Im having a networking issue in my new test environment - server core 2008, hyper-v.

I have 2 NICs on the hyper-v server, 1 for the host and the other is shared by 3 x VM through the usual virtual network switch.

Host has static IP and the 3 test VM's have static IP's too.

Whatever I try, I can only get external network communication through 2 of the VM's at any time.

Running constant pings from all 3 VM's, only 2 will communicate externally. It's any 2 of the 3 which will work. I can start any 2 VM's and they work, start the third, no IP connectivity. Shut them all down, start any 2 of the 3 VM's, both OK, whichever VM I start 3rd, will have no IP connectvity so its not specific to the VM's...or its specific to all of them!

As its my first server core 2008 build, im struggling to get information on the virtual network switch on the hyper-v host as it seems to be only allowing 2 connections through it.

Networking pic link below, (ignore the test2003x86 VM having 2 virtual interfaces as i've been trying different setups and additional virtual network cards to no avail).

So in the pic below, the test2003x86 and test2003x64 VM's both work fine but the test2008 VM has no external network, the interface on the VM sends packets but receives none. (test2008 was started last).

Any 2 from 3 working? Im sure hyper-v supports more than 2 VM's on its virtual network switch? Unless its a limitation on the NIC on the host (Intel CT gigabit card).

AFAIK, all 3 should be working...?


  • 1
    This sounds pretty weird. But you did say you were "struggling to get information about the virtual switch" so I humbly suggest as a first step you download the RSAT (Remote Server Administration Tools) to your desktop or workstation, then fire up Hyper-V Manager and connect remotely to your Hyper-V host. That's how most of us mere mortals administer Hyper-V on Core. – Ryan Ries Nov 13 '12 at 13:21
  • Hi Ryan, thanks for replying, I use hyper-v manager and MS VMM. Also using visualcore tool on server core. The issue is getting more detailed info on the hyper-v virtual switch inside server 2008 core...and the problem is the communcation from the VM's through the virtual switch and the physical NIC.....I think! – smurftech Nov 13 '12 at 13:23
  • None of your VMs have the same IPs or MAC addresses do they? – Ryan Ries Nov 13 '12 at 13:26
  • The MACs are dynamic allocated in VMM, none are the same but they are in sequence. IP's are sequential also. – smurftech Nov 13 '12 at 13:28
  • Well crap. Hopefully somebody figures it out. But I can say that yes, they should all three be working. – Ryan Ries Nov 13 '12 at 13:29

OK took me a day or 2 but I found the answer, I had totally forgot about the cisco switches we use and was convinced it was the server itself...

Here's the offending line on my switch port config:

switchport port-security maximum 2

cisco port security was the culprit!

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