Tun interface do not route packets on Windows 7 (extended no-NAT)

[Vasili Pupkin]

In my setup I have a client running Win7, the tun interface allows to
make connection from client to server but it only route packets back
for some time and then broke.

The client system is NOT behind the NAT and PersistentKeepalive=25 do
not help, the issue is local and external network route encrypted
packets as expected. Have tested it with wireshark.

I have checked the tun adapter with RawCap tool (wireshark do not let
you monitor tun interface on Win7) and decrypted packets sent by the
server actually generated inside the tun
interface on the client but aren't routed to the process nor processed
any further, they stuck on OSI level 3. If I then ping server from
client the tun interface revives but broke again after like 30 seconds
of silence. The support for Win7 will be dropped later this year but
it is still rather popular OS among users.