[lwip-users] LWIP and its keep-alive feature - does it work?

[Peter]

Hi All,

Does anyone know whether the keep-alive feature in LWIP TCP actually
works, and if so, are there any unusual limitations?

I have a system described here
https://www.eevblog.com/forum/networking/sockets-keep-alive-and-vpns/

comprising of a client and a server (both embedded, LWIP/FreeRTOS, STM
32F417). The KA option is apparently enabled with the calls described
in the above link, and it seems to do "something" (in that if running
this over a VPN, the VPN remains UP, instead of hanging up after some
time) but if say the server is rebooted during a connection, the
connection is not re-established. Maybe that is how it is supposed to
work i.e. if one wanted to re-establish a connection in such a
situation, the client should be sending out regular "real" packets,
not KA packets.

Needless to say I have googled everywhere and all I find is people
having problems with LWIP KA but nobody posting solutions.

Thank you in advance,

Peter