[En-Nut-Discussion] En-Nut-Discussion Digest, Vol 116, Issue 3

[Mingshu Wang]

Ole,

Thank you for the reply. As you said I didn't have enough listening threads to handle the incoming messages. Once I increase the threads, the problem is gone.

Thanks again.
Mingshu

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Today's Topics:

   1. TCP/HTTP problem (Mingshu Wang)
   2. Re: TCP/HTTP problem (Ole Reinhardt)


----------------------------------------------------------------------

Message: 1
Date: Wed, 5 Jun 2013 21:27:04 +0000
From: Mingshu Wang <mwang at ccontrols.com>
To: "'en-nut-discussion at egnite.de'" <en-nut-discussion at egnite.de>
Subject: [En-Nut-Discussion] TCP/HTTP problem
Message-ID:
	<24E383FC1C8DCF48ACAB94CA2BAE7A29281BB774 at exchbox01.ccsi.local>
Content-Type: text/plain; charset="us-ascii"

Hi all,

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?

Thank you very much.

Mingshu

------------------------------

Message: 2
Date: Wed, 05 Jun 2013 23:47:50 +0200
From: Ole Reinhardt <ole.reinhardt at embedded-it.de>
To: en-nut-discussion at egnite.de
Subject: Re: [En-Nut-Discussion] TCP/HTTP problem
Message-ID: <51AFB206.5060204 at embedded-it.de>
Content-Type: text/plain; charset=ISO-8859-1

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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