Re: [lwip-users] strange TCP behavior, connection stalls

[Sergio R. Caprile]

You should first validate the port by running a known to work 
application, pick one from the contrib tree. The port must not call 
basic (non-netconn or non-socket) lwIP functions from different threads.

You must specify which API you are using, and it is quite helpful if you 
post your piece of software.
You seem to be using the socket API, you are definitely using an RTOS.

Where was this capture taken ? Judging by the incorrect checksums 
reported by wireshark, this seems to be taken at the web server 
(offloading).
I can't see why your server is not accepting the first syn. If the 
capture is actually taken at the web server, it should have accepted it.
Your device is missing frames, it asks for the same sent data twice 
(thrice in total) in frames 19 to 23. This is common in bad ports and 
bad layer-2 drivers (and Wi-Fi networks...).