FreeBSD network failover

[Gabe]

I have a nat'd box which obviously has an internal and external ip address. The box has a third interface which is configured to a DSL connection. My goal is for that interface to be activated if the external side fails so that outbound traffic still flows. Any of you know of a way to accomplish this regardless of the type of failure.

I looked into CARP but I am not convinced that this would do what I need it to.

/gabe