Internet Control Message Protocol (ICMP) is used by devices on a network to send control and error messages to computers and servers. There are several different uses for ICMP, such as announcing network errors, announcing network congestion, and troubleshooting.
Ping is commonly used to test connections between computers. Ping is a simple but highly useful command-line utility used to determine whether a specific IP address is accessible. To see a list of options that you can use with the ping command, type C:\>ping /? in the Command Prompt window.
The ipconfig command is another useful command-line utility used to verify that a NIC has a valid IP address. To display full configuration information of all network adapters, type C:\> ipconfig /all in the Command Prompt window. You can ping the IP address obtained from the ipconfig /all command to test IP connectivity.
Ping works by sending an ICMP echo request to a destination computer or other network device. The receiving device then sends back an ICMP echo reply message to confirm connectivity. Echo requests and echo replies are test messages that determine if devices can send packets to each other. Four ICMP echo requests (pings) are sent to the destination computer. If it is reachable, the destination computer responds with four ICMP echo replies. The percentage of successful replies can help you to determine the reliability and accessibility of the destination computer. Other ICMP messages report undelivered packets and whether a device is too busy to handle the packet.
You can also use ping to find the IP address of a host when that host’s name is known. If you ping the name of a website, for example, cisco.com, as shown in the figure, the IP address of the server displays.