Internet Control Message Protocol (ICMP)

Some applications query the network using this protocol; ping for example.

  • Works at layer 3 to deliver connectionless packets
  • Ping works by sending echo requests

Wikipedia #

The Internet Control Message Protocol (ICMP) is a supporting protocol in the internet protocol suite. Is is used by network devices, including routers , to send error messages and operational information indicating success or failure when communicating with another IP address, for example, an error is indicated when a requested service is not available or that a host or router could not be reached. ICMP differes from transport protocols such as TCP and UDP in that it is not typically used to exchange data between systems, nor is it regularly employed by end-user network applications (with the exception of some diagnostic tools like ping and traceroute ).

Source: https://en.wikipedia.org/wiki/Internet_Control_Message_Protocol