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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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vMotion across different VDS version between onPrem and VMC

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For those of you who have attempted a vMotion (whether that is within a vCenter Server or between different vCenter Servers (including across SSO Domains), if the VM is running on a Distributed Virtual Switch (VDS) and the version of the VDS is not the same between the source and destination (VDS 6.5 to VDS 6.7), the operation will fail with the following error message (UI and API):

Currently connected network interface 'Network adapter 1' cannot use network 'DVPG-VM-Network (VDS-67)', because the destination distributed switch has a different version or vendor than the source distributed switch.


This behavior is no different on VMware Cloud on AWS (VMC) or at least, I thought it was, until I recently learned about a really neat feature that was introduced in the VMC 1.4p2 release, here is a snippet from the release notes:

Cross VDS version vMotion Compatibility
With this advanced configuration option enabled, bi-directional vMotion between on-premises and VMware Cloud on AWS can be achieved across different virtual distributed switch (VDS) versions (greater than or equal to version 6.0). This must be enabled on the on-premises vCenter.

It turns out there is actually a way to allow vMotions across different VDS versions, this is important for VMC because the software stack will always be using a newer version than what we ship to our onPrem customers. However, due to this limitation, we could not benefit from the latest VDS version but had to default it to VDS 6.0 to ensure that customers could migrate their workloads. The advanced setting mentioned in the release notes allows us to disable the strict compatibility check which is performed on the destination vCenter Server when a vMotion is initiated, this setting is now enabled by default on the VMC vCenter Server which is why you can perform migration across different VDS without having to do anything special on your onPrem vCenter Server.

UPDATE (11/07/21) - Thanks to Robert Cranedonk, it looks like you can now also vMotion across different NSX-T Logical Switches by adding vCenter advanced setting called  config.vpxd.network.allowVmotionBetweenLogicalSwitches and set the value to true.

UPDATE (01/02/21) - If you are running vSphere 7.x, an additional advanced setting must be configured called config.vmprov.enableHybridMode and set the value to true. For more details, you can refer to this VMware KB 79446. Thanks to reader Marc Alumbaugh for sharing this finding!

UPDATE (10/16/18) - With the release of vSphere 6.7 Update 1, customers can now also vMotion VMs from on-prem running on a VDS to VMC with NSX-T N-VDS.

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Bulk VM Migration using new Cross vCenter vMotion Utility Fling

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Over the last few years, I have spoken to a number of customers who have greatly benefited from the ability to live migrate Virtual Machines across different vCenter Servers that are NOT part of the same vCenter Single Sign-On (SSO) Domain, which I had first shared back in 2015 here and here. This extended capability of the Cross vCenter vMotion feature enabled customers to solve new use cases that were challenging, especially for scenarios such as Datacenter migration, consolidation or even migrating existing workloads from their current environment into new SDDC deployments such as VMware Cloud Foundation (VCF) as an example.

Although customers could initiate Cross vCenter vMotions using the vSphere API which included PowerCLI (Move-VM cmdlet was enhanced in 6.5, more details here), the overall experience was still not as friendly. This was especially true for customers who may only have a small number of VMs to migrate and prefer a UI-based interface rather than an API/CLI only option. In addition, for large number of VM migrations, there was not an easy way to perform "batch" VM migrations that was easily consumable for folks who may not have a strong background in Automation or the vSphere APIs.

Today, I am pleased to share a new VMware Fling called the Cross vCenter Migration Utility that will help simplify the consumption of initiating VM migration(s) across different vCenter Servers, especially between dispart SSO Domains where a graphical interface was not available. This solution was developed out of our VMware Cloud Foundation (VCF) Engineering group which is part of the Integrated Systems Business Unit at VMware. I had spoken to a number of folks within the group about the extended Cross vCenter vMotion capability and I was super excited when I heard they were planning to release this tool as a Fling and make it available to all customers. I was fortunately to have been involved in the project alongside the Engineering lead Vishal Gupta and we are excited that we can finally talk about this project and see how customers will be using this new tool.

UPDATE (05/07/18) - The Fling has just been updated to 2.0 with the following new features:

  • Added support to select individual host as the placement target
  • Added support for migrating VMs with shared datastore
  • Added clone functionality in addition to relocate
  • Added resource summary details for placement targets
  • Added a prompt to verify site thumbprint during SSL verification
  • Added a link to refresh vm list in the inventory view
  • Updated REST APIs to add operation type parameter

Cross vCenter Migration Utility Fling

Cross vCenter vMotion Requirements: KB 2106952

Download Fling here


Features

  • Completely UI-driven workflow for VM migration
  • Provides REST API for managing migration operations
  • Works with vCenter not part of the same SSO domain
  • Supports both live/cold migration of VMs
  • Batch migration of multiple VMs in parallel
  • Flexible network mappings b/w source and destination sites

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