DrayTek Dual WAN routers such us the Vigor2920 have two Ethernet WAN Interfaces. The Dual WAN Ports allow you to connect to two separate network connections for automatic fail over and load balance. You may refer to the figure shown below.

Configuring Automatic Failover

When WAN1 is Down, WAN2 will be Up automatically; when WAN1 is Up again, WAN2 will be Down automatically.

For your business you need a reliable connection. The downtime of even just a few minutes is equal to quite a bit of revenue loss. You can use Automatic Failover for network redundancy to keep your Internet connection always online. Assuming you have two links, one is Cable connection (WAN1) and the other is ADSL connection (WAN2). Normally you want all the traffic goes through WAN1.

Refer to the steps below to setup your Vigor 2920 series router.

1. Connect a Cable line to WAN1 port and a DSL modem to WAN2 port respectively.

2. Open the Web configurator and go to WAN >> General Setup.

3. Click the WAN1 link. Choose Always On for Active Mode. Click OK to save it and exit the page.

4. Click the WAN2 link. Choose Backup for Active Mode and choose When any WAN disconnect or When all WAN disconnect as Backup WAN.

5. Go to WAN >> Internet Access.

6. Select Static or Dynamic IP for WAN1 and PPPoE for WAN2 respectively. Then press the Details Page button to display the corresponding configuration page.

7. Configure the proper settings for Cable line and DSL line connection in those pages according to the information offered by ISP.

After the configuration, Vigor router will use ARP requests to check if WAN1/WAN2 Gateway is alive. If there is no response for a period of time, the router will drop the connection of line and then automatically dial the DSL connection for WAN2. After WAN2 is connected, all the traffic will be guided and switched to WAN2. Though WAN1 is down, Vigor router would always send ARP requests to check its status. When it receives the ARP response from the Gateway on WAN1 the connection is considered reestablished, Vigor router will use WAN1 again and disconnect WAN2 switching over all existing sessions.

More Information on DrayTek can be found in this other blogs.