When you attempt to make a PPTP connection between a computer running Windows NT Server version 4.0 Routing and Remote Access (RRAS) routers, the connection may fail with the error message "Remote PPP peer is not responding". The PPTP connection must be initiated to the correct IP address on that computer. For this reason, using the computer name in the phone book entry results in sporadically successful PPTP connections. This basic concept is also true for legacy Windows NT 4.0 RAS clients tunneling to legacy Windows NT 4.0 servers or Routing and Remote Access servers.

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The PPTP service responds to connection requests using the IP address of the interface that has the best route back to the PPTP client. You should use this address as the connection endpoint of your PPTP connection. This is important because the interface that receives the PPTP request is not necessarily the interface associated with the best route back to the PPTP client.

If the target PPTP server has a dedicated circuit, the IP address will be that of the WAN adapter. If the target PPTP server has a PPP connection to a local ISP, you will need to PPTP to the IP address assigned by the ISP.

In a rare case, you may have an end to end PPP connection between two Windows NT routers and try to bring up PPTP over that PPP link. When Windows NT routers connect through demand dial, both routers will assign each other an IP address. In this case, you would then PPTP to the PPP address that your local router assigned the peer router.

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Example

•	Router 1 has a RAS IP address pool of 192.168.0.0 mask 255.255.255.0 (address pool 192.168.0.1-254)
•	Router 2 has a RAS IP address pool of 172.16.0.0 mask 255.255.255.0 (address pool 172.16.0.1-254)

When Router 1 demand dials Router 2 over PPP, Router 1 will create an NDISWAN interface with IP address 192.168.0.1. This address is used internally by Routing and Remote Access Service. The address can be seen using the IPCONFIG command. You will also see this in the route table using the KERNROUT PRINT command. Router 1 will then be assigned an NDISWAN address of 172.16.0.2 by its peer router. This assigned address will show up in IPCONFIG as well as ROUTE PRINT, KERNROUT PRINT, and the GUI route table in Routing and Remote Access Administrator.

Router 2 will use the NDISWAN address 172.16.0.1 internally and will be assigned the NDISWAN address 192.168.0.2. To bring up the PPTP connection over PPP, Router 1 will need to connect to 192.168.0.2 (an address from its own RAS pool).

Router-to-Router PPTP Over PPP Addressing in Table Form

Router 1
RAS IP address pool statically defined as 192.168.0.0, mask 255.255.255.0
NDISWAN1 192.168.0.1 uses the first address of the pool internally
NDISWAN2 172.16.0.2 assigned during the PPP connection to Router 2
NDISWAN3 172.16.0.3 assigned during the PPTP connection to Router 2

Router 2
RAS IP address pool statically defined as 172.16.0.0, mask 255.255.255.0
NDISWAN1 172.16.0.1 uses the first address of the pool internally
NDISWAN2 192.168.0.2 assigned during the PPP connection to Router 2
NDISWAN3 192.168.0.3 assigned during the PPTP connection to Router 2

If Router 1 were a legacy Windows NT 4.0 RAS client, it could have simply tunneled to the address 172.16.0.1. Legacy Windows NT 4.0 RAS clients do not dynamically assign an IP address to the server, so the server side internal address of 172.16.0.1 can be used.

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