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Un router realizeaza 2 operatii:

1. Packet forwarding trimite pachete de la o

interfata la alta

2. Descopera si implementeaza rute ->tabelade routare ?

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Exista doua modalitati de routare:

Static Routing

Dynamic Routing: - protocoale de routare

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Un sistem autonom: ( autonomous system AS este o regiune din internet care este

administrata de o singura entitate.

Exista doua tipuri de routare: Intra-domain routing

Interd-omain routing.

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Intradomain Routing

Routare in acelasi AS

Ignora reteaua din afara AS-ului

Protocoale: Interior Gateway

Protocols or IGPs

Cele mai cunoscute:

RIP (simplu si batran)

OSPF (mai bun )

Interdomain Routing

Routare intre AS-uri Presupune ca internetul estealcatuit dintr-o colectie de AS-uriInterconectate.

Exista un router in fiecare AScare routeaza traficul intredomenii. Protocoale: Exterior GatewayProtocols or EGPs

Cele mai cunoscute:EGPBGP (recent)

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Un algoritm de routare reprezinta:

O procedura de trimitere si primire de informatiidespre retelele invecinate catre alte routere.

O procedura pentru calcularea routelor optime. Rutele sunt calculate pe principul drumului cel mai scurt.

Trebuie identificata ruta care are asociat costul cel maimic.

O procedura care sa reactioneze la schimbarile detopologie.

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2 tipuri de routare consacrate:

1. Distance Vector Routing

Fiecare nod cunoaste distanta (=cost) catre vecinii directconectati

Un nod transmite, periodic, mesaje de tip update catrevecini Nodurile noi isi fac publica prezenta vecinilor.

2. Link State Routing

Fiecare nod cunoaste distanta fata de vecini

Informatiile despre distanta sunt transmise tuturornodurilor din retea (=link state)

Fiecare nod calculeaza tabela de routare independent

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Un protocol simplu intradomain Implementare directa a Distance Vector

Routing Fiecare router isi face public (advertises)

vectorul de distanta (distance vector) lafiecare 30 s sau la o schimbare in tabela deroutare catre toti vecinii.

1 = link metric

Nr de hopuri maxim este 15 / 16 = infinit Rutele expira (timeout) (= 16) daca nu sunt

inoite in 3 min

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1988 RIPv1 (RFC 1058) classful routing

1993 RIPv2 (RFC 1388) Se permite adugarea de masti de retea in tabela de

routare classless routing

1998 Versiunea curenta RIPv2 (RFC 2453)

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RIPv2 este un RIPv1 extins: Mastile de retea (Subnet masks) sunt incluse

in informatiile de routare

Mesajele de routare sunt autentificate

Se transmit informatii despre urmatorul hop(next-hop address)

Foloseste IP multicasting

Campurile suplimentare din RIPv2 suntimplementate in campurile nefolosite aleRIPv1

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Protul 520 dedicat pentru mesaje de tip UDP

Two types of messages: Request messages

Cere o actualizare vecinilor

Response messages

Mesaj de raspuns

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Initializarea: Se transmite un pachet request(command = 1, address family=0..0) pe toate interfetele:

RIPv1 - broadcast

RIPv2 multicast 224.0.0.9,

Routerele ce primesc mesajul tranmit mesajul deraspuns cu tabela de routare

Se actualizeaza tabela de routare Se reactualizeaza odata la 30s

Actualizarile se genereaza si la schimbari de stare

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(#1) shows the normal state of thenetwork, with RBable toreach N1throughRAat a cost of 2.

#2, the link between RAand N1isbroken. RAchanges its cost to reach N1to16 (RIP infinity).

#3, Before RAcan send out this update

to RB, it receives a routine RIP messagefrom RBindicating that N1can be reachedfor a cost of 2. RAis then fooled intothinking it can use RBas an alternate routeto N1, even though RBs informationoriginally came from RAin the first place.In #4,RAthen sends this bogusinformation out, which is received by RBin

#5. RBthen increases its cost to 4, and onits next cycle will send this to RA, whichwill increase its cost to 5, and so on. Thiscycle will continue, with both routerscounting to infinity (16).

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RIPnecesita un timp mare de stabilizare

RIP mosteneste problemele distance vector count-to-Infinity

RIP foloseste split horizon pentru a evitacount-to-infinity

Nr maxim de hopuri 15