A network is when two or more computers (and network peripherals) are linked together so they can share data.
Types of Networks
When a network is inside a single room or building, it is called a LAN (Local Area Network). When a network is between two or more separate buildings, it is called a WAN (Wide Area Network. The Internet is a WAN, the biggest WAN in the world.
There are specific types of networks. A HAN, for example, is a Home Area Network, where several devices are connected within a single home. This is a type of LAN. You might also hear about CANs (Campus Area Networks), MANs (Metropolitan Area Networks), or PANs (Personal Area Networks).
Different computers use different operating systems and filesystems, making it difficult for them to communicate directly. To solve this problems, we must use protocols. Protocols are standard rules which every computer must follow so all devices can exchange data smoothly and clearly.
We have protocols in our lives. For example, there are greeting protocols. In Japan, the protocol is to bow. There are specific rules about how much to bow, based on the person's status and the situation. In America, the protocol is to shake hands; usually, three shakes, with the last one being the strongest. These protocols are not universal, meaning that if a Japanese and American person meet, especially in a place like an airport, the protocol for greeting is unclear, and this can cause problems.
For a computer, each protocol explains how computers exchange data for a specific type of interaction. For example, there is one specific protocol for exchanging web page information (HTTP); there is a different protocol for exchanging files (FTP). There is a protocol for sending email (SMTP) and one for receiving email (POP). These are common protocols; all computers have them.
The main protocol set for the Internet is TCP/IP. Every computer and any electronic device which can connect to a network "know" the TCP/IP protocol; they follow the rules of TCP/IP.
If you want your computer to use a new communication or data exchange program, you are probably using a new protocol. For example, if you download and install Skype (a text, audio, and video chat program), your computer will be able to use the Skype Protocol. Once your computer has that protocol, it can "see" and "talk to" all other computers which have and use the protocol.
In short, adding a protocol (often by installing an application or a browser plug-in) allows you to do something new on the Internet.
IP: Internet Protocol
Part of TCP/IP is the IP (Internet Protocol). This protocol controls addresses of computers on a network. It allows your computer to find other computers.
There are two IP addresses for any computer: the internal (LAN) IP address, and the external (Internet) IP address. The external IP address is public; anyone can see which external IP address you are using. Your internal IP address, however, is private.
This is similar to an apartment building. There is an address for the building (e.g., 247 Main Street) and an address for each apartment in the building (e.g., Room 1206). Everybody can see the address of your building, but to see which room you live in, they must be able to enter the building, which has security to keep people out.
Currently, most networks use an IP address format called IPv4. This is an address system begun in the 1980s, before the Internet became popular. It allows for more than 4 billion addresses. However, due to the way these addresses are distributed, there is much waste; as a result, there are not enough IPv4 addresses left. To fix this problem, a new system, called IPv6, is being introduced.
IPv4 addresses are 32-bit (4 Bytes). Usually, they are expressed as four base-10 numbers, each number being between 0 and 255. For example:
If you see an IPv4 address with a number above 255, it is a fake. Often times, movies and TV shows will use fake IP addresses in the same way they use fake telephone numbers; they do not want crowds of people contacting some poor person who uses that number. For example, in the movie Iron Man 3, Tony Stark makes an Internet connection using IPv4; his addresses look like this:
Internal IPv4 addresses are limited to these number ranges ("x" means any number between 0 and 255):
- 172.16.x.x ~ 172.31.x.x
External IPv4 addresses can be almost any other address between 0.0.0.1 and 255.255.255.254, except for a few special reserved addresses (e.g., "127.0.0.1" is an IP address which points at your own computer).
As stated above, IPv4 numbers are running out. As a result, we are, very slowly, switching to a new system called IPv6. IPv4 addresses are 32-bit, giving us 4.3 billion address combinations. IPv6 addresses are 128-bit, giving us as many as 340,000,000,000,000,000,000,000,000,000,000,000,000 addresses, or 340 undecillion (yes, that's a real word).
IPv6 addresses are not shown using base 10, as that would be too long a number (e.g., 18.104.22.168.22.214.171.124.126.96.36.199.188.8.131.52). Instead, we use base 16, or hexadecimal (0 ~ f) to show the address; for example:
That's still really long, but it's a bit easier to read.
LANs, as stated above, exist within a single building or room. To identify one computer within the network, an internal IP address is used. In our lab, the address is 172.17.2.x, with "x" being the identifying number for each computer.
Below is a "map" of what the network looks like:
In this map, the red squares are computers. They are connected using cables, shown as purple lines. Each computer has a LAN port, a socket in the back of the computer that allows a network cable to be plugged in.
To connect computers in such a LAN, we use a cable called the Ethernet cable (also called a LAN cable or network cable). It is usually light blue (though it can be any color), and the connector looks like a land-line telephone connector, except bigger.
In order to connect all computers together, we use Ethernet hubs, shown on the map as yellow circles .
An Ethernet hub has many Ethernet cable ports (usually 8, 16, or more). If you plug several computers into a hub, they can "see" and "talk" to each other.
In the case of our lab, each row of computers has a hub; one cable from each hub goes to the next hub, until we reach the back of the room. This way, all the computers are connected.
Notice that the green triangles are printers. Many peripherals have the ability to join a LAN. Another peripheral to the LAN is the orange rounded-rectangle at the bottom right; that is a file server, basically a hard disk drive connected to the network.
Finally, the blue pentagon near the bottom right is the network server.
Just above, I mentioned two kinds of servers. A server is actually not a computer, or even a device. A "server" is software. Server software does exactly what the name suggests: it serves data. When you ask for data on a network, a server gives it to you. We often refer to the computers running server software as "servers," but the real server is a software function.
There are several kinds of servers. The server most people think about is a LAN server (sometimes called a "network server," or just the "server"). A LAN server is a computer which manages a LAN. It controls the network, assigning addresses and managing data traffic between computers. It also manages the connection between the LAN and the Internet (the thick, light blue line extending to the right of the server).
Another kind of server you will find on a LAN is a file server. This is a hard drive, or part of a hard drive, which can be accessed by computers in the network. It is kind of a "meeting place," a shared storage device for everyone. In our lab, you will find the file server through the icon named "Public" (or "shortcut to public").
When you connect to the Internet, you will encounter more servers. Whenever you type a web site address into a browser, you are communicating with a web server, which then serves to you the web page. When you send email, you are using an SMTP mail server; when you receive email, you are accessing a POP mail server.
What Is Your IP Address?
You can find out your internal (LAN) IP address. In Windows:
- Go to the Start Menu and open the Control Panel;
- In the Search window at the top right, type "IP";
- You should see a result under "Network and Sharing Center" called "view network connections"; click on that link.
- You will see a Local Area Connection; double-click on it.
- Click the button marked "Details";
- In the dialog box that appears, look for "IPv4 Address"; that is your internal IP address. It should begin with "10," "172," or "192.168." An IPv6 address might also be visible below.
On a Mac:
- In the Apple Menu at top left, open System Preferences;
- Click on "Network";
- At the bottom left of the Network Preferences window, click on "Advanced";
- At the top, click the tab/bar section titled "TCP/IP";
- You will see the IPv4 address, and possibly an IPv6 address below.
To find your external IP address, just click here!