n2n is an open source Layer 2 over Layer 3

Network Layer

The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...

 VPN

Virtual private network

A virtual private network is a network that uses primarily public telecommunication infrastructure, such as the Internet, to provide remote offices or traveling users access to a central organizational network....

 application which utilises a peer-to-peer

Peer-to-peer

Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

 architecture for network membership and routing.

Contrary to many other VPN programs, n2n can also connect computers which reside behind NAT

Network address translation

In computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....

 routers. These connections are set up with help from a third computer that both computers can reach. This computer, called a supernode, can then route the information between NATed nodes.

It is free software

Free software

Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 licensed under the terms of the GNU General Public License

GNU General Public License

The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....

v3.