Application of topology：
Go to Network > Interface. Configure physical interface 1 and interface 2 as WAN1 and WAN2 respectively.
Then set WAN2 according to the above operation, as shown in the following figure:
All the WAN ports are in the Default for load Balance.When the WAN port in the group is down, the WAN port will be automatically removed from the balancing group to realize the traffic load balancing automatically.
Although your link is not down, the interface is still up. However, if your network is unavailable, the interface will be automatically removed from the load balancing.The link is automatically added back to the load balancing group.
If the WAN port link is connected, the WAN port can obtain the IP address, as shown in the figure below.
When you finish these steps above, the router could backup your line and switch data transmission between different WAN ports much flexibly as you configured.
Finally, we verify the effect of load balancing by speed measuring software.