Limit/block devices when LB2120 LTE model is in failover mode

[m8473]

Using an LB2120 as backup to cable internet service at a rental unit. It sits between the cable modem and our Netgear R6700 Nighthawk wifi router.

When the cable internet fails it is important to keep connection with the security cameras, door locks, thermostat, and weather station. But I don't want to be paying LTE data rates for other connected devices (renter devices on the guest network, TV streaming video, etc.). Is there a way to block all devices except those we need to keep active when the LB2120 is in failover (LTE) mode? It needs to be automatic - not some manual reconfiguration of the LB2120 or the Nighthawk router. Is it possible?

Thanks.

[wombat71]

According to the manual, you can filter, but as I don't see it on my LB2120, I'm guessing either:

1) feature was removed in the version of the firmware I'm running 

or more likely

2) not available in bridge mode

As you have to be in bridge mode for the failover, perhaps what you're doing isn't possible?