ORA-12528: TNS Listener all instances are blocked in Dataguard Environment

In this case, we are getting the following error when our database is start in mount / nomount / restricted state. Sometime we faced this while configuring the dataguard Environment.

Error:

C:\Windows\system32>sqlplus /nolog
SQL*Plus: Release 10.2.0.3.0 – Production on Wed Oct 1 19:40:51 2008
Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.
 
SQL> connect sys@dbname as sysdba
Enter password:
ERROR: ORA-12528: TNS:listener: all appropriate instances are blocking new connection

You might get this error if you encounter with Connections via the listener to an instance that is in RESTRICTED status or in NO MOUNT status. The lsnrctl services output will show that the service handler for this instance is in state: BLOCKED or RESTRICTED.
 
Check the status of services by listener commands:

lsnrctl status
lsnrctl services

As example show below the status is blocked for ORCL service:

lsnrctl status
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 11.2.0.1.0 - Production
Start Date                20-DEC-2014 02:39:22
Uptime                    14 days 2 hr. 26 min. 18 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /u01/oracle/product/11.2.0/grid/network/admin/listener.ora
Listener Log File /u01/oracle/diag/tnslsnr/test/listener/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=test)(PORT=1521)))
Services Summary...
Service "ORCL" has 1 instance(s).
  Instance "ORCL", status BLOCKED, has 1 handler(s) for this service...

Solution
In Some cases we need to overcome with this problem like dataguard configuration. In which our standby database is in recover mode means it’s in mounted state for apply the redo logs of primary database. In that case listener status for service is Blocked or RESTRICTED. To overcome from it we used the following parameter in tnsnames.ora file:
 
(UR=A) clause is used for TNS connect strings has been created as an enhancement.*(UR=A)* clause is intended to work with a dynamically registered handler so the use of SERVICE_NAME versus SID is preferred. (ID 362656.1)

Need to modify the tnsnames.ora file for connectivity as shown below:

DBNAME =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = xxx.xxx.xx.xx)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = hostname.rnhub.com)
            (UR = A)
    )
  )