Multicasting and Switches
After the RP discovers multicast end stations off a given segment and begins receiving multicast traffic from the server, it forwards this traffic to the segment. In today's networks, that usually means that the first networking device that receives this traffic is a switch. Switches flood the traffic throughout the VLAN, treating it like a local broadcast. This could have a serious effect on the performance of a VLAN, especially if the multicast information is a video stream.
Controlling Multicast Traffic
With the use of a multicast routing protocol running on your RPs, you've solved your Layer 3 problems in the intelligent forwarding of your multicast traffic. Now you'll have to deal with the issues of your switches ...