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Transcript of RS InstructorPPT Chapter1 Edited
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© 2008 Cisco Systems, Inc. Al l r ights reserved. Cisco ConfidentialPresentation_ID
Cha!ter " Introd#ction
to S$itched %et$or&s
Routing and Switching
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Chapter 1
.0 Introd#ction
. 'A% Design
.2 S$itched (nvironment
.) S#mmary
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Chapter 1: Objectives
*!on com!letion of this cha!ter, yo# $ill +e a+le to"
Descri+e convergence of data, voice, and video in the contet ofs$itched net$or&s.
Descri+e a s$itched net$or& in a small-to-medi#m-sied +#siness.
(!lain the !rocess of frame for$arding in a s$itched net$or&.
Com!are a collision domain to a +roadcast domain.
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Converged Networks
Growing Complexit o! Networks
#r digital $orld ischanging.
Information m#st
+e accessed fromany$here in the$orld.
%et$or&s m#st +esec#re, relia+le,
and highlyavaila+le.
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Converged Networks
"lements o! a Converged Network
Colla+oration is are#irement.
3o s#!!ort colla+oration,net$or&s em!loy
converged sol#tions.
Data services incl#devoice systems, IP !hones,voice gate$ays, videos#!!ort, and video
conferencing. Call control, voice
messaging, mo+ility, anda#tomated attendant arealso common feat#res.
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Converged Networks
#ene!its o! a Converged Network
Converged net$or&
5 a single net$or& designed to handle voice, video, and data6
5 an internal net$or& $here the 'ayer ) devices, s#ch as
ro#ters, have a com!lete ro#ting ta+le to +e a+le to
acc#rately and efficiently send data to a remote destination65 a s$itch net$or& that has com!leted calc#lations that res#lt
in a single !ath thro#gh the s$itch net$or&.
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Converged Networks
#ene!its o! a Converged Network
(lements of a Converged %et$or& ...29
5 Call control: 3ele!hone call !rocessing, caller ID, call
transfer, hold, and conference
5 $oice messaging: :oicemail
5 %obilit: ;eceive im!ortant calls $herever yo# are
5 &utomated attendant: Serve c#stomers faster +y ro#ting
calls directly to the right de!artment or individ#al
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Converged Networks
#orderless Switched Networks
3he Cisco <orderless %et$or& is a net$or& architect#re thatallo$s organiations to connect anyone, any$here, anytime,and on any device sec#rely, relia+ly, and seamlessly.
Cisco <orderless %et$or& is designed to address I3 and+#siness challenges, s#ch as s#!!orting the convergednet$or& and changing $or& !atterns.
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Converged Networks
'ierarch in the #orderless Switched
Network
<orderless
s$itched net$or&
design g#idelines
are +#ilt #!on the
follo$ing !rinci!les"
>ierarchical
*nderstanding
the role of
each device atevery tier,
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Converged Networks
'ierarch in the #orderless Switched
Network
<orderless
s$itched net$or&
design g#idelines
are +#ilt #!on the
follo$ing !rinci!les"
;esiliency
- Satisfies #ser
e!ectations for&ee!ing thenet$or& al$ayson
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Converged Networks
'ierarch in the #orderless Switched
Network
<orderless
s$itched net$or&
design g#idelines
are +#ilt #!on the
follo$ing !rinci!les"
?lei+ility
- Allo$s intelligent
traffic load
sharing +y #sing
all net$or&
reso#rces
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Converged Networks
'ierarch in the #orderless Switched
Network
<orderless
s$itched net$or&
design g#idelines
are +#ilt #!on the
follo$ing !rinci!les"
@od#larity
Allo$s seamless
net$or& e!ansionand integratedservice ena+lementon an on-demand+asis
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Converged Networks
Core (istribution access
Access layer
;e!resents the net$or& edge, $here traffic enters or eits thecam!#snet$or&.
3raditionally, the !rimary f#nction of an access layer s$itch is to!rovide net$or& access to the #ser.
Access layer s$itches connect to distri+#tion layer s$itches, $hichim!lement net$or& fo#ndation technologies s#ch as ro#ting, #ality ofservice, and sec#rity.
.
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Converged Networks
Core (istribution access
Distri+#tion 'ayer
3he distribution layer interfaces +et$een the access layer and thecore layer to !rovide many im!ortant f#nctions, incl#ding"
Aggregating large-scale $iring closet net$or&s Aggregating 'ayer 2 +roadcast domains and 'ayer ) ro#ting
+o#ndaries
Providing intelligent s$itching, ro#ting, and net$or& access !olicyf#nctions to access the rest of the net$or&
Providing high availa+ility thro#gh red#ndant distri+#tion layers$itches to the end-#ser and e#al cost !aths to the core
Providing differentiated services to vario#s classes of servicea!!lications at the edge of the net$or&
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Converged Networks
Core (istribution access
Core 'ayer
3he core layer is the net$or& +ac&+one. It connects several layers ofthe cam!#s net$or&.
3he core layer serves as the aggregator for all of the other cam!#s+loc&s and ties the cam!#s together $ith the rest of the net$or&. 3he!rimary !#r!ose of the core layer is to !rovide fa#lt isolation and high-s!eed +ac&+one connectivity.
?ig#re -4 sho$s a three-tier campus network design fororganiations $here the access, distri+#tion, and core are eachse!arate layers.
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Converged Networks
Core) (istribution) &ccess
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Switched Networks
Role o! Switched Networks
Switched Networks *1+1+,-
S$itched net$or&s are im!ortant $hen de!loying $ired 'A%s.
A net$or& !rofessional today m#st +e $ell-versed in s$itches and'A% technology in order to add commonly de!loyed devices s#ch
as PCs, !rinters, video cameras, !hones, co!iers, and scanners. Sharing and accessing net$or& devices is common in +oth the
home and +#siness net$or&.
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Switched Networks
Role o! Switched Networks
S$itching technologies are cr#cial to net$or& design.
S$itching allo$ traffic to +e sent only $here it is needed in mostcases, #sing fast methods.
A s$itched 'A%"
Allo$s more flei+ility Allo$s more traffic management
S#!!orts #ality of service, additional sec#rity, $ireless, IP
tele!hony, and mo+ility services
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Switched Networks
Role o! Switched Networks
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Switched Networks
Role o! Switched Networks
?orm ?actors ..2.29
3here are vario#s ty!es of s$itches #sed in +#siness net$or&s. It isim!ortant to de!loy the a!!ro!riate ty!es of s$itches +ased onnet$or& re#irements.
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Switched Networks
.orm .actor
.ixed/lat!orm
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Switched Networks
.orm .actor *cont+-
%odular
/lat!orm
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Switched Networks
.orm .actor *cont+-
Stackable
/lat!orm
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.rame .orwarding
Switching as a General Concept
A s$itch ma&es a decision +ased on ingress and a destination
!ort.
A 'A% s$itch &ee!s a ta+le that it #ses to determine ho$ to
for$ard traffic thro#gh the s$itch.
Cisco 'A% s$itches for$ard (thernet frames +ased on thedestination @AC address of the frames.
3he f#ndamental conce!t of s$itching refers to a devicema&ing a decision +ased on t$o criteria"
Ingress !ort Destination address
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.rame .orwarding
Switching as a General Concept
3he decision on ho$ a s$itch for$ards traffic is made inrelation to the flo$ of that traffic.
3he term ingress is #sed to descri+e a frame entering a deviceon a s!ecific !ort.
3he term egress is #sed to descri+e frames leaving the devicethro#gh a !artic#lar !ort.
hen a s$itch ma&es a decision, it is +ased on the ingress!ort and the destination address of the message.
A 'A% s$itch maintains a ta+le that it #ses to determine ho$ to
for$ard traffic thro#gh the s$itch.
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.rame .orwarding
(namicall /opulating a Switch %&C
&ddress 0able A s$itch m#st first learn $hich devices eist on each !ort +efore it
can transmit a frame.
It +#ilds a ta+le called a @AC address or content addressa+le
memory CA@9 ta+le.
3he ma!!ing device B- !ort is stored in the CA@ ta+le. CA@ is a s!ecial ty!e of memory #sed in high-s!eed searching
a!!lications.
3he information in the @AC address ta+le #sed to send frames.
hen a s$itch receives an incoming frame $ith a @AC address thatis not fo#nd in the CA@ ta+le, it floods it to all !orts, +#t the one that
received the frame.
;efer online notes ?ig#re -) to -8
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.rame .orwarding
Switch .orwarding %ethods *1+,+1+- Commonly, in earlier net$or&s, as they gre$, enter!rises +egan to
e!erience slo$er net$or& !erformance.
(thernet +ridges an early version of a s$itch9 $ere added
to net$or&s to limit the sie of the collision domains. In the ==0s,
advancements in integrated circ#it technologies allo$ed for 'A% s$itches to re!lace
(thernet
+ridges. 3hese 'A% s$itches $ere a+le to move the 'ayer 2for$arding decisions
from soft$are to application-specific-integrated circuits (ASICs). ASICs red#ce
the !ac&et-handling time $ithin the device, and allo$ the device tohandle an
increased n#m+er of !orts $itho#t degrading !erformance. 3hismethod of for$arding
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.rame .orwarding
Switch .orwarding %ethods
&dd a header
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.rame .orwarding
Store2and2.orward Switching
Allo$s the s$itch to" Chec& for errors via ?CS chec&9
3he ?CS is an error chec&ing !rocess that hel!s to ens#re that the frame is free of !hysical andata-lin& errors. If the frame is error-free, the s$itch for$ards the frame. ther$ise, the frame idro!!ed.
A#tomatic <#ffering
3he ingress !ort +#ffering !rocess #sed +y store-and-for$ard s$itches !rovides the
flei+ility to s#!!ort any mi of (thernet s!eeds. ?or eam!le, handling an incoming
frame traveling into a 00 @+s (thernet !ort that m#st +e sent o#t a E+s
interface $o#ld re#ire #sing the store-and-for$ard method. ith any mismatch in
s!eeds +et$een the ingress and egress !orts, the s$itch stores the entire frame in a
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.rame .orwarding
Store2and2.orward Switching
Allo$s the s$itch to" Perform a#tomatic +#ffering
3he ingress !ort +#ffering !rocess #sed +y store-and-for$ard s$itches !rovides the flei+ility ts#!!ort any mi of (thernet s!eeds. ?or eam!le, handling an incoming frame traveling into a00 @+s (thernet !ort that m#st +e sent o#t a E+s interface $o#ld re#ire #sing the store-and-for$ard method.
Store-and-for$ard s$itching is CiscoFs !rimary 'A% s$itchingmethod.
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.rame .orwarding
Store2and2.orward Switching *cont+-
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.rame .orwarding
Cut20hrough Switching
An advantage to c#t-thro#gh s$itching is the ca!a+ility of the s$itchto start for$arding a frame earlier than store-and-for$ard s$itching.
3here are t$o !rimary characteristics of c#t-thro#gh s$itching" ra!idframe for$arding and invalid frame !rocessing.
Allo$s the s$itch to start for$arding in a+o#t 0 microseconds
%o ?CS chec&
%o a#tomatic +#ffering
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.rame .orwarding
Cut20hrough Switching
;a!id ?rame ?or$arding As indicated in ?ig#re -20, a s$itch #sing the c#t-thro#gh method
can ma&e a for$arding decision as soon as it has loo&ed #! thedestination @AC address of the frame in its @AC address ta+le.
3he s$itch does not have to $ait for the rest of the frame to enter the
ingress !ort +efore ma&ing its for$arding decision.
3he c#t-thro#gh s$itching method does not dro! most invalidframes. ?rames $ith errors are for$arded to other segments of thenet$or&. If there is a high error rate invalid frames9 in the net$or&,c#t-thro#gh s$itching can have a negative im!act on +and$idth6
th#s, clogging #! +and$idth $ith damaged and invalid frames.
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.rame .orwarding
Cut20hrough Switching
?ragment ?ree ?ragment free s$itching is a modified form of c#t-thro#gh s$itching
in $hich the s$itch $aits for the collision $indo$ 4/ +ytes9 to !ass+efore for$arding the frame.
3his means each frame $ill +e chec&ed into the data field to ma&e
s#re no fragmentation has occ#rred.
?ragment free mode !rovides +etter error chec&ing than c#t-thro#gh,$ith !ractically no increase in latency.
ith a lo$er latency s!eed advantage of c#t-thro#gh s$itching, it ismore a!!ro!riate etremely demanding, high-!erformancecom!#ting >PC9 a!!lications that re#ire !rocess-to-!rocesslatencies of 0 microseconds or less.
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.rame .orwarding
Cut20hrough Switching *cont+-
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Switching (omains
Collision (omains
A collision domain is the segment $here devices m#st com!ete tocomm#nicate.
All !orts of a h#+ +elong to the same collision domain.
(very !ort of a s$itch is a collision domain on its o$n.
A s$itch +rea& the segment into smaller collision domains, easingdevice com!etition.
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Switching (omains
Collision (omains
A collision domain is the segment $here devices m#st com!ete tocomm#nicate.
All !orts of a h#+ +elong to the same collision domain.
(very !ort of a s$itch is a collision domain on its o$n.
A s$itch +rea& the segment into smaller collision domains, easingdevice com!etition.
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Switching (omains
#roadcast (omains
A +roadcast domain is the etend of the net$or& $here a +roadcastframe can +e heard.
S$itches for$ard +roadcast frames to all !orts6 therefore, s$itches
do not +rea& +roadcast domains.
All !orts of a s$itch, $ith its defa#lt config#ration, +elong to thesame +roadcast domain.
If t$o or more s$itches are connected, +roadcasts are for$arded to
all !orts of all s$itches, ece!t for the !ort that originally received
the +roadcast.
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Switching (omains
#roadcast (omains
<roadcasts are sometimes necessary for initially locating otherdevices and net$or& services, +#t they also red#ce net$or&efficiency.
3oo many +roadcasts and a heavy traffic load on a net$or& canres#lt in congestion" a slo$do$n in the net$or& !erformance.
;efer online notes " ?ig#re .2.2
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Switching (omains
&lleviating Network Congestion
S$itches hel! alleviating net$or& congestion +y"
?acilitating the segmentation of a 'A% into se!arate collision
domains
Providing f#ll-d#!le comm#nication +et$een devices
3a&ing advantage of their high-!ort density
<#ffering large frames
(m!loying high-s!eed !orts
3a&ing advantage of their fast internal s$itching !rocess
>aving a lo$, !er-!ort cost
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Chapter 1: Summar
In this cha!ter, yo# learned" 3he trend in net$or&s is to$ards convergence #sing a single set of
$ires and devices to handle voice, video, and data transmission.
3here has +een a dramatic shift in the $ay +#sinesses o!erate.
3here are no !hysical offices or geogra!hic +o#ndaries constraints.;eso#rces m#st no$ +e seamlessly availa+le anytime andany$here.
3he Cisco <orderless %et$or& architect#re ena+les differentelements, from access s$itches to $ireless access !oints, to $or&
together and allo$ #sers to access reso#rces from any !lace at anytime.
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Chapter 1: Summar *cont+-
3he traditional, three-layer hierarchical design model divides thenet$or& into core, distri+#tion, and access layers, and allo$s each!ortion of the net$or& to +e o!timied for s!ecific f#nctionality.
It !rovides mod#larity, resiliency, and flei+ility, $hich !rovides afo#ndation that allo$s net$or& designers to overlay sec#rity,
mo+ility, and #nified comm#nication feat#res. S$itches #se either store-and-for$ard or c#t-thro#gh s$itching.
(very !ort on a s$itch forms a se!arate collision domain allo$ing foretremely high-s!eed, f#ll-d#!le comm#nication.
S$itch !orts do not +loc& +roadcasts and connecting s$itches canetend the sie of the +roadcast domain, often res#lting in degradednet$or& !erformance.