'Return tenant\'s network associated to auto-allocated topology.
The topology will be provisioned upon return, if network is missing.'

def get_auto_allocated_topology(self, context, tenant_id, fields=None):

    fields = (fields or [])
    tenant_id = self._validate(context, tenant_id)
    if (CHECK_REQUIREMENTS in fields):
        return self._check_requirements(context, tenant_id)
    elif fields:
        raise n_exc.BadRequest(resource='auto_allocate', msg=_('Unrecognized    field'))
    network_id = self._get_auto_allocated_network(context, tenant_id)
    if network_id:
        return self._response(network_id, tenant_id, fields=fields)
    default_external_network = self._get_default_external_network(context)
    network_id = self._build_topology(context, tenant_id, default_external_network)
    return self._response(network_id, tenant_id, fields=fields)
