IronPort Systems ZyAIR B-4000 - Manual (Page 235)

ZyAIR B-4000 Hot Spot Gateway
PPTP F-1
Appendix F
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 PC 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 PC 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 PC 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.
Diagram F-1 Transport PPP frames over Ethernet
PPTP and the ZyAIR
When the ZyAIR is deployed in such a setup, it appears as a PC 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 ZyAIR's Internet connection. In NAT mode, the ZyAIR is able to
pass the PPTP packets to the internal PPTP server (i.e. NT server) behind the NAT. Users need to forward
PPTP packets to port 1723 by configuring the server in Menu 15.2 - Server Set Setup. In the case above
as the remote PPTP Client initializes the PPTP connection, the user must configure the PPTP clients. The
ZyAIR initializes the PPTP connection hence; there is no need to configure the remote PPTP clients.