[c-nsp] CEF and multicast on a 3750

[Gert Doering]

Hi,

On Tue, Jun 26, 2012 at 08:39:35AM -0600, John Neiberger wrote:
> On Tue, Jun 26, 2012 at 7:59 AM, Gert Doering <gert at greenie.muc.de> wrote:
> > On Tue, Jun 26, 2012 at 06:55:41AM -0600, John Neiberger wrote:
> >> > Odd. How intermittent? What's the traffic rate?
> >>
> >> We seem to start losing packets at around 250 Mbps of total multicast
> >> traffic, as I recall. I'll double check when I get in to work.
> >
> > Bursty ingress from multiple sources?
> >
> > This could just be the "tiny buffer" syndrome... are you seeing output
> > drops on the egress ports?
> 
> The sources are constant bit rate video sources, so they're not
> bursty. 

Ahem.  "20 packets per seconds" is "constant", but can be bursty as well,
like "send 20 packets as fast as you can go, and then wait 0.99 seconds".

Unless your sure that your sources are *really* sending their packets
equally spaced on a microsecond scale, assume microbursts.

> We are not seeing output drops on most interfaces, but I just
> noticed that we had a few thousand output discards on an interface
> facing one of our monitoring devices. I'll need to figure that out
> because it is our monitoring device that is reporting most of the
> problems. We only have about 340 Mbps of traffic facing that probe,
> though, so I have no idea why we'd be seeing output drops.

This might be good news in the end - no output drops to the customer,
only to the monitoring system.

We do not have much experience with 3750s, but I have been told that
they have the same too-small buffers as 2960s - and there, we have
seen packet drops in our audio streams ("constant bit rate" - but 
streaming servers that produce microbursts) as soon as we hit about 
25% of the egress port capacity...

Solution #1 - move stuff to a 6500 (which is what we did in the end),
or solution #2, add a 2nd GE to the link to your monitoring box
(which is what we did initially, spread out ~800 Mbit/s across a 4x GE 
channel...)

gert
-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 305 bytes
Desc: not available
URL: <https://puck.nether.net/pipermail/cisco-nsp/attachments/20120626/a6350ba5/attachment.sig>