# Migrating VMs to an older ESXi version

Hi all, just a short post about a small task I had on my desk last week. Customer needed to migrate a 3 servers from current provider to one of our older platforms. Few issues to overcome. First off only had VPN access to the provider and access to the ESXi 6.0 web UI that was running the VMs. So how to export them without downtime? No way to do something like a Veeam replication as I only had the VPN connection. Had to do an export-import scenario. Clone them? Requires vCenter. Hmm.

So what did I do? Well I asked nicely and was allowed to deploy a temporary VCSA onto the host and add the host itself to the vCenter. This allowed me to clone the 3 VMs (after removing a metric f***ton of snapshots). Then I could export the cloned VMs as OVFs to a machine in our network. It was lucky that I could do this and did not need to do the entire operation in a service window. The last copy of the machines were not needed as it was more of a “configuration copy” than anything else. So while the customers systems were running we could move the cloned VMs.

Now came the tricky part that I did not foresee but quickly identified! I exported from a vCSA 6.7 U1 and an ESXi 6.0 host. This makes a SHA256 signed OVF. Trying to import this to a 5.5 vCenter fails as the 5.5 vCenter does not support SHA256. OVFtool has a nice feature where you can convert the OVF from SHA256 to SHA1 by making a new package with the following command:

ovftool --shaAlgorithm=SHA1 .\path\to\file.ovf .\path\to\destionation.ova

Simple! Converts the OVF to an OVA with SHA1 instead of SHA256. Import now works. Wait not it did not! The machines are VMX-11 which does not run on ESXi 5.5. What to do. Recommended approaches are to use VMware converter to convert the VM and downgrade the hardware version. I took a slightly more simple but probably also more unsported route.

VMX version is defined in the OVF som it was simple to open the OVF file and locate the “SystemType” parameter and change it from “vmx-11” to “vmx-10”. This however breaks the manifest files SHA256 hash of the OVF file. This is simple to fix aswell using “certutil” on Windows. Following command generates a SHA256 has for a file:

certutil -hashfile .\path\to\file.ovf sha256

Simple replace the SHA256 thumbprint in the manifest file with the one generated above. Rerun the SHA1 conversion above and import now works. My colleague who needed the VMs converted reported back later that day and confirmed machines were booting fine and running as they should so he could continue reconfiguration of the machines.

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