User manual

L2TP Overview
303532-A Rev 00
1-5
L2TP Access Concentrator (LAC)
The L2TP access concentrator (LAC) resides at the ISP network. The LAC
establishes the L2TP tunnel between itself and the LNS.
When the remote user places a call to the ISP network, this call goes to the LAC.
The LAC then negotiates the activation of an L2TP tunnel with the LNS. This
tunnel carries data from the remote user to the corporate network.
For more information about the Bay Networks implementation of the LAC in an
L2TP network, see “Bay Networks L2TP Implementation
” on page 1-11.
Remote Access Server (RAS)
The remote access server (RAS) resides at the ISP network. If the remote host is
an L2TP client, the tunnel is established from the remote client through a RAS to
an LNS at the corporate network. In this situation, there is no need for a LAC.
The RAS does not establish the tunnel; it only forwards already tunneled data to
the destination.
Tunnel Management Server (TMS)
At the ISP network, there needs to be a mechanism for identifying L2TP tunneled
users so that the LAC can construct the L2TP tunnel. Bay Networks uses a
mechanism called a tunnel management server (TMS); other vendors may use a
different method.
Note:
In this guide, the term LAC refers to a remote access server with L2TP
capabilities. The term RAS refers to a remote access server without L2TP
capabilities.