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Analysis of the Security of  Windows NT 1 March 1999 33 Another attractive feature with PPTP is the fact that it enables Internet as a backbone network for other protocols then TCP/IP. For example, both NwLink and NetBEUI can be encapsulated in PPTP packets. The RAS protocol is an elder protocol used in NT 3.1, which is used in other operating systems’ environments as well. Due to backward compatibility promises, it is still sup- ported in NT 4.0, but we will not describe it further in this report. SLIP [51], [52] is an old communication protocol used originally on UNIX systems. This protocol is supported in NT RAS clients, but it cannot be used to connect to a RAS server. However, it can be used to connect to, for example, an Internet Service Provider (ISP), assumed that the ISP supports SLIP. Note, SLIP supports only TCP/IP.