There is nothing out of the box from Cisco that will do this. You will have to either use the LDAP directory and integrate these two Clusters together or purchase a third party tool such as Citrix Application Gateway. It can basically merge two LDAP directories and serve any and all Cisco clusters.
If that is not an option, you will need to create some sort of XML app that will be able to search each directory from CUCM. I would imagine it would not be too hard. Just have to create the first xml page to have them select which directory they search for.
for a client I have implemented something similar, it's a middleware application that imports both cluster's users via AXL (so you don't have to rely on LDAP!) and presents a consolidated directory that can be searched by users(phones) from both clusters.
This is really fast, but requires a nightly (or x hourly) import of all users
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The short answer is that you don't.... That isn't entirely true while at
the same time it kind of is, but for the most part you don't configure
the softkeys. You enable or disable them via TCL. Here is the long
answer. Be sure to read the whole thing or e...
Topology: IP Phone > Switches > Microsoft NPS setup to forward 802.1x
proxy to > ISE 2.1 patch 3 Authentication: EAP-TLS using Cisco MIC SANs
Phone Models 802.1X support? 802.1x flavor Addtl Comment EAP-MD5 EAP-TLS
Cisco 3905 Y Y N Cisco 6911 Y Y N Cisco ...