Re: [lwip-users] RE: lwIP TCP Dup Ack problem

[Kieran Mansley]

On Fri, 2007-08-03 at 22:44 +0200, Per-Henrik Lundblom wrote:
> * Ramanathan Ramadass <address@hidden> [070803 22:36]:
> 
> > Not necessarily. If I am reading the code right, the condition in
> > "tcp_output()" is;
> > 
> > if(pcb->flags & TF_ACK_NOW &&
> >     (seg == NULL ||
> >    ....)
> > 
> > Where "seg" is the "pcb->unsent" queue. Because the data is flowing one
> > way (from client to lwIP) "pcb->unsent" will be NULL and will result in a
> > Dup ACK. I think this is a bug.
> 
> I can honestly say I didn't look at your capture files but I have been
> hacking around pretty heavily in lwIP at work recently with data flows
> similar to yours. If you call for example tcp_received() in wrong ways
> you will get a lot of DUP ACKs. Even if you do everything The Right Way
> you may end up with a DUP ACK sometimes. At least in my case that mostly
> came from the fact that lwIP doesn't implement the persist timer and
> functionality for splitting TCP data in the pcb->unsent queue. I have
> implemented this functionality but haven't submitted any patches.

The persist timer implementation would be of great interest, as we
really must have it to be a compliant stack and it's causing problems
for a number of users.  Do you plan to be able to send this patch in, or
is that unlikely (e.g. due to problems with licencing of code etc)?  I
only ask so we know whether or not we need to independently work on
this.

Thanks

Kieran