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Layer 2 and Layer 3 SwitchingFreeha Khan
2nd PresentationIS 8040Data Co !nication "heory and Practice
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SwitchingToday in data communications, all switchingand routing equipment perform two basicoperations:
Switching data frames Maintenance of switching operationsSwitching is the process of taking an incomingframe from one interface and delivering it out
through another interfaceRouters use Layer switching to route apacket, and switches !Layer " switches# useLayer " switching to forward frames
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Switches
%&'%&&()bps *thernet Switches are goodresolution if *thernet L+ s are stretched to
the breaking point under the weight of new users, servers and high(end applications)ost switches provide shared or dedicated%&'%&& uplinks to other switches or networkbackbones, and some even provide one ortwo dedicated -igabit *thernet links forespecially heavy bandwidth requirements
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Layer 2 Switching
Layer " switches,operate at the
second, or data link,layer of the opensystemsinterconnection
model
OSI Model
#$$%ication
PresentationSession"rans$ort
&etwor'Data Lin'Physica%
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Layer 2 Switch
-arrett .ommunications )agnum switchescome with eight to "/ %&'%&&()bps ports andrange in price from 0122 to 0%,%223
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Layer 2 Switching
I, the Layer 2 switch does not 'now where tosend the ,ra e it +roadcasts the ,ra e o!t a%% its$orts to the networ' to %earn the correctdestination
hen the ,ra e s re$%y is ret!rned the switch
%earns the %ocation o, the new address and addsthe in,or ation to the switching ta+%e
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Layer 3 Switching
Layer switchingoperates at the
network layer
SI *ode%#$$%ication
PresentationSession"rans$ort
&etwor'Data Lin'Physica%
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Layer 3 Switch
Li ited $!r$ose
Layer 3 switches are on%y a.ai%a+%e ,orthernet"hey on%y ro!te IP/IP6 $rotoco%s
Ca$a+%e to $er,or ro!ting at wires$eed7 10 100 1000 *+$s
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Layer 3 Switching
ardware +ased $ac'et to $ac'et IPro!ting- ardware +ased ro!ters cost %ess than
traditiona% so,tware +ased ro!ters
"hey switch non ro!ta+%e tra,,ic to Layer 2
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Layer 3 Switch
Rapier T) %&'%&& Layer Switch
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Layer 3 Switching
7t e$amines packet information andforwards packets based on theirnetwork(layer destination addressesLayer switching also supportsrouter functionality
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Layer 3 Switching
Flow of intersubnet traffic with Layer 3 switches
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Di,,erence +etween Layer 2 and
Layer 3 Switches"he di,,erence +etween Layer 2 and Layer 3switching is the ty$e o, in,or ation inside the
,ra e that is !sed to deter ine the correcto!t$!t inter,aceith Layer 2 switching ,ra es are switched
+ased on *#C address in,or ationith Layer 3 switching ,ra es are switched
+ased on networ' %ayer in,or ation
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Di,,erence +etween Layer 2 and
Layer 3 SwitchesLayer " switching does not lookinside a packet for network(layerinformation as does layer switchingLayer " switching is performed bylooking at a destination )+.address within a frame
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Di,,erence +etween Layer 2 and
Layer 3 SwitchesLayer switches looks at the frame8sdestination address and sends it to the
appropriate interface if it knows thedestination address locationLayer " switching builds and maintains a
switching table that keeps track of which)+. addresses belong to each port orinterface
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9e,erences
Switched, Fast, and Gigabit Ethernet 9o+ert:reyer and Sean 9i%ey "hird dition
Business Data Communications Sta%%ingsFo!rth ditionhtt$7//www;gcn;cohtt$7//www;s%ac;stan,ord;ed!/htt$7//www;cisco;co /!ni.ercd
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9e,erences
htt$7//www;gcn;co /state/.o%(
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