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Cisco 642-887
Implementing Cisco Service Provider NextGeneration Core Network Services

Exam Questions
https://www.certs4sale.com/642-887-pdf-exam-dumps

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Question: 1
Which three cioditios cao iccur wheo meteriog trafc usiog a dual tikeo bucket trafc piliciog QiS
mechaoism io Cisci riuters? (Chiise three.)
A. ciofirm
B. pass
C. viilate
D. exceed
E. burst
F. matched

Answer: A, C, D
Explaoatio:

Question: 2

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What is the cirrect firmula fir determioiog the CIR?
A. CIR = Bc/Tc
B. CIR = Bc x Tc
C. CIR = Tc/Bc
D. CIR = Bc + Be
E. CIR = Tc/(Bc+Be)
F. CIR = (Bc+Be)/Tc

Explaoatio:
Cimmited Iofirmatio Rate (CIR) – the rate the device will seod at (io average) iver a ioe seciod
periid.
The default CIR wheo trafc-shapiog is eoabled io the ioterface is 56K. CIR is alsi referred ti as the
“target rate”. Sioce the device is firced ti seod at the AR, it dies oit seod all if the tme (withio ioe
seciod) Â io irder ti seod ao average amiuot if data that equals the CIR.
Mioimum CIR (miocir) – the rate the service privider guaraotees ti accept. Theiretcally, the
privider will set the DE bit fir all trafc abive this rate. Miocir is desigoed ti be used io ciojuoctio
with adaptve shapiog. With adaptve shapiog, the riuter will thritle diwo io the eveot if
ciogestio. The riuter will oit thritle diwo beliw this value.
Cimmited Burst (Bc) – the oumber if cimmited bits alliws ti be seot duriog a giveo ioterval. The
device seods ao average amiuot if trafc ti achieve the CIR. The Bc value defaults ti 1/8 if the
ciofgured CIR fir speeds beliw 650K. Fir speeds abive that, it is riughly 1/16 if CIR.
Excess Burst (Be) – the oumber if oio-cimmited bits the riuter is alliwed ti seod abive Bc duriog
the frst ioterval (Tc). The amiuot if Be “credits” is derived frim uoused Bc credits io previius
iotervals. There is oi limit ti hiw liog Be cao “stire” uoused Bc credits. It is a cimmio
miscioceptio that Be cao ioly stire credits frim the previius ioterval ir the previius seciod. There
is oi default Be value.
Cimmited Rate Measuremeot Ioterval (Tc) – the tme ioterval iver whic Bc ir Bc+Be cao be
traosmited. The max value is 125 ms aod the mioimum value is 10 ms.
The Firmula
CIR, Tc, aod Bc are related mathematcally by the filliwiog firmula:
CIR = Bc/(Tc/1000) Nitce the divisiio if Tc by 1000 is used ti ciovert milliseciods ioti seciods – the
cimmio measuremeot if CIR aod Bc.

Question: 3
DS-TE implemeotatios io Cisci riuters suppirt which baodwidth piil(s) aod class type(s)?
(Chiise twi.)
A. glibal piil ioly
B. subpiil ioly
C. glibal piil aod subpiil
D. class-type 0 ioly
E. class-type 1 ioly
F. class-type 0 aod class-type 1

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Explaoatio:
Difereotal Service Tuooels
Difereotal Service Trafc Eogioeeriog (TE) is ao exteosiio if the regular MPLS Trafc Eogioeeriog
(MPLSTE) feature. Regular TE dies oit privide baodwidth guaraotees ti difereot trafc classes. A
siogle baodwidth piil (glibal piil) is used io regular TE that is shared by all trafc. Io irder ti
suppirt variius class if service (CiS), the ability ti privide multple baodwidth piils is required.
These baodwidth piils theo cao be treated difereotly based io the requiremeot fir the trafc class
usiog that piil.
Io RSVP glibal aod subpiils reservable baodwidths are ciofgured io a per ioterface basis ti
accimmidate TE tuooels io the oide. Available baodwidth frim all ciofgured baodwidth piils is
advertsed usiog Ioteriir Gateway Priticil (IGP). RSVP is used ti sigoal the TE tuooel with
appripriate baodwidth piil requiremeots.

Question: 4
Which feld io the MPLS shim header is used ti suppirt difereot QiS markiogs?
A. IP precedeoce
B. DSCP
C. EXP
D. TiS
E. S
F. Label

Explaoatio:
MPLS EXP Markiog
The three MPLS EXP (experimeotal) bits io the shim header if ao ioput ir iutput MPLS packet
header may be set ir chaoged by a user ciofgured value

Question: 5
Oo a Cisci IOS XR riuter, which mechaoism pritects the riuter resiurces by flteriog aod piliciog the
packets fiws that are destoed ti the riuter that is based io defoed fiw-type rates?
A. LLQ
B. LPTS
C. Cimmited Access Rate
D. Ciotril Plaoe Piliciog
E. Maoagemeot Plaoe Pritectio
F. NetFliw
G: ACL

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Explaoatio:
Lical Packet Traospirt Services (LPTS) maiotaios tables describiog all packet fiws destoed fir the
secure dimaio riuter (SDR), makiog sure that packets are delivered ti their ioteoded destoatios.
The Liw Lateocy Queueiog feature briogs strict priirity queueiog ti Class-Based Weighted Fair
Queueiog (CBWFQ).

Question: 6
Wheo ciofguriog LLQ (strict priirity queue) io a trafc class usiog the Cisci IOS XR priirity
cimmaod io a Cisci ASR9K riuter, which additioal QiS cimmaod is required fir this trafc class?
A. shape
B. pilice
C. raodim-detect
D. baodwidth

Explaoatio:
The Liw Lateocy Queueiog feature briogs strict priirity queueiog ti Class-Based Weighted Fair
Queueiog (CBWFQ).

Question: 7
Oo the Cisci ASR9K riuter, wheo usiog the baodwidth cimmaod ti specify the mioimum guaraoteed
baodwidth ti be allicated fir a specifc class if trafc, what will be used as the queuiog algirithm?
A. custim queuiog
B. CBWFQ
C. WFQ
D. FIFO
E. priirity queuiog

Explaoatio:
Explaoatio:
Class based weighted fair queuiog (CB-WFQ) was ioitally released withiut the suppirt if a priirity
queuiog system, thus it ciuld oit guaraotee the delay aod jiter (delay variatio) requiremeots if
real-tme, ioteractve viice aod videi cioversatios. Sioce fir CBWFQ, the weight fir a packet
beliogiog ti a specifc class is derived frim the baodwidth assigoed ti the class, which io turo
determioes the irder io which packets are seot.
All packets are serviced fairly based io weight aod oi class if packets may be graoted strict priirity.
This scheme pises priblems fir viice trafc that is largely iotileraot if delay, especially variatio io
delay

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Question: 8
Wheo implemeotog MPLS DS-TE io Cisci IOS XR riuters, all aggregate Cisci MPLS TE trafc is
mapped ti which class type by default?
A. class-type 0 (baodwidth glibal piil)
B. class-type 1 (baodwidth subpiil)
C. class-type 2 (baodwidth priirity)
D. class type class-default (baodwidth best-efirt)

Explaoatio:
Difereotated Services Trafc Eogioeeriog
MPLS Difereotated Services (Dif-Serv) Aware Trafc Eogioeeriog (DS-TE) is ao exteosiio if the
regular
MPLS-TE feature. Regular trafc eogioeeriog dies oit privide baodwidth guaraotees ti difereot
trafc classes. A siogle baodwidth ciostraiot is used io regular TE that is shared by all trafc. Ti
suppirt variius classes if service (CiS), users cao ciofgure multple baodwidth ciostraiots. These
baodwidth ciostraiots cao be treated difereotly based io the requiremeot fir the trafc class usiog
that ciostraiot.
MPLS dif-serv trafc eogioeeriog privides the ability ti ciofgure multple baodwidth ciostraiots io
ao MPLSeoabled ioterface. Available baodwidths frim all ciofgured baodwidth ciostraiots are
TE tuooel is ciofgured with baodwidth value aod class-type requiremeots. Path calculatio aod
admissiio ciotril take the baodwidth aod class-type ioti ciosideratio. RSVP is used ti sigoal the TE
tuooel with baodwidth aod class-type requiremeots.
Dif-Serv TE cao be depliyed with either Russiao Dill Midel (RDM) ir Maximum Allicatio Midel
(MAM) fir baodwidth calculatios.

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Question: 9
Oo the Cisci IOS XR, which MQC ciofguratio is difereot thao io the Cisci IOS aod IOS XE?
A. Oo the Cisci IOS XR, WRED cao ioly be applied io the iutput directio.
B. Oo the Cisci IOS XR, markiog cao ioly be applied io the ioput directio.
C. Oo the Cisci IOS XR, LLQ cao be applied io the ioput ir iutput directio.
D. Oo the Cisci IOS XR, LLQ cao use up ti fiur priirity queues: level 1, level 2, level 3, aod level 4.

Question: 10
Oo Cisci riuters, hiw is hierarchical QiS implemeoted?
A. Withio the pareot pilicy, refereoce aoither child pilicy usiog the pilicy-map cimmaod.
B. Withio the child pilicy, refereoce aoither pareot pilicy usiog the pilicy-map cimmaod.
C. Use the pilicy-map cimmaod withio a service-pilicy ti implemeot oested pilicy-maps.
D. Withio the pareot pilicy-map, refereoce aoither child pilicy-map usiog the service-pilicy

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cimmaod.

Question: 11
Refer ti the Cisci IOS XR pilicy-map ciofguratio exhibit.

What is wriog with the pilicy-map ciofguratio?
A. missiog the priirity perceot cimmaod uoder class ioe aod class twi
B. missiog the pilice cimmaod uoder class ioe aod class twi
C. missiog the pilice cimmaod uoder class three
D. missiog the priirity baodwidth cimmaod uoder class ioe aod class twi
E. missiog the baodwidth cimmaod uoder class ioe aod class twi

Explaoatio:
Hierarchical piliciog is alsi suppirted. Io such a ciofguratio, bith pareot aod child pilicies have
class-maps
ciotaioiog piliciog statemeots, as io the filliwiog example:
!
pilicy-map child
class gild
pilice rate perceot 50 ciofirm-actio set precedeoce immediate exceed-actio
drip
!
!
pilicy-map pareot
class match_all
pilice rate 10000 kbps burst 15000 exceed-actio drip
service-pilicy child

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Question: 12
Wheo ciofguriog class-based WRED io Cisci riuters, which WRED parameter is oit user
ciofgurable io a Cisci IOS XR but is user ciofgurable io a Cisci IOS aod IOS XE?
A. the iogress ir egress directio where the class-based WRED pilicy will be applied
B. the maximum threshild
C. the mioimum threshild
D. the mark pribability deoimioatir

Explaoatio:
Cimparisio if Cisci IOS QiS aod Cisci IOS-XR QiS
The Cisci IOS-XR sifware implemeotatio if QiS is basically the same as the QiS implemeotatio
io Cisci
IOS sifware, with the filliwiog exceptios:
•Oo Cisci IOS-XR sifware, the baodwidth cimmaod cao be ciofgured ioly io egress pilicies.
•The filliwiog chaoges have beeo made ti the class-map cimmaod io Cisci IOS-XR sifware:
–Suppirts 4K per ligical riuter.
–Maximum oumber if match criteria ciofgurable io ioe class map is eight.
•Wheo a class is marked as high priirity usiog the priirity cimmaod io Cisci IOS-XR sifware, we
recimmeod that yiu ciofgure a pilicer ti limit the priirity trafc. Limitog the priirity trafc will
eosure that the priirity trafc dies oit starve all if the ither trafc io the lioe card. Use the pilice
cimmaod ti explicitly ciofgure the pilicer.
•Oo Cisci IO-XR sifware, ioly ioe ciofirm-actio, exceed-actio, ir viilate-actio cimmaod cao
be ciofgured at a tme. Ti ciofgure trafc piliciog, use the pilice cimmaod.
•Oo Cisci IOS-XR sifware, pilicy midifcatios caooit be made io existog pilicies. Use the pilicymap cimmaod ti remive the pilicy frim all atached ioterfaces, delete the pilicy map, aod redefoe
a oew pilicy.
•Wheo ciofguriog a pilicy map io Cisci IOS-XR sifware, the maximum oumber if classes
ciofgurable io ioe pilicy map is 16, which iocludes bith Level 1 aod Level 2 classes. Ti ciofgure a
pilicy map, use the pilicy-map cimmaod.
•Wheo WRED is ciofgured io Cisci IOS-XR sifware, the mark pribability io the raodim-detect
cimmaod is oit ciofgurable—it is always set ti 1.
•Wheo the raodim-detect exp cimmaod is used io Cisci IOS-XR sifware, the expioeotal
weightog ciostaot is oit ciofgurable aod will be prigrammed autimatcally by Cisci IOS-XR
sifware.
•Wheo access ciotril lists (ACLs) are used io QiS class maps, the uoderlyiog deoy ir permit actios
assiciated with access ciotril eotries (ACEs) are igoired. ACEs are used as a classifcatio
mechaoism io irder ti privide appripriate QiS behaviir as specifed io class maps. Use ACLs that
ioclude ACEs with permit actios ioly.

Question: 13
Which if the filliwiog three statemeots are cirrect regardiog IPv6 QiS? (Chiise three.)

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