In Windows2000 domains, the domain mode in which all domain controllers in a domain are running Windows2000 and a domain administrator has switched the domain operation mode from mixed mode to native mode. Native mode supports universal groups and nesting of groups. In native mode, domain controllers running WindowsNT4.0 or earlier are not supported. In Windows Server2003 domains, native mode is referred to as 'Windows2000 native', and it is one of three domain functional levels available.