We have put m0n0 to use in such an environment. We set up a VPN
amongst our consultants' cubicles and offices over the client's
corporate LAN (which becomes our WAN).
m0n0 protects us from them and them from us.
Everything works fine if you allow private address traffic on the WAN
> I was wondering if any of you have ever used m0n0wall with private
>IPs on the WAN and LAN interfaces?