layer 2 traffic

[binary <dreamer.binary@gmail.com>]

hello everyone,
i would like to connect my office(A), home(B) and my wife's office(C) in 
a network.
all 3 of them they do have an adsl connection with a debian wheezy box 
with 3 ethernet cards.
that box runs as files server in the local network.
i would like to connect all 3 sites but have some kind of layer 2 
network over IP.
this is due to some application that i need to run that they fail to run 
in a layer 3 network (checked with the vendor).
for example ethernet 3 on each site's box could be setup for layer 2 
traffic. then site A could send all traffic (MAC, ....) to site's B and 
C ethernet 3 attached devices.
at the moment the 3 sites are in an openvpn from the linux boxes with 
port forward from the ISP's routers on each site. but this is for the 
layer 3, i cannot carry layer 2 traffic.

could someone point me to some solutions on how to run this kind of setup?



sincerely yours.