Purpose of a routing protocol and autonomous systems

Purpose of a routing protocol and autonomous systems 

6.2.3 
This page will explain why routing protocols and autonomous systems are used.
The goal of a routing protocol is to build and maintain a routing table. This table contains the learned networks and associated ports for those networks. Routers use routing protocols to manage information received from other routers and its interfaces, as well as manually configured routes.
The routing protocol learns all available routes, places the best routes into the routing table, and removes routes when they are no longer valid. The router uses the information in the routing table to forward routed protocol packets.
The routing algorithm is fundamental to dynamic routing. Whenever the topology of a network changes because of growth, reconfiguration, or failure, the network knowledgebase must also change. The network knowledgebase needs to reflect an accurate view of the new topology.
When all routers in an internetwork operate with the same knowledge, the internetwork is said to have converged. Fast convergence is desirable because it reduces the period of time in which routers would continue to make incorrect routing decisions.
Autonomous systems divide the global internetwork into smaller and more manageable networks. Each AS has its own set of rules and policies and an AS number that will distinguish it from all other autonomous systems.
The next page will introduce the two main classes of routing algorithms.

Autonomous systems

Autonomous systems 

6.2.2

This page will define an autonomous system (AS).
An AS is a collection of networks under a common administration that share a common routing strategy. To the outside world, an AS is viewed as a single entity. The AS may be run by one or more operators while it presents a consistent view of routing to the external world.
The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns a 16-bit identification number to each AS. This autonomous system number is a 16 bit number. Routing protocols, such as Cisco IGRP, require the assignment of a unique, AS number.
The next page will explain the purpose of routing protocols and autonomous systems.

Dynamic Routing Overview /

Dynamic Routing Overview 

Introduction to routing protocols

6.2.1

This page will introduce routing protocols and how they are used.
Routing protocols are different from routed protocols in both function and task.
A routing protocol is the communication used between routers. A routing protocol allows routers to share information about networks and their proximity to each other. Routers use this information to build and maintain routing tables.
Examples of routing protocols are as follows:

• Routing Information Protocol (RIP)
• Interior Gateway Routing Protocol (IGRP)
• Enhanced Interior Gateway Routing Protocol (EIGRP)
• Open Shortest Path First (OSPF)

A routed protocol is used to direct user traffic. A routed protocol provides enough information in its network layer address to allow a packet to be forwarded from one host to another based on the addressing scheme.
Examples of routed protocols are as follows:

• Internet Protocol (IP)
• Internetwork Packet Exchange (IPX)

The next page will describe autonomous systems.