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.

Gateway

The IP address for the router that your computer uses to connect to any IP addresses not in your local subnet. If you have a router at home, then on your machines the gateway is the IP address of your router.

Hub

A hub is a little box about the size of a modem that you can interconnect a bunch of 10baseT ethernet lines with. A 10baseT line runs from each computer to the hub; the hub makes sure all the lines get all the traffic. See Routers and Hubs for more info.

Net Mask

A net mask is a 32-bit binary number that consists of a string of 1's followed by a string of 0's. It is sometimes expressed in 'quad-dot' notation, like 255.255.255.0, or simply as the number of consecutive 1's, like /24. It is used to define a sub-net which is separated from all other networks by a router. The netmask indicates which part of the IP address is on the local network, and which must go out through the router. If your ISP assigns you 8 IP addresses, then your netmask will be 255.255.255.248, which means all your IP addresses are the same except for the last 3 bits. Requests for all other IP addresses must go out over the router.

Netmask

A netmask is binary number that consists of a string of 1s followed by a string of 0s. The line between the 1s and 0s is applied to an IP address of a router to define what addresses are on the subnet, below the router, and which ones need to be passed to the higher net above it. Typical netmasks look like 255.255.255.0 (meaning "IP addresses that are the same as mine in the last 8 bits are on the local subnet, and I don't have to pass them on to the network above me. IP addresses that are different than mine in any of the first 24 bits must be passed on." If routers could talk, of course. See subnet, too.

Router

A Router can be either a box or some software that you run on a PC (Macs included, of course.) Routers are used as traffic directors between two networks, like between your local LAN and your ISP. For more details, see Routers and Hubs.

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.