4. Structuring the Internet

The Internet is often referred to as "the network of networks". It enables networks from different companies to interconnect. Its management is not centralized. Unlike address allocation, there is no authority responsible for interconnecting corporate networks. The Internet introduces the notion of an autonomous system, which can be defined as a set of networks managed by the same authority. An autonomous system is designated by a 16-bit integer. At the beginning of 1999, there were some 4,000 autonomous systems on the Internet.

Each autonomous system is responsible for defining its own network topology, allocating its own addresses and designing its own routing plan. Routing tables can be built :

• statically: knowledge of the site's other networks is acquired by direct configuration of the router. This is only feasible...