Is a nifty tool to check the online status of ips/host and do rdns check or get mx records.Using the tool is pretty simple you just input the ips/dns names that you want to ping/rdns or get the mx record and click refresh/check.
On the main page failed pings will have OFF on the toggle buttons. Succeeded pings will have ON.
Results may vary depending on your ISP and carrier if you use it trough 3G network. Also you have one field where you can test a service with port.