Interior Gateway Protocol (IGP)

Let’s start with a quick review of what’s going on within the AS itself and introduce some terminology. Within this AS we have areas: at least one unicast routing protocol and perhaps one or more multicast protocols. All of the routing protocols used within the AS are Interior Gateway Protocols (IGPs).

Routing protocols fall under the class of gateway protocols because a gateway is something that connects two networks. This gateway can either be a special hardware device or a piece of software. Items that fall under the realm of gateways are computers that provide routing services, computers that connect various physical network types together (say,Token Ring and Ethernet), and computers that allow multiple network protocols to talk to one another (perhaps TCP/IP and IPX). Now let’s take a look at the collection of popular border routing protocols.