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Re: [lwip-users] TCP connect problem

From: Adam Dunkels
Subject: Re: [lwip-users] TCP connect problem
Date: Thu, 24 Feb 2005 15:51:33 +0100

On Thu, 2005-02-24 at 14:23 +0000, Kieran Mansley wrote:
> On Thu, 2005-02-24 at 15:19 +0100, Jan Wester wrote:
> > Hi
> > Normaly I can do many TCP connect-close sequence, but if I restart my
> > system and try to do TCP connect I often got tcp_error. 
> > Is it any problem with seq no ? I using 0.7.2
> > On the sniffer I can see 
> > SYN SEQ=6525
> >         ACK=6533        Only ack ?
> > And after lot of try it connect
> > SYN SEQ=6595
> > SYN ACK=6596        Connect
> Sounds like one of the machines is interpreting the SYN as relating to a
> connection that existed before the reboot.  As it thinks it's already
> open, it responds with an ACK rather than a SYN-ACK, although I'm not
> sure this is correct behaviour: I'd have to check the RFC to be sure.
> Eventually, the connection times out and then the SYN succeeds.  

If I remember correctly, yhis is the intended behavior according to the
RFC, but with a small addition: the ACK should trigger an RST from the
side that sent the SYN. This will abort the connection. (But I'm not
sure that lwIP follows the RFC in this case.)


Adam Dunkels, Swedish Institute of Computer Science
http://www.sics.se/~adam/, <address@hidden>

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