[165248] in North American Network Operators' Group
Re: TCP Performance
daemon@ATHENA.MIT.EDU (Blake Dunlap)
Tue Aug 27 13:32:33 2013
In-Reply-To: <3c3f6faa$247b83c2$1ee532dd$@flhsi.com>
From: Blake Dunlap <ikiris@gmail.com>
Date: Tue, 27 Aug 2013 12:31:40 -0500
To: nick@flhsi.com
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
If you have a router, you can turn on shaping to the bandwidth the link
will support.
-Blake
On Tue, Aug 27, 2013 at 12:11 PM, Nick Olsen <nick@flhsi.com> wrote:
> I do indeed have stats for "TX Pause Frames" And they do increment.
> However, Our router is ignoring them since it doesn't support flow control.
>
> I guess my next question would be. In the scenario where we insert a
> switch between the radio and the router that does support flow control. Are
> we not only moving where the overflow is going to occur? Will we not see
> the router still burst traffic at line rate toward the switch, Which then
> buffer overflows sending to the radio on account of it receiving pause
> frames?
>
>
> Nick Olsen
> Network Operations
> (855) FLSPEED x106
>
>
>
> ------------------------------
> *From*: "Tim Warnock" <timoid@timoid.org>
> *Sent*: Tuesday, August 27, 2013 1:08 PM
> *To*: "Blake Dunlap" <ikiris@gmail.com>, "nick@flhsi.com" <nick@flhsi.com>
> *Cc*: "nanog@nanog.org" <nanog@nanog.org>
> *Subject*: RE: TCP Performance
>
>
> > Regardless, your problem looks like either tail drops or packet loss,
> which
> > you showed originally. The task is to find out where this is occurring,
> and
> > which of the two it is. If you want to confirm what is going on, there
> are
> > some great bandwidth calculators on the internet which will show you what
> > bandwidth you can get with a given ms delay and % packet loss.
> >
> > As far as flow control, its really outside the scope. If you ever need
> flow
> > control, there is usually a specific reason like FCoE, and if not, it's
> > generally better to just fix the backplane congestion issue if you can,
> > than ever worry about using FC. The problem with FC isn't node to node,
> its
> > when you have node to node to node with additional devices, it isn't
> smart
> > enough to discriminate, and can crater your network 3 devices over when
> it
> > would be much better to just lose a few packets.
> >
> > -Blake
>
> In my experience - if you're traversing licenced microwave links as
> indicated flow control will definitely need to be ON.
>
> Check the radio modem stats to confirm but - if you're seeing lots of
> drops there you're overflowing the buffers on the radio modem.
>
>
