I wanted to share some info on a recent issue I faced with Microsoft Hyper-V Server SP1 and trunking.

We are in an environment where we wanted to deploy a Hyper-V host to a site and have a trunk from a Cisco switch so that we could throw guests into different VLAN’s. Sounds relatively simple, and in the VMware environment it is, but Hyper-V proved a little more difficult to grasp.

Let me just run through a brief explanation of how the host is setup. We built the Hyper-V Server host, gave it an IP, added it to the domain and registered it in DNS. In SMVMM 2012 we defined a logical network in the fabric and added the VLAN and IP subnet (in CIDR) to the network site. We did not define an IP address pool for the logical network, as DHCP will be taking care of this for us. Next we added the host to VMM. We then deployed the host to the site and proceeded to modify the network settings to configure trunking remotely.

This was our downfall.

Remotely – in the host properties, we enabled logical network connectivity from out logical network, changed the NIC to trunk and made sure the subnet and VLAN details were correct. We then added the virtual network interface and granted host access through a VLAN so that we could still manage the host. Then we applied all the changed to the host.

What we did not know is that the host would apply settings one by one, and NOT send all config to the host to apply. What happened was that the host applied the trunking details and then could not apply the virtual network details as the host became offline.

After reading a tonne of unhelpful articles we solved the problem via the following:

• Cabling the second NIC.
• The second NIC got an IP via DHCP and hence moved the DNS record for the host.
• As the host was added to VMM using DNS, the network settings were applied properly which meant that the virtual network was created, bringing our trunked host back online.
• Once the host was up DNS had registered both IP’s so that we could safely shut down the second NIC, or allocate it to a management only NIC.

Hope this helps either explain a brief overview of trunking in Hyper-V or provide a solution to a similar problem.