No more actions need to be operated on the part of the trusted domain.
After you switching from a Domain level authentication to Selective authentication, you also need to be granted "Allowed to Authenticate" right on the file server if the users from the trusted forest want to access resources from the trusting forest.
To assign the permission:
- Login to local domain controller where the resource (workstation) resides. Open AD Users and computers – switch to Advanced Features view.
Find the workstation you are trying to login to – right click – properties – security tab.
- Under group or Usernames – click Add.
- Select Locations – select domain that contains the user account trying to login.
- Enter username – click OK – authenticate with account that has access.
- Select user – then in permissions for user select “allow” for allowed to authenticate.