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Where do the IP addresses come from?

You used to have to set up ip addresses, netmasks, gateways, and name resolvers all manually. Refer to any basic networking text to learn more about this aspect.

These days DHCP (Dynamic Host Control Protocol) is very popular. Let's assume that a DHCP server (typically inside your Cable/DSL modem) and issues all the network information required. The network engineer at your upstream provider has configured the modem for you so that it will work with their network.

With a typical home setup, you are assigned just one IP address and if you have more than one computer at home, you have to play games (NAT or MASQUERADE) to share the one IP address. A typical small business connection might have 5 IP addresses assigned statically so that you can publish them; a sixth address in the range lets you communicate with the router in your DSL modem.

For a 6 address block, you'd be assigned a netmask with 29 bits (255.255.255.248 in "dotted decimal" format). You don't need to know what a netmask is right now, but it divides the address into two parts, network and local. In the postcard analogy, a p.o. box number would be the local part of your address.

Let's say your first DSL provider gives you the address range from 63.63.63.1 to 63.63.63.6; your computer is at 63.63.63.1; your DSL router is at 63.63.63.6; and the remaining 4 addresses are currently unused.