ZyXEL Communications ZyXEL ZyWALL P1, User Manual

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ZyWALL P1 User’s Guide
Appendix D PPTP 291
Appendix D
PPTP
What is PPTP?
PPTP (Point-to-Point Tunneling Protocol) is a Microsoft proprietary protocol (RFC 2637 for
PPTP is informational only) to tunnel PPP frames.
How can we transport PPP frames from a computer to a broadband
modem over Ethernet?
A solution is to build PPTP into the ANT (ADSL Network Termination) where PPTP is used
only over the short haul between the computer and the modem over Ethernet. For the rest of
the connection, the PPP frames are transported with PPP over AAL5 (RFC 2364) The PPP
connection, however, is still between the computer and the ISP. The various connections in
this setup are depicted in the following diagram. The drawback of this solution is that it
requires one separate ATM VC per destination.
Figure 162 Transport PPP frames over Ethernet
PPTP and the ZyWALL
When the ZyWALL is deployed in such a setup, it appears as a computer to the ANT.
In Windows VPN or PPTP Pass-Through feature, the PPTP tunneling is created from
Windows 95, 98 and NT clients to an NT server in a remote location. The pass-through feature
allows users on the network to access a different remote server using the ZyWALL's Internet
connection. In SUA/NAT mode, the ZyWALL is able to pass the PPTP packets to the internal
PPTP server (i.e. NT server) behind the NAT. You need to configure port forwarding for port
1723 to have the ZyWALL forward PPTP packets to the server. In the case above as the
remote PPTP Client initializes the PPTP connection, the user must configure the PPTP clients.
The ZyWALL initializes the PPTP connection hence; there is no need to configure the remote
PPTP clients.