Call-LNS Scenario (Intranet Connection Through LAC Dial-Up)
This section describes the L2TP VPN networking and services in the call-LNS scenario.
In addition to providing remote access services for users, L2TP VPN interconnects the enterprise branch and headquarters so that branch users and headquarters users can communicate.
As shown in Figure 1, the L2TP Access Concentrator (LAC) serves as the egress gateway of the branch, and the LNS serves as the egress gateway of the headquarters. After L2TP VPN is configured on the LAC and LNS, the LAC proactively initiates a request to the LNS for establishing an L2TP VPN tunnel. After the L2TP VPN tunnel is established, the traffic sent by branch users to access the headquarters reach the peer device over the L2TP VPN tunnel. In the scenario, the L2TP VPN tunnel is established between the LAC and LNS. Users are not aware of the tunnel. 
The LAC and NAS are both tunnel initiators in L2TP. On a dialup network, the device that provides access services on a dialup network is called a NAS, and the device that provides access services on an Ethernet network is called a LAC.
