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CompTIA A+ Certification All-in-One Exam Guide

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Figure 21-35 The Cyberduck FTP program running on macOS

Telnet and SSH

Telnet is a terminal emulation program for TCP/IP networks that uses port 23

and enables you to connect to a server or fancy router and run commands on

that machine as if you were sitting in front of it. This way, you can remotely

administer a server and communicate with other servers on your network. As

you can imagine, this is rather risky. If you can remotely control a computer,

what’s to stop others from doing the same? Of course, Telnet does not allow

just anyone to log on and wreak havoc with your network. You must enter a

special user name and password to run Telnet. Unfortunately, Telnet shares

FTP’s bad habit of sending passwords and user names as clear text, so you

should generally use it only within your own LAN.

If you need a remote terminal that works securely across the Internet, you

need Secure Shell (SSH). In fact, today SSH has replaced Telnet in almost all

places Telnet used to be popular. To the user, SSH works just like Telnet.

Behind the scenes, SSH uses port 22, and the entire connection is encrypted,

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