IP Multicast delivery using IGMP

Unanswered Question
Aug 26th, 2009

Do I need to have PIM enabled on a local network or is IGMP enough for multicast data delivery. We have the MC source connected to a Layer 2 Cisco switch that has IGMP snooping enabled. The MC receivers are also connected to this switch. Is it possible for each multicast receiver to only subcribe to a specific MC group or do we need to have PIM enabled on this switch? Is IGMP snooping enough?

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Jon Marshall Wed, 08/26/2009 - 06:39

You need to enable PIM if


1) your source and receivers are in different vlans so you need to route the multicast traffic


OR


2) Something must makes IGMP queries for the IGMP snooping function to listen to the answers ie. IGMP snooping is a passive function, it can only listen to answers rather than send out the query itself.


However some switches have a function called the "IGMP snooping querier" where they can send out IGMP queries so IGMP snooping can listen to the answers.


If your switch has this function you do not need PIM on the vlan interface. If it doesn't you do.


Jon

Peter Paluch Wed, 08/26/2009 - 06:39

Hello,


As long as you do not need to forward your multicast traffic through a router, the IGMP snooping support on your Layer 2 switch should be fine.


However, be sure to activate the IGMP Querier support on the switch to elicit IGMP reports from connected workstations. Enter this command in your switch configuration:


ip igmp snooping querier


Best regards,

Peter


jschweng Wed, 08/26/2009 - 07:21

Everything is on one vlan. We will try that querier command. Thanks so much.

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