| Platform SDK: Active Directory, ADSI, and Directory Services |
Active Directory servers publish their addresses such that clients can find them knowing only the domain name. Active Directory servers are published using the Service Resource Records (SRV RRs) in DNS. The SRV RR is a DNS record used to map the name of a service to the address of a server offering that service. The name of a SRV RR is in this form:
<service>.<protocol>.<domain>
Active Directory servers offer the LDAP service over the TCP protocol so that published names are "ldap.tcp.<domain>". Thus, the SRV RR for Microsoft.Com is "ldap.tcp.microsoft.com". Additional information on the SRV RR indicates the priority and weight for the server, allowing clients to choose the best server for their needs.
When an Active Directory server is installed, it uses Dynamic DNS to publish itself. Since TCP/IP addresses are subject to change over time, servers periodically check their registrations to make sure they are correct, updating them if necessary.
Dynamic DNS is a recent addition to the DNS standard. Dynamic DNS defines a protocol for updating a DNS server with new or changed values dynamically. Prior to Dynamic DNS, administrators needed to manually configure the records stored by DNS servers.