Migrating Active Directory Users and Merging Domains
Imagine you are part of a company. That company is being bought out by a larger company. To ease feelings, new email accounts are created at the larger company (ie This e-mail address is being protected from spambots. You need JavaScript enabled to view it ). The computers remain on the domain of the smaller company (ie @branch.tld).
Now comes a point in time where the larger company wants to join the domains together. What are the options? How do you handle this situation?
Very good questions.
OPTION-1: 1 Forest & 2 Domains
A forest is a group of domains. It is possible to keep the domains separate but still have the same forest. @hq.tld and @branch.tld will live happily together and have a trust-relationship.
Two users would still exist. For example, This e-mail address is being protected from spambots. You need JavaScript enabled to view it and This e-mail address is being protected from spambots. You need JavaScript enabled to view it would still exist which is confusing for people.
OPTION-2: Parent-Child Domain
The parent domain is hq.tld. It is possible to have a child domain such as branch.hq.com (or is you prefer, us.company.tld).
Two users would still exist. For example, This e-mail address is being protected from spambots. You need JavaScript enabled to view it and This e-mail address is being protected from spambots. You need JavaScript enabled to view it would still exist which is confusing for people.
OPTION-3: Flat & Import
This consolidates everything down. It gets rid of messiness and flattens the company to 1 domain of hq.tld.
Only one user exist per person and this makes sense for people.
How To Flatten Domain and Import Users