Introduction to Routing · Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in...

Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr 1

13010947_05F9_c2 © 1999, Cisco Systems, Inc.

2© 1999, Cisco Systems, Inc. 3010947_05F9_c2

Introduction to RoutingIntroduction to Routing

Session 301Session 301



AgendaAgenda

•• AddressingAddressing

• Concepts

• Routing Protocols

• Statics and Defaults


Routing Information Routing Information Protocol (RIP and RIPv2)Protocol (RIP and RIPv2)

Interior Gateway RoutingInterior Gateway RoutingProtocol (IGRP)Protocol (IGRP)

Open Shortest Path First Open Shortest Path First (OSPF) Protocol(OSPF) Protocol

NetWare Link ServicesNetWare Link ServicesProtocol (NLSP)Protocol (NLSP)

Intermediate System to Intermediate System to Intermediate System (IS-IS)Intermediate System (IS-IS)

Enhanced IGRP (EIGRP)Enhanced IGRP (EIGRP)

Border Gateway Protocol (BGP)Border Gateway Protocol (BGP)

Physical LayerPhysical Layer

Network LayerNetwork Layer

TransportTransport

SessionSession

PresentationPresentation

ApplicationApplication

Data Link ControlData Link Control

L1L2L3L4L5L6L7

ISO—OSI Reference ModelISO—OSI Reference Model



Router FunctionsRouter Functions

• Routing = buildingmaps and givingdirections

• Switching =moving packetsbetween interfaces

• Routers are packetswitches

• Path determinationis overhead


UNIX HostUNIX HostUNIX HostUNIX Host

Company A Company B

InternetTCP/IP

Introduction to IP AddressesIntroduction to IP Addresses

• Unique addressing allows communicationbetween end stations

• Path choice is based on location

• Location is represented by an address



32 Bits

NetworkNetwork HostHost

172 . 16 . 122 . 204

IP AddressingIP Addressing

8 Bits 8 Bits 8 Bits 8 Bits


• Class A:

• Class B:

• Class C:

• Class D: for multicast

N = Network number assigned by NICH = Host number assigned by network administrator

NN HH HH HH

IP Address ClassesIP Address Classes

NN NN HH HH

NN NN NN HH



172.16.200.11

172.16.3.10

172.16.12.12

IP: 172.16.2.1

10.1.1.1

10.250.8.11

10.180.30.118

IP: 10.6.24.2

E0 E1

172 .16 12 12

Network Host

. . NetworkNetwork InterfaceInterface172.16.0.0172.16.0.0

10.0.0.010.0.0.0

E0E0

E1E1

Routing TableRouting Table

Host AddressesHost Addresses


172.16.2.11

172.16.2.2

172.16.2.160

IP: 172.16.2.1

172.16.3.5

172.16.3.100

172.16.3.150

IP: 172.16.3.1

NetworkNetwork InterfaceInterface172.16.2.0172.16.2.0

172.16.3.0172.16.3.0

E0E0

E1E1


Subnet AddressingSubnet Addressing

Host.160172 .16

Network Subnet.2

E0 E1



IPAddress

Subnet MaskSubnet Mask

172172 1616 00 00

DefaultSubnet

Mask

Network Host

255255 255255 00 00

Use Host Bits, Starting at the High Order Bit Position

8-bitSubnet

Mask

Network Subnet Host

255255 255255 255255 00

Network Host


.6

.13

.9

.10.14

.5

A

C

B172.16172.16.40.1

255.255.255.0

172172.16.50.1255.255.255.0

172.16172.16.60.1255.255.255.0

192.168.1.8255.255.255.252

192.168.1.4255.255.255.252

192.168.1.12255.255.255.252

Where Is 172.16.0.0?

Discontiguous IP SubnetDiscontiguous IP Subnet



.6

.13

.9

.10.14

.5

A

C

B172.16.40.1

255.255.255.0

172.16.50.1255.255.255.0

172.16.60.1255.255.255.0

172.16.1.8255.255.255.252

172.16.1.4255.255.255.252

172.16.1.12255.255.255.252

Variable Length Subnet MaskVariable Length Subnet Mask

• Conserve IP addresses


80 Bits

NetworkNetwork NodeNode

32 Bits 48 Bits

000C 15C0 0077.0650.2328

IPX AddressingIPX Addressing



• Assigns an address and subnet mask

• Starts IP processing on an interface

• Assigns a network number

• Starts IPX processing on an interface

• Must have ipx routing configured

Address ConfigurationAddress Configuration

Router (config-if) #

ip address ip-address subnet-maskip address ip-address subnet-mask

ipx network network ipx network network


131.108.48.0 /24131.108.48.0 /24

131.108.49.0 /24131.108.49.0 /24

131.108.50.0 /24131.108.50.0 /24

131.108.51.0 /24131.108.51.0 /24

131.108.52.0 /24131.108.52.0 /24

131.108.53.0 /24131.108.53.0 /24

131.108.54.0 /24131.108.54.0 /24

131.108.55.0 /24131.108.55.0 /24

Classless Prefix NotationClassless Prefix Notation

• 131.108.0.0/16 versus 255.255.0.0

• Summarizable blocks of subnets131.108.48.0 /21131.108.48.0 /21



Router (config) #

IP Address ConfigurationIP Address Configuration

• Sets format of network mask as seen in showshowcommands

• bitcount 172.16.31.6/24

• decimal 172.16.31.6 255.255.255.0

• hexadecimal 172.16.31.6 0xFFFFFF00

ip netmask-format{bitcount | decimal | hexadecimal}

ip netmask-format{bitcount | decimal | hexadecimal}


AgendaAgenda

• Addressing

•• ConceptsConcepts





x

ConvergenceConvergence

• Time required for router to identify anduse an alternate path

• Dependent on timer values and algorithm

• Difficult to predict precisely


Load BalancingLoad Balancing

• Equal cost paths

• Rapid failover

N1

R1 R4R3

R2T1

T1T1

T1

N2



Load BalancingLoad Balancing

• Unequal cost paths

N1

R1 R4R3

R2

T1

512K

N2

768K


x

HolddownHolddown

• Sets minimum convergence time

• Prevents routing loops

I Will IgnoreI Will IgnoreRoutes to XRoutes to X

While inWhile inHolddownHolddown



Packets for Network X

Routing Loop:Routing Loop:A Routing DisagreementA Routing Disagreement

• Packets do not get to the destination

• Temporary traffic surge until convergence


Do not send routing databack in the direction from

which it came

Split HorizonSplit Horizon

“

”



A

C

BD

PVC

PVC

PVCS0

DD 11


Frame Relay Network


C

BD

PVC

PVC

PVCS0

Turn off Split HorizonTurn off Split Horizon

DD 11

CC 22

BB 22

AA 22DD 22

CC 22

BB 22

AA 1,31,3

A

Frame Relay Network




A

C

BD

PVC

PVC

PVCS0.3

S0.1

Frame Relay Network

DD 11

CC 22

BB 22

DD 11

BB 22

AA 22


Metrics (Cost)Metrics (Cost)

• Numeric value used to chooseamong paths

• RIP/RIPv2 is hop count and ticks (IPX)

• OSPF/ISIS is interface cost (bandwidth)

• (E)IGRP is compound

• BGP can be complicated

• Path determination depends on metric



AgendaAgenda

• Addressing

• Concepts

•• Routing ProtocolsRouting Protocols




198.113.181.0198.113.181.0 [170/304793][170/304793]192.150.42.177192.150.42.177 02:03:5002:03:50 DD

198.113.178.0198.113.178.0

192.168.96.0192.168.96.0

192.168.97.0192.168.97.0

[110/9936][110/9936]192.150.42.177192.150.42.177 02:03:5002:03:50 OO

192.150.42.177192.150.42.177 00:00:2000:00:20 RR

CC

[120/3][120/3]

Ethernet0Ethernet0

Ethernet0Ethernet0

Ethernet0Ethernet0

Ethernet0Ethernet0

AgeAge SourceSourceNetwork #Network # InterfaceInterface Next HopNext Hop MetricMetric

One Forwarding Table Per Protocol (IP, IPX)



• Hardware state

• DynamicRoutes are learned from a protocol

• StaticRoutes are manually defined

Building the Routing TableBuilding the Routing Table


I Know About:Network XNetwork YNetwork Z

I Know About:Network ANetwork BNetwork CA

B

C

X

Y

Z

Routing Update

Exchanges Network Knowledge

Routing ProtocolsRouting Protocols

• Routers are packet switches that forward trafficbased on layer 3 logical addresses

• Routing protocol updates are exchanged by routersto learn about paths to other logical networks

• Each routing protocol offers features that can make itdesirable as part of an internetwork design



Routing Protocol GoalsRouting Protocol Goals

• Optimal path selection

• Loop-free routing

• Fast convergence

• Limited designadministration

• Minimize update traffic

• Handle address limitations

• Support hierarchicaltopology

• Incorporate rapidconvergence

• Easy to configure

• Adapts to changeseasily and quickly

• Does not create a lotof traffic

• Scales to a large size

• Compatible with existinghosts and routers

• Supports variable lengthsubnet masks anddiscontiguous subnets

• Supports policy routing


IP RIPIP RIP

• RoutingInformationProtocol

• Widely available

• Hop count metric

• Periodic update

• Easy to implement

• Usually free

• RFC 1058

• Simple = limited

• Slow convergence

• No VLSM

• No discontiguoussubnets

• Routing loops

• Count to infinity



Send Routing Table to Neighbors

Net A

Net B Net C

Net D

E0S0 S1 S0E0

R1 R2 R3

RIP—Distance VectorRIP—Distance Vector

AA E0E0BB S0S0

S0S0DDS0S0CC

NetworkNetwork InterfaceInterfaceBB S0S0CC S1S1

S1S1DDS0S0AA

NetworkNetwork InterfaceInterfaceCC S0S0DD E0E0

S0S0AAS0S0BB

NetworkNetwork InterfaceInterface

S0


RIP V1

Broadcast Routing UpdatesBroadcast Routing Updates



R1

R2

R3

T1

56k

T1

0 Hops

1 Hop

Path A

Path B

Hops

RIP MetricRIP Metric


When to Use RIPWhen to Use RIP

• Implementation in a few hours

• Good for stable links

• Good for small networks

• routed in host environment

• Multivendor environment

• Non-redundant network



RIP V2RIP V2

• RFC 1723• Cisco IOS® 11.1 support• Advertises masks• Variable length subnet masks• Route summarization• Routing updates use multicast• Authenticated updates using MD5


Multicast Routing UpdatesMulticast Routing Updates

RIP V2



When to Use RIPv2When to Use RIPv2

• Same as RIP

• Subnet mask support

• Reduce broadcast load

• Validated updates

• Multivendor environment

• Non-redundant network


IPX RIPIPX RIP

• Widely available

• Hop count metric

• Ticks (1/18 sec)

• Periodic update

• Easy to implement

• Free on servers

• Tied to SAPprotocol

• Simple = limited

• Slow convergence

• No default route

• Routing loops

• Count to infinity



IPX RIP—TicksIPX RIP—Ticks

• Ticks are usedto determineserver timeout

• Default for LANinterfaces is 1

• Default for WANinterfaces is 4

• IPXWANcalculates forits interfaces

• can be set viathe ipx delaynumber interfacesub command


IGRPIGRP

• Interior GatewayRouting Protocol

• Cisco developed

• Distance vector

• Compoundmetric

• Cisco IOS 9.21

• Periodic update

• No VLSM

• Default timersproduce slowconvergence



• Administrativeweight

• Delay

• Bandwidth

• Reliability

• Load R1

R2

R3

T1

56k

T1

(K2 * BW) (256-load)

K5 (reliability + K4))

= ((K1 * BW + + K3* delay)) *

IGRP Compound MetricIGRP Compound Metric


Delay Metric-Based on

D1 + D2 + D3

BandwidthMetric-Based

on 64kbps

D1 D2 D3

1.5 Mbps 64 kbps 1.5 Mbps

How the IGRP Metrics WorkHow the IGRP Metrics Work

• Bandwidth dominates short paths

• Delay dominates long paths

• Configure bandwidth on all interfaces



When to Use IGRPWhen to Use IGRP

• Simplicity of RIP

• Good for small and medium networks

• When metrics are important

• Reduced routing overhead


Enhanced IGRPEnhanced IGRP

• Extremely fastconvergence

• VLSM support

• Discontiguoussubnets

• Arbitrary routesummarization

• Supports prefix andhost routing

• Best of DV and LS

• Low overhead

• Guaranteedloop-free

• Reliable, incrementalupdate-based

• Multiprotocol:IP, IPX®, AppleTalk

• Easy to configure



Topology Table

On Startup Routing TablesAre Exchanged; Routing

Table Built Based on BestPaths from Topology Table

X’s Table

Y’s Table

Advanced Distance VectorAdvanced Distance Vector

• Construct neighbor tables• Construct topology tables• Compute routes

AABBCC

1113132020

AABBCC

553333

AABBCC

QQZZXX

2213131313

AA 27271155

ZZQQXX

BB.... 1212.... ZZ....

AABBCC

272712123535ZZ

XX

YYQQ


EIGRP TablesEIGRP Tables

• Topology table

• Acted upon by DUAL

• All routes advertisedby neighbors

• List of neighbors foreach route

• Routes passiveor active

• Neighbor table

• Keeps adjacentneighbor’s address

• Keeps the hold time

• Information forreliable transport



Diffusing UpdateDiffusing UpdateAlgorithm (DUAL)Algorithm (DUAL)

• DUAL is a loop-free routing algorithmthat performs a diffused computationof a routing table

Uses a new routing algorithm

Achieves fast convergence

Network changes propagate only to affectednodes (“bounded updates”)

• No need for route holddown

• Researched and developed by SRIInternational


IPX EIGRPIPX EIGRP

• Automatic redistribution of routesinto RIP/SAP

• Maximum network size is 224 hopsvs 15 for RIP

• Incremental SAPs sent, reducingbandwidth usage

• All other benefits of EIGRP



When to Use EIGRPWhen to Use EIGRP

• Very large, complex networks

• VLSM

• For fast convergence

• Little network design

• Multiprotocol support


Topology Information IsKept in a Database Separate

from the Routing Table

X’s Link State

Z’s Link StateQ’s Link State

Link State RoutingLink State Routing

• OSPF• IS-IS• NLSP• DECnet V

ZZ

XX

QQ

AABBCC

QQZZXX

2213131313YY



Link State RoutingLink State Routing

• Neighbor discovery• Constructing an LSA (Link State

Advertisement)• Distribute LSA• Compute routes using SPF

(Shortest Path First)• On network failure

New LSAs flooded

All routers recompute routing tables


OSPFOSPF

• Open ShortestPath First

• Link state or SPFtechnology

• Developed by OSPFworking group ofIETF (RFC 1253)

• Designed expresslyfor TCP/IP Internetenvironment


• Variable-lengthsubnet masks

• Discontiguoussubnets

• No periodic updates

• Route authentication

• Delivered two yearsafter IGRP



BackboneBackboneRouterRouter

OSPF Areas and RulesOSPF Areas and Rules

Area 1Area 4

Area 0

Area 2 Area 3

InternalInternalRouterRouter

AreaAreaBorderBorderRouterRouter

AutonomousAutonomousSystem (AS)System (AS)

Border RouterBorder Router

Internet

• Backbone area (0)must be present

• All other areasmust haveconnectionto backbone

• Backbone mustbe contiguous

• Do not partitionarea (0)


When to Use OSPFWhen to Use OSPF

• Large hierarchical networks

• Complex networks, except…Topology restrictive

Additional network design

• VLSM


• Multivendor



IS-ISIS-IS

• IS = IntermediateSystem

• Dual IS-IS

• Integrated IS-IS

• Metric is 6 bitswide (1-63)*

• All interfacesdefault to 10

• ISO 10589

• Two types of areas:Level-1 other areas

Level-2 backbone

• Default foreach level

• Much like OSPF


NetWare Link Services ProtocolNetWare Link Services Protocol

• Derived from ISIS

• NLSP specs 3 levels of routers

• Only 2 levels are defined

• Spec is Novell NLSP version 1.1http://developer.novell.com

/devres/langrp/specs/nlspspec.exe

http://www.novell.com/documentation

/en/kayak/nw411com/ipxrtenu/docmodul/ch3.html



BGPBGP

• RFC 1771

• Border GatewayProtocol

• Version 4 is current

• Exterior routingprotocol (vs.interior)

• Uses TCP fortransport

• Many options forpolicy enforcement

• Classless InterDomain Routing(CIDR)

• Widely used forInternet backbone

• Autonomoussystems


EE

AS 100 AS 101

AS 102

Peering

BGP BasicsBGP Basics

• Runs over TCP

• Path vectorprotocol

• Incremental update

CCAA

BB DD

EE



• BGP peer within the same AS• Not required to be directly connected• IBGP neighbors should be fully meshed• Few BGP speakers in corporate network

AS 100

Internal BGP (IBGP) PeeringInternal BGP (IBGP) Peering

BB

DD

AA

EE


AS 100 AS 101

External BGP (EBGP) PeeringExternal BGP (EBGP) Peering

• Between BGP speakers in different AS

• Should be directly connected

• Don’t run an IGP between EBGP peers

AA

BB

CC



BGP

BGP

BGP

StaticRoute

AS 100

AS 200

AS 400

AS 300

Policy DrivesPolicy DrivesBGP RequirementsBGP Requirements

• Policy for AS 100: Always use AS 300path to reach AS 400


B

Static

Advertise DefaultNetwork Via IGP Use a Static Route to

Provide Connectivity

NetworkNumber

ISP Runs BGP

When Not to Use BGPWhen Not to Use BGP

• Avoid BGP configuration by usingdefault networks and static routes

Appropriate when the local policy is thesame as the ISP policy

AA BB

CC



AgendaAgenda

• Addressing

• Concepts


•• StaticsStatics and Defaults and Defaults


Static RoutesStatic Routes

• Routes configured manually

• Useful when few or just oneroute exist

• Can be administrative burden

• Frequently used for default route



172.16.3.13

172.16.1.0C15C0

172.16.3.23

T1

ISDN

Floating Static RoutesFloating Static Routes

• A static route with a high distancedistance• Can be overridden by dynamic info

ip route 172.16.1.0 255.255.255.0 172.16.3.1 140140

ipx route C15C0 3.0000.0c15.3628 floating-static


Default RoutesDefault Routes

• Route used if no match is found inrouting table

• Can be carried by routing protocols• Two models

Special network number:0.0.0.0 (IP)-2 (IPX)

Flagged in routing protocol

• Protocols support multiple models



Creating a Default RouteCreating a Default Route

• RIP, RIPv2: network 0.0.0.0

• IGRP, EIGRP: ip default-network

• OSPF: default originate

• IPX: ipx route default

• default gateway is for “host mode”


172.16.1.0

172.16.0.0

s0 s1

Internet

Default IPDefault IP Subnet Subnet

• Two defaultsFor unknown networks

For unknown subnets

• Controlled by ip classless



Comparison of Routing ProtocolsComparison of Routing Protocols

LinkStateLinkLinkStateState

TraditionalTraditionalDistanceDistanceVectorVector

AdvancedAdvancedDistanceDistanceVectorVector

ScalabilityScalability

BandwidthBandwidth

MemoryMemory

CPUCPU

ConvergenceConvergence

ConfigurationConfiguration

GoodGood

LowLow

LowLow

HighHigh

LowLow

LowLow

HighHigh

HighHigh

ExcellentExcellent

LowLow

ModerateModerate

LowLow

FastFast

EasyEasy

FastFast

ModerateModerate

SlowSlow

EasyEasy


NameName TypeType ProprietaryProprietary FunctionFunction UpdatesUpdates MetricMetric VLSMVLSM SummSumm

RIPRIP

RIPv2RIPv2

IGRPIGRP

EIGRPEIGRP

OSPFOSPF

IS-ISIS-IS

BGPBGP

DVDV

DVDV

DVDV

Adv DVAdv DV

LSLS

LSLS

DVDV

NoNo

NoNo

YesYes

YesYes

NoNo

NoNo

NoNo

InteriorInterior

InteriorInterior

InteriorInterior

InteriorInterior

InteriorInterior

Int/ExtInt/Ext

ExteriorExterior

30 Sec30 Sec

30 Sec30 Sec

90 Sec90 Sec

TrigTrig

TrigTrig

TrigTrig

TrigTrig

HopsHops

HopsHops

CompComp

CompComp

CostCost

CostCost

N/AN/A

NoNo

YesYes

NoNo

YesYes

YesYes

YesYes

N/AN/A

AutoAuto

AutoAuto

AutoAuto

BothBoth

ManMan

AutoAuto

ManMan

Internet Routing ProtocolsInternet Routing Protocols

• IP routing protocols arecharacterized as



Topology/TechnologyTopology/TechnologyConsiderationsConsiderations

• Routing and services overhead is usuallynot a big deal when you have a lot ofbandwidth (i.e. LANs)

• Protect WAN bandwidth using update-basedprotocols—more bandwidth and buffers forapplication traffic

• High densities of sub(interfaces) can cause“hot spots” and router CPU overload

• NBMA (Non-Broadcast Multi-Access)technologies always require gooddesign practices


For Further Reference…For Further Reference…

•• Computer Networks, Third EditionComputer Networks, Third Editionby Andrew Tanenbaum (ISBN: 0-13349-945-6)

•• Interconnections : Bridges and RoutersInterconnections : Bridges and Routersby Radia Perlman (ISBN: 0-20156-332-0)

•• Internetworking with TCP / IP, Volume 1:Internetworking with TCP / IP, Volume 1:Principles, Protocols, and ArchitecturePrinciples, Protocols, and Architectureby Douglas Comer (ISBN: 0-13216-987-8)

•• IP Routing FundamentalsIP Routing Fundamentalsby Mark Sportack (ISBN: 1-57870-071-x)

•• IP Routing PrimerIP Routing Primerby Robert Wright (ISBN: 1-57870-108-2)

•• OSPF Network Design SolutionsOSPF Network Design Solutionsby Thomas, Thomas M. (ISBN: 1-57870-046-9)



Thank You!Thank You!

• Please fill out the survey• This was #301 Introduction

to Routing• Related sessions:

304 Intro to IP Switching307 Deploying IGRP/EIGRP308 Deploying OSPF/NLSP/IS-IS

309 Deploying BGP

Introduction to Routing

Session 301


Introduction to Routing · Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in...

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Transcript of Introduction to Routing · Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in...