[c-nsp] Weird Multicast microburst amplification issue

[Matthew Huff]

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?

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