@Davanum, I am using devstack from the master branch and it is a nova network.

Below is the stack trace from nova-net:

2015-02-10 08:34:09.180 ERROR oslo_messaging.rpc.dispatcher [req-8b1e1d6e-c0d8-49d2-b371-c9e8b3095c84 admin admin] Exception during message handling: Detect
ed existing vlan with id 100
Traceback (most recent call last):

  File "/opt/stack/nova/nova/conductor/manager.py", line 412, in _object_dispatch
    return getattr(target, method)(context, *args, **kwargs)

  File "/opt/stack/nova/nova/objects/base.py", line 206, in wrapper
    return fn(self, ctxt, *args, **kwargs)

  File "/opt/stack/nova/nova/objects/network.py", line 177, in create
    db_network = db.network_create_safe(context, updates)

  File "/opt/stack/nova/nova/db/api.py", line 973, in network_create_safe
    return IMPL.network_create_safe(context, values)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 125, in wrapper
    return f(*args, **kwargs)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 2743, in network_create_safe
    raise exception.DuplicateVlan(vlan=values['vlan'])

DuplicateVlan: Detected existing vlan with id 100

2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher Traceback (most recent call last):
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 142, in _
dispatch_and_reply
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     executor_callback))
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 186, in _
dispatch
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     executor_callback)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 130, in _
do_dispatch
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     result = func(ctxt, **new_args)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/network/manager.py", line 2068, in create_networks
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     self, context, vpn=True, **kwargs)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/network/manager.py", line 1207, in create_networks
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     return self._do_create_networks(context, **kwargs)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/network/manager.py", line 1380, in _do_create_networks
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     net.create()
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/objects/base.py", line 191, in wrapper
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     ctxt, self, fn.__name__, args, kwargs)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/conductor/rpcapi.py", line 370, in object_action
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     objmethod=objmethod, args=args, kwargs=kwargs)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/client.py", line 156, in call
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     retry=self.retry)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/transport.py", line 90, in _send
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     timeout=timeout, retry=retry)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/_drivers/amqpdriver.py", line 417,
 in send
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     retry=retry)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/_drivers/amqpdriver.py", line 408,
 in _send
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     raise result
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher DuplicateVlan_Remote: Detected existing vlan with id 100
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher Traceback (most recent call last):
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/conductor/manager.py", line 412, in _object_dispatch
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     return getattr(target, method)(context, *args, **kwargs)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/objects/base.py", line 206, in wrapper
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     return fn(self, ctxt, *args, **kwargs)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/objects/network.py", line 177, in create
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     db_network = db.network_create_safe(context, updates)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/db/api.py", line 973, in network_create_safe
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     return IMPL.network_create_safe(context, values)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 125, in wrapper
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     return f(*args, **kwargs)
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher   File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 2743, in network_create_safe
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher     raise exception.DuplicateVlan(vlan=values['vlan'])
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher DuplicateVlan: Detected existing vlan with id 100
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.180 TRACE oslo_messaging.rpc.dispatcher 
2015-02-10 08:34:09.182 ERROR oslo_messaging._drivers.common [req-8b1e1d6e-c0d8-49d2-b371-c9e8b3095c84 admin admin] Returning exception Detected existing vl
an with id 100
Traceback (most recent call last):

  File "/opt/stack/nova/nova/conductor/manager.py", line 412, in _object_dispatch
    return getattr(target, method)(context, *args, **kwargs)

  File "/opt/stack/nova/nova/objects/base.py", line 206, in wrapper
    return fn(self, ctxt, *args, **kwargs)

  File "/opt/stack/nova/nova/objects/network.py", line 177, in create
    db_network = db.network_create_safe(context, updates)

  File "/opt/stack/nova/nova/db/api.py", line 973, in network_create_safe
    return IMPL.network_create_safe(context, values)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 125, in wrapper
    return f(*args, **kwargs)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 2743, in network_create_safe
    raise exception.DuplicateVlan(vlan=values['vlan'])

DuplicateVlan: Detected existing vlan with id 100
 to caller
2015-02-10 08:34:09.182 ERROR oslo_messaging._drivers.common [req-8b1e1d6e-c0d8-49d2-b371-c9e8b3095c84 admin admin] ['Traceback (most recent call last):\n',
 '  File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 142, in _dispatch_and_reply\n    executor_callback))\n', '  File "/
usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 186, in _dispatch\n    executor_callback)\n', '  File "/usr/local/lib/python2.
7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 130, in _do_dispatch\n    result = func(ctxt, **new_args)\n', '  File "/opt/stack/nova/nova/network/
manager.py", line 2068, in create_networks\n    self, context, vpn=True, **kwargs)\n', '  File "/opt/stack/nova/nova/network/manager.py", line 1207, in crea
te_networks\n    return self._do_create_networks(context, **kwargs)\n', '  File "/opt/stack/nova/nova/network/manager.py", line 1380, in _do_create_networks
\n    net.create()\n', '  File "/opt/stack/nova/nova/objects/base.py", line 191, in wrapper\n    ctxt, self, fn.__name__, args, kwargs)\n', '  File "/opt/st
ack/nova/nova/conductor/rpcapi.py", line 370, in object_action\n    objmethod=objmethod, args=args, kwargs=kwargs)\n', '  File "/usr/local/lib/python2.7/dis
t-packages/oslo_messaging/rpc/client.py", line 156, in call\n    retry=self.retry)\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/transp
ort.py", line 90, in _send\n    timeout=timeout, retry=retry)\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/_drivers/amqpdriver.py", li
ne 417, in send\n    retry=retry)\n', '  File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/_drivers/amqpdriver.py", line 408, in _send\n    raise 
result\n', 'DuplicateVlan_Remote: Detected existing vlan with id 100\nTraceback (most recent call last):\n\n  File "/opt/stack/nova/nova/conductor/manager.p
y", line 412, in _object_dispatch\n    return getattr(target, method)(context, *args, **kwargs)\n\n  File "/opt/stack/nova/nova/objects/base.py", line 206, 
in wrapper\n    return fn(self, ctxt, *args, **kwargs)\n\n  File "/opt/stack/nova/nova/objects/network.py", line 177, in create\n    db_network = db.network
_create_safe(context, updates)\n\n  File "/opt/stack/nova/nova/db/api.py", line 973, in network_create_safe\n    return IMPL.network_create_safe(context, va
lues)\n\n  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 125, in wrapper\n    return f(*args, **kwargs)\n\n  File "/opt/stack/nova/nova/db/sqlalche
my/api.py", line 2743, in network_create_safe\n    raise exception.DuplicateVlan(vlan=values[\'vlan\'])\n\nDuplicateVlan: Detected existing vlan with id 100
\n\n']