by Alan Fernald

Created on: October 21, 2008   Last Updated: June 04, 2011

As most people know it, the Internet is a myth.

Most people picture the Internet as a single network the spans the globe and reaches into the businesses and households of everyone who connects. In reality, it was the interconnection of millions of smaller networks that created the global network now known as the Internet.

To achieve this incredible feat, Al Gore, the Advanced Research Projects Agency (ARPA), and various universities joined together to outline the rules that would permit the widest range of technologies to unite and form the information superhighway.

These rules defined the construction of the Internet.

To implement a global network while permitting decentralized administration of that network, they created several standards that are now the mainstays of modern computer networks.

These achievements included the definition of Domain Name Services (DNS), the TCP/IP protocol, and TCP/IP networks and subnetworks. This article will specifically address the basics of subnetworks.

Subnetting, or the process of creating subnetworks, is the method used to partition or divide a single network into smaller networks. We can continue to create subnets on each of these smaller networks in turn until we reach the minimum network size of two network "nodes". For each network, we must have a network identity, and for each network node, we need to have a node address. The combination of the network identity with the node address must result in a totally unique address.

With TCP/IP v4, this unique address is actually a 32-bit binary number that is normally written as a four-digit decimal number similar to 208.112.8.62. The lower boundary of this range is 0.0.0.0, whereas the upper boundary is 255.255.255.255. This permits a total of over 4 billion addresses available on the global network.

To determine the actual network identity and node address of a particular device connected to the internet, we use another number often referred to as the "network mask" or "net mask". To differentiate between the two components, the entire address is written in binary and the net mask is used to "mask" the network identity, and all other digits left over become the node address. This is easier to understand if you see it in action.

Assume that we have an address of 208.112.8.255 (not a valid address, this is used for explanation only), with a net mask of 255.255.255.0. This would be written as:

• 11010000.01110000.00001000.11111111 Unique Address

• 11111111.11111111.11111111.00000000

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