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 that the Internet is a point-to-point network.
- 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.
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? Image? Bank balance? Web page? It doesn’t care. It’s all just numbers. The higher layers figure out what the numbers mean.
It can’t be all just numbers. Web pages have more text than numbers. Where do all the letters come from? And photos?
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, “*” (geeks call this a “splat”) is 42, and so on.
To represent “Renata,” a computer could use 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. Higher layers figure out what the numbers mean.
Point-to-point
The Internet links millions of computers together. Millions and millions and millions!
There is no Central Internet Secret Base Under a Volcano (CISBUV) that all traffic goes to. That is, the Internet is not like this:
Figure 1. Star network
This arrangement is called a star network. It’s common for local area networks (LANs), where the computers are all close together. But it wouldn’t work for the Internet, which is spread out all over the world. There’d be too much delay in sending all that traffic to the one central point.
Here’s what the Internet really looks like:
Figure 2. Point-to-point network
There are lots of computers, connected with a bunch of point-to-point 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 2, nodes A and I are gateway computers.
How does data get sent around? Look at this:
Figure 3. Two computers on the Internet
Larry’s computer wants to send some data to Ivan’s computer. The data goes first to node A, and it ends up at node I, where it gets passed to Ivan’s computer.
There are lots of ways the data could travel. It could follow the path A-B-E-F-I, A-B-E-G-H-I, A-D-G-H-I, ... The Internet automatically chooses the path with the least traffic. This can vary from moment to moment. Suppose Larry and Ivan are IMing (instant messaging). Larry’s first message could follow one path. His next message, sent two minutes later, could follow a different path.
All computer on the Internet talk to each other using a protocol called TCP/IP. The details don’t matter. Just remember that the bucket o’ numbers layer use TCP/IP to send data to each other.
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 answer 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.
Right. That’s a protocol for people.
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 is receiving them, what the numbers are, and other stuff.
There’s software in your Windows PC, Mac, Linux machine, or whatever, that knows how to talk TCP/IP.
IP addresses
Computers on the Internet have to know how to identify each other. Each computer has an IP address. It’s four sets of digits with periods (.) in between. For example: 123.21.22.11, 211.22.92.91, and 88.120.233.9.
Every computer on the Internet has to have an IP address, somehow or other. There are lots of tricks for using one IP address to support multiple computers. But that’s not important for our purposes.
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 (hold down the Windows key and press R). Type cmd and press Enter. You’ll see a command line window. Type ipconfig and press Enter. You’ll get a bunch o’ output. The IP address will be labeled something like IPv4.
If you have a different type of computer, use Google (or Yahoo, Bing, whatever) to find out how to get your computer’s IP address. Explain how in the exercise discussion.
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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 219.32.228.181 today!” Ack!
Instead, we have the domain name system. When you register a domain name like doomdogs.com, you get the right to associate the domain name with an IP address. So your ad can read: “Free download! Go to doomdogs.com 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:
ping coredogs.com
Your computer will ping the computer associated with the domain name. A “ping” is basically 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.
Note that some servers won’t respond to pings. The server that answers to microsoft.com, for example, ignores pings. But you still get an IP address.
Find the IP addresses of some of your favorite Web sites. (I like masalatime.com and failblog.org.)
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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 |
|---|---|
| sitepoint.com | 69.20.16.232 |
| whitehouse.gov | 96.16.226.135 |
| ... | ... |
When you type a domain name, your computer sends the DNS server the domain name, and gets back the IP address. Your computer then 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 is propagated throughout 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 deathpoodles.com. Go to http://www.networksolutions.com/whois/index.jsp and type it in. The one who comes up with the strangest name wins.
You can find some strange stuff. (There is a strangestuff.com.)
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Summary
- The Internet is a point-to-point network.
- 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.
