Debugging a broken Internet connection

I was sitting in my living room, minding my own business, when all of a sudden I couldn't access a website. Then another and another. What to do?

Many years have taught me that the hardest part of debugging a computer problem is understanding it. With that in mind, the first thing to do is to narrow down the problem, to find the specific link in the chain that broke. The following steps should help you do just that.

1. Try a different web browser

Any computer that has only one web browser is, in my opinion, mis-configured,  if for no other reason than all things break and having a second (or third) browser available is like a spare tire in the trunk.

2. Try websites by IP address

The name of a website is just a convenience for humans. In reality, computers pass data using numbers (IP addresses) rather than names. The problem might be in the system used to translate names to numbers (DNS and/or hosts file).

Testing the translation system is easy, if you prepare for it ahead of time by bookmarking the IP address of a few websites.

An excellent IP address to bookmark is the OpenDNS system status page at 

http://208.69.38.170

Its a great test because OpenDNS has published their IP address and thus (sort of) promised not to change it.

It's rare for any organization to publish their IP address as it may change over time. For example, a website hosted in Florida that moves to Utah, will get a new IP address. But since the name won't change, no one should care.

Thus, it's a good idea to bookmark a handful of IP addresses because some are bound to change over time. The TCP/IP ping command, available in all desktop operating systems, can be used to find the current IP address of any website.

Here are a few randomly chosen examples:

 yahoo.com      http://98.137.149.56

 boston.com     http://66.151.183.41

 microsoft.com  http://207.46.197.32  

 reuters.com     http://206.132.6.134    

If websites are visible by IP address, but not by name, you have greatly narrowed down the problem.     

3. Try to access your router 

Routers are normally accessed by their IP address. On home networks, the address is most likely 192.168.x.x where the Xs are numbers between zero and 255.

Windows users can learn the IP address of their router with the ipconfig command, look for the default gateway. The concept of a default gateway applies to all computing devices using TCP/IP, which is pretty much all computing devices.

No matter what your operating system is, the default gateway is a basic networking concept and should be displayed in the properties of your network connection. When you learn the IP address of your router, bookmark it. It also can't hurt to tape it to the router.

If all goes well, accessing the router should produce a prompt to enter a userid and password. If, however, the page fails to load, that tells you the problem is inside the LAN, not outside.

4. Re-establish a WiFi connection

If the home page of the router fails to load and you are using a wireless network, try to disconnect from the network and then re-connect. In my case, this fixed my problem.

5. Look at your LAN

There are few parts to this. The most obvious is to reboot the problematic computer. Then, if possible, try another computing device (computer, tablet or smartphone). Also, if WiFi is not working, try Ethernet and vice versa.    

6. Reboot modem and router

If you can access the router but nothing in the outside world, reboot the device(s) that give you access to the outside world. There are often two devices, a router and a modem, but some ISPs provide a single box that does both functions.

If you have two devices, reboot the modem first, then the router. By reboot, I mean unplug the device from electricity, wait a minute, plug it back in and then wait another minute for it to restart. 

Afterwards, it's also a good idea to reboot the computers connected to the router. It may not be needed, but it can't hurt.  

You should be prepared to do all these steps now; it's good Defensive Computing.

For extra credit, make a note of the normal state of all the lights on your modem and/or router. Which ones are on, what color they are, whether they blink or not, etc. Write it on a piece of paper and tape it to the device.

If the problem is outside your home/office, the state of these lights can be helpful to your ISP.  

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