[PATCH wireguard-windows] Calculate the actual route metric by summing interface and route metric.

[Ludwig Herzog]

Hi,

I'm reading this maillist since a longer time and was never brave enough
to mention my problem since I'm not a developer or programmer and don't
know if I can describe it properly. Now this windows/metric stuff came
up, so I take a heart ;-)

In short: I have windows 10 client softwares which only work properly
with manually set adapter and gateway metrics in the VPN network
adapter, what works for openVPN (even better for a logmein test setup)
but not for wireguard, since manual metric settings are not recognized /
overwritten by the windows wireguard app. Is it possible to set the
metrics somehow in the config file? Or prevent the windows wireguard app
from overwriting?

Regards

Ludwig


Am 30.03.2020 um 07:31 schrieb Jason A. Donenfeld:
> On Sun, Mar 29, 2020 at 8:29 PM Philipp Czerner <suyjuris.gi at nicze.de> wrote:
>> Signed-off-by: Philipp Czerner <suyjuris.gi at nicze.de>
>> ---
>> Hi,
>>
>> I had some issues setting up Wireguard behind another VPN. Curiously, it bound the physical interface instead of the other VPN, which was the default route. According to MSDN "the actual route metric used to compute the route preference is the summation of interface metric specified in the Metric member of the MIB_IPINTERFACE_ROW structure and the route metric offset specified in this member" (documentation for MIB_IPFORWARD_ROW2), but the code did not seem to consider this. After I changed the calculation, I got the expected behaviour.
>>
>> Cheers,
>> Philipp
>>
>>   tunnel/defaultroutemonitor.go | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/tunnel/defaultroutemonitor.go b/tunnel/defaultroutemonitor.go
>> index c102b64..4b24e8e 100644
>> --- a/tunnel/defaultroutemonitor.go
>> +++ b/tunnel/defaultroutemonitor.go
>> @@ -33,8 +33,14 @@ func bindSocketRoute(family winipcfg.AddressFamily, device *device.Device, ourLU
>>                  if err != nil || ifrow.OperStatus != winipcfg.IfOperStatusUp {
>>                          continue
>>                  }
>> -               if r[i].Metric < lowestMetric {
>> -                       lowestMetric = r[i].Metric
>> +
>> +               iface, err := r[i].InterfaceLUID.IPInterface(family)
>> +               if err != nil {
>> +                       continue
>> +               }
>> +
>> +               if r[i].Metric + iface.Metric < lowestMetric {
>> +                       lowestMetric = r[i].Metric + iface.Metric;
> Nice semicolon ;-).
>
> Thanks a lot for this patch and triaging the issue. Nice to hear that
> nested VPNs work. If you don't mind sharing, I'd be interested to
> learn what software sets up its routes in this manner.
>
> Anyway, applied here:
> https://git.zx2c4.com/wireguard-windows/commit/?id=66ad537f4e2144112cb6686c4fc4856d70bf6a3d
>
> Jason