I'm fairly new to IP Multicast. I've been reading up on it and it is getting harder and harder to grasp. I have a Cisco 4506 running as my core switch. It is doing all my inter vlan routing. It is the only router on our LAN. I have about 30 other edge switches. about 30 vlans total with roughly 800 hosts. I inherited this network and at first everything was running on vlan 1. Now i have segmented it a little but there is still about 50% of the hosts on vlan 1. I'm trying to configure multicast on our network. I first realized i needed multicast when our Ghost stopped working. I have enabled IP Multicast-routing, igmp snooping is enabled, Loopback interface on 4506 is the RP, IP PIM Sparse-mode on necessary vlans. When i turn on IP Pim SM on a vlan other than vlan 1, the CPU is fine. But when i enable it on vlan 1, the cpu stays at 80-90%. It eventually drops to around 70 but it spikes. I know vlan 1 is the problem, but i want to know if i have configured multicast right. Like i said, all of this is on my 4506. Also, when i run SHOW IP IGMP GROUPS, i get a huge list of groups. A lot of printers, servers, and weird things like our proximity panels. any ideas?