[En-Nut-Discussion] TCP/HTTP problem

[Ole Reinhardt]

Hi,

> We made a product with AT91_SAM7X256 and Nut/OS 4.8.7. Recently we
> found a problem with accessing the webpage via Internet. We can
> replicate the issue with one IP router (we use port forwarding from
> port 80 to 80). The webpage becomes inaccessible for a while but then
> returns to the working condition after about a minute. In the
> inaccessible state, the webpage is not reachable via both the LAN
> side &the WAN side but pings work. We watch the messages with
> Wireshark during the test. We see TCP RST sent by our product
> (Nut/OS) during the inaccessible state.
> 
> Did anyone see this problem before? Is there a solution for this
> problem?

No, I have not seen exactly this problem before, but might have an idea
what is happening.

TCP RST packages are send (beside others) in the following conditions:

- PC tries a connection to a closed port
- Ethernut tries to abort a connection.

I assume you hit the first situation.

AFAIK Nut/OS 4.8.7 did not yet implement TCP connection back-log. It
might be possible, that your Web-Server does not provide enough
listening threads to handle all incomming requests at a time (especially
if you have lots of included files like images, css, js, etc.) which
must be loaded to completely render the web-page. In this case your
Web-Server might not be able to accept more connections and the TCP
stack will send out RST packages for all incomming connections that can
not be handled.

And a few moments later all previous connections got closed, and are now
free to handle further requests, so you can access the page a few
moments later again without problems.

It might be a good idea to upgrade to the latest stable Nut/OS version,
which supports TCP connection backlog.

Best regards,

Ole

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