Jumbo frame Question

Fri Nov 26 17:23:06 UTC 2010

Jon,

Do you have something blocking MTU Path Discovery?  Unless I'm off base on this, shouldn't that be taking care of your issue?

-Richard

-----Original Message-----
From: Jon Meek [mailto:meekjt at gmail.com] 
Sent: Friday, November 26, 2010 12:17 PM
To: nanog at nanog.org
Subject: Re: Jumbo frame Question

I have the "opposite problem". I use iperf to test WAN and VPN
throughput and packet loss, but find that the sending Linux system
starts out with the expected MTU / MSS but then ramps up the packet
size to way beyond 1500. The result is that network equipment must
fragment the packets. On higher bandwidth circuits there are a lot of
re-transmits that mask any real packet loss that might exist in the
path.

I have tried multiple methods to clamp the MTU, but nothing has worked
so far. This leads me to wonder how often real bulk transfer
applications start using jumbo packets that just end up getting
fragmented downstream.

The jumbo packets from iperf occur on various versions of the Linux
kernel and different distributions. It might only happen on GigE.

Suggestions on clamping the MTU are welcome.

Thanks,

Jon

On Thu, Nov 25, 2010 at 7:13 PM, Harris Hui <harris.hui at hk1.ibm.com> wrote:
>
> Hi
>
> Does anyone have experience on design / implementing the Jumbo frame
> enabled network?