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Ping Tutorials in More Details

Page 2: How to Use Ping for Network Diagnostics

Ping is a network tool that comes with most computer operating system. For Windows user, you can use the MS DOS window to perform the ping test.

To see all the ping command line options, you can use the /? switch. The following diagram show the result of using ping /? command in MS DOS window:

ping network diagnostics

Now let’s do some ping examples to see how to analyze the results.

A Ping (Success) Example:

Open the MS DOS window and do a ping as shown in the following example:

how to use ping

If you do a ping without any option, it will use the default value in the network configuration file. In the above example:

  • Number of echo requests to send = 4
  • Time to live (TTL) = 128

(Actually, you can set the original number of TTL to any number. When the packet pass through a node, server, gateway or routers, the number of TTL will be decreased by 1, ie. 255, 254, 253…..100, 99……50, 49, 48, 47. When the number of TTL = 0, then the packets will be discard by the last router. We usually call that the packet is lost! This is very important to discard the packets that are "wandering" on the Internet, otherwise the Internet will be jammed with “wandering” packets.)

  • Timeout = 2 seconds

(if a packet cannot received within two seconds, it will be discard and consider to be lost.)

Troubleshooting Ping Results:

Take the above as an example, it shows:

  • The connectivity between the two computer is successful.
  • All packets were received, i.e. no packets are lost.
  • The average round trip is 373 mini-seconds (0.373 seconds). This should consider to be a very good connectivity.

A Ping (Fail) Example

Let’s see what is the ping result when a host is unreachable.

ping example

Troubleshooting Ping Results:

A failed ping can be the result of many possible problems:

  • The destination host is down or incapable of responding.
  • A firewall or other security mechanism blocking ICMP echo requests or replies.
  • Invalid routing information on the source or destination host.
  • Invalid routing information on an intermediate router.
  • Physical connectivity problems on the source or destination host, or on an intermediate router.
  • Other possible problems…..

Unfortunately, unsuccessful pings are not so meaningful and doesn’t help much in diagnosing the problem. However, the Traceroute command, which will be discussed in another post later, can be used to help isolating some of these problems.

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