Re: Actual window sized used

["Chris McFarling" <cmcfarling_lists --at-- pacificpremedia.com>]

>
> Do TCP window parameter settings in the OS affect the window size used
> by
> iperf? For example, if I make the following registry edits in Win2K:
>
>   GlobalMaxTcpWindowSize=17520
>   Tcp1323Opts=1
>   TcpWindowSize=17520
>
> and the start iperf with the following:
>
> iperf -s -w 65700
>
>
> will iperf use a 65700 byte window or will it use a 17520 window? It
> reports
> that is using a window size of 64K but I just want to verify that what
> it's
> reporting is actually true.
>
> Thanks
>
>
> Whatever window size you set on iperf's command line will override the
> OS setting. If you don't specify a window using -w then iperf will use
> the window size your OS specifies.
>
> --Andy


Taking that a step further, I've noticed the requested and actual window
sizes are always the exact same. For example, on OS X when I request a
window size of 17520 iperf reports:

TCP window size: 18.4 KByte (WARNING: requested 17.1 KByte)

Does iperf automatically choose a window size that is a multiple of the MSS?
In the case of OS X the MSS is 1448. 17520 is a multiple of 1460. The closet
multiple of 1448 (rounding up) would be 18824, or 18.4K.

Just looking for verification on that.

Thanks