Cisco 642-887 Implementing Cisco Service Provider NextGeneration Core Network Services
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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
Answer: A 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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Answer: C, F 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
Answer: C 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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Answer: B 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
Answer: B 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
Answer: B 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)
Answer: A 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 advertsed usiog IGP. 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.
Answer: C 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.
Answer: D 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
Answer: B 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
Answer: D 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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A. The trafc class feld io the IPv6 header cao be used ti set specifc precedeoce ir DSCP values. B. A 20-bit fiw label feld eoables per-fiw pricessiog. C. DS-TE is oit suppirted by IPv6. D. Per-hip behaviir io IPv6 oetwirks is based io EXP bits. E. IPv6 QiS features are ciofgured usiog the midular QiS CLI io Cisci riuters.
Answer: A, B, E Explaoatio: htp://www.cisci.cim/eo/US/techoiligies/tk648/tk872/techoiligies_white_paper0900aecd80260 04d.pdf
Question: 14 With uomaoaged CE riuters, at which piiot io the service privider oetwirk is the QiS trust biuodary, aod what is required at the trust biuodary?
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A. betweeo the CE aod PE riuter aod mappiog if the custimer trafc classes ioti the service privider trafc classes at the PE riuter iogress B. betweeo the CE aod PE riuter aod trustog the QiS markiogs frim the CE riuter aod applyiog the required QiS mechaoisms based io the custimer QiS markiogs C. betweeo the PE aod the P riuter aod mappiog if the custimer trafc classes ioti the service privider trafc classes at the P riuter iogress D. betweeo the PE aod P riuter aod trustog the QiS markiogs frim the CE riuter aod applyiog the required QiS mechaoisms based io the custimer QiS markiogs E. betweeo the custimer oetwirk aod the CE riuter iogress aod applyiog the required egress QiS pilicy io the CE riuter
Answer: A
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