Reference model

[tbarbette]

There are multiple reference models for a router lying around, but I would like to be able to provide a few reference models for some features, like a switch, a basic IP router, and a more full-fledged router like VPP with a NAT etc.

There is one fundamental limitation to the Click model : we can't have a "for loop" around a pipeline. The obvious case is I/O. We need to have a way to duplicate a path (say an elementclass) according to a list of something, like NICs.

I'm not sure about the right abstraction for that, so I leave it up for discussion.