Dynamic Routing Protocol Concepts

Dynamic Routing Protocol Concepts

Perspective and Background

As networks have evolved and become more complex, new routing protocols have emerged. One of the earliest routing protocols, Routing Information Protocol (RIP), has evolved into a newer version, RIPv2. To address the needs of larger networks, two advanced routing protocols were developed: Open Shortest Path First (OSPF) and Intermediate System–to–Intermediate System (IS-IS). Cisco developed Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP), which also scales well in larger network implementations.

Additionally, there was the need to interconnect different internetworks and provide routing among them. Border Gateway Protocol (BGP) is now used between Internet service providers (ISP) as well as between ISPs and their larger private clients to exchange routing information. With the advent of numerous consumer devices using IP, the IPv4 addressing space is nearly exhausted. Thus, IPv6 has emerged, which has required newer versions of the IP routing protocols to be developed.


Role of Dynamic Routing Protocols

Routing protocols determine the best path to each network, which is then added to the routing table. One of the primary benefits of using a dynamic routing protocol is that routers exchange routing information whenever there is a topology change.

Compared to static routing, dynamic routing protocols require less administrative overhead. However, the expense of using dynamic routing protocols is dedicating part of a router’s resources for protocol operation, including CPU time and network link bandwidth.

Purpose of Dynamic Routing Protocols

A routing protocol is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol’s choice of best paths.

List the four purposes of a routing protocol.

■ Discovery of remote networks
■ Maintaining up-to-date routing information
■ Choosing the best path to destination networks
■ Ability to find a new best path if the current path is no longer available

List and briefly describe the main components of a routing protocol.

■ Data structures: Some routing protocols use tables and/or databases for their operations. This information is kept in RAM.
■ Algorithm: An algorithm is a finite list of steps used in accomplishing a task. Routing protocols use algorithms for facilitating routing information and for best-path determination.
■ Routing protocol messages: Routing protocols use various types of messages to discover neighboring routers and exchange routing information, and do other tasks to learn and maintain accurate information about the network.

Dynamic Routing Protocol Operation

The method that a routing protocol uses to accomplish its purpose depends on the algorithm it uses
and the operational characteristics of that protocol.

Describe the basic operations of a dynamic routing protocol.

■ The router sends and receives routing messages on its interfaces.
■ The router shares routing messages and routing information with other routers that are using the same routing protocol.
■ Routers exchange routing information to learn about remote networks.
■ When a router detects a topology change, the routing protocol can advertise this change to other routers.