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. Please refer to the dns_discovery_domain parameter in the sssd.conf 5 manual page for more defails. The queries usually specify _tcp as the protocol. Exceptions are documented in respective option description. For more information on the service discovery mechanism, refer to RFC 2782.