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RE: [Openvpn-users] TAP32 Driver question (James Yonan?)

  • Subject: RE: [Openvpn-users] TAP32 Driver question (James Yonan?)
  • From: Andreas Iwanowski <namezero@xxxxxxxxx>
  • Date: Wed, 26 Jan 2005 22:32:45 -0500

I think I didn't make myself clear enough about what I had in mind.
What I meant was some kind of an "emulated" TAP32 driver that still
functions the same but looks like a modem to windows.
This way, OpenVPN would look to Windows like a Dial-Up connection
and could also be used to log on to domains using the "Log on using
dial up connection" checkbox at the logon prompt.

However, this setup would require this "modem driver" to implement
a completely functional TAP32 interface. Probably there would also
be some OpenVPN code that would have to be changed.

Maybe this here makes things clearer:

Right now:
TCP/UDP carrier<---->OpenVPN<---->Tap32Adapter<---->O/S(Windows)

What I have in mind:
TCP/UDP carrier<---->OpenVPN<---->Modem_emulation_driver<---->O/S(Windows)

I'm not saying the TAP32 adapter should be replaced, but in some
setup scenarios (like road warriors who need to log on to a domain)
a modem driver based implementation would be easier.

    Andreas Iwanowski

-----Original Message-----
From: James Yonan [mailto:jim@xxxxxxxxx] 
Sent: Wednesday, January 26, 2005 9:48 PM
To: Andreas Iwanowski
Cc: Openvpn Users (openvpn-users@xxxxxxxxxxxxxxxxxxxxx)
Subject: Re: [Openvpn-users] TAP32 Driver question (James Yonan?)

On Wed, 26 Jan 2005, Andreas Iwanowski wrote:

> Hello folks!
>  I have a question about the TAP32 driver used by OpenVPN. I have done 
> some research and skimmed through the source code of OpenVPN and the
> TAP32 driver.
> My question originated from the lack of "Logon using Dialup" in 
> OpenVPN and the discussion about root/admin rights to run OpenVPN.

OpenVPN can connect over dialup or any other IP-capable network device.
> My question (especially to James Yonan) is if OpenVPN would still work 
> with a modem driver that emulates a P2P connection (obviously, OpenVPN 
> would only run in TUN mode using this expecially modified driver), and 
> Windows would have the control over the connection.

Yes, and it could run in both TUN or TAP mode.  The only thing that might need to be tweaked is the MTU size to make sure the different levels of encapsulation do not end up overflowing any packet size limits.  Use --mssfix and/or --fragment to reduce the MTU size.

> This setup would require the following changes/additions: - A modem 
> driver that emulates a TAP32 interface (emulating an emulated device?) 
> - OpenVPN control interface so that Windows' "Disconnect" and IP 
> options work. (Isn't there a management interface in the new v2_rc6 version?

I think you are confusing the TAP-Win32 driver with the network interface over which the encrypted UDP or TCP carrier operates.  They are quite independent.  If you want to run OpenVPN over a modem connection, just do it.  The TAP-Win32 driver doesn't need to know anything about it.


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