- [Instructor] A very useful tool
with unexpected uses is Telnet.
By default, it isn't installed on Windows anymore,
but a simple Google can give you the steps to install.
On my Windows 10 machine,
I can enter the following command to install it.
(keyboard clicking)
Now, from a command prompt, I can simply type, "telnet"
to enter the program.
While the Telnet utility allows me to Telnet into equipment
for remote administrative purposes,
it's also extremely useful for troubleshooting.
I looked up google.com's MX record,
then traced down the A record associated with that entry.
I'm going to test SMTP on that mail server
by Telnetting into it.
From the command line, I'll simply enter "telnet"
then the IP address to connect to,
and last, the port to connect on.
In this case, telnet 142.250.138.26 25.
By default, Telnet that wants to connect on port 23.
But in this case, I'll change it to port 25.
I have the prompt available from the mail server.
I can give the server an hello command
and see if it responds.
This is great for testing simple connectivity
to a mail server or relay server.
I can also verify a web server using Telnet.
I'm going to telnet gregsowell.com on port 80
the standard HTTP port.
Telnet gregsowell.com on port 80.
If the session shows a blinking cursor in the top left,
that means I have an established TCP session.
From here, I can type any letter and hit Enter.
The server spits some info back at me with an error message.
Sometimes the server won't spit anything back
but I can still see if the session is established.
Telnet is a quick and simple way to verify
if a TCP session can be established.