VMware Horizon 7.3.x – Resolving “Protocol failure” status on VMs

Recently I went through the process of upgrading a VMware Horizon 6.1.1 VDI environment to 7.3.1 which was just released, and apart from some small teething issues with licensing during the upgrade due to a slight oversight in the VMware documentation everything else appeared to go smoothly.

As this environment uses View Composer Linked-Clones for non-persistent desktop pools part of the upgrade involves installing the new Horizon 7.3.1 agent onto the gold master VM template for each desktop pool then performing a recompose of the VMs in those pools.This is where I ran into an issue.

After upgrading the agent and performing a recompose operation on the VMs within each desktop pool they then displayed a Protocol failure” status within Horizon Administrator although I could still login to them as normal through the Horizon Client.

On doing a bit of research it appears this error can be generated if the firewall ports for a particular display protocol aren’t opened between the Horizon guest VM agent and Horizon Connection servers – in the case of Horizon this can be the Remote Desktop Protocol or PCoIP (PC over Internet Protocol) depending on how you have configured your desktops. In my case PCoIP was being used and all required ports between the guest VM agent and Horizon Connection servers were opened.

Verifying that everything within the environment was how it should be I then turned my attention back to the Horizon agent on the gold master VM template. Thinking that perhaps the upgrade from 6.1.1 to 7.3.1 had affected something I decided to completely uninstall the agent, reboot and install 7.3.1 again from fresh then recompose the VMs in desktop pools from the new snapshot.

This time after the VMs had passed their customizing stage and I was then presented with the “Available” status as normal. Success!

So with that here are some takeaways from this after doing some extensive reading.

If you have VMs displaying a “Protocol failure” status within Horizon Administrator do one or more of the following;

  • Verify the required TCP ports are opened on the guest VMs with the Horizon Agent installed – a list of these can be found here
  • Verify the Horizon Agent services are running on the guest VMs – a list of these can be found here
  • Check for a “ghosted” network adapter on the gold master template VM and remove it – more info can be found here
  • Uninstall the previous version of the Horizon Agent first if upgrading to a newer version.

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