Re: [lwip-users] Connection abort due to max SYN retries reached

[D.C. van Moolenbroek]

Hi,

On 3/22/2017 18:11, Axel Lin wrote:
> I recently found it's easy to get connection abort when I test
> connecting web server.
> (test by just repeating send http request)
>
> It's easy to get below debug message:
> tcp_slowtmr: max SYN retries reached

Just a guess: could it be that your test is making so many connections 
so fast that you're cycling through all local port numbers and thus end 
up reusing them, while previous connections with those port numbers are 
still in TIME_WAIT state on the web server side at the time that the 
first SYN is sent for the new connection on the client side? It should 
be fairly easy to check this with netstat on the server side, if you 
have access to such a tool there of course.

If that is indeed the case, behavior would definitely differ between 
1.4.1 and 2.0.x due to patch #9039 and bug #50498, although it would 
then be a matter of perspective as to whether the issue is with lwIP or 
your test..

Regards,
David