effect of the interior gateway routing protocols in the mult.pdf
TRANSCRIPT
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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 $3ET Modeler then an in depth
anal-ses of the netor! performance ill be pro.ide "
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Keywords: IP, MPLS, VPN, MPLS VPN, OSPF,IS-IS
"! "#$% &" '" ) ( $ &( (* ! +, -
.&" % $/ 412 30 $ 54% 6 " ) 7 89 :; -
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%( DEDCAT$3
AC53$60ED7EME3T ABST,ACT 2! 2TAB0E $+ C$3TE3TS 20ST $+ +78,ES 9
0ST $+ TAB0ES 9
CHAPT! "#
'Bac!ground ''"%roblem Statement '"roposed Solution
'";$b#ecti.es ;
'"
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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 an- other 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 an- other 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'
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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- an- other 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:
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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"
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+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"
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""%" !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)"
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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"
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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 ,
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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'
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+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
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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 "''):
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+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
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%-%'% 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"
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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'
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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"
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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 $S+ netor!"G'
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+igure "' 0in! state ad.ertisements
%-%'%3 "SP* Pac,et *ormat:
C$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 (
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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-
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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
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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