Re: [lwip-users] lwip does not ack retransmissions

[john bougs]

--- On Tue, 1/27/09, Alain M. <address@hidden> wrote:

> From: Alain M. <address@hidden>
> Subject: Re: [lwip-users] lwip does not ack retransmissions
> To: "Mailing list for lwIP users" <address@hidden>
> Date: Tuesday, January 27, 2009, 6:19 PM
> Hi John,
> 
> I have read this thread carefully but I managed to get
> lost. Now that you solved the problem, could you please give
> us a quick description of what caused the problem and the
> solution??
> 
> This could happen to any of us...
> 
> Thanks,
> Alain


The problem happens sometimes when lwip misses a TCP packet.  This results in a 
bunch of out of sequence packets (in in my specific example the first few are 
smaller than the original resulting in the new vs old being skewed).  
Eventuality the OOS packets end up filling up the pbuf_pool so no more packets 
can be received.  This locks up lwip because the correct packets can not be 
received.  John has indicated that these packets should eventually be cleared 
due to timeouts, but in my case the telnet session  indicates the connection 
has been lost and shuts down before this happens.

There were 2 fixes we discussed. The fist is to set TCP_QUEUE_OOSEQ to 0.  this 
will cause lwip to reject OOS packets.  The second was a patch that cleared the 
OOS pbufs if we run out of space in pbuf_pool.