3Com 3C13636 Configuration Manual page 1212

3Com Router 3000 Ethernet Family
Configuration Guide
PC
Figure 2-4 Typical L2TP application network
Call setup flow of L2TP tunnel is shown in the following figure:
PC
(3) PAP or CHAP authentication
Figure 2-5 Call setup flow of L2TP channel
The following is the call setup process using L2TP tunnel:
1) The PC at user side initiates setup request;
2) The PC and LAC equipment (Router A) negotiate PPP LCP parameters;
3) LAC performs PAP or CHAP authentication based on the information provided by
the PC;
4) LAC sends access request including VPN user's name and password to RADIUS
server for authentication;
RADIUS Server
IP network
PSTN/ISDN
Router A
LAC
LAC
Router A
(1) Call Setup
(2) PPP LCP Setup
(4) access request
(5) access accept
(12) CHAP authentication twice(challenge/response)
(15) authentication passes
3Com Corporation
RADIUS Server
WAN
LAC
RADIUS Server
(6) Tunnel establishment
(7) PAP or CHAP authentication
(challenge/response)
(8) authentication passes
(9) user CHAP response, ppp
negotiation parameter
2-5
Chapter 2 Configuration of L2TP
IP network
PC
Router B
PC
LNS
LNS
LNS
Router B
RADIUS Server
(10) access request
(11) access accept
(13) access request
(14) access accept