Ping

2.  A ping is perhaps the most commonly used tool when
troubleshooting a network.
 Ping (Packet Internet Groper) tool is included with most
operating systems.
 It is invoked using a ping command.
 Ping command uses ICMP (Internet Control Message
Protocol).
 Ping works by sending an ICMP echo request message to
the specified IP address.
 If the computer with the destination IP address is
reachable, it responds with an ICMP echo reply message.
 A ping command usually outputs some other information
about a network performance, e.g. a round-trip time, a time
to send an ICMP request packet and receive an ICMP
reply packet.

3.  Here is an output of the ping command from Windows 7:
 In the example above we have pinged the ip address
10.10.100.1. By default, ping on Windows sends four ICMP
request packets. As you can see from the output above, the
host with the IP address of 10.10.100.1 is reachable and has
replied with four ICMP reply packets. You can also see that
the remote host has replied within 1 ms, which indicates that
the network is not congested.