A word about IP Addresses:

The identity of your network and every computer on it depends on Internet Protocol addresses of the form 204.144 .169.10. Typically, you will need a Class C IP address block for up to 255 machines (204.144.169.0 through 204 0.144.169.254, for example). You can use multiple Class Cs for more machines. In theory, these are your addresses, and until 1995 you would typically obtain them directly from the InterNIC, and they were yours for life.

The growth of the Net brought on some problems in the speed and design of packet routers. A router receives packets in one port, opens the packet, examines the header for address information, and sends the packet on its way via one of several routes depending on its ultimate destination and the connections the router has. To do this, it maintains a table of "routes."

As the network has grown, the size of this router table has grown correspondingly - and somewhat alarmingly. To alleviate this, the Internet community developed a concept referred to as Classless Inter Domain Routing or CIDR. In its most basic form, CIDR is a shorthand notation for routers that replaces thousands of addresses with a simple reference to another backbone provider that services those addresses. So all packets destined for any of these gazillion addresses can simply be routed to Sprint, for example, and the machine knows how to route from there.

The problem is that as the routing tables have grown, addresses that do NOT fall into a block of some size somewhere, have been eliminated from some routing tables. Sprint was the first to employ this obnoxious tactic beginning in June of 1995. Its version of the Internet simply didn't include some addresses in the 204.xxx.xxx.xxxx and 206.xxx. xxx.xxx ranges. So if you were in one of those address ranges, anyone connected to the Sprint backbone couldn't reach you. This has the potential of fracturing the Internet into several networks based on addresses.

In practice, it doesn't quite. It simply strands a few small companies. But it ends the concept of independent Internet addresses. In general, you will have to obtain an IP address from your Internet service provider and so exist as part of the provider's CIDR block to be assured of being reachable. The downside to this is that if you change Internet service providers-after being notified of a 400 percent price increase, for example- you will have to reconfigure every machine in your network, a tedious, expensive, and error prone process given the current software and operating systems. As a result, Internet service providers have a bit of a hold on you as a customer. This makes the initial selection of an Internet service provider perhaps more important than it might otherwise be.