LISTENERS arguments in RAC installation

 As part of RAC installation, prior to the creation of ASM and Database instances, we ran the netca tool

from ASM_HOME/bin and created a listener on the cluster. The configuration completed successfully and it 

created listener.ora on both nodes

NODE-1

LISTENER_RACNODE1 =

  (DESCRIPTION_LIST =

    (DESCRIPTION =

      (ADDRESS = (PROTOCOL = TCP)(HOST = RACNODE1-vip)(PORT = 1521)(IP = FIRST))

      (ADDRESS = (PROTOCOL = TCP)(HOST = RACNODE1)(PORT = 1521)(IP = FIRST))

    )

  )

NODE-2

LISTENER_RACNODE2 =

  (DESCRIPTION_LIST =

    (DESCRIPTION =

      (ADDRESS = (PROTOCOL = TCP)(HOST = RACNODE2-vip)(PORT = 1521)(IP = FIRST))

      (ADDRESS = (PROTOCOL = TCP)(HOST = RACNODE2)(PORT = 1521)(IP = FIRST))

    )

  )

Questions:

1.Why does the listener.ora have VIP as the first address and the public ip of the node as second address? What does this acheive?