It is possible to login to child and parent domain using a single user id which user id has been created in parent domain .

Hello, you can create a root domain and a child domain using a user that is member of the Enterprise Administrator Builtin group. This posting is provided "AS IS" with no warranties or guarantees , and confers no rights. Microsoft Student Partner Microsoft Certified Professional Microsoft Certified Systems Administrator: Security Microsoft Certified Systems Engineer: Security Microsoft Certified Technology Specialist: Windows Server 2008 Active Directory, Configuration Microsoft Certified Technology Specialist: Windows Server 2008 Network Infrastructure, Configuration Microsoft Certified Technology Specialist: Windows Server 2008 Applications Infrastructure, Configuration

It is possible to login to child and parent domain using a single user id which user id has been created in parent domain . Yes, in order for that user to have permissions in any part of the part of the parent domain, it will need to be part of a Global Security Group within that domain. It's domain trusts and federation services that are more tricky to deal with... Best Regards,Steve Kline Microsoft Certified IT Professional: Server Administrator Microsoft Certified Technology Specialist: Active Directory, Network Infrastructure, Application Platform, Windows 7 Microsoft Certified Product Specialist & Network Product Specialist Red Hat Certified System Administrator This posting is "as is" without warranties and confers no rights.