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12/02/2015
Internetworking Basics
Heres a list of some of the things that commonly cause LAN traffic
congestion
!oo many hosts in a collision or "roa#cast #omain
Broa#cast storms !oo much multicast traffic
Low "an#wi#th
A##ing hu"s for connecti$ity to the network
A "unch of A%& "roa#casts
!here are two a#$antages to using routers in your network
!hey #ont forwar# "roa#casts "y #efault'!hey can filter the network "ase# on layer () Network layer) information
such as an I& a##ress'Here are four ways a router functions in your network&acket switching
&acket filteringInternetwork communication
&ath selection
*witches create se+arate collision #omains within a single "roa#cast
#omain' %outers +ro$i#e a se+arate "roa#cast #omain for each
interface'
,ont let this e$er confuse you
-ou woul# use a "ri#ge in a network to re#uce collisions within
"roa#cast
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#omains an# to increase the num"er of collision #omains in your
network'
,oing this +ro$i#es more "an#wi#th for users' An# ne$er forget that
using
hu"s in your .thernet network can contri"ute to congestion' As
always) +lan your network #esign carefully
LANs) which are use# when you logically "reak u+
"roa#cast #omains in a layer 2) switche# network
Internetworking o#els
A#$antages of %eference o#els
!he *I mo#el is hierarchical) an# there are many a#$antages that
can "e a++lie# to any layere# mo#el) "ut as I sai#) the *I mo#els +rimary +ur+ose is to
allow #ifferent $en#ors
networks to intero+erate'
Heres a list of some of the more im+ortant "enefits for using the *I
layere# mo#el
!he 3++er Layers
!he Lower Layers
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It #i$i#es the network communication +rocess into smaller an# sim+ler
com+onents)
facilitating com+onent #e$elo+ment) #esign) an# trou"leshooting'
It allows multi+le4$en#or #e$elo+ment through the stan#ar#iation of
network
com+onents'
It encourages in#ustry stan#ar#iation "y clearly #efining what
functions occur at each
layer of the mo#el'
It allows $arious ty+es of network har#ware an# software to
communicate'
It +re$ents changes in one layer from affecting other layers to
e6+e#ite #e$elo+ment
!he u++er layers
!he following network #e$ices o+erate at all se$en layers of the *I
mo#el
Network management stations 7N*s8
9e" an# a++lication ser$ers
:ateways 7not #efault gateways8
*er$ers
Network hosts
!he *I reference mo#el has the following se$en layers
A++lication layer 7layer ;8
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&resentation layer 7layer unctions
!he Layere# A++roach
!he A++lication layer of the *I mo#el marks the s+ot where users
actually communicate
to the com+uter an# comes into +lay only when its clear that access to
the network will "e nee#e# soon' !ake the case of Internet .6+lorer 7I.8' -oucoul# actually uninstall e$ery trace of networking com+onents like !?&/I&)
the NI? car#) an# so on an# still use I. to $iew a local H!L #ocument'
!he A++lication layer works as the interface "etween actual a++lication
+rograms' !his means en#4user +rograms like icrosoft 9or# #ont
resi#e
at the A++lication layer) they interface with the A++lication layer
+rotocols'
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!he &resentation layer ensures that #ata transferre# from the
A++lication layer of one system can "e rea# "y the A++lication layer of
another one'
!he *ession layer is res+onsi"le for setting u+) managing) an##ismantling sessions "etween &resentation layer entities an# kee+ing user
#ata se+arate' ,ialog control "etween #e$ices also occurs at this layer
!he !rans+ort layer segments an# reassem"les #ata into a single #ata
stream' !he term relia"le networking can "e use# at the !rans+ort layer'
%elia"le networking re@uires that acknowle#gments) se@uencing) an# flowcontrol will all "e use#'
?onnection4riente# ?ommunication
>or relia"le trans+ort to occur) a #e$ice that wants to transmit mustfirst esta"lish a connection4oriente# communication session with a remote
#e$iceits +eer systemknown as a call setu+ or a three4way han#shake'
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>low ?ontrol
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!he +ur+ose of flow control is to +ro$i#e a way for the recei$ing #e$ice
to
control the amount of #ata sent "y the sen#er'
A ser$ice is consi#ere# connection4oriente# if it has the following
characteristics
A $irtual circuit) or three4way han#shakeC is set u+'
It uses se@uencing'
It uses acknowle#gments'
It uses flow control'
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9in#owing
!he @uantity of #ata segments) measure# in "ytes)
that the transmitting machine is allowe# to sen# without recei$ing an
acknowle#gment is calle# a win#ow'
9in#ows are use# to control the amount of outstan#ing)
unacknowle#ge#
#ata segments'
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If a recei$ing host fails to recei$e all the "ytes that it shoul#
acknowle#ge)
the host can im+ro$e the communication session "y #ecreasing the
win#ow sie'
Acknowle#gments
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%elia"le #ata #eli$ery ensures the integrity of a stream of #ata sent
from one machine to the other through a fully functional #ata link' It
guarantees that the #ata wont "e #u+licate# or lost'
!he Network layer) or layer () manages #e$ice a##ressing) tracks the
location of #e$ices on the network) an# #etermines the "est way to mo$e
#ata'
Here are some router characteristics that you shoul# ne$er forget
%outers) "y #efault) will not forwar# any "roa#cast or multicast
+ackets'
%outers use the logical a##ress in a Network layer hea#er to #etermine
the ne6t4ho+ router to forwar# the +acket to'
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%outers can use access lists) create# "y an a#ministrator) to control
security "ase# on the ty+es of +ackets allowe# to enter or e6it an interface'
%outers can +ro$i#e layer 2 "ri#ging functions if nee#e# an# can
simultaneously route through the same interface'
Layer ( #e$icesin this case) routers+ro$i#e connections "etween
$irtual LANs 7LANs8'
%outers can +ro$i#e @uality of ser$ice 7Do*8 for s+ecific ty+es of
network traffic'
!he ,ata Link layer +ro$i#es for the +hysical transmission of #ata an#
han#les error notification) network to+ology) an# flow control'
!he I... .thernet ,ata Link layer has two su"layers
e#ia Access ?ontrol 7A?8
,efines how +ackets are +lace# on the me#ia' ?ontention me#ia
access is first come/first ser$e#C access where e$eryone shares the same"an#wi#thhence the name' &hysical a##ressing is #efine# here as well as
logical to+ologies'
9hats a logical to+ologyE Its the signal +ath through a +hysical
to+ology' Line #isci+line) error notification 7"ut not correction8) the or#ere#
#eli$ery of frames) an# o+tional flow control can also "e use# at thissu"layer'
Logical Link ?ontrol 7LL?8%es+onsi"le for i#entifying Network layer +rotocols an# then
enca+sulating them' An LL? hea#er tells the ,ata Link layer what to #o witha +acket once a frame is recei$e#' It works like this a host recei$es a frame
an# looks in the LL? hea#er to fin# out where the +acket is #estine#forinstance) the I& +rotocol at the Network layer'
!he LL? can also +ro$i#e flow control an# se@uencing of control "its'
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*witches an# Bri#ges at the ,ata Link Layer
Layer 2 switching is consi#ere# har#ware4"ase# "ri#ging "ecause it
uses s+ecialie# har#ware calle# an a++lication4s+ecific integrate# circuit
7A*I?8' A*I?s can run u+ to high giga"it s+ee#s with $ery low latency rates'
*o) networks are to routers as in#i$i#ual #e$ices are to switches an#
"ri#ges' An# routing ta"les that ma+C the internetwork are for routers) as
filter ta"les that ma+C in#i$i#ual #e$ices are for switches an# "ri#ges'
!he &hysical Layer
>inally arri$ing at the "ottom) we fin# that the &hysical layer #oes two
things it sen#s "its an# recei$es "its' Bits come only in $alues of 1 or 0a
orse co#e with numerical $alues'
Hu"s at the &hysical Layer
A hu" is really a multi+le4+ort re+eater' A re+eater recei$es a #igital
signal) ream+lifies or regenerates that signal) then forwar#s the signal outthe other +ort without looking at any #ata'
.6am .ssentials
I#entify the +ossi"le causes of LAN traffic congestion' !oo many hosts
in a "roa#cast #omain) "roa#cast storms) multicasting) an# low "an#wi#th
are all +ossi"le causes of LAN traffic congestion'
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,escri"e the #ifference "etween a collision #omain an# a "roa#cast
#omain' ?ollision #omain is an .thernet term use# to #escri"e a network
collection of #e$ices in which one +articular #e$ice sen#s a +acket on a
network segment) forcing e$ery other #e$ice on that same segment to +ayattention to it' 9ith a "roa#cast #omain) a set of all #e$ices on a network
hear all "roa#casts sent on all segments' ,ifferentiate a A? a##ress an# an I& a##ress an# #escri"e how an#
when each a##ress ty+e is use# in a network' A A? a##ress is a
he6a#ecimal num"er i#entifying the +hysical connection of a host' A?
a##resses are sai# to o+erate on layer 2 of the *I mo#el'
I& a##resses) which can "e e6+resse# in "inary or #ecimal format) are
logical i#entifiers that are sai# to "e on layer ( of the *I mo#el' Hosts onthe same +hysical segment locate one another with A? a##resses) while I&
a##resses are use# when they resi#e on #ifferent LAN segments or su"nets'
3n#erstan# the #ifference "etween a hu") a "ri#ge) a switch) an# a
router' A hu" creates one collision #omain an# one "roa#cast #omain' A"ri#ge "reaks u+ collision #omains "ut creates one large "roa#cast #omain'
!hey use har#ware a##resses to filter the network' *witches are really Fustmulti+le4+ort "ri#ges with more intelligenceG they "reak u+ collision #omains
"ut
creates one large "roa#cast #omain "y #efault' Bri#ges an# switches
use har#ware a##resses to filter the network' %outers "reak u+ "roa#cast
#omains 7an# collision #omains8 an# use logical a##ressing to filter thenetwork'
I#entify the functions an# a#$antages of routers' %outers +erform
+acket switching) filtering) an# +ath selection) an# they facilitate
internetwork communication' ne a#$antage of routers is that they re#uce"roa#cast traffic'
,ifferentiate connection4oriente# an# connectionless network ser$ices
an# #escri"e how each is han#le# #uring network communications'
?onnection4oriente# ser$ices use acknowle#gments an# flow control to
create a relia"le session' ore o$erhea# is use# than in a connectionlessnetwork ser$ice' ?onnectionless ser$ices are use# to sen# #ata with no
acknowle#gments or flow control' !his is consi#ere# unrelia"le'
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,efine the *I layers) un#erstan# the function of each) an# #escri"e
how #e$ices an# networking +rotocols can "e ma++e# to each layer' -ou
must remem"er the se$en layers of the *I mo#el an# what function each
layer +ro$i#es' !he A++lication) &resentation) an# *ession layers are u++erlayers an# are res+onsi"le for communicating from a user interface to an
a++lication' !he !rans+ort layer +ro$i#es segmentation) se@uencing) an#$irtual circuits' !he Network layer +ro$i#es logical network a##ressing an#
routing through an internetwork' !he ,ata Link layer +ro$i#es framing an#
+lacing of #ata on the network me#ium' !he &hysical layer is res+onsi"le fortaking 1s an# 0s an# enco#ing them into a #igital signal for transmission on
the network segment'
.thernet Networks in %e$iew
.thernet is a contention4"ase# me#ia access metho# that allows all
hosts on a network to share the same links "an#wi#th'
Broa#cast ,omain
Let me start "y gi$ing you the formal #efinition "roa#cast #omain
refers to a grou+ of #e$ices on a s+ecific network segment that hear all the
"roa#casts sent out on that s+ecific network segment'
?*A/?,
.thernet networking uses a +rotocol calle# ?arrier *ense ulti+le
Access with ?ollision ,etection 7?*A/?,8) which hel+s #e$ices share the
"an#wi#th e$enly while +re$enting two #e$ices from transmittingsimultaneously on the same network me#ium'
9hen a collision occurs on an .thernet LAN) the following ha++ens
1' A Fam signal informs all #e$ices that a collision occurre#'
2' !he collision in$okes a ran#om "ackoff algorithm'
(' .ach #e$ice on the .thernet segment sto+s transmitting for a short
time until its "ackoff timer e6+ires'
=' All hosts ha$e e@ual +riority to transmit after the timers ha$e
e6+ire#'
.thernet at the ,ata Link Layer
.thernet at the ,ata Link layer is res+onsi"le for .thernet a##ressing)
commonly referre# to as A? or har#ware a##ressing
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.thernet >rames !he ,ata Link layer is res+onsi"le for com"ining "its into "ytes an#
"ytes into frames' >rames are use# at the ,ata Link layer to enca+sulate+ackets han#e# #own from the Network layer for transmission on a ty+e of
me#ia access'
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.thernet at the &hysical Layer
.thernet was first im+lemente# "y a grou+ calle# ,I) which stan#s
for ,igital) Intel) an# ero6' !hey create# an# im+lemente# the first
.thernet LAN s+ecification) which the I... use# to create the I... 02'(
committee' !his was a 10 "+s network that ran on coa6 an# thene$entually twiste#4+air an# fi"er +hysical me#ia'
!he .IA/!IA s+ecifies that .thernet use a registere# Fack 7%J8
connector on
unshiel#e# twiste#4+air 73!&8 ca"ling 7%J=58'
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.thernet ?a"ling
*traight4through ca"le
?rosso$er ca"le %olle# ca"le
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>i"er +tic
>i"er4o+tic ca"ling has "een aroun# for a long time an# has some soli#
stan#ar#s' !he ca"le allows for $ery fast transmission of #ata) is ma#e of
glass 7or e$en +lastic8) is $ery thin) an# works as a wa$egui#e to transmit
light "etween two en#s of the fi"er' >i"er o+tics has "een use# to go $ery
long #istances) as in intercontinental connections) "ut it is "ecoming more an# more +o+ular in .thernet LAN networks #ue to the fast s+ee#s
a$aila"le an# "ecause) unlike 3!&) its immune to interference like cross4talk'
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!he ?isco three4Layer Hierarchical o#el
!he ?ore Layer
!he core layer is literally the core of the network' At the to+ of the
hierarchy) the core layer is res+onsi"le for trans+orting large amounts of
traffic "oth relia"ly an# @uickly' !he only +ur+ose of the networks core layeris to switch traffic as fast as +ossi"le'
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!elnet was one of the first Internet stan#ar#s) #e$elo+e# in 1K
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*ecure *hell 7**H8 +rotocol sets u+ a secure session thats similar to
!elnet o$er a stan#ar# !?&/I& connection an# is em+loye# for #oing things
like logging into systems) running +rograms on remote systems) an# mo$ing
files from one system to another' An# it #oes all of this while maintaining anencry+te# connection
>ile !ransfer &rotocol 7>!&8 actually lets us transfer files) an# it can
accom+lish this "etween any two machines using it' But >!& isnt Fust a+rotocolG its also a +rogram' +erating as a +rotocol) >!& is use# "y
a++lications
!ri$ial >ile !ransfer &rotocol 7!>!&8 is the stri++e#4#own) stock $ersion
of >!&) "ut its the +rotocol of choice if you know e6actly what you want an#
where to fin# it "ecause its fast an# so easy to use
*im+le Network anagement &rotocol 7*N&8 collects an#mani+ulates $alua"le network information) as you can see in >igure (';' Itgathers #ata "y +olling the #e$ices on the network from a network
management station 7N*8 at fi6e# or ran#om inter$als) re@uiring them to
#isclose certain information) or e$en asking for certain information from the#e$ice' In a##ition) network #e$ices can inform the N* station a"out
+ro"lems
as they occur so the network a#ministrator is alerte#
Hy+erte6t !ransfer &rotocol 7H!!&8 to make it all +ossi"le 7>igure ('8'
Its use# to manage communications "etween we" "rowsers an# we"ser$ers an# o+ens the right resource when you click a link) where$er thatresource may actually resi#e'