Editing Tunneling protocol (section)

== Technical overview ==
As an example of network layer over network layer, [[Generic Routing Encapsulation]] (GRE), a protocol running over IP ([[List of IP protocol numbers|IP protocol number]] 47), often serves to carry IP packets, with RFC 1918 private addresses, over the Internet using delivery packets with public IP addresses. In this case, the delivery and payload protocols are the same, but the payload addresses are incompatible with those of the delivery network.

It is also possible to establish a connection using the data link layer. The [[Layer 2 Tunneling Protocol]] (L2TP) allows the transmission of [[Frame (networking)|frames]] between two nodes. A tunnel is not encrypted by default: the [[TCP/IP]] protocol chosen determines the level of security.

[[Secure Shell|SSH]] uses port 22 to enable data encryption of payloads being transmitted over a public network (such as the Internet) connection, thereby providing [[VPN]] functionality. [[IPsec]] has an end-to-end Transport Mode, but can also operate in a tunneling mode through a trusted security gateway.

To understand a particular protocol stack imposed by tunneling, network engineers must understand both the payload and delivery protocol sets.