>In the same communication line we have 2 domains. I like to give access to some users of domain1 to resources in Domain2.
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>How can I give access to users of Domain1 to the resources of Domain2?

You need to set up a trust relation between Domain2 and Domain1, such that some set of users in Domain1 are recognized as trusted users of Domain2. Domain2 then relies on Domain1's validation of group membership or user identity to grant access to Domain2 resources. You do not need to set up a reciprocal trust relation unless you need members of DOmain2 to access resources of Domain1.

There's a good deal of information on trust relations at John Savill's NT FAQ Web Page; it's one of the best open resources on NT on the Web, and it's updated at least weekly with new information. Add it to your favorites...