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- [Instructor] A very useful tool

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with unexpected uses is Telnet.

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By default, it isn't installed on Windows anymore,

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but a simple Google can give you the steps to install.

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On my Windows 10 machine,

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I can enter the following command to install it.

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(keyboard clicking)

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Now, from a command prompt, I can simply type, "telnet"

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to enter the program.

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While the Telnet utility allows me to Telnet into equipment

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for remote administrative purposes,

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it's also extremely useful for troubleshooting.

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I looked up google.com's MX record,

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then traced down the A record associated with that entry.

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I'm going to test SMTP on that mail server

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by Telnetting into it.

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From the command line, I'll simply enter "telnet"

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then the IP address to connect to,

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and last, the port to connect on.

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In this case, telnet 142.250.138.26 25.

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By default, Telnet that wants to connect on port 23.

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But in this case, I'll change it to port 25.

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I have the prompt available from the mail server.

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I can give the server an hello command

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and see if it responds.

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This is great for testing simple connectivity

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to a mail server or relay server.

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I can also verify a web server using Telnet.

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I'm going to telnet gregsowell.com on port 80

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the standard HTTP port.

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Telnet gregsowell.com on port 80.

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If the session shows a blinking cursor in the top left,

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that means I have an established TCP session.

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From here, I can type any letter and hit Enter.

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The server spits some info back at me with an error message.

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Sometimes the server won't spit anything back

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but I can still see if the session is established.

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Telnet is a quick and simple way to verify

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if a TCP session can be established.