Re: Odd sequence....

[Andi Kleen]

On Sun, Jun 04, 2000 at 05:55:18PM +0200, Rogier Wolff wrote:
> 
> 
> Hi,
> 
> I just caught a TCP dump that looks kind of funny to me:
> 
>  1 16:58:19.895993 bwww.ssh > 14dyn184.61101: . 864:864(0) ack 816   
>  2 16:58:19.909331 14dyn184.61101 > bwww.ssh: P 816:836(20) ack 784   
>  3 16:58:19.915995 bwww.ssh > 14dyn184.61101: P 784:824(40) ack 816   
>  4 16:58:19.929933 14dyn184.61101 > bwww.ssh: . 836:836(0) ack 864   
>  5 16:58:20.090871 14dyn184.61101 > bwww.ssh: P 836:856(20) ack 864   
>  6 16:58:20.136009 bwww.ssh > 14dyn184.61101: P 864:884(20) ack 836   
>  7 16:58:20.149553 14dyn184.61101 > bwww.ssh: . 856:856(0) ack 884   
>  8 16:58:20.155974 bwww.ssh > 14dyn184.61101: P 884:904(20) ack 836   
>  9 16:58:20.169551 14dyn184.61101 > bwww.ssh: . 856:856(0) ack 904   
> 10 16:58:20.315990 bwww.ssh > 14dyn184.61101: . 904:904(0) ack 856   
> 11 16:58:20.316002 bwww.ssh > 14dyn184.61101: P 904:924(20) ack 856   
> 12 16:58:20.329548 14dyn184.61101 > bwww.ssh: . 856:856(0) ack 924   
> 13 16:58:40.477658 14dyn184.61101 > bwww.ssh: P 856:876(20) ack 924   
> 14 16:58:40.744978 bwww.ssh > 14dyn184.61101: . 1696:1696(0) ack 876   

Some packet got lost.

> 15 16:59:19.536500 14dyn184.61101 > bwww.ssh: P 876:896(20) ack 924   

14dyn acks immediately, but piggy backs some data in the ack.

> 16 16:59:19.803107 bwww.ssh > 14dyn184.61101: . 1696:1696(0) ack 896  

bwww acks it.  A bit later a retransmit would occur (fast retransmit
only really works for bulk data where the full window triggers enough
out of order acks) 

> 
> (all packets had win 32120 (DF) [tos 0x10], which is not show above). 
> 
> 
> If I'm not mistaken, packet 4, is the one that messes things up:
> it acknowledges 40 bytes it hasn't recieved. 

But it has. See packet 1.
> 
> After 20 seconds of patience (*), at 16:58:40 I type another "return"
> to try and get things moving again. At that moment bwww, sends a
> packet indicating that we've missed 864-1696. Rosie then doesn't react
> and acks whatever it HAS recieved, to try to tempt bwww to perform a
> fast(!)-retransmit.

I see nothing wrong.

-Andi