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"CM down, feature Disabled" error


We hace CCM 4.0(2a) sr2a integrated with IPCC express 3.5(2).

When users are speaking over the phone,suddenly there call gets disconnected & they see an error "CM down, feature Disabled” on their IP phone.

This is happening inconsistently say 2 in 100 phones in 8 hrs shift.

I have set all the ports to 100 full on catalyst 3750 switch to which phones are connected.phones and agent desktop are connected to seperate ports on the switch.CCM server NIC & associated port on switch is set to 100 full.

Network looks quiet stable.Is there any thing to be checked on the CCM server.



Rising star

Re: "CM down, feature Disabled" error

The error means that the phones lost connectivity with callmanager. If it is only 2 phones, I do not think that callmanager service is stopping, but you check the event logs to verify. You may want to check the NIC settings on callmanager again, some upgrades actually set the NIC back to auto. You should also check CPU. If CPU is spiking, it could also cause this issue.



Re: "CM down, feature Disabled" error

You might also check your MTU configuration on your Call Manager(s). If you are running CSA, or if your Call Manager(s) are behind a firewall, you may be having a TCP MTU discovery issue. You can check this by doing the following:

Disable PMTUD:

PMTU discovery is enabled by default, but can be controlled by adding the following value to the registry:


PMTU Discovery: 0 or 1 (Default = 1)

Data Type: DWORD

A "1" enables discovery while a "0" disables it. When PMTU discovery is disabled, a MTU of 1500 bytes is used for all non local destination IP addresses. The TCP MSS=1460.

Setting this parameter to 1 (True) causes TCP to attempt to discover the Maximum Transmission Unit (MTU or largest packet size) over the path to a remote host. By discovering the Path MTU and limiting TCP segments to this size, TCP can eliminate fragmentation at routers along the path that connect networks with different MTUs. Fragmentation adversely affects TCP throughput and network congestion.


Re: "CM down, feature Disabled" error


I found only in the server registry this path


I didn`t found \EnablePMTUDiscovery\

So could anyone help me?



Re: "CM down, feature Disabled" error

Did you check your switch interfaces for errors after you set them to 100/full? AUTO is the preferred setting. Because some devices still expect an autonegotiating link partner even when manually configured for full duplex, they may be "helpful" and drop back to half duplex since they think they're connect to a device not capable of half duplex.

It can be frustrating to troubleshoot this behavior. The best course of action with modern devices is to leave them set to AUTO and avoid the problem altogether.



Rising star

Re: "CM down, feature Disabled" error

If voice media stops and the phone produces this error at the same time, the phone is what's having the problem and not CCM. Even if the phone is cut off from CallManager, that call will continue to be up at least for a short while. That's what that "CM Down, Features Disabled" message is all about. It's waiting for you to finish your call and hang up before it tries to re-register. The fact that voice media stops at the same time and (almost) everyone else is fine indicates a problem local to that phone.

As another poster mentioned, do not attempt to lock speed and duplex to the phones. You will cause far more problems doing this than you will solve. Speed and duplex are best left to auto.


Re: "CM down, feature Disabled" error

Are the phones on the LAN with the CM server or across a WAN?

My guess is the Phone Firmware...Try updating to the newest firmware on the phones...I had a problem with phones saying CM down Features disabled, but mine was being caused by a user hanging up the phone after being in a call....Then the phone would try to tell the callmanager (over a WAN) that it was ending the call but couldnt get through(dont know why) would then lock up and say CM down Features disabled and you would have to unplug the phone to get it back...Updating the firmware fixed how the phone handled this situation...

I was having the same frequency as you also...1 or 2 out of a 100 a day...


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