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IGMP snooping needs a router?

Hi there,

I've just purchased a Cisco Express 500, because it supports IGMP snooping. I want to prevent multicast packets to flood all the port on the switch, but I am unable to do so still. I've read a few posts on this forum, but am having a hard time to understand it clearly.

So, I have this one switch, no other switches or routers are involved. I have a streaming server which sends video streams on some multicast adresses. I have all the ports on the switch in the same VLAN, with IGMP enabled. When I trace on any of the ports (e.g. with ethereal) I still see all the multicast traffic, even though there is no client requesting any of the streams.

What am I doing wrong? I expected the switch to block all multicast traffic on all ports, and use IGMP snooping to see IGMP messages from clients requesting the video streams. I read something about an mrouter being needed. What is this / how does this work? Is there some way I can get this to work without purchasing extra equipment, e.g. with some additional software on a PC or something?

Thanx, Hans

Hall of Fame Super Blue

Re: IGMP snooping needs a router?

Hi Hans

Usually a multicast router (mrouter) acts as as the IGMP querier. However if you only need the traffic on the same vlan then you don't need a multicast router but you still need an IGMP querier.

On most of the cisco switches you can enable it to be the IGMP querier instead of a router with the "ip igmp snooping querier command".

But i had a quick look at the CE500 user guide and there doesn't seem to be an option to enable it.


Hall of Fame Super Blue

Re: IGMP snooping needs a router?


one other option is to statically map the multicast address to the switch ports but i'm not sure how easy it would be to do this on the CE 500. Sorry have used one of these before.

excerpt from cisco doc below.

Solution 4: Configure Static Multicast MAC Entries on All the Switches

You can make a static content-addressable memory (CAM) entry for the multicast MAC address on all the switches for all the receiver ports and the downstream switch ports. Any switch obeys the static CAM entry rules and sends the packet out all the interfaces that are specified in the CAM table. This is the least-scalable solution for an environment that has a lot of multicast applications.

Switch1(config)#mac-address-table static 0100.5e6f.efef vlan 1 interface

gigabitethernet 2/46 gigabitethernet 2/48

!--- Note: This command should be on one line.

Switch1#show mac-address-table multicast vlan 1

vlan mac address type learn qos ports


1 0100.5e6f.efef static Yes - Gi2/46,Gi2/48

Switch2(config)#mac-address-table static 0100.5e6f.efef vlan 1 interface

fastethernet 1/0/47

!--- Note: This command should be on one line.

Switch2#show mac-address-table multicast vlan 1

Vlan Mac Address Type Ports

---- ----------- ---- -----

1 0100.5e6f.efef USER Fa1/0/47


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