Hyper-V Virtual Network configuration changes automatically after reboot of host

leadwave used Ask the Experts™
So here's the situation:

I have a Windows 2008 Enterprise with Hyper-V setup with 4 VM's.

I have 1 broadcom nic dedicated to each VM.  So I've setup 4 virtual networks on each nic so that each host would be using their own nic.

In device manager the nics are named as such: Broadcom, Broadcom #2, Broadcom #3, Broadcom #4

So the virtual networks are assigned so that VN1 is Broadcom, VN2 is Broadcom #2, etc.

Well, after we reboot the Hyper-V host, the nics somehow get renamed to Broadcom #5, Broadcom #6, Broadcom #7, and Broadcom #8.

What happens then is that none of my VM's can communicate on the network because the Virtual Networks they're associated to are linked to nics that no longer exist.  So then I have to re-associate the virtual networks with the newly renamed nics and that works until the next reboot.

Any idea what is causing this and how I may go about fixing it?

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So you have 4 NICs only ?
Which Nic are you using for your Hyper-V Host management ? (A separate one is recommended)

I haven't faced this situation exactly - but I will try to help :

a) Arrange downtime
b) Delete all virtual networks
c) Delete All Network cards (device manager delete all NICs)
d) reboot host - let windows identify / install drivers for your nics or update your nics to the latest drivers from dell

Now Just create "ONE" (1) Virtual Network (Separate from the ONE you are using for your HOST BOX), make sure the Virtual Network type is "External".

Once that is created, go into each of your VM's settings and make sure they are all using that ONE Virtual Network you created.

They will communicate !!


So now you are left with 2 NICS :

If you have really high traffic VMs then create a 2nd Virtual Network of type External (binding it to  your 3rd NIC) and assign your desired VMs to that Virtual Network.

What Hyper-V Does is it creates a Virtual Switch on your NIC, so you don't necessarily need to have 4 virtual networks for 4 servers, we run 10 Servers with 1 Virtual Network for 80 - 100 users at one site and another 10 virtual servers with 200 - 300 users with 2 virtual networks, as long as you have a good switch connected to your servers you won't feel the need of this, unless the traffic is really high.



Hope that Helps


Thanks.  I'll give that a try and assign points when I see the results.  And thanks also for the insight on the Virtual Networks.
Syed Mutahir Alibinarybonsai

Glad to help, let me know if you need any further clarifications

Also, let me know what roles are those servers (VMs) for, any role installed on the Hyper-V Host apart from Hyper-V ?

It is good (recommended) to Just have the Hyper-V role installed on the Host server

I would just like to add to the first post by mutahir. In the step provided by him, before deleting all NICs you might have better result if you, at an elevated command prompt use "SET DEVMGR_SHOW_NONPRESENT_DEVICES=ENABLED" without quotes and while using device manager, from the drop down menu, select "show hidden devices"
This will let you see and delete hidden NICs in your system.


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