SSH Tunneling

What is SSH Tunneling?
SSH tunneling is used to securely access private services that are not exposed to the internet.

• It works only over SSH
• It uses port 22 to encrypt and forward traffic
• It can carry other traffic like HTTP, databases, or RDP

Why do we need SSH Tunneling?
Some services are internal only and cannot be accessed directly:

• Databases (MySQL, PostgreSQL)
• Internal web applications
• Admin dashboards
• RDP or SSH on other machines

Exposing these services to the internet would be insecure.

Solution: An SSH tunnel allows access to these internal services through one secure entry point: 👉 SSH (port 22).

Security (encryption)
Some services:

• Don’t encrypt traffic
• Use weak auth
• Were never designed for the public internet

SSH tunnel:

• Encrypts everything
• Hides credentials
• Protects against sniffing

Example

ssh -L 9000:localhost:80 10.5.2.1

What happens here?

• Server 10.5.2.1 runs:

  • SSH (port 22)
  • A web service (port 80)

• Alice:

  1. Runs the SSH command (ssh -L 9000:localhost:80 10.5.2.1)
  2. Logs in successfully
  3. Opens her browser and goes to: http://localhost:9000

-L: Means local port

➡️ This securely connects her to the web service on 10.5.2.1 without server exposing the webservice to the internet.

Difference between SSH login vs SSH Tunneling

Articles recommended by the author

• SSH: Unlocking Its Power – A Beginners Guide to SSH

References

• [Neme11] E. Nemeth, UNIX and Linux System Administration Handbook. Prentice Hall, 2011. [Online]. Available: https://books.google.de/books?id=0SIdBAAAQBAJ