Link aggregation(802.3ad) allows you to combine two or more physical interfaces together to form an aggregated link. This new link has the bandwidth of all the links combined. If a link in the group fails, traffic is automatically transferred to the remaining interfaces with the only noticeable effect being reduced bandwidth.
This is similar to redundant interfaces, with the major difference being that a redundant interface group uses only one link at a time, while an aggregate link group uses the total bandwidth of the functioning links in the group.
Steps to configure are as below:
1. Go to Network / Interface Settings / Wan Settings
2. Click on Add LAG
3. Select Member Interfaeces
4. Select Load Balancing Mode as per the requirement and press save