[tyingq]

Works fine on a pi with either usb interfaces or virtual ones.

If you want to experiment at a low cost, though, there's the Banana PI BPI-R1. A ~$70 linux ARM dev board with 5 GB ethernet interfaces.

[pjc50]

You can even bridge an interface to a tun/tap device, which is quite useful for VPNs and doing your own packet-twiddling code.