CUCM 11.0 upgrade to 12.5 ESXi mismatch

[m.goretti]

My customer would like to upgrade his collaboration infrastructure (CUCM, IM&P, Unity Conn) version 11.0 to version 12.5
There are currently 2 x BE6000s with VMWARE 6.
From the compatibility matrix VMWARE 6 is not supported by CUCM 12.5 and of course version 11.0 is not compatible with version 6.7

11.0
https://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/uc_system/virtualization/older_pages/virtualization-cisco-unified-communications-manager-older.html#v11

12.5
https://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/uc_system/virtualization/older_pages/virtualization-cisco-unified-communications-manager-older.html#v12.5

However, I saw from the VMWARE compatibility matrix (https://kb.vmware.com/s/article/2007240) that the VM hardware number (8) of the CUCM, IM & P is supported by version 6.7

What is the correct upgrade procedure?

Can I upgrade ESXi to version 6.7 first and then the Collaboration infrastructure?

Can I upgrade the ESXi version even if the applications are not supported? I tested in lab environment the operation of a CUCM 11.0 on VMWARE 6.7 and the VM did not give any problems.

Or first upgrade Collaboration Apps and then upgrade ESXi ?

I found this recommendation from Cisco. It's correct?

You must install a version of vSphere ESXi hypervisor that meets the requirements of the release. We recommend that you upgrade the ESXi hypervisor before you begin an upgrade of Cisco Unified Communications Manager or IM and Presence Service; however, if your currently installed version of these applications is not compatible with the ESXi version required for the new release, you can upgrade the ESXi version after you upgrade the Cisco applications

[Nithin Eluvathingal]

Upgrade the Vmware first and upgrade your UC applications. 

[Deepak Kumar R]

Hello @m.goretti I came cross the same situation earlier this year. I had to plan the activity in two phases ( 2 x maintenance windows), first one to gracefully shutdown all VM on the ESXi host and upgrade it to the compatible 6.x version. During the second maintenance window we upgraded the collab applications. You will have to upgrade your exsi first and then the collab apps. There is no choice here. Also ensure your Vmware Esxi's support contract is current. Other wise you wont be able to upgrade your esxi.

[Nithin Eluvathingal]

If you are on version 6.0 and upgrading the version to 6.7 doesn't need a contract as you will use the same license key.

Use Cisco Custom Vmware which you can download from the link

Another main thing which you must do before upgrading the Vmware is upgrade your CIMC version asper the Vmware compatibility.