PING – Network Tool Tutorial – 2

OUTPUT ANALYSIS:

In previous tutorial PING – Network Tool Tutorial – 1 we seen how PING Command works

if you want to clearly understand about PING command go through Tutorial – 1.

we catched echo_request and echo_response by using wireshark(A Popular Network Sniffing Tool)

ping gives us three major information

-Host Reachability
-Network Congestion
-Time To Live

Host Reachability

The Ping results in the previous tutorial show that four ICMP packets have been sent and four received. This result indicates you that the host is alive at the ICMP level. However, no other information, such as whether or not a a webserver is running, is given.

What’s does it mean if I receive a negative result?
Let’s see an example:

C:>ping www.abcdefg.com

Pinging abcdefg.com [192.168.88.15] with 32 bytes of data:

Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 192.168.88.15:
      Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Host www.abcdefg.com, which has IP address 192.168.88.15, did not answer to the Ping command. It’s interesting to note that the negative answer does not always mean that the recipient is not alive (in our example, it is alive and runs a webserver). In this case, the result simply means that the host just doesn’t answer to ICMP request.

What could be the reason for this “no-answer” ?
It is not always possible to know the exact reason behind a “no-answer”. As a matter of fact, there may be a lot of different reasons. In the following picture, we summarize the four major reasons.

In the first case, an external firewall blocks the ICMP requests. ICMP can be used as a first step in an attack because it can determine the alive hosts before attacking. In this case the network behind the firewall is hidden from the external world even it is well alive.

Blocking ICMP messages is a first security recommendation to secure a network. The external firewall is more often used to secure professional network because it is expensive and requires advanced skills for configuring.

In the second case, the workstation has a personal firewall that blocks the ICMP message. A personal firewall is recommended for home computers for the same reasons mentioned above.

In the thrid case, the “pinged” machine is not connected to the IP network, for instance, because the network cable is unplugged.
The echo_request message will be discarded on the last router of the layer 3 device before the remote host.

In the fourth case, the host is down or has its network card deactivated. Such as in the previous case, the echo_request message will die on the last router of the layer 3 device before the remote host.

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If a device called Geneva can ping another called Dallas, does it mean that the opposite, in other words Dallas can ping Geneva, is always true?

The response is no. As you can see below, you can have a firewall only preventing echo_request in a single direction.

When Dallas pings Geneva, the ICMP echo_request is blocked on the firewall and Dallas receives no answer from Geneva.

When Geneva pings Dallas, the ICMP echo_request reaches Dallas and Geneva receives the echo_response in return, so the ping is successful. In this case, the ICMP packets are not blocked since the firewall only stops echo_request coming from outside. Here, we have an echo_request from inside and an echo_response from outside.

Remaining things will be seen in tutorial -3..

(Taken from openmaniak.com)

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