ORA-12520 TNS listener could not find available handler

ORA-12520 TNS listener could not find available handler for requested.

This error received from the application team saying that connectivity issue from apps server .

Error: ORA-12520

Verification:

Verified the listener and found it is running.
Verified the connectivity from DBA end with remote connectivity connectivity method.

For example:

$ sqlplus scott/tiger@ORCLP

SQL>

Verified the connectivity from SQL tools like SQL developer and Toad, no connectivity issues found.
Then ruled out that there is no issue from DBA end.
After verifying the issue further with apps team if there is any change on the apps server , found that some n/w changes happened.

Reason :

In the application server ,netmask vale of the front end IP was changed during the maintenance.

Solution:

Platform team reverted the netmask value of the front end IP of the Apps server , issue resolved.

Summary :

Many times issue comes because of change requests(CRs) that were not properly analyzed and implemented.

See also:

ORA-12520 TNS listener could not find available handler