Troubleshooting Step by Step

Think in layers, not guesses

"The internet is down" is the most common and least useful bug report there is. It can mean a dozen different things. The way to fix network problems is to stop guessing and check things in order, from the bottom up.

Each step proves that one part works and rules it out. When a step fails, you have found the layer where the problem is, and you only need to look there.

Step 1: Is anything physically connected?

• Is the cable plugged in, or is WiFi turned on?
• Are the lights on the router on and blinking normally?
• Is airplane mode off?

It sounds too simple, but a loose cable or a disabled WiFi switch is the answer more often than anyone expects. Check this first, every time.

Step 2: Do I have an IP address?

ip addr          # Linux
ipconfig         # Windows

You should see an address that matches your network, such as 192.168.1.x. If you see 169.254.x.x or no address at all, DHCP failed. Reconnect to the network, renew the lease, or restart the router.

Step 3: Can I reach my own router?

ping 192.168.1.1

Use the address of your default gateway. Replies mean the local network works. No replies mean the problem is between your device and the router: WiFi signal, cable or the router itself.

Step 4: Can I reach the internet by number?

ping 8.8.8.8

This sends a message to a well-known public address and skips DNS entirely. If it works but websites do not open, you already know the problem is name lookup. If it fails, the problem is beyond your router, for example with your internet provider.

Step 5: Can I resolve names?

nslookup example.com
ping example.com

If ping 8.8.8.8 works and ping example.com fails, DNS is the broken part. Try changing your DNS server to a public one such as 1.1.1.1 and test again.

The sequence in one line

Cable, then IP address, then router, then the outside world, then DNS. Each step answers one question and points to one layer:

1. Is it connected? (physical)
2. Do I have an address? (DHCP and IP)
3. Can I reach the router? (local network)
4. Can I reach the internet by number? (routing and provider)
5. Can I resolve names? (DNS)

Handy tools along the way

• ping: is the other side reachable, and how fast does it answer?
• traceroute or tracert: where on the path does it stop?
• nslookup or dig: is DNS answering correctly?
• ss -tuln or netstat: what is listening on my machine?
• curl -I: does the website answer at the HTTP level?

Reading ping output

64 bytes from 8.8.8.8: icmp_seq=1 ttl=117 time=14.2 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=117 time=13.9 ms

--- 8.8.8.8 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss

• time is the round-trip delay in milliseconds. Lower is better.
• packet loss should be 0%. Higher numbers point to an unreliable link.
• Request timed out means no reply came back.

Calculating packet loss

Packet loss is the share of packets that did not come back. Divide the number lost by the number sent, then multiply by 100.

20 pings sent, 15 replies, 5 lost
5 / 20 = 0.25  ->  25% packet loss

Even 1 or 2 percent can make a video call glitchy. A lot of loss usually means a bad cable, a weak WiFi signal or an overloaded link.

Also look at the time values. If most replies take 15 ms but a few take 400 ms, the connection is unstable even though nothing was lost.

Three examples to practise on

Example 1: "I have WiFi but nothing loads." The laptop shows 169.254.3.9. That means no DHCP reply came back. Check the router and renew the lease.

Example 2: "Google works but my work site does not." Both ping 8.8.8.8 and Google work, so your connection and DNS are fine. The problem is with that one site or the path to it. Use traceroute and curl -I to see where it stops.

Example 3: "I can ping 8.8.8.8, but websites do not open." This points to DNS. Run nslookup example.com. If it fails, switch to 1.1.1.1 and test again.

Habits of a good troubleshooter

• Change one thing at a time, then test again. Otherwise you will not know what fixed it.
• Write down what you tried. It avoids repeating tests and lets a colleague take over.
• Ask what changed. Most problems start right after an update, a new cable or a settings change.
• Check the simple things first. Cables and power fail far more often than software.
• Compare with a working device. If your phone works on the same WiFi, the network is fine and the problem is on your laptop.