In this scenario you have an ESXi host with 1Gb physical adapters, and a virtual machine with the guest network speed showing connected at 10Gbps.
The host configuration looks like this;
But the guest VM shows this;
This is rather confusing at first, especially considering that you don’t have any 10Gb interfaces in your hosts.
So how is this possible?
If you think about the virtual networking and how this VM is connected, then it makes perfect sense. The VM has a VMXNET3 adapter (see KB1001805 for adapter types) with the VM Tools installed and is connected to a virtual switch and since both of these components understand 10Gb so it’s expected behaviour.
The same would apply in a scenario with physical servers, you would see the speed that your server is connected to the physical switch.
I always find it easier to understand with visuals so sketched this up to help explain;
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