This is a question about the traceability of MAC adresses beyond their immediate router/gateway.
I've been wondering how far beyond a router a LAN computer's MAC address is broadcast and/or traceable? Let's say there's a cafe with free internet access, and for an hour a user will occupy 192.168.0.XXX, broadcasting his MAC address to the router. Is this traceable by the upstream ISP, or anyone else, and if so, how?
As a sidenote, most routers I don't think keep good logs by default - so once the user is gone from the cafe/IP address, where are there any traces of him having been there?
Any information WITH solid documentation (on the Internet) is most welcome.