Re: [lwip-users] LwIP - 2 netifs and VPN

[Sergio R. Caprile]

You have two interfaces, one in 10.something and another in 192.168.1.
You can communicate with hosts in either network but you can't be the
one letting the WiFi access "the board" nor "the board" access the WiFi,
that is routing, and lwIP does not route.
Somehow you have built a "gateway" in the ITU-T way, an application
gateway, instead of routing you piped at the application level...

Then you somehow connected something via VPN to something somewhere in
some mode. Then you try to connect other something to that VPN via some
other something I fail to see because you don't describe.

I can only comment some basic stuff then. My best guess was that PPP has
set a default and so you send "the other way", but then I fail to see
why UDP yes and TCP no. Anyway, what you are doing is a hack, ad hoc,
and not very flexible. If it works for you, fine, but I think you need
routing.
If you need to route, then you have to use some ad hoc hooks. Search the
list, Simon has already answered some routing hook questions before.
I can't help you here, and be aware that the ESP8266 TCP/IP is a
proprietary patched stack, forked some time in the 1.4.1 days of yore,
perhaps older. So... your mileage may (will) vary.