it's just a config of the tns.

You would have the tnsnames.ora look something like:

TRAP.oracle.com =
(description =
(LOAD_BALANCE=off)
(FAILOVER=ON)
(ADDRESS = (PROTOCOL = TCP)(HOST = xxx.xxx.xxx.xx1)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = xxx.xxx.xxx.xx2)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = xxx.xxx.xxx.xx3)(PORT = 1521))
(CONNECT_DATA =
(SERVICE_NAME = )
)
)

You could subsequently turn on load balancing if you want in this as well. Essentially it tries to connect to the first address and if it cannot then it tries the second address. There are a lot of other options as well. Check out:

http://download-east.oracle.com/docs...cfg.htm#473298