Ping is one of the easiest utilities to understand at a high level.
The client sends a probe sourced from its local IP address,
in this case 10.1.4.4,
towards some arbitrary target to which it wants to test connectivity.
The probe message is known as an ICMP echo or echo‑request.
The target in this case is a server at Wired Brain Coffee
Company with an IP address of 10.2.5.5.
Upon receipt, the server opens the packet and decides what to do.
In almost all cases, the target needs to reply back to the sender.
The sender receives this probe and replies with an echo‑reply message sourced
from its local address towards the originator of the probe,
which was our client.
Most operating systems also reflect the same payload as well,
giving the center an opportunity to validate that the
payload was not modified in transit.
Okay, enough talk. Let's see if our Globomantics clients can reach
this spiffy new Wired Brain Coffee server for real.
I'm currently logged into the Globomantics CLIENT device, which,
again, is just a Cisco IOS router for simplicity.
The goal of this demonstration is to ping from this client to the new Wired
Brain Coffee Company server at the other end of the network. We simply want to
test connectivity from the client to the server.
The command in almost all operating systems is ping followed by
the target IP address the administrator wants to probe. In this
case, the remote server is 10.2.5.5.
After typing the command press Enter and wait until the test is complete.
Each exclamation mark represents that an echo‑request was sent
and a corresponding echo‑reply was received.
This test sent five probes and received five replies,
which indicates a successful test.
To quickly demonstrate a failed test, we can ping a
non‑existent IP address such as 10.2.5.6.
This time we see a period character.
This represents a single echo‑request being sent with
no corresponding reply of any kind.
Some operating systems will provide more verbose feedback,
printing request timed out or something similar.
Also, notice that it took about 10 seconds for this test to fail while it
took only a few milliseconds for the first test to succeed.
Most operating systems will give each probe a few seconds, 2 in
this case, to complete before declaring a timeout. Ping has many
minor options such as changing the packet size, timeout, source
IP address, and more.
We will explore some of these options in later videos as their real‑life use
cases become relevant for Globomantics. To reinforce learning,
I'll enable ICMP debugging and kick off another successful ping.
We can see the requests being sent and the replies being received, which
is a great way to further validate ICMP operations.
This becomes even more useful when looking at more
interesting ICMP packet types. Stay tuned