state:blocked in the listener service view

PROBLEM

When I try to log in to the listener service for a particular listener, I found the state has been specified as BLOCKED.

oracle> lsnrctl service LISTENER_SCAN1

LSNRCTL for Linux: Version 11.2.0.2.0 - Production on 20-DEC-2011 13:13:13

Copyright (c) 1991, 2010, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1)))

Services Summary...

Service "BHU_A" has 1 instance(s).

  Instance "BHU_2", status READY, has 1 handler(s) for this service...

    Handler(s):

      "DEDICATED" established:0 refused:0 state:blocked

         REMOTE SERVER

         (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=bhuora02-vip)(PORT=1532)))

Service "BHU_B" has 2 instance(s).

  Instance "BHU_1", status READY, has 1 handler(s) for this service...

    Handler(s):

      "DEDICATED" established:0 refused:0 state:ready

         REMOTE SERVER

         (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=bhuora01-vip)(PORT=1532)))

  Instance "BHU_2", status READY, has 1 handler(s) for this service...

    Handler(s):

      "DEDICATED" established:1 refused:0 state:ready

         REMOTE SERVER

         (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=bhuora02-vip)(PORT=1532)))

POSSIBLE CAUSE OF THIS ISSUE

1) When the listener believes the current number of connections has reached maximum load, it may set the state of the service handler for an instance to "blocked" and begin refusing incoming client connections with either of the following errors:

Below error will be appeared on the listener log

TNS-12516 , TNS-12519 , TNS-12520

Sol: check the select * from gv$resource_limit;

Check for the sessions & processes, whether it has reached the MAX_UTILIZATION & CURRENT_UTILIZATION. It is nearing to the allocate value then try to increase the sessions & processes values for the database.

2) In RAC scenarios, if any one modifies(put a incorrect)  either primary instance or standby instance listener parameters like local_listener,remote_listener & listener_networks. Then primary database listener might registries in the standby database – vice versa then it will place the state as BLOCKED.

Sol: verify all the listener parameters & ports are property specified for each instance in the cluster database