nt-part2_31
Analysis of the Security of Windows NT
1 March 1999
31
both ends. Moreover, both sides must have an ISDN card in place of modems. The cost
for ISDN equipment and lines is still higher than standard modems and phone lines.
Another possibility is connecting clients with a RAS server through the standard X.25
protocol.
Assume a company with two LANs at the same location, but not physically connected.
Then, assume that there is one computer connected to one of the networks, that also
need resources on the other. How could this be solved? One simple and cost effective
method is to configure a RAS client on the computer that wants access to resources on
both networks and then select a computer on the other network, on which a RAS server
is installed. Further, connect these two computers with a RS-232C Null modem cable,
see Figure 10. Now the RAS client in the figure is able to utilize resources on both net-
works.
FIGURE 10. Connecting two LANs using RAS as gateway
4.7.3 Telephone Application Programming Interface (TAPI)
NT 4.0 provides a new interface called TAPI. This interface allows programmers to
build programs, which are (more) independent, on how a specific modem works. With
TAPI, various behaviors of a modem can be controlled. Modem vendors will be
encouraged to write NT modem drivers [34].
4.7.4 Remote Access Protocols
RAS supports several modem protocols, including:
• Point-to-Point Protocol (PPP)
• PPP Multi-Link Protocol (MP)
• Point-to-Point Tunneling Protocol (PPTP)
• RAS protocol
• Serial Line Internet Protocol (SLIP)
Local
Host
Local
Host
Local
Host
RAS
server
LAN 1
RAS
Client
LAN 2
Null Modem Cable
Local
Host
Local
Host
Local
Host