This is useful when you have domain application which frequently requires access to one of the domain controllers. Since the domain controller is busy responding to application requests, sometimes it may fail to respond to client authentication requests. To alleviate this, you may designate a domain controller for client authentications so that clients always use this domain controller as their primary authenticator. When clients query DNS Server for the domain controllers, they get a list of domain controllers with priority.
For example, query returns:
_exmp1.tcp.domain.com IN SRV 10 50 389 server1.domain.com _exmp1.tcp.domain.com IN SRV 10 50 389 server2.domain.com _exmp1.tcp.domain.com IN SRV 10 50 389 server3.domain.com
In above example, 10 is the priority and 50 is the weight of the server1.domain.com. Clients will always use server1.domain.com for authentication purpose if it is available on the network. If you want your client machines to always use Server2.domain.com then change the priority of Server2.domain.com in DNS management snap-in.
Clients will always use the server name with lowest priority first. For example, you have changed SRV priority of Server2 from 10 to 6. After changing the priority, the DNS query will return the list of domain controllers in the following order:
_exmp1.tcp.domain.com IN SRV 6 50 389 server2.domain.com _exmp1.tcp.domain.com IN SRV 10 50 389 server1.domain.com _exmp1.tcp.domain.com IN SRV 10 50 389 server3.domain.com
For more information on SRV Records, please check out here: Description of DNS SRV Records.