Implementing Extension Mobility Redundancy

Unanswered Question
Aug 4th, 2010

hi all,

I have installed CUCM version 7.1.3 (2 servers : Publisher and Subscriber).

I have implemented EM redundancy using DNS,

i've created hostname in my DNS poiting to both nodes ( PUB & SUB) IP adresses and i've changed the URL service from IP adresse to the hostname.

Everything work fine when both nodes are up. Once one fo node goes down some ip phone take a very long time requesting the EM service. from my observation, i noticed that some ip phone point always to the Publisher and other point always to the Subscriber, once the server that they point to is down they take a long time to process EM login operation.

i'm wondering if there is any solution that makes this kind rendundancy work more  quickley.

thx in advance for your valuable help.

Best Regards,


I have this problem too.
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Jonathan Schulenberg Wed, 08/04/2010 - 05:08

Yes, use a load balancer such as Cisco ACE.

Your DNS server is providing two IP addresses to the phone. Typically it round robins the addresses on queries which is why some of your phones have the publisher while others the subscriber. The phone has to wait for the maximum timeout (not adjustable) to expire prior to moving on to the second address provided by DNS. Newer firmware at leasts retains the secondary address after successfully loading the initial URL for subsiquent operations (e.g. login submission).

Criss Sawyer Wed, 08/04/2010 - 05:51

hi Jonathan,

do you think that upgrading ip phones firmwares will help to minimize waiting time for this opertion?

in fact, 7912 ip phones display "Connection failed" message  during their subsequent login submission. other types take a very long time to recognize their subsequent Server.

Jonathan Schulenberg Wed, 08/04/2010 - 05:55

It's usally worth trying. You can do it on only one or two phones first if you want to test it. 8.5(3) or 8.5(4) have been stable releases.

Criss Sawyer Wed, 08/04/2010 - 07:26

hi jonathan,

wich type of ip phones do you mean? if yes,  i did not find 8.5(3) or 8.5(4) releases in cisco web site, i already upgrade 7912G phone to 8.0(4) release but it did not work and i still get the "Connection failed" message.


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