IP - Internet Protocol (continued)

What's the IP address of your current host? (Recall, the term host simply refers to a computer that is connected to the Internet.)

Click here to find out your IP address. This is the location your computer currently occupies on the Internet.

What makes Calvin College a place on the Internet?

Actually, it is not the fact that Calvin's computers all reside on Calvin's campus. The Internet is not structured in terms of geographic location. Rather, it is defined in terms of IP addresses.

A defined range of IP addresses is called a domain. Calvin College is an Internet domain (calvin.edu) because the IP addresses of all of its computers fall within the range of IP addresses that Calvin has registered.

There are several different classes of domains. Recall that each IP address is comprised of four numbers between 0 and 255; including 0, this amounts to 256 different possible values for each number.

In a Class A registration, the first of the four numbers that make up an IP address would be fixed, while the other three would be allowed to vary between 0 and 255. Thus, given a Class A license, the number of IP addresses available to you to "hand out" to the computers in your domain would be: 256 x 256 x 256 = 16,777,216—over 16 million possible addresses! Needless to say, Class A registrations are very rare and very expensive. Typically, they are used only by Internet Service Providers and companies in need of such a large number of IP addresses.

In a Class B registration, the first two numbers would be fixed and the other two would be allowed to vary between 0 and 255. Given a Class B license, the number of IP addresses available to assign to the computers in your domain would be: 256 x 256 = 65,536. Class B registrations are much more common, although still fairly expensive.

In a Class C registration, the first three numbers would be fixed and the last one would be allowed to vary between 0 and 255. Given a Class C license, only 256 IP addresses are available to assign to the computers in your domain. Class C registrations are very, very common and quite inexpensive. However, 256 IP addresses does not stretch very far: a network printer, for instance, may require its own IP address.

Note: the first number of IP address is the most significant in terms of the Internet's IP address scheme. Each following number reflects a narrower and narrower scope of the Internet.

Calvin College has a Class B registration. Thus, the first two numbers in Calvin's IP addresses are fixed at 153.106, and so the IP address of every computer within the Calvin domain begins with 153.106. Also, this means that no other computer anywhere on the Internet has an IP address that begins with 153.106.

 

If we wish, we can restrict certain Web materials, allowing only computers within our domain to access them. Remember: this is your IP address. Now, click on this Web link. If you are currently at a computer whose IP address begins with 153.106., then you are able to see this page. If not, then the Web server forbids you from viewing it.

How does this work? Every time you type a Web address into a Web browser or click on a link, your browser sends a request to a Web server somewhere. The browser must provide the IP address of the computer on which it is running so that the server knows where to send the page!

Thus, do not be lulled into believing in Internet anonymity! Practically every site you contact knows the IP address of the computer you are using.

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This chapter was written by Jeff Nyhoff and Joel Adams. Copy editing by Nancy Zylstra
©2005 Calvin College, All Rights Reserved

If you encounter technical errors, contact rit@calvin.edu.