Chpt4 Distance Vector Routing Protocols-2009-Good

7/27/2019 Chpt4 Distance Vector Routing Protocols-2009-Good

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ESMT RA

Distance VectorRouting Protocols

Routing Protocols and Concepts Chapter 4

.

E-mail: [email protected]

2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version 4.0


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Objectives Identif the characteristics of distance vector routin

protocols.

vector routing protocols using Routing InformationProtocol (RIP).

Describe the processes to maintain accurate routingtables used by distance vector routing protocols.

Identify the conditions leading to a routing loop and

explain the implications for router performance.

Recognize that distance vector routing protocols arein use today.

2 2007 Cisco Systems, Inc. All rights reserved. Cisco Public


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Distance Vector Routing Protocols Exam les of Distance Vector routin rotocols:

Routing Information Protocol (RIP)Interior Gateway Routing Protocol (IGRP)

Enhanced Interior Gateway Routing Protocol

(EIGRP)



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Distance Vector Routing Protocols -

Distance Vector

A router usin distance vector routin rotocolsknows 2 things:

Vector, or direction, traffic should be directed



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Distance Vector Routing Protocols Characteristics of Distance Vector routin

protocols:

Periodic updates

Neighbors

Broadcast updates

nt re rout ng ta e s nc u e w t rout ng up ate



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Distance Vector Routing Protocols Routin Protocol Al orithm:

Defined as a procedure for accomplishing a certain task



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Distance Vector Routing Protocols Routin Protocol Characteristics

Criteria used to compare routing protocols includes

Scalability

Resource usa e

Implementation & maintenance



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Distance Vector Routing Protocols



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Network Discovery Router initial start u Cold Starts

Init ial network discovery

in routing table



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Network Discovery Initial Exchan e of Routin Information

Ifa routing protocol is configured then:

Routers will exchange routing information

Router checks update for new informationIfthere is new information:

Metric is updated New information is stored in routing table



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Network Discovery Exchan e of Routin Information

Router convergence is reached when

All routing tables in the network contain the same networkn orma on

Routers continue to exchange routing information



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Network Discovery Conver ence must be reached before a network is

considered completely operable

interdependent categories

S eed of broadcastin routin information

Speed of calculating routes



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Routing Table Maintenance Periodic U dates: RIPv1 & RIPv2

These are time intervals in which a router sends out

its entire routin table



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Routing Table Maintenance RIP uses 4 timers

Update timer (30s)

Holddown timer (240s)

us mer (180s)



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Routing Table Maintenance Bounded U dates: EIGRP

EIRPG routing updates are:

Triggered by topology changes

Non periodic



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ou ng a e a n enance Triggered Updates

oConditions in which triggered updates are sent

Interface changes stateRoute becomes unreachable

Route is laced in routin table



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ou ng a e a n enance Random Jitter (Gigue alatoire)

Synchronized updates - a condition where multiple routers onmulti access LAN segments transmit routing updates at the

same time.

Problems with synchronized updates

Bandwidth consumption

Packet collisions Solution to problems with

Use of random variable

called RIP_JITTER



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Routing Loops Routin loo s are

A condition in

which a acket iscontinuously transmittedwithin a series of routers

destination.



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Routing Loops

Incorrectly configured static routes

Slow convergence

Routing loops can create the following issues:

Excess use of bandwidth

CPU resources may be strainedNetwork convergence is degraded

Routing updates may be lost or not processed in a timely


manner


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Problem: Count to Infinity

s s a rou ng oop w ere y pac e s ounce n n e yaround a network



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Routing Loops

.

Distance Vector routing protocols set a specified metric

Once a router counts to infinity it marks the route as unreachable



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ou ng oops .

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 routin u dates to ro a ate throu h

network with the most current information



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Routing Loops The 3. S lit Horizon Rule is used to revent routin loo s

Split Horizon rule:

which the update came



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Routing Loops 4. S lit horizon with

poison reverse

The rule states thatonce a router learns ofan unreachable route

,advertise it asunreachable backthrough the sameinterface



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Routing Loops 5. IP & TTL

Purpose of the TTL field

prevent packets from endlessly traveling on a network

How the TTL field works

TTL field contains a numeric value The numeric value is decreased b one b ever router on

the route to the destination

Ifnumeric value reaches 0 then Packet is discarded



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Routing Protocols Today

EIGRP include

Network size Compatibility between models of routers

Administrative knowledge



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Routing Protocols Today RIP

Features of RIP:

reverse

Easy to configure



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Routing Protocols Today EIGRP

Features of EIGRP:

EIGRP hello protocol used to establish neighboradjacencies

Supports VLSM & route summarization Use of topology table to maintain all routes

Classless distance vector routing protocol

Cisco proprietary protocol



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Summary Characteristics of Distance Vector routin rotocols

Periodic updates

RIP routing updates include the entire routing table

Neighbors are defined as routers that share a link and areconfigured to use the same protocol

The network discovery process for D.V. routingprotocol

Directly connected routes are placed in routing table 1s

If a routing protocol is configured then

Convergence is reached when all network routers have the



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Summary D.V. routin rotocols maintains routin tables b

RIP sending out periodic updates

RIP using 4 different timers to ensure information is accurateand convergence is achieved in a timely manner

EIGRP sending out triggered updates

D.V. routing protocols may be prone to routing loops routing loops are a condition in which packets continuously

Mechanisms used to minimize routing loops include defining

maximum hop count, holddown timers, split horizon, routepoisoning and triggered updates



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Summary Conditions that can lead to routin loo s include

Incorrectly configured static routes

Incorrectly configured route redistribution

Slow convergence

Incorrectly configured discard routes

How routing loops can impact network performanceincludes:

Excess use of bandwidth

CPU resources may be strained

Network convergence is degraded

Routing updates may be lost or not processed



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Summary Routin Information Protocol RIP

A distance vector protocol that has 2 versions

RIPv1 - a classful routing protocol

RIPv2 - a classless routing protocol

(EIGRP)A distance vector routing protocols that has some features of

link state routing protocols

A Cisco proprietary routing protocol



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Quest ions ?Quest ions ?



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Activities & Labs

PT 4.4.1: Routing Loops (A)

PT 4.7.1: Packet Tracer Skills Integration Challenge Activity (A)


Chpt4 Distance Vector Routing Protocols-2009-Good

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