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Old Geezer
Asked: 2021-08-17 22:37:09 +0800 CST

Setting up unsecure telnet [duplicate]

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I want to demonstrate serial communications in a class. Is it possible/how to set up a good old port 23 unencrypted console service in Ubuntu?

command-line

1 Answers

  1. You can install and start a telnet server with this small process. For your information, telnet default port is not 22 (ssh) but 23.

    sudo apt install inetutils-telnetd telnet

    Edit the file /etc/inetd.conf and comment out the following line

    telnet  stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/sbin/telnetd

    Then restart inet server.

    sudo systemctl restart inetutils-inetd

    To snif packages, use then tcpdump. You can install with the following command.

    sudo apt install tcpdump

    Use the following command to display the traffic on port 23 (keep the terminal open, and open a new one).

    sudo tcpdump -A -i lo dst port 23

    Finally, run telnet on your computer.

    telnet localhost 23

    Login with your local account, you will see the written text in clear into tcpdump.

    telnet

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