 - Layer Two Tunneling Protocol (L2TP) is an extension
of the Point-to-Point Tunneling Protocol (PPTP) used
by an Internet service provider (ISP) to enable the operation of a virtual private
network (VPN) over the Internet. L2TP merges the best
features of two other tunneling protocols: PPTP from Microsoft and L2F
from Cisco Systems. The two main components that make up L2TP are the L2TP
Access Concentrator (LAC), which is the device that physically terminates
a call and the L2TP Network Server (LNS), which is the device that terminates
and possibly authenticates the PPP stream.
PPP defines a means of encapsulation
to transmit multiprotocol packets over layer two (L2) point-to-point links.
Generally, a user connects to a network access server (NAS) through
ISDN, ADSL, dialup POTS or other service and runs PPP over that connection.
In this configuration, the L2 and PPP session endpoints are both on the
same NAS.
L2TP uses packet-switched network connections
to make it possible for the endpoints to be located on different machines.
The user has an L2 connection to an access concentrator, which then tunnels
individual PPP frames to the NAS, so that the packets can be processed
separately from the location of the circuit termination. This means that
the connection can terminate at a local circuit concentrator, eliminating
possible long-distance charges, among other benefits. From the user's point
of view, there is no difference in the operation.
| LAST UPDATED: |
18 Apr 2007
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