Hands-On: See the Internet in Action

These exercises use free tools that work on any smartphone or laptop browser. You do not need to install anything — except for Exercise 1, which uses a built-in command that every phone and laptop already has.

Exercise 1 — Run Your First DNS Lookup

Before You Start: DNS translates names to IP addresses. This exercise lets you run the lookup yourself, from your own device, the same way your browser does it every time you load a page.

On a laptop (Windows or Mac):

  1. Open Terminal (Mac) or Command Prompt (Windows — press Windows key, type cmd, press Enter)
  2. Type the following and press Enter: 
    nslookup google.com
  3. You will see output like: 
    Server:   192.168.1.1
Address:  192.168.1.1#53

Non-authoritative answer:
Name:    google.com
Address: 142.250.192.46
  4. Note the IP address returned
  5. Now try with other domains — type each and press Enter: 
    nslookup sbi.co.in
nslookup gmail.com
nslookup irctc.co.in

On Android:

  • Download a free terminal app (like “Termux” from the Play Store) and run nslookup google.com
  • Or use the dnschecker.org website from the next step as an alternative

What You’re Seeing

The “Server” line is your local DNS resolver — usually your router or ISP’s DNS server. The “Address” line is the IP address that google.com maps to. Notice that gmail.com and google.com may return the same or different IPs — Google has many servers. sbi.co.in returns a smaller set of IPs because SBI’s infrastructure is more centralised.

The key insight: If DNS fails, nothing works. Your browser cannot connect to anything by name. Every website, every app, every service starts here.

Deepa Asks

“What if I type the wrong domain — does DNS return an error?”

Yes. If you type nslookup nosuchwbsite12345.com, you will get a “NXDOMAIN” (Non-Existent Domain) response. Your browser translates this into “Hmm, we can’t find that site.” The problem is always at one of the four layers — DNS is often where to look first.

Discussion Prompt: Run nslookup google.com twice. Do you get the same IP both times? Google may return different IPs for the same domain name because they have thousands of servers worldwide and route you to the nearest one.

Exercise 2 — Find Your Public IP Address

Before You Start: Your phone or laptop has a private IP on your local network. But the internet sees a different address — the public IP of your router. This exercise shows you the public one.

  1. Open your phone’s browser (Chrome, Firefox, or Safari)
  2. Go to toolbox.googleapps.com
  3. In the top menu, tap Check Header — or simply search “what is my ip” in any search engine
  4. Note the IP address shown
  5. Now switch from mobile data to Wi-Fi (or vice versa) and check again

What You’re Seeing

The two IP addresses are different because your mobile network and your home Wi-Fi connect to the internet through different routers, each with its own public IP. The internet sees your traffic coming from that router’s IP, not your device’s private IP.

Discussion Prompt: If two phones on the same Wi-Fi network both visit google.com, which IP does Google see? The router’s public IP — the same one for both phones.

Exercise 3 — Watch Packets Travel (Traceroute)

Before You Start: A traceroute shows you every router your data passes through on its way to a destination. Each router is one “hop.” This is the TCP/IP stack’s Network layer made visible.

  1. Open your browser and go to ping.eu
  2. In the top menu, tap Traceroute
  3. In the hostname field, type google.com and tap Go
  4. Watch the results load — each numbered line is one hop
  5. Look at the response times in milliseconds (ms) for each hop
  6. Try the same with irctc.co.in — notice where the path diverges

What You’re Seeing

The hops with low response times (5–20 ms) are nearby routers — probably within your city or state. Hops with higher response times (50–150 ms) are farther away — possibly in another city or country. If a hop shows * * *, that router is configured to not respond to traceroute probes (common on backbone networks).

Deepa Asks

“Some hops show three times, like 12 ms, 15 ms, 11 ms — why three?”

The traceroute sends three separate packets to each hop, so you get three timing measurements. The variation is normal — it shows that network conditions fluctuate slightly even over milliseconds.

Discussion Prompt: When you do a traceroute from your phone in India to google.com, do the packets ever leave India? How can you tell from the response times?

Tying It Together

You have now seen the internet’s fundamental mechanisms in action:

  • DNS — names get translated to addresses (Exercise 1). If this fails, nothing works.
  • IP addresses — every device and every server has one (Exercise 2)
  • Routing — packets hop through multiple routers to reach their destination (Exercise 3)

Next session, we will ask the question that follows naturally from all of this: if your data is travelling through all those routers and networks — many of which you do not control — how do you keep it private and secure?