I installed a Cisco RV042 to a Cable connection and DSL line..
When I set the DSL line as primary and Cables and secondary and unplug the DSL line to check if it switched everything works fine and the computers switch to cable like nothing happened.
When I set cable and Primary and DSL as secondary and I unplug the cable line, it does not switch.. nothing happens.
and worse (not all) but some of the computers will not connect back to the internet again when I plug the line back in nothing works I have to reboot the switch router and computers to get anything back online..
FYI I disconnected the line running into the providers routers.