PPTP clients cannot establish connections to the PPTP server behind the SonicWall
The Generic Route Encapsulation (GRE) protocol is used in conjunction with PPTP. Data or payload that is going to pass through the tunnel is given a Point-to-Point Protocol (PPP) header and then placed inside a GRE packet. The GRE packet carries the data between the two tunnel endpoints. After the GRE packet has arrived at the final destination (the endpoint of the tunnel), it is discarded and the encapsulated packet is then transmitted to its final destination.
Check the following:
Make sure the following ports are open: TCP port 1723 and GRE (IP protocol 47)
Double check your configurations as follows:
Login to the firewall and click Firewall -> Service. At the bottom click ADD.
On the new window, name the service GRE
From the protocol drop down, click on GRE (47) and Click OK. (Port 1723 is already predefined in sonicwall as PPTP).
Click Firewall-> Service-> Add Group
Name this group PPTP Group and add PPTP and GRE from the left to right using the arrow. Click OK to save.
Create a NAT Policy using the service PPTP Group pointing to the PPTP server IP.
NOTE: If SonicWall is configured in Transparent Mode, then skip this step.
Create an access rule which allows PPTP (GRE) Protocol from WAN to LAN using the service PPTP Group.
Clients should now be able to connect to the PPTP server from the WAN.
3. If you still experience a problem, it is recommended that you upgrade your firmware to the latest version.