ntop/n2n

N2N is a peer-to-peer virtual private network (VPN) tool written in C. A VPN creates an encrypted tunnel between computers so they can communicate as if they were on the same local network, even when separated across the internet. Most VPNs route all traffic through a central server. N2N takes a different approach: once the initial connection is established, computers talk directly to each other, bypassing the central relay for ongoing traffic. N2N uses two types of components. The first is called an edge node, which runs on each machine you want to connect. The second is called a supernode, which acts as a coordinator to help edge nodes find each other. You start the supernode once, then start an edge process on each machine you want on the network, passing arguments that specify a shared community name, an encryption key, an IP address for that machine on the virtual network, and the address of the supernode. Once two edge nodes have located each other through the supernode, traffic between them flows directly. On Linux and similar systems, the edge process creates a virtual network interface, which requires brief elevated permissions at startup. The README explains how to drop those privileges after setup and how to install the edge binary as SUID-root so any user can start it without a separate privilege step. The README also covers IPv6 packet support within the tunnel (the underlying transport between nodes remains IPv4), cipher options including AES with measured performance figures, and instructions for running the supernode as a Docker container. The project is maintained by ntop.org and covers Windows alongside the Unix platforms, though some command-line flags differ between operating systems.