3com 3031 Instruccion De Instalación
880
C
HAPTER
63: C
ONFIGURATION
OF
L2TP
Introduction to L2TP
Protocol
Protocol
Protocol background
PPP protocol defines a kind of encapsulation technology, which can transmit
various kinds of data packets on point-to-point link of layer 2. Meanwhile, PPP
protocol is performed to create links between users and NAS, with endpoint of
layer 2 link and PPP session sticking on the same hardware.
various kinds of data packets on point-to-point link of layer 2. Meanwhile, PPP
protocol is performed to create links between users and NAS, with endpoint of
layer 2 link and PPP session sticking on the same hardware.
L2TP (Layer 2 tunneling protocol) provides transmission support to PPP link layer
packets in the tunnel. It extents PPP model in that it permits link endpoint of layer
2 and PPP session point staying at different devices and realizes information
interaction by packet exchange network technology. It combines the advantages
of Point-to-Point Tunneling Protocol (PPTP) and Layer 2 Forwarding Protocol (L2F).
Therefore, it becomes the industrial standard of IETF's Layer 2 Tunneling Protocols.
packets in the tunnel. It extents PPP model in that it permits link endpoint of layer
2 and PPP session point staying at different devices and realizes information
interaction by packet exchange network technology. It combines the advantages
of Point-to-Point Tunneling Protocol (PPTP) and Layer 2 Forwarding Protocol (L2F).
Therefore, it becomes the industrial standard of IETF's Layer 2 Tunneling Protocols.
Typical L2TP networking
application
Typical networking of VPDN application created by L2TP protocol is in Figure 207.
Figure 207 Networking diagram of typical VPDN application created by L2TP
In Figure 207, LAC stands for L2TP Access Concentrator, which is a switch network
device with the ability to process PPP and L2TP request. Usually, LAC is a NAS
(Network Access Server), which provides access service to users through
PSTN/ISDN. LNS stands for L2TP Network Server, which is a device to serve as a
part of PPP system and to function as L2TP server.
device with the ability to process PPP and L2TP request. Usually, LAC is a NAS
(Network Access Server), which provides access service to users through
PSTN/ISDN. LNS stands for L2TP Network Server, which is a device to serve as a
part of PPP system and to function as L2TP server.
LAC lies between LNS and remote system (remote users and remote branches),
used for transmitting information packet between them, encapsulating
information packets received from remote system according to L2TP protocol and
sending to LNS, and decapsulating information packets received from LNS and
sending to remote system. Local connection or PPP link can be adopted between
LAC and remote system, but PPP link is always involved in VPDN applications. As
one end of the L2TP tunnel, LNS is the peer device of LAC, and also is the logic
terminating point of PPP session transmitted in tunnel by LAC.
used for transmitting information packet between them, encapsulating
information packets received from remote system according to L2TP protocol and
sending to LNS, and decapsulating information packets received from LNS and
sending to remote system. Local connection or PPP link can be adopted between
LAC and remote system, but PPP link is always involved in VPDN applications. As
one end of the L2TP tunnel, LNS is the peer device of LAC, and also is the logic
terminating point of PPP session transmitted in tunnel by LAC.
PC
PSTN/ISDN
Remote users
LAC
LNS
Remote users
Access server
Internet
backbone network
Internal server
L2TP channel