Free course

Telnet Course

Learn Telnet as a readable application protocol, inspect its commands and option negotiation, use a client to explore text protocols, and understand why SSH replaced it.

5 modules · 25 lessons · No signup

Prerequisites: Shell Commands

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What you'll learn

Decode a Telnet session, run a safe local lab, inspect HTTP and SMTP conversations over TCP, and choose safer tools for real remote access.

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Course contents

  1. How Telnet works

    Understand the TCP connection, Network Virtual Terminal, byte stream, commands, and port 23.

    1. ✓ What Telnet is
    2. ✓ The TCP connection and port 23
    3. ✓ The Network Virtual Terminal
    4. ✓ Data and commands share one stream
    5. ✓ Check your understanding: Telnet foundations

  2. Commands and option negotiation

    Read IAC commands, WILL and DO exchanges, echo behavior, and terminal subnegotiation.

    1. ✓ Read IAC commands
    2. ✓ Negotiate with WILL and DO
    3. ✓ Echo and Suppress Go Ahead
    4. ✓ Subnegotiation and terminal details
    5. ✓ Check your understanding: commands and options

  3. Build a local Telnet lab

    Create a loopback server, connect a client, use command mode, and inspect the bytes exchanged.

    1. ✓ Choose a Telnet client
    2. ✓ Start a loopback server
    3. ✓ Connect and use command mode
    4. ✓ Observe option negotiation bytes
    5. ✓ Check your understanding: the local lab

  4. Inspect text protocols

    Use the Telnet client to test TCP and manually read HTTP and SMTP conversations.

    1. ✓ Separate the tool from the protocol
    2. ✓ Test TCP reachability
    3. ✓ Send an HTTP request by hand
    4. ✓ Read an SMTP greeting
    5. ✓ Check your understanding: inspecting protocols

  5. Security and troubleshooting

    Recognize plaintext risks, replace remote login with SSH, diagnose failures, and design a tiny protocol.

    1. ✓ Understand the plaintext risk
    2. ✓ Replace remote login with SSH
    3. ✓ Diagnose a failed session by layer
    4. ✓ Design a tiny text protocol
    5. ✓ Check your understanding: security and troubleshooting