What in detail does tnsping checks ?

Hi Community,

I have a question concerning functionality of "tnsping" command.

I have a 11gR2 RAC Cluster with an Oracle 11gR2 database running.
Entry in "/u01/app/11.2.0/grid/network/admin/tnsnames.ora:

---snip---
I99 =
  (DESCRIPTION =
    (FAILOVER = yes)
    (ADDRESS = (PROTOCOL = TCP)(HOST = scan1.ora.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = I99)
      (FAILOVER_MODE =
        (TYPE = SELECT)
        (METHOD = BASIC)
      )
    )
  )

I991 =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.ora.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = I99)
      (INSTANCE_NAME = I991)
    )
  )

I992 =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.ora.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = I99)
      (INSTANCE_NAME = I992)