Symmetric Digital Subscriber Line. An uncommon flavor of DSL, in which downstream and upstream speeds are equal. It is most widely accepted in Europe.


A computer that provides services to other computers on the same network.

In the context of sharing an Internet connection, the server computer typically has 2 NICs and runs sharing software. It “serves” Internet access to one or more client computers.


Networking software that provides instructions for an activity.

On Windows computers, the most popular service is File and Printer Sharing for Microsoft Networks. Its name is fairly self-explanatory.

sharing software

Software that allows multiple computers to connect to the Internet using the same public IP address.

Sharing software only needs to be installed on a server computer. Then, one or more client computers can be configured to use the server computer as a gateway. When these client(s) make Internet requests, the sharing software kicks in to “translate” requests back and forth between client computers and the Internet.

Most sharing software is based on a technology called NAT; as such, most sharing software has the same basic functionality. However, there are often wide variations in performance, features, and ease-of-configuration. Confusion about these choices has contributed to the popularity of cable/DSL routers, which offer the same technology with much less hassle.


To force a device to use the MAC address of another device. Cable/DSL routers often allow users to spoof the MAC address of their computer’s NIC, making it appear as if their DSL or cable modem is still directly connected to a computer.

star topology

A network configuration in which all devices are connected to a central hub or switch. Almost all home networks use star topology.

Also see topology.

static IP

An IP address that is not subject to change. Typically reserved for business Internet services, while consumer Internet services use dynamic IPs.


A category 5 cable in which the internal wires have the same arrangements at each end. The opposite of crossover. Most Cat-5 cables are wired in this way.


A group of computers that have the same IP address prefix.

subnet mask

A set of numbers that tells a router which parts of an IP address must be read. In a subnet mask, a binary digit of 1 says “read”, and 0 says “don’t read.” Subnet masks save routers from having to process an entire IP address, which makes routing more efficient.

Example: a subnet mask of, when translated into binary digits, is:


This tells a router to look at the first three parts of the IP address and ignore the last part.


A device that serves as the central connection point for computers on a LAN. While it serves the same basic function as a hub, it does so more intelligently by forwarding packets directly to their destinations.