1. Definitions and principles

Before we start describing the technical methods used on the Internet, it's worth clarifying the vocabulary, as there's a certain ambiguity in the terms used:

• The term routing is often confused with forwarding, which refers to the main function of a router. This function consists of copying a packet to the output interface as quickly as possible. Initially, interconnection equipment memorized all the information before retransmitting it (storage and retransmission), but to optimize performance, some equipment takes the decision as soon as the header is received. This technology is called switching;

• the routing function builds databases (called routing tables) indicating the output interface for a destination. This information is used for relaying.

At first glance, these...