The Local Area Network (LAN) is by far the most common type of data network. As the name suggests, a LAN serves a local area (typically the area of a floor of a building, but in some cases spanning a distance of several kilometers). Typical installations are in industrial plants, office buildings, college or university campuses, or similar locations.

Intermediate nodes (i.e. repeaters, bridges and switches)- small hardware device that joins multiple computers together within one local area network (LAN) They allow LANs to be connected together to form larger LANs.

In summary, a LAN is a communications network which is:

• Local (i.e. one building or group of buildings)
  Controlled by one administrative authority
  Assumes other users of the LAN are trusted
  Usually high speed and is always share
  
  

Network Security consists of the provisions made in an underlying computer network infrastructure, policies adopted by the network administrator to protect the network and the network-accessible resources from unauthorized access and the effectiveness (or lack) of these measures combined together.

The preventive measures attempt to secure the access to individual computers--the network itself--thereby protecting the computers and other shared resources such as printers, network-attached storage connected by the network. Attacks could be stopped at their entry points before they spread

Examples include:

Authentication of users through use of firewalls
An intrusion prevention system (IPS) helps detect and prevent malware and worms.
Network Security Analysis
Use of Network Security Software

A wide area network (WAN) is a computer network that covers a broad geographical area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries ). Or, less formally, a network that uses routers and public communications links . The largest and most well-known example of a WAN is the Inernet.

WANs are used to connect (LANs) and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations.

A virtual private network (VPN) is a private communications network often used within a company, or by several companies or organizations, to communicate confidentially over a non-private network. VPN traffic can be carried over a public networking infrastructure (e.g. the Internet) on top of standard protocols, or over a service provider's private network with a defined Service Level Agreement (SLA) between the VPN customer and the VPN service provider