When thinking of deploying a large XenDesktop infrastructure, there is a not that well known challenge, which may impact seriously on your deployment and production lifecycle. This is MAC address conflicts.

Depending on the virtual infrastructure of your choice, each behave differently on MAC address assignment.

This is something to care about because of 2 important things:

With Provisioning Services

In case of using Provisioning Services, virtual machines are created as target devices being their MAC address their unique identifier.

In my case, I came across this issue when implementing PVS on a multisite configuration with 2 different vCenters. When using XenDesktop Setup wizard we started to receive VM`s creation errors from Provisoining Servers stating there were “DuplicateKey”. Drilling down a bit, I could check VM’s were successfully created from templates on both vCenters. So I decided to give it a try and tried to create target devices on Provisioning Services console right away.

Receiving same error as before, I decided to browse collections for that same MAC address and BINGO!!! There was an existing device already there with the same MAC address.

The issue started to impact us, as we were creating thousands of desktops, and around 20% of them were failing because both vCenters where assigning the same MAC addresses.

We escalate this to Vmware’s partner engaging on this project stating it was not possible to change the MAC address vCenter instance ID. So I raised this issue within the Citrix Consulting Team, and Kenichi Mineta pointed me to Vmware’s site article below. Thanks Kenichi.

Even if you are not using Provisioning Services

You may have serious issues with VM’s purely from the networking perspective. On this case, it will be a bit more painful to identify it and will very likely require traffic sniffing as the way to debug it.

Design considerations:

So for Vmware’s deployments take into consideration each vCenter default address pool is: 00:50:56:00:00:00 – 00:50:56:3F:FF:FF

Vmware already explains on this article this issue may happen and how to modify MAC address vCenter instance ID:

http://kb.vmware.com/kb/1024025

Seriously consider to assign a different MAC address vCenter instance ID range for each vCenter, so you will avoid MAC address overlapping and conflicts.

Stay tuned for next post on design considerations with XenServer and VMM.