Re: Problem with -w option for TCP window size

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