Routing Protocols Overview / Path determination

Routing Protocols Overview

Path determination

6.3.1
This page will explain how a router determines the path of a packet from one data link to another. The router uses two basic functions:

A path determination function
A switching function

Path determination occurs at the network layer. The path determination function enables a router to evaluate the paths to a destination and to establish the preferred way to handle a packet. The router uses the routing table to determine the best path and then uses the switching function to forward the packet.

The switching function is the internal process used by a router to accept a packet on one interface and forward it to a second interface on the same router. A key responsibility of the switching function of the router is to encapsulate packets in the appropriate frame type for the next data link.
Figure

illustrates how routers use addressing for these routing and switching functions. The router uses the network portion of the address to make path selections to pass the packet to the next router along the path.
The next page will describe the commands that are used to configure a routing protocol.

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