8.the routing table

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2012 ccna.ro, Toate drepturile rezervate.

2012 ccna.ro, Toate drepturile rezervate. 1

Capitolul8:Tabeladerutare

(detaliere)

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Tabeladerutare (1) Organizareierarhic Rutelesuntstocatepenivele Conine:

adreselereelelordirectconectate rutestatice rutenvateprinprotocoalederutaredinamice

Tabeladerutarereprezintoorganizareierarhicarutelorprezentepeechipamentuldereealaunmomentdat.AceastaestesalvatnRAM,motivpentrucarese refaceautomat la fiecare repornirea ruterului.Pentrueficien,tabeladerutareestempritnrutedenivel1i2.Tabeladerutareconinemaimultetipuriderute:Reelele direct conectate: sunt adugate automat n tabel laconfigurareainterfeeiaferenteRutestatice:suntconfiguratemanualdectreadministratorivorfipreferatentotdeaunauneiruteobinuteprintrunprotocoldinamicRute nvate prin protocoale dinamice: sunt introduse automat ntabeladerutareulteriorconfigurriiprotocoluluirespectiviaprimiriiinformaiilor despre rute de la echipamentele vecine; cu ajutorul adiferiialgoritmi,updateurilederutaresuntpropagatentotdomeniulderutare.

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Tabeladerutare (2) Exemplu

Router#show ip route Codes: I - IGRP derived, R - RIP derived, O - OSPF derived, C - connected, S - static, E - EGP derived, B - BGP derived, * - candidate default route, IA - OSPF inter area route, i - IS-IS derived, ia - IS-IS, U - per-user static route, o - on-demand routing, M - mobile, P - periodic downloaded static route, D - EIGRP, EX - EIGRP external, E1 - OSPF external type 1 route, E2 - OSPF external type 2 route, N1 - OSPF NSSA external type 1 route, N2 - OSPF NSSA external type 2 route Gateway of last resort is 10.119.254.240 to network 10.140.0.0 O E2 10.130.0.0 [160/5] via 10.119.254.6, 0:00:59, Ethernet2 E 10.10.0.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2

172.110.0.0 is variably subnetted, 2 subnets, 2 masks C 172.110.232.32/28 is directly connected, Ethernet0 S 172.110.0.0/16 is directly connected, Ethernet0

Pentru a afia tabela de rutare a unui ruter, se folosete comandashow ip route. Iniial este prezentat o legend a acronimelorutilizate n afiarea rutelor, apoi un tabel cu detalii sumare privindrutelenvate.Tabelulcuprinde:Modul cum a fost nvat ruta respectiv: static (S), dinamic (semenioneazprotocolulutilizat:O OSPF,DEIGRP),directconectatAdresaIPareeleidestinaie(10.130.0.0)Distana administrativ mpreun cu metrica specificate ntreparantezedrepteAdresaIPnexthopTimpulpncndorutdevineinvalidInterfaadeieirepentrupachetultrimisspredestinaiarespectiv

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Tabeladerutare (3) Deitabelasuportattadresareclassfulcticlassless,structuraeiestebazatpeadresareaclassful

Ierarhizareatabeleiajutladeterminarearapidaciipecaresfietrimispachetul

Rutelesuntorganizatepedouniveluri

Pentru pstrarea compatibilitii vizuale, tabela de rutareimplementeaz o structur de tip classful, dar n acelai timp suntintegrate i rutelecare folosesc adresarea classless.Structuraclassfulpermite oierarhizare eficientarutelor, ceea ce duceladeterminarearapid a cii spre destinaie. Se remarc faptul c, dei parcurgereatabeleiderutaresefacesecvenial, ncepndcuprimarutexistent,n construcia tabelei inserarea unei noi rute se face naintea primeirute cu un prefix mai general dect aceasta. Astfel, informaiilereferitoare la reelelemai specifice se vor gsi naintea informaiilordesprereelelededimensiunimaimari.Rutele potficlasificatenfunciedenivelulacestoraastfel:Rutedenivel1 rutele cuomascde reeadeodimensiunemaimicsauegaldectceaclassfulaadreseirespectiveRutedenivel2rutecarereprezintsubreelealereelelorclassful

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Level1Routes Aumascadereeamaimicsauegalcumascaclassfulareelei Potfuncionaca:

DefaultRoute

SupernetRoute (mascadereeastrictmaimicdectmascaclassful)

NetworkRoute (mascadereeaegalcumascaclassful)C 192.168.2.0/22 is directly connected, Ethernet0

C 128.137.0.0/16 is directly connected, Ethernet0

S* 0.0.0.0 [1/0] via 192.168.1.2

Orutdenivel1aremascadereeamaimicsauegaldectmascade reeaa reeleiclassfuldin care faceparte, i la rnduleipoate fincadratnurmtoareletipuriderute:Rutdefault,care reprezinto rutstaticcuadresa0.0.0.0/0,sprecare vor fi trimise toate pachetele pentru care nu se cunoate odestinaiespecificSupernetRoute, rutacreiadresde reeaareomascmaimicdectreeauaclassfulNetworkRoute,rutcarearemascadereeaegalcumascareeleiclassful;aceastapoatefiiorutprinte,nmomentulncarentabelexist reele sau subreele care aparin aceluiai bloc de adrese IPclassful,darcuomascdereeamaispecificRutele de nivel 1 pot fi de tipul direct conectate, definite static saunvateprintrunprotocolderutaredinamic.

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UltimateRoutes Rutelecareinclud:

oadresnexthop i/sauointerfadeieire

PotfiattruteLevel1ctiruteLevel2 Exemplu

S* 192.168.2.0 [1/0] via 192.168.1.2is directly connected, FastEthernet1/0

Ultimate routes sunt acele rutele care includo adres IP nexthopi/sauointerfadeieire.Practicreprezintrutelepecareunpachetvafacematch naintedeafitrimisctredestinaie.ntructruteleLevel1iruteleLevel2potfidefiniteprintroadresIPnext hop sau o interfa de ieire, rutele ultimate pot aparineoricruiadintreceledouniveluri.Astfel,orutdetipultimatepoates aib masca de reea mai mic, egal sau mai mare dect cea areeleiclassfuldincare faceparte,darniciodatnuvaputeas fieorutprinte.n exemplul demai sus se poate observa o rut ultimate de nivel 1definitattprintrunIPnexthop ctiprintrointerfadeieire.

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Parent&ChildRoutes Parentroute

rutLevel1 nuconineoadresdestinaiesauointerfadeieireesteadugatautomat cndeste introdus n tabelo subreea auneireeleclassful(rutLevel2)

ChildrouterutLevel2reprezintosubreeaauneireeleclassful conineoadresdestinaiei/sauointerfadeieire

192.168.1.0/25 is subnetted, 2 subnets

Level2ChildRoutes

Level1ParentRouteS 192.168.1.0 [1/0] via 10.0.0.2S 192.168.1.128 [1/0] via 10.1.0.2

ncadrulrutelordenivel1i2sedistingruteledetipParentroute irutele de tip Child route. Astfel, rutele printe se ncadreaz ncategoria rutelor Level1 inu suntdefiniteprintroadres IP nexthop sauo interfade ieire.O rutprinteestecreatautomatdefiecaredatcndunnousubnetesteintrodusntabeladerutare.Rutacumascadereeamaimaredect rutaprintese ncadreaz n tipulChildroute.RuteleChildroute facpartedincategoriarutelornivel2 i reprezintunsubnetaluneiclasemajore.La felcai ncazulrutelordenivel1,acesteapot fi introduse n tabelade rutare ca rutedirect conectate,rutestaticesauprintrunprotocolderutaredinamic.Datoritfaptuluictabeladerutarefoloseteoadresareclassful,chiarincazulncareunsubnetinstalatntabelarecasursunprotocolde rutare classless, va fi introdusautomato rutprintedenivel1avndcaadresIPreeauamajorclassfularuteichild.

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Parent&ChildRoutes:Classful AdresareeleidinrutaParent esteadresaclaseimajore Masca de reea a rutei Parent estemasca pentru rutele saleChild

192.168.1.0 /25 is subnetted, 2 subnetsS 192.168.1.0 [1/0] via 10.0.0.2S 192.168.1.128 [1/0] via 10.0.0.2

Adresaclassful:192.168.1.0/24MascarutelorChild:/25

Modulde ierarhizarealrutelor ntabeladerutaredifer nfunciedetipuldeadresare,classfulsauclassless. ncazuladresriiclassful,rutaParent va indica vizual adresa clasei majore i masca de reea asubreelelor din care fac parte rutele Child. Masca de reeamenionat imediat ndreaptaadreseiclassfulesteafiatdoardacrutele Child au ataat aceeai masc de reea. De asemenea, noutputultabeleiderutarese indicpeaceeai liniecurutaprinteinumrul de rute Child existente pentru o anumit rut printe. ncazuldefa,2subnets.RuteleChild suntrutedenivel2isuntconsiderateruteUltimatentructconinoadresIPnexthopi/sauointerfadeieire.

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Parent&ChildRoutes:Classless AdresaimascareeleidinrutaParentcorespundclaseimajore Esteprecizatnumruldesubreeleinumruldemtifolosit Fiecaresubreeaspecificadresasubreeleiimasca

172.16.0.0/16 is variably subnetted, 3 subnets, 2 masksC 172.16.1.4/30 is directly connected, Serial0/0/0C 172.16.1.8/30 is directly connected, Serial0/0/1C 172.16.1.16/24 is directly connected, Serial0/1/0

ncazul ncareruteleChildaleuneiruteprinte folosescoschemdeadresareVLSM,adicaumascdereeadelungimevariabil,acestlucruesteindicatntabeladerutareprintextulisvariablysubneted,menionatcaoscurtdescrierearuteiprinte.Existctevadiferenemajoredeierarhizarencazulrutelorprinteichildce folosesco schemdeadresare classless spredeosebiredeceaclassful:Ruta printe are afiat n dreptul acesteiamasca de reea classfulproprieinuceaarutelorChildSunt menionate numrul de subreele (rute Child) i numrul demtidereeadiferiteutilizatedesubreelelerespectiveFiecarerutChildesteafiatmpreuncumascadereeaproprie

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Cutareantabeladerutare (Classful)

Da

Da

Da

Nu

Nu

Nu

Modulncareruteruldeterminceamaibunrutdestinaiepentruatrimitepacheteleestediferit n funciede tipulde cutare: classfulsauclassless.Astfel, ncazul rutriicucomportamentclassful, ruterulvacomparainiialadresaIPdestinaiecufiecarerutdenivel1pentruagsiopotrivire. ncazc rutagsitestede tipultimate,adicarespecificato interfade ieirei/sauoadres IPnexthop,aceastava fi folositpentru trimitereapachetului ctredestinaie.Dac rutagsitnuesteorutultimate,acestavafiorutprinteidecisevacutaopotrivirecuruteleChilddenivel2.Dacestedescoperitopotrivirecuoastfelderut,pachetulvafitrimismaideparte,iarncazcontrarpachetulvafiaruncat.Odat ce sa realizat o potrivire cu o rut printe, comportamentulclassfulnu vamaipermiteexistenauneialtepotriviri cuoalt rutprintesauorutdefault.

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Cutareantabeladerutare (Classless)Da

Da

Da

Nu

Nu

Nu

Da

Da

Nu

Nu

Odat cu implementarea conceptuluideVLSM i autilizrii adresriiclassless, limitrile comportamentului de rutare classful a dus lautilizarea pe o scar din ce n cemai larg a procesului classless delocalizareainformaiilorderutare.ncepndcuversiuneadeIOS11.3,datoritcreteriinpopularitateaschemeideadresareclassless,afostnecesarfolosireaprocesuluidecutareclasslessbydefault.Cutareaclasslessntabeladerutareesteidenticcuceaclassfulpnla momentul localizrii unei potriviri cu rutele child a unei ruteprinte. nmomentul n care nu este gsit nicio potrivire cu rutelechild, pachetul nu va fi aruncat (deosebire fa de comportamentulclassful),cisevacontinuacutareauneipotriviriprintrecelelalteruteSupernet denivel1.Pachetulva fiaruncatdoar ncazul ncarenuestegsitniciopotrivirecuorutSupernetsaunuesteconfiguratntabelorutimplicit.

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Classfulvs.Classless Activaremodclassless

(config)#ip classless esteimplicitpeversiuniledeIOS>=11.3

Activaremodclassful (config)#no ip classless

Comportamentulutilizatpentru localizarea informaiilordintabeladerutare poate fi modificat manual de ctre administrator. AnteriorversiuniideIOS11.3comportamentuldefault ncazulruterelorCiscoera classful. Acest lucru poate fi verificat prin afiarea fiierului deconfigurare,observnduseprezenacomenziino ip classless.IdeeainiialdelacareapornitimplementareaunuicomportamentderutareclassfuleraexistenaschemeideadresareIPmpritepeclase.Astfel, nainte ca Internetul s ajung la dimensiunile actuale,organizaiiledediferitedimensiuniprimeauadrese IPdoardincadrulcelor3clasedereelemajore:A,BsauC.Dinaceastcauz,realizareauneicutrinafaraspaiuluideadresealocaterainutil.Activarea procesului de rutare classless se face prin introducerea nmodul global de configurare a comenzii ip classless. Ulteriorversiunii de IOS 11.3, modul implicit de cutare este setat ca fiindclassless.

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Rezumat

Structuratabeleiderutare ComportamentClassful ComportamentClassless Cutareauneiadresedestinaientabeladerutare

1. Caresunttipurilederutecarepotexista ntrotabelderutare launmomentdat?

2. Careestemotivulpentrucaretrebuiereconstruittabeladerutarelafiecarepornireaunuiruter?

3. Cereprezintruteledenivel2?4. CruinivelpoateaparineorutUltimate ?5. n cazul rutarii cu comportament classful, este posibil trimiterea

unuipachetpeorutdefault?

8.the routing table

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