Dynamic routing

Briefintroduction

Dynamicroutingisaconceptoppositetostaticrouting.Itmeansthatrouterscanautomaticallyestablishtheirownroutingtablebasedonthespecificroutinginformationexchangedbetweenrouters,andcanbebasedonChangesinlinksandnodesareautomaticallyadjustedinatimelymanner.Whenanodeorlinkbetweennodesinthenetworkfails,orthereareotheravailableroutes,dynamicroutingcanselectthebestavailableroutebyitselfandcontinueforwardingpackets.

Principle

Theoperationofthedynamicroutingmechanismreliesontwobasicfunctionsofrouters:timelyroutinginformationexchangebetweenrouters,andmaintenanceofroutingtables:

1.Theroutersexchangeroutinginformationinatimelymanner.

Thereasonwhydynamicroutingcanautomaticallycalculateroutesandselectforwardingpathsbasedonnetworkconditionsisthatwhenthenetworkchanges,theroutinginformationexchangedbetweenrouterswillinformeachotherofthischangeinthenetwork.Informationdiffusionenablesallrouterstobeawareofnetworkchanges.

2.Therouterprocessesthecollectedroutinginformationintoaroutingtableaccordingtoacertainroutingalgorithm(differentdynamicroutingprotocolalgorithmsaredifferent)fortheroutertoconsultwhenforwardingIPpackets.

Whenthenetworkchanges,afterthelatestroutinginformationiscollected,theroutingalgorithmisrecalculated,sothatthelatestroutingtablecanbeobtained.

Itshouldbenotedthattheprocessandprinciplesofroutinginformationexchangebetweenroutersindifferentroutingprotocolsaredifferent.Theultimategoalofexchangingroutinginformationistofinda"best"pathforforwardingIPpacketsthroughtheroutingtable.Eachroutingalgorithmhasitsownsetofprinciplesformeasuringthe"best",mostofwhicharecalculatedonthebasisofintegratingmultiplecharacteristics.Thesecharacteristicsinclude:thenumberofrouternodes(hopcount)includedinthepath,andthenetworktransmissioncost(Cost),bandwidth(bandwidth),delay(delay),load(load),reliability(reliability)andmaximumtransmissionunitMTU(maximumtransmissionunit).

Commondynamicroutingprotocolsare:RIP,OSPF,IS-IS,BGP,IGRP/EIGRP.Theworkingmethodsandroutingprinciplesofeachroutingprotocolaredifferent.

Commondynamicroutingprotocols

Thecommondynamicroutingprotocolsareasfollows:

RIP

RoutingInformationProtocol(RIP)YesThefirstwidelyusedprotocolamongtheinteriorgatewayprotocolIGP.RIPisadistributedroutingprotocolbasedondistancevectorandthestandardprotocoloftheInternet.Itsgreatestadvantageissimpleimplementationandlowoverhead.

OSPF

OSPF(OpenShortestPathFirst)isanInteriorGatewayProtocol(InteriorGatewayProtocol,referredtoasIGP),usedinasingleautonomoussystem(autonomoussystem).,AS)decision-makingrouting.

IS-IS

IS-IS(IntermediateSystem-to-IntermediateSystem)routingprotocolwasoriginallyISO(theInternationalOrganizationforStandardization))AdynamicroutingprotocoldesignedforCLNP(ConnectionLessNetworkProtocol).

BGP

BorderGatewayProtocol(BGP)isanautonomoussystemroutingprotocolrunningonTCP.BGPistheonlyprotocolusedtohandlenetworksthesizeoftheInternet,anditisalsotheonlyprotocolthatcanproperlyhandlemultipleconnectionsbetweenunrelatedroutingdomains.

Features

1.Nomanualmaintenancebytheadministratorisrequired,whichreducestheworkloadoftheadministrator.

2,Occupiesnetworkbandwidth.

3.Runaroutingprotocolontheroutersothattheroutercanautomaticallyadjustroutingentriesaccordingtochangesinthenetworktopology;

4.Networkswithlargenetworkscaleandcomplextopology

Dynamicroutingconfigurationexample

Setthecomputer’sIP

[root#PCAroot]#ifconfigeth010.65.1.1netmask255.255.0.0[root#PCBroot]#ifconfigeth010.66.1.1netmask255.255.0.0

[root#PCCroot]#ifconfigeth010.69.1.1netmask255.255.0.0

[root#PCDroot]#ifconfigeth010.70.1.1netmask255.255.0.0

[root#PCAroot]#routeadddefaultgw10.65.1.2

[root#PCBroot]#routeadddefaultgw10.66.1.2

[root#PCCroot]#routeadddefaultgw10.69.1.2

[root#PCDroot]#routeadddefaultgw10.70.1.2

SetrouterIPAddress

RouterA(config)intf0/0

RouterA(config-if)#ipaddress10.65.1.2255.255.0.0

RouterA(config-if)#noshutdown

RouterA(config-if)#intf0/1

RouterA(config-if)#ipaddress10.66.1.2255.255.0.0

RouterA(config-if)#noshutdown

RouterA(config-if)#ints0/1

RouterA(config-if)#ipaddress10.68.1.2255.255.0.0

RouterA(config-if)#noshutdown

RouterA(config-if)#clockrate64000

RouterA(config-if)#exit

RouterA(config)#iprouting

RouterA(config)#routerrip

RouterA(config-router)#networkall

RouterA(config-router)#end

RouterA#

RouterCconfig)ints0/0

RouterC(config-if)#ipaddress10.68.1.1255.255.0.0

RouterC(config-if)#noshutdown

RouterC(config-if)#ints0/1

RouterC(config-if)#ipaddress10.78.1.1255.255.0.0

RouterC(config-if)#noshutdown

RouterC(config-if)#clockrate64000

RouterC(config-if)#exit

RouterC(config)#iprouting

RouterC(config)#routerrip

RouterC(config-router)#networkall

RouterC(config-router)#end

RouterC#

RouterB(config)intf0/0

RouterB(config-if)#ipaddress10.69.1.2255.255.0.0

RouterB(config-if)#noshutdown

RouterB(config-if)#intf0/1

RouterB(config-if)#ipaddress10.70.1.2255.255.0.0

RouterB(config-if)#noshutdown

RouterB(config-if)#ints0/0

RouterB(config-if)#ipaddress10.78.1.2255.255.0.0

RouterB(config-if)#noshutdown

RouterB(config-if)#exit

RouterB(config)#iprouting

RouterB(config)#routerrip

RouterB(config-router)#networkall

RouterB(config-router)#end

RouterB#

RouterA#shiproute

RouterC#shiproute

RouterB#shiproute

Didyouseethedynamicroutingtable?Ifyoucanseeit,payattentiontothedestinationnetworkandnexthopaddress.Ifyoucan’tseeit,pleasecheckwhethertheroutedinterfaceisactivatedandwhetherthenetworksettingincludesthespecifiednetwork.Iftheroutingtableiscorrect,

PleasetesttheconnectivitytoeachpointfromthecomputerPCA.

Testnetworkconnectivity

[root@PCAroot]#ping10.65.1.2(通)

[root@PCAroot]#ping10.66.1.1(通)

[root@PCAroot]#ping10.66.1.2(通)

[root@PCAroot]#ping10.68.1.1(通)

[root@PCAroot]#ping10.68.1.2(通)

[root@PCAroot]#ping10.78.1.1(通)

[root@PCAroot]#ping10.78.1.2(通)

[root@PCAroot]#ping10.69.1.1(通)

[root@PCAroot]#ping10.69.1.2(通)

[root@PCAroot]#ping10.70.1.1(通)

[root@PCAroot]#ping10.70.1.2(通)

offOpenaroutingrouterconnection,orexecutenoiprouting,orexecuteshutdowonaninterface,andthenusetheshiprocommandtoviewtheroutingtable.

SettherouterrouterAs0/0ip:10.67.1.2,routerBs0/1ip:10.67.1.1,andthen

connectthesetwopoints,andusetheshiprocommandtoviewtherouteTable,payattentiontothechangeofthenexthopIPaddressandthenumberofhops.

Youcanalsoaddanotherrouter.Aftersettingitup,checktheworkingconditionbylookingattheroutingtable.