TCP/IP Guide

BGP Path Attributes and Algorithm Overview

Routing protocols that use a distance-vector algorithm, such as RIP, are relatively simple in large part because the information each device stores about each route is itself simple. Each router only knows that it can reach a network at a specific cost through a particular next-hop router. It doesn't have knowledge of the route that datagrams will take to reach any of these networks. This level of knowledge is simply insufficient for the needs of a protocol like BGP.

In order to handle the calculation of efficient, nonlooping routes in an arbitrary topology of ASes, we need to know not just that we must get Network N7 to send to Router R4, but also the characteristics of the entire path between ourselves ...