When you add a new network adapter to Hyper-V, you’ll notice (see the Figure below) that you have two options from which to choose: “Network Adapter” and “Legacy Network Adapter”. How do you know when to choose one or the other
Here’s a simple rule of thumb:
- If the virtual machine needs to boot using a Pre-eXecution Environment (PXE) or if your operating system requires access to the network before you’re able to install the Hyper-V Integration Services. Likewise, if you need to install your virtual machine over the network, you’ll need to use the legacy network adapter. The legacy network adapter uses software to emulate a well-supported network adapter (DEC 21140). However, software emulations costs in the form of processing resources, making the legacy adapter less efficient than the high speed Network Adapter option. Note that many 64-bit operating systems do not provide native support for the legacy network adapter, but you may still need to use it for PXE purposes.
- Otherwise, use the non-legacy network adapter option. Integration Services installs bits that are necessary for the non-legacy network adapter to operate under operating systems that do not provide automatic support for this virtual adapter. Windows Server 2008 and the R2 release already include support for the Network Adapter. The synthetic driver that supports the more modern and virtualization-friendly Network Adapter is orders of magnitude more efficient than the legacy network adapter option.
I hope that clears things up a bit!