The service discovery feature allows back ends to automatically find the appropriate servers to connect to using a special DNS query. If no servers are specified, the back end automatically uses service discovery to try to find a server. Optionally, the user may choose to use both fixed server addresses and service discovery by inserting a special keyword, _srv_, in the list of servers. The order of preference is maintained. This feature is useful if, for example, the user prefers to use service discovery whenever possible, and fall back to a specific server when no servers can be discovered using DNS. The name of the SSSD domain is used as the domain part of the service discovery DNS query. For more information on the service discovery mechanism, refer to RFC 2782.