The Ping command


Ping (Packet InterNet Grouper) is one of the simplest troubleshooting commands. However, when asked for an explanation of various “components” in Ping many people would struggle including myself. Hence I would like to post about this incredible command we system administrators use it almost everyday.

Use of Ping:

  1. We can check the connectivity of a system / server.
  2. We can identify whether there is any network latency while trying to contact the system. Lesser the time generally means the network connectivity is fast. However, this depends, when you try to connect to a server in different continent and through a VPN using public internet, the latency will be high (time will be high)

Technically Ping command send a echo request

So what is this Ping command and what its output means ?

Let us take a look at the below ping result:

 

ping

Here I am trying to ping a system (IP 10.208.33.41).

bytes – Size of the ping packet.

Time – Simply shows the latency to reach the destination. More milli seconds (ms) means it take long time to reach the destination.

TTL – Time to Live. TTL in Ping generally means, when you start ping command, the TTL value is initially set at 255. With every hops (traversing through every router), the value decreases. If the TTL value of a Ping decreases to zero, Router will discard the ping request.

In otherwords, it defines the number of routers that a packet can be forwarded. Each router that forwards a packet decrements the TTL value by one.

Ping command options:

ping options

Other small but significant things.

  • By default, if the time is > 4000ms (0r 4 seconds), we will get a timeout. That means, it will appear blank in the output.
  • Ping forms the basis of DDoS attacks (DDoS – Denial of Service Attacks).

More read:

Here is Ramesh Natarajan’s 15 examples’ worth a read regarding Ping:

http://www.thegeekstuff.com/2009/11/ping-tutorial-13-effective-ping-command-examples/

 

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