Isp Routing

7/25/2019 Isp Routing

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Routing BasicRouting Basic

Routing is delivering the incoming packets to the

destination.

Routing involves two basic activities:-

Determination of optimal path to the destination.

Transport or delivery of packets to the

destination.


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Two methods of delivery of packets

Direct Delivery

Indirect Delivery


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Direct DeliveryDirect Delivery

In Direct Delivery the final destination of the packet is ahost connected to the same physical network as the

sender.

This will occur when the source and the destination are

located in the same physical network or if the delivery is

between the last and the destination host.

The sender uses the destination I address to find the

destination!s physical address.

The I software then delivers the destination I address

with the destination"s physical address to the data #ink.


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To rest of Internet

Direct Delivery

$ost %

$ost &

Direct Delivery


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Indirect deliveryIndirect delivery

If the destination is not on the same network as

the sender the packet goes from router to router. The packet travels until reaches the router

connected to the same physical network as its

final destination.

The last delivery is always direct delivery.


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R3

Indirectdelivery

Indirect delivery

Indirect delivery

Direct delivery

$ost %

$ost &

R1

R2

Indirect Delivery


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Routing MethodsRouting Methods

Routing re'uires a host or a router to have a

routing table. (everal techni'ues can make the si)e of the

routing table manageable.

They are:*e+t $op Routing

*etwork (pecific Routing

$ost specific Routing

Default Routing.


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Routing MethodsRouting Methods

*e+t hop routing:

In this method the routing table holds only the address ofthe ne+t hop, instead of holding complete route

information.

*etwork (pecific Routing:

Instead of having an entry for every host connected to thesame physical network, only one entry to define the address

of the network.

$ost (pecific Routing:

The host address is given in the routing table.

Default Routing:

Instead of listing all networks in the entire Internet a host

can ust have one entry called the default address.


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R1

Network 2 Network 3*etwork

R2

Destn *e+t $op

$ost & R

Destn *e+t $op

$ost & R/

Destn *e+t $op

$ost & ----

$ost %

$ost &

Next Hop Routing


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N2N1

S A B C

D E

R1

Destn *e+t $op

% R

& R

0 R

D R

1 R

Destn *e+t $op

*/ R

Network Specific Routing

Host Specific Routing


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*

*/*2

RR2

R/

Destn *e+t $op

$ost & R2

*/ R

*2 R2

&

%

Host Specific Routing


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*/*

R1

R1

Internet

Dest *e+t $op

*/ R

Default R/

R i B iR i B i


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3hen looking for the route, the router must first

check for direct delivery, then host specific delivery,then network specific delivery and finally default

delivery.

% host or a router keeps a routing table,

with an entry for each destination , to route

I packets.

The routing table may be4 (tatic

4 Dynamic


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Static RoutingStatic Routing

(tatic routing table mappings are established

manually by the network administrator.

(tatic routing system cannot react to networkchanges.

They are not suitable for Today!s large

Internetwork.

D i iD i ti


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Dynamic routingDynamic routing

&y using Routing protocol the routers can

automatically update any change in the routeDynamically. This is known as Dynamic routing.

In large 3%* with multiple links between

networks Routers perform more effectively when

they under stand how the network is linked.

Routers does this by e+changing information

with other Routers.

%s as result Routers create Routing Table thatshows the best path between the various links.

R ti B iR ti B i


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3ide variety of Routing rotocols can be found

(ome are roprietary or (ingle vendor for their own

products.5thers are open that have been standardised by official

sanctioning %gencies.

%mong the roprietary are

I6

I7R

5pen rotocols 8They are standardised by Internet %ctivity

&oard 8I%&9 and I(5RI

5(

Intermediate (ystem to Intermediate (ystem


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Routing AlgorithmsRouting Algorithms

%ll dynamic routing protocols are based on some

algorithms. %lgorithms must be able to 'uickly determine the

*etwork topology.

This process is called 0onvergence.

0onvergence must take place rapidly.

1ach algorithm has a different impact on *etwork

and Routers.

Routing algorithms use a variety of ;etrics

that affect calculation of 5ptimal Routs.


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0ommonly used algorithms are

Distance


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3hen there are multiple routes to the same destination,a router must have a mechanism for calculating the

best path.

% metric is a variable assigned to routers as a

means of ranking them from best to worst or from

most preferred to least preferred.

Different routing protocols use different and

sometimes multiple metrics.

Path DeterminationPath Determination

M t iM t i


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MetricsMetrics

The following are the metrics used.

$op 0ount

&andwidth

#oad

Delay

Reliability

0ost

Di t V t P t lDistance Vector Protocol


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Distance Vector ProtocolDistance Vector Protocol

In Distance


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Distance Vector ProtocolDistance Vector Protocol

Routers create a network map by communicating in a

periodic and progressive se'uence with other. This information e+change helps them determine the

scope of their network in a series of router hops that

reveals more information about the network.

3hen the router is started it knows only the networks it

is connected directly.

Then advertises information about its immediate

connections to the other routers directly connected. The Distance vector routing protocol uses second hand

information from their neighbor.

Link Status ProtocolLink Status Protocol


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Link Status ProtocolLink Status Protocol

&ased on (hortest ath irst or Dikstra %lgorithm.

(ending of link state advertisements 8#(%s9 to all other routers

within the same hierarchical area.

( routers send link-state data to all routers.

The routers perform two task

irst they use the link-state data to build a complete table ofrouter and network connections.

Then each router calculates the optimal path to each link.

3hen a router detects changes in the state of its direct link the

router broadcast the change to all others through a process called

flooding.



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Routing protocols are divided into

Interior Gatewa Routing !rotoco" #IG!$

Exterior Gatewa Routing !rotoco" #EG!$



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Interior Gateway ProtocolInterior Gateway Protocol


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Interior Gateway ProtocolInterior Gateway Protocol

Interior 7ateway rotocol are used within an %utonomous

(ystem to dynamically determine the best route.

They are

Distance %ector

4Routing Infor&ation !rotoco" #RI!$

4 Routing Infor&ation !rotoco" 2 #RI! 2$

'ink Status !rotoco"

4 (pen S)ortest pat) first#(S!*$

4 Internet Gatewa Routing !rotoco" #IGR!$

4 En)ance+ IGR!

4 Integrate+ Inter&e+iate Sste& to Inter&e+iate Sste&


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!terior Gateway Protocol!terior Gateway Protocol

1+terior 7ateway protocol is known as inter domain

rotocol.

=sed to e+change routing information between

different %utonomous systems. administration.

1+terior gateway protocols re'uire the following three

sets of information before routing can begin.

% list of neighbor 8or eer9 routers with which to

e+change routing information.

% list of *etworks to advertise as directly reachable.The %utonomous system number of the #ocal

Router.


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!terior Gateway Protocol!terior Gateway Protocol

1+terior 7ateway rotocol 8179

&order 7ateway rotocol 8&79

&order 7ateway rotocol > 8&7 >9

Routing In"ormation ProtocolRouting In"ormation Protocol


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RI is a Distance


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RI maintains only the best route to a destination.

3hen a new information provides a better route

this will replace old route information. RI uses single routing metric 8$op count9.


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RIP %RIP %


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RIP %RIP %

(upport


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Interior Gateway Routing ProtocolInterior Gateway Routing Protocol

Developed by 0I(05 in the mid B@?!s.

I7R uses a combination of matrics4 Internetwork Delay

4 &andwidth 8/?? bps to ? gigabits9

4 Reliability4 #oad 8


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nhanced IGRPnhanced IGRP

3ith (oftware Release B./ 0isco introduced1I7R.

It combines advantage of #ink status with the

Distance vector protocols.1I7R incorporates the Diffusing =pdate

%lgorithm.

#eatures o" IGRP#eatures o" IGRP


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#eatures o" IGRP#eatures o" IGRP

ast 0onvergence : 1I7R stores all of its

neighbors routing tables so that it can 'uickly

adapt to alternate route.

If no appropriate route e+ists 1I7R 'ueries

its neighbor routers to discover an alternate

route.(upports


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&'en Shortest Path #irst&'en Shortest Path #irst

=sing #ink (tate algorithm.

Introduced in B@B

;uch lower traffic overhead.

1limination of count to infinity problem.

=sing cost as metric, ;etric can be as large as

CAA2A.

(upport


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&'en Shortest Path #irst&'en Shortest Path #irst

1ach Router builds a database of the *etwork.

1+change only when tables are updated

rovides #oad balancing.

4 ;ultiple routes to a single destination.

#ooping is not formed since each router hasthe complete information.

aster convergence.

(ending link (tate advertisement to all otherrouters.


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0..(undaram

(D1 0omputer

R7; TT0, 0hennai C?? ?/E

Isp Routing

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