cisco ip telephony flash cards

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Cisco IP Telephony Flash Cards: Weighted

Random Early Detection (WRED)

Date: Nov 24, 2004 By Kevin Wallace. Sample Chapter is provided courtesy o Cisco !ress.

"his chapter provides an overve# o Wei$hted %andom &arly Detection 'W%&D( or Cisco

)! "elephony, includin$ *uestion + ns#er lash cards to help you prepare or the Cisco )!

"elephony &-am.

Why You eed !uality o" #er$ice (!o#)

"he net#ors o yesteryear physically separated voice, video, and data traic. /iterally, these

traic types lo#ed over separate media 'or e-ample, leased lines or ier1optic cale

plants(. "oday, ho#ever, net#or desi$ners are levera$in$ the po#er o the data net#or totransmit voice and video, thus achievin$ si$niicant cost savin$s y reducin$ euipment,

maintenance, and even stain$ costs.

"he challen$e, ho#ever, #ith today3s conver$ed net#ors is that multiple applications are

contendin$ or and#idth, and some applications such as, voice can e more intolerant o

delay 'that is, latency( than other applications such as, an "! ile transer. lac o

and#idth is the overshado#in$ issue or most uality prolems.

When a lac o and#idth e-ists, pacets can suer rom one or more o the ollo#in$

symptoms:

Delay5Delay is the time that is reuired or a pacet to travel rom its source to its

destination. 6ou mi$ht #itness delay on the evenin$ ne#s, #hen the ne#s anchor is

talin$ throu$h satellite to a orei$n ne#s correspondent. Because o the satellite

delay, the conversation e$ins to eel unnatural.

%itter57itter is the uneven arrival o pacets. or e-ample, consider that in a 8oice

over )! '8o)!( conversation, pacet 9 arrives. "hen, 20 ms later, pacet 2 arrives.

ter another 0 ms, pacet ; arrives, and then pacet 4 arrives 20 ms ehind pacet

;. "his variation in arrival times 'that is, variale delay( is not droppin$ pacets, ut

this


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smallest diameter. Similarly, as a pacet travels rom its source to its destination, its eective

and#idth is the and#idth o the slo#est lin alon$ that path.

Figure &

Because your primary challen$e is a lac o and#idth, the lo$ical uestion is, ?o# do you

increase availale and#idth@ nee1ed durin$ other periods o the day.

)nstead o


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!o# 'asics

"he mission statement o *oS could read somethin$ lie ?to cate$ori>e traic and apply a

policy to those traic cate$ories, in accordance #ith a *oS policy.@ Speciically, *oS

coni$uration involves the ollo#in$ three asic steps:

#tep & Determine net#or perormance reuirements or various traic types. or e-ample,

consider the ollo#in$ desi$n rules o thum or voice, video, and data traic:

oice:

No more than 9E0 ms o one1#ay delay

No more than ;0 ms o


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or Custom *ueuin$ 'C*(, #hich are coni$ured throu$h the C/), have een availale

or many years.

-odular !o# C,I (-!C)5)nstead o usin$ the C/) to coni$ure *oS parameters

or one interace at a time, the three1step *C process allo#s you to '9( place

pacets into dierent classes, '2( assi$n a policy or those classes, and ';( apply thepolicy to an interace. Because the approach is modular, you can apply a sin$le policy

to multiple interaces.

.uto!o#5uto*oS is a script that is e-ecuted on routers or s#itches that automates

the process o *oS coni$uration. Speciically, this automatic coni$uration helps

optimi>e *oS perormance or 8o)! traic.

!o# Policy -anager (!P-)5*!, in cones

*oS coni$uration. !olicies that are created #ith *! can e pushed out to routers

throu$hout an enterprise, thus reducin$ the potential or misconi$uration.

!o# Components

Cisco oers a #ealth o *oS resources on its s#itch and router platorms. "hese resources

are classiied into one o three cate$ories, #hich are discussed in this section. "he cate$ory o

*oS resources used most oten in production, ho#ever, is the Dierentiated Services

cate$ory, #hich oers $reater scalaility and le-iility than the resources ound in the Best1

&ort or )nte$rated Services cate$ories.

!o# Categories

ll o the Cisco *oS eatures are cate$ori>ed into one o the ollo#in$ three cate$ories:

'est+E""ort5Best1&ort does not truly provide *oS, ecause there is no reorderin$

o pacets. Best1&ort uses the irst1in irst1out ')F( ueuin$ strate$y, #here

pacets are emptied rom a ueue in the same order in #hich they entered it.

Integrated #er$ices (Int#er$)5)ntServ is oten reerred to as ?ard *oS,@ ecause

it can mae strict and#idth reservations. )ntServ uses si$nalin$ amon$ net#or

devices to provide and#idth reservations. %esource %eservation !rotocol '%S8!( is

an e-ample o an )ntServ approach to *oS. Because )ntServ must e coni$ured onevery router alon$ a pacet3s path, the main dra#ac o )ntServ is its lac o

scalaility.

Di""erentiated #er$ices (Di""#er$)5DiServ, as the name su$$ests, dierentiates

et#een multiple traic lo#s. Speciically, pacets are ?mared,@ and routers and

s#itches can then mae decisions 'or e-ample, droppin$ or or#ardin$ decisions(

ased on those marin$s. Because DiServ does not mae an e-plicit reservation, it is

oten called ?Sot *oS.@ "he ocus o these *uic %eerence Sheets is DiServ, as

opposed to )ntServ or Best1&ort.


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Figure

Di""#er$

No# that you understand the importance that marin$ plays in a DiServ *oS solution, you

can learn ho# pacets can e mared. )nside an )!v4 header is a yte called the type of

service (ToS) byte.6ou can mar pacets, usin$ its #ithin the "oS yte, #ith either )!!recedence or Dierentiated Service Code !oint 'DSC!( marin$s.

Figure *

)! !recedence uses the ; letmost its in the "oS yte. With ; its at its disposal, )!

!recedence marin$s can ran$e rom 0 to . o#ever, values G and should not e used,

ecause those values are reserved or net#or use.

or more $ranularity, you can choose DSC!, #hich uses the G letmost its in the "oS yte.

Si- its yield G4 possile values '0 to G;(. "he challen$e #ith so many values at your

disposal is that the value you choose to represent a certain level o priority can e treated

dierently y a router or s#itch under someone else3s administration.

"o maintain relative levels o priority amon$ devices, the )nternet &n$ineerin$ "as orce

')&"( selected a suset o those G4 values or use. "hese values are called per-hop

behaviors (PHBs), ecause they indicate ho# pacets should e treated y each router hop

alon$ the path rom the source to the destination.

"he our cate$ories o !Bs are as ollo#s:

De"ault5"raic that only needs est1eort treatment can e mared #ith the Deault

!B, #hich simply means that the G letmost its in the pacet3s "oS yte 'that is, the

DSC! its( are all 0 'that is, a DSC! value o 0(.

E/pedited For0arding (EF)5"he & !B has a DSC! value o 4G. /atency1

sensitive traic, such as voice, typically has a !B o &.

.ssured For0arding (.F)5"he roadest cate$ory o !Bs is the !B.

Speciically, 92 !Bs e-ist, as sho#n in the ollo#in$ tale.
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P1' ,o0 Drop

Pre"erence

-edium Drop

Pre"erence

1igh Drop

Pre"erence

Class 9 99 '90(

009090

92 '92(

009900

9; '94(

009990

Class 2 29 '9A(

090090

22 '20(

090900

2; '22(

090990

Class ; ;9 '2G(

099090

;2 '2A(

099900

;; ';0(

099990

Class 4 49 ';4(

900090

42 ';G(

900900

4; ';A(

900990

Notice that the ssured or#ardin$ !Bs are $rouped into our classes. &-aminin$

these DSC! values in inary reveals that the ; letmost its o all the Class 9

!Bs are 009 'that is, a decimal value o 9(H the ; letmost its o all the Class 2

!Bs are 090 'that is, a decimal value o 2(H the ; letmost its o all the Class ;

!Bs are 099 'that is, a decimal value o ;(H and the ; letmost its o all the Class 4

!Bs are 900 'that is, a decimal value o 4(. Because )! !recedence e-amines

these ; letmost its, all Class 9 DSC! values #ould e interpreted y an )!

!recedenceIa#are router as an )! !recedence value o 9. "he same applies to the

Class 2, ;, and 4 !B values.

Within each !B class are three distinct values, #hich indicate a pacet3s ?drop

preerence.@ i$her values in an !B class are more liely to e discarded durin$

periods o con$estion. or e-ample, an 9; pacet is more liely to e discarded

than an 99 pacet.

Class #elector (C#)5"o have ac#ard compatiility #ith )! !recedence, you can

use CS !Bs, ecause,


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as E, ecause only the ; letmost its are considered, and ecause 909 in inary euals

E in decimal.

!o# Tools

No# that you understand ho# marin$s can e perormed #ith the DiServ *oS model,reali>e that marin$ alone does not alter the ehavior o pacets. 6ou must have a *oS tool

that reerences those marin$ and alters the pacets3 treatment ased on those marin$s.

ollo#in$ are some o the *oS tools that are addressed later in these *uic %eerence

Sheets:

Classi"ication5Classiication is the process o placin$ traic into dierent

cate$ories. ultiple characteristics can e used or classiication. or e-ample, !F!;,

)!, S"!, and &-chan$e traic could all e placed in an ?&)/@ class.

Classiication does not, ho#ever, alter its in the rame or pacet.

-ar2ing5arin$ alters its 'or e-ample, its in the "oS yte( #ithin a rame, cell,

or pacet to indicate ho# the net#or should treat that traic. arin$ alone does not

chan$e ho# the net#or treats a pacet. Fther tools 'or e-ample, ueuin$ tools( can,

ho#ever, reerence those marin$s and mae decisions ased on them.

Congestion management5When you hear the term congestion management, thin

queuing."hese concepts are the same. When an interace3s output sot#are ueue

contains pacets, the interace3s ueuin$ strate$y determines ho# the pacets are

emptied rom the ueue. or e-ample, some traic types can e $iven priority

treatment, and and#idth amounts can e made availale or speciic classes o

traic.

Congestion a$oidance5) an interace3s output ueue ills to capacity, ne#ly

arrivin$ pacets are discarded 'that is, ?tail1dropped@(, re$ardless o the priority that is

assi$ned to the discarded pacet. "o prevent this ehavior, Cisco uses a con$estion

avoidance techniue called Wei$hted %andom &arly Detection 'W%&D(. ter the

ueue depth reaches a coni$urale level 'that is, the minimum threshold( or a

particular priority marin$ 'or e-ample, )! !recedence or DSC!(, W%&D introduces

the possiility o discard or pacets #ith those marin$s. s the ueue depth

continues to increase, the possiility o discard increases until a coni$urale

ma-imum threshold is reached. ter the ueue depth has e-ceeded the ma-imum

threshold or traic #ith a speciic priority, there is a 900 percent chance o discardor those traic types.

Figure 3

Policing and shaping5Sometimes, instead o main$ a minimum amount o

and#idth availale or speciic traic types, you mi$ht #ant to limit the availale

and#idth. Both policin$ and shapin$ tools can accomplish this o


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!olicin$ can e used in either the inound or outound direction, and it typically

discards pacets that e-ceed the coni$ured rate limit, #hich you can thin o as a

?speed limit@ or particular traic types. Because policin$ drops pacets, resultin$ in

retransmissions, it is recommended or use on hi$her1speed interaces. !olicin$

mechanisms also allo# you to re#rite pacet marin$s 'or e-ample, )! !recedence

marin$s(.

Shapin$ can e applied only in the outound direction. )nstead o discardin$ traic

that e-ceeds the coni$ured rate limit, shapin$ delays the e-ceedin$ traic y

uerin$ it until and#idth ecomes availale. "hat is #hy shapin$ preserves

and#idth, as compared to policin$, at the e-pense o increased delay. "hereore,

shapin$ is recommended or use on slo#er1speed interaces. lso, shapin$ does not

have policin$3s aility to re#rite pacet marin$s.

,in2 e""iciency5"o mae the most o the limited and#idth that is availale on

slo#er1speed lins, you can choose to implement compression or /in ra$mentation

and )nterleavin$ '/)(. =sin$ header compression on smaller pacets candramatically increase a lin3s availale and#idth.

/) addresses the issue o ?seriali>ation delay,@ #hich is the amount o time reuired

or a pacet to e-it an interace. lar$e data pacet, or e-ample, on a slo#er1speed

lin could create e-cessive delay or a voice pacet ecause o the time reuired or

the data pacet to e-it the interace. /) ra$ments the lar$e pacets and interleaves

the smaller pacets amon$ the ra$ments, reducin$ the seriali>ation delay that the

smaller pacets e-perience.

Figure 4

'asic !o# Con"iguration

Cisco continues to improve the ease and eiciency #ith #hich *oS mechanisms can e

coni$ured. "his section addresses t#o o the Cisco more recent developments: *C and

uto*oS.

5sing -!C

Fne o the most po#erul approaches to *oS coni$uration is the odular *uality o Service

Command1/ine )nterace '*C(. ter you master the three asic steps o *C, you can

use them to coni$ure a #ide ran$e o *oS tools, includin$ ueuin$, policin$, shapin$,

header compression, W%&D, and marin$.

Figure 6


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"he irst step o *C is to create class1maps, #hich cate$ori>e traic types. "he ollo#in$

command enters you into class1map coni$uration mode:

Router(config)#class-map [match-any | match-all] class-name

ter you are in class1map coni$uration mode, you can speciy multiple match statements tomatch traic, and all traic that meets the criteria that you speciied #ith the match

commands is cate$ori>ed under the class1map. ) multiple match statements are speciied, y

deault, all match statements must e met eore a pacet is classiied y the class1map.

o#ever, i you use the match+anyoption, i any individual match condition is met, the

pacet is classiied y the class1map. ter the class1maps are deined, the irst step o *C

is complete. "he second step is to create a policy1map, #hich assi$ns characteristics 'or

e-ample, marin$( to the classiied traic.

"o enter policy1map coni$uration mode, issue the ollo#in$ command:

Router(config)#policy-mappolicy-name

rom policy1map coni$uration mode, enter policy1map1class coni$uration mode #ith the

ollo#in$ command:

Router(config-pmap)#class class-name

rom policy1map1class coni$uration mode, you can assi$n *oS policies to traic that is

classiied y the class1map. 6ou can also have a situation in #hich a pacet matches more

than one class1map. )n that case, the irst class1map that is identiied in the policy1map is

used. =p to 2EG class1maps can e associated #ith a sin$le policy1map.

inally, in the third step o *C, the policy1map is applied to an interace, rame %elay

map1class, or synchronous "ranser ode '"( virtual circuit #ith the ollo#in$

command:

Router(config-if)#service-policy {input | output}policy-map-name

ollo#in$ is an *C e-ample in #hich you are classiyin$ various types o e1mail traic

'or e-ample, S"!, )!, and !F!;( into one class1map. "he KaJaa protocol, #hich is

used reuently or music do#nloads, is placed in another class1map. 8oice over )! '8o)!(

traic is placed in yet another class1map. "hen, the policy1map assi$ns and#idth allocations

or limitations to these traic types. "he *C e-ample is as ollo#s:

Router(config)#class-map match-any EM!"Router(config-cmap)#match protocol popRouter(config-cmap)#match protocol imapRouter(config-cmap)#match protocol smtpRouter(config-cmap)#e$itRouter(config)#class-map M%&!'Router(config-cmap)#match protocol aaa*Router(config-cmap)#e$itRouter(config)#class-map +,!'ERouter(config-cmap)#match protocol rtpRouter(config-cmap)#e$itRouter(config)#policy-map ,&-&.%/0Router(config-pmap)#class EM!"


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Router(config-pmap-c)#1an23i2th 4*5Router(config-pmap-c)#e$itRouter(config-pmap)#class M%&!'Router(config-pmap-c)#police *666Router(config-pmap-c)#e$itRouter(config-pmap)#class-map +,!'E

Router(config-pmap-c)#priority *78Router(config-pmap-c)#e$itRouter(config-pmap)#e$itRouter(config)#interface serial 694Router(config-if)#service-policy output ,&-&.%/0

Notice that the !7#+#T5DYpolicy1map maes 92A ps o and#idth availale to e1mail

traic. o#ever, KaJaa version 2 traic and#idth is limited to ;2 ps. 8oice pacets not

only have access to 2EG ps o and#idth, ut they also receive ?priority@ treatment,

meanin$ that they are sent irst 'that is, ahead o other traic( up to the 2EG1ps limit.

"he ne-t lo$ical uestion is, ?What happens to all o the traic that you did not classiy@

)nterestin$ly, the )FS created the class+de"aultclass1map, #hich cate$ori>es any traic thatis not matched y one o the deined class1maps. inally, in the previous e-ample, the policy1

map is applied in the outound direction on the Serial 09 interace.

"he ollo#in$ sho0commands can e used or veriication and trouleshootin$ o an *C

coni$uration:

Router#sho3 class-map [class-map-name]

'=sed to vie# #hat a class1map is matchin$(

Router#sho3 policy-map [policy-map-name]

'=sed to vie# the policy that is applied to the classes #ithin a policy1map(

Router#sho3 policy-map interface interface-identifier [input | output]

'=sed to vie# policy1map statistics or pacets that are crossin$ a speciic interace(

5sing .uto!o#

Fptimi>in$ a *oS coni$uration or 8o)! can e a dauntin$ tas. ortunately, Cisco added a

eature calleduto!oSto many o its router and s#itch platorms to automatically $enerate

router1ased or s#itch1ased 8o)! *oS coni$urations.

"he ollo#in$ router platorms support uto*oS:

900 Series

2G00 Series

;G00 Series

;00 Series


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200 Series

Cisco also supports the uto*oS eature on the ollo#in$ Catalyst s#itch series:

2LE0 '&)(

;EE0

4E00

GE00

Fn a router platorm, the ollo#in$ command enales uto*oS rom either interace1

coni$uration mode or rom D/C)1coni$uration mode 'or a rame %elay circuit(:

Router(config-if)#auto :os voip [trust] [fr-atm]

"he trustoption indicates that uto *oS should classiy voice traic ased on DSC!

marin$s, instead o usin$ NB%. "he "r+atmoption enales the uto*oS eature or rame

%elayItoI" lins and is issued rom D/C)1coni$uration mode.

Beore enalin$ uto*oS on a router interace, consider the ollo#in$ prereuisites:

Cisco &-press or#ardin$ 'C&( must e enaled, ecause uto*oS uses NB%,

#hich reuires the C& eature.

*oS policy must not e attached to the interace.

"he correct and#idth should e coni$ured on the interace.

n )! address must e coni$ured on an interace i its speed is less than GA ps.

"he interace must not e administratively shut do#n.

Note that the interace3s and#idth determines #hich uto*oS eatures are enaled. ) an

interace3s and#idth is less than GA ps, it is considered a lo#1speed interace. Fn a lo#1

speed interace, uto*oS coni$ures ultilin !!! '/!(, #hich reuires an )! address on

the physical interace. uto*oS taes that )! address rom the physical interace and uses itor the virtual multilin interace that it creates.

"o veriy that uto*oS is coni$ured or a router interace, use the ollo#in$ command:

Router#sho3 auto :os [interface interface-identifier]

Figure 8
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"he Catalyst GE00 runnin$ in yrid mode 'that is, usin$ the Cat FS or s#itch unctions(

also supports uto*oS. "o enale uto*oS on a yrid mode Catalyst GE00, you must irst

enale uto*oS $loally and then or a speciic port. ollo#in$ are the reuired commands:

&3itch#set :os auto:os

'Mloally enales uto*oS(

&3itch#set :os auto:os ;mod/port< trust [cos | 2scp]

'&nales uto*oS or a speciic port(

Note that the Catalyst GE00 can trust either CoS or DSC! values or its ueuin$ decision. )

the port is trustin$ DSC! marin$s, you can add the ollo#in$ command, #hich reco$ni>es

that the port is connected to a Cisco )! !hone or a Cisco Sot!hone 'sot#are that runs on a

!C(:

&3itch#set port :os ;mod/port< auto:os voip [ciscosoftphone | ciscoipphone]

"he port must have Cisco Discovery !rotocol 'CD!( version 2 enaled to reco$ni>e an

attached Cisco )! !hone. lthou$h some s#itches do not reco$ni>e a Cisco Sot!hone,

uto*oS can e coni$ured on Catalyst 2LE0 '&)( and ;EE0 s#itches, and the uto*oS

eature on these s#itches does reco$ni>e a Cisco )! !hone. "o coni$ure uto*oS on these

platorms, issue the ollo#in$ commands rom interace1coni$uration mode:

&3itch(config-if)#auto :os voip trust

'Coni$ures the interace to trust CoS marin$s or classiyin$ 8o)! traic(

&3itch(config-if)#auto :os voip cisco-phone

'Detects the presence o a Cisco )! !hone, usin$ CD!(

"o trouleshoot and veriy uto*oS on a Catalyst s#itch, use the ollo#in$ commands:

&3itch#sho3 auto :os [interface interface-identifier]

'Displays the coni$uration that is applied y uto*oS(

&3itch#sho3 mls :os interface [interface-identifier]

'Displays interace1level *oS statistics(

"his section has roadly addressed the eatures that are enaled y uto*oS. "he speciic

eatures are sho#n in the ollo#in$ tale.

!o# -echanism Router Feature #0itch

Feature


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Classiication NB% and DSC! !ort trust states

arin$ CB1arin$ CoS1to1DSC!remarin$

Con$estionmana$ement

//* W%%

Shapin$ CB1Shapin$ or %"S 5

/in eiciency eader Compressionand /)

5

Tra""ic Classi"ication and -ar2ing

Classiication and marin$ allo# *oS1enaled net#ors to identiy traic types near the

source and assi$n speciic marin$s to those traic types. "his section addresses the need or

and various approaches used to perorm classiication and marin$.

Classi"ication and -ar2ing 'asics

Fne o the irst *oS mechanisms that you apply to your traic is c"assification,#hich

reco$ni>es the types o traic that are lo#in$ across the net#or. or e-ample, you mi$ht

reco$ni>e "elnet, "!, and ""! traic and cate$ori>e those applications to$ether in a

speciic class o traic.

lthou$h classiication is $reat, you proaly do not #ant to coni$ure classiication on every

router. "hereore, ater the traic is classiied, you can ?mar@ it. t that point, other routers

and s#itches in the net#or can reerence those marin$s and mae decisions 'or e-ample,or#ardin$ or droppin$ decisions( ased on those marin$s.

Some o these marin$s are /ayer 2 'that is, the Data /in /ayer( marin$s, #hereas other

marin$s are at /ayer ; 'that is, the Net#or /ayer(. irst, consider the /ayer 2 marin$s.

Fn an &thernet trun, you can mar rames #ith a class o service 'CoS( value. CoS value

can ran$e rom 0 throu$h , althou$h Cisco recommends that you never use G or . "he its

that create the CoS marin$ depend on the type o trun that is ein$ used, as ollo#s:

IEEE 9;&! trun25=ses ; its in a "a$ Control yte to mar a CoS value. 'Note:

"his method is reerred to as )&&& A02.9p.(


14/48

I#, trun25=ses ; its in the )S/ header to mar a CoS value.

Figure 9

/ayer 2 marin$s also can e-tend to the WN. Consider a rame %elay net#or. Within a

rame %elay header is a it called the#iscard $"igib"e (#$) bit,#hich identiies rames that

the service provider can drop durin$ periods o con$estion. 6ou can levera$e that D& it to

identiy less important traic that you send to the rame %elay service provider. Similarly,

you can mar the Cell /oss !riority 'C/!( it in an " cell to identiy less important "

traic.

Service providers oten use ultiprotocol /ael S#itchin$ '!/S( to or#ard traic. "hree

its in the !/S lael can e used to identiy priority or traic that is lo#in$ throu$h theservice provider3s cloud.

s mentioned earlier, /ayer ; marin$s are made possile y usin$ its #ithin an )!v4

header3s "oS yte. "hese marin$s are )! !recedence '#hich uses the ; letmost its in the

"oS yte( and DSC! '#hich uses the G letmost its in the "oS yte(.

mae traic ased on any o the ollo#in$ criteria:

ccess control lists 'C/s(

&-istin$ marin$s 'or e-ample, CoS, )! !recedence, or DSC!(


15/48

*oS $roup 'a locally si$niicant $roupin$ o pacets(

!rotocol 'usin$ NB%(

"raic matchin$ another class1map

)ncomin$ interace

C address 'source or destination(

%an$e o =D! port numers

)n the ollo#in$ e-ample, you are matchin$ traic ased on a variety o the precedin$

criteria:

Router(config)#class-map match-any !=.

Router(config-cmap)#match input-interface ethernet 696Router(config-cmap)#match input-interface ethernet 694Router(config-cmap)#e$itRouter(config)#class-map '"Router(config-cmap)#match access-group 464Router(config-cmap)#e$itRouter(config)#class-map ',&Router(config-cmap)#match cos 6 4 * Router(config-cmap)#e$itRouter(config)#access-list 464 permit tcp any any e: *

)n this e-ample, the ITclass1map matches traic that came into the router on any o the

speciied interaces. "he .C,class1map matches traic that is matched y access1list 909.inally, the C7#class1map cate$ori>es traic #ith a CoS marin$ o 0, 9, 2, or ;.

-odular -ar2ing 0ith -!C

ter you have classiied your traic usin$ class1maps, you can use a policy1map to mar the

traic. ollo#in$ is a listin$ o supported marin$s and the correspondin$ synta-:

)! !recedence 'set ip precedence value(

DSC! 'set ip dscp value(

*oS $roup'set ip precedence value(

!/S e-perimental its 'set mpls e/perimental value(

CoS value 'set cos value(

rame %elay D& it 'set "r+de(

" C/! it 'set atm+clp(


16/48

)n the ollo#in$ e-ample, you use *C to remar CoS values that are enterin$ a router to

DSC! values:

Figure &

Router(config)#class-map >!-?R!Router(config-cmap)#match cos 7 8 @Router(config-cmap)#e$itRouter(config)#class-map ME/-?R!Router(config-cmap)#match cos * ARouter(config-cmap)#e$itRouter(config)#class-map ",B-?R!Router(config-cmap)#match cos 6 4Router(config-cmap)#e$it

Router(config)#policy-map REMRCRouter(config-pmap)#class >!-?R!Router(config-pmap-c)#set ip 2scp af4Router(config-pmap-c)#e$itRouter(config-pmap)#class ME/-?R!Router(config-pmap-c)#set ip 2scp af*4Router(config-pmap-c)#e$itRouter(config-pmap)#class-map ",B-?R!Router(config-pmap-c)#set ip 2scp af44Router(config-pmap-c)#e$itRouter(config-pmap)#e$itRouter(config)#interface fastethernet 694Router(config-if)#service-policy input REMRC

)n this e-ample, traic mared #ith CoS values o E, G, or is classiied in the 1I+PRIclass1

map, #hereas traic #ith CoS values o 2, ;, or 4 $oes into the -ED+PRIclass1map.

inally, CoS values o 0 and 9 are placed in the ,7W+PRIclass1map. "he RE-.R=

policy1map assi$ns a DSC! value o ;9 to the )1!%) traic, a DSC! value o 29 to the

&D1!%) traic, and a DSC! value o 99 to the /FW1!%) traic. "he third step o *C

applies a policy1map to an interace. )n this case, you are applyin$ the RE-.R=policy1map

to the ast&thernet 09 interace in the inound direction. )t is critical that you apply the

policy1map in the inound direction. By doin$ so, you are remarin$ the CoS values eore

the route processor strips them.

s you learned earlier, to see #hat policies are applied to your class1maps, use the sho0policy+mapcommand. Fr, to see interace1speciic statistics or a policy1map, the sho0

policy+map inter"ace interface-identifiercommand is appropriate.

Classi"ying 0ith '.R

"he most po#erul and le-ile approach to classiyin$ traic is the Net#or Based

pplication %eco$nition 'NB%( eature. NB% can loo eyond /ayer ; and /ayer 4

inormation, all the #ay up to /ayer . !rotocols that chan$e port numer 'that is, stateul

protocols( can e traced, and even =%/ strin$s can e matched #ith NB%.

lthou$h the )FS comes #ith multiple NB% application si$natures, a continuin$ need

e-ists or additional si$nature reco$nition. or e-ample, even thou$h your router mi$ht e


17/48

ale to reco$ni>e KaJaa traic, it mi$ht not e ale to reco$ni>e e1Doney traic.

ortunately, you can install !acet Description /an$ua$e odules '!D/s( into the router3s

lash, and these !D/s e-tend the )FS3s aility to reco$ni>e traic. !D/s are availale or

do#nload rom http:###.cisco.comc$i1intaleuild.plpdlm.

Note that this site reuires a Cisco.com lo$in. lso, note that the conte-t1sensitive help in the)FS mi$ht deine the !D/ as !rotocol Description /an$ua$e odule instead o !acet

Description /an$ua$e odule.

Figure &&

)n addition to NB%3s useulness in classiyin$, it can unction as a protocol discovery tool.

or e-ample, NB% protocol discovery could e enaled on an interace to determine the

applications that are consumin$ the most and#idth on that interace 'that is, the ?top

talers@(.

"he ollo#in$ command coni$ures NB% protocol discovery:

Router(config-if)#ip n1ar protocol-2iscovery

ter NB% has collected traic statistics or an interace, use the ollo#in$ command to

vie# the statistics:

Router#sho3 ip n1ar protocol-2iscovery

"o use NB% to classiy traic, as part o a class1map, use the ey#ord protocolin the

matchcommand, as ollo#s:

Router(config-cmap)#match protocolprotocol

6ou can reerence the previously mentioned !D/ ile #ith the ollo#in$ command:

Router(config)#ip n1ar p2lmpdlm-file

)n the ollo#in$ e-ample, NB% classiies KaJaa 8ersion 2 traic and ""! traic:

Figure &

Router(config)#class-map M%&!'Router(config-cmap)#match protocol aaa*Router(config-cmap)#e$itRouter(config)#class-map BEDRouter(config-cmap)#match protocol http

Router(config-cmap)#e$itRouter(config)#policy-map =DR.E&.
http://www.cisco.com/cgi-bin/tablebuild.pl/pdlmhttp://popup%28%27/content/images/chap06_1587201283/elementLinks/fig11.jpg')http://popup%28%27/content/images/chap06_1587201283/elementLinks/fig12.jpg')http://www.cisco.com/cgi-bin/tablebuild.pl/pdlmhttp://popup%28%27/content/images/chap06_1587201283/elementLinks/fig11.jpg')http://popup%28%27/content/images/chap06_1587201283/elementLinks/fig12.jpg')


18/48

Router(config-pmap)#class M%&!'Router(config-pmap-c)#police *666Router(config-pmap-c)#e$itRouter(config-pmap)#class-map BEDRouter(config-pmap-c)#1an23i2th 4*5Router(config-pmap-c)#e$it

Router(config-pmap)#e$itRouter(config)#interface ethernet 694Router(config-if)#service-policy output =DR.E&.

)n this e-ample, KaJaa version 2 traic is classiied y the -5#ICclass1map, #hereas http

traic is classiied y the WE'class1map. "hen, the '.RTE#Tpolicy1map limits the

=S)C class to ;2 ps #hile allocatin$ 92A ps o and#idth or the W&B class. inally,

the policy1map is applied outound to the ethernet 09 interace.

Consider the priority that you should assi$n to #e traic. ) you have an e1commerce site, as

an e-ample, #e traic mi$ht need varyin$ levels o priority, dependin$ on the content o the

#e traic. "he $ood ne#s is that NB% can reco$ni>e the content o #e traic usin$commands such as the ollo#in$:

Router(config-cmap)#match protocol http url url-string

'atches a strin$ that is contained in the =%/(

s an e-ample, you could match traic that contains the #ord ciscoin the =%/ #ith the

ollo#in$ command:

match protocol http url FciscoFG

"he asteriss are actin$ as #ildcards, matchin$ any characters eore or ater the #ord cisco.

!o# o$er Tunnel Connections

8irtual private net#ors '8!Ns( are $ainin$ tremendous popularity ecause o their aility to

provide secure connectivity throu$h a pulic net#or, such as an )S!. 8!Ns are made

possile thans to tunne"ing.

"he challen$e #ith *oS in a tunnel environment is that the tunnels encapsulate traic, #hich

hides the ori$inal inormation in a pacet3s header. ter pacets enter a tunnel, they have a

tunnel header. "hereore, all pacets have the same level o priority, ecause the classiicationo encapsulated pacets is ased on the tunnel header. "he Cisco pre1classiy eature

overcomes this issue y applyin$ *oS eatures to pacets eore they enter the tunnel. !re1

classiication, ho#ever, is only necessary #hen you are classiyin$ ased on a criterion other

than a pacet3s "oS yte. "he )FS automatically copies its rom a pacet3s "oS yte into the

"oS yte o the tunnel header.

Figure &*>>>


19/48

"o enale the pre1classiication eature, in tunnel1interace1coni$uration mode 'or in crypto1

map coni$uration mode or an )!Sec tunnel(, enter the ollo#in$ command:

:os pre-classify

!o# o$er '?P et0or2s

)n a service provider environment, you mi$ht not #ant to use access1lists or other

classiication mechanisms throu$h the service provider3s net#or. n alternate option is to

use *oS !olicy !ropa$ation "hrou$h BM! '*!!B(.

*!!B lets you encode *oS inormation y assi$nin$ BM! attriutes such as an autonomous

system numer, community strin$, or an )! prei-.

or e-ample, instead o settin$ the )! !recedence marin$ to a 4 inside every pacet, you

could send the traic #ith a certain community strin$. When the ar1end autonomous system

receives the traic #ith that community strin$, it can mar those pacets #ith an )!!recedence o 4.

)n the ollo#in$ e-ample or router %9, the community attriute determines ho# the )!

!recedence value is set. Speciically, traic #ith a community strin$ o 20:9 has its )!

!recedence set to a 2, and traic #ith a community strin$ o 20:2 has its )! !recedence set to

a ;. "he @gp+policy sourcecommand applies this policy to interace Serial 09.

Figure &3>>>

router 1gp 466 ta1le-map prece2ence-map neigh1or 4H4H4H* remote-as *66 neigh1or 4H4H4H* sen2-communityIroute-map prece2ence-map permit 46 match community 4 set ip prece2ence *Iroute-map prece2ence-map permit *6

match community * set ip prece2ence Iip community-list 4 permit *6J4ip community-list * permit *6J*Iinterface serial 694 ip a22ress 4H4H4H4 *77H*77H*77H6 1gp-policy source ip-prec-map

Catalyst+'ased Classi"ication and -ar2ing

6ou can perorm classiication and marin$ unctions, not


20/48

technolo$y, proper *oS coni$uration in a enterprise net#or3s inrastructure is also critical.

or e-ample, a s#itch mi$ht have interaces that run at dierent speeds 'or e-ample, 90

ps and 9 Mps(. Such a scenario could lead to a s#itch ueue overlo#in$. lso, traic

can enter a s#itch mared #ith a /ayer 2 CoS value. "hese /ayer 2 values do not pass

throu$h a route processor. "hereore, a Catalyst s#itch is an e-cellent place to perorm CoS1

to1DSC! remarin$. So, #hen the traic reaches the route processor, it has a /ayer ;marin$, #hich can pass successully throu$h the route processor.

pplyin$ *oS eatures at the ed$e o the net#or 'or e-ample, in a #irin$ closet( oers the

ollo#in$ eneits:

!rovides immediate traic classiication

%educes con$estion #ithin the remainder o the net#or

&ases the processor urden on the distriution and core routers

"hese *uic %eerence Sheets primarily ocus on the Catalyst 2LE0 Series o s#itches. 6ou

can coni$ure the Catalyst 2LE0 ports to trust CoS or DSC! marin$s. o#ever, y deault,

these ports are ?untrusted,@ meanin$ that they disre$ard priority marin$s on incomin$

traic. When a port is untrusted, traic is assi$ned the coni$urale CoS value o the port.

"he Catalyst 2LE0 can place rames in one o our ueues. /ater in these *uic %eerence

Sheets, you use these ueues or Wei$hted %ound %oin 'W%%( ueuin$. or no#, ho#ever,

you should e amiliar #ith ho# the s#itch places rames #ith various CoS marin$s into its

our ueues, as descried in the ollo#in$ tale.

De"ault !ueue .ssignment

Co# alue !ueue

0 and 9 9

2 and ; 2

4 and E ;

G and 4


21/48

or internal *oS processin$, all traic 'even non1)! traic( is assi$ned an internal DSC!

numer. "he deault CoS1to1DSC! mappin$s are sho#n in the ollo#in$ tale.

Co#+to+D#CP -appings

Co# alue D#CP alue

0 0

9 A

2 9G

; 24

4 ;2

E 40

G 4A

EG

Because the Catalyst 2LE0 uses CoS values to mae ueuin$ decisions, eore the ueuin$

process, the internal DSC! value is e-trapolated to a CoS value. lthou$h mappin$s are

coni$urale, the deault values are sho#n in the ollo#in$ tale.

D#CP+to+Co# -appings

D#CP alues Co# alue


22/48

0 0

A and 90 9

9G and 9A 2

24 and 2G ;

;2 and ;4 4

40 and 4G E

4A G

EG

With your understandin$ o the deault s#itch ehavior, you can e-plore ho# to manipulate

the trust settin$s and the CoS1to1DSC! mappin$s. "he ollo#in$ command tells a port #hat

to trust:

&3itch(config-if)#mls :os trust [cos [pass-through 2scp] | 2evice cisco-phone | 2scp]

"he pass+through dscpoption does not modiy the DSC! values 'that is, remar them ased

on CoS values(.

6ou can use the ollo#in$ command to assi$n a deault CoS value or a port:

&3itch(config-if)#mls :os cos {default-cos| overri2e}

"he o$errideoption applies the deault CoS value to a rame, even thou$h a rame mi$ht

already have a CoS marin$.

"he ollo#in$ commands allo# you to manipulate the deault CoS1to1DSC! and DSC!1to1

CoS mappin$s:

&3itch(config)#mls :os map cos-2scp 2scpvalue4 2scpvalue* HHH 2scpvalue5


23/48

'Coni$ures CoS1to1DSC! mappin$(

or e-ample:

&3itch(config)#mls :os map cos-2scp 6 48 *A * A A6 A5 78

)n this e-ample, the ei$ht DSC! values that are entered correspond to CoS values 0 throu$h

.

&3itch(config)#mls :os map 2scp-cos dscp-listto cos

'Coni$ures DSC!1to1CoS mappin$(

or e-ample:

&3itch(config)#mls :os map 2scp-cos 48 *5 *A *8 to 4

Figure &4>>>

6ou can associate up to 9; DSC! values #ith a sin$le CoS value.

"he three1step *C process can also e used on a Catalyst 2LE0 to perorm classiication

and marin$, #ithout as many ?match@ options as are availale on a router platorm.

"ypically, you create a standard or e-tended )! access1list 'or a /ayer 2 C C/ or non1)!

traic(. "hat access1list can then serve as the match criterion in a class1map. Note, ho#ever,

that the e-tended )! access1lists that are availale on the Catalyst 2LE0 do not have all the

options that are availale on a router. Speciically, you cannot use the access1list to match a

ran$e o port numers.

)n the ollo#in$ e-ample, an e-tended )! access1list matches traic that is destined or )!

address 9L2.9GA.0.909. policy1map then mars traic that is destined or that host #ith a

DSC! value o ;4. inally, the policy is applied to interace Mi$ait &thernet 0; in the

inound direction. "he e-ample is as ollo#s:

&3itch(config)#access-list 466 permit ip any host 4K*H485H6H464&3itch(config)#class-map '.'"&&&3itch(config-cmap)#match access-group 466&3itch(config-cmap)#e$it&3itch(config)#policy-map '.?,"!'0&3itch(config-pmap)#class '.'"&&&3itch(config-pmap-c)#set ip 2scp A&3itch(config-pmap-c)#interface gig 69&3itch(config-if)#service-policy input '.?,"!'0

s#itch3s *oS interace coni$uration can e veriied #ith the ollo#in$ command:

&3itch#sho3 mls :os interface interface-identifier

=se the ollo#in$ command to see ho# CoS and DSC! values are mapped to one another:


24/48

&3itch#sho3 mls :os maps [cos-2scp | 2scp-cos]

!ueuing

Sometimes reerred to as con$estion mana$ement, ueuin$ mechanisms identiy ho# traic

rom multiple streams is sent out o an interace that is currently e-periencin$ con$estion.

"his section e-amines various approaches to ueuin$ and emphasi>es the ueuin$ approaches

coni$ured via *C.

!ueuing 'asics

When a device, such as a s#itch or a router, is receivin$ traic aster than it can e

transmitted, the device attempts to uer the e-tra traic until and#idth is availale. "his

uerin$ process is called queuing.6ou can use ueuin$ mechanisms to inluence in #hat

order various traic types are emptied rom the ueue.

Figure &6

Con$estion occurs not


25/48

De"icit Round Ro@in (DRR) Aueuing5"his type o ueuin$ can suer rom a

?deicit@ issue. or e-ample, i you coni$ured C* to removed 9E00 ytes rom a

ueue durin$ each round1roin cycle, and you had a 94LL1yte pacet and a 9E001

yte pacet in the ueue, oth pacets #ould e sent. "his is ecause C* cannot send

a partial pacet. Because the 94LL1yte pacet #as transmitted and ecause another

yte still had to e serviced, C* #ould start servicin$ the 9E001yte pacet. D%%eeps trac o the numer o e-tra ytes that are sent durin$ a round and sutracts that

numer rom the numer o ytes that can e sent durin$ the ne-t round.

router has t#o types o ueues: a hard#are ueue and a sot#are ueue. "he hard#are

ueue, #hich is sometimes reerred to as the transmit ueue '"-*(, al#ays uses )F

ueuin$, and only #hen the hard#are ueue is ull does the sot#are ueue handle pacets.

"hereore, your ueuin$ coni$uration only taes eect durin$ periods o interace

con$estion, #hen the hard#are ueue has overlo#ed. With this asic understandin$ o

ueuin$, you e$in to e-amine several ueuin$ methods in more detail.

FIF7

=sin$ )F in the sot#are ueue #ors


26/48

With W*, a pacet3s )! !recedence inluences the order in #hich that pacet is emptied

rom a ueue. Consider the previous scenario #ith the addition o )! !recedence marin$s. )n

this scenario, lo# 3s pacets are mared #ith an )! !recedence o E, #hereas lo# B and

lo# C have deault )! !recedence marin$s o 0. "he order o pacet servicin$ #ith W* is

ased onsequence numbers,#here pacets #ith the lo#est seuence numers are transmitted

irst.

"he seuence numer is the #ei$ht o the pacet multiplied y the numer o yte1y1yte

rounds that must e completed to service the pacet '


27/48

With W*, each lo# is placed in its o#n ueue, up to a ma-imum numer o ueues as

deined y the dynamic-queuesparameter. "he deault numer o ueues that is created

dynamically 'that is, dynamic1ueues( is 2EG.

"hereservable-queuesparameter deines the numer o ueues that are made availale to

interace eatures such as %S8!. "he deault numer o reservale ueues is 0.

lthou$h W* is easy to coni$ure 'or e-ample, it is enaled y deault on interaces that

run at or elo# 2.04A ps(, and althou$h W* is supported on all )FS versions, it has its

limitations. Speciically, W* cannot $uarantee a speciic amount o and#idth or an

application. lso, i more than 2EG lo#s e-ist, y deault, more than one lo# can e orced

to share the same ueue.

6ou can vie# statistics or W* #ith the sho0 inter"ace interface-identifiercommand. "he

output rom this command not only veriies that W* is enaled on the speciied interace,

ut it also sho#s such inormation as the current ueue depth and the ma-imum numer o

ueues allo#ed.

C'+WF!

"he W* mechanism made sure that no traic #as starved out. o#ever, W* did not mae

a speciic amount o and#idth availale or deined traic types. 6ou can, ho#ever, speciy

a minimum amount o and#idth to mae availale or various traic types usin$ the CB1

W* mechanism.

CB1W* is coni$ured throu$h the three1step *C process. =sin$ *C, you can create up

to G; class1maps and assi$n a minimum amount o and#idth or each one. Note that thereason you cannot create G4 class1maps is that the class+de"aultclass1map has already een

created.

"raic or each class1map $oes into a separate ueue. "hereore, one ueue 'or e-ample, or

C)"%) traic( can e overlo#in$, #hile other ueues are still acceptin$ pacets.

Band#idth allocations or various class1maps can e speciied in one o three #ays:

and#idth, percenta$e o and#idth, and percenta$e o remainin$ and#idth. "he ollo#in$

para$raphs descrie each o these allocations.

6ou can mae a speciic amount o and#idth availale or classiied traic. "o allocate a

and#idth amount, use the ollo#in$ command, notin$ that the units o measure are in ps:

Router(config-pmap-c)#1an23i2th bandwidth

)nstead o speciyin$ an e-act amount o and#idth, you can speciy a percenta$e o the

interace and#idth. or e-ample, a policy1map could allocate 2E percent o an interace3s

and#idth. "hen, that policy1map could e applied to, or e-ample, a ast &thernet interace

and also to a slo#er1speed serial interace. "o allocate a percenta$e o the interace

and#idth, use the ollo#in$ command:

Router(config-pmap-c)#1an23i2th percentpercent


28/48

s an alternative to allocatin$ a percenta$e o the total interace and#idth, you can also

allocate a percenta$e o the remainin$ and#idth 'that is, ater other and#idth allocations

have already een made(. "o allocate a percenta$e o the remainin$ interace and#idth, use

the ollo#in$ command:

Router(config-pmap-c)#1an23i2th remaining percentpercent

By deault, each ueue that is used y CB1W* has a capacity o G4 pacets. o#ever, this

limit is coni$urale #ith the ollo#in$ command:

Router(config-pmap-c)#:ueue-limit number_of_packets

lthou$h CB1W* ueues typically use )F or traic #ithin a particular ueue, the class1

deault ueue can e enaled or W* #ith the ollo#in$ command:

Router(config-pmap-c)#fair-:ueue [dynamic-queues]

s noted earlier, CB1W* is coni$ured throu$h *C. "hereore, the standard *C

veriication and trouleshootin$ commands, such as sho0 policy+map inter"ace interface-

identifier, are applicale or CB1W*.

By deault, only E percent o an interace3s and#idth can e allocated. "he remainin$ 2E

percent is reserved or nonclassiied or overhead traic 'or e-ample, CD!, /), or routin$

protocols(. "his limitation can e overcome #ith the ma/+reser$ed+@and0idth percentage

interace1coni$uration1mode command, #here thepercentageoption is the percenta$e o an

interace3s and#idth that can e allocated.

CB1W* is thereore an attractive ueuin$ mechanism, thans to its *C coni$urationstyle and its aility to assi$n a minimum and#idth allocation. "he only mae that #hen you

place pacets in a priority ueue, you are not only allocatin$ a and#idth amount or that

traic, ut you also are policin$ 'that is, limitin$ the availale and#idth or( that traic. "hepolicin$ option is necessary to prevent hi$her1priority traic rom starvin$ out lo#er1priority

traic.

Note that i you tell multiple class1maps to $ive priority treatment to their pacets, all priority

pacets $o into the same ueue. "hereore, priority traic could suer rom havin$ too many

priority classes. !acets that are ueued in the priority ueue cannot e ra$mented, #hich is

a consideration or slo#er1speed lins 'that is, lin speeds o less than GA ps(. //*, ased

on all the listed eneits, is the Cisco preerred ueuin$ method or latency1sensitive traic,

such as voice and video.

6ou can use either o the ollo#in$ commands to direct pacets to the priority ueue:


29/48

Router(config-pmap-c)#priority bandwidth

'Note that the and#idth units o measure are in ps.(

Router(config-pmap-c)#priority percentpercent

'Note that thepercentoption reerences a percenta$e o the interace and#idth.(

Consider the ollo#in$ //* e-ample.

Figure &e http traic, and that traic is placed in the

#5RFI?class. Note that NB% is invoed #ith the ollo#in$ command:

Router(config-cmap)# match protocol

8oice pacets are placed in the 7ICEclass. "he !7#B#T5DYpolicy1map $ives 92A ps

o and#idth to the http traic #hile $ivin$ 2EG ps o priority and#idth to voice traic.

"hen the policy1map is applied outound to interace serial 09.

Catalyst+'ased !ueuing

Some Cisco Catalyst s#itches also support their o#n ueuin$ method, called Wei$hted

%ound %oin 'W%%( ueuin$. or e-ample, a Catalyst 2LE0 s#itch has our ueues, and

W%% can e coni$ured to place rames #ith speciic CoS marin$s into certain ueues. 'or

e-ample, CoS values 0 and 9 are placed in *ueue 9.(

Wei$hts can e assi$ned to the ueues, inluencin$ ho# much and#idth the various

marin$s receive. "he ueues are then serviced in a round1roin ashion. Fn the Catalyst

2LE0, ueue numer 4 can e desi$nated as an ?e-pedite@ ueue, #hich $ives priority

treatment to rames in that ueue. Speciically, the e-pedite ueue must e empty eore anyadditional ueues are serviced. "his ehavior can lead to protocol starvation.


30/48

Fn a Catalyst 2LE0, rames are ueued ased on their CoS values. "he ollo#in$ command

can e used to alter the deault ueue assi$nments:

&3itch(config)#3rr-:ueue cos-map :ueuePnum1er cosPvalueP4 cosPvalueP* QcosPvaluePn

or e-ample, the ollo#in$ command #ould map CoS values o 0, 9, and 2 to ueue numer

9 on a Catalyst 2LE0:

&3itch(config)#3rr-:ueue cos-map 4 6 4 *

"he #ei$ht that is assi$ned to a ueue speciies ho# many pacets are emptied rom a ueue

durin$ each round1roin cycle, relative to other ueues. 6ou can coni$ure ueue #ei$hts

#ith the ollo#in$ command:

&3itch(config)#3rr-:ueue 1an23i2th 3eightP4 3eightP* 3eightP 3eightPA

%ememer that ueue numer 4 on a Catalyst 2LE0 can e coni$ured as an e-pedite ueue

'that is, a priority ueue(. "o coni$ure ueue numer 4 as an e-pedite ueue, set its #ei$ht to

0.

ollo#in$ is an e-ample o a W%% coni$uration.

Figure

&3itch(config)#interface gig 697&3itch(config-if)#3rr-:ueue 1an23i2th 4 * A&3itch(config-if)#3rr cos-map A 7

)n this e-ample, the 0rr+Aueue command is assi$nin$ the #ei$hts 9, 2, ;, and 4 to the

s#itch3s our ueues. "he irst ueue, #ith a #ei$ht o 9, or e-ample, only $ets one1third the

and#idth that is $iven to the third ueue, #hich has a #ei$ht o ;. "he 0rr cos+map 3 4

command is instructin$ rames that are mared #ith a CoS o E to enter the ourth ueue.

"o veriy ho# a Catalyst 2LE0 is mappin$ CoS values to DSC! values 'or vice versa(, use the

ollo#in$ command:

&3itch#sho3 mls :os maps [cos-2scp | 2scp-cos]

6ou can use the ollo#in$ command to vie# the #ei$ht that is assi$ned to each ueue:

&3itch#sho3 3rr-:ueue 1an23i2th

nother useul W%% command, #hich sho#s ho# CoS values are ein$ mapped to s#itch

ueues sho#s is as ollo#s:

&3itch#sho3 3rr-:ueue cos-map


31/48

inally, you can see the *oS coni$uration or an interace 'or e-ample, trust state and the

interace3s deault CoS value( #ith the ollo#in$ command:

&3itch#sho3 mls :os interface [interface-identifier]

Weighted Random Early Detection (WRED)

Whereas ueuin$ provides con$estion mana$ement, mechanisms such as W%&D provide

con$estion avoidance. Speciically, W%&D can prevent an output ueue rom ever illin$ to

capacity, #hich #ould result in pacet loss or all incomin$ pacets. "his section e-amines

the need or and the coni$uration o W%&D on Cisco routers.

1o0 TCP 1andles Drops

%ecall rom your early studies o net#orin$ technolo$y ho# "ransport Control !rotocol

'"C!( #indo#in$unctions. sender sends a sin$le se$ment, and i the sender receives asuccessul acno#led$ment rom the receiver, it then sends t#o se$ments 'that is, a

?#indo#s si>e@ o 2(. ) those t#o se$ments #ere acno#led$ed successully, the sender

sends our se$ments, and so on, increasin$ the #indo# si>e e-ponentially.

o#ever, i one o the se$ments is dropped, the "C! lo# $oes into "C! slo# start, #here

the #indo# si>e is reduced to 9. "he "C! lo# then e-ponentially increases its #indo# si>e

until the #indo# si>e reaches hal o the #indo# si>e #hen con$estion ori$inally occurred.

t that point, the "C! lo#3s #indo# si>e increases linearly.

"C! slo# start is relevant to *oS, ecause #hen an interace3s output ueue is ull, all ne#ly

arrivin$ pacets are discarded 'that is, ?tail dropped@(, and all o those "C! lo#ssimultaneously $o into "C! slo# start.

Note that the process o multiple "C! lo#s simultaneously enterin$ "C! slo# start is called

g"oba" synchroni%ationor T&P synchroni%ation.When "C! synchroni>ation occurs, the lin3s

and#idth is underutili>ed, resultin$ in #asted and#idth.

RED 'asics

"he purpose o %andom &arly Detection '%&D( is to prevent "C! synchroni>ation y

randomly discardin$ pacets as an interace3s output ueue e$ins to ill. o# a$$ressively

%&D discards pacets depends on the current ueue depth.

"he ollo#in$ three parameters inluence #hen a ne#ly arrivin$ pacet is discarded:

inimum threshold

a-imum threshold

ar !roaility Denominator '!D(

"he minimum thresho"dspeciies the numer o pacets in a ueue eore the ueueconsiders discardin$ pacets. "he proaility o discard increases until the ueue depth


32/48

reaches the ma'imum thresho"d.ter a ueue depth e-ceeds the ma-imum threshold, all

other pacets that attempt to enter the ueue are discarded.

o#ever, the proaility o pacet discard #hen the ueue depth euals the ma-imum

threshold is 9'!D(. or e-ample, i the mar proaility denominator #ere set to 90, #hen

the ueue depth reached the ma-imum threshold, the proaility o discard #ould e 990'that is, a 90 percent chance o discard(.

Figure &

"he minimum threshold, ma-imum threshold, and !D comprise the %&D proile. "he

ollo#in$ i$ure sho#s the three distinct ran$es in a %&D proile: no drop, random drop, and

ull drop.

Figure

%&D is most useul on router interaces #here con$estion is liely. or e-ample, a WN

interace mi$ht e a $ood candidate or %&D.

C'+WRED

Cisco does not support %&D, ut ortunately it supports somethin$ etter: Wei$hted %andom

&arly Detection 'W%&D(. =nlie %&D, W%&D has a proile or each priority marin$. or

e-ample, a pacet #ith an )! !recedence value o 0 mi$ht have a minimum threshold o 20

pacets, #hereas a pacet #ith an )! !recedence o 9 mi$ht have a minimum threshold o 2E

pacets. )n this e-ample, pacets #ith an )! !recedence o 0 #ould start to e discarded

eore pacets #ith an )! !recedence o 9.

lthou$h W%&D can e coni$ured rom interace1coni$uration mode or rom virtual1

circuit1coni$uration mode, these *uic %eerence Sheets ocus on an *C1ased W%&D

coni$uration. "o enale W%&D and to speciy the marin$ that W%&D pays attention to

'that is, )! !recedence or DSC!(, issue the ollo#in$ policy1map1class coni$uration1mode

command:

Router(config-pmap-c)#ran2om-2etect [2scp-1ase2 | prec-1ase2]

) neither dscp+@asednor prec+@asedis speciied, W%&D deaults to prec+@ased. ter

W%&D is coni$ured, the )FS assi$ns deault minimum threshold, ma-imum threshold, and

!D values. o#ever, you can alter those deault parameters #ith the ollo#in$ commands:

Router(config-pmap-c)#ran2om-2etect prece2ence prece2encePvalue minimum-threshol2 ma$imum-threshol2 mar-pro1a1ility-2enominator

'=sed or prec1ased W%&D(


33/48

Router(config-pmap-c)#ran2om-2etect 2scp 2scpPvalue minimum-threshol2ma$imum-threshol2 mar-pro1a1ility-2enominator

'=sed or dscp1ased W%&D(

"o reinorce this synta-, consider the ollo#in$ e-ample, #here the $oal is to coni$ureW%&D or the WREDTE#Tclass1map. ter the class1map3s ueue depth reaches 2E

pacets, a DSC! value o 9; mi$ht e discarded. !acets that are mared #ith a DSC!

value o 92 should not e discarded until the ueue depth reaches ;0 pacets, and inally,

pacets that are mared #ith a DSC! value o 99 should have no chance o discard until

the ueue depth reaches ;E pacets. ) the ueue depth e-ceeds 900 pacets, there should e a

900 percent chance o discard or these three DSC! values. o#ever, #hen the ueue depth

is e-actly 900 pacets, the chance o discard or these various pacet types should e 2E

percent. lso, CB1W%&D reuires that CB1W* e coni$ured or the interace. So, as an

additional reuirement, you mae 2E percent o the interace3s and#idth availale to the

WREDTE#Tclass o traic.

Figure *

Router(config-pmap)#class BRE/.E&.Router(config-pmap-c)#1an23i2th percent *7Router(config-pmap-c)#ran2om-2etect 2scp-1ase2Router(config-pmap-c)#ran2om-2etect 2scp af4 *7 466 ARouter(config-pmap-c)#ran2om-2etect 2scp af4* 6 466 ARouter(config-pmap-c)#ran2om-2etect 2scp af44 7 466 A

&-amine the solution, and notice that the !D is 4. "his value #as chosen to meet the

reuirement o a 2E percent chance o discard #hen the ueue depth euals the ma-imum

threshold 'that is, 94 O .2E(. lso, notice that a DSC! value o 9; is dropped eore a

DSC! value o 92, #hich is dropped eore a DSC! value o 99. "his approach is

consistent #ith the deinition o the per1hop ehaviors '!Bs(, ecause the last di$it in the

ssured or#ardin$ '( DSC! name indicates its drop preerence. or e-ample, a value o

9; #ould drop eore a value o 92.

"o vie# the minimum threshold, ma-imum threshold, and !D settin$s or the various )!

!recedence or DSC! values, you can issue the sho0 policy+map inter"ace interface-identifiercommand.

EC Con"iguration

W%&D discards pacets, and that is one #ay or the router to indicate con$estion. o#ever,

routers can no# indicate a con$estion condition y si$nalin$, usin$ an approach called

&-plicit Con$estion Notiication '&CN(.

&CN uses the 2 last its in the "oS yte to indicate #hether a device is &CN capale, and i

so, #hether con$estion is ein$ e-perienced.


34/48

Figure 3

Cisco routers can use &CN as an e-tension to W%&D and mar pacets that e-ceed aspeciied value, instead o droppin$ the pacets. ) the ueue depth is at or elo# the W%&D

minimum threshold, the pacets are sent normally,


35/48

Policing5!olicin$ typically limits and#idth y discardin$ traic that e-ceeds a

speciied rate. o#ever, policin$ also can remar traic that e-ceeds the speciied

rate and attempt to send the traic any#ay. Because policin$3s drop ehavior causes

"C! retransmits, it is recommended or use on hi$her1speed interaces. lso, note that

policin$ can e applied inound or outound on an interace.

#haping5Shapin$ limits e-cess traic, not y droppin$ it ut y uerin$ it. "his

uerin$ o e-cess traic can lead to delay. Because o this delay, shapin$ is

recommended or slo#er1speed interaces. =nlie policin$, shapin$ cannot remar

traic. s a inal contrast, shapin$ can e applied only in the outound direction on

an interace.

"he uestion ecomes this: o# do you send traic out o an interace at a rate that is less

than the physical cloc rate o the interace )t is impossile or an interace to send at a rate

that is slo#er than the line rate. o#ever, you can send at an ?avera$e@ rate that is less than

the cloc rate y usin$ policin$ or shapin$ tools that do not transmit all the time. Speciically,

these tools send a certain numer o its or ytes at line rate, and then they stop sendin$ untila speciic timin$ interval 'or e-ample, 9A o a second( is reached. When the timin$ interval

is reached, the interace a$ain sends a speciic amount o traic at line rate, it stops, and then

it #aits or the ne-t timin$ interval to occur. "his process continually repeats, allo#in$ an

interace to send an avera$e and#idth that can e elo# the physical speed o the interace.

"his avera$e and#idth is called the Committed )normation %ate 'C)%(. "he numer o its

'the unit o measure that is used #ith shapin$ tools( or ytes 'the unit o measure that is used

#ith policin$ tools( that is sent durin$ a timin$ interval is called the Committed Burst 'Bc(.

"he timin$ interval is #ritten as "c.

or e-ample, consider that you have a physical line rate o 92A ps, ut the C)% is only G4ps. lso consider that there are ei$ht timin$ intervals in a second 'that is, "c O 9A o a

second O 92E ms(, and durin$ each o those timin$ intervals, A000 its 'that is, the committed

urst parameter( are sent at line rate. "hereore, over the period o a second, A000 its #ere

sent 'at line rate( ei$ht times, or a $rand total o G4,000 its per second, #hich is the C)%.

Figure 4

o#ever, i all the Bc its 'or ytes( #ere not sent durin$ a timin$ interval, you have anoption to ?an@ those its and use them durin$ a uture timin$ interval. "he parameter that

allo#s this storin$ o unused potential and#idth is called the &-cess Burst 'Be( parameter.

"he Be parameter in a shapin$ coni$uration speciies the ma-imum numer o its or ytes

that can e sent in e-cess o the Bc durin$ a timin$ interval, i those its are indeed availale.

or those its or ytes to e availale, they must have $one unused durin$ previous timin$

intervals. !olicin$ tools, ho#ever, use the Be parameter to speciy the ma-imum numer o

ytes that can e sent durin$ a timin$ interval. "hereore, in a policin$ coni$uration, i the

Bc euals the Be, no e-cess urstin$ occurs. ) e-cess urstin$ does occur, policin$ tools

consider this e-cess traic as e'ceeding traffic. "raic that conorms to 'that is, does not

e-ceed( the speciied C)% is considered y a policin$ tool to e conforming traffic.s part o

your policin$ coni$uration, you can speciy #hat action to tae #hen traic conorms to theC)% and #hat other action to tae #hen the traic e-ceeds the C)%.


36/48

"he relationship et#een the "c, Bc, and C)% is $iven #ith the ollo#in$ ormula:

'!R L Dc 9 .c

lternatively, the ormula can e #ritten as ollo#s:

.c L Dc 9 '!R

"hereore, i you #ant a smaller timin$ interval, you could coni$ure a smaller Bc.

"o illustrate the operation o traic conditioners, Cisco allo#s the metaphor o a ?toen

ucet,@ #here you place Bc toens in the ucet durin$ each timin$ interval. lso, the

ucet can hold a total o Be toens. )n a policin$ coni$uration, traic that reuires no more

than the Bc numer o its or ytes to e transmitted is called conforming traffic."raic that

reuires more than the Bc numer o its or ytes is said to e e'ceeding traffic.

Consider a policin$ e-ample, #here E00 ytes are currently in the toen ucet. pacetcomes throu$h reuirin$ ;00 ytes. "he ytes are removed rom the ucet, and the pacet is

sent. "hen, eore the ucet has een replenished #ith more toens, another ;001yte pacet

comes alon$. Because only 200 ytes remain in the ucet, the pacet cannot e sent and is

discarded.

Figure 6

"his illustration descries ho# policin$ unctions #ith asing"e toen bucet ho#ever Cisco

supports a dua" toen bucet.

With a dual toen ucet, t#o ucets e-ist. "he irst ucet has a depth o Bc, and the

second ucet has a depth o Be. ) a pacet can e or#arded usin$ ytes in the Bc ucet, it

is said to e conormin$. ) the pacet cannot e or#arded usin$ the ytes in the Bc ucet,

ut it can e or#arded usin$ the ytes in the Be ucet, it is said to e e-ceedin$. ) the

pacet cannot e or#arded usin$ either o the ucets individually, it is said to e violatin$.

%eali>e, ho#ever, that a violatin$ pacet can still e transmitted i it can e or#arded usin$

the comined ytes in oth the Bc and Be ucets.

Figure 8

)nstead o policin$ traic to a sin$le rate, Cisco also supports dual1rate policin$. With dual1

rate policin$, you still have t#o toen ucets. "he irst ucet is the Committed )normation

%ate 'C)%( ucet, and the second ucet is the !ea )normation %ate '!)%( ucet. "hese

ucets are replenished #ith toens at dierent rates, #ith the !)% ucet ein$ illed at a

aster rate.


37/48

When a pacet arrives, the dual1rate policer checs to see #hether the !)% ucet has enou$h

toens 'that is, ytes( to send the pacet. ) there are not suicient toens, the pacet is said

to e vio"ating,and it is discarded. Fther#ise, the policer checs to see #hether the C)%

ucet has enou$h toens to or#ard the pacet. ) the pacet can e sent usin$ the C)%

ucet3s toens, the pacet is conforming.) the C)% ucet3s toens are not suicient, ut

the !)% ucet3s toens are suicient, the pacet is said to e e'ceeding,and the e-ceedaction 'or e-ample, transmit #ith a DSC! value o 99( is applied.

Figure 9

With a policin$ mechanism, you can speciy various actions to perorm ased on #hether a

pacet is conormin$, e-ceedin$, or violatin$. &-amples o these actions are as ollo#s:

Transmit5Send the pacet on to the scheduler.

Drop5Discard the pacet.

-ar25Set priority its or the pacet.

-ultiaction5!erorm more than one action, such as mar the pacet #ith a DSC!

value o 92 and set the C/! it to a 9.

C'+Policing Con"iguration

irst, consider the coni$uration o Class1Based !olicin$ 'CB1!olicin$( or a sin$le rate. 6ou

can coni$ure CB1!olicin$ #ith the ollo#in$ command:

Router(config-pmap-c)#police cir[bc[be]] [conform-action action] [e$cee2-action action] [violate-action action]

Note that you do not have to speciy the Bc or Be values. ) you speciy only the C)%, the

)FS calculates Bc as C)%;2 or 9E00 '#hichever is hi$her(. lso, the deault Be value euals

Bc, meanin$ that the toen ucet never holds more than Bc ytes.

)n the ollo#in$ e-ample, you #ant to limit #e traic to 900 ps and "elnet traic to E0ps on interace &thernet 00.

Figure


38/48

Router(config)#policy-map ?,"!'!=OPEM?"ERouter(config-pmap)#class BEDRouter(config-pmap-c)#police 466666Router(config-pmap-c)#e$itRouter(config-pmap)#class-map .E"=E.Router(config-pmap-c)#police 76666

Router(config-pmap-c)#e$itRouter(config-pmap-c)#e$itRouter(config-pmap)#e$itRouter(config)#interface Ethernet 696Router(config-if)#service-policy output ?,"!'!=OPEM?"E

s mentioned earlier, you can coni$ure dual1rate CB1!olicin$, #here you police to t#o

distinct rates: the C)% and !)%. "he ollo#in$ command coni$ures dual1rate CB1!olicin$:

Router(config-pmap-c)#police cir cir[1c bc] [pirpir] [1e be] [conform-action action] [e$cee2-action action] [violate-action action]

Similar to CB1W* and //*, dual1rate CB1!olicin$ allo#s you to limit the and#idth ospeciic traic y a percenta$e o an interace3s and#idth. "his can e accomplished #ith


Router(config-pmap-c)#police cir percentpercent [1c bc] [pir percentpercent] [1e be] [conform-action action] [e$cee2-action action] [violate-action action]

C'+#haping Con"iguration

Fne o t#o approaches can e used #hen coni$urin$ Class1Based Shapin$ 'CB1Shapin$(:

shapin$ to avera$e and shapin$ to pea. When you coni$ure CB1Shapin$ to shape toavera$e, you only #ant to send traic at the C)%. o#ever, i you coni$ure shapin$ to pea,

you are attemptin$ to send aove the C)%, i and#idth is availale. Speciically, #hen you

shape to pea, instead o


39/48

Router(config)#class-map +EROE'"&&Router(config-cmap)#match protocol telnetRouter(config-cmap)#e$itRouter(config)#class-map ?EC'"&&Router(config-cmap)#match protocol httpRouter(config-cmap)#e$it

Router(config)#policy-map +EROE?,"!'0Router(config-pmap)#class +EROE'"&&Router(config-pmap-c)#shape average 8A666Router(config-pmap-c)#e$itRouter(config-pmap)#e$itRouter(config)#policy-map ?EC?,"!'0Router(config-pmap)#class ?EC'"&&Router(config-pmap-c)#shape pea 8A666

)n this e-ample, the .ER.?EP7,ICYpolicy1map is shapin$ "elnet traic to avera$e,

meanin$ that "elnet traic is shaped to the C)% o G4 ps. o#ever, that is not the case or

the PE.=P7,ICYpolicy1map.

"he PE.=P7,ICYpolicy1map is shapin$ traic to a pea rate o C)% Q R9 P 'BeBc(.

Because you let the )FS calculate the Bc and Be values, they are eual, #hich means that you

are shapin$ to a rate o G4000 Q '9 P 9( O 92A ps.

Ena@ling C'+#haping "or Frame Relay et0or2s

Fn rame %elay net#ors, you mi$ht need not only to shape your traic, ut you mi$ht also

need your router to respond to con$estion occurrin$ in the service provider3s cloud, y

reducin$ the C)% to a lo#er value.

When a service provider ecomes con$ested and needs to discard rames, it irst discardsrames #ith their Discard &li$ile 'D&( it set to a 9. "he service provider also can reuest

that the sendin$ router slo# its transmission rate, y marin$ the Bac#ard &-plicit

Con$estion Notiication 'B&CN( it to a 9, in a rame $oin$ ac to the sender. When this

occurs, i the router is coni$ured to respond to B&CNs, the router reduces its C)% y 2E

percent. ) the router receives another B&CN in the ne-t time interval, it decreases its

transmission rate y 2E percent o the current rate. "his ehavior can continue until the rate

drops to the router3s coni$ured minimum C)%.

Figure *

6ou can, ho#ever, encounter a situation in #hich the vast ma


40/48

Figure *&

ter a sender has slo#ed its transmission rate ecause o B&CNs, 9G timin$ intervals mustelapse eore the sender e$ins to increase its transmission rate. When the sender does e$in

to increase its transmission rate, it does so at a much more cautious rate than #hen it reduced

its rate. Speciically, the sender only increases its transmission rate y 'Be P Bc( 9G its per

timin$ interval.

Consider the ollo#in$ e-ample, #here CB1Shapin$ is ein$ comined #ith CB1W* to

allocate at least one amount o and#idth, #hile shapin$ 'that is, limitin$ the traic rate( to a

hi$her and#idth.

Router(config)#policy-map NRME&>?E

Router(config-pmap)#class NRME'"&&Router(config-pmap-c)#shape average 4*5666Router(config-pmap-c)#shape a2aptive K8666Router(config-pmap-c)#1an23i2th K8

)n this e-ample, traic classiied y the FR.-EC,.##class1map is shaped to an avera$e

rate o 92A ps. lso, the shape adapti$e mincircommand is used to speciy the minimum

value to #hich the C)% can drop in the presence o B&CNs. )n this e-ample, the router can

reduce its transmission rate to a C)% o LG ps. 'Note that the units o measure or the

mincirparameter are its per second.( lso, CB1W* speciies that at least LG ps o

and#idth is availale or this class o traic. Note that, as sho#n in the previous e-ample,

minimum C)% 'as speciied y the shape adapti$ecommand( should not e less than theand#idth that is allocated y CB1W*.

!o# on #lo0+#peed ,in2s

)n this section, you mae the most o your limited and#idth on lo#er1speed WN

interaces. Speciically, you are introduced to compression technolo$ies, #hich send e#er

its across the lin, and lin ra$mentation and interleavin$ technolo$ies, #hich ra$ment

lar$e payloads to reduce the seriali>ation delay that is e-perienced y smaller payloads.

Tools "or 5sing 'and0idth E""iciently

"he t#o road cate$ories o compression are as ollo#s:

Payload compression5%educes the payload si>e, usin$ approaches such as S"C,

!redictor, or !!C.

1eader compression5%educes the si>e o the "C! and %"! headers.

"he $oal o compression technolo$ies is to increase the throu$hput over a WN lin #hile

reducin$ the delay. o#ever, particularly #ith payload1compression approaches, the time

that is reuired y lo#er1end routers to run the compression al$orithm can increase theoverall delay. ortunately, these routers can have hard#are acceleration modules that you can


41/48

add to dramatically improve the router3s aility to perorm compression in a timely manner.

or e-ample, a Compression dvanced )nte$ration odule 'C)( is availale to oload

compression tass rom 2G00 Series routers.

"hese *uic %eerence Sheets, ho#ever, ocus on header compression. With header

compression, a header typically is reduced rom appro-imately 40 ytes in si>e toappro-imately ; to E ytes Ror "ransport Control !rotocol '"C!( header compression or 2 to

4 ytes Ror %eal1"ime "ransport !rotocol '%"!( header compression. o#ever, the routers

technically are not doin$ compression. %ather, these routers cache inormation that does not

chan$e durin$ a conversation, such as source and destination )! addresses and "C!=D! port

numers. "he compressed header then carries such inormation as =D! checsums and a

session conte-t )D 'C)D(, #hich identiies #hich lo# the pacet is a part o.

Figure *

nother *oS mechanism that is useul or slo#er lin speeds is /in ra$mentation and

)nterleavin$ '/)(. Consider a 9E001yte data rame that is ein$ sent out o a G41ps serial

interace. "he interace, in this case, needs 9A ms


42/48

Beore coni$urin$ header compression, reali>e that header compression is most eective or

slo# lins that are carryin$ pacets #ith relatively small payloads, such as voice or "elnet

traic.

CB1eader Compression can e coni$ured rom policy1map1class coni$uration mode #ith


Router(config-pmap-c)#compression hea2er ip [tcp | rtp]

Note that i you do not speciy tcpor rtp, this command perorms oth "C! and %"! header

compression. =nlie previous versions o header compression, you do not need to speciy the

ma-imum numer o simultaneous compressed sessions supported. With CB1eader

Compression, the numer o connections is determined automatically y the )FS.

Consider the ollo#in$ CB1eader Compression e-ample:

Router(config)#class-map +,!'ERouter(config-cmap)#match protocol rtpRouter(config-cmap)#e$itRouter(config)#policy-map ',M?RE&&Router(config-pmap)#class +,!'ERouter(config-pmap-c)#compression hea2er ip rtpRouter(config-pmap-c)#e$itRouter(config-pmap)#e$itRouter(config)#interface serial 694Router(config-if)#service-policy output ',M?RE&&

)n this e-ample, you are matchin$ voice traic 'that is, %"! pacets( usin$ NB%. "hen, you

are applyin$ CB1eader Compression to those %"! pacets #ith the C7-PRE##policy1map. "he policy1map is then applied outound to interace serial 09. Because you coni$ured

header compression usin$ the *C approach, the same veriication commands that you

learned earlier 'that is, sho0 policy+map and sho0 policy+map inter"ace interface-

identifier( are still applicale.

5sing -,P and FRF;& "or ,FI

"he seriali>ation delay $oal that you have #hen coni$urin$ an /) mechanism is in the

ran$e o 90 to 9E ms. "o determine the seriali>ation delay or a speciic rame si>e on a

speciic lin speed, use the ollo#in$ ormula:

&erialiation /elay L (NrameP&ie F 5) 9 "inP&pee2

"he reason that you multiply the rame si>e y A is to convert ytes into its. Consider a

rame si>e o E92 ytes on a lin speed o 92A ps, as ollo#s:

&erialiation /elay L (74* F 5) 9 4*5 L * ms

lthou$h Cisco supports %.99 nne- C as an /) mechanism or 8o% net#ors, these

*uic %eerence Sheets ocus on the coni$uration o ultilin !!! '/!( and %.92.

irst, consider the coni$uration o /!.


43/48

ultilin !!!, y deault, ra$ments traic. 6ou can levera$e that act and run /!, even

over a sin$le lin. 6ou perorm the /! coni$uration under a virtual multilin interace, and

then you can assi$n one or more physical interaces to the multilin $roup. "he physical

interace does not have an )! address assi$ned, ut the virtual multilin interace does.

"ypically, you use a sin$le interace as a memer o the multilin $roup. ollo#in$ is the

synta- to coni$ure /!:

Router(config)#interface multilin multilink_interface_number

'Creates a virtual multilin interace.(

Router(config-if)#ip a22ress ip_address subnet_mask

'ssi$ns an )! address to the virtual multilin interace.(

Router(config-if)#ppp multilin

'Coni$ures ra$mentation on the multilin interace.(

Router(config-if)#ppp multilin interleave

'Shules the ra$ments to$ether.(

Router(config-if)#ppp fragment-2elay serialization_delay

'Speciies ho# lon$ it #ill tae or a ra$ment to e-it the interace, in milliseconds. Note that

the )FS automatically calculates the appropriate pacet si>e to meet the speciied seriali>ation

delay.(

Router(config-if)#encapsulation ppp

'&nales ppp encapsulation on the physical interace.(

Router(config-if)#no ip a22ress

'%emoves the )! address rom the physical interace.(

Router(config-if)#multilin-group multilink_group_number

'ssociates the physical interace #ith the multilin $roup.(

)n the ollo#in$ e-ample, the $oal is to coni$ure /! on routers %9 and %2 so that you are

achievin$ a seriali>ation delay o 90 ms on their serial 00 interaces.

Figure *3

R4(config)#interface multilin 4R4(config-if)#ip a22ress 46H4H4H4 *77H*77H*77H6


44/48

R4(config-if)#ppp multilinR4(config-if)#ppp multilin interleaveR4(config-if)#ppp fragment-2elay 46R4(config-if)#e$itR4(config)#interface serial 696R4(config-if)#encapsulation ppp

R4(config-if)#no ip a22ressR4(config-if)#multilin-group 4

R*(config)#interface multilin 4R*(config-if)#ip a22ress 46H4H4H* *77H*77H*77H6R*(config-if)#ppp multilinR*(config-if)#ppp multilin interleaveR*(config-if)#ppp fragment-2elay 46R*(config-if)#e$itR*(config)#interface serial 696R*(config-if)#encapsulation pppR*(config-if)#no ip a22ressR*(config-if)#multilin-group 4

"o veriy the /! coni$uration, you can use the sho0 inter"aces multilin2 interface-

identifiercommand. "he output rom this command sho#s ho# many interleaves have een

perormed. "hereore, this is an e-cellent command to veriy that /! is indeed unctionin$.

%.92 is coni$ured as part o a rame %elay map1class. =nlie /!, #here you can

speciy a desired seriali>ation delay, #ith %.92, you must speciy the si>e that you #ant to

ra$ment rames to. s a rule o thum, divide the line speed y A00 to $et a ra$ment si>e

that results in a 901ms seriali>ation delay. or e-ample, on a G4,0001ps lin, divide G4,000

y A00 to $et A0. "his means that i you speciy a ra$ment si>e o A0, your ra$ments #ill

have a seriali>ation delay o 90 ms.

ollo#in$ is the synta- to coni$ure %.92:

Router(config)#map-class frame-relay name

'Creates the map1class and enters map1class coni$uration mode.(

Router(config-map-class)#frame-relay fragment fragment-size

'Speciies the si>e to #hich %.92 #ill ra$ment rames. Note that the )FS does not

automatically calculate the ra$ment si>e ased on a speciied delay, as the /! mechanism

did.(

Router(config-if)#frame-relay traffic-shaping

'&nales rame %elay traic shapin$ on the physical interace.(

Router(config-if | config-su1if)#frame-relay class name

'ssociates the map1class #ith an interace or a suinterace.(

Router(config-fr-2lci)#class name


45/48

'ssociates the map1class #ith a rame %elay D/C).(

)n the ollo#in$ e-ample, you coni$ure %.92 to create a seriali>ation delay o 90 ms on a

lin that is cloced at a rate o G4 ps. "he map1class then is applied to D/C) 909. Because

%.92 is coni$ured as a part o rame %elay traic shapin$, you also speciy a C)% o G4

ps and a Bc o G40.

Figure *4

R4(config)#map-class frame-relay NRN4*-EM?"ER4(config-map-class)#frame-relay cir 8A666R4(config-map-class)#frame-relay 1c 8A6R4(config-map-class)#frame-relay fragment 56

R4(config-map-class)#e$itR4(config)#interface serial 694R4(config-if)#frame-relay traffic-shapingR4(config-if)#interface serial 694H4 point-to-pointR4(config-su1if)#frame-relay interface-2lci 464R4(config-fr-2lci)#class NRN4*-EM?"E

6ou can use the sho0 "rame+relay "ragmentcommand to vie# the ra$ment si>e that is

ein$ used. lso, use the sho0 "rame+relay p$ccommand to vie# the ra$ment si>e that is

used on a particular D/C).

!o# Design ?uidelines

"his section revie#s, in a desi$n conte-t, many o the concepts presented earlier in these

*uic %eerence Sheets. or e-ample, voice, data, and video applications each have uniue

desi$n $uidelines. "hese $uidelines are e-amined in this section.

Classi"ication Re$ie0

s a revie#, recall ho# you perormed classiication and marin$ early on in these *uic

%eerence Sheets. =sin$ the three1step *C approach, you sa# ho# to classiy traic y

such characteristics as an incomin$ interace, an access1list match, or an NB%. "he

Net#or Based pplication %eco$nition 'NB%( classiication mechanism oered the most$ranular classiication, ecause NB% can loo eyond /ayer ; or /ayer 4 inormation, all

the #ay up to /ayer .

arin$ could then e done at /ayer 2 or /ayer ; usin$ marin$s such as CoS 'at /ayer 2(,

)! !recedence 'at /ayer ;(, or DSC! 'at /ayer ;(.

Figure *6


46/48

!ueuing Re$ie0

arin$ traic alone does not chan$e the ehavior o the traic. "o inluence the traic3s

ehavior, you can use the ollo#in$ other *oS mechanisms:

!ueuing'or e-ample, //*, CB1W*, and W%%(

Congestion a$oidance'or e-ample, W%&D and &CN(

Compression'or e-ample, "C! and %"! CB1eader Compression(

Tra""ic conditioning'or e-ample, CB1!olicin$ and CB1Shapin$(

,in2 e""iciency 'or e-ample, /in ra$mentation and )nterleavin$ mechanisms such

as /! and compression mechanisms, such as %"!(

With the covera$e o each o these *oS mechanisms, you can no# select the appropriate tool

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