Unable to join Data Domain to a Specific Organizational Unit (OU) of Active Directory

Verify Forward Lookup & Reverse lookup if DNS is working properly or not.

1. Use the below set of commands to verify both the lookup are working properly.
   • net lookup <Data Domain Host Name>
   • net lookup <Data Domain Interface (ideally the Management interface) IP Address>
   • net lookup <Domain Controller Name>
   • net lookup <Realm Name>

Note : you can use any Windows host in the same Active Directory environment to perform the DNS lookup is the same way, for that the command will be as follows..

• nslookup <Data Domain Host Name>
• nslookup <Data Domain Interface (ideally the Management interface) IP Address>
• nslookup <Domain Controller Name>
• nslookup <Realm Name>  

While joining a Data Domain to a Specific Organizational Unit (OU) of Active Directory it fails, but it joins to the default "Computers" Organizational Unit (OU) successfully.

Two possible causes are there.

1. The Organizational Unit (OU) Specified to join is not following the correct syntax what is expected from Data Domain Operating System.
2. The Administrator does not have privileges to join the Data Domain to that specified Organizational Unit (OU).

Requirements to join the Specific OU of Active directory is very simple and as follows.

• Realm Name (Domain Name) of the active Directory.
• Exact OU Location details as "Parent OU/Child OU/Child OU".
• An Active Directory Administrator who have the permission to join the host to the specified Organizational Unit.

Setting up the organizational-unit in CIFS option
cifs option set organizational-unit "Parent OU Name/Child OU Name"

For example if the OU is INFRA/NAS then the command will be 
cifs option set organizational-unit "INFRA/NAS"

Remember : the "/" is important and it should be Unix type not windows type

Check if the organizational-unit is set to right one or not, command to check is 
cifs option show (Upto DDOS 5.6)
cifs option show all (DDOS 5.7.x and after)

Make sure admin access authentication for CIFS is enabled
Form Data Domain Command Prompt
adminaccess authentication show : Displays the access for CIFS is enabled or not
adminaccess authentication add cifs : Adds the Authentication for CIFS

Joining the Active Directory
cifs set authentication active-directory <Active Directory Realm Name>
Hit Enter, it asks for credential to join Active Directory, The Administrator should have required Admin privilege to join the data domain host to AD.