Question : RMAN LISTENER SETUP

Hello, i have to configure oracle data guard on oracle 11g R2 ,  the  connect  to the  auxiliary oracle instance
must be performed on unmounted database and with @dblink format  , this is my result :

RMAN> connect auxiliary sys/****@stanbyDB  
RMAN-04006: error from auxiliary database: ORA-12528: TNS:listener: all appropriate instances are blocking new connections

What is the listener config  for that ?  

Best regards,
Pablo.

Answer : RMAN LISTENER SETUP

does
select system_user
give you what you want.