Internet Service Providers (ISPs) connect clients, who represent the lowest part of the routing hierarchy, with other clients of other ISPs through higher network layers or at the same level. At the top of the routing hierarchy are layer 1 networks, large telecommunications companies that exchange traffic directly with others through interconnection agreements. Layer 2 and lower-level networks buy Internet traffic from other providers to reach at least some parts of the global Internet, although they can also participate in interconnection. An ISP can use a single provider for connectivity or implement multihoming to achieve redundancy and load balancing. The neutral points have the most important traffic loads and have physical connections to multiple ISPs.
Computers and routers use routing tables to direct IP packets between locally connected machines. Tables can be built manually or automatically through DHCP for an individual team or a routing protocol for the routers themselves. In a single homed situations, a default route usually points "up" towards an ISP providing transport. Higher-level ISPs use the Border Gateway Protocol to solve access routes to a certain range of IP addresses through the complex connections of the global Internet.
Academic institutions, large companies, governments and other organizations can perform the same role as ISPs, with the participation in the exchange of traffic and transit of the purchase on behalf of their internal networks of individual computers. Research networks tend to interconnect in large subnets such as GEANT, GLORIAD, Internet2, and national research in the United Kingdom and the education network, Janet. These in turn are built around the smaller networks (see list of academic organizations of computer networks)
Not all computer networks are connected to the Internet. For example, some classified States websites are only accessible from independent secure networks. Until here hope we expanded our thinking, lets grow together
