Sybex CCENT 640-822Chapter 8: IP RoutingInstructor & Todd Lammle

Chapter 8 Objectives

• Understanding IP routing• Static routing• Dynamic routing

– RIP– RIPv2– Verifying routing

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To route a router need to know:– Remote Networks

– Neighbor Routers

– All Possible routes to remote network

– The absolute best route to all remote networks

– Maintain and verify the routing information

What is Routing?

C B AD

Basic Path Selection

What interface will the router send out a packet if it has destination address of 10.10.10.18?

Simple IP Routing

Routing/PDU Example:Host A Web browses to the HTTP

Server….

Routing/PDU Example 2

ICMP Error example

Basic Routing Using MAC and IP Addresses

Testing basic routingKnowledge

Configuring IP RoutingNetwork

ip route remote network

[mask]

{address|interface}

[distance]

[permanent]

Router(config)#ip route remote_network mask next_hop

Static Route Configuration

ip route 172.16.1.0 255.255.255.0 172.16.3.2or

ip route 172.16.1.0 255.255.255.0 s0

Static Route Example

172.16.3.2

SO

172.16.1.0

B172.16.3.1

A B

Stub Network

172.16.2.0

SO

Default Routes

172.16.3.2

SO

172.16.1.0

B172.16.3.1

A B

Stub Network

172.16.2.0

SO

ip route 0.0.0.0 0.0.0.0 172.16.3.1

ip classless

Configuring a gateway of Last resort

• Routing protocols are used between routers to: – Determine the path of a packet through a network– Maintain routing tables– Examples?

• Routed protocols are:– Assigned to an interface– Once the path is determined by the Routing

protocol, determines method of delivery– Examples?

Routing vs. Routed

Autonomous System 1 Autonomous System 2

IGPs: RIP, IGRP EGPs: BGP

Routing Protocols

•An autonomous system is a collection of networks under a common administrative domain.

•IGPs operate within an autonomous system.

•EGPs connect different autonomous systems.

Classful Routing Overview

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

– Within the same network, consistency of the subnet masks is assumed.

– Summary routes are exchanged between foreign networks.

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

Classless Routing Overview

Classless routing protocols include the subnet mask with the route advertisement.

– Classless routing protocols support variable-length subnet masking (VLSM).

– Summary routes can be manually controlled within the network.

– Examples of classless routing protocols:• RIP Version 2 (RIPv2)• EIGRP• OSPF• IS-IS

IGRPAdministrative Distance=100

Router D

Router BRouter A

Router C

RIPAdministrative Distance=120

Default Administrative DistanceDirectly Connected: 0Static Route: 1RIP: 120IGRP: 100EIGRP: 90OSPF: 110

Administrative Distance

C B AD

RoutingTable

RoutingTable

RoutingTable

RoutingTable

RoutingTable

RoutingTable

RoutingTable

RoutingTable

Distance—How farVector—In which direction

Distance—How farVector—In which direction

Distance vector algorithms do not allow a router to know the exact topology of an internetwork.

All routers just broadcast their entire routing table out all active interfaces on periodic time intervals

Distance Vector

Pinhole Congestion

Discovering RoutesDiscovering Routes

Converged RoutesConverged Routes

Routing Loops

64kbps

T1

T1 T1

– Hop count metric selects the path, 16 is unreachable

– Full route table broadcast every 30 seconds

– Load balance maximum of 6 equal cost paths (default = 4)

– RIPv2 supports VLSM and Discontiguous networks

RIP Overview

Router(config)#router rip

Router(config-router)#network network-number*

network 172.16.0.0network 192.168.10.0

router RIPnetwork 172.16.0.0network 10.0.0.0

router RIP

*Network is a classful network address.

Every device on network uses the same subnet mask

172.16.10.0 192.168.10.010.3.5.0

RIP Routing Configuration

RIP Routing Example 2

RIP Version 2• Allows the use of variable length subnet

masks (VLSM) by sending subnet mask information with each route update

• Distance Vector – same AD, and timers.• Easy configuration, just add the command

“version 2” under the router rip configuration

router ripnetwork 10.0.0.0version 2

Discontiguous Addressing

• Two networks of the same classful networks are separated by a different network address

192.168.10.0/24

10.1.1.0/24

192.168.10.0/24

– RIPv1 and IGRP do not advertise subnet masks, and therefore cannot support discontiguous subnets.

– OSPF, EIGRP, and RIPv2 can advertise subnet masks, and therefore can support discontiguous subnets.

A Discontiguous network

Verifying RIP

Router#show ip protocols

Router#show ip route

Router#debug ip rip

Router#undebug all (un all)

Summary

– Open your books and go through all the written labs and the review questions.

– Review the answers in class.

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