How to resolve ORA-12518: TNS:listener could not hand off client connection

Step1) Try to connect with db string

C:\Windows\System32>sqlplus sys/oracle_4U@db11g as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Wed Jan 31 16:43:40 2018

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

ERROR:
ORA-12518: TNS:listener could not hand off client connection

We observe  the ORA-12518 error.

Step 2) This issue occurs usually in window server if oracle services are not running. Lets check the services in services.msc. In my case its not running so I started the services and issue resolved.

C:\Windows\System32>net start oracleservicedb11g
The OracleServicedb11g service is starting.
The OracleServicedb11g service was started successfully.


C:\Windows\System32>SQLPLUS sys/oracle_4U@db11g as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Wed Jan 31 16:43:59 2018

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area 3390558208 bytes
Fixed Size                  2259920 bytes
Variable Size            2432697392 bytes
Database Buffers          939524096 bytes
Redo Buffers               16076800 bytes
Database mounted.
Database opened.