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Automating the retrieval & reclamation of VM MAC address blocklist for vCenter Server using the vSphere MOB

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As shared in this blog post HERE and HERE, vCenter Server has a built-in mechanism for managing VM MAC addresses where the original VM has been migrated to a different vCenter Server (regardless of the vCenter SSO Domain) using a VM MAC Address blocklist.

The VM MAC address blocklist functionality is still only available using a private API and the only way to find out what VM MAC addresses are currently in the list is by interactively using the vSphere MOB and the fetchRelocatedMACAddress API.

Recently, I had a question from a customer who was looking to clear the VM MAC address blocklist and was wondering if that was possible and whether there was an API to perform this operation?

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Does vCenter Server recycle VM MAC Addresses after Cross vCenter vMotion?

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I recently received a question from a customer who was concerned that after a VM has been migrated from one vCenter Server to another using Cross vCenter vMotion, that the original source VM MAC Address could potentially be recycled and re-used at a later point. Back in 2015, I actually wrote about this very topic and the concerns around VM MAC Address duplication after a Cross vCenter vMotion, which I highly encourage folks to check out if you have not seen this article already.

While re-reading the article, I realized that the article had primarily focused on vCenter Servers that were in Linked Mode or under the same vSphere Single Sign-On (SSO) domain and although I did mention the Cross vCenter vMotion across across different vSphere SSO domains scenario, it looks like the details were a tad bit light.

To quickly summarize, when a VM is migrated from a source vCenter Server to the designation vCenter Server, the VM's MAC Address is added to a MAC Address "block list" on the source vCenter Server. This ensures that the VM MAC Address will not be reallocated by the source vCenter Server which would cause a network conflict. This has been the default behavior since vSphere 6.0 and no additional configuration change is required by customers.

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How to deploy the vCenter Server Appliance (VCSA) with a custom MAC Address?

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I recently had a question that came in from our field where a customer needed to deploy the vCenter Server Appliance (VCSA) with a specific MAC Address which was a requirement to ensure property connectivity within their network. This type of network requirement is not really new or unique, it is a common practice used to ensure only valid VMs with a static DHCP reservation can actually connect to a specific network but it certainly was the first time I had heard of this request for the VCSA.

With the default VCSA installer workflow, there is currently not a way to modify the network MAC Address which is automatically generated after the deployment of the OVA. Having said that, I have spent quite a bit of time exploring the various non-standard methods of deploying the VCSA in the past (see here, here and here) and with that information, you definitely can affect the MAC Address while still maintaining a valid VCSA deployment. With a bit of trial/error, there are two options depending if you are deploying the VCSA directly to an ESXi host (for initial setup) or to an existing vCenter Server. To demonstrate how this works, I have created a basic shell script called VCSAStaticMACAddress.sh which you can easily adapt to for a Windows-based environment.

The trick is that when you deploy to a vCenter Server endpoint, the required OVF properties are persisted which would allow you to only deploy the VCSA but not actually power it on and there you can easily augment a number of settings including the MAC Address. In the case of deploying directly to an ESXi host, OVF properties are not persisted and hence a challenge if you wish to make changes prior to powering on the VM. In earlier versions, it was possible to set these OVF properties by way of using the extraConfig property of the VM but it looks like this trick no longer works and requires a slight variation of the workflow which is described in the instructions below.

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