Some network services can only be used by SCS hosts, either because access has been restricted to particular host names or IP addresses, or because of the way the network is configured. Services that can usually only be done by SCS hosts include:

Access to the network neighborhood to browse our Windows domain
Access to certain protected web pages.
Use of the SCS netnews server, dnntp.srv.cs.cmu.edu, to read netnews.
Use of our mail servers to relay mail.