TCP/IP routing over PPTP for dummies with win2k3 server

[tech4ip01]

Hello everyone,

I am having a bit of a problem connecting my network (16 public IPs provided by our ISP) over a PPTP connection to to the same ISP (located in same building) via a cable they dropped directly into our office. We are using Windows 2003 Server as our router to establish the PPTP to the ISP. I can get the PPTP to connect just fine via the RRAS console, however, I am having difficulty with the routing side of things. The IP that the PPTP is assiging me is different from any of the IPS they gave me when talking to them in person. Could this be right? If so, how then would I establish a route between the IPs they assigned me and this IP that is coming up automatically from their PPTP server?

Any thoughts or suggestions would be greatly appreciated.

Patrick

 

[John Lewis]

OK, here goes it.

There are four IP addresses involved in a pptp connection. The pptp client will have a 'physical' IP address. In this case, it would be the public IP your ISP has assigned for the computer in your office. The pptp server also has a physical IP address. This would be the IP your ISP uses for the pptp server you are connecting to -- the same one you used in the RRAS console.

Now the fun begins. When you make the pptp connection, a 'virtual' network adapter is added to your client machine and the ISP's server. Each side is assigned it's own IP address, so you will now have a virtual IP address on your computer as will the ISP. If you activate the connection, then open the properties of the connection, both of these addresses should be listed in the details. Also, these addresses should be 'private' addresses that are not directly routed over the internet. That's not really important in your case, the ISP should handle the routing internally, but it explains why they are not similar to the other addresses.

Any traffic that needs to traverse the pptp tunnel should be routed through the virtual addresses, so you will need to use those to build your routes. You can't control the routes on their end, so you have to hope they are dealing with it correctly. All you can do is add the route to your other computers using the virtual IP and cross your fingers.