You cannot connect multiple NICs to a single Hyper-V vSwitch without teaming on the host

Can you connect multiple NICs to a single Hyper-V vSwitch without teaming on the host

Recently I got a question on whether a Hyper-V virtual switch can be connected to multiple NICs without teaming. The answer is no. You cannot connect multiple NICs to a single Hyper-V vSwitch without teaming on the host.

This question makes sense as many people are interested in the ease of use and the great results of SMB Multichannel when it comes to aggregation and redundancy. But the answer lies in the name “SMB”. It’s only available for SMB traffic. Believe it or not but there is still a massive amount of network traffic that is not SMB and all that traffic has to pass through the Hyper-v vSwitch.

What can we do?

Which means that any redundant scenario that requires other traffic to be supported than SMB 3 will need to use a different solution than SMB Multichannel. Basically, this means using NIC teaming on a server. In the pre Windows Server 2012 era that meant 3rd party products. Since Windows Server 2012 it means native LBFO (switch independent, static or LACP). In Windows Server 2016 Switch Embedded Teaming (SET) was added to your choice op options. SET only supports switch independent teaming (for now?).

If redundancy on the vSwitch is not an option you can use multiple vSwitches connected to separate NIC and physical switches with Windows native LBFO inside the guests. That works but it’s a lot of extra work and overhead so you only do this when it makes sense. One such an example is SR-IOV which isn’t exposed on top of  a LBFO team.

DELL EMC World 2017 Concludes

Today DELL EMC World 2017 ends with a dinner with DELL EMC management and engineers to discus our impressions on the information we took away from DELL EMC World 2017. I would like to thank the ever hard working Sarah Vela for making this possible. It’s much appreciated.


Professionally I’m blessed with multiple opportunities to attend conferences and summits. That’s where I get to talk to the skilled and passionate people who work on the technologies we work with intensively. This is very much a two way street where we learn from each other. And on many conferences I might also be a speaker or participate in advisory boards to provide feedback. Some of those latter discussions are under NDA. This is normal and I have NDA’s with other companies as well. That’s the legal side of the trust we place in each other in order to discuss evolving and future technologies.

I attend multiple events from different players. Some of these disagree with me and that is fine. We learn from being challenged. It helps us define more clearly what we design and build as well as why and how. More and more solutions become a more diverse, multi pronged combination of components with their specific capabilities at our disposal. These change fast and so do our solutions. An element not to be ignored in designing those solutions. That’s one take away from DELL EMC world that seems to have hit home. The other is that some companies are in a rather dire IT condition due to years of stand still.

I’m happy to see that today and tomorrow DELL EMC has the technologies needed for us to deliver modern IT solutions. The way in which we choose to do so is our choice and DELL EMC states it is committed to supporting that. As a testimonial to that we got to see the the DELL EMC Storage Spaces Direct Ready nodes based on the soon to be available generation 14 PowerEdge servers.


That is how we worked for many years with DELL and we have been assured we can continue to work with DELL EMC. That what Michael Dell committed to and I have seen them deliver on that promise for many years. For me that’s enough to be confident in that until proven different. Even if that message was sometimes brought in a way that made me think Las Vegas had gotten the better of some conference managers. But let’s not get the form in the way of the content.

On a final note, Dell EMC is not anti public cloud or pro on-premises. That’s how it should be and that how we deliver IT. We use the tools at our disposal to build the best possible solutions we can. What we use depends on the needs and changes as technology evolves. That’s OK. Saying you need hardware doesn’t make you a cloud hater or vice versa. The world is not that simple.

vNIC Speed in guests on Windows Server 2016 Hyper-V

Prior to Windows Server 2016 Hyper-V the speed a vNIC reported was an arbitrary fixed value. In Windows 2012 R2 Hyper-V that was 10Gbps.

This is a screen shot of a Windows Server 2012 R2 VM attached to a vSwitch on an LBFO of 2*1Gbps running on Windows Server 2012 R2 Hyper-V.


This is a screen shot of a Windows Server 2016 VM attached to a vSwitch on an LBFO of 2*10Gbp running on Windows Server 2012 R2 Hyper-V.


As you can see the fixed speed of 10Gbps meant that even when the switch was attached to a LBFO with 2 1Gbps NIC it would show 10Gbps etc. Obviously that would not happen unless the 2 VMs are on the same host and the limitations of the NIC don’t come into play as these are bypassed.Do note that the version of Windows in the guest doesn’t matter here as demonstrated above.

The reported speed behavior has changed in Windows Server 2016 Hyper-V. You’ll get a more realistic view of the network capabilities of the VM in some scenarios and configurations.

Here’s a screenshot of a VM attached to a vSwitch on a 1Gbps NIC.


As you can see it reports the speed the vSwitch can achieve, 1Gbps. Now let’s look at a VM who’s vNIC is attached to a LFBO of two 10Gbps NICs.


This NIC reports 20Gbps inside of the VM, so that’s 2 * 10Gbps.

You get the idea. the vNIC reports the aggregated maximum bandwidth of the NICs used for the  vSwitch. If we had four 10Gbps NICs in the LBFO used for the vSwitch we could see 40Gbps.

You do have to realize some things:

  • Whether a VM has access to the the entire aggregated bandwidth depends on the model of the aggregation. Just consider Switch independent teaming versus LACP teaming modes.
  • The reported bandwidth has no knowledge of any type of QoS. Not hardware based, or virtual via Hyper-V itself.
  • The bandwidth also depends on the capabilities of the other components involved (CPU, PCIe, VMQ, uplink speed, potentially disk speed etc.)
  • Traffic within a host bypasses the physical NIC and as such isn’t constraint  by the NIC capabilities it self.
  • As before the BIOS power configuration has an impact on the speed of your 10Gbps or higher NICs.

Simplified SMB Multichannel and Multi-NIC Cluster Networks

Simplified SMB Multichannel and Multi-NIC Cluster Networks

One of the seemingly small feature enhancements in Windows Server 2016 Failover clustering is simplified SMB multichannel and multi-NIC cluster networks. In Windows 2016 failover clustering now recognizes and uses multiple NICs on the same subnet for cluster networking (Cluster & client access).


Why was this introduced?

The growth in the capabilities of the hardware ( Compute, memory, storage & networking) meant that failover clustering had to leverage this capability more easily and for more use cases than before. Talking about SMB, that now also is used for not “only” CSV and live migration but also for Storage Spaces Direct and Storage Replica.

  • It gives us better utilization of the network capabilities and throughput with Storage Spaces Direct, CSV, SQL, Storage Replica etc.
  • Failover clustering now works with multichannel as any other workload without the extra requirement of needing multiple subnets. This is more important that it seems to me at first. But in many environment getting another VLAN and/or extra subnet is a hurdle. Well that hurdle has gone.
  • For IPv6 Link local Subnets it just works, these are auto configured as cluster only networks.
  • The cluster Validation wizard won’t nag about it anymore and knows it’s a valid failover cluster configuration

See it in action!

You can find a quick demo of simplified SMB multichannel and multi-NIC cluster networks on my Vimeo channel here


In this video I demo 2 features. One is new and that is virtual machine compute resiliency. The other is an improved feature, simplified SMB multichannel and multi NIC cluster networks. The Multichannel demo is the first part of the video. Yes, it’s with RDMA RoCEv2, you know I just have to do SMB Direct when I can!

You can read more about simplified SMB multichannel and multi-NIC cluster networks on TechNet in here. Happy Reading!