n2n is a layer-two peer-to-peer virtual private network (VPN) which
allows users to exploit features typical of P2P applications at
network instead of application level. This means that users can gain
native IP visibility (e.g. two PCs belonging to the same n2n network
can ping each other) and be reachable with the same network IP address
regardless of the network where they currently belong. In a nutshell,
as OpenVPN moved SSL from application (e.g. used to implement the
HTTPS protocol) to network protocol, n2n moves P2P from application to
network level.