All things related to multicast

[John Meylor <>]

Mark Boolootian wrote:
> 
> I'm interested in knowing how folks deal with multicast across a
> layer 2 core.  Our campus backbone currently has a layer two core which
> is treated as a common backbone subnet.  While that makes traceroutes look
> nice, multicast traffic floods and all the backbone router interfaces see
> it, whether they need to or not.
> 
> As we roll out gigE in the backbone, the topology is moving towards a
> collection of point-to-point links, so the multicast flooding over a
> layer 2 core problem will go away.  Nonetheless, I'm interested in knowing
> how others have dealt with this issue.  It would seem your choices are
> 
>   o Overlay the layer 2 core with layer 3 point-to-point links
> 
>   o Run the appropriate protocol for mitigating this problem.  Cisco has
>     RGMP, which sounds like CGMP all over again.  Foundry, and perhaps
>     others, is doing PIM snooping, which sounds like the right way to do
>     it to me.

I wouldn't discount value of RGMP so quickly, its provided
a simple, effective solution to these router-only L2 forwarding 
problems in many deployments for some time now.  It does require
the router to talk to the switch, but as its sw solution in L3
it also can be used in most cases today.

 john



> 
>   o Live with it.
> 
> Any experience/comments would be appreciated.
> 
> thanks,
> mb
> ---
> Mark Boolootian
> UC Santa Cruz