ORA-16665: timeout waiting for the result from a database

$ oerr ora 16665
16665, 0000, "timeout waiting for the result from a database"
// *Cause: The Oracle Data Guard broker was forced to time out a network
// connection to a remote database because:
// - The network call to the remote database did not complete in
// a timely manner.
// - The remote database was unable to execute the command due to
// an instance failure.
// *Action: Check Data Guard broker log files for the details of the failure.
// If the network call did not complete in a timely manner, increase
// the CommunicationTimeout configuration property value and reissue
// the command.