Windows 2008 R2 Domain Forest Trust to Windows 2012 R2

To create a forest trust, the minimum forest functional level for the forests that are involved in the trust relationship is Windows Server 2003.

You can create a forest trust between two Windows Server 2003 forests, between two Windows Server 2008 forests, between two Windows Server 2008 R2 forests, between a Windows Server 2003 forest and a Windows Server 2008 forest, between a Windows Server 2003 forest and a Windows Server 2008 R2 forest, or between a Windows Server 2008 forest and a Windows Server 2008 R2 forest.

Configuring Selective Authentication Settings

Trusts that are created between Windows Server 2008 forests can use legacy authentication settings (settings that were used in Windows 2000 Server) or selective authentication. Selective authentication is a security setting that can be enabled on external trusts and forest trusts between Windows Server 2003 forests and Windows Server 2008 forests, in any combination. Selective authentication provides Active Directory administrators who manage a trusting forest more control over which groups of users in a trusted forest can access shared resources in the trusting forest. Because creating an external trust or forest trust provides a pathway for all authentication requests between the forests, this increased control is especially important when administrators need to grant access to shared resources in their organization’s forest to a limited set of users in another organization’s forest.


-- Kindly take a look at the below document, hope it helps.

https://technet.microsoft.com/en-us/library/cc816580(v=ws.10).aspx

Thank you very much for your feed back... The one item I am still fuzzy on is after the trust is setup, this does not automatically provide authentication or does it if using domain wide authentication????

When establishing a domain trust there is two options for defining the way that users from the trusted domain authenticate to the trusting domain.
1.
The domain-wide authentication setting permits unrestricted access by any users in the trusted domain to all available shared resources in the trusting domain. This is the default authentication setting for external trusts.
With this method users from the trusted domain are able to access servers, services, shares and files with normal NTFS and share permissions.

2.
Selective authentication” takes a “deny all” approach explicitly blocking all access at the server level to all users who are not explicitly granted the “Allowed to authenticate” permission.
*With this method administrators must grant rights to each system they wish to allow access to in addition to the NTFS and share permissions. It is an extra level and security and may give your domain administrators a little ease when considering the domain trust risks.

Thank you very much.. I understand the difference between domain wide and selective authentication but trying to confirm that just setting up a trust does not grant permission correct? Or does it if using domain wide?

Hi

It is totally depends on the What type authentication you have set up.

Domain-wide : Authentication External Permits unrestricted access by any users. Default authentication setting for external trusts.
Forest-wide : Authentication Forest Permits unrestricted access by any users. Default authentication setting for forest trusts.
Selective Authentication :  External and Forest Restricts access over an external Authentication setting must be manually enabled


For more info refer below links:

https://araihan.wordpress.com/2009/08/05/how-to-create-an-external-trust-between-two-domains/

http://www.tech-faq.com/understanding-trust-relationships.html

So if you setup the trust with domain wide authentication that access is automatically granted correct?