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Is IGMP snooping the same as multicast?

I was asked to enable multicasting on my network (4507R core, 3750G distribution, 3560G access). I ensured IGMP snooping was enabled and used a packet sniffer to check for activity such as joining and leaving a session while using a chat program that uses multicast. I saw the exepcted traffic and the application worked. Is this enough to enable basic multicast support? or is there something more that is needed? I had a look at the Cisco documentation but I see a lot of information on IP Multicasting which I'm not sure is the same thing.

thanks

Reply to
1crazyrican
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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

Reply to
Oliver Garraux

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.

Reply to
1crazyrican

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..

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Reply to
Thrill5

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.

Reply to
1crazyrican

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.

Reply to
1crazyrican

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