[c-nsp] Multicast Behavior on a Cat issue...

[Tim Stevenson]

Don't know your span configuration, but I think you are probably 
hitting a known limitation of SPAN in conjunction with 
multicast/flood traffic, ie, CSCds22021.

You are right, we are not actually sending the packet back out on the 
receiving port in this case.

Tim

At 05:26 PM 9/1/2005, Dave Temkin noted:
>Does anyone have a link to how multicast should behave on a Catalyst?
>
>It's my understanding that when a host sends out traffic to a group it's
>subscribed to, the Cat is smart enough to check the source MAC address of
>the traffic and not forward the traffic back to the port that sent it into
>the network.   I'm seeing an issue where this isn't happening - a host is
>publishing a significant amount of multicast, and when we span the port we
>see two copies of the traffic (from the host out to the switch, and then
>from the switch back to the host).
>
>Cisco hasn't been much help to us thus far, but we can't imagine this is
>the intended behavior.
>
>Thanks,
>-Dave
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Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Technical Marketing Engineer, Catalyst 6500
Cisco Systems, http://www.cisco.com
IP Phone: 408-526-6759
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