Using Dual NICs on a single subnet

Question

Hi,

I am setting up a Dell 1950 III running Windows Server 2008 x64 Server. The server comes with dual NICs. I am also installing Hyper-V. The Hyper-V documentation states that for security reasons I should setup a separate NIC for the virtual machines that run under Hyper-V. I am running a single subnet (10.0.0.x).

I plugged both NICs into the same router, gave them different static IP's as 10.0.0.3 and 10.0.0.4 with the same subnet 255.255.255.0 and the same gateway of 10.0.0.15. I didn't receive any errors during the configuration process but I did get a warning about having the same gateway address for both NICs.

I added 10.0.0.3 to DNS and setup 10.0.0.4 in Hyper-V as the physical NIC to use for virtualization.

I can ping my server, I can access the server using remote access but when I tried to access a shared drive on the server I get an error message that the computer name is a duplicate.

I've looked but I cannot find anything that states how to correctly set this up. To the contrary most of the info I can find states that this is a bad idea. I wouldn't have tried it if the Hyper-V documentation hadn't told me to.

Is there a way to do setup dual NICs on the same subnet as it states in the documentation? Am I mis-interpreting the documentation? Any help would be greatly appreciated.

Dev Mgr · Answer

I'd suggest teaming the NICs instead. This makes administration a lot easier and gives your VMs more bandwidth.

Using 2 NICs on 1 subnet seems to cause issues from what I've seen (mostly I see it when trying to set up redundant iSCSI networks and 2 seperate subnets aren't reserved for this).

deriderj · Answer

>> I'd suggest teaming the NICs instead. This makes administration a lot easier and

>> gives your VMs more bandwidth.

Thanks for the idea but I don't think that's going to satisify the Microsoft requirement. I'm trying to follow the guidelines that Microsoft put in their documentation on setting up Hyper-V that states for security reasons always setup a separate network connection for VM's running under Hyper-V. Teaming the NIC's doesn't provide the security that Microsoft is recommending. I'm still wondering how to successfully setup Dual NIC's on a single subnet or might it be possible that I am misinterpreting the Microsoft documentation (it seems very clear, but stranger things have happened).

Thanks.

Dev Mgr · Answer

If you want to follow Microsoft's guidelines, have you contacted them to ask how they suggest to make it work?

deriderj · Answer

>> If you want to follow Microsoft's guidelines, have you contacted them to ask
>> how they suggest to make it work?

Is there a way to contact Microsoft? I purchased my system through Dell and the usual support is through Dell support. I posed this question to Dell support but they were unfamiliar with Hyper-V and could only tell me that most people use two NIC's on different subnets. There wasn’t much depth of knowledge on this subject with the person I spoke to at Dell although I really think they tried to help. With the purchase of an OEM Windows 2008 O/S do I have any support available through Microsoft?

I got this to sort of work but it was terribly awkward and I don't know that it will be stable because I don't understand it completely. I enabled both NIC's with different static IP addresses (10.0.0.3 and 10.0.0.4). Then in Hyper-V I created a “Virtual Network” using the 2nd NIC (10.0.0.4). Creating a Virtual Network somehow alters the network connection configuration of the 2nd NIC so that it acts as a network switch. When I look at the network connection configuration all the protocols are unchecked except the “Microsoft Virtual Network Switch”. Then I see that a 3rd network connection has been created that mimics what the 2nd network connection use to look like.

Next I went into WINS and deleted any mention of my server name or anything with 10.0.0.3 and 10.0.0.4 associated with it. I hard coded 10.0.0.3 into DNS and deleted the 10.0.0.4 entry from DNS. I rebooted my server and when it came up I created a new Virtual Machine in Hyper-V and specified the “Virtual Network” name I had created earlier as the VM’s “Network Adapter”. I then configured the rest of the VM settings and installed Vista. When Vista came up it had its own IP 10.0.0.14 through DHCP and everything seemed to work normally.

This cannot possibly be the correct procedure! If I had not deleted the entries from WINS and DNS nothing would have worked (in fact it didn’t work until I deleted those entries; before I deleted them I received a duplicate machine name on the network error messages). The WINS and DNS entries for my two NICs were added automatically and probably initially correctly into DNS and WINS. Since these are automatic entries at some point will they come back? So far they have not come back and everything is working the way I hoped it would.

Does anyone have any comments on this? I’ve searched the Internet but could find nothing definitive on how to configure this two NIC approach properly although I have seen posts alluding to the fact that the two NIC approach should be used.

Should I be worried that this configuration is going to fail over time?

Thanks again for the help.

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Using Dual NICs on a single subnet

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