Re: [lwip-users] transfer stucks when snd_wnd is less than TCP_MSS

[Vlad]

I forgot to say - lwip are in vmware. I.e. network structure are following:

lwip (in vmware) <--- 1gb virtual vmware network ----> virtual vmware hub 
<-vmware network driver-> 192.168.0.2 (my real machine) <---- 1gb 
ethernet ----> linux router <----128k adsl ----> internet <----> linux server

seems that vmware hub responses very fast with ack-s before packets really 
have sent.
at "hang" moment vmware hub sent acks for near 1000000 bytes (within 1-2 
seconds ) sent (sent window starts with big value - near 60000 and decreases 
down to small value).
but at real eth interface (on 192.168.0.2 - real machine with vmware 
installed) i see ack's only for 80-90kb. and send window size doesn't grow 
more than 137 bytes.

BUT, windows tcp/ip stack works fine in same virtual machine. seems that 
problem in lwip.

On Friday 09 March 2007 11:46, Kieran Mansley wrote:

> On Fri, 2007-03-09 at 11:17 +0200, Vlad wrote:
> > lwip connected to internet throught router:
> >
> > lwip(192.168.0.2) <--- 1 GB ethernet ---> router(192.168.0.1/x.x.x.x real
> > ip) <--- 128k adsl connection ----> internet <----> remoute linux server
> > (to which lwip connects)
> >
> > router is masquerading linux 2.6 server.
> >
> > router returns quickly ack-s on most of my outgoing packets, returning
> > less window size on each ack. lwip transfers 365kbytes traffic out and
> > then hangs because of small window.
> >
> > i see with tcpdump that router transfers out only 86kbytes and then stops
> > transfering.
> >
> > if i connect lwip to internet directly, all works fine.
>
> Very strange - the router should not be acking packets as you suggest it
> is.  Packets should only be acked by the remote linux server to which
> lwIP connects.  It sounds like you have a problem with your router,
> particularly as lwIP works fine when you remove the router.
>
> > is "slow start" will be a solution for me ?
>
> slow start is an internal TCP mechanism that the stack should invoke
> when appropriate.  It's not something you should need to worry about in
> your application.
>
> Again, it sounds like lwIP is not at fault here and is doing the right
> thing, so I'm not sure what help I can be.
>
> Kieran
>
>
>
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