introduction to routing protocols · 2018-10-09 · eigrp • • • • •

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

1© 2000, Cisco Systems, Inc. 22041241_05_2000_c1


Introduction to RoutingProtocols


Session 2204Session 2204



AgendaAgenda

•• IP, IPX Addressing ConceptsIP, IPX Addressing Concepts

• Generic Routing Concepts

• Specific Routing Protocols

• Static and Defaults Routes


MAC AddressMAC Address

1234.5678.9ABC1234.5678.9ABC

0000.0c0000.0cXX.XXXXXX.XXXX

First 24 bits = Manufacture Code assigned by IEEE

XXXX.XXXXXX.XX00.000100.0001

Second 24 bits = Specific interface,assigned by Manufacture

FFFF.FFFF.FFFFFFFF.FFFF.FFFFAll F’s= Broadcast

48 Bit Hexadecimal (Base16) Unique Layer two address



32 Bits

NetworkNetwork HostHost

172 . 16 . 122 . 204

IP AddressingIP Addressing

8 Bits 8 Bits 8 Bits 8 Bits


IPAddress

IP Subnetting, Mask IP Subnetting, 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



IP Address ClassesIP Address Classes

11 00 00 00126126 255255 255255 254254

StartStartEndEnd

128128 00 00 00192192 255255 255255 254254

StartStartEndEnd

192192 00 00 00223223 255255 255255 254254

StartStartEndEnd

255255 00 00 00MaskMask

255255 255255 00 00MaskMask

255255 255255 255255 00MaskMask

Class A:

Class B:

Class C:Class D: for multicast


IP Address Mask FormatsIP Address Mask Formats

• bitcount ---172.16.31.6/24

• decimal ---- 172.16.31.6 255.255.255.0

• hexadecimal 172.16.31.6 0xFFFFFF00

The Router will display different Maskformats at different times.



UNIX Host AUNIX Host A

1111.1111.11111111.1111.1111

3333.3333.33333333.3333.3333

4444.4444.44444444.4444.4444

R1R1

R2R2

2222.2222.22222222.2222.2222

5555.5555.55555555.5555.5555

Finding the IP Addresson the LAN

Finding the IP Addresson the LAN

• ARP = Address ResolutionProtocol

• Host and routers have preassigned MAC addresses

• Host A sends a ARP request forrouter R1

• The ARP request is a broadcastpacket

• R1 replies with ARP responseunicast address

• Now both Host A and Router R1have the IP and MAC address foreach other in their ARP Table


UNIX HostUNIX HostUNIX HostUNIX Host

Street A Street H

How Do I Get there From Here?How Do I Get there From Here?

• Path choice is based on location

• Location is represented by an address



172. 16. 200.11255.255. 0. 0

172. 16.3.10255.255.0.0

172.16.12.12/16

IP: 172.16.2.1/16

10.1.1.1/8

10.250.8.11255. 0. 0. 0

10.180.30.118/8

IP: 10.6.24.2/8

E0 E1

172 .16 12 12

Network Host

.NetworkNetwork InterfaceInterface

172.16.0.0

10.0.0.0

172.16.0.0

10.0.0.0

E0

E1

E0

E1

Forwarding TableForwarding Table

Host AddressesHost Addresses

255.255255.255 0 . 00 . 0


172.16.2.11/24

172. 16. 2 . 2255.255.255.0

172.16.2.160/24

IP: 172.16.2.1/24

172.16. 3 . 5255.255.255.0

172.16.3.100/24

172.16.3.150/24

IP: 172.16.3.1/24

NetworkNetwork InterfaceInterface172.16.2.0

172.16.3.0

172.16.2.0

172.16.3.0

E0

E1

E0

E1


Subnet AddressingSubnet Addressing

Host

160172 .16

Network Subnet

2

E0 E1

255.255255.255 .255.255 .0.0



.6

.13

.9

.10.14

.5

A

C

B172.16172.16.40.1

255.255.255.0

172172.16.50.1255.255.255.0

172.16.60.1255.255.255.0

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

Routing Protocols will by DefaultSummarize Major Networks

Routing Protocols will by DefaultSummarize Major Networks


.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

172.16.1.X With a255.255.255.252 mask

Or /30 the 1 subnetmy be broken into 64

Subnets



80 Bits

NetworkNetwork NodeNode

32 Bits 48 Bits

000C 15C0 0077.0650.2328

IPX AddressingIPX Addressing

IPX Network #IPX Network # IPX STATION #IPX STATION #Usulay same a MAC addressUsulay same a MAC address


• 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



AgendaAgenda


• Generic Routing Concepts




ConvergenceConvergence

• Time required for router to identify anduse an alternate path

• Dependent on timer values and algorithm

• Difficult to predict precisely

AABB CC DD EE FF

A,B,CA,B,CD,E,FD,E,F




B,CB,CD,E,FD,E,F

B,CB,CD,E,FD,E,F

11

22

33

44 66

55

Router’s 5 and 6Router’s 5 and 6Have no knowledge of Have no knowledge of the new Network A Yetthe new Network A Yet



Load BalancingLoad Balancing

• Equal cost paths

• Rapid failover

N1

R1 R4R3

R2T1

T1T1

T1

N2


Load BalancingLoad Balancing

• Unequal cost load balancing: Eigrp

N1

R1 R4R3

R2

T1

512K

N2

768K256K



x

HolddownHolddown

• Sets minimum convergence time

• Prevents forwarding loops

I Will IgnoreRoutes to X

While inHolddown


Packets for Network X

Forwarding Loop:A Routing Disagreement

Forwarding Loop:A 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

“

”


C

BD

PVC

PVC

PVCS0


A

Frame Relay Multipoint Network

11

22

33

44

A

C

Router 2,3,4All advertise their Respective

Ethernets to Router D, Router Dknows all networks

B



A

C

BD

PVC

PVC

PVCS0


Frame Relay NetworkRouter 1

Advertises network D to routers 2,3,4

11

22

33

44Router 1Knows all networks but

Will only advertise D out of S0Because it learned A,B,C from S0


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


• Generic Routing Categories





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 RouterOne Forwarding Table per Network Protocol



• Directly connectedRoutes that the router is attached to

• StaticRoutes are manually defined

• DynamicRoutes protocol are learned from a Protocol

Building the Forwarding TableBuilding the Forwarding 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

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

• Each routing protocol offers features that can makeit desirable 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

• Routing InformationProtocol

• Widely available

• Hop count metric

• Periodic update

• Easy to implement

• One of the firstavailable

• RFC 1058

• Simple = limited

• Slow convergence

• No VLSM

• No discontiguoussubnets

• Max 15 Hops



Send RIP 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

S 10.1.1.1 D 255.255.255.255S 10.1.1.1 D 255.255.255.255

All Stations Have to Listen to Rip Broadcast’sAll Stations Have to Listen to Rip Broadcast’s



R1

R2

R3

T1

56k

T1

1 Hop

Path AHops

RIP MetricRIP Metric

Path B0 Hops


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

• Subnet mask support

• Reduce broadcast load

• Validated updates

• Multivendor environment



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

• Max 15 hops


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

• LoadR1

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 64 kbps

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


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

B..B.. 12..

12.. Z..Z..

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 UpdateAlgorithm (DUAL)Diffusing UpdateAlgorithm (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


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 Separatefrom the Forwarding Table

X’s Link State

Z’s Link StateQ’s Link State

Link State RoutingLink State Routing

• OSPF• IS-IS• NLSP

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 failureNew LSAs floodedAll routers recompute link state databases


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



BackboneRouter

BackboneRouter

OSPF Areas and RulesOSPF Areas and Rules

Area 1Area 4

Area 0

Area 2 Area 3

InternalRouterInternalRouter

AreaBorderRouter

AreaBorderRouter

AutonomousSystem (AS)

Border Router

AutonomousSystem (AS)

Border 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 10 bitswide

• 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 two levels are defined

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

http://developer.novell.com/research



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

• AS=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 DrivesBGP Requirements

Policy DrivesBGP 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


• Generic Routing Categories




Static RoutesStatic Routes

• Routes configured manually

• Useful when few or just oneroute exist

• Can be administrative burden

• Frequently used for default route



Administrative DistanceAdministrative Distance• The router treats different routing protocols with a different preference

Route SourceRoute Source Default DistanceDefault Distance

Connected InterfaceConnected InterfaceStatic RouteStatic RouteEnhanced IGRP Summary RouteEnhanced IGRP Summary RouteExternal BGPExternal BGPInternal Enhanced IGRPInternal Enhanced IGRPIGRPIGRPOSPFOSPFIS-ISIS-ISRIPRIPEGPEGPExternal Enhanced IGRPExternal Enhanced IGRPInternal BGPInternal BGPUnknown, Discard RouteUnknown, Discard Route

00115520209090100100110110115115120120140140170170200200255255


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 inforwarding 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:ISIS default originate

• IPX: ipx route default• default gateway is for “host mode”



172.16.1.0

172.16.0.0

s0 s1

Internet

Default IP SubnetDefault IP Subnet

• Two defaultsFor unknown networks

For unknown subnets

• Controlled by ip classless


Comparison of Routing ProtocolsComparison of Routing Protocols

LinkStateLinkState

TraditionalDistanceVector

TraditionalDistanceVector

AdvancedDistanceVector

AdvancedDistanceVector

Scalability

Bandwidth

Scalability

Bandwidth

Memory

CPU

Memory

CPU

Convergence

Configuration

Convergence

Configuration

Good

Low

Good

Low

Low

High

Low

High

Low

Low

Low

Low

High

High

High

High

Excellent

Low

Excellent

Low

Moderate

Low

Moderate

Low

Fast

Easy

Fast

Easy

Fast

Moderate

Fast

Moderate

Slow

Easy

Slow

Easy

PathVectorPath

Vector

Outstanding

Low

Outstanding

Low

High

Moderate

High

Moderate

Moderate

Hard

Moderate

Hard



NameName

RIPRIP

RIPv2RIPv2

IGRPIGRP

EIGRPEIGRP

OSPFOSPF

IS-ISIS-IS

BGPBGP

TypeType

DVDV

DVDV

DVDV

Adv DVAdv DV

LSLS

LSLS

Path VecPath Vec

ProprietaryProprietary

NoNo

NoNo

YesYes

YesYes

NoNo

NoNo

NoNo

FunctionFunction

InteriorInterior

InteriorInterior

InteriorInterior

InteriorInterior

InteriorInterior

InteriorInterior

ExteriorExterior

UpdatesUpdates

30 Sec30 Sec

30 Sec30 Sec

90 Sec90 Sec

TrigTrig

TrigTrig

TrigTrig

IncrIncr

MetricMetric

HopsHops

HopsHops

CompComp

CompComp

CostCost

CostCost

N/AN/A

VLSMVLSM

NoNo

YesYes

NoNo

YesYes

YesYes

YesYes

SummSumm

AutoAuto

AutoAuto

AutoAuto

BothBoth

ManMan

AutoAuto

AutoAuto

• IP routing protocols are characterized as

YesYes

Internet Routing ProtocolsInternet Routing Protocols


Topology/TechnologyConsiderations

Topology/TechnologyConsiderations

• 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…

•• EIGRP Network Design SolutionsEIGRP Network Design Solutionsby Ivan Pepelnjak,(ISBN: 1578701651)

•• 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)


For Further Reference…For Further Reference…

•• Routing in the InternetRouting in the Internetby Christian Huitema (ISBN: 0-13132-192-7)

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

•• ISP Survival Guide : Strategies for Running aISP Survival Guide : Strategies for Running aCompetitive ISPCompetitive ISPby Geoff Huston (ISBN:0-47131-499-4)

•• Internet Routing ArchitecturesInternet Routing Architecturesby Bassam Halabi (ISBN: 1-56205-652-2)



Thank You!Thank You!

• Related sessions:2208 Deploying IGRP/EIGRP

2205 Deploying OSPF

2209 Deploying BGP

2200 Advanced IP Routing



Session 2204Session 2204




Please Complete YourEvaluation Form

Session 2204



introduction to routing protocols · 2018-10-09 · eigrp • • • • •

Documents