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

[Vlad]

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.

is "slow start" will be a solution for me ? 

On Friday 09 March 2007 10:15, Kieran Mansley wrote:

> On Thu, 2007-03-08 at 19:18 +0200, Vlad wrote:
> > I mean second. lwip receives ack packets that sets snd_wnd less and less
> > with every packet:
> >
> > 19:11:10.246024 IP x1:port1 > x2:port2: P 61680:63140(1460) ack 1 win
> > 20480 19:11:10.246055 IP x2:port2 > x1:port1: . ack 63140 win 15340
> > 19:11:10.246604 IP x1:port1 > x2:port2: P 63140:64600(1460) ack 1 win
> > 20480 19:11:10.246641 IP x2:port2 > x1:port1: . ack 64600 win 13880
> > 19:11:10.247193 IP x1:port1 > x2:port2: P 64600:66060(1460) ack 1 win
> > 20480 19:11:10.247224 IP x2:port2 > x1:port1: . ack 66060 win 12420
> > 19:11:10.248301 IP x1:port1 > x2:port2: P 66060:67520(1460) ack 1 win
> > 20480 19:11:10.248340 IP x2:port2 > x1:port1: . ack 67520 win 10960
> > 19:11:10.248974 IP x1:port1 > x2:port2: P 67520:68980(1460) ack 1 win
> > 20480 19:11:10.249011 IP x2:port2 > x1:port1: . ack 68980 win 9500
> > 19:11:10.249588 IP x1:port1 > x2:port2: P 68980:70440(1460) ack 1 win
> > 20480 19:11:10.249619 IP x2:port2 > x1:port1: . ack 70440 win 8040
> > 19:11:10.250184 IP x1:port1 > x2:port2: P 70440:71900(1460) ack 1 win
> > 20480 19:11:10.250215 IP x2:port2 > x1:port1: . ack 71900 win 6580
> > 19:11:10.250778 IP x1:port1 > x2:port2: P 71900:73360(1460) ack 1 win
> > 20480 19:11:10.250814 IP x2:port2 > x1:port1: . ack 73360 win 5120
> > 19:11:10.251726 IP x1:port1 > x2:port2: P 73360:74820(1460) ack 1 win
> > 20480 19:11:10.251764 IP x2:port2 > x1:port1: . ack 74820 win 3660
> > 19:11:10.252660 IP x1:port1 > x2:port2: P 74820:76280(1460) ack 1 win
> > 20480 19:11:10.252705 IP x2:port2 > x1:port1: . ack 76280 win 2200
> > 19:11:10.253375 IP x1:port1 > x2:port2: P 76280:77740(1460) ack 1 win
> > 20480 19:11:10.253409 IP x2:port2 > x1:port1: . ack 77740 win 740
> >
> > At this moment remote server (x2 - remote, x1 - local) stops send
> > packets, and my program cannot send packets (they stays in queue) because
> > snd_wnd == 740, segment size is 1460 == TCP_MSS. Connection times out in
> > 1 minute.
>
> Hmmm, seems like the network stack you're talking to is being rather
> uncooperative.  Normally a stack would try not to advertise less than 1
> MSS of receive window, and to send an update with more window space as
> soon as possible if it did close the window in this way.  We shouldn't
> drop any packets due to this though - lwIP will just wait until the
> other side advertises more window space and then carry on.  I'm also
> surprised that the connection times out in 1 minute - that's a very fast
> timeout.  Does the other stack not eventually advertise more window
> space?  If not, I think the problem is at that end.  Looks like lwIP is
> doing the right thing to me.
>
> Kieran
>
>
>
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