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

[Dave Temkin]

Tim,

	This sounds about right.  I'm going to test this with a machine
running snoop on the actual publisher on Tuesday and see if I see the same
results (doubles in the SPAN sniff, but not on the actual machine).

Thanks,
-Dave

On Fri, 2 Sep 2005, Tim Stevenson wrote:

> 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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