IP advanced.pdf

8/22/2019 IP advanced.pdf

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Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 1

Alcatel University - 8AS 90200 1140 VT ZZA Ed.011

Routing


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1 TitleSession presentation

Objective: to be able to configure RIP and OSPF dynamic

routing

program:

1 Overview

2 RIP protocol

3 OSPF protocol


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Routing

1. Overview


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1- OverviewVarious types of routing

Static

Prevent traffic due to routing protocol

Easy design on small network

Risk of errors

Programmed manually

No re-routing in case of failure

Dynamic

Re-route automatically the traffic in case of network failure

Ideal for large network

Involve over processing in the routers

Generate over traffic on the network

Static routing

Static routing is manually performed by the network administrator. The administrator is responsible for discoveringand propagating routes through the network. These definitions are manually programmed in every routing devicein the environment.

Once a device has been configured, it simply forwards packets out the predetermined ports. There is nocommunication between routers regarding the current topology of the network.

In small networks with minimal redundancy, this process is relatively simple to administer. However, there areseveral disadvantages to this approach for maintaining IP routing tables:

Static routes require a considerable amount of coordination and maintenance in non-trivial networkenvironments.

Static routes cannot dynamically adapt to the current operational state of the network. If a destinationsubnetwork becomes unreachable, the static routes pointing to that network remain in the routing table. Trafficcontinues to be forwarded toward that destination. Unless the network administrator updates the static routes toreflect the new topology, traffic is unable to use any alternate paths that may exist.

Dynamic routing:

Dynamic routing algorithms allow routers to automatically discover and maintain awareness of the paths throughthe network.


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1- OverviewPrinciple of routing tables :

Fill-in this table

Network Mask Next hop If


204.92.77.0 255.255.255.0

192.168.201.0 255.255.255.0

204.92.76.0 255.255.255.0 e0

e1

204.92.76.2

204.92.75.0 255.255.255.0 e2

204.92.75204.92.75.0.0

192.168.201192.168.201.0.0204.92.76204.92.76.0.0204.92.77204.92.77.0.0R1

R2R2

.1.1 .1.1.1.1.2.2

0.0.0.0(default) 0.0.0.0

192.168.201.0 255.255.255.0

204.92.76.0 255.255.255.0 e1e1

204.92.76.1

e0

.2.2

e0e0e1e1

e2

e1e1

e0

Fill-in this table


An important function of the IP layer is IP routing. This provides the basic mechanism for routers to interconnectdifferent physical networks.

The router only has information about various kinds of destinations:

networks that are directly attached to one of the physical networks to which the router is attached.

Hosts or networks for which the router has been given explicit definitions.

The metrics provide indication about cost of a route to a destination.

Metrics are based on :

the number of hops,

the bandwidth,

the delay, ...


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1- OverviewRouting table : the metric

R1

R2

192.168.201.0

204.92.76.0

204.92.77.0

.1 .1.1.2

204.92.75.0

.2

.2

Network Mask Next hop metric

204.92.77.0 255.255.255.0192.168.201.0 255.255.255.0204.92.76.0 255.255.255.0

204.92.76.1

204.92.75.0 255.255.255.0 204.92.76.1 e1

204.92.77.0 255.255.255.0 e2

001

1

0

Secondary route

Primary routePrimary route

204.92.75.0 255.255.255.0 204.92.77.1 e2 1

If

e1e1e0

e1e1

e0e0e1e1

e2

e2

The metrics provide indication about cost of a route to a destination and allow the choice when several routes areavailable.


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ISDN

1- OverviewOther advantage of static routing

If dynamic routing on ISDN linkIf dynamic routing on ISDN link

The connection should beThe connection should be continiouselycontiniousely onon

for routing information updatefor routing information updateHigh costHigh cost

Normally, static routes are used only in simple network topologies. However, there are additional circumstanceswhen static routing can be attractive. For example, static routes can be used:

To manually define a default route. This route is used to forward traffic when the routing table does not contain amore specific route to the destination.

To define a route that is not automatically advertised within a network.

When utilization or line tariffs make it undesirable to send routing advertisement traffic through lower-capacityWAN connections.

When complex routing policies are required. For example, static routes can be used to guarantee that trafficdestined for a specific host traverses a designated network path.

To provide a more secure network environment. The administrator is aware of all subnetworks defined in theenvironment. The administrator specifically authorizes all communication permitted between these subnetworks.

To provide more efficient resource utilization. This method of routing table management requires no networkbandwidth to advertise routes between neighboring devices. It also uses less processor memory and CPU cyclesto calculate network paths.


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network

140.252.13.32

1- OverviewExample of routing (1)

140.252.1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33 140.252.13. 34140. 252.13.35

140.252.13.66

140.252.13.65

network

140.252.1

140 252. .13 35.IP @ :

1 0 0 0 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 0 0 0 1 10 0 0 0 1 1 0 1

140 252. .13 32.Network :

1 0 0 0 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 0 0 0 0 00 0 0 0 1 1 0 1

1 1 1 1 1 1 1 11 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0

Masque :

/27


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Destination Gateway Flags InterfaceRefcnt Use

1- OverviewExample of routing (2)- Routing table

140.252.1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33 140.252.13. 34140. 252.13.35

140.252.13.66

140.252.13.65Network

140.252.13.32

Network

140.252.1

140.252.13.65/32

To go to :

UU

U: This routeU: This route isis UpUp

Refcnt: nb of TCP session

Use : nb of packets sent on this @

0 0 eth0

ethernet

140.252.13.35

G: Go througth Gateway

G

H: This address is a full IP@ of host

H


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Network

140.252.13.32


140.252.1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.1

Direct route : route connected to this machine , on this interface

140.252.13.34


140.252.13.65/32 140.252.13.35 U G H eth00 0

To go to :

140.252.13.32/27

U: This routeThis route isis UpUp

U 4 2543

_: This address is an IP@ of network

_

_: direct route

140.252.13.34 _ eth0

ethernet


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140.252.1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1

Destination Gateway Flags

140.252.13.65/32 140.252.13.35 U G H

140.252.13.32/27 140.252.13.34 U _ _

Loopback between 2 applications

Interface

eth0

Refcnt Use

0 0

140.252.13.34

eth04 2543

To go to :

127.0.0.1 /32

U:U: thisthis routeroute isis UpUp

UU 0 0 lo0

loopback

_: direct route

127.0.0.1 _


H


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140.252.1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1


140.252.13.65 /32 140.252.13.35 U G H

140.252.13.32 /27 140.252.13.34U _ _

InterfaceRefcnt Use

0 0

140.252.13.34

eth04 2543

127.0.0.1 /32U _ H

lo00 0127.0.0.1default

Default route

U


eth0

140.252.13.33

Go through

G: indirect route

G_ 0 0 eth0

ethernet


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1- OverviewExample of routing (6)- routing table using

140.252.1.92 140.252.1.32 140.252.1.11140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1

140.252.13.34


140.252.13.65 /32 140.252.13.35 U G H

140.252.13.32 /27 140.252.13.34 U _ _

Interface

eth0

Refcnt Use

0 0

eth04 2543

default 140.252.13.33 eth00 0U G _

127.0.0.1 /32 U _ H lo00 0127.0.0.1

Example :Search IP@ 140.252.13.35

1- Search of precise IP @ (among entries with flag=H)=> fail

2- Search on network@, The network@ 140.252.13.32 is found=> send the packet to the MAC@ of the search host (140.252.13.35) on Ethernet interface : eth0


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140.252.1.92 140.252.1.32 140.252.1.11 140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65Network

140.252.13.32

Network

140.252.1

140.252.13.34


140.252.13.65 /32 140.252.13.35 U G H

140.252.13.32 /27 140.252.13.34 U _ _

Interface

eth0

Refcnt Use

0 0

eth04 2543

default 140.252.13.33 eth00 0U G _

127.0.0.1 /32 U _ H lo00 0127.0.0.1

Example :search IP @ 140.252.13.65

1- Search of precise IP @ (among entries with flag=H)=>the @ 140.252.13.65 is found

=> indirect route (G), sends the packet to MAC@ of the router (140.252.13.35) on Ethernet interface : eth0


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140.252.1.92 140.252.1.32 140.252.1.11140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1

140.252.13.34


140.252.13.65 /32 140.252.13.35 U G H

140.252.13.32 /27 140.252.13.34 U _ _

Interface

eth0

Refcnt Use

0 0

eth04 2543

default 140.252.13.33 eth00 0U G _

127.0.0.1 /32 U _ H lo00 0127.0.0.1

1- Search of precise IP @ (among entries with flag=H)=> fail

3- Selection of dfault => indirect route (G), sends the packet to MAC@ of the router (140.252.13.33)on Ethernet interface : eth0

Exemple :recherche @IP 192.207.117.2

2- Search on network@, => fail


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1- OverviewExample of routing (9)- Configuration

% netstat -rnDestination Gateway Flags InterfaceRefcnt Use

140.252.1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1

140.252.13.34

Creation of direct routes : at the (ifconfig) : route creation : command route .Examples:

default 140.252.13.33 eth00 0U G _

route add default 140.252.13.33

140.252.13.65 /32 140.252.13.35 U G H 0 0 eth0

route add -host 140.252.13.65 140.252.13.35

127.0.0.1 /32U _ H

lo00 0127.0.0.1

One entry for loopback

140.252.13.32 /27 140.252.13.34 U _ _ eth00 0

One entry for the local network


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140.252.1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33 140.252.13.34140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1


0 0


H140.252.13.65 /32

To go to :

UU


eth0

ethernet

140.252.13.35

G: go through Gateway

G


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140.252. 1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

network

140.252.13.32

network

140.252.1

140.252.13.34

Direct route : route connected to this machine , on this interface


140.252.13.65 /32 140.252.13.35 U G H

Interface

eth0

Refcnt Use

0 0

eth0

ethernet

_: H: This address is a network IP @

_

To go to :

140.252.13.32 /27

_: direct route

140.252.13.33 _

U: This route is Up

U 0 0


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140.252. 1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1

140.252.13.34


140.252.13.65 /32 140.252.13.35 U G H

Interface

eth0

Refcnt Use

0 0

eth0_140.252.13.32 /27 140.252.13.33 _U 0 0

Loopback between 2 applications

127.0.0.1 /32 UU 0 0 lo0

loopback

127.0.0.1_ H


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140.252. 1.92 140.252.1.32 140.252.1.11

140.252.1.4

Internet

140.252.1.183

140.252.1.29

140.252.13.33140.252.13.35

140.252.13.66

140.252.13.65

Network

140.252.13.32

Network

140.252.1

140.252.13.34


140.252.13.65 /32 140.252.13.35 U G H

Interface

eth0

Refcnt Use

0 0

eth0_140.252.13.32 /27 140.252.13.33 _

U

0 0

127.0.0.1 /32

UU

0 0 lo0127.0.0.1 _ H

140.252.1.29

G: go through Gateway

G s0

SerialInterface

To go to :

default


UU 0 0_


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Cisco- Static route command

ipip routeroute netnet--idid netmasknetmask {nextnext--hophop--ipip@@ | interface} [distancedistance]

ipip routeroute 172.31.10.0172.31.10.0 255.255.255.0255.255.255.0 10.10.10.210.10.10.2 101101

Examples :

ipip routeroute 0.0.0.00.0.0.0 0.0.0.00.0.0.0 Serial3Serial3 192.168.20.1192.168.20.1

2- Get out by this interface

3- pass by this gateway1- To go to this destination

4- The cost to reach the destination is

ipip routeroute 0.0.0.00.0.0.0 0.0.0.00.0.0.0 Ethernet0Ethernet0broadcast interface : the route will be insertedinto the routing table only when the broadcast

interface is up

If you point a static route to a broadcast interface,

for example, ip route 0.0.0.0 0.0.0.0 Ethernet0

the route will be inserted into the routing table only when the broadcast interface is up.

This configuration is not recommended because when the next hop of a static route points to an interface, the router considerseach of the hosts within the range of the route to be directly connected through that interface.

With this type of configuration, a router will perform Address Resolution Protocol (ARP) on the Ethernet for every destination therouter finds through the default route because the router will consider all of these destinations as directly connected to Ethernet0.

Specifying a numerical next hop on a directly connected interface will prevent the router from performing ARP or eachdestination address.

However, if the interface with the next hop goes down and the numerical next hop is reachable through a recursive route, youshould specify both the next hop IP address and the interface through which the next hop should be found.

For example, ip route 0.0.0.0 0.0.0.0 Serial3 192.168.20.1

Administrative distance is the feature used by routers to select the best path when there are two or more different routes tothe same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol.

Each routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. Thesmaller the administrative distance value, the more reliable the protocol.


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172.31.10.0172.31.10.0

/24/24

E0

.2.2

.1.1

192.168.20.0 /30192.168.20.0 /30

.11

S3.22

S1

10.10.10.0 /3010.10.10.0 /30

.11

S2

.22S0

192.168.10.0 /30192.168.10.0 /30

.22

S0.11S0

Cisco - Static routing configuration example

Internet R1R1 R2R2

64kb/s

2Mb/s2Mb/s

R2#show ip route

Codes: C - connected, S - static, * - candidate default

Gateway of last resort is 10.10.10.1 to network 0.0.0.0

C 172.31.10.0172.31.10.0/24 is directly connected, Ethernet0

C 192.168.20.0192.168.20.0/30 is directly connected, Serial1


ip route 0.0.0.0 0.0.0.0 Serial0 10.10.10.110.10.10.1default route

Other administrative distance

ip route 0.0.0.0 0.0.0.0 Serial1 192.168.20.1192.168.20.1 250250

Defaultadministrativedistance = 1

S* 0.0.0.0/0 [1/0] via 10.10.10.110.10.10.1

Only the primary route is inserted

R1#show ip route

Codes: C - connected, S - static, * - candidate default

Gateway of last resort is 0.0.0.0 to network 0.0.0.0


C 192.168.10.0192.168.10.0/30is directly connected, Serial0

C 192.168.20.0192.168.20.0/30is directly connected, Serial3

ip route 0.0.0.0 0.0.0.0 Serial3/0

ip route 172.31.10.0172.31.10.0 255.255.255.0 Serial3 192.168.20.2192.168.20.2 250250

ip route 172.31.10.0172.31.10.0 255.255.255.0 Serial2 10.10.10.210.10.10.2

primary

S* 0.0.0.0/0 is directly connected, Serial3/0

S 172.31.10.0172.31.10.0/24 [250/0] via 10.10.10.210.10.10.2, Serial2

By default, static routes have an administrative distance of one, which gives them precedence over routes fromdynamic routing protocols. By increasing the administrative distance to a value greater than that of a dynamicrouting protocol, the static route can be a safety net in the event that dynamic routing fai ls.

If you would specify an administrative distance for a static route.This kind of static route is called "floating" static.It is installed in the routing table only when the preferred route disappears.


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1- OverviewExercise : Static routing

Internet

172.16.0.0

/16

10.2.0.0/16

10.1.0.0/16

192.168.2.0

/24

192.168.1.0

/24

172.17.0.0/16

IP@:1

IP@:2

IP@:3

IP@:4

IP@:5

IP@:6

IP@:7

IP@:8

IP@:9

IP@:10

10.1.0.0/16@IP1

10.2.0.0/16@IP2

Routing Table

172.16.0.0/16@IP4

10.2.0.0/16@IP3

Routing Table

172.17.0.0/16@IP5

172.16.0.0/16@IP9

Routing Table

192.168.1.0/24@IP7

172.17.0.0/16@IP6

Routing Table

192.168.2.0/24@IP8

0.0.0.0 / 00.0.0.0 / 0 @IP3@IP3

0.0.0.0 / 00.0.0.0 / 0 @IP5@IP5

192.168.0.0/16192.168.0.0/16 @IP6@IP6

10.1.0.0/1610.1.0.0/16 @IP2@IP2

0.0.0.0 / 00.0.0.0 / 0 @IP10@IP10

10.0.0.0 / 810.0.0.0 / 8 @IP4@IP4

192.168.0.0/16192.168.0.0/16 @IP4@IP4

172.17.0.0/16172.17.0.0/16 @IP4@IP4

0.0.0.0 / 00.0.0.0 / 0 @IP9@IP9

Complete the routing tables of the various routers to get access to all destinations.


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1- OverviewDynamic routing principle

Routers advertise the networks

they can reach

Routers calculate the routes from

advertisementsadvertisements


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1- OverviewVarious routing protocols algorithms

Algorithm of routing

Distance VectorDistance Vector Link StateLink State

RIP

BGP

IGRP (CISCO)DECnet (Phase IV)

OSPF

IS-IS

DECnet (Phase V)

RIP : Routing Information Protocol

IS-IS : Intermediate System to Intermediate System

OSPF : Open Shortest Path First

IGRP: Internet Gateway Routing Protocol

BGP: Border Gateway Protocol

The automatic discovery of routes can use a number of currently available dynamic routing protocols. Thedifference between these protocols is the way they discover and calculate new routes to destination networks.They can be classified into three broad categories:

- Distance vector protocols

- Link state protocols


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1- OverviewDistance vector : principle

NetworkNetwork11 NetworkNetwork

55

NetworkNetwork44R1R1

R2R2 R3R3

R4R4

NetworkNetwork22

NetworkNetwork33

Network 2Network 2

Network

2

Network

2(1hop,R

3)

Network 3Network 3Network 3Network 3 (1 hop, R4)

Network 4Network 4

Network4Network4(0hop,e0)

Network 5Network 5

Network5

Network5(0hop,e2)

Routers based onRouters based on

number of hopsnumber of hops

(D, V)

(Alternative routes are not kept.)

Netw

ork1

Netw

ork1(0hop

,e1)

Network 1Network 1

R1R1View of R1

e0

e2e1

Distance vector algorithms

they allow each device in the network to automatically build and maintain a local IP routing table. The principlebehind distance vector routing is simple.

Each router in the internetwork maintains the distance orcostfrom itself to every known destination. This valuerepresents the overall desirability of the path. Paths associated with a smaller cost value are more attractive to usethan paths associated with a larger value. The path represented by the smallest cost becomes the preferred pathto reach the destination. This information is maintained in a distance vector table.

The table is periodically advertised to each neighboring router. Each router processes these advertisements todetermine the best paths through the network.


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(no optimal route)

1- OverviewDistance vector : cost problem

NetworkNetwork11

R1R1

R2R2

R3R3

NetworkNetwork22

NetworkNetwork33

High throughput

High throughput

Low throughput

Network 3Network 3 (1 hop, R3)

Network 2Network 2 (0 hop, e1)

Network 1Network 1 (0 hop, e0)

R1R1

e0

e1


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1- OverviewLink state

NetworkNetwork11 NetworkNetwork

55

NetworkNetwork44R1R1

R2R2 R3R3

R4R4

NetworkNetwork22

NetworkNetwork33

NetworkNetwork11

R4R4

R3R3R2R2

NetworkNetwork

44

NetworkNetwork33

NetworkNetwork22

Network

Network55

Each router makes the network

topology

R1R1View of R1

Link state routing

The growth in the size and complexity of networks in recent years has necessitated the development of morerobust routing algorithms. These algorithms address the shortcoming observed in distance vector protocols. Thesealgorithms use the principle of a link state to determine network topology. A link state is the description of aninterface on a router (for example, IP address, subnet mask, type of network) and its relationship to neighboringrouters. The collection of these link states forms a link state database. The process used by link state algorithmsto determine network topology is straightforward:

Each router identifies all other routing devices on the directly connected networks.

Each router advertises a list of all directly connected network links and the associated cost of each link. This isperformed through the exchange of link state advertisements (LSAs) with other routers in the network.

Using these advertisements, each router creates a database detailing the current network topology. Thetopology database in each router is identical.

Each router uses the information in the topology database to compute the most desirable routes to eachdestination network. This information is used to update the IP routing table.


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2 classes of protocols:2 classes of protocols:

INTERNETINTERNET

1- OverviewVarious routing protocol classes

SprintSprintDFNDFN

RenaterRenater

Autonomous

system

IInteriornterior GGatewayateway PProtocolrotocol (RIP, IGRP, OSPF, )

EExteriorxterior GGatewayateway PProtocolrotocol (EGP, BGP, IS-IS, )

Autonomous

system

SphinxSphinx

JanetJanet

BGPBGP

(OSPF)

(RIP)

(OSPF)

(EIGRP)

(IGRP)

An AS is defined as a logical portion of a larger IP network. An AS is normally comprised of an internetwork withinan organization. It is administered by a single management authority.

Some routing protocols are used to determine routing paths within an AS. Others are used to interconnect a set ofautonomous systems:

Interior Gateway Protocols (IGPs): Interior gateway protocols allow routers to exchange informationwithin an AS. Examples of these protocols are Open Short Path First (OSPF) and Routing InformationProtocol (RIP).

Exterior Gateway Protocols (EGPs): Exterior gateway protocols allow the exchange of summaryinformation between autonomous systems. An example of this type of routing protocol is Border GatewayProtocol (BGP).

The interior protocols used to maintain routing information within each AS. The figure also shows the exteriorprotocols maintaining the routing information between autonomous systems.

Within an AS, multiple interior routing processes may be used. When this occurs, the AS must appear to otherautonomous systems as having a single, coherent interior routing plan. The AS must present a consistent view of

the internal destinations


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Routing

2 RIP protocol

RFC 1058 and 1723

Routing Information Protocol (RIP)

RIP is an example of an interior gateway protocol designed for use within small autonomous systems.

In mid-1988, the IETF issued RFC 1058, which describes the standard operations of a RIP system. However, the RFCwas issued after many RIP implementations had been completed. For this reason, some RIP systems do not supportthe entire set of enhancements to the basic distance vector algorithm (for example, poison reverse and triggeredupdates).


34/306


34


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35

RIP: router start-up

A B

C

D E

N1N1 N2N2

N6N6

N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N1 11

0N3 3

20

Net HopCost

N1 12

0

N2 21

0N4 4

10

Net HopCost

N3 31

0

N6 62

0

Net HopCost

N5 51

0

N2 22

0

Net HopCost

N5 52

0

N6 61

0N4 4

20

Net HopCost

The distance vector table describes each destination network. The entries in

this table contain the following information:

The destination network (vector) described by this entry in the table.

The associated cost (distance) of the most attractive path to reach this destination. This provides theability to differentiate between multiple paths to a destination. In this context, the terms distance and costcan be misleading. They have no direct relationship to physical distance or monetary cost.

The IP address of the next-hop device used to reach the destination network.

At router initialization, each device contains a distance vector table listing each directly attached networks andconfigured cost. Typically, each network is assigned a cost of 1.


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36

IP@src

:3.2IP@

dest:broadcast

IP@src

:1.11.1IP@

dest:broadcast

N1 1

N3 1

RIP : Update of the routing tables (1)

N1 11

0

N3 32

0N1 1

20

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0

Net HopCost Net HopCost

Net HopCost

Net HopCost

Net HopCost

N3 11

+1+1

N1 1

N1 1N3 1

1111

32

RIP packet types

The RIP protocol specifies two packet types. These packets may be sent by any device running the RIP protocol:

Request packets: A request packet queries neighboring RIP devices to obtain their distance vector table.The request indicates if the neighbor should return either a specific subset or the entire contents of thetable.

Response packets: A response packet is sent by a device to advertise the information maintained in itslocal distance vector table.

- The table is automatically sent every 30 seconds.

- The table is sent as a response to a request packet generated by another RIP node.

When a response packet is received by a device, the information contained in the update is compared against thelocal distance vector table. If the update contains a lower cost route to a destination, the table is updated to reflectthe new path.


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37

RIP : Update of the routing tables(2)

N1 11

0

N3 32

0N1 1

20

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0


Net HopCost

Net HopCost

Net HopCost

N3 1111

11

N1 32

1

N3 1

N6 1N1 2

+1

N3 62

1

N1 62

2

N3 1N6 1N1 2

+1

N6 31

1


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38


N1 11

0

N3 32

0N1 1

20

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0


Net HopCost

Net HopCost

Net HopCost

N3 1111

11

N1 32

1

N3 62

1

N1 62

2

N1 1

N2 1

N4 1N3 22

+1

N1 41

1

N2 41

1

N1 1N2 1N4 1

N3 22

N1 21

1N4 2

11

N3 2211

22

+1N6 3

11


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39

N2 61

2

N5 42

1


N1 11

0

N3 32

0N1 1

20

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0


Net HopCost

Net HopCost

Net HopCost

N3 1111

11

N1 32

1

N3 62

1

N1 41

1

N2 41

1

N5 1

N6 1N4 1N3 2

N1 2N2 2

N1 21

1N4 2

11

N3 2211

22

N6 52

1

+1

N5 1N6 1N4 1N3 2N1 2N2 2

+1

N6 31

1

N5 1N6 1N4 1N3 2N1 2N2 2

N5 61

1

N4 61

1

+1

N6 42 1


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40

N2 61

2

N5 42

1


N1 11

0N3 3

20

N1 12

0

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0


Net HopCost

Net HopCost

Net HopCost

N3 1111

11

N1 32

1

N3 62

1

N1 61

2N1 41

1

N2 41

1

N1 21

1N4 2

11

N3 2211

22

N6 52

1

N6 31

1

N5 61

1

N4 61

1

N6 42 1

N5 2

N1 1N2 1

N4 1N3 22

N6 2

+1

N5 2

N1 1

N2 1N4 1N3 22

N6 2

+1

N5 12 2

N2 12

1N4 1

21

N5 2

N1 1N2 1N4 1N3 22

N6 2

+1


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41

N2 61

2

N5 42

1


N1 11

0N3 3

20

N1 12

0

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0


Net HopCost

Net HopCost

Net HopCost

N3 1111

11

N1 32

1

N3 62

1

N1 61

2N1 41

1

N2 41

1

N1 21

1N4 2

11

N3 2211

22

N6 52

1

N6 31

1

N5 61

1

N4 61

1

N6 42 1N5 12 2

N2 12

1N4 1

21

N1 1

N3 1N6 2

N5 3

N2 2N4 2

N1 1

N3 1N6 2

N5 3

N2 2N4 2

+1

+1


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42

N2 61

2

N5 42

1


N1 12

0

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

Net HopCost


N3 1111

11

N1 32

1

N3 62

1

N1 61

2N1 41

1

N2 41

1

N5 61

1

N4 61

1

N6 42 1+1

N5 1N2 1

N1 2

N4 2

N3 33N6 2

N5 1N2 1

N1 2N4 2N3 33

N6 2

+1

N1 11

0N3 3

20

Net HopCost

N6 31

1

N5 12 2

N2 12

1N4 1

21

N5 51

0

N2 22

0

Net HopCost

N1 21

1N4 2

11

N3 2211

22

N6 52

1

During an adverse condition, the length of time for every device in the network to produce an accurate routingtable is called the convergence time.


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43

RIP: slow convergence

B CAN1N1

30s

N1;N1;costcost=1=1

advertisementadvertisement

30s

N1;N1;costcost=2=2


In RIP the time convergence could be very long:


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44

The route selected by RIP is not the fastest

RIP: metric = hop count

A

B

C

2Mb/s2Mb/s

64kb/s64kb/s

2Mb/s2Mb/sN5N5

N4N4

N1N1 1

2

E1

Solution : Assign a minimum cost to a route

N2N2

N3N3

2

N6N6

1

21

N1 11

0

N2 21

0N3 3

10

Net HopCost

N4 22

1

N5 32

1

N6 22 1


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45

N2 61

2

N5 42

1

RIP: Failure in the network (1)

N1 12

0

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0

Net HopCost

Net HopCost

Net HopCost

Net HopCost

N3 1111

11

N1 32

1

N3 62

1

N1 61

2N1 41

1

N2 41

1

N1 21

1N4 2

11

N3 2211

22

N6 52

1

N5 61

1

N4 61

1

N6 42 1

N1 11

0N3 3

20

Net HopCost

N6 31

1

N5 12 2

N2 12

1N4 1

21

N3 1N6 2

N5 2

N2 1

N4 1

N6 2

N5 2

N2 1N4 1

N6 2

+1

+1

+1

While the routing tables are converging, networks are susceptible to inconsistent routing behaviour. This cancause routing loops or other types of unstable packet forwarding.


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46

N2 61

2

N5 42

1

RIP: Failure in the network(2)

N1 12

0

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0

Net HopCost

Net HopCost

Net HopCost

Net HopCost

N3 1111

11

N1 32

1

N3 62

1

N1 61

2N1 41

1

N2 41

1

N1 21

1N4 2

11

N3 2211

22

N6 52

1

N5 61

1

N4 61

1

N6 42 1

N1 11

N3 32

0

Net HopCost

N6 31

1

N5 12

N2 12

N4 12

N2 3

N3 1

N6 1

N5 2N4 2

+1

N2 3

N3 1N6 1

N5 2

N4 2

+1

231

331

231


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47

N2 61

2

N5 42

1

RIP: Failure in the network(3)

N1 12

0

N2 21

0

A B

C

D E

N1N1

N2N2

N6N6 N5N5

N3N3 N4N4

12

2

1

2

2

2

1

1

1

1

2

N4 41

0

N5 52

0

N6 61

0N4 4

20

N3 31

0

N6 62

0

N5 51

0

N2 22

0

Net HopCost

Net HopCost

Net HopCost

Net HopCost

N3 1111

N1 32

1

N3 62

1

N1 61

2N1 41

1

N2 41

1

N1 21

1N4 2

11

N3 2211

N6 52

1

N5 61

1

N4 61

1

N6 42 1

N1 11

N3 32

0

Net HopCost

N6 31

1

N5 31

N2 31

N4 31

2

2

3

N5 1N6 1N4 1N3 2

N1N2 2

N5 1

N6 1N4 1N3 2

N1N2 2

N5 1N6 1N4 1N3 2N1N1N2 2

+1

+1

224422

225522

+1


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48

Counting to infinity (1)

BA

N1N1 N2N2 N3N3

N1 11

N2 22

0

Net HopCost

N3 21

1

0

112 2

N1 22

N2 21

0

Net HopCost

N3 32

0

1

30s

30sRouting table broacasting

Routing table broacasting




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49

2.1broadcast

2.2broadcast

2.1broadcast

Counting to infinity(2)

BA

N1N1 N2N2 N3N3

112 2

t0

30s

N1 11N2 2

20

Net Hop Cost

N3 21

1

0 N1 22

N2 21

0Net HopCost

N3 32

0

1

30s

30s

N1 11N2 2

20

Net Hop Cost

N3 21 1

0

N1N2 1N3 1

2+1N1 1

1

N2 22 0

Net Hop Cost

N3 21 1

2

N1 22

N2 21

0

Net HopCost

N3 32

0

13N1N2 1N3 2

3

N1N2 1N3 1

4+1N1 21

N2 22 0

Net Hop Cost

N3 21 1

24

21

+1

Convergence and counting to infinity

Given sufficient time, this algorithm will correctly calculate the distance vector table on each device. However,during this convergence time, erroneous routes may propagate through the network.

The manner in which the costs in the distance vector table increment gives rise to the term counting to infinity. Thecosts continues to increment, theoretically to infinity. To minimize this exposure, whenever a network isunavailable, the incrementing of metrics through routing updates must be halted as soon as it is practical to do so.In a RIP environment, costs continue to increment until they reach a maximum value of 16. This limit is definedin the RFC.

A side effect of the metric limit is that it also limits the number of hops a packet can traverse from source networkto destination network. In a RIP environment, any path exceeding 15 hops is considered invalid. The routingalgorithm will discard these paths.


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50

2.1broadcast

Split horizon

BA

N1N1 N2N2 N3N3

112 2

t0

30s

N1 11N2 2

20

Net Hop Cost

N3 21

1

0 N1 22

N2 21

0Net HopCost

N3 32

0

1

30s

30s

N1 11N2 2

20

Net Hop Cost

N3 21 1

0

N3 1 +1N1 11N2 22 0

Net Hop Cost

N3 21 1

N1 22

N2 21

0

Net HopCost

N3 32

0

1

N1 22N2 22 0

Net Hop Cost

N3 21 1

2.2

broadcast

N1 1+1

2.1broadcast

N3 1 +1

2.2

broadcast+1

There are two enhancements to the basic distance vector algorithm that can minimize the counting to infinityproblem:

Split horizon with poison reverse

Triggered updates

These enhancements do not impact the maximum metric limit.

Split horizon

The excessive convergence time caused by counting to infinity may be reduced with the use of split horizon. Thisrule dictates that routing information is prevented from exiting the router on an interface through which theinformation was received.

The convergence occurs considerably faster using the split horizon rule. The limitation to this rule is that eachnode must wait for the route to the unreachable destination to time out before the route is removed from thedistance vector table. In RIP environments, this timeout is at least three minutes after the initial outage. During thattime, the device continues to provide erroneous information to other nodes about the unreachable destination.This propagates routing loops and other routing anomalies.


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51

Poison Reverse

BA

N1N1 N2N2 N3N3

112 2

t0

N1 11N2 2

20

Net Hop Cost

N3 21 1

0

N1 22

N2 21

0

Net HopCost

N3 32

0

1

N1 11N2 22 0

Net Hop Cost

N3 21 1

0N1

Poison reversePoison reverse

Split horizonSplit horizon

N1 22

N2 21

0

Net HopCost

N3 32

0

1-

N3 1 +1N1 11N2 22 0

Net Hop Cost

N3 21 1

0

30s

30s

N1 1

30s

30s

+1

Poison reverse

Poison reverse is an enhancement to the standard split horizon implementation. It is supported in RFC 1058. Withpoison reverse, all known networks are advertised in each routing update. However, those networks learnedthrough a specific interface are advertised as unreachable in the routing announcements sent out to that interface.

This drastically improves convergence time in complex, highly-redundant environments. With poison reverse,when a routing update indicates that a network is unreachable, routes are immediately removed from the routingtable. This breaks erroneous, looping routes before they can propagate through the network. This approach differsfrom the basic split horizon rule where routes are eliminated through timeouts.

Triggered updates

Like split horizon with poison reverse, algorithms implementing triggered updates are designed to reduce networkconvergence time. With triggered updates, whenever a router changes the cost of a route, it immediately sendsthe modified distance vector table to neighboring devices. This mechanism ensures that topology changenotifications are propagated quickly, rather than at the normal periodic interval.


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52

Hold-Down

BAN1N1 N2N2 N3N3

1

12 2

N1 11N2 2

20

Net Hop Cost

N3 21 1

N1 22N2 21

0

Net HopCost

N3 32

0

N1N1

1

/0

C1

N1N2 1

Net Cost

N3 2

1

N1N2 1

NetCost

N3 1

2

30s

N1N2 1

Net Cost

N3 2

1

N1N2 1

NetCost

N3 2

1

30s

66 Th.Th.


30s

N1N2 1

Net Cost

N3 1

2

N1N2

Net

N31

Cost

1

2

N1 22

N2 21

0

Net HopCost

N3 32

0

/11

N1 32N2 32

1

Net HopCost

N3 31

0

N1 32

N2 32

1

Net HopCost

N3 31

0

/22

End of failureEnd of failure

N1 22

N2 21

0

Net HopCost

N3 32

0

/1N1 3

2

N2 32

1

Net HopCost

N3 31

0

/2

N1 11

N2 22

0

Net Hop Cost

N3 21 1

/00

N1 11

N2 22

0

Net Hop Cost

N3 21

1

/0

N1 22

N2 21

0

Net HopCost

N3 32

0

/1

N1 32

N2 32

1

Net HopCost

N3 31

0

/2

Hold-down is the amount of time the router will wait before sending flashes about RIP changes. RIP has a 3-minute hold-down timer.


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53

Format of the RIP 1 message

0 8 16 24 31

Command Version

Address Family Id

Network 1 IP address

Metric (Distance to network 1)

1 : Request

2 : Response

Value 1 to 15Value 1 to 15

Version =1

2 for IP2 for IP

Address Family Id



RIP packet types

The RIP protocol specifies two packet types. These packets may be sent by any device running the RIP protocol: Request packets: A request packet queries neighboring RIP devices to obtain their distance vector table.

The request indicates if the neighbor should return either a specific subset or the entire contents of thetable.

Response packets: A response packet is sent by a device to advertise the information maintained in itslocal distance vector table.

RIPv1 does not manage subnet mask


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54

Encapsulation of the RIPv1 messages

Version Headerlength

Type OfService Datagram length

Identification Flag Datagram Offset

TTL Protocol: 1717 Checksum

Source IP address

Destination IPDestination IP addressaddress::

IPheader

UDPheader

UDP source port UDP destination port :

UDP message length Checksum UDP

RIP messageRIP message(25 routes maxi)(25 routes maxi)

512 bytesmax

UDPUDP

RIPRIP520520

BroadcastBroadcast255.255.255.255255.255.255.255

MAC src :--.--.--.--.--.--

MAC dest: ffff..ffff..ffff..ffff..ffff..ffff


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Advantages / disadvantages of RIPv1

Easy to implement,Easy to implement,

Easy to configure, to maintain, to useEasy to configure, to maintain, to use

Very useful in small networksVery useful in small networks

Vulnerable while convergence timeVulnerable while convergence time,,

Slow convergenceSlow convergence

Large bandwidth used by the protocolLarge bandwidth used by the protocol

Metric difficult to interpretMetric difficult to interpret

no multiple pathsno multiple paths

Arbitrary External route costsArbitrary External route costs

No managing of subnetsNo managing of subnets

No authentication of routing messagesNo authentication of routing messages

The main advantage of distance vector algorithms is that they are typically easy to implement and debug. Theyare very useful in small networks with limited redundancy.

RIP limitations

There are a number of limitations observed in RIP environments:

Path cost limits: The resolution to the counting to infinity problem enforces a maximum cost for a network path.This places an upper limit on the maximum network diameter. Networks requiring paths greater than 15 hops mustuse an alternate routing protocol.

Network-intensive table updates: Periodic broadcasting of the distance vector table can result in increasedutilization of network resources. This can be a concern in reduced-capacity segments.

Relatively slow convergence: RIP, like other distance vector protocols, is relatively slow to converge. Thealgorithms rely on timers to initiate routing table advertisements.

No support for variable length subnet masking: Route advertisements in a RIP environment do not includesubnet masking information. This makes it impossible for RIP networks to deploy variable length subnet masks.


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RIPv2

Allows subnet routingAllows subnet routing

Authentication of the routing messagesAuthentication of the routing messages

Multicast transmissionMulticast transmission

Advantages of RIPv2 compared with RIPv1 :Advantages of RIPv2 compared with RIPv1 :

RIP-2 is described in RFC 1723. The standard was published in late 1994.


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Multicast

MAC 00.6f.66.32.0b.0800.6f.66.32.0b.08MAC

00.53.27.32.02.c800.53.27.32.02.c8MAC MAC

00.18.55.92.a2.0800.18.55.92.a2.08

00.35.d6.39.00.35.d6.39.cbcb.0a.0a

DestDest :: 01.00.5e.00.00.09 ..01.00.5e.00.00.09 ..

00.80.9f.00.02.0300.80.9f.00.02.03MAC 01.00.5e.00.00.0901.00.5e.00.00.09

01.00.5e.00.00.0901.00.5e.00.00.09

For each multicast address, there exists a set of zero or more hosts that listen for packets transmitted to theaddress. This set of devices is called a host group.

224.0.0.9: All RIP2 routers


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58

Format of the RIP 2 message

0 8 16 24 31

Command Version1 : Request

2 : Response

Value 1 to 15Value 1 to 15

Version =2

Authentic type0: no authentic

2: Password data

Authentication data

2 for IP2 for IP

Address Family Id

x FF FF forauthentication entry

Address Family Id


Subnet Mask

Next Hop


Route tag

InternalInternal ororexternalexternal routeroute

RIP-2 is described in RFC 1723 it provides these additional benefits not available in RIP-1:

Support for CIDR and VLSM: RIP-2 supports supernetting (that is, CIDR) and variable-length subnet masking.This support was the major reason the new standard was developed. This enhancement positions the standard to

accommodate a degree of addressing complexity not supported in RIP-1.

Support for multicasting: RIP-2 supports the use of multicasting rather than simple broadcasting of routingannoucements. This reduces the processing load on hosts not listening for RIP-2 messages. To ensureinteroperability with RIP-1 environments, this option is configured on each network interface.

Support for authentication: RIP-2 supports authentication of any node transmitting route advertisements. Thisprevents fraudulent sources from corrupting the routing table.

Support for RIP-1: RIP-2 is fully interoperable with RIP-1. This provides backward-compatibility between thetwo standards.

The first entry in the update contains either a routing entry or an authentication entry.

- Route Tag: This field is intended to differentiate between internal and external routes. Internal routes arelearned via RIP-2 within the same network or AS.

- Subnet Mask: This field contains the subnet mask of the referenced network.

- Next Hop: This field contains a recommendation about the next hop the router should use when sendingdatagrams to the referenced network.

The RIP-2 standard does not encrypt the authentication password. It is transmitted in clear text. This makes thenetwork vulnerable to attack by anyone with direct physical access to the environment.


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59

Encapsulation of the RIPv2 messages

Version Headerlength

Type OfService Datagramme length

Identification Flag Datagramme Offset

TTL Protocol: 1717 Checksum

Source IP address

Destination IPDestination IP addressaddress::

IPheader

UDPheader

UDP source port UDP destination port :

UDP message length Checksum UDP

RIP messageRIP message(25 routes maxi)(25 routes maxi)

512 bytesmax

UDPUDP

RIPRIP520520

MulticastMulticast224.0.0.9224.0.0.9

MAC src :--.--.--.--.--.--

MAC dest: 01.00.5E.00.00.0901.00.5E.00.00.09

RIP uses a specific packet format to share information about the distances to known network destinations. RIPpackets are transmitted using UDP datagrams. RIP sends and receives datagrams using UDP port 520. RIPdatagrams have a maximum size of 512 octets.

Updates larger than this size must be advertised in multiple datagrams. In LAN environments, RIP datagrams aresent using the MAC all-stations broadcast address and an IP network broadcast address. In point-to-point or non-broadcast environments, datagrams are specifically addressed to the destination device.

A 512 byte packet size allows a maximum of 25 routing entries to be included in a single RIP advertisement.


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60

Relationship between IP and MAC in multicast mode

MulticastMulticast MACMAC addressaddress

1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1

0 0 0 0 0 0 0 11 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0 0

0 1 - 0 0 5 E- - - -

MulticastMulticast IPIP AddressAddress

Classe D

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1

AddressAddress of groupof group

0 00 0 0 00 0 0 90 9

224 . .0 00 0 0 00 0 0 90 9.

AddressAddress translationtranslation

Multicast addressing

Multicast devices use Class D IP addresses to communicate. These addresses are contained in the rangeencompassing 224.0.0.0 through 239.255.255.255.

The mapping between the IP multicast destination address and the data-link address is not done with ARP.Instead, a static mapping has been defined. In an Ethernet network, multicasting is supported if the high-orderoctet of the data-link address is 0x'01'. The IANA has reserved the range 0x01005E000000' through0x'01005E7FFFFF' for multicast addresses. This range provides 23 usable bits. The 32-bit multicast IP address ismapped to an Ethernet address by placing the low-order 23 bits of the Class D address into the low-order 23 bitsof the IANA reserved address block.


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61

netid2

netid1

netid3netid4

CISCO : RIP Configuration

R2#

R2(config)#

config terminal

routerrip

R2(config-router)#

Routing protocol

R2

R3

R1

netid5

R2(config-router)#version 2 RIPv2

network

R2(config-router)# network

R2(config-router)# network

RIP routing updates will be sent and

received only through interfaces on

these networks

router rip : Enable a RIP routing process

network network-number :Associate a network with a RIP routing process. RIP routing updates will be sent and received onlythrough interfaces on this network. RIP sends updates to the interfaces in the specified networks. Also, if an interfaces network isnot specified, it will not be advertised in any RIP update.

version 2 : RIP v2 supports authentication, key management, route summarization, classless interdomain routing (CIDR), andvariable-length subnet masks (VLSMs).

no auto-summary Disable automatic summarization. RIP Version 2 supports automatic route summarization by default. Thesoftware summarizes subprefixes to the classful network boundary when crossing classful network boundaries. If you havedisconnected subnets, disable automatic route summarization to advertise the subnets.

Static routes that point to an interface will be advertised via RIP, IGRP, and other dynamic routing protocols, regardless of whetherredistribute static router configuration commands were specified for those routing protocols. These static routes are advertisedbecause static routes that point to an interface are considered in the routing table to be connected and hence lose their staticnature. However, if you define a static route to an interface that is not one of the networks defined in a network command, nodynamic routing protocols will advertise the route unless a redistribute static command is specified for these protocols.


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62

Interface configuration

OnlyOnly one router onone router on thisthis LANLAN((broadcastingbroadcasting of RIPof RIP

messages notmessages not requiredrequired))

RIPRIP should be implementedshould be implemented ininthisthis hosthost havinghaving 2 interfaces in2 interfaces inorderorder to selectto select thethe best routebest route

OnlyOnly one routerone routeronon thisthis LAN but,LAN but,

Passive-interface

PSTN

static route

Example: (config)# router rip

(config-router)# network network-to-be-advertised

(config-router)# network network-to-be- advertised

(config-router)# passive-interface interface

RIP modes of operation

RIP hosts have two modes of operation:

Active mode: Devices operating in active mode advertise their distance vector table and also receive routingupdates from neighboring RIP hosts. Routing devices are typically configured to operate in active mode.

Passive (or silent) mode: Devices operating in this mode simply receive routing updates from neighboring RIPdevices. They do not advertise their distance vector table. End stations are typically configured to operate inpassive mode.


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63

CISCO : Show RIP protocol

#show ip protocolsRouting Protocol is "rip"

Sending updates every 30 seconds, next due in 13 seconds

Invalid after 180 seconds, hold down 180, flushed after 240

Outgoing update filter list for all interfaces is

Incoming update filter list for all interfaces is

Redistributing: rip

Default version control: send version 1, receive any version

Interface Send Recv Key-chain

Ethernet0 1 1 2

Ethernet1 1 1 2

Routing for Networks:

172.16.0.0

Routing Information Sources:

Gateway Distance Last Update

172.16.200.4 120 00:00:22

172.16.200.1 120 00:00:12

172.16.200.3 120 00:00:07

172.16.200.200 120 00:00:05

Distance: (default is 120)

Weight added to the original metric which is function

of routing protocol : RIP120, OSPF110, IGRP100, ...

Next routing table transmissionRouting table

broadcastedevery 30

Route becomesinvalid after 180

without information

After the end offailure, the routekept invalid 180

When a route becomesinvalid (metric=16),router keeps it in

memory during 240

Administrative distance is the feature used by routers to select the best path when there are two or more different routes to thesame destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol. Each

routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. Administrative distance is the first criterion that a router uses to determine which routing protocol to use. The smaller the

administrative distance value, the more reliable the protocol.

If two protocols provide route information for the same destination.When several routing protocols are implemented in CISCOrouter, it adds a distance (weight) to the original metric, RIP: 120, OSPF:110, IGRP:100. If there are two routes with the samemetric to a destination, example: one got by Rip and another by Ospf, the router will select the ospf route,

The Cisco IOS software sends routing information updates every 30 seconds; this process is termed advertising.

If a router does not receive an update from another router for 180 seconds or more, it marks the routes served by the nonupdatingrouter as being unusable.

If there is still no update after 240 seconds, the router removes all routing table entries for the nonupdating router.


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64

r202#

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default

U - per-user static route, o - ODR

T - traffic engineered route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 14 subnets

R 172.16.204.0 [120/1] via 172.16.200.4, 00:00:00, Ethernet0

C 172.16.200.0 is directly connected, Ethernet0R 172.16.201.0 [120/1] via 172.16.200.1, 00:00:20, Ethernet0

C 172.16.202.0 is directly connected, Ethernet1

R 172.16.203.0 [120/1] via 172.16.200.3, 00:00:14, Ethernet0

R 172.16.1.0 [120/1] via 172.16.200.200, 00:00:14, Ethernet0

show ip route

CISCO : show IP route

If two protocols provide route information for the same destination.When several routing protocols are implemented in CISCOrouter, it adds a administrative distance (weight) to the original metric, RIP: 120, OSPF:110, IGRP:100. If there are two routes withthe same metric to a destination, example: one got by Rip and another by Ospf, the router will select the ospf route,

Connected interface 0

Static route 1

Enhanced Interior Gateway Routing Protocol (EIGRP) summary route 5

External Border Gateway Protocol (BGP) 20

Internal EIGRP 90

IGRP 100

OSPF 110

Intermediate System-to-Intermediate System (IS-IS) 115

Routing Information Protocol (RIP) 120

Exterior Gateway Protocol (EGP) 140

On Demand Routing (ODR) 160

External EIGRP 170

Internal BGP 200

Unknown* 255


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65

CISCO : Debug RIP events

r202#deb ip rip events

RIP event debugging is on

r202#

00:45:46: RIP: received v1 update from 172.16.200.4 on Ethernet0

00:45:46: RIP: Update contains 1 routes00:45:52: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.16.200.2)

00:45:52: RIP: Update contains 1 routes

00:45:52: RIP: Update queued

00:45:52: RIP: sending v1 update to 255.255.255.255 via Ethernet1 (172.16.202.1)

00:45:52: RIP: Update sent via Ethernet0


00:45:52: RIP: Update queued

00:45:52: RIP: Update sent via Ethernet1





00:46:05: RIP: received v1 update from 172.16.200.3 on Ethernet000:46:05: RIP: Update contains 1 routes

r202#u all


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CISCO : Debug RIP

r202#deb ip ripRIP protocol debugging is onr202#00:46:24: RIP: received v1 update from 172.16.200.1 on Ethernet000:46:24: 172.16.201.0 in 1 hops00:46:31: RIP: received v1 update from 172.16.200.200 on Ethernet000:46:31: 172.16.1.0 in 1 hops00:46:31: 172.16.2.0 in 1 hops

00:46:31: 172.16.104.0 in 3 hops00:46:31: 172.16.105.0 in 3 hops00:46:31: 172.16.106.0 in 3 hops00:46:31: 172.16.100.0 in 2 hops00:46:31: 172.16.101.0 in 3 hops00:46:31: 172.16.102.0 in 3 hops00:46:31: 172.16.103.0 in 3 hops00:46:34: RIP: received v1 update from 172.16.200.3 on Ethernet000:46:34: 172.16.203.0 in 1 hops00:46:43: RIP: received v1 update from 172.16.200.4 on Ethernet000:46:43: 172.16.204.0 in 1 hops00:46:46: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.16.200.2)00:46:46: subnet 172.16.202.0, metric 100:46:46: RIP: sending v1 update to 255.255.255.255 via Ethernet1 (172.16.202.1)00:46:46: subnet 172.16.204.0, metric 200:46:46: subnet 172.16.200.0, metric 100:46:46: subnet 172.16.201.0, metric 200:46:46: subnet 172.16.203.0, metric 200:46:46: subnet 172.16.1.0, metric 2

00:46:46: subnet 172.16.2.0, metric 200:46:46: subnet 172.16.104.0, metric 400:46:46: subnet 172.16.105.0, metric 400:46:46: subnet 172.16.106.0, metric 400:46:46: subnet 172.16.100.0, metric 300:46:46: subnet 172.16.101.0, metric 400:46:46: subnet 172.16.102.0, metric 400:46:46: subnet 172.16.103.0, metric 400:46:52: RIP: received v1 update from 172.16.200.1 on Ethernet000:46:52: 172.16.201.0 in 1 hops


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Routing

3. OSPF protocol

Open Shortest Path First (OSPF)

The Open Shortest Path First (OSPF) protocol is another example of an interior gateway protocol. It was developed as a non-proprietary routing alternative to address the limitations of RIP. Initial development started in 1988 and was finalized in 1991.Subsequent updates to the protocol continue to be published. The current version of the standard is documented in RFC 2328.

OSPF provides a number of features not found in distance vector protocols. Support for these features has made OSPF a widely-deployed routing protocol in large networking environments. In fact, RFC 1812 Requirements for IPv4 Routers, lists OSPF as theonly required dynamic routing protocol.

Equal cost load balancing: The simultaneous use of multiple paths may provide more efficient utilization of network resources.

Logical partitioning of the network: This reduces the propagation of outage information during adverse conditions. It also provides theability to aggregate routing announcements that limit the advertisement of unnecessary subnet information.

Support for authentication: OSPF supports the authentication of any node transmitting route advertisements. This prevents fraudulentsources from corrupting the routing tables.

Faster convergence time: OSPF provides instantaneous propagation of routing changes. This expedites the convergence timerequired to update network topologies.

Support for CIDR and VLSM: This allows the network administrator to efficiently allocate IP address resources.


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68

NetworkNetwork

222.211.10222.211.10.00

NetworkNetwork

192.213.11192.213.11.00

Network : 128.213Network : 128.213.0.0.0.0

Shortest path tree

RbRb

RdRd

RcRc

Each router makes a tree-representation of the network

RaRa (view of R1)RaRa

NetworkNetwork

128.213128.213.0.0.0.0

LinkLink--costcost= 100 000 000 / bandwidthbps

55

55

1010

RbRb

1010

RcRc

1010

1010

NetworkNetwork

192.213.11192.213.11.00

55

NetworkNetwork222.211.10222.211.10.00

RdRd

55

55

1010

costcost

00

costcost

The SPF algorithm is used to process the information in the topology database. It provides a tree-representation of the network.The device running the SPF algorithm is the root of the tree. The output of the algorithm is the list of shortest-paths to each

destination network. Because each router is processing the same set of LSAs, each router creates an identical link state database. However,

because each device occupies a different place in the network topology, application of the SPF algorithm produces a differenttree for each router.

cost= 100 000 000 / bandwidthbps

Example :

Cost of 10Mb/s Ethernet link : 108 / 107 = 10

Cost of link T1 1,544Mb/s: 108 / 1544x103 = 64


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69

From To L CostFrom To L Cost

From To L Cost

SPF database (Initialisation)

RbRb

RdRd

RcRc

RaRa

Net: 3Net: 3

Net: 2Net: 2

Net: 1Net: 1

11

11

11

22

22

22

33

AA B 1B 111 33AA C 1C 111 33

From To L Cost

C3

C1

C1

C3

C2

C3

C4

Toutes les Databases sont identiques

AA NN11 1111 33

CC A 1A 133 22CC B 1B 133 22

CC NN11 1133 22CC NN33 3322 11

CC D 3D 322 11

DD B 2B 222 44DD C 3C 311 33

DD NN33 3311 33

BB A 1A 122 11

BB D 2D 211 33

BB NN11 1122 11BB NN22 2211 33

BB C 1C 122 11

DD NN22 2222 44

Link state database

The link state database is also called the topology database. It contains the set of link state advertisements describing theOSPF network and any external connections.


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70

From To L Cost

From To L Cost

SPF database (Updating)

RbRb

RdRd

RcRc

RaRa

Net: 3Net: 3

Net: 2Net: 2

Net: 1Net: 1

11

11

11

22

22

22

33

AA B 1B 111 33AA C 1C 111 33

From To L Cost

C3

C1

C1

C3

C2

C3

C4

All the Databases are identical

AA NN11 1111 33

From To L Cost

CC A 1A 133 22CC B 1B 133 22

CC NN11 1133 22CC NN33 3322 11

CC D 3D 322 11

BB A 1A 122 11

BB D 2D 211 33CC NN11 1133 22

DD B 2B 222 44DD C 3C 311 33

CC A 1A 133 22

DD NN33 3311 33

BB NN11 1122 11BB NN22 2211 33

CC D 3D 322 11CC NN33 3322 11

DD NN22 2222 44

CC B 1B 133 22

BB C 1C 122 11

DD B 2B 222 44DD C 3C 311 33

DD NN33 3311 33

BB A 1A 122 11BB C 1C 122 11

BB NN11 1122 11BB NN22 2211 33

BB D 2D 211 33

CC A 1A 133 22CC B 1B 133 22

CC NN11 1133 22CC NN33 3322 11

AA B 1B 111 33AA C 1C 111 33

AA NN11 1111 33CC D 3D 322 11

BB A 1A 122 11

BB D 2D 211 33

BB NN11 1122 11BB NN22 2211 33

BB C 1C 122 11

AA B 1B 111 33AA C 1C 111 33

AA NN11 1111 33

CC NN11 1133 22

DD B 2B 222 44DD C 3C 311 33

CC A 1A 133 22

DD NN33 3311 33

CC D 3D 322 11CC NN33 3322 11

DD NN22 2222 44

CC B 1B 133 22

DD NN22 2222 44

DD B 2B 222 44DD C 3C 311 33

BB A 1A 122 11BB C 1C 122 11

AA B 1B 111 33AA C 1C 111 33

AA NN11 1111 33

DD NN33 3311 33

BB NN11 1122 11BB NN22 2211 33

BB D 2D 211 33

DD NN22 2222 44

Each router within the area maintains an identical copy of the link state database.


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71CC

AA BB CC DD

AA BB CC DD

BB

CC

DD

AA

BB

AA BB CC DD

BB CC DD

Route

A to

Route

Route

SPF calculation

From To L Cost

RaRaAA B 1B 111 33AA C 1C 111 33

AA NN11 1111 33

BB A 1A 122 11

BB D 2D 211 33CC NN11 1133 22

DD B 2B 222 44DD C 3C 311 33

CC A 1A 133 22

DD NN33 3311 33

BB NN11 1122 11BB NN22 2211 33

CC D 3D 322 11CC NN33 3322 11

DD NN22 2222 44

CC B 1B 133 22

BB

C 1C 122 11

33 3300

00 1111 33

112222

44 33

00

00

3+3+00 3+3+113+3+11 3+3+33

A,B

C=3

A,C

C=3

A,B,DC=6

3+3+113+3+223+3+22 3+3+00

A,C,DC=4

+3+3+3+3

RbRb

RdRd

RcRc

Net: 3Net: 3

Net: 2Net: 2

Net: 1Net: 1

11

11

11

22

22

22

33

C3

C1

C1

C3

C2

C3

C4

primaryprimary

secondarysecondary

There are two algorithms for computing a routing table from a link table. These are:

the forward search algorithm (Also known as Dijkstra's Algorithm) and,

the backward search algorithm (Also known as the Bellman-Ford Algorithm)


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72

SPF example : Network topology

slipslip

11

E12E12

E15E15

N3N3

E12E12 E13E13 E14E14N1N1

N2N2 N4N4

N9N9

N12N12

N11N11

N8N8

N7N7

R1R1

R2R2 R3R3

R4R4 R5R5

R9R9

R12R12

N10N10

R11R11

R7R7

R8R8

R6R6

N6N6R10R10

8888

88 88 88

77

6688

11

33

11

11

11

101022

11 2211

11

44

55

77

66

66

22

99

22

33

33

1133

11

11

66

Inter networks example:


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73

SPF example : Init

E12E12 E13E13 E14E14

8888

88 88 88

77

88

11

1010

22

11 2211

11

44

E12E12

E15E15

55

77

66

66

22

99

22

33

R1R1

R2R2 R3R3

R4R4 R5R5

R9R9

R12R12R11R11

R7R7

R8R8

R6R6

N6N61133 R10R10

11

11

66

N3N3

N2N2

33N1N1

33 N11N11

N9N9

N10N10 N12N12

N8N8

N4N4

11

11

11

Dest Cost

R6R6R10R10 77R6R6R3R3 66R6R6R5R5 66

N7N7

66

Dest Cost

R3R3R6R6 88R3R3N4N4 22R3R3N3N3 11

Dest Cost

R4R4

R5R5 88R4R4N3N3 11

Dest Cost

R1R1N1N1 33R1R1N3N3 11

Dest Cost

R2R2N2N2 33R2R2N3N3 11

Dest Cost

R9R9N11N11 33R9R9N9N9 11

Dest Cost

R12R12N9N9 11

R12R12N10N10 22R12R12N12N12 1010

Dest Cost

R11R11N9N9 11R11R11N8N8 22

Dest Cost

R10R10R6R6 55R10R10N6N6 11R10R10N8N8 33

Dest Cost

R8R8N6N6 11R8R8N7N7 44

Dest Cost

R7R7R5R5 66

R7R7N6N6 11R7R7E12E12 22R7R7E16E16 99

Dest Cost

R5R5R4R4 88R5R5R6R6 77R5R5R7R7 66R5R5E12E12 88R5R5E13E13 88R5R5E14E14 88

Each node knows the directly connected links as well as the adjacent routers.


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74

SPF example : Database exchange

E12E12 E13E13 E14E14

8888

88 88 88

77

88

11

1010

22

11 2211

11

44

E12E12

E15E15

55

77

66

66

22

99

22

33

R1R1

R2R2 R3R3

R4R4 R5R5

R9R9

R12R12R11R11

R7R7

R8R8

R6R6

N6N61133 R10R10

11

11

66

N3N3

N2N2

33N1N1

33 N11N11

N9N9

N10N10 N12N12

N8N8

N4N4

11

11

11

N7N7

66

R6R6Dest Cost

R6R6R10R10 77R6R6R3R3 66R6R6R5R5 66R3R3R6R6 88R3R3N4N4 22

R3R3N3N3 11R2R2N2N2 33R2R2N3N3 11R1R1N1N1 33R1R1N3N3 11R4R4R5R5 88R4R4N3N3 11R9R9N11N11 33R9R9N9N9 11R12R12N9N9 11R12R12N10N10 22R12R12N12N12 1010R11R11N9N9 11R11R11N8N8 22R10R10R6R6 55R10R10N6N6 11R10R10N8N8 33R8R8N6N6 11

R8R8N7N7 44R7R7R5R5 66R7R7N6N6 11R7R7E12E12 22R7R7E15E15 99R5R5R4R4 88R5R5R6R6 77R5R5R7R7 66R5R5E12E12 88R5R5E13E13 88R5R5E14E14 88

After exchanges between routers, each router within the area maintains an identical copy of the link state database.


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75

SPF example : Graph

E12E12 E13E13 E14E1488 88 88

E12E12

E15E15

22

99

R1R1

R2R2 R3R3

R4R4 R5R5

R9R9

R12R12R11R11

R7R7

R8R8

R6R6

N6N6R10R10

N3N3

N2N2

N1N1

N11N11

N9N9

N10N10 N12N12

N8N8

N4N4

N7N7

88

66

11

11

22 22

11

1133

33

11

11

33

33 11

1188

88

66

66

557733

33

1111

11

11

11

11

1010

101022

22

22

22

33

33

11

11

1111

4444

1111

7766

R6R6Dest Cost

R6R6R10R10 77R6R6R3R3 66R6R6R5R5 66R3R3R6R6 88R3R3N4N4 22

R3R3N3N3 11R2R2N2N2 33R2R2N3N3 11R1R1N1N1 33R1R1N3N3 11R4R4R5R5 88R4R4N3N3 11R9R9N11N11 33R9R9N9N9 11R12R12N9N9 11R12R12N10N10 22R12R12N12N12 1010R11R11N9N9 11R11R11N8N8 22R10R10R6R6 55R10R10N6N6 11R10R10N8N8 33R8R8N6N6 11

R8R8N7N7 44R7R7R5R5 66R7R7N6N6 11R7R7E12E12 22R7R7E15E15 99R5R5R4R4 88R5R5R6R6 77R5R5R7R7 66R5R5E12E12 88R5R5E13E13 88R5R5E14E14 88

From its topology database, any router can know the network topology.


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SPF example : Routing table of R6

E13E13 E14E14

88 88

E12E12E15E15

99

R1R1

R2R2R3R3

R4R4R5R5

R9R9

R12R12

R11R11

R7R7

R8R8

R6R6

N6N6R10R10

N3N3

N2N2

N1N1

N11N11

N9N9

N10N10 N12N12

N8N8

N4N4

N7N7

11

11

66

33

33

6622

77

33

33

11

11

1010

22

11

44

22

Dest. Next Costhop

N1 R3 10

N2 R3 10

N3 R3 7

N4 R3 8N6 R10 8

N7 R10 12

N8 R10 10

N9 R10 11

N10 R10 13

N11 R10 14

N12 R10 21

RT5 R5 6

RT7 R10 8

E12 R10 10

E13 R5 14

N14 R5 14

N15 R10 17

22

11

11

1111

11

Routing tables are constructed by examining a link table whose entries detail the cost of each link in the network.


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SPF example : Tree seen by R6

E13E13 E14E14

E12E12 E15E15

R1R1 R2R2

R3R3

R4R4

R5R5

R9R9 R12R12

R11R11 R7R7R8R8

R6R6

N6N6

R10R10

N3N3

N2N2N1N1

N11N11

N9N9

N10N10 N12N12

N8N8

N4N4 N7N7

Each router can see the network as a tree.


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OSPF: Router Identifier

IP@= 3.3.3.3IP@= 3.3.3.3

IP@=1.1.1.1IP@=1.1.1.1

IP@=2.2.2.2IP@=2.2.2.2

LoopbackLoopback

IP@= 5.5.5.5IP@= 5.5.5.5

LoopbackLoopbackIP@= 7.7.7.7IP@= 7.7.7.7

IP@= 9.9.9.9IP@= 9.9.9.9

IP@=4.4.4.4IP@=4.4.4.4

RID=RID=

if no loopback,

RID=RID=

RID= (Router ID) highest loopback IP@,

the highest interface IP@.

7.7.7.77.7.7.7

3.3.3.33.3.3.3

In OSPF, an unique identifier is assigned to each node : RID (Router Identity)

The RID is the highest IP address on the box or the loopback interface, calculated at boot time or whenever the OSPF processis restarted.

IP advanced.pdf

Documents

Transcript of IP advanced.pdf