Could you run a ping script to the given monitored IPs (or use something 
like Nagios) and then run a script to update the routing configuration 
on a router that can take external commands easily?  That's the approach 
I would take from a cost to performance standpoint, unless I 
misunderstand what you are trying to do.  I did something similar to 
that years ago with a cheap Linksys router (but I opened and closed 
ports within  a LAN rather than modifying the route between two WANS in 
that case) to do primitive failover.  It worked perfectly.

Jeff

Mark Gilbert wrote:
> I was wondering if someone knows of an open source free router product
> which can do object tracking.  Object tracking tracks to ip's and
> depending if one becomes unavailable it will dynamically change the
> routing to another path.  I am assuming this is not possible with
> M0n0wall but would be delighted if it were possible. 
>
>  
>
> Thanks
>
>
>