Every path to the Internet leads through a router. In fact, Internet pathways generally pass through many, many routers, and the worldwide Internet can be visualized as a branching, maze-like galaxy of routers, each defining the intersection points between millions of smaller networks. Among the millions of routers constituting the worldwide Internet, we are going to assume that you've purchased - one - of them that is of special significance to you, because it is installed inside your home or small office, and it will use "NAT" (Network Address Translation) technology (as described in other movies here on AskMisterWizard.com) to help you manage multiple IP addresses.
If you aren't familiar with NAT technology, then you should watch the two movies entitled - "Simple Routers for Small Networks Part 1: Client Firewalls" - and - "Simple NAT Routers Part 2: Multiple PCs", before proceeding here, because - this - movie builds on - those - concepts.
If yours is a typical small network using a low-cost Cable or DSL Internet connection, the - "external" - ethernet interface of your router will be assigned a single IP address by your Internet Service Provider. (That - "public" - IP address will probably change from time to time because most ISPs like to assign and re-assign public addresses dynamically, as they are needed).
The - "internal" - interface of your router will use NAT technology to help you manage a group of local IP addresses. When you connect a computer, print server, or file server to your local area network, its ethernet interface will need an IP address from that group. Most small NAT routers can manage a group of 256 local IP addresses.
Technically, an IP address is a unique 32-bit, binary number that identifies a piece of Internet equipment. Computers use binary numbers because binary hardware is a lot simpler (and less expensive) than hardware built to understand decimal or other number systems. If you were to examine an Internet Address as it arrives from an Ethernet cable, it would look something like this:
11000000101010000000000000000010
Although that binary system is efficient for computer hardware, it's unwieldy for us humans! If we convert that number into the familiar decimal form that we use for normal human mathematics, it looks like this:
3232235522
But Internet addresses are not just ordinary numbers; the format has a functional, unique structure. They are assigned by an - "Internet Architecture Board" - in patterns that can be analyzed to give hints as to the location of the associated equipment within the grand scheme of the worldwide Internet. Within that - Grand Scheme, it turns out that the most important characteristics of an individual address can be deduced by examining eight-bit blocks. Unfortunately, if we convert an Internet Address into a decimal number, the 8-bit boundaries become hopelessly obscured. This led the Internet gurus of yesteryear to abandon decimal address representations. Instead, they prefer to visualize the 32 bits as four segments of eight bits each like this:
11000000 10101000 00000000 00000010
By common agreement, Internet folk have decided to represent each of those four, eight-bit binary segments as an individual number which can be converted to decimal, ranging between 0 and 255 (base 10). The usual and customary arrangement separates each of those segments with a period (pronounced - "dot" - among the Internet Cogniscenti). This results in IP addresses that look like this:
192.168.0.2
All of your Internet-compatible computers and equipment must somehow become aware of an Internet address by which it can communicate with everybody else using the IP protocol
The methods by which your computers and equipment learn their IP addresses fall into two broad categories as follows:
1 of 2: They can be automatically configured with a "dynamic" IP address,
or
2 of 2: They can be manually configured with a "static" IP address.
Most people start out using the first of these options, resulting in - "dynamic" IP addresses. Later, as they become more experienced and as they activate increasingly sophisticated services, it is commonplace to configure some of their equipment with static IP addresses.
Let's examine Dynamic IP address configuration first. (Later on, we'll view other movies to tackle the manual configuration methods that are necessary for static IP addresses).
DHCP: The "Dynamic Host Control Protocol"
Long ago, as well-established Local-Area Networks based on - Ethernet - began to evolve into globe-spanning networks using Internet Protocols, some very smart people determined that it would be a - Good Thing - to have an Ethernet-compatible server that might help a population of computers to migrate to the Internet, automatically obtaining IP addresses and every other necessary detail. As a result of this foresight, they agreed on a protocol by which ethernet-based computers that needed an IP address could use ethernet to ask for and receive one from a nearby - "server" - authority that understood both Ethernet and Internet protocols. They named this - "DHCP" - the - "Dynamic Host Control Protocol", and it has become very popular. Basically, any computer (or other piece of network equipment with an ethernet interface) that needs an IP address can use ethernet to - "broadcast" - a request for help like this:
"Hey! Everybody listen up: I need an IP address. If there's anybody here that understands the DHCP protocol and knows about available IP addresses that are compatible with this local area network, please respond back to me on my ethernet address so I can use IP along with the rest of you."
If a - "DHCP server" - has been installed on that ethernet broadcast domain, it will respond with a message like this:
"I am the DHCP server for this network. According to my records, you should use IP address 192.168.0.2 until further notice. The netmask for this network is 255.255.255.0, the default gateway address is 192.168.0.1, and Domain Name Services are always available from a computer at 65.130.221.8."
This information will permit any ethernet-equipped computer to configure itself for the Internet Protocol and to communicate with all of the other computers on the Internet.
Most modern, low-cost NAT routers include a built-in DHCP server that can handle DHCP requests for all of your computers and other network equipment.
As illustrated in this example, the DHCP protocol provides more than just an IP address. It's now time for us to proceed with brief discussions of that other information.
