It is normal that users would like to know if the server is available. The title e ping works great in such situations. It is the most needed diagnostic tool in TCP/IP networks. Ping is implemented in all operating systems. It can check an active connection between two computers and measure how quickly data of packets are transmitted. Ping uses the ICMP (Internet Control Message Protocol) protocol. The principle of operation of ping command may be compared to the sonar installed on a submarine. Ping sends ICMP Echo Request and receives ICMP Echo Reply. In the first step, host sends the ICMP Echo Request packet to the server. The next, the host waits for the ICMP Echo Reply packet sent by the server. A lot of public server use these packets. A smaller value of ping measurement means that the connection is better. If the host does not get back the ping reply, it usually means that the server is offline. This may happen when:
The height of the ping depends on: link speed, network load and the nearest bandwidth on the path between the server and the host.
Some firewalls block the ICMP scanning. It is popular protection method against attacks. Usually, the ping allows us to determine the type of operating system. It greatly simplifies attack . This knowledge affords, in the wrong hands, to get an access to the computer. There are many free websites, where users can check not only ping but also the speed of their interrnet connection. It is also possible to run “ping” command from local machine. All operation systems have an implementation of this protocol and an appropriate application.