When using two Internet connections from the same ISP, both links cannot be active at the same time if they are connecting to the same remote network and using the same remote gateway IP address. Since it is not possible to have two default routes each using the same remote gateway, the backup uplink must be used in standby mode only and used if the primary connection goes down. A second virtual server is used to monitor the primary uplink. When the primary uplink becomes unavailable, a script is executed to activate the secondary uplink. Lowering the route metric of the secondary uplink ensures that the backup uplink is used. When the primary uplink becomes available again (probing is successful), a script will place the secondary uplink into standby again.
In this article:
Step 1. Configure Two DHCP Connections
Configure two DHCP WAN connections. For more information, see How to Configure an ISP with Dynamic IP Addresses (DHCP).
For the primary and secondary DHCP uplink, use the following settings:
|Setting||Primary DHCP Connection||Secondary DHCP Connection|
Step 2. Create an Additional Virtual Server
Create an additional virtual server and configure a monitoring policy of the virtual server to execute a custom script in case of failure / success.
- Navigate to your box (Config > Full Config).
- Right-click Virtual Servers and select Create Server.
- Enter a Server Name.
- In the First-IP [IP1] field, enter
- Click Next.
- From the IP Monitoring Policy list, select all-OR-all-present.
- In the Monitored IPs I table, add the IP address to be monitored. This is typically an IP address in the Internet or from your ISP that indicates that a connection to the Internet is available.
- Click Next.
In the Start Script field, add the following script for the secondary DHCP uplink:
In the Stop Script field, add the following script for the secondary DHCP uplink:
If the monitoring IP address is unreachable, the virtual server stops and enables the secondary DHCP uplink by executing the stop script. If the monitoring IP address is available again, the virtual server starts and disables the secondary DHCP uplink by executing the the start script.
Step 3. Create a Host Firewall Rule
Create a Host Firewall rule to make sure that IP address probing is always done through the primary DHCP uplink (using the DHCP interface).
- Open the Host Firewall Rules page (Config > Full Config >Box > Infrastructure Services).
- Click Lock.
- Select the Outbound rule set on top of the rule list.
- Right-click in the rule list and select New > Rule.
- Select Pass as the action.
- Enter a name for the rule. For example,
- Specify the following settings that must be matched by the traffic handled by the access rule:
- Source – Select All-LocalIPs.
- Destination – Enter the IP address to be monitored.
- Service – Select ICMP.
- In the left pane, select the Object Viewer check box. The Object Viewer window opens.
- Open the Connections tab and create the connection object:
- Right-click the table and select New Connection. The Edit/Create a Connection Object window opens.
- Enter a Name for the connection object. E.g.,
From the NAT Address list, select From Interface.
In the Interface Name field, enter
- Click OK.
- In the Edit Rule window, select the new connection object in the Connection Method section.
- Click OK.
- Drag and drop the new access rule in the rule set so no rule above it matches the traffic you want to forward.
- Click Send Changes and Activate.
You can now see the active routes of the primary uplink and the pending route of the secondary uplink. If the primary uplink goes down, the virtual server is stopped and the stop script is executed - activating the secondary uplink. When the primary connection is available again, the virtual server executes the start script, which places the secondary link into standby mode again.