layers 2, 3, 4 and 7.
Basically, you forge each layer of a frame (Net::Packet::IPv4 for layer 3,
Net::Packet::TCP for layer 4 ; for example), and pack all of this into a
Net::Packet::Frame object. Then, you can send the frame to the network, and
receive it easily, since the response is automatically searched for and
matched against the request.
