The bucket o' numbers layer

Where are we?

On the previous page, you learned that thinking in layers is important. Otherwise, your brain might get overloaded.

This page explains what you need to know about the bottom layer: the bucket o’ numbers layer.

This lesson’s goals

By the end of this lesson, you should:

  • Know what TCP/IP is.
  • Know what an IP address is.
  • Be able to find the IP address of your computer.
  • Be able to find the find the IP address of a Web site.
  • Know what DNS is and why it is used.
  • Be able to find the owner of a domain name.

Ouch! That’s a lot of acronyms. My brain is already switching off.


I hear you. Some books throw lots of complicated stuff at you all at once. Your brain gets into the habit of giving up.

Tell your brain to try again. CoreDogs is slow and gentle. Your brain has a chance here.

It’s all in the numbers

The bucket o’ numbers layer sends numbers from one computer to another. It doesn’t care what the numbers are. Email? Photo? Bank balance? Web page? It doesn’t care. It’s all just numbers. The higher layers (the services and display layers) figure out what the numbers mean.


It can’t be just numbers. Web pages have letters, A, B, C, and the rest. Where do all the letters come from? And photos. They aren’t numbers.


Good question! Actually, it is all numbers. That’s all computers ever deal in.

Computers use numbers to represent letters and symbols. Each one is given a code. For example, “A” is 65, “B” is 66, “*” (an asterisk – geeks call it a “splat”) is 42, etc.

To send the word “Renata,” a computer could send the numbers: 82 101 110 97 116 97.

Photos are made of numbers as well. The numbers represent colors for dots on the screen.

At the bucket o’ numbers layer, everything is just numbers.

The Internet links millions of computers together. Millions and millions and millions!

Here’s what the Internet looks like:

Lots of simple links

Figure 1. Lots of simple links

The computers are connected by simple links. Each link connects only two computers. Computers in the network are often called nodes.

When you connect your home computer to the Internet (over cable, telephone, or whatever), you connect to an Internet gateway. This is a computer that passes data back and forth between the Internet and individual computers. In Figure 1, node A is a gateway computer.

All computers on the Internet talk to each other using a protocol called TCP/IP. The details don’t matter. We don’t even care what TCP/IP stands for.


I hear the word “protocol” a lot. What does it mean?


A protocol is a set of rules for communicating. For example, suppose the telephone rings. What do you do?


I pick it and say “Hello.”


Right. You could say “My brain is made of meat” instead of “Hello.” Why don’t you?


When I say “Hello,” the caller knows what to do. “Hello” means “I’m ready to listen.” If I talked about brains, the caller wouldn’t know what to do. Maybe hang up and call the cops.


The “hello” thing is a protocol for people. A rule for communicating.

It’s the same with computers. TCP/IP is a set of rules for one computer sending numbers to another. A TCP/IP message has data about which computer is sending the numbers, which computer the numbers are being sent to, the numbers themselves, and other stuff.

There’s software in your Windows PC, Mac, Linux machine, or whatever, that knows how to talk TCP/IP. They all have to talk TCP/IP, if they want to use the Internet.

IP addresses

Computers on the Internet need to know how to identify each other, so each machine can send numbers to the right destination computer. Each computer has an IP address. It’s four sets of digits with periods (.) in between. For example:,, and

Every computer on the Internet has to have an IP address. There are tricks for using one IP address for several computers. But, in the end, each machine has an IP address.

Exercise: Find your computer's IP address

You can find out the IP address of your computer. On a Windows PC, bring up the Run dialog. The easiest way is to hold down the Windows key and press R. The Windows key looks like this:

Windows key

Type cmd and press Enter. You’ll see a command line window. Mine looks like this:

Command line window

Type ipconfig and press Enter. You’ll get a bunch o’ output. The IP address will be labeled something like IPv4. Type it in the solution section below.

If you have a different type of computer, use Google to find out how to get your computer’s IP address. Explain how in the exercise discussion.

(Log in to enter your solution to this exercise.)

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Domain names

IP addresses are used for all Internet traffic, including the Web. But numbers are hard for people to remember. Imagine an ad that says: “Free download! Go to today!” Ack!

Instead, we have the domain name system (DNS). When you register a domain name, maybe, you associate the domain name with an IP address. So your ad can read: “Free download! Go to today!” Much better.

Exercise: Find a Web site's IP address

You can find the IP addresses of Web sites. There are several ways to do it. One way is to use the ping command.

Go to your computer’s command line. (On a Windows machine, hold down the Windows key and press R, type cmd and press Enter.) Type ping and then a domain, like:


Your computer will ping the computer associated with the domain name. A “ping” is an “are you there?” message, used to tell if a server is running. As a side effect, ping will tell you the IP address of the server.

Some servers won’t respond to pings. The server that answers to, for example, ignores pings.

Find the IP addresses of some of your favorite Web sites. (I like and

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How does your computer know what IP address matches what domain? By asking a domain name system (DNS) server. A DNS server is a computer with a table in its memory (or on disk), like this:

Domain name IP address
... ...

When you type a domain name like into a browser, your computer sends the DNS server the domain name, and gets back the IP address. Your computer uses the IP address to send the actual message.

When you register a domain name and associate it with an IP address, the new name and IP address spread across the Internet. That is, the DNS servers tell each other that there is a new table entry.

You can find out who registered a domain name using a whois service. Try this exercise.

Exercise: Play the Weird Domain Game

Think up a strange domain name, like Go to and type it in. The one who comes up with the strangest name wins.

You can find some strange stuff. (There is a

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  • Computers on the Internet use TCP/IP.
  • Computers have IP addresses to identify them on the Internet.
  • You know how to find the IP address of your computer.
  • You know how to find the IP address of a Web server.
  • DNS servers associate domain names with IP addresses.
  • You know how to find the owner of a domain name.

What now?

You know all you need to know about the BoNL. Let’s talk about the services layer.