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New Member

Configure Extension Mobility in failover


I have installed 2 server Call Manager version 7.1.3 (Publisher and Subscriber).

I want to configure Extension mobility in failover using server Load Balancing (SLB) as recommanded by Cisco.

I want to know which type of server can I use for SLB? because I use NLB Manager in server Windows 2003 but he can't to connect to my servers Call Manager, I have a message: Could not locate NLB on the specified computer.

It's not possible to configure Load Balancing using a server Windows 2003 with Cisco Call Manager version 7?

Thanks in advanced,

best Regards,



Re: Configure Extension Mobility in failover

I have seen normally ACE as SLB or IOS SLB feature for EM working.

Any other device that is capable of getting detailed down to the
HTTP URL, should work fine as well - especially if this Virtual IP is
specifically used for EM logins.  It doesn't have to follow through with the
whole login process ... just initiate an HTTP GET to the EM Service URL and
ensure that it gets a response prompting for username & PIN:

Have you manage to use SLB with other HTTP applications not only EM?


Super Bronze

Re: Configure Extension Mobility in failover


Windows NLB isn't meant to be used that way - it's used to make a HA virtual cluster out of several Windows servers. Linux doesn't have that feature, and the ability to use Windows admin tools to administer anything on Linux is very rare.

Theoretically you could create a Windows NLB cluster and write your own app to check for an active CCM EM service and redirect the user (phone) web session to that; however you'd need some reasonable web dev skills.

The easy option is to

- create multiple DNS A records for the same name (such as '') pointing to at least two CCM servers running the EM service

- point your initial EM service URL at that hostname instead of the publisher IP

- point the servicess URL at the same hostname instead of IP

- ensure your phones have valid DNS servers assigned to resolve the above

In failover scenarios, the phones often have delays as they try the failed server before switching, but it's better than nothing.

Otherwise get a hardware load balancer...


Please rate helpful posts...

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
New Member

Re: Configure Extension Mobility in failover

Hi Aaron,

Thanks for your answer,

Yes, the problem of using DNS to configure EM redundancy is the delay that can take some phone...

But I have other problem with the IP phone 7912, these phones return the message "Connection error " if the name Cluster check the server that's down.

Do you have any idea? is the type 7912 supported with the olution of DNS?

Thanks a lot,

bets Regards,


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