It is just an idea, I am not sure if it is possible to do. I have an application used as a server for something. I'd need a script executed every time internet connection is lost, actually when it is regained. ISP is pretty regular and they only change my ip in 7am once a day so I have cron scheduled to run a script at that time, but every now and then there is some other reason for disconnection at different time so I could use some solution for script to be executed after internet connection is established.

And another thing. I'd like to setup another machine that would serve as a backup option if for some reason the first one looses internet connection for longer period. Maybe some script to ping first machine all the time and to execute a script when there is no valid response for more then 5 minutes. Or if 5 minutes are not possible then to execute script as soon as it gets invalid response on ping.
I guess it doesn't have to be done by using ping, but that is only thing that I could think of.

Any suggestions would be much appreciated.