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Hyper-V internal network woes

by Alex Peck on April 22nd, 2009

System Center Virtual Machine Manager is a rubbish name for a product. Beyond that, SCVMM seems pretty good. I recently p2v’d a lab environment with a DC, Exchange, SQL, App Server and Vista client. Even hot-imaging the DC was smooth, although I would recomend telling the DC not to update machine passwords before you start.

So, I thought, clearly what I need is another application server and client. I cloned the VMs I had, then turned them into templates. This is where things went a bit wrong. When I p2v’d the originals, SCVMM cloned the MAC addresses of the physical machines. If I were replacing physical machines in an enterprise, this is probably what I would have wanted. With just one of each machine (and each MAC), the network works fine.

However, when you create a new machine from a template taken from a p2v’d VM, the template also inherits the physical machines MAC, as does the instance of the template. At no point in any of the template/new machine wizards was there a mention of a MAC address. I had previously read an article about how MACs are assigned dynamically, so I assumed this was happening seamlessly. It wasn’t.

In the beginning, I only used one of the two clients at a time, and didn’t notice the intermittent network problems. Then suddenly it seemed like only one of the clients could connect to the network at a time. I could only see file shares from one of them on other machines: I’d connect to one client, and the share on the other would close. Prior to this, I had intermittent problems accessing the app server.

After a considerable amount of time spent measuring the network speed at each client (which worked fine, since I only accessed one of them at a time), I went back to basics with my old friend ipconfig. I’m still quite surprised that I noticed that the MAC addresses on the clients were the same, it’s not something I would normally look at.

The moral of this story: be careful when assigning MAC addresses.

From → Virtualization

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