Is IGMP snooping the same as multicast?

Have you configured multicast routing? Multicast routing is required if you want to be able to multicast between subnets/VLAN's. IGMP snooping lets the switches know which ports it needs to forward the multicast traffic to (L2), whereas multicast routing is responsible for getting the multicast traffic from the source to all of the destination subnets (L3). Unless you already had multicast routing enabled on your L3 switches you probably will not be able to send multicast traffic from one VLAN to another. Try your chat program with your client on a different subnet from the server and see if multicast still works with it.

Oliver

Thanks for the explanation. I have IP multicast-routing enabled at the core switch (4507R). Since IGMP is enabled on my L2 switches I should be fine. I will test the chat probram again and try disabling/enabling multicast-routing to see what happens.

Enabling multicast routing will allow subnets on the same router to receive a multicast stream, also sourced on that router. To get multicast to got between routers, you need to enable PIM (Protocol Independent Multicast). It's pretty simple, see the following doc..

Okay, I read the documentation but I am not 100% sure I understand. I have a 4507 at the core which has multicast routing enabled. The examples seem to suggest that PIM is configured on a router, which I am guessing must also be the 4507 since I have no other router. I have a 3750G connected to the 4507 using a trunk and vlans, no routing. So, do I configure PIM on the 4507? If so, is it configured on the physical interface or the vlan? It looks as though I do not have to configure the 3750G.

Thanks for your help.

I used my smartnet contract and called Cisco. The tech told me to enable multicast routing on the 4507 and configure PIM on all my vlans (also on the 4507). IGMP snooping should be enabled on all my other switches (it is enabled by default).

Here are some commands the tech used: You can find the group address by "sh ip mroute" command and look for the source address. On the distribution switches, "sh ip igmp snooping mrouter" should point towards 4500 switch.

Thanks to all who responded, hopefully someone else will benefit from this.