ALL OR NONE

The night before last night we encountered the following on one of our instances (Oracle 11.1.0.7 on RedHat Linux 64bit OS):

sqlplus / as sysdba resulted in the following error message:
ORA-01031: insufficient privileges

After some troubleshooting I found that I could connect as follows:
sqlplus /nolog
Connect sys/ as sysdba

I brought down the rdbms instance and then I brought down the ASM instance and the server was rebooted. Post reboot I brought up the ASM instance with no issues and then proceeded to attempt to startup the rdbms instance. However, this failed with the following errors:

ORA-00210: cannot open the specified control file
ORA-00202: control file: '+DGRP_RAID5_01_0000/control03.ctl'
ORA-17503: ksfdopn:2 Failed to open file +DGRP_RAID5_01_0000/control03.ctl
ORA-15001: diskgroup "DGRP_RAID5_01_0000" does not exist or is not mounted
ORA-15055: unable to connect to ASM instance
ORA-01031: insufficient privileges

I connected to the ASM instance and confirmed that the diskgroup was mounted and that the controlfiles were really there:

select group_number,name,state from v$asm_diskgroup;

GROUP_NUMBER NAME STATE
------------------ ------------------------------ -----------
1 DGRP_RAID5_01_0000 MOUNTED

select a.name FILE_ALIAS, b.name DISKGROUP_NAME
from v$asm_alias a, v$asm_diskgroup b
where a.group_number=b.group_number
order by a.name;

FILE_ALIAS DISKGROUP_NAME
---------------------------------------------------------------------- ------------------------
CONTROLFILE DGRP_RAID5_01_0000
CONTROLFILE DGRP_RAID5_01_0000
CONTROLFILE DGRP_RAID5_01_0000


I then traced it down to an entry in the sqlnet.ora file:
SQLNET.AUTHENTICATION_SERVICES= (NONE)

I changed this to:
SQLNET.AUTHENTICATION_SERVICES= (ALL)

I was then able to login to sqlplus / as sysdba as expected and start the rdbms instance with no issues.