Sqlnet Listener :- status READY, has 0 handler(s) for this service...

User reported Application servers were unable to connect to sqlnet listener service.
Listener was running, service was READY, but there were 0 handlers for the service.

Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=xxx)(PORT=1560)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=yyy)(PORT=1560)))

Service "TEST" has 1 instance(s).
Instance "zzz", status READY, has 0 handler(s) for this service...

According to Metalink note 885431.1 we can avoid this issue if our listeners use only one end-point. We need to listen on the VIP address, but don't need to listen on the HOST address.

E.g change

LISTENER_XXX =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = myvip)(PORT = 1560)(IP = FIRST))
(ADDRESS = (PROTOCOL = TCP)(HOST = myhost)(PORT = 1560)(IP = FIRST))
)
)

To

LISTENER_XXX =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = myvip)(PORT = 1562)(IP = FIRST))
)
)