cap. 13 forouzan. chapter 13 routing protocols (rip, ospf, bgp)

Cap. 13 ForouzanCap. 13 Forouzan

Chapter 13

Routing Protocols(RIP, OSPF, BGP)

Servicios:Servicios:

Crear o Actualizar una tabla de ruteo basado en la trayectoria de mínimo atraso entre el fuente y el destino. Conociendo totalmente a la red. Basándome en un conocimiento

Parcial de la red

Tipos de Protocolos de RuteoTipos de Protocolos de Ruteo

Static: A parameter is minimized outline; the router is manually configured given the result of

the minimization process. Protocols:

1-MD + backtracking n-MD + backtracking (p.e. bifurcación) Flooding Flow based

Dynamic (Adaptable) Centralized:

All information is sent to a RCC (Routing Center Control) node. Aislado: Cada nodo colecta informacion SIN intercambiar mensajes.

Papa caliente: en la fila mas corta Distributed: Each node collect information to send to the others.

Vector de distancias (Bellman-Ford distribuido o Ford-Fulkerson) Estado-del-enlace

Static: A parameter is minimized outline; the router is manually configured given the result of

the minimization process. Protocols:

1-MD + backtracking n-MD + backtracking (p.e. bifurcación) Flooding Flow based

Dynamic (Adaptable) Centralized:

All information is sent to a RCC (Routing Center Control) node. Aislado: Cada nodo colecta informacion SIN intercambiar mensajes.

Papa caliente: en la fila mas corta Distributed: Each node collect information to send to the others.

Vector de distancias (Bellman-Ford distribuido o Ford-Fulkerson) Estado-del-enlace

MetricsMetrics

Hop number Delay Throughput

Autonomous SystemAutonomous System

Exterior Routing

Interior and Exterior RoutingInterior and Exterior Routing

Autonomous SystemAutonomous System

Interior Routing

Interior Routing

Interior Routing

Interior Routing

Exterior Routing

RIP (Routing Information Protocol)RIP (Routing Information Protocol)

RIP (Routing Information

Protocol)

RIP (Routing Information

Protocol) It is a vector distance algorithm which

uses the Bellman-Ford Algorithm to calculate the routing tables to be used inside an AS.

Hop count is used as the metric for path selection.

If the hop count is greater than 15, the packet will be discarded.

By default, routing updates are broadcast every 30 seconds.

EnvironmentEnvironment

Enlace Datos

Red

Físico

Transporte

Sesión

Presentación

Aplicación

Varies

IP, ICMP

TCP, UDP

HTTP, SNMP,

Telnet, ftp

Varies

IP,ICMP,RIP

Varies

IP,ICMP,RIP

Varies

IP,ICMP,RIP

Varies

IP,ICMP,RIP

Varies

IP,ICMP,RIP

Enlace Datos

Red

Físico

Transporte

Sesión

Presentación

Aplicación

Varies

IP, ICMP

TCP, UDP

HTTP, SNMP,

Telnet, ftp

Léxico: RIP (Routing Information

Protocol)

Léxico: RIP (Routing Information

Protocol) Request Response

Solicited Unsolicited

Update Message

Semantics:Semantics: Request

Send for a router that just come up or by a router that some has some time-out entries.

Unicast, multicast or broadcast. Response

Solicited: Send only in answer to a request

Unsolicited: Sent periodically, every 30 seconds.

Update Message: Periodic Timer Controls the advertising of regular update

messages.

Figure 13-7

Sintaxis:Formato del Frame de un

Request


Request


Response


ResponseComando (1-5) ReservedVesion(1)

Familia de Red 1 (For TCP/IP=2)

Dirección IP de la Red 1

0 24168 31

Debe de estar puesto a cero.



Distancia hacia la Red 1: Hop count from the advertising router to the destination network

Familia de Red 2

Dirección IP de la Red 2




…Distancia hacia la Red 2: Hop count from the advertising router to the destination network

Figure 13-8

Routing TableRouting Table

Each entry in the routing table has: destination network IP address, shortest distance to reach the destination

in hop count and next hop (interface) to which the packet

should be deliver to reach its final destination..

Figure 13-4

Figure 13-5

Reglas de Procedimiento: RIP (Routing Information

Protocol)

Reglas de Procedimiento: RIP (Routing Information

Protocol) Incialization. Every T msec:

1. Node’s distance calculation.2. Send information(vector of

estimates) to its neighbors.3. Recieve information from its

neighbors.4. For each value of vector adds the

calculated distance.5. Updates Routing Table (RIP

Updating algorithm).

2. Nodes sending information,3. Neighbors receiving information

2. Nodes sending information,3. Neighbors receiving information

En realidad los nodos NO estan sincronizados, y eso hace que una grafica mas real para un tiempo t1 sea:

Nota: Utiliza broadcast al enviar mensajes a sus vecinos

5. RIP Updating algorithm5. RIP Updating algorithm

Receive: a response RIP message1. Add one hop to the hop count for each advertising

destination.2. Repeat the following steps for each advertised destination:

1. If (destination not in the routing table) // New router1. Add the advertised information to the table

2. Else1. If (next-hop field is the same)

1. Replace entry in the table with the advertising one

2. Else1. If (advertised hop count < than the one in the

table)1. Add it to the routing table.

2. Else1. Do nothing.

A router receive a RIP messageA router receive a RIP message

Net2 4Net3 8Net6 4Net8 3Net9 5

Net1 7 ANet2 2 CNet6 8 FNet8 4 ENet9 5 F

RIP message from C

Old routing table





RIP message from C

1. RIP message from C

After increment

Old routing table

Updating Algorithm





Updating Algorithm

RIP message from C

RIP message from C

After increment

Old routing table





Updating Algorithm

Net1 7 A

RIP message from C

RIP message from C

After increment

Old routing tableNew routing table

Rules:

Net1: No news, don’t change.





Updating Algorithm

Net1 7 ANet2 5 C

RIP message from C

RIP message from C

After increment


Rules:

Net2: Same next hope, replace.





Updating Algorithm

Net1 7 ANet2 5 CNet3 9 C

RIP message from C

RIP message from C

After increment


Rules:

Net3: A new router, add.





Updating Algorithm

Net1 7 ANet2 5 CNet3 9 CNet6 5 C

RIP message from C

RIP message from C

After increment


Rules:

Net6: Different next hope, new hop count smaller, replace.

A router recive a RIP messageA router recive a RIP message




Updating Algorithm

Net1 7 ANet2 5 CNet3 9 CNet6 5 CNet8 4 E

RIP message from C

RIP message from C

After increment


Rules:

Net8: Different next hope, new hop count the same, don’t change.

A router recive a RIP messageA router recive a RIP message




Updating Algorithm

Net1 7 ANet2 5 CNet3 9 CNet6 5 CNet8 4 ENet9 5 F

RIP message from C

RIP message from C

After increment


Rules:

Net9: Different next hope, new hop count larger, don’t change.

Timers en RIPTimers en RIP

Sending of messages(distance’s vector)

Validity of a route(route is invalid, but the route is not still purged from the table )

Failure of a Router(after this time, finally the route is purged from the table )

Problems:Problems:

Slow Convergence: Since information is on the neigbors, it shows very

slow Convergece (Infinite Counting Problem: reacts faster to the good news than to the bad news).

Solution: Limiting the number of hops (AS Diameter) a 15.

Instability: messages can go from one router to another in a

loop. Solutions:

Triggered Update Split Horizon Poison Reverse

Tiempo esperado entes que un cambio alcance un ruteador:

Entonces, el tiempo de le toma actualizar un ruteador que está a N ruteadores, entonces

sec152

}{30

===

RIPpt

ptxE

sec152

×=× Nt

NRIPpt

p

Figure 13-10

Ejemplo:Ejemplo: Si hay 10 enrutadores:

Suponiendo que la tecnología de red utilizada es Ethrenet, entonces la cantidad de bits transmitidos en este tiempo es:

sec1502

10,30

=×== Nt

p

RIPp

tN

Mbps150

Problems:Problems:

Slow Convergence: Since information is on the neigbors,

it shows very slow Convergece (Infinite Counting Problem: reacts faster to the good news than to the bad news).

Solution: Limiting the number of hops (AS

Diameter) a 15.

Figure 13-11

Problems:Problems:

Instability: messages can go from one router to

another in a loop. Solutions:

Limiting the number of Hops, reduce the problem but do NOT eliminate it.

Triggered Update Split Horizon Poison Reverse

Figure 13-12

3

Figure 13-12

45 B

5 B 6

7 6

Triggered UpdateTriggered Update

If there is a change in the network, the router springs into action inmediatly by sending out its new table.

Split HorizonSplit Horizon

If a router receive a packege from an interface, then the same update information must not be send back for the same interface.

Figure 13-12

Eenvia información de Net3, pero NO de Net1,

16 - 16 -

Eenvia información de Net1, pero NO de Net3,

Figure 13-13

Poisson ReversePoisson Reverse

Information receive by the router is used to update the routing table and then passed out to all interfaces. However, a table entry that has come through one interface is set to a metric of 16 as it goes out through the same interface.

Figure 13-14

RIP v2RIP v2

Enables RIP to receive information of an exterior routing protocol.

Authentication is added to protect message against unauthorized advertisement.

Utiliza la dirección de multicast: 224.0.0.9

Figure 13-15

Figure 13-16

OSPFOSPF

Interior Routing Protocol. Divide the AS in areas (colection of

networks, hosts and routers inside an AS). Routers inside an area floods the area

with routing information. There is a special area called ¨backbone¨. All areas inside an AS must be connected

to the “backbone”. Allow the administrator to assign cost

(based on delay, maximum throughput, etc.) to each router.

OSPF:OSPF:

Interior Routing Protocol. Divide the AS in areas (colection of

networks, hosts and routers inside an AS).

Routers inside an area floods the area with routing information.

Allow the administrator to assign cost (based on delay, maximum throughput, etc.) to each router.

Routers inside the Area flood the area with routing information.

At the border of an area, a special router summarize the information about the area and send it to other areas.

All the areas inside an autonomous system must be connected to the backbone. If, due to some problem, the connectivity between a backbone and an area is broken, a virtual link between routers must be created by the administration to allow continuity of the functions of the backbone.

Figure 13-19

a. Transient link phisical representation.b. Transient link “possible” phyisical representation: Even if they are connected to the same LAN, in this case each router would had to advertise the other routers the status of the links!!!c. Transient link “convenient” logical representation: there is a special router who is a true router and a designeted router. The designated router collect the interface information attached to the LAN.

Graphical RepresentationGraphical Representation

Figure 13-24

Figure 13-30-Part 1

Figure 13-30-Part 2

Figure 13-30 Part 3

Figure 13-31

Test Reacheability.First step in the link state routing.

When a router in connected for first time to the network, it needs to know the the complete link state database.

A router needs information about specific route or routes.It is answered with a link State update packet.

All the links of the router

All the links connected to a networkOne for each network. It sends the network masks and the metrics

To which network, the border router is attached.One for each network. It

sends the network masks and the metrics

Figure 13-32

Link State Request

Database Description

Link State Update

Figure 13-33

Figure 13-36

Figure 13-41

BGPBGP

The autonomous boundary routers advertise the reachability of the networks in their own autonomous systems to neighbor autonomous boundary routers.

Each router that receive a path vector message verifies that the advertised path is in agreement with its policy.

If it is, the router updates its routing table modifies the message (

adds its number to the path and replaces the next routing with its own

identification) sending it to the next neighbor.

Figure 13-42

Loop Prevention: Can be avoided using the path

vector routing. Policy Routing:

The path is not based in minmium delay or minimum number of hops, but in policies.

FinFin

Figure 13-43

Figure 13-44

Figure 13-45

Figure 13-46

Figure 13-47

Figure 13-48

Figure 13-49

Figure 13-50

cap. 13 forouzan. chapter 13 routing protocols (rip, ospf, bgp)

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