igmp/cgmp doubts

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Nov 22nd, 2008
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in multicasting..

-is it possible to have pure igmp working on routers and igmp snooping on the switches? in this case i dont need cgmp.

-or igmp/cgmp on the router along with cgmp on the switch?

am confused coz of the ff;

1-igmp snooping could watch the igmp request/report and forward multicast to the correspondig switchport found on EARL table.

2-cgmp on the router could inform the switch thru cgmp as to the mac of the host who have requested/reported for a multicast which is the same thing as 1

please help me clarify this doubts

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Joseph W. Doherty Sat, 11/22/2008 - 12:07
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If I remember correctly, cgmp was an early Cisco proprietary feature preventing multicast flooding all ports. If the switch supports igmp snooping, suggest you use it instead. Unsure whether you can mix the two.

Paper with additonal information on both. http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00800b0871.shtml

Jon Marshall Sat, 11/22/2008 - 14:01
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You generally use either IGMP or CGMP for switches. IGMP is the more modern one and is implemented in hardware on switches.

If you use IGMP there is no need to implement CGMP. IGMP works on a switch by listening to the answers to IGMP queries which are usually made by any PIM enabled L3 interface. There is also an IGMP querier function that can be used on some switches if you don't have a L3 PIM enabled interface.

CGMP is a software based solution that relies on the L3 router to inform the switch which ports to add to a multicast group.

They achieve the same thing in different ways. If you can run IGMP this is the one you should run.



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