Distance Vector Routing - PowerPoint Presentation

Slide1

Distance Vector Routing Protocols and RIP V.1

Routing Protocols and Concepts – Chapter

4, 5

Editted

by

Nugroho

Agus

H.,

M.Si

.Slide2

Routing Protocol Algorithm:Slide3

Routing Protocol Characteristics

Criteria

used to compare routing protocols

includes

Time to convergence

Scalability

Resource usage

Implementation & maintenance Slide4

Network DiscoveryRouter initial start up (Cold Starts)

Initial network discovery

Directly connected networks are initially placed in routing table Slide5

Network Discovery

Initial Exchange

of Routing Information

If

a routing protocol

is

configured

then:

Routers will exchange routing information

Routing updates received from other routers

Router checks update for new informationIf there is new information:Metric is updatedNew information is stored in routing tableSlide6

Network Discovery

Exchange of Routing Information

Router convergence

is reached when

All

routing tables

in the network

contain the same network information

Routers continue to exchange routing information

If

no new information is found then Convergence is reachedSlide7

Network Discovery

Convergence must be reached

before a network is considered completely operable

Speed of achieving convergence consists of 2 interdependent categories

Speed of broadcasting routing information

Speed of calculating routesSlide8

Distance Vector Technology- The Meaning of Distance Vector

A router using distance vector routing protocols knows 2 things:

Distance

to final destination

Vector, or direction,

traffic should be directedSlide9

Characteristics of Distance Vector routing protocols:

Periodic

updates

Neighbors

Broadcast updates

Entire routing table is included with routing update

Slide10

Examples of Distance Vector routing protocols:

Routing

Information Protocol

(RIP)

Interior Gateway Routing Protocol

(

IGRP

)

Enhanced Interior Gateway Routing Protocol

(

EIGRP) Slide11

Distance Vector Routing ProtocolsSlide12

Routing Table MaintenancePeriodic Updates:

RIPv1

&

RIPv2

These are

time intervals

in which a router sends out its entire routing

table

RIP uses 4 timers

Update timer

Invalid timer Holddown timer Flush timer Slide13

Routing LoopsRouting loops

are

A condition in which

a packet is continuously transmitted

within a series of routers without ever reaching its destination.Slide14

Routing LoopsRouting loops

may be

caused by

:

Incorrectly configured static routes

Incorrectly configured route redistribution

Slow convergence

Incorrectly configured discard routes

Routing loops

can

create the following issues: Excess use of bandwidth CPU resources may be strained Network convergence is degraded Routing updates may be lost or not processed in a timely mannerSlide15

Routing Loops Count to Infinity

This is

a routing loop whereby packets bounce infinitely around a networkSlide16

Routing LoopsSetting a maximumDistance Vector routing protocols

set a specified metric value to indicate infinity

Once a router “counts to infinity” it marks the route as unreachableSlide17

Routing Loops

Preventing loops with

holddown

timers

Holddown

timers

allow a router to not accept any changes to a route for a specified period of time

Point of using

holddown

timers

Allows routing updates to propagate through network with the most current informationSlide18

Routing LoopsThe

Split Horizon Rule

is

used to prevent routing loops

Split Horizon rule

:

A router should not advertise a network through the interface from which the update cameSlide19

Routing LoopsSplit horizon

with

poison reverse

The rule states that once a router learns of an unreachable route through an interface, advertise it as unreachable back through the same interfaceSlide20

Routing LoopsIP &

TTL

Purpose of the

TTL

field

The

TTL

field is found in an IP header and is

used to prevent packets from endlessly traveling on a network

How the

TTL field works TTL field contains a numeric valueThe numeric value is decreased by one by every router on the route to the destinationIf numeric value reaches

0

then Packet is discardedSlide21

Routing Protocols Today

Factors used to determine whether to use RIP or EIGRP include

Network size

Compatibility between models of routers

Administrative knowledgeSlide22

Routing Protocols TodayRIP

Features of RIP:

Supports

split horizon & split horizon with poison reverse

Capable of

load balancing

Easy to configure

Works in a multi vendor router environmentSlide23

Routing Protocols TodayEIGRP

Features of

EIGRP

:

Triggered updates

EIGRP

hello protocol used to establish neighbor adjacencies

Supports

VLSM

& route summarization

Use of topology table to maintain all routesClassless distance vector routing protocolCisco proprietary protocolSlide24

Routing Information Protocol (RIP)A distance vector protocol that has 2 versionsRIPv1

- a

classful

routing protocol

RIPv2

- a classless routing

protocolSlide25

RIPv1RIP Characteristics

A

classful

, Distance Vector (

DV

) routing protocol

Metric = hop count

Routes with a hop count > 15 are unreachable

Updates are broadcast every 30 secondsSlide26

RIPv1RIP Operation

RIP uses 2 message types:

Request message

This is sent out on startup by each RIP enabled interface

Requests all RIP enabled neighbors to send routing table

Response message

Message sent to requesting router containing routing tableSlide27

RIPv1IP addresses initially divided into classes

Class A

Class B

Class C

RIP is a

classful

routing protocol

Does not send subnet masks in routing updatesSlide28

RIPv1Administrative Distance

RIP’s

default administrative distance is 120Slide29

Basic RIPv1 Configuration

A typical topology suitable for use by

RIPv1

includes:

Three router set up

No PCs attached to LANs

Use of 5 different IP subnetsSlide30

Basic RIPv1 ConfigurationRouter RIP Command

To enable RIP enter:

Router rip

at the global configuration prompt

Prompt will look like

R1(config-router)#Slide31

Basic RIPv1 Configuration

Specifying Networks

Use the

network

command to:

Enable RIP on all interfaces that belong to this network

Advertise this network in RIP updates sent to other routers every 30 secondsSlide32

Verification and Troubleshooting

Show

ip

Route

To verify and troubleshoot routing

Use the following commands:

show

ip

route

show

ip protocols debug ip rip Slide33

Verification and Troubleshooting

show

ip

protocols

command

Displays routing protocol configured on routerSlide34

Verification and Troubleshooting

Debug

ip

rip

command

Used to display RIP routing updates as they are happening

Slide35

Verification and Troubleshooting

Passive interface

command

Used to prevent a router from sending updates through an interface

Example:

Router(

config

-router)#passive-interface interface-type interface-numberSlide36

Passive interfacesSlide37

Automatic Summarization

Modified Topology

The original scenario has been modified such that:

Three

classful

networks are used:

172.30.0.0/16

192.168.4.0/24

192.168.5.0/24

The 172.30.0.0/16 network is

subnetted

into three subnets:

172.30.1.0/24

172.30.2.0/24

172.30.3.0/24

The following devices are part of the 172.30.0.0/16

classful

network address:

All interfaces on

R1

S0

/0/0 and

Fa0

/0 on

R2Slide38

Configuration Details

To

remove the RIP routing process use the following command

No router rip

To check the configuration use the following command

Show runSlide39

Boundary Routers

RIP

automatically summarizes

classful

networks

Boundary routers summarize RIP subnets from one major network to anotherSlide40

Automatic SummarizationAdvantages of automatic summarization:

The size of routing updates is reduced

Single routes are used to represent multiple routes which results in faster lookup in the routing tableSlide41

Automatic SummarizationDisadvantage of Automatic Summarization:

Does not support

discontiguous

networks

Slide42

Automatic Summarization

Discontiguous Topologies do not converge with RIPv1

A router will only advertise major network addresses out interfaces that do not belong to the advertised routeSlide43

Default Route and RIPv1Modified Topology: Scenario

C

Default routes

Packets that are not defined specifically in a routing table will go to the specified interface for the default route

Example: Customer routers use default routes to connect to an ISP router

Command used to configure a default route is

ip route 0.0.0.0 0.0.0.0 s0/0/1Slide44

Default Route and RIPv1Slide45

Default Route and RIPv1

Propagating the Default Route in

RIPv1

Default-information originate

command

This command is used to specify that the router is to originate default information, by propagating the static default route in RIP updateSlide46

SummaryRIP characteristics include:

Classful

, distance vector routing protocol

Metric is Hop Count

Does not support

VLSM

or

discontiguous

subnets

Updates every 30 seconds

Rip messages are encapsulated in a UDP segment with source and destination ports of 520 Slide47

Summary: Commands used by RIP

Command

Command’s purpose

Rtr(config)#router rip

Enables RIP routing process

Rtr

(

config

-router)#network …. …. …

…

Associates a network with a RIP routing process

Rtr#debug ip rip

used to view real time RIP routing updates

Rtr(config-router)#passive-interface fa0/0

Prevent RIP updates from going out an interface

Rtr(config-router)#default-information originate

Used by RIP to propagate default routes

Rtr#show ip protocols

Used to display timers used by RIPSlide48