Class - "C" - (Small Commercial Grade) Internet Services

The world wide Internet consists of the Local Area Networks of millions of businesses and homes, all interconnected under the authority of the - "Internet Architecture Board". When a new business wishes to join the Internet, they generally configure their local Ethernet first, as described in our first - "Ethernet Series", and then they purchase a class - "C" - address space connection from an Internet Service Provider.

Under the original design of the Internet, a class - "C" - address space was the smallest and most modular connection a business could purchase, and even though it's the smallest modular connection originally anticipated, it turns out that a class C address space and a class C connection is really quite powerful. In fact, it's more powerful than most small businesses need, and it certainly provides more services than would be needed by a typical home office. Furthermore, if a class C Internet connection is fully exploited in the most efficient possible manner, it allows over 33 million simultaneous networking processes to communicate between the Local Area Network (LAN) and the worldwide Internet. It is commonly stated that a class C address space allows up to 256 new computers to be connected to the Internet. However, generally 3 of those 256 IP addresses are lost to networking overhead, so the real number is 253 new computers.

Because the Internet is quickly running out of IP addresses, a class C connection like this with a block of 256 real Internet addresses is quite expensive, since any company that buys one is competing with other companies who want that rapidly diminishing address space resource. If you've seen our - "OSI 7-Layer Vocabulary of Modern Internetnetworking" - movie here on, then you also know that layer four of this architecture makes provision to address many, many different application services inside each computer.

Internet addressing commonly makes provision for selecting among up to 65535 TCP processes and up to 65535 UDP style processes for networking within each computer. Very, very few computers will ever be expanded and exploited to the point where they use up all of that process addressing space. But that addressing system works splendidly on the Internet, and so any of over 33 million potential processes can be running anywhere in a class C address space, and each of those processes can address any other process anywhere else out in the entire world wide Internet.

Cisco 1603 Router

After a small business makes a commitment to purchase a class C address space from a commercial grade Internet service provider, they must then purchase a commercial grade router. This is a fairly expensive and sophisticated device costing on the order of several hundred to several thousand American dollars. The dominant supplier of business class routers in the industry is "Cisco". The business class router will provide an Ethernet connection that can feed all of the computers in a Local Area Network, and it's typically expanded by a combination of hubs or switches. You can learn more about hubs and switches here on by visiting our - "Ethernet" - section and looking for short movies with those corresponding titles.

After installing the router and an appropriate assortment of hubs and switches, all of the computers constituting the small business's Local Area Network are then given IP addresses from among the group of 256 Internet addresses represented by the class C address space, and are connected through the hubs and switches back through the router and to one another.

(For the sake of simplicity, this diagram illustrates only two computers, but as many as 253 computers can be interconnected in this way).

In common Internet parlance we would say that each of these 253 computers is directly connected to the Internet. Each can run any combination of network clients or network server processes. Each of those processes can address any other computer with it's processes directly connected to the Internet. So, in this fully developed, business oriented, class C connection situation, there are multiple computers per router (up to 253), and there are multiple processes per computer (more than 130 thousand), for a grand total, potentially, of more than 33 million network oriented processes on this small network, all of which can simultaneously address the world wide Internet and speak with any other process anywhere else. It's really powerful. For most people it's over kill.

Any of these network processes can be - "clients"- (with processes originating inside the LAN and accessing Internet services), or - "Servers" - (constantly listening for conversations originating out on the Internet requesting access to local services).

Every time you install an additional computer on this kind of network another one hundred thirty one thousand new local network processes (either clients or servers) can potentially interact with the world wide Internet.

Of course, a configuration like this leaves all of those processes on the Local Area Network vulnerable to attack and access from the world wide Internet, and so this situation cries out for security. Security can be enforced inside the router, or by inserting other boxes in between routers and the computers being protected, or protection can be built into each of the computers. You can learn a lot more about security from other movies here on

Because this class C Internet address space has so much excess power beyond what would normally be needed by a small business or home environment, clever people have figured out a way to trade off the excess process addressing space and to allow multiple computers to access the Internet, hidden behind a home or small office router, using a lower cost Internet connection intended for just one computer. You can learn more about these systems here at from our video entitled - "Low Cost Internet Access for Small Office Networks and Home Office Networks.