Identical Usernames In 1 Forest

[Frank A, Zanotti]

Hi,
I just want to confirm something I was testing in my lab. I have one AD
forest with two domains. One Parent and one child (abc.com) and
(xyz.abc.com) which are both in Mixed Mode. I shouldn't be able to create
the same username in both domains even with a different UPN suffix
(@abc.com) and (@xyz.abc.com) because of NetBIOS. Then I switched the child
to Native mode and left the parent in mixed mode and I was able to create
Identical usernames in both domains. Is my testing correct. And my second
question is what happens if I switch the parent to native mode, is it ok to
have identical usernames as long as the UPN suffix is different.

Thanks in Advance
Frank A, Zanotti
(e-mail address removed)

 

[Frank A, Zanotti]

I think I got confused here, In technet it states "A security principal name
is not unique across domains, but, for backward compatibility, it must be
unique within its own domain. I should have read before I Posted.
Sorry for the question.