A NIC that talks ethernet doesn't mean it's in the hardware. It's more about the ASICs on the ports to handle high traffic rates. The NIC can send the packet

A NIC that talks ethernet doesn't mean it's in the hardware. It's more about the ASICs on the ports to handle high traffic rates. The NIC can send the packet on the wire, but inserting the IPv6 headers is done in hardware with ASICs. This is the difference between millions of packets per second versus tens of thousands.