Many of you have already heard about the new VMware vNetwork Distributed switch. It has been a really great innovation by VMware. I believe most of us has already learned something about its benefit like:

1- Simplify Virtual Machine Networking: As you get to create one switch per cluster & create the policy across all your ESX hosts at once instead of repeating the process endlessly.

2- Enhance Virtual Machine Networking:

• VMware vNetwork Distributed Switch maintains network runtime state for VMs as they move across multiple hosts, enabling inline monitoring and centralized firewall services.
• It provides a  framework for monitoring and maintaining the security of virtual machines as they move from physical server to physical server
• It enables the use of third party virtual switches such as the Cisco Nexus 1000V to extend familiar physical network features and controls to virtual networks.

I agree that VMware has succeeded greatly with the VMware vNetwork Distribute Switch, but there is a bug or shall I call it a limitation that really bug me and many other VMware Implementers & admins. Read below to find more about this bug & I hope someone of VMware give this post an attention and resolve this issue in the next release.

What bug me is that, if you lose virtual Center you will have no way in moving virtual machines between different port groups on the vNetwork Distribute Switch. In addition, you will not be able to get a virtual machine from the traditional virtual switch to a port group on the vNetwork Distributed Switch. Extra to that, you can’t move a VM to another VMware vNetwork Distribute Switch. So that means if you are using VMware vSphere vNetwork Distribute Switches & you lose virtual center you are almost disabled on the networking part. If you lose connectivity on the classic virtual switch & your adapter on the distributed switch are OK you still can’t move your virtual machines to that distributed switch till Virtual Center is back. I understand that VMware has to protect their licensing schema and that why this done this way, but it seems to me they are getting their vNetwork Distribute Switch to be too vurnable if vCenter go down.

The below images should illustrate the problem:

If you look at the above two images you will notice they are for the same virtual machine which is connected to a port group on a VMware vNetwork Distribute Switch. The first one is showing the networks your VM can join when connected using virtual Center & the second one show the networks your VM is allowed to join when VC is down. Notice that you don’t see most of the vNetwork Distribute Switch port groups in the second image.

Again the two images above shows a virtual machine which is not connected on vDistribute Switch. The first one show you the network your VM can connect to when managing the server from vCenter & the second one show you the networks your VM can connect to when managing the server without vCenter.

As you can tell when ever you lose virtual center in your enviornment you will have a scary less control of you networking in the case of vNetwork Distribute Switches than the classic VMware virtual Switches. I hope some one of VMware take my words, verify it & send it to the development team to fix it. Ah I would not mind a nice comment as well :).