A very useful tool with unexpected results is Telnet. By default it isn’t installed on Windows anymore, but a simple Google can give you the steps to install. On Windows 10, I can enter a simple command line statement to install it. The ISM /online /Enable-Feature/FeatureName:TelnetClient. All right. Now that I’ve got the “operation completed successfully” message, I’ll go ahead and clear the screen.
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What is telnet
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. So in this case, telnet 22.214.171.124, then a space and the port number of 25.
By default, Telnet wants to connect to port 23, but in this case, you can see I changed it to port 25. I have the prompt available for the mail server. I can give the server a HELO command and see it respond. (typing) At this point, I’ll enter the quit command, but I could actually send an entire e-mail via Telnet. (typing) This is great for testing connectivity to a mail server or a relay server. At this point, I’m gonna go ahead and clear the screen.
I can also verify a web server using Telnet. I’m going to Telnet to Google on port 80, the standard HTTP port. Telnet Google.com on port 80. If the session shows a blinking cursor on the top left, that means I’ve established a TCP session. From there, I can type anything and hit enter. The server spits back some info at me with an error message. Sometimes a 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 has been established.
How to configure telnet
So, for that you have first of all open packet trace you need 1 pc and 1 pc switch you can take any switch and pc, first of all make connection between them and connect with telnet port.
Open the switch and go to CLI mode and start typing
#Line console 0
#line vty pass 0 4
#enable password cisco
#interface vlan 1
#ip add 172.17.1.1 255.255.0.0
Now open the PC and go to desktop and assign a ip address to the PC, give it static IP 172.17.1.2 255.255.0.0, open the command prompt.
PC> telnet 172.17.1.1
switch# config terminal
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