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Re: [lwip-users] [TCP Previous segment lost] / [TCP Out-Of-Order] (HTTPd

From: Kieran Mansley
Subject: Re: [lwip-users] [TCP Previous segment lost] / [TCP Out-Of-Order] (HTTPd-RAW)
Date: Mon, 10 Aug 2009 11:50:59 +0100

On Thu, 2009-08-06 at 09:44 -0700, Chris_S wrote:
> Working on getting my server code finished, everything working pretty
> good now.  
> However a question:
> I'm getting the above pair of packet msgs shown in Wireshark
> displaying a http page.  Same result in IE or FF.
> The page shows correctly everytime without errors, so I'm not sure if
> this is something significant or not.  No errors or odd things shown
> in lwIP at all (1.31.RC2).  Everything in stats appear good.  I've
> attached the PCAP file for one page refresh.  There are 3 files in the
> http page.  It always comes after the 3rd file request.

That is odd - the two packets in question are being shown out of order,
and looking at the IP ID field in their headers they were generated in
the correct order.  The reason there is no retransmission is that the
"missing" packet is the second one, and so it is received almost
immediately and no retransmission is required.

If you get the time to look into this in more detail I think it would be
worth it.  The re-ordering must be happening after the IP header is
generated (due to the IP IDs).  I wonder if your driver could be doing
something odd, or if one of the packet lists inside lwIP is improperly


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