For questions about network tunnels.
A tunnel in a network is a logical link that encapsulates packets as the payload of another network protocol (or even the same). This allows the encapsulated protocol(s) to be hidden from the network through which the encapsulating packets travel. For example, IPv6 packets can be encapsulated inside IPv4 packets in order to travel across an IPv4-only network.
The original packets may optionally be encrypted. In this case, the tunnel is often called a Virtual Private Network (VPN).