Introduction To L2Tp - H3C SecPath F1800-A Operation Manual

Operation Manual - VPN
H3C SecPath F1800-A Firewall
Its disadvantages are:
Users need to install dedicated software (usually Win2000 platform), which limits
platforms available for users.
There are three types of VPDN tunneling protocol: PPTP, L2F, and L2TP; among
them, L2TP is the most popular.

2.1.2 Introduction to L2TP

I. Protocol Background
PPP defines a kind of encapsulation technology, which can transmit kinds of data
packets on point-to-point link of layer 2. Meanwhile, PPP runs between users and
NAS, with link endpoint of layer 2 and PPP session point staying at the same
hardware device.
L2TP supports transmitting PPP link layer packets in the tunnel. It permits that link
endpoint of layer 2 and PPP session point stay at different devices; it realizes
information interaction by packet exchange network technology. In this way, it extends
the PPP model.
L2TP combines the advantages of PPTP and L2F. Therefore, it becomes the
industrial standard of IETF's L2TP.
II. Typical L2TP Networking Application
Typical networking of VPDN application created by the L2TP protocol is shown in
Figure 2-1.
Figure 2-1 Networking diagram of VPDN service created by L2TP
In Figure
and used to process PPP end system and L2TP.
The L2TP Network Server (LNS) is used to process L2TP server port in PPP end
system.
Usually, LAC is a NAS, which provides access service for users through PSTN or
ISDN. LAC is placed between LNS and remote system (remote users and remote
Remote
User
LAC
PSTN/
ISDN
NAS
Remote
Branch
2-1, the L2TP Access Concentrator (LAC) is attached to the switch network
L2TP tunel
Internet
7-8
Chapter 2 L2TP Configuration
LNS
Internal Server