Active Directory servers publish their addresses so that clients can find from their own domain names. Active Directory servers are published in the DNS resource records through services (SRV RR - Resource Record Service). The resource record of service is a DNS record used to map the name of a service address of a server offering that service. Its name is of the form:
<Service>. <Protocol>. <Domain>Active Directory servers offer the service LDAP (Lightweight Directory Access Protocol) over TCP so that the names published in the form:
ldap.tcp.Thus, the registration service resource for "Microsoft.com" is "ldap.tcp.microsoft.com".