Virtual private networks

Organizations build networks to meet their IT networking needs. Each network carries data and applications that are specific to that organization only. Hence, the networks so built are private to that extent. Building a network that is restricted to a campus is manageable from a cost perspective, as the distances are small, and fiber can be laid to connect the various buildings within a campus. The challenge is when the connectivity is required over long distances. Every organization cannot set up a private network covering such large distances, as it is very capital intensive. Thus, the organizations use the services of a service provider who provides connectivity services. The services so provided are such that the SP infrastructure is logically partitioned into small blocks that are dedicated to each organization. Such networks, though built on public infrastructures, are virtually private, and are known as VPNs.

The simplest form of such a case is where an organization...