Glossary

Note: these aren't the definitions you'd find in a book. If that's what you want, then go look in a book. These are they way I would explain the terms to someone. I'd appreciate it if you'd let me know of anything that's misleading or just plain wrong, but I'm not trying to be too strict. Life is tough enough. Sometimes, I may show some sarcasm, though.

Firewall

A way to block unwanted traffic from a company's internal network. It can be as simple as a router that simply prohibits TCP/IP packets of a certain type from crossing the boundary between the company's LAN and the Internet. In a complex system, it will allow traffic only from certain IP addresses, or only certain kinds of traffic, or only traffic that has been authenticated somehow.

Internet

A "public" communications network using TCP/IP protocols. To access the Internet, you must be running TCP/IP at the point of connection and you must arrive there with a unique IP address - a "quad-dot" number like 216.71.126.178. Each of the four numbers ranges from 0 to 255. No other machine in the world has the same address. TCP/IP requires that you send a "packet" addressed to a machine with another IP address. The internet will do all the routing to get it there. If one route breaks down, it will find another. Packets are re-assembled in the right order at the other end. It's magnificent.

Intranet

A "private" version of the Internet. Typically a TCP/IP network running within a company that excludes access from computers not connected directly to the company's network.

TCP/IP

The protocol of the internet - by definition. The IP stands for "Internet Protocol". The TCP is something else I can't remember. TCP/IP works off a few very simple principles:

• Every connected machine has a unique 32-bit address, usually expressed as a "quad-dot" like 216.71.1267.178.
• Transmission are made in fairly small packets of bits, with headers containing the source and destination IP addresses.
• The network consists of routers each of which will forward the packet to a router closer to the destination. If the packet doesn't get through, it will try another path. Eventually, unless the whole network is down, the packet will get through.

TCP/IP is way cool.