But you won't have to log into it to check if the host is up. Your rsh call basically does that and that's not what you want.

You need to use something like ping to check for a network response before trying to log into the host (via rsh, etc). If pinging the host indicates that it is up then try something like rping to see if the OS is up because I've had many a machine lock up tight yet still respond to pings. This is just an extra measure to ensure that you will get the results you need.