When configuring the user segment sharing feature, you must specify an ATG server to act as the user segment server. This server responds to requests for the list of ATG user segments. You should use the Content Administration server as the user segment server. Doing so ensures that the list of user segments that is passed to Experience Manager only contains segments that have been checked into Content Administration and deployed to the production server. It also ensures that user segment requests and responses occur in a secure environment. By default, a Content Administration server, as configured via CIM, is able to function as the user segment server.