Layer 2 Tunneling Protocol (L2TP)
An example of network layer VPN: use IP packets to encapsulate Layer 2 frames
a standard method for tunneling Point-to-Point Protocol (PPP) [RFC1661] sessions.
L2TP has since been adopted for tunneling a number of other L2 protocols (e.g., Ethernet, Frame Relay, etc).
L2TPv3 defines the base control protocol and encapsulation for tunneling multiple Layer 2 connections between two IP nodes.
L2TPv3 consists of
the control protocol for dynamic creation, maintenance, and teardown of L2TP sessions, and
the L2TP data encapsulation to multiplex and demultiplex L2 data streams between two L2TP nodes across an IP network.