How Computers Work · Your Computer on a Network · Lesson 5 of 5

Challenge: The Family Internet Is Down

Help your sister's family get back online, one clue at a time.

Is it one device or the whole house

You're visiting your sister's family. Everyone is upset. "The internet isn't working," your niece says.

You start by asking questions. A good troubleshooter narrows things down before fixing anything.

• Her laptop shows Wi-Fi connected, but no website opens.
• Her phone, on the same Wi-Fi, can't load anything either.
• Your brother-in-law's phone works fine on cellular data, with Wi-Fi turned off.

Think about what these clues share. Two different devices fail, but only on the home Wi-Fi. When several devices fail on the same network at once, the problem is rarely inside any one of them. It's more likely in the boxes they all share.

The modem and the router sit in the hallway. Their lights look normal, but nobody has touched them in months.

A strange address

You restart the modem, then the router, and wait a few minutes. The family desktop PC, plugged in with an Ethernet cable, now works. The phones are back too.

But the laptop still says "No internet". You open the terminal and type ipconfig. Its IPv4 address starts with 169.254.

That address is a clue. The laptop never got a proper address from the router, so it made one up.

Connected, but no sites

You turn the laptop's Wi-Fi off and on. Now it has a normal address, 192.168.1.37. Progress.

Yet every website shows "Server not found". Your niece's chat app, which was already open, still gets messages. In Settings, you notice the DNS server assignment was changed by hand to a strange address. Your niece says a "speed booster" app she downloaded did it.

Keep the doors closed

Everything works now. Then your niece's game shows a message: "For best results, turn off your firewall."

Later, Windows Security also asks if the game may communicate on Private networks, Public networks, or both. The game is from a store she trusts, and she plays it at home and sometimes at the library.