Routing in Internet networks

Routers make it possible to design networks with no limits on size or number of devices. Routing is becoming indispensable for interconnecting a network to the rest of the Internet, building a large network or managing flows within the network. The difficulty of configuring a routed network is not only linked to the administration of the router itself. An addressing plan (i.e. the set of rules applied to assign an address to a piece of equipment) must be designed and managed by the network administrator.

This article presents the various engineering aspects of routing. After some basic definitions, the reader will find the address allocation rules implemented in Internet networks, as well as their evolution over time, notably the CIDR hierarchical allocation technique and private addressing. The presentation of the IP protocol and packet format focuses on the fields used for routing. The architecture of a router and its configuration rules are also described, as well as the Internet's division into domains and the different families of routing protocols. The protocols implemented within a site (RIP, OSPF, IS-IS) and the routing protocols implemented between sites (BGP) are presented, before describing routing evolutions and in particular the recent IPv6 protocol.