Networking

Virtual Network Adapter Types

There are two types of virtual network adapters (vNICs) in Hyper-V: Legacy Network Adapter and Network Adapter. As of Windows Server 2025, when a VM is created, all VMs get a Network Adapter which is a synthetic network adapter designed and optimized for Hyper-V.

Generation 1 VMs also support the Legacy Network Adapter which is an emulated Intel 21140 adapter. The biggest difference that matters is that the Legacy Network Adapter is capped at around 100 Mb and has higher CPU utilization. If using Generation 1 VMs, always use Network Adapter for any vNIC, not Legacy Network Adapter.

A vNIC must be connected to the correct vSwitch.

To understand how vNICs work in a VM, read the Microsoft Learn article “Virtual Machine Network Adapters”.

Virtual Network Adapter Configuration

As documented in the capacity specification article from Microsoft, there can be 64 Network Adapters, and if using a Generation 1 VM, an additional four Legacy Network Adapters.

Understand your requirements and plan the architecture accordingly. For most configurations, a single vNIC is sufficient for the workload. Some workloads and architectures have more specific demands that could justify using more than one vNIC, but more than one should never be configured “just because” or that is the way certain configurations were done in the past on physical hardware or other virtual platforms.

Examples of requiring multiple vNICs include, but are not limited to:

• In-guest iSCSI using a dedicated network

• An isolated network to leverage a shared SMB path on a specific network for security

• A dedicated backup network

The isolation could be a logical network via a VLAN tag on the physical network or could be a truly separated and dedicated network for these purposes.

For moderate or higher demand workloads, in-guest network tuning is recommended. Just like the Hyper-V host, enabling RSS is recommended to better distribute the network traffic handling within the OS.