network failover; but not bonding

[sean darcy]

I have a machine with 2 nic's. One nic (ETH0) is connected to a cable 
modem. The other nic (ETH1) is connected to an internal lan. The 
internal lan also has access to the internet.

The cable service, Time-Warner RoadRunner, is great when up, but is not 
reliable. The connection through the internal lan (Verizon DSL) is 
reliable but lousy. Sigh.

When the cable is down, the interface connection to the cable modem 
stays up. An ifconfig shows ETH0 as up. The only way to tell is to ping 
an outside address.

I thought of bonding. But that won't work since it will see ETH0 as up, 
even if the cable service is down.

Is there a way to implement network failover that actually checks for 
true internet connection?

sean