Introduction to Dynamic Routing Protocols - Routing Protocols and Concepts - page 145

Distance Vector Routing Protocol Operation

Distance vector means that routes are advertised as vectors of distance and direction . Distance is
defined in terms of a metric , such as hop count, and direction is simply the next - hop router or exit
interface . Distance vector protocols typically use the Bellman - Ford algorithm for the best-path route
determination.

Some distance vector protocols periodically send complete routing tables to all connected neighbors.
In large networks, these routing updates can become enormous, causing significant traffic on the links.

Distance vector protocols use routers as sign posts along the path to the final destination. The only
information a router knows about a remote network is the distance or metric to reach that network and
which path or interface to use to get there. Distance vector routing protocols do not have an actual
map of the network topology .

List four situations in which distance vector routing protocols are a good choice.

The network is simple and flat and does not require a special hierarchical design.

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The administrators do not have enough knowledge to configure and troubleshoot link-state pro-
tocols.

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Specific types of networks, such as hub-and-spoke networks, are being implemented.

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Worst-case convergence times in a network are not a concern.

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Link-State Protocol Operation

In contrast to distance vector routing protocol operation, a router configured with a link-state routing
protocol can create a “complete view,” or topology , of the network. A link-state router uses link - state
information to create a topology map and to select the best path to all destination networks in the
topology .

Link-state routing protocols do not use periodic updates. After the network has converged , a link-state
update is only sent when there is a change in the topology.

List three situations in which link-state routing protocols are a good choice.

The network design is hierarchical, usually occurring in large networks.

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The administrators have a good knowledge of the implemented link-state routing protocol.

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Fast convergence of the network is crucial.

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Classful and Classless Protocols

All routing protocols can also be classified as either

Classful routing protocols

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Classless routing protocols

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Classful Routing Protocols

What feature makes a routing protocol a classful routing protocol?

Classful routing protocols do not send subnet mask information in routing updates.

There are other limitations to classful routing protocols, including their inability to support discontigu-
ous networks—a topology that consists of a major network separating the subnets of another major
network.

Classful routing protocols include RIPv1 and IGRP .