Re: iperf - MSS
On Tue, Apr 1, 2008 at 2:00 AM, Mittal Patel <mp.mpatelp --at-- googlemail.com> wrote:
> Hi,
>
> I would like to ask two question :
>
> 1) I specified the MSS in iperf to 1460 using
> > iperf -s -w 2500000 -M 1460 -m
>
> It shows the MTU as 1500 after the running iperf as follows:
> WARNING: attempt to set TCP maximum segment size to 1460, but got 536
> ------------------------------------------------------------
> Server listening on TCP port 5001
> TCP window size: 47.7 MByte (WARNING: requested 24.4 MByte)
> ------------------------------------------------------------
> [ 4] local 192.1.11.253 port 5001 connected with 192.1.10.253 port 44831
> [ 4] 0.0-10.1 sec 871 MBytes 726 Mbits/sec
> [ 4] MSS size 1448 bytes (MTU 1500 bytes, Ethernet)
>
> But when i collect the packet by tcpdump, i found that the MSS is
> around 3000. Could you please give the reason behind this. Also the
> warning says that attempt to set TCP maximum size to 1460 but got 536.
> why?
Not sure about this... TCP in the Linux kernel often takes what you
say as advice rather than a requirement. However I would have thought
it would obey MSS so maybe a bug??
>
> 2)How i can know which TCP flavor does iperf is using? It is same as
> kernel tcp flavor?
>
> Thank you,
>
> Mittal
>
>
It will use your default. There are patches from Gerrit Renker and
myself to override the default:
http://www.erg.abdn.ac.uk/users/gerrit/dccp/apps/iperf/patches/
http://wand.cs.waikato.ac.nz/~iam4/software/index.html
Gerrit's is a more developed version than mine and he has added more
features in his patch set. We both added support for DCCP.
We are both happy for our changes to be merged upstream but neither
have the time to resync the codebase so if someone else picks up our
changes we would be most grateful.
Regards
Ian
--
Web: http://wand.net.nz/~iam4/
Blog: http://iansblog.jandi.co.nz