def add_snmp(data, interfaces):
    """
    Format data for adding SNMP to an engine.
    
    :param list data: list of interfaces as provided by kw
    :param list interfaces: interfaces to enable SNMP by id
    """
    snmp_interface = []
    if interfaces: # Not providing interfaces will enable SNMP on all NDIs
        interfaces = map(str, interfaces)
        for interface in data:
            interface_id = str(interface.get('interface_id'))
            for if_def in interface.get('interfaces', []):
                _interface_id = None
                if 'vlan_id' in if_def:
                    _interface_id = '{}.{}'.format(
                        interface_id, if_def['vlan_id'])
                else:
                    _interface_id = interface_id
                if _interface_id in interfaces and 'type' not in interface:
                    for node in if_def.get('nodes', []):
                        snmp_interface.append(
                            {'address': node.get('address'),
                             'nicid': _interface_id})
    return snmp_interface