Product specifications

Chapter 6: Connection Management Efficient Networks
®
Router family
Command Line Interface Guide
Page 6-28 Efficient Networks
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Tunnels
• Tunnels are virtual paths that exist between an L2TP client and an L2TP
server.
• An L2TP server can communicate simultaneously with more than one L2TP
client.
• An L2TP client can communicate simultaneously with more than one L2TP
server.
• Some L2TP implementations including the one discussed in this section
allow the same router to act as both an L2TP client and an L2TP server
simultaneously, if so configured.
CAUTION:
Verify that the IP address of the other end of the tunnel is correctly routed through the
right, local interface/remote and will not appear to be routed through the tunnel. An
attempt to route the tunnel endpoint within itself will fail.
Sessions
Sessions can be thought of as switched virtual circuit “calls” carried within a tunnel
and can only exist within tunnels. One session carries one “call”. This “call” is one
PPP session. Multiple sessions can exist within a tunnel. The following briefly
discusses how sessions are created and destroyed.
• Session creation
Traffic destined to a remote entry (located at the end of the tunnel) initiates a tunnel
session. When the L2TP client wishes to establish a session to an LNS, the L2TP
client assumes the role of a LAC and sends control packets containing incoming call
information to the LNS over the tunnel.
• Session destruction
Figure 6-1: L2TP Example
INTERNET
L2TP Client:
Dial User+LAC
(ISDN router)
LNS Router
Remote User
Company
Company
LAN/server
PC
TUNNEL
Logical Link
Physical Link
Physical Link
IP traffic to the Internet
PPP session
ISDN line
DSL/ATM traffic
PPP session running over the tunnel