As you know a network is a collection of devices connected together. Networks are further classified into various types depending on their size, expanse, security, purpose and many other parameters. While covering all these classifications is beyond the scope of the CCNA exam, there are two important network classifications that you need to know about for the exam. In fact a large part of the CCNA exam revolves around these two types of networks:

  •  Local Area Network (LAN) – This is a term used to describe a network covering a limited geographical area such as a floor, building or a campus. LAN usually has a high data-transfer rate. The Ethernet standard is the most commonly used technology in LANs. Ethernet is so common that it is almost synonymous with LAN today. As of late, wireless technology is also becoming increasingly common for a local LAN. Both these standards are covered in depth further in the book.
  • Wide Area Network (WAN) – This is a term used to describe a network covering a large geographical area such as a multiple cities, a country or even across the world. They are used to connect LANs across the area they cover. A typical example would be the LANs at various offices of a company connected by WAN. Various technology standards used in WAN will be covered later in the book.

Internetworking Models

As the importance of computers grew, vendors recognized the need for networking them. They created various protocols whose specifications were not made public. Hence each vendor had different ways of networking computers and these ways were not compatible to each other. This means that computers of one vendor could not be networked with another vendor’s computers. Slowly these specifications were made public and some inter-vendor compatibility was created but this still represented too many complications. In 1977 the International Organization for Standardization (ISO) started working on an open standard networking model that all vendors would support to promote inter-operability. This standard was published in 1984 and was known as the Open Systems Interconnection (OSI). During the same time period (1973 to 1985) another effort by the Defense Advanced Research Projects Agency (DAPRA) was underway to create an open standard network model. This network model came to be known as the TCP/IP Model. By 1985, the TCP/IP model started gaining more prominence and support from vendors and eventually replaced the OSI model.

This section starts by discussing the OSI Reference model in some depth before moving into a deep discussion on the TCP/IP model and its protocols.