25.1_determining ip routes

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2002, Cisco Systems, Inc. All rights reserved.


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2002, Cisco Systems, Inc. All rights reserved. 2

Determining IP Routes

Module 5


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2002, Cisco Systems, Inc. All rights reserved. ICND v2.05-3

Objectives

Upon completing this lesson, you will be able to:

Describe the features and operation of static routing

Describe the features and operation of dynamic routingprotocols, including RIP, IGRP, EIGRP,and OSPF

Build a functional router configuration to support thespecified network operational requirements, given anetwork design

Use show commands to identify anomalies in routingoperation, given an operational router

Use debug commands to identify events and anomalies inrouting operation, given an operational router


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2002, Cisco Systems, Inc. All rights reserved. 4

Routing Overview


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Objectives

Upon completing this lesson, you will beable to:

Explain the differences between static routingand dynamic routing

Identify the classes of routing protocols

Use Cisco IOS commands to configure staticroutes and default route forwarding, given a

functioning router Use show commands to identify anomalies in

static routing operation, given an operationalrouter


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To route, a router needs to do the following:

Know the destination address

Identify the sources it can learn from

Discover possible routes

Select the best route

Maintain and verify routing information

What Is Routing?


7/27 2002, Cisco Systems, Inc. All rights reserved. ICND v2.05-7

Routers must learn destinations that are

not directly connected.

What Is Routing? (Cont.)



Static Route

Uses a route that anetwork administratorenters into the routermanually

Dynamic Route

Uses a route that anetwork routingprotocol adjustsautomatically for

topology or trafficchanges

Identifying Static and Dynamic Routes



Static Routes

Configure unidirectional static routes to and froma stub network to allow communications to occur.



Defines a path to an IP destination network or subnet or host

Router(config)#ip route network [mask]

{address

|interface

}[distance

] [permanent]

Static Route Configuration



Static Route Example

This is a unidirectional route. You must have a route

configured in the opposite direction.



Default Routes

This route allows the stub network to reach all known

networks beyond router A.



Verifying the StaticRoute Configuration

router#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default

U - per-user static route

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

10.0.0.0/8 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, Serial0S* 0.0.0.0/0 is directly connected, Serial0



Routing protocols areused between

routers to determinepaths and maintainrouting tables.

Once the path isdetermined, a router canroute a routed protocol.

What Is a Routing Protocol?



An autonomous system is a collection of networksunder a common administrative domain.

IGPs operate within an autonomous system.

EGPs connect different autonomous systems.

Autonomous Systems: Interior orExterior Routing Protocols



Administrative Distance:Ranking Routes



Determining the route AdministrativeDistance

AD is a number that measures thetrustworthiness of the source of a routinginformation.

The higher the number, the lower thetrustworthiness rating.

Example:Directed connection 0

Static route (by default) 1IGRP 100OSPF 110RIP 120



Classes of Routing Protocols



Classful Routing Overview

Classful routing protocols do not include thesubnet mask with the route advertisement.

Within the same network, consistency of thesubnet masks is assumed.

Summary routes are exchanged between foreignnetworks.

Examples of classful routing protocols:RIP Version 1 (RIPv1)

IGRP



Classless Routing Overview

Classless routing protocols include the subnet maskwith the route advertisement.

Classless routing protocols support variable-lengthsubnet masking (VLSM).

Summary routes can be manually controlled withinthe network.

Examples of classless routing protocols:

RIP Version 2 (RIPv2)

EIGRP

OSPF

IS-IS


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Routing ProtocolComparison Chart


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Using the ip classless Command


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Without ip classless command

BHMGAD

S0/0

192.168.13.2

To

10.2.2.4

192.168.1.4/30

10.1.1.0

10.3.3.0

Fa0/1

Fa0/0

Destination network Outbound interface

10.3.3.0 Fa0/1

10.1.1.0 Fa0/0

0.0.0.0 S0/0


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With ip classless command

BHMGAD

S0/0

192.168.13.2

To

10.2.2.4

192.168.1.4/30

10.1.1.0

10.3.3.0

Fa0/1

Fa0/0

Destination network Outbound interface

10.3.3.0 Fa0/1

10.1.1.0 Fa0/0

0.0.0.0 S0/0


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Summary

Routing is the process by which an item gets from onelocation to another. In networking, a router is the deviceused to route traffic.

Routers can forward packets over static routes or

dynamic routes, based on the router configuration. Static routes can be important if the Cisco IOS software

cannot build a route to a particular destination. Staticroutes are also useful for specifying a gateway of lastresort to which all unroutable packets will be sent.

A default route is a special type of static route used forsituations when the route from a source to a destinationis not known or when it is unfeasible for the routing tableto store sufficient information about the route.


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