Introduction
In Chapter I, we outlined the many causes of insecurity in the information communication technology (ICT) infrastructure. We indicated one particular weakness as users with little knowledge of the working of the communication infrastructure. In this chapter, we intend to address that concern. We give a very elementary treatment of the theory of networks and then outline the best network security solutions.
Computer.Network.Basics
What is a computer network? A computer network is a distributed system consisting of loosely coupled computers and other devices as network nodes. Any two nodes of this network can communicate with each other through a communications medium by observing a set of communicating rules or protocols that each device in the network must follow to communicate with another in the network. The resulting combination, consisting of hardware and software, is a computer communication network, or computer network, in short. Figure 1 shows a computer network.
Network nodes may own resources individually that are locally or globally accessible. Each network has application programs and network protocols that are used to synchronize, coordinate, and bring about the sharing and exchange of data among the network elements. Network software also makes the sharing of expensive resources in the network possible. Network elements, network software, and users all work together so that individual users get to exchange messages and share resources on other systems that are not readily available locally. The network elements, together with their resources, may be of diverse hardware technologies and the software may be as different as possible, but the whole combination must work together in unison.
Computer networks are used in a variety of ways and in different settings including business, like baking, and education, like computing laboratories and research. Whether in special setting or in a home connected to the Internet via an Internet service provider (ISP), like BellSouth or AT&T, computer networks provide a variety of services including:
Ethernet Laser prnter Laptop Laptop Laptop Laptop Figure.1..A.computer.network
• Communication: E-mail service being the Internet’s largest commu- nication service. Millions of people communicate via e-mail and it is becoming, if not already is, the main communication medium.
• Data.exchange: Many network servers store large quantities of data.
Besides, data exchange is probably the second largest service of com- puter networks. One can search Google databases for information and Amazon databases for books. With the race heating up for the big three data storage companies, Google, Yahoo, and Microsoft, it looks like data storage will soon become the dominant service.
• Shared.resources:.Sharing of resources on a network now makes it
possible for a pool of employees to share computer resources, like a printer down the hall, saving businesses millions of dollars in equipment purchases.
Computer.Network.Types
Because most computer networks are private and owned by organizations, institutions, and individuals, each network is built to meet the needs of the organization that commissions it. This meeting of organizational needs dictates the type and size of the network. All computer networks are not the same. They are designed and built with a goal in mind and for different organiza-
tions, the goals vary. Remember that from our definition of a network, each
network is a cluster of network elements and their resources. The size of the cluster determines the network type. There are, in general, two main network types: the local area network (LAN) and a wide area network (WAN).
Local.Area.Network.(LAN)
Two or more computers connected in close proximity form a LAN. Each com- puter must have a network card (NIC) or a network adapter. The computers are connected by a common medium of cabling like coaxial, twisted pair, or
optical fiber. The network must also have common protocols that include:
• Access methods based on a chosen lan technology. For example if ethernet technology is to be used, then it comes with its carrier sense multiple access with collision detection (csma/cd) protocol.
• Network communication protocol like internet protocol (ip) or internet- work packet exchange (ipx).
Purpose.of.a.LAN
These special computer networks are set up for several reasons including:
• Sharing expensive resources like printers, disks, scanners, internet ac- cess, and others. For a company, this sharing of peripherals can mean great savings.
• Provide communication to shared data and programs. This is both a saving and security option. Savings can be made if instead of buying software products for each and every computer in the company, you only buy one copy that is installed on the server and can be shared by all. It is also a security bonanza, because if software and company data is kept by every employee, there are chances that the data and programs will be stolen or lost.
• Makes making updates easy and cheap. Again because of the same reasons, if hundreds of copies of a software product were bought for every computer in the company and there is a patch for the software, it would take days to get all the computers updated, costing the company money and time.
• Good for controlled administration of the network. Few experienced people can be hired and the network can be administered from one location. Ethernet Scanner Laser prnter Laptop Laptop Laptop Laptop Figure.2..A.LAN.network
Wide.Area.Networks.(WANs)
A WAN, on the other hand, is a network made up of one or more clusters
of network elements and their resources, but instead of being confined to a
small area, the elements of the clusters or the clusters themselves are scat- tered over a wide geographical area, like in a region of a country or across the whole country, several countries, or the entire globe, like the Internet, for example. Some advantages of a WAN include distributing services to a wider community and the availability of a wide array of both hardware and software resources that may not be available in a LAN. However, because of the large geographical areas covered by WANs, communication media are slow and often unreliable. Figure 4 shows a WAN network.
Metropolitan.Area.Networks.(MANs)
Between the LAN and WAN, there is also a special middle network called the metropolitan area network (MAN), because it covers a slightly wider area than the LAN, but not so wide as to be considered a WAN. Civic networks that cover a city or part of a city are a good example of a MAN. MANs are rarely talked about because they are quiet often overshadowed by cousin LAN to the left and cousin WAN to the right.
Server Laptop Laptop Router Router Prnter Internet Server Laptop Laptop Figure.4..A.WAN.network