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.

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