Implement Multicast Tomorrow

Unanswered Question
Jul 11th, 2007
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I have been asked to implement multicast within our network tomorrow and just wanted to ask a few questions.

We have a 3550 core (HSRP) and 2950 and 3560 poe switches for the access layers.

I was proposing to configure the core as per:

ip mutlicast-routing

ip pim send-rp-announcce vlan1 scope 16 ip pim send-rp-discovery scope 16

interface vlan 1

ip cgmp

Then on the access switches

ip multicast-routing

int vlan 1

ip pim sparse-mode

ip cgmp enable

But I do not know if i should enable igmp snooping on the access switches for if the IGMP on the core is enough to stop the multicast propogating.

I also didn't know whether to duplicate the config on the hsrp other switch.

Thanks for any advice


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Jon Marshall Wed, 07/11/2007 - 09:29
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Hi Sam

You need to enable IGMP snooping on all your switches. If you don't then say a client on one of your access switches wants to receive a multicast stream. The packet is sent down to the switch but if it doesn't have IGMP snooping turned on it will have to flood the packet out all ports.

You have ip cgmp turned on. This is an either or thing. Either you run IGMP snooping or you run CGMP - you don't need both. It is recommened to run IGMP snooping if it is supported in hardware.

Yes if you want resilience you will need to configure both your core switches with the multicast details.

Good luck



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