Part 1 · Lesson 3 · Beginner

Ports: Many Doors, One Machine

One machine, many ports — each a different process.

In this interactive Infrastructure lesson from Stencel Academy you don't just read — you type real commands like ss -tlnp, curl web-01:8080 and watch the machine respond on a live, animated map. It is part of the free How Infrastructure Works course.

Key takeaway: A port is a numbered door into one process; 'connection refused' means nobody is listening there.

Before this lesson

Builds on: Names to Addresses.

What you'll practise

curl -s web-01 — No port given → 80 is implied. nginx answers the door.
ss -tln — Without -p you see the doors but not who's behind them.
sudo lsof -i :80 — The other direction: which process owns this port?
nc -zv web-01 5432 — Postgres listens on 127.0.0.1 only — invisible from outside.

Terms you'll learn

portsocketlisteningconnection refusedwell-known ports

Check your understanding

`curl web-01:8080` says 'connection refused'. Why?

No process is listening on port 8080
Port 8080 doesn't exist on Linux machines
The internet dropped the packet on the way

Open the interactive lesson →