Re: question about the set tcp window size in iperf 1.6.3
On 29 Nov, Chong Zhang wrote:
> Hi Marc,
>
> Thanks for the link and the patch.
and did you use it below ?
> I have another question and hope you could help me a bit:
> I have two linux boxes connected via internet, and both
> have default 16k buffer size on client mode and 85.3k on server mode.
... and you use these defaults ? (i.e., no iperf -w option?)
> But I got different Bandwidth result on the two direction:
>
> A--> B ( 400K)
> B--> A(1.4M)
Moctets/s (or Mbits/s ?)
> They are not identical boxes but I don't see too much difference (>1G,
>>=256M, low cpu load)
What is the linux kernel version ?
> the tcpdump on node A shows the following ( I don't have root permission on
> node B)
> A--> B
> A.32787 > B.5001 nnn:nnn(1448) ack 1 win 5840
> B.5001 > A.32787 ack nnn win 63712
> B--> A
> B.1052 > A.5001 nnn:nnn(1448) ack 1 win 16060
> A.5001 > B.1052 ack nnn win 63712
>
> Why they have different win advertisements?
>
Assuming the latency between your boxes is in the 10ms range (true?),
yes it seems the receiver window is your bottleneck indeed, as opposed
to some other asymetry in the network...
suggested reading:
Documentation/networking/ip-sysctl.txt in the linux source.
Hopefully these short hints/questions will help.
--
Marc.
--
Mitch Kutzko | mitch --at-- dast.nlanr.net | mitch --at-- ncsa.uiuc.edu | 217-333-1199
http://hobbes.ncsa.uiuc.edu/