about authentication root of linux in active directory

[Sonoe]

hi.
I'm trying to do the authentication of linux by active
directory.

Environment;
Linux Redhat 8
Windows 2000 Server

I installed pam_krb5 and krb5-libs in the linux, and configure
krb5.conf file and system-auth file, and created 'testuser' both
in linux and w2k machine. then I could login from 'testuser'
of linux by using authentication of Active directory.
However, I don't want to use authentication of active
directory when 'root'(su -) in linux login. What should I do?
When I create 'root' user in active directory, it'll work well.
but I don't think it's good solution.
I created .k5login and .klogin file in '/root' directory
though, it doesn't work...

sononon