The NetScaler appliance supports Application Layer Gateways (ALGs) for the Point-to-Point Tunneling Protocol (PPTP).

PPTP is a network protocol that enables secure transfer of data from a remote client to an enterprise server by creating a tunnel across TCP/IP-based data networks. PPTP encapsulates PPP packets into IP packets for transmission over the Internet. PPTP establishes a tunnel for each communicating PPTP network server (PNS)-PPTP Access Concentrator (PAC) pair. After the tunnel is set up, enhanced generic routing encapsulation (GRE) is used to exchange PPP packets. A call ID in the GRE header indicates the session to which a particular PPP packet belongs.

The NetScaler appliance recognizes PPTP packets that arrive on the default TCP port, 1723. The appliance parses PPTP control packets, translates the call ID, and assigns a NAT IP address. For two-way data communication between the client and server, the NetScaler appliance creates an LSN session entry based on the server call ID, and an LSN session based on the client call ID. The appliance then parses the GRE data packets and translates call IDs on the basis of the two LSN session entries.

For PPTP protocol, the NetScaler appliance also includes timeout setting for any idle PPTP LSN sessions. If a PPTP LSN session is idle for a time that exceeds the timeout setting, the NetScaler appliance removes the session.

Limitations:

The following are the limitations of PPTP ALG on a NetScaler appliance: