How the Internet Works is a series of articles covering the different aspects of the internet in detail. Not in exhaustive, expert-level detail, like the many books on the subject do, but in enough detail to give a solid understanding of those different aspects and how they interact to move data around the internet.

My intended audience is people like myself: web developers who feel the need to have a good overall knowledge of how the internet works. I feel the need because I believe that a good understanding of the geography upon which a web application travels and resides facilitates good practice in addressing development concerns such as security, scalability, availability, stability and performance, among others.

Let’s begin at the beginning.

What Is the Internet, Anyway?

The internet is a worldwide system of interconnected computer networks. These computer networks can be anything from a small Local Area Network (LAN), to a Wide Area Network (WAN) of global scope.

Machines networked together in an office are an example of a LAN. Cell phone networks and Internet Service Provider (ISP) networks are examples of WANs. The internet, then, is the system by which all these LANs and WANs communicate with each other.

The internet is organized similarly to a postal system. In a mail service, a residential user might put a letter in a mailbox. A mail carrier would then bring it to the post office to be sorted and routed and sent to the post office that serves the destination address. At the other end, another mail carrier would pick up the letter from the post office and deliver it to that address. A similar process happens on the internet.

Carrying the post office analogy further, a business office usually has an office mail department. This department sorts mail coming from the office and arranges delivery to the post office. This is like a shared internet connection on a LAN: all internet traffic on the LAN is routed to one machine that is responsible for sending it out onto the internet.

Internet users connect to the internet via an internet service provider, or ISP. The ISP is a WAN that services a large number of individual internet users and/or LANs. In the postal system analogy, the ISP is like the post office.

The TCP/IP Model

The architecture of the internet is organized around the TCP/IP model. In the next dozen or so articles, we’ll take up the TCP/IP model in detail.