Home page
The Laboratory
Research taking place
Educational activities
Laboratory people
News / Events
Miscellaneous stuff
Server contents

Go to the previous, next section.

Internet Numbers

invisible.xbm invisible.xbm

Every single machine on the Internet has a unique address,(2) called its Internet number or IP Address. It's actually a 32-bit number, but is most commonly represented as four numbers joined by periods (`.'), like This is sometimes also called a dotted quad; there are literally thousands of different possible dotted quads. The ARPAnet (the mother to today's Internet) originally only had the capacity to have up to 256 systems on it because of the way each system was addressed. In the early eighties, it became clear that things would fast outgrow such a small limit; the 32-bit addressing method was born, freeing thousands of host numbers.

Each piece of an Internet address (like 192) is called an "octet," representing one of four sets of eight bits. The first two or three pieces (e.g. 192.55.239) represent the network that a system is on, called its subnet. For example, all of the computers for Wesleyan University are in the subnet 129.133. They can have numbers like,, up to 65 thousand possible combinations (possible computers). invisible.xbm invisible.xbm

IP addresses and domain names aren't assigned arbitrarily--that would lead to unbelievable confusion. An application must be filed with the Network Information Center (NIC), either electronically (to hostmaster@nic.ddn.mil) or via regular mail.

Go to the previous, next section.


Copyright © 1998, Software Engineering Laboratory
National Technical University of Athens