Overview
Tunneling is an encapsulation technology. One network protocol encapsulates packets of another network protocol and transfers them over a virtual point-to-point connection. The virtual connection is called a tunnel. Packets are encapsulated at the tunnel source end and de-encapsulated at the tunnel destination end. Tunneling refers to the whole process from data encapsulation to data transfer to data de-encapsulation.
Tunneling supports the following technologies:
Transition techniques, such as IPv6 over IPv4 tunneling, to interconnect IPv4 and IPv6 networks.
VPN, such as IPv4 over IPv4 tunneling, IPv4/IPv6 over IPv6 tunneling, GRE, and IPsec tunneling.
Traffic engineering, such as MPLS TE to prevent network congestion.
Unless otherwise specified, the term "tunnel" in this document refers to IPv6 over IPv4, IPv4 over IPv4, IPv4 over IPv6, and IPv6 over IPv6 tunnels.