H3C SR8800-F Configuration Manual page 269

In steps 12 and 13, the LAC forwards packets for the remote system and LNS. Host A and LAC
exchange PPP frames, and the LAC and LNS exchange L2TP packets.
Client-initiated tunneling mode
As shown in
communicate with the LNS through the Internet. The LAC client can directly initiate a tunneling
request to the LNS without any dedicated LAC devices.
Figure 78 Client-initiated tunneling mode
A client-initiated tunnel has the following characteristics:
•
A client-initiated tunnel has higher security because it is established between a remote system
and the LNS.
•
The remote system must support L2TP and be able to communicate with the LNS. This causes
poor expandability.
As shown in
establishing a NAS-initiated tunnel. (Details not shown.)
Figure 79 Client-initiated tunnel establishment process
LAC-auto-initiated tunneling mode
In NAS-initiated mode, a remote system must successfully dial in to the LAC through PPPoE or
ISDN.
In LAC-auto-initiated mode, you can use the l2tp-auto-client command on the LAC to trigger the
LAC to initiate a tunneling request to the LNS. When a remote system accesses the private network,
the LAC forwards data through the L2TP tunnel.
Figure 78, a remote system running L2TP (LAC client) has a public IP address to
Figure 79, the workflow for establishing a client-initiated tunnel is similar to that for
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