Why is the host PC using a virtual external network interface?

Hi everyone,

Hope everybody is doing well and keeping safe.

I'm running a CentOS vm in Hyper-V that I needed to expose to my home network so I created an external switch and connected to it. All is working well on this front, no complaints.

What's confusing me is..my host Win 10 Pro (version 20H2) PC seems to be using that external switch instead of the default and physical LAN (where the ethernet cable is plugged in). I mean the thing is showing as connected but when I checked its properties, only "Microsoft LLDP Protocol Driver" and "Hyper-V Extensible Virtual Switch" are selected, the rest are unchecked.

Why is this? I ask because in the future I plan to populate more VMs and intend to expose them to my home network as well..so I kind of need to understand how this is working.

Sorry if this is a dumb question, my networking is quite weak.

Thank you.

Ah yes, this is quite a confusing area even for those of us seasoned network peeps.

When you designate an external adapter (your physical adapter that your network cable plugs into) to use, hyper v creates a virtual switch and then binds it to this physical adapter. All communication from the host computer now passes through that virtual switch. Your physical adapter can still be seen on your host (as you have noted), but hyper v will remove all of the bindings and will link this adapter to the hyper v virtual switch.

You should now see a vethernet adapter which is the virtual adapter location where you would now set things like static ip addresses and other settings in this location rather than your physical network adapter.

pparks1 said:

Ah yes, this is quite a confusing area even for those of us seasoned network peeps.

When you designate an external adapter (your physical adapter that your network cable plugs into) to use, hyper v creates a virtual switch and then binds it to this physical adapter. All communication from the host computer now passes through that virtual switch. Your physical adapter can still be seen on your host (as you have noted), but hyper v will remove all of the bindings and will link this adapter to the hyper v virtual switch.

You should now see a vethernet adapter which is the virtual adapter location where you would now set things like static ip addresses and other settings in this location rather than your physical network adapter.

Thank you for replying.

So, a hypervisor is making changes on host because I told it create a new external virtual switch? And has since removed the binding between my host and its physical network adapter? That's incredibly confusing.

• So, what has this situation turned my physical network adapter into then?
• I mean the host is still connected to the router from here..so it is still being used, right?
• What would happen if I create another virtual external adapter (so that another VM can also be on the homenetwork)? Would the host PC use the second one or remain with this one?

This page here does a pretty good job explaining it, I'm going to steal a few relevant parts here to try to answer your questions
What is the Hyper-V Virtual Switch and how does it work? (altaro.com)



Your physical adapter is still there and it acts pretty much as a bridge/pass through to the rest of your network and the Internet further upstream.

All further VM's you create, you can attach to your virtual switch and they will automatically be on your network. In the bottom right of the above picture, all of these virtual machine virtual adapters are the Network interfaces from each virtual machine you create.

raava said:

What's confusing me is..my host Win 10 Pro (version 20H2) PC seems to be using that external switch instead of the default and physical LAN (where the ethernet cable is plugged in).

Yes, Hyper-V does that. It is because Hyper-V is a Type 1 Hypervisor, as explained by cereberus here:

cereberus said:

Type 1 Hypervisors sit between the hardware and your virtual machines AND your Host OS.
In effect, your Host OS is turned into a virtual machine as well....

Hypervisor Type 1 and Type 2

pparks1 said:

This page here does a pretty good job explaining it, I'm going to steal a few relevant parts here to try to answer your questions
What is the Hyper-V Virtual Switch and how does it work? (altaro.com)



Your physical adapter is still there and it acts pretty much as a bridge/pass through to the rest of your network and the Internet further upstream.

All further VM's you create, you can attach to your virtual switch and they will automatically be on your network. In the bottom right of the above picture, all of these virtual machine virtual adapters are the Network interfaces from each virtual machine you create.

This is why I LOVE the Internet. So many experts who are willing to get down to the nitty-gritty.

Thank you again for that article and for your own explanation. I've read it, gonna sleep on it tonight and read it again tomorrow for better comprehension.

What struck out to me was that a virtual switch can have multiple virtual network adapters..which I didn't grasp before.

However, the bit that I don't quite get is this.

"The only reason to check the box is if you need the management operating system to be able to communicate directly with the virtual machines on the created virtual switch or with the physical network connected to the particular physical adapter or team that hosts the virtual switch."

Had I chosen not to allow the management OS to "share" the switch, it would not have created management OS' virtual network adapter (and plugged it into the vSwitch), correct?

In that scenario, would the management OS be isolated? Because it won't be able to reach out to VMs directly nor would it be able to get the network that was plugged into the physical switch?

raava said:

...would the management OS be isolated? Because it won't be able to reach out to VMs directly nor would it be able to get the network that was plugged into the physical switch?

With Hyper-V the host machine and the guest VMs will always see each other on the network, regardless of whether the VM uses the default switch or a switch that you have set up. Only if the VM has no network connection will it not be able to see shares on the host machine.

Using the default switch a VM can only see the host machine and the internet. With a virtual switch the VM can also see any other machines on your local network.

Bree said:

Yes, Hyper-V does that. It is because Hyper-V is a Type 1 Hypervisor, as explained by cereberus here:

Hypervisor Type 1 and Type 2

Thank you. Until I saw the picture, I had no idea about that lol. Shows how much I didn't know.
Gonna read through the page now.

- - - Updated - - -

Bree said:

With Hyper-V the host machine and the guest VMs will always see each other on the network, regardless of whether the VM uses the default switch or a switch that you have set up.

Using the default switch a VM can only see the host machine and the internet. With a virtual switch the VM can also see any other machines on your local network.

Yes, I wanted the VM to see other machines on my home network and vice versa. That's why I went with the vExternalSwitch. And one of its default option selected was to 'Allow management OS to share it'.

What I'm wondering (after reading that article) is had I left it unchecked, how would it have been different?
Will the management OS' not have its virtual adapter plugged into vExternalSwitch (like I currently have)?

raava said:

...What I'm wondering (after reading that article) is had I left it unchecked, how would it have been different?
Will the management OS' not have its virtual adapter plugged into vExternalSwitch (like I currently have)?

Like you, I took the defaults when setting up a virtual switch and everything just works. Kari s a Hyper-V Guru and in Part Three of his tutorial....

Hyper-V virtualization - Setup and Use in Windows 10

...he references his Virtual Switch tutorial on sister site Eight Forums. There he says to... "Name the switch as you wish, select which of host NICs it will be connected to. Please check that the option Allow management operating system to share this network adapter is selected, otherwise you might lose all connectivity..."

Hyper-V Virtual Switch Manager | Windows 8 Help Forums

you will want that box checked and that's why it's the default. With the box unchecked, you wouldn't be connected to that virtual switch, and in turn your host machine would lose access to the Internet and rest of the network.

I think that guide should say that you should leave it checked unless you don't want it to communicate with the VM's.