Telnet¶

Understanding Telnet¶

Telnet (port 23) is a text-based protocol used to connect to remote systems. It provides a command-line interface for communication with other servers or services over TCP. Though it's largely replaced by SSH due to lack of encryption, it's still useful for manual testing, service probing, and understanding protocols.

Telnet is commonly used to simulate client requests to test whether a server responds correctly on certain ports.

Using Telnet to Interact with Protocols¶

1. Echo Server (Port 7)¶

Purpose:¶

Echoes whatever data you send.

Example:¶

telnet example.com 7

Then type:

Hello World!

The server will return:

Hello World!

2. Daytime Server (Port 13)¶

Purpose:¶

Returns current date and time as plain text.

Example:¶

telnet time.nist.gov 13

Output:

58969 21-08-03 11:26:33 50 0 0 762.1 UTC(NIST)

3. HTTP Server (Port 80)¶

Purpose:¶

Used to interact with web servers.

Commands and Examples:¶

telnet example.com 80

- GET request:¶

GET / HTTP/1.1
Host: example.com

(Press Enter twice)
Server responds with HTML page.

- POST (simulate form submission):¶

POST /form HTTP/1.1
Host: example.com
Content-Length: 13
Content-Type: application/x-www-form-urlencoded

name=Subrat

- PUT:¶

Creates or replaces a resource

PUT /file.txt HTTP/1.1
Host: example.com
Content-Length: 11

Hello World

- DELETE:¶

Deletes a resource

DELETE /file.txt HTTP/1.1
Host: example.com

4. FTP Server (Port 21)¶

Purpose:¶

Used for file transfer.

Example:¶

telnet ftp.example.com 21

Commands:¶

USER yourname
PASS yourpassword
RETR test.txt     <-- Download file
STOR upload.txt   <-- Upload file

5. SMTP Server (Port 25)¶

Purpose:¶

Send emails.

Example:¶

telnet smtp.example.com 25

Commands:¶

HELO yourdomain.com
MAIL FROM:<sender@example.com>
RCPT TO:<receiver@example.com>
DATA
Subject: Test Email

This is a test message.
.
QUIT

6. POP3 Server (Port 110)¶

Purpose:¶

Retrieve emails from the server (inbox download).

Example:¶

telnet pop.example.com 110

Commands:¶

USER yourname
PASS yourpassword
STAT
LIST
RETR 1
DELE 1
QUIT

7. IMAP Server (Port 143)¶

Purpose:¶

Access and manage mailbox on the server.

Example:¶

telnet imap.example.com 143

Commands:¶

a LOGIN yourname yourpassword
b SELECT INBOX
c FETCH 1 BODY[]
d COPY 1 "Archive"
e LOGOUT

Summary Table¶

Protocol	Default Port	Telnet Usage	Main Purpose
Echo	7	`telnet host 7`	Echo input
Daytime	13	`telnet host 13`	Get date & time
HTTP	80	`telnet host 80`	Web page requests (GET/POST/PUT/DELETE)
FTP	21	`telnet host 21`	File transfer
SMTP	25	`telnet host 25`	Send emails
POP3	110	`telnet host 110`	Retrieve inbox messages
IMAP	143	`telnet host 143`	Manage mailbox folders

Additional Notes:¶

Telnet won't work with encrypted (SSL/TLS) services like HTTPS (port 443), FTPS, or SMTPS.
Useful for manual protocol testing, learning, or network debugging.
Use Ctrl + ] followed by quit to exit Telnet.