Table of Contents
Advertisement
E-1
Appendix E
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 E-1 Transport PPP frames over Ethernet
PPTP and the Contivity 221
When the Contivity 221 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 Contivity 221's Internet connection. In
SUA/NAT mode, the Contivity 221 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
Contivity 221 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 Contivity 221
initializes the PPTP connection hence; there is no need to configure the remote PPTP clients.
PPTP Protocol Overview
Contivity 221 VPN Switch User's Guide
Advertisement
Table of Contents
