Understanding 3G/4G Failover

It is important to note that the failover behavior when the primary WAN interface goes down depends on the Connection Type setting that is configured for the 3G/4G Connection Profile. In order for the 3G/4G interface to function as a backup interface, it must be configured as the Final Backup interface in the default load balancing group on the Network > Failover & LB Group page.

The following sections describe the three different methods of WAN-to-3G/4G failover. All of these sections assume that the U0/U1/M0 interface is configured as the Final Backup interface in the load balancing group.

Topics:
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Persistent Connection 3G/4G Failover
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Connect on Data 3G/4G Failover
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Manual Dial 3G/4G Failover

Persistent Connection 3G/4G Failover

3G/4G Failover: Persistent Connection Configuration depicts the sequence of events that occur when the WAN ethernet connection fails and the 3G/4G Connection Profile is configured for Persistent Connection.

3G/4G Failover: Persistent Connection Configuration

1
Primary Ethernet connection available – The Ethernet WAN interface is connected and used as the primary connection. The U0/U1/M0 interface is never connected while the Ethernet WAN interface is available (unless an explicit route has been configured which specifies 3G/4G as the destination interface).
2
Primary Ethernet connection fails – The U0/U1/M0 interface is initiated and remains in an “always-on” state while the Ethernet WAN connection is down.

If another Ethernet WAN interface is configured as part of the load balancing group, the appliance will first failover to the secondary Ethernet WAN before failing over to the U0/U1/M0 interface. In this situation, failover to the U0/U1/M0 interface will only occur when both the primary and secondary WAN paths are unavailable.

3
Reestablishing Primary Ethernet Connectivity After Failover – When the Ethernet WAN connection (either the primary WAN port or the secondary WAN port, if so configured) becomes available again, all LAN-to-WAN traffic is automatically routed back to the available Ethernet WAN connection. This includes active connections and VPN connections. The U0/U1/M0 interface connection is closed.
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CAUTION: It is not recommended to configure a policy-based route that uses the U0/U1/M0 interface when the U0/U1/M0 interface is configured as the Final Backup in the load balancing group. If a policy-based route is configured to use the U0/U1/M0 interface, the connection will remain up until the Maximum Connection Time (if configured) is reached.