About "ping" Tool

               PING (short for Packet Internet Groper) is a universal command that is available on every operating system to test the reachability of a network. When ping command is entered with an IP address as its argument, the machine will try to send some bits of raw data towards the machine owning that IP address .If some machine exits with that IP address ,it will send back certain bits.Thus the machine receive the bits and it confirms that a path is available from the current machine to the other through a network.

How 2?  Check the reachability of the machine 192.168.1.1 (IP address)

1:open terminal

2:type ping 192.168.1.1

You will get a an output like this:

if not :

 This results when destination is not reachable, try with host address IP is unknown:

 ping www.google.com

Thus, the ping command's output gives:

 Description:

Think of this application as network SONAR.

 The 'ping' application sends ICMP ECHO_REQUEST packets to any network addressable host (i.e. a server, a gateway router, etc.). The piece of equipment must be IP (Internet Protocol) addressable in order for this function to work

Usage:

This application is useful for determining whether a host is up and running on the network. The 'ping' application will return information regarding the hosts response to the ICMP ECHO_REQUEST packets.

 Thus, the ping command's output gives:

• The IP address which corresponds to the name of the remote machine;
• The ICMP sequence number;
• The packet's time to live (TTL). The time to live (TTL) field shows how many routers the packet went through as it travelled between the two machines. Each IP packet has a TTL field with a relatively high value. Each time it goes through a router, the value is reduced. If this number ever reaches zero, the router interprets this to mean that the packet is going around in circles, and terminates it;
• The round-trip delay field corresponds to the length of time in milliseconds of a round trip between the source and target machines. As a general rule, a packet must have a delay no longer than 200 ms;
• The number of lost packets.

EXACT WORKING

When one machine pings another machine which is remotely connected it actually send ICMP packets to and fro during the conversion.

Machine A pings-------------ICMP PACKET PING REQUEST------------> Machine B

Machine B replies------------ICMP Reply---------------------------------->Machine A (Identifies the machine)

HOw this Works??

Machine A ------------>create ICMP REQUEST Packet

=========> Randamoly Generated DATA '1247sd'+ Destination 'B'+ Source 'A'

Machine B------------->Create ICMP Reply PACKET

==========>(Same DATA from ICMP request is extracted and stuffed) '1247sd' + Destination 'A'+ Source 'B'

MAchine ------------->Recives tha ICMP REply from B and cheks the vaue in data part for conforming that the HOST N itself has responded. '147sd''1247sd' if yes it confirms the host is alive.

 NOTE:The main component in PACKET is only mentioned here.This is not exact content in packet ,it consist other data also like type cheksum TTL value etc.                                                           

 Possible errors:

 ping: opern.org

The host you pinged isn't a valid fully qualified domain name.

 10 packets transmitted, 0 packets received, 100% packet loss

The host you pinged is a valid fully qualified domain name, but ping could not establish a network connection to it. Could be that the host is down. Another possibility is that your local machine has fallen off the network. Maybe the local gatewy router is down.

 10 packets transmitted, 5 packets received, 50% packet loss

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