HP VPN Firewall Appliances VPN Configuration Guide

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establish an L2TP tunnel for the virtual PPP user. When a remote system accesses the internal
network, the LAC forwards data through the L2TP tunnel. In this mode, the connection between a
remote system and the LAC is not confined to a dial-up connection and can be any IP-based
connection.
Figure 154 LAC-auto-initiated tunneling mode
L2TP tunnel establishment process
Figure 155 Typical L2TP network
Figure 156 shows an L2TP call's setup procedure in NAS-initiated mode.