FOSS Network Infrastructure and Security/Network Concepts and Architectures

 FOSS Network Infrastructure and Security 

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Foreword — List of Abbreviations — Introduction to FOSS and GNU/Linux — Network Concepts and Architectures — Major Networking Functions with FOSS — Security Functions with FOSS — Network Planning — Further References — Glossary — About the Author — Acknowledgements — About APDIP — About IOSN

Computer Networks

A network is a mechanism that enables distributed computers and users to communicate and share resources. Sharing of resources may mean sharing a printer, a scanner or even a large hard disk on a particular computer. A computer network connects two or more computers or peripherals so that all users on the network have access to these resources.

There are two major types of computer networks:

• Server-based networks; and

• Peer-to-peer networks.

In a server-based network, there exists one or more computer(s) on which the resources are centralized. The network is also more or less controlled by the server. Servers generally have superior processing power, memory and hard disk space compared to desktop systems.

In a peer-to-peer network, all computers on the network are responsible for sharing resources. Each computer shares the resources that it has. All computers are servers as well as clients. There is no central control over the resources. Peer-to-peer networks are based on peer relationships among computers in the network.

Network Topology

Topology refers to the arrangement of computers in a network. In physical terms, there are two main topologies that are commonly used:

• Bus topology; and

• Star topology

The simplest arrangement is Bus topology in which all computers are connected in a series to a single stretch of cable. This means that the entire length of the cable must be intact for the network to work properly; which makes larger networks prone to failure.

A hub or a switch is used as the central exchange point in a Star topology. All computers are connected to the hub in a star-like configuration of wires going in all directions from the hub. A Star topology is easier to maintain and to expand.

LAN Architecture

Two computers can communicate in different ways through different Local Area Network (LAN) architectures. Of the two well-known architectures — Ethernet and Token Ring — the former is more popular.

Ethernet

Ethernet is independent of any vendor, which accounts for its great success. Basic Ethernet architecture operates at a speed of 10 Mbps (mega bits per second). Other variations include Fast Ethernet, operating at 100 Mbps, and Gigabit Ethernet operating at 1 Giga bit per second. The Ethernet standards are referred to in the 802.nn notation, an Institute of Electrical and Electronics Engineers (IEEE) standard. WiFi (wireless fidelity) networks also follow the same standards, and are thus characterized as 802.11x.

Token Ring

Token-Ring LAN technology was developed and promoted by IBM in the early 1980s and was later standardized as IEEE 802.5. Initially very successful, its popularity went into steep decline after the introduction of the 10 Mbps Ethernet standard in the early 1990s.

Network Hardware

Network Cabling

Cables play a fundamental role in any network, and exist at the most primary level of the network. Two types of cables are in common use – co-axial cables (similar to cable TV cables) and twisted pair cables (similar to telephone cables). Co-axial cables are generally used with T-connectors in a Bus topology network. Twisted pair cables are used mostly in Hub-based networks.

Network Adapter Cards

Network Interface Cards (NICs) or Network Adapter Cards, as they are commonly known, provide an interface on the computer to connect to the network cable. Today, most computers come with a built-in network card. However, if it is not built into the system, an additional card can be inserted inside the computer, which will then connect to the network cable.

Networks Operation and Layers

Computer networks operate at different layers, each of which is independent of the others. The layers are stacked on top of each other, with each layer providing service to the layer above it. Network layers, as these layers are commonly known, provide general understanding of any computer network. A very simple form of these layers is illustrated below.

Operating Software Layer (with Internet Protocol)

Network Applications

Application Layer

Transmission Control Protocol / User Datagram Protocol	Transport Layer
Internet Protocol	Network Layer

Hardware Layer Network Interface Card Layer Electronic Layer

Network Interface Card Layer

Electronic Layer