[c-nsp] Weird Multicast microburst amplification issue

Matthew Huff mhuff at ox.com
Fri Dec 9 14:24:45 EST 2011

Unfortunately, it isn't something simple like that. The output drops are continuously happening. The network is very stable. There are not other issues during this time. It's something amplifying the burst of the stream, either the multicast replication or passing through the layer 3 interface.

IF we run a test with a server on switch a, a client on switch a, and a client on switch b, only the client on switch b is seeing the problem. The problem isn't passing the data from switch-a to b, but rather something during the transmission that changes the shape of the data to be a heavier burst.

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: Chuck Church [mailto:chuckchurch at gmail.com]
> Sent: Friday, December 09, 2011 2:11 PM
> To: Matthew Huff; 'cisco-nsp'
> Subject: RE: [c-nsp] Weird Multicast microburst amplification issue
> Are there multiple streams passing through the switch?  A spanning tree
> recalculation will cause IGMP to flush associations, and flood all
> streams out all ports until they're relearned.  Portfast will fix it,
> as will a multicast-specific interface command, would need to look it
> up.
> Chuck
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Matthew Huff
> Sent: Friday, December 09, 2011 1:49 PM
> To: 'cisco-nsp (cisco-nsp at puck.nether.net)'
> Subject: [c-nsp] Weird Multicast microburst amplification issue
> 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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