Sybex CCNA 640-802Chapter 6: IP RoutingInstructor & Todd Lammle

Chapter 6 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

172.16.1.0

BA

172.16.2.0

172.16.2.2

172.16.1.2172.16.2.1 172.16.1.1

e0 e0

>ping 172.16.1.2>ping 172.16.1.2

B

172.16.3.1 172.16.3.2

s0s0

Host A

Host B

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

Server….

3. The destination port number in a segment header will have a value of __

1. The destination address of a frame will be the _______________________2. The destination IP address of a packet will be the IP address of the________________________________

172.16.3.2

SO

Static Routes

172.16.1.0

B172.16.3.1

A B

Stub Network

172.16.2.0

SOA

Routes must be unidirectional

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

To send packets with a remote destination network not in the routing table to the next-hop router, only used for stub networks.

ip route 0.0.0.0 0.0.0.0 172.16.3.1

ip classless

• Routing protocols are used between routers to: – Determine the path of a packet through a

network– Maintain routing tables– Two types: interior/exterior gateway

protocols (I/EGPs)– Examples:

• IGP: RIP, IGRP; • EGP: Border Gateway Protocol (BGP)

Routing Protocols

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, i.e., all routers sharing the same routing table are in the same AS.

•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

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

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

Distance Vector

Discovering RoutesDiscovering Routes

Discovering Routes: Converged Routing TablesDiscovering Routes: Converged Routing Tables

Routing Loops

Stop Router Loops

• Maximum hop count: RIP permits a hop count of up to 15.

• Split horizon: routing information cannot be sent back in the direction from which it was received.

• Route poisoning: advertising the downed network as unreachable

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 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

RIPv1 vs. RIPv2

RIPv1 RIPv2

Distance vector Distance vector

Maximum hop count 15

Maximum hop count 15

Classful Classless

Broadcast based Multicast 224.0.0.9

No support for VLSM Supports VLSM

No authentication MD5 authentication

No support for discontiguous networks

Supports discontiguous networks

Interior Gateway Routing Protocol

• Maximum hop count: 255 for larger network, default 100

• Composite metric: bandwidth and delay of the line.

Config trouter igrp 10

IGRP vs. RIP

Large network Small network

Uses AS number for activation

Uses network address, with all subnet and host bits off

Full route table update per 90 sec

Full route table update per 30 sec

AD 100 AD 120

Uses bandwidth and delay of the line as metric, maximum hop count 255

Uses only hop count to determine the best path to a remote network, max 15

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.

Passive Interface

Maybe you don’t want to send RIP updates out your router interface connected to the Internet. Use the passive-interface command:Router(config)#router rip

Router(config-router)#passive-interface serial0

This allows a router to receive route updates on an interface,

but not send updates via that interface

S0 GatewayInternet

Updates

XX

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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