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World L3: Phone Lines

ping and traceroute

You will learn: to check if a machine answers, and which exchanges a call passes.

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

Two hellos, no reply: 100% packet loss. Is the shop closed? Or is the road broken on the way?

Watch

ping: Hello, can you hear me? It sends a tiny message and times the echo. sends a tiny hello and times the echo. -c 3 sends three, then stops. Tap the line that says how many came back.

Tap the summary line.

0 of 1 found

Try it

Ping pasar.example three times. Without -c, ping never stops: then press Ctrl+C.

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

kedai (lab)
traceroute kedai.example
traceroute to kedai.example (203.0.113.10), 30 hops max, 60 byte packets
1 gateway.kedai (10.0.0.1) 0.026 ms 0.003 ms 0.002 ms
2 exchange.example (198.51.100.1) 0.012 ms 0.004 ms 0.003 ms
3 kedai.example (203.0.113.10) 0.024 ms 0.004 ms 0.005 ms

traceroute: Lists every telephone exchange (hop) a call passes on its way. lists every exchange on the way. Each line is a hop. This lab sits on one machine, so the times are tiny.

Predict

Another day, the same traceroute shows this. Is the road broken at hop 2?

 1  gateway.kedai (10.0.0.1)  0.040 ms  0.004 ms  0.004 ms
 2  * * *
 3  kedai.example (203.0.113.10)  0.015 ms  0.007 ms  0.007 ms

Check

What does each ping result tell you?

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

        You did it!

        You can now ping a machine and trace the road to it.

        Go deeper (optional)

        Many servers block ping on purpose. No reply does not always mean down: test the real port with curl. mtr mixes ping and traceroute into one live table. Our traceroute outputs came from a real Debian 13 lab.

        Real mission

        1. ping -c 3 example.com
        2. sudo apt install traceroute
        3. traceroute example.com

        0 of 3 steps done · Your ticks are saved.