Windows TAP driver issues

[Etienne Dechamps]

Hi Todd,

I did some tests with NDIS 6 TAP-Windows about three years ago. The outcome
of that was https://github.com/gsliepen/tinc/pull/73/commits/
0c010ff9fe50b4046b5c7977bafac3e74037f075

It was a long time ago and I don't remember the details, but I remember I
was quite confused because I couldn't explain why OpenVPN did not seem to
exhibit any performance issues on the same driver, even though the code
paths around device I/O looked very similar. In the end I gave up because
I'm not familiar enough with Windows driver development to investigate any
further.

Note that in order to make the NDIS 6 drivers work reliably with tinc, I
first had to mess with tinc a bit, see https://github.com/gsliepen/
tinc/pull/71 - I'm not sure these patches made it to the 1.0 branch, so you
might want to stick to tinc 1.1 for your testing. Even with these fixes, as
I explain above the performance is still problematic.

On 16 January 2018 at 17:34, Todd C. Miller <Todd.Miller at sudo.ws> wrote:

> While I'm aware that tinc is known to have problems with the latest
> Windows TAP driver (NDIS 6), we want to run tinc on Windows server
> 2016 which doesn't support NDIS 5 drivers.  Since using the old
> version of the TAP driver is not an option, I'd like to better
> understand the issues with tinc and the NDIS 6 TAP driver.
>
> Can anyone point me to a discussion of the known issues?  From
> experience it seems like the driver has problems immediately after
> tinc is started and sometimes falls over when there is a lot of
> traffic.  The suggestions from the OpenVPN folks are generally
> things like increasing the MTU but this has not had much effect in
> my testing.
>
> I'm planning to familiarize myself with NDIS drivers so I can try
> and improve the current state of affairs but I don't have prior
> experience writing NDIS drivers.
>
> Thanks!
>
>  - todd
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