1. Upgrade your NCOS to 6.5.0 or later. This process can be found here (NCOS: How to update the NCOS of a Cradlepoint router
2. Log into your Cradlepoint administration web page or access the device from NetCloud Manager.
3. Go to Connection Manager.
4. Locate your primary WAN connection. This is usually the ethernet WAN profile.
5. Set the WAN verify setting to active ping. Google's DNS server is often used as the target IP (126.96.36.199).
6. Reduce the retry interval to 1 second and the retry count to 1 second.
7. Reduce the idle check interval to 2 seconds.
8. Set the secondary connection (usually an LTE modem) profile from on-demand to Standby.
These settings will make the Cradlepoint check for an active connection every 2 seconds and spend 1 second trying a second time. After that, failover will occur to the secondary connection.