1:1 Inter-Board Backup on the LNS

Usage Scenario

In the 1:1 backup scenario on the LNS, two boards need to be bound to an LNS backup group to function as the master and backup tunnel boards.

Figure 1 Networking for LNS-side 1:1 inter-board backup
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Inter-Board Hot Backup Fundamentals

A logical interface Loopback0 is specified on the LNS, and an L2TP tunnel is established between the LNS and the LAC using the IP address of the interface.

When no fault occurs, the tunnel is established on the master tunnel board and the entries are backed up to the slave tunnel board. In this case, the entries on the master and slave tunnel boards are the same, and user services run on the master tunnel board.
When the master tunnel board is faulty, the route between the LAC and LNS is reachable because the loopback interface is used as the tunnel interface. The control plane sets the status of the slave tunnel board to master. The entries on the slave tunnel board remain unchanged and are the same as those on the faulty master tunnel board. Therefore, users stay online, and the control plane directs user traffic to the new master tunnel board.