Configuring L2Tp; Overview; Typical L2Tp Networking; L2Tp Message Types And Encapsulation Structure - HPE FlexNetwork MSR series Configuration Manual

Configuring L2TP

Overview

The Layer 2 Tunneling Protocol (L2TP) is a Virtual Private Dialup Network (VPDN) tunneling
protocol. L2TP sets up point-to-point tunnels across a public network (for example, the Internet) and
transmits encapsulated PPP frames (L2TP packets) over the tunnels. With L2TP, remote users can
access the private networks through L2TP tunnels after connecting to a public network by using PPP.
As a Layer 2 VPN technology, L2TP provides a secure, cost-effective solution for remote users to
access private networks.

Typical L2TP networking

Figure 20 L2TP network diagram
Remote
branch
As shown in
•
Remote system—A remote system is usually a remote user's host or a remote branch's device
that needs to access the private network.
•
LAC—An L2TP access concentrator (LAC) is both PPP and L2TP capable. It is usually a
network access server (NAS) located at a local ISP, which provides access services mainly for
PPP users.
An LAC is an endpoint of an L2TP tunnel and lies between an LNS and a remote system. It
encapsulates packets received from a remote system by using L2TP and then sends the
encapsulated packets to the LNS. It decapsulates packets received from the LNS and then
sends the decapsulated packets to the intended remote system.
•
LNS—An L2TP network server (LNS) is both PPP and L2TP capable. It is usually an edge
device on an enterprise network.
An LNS is the other endpoint of an L2TP tunnel. It is the logical termination point of a PPP
session tunneled by the LAC. L2TP extends the termination point of a PPP session from a NAS
to an LNS by establishing a tunnel.

L2TP message types and encapsulation structure

L2TP uses the following types of messages:
Remote user
LAC
PPPoE/ISDN
Figure 20, a typical L2TP network has the following components:
LNS
Internet
L2TP tunnel
67
Private
network