This is based on the ping command. To check a host's availability (alive/down) on the Internet, we use the ping command from our command prompt. The most simple command of ping is ping hostname. Here we are implementing a mechanism which will take the host name from user as input and then use the ping command and give the output on the page. A host name can be a valid FQDN (e.g. www.yahoo.com) or simply an IP address (e.g. 64.86.4.3). Here we have set it to ping a host for five times. So if a host is reachable, you'll get five replies. If there is some kind of difficulty to connect to the host, you may not get all five replies. And if you get no reply, then the host is either down or there is no such alive host. Just take a look on the results and you'll understand.

Please Enter the host here:

 

Result: