Windows 2000 Active Directory (AD) uses the service-location mechanism that the Internet Engineering Task Force (IETF) Request for Comments (RFC) 2782 specifies. This RFC shows how clients can use DNS SRV records to locate network services on the network. Each SRV record has the following format:
_Service is the symbolic name of the desired service. AD domain controllers (DCs) publish SRV records for the services that Table A lists. _Proto is the symbolic name of the desired protocol. AD provides services over UDP and TCP. Name is the domain name in which the service is advertised. TTL is the time-to-live value for the SRV record, as RFC 1035 defines. Class is the class of record, as RFC 1035 defines. Priority is a number between 0 and 65,535 that defines in which order a client should attempt to contact the available hosts: Clients must contact target hosts with lower-priority values before hosts with higher values. Weight is a number between 0 and 65,535 that determines how likely the client will be to select this target host, with higher weights having a proportionately higher likelihood of being selected. Port is a number between 0 and 65,535 that signifies the IP port on which the advertised service is available. Target is the Fully Qualified Domain Name (FQDN) of the host providing the service.