In a nationwide network such as the current Internet, it is very unlikely that a single routing protocol will used for the whole network. Rather, the network will be organized as a collection of “autonomous systems”. An autonomous system will in general be administered by a single entity, or at least will have some reasonable degree of technical and administrative control. Each autonomous system will have its own routing technology.
– C. Hedrick; Routing Information Protocol; RFC 1058; June 1988.
Interior Gateway Protocols (IGP) are used to route Internet communications within a local area network, such as within an office building. The two main types of IGP protocols are described in the following sections, along with an example proprietary protocol for comparison purposes.