User guide

106 Chapter 4. Configuring Special Features

L2TP Tunneling Ñ Virtual Dial-Up

This section has four parts:

¥ The Introduction provides a general overview of L2TP tunneling.

¥ The L2TP Concepts section explains LNS, L2TP client, LAC, dial user, tunnels, and sessions.

¥ Configuration describes preliminary configuration steps and verification steps and lists commands associated

with the configuration of L2TP and PPP sessions.

¥ The Sample Configurations section provides two examples with step-by-step instructions: a simple L2TP

client configuration example and a complete LNS and L2TP client configuration example.

The installation CD also contains sample configuration files. These files can be edited for your installation

and copied to the router using TFTP or the Windows Quick Start application. For more information on TFTP

use, see Batch File Command Execution, page 279.

Introduction

L2TP (Layer 2 Tunneling Protocol) is used to forward a PPP link from a remote site to a corporate site across the

Internet, thus creating virtual paths called tunnels. Because tunneling involves encapsulating data, packets can be

transported across networks using different protocols. The advantages for tunneling the PPP protocol are listed

below:

¥ Different network protocols such as NetBEUI, IPX, and Appletalk can be transported through the Internet

using a tunnel. The protocol packets are encapsulated and routed across the network through the Internet.

¥ Tunnels provide a way to reduce costs and complexity associated with remote dial-up networking by using a

local ISP: users connect to the remote site by dialing into their local ISP and letting the Internet handle the

long-distance connections, thus avoiding long-distance phone charges.

¥ Tunneling PPP allows compression of data through the entire tunnel, which translates into greater throughput.

¥ By allowing encryption over the PPP link, L2TP contributes to more secure networks over the Internet.

¥ Remote users can access the company network, even if there is a company firewall (provided, of course, that

tunnels can come through the firewall).

Note: This feature can interoperate with any vendor that supports L2TP - Draft II.

L2TP Concepts

This section defines the major L2TP concepts such as LNS, L2TP client, LAC, and Dial user. These concepts are

illustrated with L2TP client examples. Also described are tunnels and sessionsÕ creations and destructions.