UNIX for Advanced & Expert Users

Here we want to implement the network redundancy on UNIX with the software.
The two network interface cards are configured on the UNIX node,once one card is down or unnormal,the other can take over. Those aplications that used the tcp ,udp,multicast protocol can also been switched at the same time.
The question is :
1. how to monitor the network interface card is falied.(niff daemon might been ok?)
2. How to monitor the network traffic ?(include the switch port)
3. Once find the card failed or network traffic was high, are there any good ideas to switch the application?

If not the above, any other suggestions?
By the way, the above implementation should be finished with the programing instead of hardware.
Thanks

post your unix version, the most of the unices already have daemons or tools for that, like on Solaris the IPMP/mpathd

post an output from "uname -a"

regards PRESSY

As you know, we develop our software on the different platform, Then the UNIX version has two version:One is the True 64 UNIX, the other is HP-UX.
By the way, we want to immplement it by our program.