If one wants to extend a private network across a public network, then one should make use of the VPN or the virtual private network. VPNs have several classifications. Thusly, they're categorized by the OSI layer presented to the network connection (e.g., Layer 3 network connectivity or Layer 2 circuits), the levels of security offered, whether site-to-site or remote-access connectivity is offered, the termination point location of the tunnel (e.g., network-provider edge or customer edge), and the protocols utilized to tunnel traffic with the paid or free vpn software. As for routing, it's all about operating tech of the point-to-point network topology that could, in theory, technically constitute as not a VPN.