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Catalyst multi-cast traffic on trunks

Can anyone explain why the counters on our catalyst switches are seeing multi-cast frames. We are not running any IP Multicast traffic, but the port counters on the trunk ports are counting ethernet multi-cast frames. I guess I don't understand L2 multi-cast. Any links to documentation appreicated...

Thanks

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Cisco Employee

Re: Catalyst multi-cast traffic on trunks

There is lot of other switch control traffic which is multicast(examples: BPDUs, HSRP). Also if you have CAT5000 series switches, when traffic is transmitted over an ISL trunk, the output from the show mac command shows transmitted unicast and broadcast packets as multicast packets.

http://www.cisco.com/cgi-bin/bugtool/onebug.pl?bugid=CSCdm32224

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