Typical L2Tp Networking Application - H3C SR6600 Configuration Manual

However, users must install dedicated software, which means that they must use
platforms supporting L2TP client. Usually, Windows 2000 platform is used.
In general, a VPDN gateway can be a router or a dedicated VPN server.
There are primarily three VPDN tunneling protocols:
PPTP: Point-to-Point Tunneling Protocol
L2F: Layer 2 Forwarding
L2TP: Layer 2 Tunneling Protocol.
L2TP is currently the most widely-used VPDN tunneling protocol.

Typical L2TP Networking Application

Figure 4-1 shows a typical VPDN built by using L2TP.
Figure 4-1 VPDN built by using L2TP
A VPDN built by using L2TP comprises three components:
Remote system
A remote system is usually a remote user 's host or a remote branch's routing device that
needs to access the VPDN network.
LAC
An L2TP access concentrator (LAC) is a router that has PPP and L2TP capabilities. An LAC
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 using L2TP and then sends the
resulting packets to the LNS. It de-encapsulates packets received from the LNS and then
sends the resulting packets to the intended remote system.
The connection between an LAC and a remote system is a local connection or a PPP link.
Usually, a PPP link is used in a VPDN application.
LNS
An L2TP network server (LNS) functions as both the L2TP server and the PPP end system.
It is usually an edge router on an enterprise network.
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