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I am trying to get a concrete confirmation with supporting documentation on how vms communicate to each other if residing on the same host. From what I have read on multiple threads:

'VM's will not use the physical NIC if the two VMs are on the same vSwitch.'

Here is my scenario: 2 node cluster

VMa

VMb

IP: 192.168.100.0/24

NETWORK: Physical NIC <-> NIC Team <-> (External) vSwitch <-> VM

So that I'm know I'm 100% correct.

ANY/ALL traffic, with an origin/destination, from/for, a VM residing on the same host server, using the same vSwitch, will traverse via that said vSwitch.

Correct:

VMa <-> (External) vSwitch <-> VMb

NOT

VMa <-> (External) vSwitch <-> NIC Team <-> Physical NIC <-> NIC Team <-> (External) vSwitch <-> VMb

If I could get some supporting documentation for this that would be most helpful. I have had no luck finding it myself.

Dave
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3 Answers3

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I'm new to Hyper-V but shouldn't inter-VM communication be done through a Private or Internal Switch?

"Hyper-V’s Private Switch The private switch allows communications among the virtual machines on its host and nothing else. Even the management operating system is not allowed to participate. This switch is purely logical and does not use any physical adapter in any way. “Private” in this sense is not related to private IP addressing. You can mentally think of this as a switch that has no ability to uplink to other switches.

Hyper-V’s Internal Switch The internal switch is similar to the private switch with one exception: the management operating system can have a virtual adapter on this type of switch. This allows the management operating system to directly communicate with any virtual machines that also have virtual adapters on the same internal switch. Like the private switch, the internal switch does not have any relation to a physical adapter and therefore also cannot uplink to any another switch.

Hyper-V’s External Switch The external switch type must be connected to a physical adapter. It allows communications between the physical network and the management operating system and the virtual adapters on virtual machines. Do not confuse this switch type with public IP addressing schemes or let its name suggest that it needs to be connected to an Internet-facing system. You can use the same private IP address range for the adapters on an external virtual switch that you’re using on the physical network it’s attached to. External in this usage means that it can connect to systems that are external to the Hyper-V host."

https://www.altaro.com/hyper-v/virtual-networking-configuration-best-practices/

Rich M
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-HyperV Virtual - Layer 2 Device (Switch) -Physical NIC - ACT like Layer 3 Device (Router)

1.If your having two VM's in the same subnet and connected to same HyperV Virtual switch the communication between two virtual adapters will be like this

VM1 <-> HyperV Virtual <-> Physical NIC <-> VM2

2.If your having two VM's in the different subnet and connected to different HyperV Virtual switch the communication between two virtual adapters will be like this

VM1 <-> HyperV Virtual <-> Physical NIC <-> HyperV Virtual <-> VM2.

Note : Basically all VM's will be connected to HyperV Virtual switch using Virtual NIC's.

By default, Physical NIC is bounded to Management Network (Through which all communication and network commissioning and decommissioning happens)

In this scenario, if you have more than one VM you can connect all VM to Single HyperV Virtual switch (if all in the same subnet) or to Individual HyperV Virtual switch (for individual subnet).

Better go for individual virtual subnet setup if have more than one subnet to have better working and understanding.

https://www.altaro.com/hyper-v/the-hyper-v-virtual-switch-explained-part-1/

Aiden
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The following link suggests differently: TechNet

Also, the Altaro link states:

Ethernet Frame Switching The Hyper-V virtual switch is able to read the MAC addresses in an Ethernet packet and deliver it to the correct destination if it is present on the virtual switch. It is aware of the MAC addresses of all virtual network adapters attached to it. An external virtual switch also knows about the MAC addresses on any layer-2 networks that it has visibility to via its assigned physical adapter or team.

Would this not suggest that no traffic would traverse the physical switch?

Both VMs are connected to the same vSwitch, are within the same subnet and reside on the same host?

Dave
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