Effect of the Interior Gateway Routing Protocols in the Mult.pdf

7/27/2019 Effect of the Interior Gateway Routing Protocols in the Mult.pdf

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Sudan University of Science &Technology

College of Graduated Studies

Effect of the Interior Gateway RoutingProtocols in the Multiprotocol Label

Switching Networks

A thesis submitted as partial fulfillment for the requirement

of the MSC Degree in Electronic Engineering

(Telecommunications Engineering)

Submitted by:

Suhail Badai Abdel!arim ahmed


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Supervised by:

Dr" Sara Mustafa El#ac!

$ctober %&'%

!"# $%&'!(#)* %+,#-#.# /#0!'12%3*4!'#(#)#0!2!&5!6#"#7#&8!9:*(!2*%"#7#";


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To the man who gave me faith, power andorganized my life to My Father.And to our

continuou ource of love My Mother


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QNTULEVGEMENW!t wa a great honor and e"tremely great

opportunity that Allah gave to me to #e under

upervied and one of tudent of great teacher

li$e Dr. Sara Mustafa Eljackhe wa very helpful

,with unlimited $indne and he gave me her #et

effort to ma$e thi wo$ true. Than$ you very much.

%pecial than$ to my #et friend Eng.Waleed

Mohammed Elhassanfor hi upport and valua#le

advie.

And ! would li$e to give my than$ toEng.Mohammed Foad Mekkifrom &apital 'ne co.

for hi upport and uggetion.

And of coure my limitle than$ and wonderful

feeling to my fianc(e Gamerfor her upport,

patient and undertanding.


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Abstract

Traditional based netor!s* +rame ,ela- and ATM netor!s ha.e man-

disad.antages in the management operation of large netor!s li!e cost* securit-*

scalabilit- and fle/ibilit-" To sol.e this* an M0S1based 23 netor!ing is

introduced that can or! ith e/isting deplo-ed bac!bones and allo

organi4ations to interconnect the dispersed sites and remote or!ers through

secure lin!s b- using public internet"

This thesis tries to pro.ide a better understand of the operation of ser.ice

pro.iders large netor!s management operation through focusing in the M0S

23 technolog-" t offers a detailed description of the ma#or operation of the

M0S 23 netor!s to met a customer requirement in the content deli.er-

mission" To get better understand of the beha.ior of the M0S 23 netor!s* the

interaction beteen routing protocols as chosen as a case stud- of the M0S

23 netor!s performance" This thesis or! is mainl- focusing in stud-ing the

effect of the interior gatea- routing protocols in the M0S 23 netor!s" To

famous protocols chose to be in.estigated ($S+ and S1S) and to proposed

designs are introduced to be simulated ith $3ET Modeler then an in depth

anal-ses of the netor! performance ill be pro.ide "


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Keywords: IP, MPLS, VPN, MPLS VPN, OSPF,IS-IS

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'Bac!ground ''"%roblem Statement '"roposed Solution

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()ST "* *)GU!S

*igure #umber Title Page

+igure '"' Con.ergence in M0S netor!s %

+igure %"' Traditional 0a-er % Bac!bone 3etor! ?

+igure %"% M0S netor! '&

+igure %"Basic Architecture of an M0S 3ode erforming

,outing

''

+igure %"; 0abel Sitched ,outer '%

+igure %"< 0abel Sitched ath '

+igure %"= 7eneric label format ' frame rela- as a data lin! la-er ' Di#!stras algorithm ;=

+igure "?"The lin! state database

;>

+igure "'&S+ routing


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+igure ;"% 0oad in 0arge $S+ netor! (ello23) ?=

+igure ;"% 23s load comparison ?@

+igure ;"%; Throughput in 0arge $S+ netor! (,ed23) ?>

+igure ;"%< Throughput in 0arge $S+ netor! (ello23) ?>

+igure ;"%= 23s Throuput comparison ??+igure ;"%@ Con.ergence duration of $S+ '&&

+igure ;"%> End to end dela- in 0arge S1S netor! (,ed23) '&&

+igure ;"%?end to end dela- in 0arge S1S netor!

(ello23)'&'

+igure ;"& 23s dela- comparison '&'

+igure ;"%' 0oad in 0arge S1S netor! (,ed23) '&%

+igure ;"% 0oad in 0arge $S+ netor! (ello23) '&

+igure ;" 23s load comparison '&

+igure ;"; Throughput in 0arge S1S netor! (,ed23) '&;+igure ;"< Throughput in 0arge S1S netor! (ello23) '& *or4ard 9uivalence Class 6*C7: A group of pac!ets that has the same transmission path and forarding

mechanism is !non as +EC" The pac!ets belonging to the same +EC ha.e the

same label" But some pac!ets do not belong to same +EC and forarding

mechanism due to a different E9 .alue" ngress 0S,s decides hich pac!et

belongs to hich +EC and this is done onl- once in M0S netor! G=H"

$%$%$ (abels and (abel +indings:

A label* in its simplest form* identifies the path that a pac!et should tra.erse" A

label is carried or encapsulated in a 0a-er % header along ith the pac!et" The

recei.ing router e/amines the pac!et for its label content to determine the ne/t

hop" After a pac!et has been labeled* the rest of the #ourne- of the pac!et through

the bac!bone is based on label sitching" The label .alues are of local significance

onl-* meaning that the- pertain onl- to hops beteen 0S,s" After a pac!et has

been classified as a ne or e/isting +EC* a label is assigned to the pac!et" The

label .alues are deri.ed from the underl-ing data lin! la-er" These data lin! la-er

identifiers* such as +rame ,ela- D0Cs or ATM 2K2Cs* can be used directl- as

labels" The pac!ets are then forarded based on their label .alue"

0abels are bound to an +EC as a result of some e.ent or polic- that indicates a

need for such binding" These e.ents can be either data1dri.en bindings or control1

dri.en bindings" The latter is preferable because of its ad.anced scaling properties

that can be used in M0S"


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0abel assignment decisions can be based on forarding criteria such as the

folloing:

Destination unicast routing"

Traffic engineering (TE)"

Multicast"

2irtual pri.ate netor! (23)"

Jualit- of Ser.ice (JoS)"

%"%"%"' Generic (abel *ormat:

7eneric label format is illustrated in +igure %"= "The label can be embedded inthe header of the data lin! la-er(the ATM 2CK2 is shon in +igure %"@ and

frame1rela- D0C in +igure %">) or in the shim (beteen la-er % and la-er

netor! header as shon in +igure %"?" G=H

+igure %"= 7eneric label format


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+igure %"@ ATM as a data lin! la-er

+igure %"> frame rela- as a data lin! la-er

$%$%$%$ (abel Creation:

Topologybased methodI uses normal processing of routing protocols (such

as $S+ and B7)"

!e9uestbased methodI uses processing of request1based control traffic (such

as ,S2)"

Trafficbased method I uses the reception of a pac!et to trigger the

assignment and distribution of a label"

The topolog-1 and request1based methods are e/amples of control1dri.en label

bindings* hile the traffic1based method is an e/ample of data1dri.en binding"

$%$%$% (abel 8istribution


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M0S architecture dose not mandate a single method of signaling for label

distribution" E/isting routing protocols* such as the border gatea- protocol

(B7)* ha.e been enhanced to pigg-bac! the label information ithin the

contents of the protocol" The ,S2 has been e/tended to support pigg-bac!ed

e/change of labels" The ET+ has also defined a ne protocol !non as the label

distribution protocol (0D) for e/plicit signaling and management of the label

space"

A summar- of the .arious schemes for label e/change is as follos:

'" (8PI maps unicast destination into labels

%" !S;P


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nodes through hich the pac!et tra.erses" The path specified could be non1

optimal* as ell" Along the path* the resources ma- be reser.ed to ensure JoS to

the data traffic" This eases traffic engineering through out the netor!* and

differentiated ser.ices can be pro.ided using flos based on policies or netor!

management methods" The 0S setup for an +EC is unidirectional" The return

traffic must ta!e another 0S" +igure %"? shos a basic operation for the and

interaction beteen the M0S netor! elements"G=H*G?H"


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+igure %"? Basic M0S $peration

The folloing steps must be ta!en for a data pac!et to tra.el through an M0S

domain:

label creation and distribution"

Table creation at each router"

label1sitched path creation"

0abel insertionKtable loo!up"

ac!et forarding"

The source sends its data to the destination" n an M0S domain* not all of the

source traffic is necessaril- transported through the same path" Depending on the

traffic characteristics* different 0Ss could be created for pac!ets ith different

requirements"

$%$% Signaling 5echanisms

'" label re9uestO8sing this mechanism* an 0S, requests a label from its

donstream neighbor so that it can bind to a specific +EC" This mechanism can

be emplo-ed don the chain of 0S,s up until the egress 0E, (i"e"* the point at

hich the pac!et e/its the M0S domain)"

%" label mappingOn response to a label request* a donstream 0S, ill send a

label to the upstream initiator using the label mapping mechanism"

Concepts for label request and label mapping are e/plained in +igure %"'&:


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+igure %"'& M0S signaling

$%$%- Tunneling in 5P(S

A unique feature of M0S is that it can control the entire path of a pac!et

ithout e/plicitl- specif-ing the intermediate routers" t does this b- creating

tunnels through the intermediar- routers that can span multiple segments" This

concept is used in pro.isioning M0SIbased 23s"

Consider the scenario in +igure %"''" 0E,s (0E,'* 0E,%* 0E,* and 0E,;) all

use B7 and create an 0S beteen them (0S ')" 0E,' is aare that its ne/t

destination is 0E,%* as it is transporting data for the source* hich must go

through to segments of the netor!" n turn* 0E,% is aare that 0E, is its ne/t

destination* and so on" These 0E,s ill use the 0D to recei.e and store labels

from the egress 0E, (0E,; in this scenario) all the a- to the ingress 0E,

(0E,')"G=H"


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+igure %"''" Tunneling in M0S

+or 0E,' to send its data to 0E,%* it must go through se.eral 0S,s" Therefore*

a separate 0S (0S %) is created beteen the to 0E,s (0E,' and 0E,%) that

spans 0S,'* 0S,%* and 0S," This* in effect* represents a tunnel beteen the to

0E,s" The labels in this path are different from the labels that the 0E,s created

for 0S'" This holds true for 0E, and 0E,;* as ell as for the 0S,s in beteen

them" 0S is created for this segment"

To achie.e this* the concept of a label stac! is used hen transporting the pac!et

through to netor! segments" As a pac!et must tra.el through 0S '* 0S %*and

0S * it ill carr- to complete labels at a time" The pair used for each segment

is (') first segment* label for 0S ' and 0S % and (%) second segment* label for0S ' and 0S "

6hen the pac!et e/its the first netor! and is recei.ed b- 0E,* it ill remo.e

the label for 0S % and replace it ith 0S label* hile sapping 0S ' label

ithin the pac!et ith the ne/t hop label" 0E,; ill remo.e both labels before

sending the pac!et to the destination"G=H"

$%$%/ 5P(S effects in )P #et4or,:

M0S technolog- pla-s a main rule in the enhancement of the traditional

netor!s this section gi.es a brief discussion about these enhancement" n

traditional netor!s* pac!ets are routed according to information contained in


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the header of each pac!et" As the pac!ets ma!e their a- across the netor!* the-

are e/amined b- each sitchKrouter the- pass through to determine ho the pac!et

should be handled in terms of Jualit- of Ser.ice (JoS) and outbound routing" n

man- cases* each pac!et is encr-pted before it enters the netor! to ensure

confidentialit- +igure %"'%

+igure %"'% Traditional netor!

All of these functions (e"g"* chec!ing for errors* .erif-ing address* repac!aging*re1

transmitting)* hile necessar-* ta!e time to perform and introduce dela- into the

equation I an unacceptable fact for dela-1sensiti.e applications li!e .oice and

.ideo* both of hich are becoming ma#or elements in enterprise netor!s"

M0S eliminates this problem* as +igure %"' illustrates" As pac!ets are created

for transport in an M0S netor!* the- are gi.en a Llabel that identifies not onl-

the priorit- of the pa-load the- contain* but also the relati.e priorit- of each pac!et

as ell" B- rel-ing on this unique prioriti4ation scheme* traffic deli.ered o.er an

1based M0S netor! demonstrates JoS le.els that are identical to those

pre.iousl- a.ailable onl- on +rame ,ela-* ATM* and ri.ate 0ine netor!s"

M0S or!s because it performs to tas!s .er- ell: tprioriti%es traffic based on

header information* and it s!apes the traffic according to its !noledge of netor!

topolog- and current load (Shaping is simpl- the process of spreading traffic


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across all paths in the netor! to guarantee optimal traffic handling b- the

resources a.ailable ithin the netor!)"G'?H

+igure %"' M0S 3etor!

$% ;irtual Private #et4or,s 6;P#7:

A $irtual %ri$ate network 45/86 i a data networ$ compoed of

private and pu#lic ection that permit ending confidential data

over unprotected pu#lic connection without the ri$ of

compromie #y eavedropper, thieve, or thoe who would

a#otage information. To the uer, a 5/8 appear a a private

networ$. The ucce of the !nternet ha inpired companie and

organization to ditri#ute an increaing amount of information

over circuit uing !nternet protocol. !n a format made eay to

read #y incorporating the graphical interface and hyperte"t


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techni9ue of the e#, companie and organization are a#le to

provide proprietary information to employee and product

information to the pu#lic. To erve them, companie and

organization ue the pu#lic !nternet. To erve their internal

need, companie and organization ue private internet called

intranets. At firt, uer from inide and outide the enterprie

were pleaed to communicate with one another and do #uine

together. Bowever, once the uer community had uffered a few

epiode of eavedropping, hac$ing, or theft of information, they

ought to achieve privacy without acrificing the fle"i#ilityac9uired from uing the pu#lic !nternet. To do thi, they created a

5/8. Bowever, it would #e wrong to imagine that 5/8 can #e

created olely from pu#lic !nternet facilitie. They ue the full3

range of communication facilitie including leaed telephone

circuit, frame relay or ATM lin$, communication atellite hop,

!%C8, and /'T%.

$%%'Types of ;P#s

23s can be di.ided in se.eral a-s" $ne set of configurations is:

P Intranet VPN: A 23 in hich se.eral enterprise campus netor!s are

interconnected b- tunnels o.er nternet connections (distributed bac!bone)"

PExtranet VPN:An intranet 23 used b- customers* suppliers* and enders"

Tunnels are established o.er nternet connections to a secure enterprise ser.er"

= Remote access VPN: A 23 in hich enterprise emplo-ees on the mo.e can

establish a dial1up connection to a remote S and create tunnels to enterprise

campus netor!s"


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P Intracompany VPN: A single campus netor! or an intranet 23* in hich

encr-pted communications are used to protect against securit- breaches ithin the

enterprise"

8sing an- of these arrangements ensures the oner has a significant le.el of

control o.er ho can read information (i"e"* read onl-)* or! ith information

(i"e"*donload)* and contribute or change information (i"e"* author or edit)"

+urthermore* the- can restrict electronic mail and other traffic to ithin the

compan-" n addition* the netor! uses a popular set of protocols that are familiar

to man- persons" Moreo.er* campus netor!s (intranets) can be connected o.er a

distributed bac!bone supplied b- the nternet"G'%H

$%%$ ;P# Approaches: 23 technologies ha.e e.ol.ed into to ma#or approaches toard

implementing 23 ser.ices:

'" Connectionoriented ;P#O The E de.ices pro.ide .irtual leased lines

beteen the CE de.ices" These .irtual leased lines are called &irtual circuits

(2Cs)" The 2Cs can be permanent* established out1of1band b- the ser.ice pro.ider

netor! management team (calledper'a"e"t &irtual circuits, orPV(s)" The- can

also be temporar-* established on demand b- the CE de.ices through a signaling

protocol that the E de.ices understand"

(These 2Cs are called switc!ed &irtual circuits, or SV(s)+igure G%"';H"G'&H


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+igure %"'; Connection1oriented 23

%" Connectionless ;P#O The E de.ices participate in the connectionless data

transport beteen CE de.ices" t is unnecessar- for the ser.ice pro.ider or the

customer to establish 2Cs in these 23s* e/cept perhaps beteen the E and CE

routers if the ser.ice pro.ider uses sitched 6A3 as its access netor!

technolog- figure G%"'


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o.erhead on the de.ices)" +urthermore* se.eral additional mechanisms ha.e been

implemented to allo the customers to use o.erlapping address spaces"n a t-pical

M0S123 netor!* the CE routers and E routers e/change the customer routes

using an- suitable routing protocol" These routes are inserted into 2,+s on the

E routers* hich guarantees the perfect isolation beteen customers" This process

is illustrated in +igure %"'=* hich details the internal structure of a E router (San

Qose) to hich to 23 customers are connected (+ast+ood and EuroBan!) and

hich also connects to a router"G'&H

+igure %"'= 2irtual ,outing Table in E routers

6hen customer routes are placed into 2,+s* the E routers allocate a separate

M0S label that ill be needed for 23 data forarding to each customer route"

The customer routes and associated M0S labels are transported across the 1

netor! using multiprotocol B7" The customer addresses are augmented ith

a =;1bit route distinguisher before being inserted into the pro.iders B7 to ensure

global uniqueness of potentiall- no unique customer addresses" Additional B7

attributes (e/tended B7 communities) are used to control the e/change of routes


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beteen 2,+s to allo the ser.ice pro.iders to build 23 topologies that are

almost impossible to build ith another 23 technolog-"

$%-%' !outing Protocols "ptions:

E/tended range of routing protocols that are supported beteen the E

routers and the CE routers" Enhanced 7, (E7,) and ntegrated ntermediate

S-stem1to1ntermediate S-stem (ntegrated S1S) are supported* as ell as

additional $S+ connecti.it- options* including .irtual $S+ lin!s beteen E

routers (s!a' li")s)"

+urthermore* it supports Multicast inside the M0S 23 and per12,+ netor!

address translation (3AT) on the E router G'&H"This thesis is gi.e a detailed

discussion in routing protocol in chapter "

$%-%$ 5P(S ;P# as choice for service providers:

Man- ser.ice pro.iders that anted to minimi4e their costs of pro.isioning and

operations b- offering all their ser.ices (23 and public nternet) o.er a common

infrastructure ha.e enthusiasticall- embraced M0S1based 23 netor!s"

+urthermore* these ser.ice pro.iders ha.e achie.ed significant cost sa.ings due to

the pro.isioning simplicit- offered b- M0S 23s integration ith the benefits

of both connectionless and connection1oriented 23 approaches"

An end1to1end M0S 23 solution is* li!e another 23 solution* di.ided

into the central netor! to hich a large number of customer sites (sites in the C1

netor!) are attached" The customer sites are attached to the E de.ices (E

routers) through CE de.ices (CE routers)"Each E router contains se.eral .irtual

routing and forarding tables (2,+s)Oat least one per 23 customer" These

tables are used together ith Multiprotocol B7 run beteen the E routers to

e/change customer routes and to propagate customer datagrams across the M0S


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23 netor!" The E routers perform the label imposition (ingress E router) and

remo.al (egress E router)" The central de.ices in the M0S 23 netor! (

routers) perform simple label sitching"

M0S1based 23s ha.e been significantl- enhanced since their initial rollout"

The ne M0S 23 features allo better integration of access technologies*

support of additional E1CE routing protocols* as ell as support of ne transport

options across M0S bac!bones.G'&H


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CHAPT! TH!

RTYWING IN MPLS

%' Autonomous systems:

The definition of an autonomous s-stem (AS) is integral to understanding

the function and scope of a routing protocol" An AS is defined as a logical portion

of a larger netor!" An AS is normall- comprised of an internetor! ithin an


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organi4ation" t is administered b- a single management authorit-" As shon in

+igure "'* an AS ma- connect to other autonomous s-stems managed b- the same

organi4ation" Alternati.el-* it ma- connect to other public or pri.ate netor!s"

+igure "' Autonomous S-stem

Some routing protocols are used to determine routing paths ithin an AS" $thers

are used to interconnect a set of autonomous s-stems:

%'%' )nterior Gate4ay Protocols 6)GPs7: nterior gatea- protocols allo

routers to e/change information ithin an AS" E/amples of these protocols are

$pen Short ath +irst ($S+) and ,outing nformation rotocol (,)"

%'%$ 0terior Gate4ay Protocols 6GPs7:E/terior gatea- protocols allo thee/change of summar- information beteen autonomous s-stems" An e/ample of

this t-pe of routing protocol is Border 7atea- rotocol (B7)"

+igure "' depicts the interaction beteen interior and e/terior protocols" t

shos the interior protocols used to maintain routing information ithin each


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AS"The figure also shos the e/terior protocols maintaining the routing

information beteen autonomous s-stems"

6ithin an AS* multiple interior routing processes ma- be used" 6hen this occurs*

the AS must appear to other autonomous s-stems as ha.ing a single* coherent

interior routing plan" The AS must present a consistent .ie of the internal

destinations"G'


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+igure "% routing operation e/ample

%$%' !outer:

+igure " is a functional diagram of a router" A database of routes is stored

and maintained b- all routers" Called a routi"# tale* it contains information

concerning routes beteen the node oning the table and the potential destination

nodes" At a minimum it includes the destination D* intermediate interface D(s)

and forarding address(es)* and information to distinguish the best route to use

hen multiple routes are possible" t is significantl- more comple/ than the table

maintained b- bridging de.ices" oe.er* its e/tent is limited to the immediatel-

reachable nodes that surround it* so that it is significantl- smaller" Searching a

routing table is a relati.el- simple tas!" +or each route* a t-pical routing table ill

include the folloing

fields:

=Destination address: The address of the node to hich the source directs the

pac!et to be deli.ered" +or direct deli.eries* the destination address carries the

same netor! D as the router" +or i"direct deli.eries* the destination address does

not carr- the same netor! D as the router* and the datagram is sent to the

forarding address contained in the table entr-"


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=Network mask: A bit mas! is used to determine the netor! D of the destination

address" An datagram ith a destination address that contains the specific

netor! D for this route ill be forarded o.er it"

P Forwarding IP address: +or i"direct deli.eries* the address of a directl-

reachable router to hich the datagram is forarded for e.entual deli.er- to the

destination address" The address to hich the datagram is to be forarded

on its ne/t hop"

6hile the routing table contains information on all routes ithin the routers

pur.ie* the router maintains a separate loo)-up table in hich all recentl- used

routes are recorded" f the- are not used again ithin a specified time* the- are

purged" Because it does not ha.e to search the larger routing table for directions* the

router can pro.ide rapid ser.ice if the routes are called for again before time runs

out" riorit- routes can be stored permanentl- in the

loo! up table"G'%H


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+igure " +unctional diagram of router

%$%$ !outing classification:

,outing algorithms are used to build and maintain the routing table on a

de.ice" There are to primar- methods used to build the routing table:

%$%$%' Static routing

Static routing is manuall- performed b- the netor! administrator" The

administrator is responsible for disco.ering and propagating routes through the

netor!" These definitions are manuall- programmed in e.er- routing de.ice in

the en.ironment"


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$nce a de.ice has been configured* it simpl- forards pac!ets out the

predetermined ports" There is no communication beteen routers regarding the

current topolog- of the netor!"G'


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" -brid protocols"

'% 8istance vector routing:

The principle behind distance .ector routing is simple" Each router in theinternetor! maintains the dista"ce or cost from itself to e.er- !non destination"

This .alue represents the o.erall desirabilit- of the path" aths associated ith a

smaller cost .alue are more attracti.e to use than paths associated ith a larger

.alue" The path represented b- the smallest cost becomes the preferred path to

reach the destination"G'


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nformation for a particular destination prefi/ originates in some router" The router

learns the information in one of three a-s:

The destination prefi/ is associated ith one of the routers attached

interfaces"

The router is manuall- configured to originate the destination prefi/"

The router learns the destination prefi/ from another routing protocol"

A .ector protocol transmits the destination prefi/ to its directl- connected

neighbors" Each neighbor* hen it recei.es the route information* modifies the

information in such a a- that the route information indicates the distance from

that router to the originating router" +or e/ample* !)P increases the router hop

count b- one" The modified route is then added into the routers routing table" $nl-

then is the route sent to that routers on directl- connected neighbors* to be

modified again b- those neighbors"G'H

, and B7 are to popular e/amples of distance .ector routing protocols"

$% (in, State 8ynamic !outing:

The groth in the si4e and comple/it- of netor!s in recent -ears has

necessitated the de.elopment of more robust routing algorithms" These algorithms

address the shortcoming obser.ed in distance .ector protocols"

These algorithms use the principle of a link stateto determine netor! topolog-" A

lin! state is the description of an interface on a router (for e/ample* address*

subnet mas!* t-pe of netor!) and its relationship to neighboring routers" The

collection of these lin! states forms a lin! state database"G'


54/142

The idea behind lin! state routing is simple and can be stated as fi.e parts" Each

router must do the folloing:

'" Disco.er its neighbors and learn their netor! addresses"

%" Measure the dela- or cost to each of its neighbors"

" Construct a pac!et telling all it has #ust learned"

;" Send this pac!et to all other routers"


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;" SPF: calculations o a router actuall- uses the information in the lin! state

database to calculate routes"

%%' Ad.acencies:

Before lin! state routers can begin sending and recei.ing announcements

and building their databases* the- must be able to identif- their neighbors" And it is

not enough to #ust identif- directl- connected routers in some netor!s* routers

might be spea!ing se.eral routing protocols" A router running a specific lin! state

protocol must be able to find #ust those directl- connected routers running the same

protocol" And e.en this requirement is not good enough" 6ithin the domain of asingle routing protocol* there can be constraints on hich routers are alloed to

e/change route information"

rerequisite to the operation of a lin! state protocol is the abilit- for e.er- router to

identif- itself" Therefore* each lin! state router has a router D (,D)* hich is an

address unique to each router ithin a single routing domain" The router D can be

administrati.el- assigned* or it can be automaticall- deri.ed b- some means such

as using an interface address" The onl- requirement is that it must be different from

the D used b- another router in the domain* and the router cannot identif- itself

differentl- to different neighbors"

To identif- itself and to disco.er neighbors* a lin! state protocol uses ello

messages" At the least* a ello message includes the D of the router that

originated the message" The ello also includes information specific to the routing

protocol and rele.ant to the sending router such as timer settings* interface

parameters* and authentication information" Such information is used to ensure*

before forming an ad#acenc-* that the to routers are in agreement:


56/142

About ho to e/change information and maintain their ad#acenc-*

That the information can be e/changed reliabl-*

And that the neighbors can trust each other"

6hen a routing protocol is enabled on a router* there is usuall- some method of

specif-ing hich connected lin!s from one lin! to all lin!s are to be included in the

protocol operations" 0in! state protocols then transmit ello messages on these

lin!s at some regular inter.al" The messages must be broadcast or multicast* so that

an- as1-et1undisco.ered neighbors ill hear them" Because the ello protocol is

used to disco.er onl- directl- connected neighbors* it is important that no ellomessage is e.er forarded be-ond the lin! on hich it is transmitted" The

originating router can ensure this b- methods such as setting the TT0 of the

pac!et containing the message to ' or using a multicast address that is specificall-

scoped to a single lin!"

Handshakingis an eas- a- to .erif- to1a- communication is for each router

to include in its ellos on a lin! a list of all routers from hich it has recei.ed

ellos on that lin!" ,outer A in *igure %1has recei.ed a ello from router B" n

its ne/t ello* A includes Bs router D" 6hen router B recei.es this ello* it sees

its D and !nos that A is aare of it" ,outer B responds in !ind b- including As

D in its ellos" 6hen A sees its D in Bs ellos* it !nos B is aare of it" 3o

both routers ha.e .erified to1a- communication* and are ad#acent" This method

of handsha!ing is called three1a- handsha!ing"


57/142

+igure "= hello pac!ets

After an ad#acenc- is formed* ellos ser.e as !eepali.es for the ad#acenc-" $ne

of the protocol parameters that a router can include in its ello messages is a

specification of ho often it sends ellos" A recei.ing router then !nos ho

often to e/pect ellos from that neighbor" f the specified time period elapses

ithout the reception of a ello (alloing some e/tra time for lost ellos)* a router

can assume that the neighbor is no longer acti.e on the lin! and therefore the

ad#acenc- ith that neighbor is in.alid" Depending on the lin! state protocol* the

ello period beteen routers might be predetermined and non1negotiable* the

routers might be able to negotiate a ello period* or the ello periods of the to

routers might be independent (each router #ust accepts its neighbors period)"G'H

%%$ *looding

6ithin a netor! of ad#acent routers* each router originates an announcement

of its directl- connected lin!s and neighbors" E.er- router in the netor! must

recei.e e.er- announcement and record a cop- in its database" The process of

getting the announcement to e.er- router is called flooding" +looding in the


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netor! shon in +igure "@ is an eas- process: Each router sends its

announcement to all of its ad#acent neighbors* and each of these neighbors

forards a cop- of the announcement to each of its on ad#acent neighbors" f split

hori4on is practiced (no router sends an announcement bac! to the neighbor it

recei.ed the announcement from)* e.er- router gets a cop- of e.er- announcement

and the flooding then stops"

The netor! in +igure "@presents more of a challenge for flooding because of all

the loops" Qust as split hori4on rules are insufficient to stop the looping of .ector

protocol updates in such a topolog-* split hori4on rules are insufficient to control

the flooding of lin! state announcements" A better process is needed to stop the

flooding of an announcement after all routers ha.e a cop-"

+igure "@" A ell1meshed netor! poses challenges for flooding"

There are other considerations be-ond #ust !noing hen to stop flooding" f a

router originates an announcement and then fails* ho do the other routers !no

that its announcement no longer is .alid f a router recei.es differing

announcements from the same router* hich announcement should be belie.ed f

an announcement becomes corrupted either in transit or in a database* ho can a

router detect the corruption


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Three mechanisms used to create a more reliable flooding process are aging*

sequence numbers* and chec!sums"

%%$%' Timely *looding: Aging

$ne of the essential concepts of a lin! state protocol is that the information in

e.er- routers database must be the same as the information in e.er- other routers

database" To guarantee Usameness*U no router can modif- another routers

announcement" That means that e.er- router is responsible for its on

announcements"6hat happens* then* if a router fails after flooding an

announcement f the failure is due to a lin! problem* the neighbors on the lin!ill detect the failure through the 0a-er % protocol" f the failure is a protocol

daemon or the router itself* neighbors ill detect the failure through the loss of

ello messages" n either case* the effected neighbors send ne announcements

indicating the change"

0in! state protocols include an age field in each lin! announcement" 6hen a

router originates an announcement* it sets a .alue in the age field" This .alue is

changed either incremented or decremented ($S+ increments the age* hereas

S1S decrements it) b- other routers during flooding* and b- e.er- router as the

announcement resides in its database" Some absolute .alue is specified in the

protocol at hich* if the age reaches this .alue* the announcement is declared

in.alid or Uaged out*U and is deleted from the database" The originating router is

responsible for sending a ne cop- of the announcement at some time prior to thisage e/piration" The origination of a ne announcement is called a refresh"

An age counter can be either up1counting or don1counting" An up1counting

age is less fle/ible because it is set beteen to absolutes: 4ero and the ma/imum


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age specified in the protocol design" $n the other hand* a don1counting age can

start at some arbitrar- .alue* bounded at the upper end onl- b- the si4e of the age

field* and counts don to 4ero"

%%$%$ Se9uential *looding: Se9uence #umbers

6hene.er a router recei.es a lin! announcement* it sends a cop- out each of

its donstream interfaces" t is ob.ious in a ell1meshed netor! such as the one

depicted in +igure "@ that an announcement ill be replicated numerous times

during flooding* and as a result some routers ill recei.e multiple copies of the

same announcement" f all announcements arri.e at the same time* an-announcement can be chosen" $f course* dela-s across different netor! paths

bac! to the originator are going to .ar-* so in most cases the multiple copies of the

same announcement arri.e at different times" n this case* the router might simpl-

accept the announcement ith the loest age* on the grounds that the loest age

indicates the neest announcement"

As ith aging* the design of the sequence counter is important" The simplest

sequence numbering scheme is a linear one: A sequence number starts at 4ero* and

increments up to some ma/imum" +or e/ample* a %1bit sequence number (used b-

both $S+ and S1S) can range from 4ero to % %* or about ;" billion" f a router

ala-s starts numbering its announcements at sequence number one* this man-

a.ailable numbers should last far be-ond the lifetime of the router" E.en if a router

produces a ne announcement e.er- second sign of a .er- unstable lin! thema/imum sequence number ould not be reached for more than '& -ears"

resumabl- someone ould repair the instabilit- before then"


61/142

""%" !eliable *looding: Chec,sums

a.ing a consistent information in all databases ithin a lin! state netor! is

.er- important in routing" et in netor!s a lin! state announcement can become

corrupted in man- a-s" An announcement can be changed due to noise on a lin!*

or it can be corrupted hile it resides in a routers database" Because of the

possibilit- of the announcement being altered* there should be a mechanism for

chec!ing to ensure that the announcement is accurate"

The concern o.er information corruption certainl- e/tends be-ond lin! state

protocols" Most pac!ets and messages include error chec!ing* most often in theform of a chec!sum" A chec!sum is performed o.er the entire contents of a lin!

state announcement ith the e/ception of the age field" Because the age changes as

the announcement passes through routers during flooding* including it in the

chec!sum ould mean recalculating the chec!sum e.er- time the age changes"G'H

%% Announcement Headers

Se.eral !inds of identifiers associated ith a lin! state announcement ere

discussed till no" Some identifiers* such as the router D* are used to differentiate

the announcement from other routers announcements" $ther identifiers* such as

the sequence number* age* and chec!sum* are used to differentiate beteen

specific instances of an announcement from the same router"

All of these identifiers are included in a header that precedes the actual route

information of the announcement" This a-* none of the information in the

announcement itself must be e/amined during the flooding processonl- the header

must be e/amined"


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There is also another benefit to ha.ing such identifiers in a header" 6hen a router

must describe to a neighbor hat announcements it has in its database* or hen a

router must request a cop- of an announcement from a neighbor* the

announcements can be full- described b- sending #ust the header rather than the

entire announcement" G'H

%%- SP* Calculations

6ith a complete database* the router can begin calculating a shortest path to all

other routers in the netor!" 6hen a path to all routers is !non* a path to an- of

the routers connected subnets is also !non"

There is a set of rules comes from graph theor- and as formulated b-ds#er

./ 0i+)stra" A netor! is .ieed as a graph of nodes* in hich the routers are the

nodes" 5eep in mind that to calculate shortest paths* some a- to assign a cost to

each lin! connecting to nodes is needed" The sum of the costs across a route is

the distance of the route" 6e could* if e anted* #ust use router hops" n this case*

each lin! ould ha.e a cost of one hop" But router hops limits us in the a-s e

can define and control traffic patterns in the netor!" A better scheme is to assign

a dimensionless number to each lin!* as shon in +igure ">" Each number then

represents the cost of sending a pac!et out the interface connected to the lin!" A

shortest path is the one in hich the total cost of all outgoing interfaces from the

source to the destination is the loest (or UcheapestU)"


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+igure ">" A lin! cost on each path in the netor! ill factor into Di#!stras algorithm for

calculating the shortest1path routing tree in a lin! state netor!"

Construct GaH tree of minimum total length beteen the n nodes" (The tree is agraph ith one and onl- one path beteen e.er- to nodes")

n the course of the construction that presented here* the branches are di.ided into

three sets:

" The branches definitel- assigned to the tree under construction (the- ill be in a

subtree)

" The branches from hich the ne/t branch to be added to set * ill be selected

" The remaining branches (re#ected or not considered)"

The nodes are di.ided into to sets:

A" the nodes connected b- the branches of set *

B" the remaining nodes (one and onl- one branch of set ill lead to each of

these nodes)"


64/142

6e start the construction b- choosing an arbitrar- node as the onl- member of set

A* and b- placing all branches that end in this node in set " To start ith* set is

empt-" +rom then onards e perform the folloing to steps repeatedl-"

Step '% The shortest branch of set is remo.ed from this set and added to set "

As a result* one node is transferred from set B to set A"

Step $% Consider the branches leading from the node* that has #ust been

transferred to set A* to the nodes that are still in set B" f the branch under

construction is longer than the corresponding branch in set * it is

re#ected if it is shorter* it replaces the corresponding branch in set * and

the latter is re#ected"

6e then return to step ' and repeat the process until sets and B are empt-" The

branches in set form the tree required"

3o e can adapt Di#!stras rules for routers and netor!s" +irst* e define the

sets" Di#!stra defines three sets of branches: * * and " 6e define these three sets

as follos:

Set : The tree database 0in!s (branches) are added to the shortest1path tree

b- adding them to this database" 6hen the algorithm is finished* this

database ill contain the shortest1path tree"

Set : The temporar- database 0in!s are copied from the lin! state database

to this list in a prescribed order* here the- become candidates to be addedto the tree" 6hen this database becomes empt-* e !no the calculation is

finished"


65/142

Set : The lin! state database This is the complete routing database for the

netor!* containing the shortest path to each destination"

Di#!stra also specifies to sets of nodes* A and B* as follos:

Set A The routers connected to the lin!s in the tree database"

Set B All other routers" 6hen the calculation is finished* this set ill be

empt-" n other ords* all routers ill be accounted for in the tree database"

+igure "?shos the netor! of +igure ">along ith the lin! state database for

the netor!" Each of the entries is in the form Goriginating router neighbor* cost to

neighborH" The a- to read this database is* for instance* that router ,' has sent an

announcement indicating to neighbors: neighbor ,%* at a cost of '* and ,


66/142

Each router then creates a tree database and a candidate database* and performs the

folloing steps:

'% The router adds itself to the tree database as the root of the tree" t shos itself

as its on neighbor* ith a cost of &"

$% All entries in the lin! state database describing lin!s from the root to its

neighbors are added to the candidate database"

% The cost from the root to each node in the candidate database is calculated" The

lin! in the candidate database ith the loest cost is mo.ed to the tree database*

along ith the cost from the root" f to or more lin!s are an equall- lo costfrom the root* choose one" f an- entries are left in the candidate database ith a

lin! to the neighbor #ust mo.ed to the tree* those entries are deleted from the

candidate database"

-% The router D of the neighbor on the lin! #ust added to the tree is e/amined"

Entries originated b- that neighbor are added to the candidate database* e/cept

for entries in hich the D of the neighbor is alread- in the tree database"

/% f entries remain in the candidate database* return to Step " f the candidate

database is empt-* terminate the calculation" At this time e.er- router in the

netor! should be represented as a neighbor on one of the lin!s in the tree

database* and e.er- router should be represented #ust once"G'


67/142

+igure "'& S+ routing

%- 0amples of )nterior Gate4ay !outing Protocols:

This thesis is focusing in the effect of the 7s in the M0S 23 netor!

ill ta!e $S+ and S1S as e/amples ith detailed description in the folloing

sections:

%-%' "pen Shortest Path *irst 6"SP*7:

$S+ is an 7 that routes pac!ets ithin a single autonomous s-stem (AS)"

$S+ uses lin!1state information to ma!e routing decisions* ma!ing route

calculations using the shortest path first (S+) algorithm ( Di#!stra algorithm)"

Each router running $S+ floods lin!1state ad.ertisements throughout the AS that

contain information about that routers attached interfaces and routing metrics"

Each router ta!es the information in these lin!1state ad.ertisements and creates a

complete routing table for the netor!"G%=H

$S+ routes pac!ets based solel- on the destination address contained in the

pac!et header" $S+ quic!l- detects topological changes* such as hen router


68/142

interfaces become una.ailable* and calculates ne loop1free routes quic!l- and

ith a minimumof routing o.erhead traffic"

All $S+ interfaces ha.e a cost* hich is described b- a single dimensionless

metric that is determined using the folloing formula:

cost > referenceband4idth ? interface band4idthNNNNNN"("')

%-%'%' #et4or, Hierarchy:

$S+ pro.ides the functionalit- to di.ide an intradomain netor! (an

autonomous s-stem) into subdomains* commonl- referred to as areas" E.er-

intradomain must ha.e a core area* referred to as a backbone area this is

identified ith Area D &" Areas are identified through a %1bit area field thus

Area D & is the same as &"&"&"&"

8suall-* areas (other than the bac!bone) are sequentiall- numbered as Area ' (i"e"*

&"&"&"')*Area %* and so on" $S+ allos a hierarchical setup ith the bac!bone

area as the top le.el hile all other areas* connected to the bac!bone area* are

referred to as lo1le.el areas this also means that the bac!bone area is in charge of

summari4ing the topolog- of one area to another area* and .ice .ersa" +igure "''

illustrate netor! hierarch- using lo1le.el areas"

%-%'%$ !outer Classification

6ith the functionalit- pro.ided to di.ide an $S+ netor! into areas* the routers

are classified into four different t-pes (+igure "''):


69/142

+igure "'' $S+ bac!bone and lo1le.el areas

'"rea!"order Ro#ters: These are the routers that sit on the border beteen the

bac!bone and the lo1le.el areas" Each area1border router must ha.e at least one

interface to the bac!bone it also has at least one interface to each area to hich it

is connected"

%"Internal Ro#ters: These are the routers in each lo1le.el area that ha.e

interfaces onl- to other internal routers in the same area"

""ackbone Ro#ters: These are the routers located in Area & ith at least one

interface to other routers in the bac!bone" Area1border routers can also be

considered as bac!bone routers"

;"$ "o#ndary Ro#ters: These routers are located in Area & ith connecti.it- to

other ASthe- must be able to handle more than one routing protocol" +or

e/ample* to e/change information ith another AS* the- must be able to spea!

B7" These routers also ha.e internal interfaces for connecti.it- to other

bac!bone routers"G';H


70/142

%-%'% Physical net4or, types:

$S+ categori4es netor! segments into three t-pes"The frequenc- and

t-pes of communication occurring beteen $S+ de.ices connected to these

netor!s is impacted b- the netor! t-pe:

= Pointtopoint: oint1to1point netor!s directl- lin! to routers"

P 5ultiaccess:Multi1access netor!s support the attachment of more than to

routers" The- are further subdi.ided into to t-pes:

1 Broadcast netor!s ha.e the capabilit- of simultaneousl- directing a pac!et to all

attached routers" This capabilit- uses an address that is recogni4ed b- all de.ices"

Ethernet and to!en1ring 0A3s are e/amples of $S+ broadcast multi1access

netor!s"

1 3on1broadcast netor!s do not ha.e broadcasting capabilities" Each pac!et must

be specificall- addressed to e.er- router in the netor!"

9"%< and frame rela- netor!s are e/amples of $S+ non1broadcast multi1access

netor!s"

P oint1to1Multipoint: oint1to1multipoint netor!s are a special case of multi1

access* non1broadcast netor!s" n a point1to1multipoint netor!* a de.ice is not

required to ha.e a direct connection to e.er- other de.ice"

This is !non as a partiall- meshed en.ironment"

%-%'%- #eighbor routers and ad.acencies:

,outers that share a common netor! segment establish a neighbor

relationship on the segment" ,outers must agree on the folloing information to

become neighbors:

P Area1id: The routers must belong to the same $S+ area"


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P Authentication: f authentication is defined* the routers must specif- the same

passord"

P ello and dead inter.als: The routers must specif- the same timer inter.als used

in the ello protocol"

P Stub area flag: The routers must agree that the area is configured as a stub area"

$nce to routers ha.e become neighbors* an ad#acenc- relationship can be formed

beteen the de.ices" 3eighboring routers are considered ad#acent hen the- ha.e

s-nchroni4ed their topolog- databases" This occurs through the e/change of lin!

state information"

%-%'%/ 8esignated and bac,up designated router:

The e/change of lin! state information beteen neighbors can create

significant quantities of netor! traffic" To reduce the total bandidth required to

s-nchroni4e databases and ad.ertise lin! state information* a router does not

necessaril- de.elop ad#acencies ith e.er- neighboring de.ice:

P Multi1access netor!s: Ad#acencies are formed beteen an indi.idual router and

the (bac!up) designated router"

P oint1to1point netor!s: An ad#acenc- is formed beteen both de.ices"

Each multi1access netor! elects a designated router (D,) and bac!up designated

router (BD,)" The D, performs to !e- functions on the netor! segment:

P t forms ad#acencies ith all routers on the multi1access netor!" This causes the

D, to become the focal point for forarding 0SAs"

P t generates netor! lin! ad.ertisements listing each router connected to the

multi1access netor!"

The BD, forms the same ad#acencies as the designated router" t assumes D,

functionalit- hen the D, fails"


72/142

Each router is assigned an >1bit priorit-* indicating its abilit- to be selected as the

D, or BD," A router priorit- of 4ero indicates that the router is not eligible to be

selected" The priorit- is configured on each interface in the router"

+igure "'% illustrates the relationship beteen neighbors" 3o ad#acencies are

formed beteen routers that are not selected to be the D, or BD,"G';HG'


73/142

The contents of an 0SA describes an indi.idual netor! component (that

is*router* segment* or e/ternal destination)" 0SAs are e/changed beteen ad#acent

$S+ routers" This is done to s-nchroni4e the lin! state database on each de.ice"

6hen a router generates or modifies an 0SA* it must communicate this

change throughout the netor!" The router starts this process b- forarding the

0SA to each ad#acent de.ice" 8pon receipt of the 0SA* these neighbors store the

information in their lin! state batabase and communicate the 0SA to their

neighbors" This store and forard acti.it- continues until all de.ices recei.e the

update" This process is called reliale $loodi"#" To steps are ta!en to ensure this

flooding effecti.el- transmits changes ithout o.erloading the netor! ith

e/cessi.e quantities of 0SA traffic:

P Each router stores the 0SA for a period of time before propagating the

information to its neighbors" f* during that time* a ne cop- of the 0SA arri.es*

the router replaces the stored .ersion" oe.er* if the ne cop- is outdated* it is

discarded"

P To ensure reliabilit-* each lin! state ad.ertisement must be ac!noledged"

Multiple ac!noledgements can be grouped together into a single

ac!noledgement pac!et" f an ac!noledgement is not recei.ed*the original lin!

state update pac!et is retransmitted"

0in! state ad.ertisements contain fi.e t-pes of information" Together these

ad.ertisements pro.ide the necessar- information needed to describe the entire

$S+ netor! and an- e/ternal en.ironments:

P ,outer 0SAs: This t-pe of ad.ertisement describes the state of the routers

interfaces (lin!s) ithin the area" The- are generated b- e.er- $S+ router" The

ad.ertisements are flooded throughout the area"


74/142

P 3etor! 0SAs: This t-pe of ad.ertisement lists the routers connected to a multi1

access netor!" The- are generated b- the D, on a multi1access segment" The

ad.ertisements are flooded throughout the area"

P Summar- 0SAs (T-pe1 and T-pe1;): This t-pe of ad.ertisement is generated b-

an AB," There are to t-pes of summar- lin! ad.ertisements:

1 T-pe1 summar- 0SAs describe routes to destinations in other areas ithin the

$S+ netor! (inter1area destinations)"

1 T-pe1; summar- 0SAs describe routes to ASB,s"

Summar- 0SAs are used to e/change reachabilit- information beteen areas"

3ormall-* information is announced into the bac!bone area" The bac!bone then

in#ects this information into other areas"

P AS e/ternal 0SAs: This t-pe of ad.ertisement describes routes to destinations

e/ternal to the $S+ netor!" The- are generated b- an ASB," The

ad.ertisements are flooded throughout all areas in the $S+ netor!"G'


75/142

+igure "' 0in! state ad.ertisements

%-%'%3 "SP* Pac,et *ormat:

C$MM$3 EADE,:

The common header has the folloing !e- fields (*igure %'-):

P Version:This field represents the $S+ .ersion number the current .ersion is %"

P %ype: This field specifies the t-pe of pac!et to follo" $S+ has fi.e pac!et

t-pes: hello (')*

database description (%)* lin! state request ()* lin! state update (;)* and 0SA (


76/142

P rea ID: This is the D of the area here the $S+ pac!et originated" 2alue

&"&"&"& is reser.edfor the bac!bone area"

'hecks#m:This is the chec!sum o.er the entire $S+ pac!et"

+igure "'; $S+ Common eader

*uype and*ut!e"ticatio" Field: AuT-pe or!s ith the Authentication field

for authentication"

There are three authentication t-pes:

AuT-pe Meaning Authentication +ield

& 3o authentication Can be an-thing

' Simple* clear te/t passord1based authentication An >1b-te passord

% Cr-ptographic MD< chec!sum authentication >1b-te is di.ided as

shon in

+igure "';

Table "' Authentication t-pes


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hen AuT-pe is %* it contains a 5e-D* an Authentication Data 0ength* and a

Cr-ptographic Sequence 3umber" MD< chec!sum is used to produce a '=1b-te

message digest that is not part of the $S+ pac!et rather* it is appended to the end

of the $S+ pac!et"G';H

+igure "'< MD< message

%-%$ )ntermediate System to )ntermediate System 6)S)S7:

n recent -ears* the S1S routing protocol has become increasingl- popular*

ith idespread usage among Ser.ice ro.iders" t is a lin! state protocol* hich

enables .er- fast con.ergence ith large scalabilit-" t is also a .er- fle/ible

protocol and has been e/tended to incorporate leading edge features such as M0S

Traffic Engineering"G'=H

A to1le.el hierarch- is used to support large routing domains" A large

domain ma- be administrati.el- di.ided into areas" Each s-stem resides in e/actl-


78/142

one area",outing ithin an area is referred to as (evel ' routing" ,outing beteen

areas is referred to as (evel $ routing" A 0e.el % ntermediate S-stem (S) !eeps

trac! of the paths to destination areas" A 0e.el ' (S) !eeps trac! of the routing

ithin its on area" +or a pac!et destined for another area* a 0e.el ' S sends the

pac!et to the nearest 0e.el % S in its on area* regardless of hat the destination

area is" Then the pac!et tra.els .ia 0e.el % routing to the destination area* here it

ma- tra.el .ia 0e.el ' routing to the destination" t should be noted that selecting

an e/it from an area based on 0e.el ' routing to the closest 0e.el % S might result

in suboptimal routing"

%-%$%' )S)S "perations :

From a high le(el) I$!I$ operates as *ollows:

P ,outers running S1S ill send hello pac!ets out all S1S1enabled interfaces to

disco.er neighbors and establish ad#acencies"

P ,outers sharing a common data lin! ill become S1S neighbors if their hello

pac!ets contain information that meets the criteria for forming an ad#acenc-" The

criteria differ slightl- depending on the t-pe of media being used (p%p or

broadcast)"

P ,outers ma- build a lin,state pac,et 6(SP7based upon their local interfaces

that are configured for S1S and prefi/es learned from other ad#acent routers"

P 7enerall-* routers flood 0Ss to all ad#acent neighbors e/cept the neighbor

from hich the- recei.ed the same 0S" oe.er* there are different forms of

flooding and also a number of scenarios in hich the flooding operation ma-

differ"


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P All routers ill construct their lin!1state database from these 0Ss"

P A shortest1path tree (ST) is calculated b- each S* and from this ST the

routing table is built.

%-%$%$ )S)S 8ata*lo4 8iagram:

The flo of information ithin the S1S routing function is represented b-

the S1S data1flo diagram 6*igure %'17* hich consists of four processes and a

,outing nformation Base (,B)" The ,B consists of the lin!1state database and

the forarding database" The four processes in the S1S data1flo diagram are:

recei&e, update, decisio", and $orward/

+igure "'= data flo in S1S

The recei&eprocess is the entr- point for all data* including user data* error

reports* routing information* and control pac!ets" t passes user data and error

reports to the forard process and passes routing information and control pac!ets

(hellos* 0Ss* and sequence number pac!ets) to the update process"


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The update process generates local lin! information that is flooded to ad#acent

routers in addition* the update process recei.es* processes* and forards lin!

information recei.ed from ad#acent routers" This process manages the 0e.el ' and

0e.el % lin!1state databases and floods 0e.el ' and 0e.el % 0Ss throughout an

area"

The decisio" process runs shortest1path1first (S+) algorithm on the lin!1state

database* and creates the forarding database" t computes ne/t1hop information

and computes sets of equal1cost paths* creating an ad#acenc- set that is used for

load balancing" $n a Cisco router* S1S supports load balancing o.er and up to si/

equal1cost paths" The $orwardprocess gets its input from the recei&eprocess and

uses the forarding database to forard data pac!ets toard their destination" t

also redirects load sharing and generates error reports"

%-%$% Areas and the !outing 8omain

An S1S routing domain is similar to a B7 autonomous s-stem" A routing

domain is a collection of areas under an administration that implements routing

policies ithin the domain"

+ac,bone

S1S does not ha.e a bac!bone area li!e the $S+ area &" The S1S bac!bone

is a contiguous collection of 0e.el %1capable routers* each of hich can be in a

different area (+igure "'@)"


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+igure "'@ S1S Bac!bone

Areas

6ith S1S* an indi.idual router is in onl- one area* and the border beteen areas is

on the lin! that connects to routers that are in different areas (+igure "'>)" This

is in contrast to $S+* in hich the area borders are ithin the Area Border

,outers (AB,s) (+igure "'?)" The reason for this difference is that an S1S router

generall- has one netor! ser.ice access point (3SA) address* and an router

generall- has multiple addresses"


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+igure "'> S1S Areas: Area Borders Are on 0in!s Beteen ,outers

Figure 3.19 OSPF Areas: Area Borders Are Within Routers

(evel ' !outer :

A 0e.el ' router !nos the topolog- onl- of its on area and has 0e.el ' or

0e.el'K0e.el% neighbors in this area" t has a 0e.el ' lin!1state database ith all

the information for intra1area routing"

(evel $ !outer :

A 0e.el % router ma- ha.e neighbors in the same or in different areas* and it has a

0e.el % lin!1state database ith all information for inter1area routing" 0e.el

% routers !no about other areas but ill not ha.e 0e.el ' information from

its on area" n the $S orld* a router must !no the topolog- of its on

area so a 0e.el % router should not be configured hen onl- $S traffic is

being routed" f the traffic in an area is 1onl-* all the routers can be

configured as 0e.el %"


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(evel '?(evel $ !outer :

A 0e.el 'K0e.el % router ma- ha.e neighbors in an- area" t has to lin!1state

databases: a 0e.el ' lin!1state database for intra1area routing and a 0e.el % lin!1state database for inter1area routing" A 0e.el 'K0e.el % router runs to S+s and

ma- require more memor- and processing as a result" G%@H"

%-%$%- SH"!TST PATH CA(CU(AT)"#:

Shortest path calculation is based on Di#!stras algorithm" $nce a router

recei.es a ne 0S* it aits for < sec before running the shortest path calculation"

There is a '& sec hold1don timer beteen to consecuti.e shortest1path

calculations ithin the same area" 0'K0% routers that reside in 0' areas must run

separate shortest path calculations* one for the 0' area and the other for the 0%

area"

0in! metric in S1S has been originall- limited to = bits and* thus* the .alue ranges

from & to = and the total path cost in an S1S domain can ha.e a ma/imum .alue

of '&%" This =1bit metric is !non as a "arrow 'etric" A wide 'etric e/tension is

no a.ailable through traffic engineering e/tensions to S1S that permits a %;1bit

metric* thus alloing a range of & to '=*@@@*%'< (V%%; W')"G%@H

%-%$%/ Pac,et Types :

There are four general t-pes of pac!ets* and each t-pe can be 0e.el ' or 0e.el %"

P ntermediate S-stem1to1ntermediate S-stem ello ()O8sed b- routers to

detect neighbors and form ad#acencies" n addition to the * hich is an S1S

protocol data unit (D8)* there is an S and an ES* hich are End S-stem1to1

ntermediate S-stem (ES1S) D8s"


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P 0in!1state pac!et (0S)OThere are four t-pes of 0Ss: 0e.el ' pseudonode*

0e.el ' nonpseudonode* 0e.el % pseudonode* and 0e.el % nonpseudonode"

P Complete sequence number D8 (CS3)OCS3s contain a list of all 0Ss

from the current database" CS3s are used to inform other routers of 0Ss that

ma- be outdated or missing from their on database" This ensures that all routers

ha.e the same information and are s-nchroni4ed" The pac!ets are similar to an

$S+ database description pac!et"

P artial sequence number D8 (S3)OS3s are used to request an 0S (or

0Ss) and ac!noledge receipt of an 0S (or 0Ss)"

The folloing information is included in D8s:

P 6hether the D8 is a point1to1point (6A3) D8 or a 0A3 D8"

P Source DOS-stem D of the sending router"

P olding timeOTime period to ait to hear a hello before declaring theneighbor dead" Similar to the $S+ dead inter.al* the default .alue is three times

the hello inter.al but can be changed ith the S1S hello1multiplier command"

P Circuit t-pe indicating hether the interface on hich the D8 as sent is

0e.el '* 0e.el %* or 0e.el 'K0e.el %"

P D8 length"

P 0ocal circuit D on the sending interface (in point1to1point hello D8s)"

P 0A3 DOS-stem D of the DS plus the pseudonode D (circuit D) to

differentiate 0A3 Ds on the same DS"


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P riorit-Oigher is better" 8sed in DS election (in 0A3 hello D8s* there is

no D, (Designated ,outer) election on a point1to1point lin!)"

B- default* S1S hellos are padded to the full ma/imum transmission unit (MT8)

si4e"

The benefit of padding s to the full MT8 is earl- detection of errors caused b-

transmission problems ith large frames or MT8 mismatched on ad#acent

interfaces"G'=H

%1 Similarities and 8ifferences +et4een )S)S and "SP*:

t is helpful to consider the similarities and differences beteen S1S and

$S+" +irst* it should be noted that fundamentall- there is little difference beteen

$S+ and S1S" Thus*the differences center more on ho certain things are done*

often st-listic differences"

+, $I-I&RI%IE$:

There are se.eral similarities beteen S1S and $S+:

P Both protocols pro.ide netor! hierarch- through to1le.el areas"

P Both protocols use ello pac!ets to initiall- form ad#acencies and then continue

to maintain them"

P Both protocols ha.e the abilit- to do address summari4ation beteen areas"

P Both protocols maintain a lin! state database* and shortest path computation

performed using Di#!stras algorithm"


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P Both protocols ha.e the pro.ision to elect a designated router for representing a

broadcast netor!"

., DIFFEREN'E$:

6hile there are similarities as noted abo.e* there are se.eral differences:

P 6ith $S+* an area border router can sit on the boundar- beteen the bac!bone

area and a lo1le.el area ith some interfaces in the area hile other interfaces are

in the other area" n S1S* routers are entirel- ithin one or the other areaOthe

area borders are on lin!s* not on routers"

P 6hile $S+ pac!ets are encapsulated in datagrams* S1S pac!ets are directl-

encapsulated in lin! la-er frames"

P The $S+ dimension1less lin! metric .alue is in the range ' to =


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CHAPT! *"U!

EMPIRIQL SWYV[


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-% mpirical !esearch:

Empirical ,esearch based on e/perimentation or direct obser.ation* i"e"

e.idence" This !ind of research often conducted to anser specific questions or to

test h-pothesis" This chapter focus in presenting the result of empirical research

and the detailed anal-sis in respect to the research questions"

-%' Simulation:

The term simulation is used in different a-s b- different people" As used here*

simulation is defined as the process of creating a 'odelof an e/isting or proposed

syste' in order to identif- and understand those factors hich control the s-stem

andKor to predict the future beha.ior of the s-stem" Almost an- s-stem hich can

be quantitati.el- described using equations andKor rules can be simulated"G'H This

gi.e the abilit- the get a clear .ie about points of ea!ness and help to impro.e

the performance of it"

;"'"' Simulation Tools:


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Some of the popular discrete-e&e"t si'ulators (DES) for netor!s are:

-%'%'%'G#S:

s a graphical netor! simulator that allos simulation of comple/ netor!s"

To pro.ide complete and accurate simulations* 73S is strongl- lin!ed ith:

D-namips* a Cisco $S emulator* D-nagen* a te/t1based front end for D-namips*

Jemu*a generic and open source machine emulator and .irtuali4er and 2irtualBo/*

a free and poerful .irtuali4ation softare"

73S is an e/cellent complementar- tool to real labs for netor! engineers and

administrators" t can also be used to e/periment features of Cisco $S* Quniper

Qun$S or to chec! configurations that need to be deplo-ed later on real routers"

73S pro#ect is an open source* free program that ma- be used on multiple

operating s-stems* including 6indos* 0inu/* and Mac$S 9"G%H

-%'%'%$ #et4or, Simulator 6ns7:

3s1 is a discrete1e.ent netor! simulator* targeted primaril- for research and

educational use" ns1 is free softare* and is publicl- a.ailable for research*

de.elopment* and use" The goal of the ns1 pro#ect is to de.elop a preferred* open

simulation en.ironment for netor!ing research: it should be aligned ith the

simulation needs of modern netor!ing research and should encourage communit-

contribution* peer re.ie* and .alidation of the softare"GH

-%'%'% "P#T 5odeler:

stands for $ptimi4ed 3etor! Engineering Tools* $3ET Modeler

accelerates the research and de.elopment process for anal-4ing and designing


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communication netor!s* de.ices* protocols* and applications" 8sers can anal-4e

simulated netor!s to compare the impact of different technolog- designs on end1

to1end beha.ior" Modeler incorporates a broad suite of protocols and technologies*

and includes a de.elopment en.ironment to enable modeling of all netor! t-pes

and technologies including: 2o* TCK*8MTS*$S+*M0S *.= and man-

other applications"G;H $3ET Technologies has also offered free of cost .ersion

!non as T 7uru for academic use" The eas- to use 78 structure of this modeler

enable users to design* simulate and .ie the results ithout ha.ing good

programming !noledge" The stabilit-* accurate results * large number of .enders

de.ices and the ease of using ere the main reasons to choose the $3ET

modeler as the simulation tool to be used in this research or!"

-%$ "P#T Simulation:

+olloing section include in depth stud- of the $3ET simulator tool to

anal-ses the M0S 23 netor! beha.ior:

-%$%' Tas,:

The main tas! of this empirical stud- is to gi.e in depth anal-sis for the

performance of the M0S 23 netor!s b- stud-ing the effect of the interior

gatea- protocols ($S+ and S1S) in the netor! performance hen the-

interaction ith e/terior gatea- protocols (B7)" This can be achie.ed b- ta!ing

into stud- the different performance metrics li!e con.ergence time* 23 dela-*23 load and throughput (bitKseconds)"The results obtained b- the simulation are

anal-4ed to determine the beha.ior of M0S 23 bac!bone"

-%$%$ Assumptions:


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t is .er- hard to predicts the beha.ior of M0S 23 bac!bone because of the

different designs and implementation factors are in.ol.ed in the netor! such as

configuring the 23*M0S routers* 0Ss * traffic* data lin!s* etc" This or!

pro.ide a simulation results for different M0S 23 models b- considering $S+

or S1S as 7 and B7 as E7" oint to point S$3ET ($C) lin!s used to

connect each router in the simulation design"

-%$% Analysis 5ethodology:

n this section the proposed designs of the M0S 23 netor!s ill be

presented ith it is relati.e configurations and thereb- determining the optimum

connection matri/ and location of netor! de.ices"

-%$%%' #et4or, Scenarios:

To get a clear and better understanding of the beha.ior of M0S 23

netor! according to the chosen interior gatea- protocol ($S+ or S1S) used

in it* to netor!s scenario ere pro.ided and implemented in the simulation tool:

'" Medium ser.ice pro.ider M0S 23 netor! bac!bone ith interior

gatea- protocol and e/terior gatea- protocol (B7)"

%" 0arge ser.ice pro.ider M0S 23 netor! bac!bone ith interior gatea-

protocol and e/terior gatea- (B7)"

Each scenario as implemented for to times according to the 7 used* one time

b- using $S+ and other time using S1S"


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-%$%%$ #et4or, Topology:

A ph-sical communication scheme consisting of connected de.ices is

!non as netor! topolog-" To netor! topologies are simulated in this thesis as

mentioned before:

'" +irst topolog-: Medium ser.ice pro.ider M0S 23 netor!

bac!bone ith interior gatea- protocol and e/terior gatea-

protocol (B7):

The considered topolog- for medium ser.ice pro.ider netor! in both cases of7 is shon in +igure ;"':

+igure ;"' medium ser.ice pro.ider netor!

3etor! component:


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As mentioned before this topolog- used for the to test cases first b- using

$S+ routing protocol as 7 and in the second case b- using S1S routing

protocols but in both test case the same component and initial confirmation are

used" This topolog- constructed from:

To autonomous s-stems:

'" Ser.ice pro.ider autonomous s-stem named AS1' contain of:

a) To pro.ider edge (E) routers for recei.ing and transmitting data from the

customer sites router through the M0S 23 bac!bone"

b)Three pro.ider () routers hich handling the traffic and routing through the

ser.ice pro.ider netor!"

%" Costumer autonomous s-stem called AS1' contain an enterprise netor! named

S Microsyste's (o'pa"y this comapna- ha.e to sites need to be connecting .ia

M0S 23 and each site ha.e:

a) Costumer edge router: to transmit and recei.e data for ser.ice pro.ider

netor!"

b)To costumer routers"

" To ma!e a communication beteen each compan- site Virtual Pri&ate Networ)

through M0S cloud is used and named VPN redas shon in +igure ;"%:


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+igure ;"% enterprise 23

As mentioned pre.iousl- lin!s beteen routes are S$3ET$C

('


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+igure ;" large ser.ice pro.ider netor!

3etor! component:

The main reason of suggesting this topolog- is to gi.e more anal-ses for the

beha.ior of M0S 23 netor! according to the interaction beteen the interior

gatea- protocols and e/terior gatea- protocols under more complicated

circumstances" Again this scenario as simulated for to times b- using $S+ as

7 ones and second using S1S as 7" This topolog- constructed from:

Three autonomous systems:

Ser.ice pro.ider autonomous s-stem named AS1' contain of:

'" Three pro.ider edge (E) routers"

%" +our pro.ider () routers "

'" +irst costumer autonomous s-stem named AS1% contain an enterprise netor!

belongs to compan- ' hich ha.e three sites need to be connected .ia M0S

23 each site from them ha.e:

'" Costumer Edge router (CE)"

%" To customer routers"

%" Second costumer autonomous s-stem named AS1 contain an enterprise

netor! belongs to compan- % hich ha.e three sites need to be connected .ia

M0S 23 each site from them ha.e:


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'" Costumer Edge router (CE)"

%" To customer routers"

" To ma!e a communication beteen each compan- site to 23s ere made

one for each compan- named ,ed 23 and ello 23 as shon in +igure ;";"

;"%"" nitial configurations:

The rocess of the initial configuration for M0S 23 compounded from three

main steps:

'" M0S routers configuration"

%" 2irtual pri.ate netor!s"

" 0abel sitching paths 0Ss"

5P(S routers configuration:

;igure D.D5/8E


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Each router ha.e to be able to enable M0S on it as shon in +igure ;";"And

the pro.iders edge (E) routers must be configured ith e/terior gatea- routing

protocols (B7) beteen all Es* i"e" all Es are B7 neighbors as shon in

+igure ;"< *and 7 ($S+ or S1S) for communicate ith other pro.ider ()

router" ro.ider routers need to be configured ith the same 7 used for Es

routers:

+igure ;"; M0S routers enable +igure ;"< B7 neighbors

;P# configuration:


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23s in both scenario ha.e the same configurations settings as mention before the

first scenario ha.e #ust one 23 named red 23 and the second scenario ha.e to

23s named red 23 and -ello 23" +igure ;"= shos the initial configuration

for them:

+igure ;"= 23s configurations

0S configuration:

0Ss ha.e been configured beteen each E in the to netor!s as shon in

+igure ;"@"+or e/ample in the medium netor! the label sitch path as set as

Site'E1to1Site%E"


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+igure ;"@ 0S beteen E routers

1%/


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-%$%%- #et4or, Traffic:

Traffic that used for purpose of the testing the effect of the 7 on the beha.ior of

M0s 23 as same traffic for both scenarios and it had the folloingspecifications:

traffic flo represented as


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+igure ;"> traffic configurations

-%$%%/ Test Parameters:

To get a fair #udgment for hich is the best 7 protocol to be used in M0S

23 netor!s* and for better understand of the effect of the 7 in M0S 23

netor!s man- factor ha.e been e/amined and these factors can be classified as:

'" arameters related to the protocol itself: con.ergence time"

arameters related to the 23: dela-* load and throughput"

Protocol parameter: Convergence time:

n d-namic routing* routing tables are created d-namicall- b- obtaining the

netor! information from other routers" ,outers in the netor! must be constantl-

updated to changes in the netor! topolog-" ,outes ma- be added or remo.ed* or

routes ma- fail due to a brea! in the ph-sical lin!"6hen a ne lin! is added or a

lin! fails or changes* updates are sent b- routers across the netor! that describe

changes in the netor! topolog-" $ther routers in the netor! then runs a routing

algorithm to recalculate routes and build ne routing tables based on the update

information" After recalculation* all the routing tables ha.e arri.ed at a common

.ie of the netor! topolog-" A con.erged netor! topolog- .ie means all the
http://www.omnisecu.com/cisco-certified-network-associate-ccna/what-is-dynamic-routing-and-different-types-of-dynamic-routing.htmhttp://www.omnisecu.com/cisco-certified-network-associate-ccna/what-is-dynamic-routing-and-different-types-of-dynamic-routing.htm


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routers agree on hich lin!s are up* hich lin!s are don* hich lin!s are running

fastest etc" 'on(ergence timeis the time* hich a group of routers reach the state

of con.ergence" $ptimall- the routing protocols must ha.e fast con.ergence time"

G%'H

;P# parameters:

To stud- the effect of the 7s in the M0S 23 some parameters related to the

23 ha.e to be considered:

'% nd to nd delay:

This parameters as used to get the time elapsed beteen traffic entering the

Uro.iders 3etor!U through ngress E and traffic lea.ing the Uro.iders

3etor!U through Egress E" The end to end dela- measurement usuall- is a hard

operation according to it is relationship ith man- other factors " 7enerall- the

total end to end dela- is sum of man- t-pes of dela- as describes b- the folloing

formula:

dendend> #@ dtransdpropdprocBNNNNN(;"')

here:

dend1endV end1to

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