The utility iftop allows you to monitor bandwidth usage. It is in some sense similar to tools like iptraf, dstat and bwm-ng. Iftop is more special than those. Because iftop lets you monitor the speed of individual TCP / UDP connections. Basically, you will be able to determine how much traffic is flowing between two hosts.
Since I could not find a WAN failover script for Linux to my likening, I wrote one myself. If you have any use for it: I put it on a Google code project.
WFS tests the availability of your primary WAN connection and switches to your secondary / backup connection when a failure is detected. When in failover mode, WFS continues to monitor the availability of the primary WAN connection and once it becomes available again, it switches back.
For more information and a download, please take a look at the project:
