Draytek Vigor2862 Series User Manual page 246

5. Configure LAN on the secondary router. Mind that the IP should be different and larger
than it on the primary router.
Info
6. We have setup High Availability on both routers, and before we link up both routers, it's
time to setup all other functions on the primary router so later we can see the
configuration sync taking place. If your primary router is already settled please proceed
to the next step. Here we configure the WAN as the representative example.
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If you have more than one LAN, you should set all the LAN IP of each LAN on
Primary and Secondary routers to different IP addresses to avoid IP conflict.
Here is the example, there are several LAN and all of them are under the
protection of hardware redundancy:
Vigor2862 Series User's Guide