Do have Cisco fallback scenario if the migration fails.
At the migration from CUCM 8.6 to CUCM 10.5 we have to go back to CUCM 8.6.
You need to provide more information on the scenario you are asking about. The simple answer is turn off the 10.5 cluster and restart the 8.6, but that is assuming you did a migration from one server to another. Did you actually migrate to different hardware? Did you upgrade on the same server? Did you make a DRS backup of your 8.6 cluster?
Normally, a switch version takes you back to the previous version, but your question implies that you cannot do this operation. So I would be interested in why you cannot revert version.
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We are not using DRS reason we are going from Unrestricted to restricted then you are need to export/import configuration to CUCM 10.5
CUCM 8.6 are installed on MCS server we do not use PCD not possible
When we migrate from CUCM 8.6 to CUCM 10.5 at the migration we hit defect in the software.
Regarding CTL, ITL certificates and TFTP problem.
We are used the Enterprise parameter fallback to 8.0.
Only the phones are not more willing to register to the CUCM 8.6 cluster.
The phones were in random state.
Solution power off/on the phones.
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