[c-nsp] Weird Multicast microburst amplification issue

[Matthew Huff]

No span sessions enabled.

It definitely looks like a classic microburst output buffer overflow problem, but with a Sup720 and a 6748 module, I haven't seen this at this volume. Ticker volume has peeked recently, and that might contribute to it. It appears to start happening with more than 120Mbps and/or 12,000 pps output on the port. Other than moving to 10GB, I don't see any solutions. Given the 6748 buffer size, I'm surprised it's overrunning it at this volume.



----
Matthew Huff             | 1 Manhattanville Rd
Director of Operations   | Purchase, NY 10577
OTA Management LLC       | Phone: 914-460-4039
aim: matthewbhuff        | Fax:   914-460-4139


> -----Original Message-----
> From: Dale W. Carder [mailto:dwcarder at wisc.edu]
> Sent: Monday, December 12, 2011 10:10 AM
> To: Matthew Huff
> Cc: 'cisco-nsp (cisco-nsp at puck.nether.net)'
> Subject: Re: [c-nsp] Weird Multicast microburst amplification issue
> 
> Do you have any span sessions enabled?
> 
> Dale
> 
> Thus spake Matthew Huff (mhuff at ox.com) on Fri, Dec 09, 2011 at
> 01:48:35PM -0500:
> > We have a multicast data stream (real-time ticker data) that by its
> nature is very bursty.
> >
> > When we connect a source server via gigabit Ethernet to our
> 6500/sup720 switch via a 6748 module and a destination server via
> gigabit to  the same or different module in the same switch, everything
> works fine. If the destination server is on a different switch
> connected by a layer3 10GB connection then we have significant output
> drops on the Ethernet connected to the destination server.
> >
> > All switches are 6509/sup720 with 6748 line cards. QoS is disabled
> globally. The servers are identical. The output drops only occur on the
> Ethernet drop connected to the server.
> >
> > The only thing I can think is happening is that by routing the
> traffic via the 10gb L3 interface, something is causing the traffic
> burst to amplify, overrunning the output port. Has anyone seen this,
> and does anyone know how to mitigate this?
> >
> > ----
> > Matthew Huff             | 1 Manhattanville Rd
> > Director of Operations   | Purchase, NY 10577
> > OTA Management LLC       | Phone: 914-460-4039
> > aim: matthewbhuff        | Fax:   914-460-4139
> >
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