Tunneling is generally done by encapsulating the private network data and protocol information within the public network transmission units so that the private network protocol information appears to the public network as data. Tunneling allows the use of the Internet, a public network, to convey data on behalf of a private network.
One approach to tunneling is the Point-to-Point Tunneling Protocol (PPTP) developed by Microsoft and several other companies. The PPTP keeps proprietary data reasonably secure, even though part of the path(s) between or among end users exists in public communication channels. The PPTP allows authorized users to access a private network – called a virtual private network (VPN) -through an Internet service provider (ISP) or online service. Another common tunneling protocol is generic routing encapsulation (GRE), developed by Cisco Systems. There are numerous, less common tunneling protocols.
Tunneling and using a VPN is not intended as a substitute for encryption/decryption. In cases where a high level of security is necessary, the strongest possible encryption should be used within the VPN itself, and tunneling should serve only as a convenience.
