cd0-138f-4397-8d78-86f5196260ca None None] Returning exception update_port_postcommit failed. to caller
2014-12-06 17:09:26.067 ERROR oslo.messaging._drivers.common [req-d8c65cd0-138f-4397-8d78-86f5196260ca None None] ['Traceback (most recent call last):\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 134, in _dispatch_and_reply\n    incoming.message))\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 177, in _dispatch\n    return self._do_dispatch(endpoint, method, ctxt, args)\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 123, in _do_dispatch\n    result = getattr(endpoint, method)(ctxt, **new_args)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/rpc.py", line 161, in update_device_up\n    host)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/plugin.py", line 1196, in update_port_status\n    self.mechanism_manager.update_port_postcommit(mech_context)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 535, in update_port_postcommit\n    continue_on_failure=True)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 310, in _call_on_drivers\n    method=method_name\n', 'MechanismDriverError: update_port_postcommit failed.\n']
2014-12-06 17:09:26.248 ERROR neutron.plugins.ml2.managers [req-8ddb58ad-69a3-4310-9757-c444ae0bccaf None None] Mechanism driver 'cisco_nexus' failed in update_port_postcommit
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers Traceback (most recent call last):
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 299, in _call_on_drivers
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     getattr(driver.obj, method_name)(context)
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/mech_cisco_nexus.py", line 378, in update_port_postcommit
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     self._configure_nve_member) if vxlan_segment else 0
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/mech_cisco_nexus.py", line 325, in _port_action_vxlan
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     func(vni, device_id, mcast_group, host_id)
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/mech_cisco_nexus.py", line 135, in _configure_nve_member
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     vni, mcast_group)
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/nexus_network_driver.py", line 308, in create_nve_member
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     self._edit_config(nexus_host, config=confstr)
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers   File "/opt/stack/neutron/neutron/plugins/ml2/drivers/cisco/nexus/nexus_network_driver.py", line 94, in _edit_config
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     raise cexc.NexusConfigFailed(config=config, exc=e)
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers NexusConfigFailed: Failed to configure Nexus: 
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers       <config xmlns:xc="urn:ietf:params:xml:ns:netconf:base:1.0">
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers         <configure>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers           <__XML__MODE__exec_configure>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers <interface>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     <nve>nve1</nve>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     <__XML__MODE_if-nve>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers         <member>member vni 9000 mcast-group 225.1.1.1</member>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers     </__XML__MODE_if-nve>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers </interface>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers 
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers           </__XML__MODE__exec_configure>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers         </configure>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers       </config>
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers . Reason: Unexpected session close
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers IN_BUFFER: `Unexpected session close`.
2014-12-06 17:09:26.248 TRACE neutron.plugins.ml2.managers 
2014-12-06 17:09:26.249 ERROR oslo.messaging.rpc.dispatcher [req-8ddb58ad-69a3-4310-9757-c444ae0bccaf None None] Exception during message handling: update_port_postcommit failed.
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher Traceback (most recent call last):
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 134, in _dispatch_and_reply
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher     incoming.message))
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 177, in _dispatch
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher     return self._do_dispatch(endpoint, method, ctxt, args)
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 123, in _do_dispatch
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher     result = getattr(endpoint, method)(ctxt, **new_args)
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/rpc.py", line 161, in update_device_up
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher     host)
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/plugin.py", line 1196, in update_port_status
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher     self.mechanism_manager.update_port_postcommit(mech_context)
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 535, in update_port_postcommit
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher     continue_on_failure=True)
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher   File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 310, in _call_on_drivers
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher     method=method_name
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher MechanismDriverError: update_port_postcommit failed.
2014-12-06 17:09:26.249 TRACE oslo.messaging.rpc.dispatcher 
2014-12-06 17:09:26.251 ERROR oslo.messaging._drivers.common [req-8ddb58ad-69a3-4310-9757-c444ae0bccaf None None] Returning exception update_port_postcommit failed. to caller
2014-12-06 17:09:26.251 ERROR oslo.messaging._drivers.common [req-8ddb58ad-69a3-4310-9757-c444ae0bccaf None None] ['Traceback (most recent call last):\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 134, in _dispatch_and_reply\n    incoming.message))\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 177, in _dispatch\n    return self._do_dispatch(endpoint, method, ctxt, args)\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo/messaging/rpc/dispatcher.py", line 123, in _do_dispatch\n    result = getattr(endpoint, method)(ctxt, **new_args)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/rpc.py", line 161, in update_device_up\n    host)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/plugin.py", line 1196, in update_port_status\n    self.mechanism_manager.update_port_postcommit(mech_context)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 535, in update_port_postcommit\n    continue_on_failure=True)\n', '  File "/opt/stack/neutron/neutron/plugins/ml2/managers.py", line 310, in _call_on_drivers\n    method=method_name\n', 'MechanismDriverError: update_port_postcommit failed.\n']