CCNA for Dummies by Unknown

Author:Unknown
Language: eng
Format: mobi, pdf
Published: 2011-12-29T16:35:12+00:00

The state of the network

Although link−state routing is not covered extensively on the CCNA exam, you should at least understand what it is so that you can eliminate it as a possible wrong multiple−choice answer.

Link−state routing, which is also called shortest−path−first (SPF), is more complex and requires more processing and more memory than distance−vector routing. In this routing technique, each router keeps track of the state (the health) of its directly connected neighbors. It does this by broadcasting link−state packets (LSPs, also known as link−state advertisements [LSA], or simply hello packets) containing information about the networks to which the router is connected. The router uses the LSPs it receives from other routers to build a database about the network, and then uses the SPF algorithm to determine the shortest route to each network, which is stored in its routing table. When a change occurs in the topology, the use of LSPs results in faster network convergence than is possible with distance−vector routers.

Remember There are several link−state routing algorithm schemes used on Cisco routers, including NLSP

(NetWare Link Services Protocol), OSPF (Open Shortest Path First), and IS−IS (Intermediate System−to−Intermediate System).

Classful Routing

The CCNA exam expects you to be proficient at adding RIP and IGRP protocol statements to a router configuration. In an effort to live up to your expectations when you purchased this book, in this section we review the process used to add statements in both protocols.

You may encounter classful routing on the exam used to describe a routing protocol. Classful routing uses network identities to identify specific routes. RIP and IGRP, the routing protocols you should study the most, are classful routing protocols.

On the other hand, classless routing allows a block of IP addresses to be represented as a single route. CIDR

(Classless Interdomain Routing) is the primary classless routing strategy. Protocols that use the classless routing strategy are also called prefix routing protocols.

Time−Saver Concentrate on classful router configurations. While youll see CIDR addressing references on the exam, you probably wont see any configuration command statements involving CIDR

classless notations.

Let er RIP

Remember RIP (Routing Information Protocol) is a classful, distance−vector routing protocol. As such, it uses information provided to it by its neighboring routers to maintain information in a routing table about the cost, in terms of hops and other metrics, of a particular route.

Your focus on RIP when preparing for the CCNA exam should be adding RIP statements to the router. This is something you really should practice using a router, if at all possible. We dont mean that you absolutely cannot pass the test without using a router to study. What we mean is that it sure will be a lot easier to get ready using a router.

Showing your RIP

To display the current routing information on the router, including all types of existing routes, use the command

CCNA_4_Dummies#show ip route

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