PPTP Connection sharing behind NAT

["J. Theriault" <administrator () maginetworks com>]

Hello,


I would like to set up a Linux machine to route connections over a PPTP 
connection to a secondary ISP inside a pre-existing network, so that 
internal machines generally use the "standard" ISP connection, and 
others can be configured to use the Linux machine's PPTP connection as a 
gateway/tunnel for their internet access.

I have no previous practical experience with PPTP and most of the Linux 
PPTP documentation seems quite daunting, so if anyone knows a simple way 
to do this, I'd appreciate any help or advice before I get started.

-----

So far, I'm visualizing it like so:

U = Standard Unencrypted connection
E = PPTP Encryption connection

------------     -------     ----------           -----------
| Internet |--U--| ISP |--U--| Router |-----U-----| Clients |
|          |     |     |     |        |           |         |
|          |     |     |     |        |           |         |
|          |     |     |     |        |           |         |
|       E--|--E--|--E--|--E--|----E   |           |         |
------------     -------     ----------           -----------
    |   |                WAN DHCP/LAN 10.0.0.1    (10.0.0.0/8)
    U   E                         |
    |   |                         E
  ---------                       |
  | ISP-2 |                       E   ----------   -----------
  ---------                       |-E-| Linux* |-E-| Clients |
                                      ----------   -----------
                                                  (192.168.0.0/24)

* Linux (Ubuntu 6.10):

WAN: 10.0.1.0/8 (For PPTP connection both DNS/routing are required)
LAN: 192.168.0.0/24 (For the few clients who are to use ISP-2)
PPP: PPTP connection to ISP-2

IPTables:
 - Incoming from WAN/PPP blocked
 - Outgoing LAN to WAN blocked
 - Outgoing LAN to PPP passed

Routing/DNS forwarding: Set to use ISP-2's gateway and DNS for all

-----

So, does anyone know a simple way to do this, such as if m0n0wall (which 
has support for a PPTP WAN but does not seem to allow me to set DNS or 
gateway options to be able to resolve and contact the PPTP server in the 
first place to establish the connection) can be configured to do this, 
or is there going to be a lot of trial and error? ;)


Thank you,

Joseph Theriault
administrator () maginetworks com

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