MoH Multicast on CME to 3560G

Answered Question
Jan 27th, 2009

CME 7.0(1) on 2811

3560G 24 Port PoE switch

The ports on the 3560G were very chatty, which I assumed was from the Multicast MoH stream send by CME. I configured IP Multicast routing on the voice VLAN for both the 2811 and 3560G. The excess traffic on the 3560G has subsided except the Ethernet trunk that links the 3560G and 2811 is still extremely chatty.

Should I be concerned or is this normal behavior?

Correct Answer by Nicholas Matthews about 8 years 3 weeks ago

CME by default will just start streaming the multicast when it is configured. It isn't 'kicked off' when MoH is called like one may expect.

In this scenario, the router is a simple multicast source. Meaning, you don't even need full multicast configuration on it. In this situation, it means that CME will stream the MoH towards the switch. This means your best case scenario is MoH on your trunk at all times, plus the ports for the IP phones.

hth,

nick

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Nicholas Matthews Tue, 01/27/2009 - 10:14

We find that in many cases we require to turn off IGMP snooping in order to get CME multicast to work.

This is because the phone does not send an IGMP join message to join the stream. Because of this, the switch floods it everywhere, all the time.

When the phone is told to listen to multicast, it just changes it's listen port to listen to the multicast.

hth,

nick

voipis4me Tue, 01/27/2009 - 12:48

Nick,

I disabled IGMP snooping on the 3560G and the switchports went back to being chatty.

MoH works fine. I am just concerned about the chatty trunk port.

Do you have any other suggestions?

Correct Answer
Nicholas Matthews Tue, 01/27/2009 - 13:24

CME by default will just start streaming the multicast when it is configured. It isn't 'kicked off' when MoH is called like one may expect.

In this scenario, the router is a simple multicast source. Meaning, you don't even need full multicast configuration on it. In this situation, it means that CME will stream the MoH towards the switch. This means your best case scenario is MoH on your trunk at all times, plus the ports for the IP phones.

hth,

nick

voipis4me Tue, 01/27/2009 - 13:49

Nick,

I checked the counters on the switchport, plus periodically checked cpu utilization and they are all minimal. I guess I was just being paranoid.

Thank you for the insight.

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