SYMPTOMS
After applied 11.2.0.4 Windows Bundle Patch 10, ORA-12638
occurred when trying to connect to database using SQL*Plus:
sqlplus system/password => ORA-12638
CAUSE
NTS is Windows Native authentication where the user is authenticated to the db
based on the OS credentials. NTS code checks group
membership for the OS user.
For example, if the OS user is a member of the ORA_DBA group
then that user can login as sqlplus / as sysdba using NTS authentication.
.
When you specify sqlnet.authentication_services=(NTS) in the sqlnet.ora it is expected that the
client will be authenticated and login to database
using the OS credentials via Windows Native Authentication. No external
password is needed.
.
If you have specified sqlnet.authentication_services=(NTS) in the sqlnet.ora and provide
a username/password the connection should fail with an error.
.
The Oracle documentation recommends to set
'sqlnet.authentication_services=(NONE)' for for regular username/password
based authentication.
http://docs.oracle.com/cd/B19306_01/network.102/b14213/sqlnet.htm
SOLUTION
Use: sqlnet.authentication_services=(NTS) in the sqlnet.ora for OS authentication: sqlplus / as sysdba
Use: sqlnet.authentication_services=None in the sqlnet.ora for External authentication: sqlplus system/password