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RE: [lwip-users] LWIP TCP issues

From: Kieran Mansley
Subject: RE: [lwip-users] LWIP TCP issues
Date: Fri, 15 Sep 2006 09:02:54 +0100

> > 
> >      We are using LWIP in an ecos based environment. We are having
> > problems with LWIP TCP. The udp part is communicating successfully to
> > a external TCP/IP stack from our system. But while using TCP client to
> > connect to a external TCP server from with in the system, it is not
> > working. The tcp_connect results in a SYNC to the external server. The
> > server acks with a SYNC -ACK. Then a RST goes from the LWIP instead of
> > an ACK to complete the initialization handshake.

Hmm, that is strange.  It sends a RST, and then immediately follows that
with the correct ACK to the SYNACK.  There is some odd ARP traffic going
on too - it ARPs before sending the SYN (which is expected) but then
sends another ARP request before sending the RST and ACK.  At the top of
the trace it is sending ARP requests asking for the replies to be sent
to which is obviously wrong.

I'm not an expert on the ARP code in lwIP, so can't really comment about
that - perhaps someone else can help there.

There are only a few places in the stack that send a RST packet.  The
simplest way to find out why it is sending a RST is to turn on some
debugging print statements in each of these.  Once we know why it sends
the RST, fixing the problem should be much easier.


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