Limiting Multicast for Cisco CME - MOH

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May 17th, 2009
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Greetings, i have a relatively small CME setup with approx 50 handsets spread across three 2960 switches and a 2851 ISR running CME 7.1.

The CME router itself is connected to a 24 Port Gigabit 2960 whilst the phones are connected across two 24 Port 2960 PoE switches. Each PoE switch is trunked to the gigabit switch.

Im trying to limit multicast traffic to the voice vlan 102 without flooding the rest of the network.

So far i have done the following:

- Disabled IGMP snooping on all other vlans except 102 across all switches

- Configured a multicast group on all switches matching the address used on the CME system "" placing relevant ports into the group whether they be connected to phones or the CME system itself

- Configured the port which is connected to the CME router as a MRouter port

- Disabled immediate leave on vlan 102 across all switches

- Specified PIM-DVMRP as the protocol on all switches.

Unfortunately i am unable to get MOH for internal users when implementing this configuration, if i remove all the config it works as expected but the switches literally go nuts in the process.

I admit i know little about multicast, any assistance or a nudge in the right direction would be much appreciated.


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paolo bevilacqua Sun, 05/17/2009 - 09:22
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You should leave things as they are and forget about it.

CME MOH is a quite low bandwidth traffic and will not hinder anything else on your network.

Never heard of anyone having problems with it.

Giuseppe Larosa Sun, 05/17/2009 - 10:40
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Hello Mark,

>> Disabled IGMP snooping on all other vlans except 102 across all switches

this has a terrible impact on the switches making them to flood all multicast in all vlans !

Stay with default config and enable

ip multicast routing


ip pim sparse-dense-mode on router subif in vlan102 so that it will performs as IGMP querier.

access-list 2 deny host

access-list 2 permit any

if you want to be sure that it is not used on other subnets use

ip pim rp-address

ip igmp-group 2

out all other subinterfaces of router using the acl 2 as defined above.

In this way PIM SM will be used and igmp joins to will be not accepted on other subnets.


Hope to help



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