CCNA Notes on Basic Network Concepts required for the CCNA certification

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The following article is basically a CCNA mini guide on the basic networking concepts you are required to know to become certified as a CCNA. It is not intended to be all encompassing but rather to give you an idea of the basic concepts involved in networking.

We will cover the following topics:

What is a network

A network in an IT environment term which describes a series or group of connected devices that share various services and data. A network allows users who are connected to the network to share documents, websites, databases, emails, messages, music, printers, faxes and other devices. There are various types of networks depending on the size and functionality of the network. Two of the most common network types include the Local Area Network and the Wide Area Network. Give yourself the CCNA Kick Start training advantage with this course.

Types of Networks

A Local Area Network or LAN, is normally a high speed computer network that is limited to a relatively small geographical area. LANs are generally networks that cover a building or set of buildings like a university or campus. LANs are generally administered by a single company or person. LANs usually rely on Ethernet technology to enable connection to the LAN.

WAN’s on the other hand are networks that span large geographical areas. WANs connect a series of Local Area Networks and WANs are created using various WAN technologies. Wide Area networks are often administered by various different companies or administrators.

Storage Area Networks are networks that are set up to function as high speed secure storage devices. Storage Area Networks are called SANs.

A VPN is a Virtual Private Network. VPNs allow information to be sent across public networks like the internet. Virtual Private Networks are often used to connect branch offices to the main office or to connect remote users to the branch or main offices of a corporation.

Multiple networks that are connected together are often referred to as an internetwork. The internet is an example of an giant internetwork.

For a network to function properly, there must be rules and standards that allow users to connect to the network, and that allow users access to the various elements of the network.

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Network protocols

Network protocols are rules that determine how the users can share the data and devices. Network protocols are used to define how devices connect and communicate with one another via the network. Examples of network protocols include IP or Internet Protocol, HTTP or Hyper Text Transfer Protocol and SMTP or Simple Mail Transfer Protocol.

Network Reference Models

Network protocols often work together or communicate with one another to allow for communication between wide varieties of devices. Due to the differences in these protocols and the various different devices that form the network, Network Reference Models were developed to provide a structure for incorporating different devices on the network. Network Reference Models provide a set of standards and procedures on how network protocol communication should occur. The most common network reference models are the OSI and DoD models.

The Open Systems Interconnection Reference Model

Networks are often composed of different devices from different manufacturers. In fact, the fact that networks can be created using devices from different manufacturers is one of the reasons that networks have become as powerful as they are today. The internet would not have been possible had it not been for the different devices and data being shared around the world. But using devices from different manufacturers presents its own set of challenges. Consistent network standards are required to ensure connectivity between these devices. This is where the Network Reference Models like the Open Systems Interconnection models become important.

The OSI model was developed by the International Organization for Standardization in 1984 to govern how information should be sent across a network. The OSI model is composed of seven layers that each correspond to a different function within the network. The seven layers of the OSI are:

Physical
Data link
Network
Transport
Session
Presentation
Application

The layers of the OSI can be learnt using the following mnemonic: Please Do Not Throw Saucy Pizzas Away.

Although the OSI model is now somewhat antiquated, the bottom four layers of the model is still widely applied in the field today.

Basic functions and descriptions of the OSI layers

The last three layers of the OSI model are often grouped and referred to as the upper layers of the OSI. The application, session and presentation layers normally manage application level functions. These layers are also normally implemented in the software used on the network.

The application layer provides standards for the interface between the user and various applications. The application layer determines resource availability and it synchronizes the communication. The application layer also interacts with the presentation layer. Examples of the application layer include FTP or File Transfer Protocol via an FTP client, HTTP via a web browser, and POP3 and SMTP via an email client.

The presentation layer controls the format and presentation of the user data for the application layer. Examples of standard formatting types include text formats like RTF, image formats like GIF and JPG, standard audio formats like MP3 and WAV and standard movie formats like MPEG and AVI.

The session layer is the layer responsible for the creation and termination of sessions between the various users and devices on the network. Sessions that are lost or prematurely terminated can be reinitiated through a recovery process. The session layer has fallen out of use and it not used in a lot of the modern protocols like TCP/IP.

The transport layer controls the transfer of data. This layer ensures that data is send and arrives in order and error free. The transport layer can function as a connection oriented layer or as a connectionless layer.

The network layer contains the standards for all internetwork communication. This layer provides unique addresses that are used to identify the host and network and this layer is responsible for determining the best path to a particular destination network.

The data link layer is responsible for the transportation of data within networks themselves. The data link layer consists of two separate sub layers: the logical link control and the Media Access Control layers.

Finally the physical layer is responsible for transporting the raw bits onto the physical medium itself. The physical layer provides a number of specifications for the actual networking hardware.