MORE INFORMATION
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.
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.