World map

 

BM

World L3: Phone Lines

IP addresses: the shop's number

You will learn: what an IP address is, and how to find your server's.

Checked with Linux (Debian 13) on 1 Nov 2026

The problem

You are hereyou@kedai:~$

Folder ~

Empty folder

+ 3 hidden (ls -a)

Services

  • cronrunningstarts at boot
  • sshrunningstarts at boot
  • nginxrunningstarts at boot

Phone lines (network) Address 10.0.0.5

Listening ports

  • :22 sshd
  • :80 nginx

Aina needs the shop server’s number to call it. ip -br addr printed two lines. Which number is it?

Try it

An IP address: A computer's phone number: four numbers from 0 to 255 with dots, like 10.0.0.5. is a computer’s phone number. It has four numbers, each 0 to 255, joined by dots. Real address or not?

Swipe right for good, left for needs work. Or use the buttons.

1 / 510.0.0.5

Watch

kedai has two lines. lo is 127.0.0.1, the loopback: the shop’s intercom. eth0 is 10.0.0.5: the line to the street. Which one can Aina’s laptop call?

Try it

Your turn. Show kedai’s addresses with ip -br addr (or hostname -I).

You are hereyou@kedai:~$

Folder ~

Empty folder

+ 3 hidden (ls -a)

Services

  • cronrunningstarts at boot
  • sshrunningstarts at boot
  • nginxrunningstarts at boot

Phone lines (network) Address 10.0.0.5

Listening ports

  • :22 sshd
  • :80 nginx

Watch

Some numbers only work inside one building. These are private address: A number that only works inside one building: 10.x, 172.16-31.x or 192.168.x.: 10.x, 192.168.x and 172.16–31.x. Sort them.

Drag a card into a box. Or tap the card, then tap the box.

      Predict

      On your laptop you open http://127.0.0.1. Whose page could answer?

      You did it!

      You can now find a server’s address and tell private from public.

      Go deeper (optional)

      Newer IPv6 addresses look like 2001:db8::5. Our practice server has none. Numbers like 203.0.113.x are kept for examples, like fake phone numbers in films.

      Real rep (optional): find your own computer’s number.

      Real mission

      1. ip -br addr
      2. ipconfig getifaddr en0
      3. ipconfig

      0 of 4 steps done · Your ticks are saved.