Networking Glossary

Introduction

This page explains some of the fundamental concepts, components and terminology associated with standard computer networks. These networks are often referred to as local area networks (LAN). This type of network is technically known as an Ethernet network.

Network

An Ethernet network consists of two or more devices effectively connected together as shown in the diagram.

Addressing

IP Address

An IP address is a series of 4 numbers, in the range 0 to 255, assigned to each device on the network. Each device on the network needs a unique IP address to communicate with other devices. Problems will occur if two devices on the network have the same IP address.

Subnet Mask

A subnet mask is a series of 4 numbers, in the range 0 to 255, assigned to devices on the network. It is used as a filter, in conjunction with the IP address, to decide which other devices should be communicated with.

Assignment

There are two ways to assign IP addresses and subnet masks to a device on the network, static assignmant and dynamic assignment.

Static Assignment (Manual)

Static (fixed) assignment is where a fixed IP address is manually programmed into the device. This is normally done using a settings menu on the device. Some devices do not support static IP assignment.

Dynamic Assignment (Automatic)

Dynamic assignment is where the IP address is assigned automatically, by the network. Each device sends a request for an IP address onto the network. It then waits for a response containing the address it should use. This is done using a mechanism called DHCP.

DHCP

DHCP (Dynamic Host Configuration Protocol) is a standard protocol used for automatic assignment of IP addresses to devices on a network. Devices, that are configured for DHCP, send a request then wait to receive a response containing the IP address that they have been allocated. A major advantage of this approach is a device can be moved to a different network without the need for reconfiguration. Some devices send a DHCP request every time they are connected to a network. Other devices only send a request at power up, meaning they have to be power cycled whenever they are moved to a new network.

DHCP Server

A DHCP server is a small configurable software component that processes DHCP requests from devices on the network. It replies to each request with a response containing a valid IP address for that device. It keeps a record of the devices who sent requests, and the IP addresses that it assigned to them, ensuring that no two devices are supplied with the same address. It is important that only one DHCP server exists on the network. Problems will occur if more than one is present since devices would then receive multiple responses to their DHCP requests. Typically, DHCP server functionality is integrated into the router device on the network.

Dynamic Fixed Assignment

Dynamic fixed assignment (also known as Address Reservation) is a feature, supported by some DHCP servers, that allows devices to be dynamically assigned the same IP address every time. The advantage of this approach is that it harnesses the advantages of both static and dynamic assignment techniques.

Subnet

A subnet (subnetwork) is a subdivision of a larger network. Most networks are classed as subnets since they are typically connected to the internet and are thus a subdivision of that network. A subnet is defined by the range of IP addresses that are deemed valid on it's network.

Network Switch

A network switch, often just referred to as a switch, allows multiple network devices to be connected together in a star formation. Switches come in different types and sizes. The most common type of switch is known as a "dumb" switch because it is not user configurable. A switch's size is defined by the number of network sockets, or ports, it has. The diagram below shows a four port switch.

A switch functions as a multipoint connector where any device, attached to any of the switch ports, is effectively connected to all other devices connected to any of the other ports.

Router

A router is a device that manages the boundary between two networks or subnets.

Wireless Access Point (WAP)

A WAP is device that provides wireless access to the network.

Combination Boxes

Router-Switch

Router-Switch-WAP

Appendix

Advantages/Disadvantages Of IP Assignment Methods

Static IP Advantages

• The IP address is reliable as it always remains the same.

Static IP Disadvantages

• There is a small time/labour overhead in manual configuration
• There is a potential for error such as address conflicts
• If the device is moved to another network it will probably need a new address
• Need to keep a record of all addresses on the network