Re: Problem with -w option for TCP window size
It is called window scaling please refer to RFC 1323 for more information.
Kevin
On Wed, 9 Jul 2003, Dan S wrote:
> Thank you very much for your useful information. I just wondering if I have set the receiver window size to some value greater than 64k, how the receiver informs the sender of its window size through TCP header? (since there are only 16 bits for TCP window advertisment field)
>
>
> Thank you very much for your time and useful information.
>
> Best Regards,
> Dan
>
> Kevin Gibbs <kgibbs --at-- ncsa.uiuc.edu> wrote:
> Dan,
> Iperf does not set window sizes but simply requests that the OS set it
> to a certain size. Many OSes do not listen directly to the suggest. I
> assume you are running Linux as it is its habit of setting the window to
> 2x the suggested size. This is not a problem with Iperf, but an effect of
> the OS. The maximum window size is not limited by 16bits and can be set as
> high as 2GB I believe. Please refer to some of the tuning guides that are
> linked from our website for more information about using large window
> sizes.
>
> Kevin
>
> On Sat, 5 Jul 2003, Dan S wrote:
>
> > Hi all,
> > I have problems with -w option to set TCP window size. Everytime I
> > specify the TCP window size by using -w option, iperf never allows me to
> > get the specific window size as I have specified. For example, when I
> > use iperf -c "host name" -w 7k, it shows TCP window size: 14 KByte
> > (WARNING: requested 7.00 KByte). Which one is the allowed TCP window
> > size? From the throughput result, I think that iperf set the window size
> > to 14 KByte according to this example.
> >
> > Another question is about the maximum TCP window size that iperf allows
> > us to set. I am wondering what is the maximum size it allows. As far as
> > I know, the maximum allowable TCP window size in which we can set is 64
> > Kbytes according to 16 bit window size allowable in TCP header. If the
> > window size can be set to any value larger than this in iperf, please
> > let me know how it works and how it can be possible.
> >
> > Thank you very much for all responses.
> >
> > Regards,
> > Dan
>
>
>
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