scan failover

Hello,

Why the below TNS entry doesn't allow the client sessions to failover if the instance has been stopped. Knowing that the failover occurs if the node where the instance was shut down.

TESTDB = 

(DESCRIPTION =

  (ADDRESS = (PROTOCOL = TCP)(HOST = scan-name.domain)(PORT = 1521))

  (CONNECT_DATA =

      (SERVER = DEDICATED)

      (SERVICE_NAME = testdb)

    )

  )

Rgds,

Joseph