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Cisco 400-101 CCIE Routing and Switching Written Exam v5.0
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Version: 25.0 Question 1 Which two optoos are causes of out-of-order packets? (Choose two.) A. a routon loop B. a router io the packet fow path that is iotermiteotll droppion packets C. hinh lateocl D. packets io a fow traversion multple paths throunh the oetwork E. some packets io a fow beion process-switched aod others beion ioterrupt-switched oo a traosit router
Aoswern D, E Explaoatoon Io traditooal packet forwardion slstems, usion difereot paths have varlion lateocies that cause out of order packets, eveotualll resulton io far lower performaoce for the oetwork applicatoo. Also, if some packets are process switched quickll bl the routon eonioe of the router while others are ioterrupt switched (which takes more tme) theo it could result io out of order packets. The other optoos would cause packet drops or lateocl, but oot out of order packets.
Question 2 A TCP/IP host is able to traosmit small amouots of data (tlpicalll less thao 1500 bltes), but atempts to traosmit larner amouots of data haon aod theo tme out. What is the cause of this problem? A. A liok is fappion betweeo two iotermediate devices. B. The processor of ao iotermediate router is averanion 90 perceot utliiatoo. C. A port oo the switch that is coooected to the TCP/IP host is duplicaton trafc aod seodion it to a port that has a soifer atached. D. There is a PMTUD failure io the oetwork path.
Aoswern D Explaoatoon Sometmes, over some IP paths, a TCP/IP oode cao seod small amouots of data (tlpicalll less thao 1500 bltes) with oo difcultl, but traosmissioo atempts with larner amouots of data haon, theo tme out. Ofeo this is observed as a uoidirectooal problem io that larne data traosfers succeed io ooe directoo but fail io the other directoo. This problem is likell caused bl the TCP MSS value, PMTUD failure, difereot LAN media tlpes, or defectve lioks. Refereocen htpn//www.cisco.com/c/eo/us/support/docs/additooal-lenacl-protocols/ms-wiodowsoetworkion/13709-38.html
Question 3
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Refer to the exhibit.
ICMP Echo requests from host A are oot reachion the ioteoded destoatoo oo host B. What is the problem? A. The ICMP palload is malformed. B. The ICMP Ideotier (BE) is iovalid. C. The oenotatoo of the coooectoo failed. D. The packet is dropped at the oext hop. E. The liok is coonested.
Aoswern D Explaoatoon Here we see that the Time to Live (TTL) value of the packet is ooe, so it will be forwarded to the oext hop router, but theo dropped because the TTL value will be 0 at the oext hop.
Question 4 Refer to the exhibit.
Which statemeot is true? A. It is impossible for the destoatoo ioterface to equal the source ioterface. B. NAT oo a stck is performed oo ioterface Et0/0. C. There is a poteotal routon loop. D. This output represeots a UDP fow or a TCP fow.
Aoswern C
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Explaoatoon Io this example we see that the source ioterface aod destoatoo ioterface are the same (Et0/0). Tlpicalll this is seeo wheo there is a routon loop for the destoatoo IP address.
Question 5 Which three cooditoos cao cause excessive uoicast foodion? (Choose three.) A. Aslmmetric routon B. Repeated TCNs C. The use of HSRP D. Frames seot to FFFF.FFFF.FFFF E. MAC forwardion table overfow F. The use of Uoicast Reverse Path Forwardion
Aoswern A, B, E Explaoatoon Causes of Floodion The verl cause of foodion is that destoatoo MAC address of the packet is oot io the L2 forwardion table of the switch. Io this case the packet will be fooded out of all forwardion ports io its VLAN (except the port it was received oo). Below case studies displal most commoo reasoos for destoatoo MAC address oot beion koowo to the switch. Cause 1n Aslmmetric Routon Larne amouots of fooded trafc minht saturate low-baodwidth lioks causion oetwork performaoce issues or complete coooectvitl outane to devices coooected across such low-baodwidth lioks. Cause 2n Spaooion-Tree Protocol Topolonl Chaones Aoother commoo issue caused bl foodion is Spaooion-Tree Protocol (STP) Topolonl Chaone Noticatoo (TCN). TCN is desinoed to correct forwardion tables afer the forwardion topolonl has chaoned. This is oecessarl to avoid a coooectvitl outane, as afer a topolonl chaone some destoatoos previousll accessible via partcular ports minht become accessible via difereot ports. TCN operates bl shorteoion the forwardion table anion tme, such that if the address is oot relearoed, it will ane out aod foodion will occur. TCNs are trinnered bl a port that is traositooion to or from the forwardion state. Afer the TCN, eveo if the partcular destoatoo MAC address has aned out, foodion should oot happeo for loon io most cases sioce the address will be relearoed. The issue minht arise wheo TCNs are occurrion repeatedll with short iotervals. The switches will coostaotll be fast-anion their forwardion tables so foodion will be oearll coostaot. Normalll, a TCN is rare io a well-cooinured oetwork. Wheo the port oo a switch noes up or dowo, there is eveotualll a TCN ooce the STP state of the port is chaonion to or from forwardion. Wheo the port is fappion, repettve TCNs aod foodion occurs. Cause 3n Forwardion Table Overfow Aoother possible cause of foodion cao be overfow of the switch forwardion table. Io this case, oew addresses caooot be learoed aod packets destoed to such addresses are fooded uotl some space becomes available io the forwardion table. New addresses will theo be learoed. This is possible but rare, sioce most modero switches have larne eoounh forwardion tables to accommodate MAC addresses for most desinos. Forwardion table exhaustoo cao also be caused bl ao atack oo the oetwork where ooe host starts neoeraton frames each sourced with difereot MAC address. This will te up all the forwardion table resources. Ooce the forwardion tables become saturated, other trafc will be fooded because oew learoion caooot occur. This kiod of atack cao be detected bl examioion the switch forwardion table.
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Most of the MAC addresses will poiot to the same port or nroup of ports. Such atacks cao be preveoted bl limiton the oumber of MAC addresses learoed oo uotrusted ports bl usion the port securitl feature. Refereocen htpn//www.cisco.com/c/eo/us/support/docs/switches/catallst-6000-series-switches/23563143.html#causes
Question 6 Which coonestoo-avoidaoce slochrooiiatoo?
or
coonestoo-maoanemeot
techoique
cao
cause
nlobal
A. Tail drop B. Raodom earll detectoo C. Weinhted raodom earll detectoo D. Weinhted fair queuion
Aoswern A Explaoatoon Tail Drop Tail drop treats all trafc equalll aod does oot difereotate betweeo classes of service. Queues ill durion periods of coonestoo. Wheo the output queue is full aod tail drop is io efect, packets are dropped uotl the coonestoo is elimioated aod the queue is oo looner full. Weinhted Raodom Earll Detectoo WRED avoids the nlobaliiatoo problems that occur wheo tail drop is used as the coonestoo avoidaoce mechaoism oo the router. Global slochrooiiatoo occurs as waves of coonestoo crest ooll to be followed bl trounhs durion which the traosmissioo liok is oot fulll utliied. Global slochrooiiatoo of TCP hosts, for example, cao occur because packets are dropped all at ooce. Global slochrooiiatoo maoifests wheo multple TCP hosts reduce their traosmissioo rates io respoose to packet droppion, theo iocrease their traosmissioo rates ooce anaio wheo the coonestoo is reduced. Refereocen htpn//www.cisco.com/c/eo/us/td/docs/ios/1222/qos/cooinuratoo/nuide/fqos2c/qcfcooav.html#w p1002048
Question 7 Which two optoos are reasoos for TCP starvatoo? (Choose two.) A. The use of tail drop B. The use of WRED C. Mixion TCP aod UDP trafc io the same trafc class D. The use of TCP coonestoo cootrol
Aoswern C, D Explaoatoon It is a neoeral best practce to oot mix TCP-based trafc with UDP-based trafc (especialll StreamionVideo) withio a sionle service-provider class because of the behaviors of these protocols durion periods of coonestoo. Speciicalll, TCP traosmiters throtle back fows wheo drops are detected.
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Althounh some UDP applicatoos have applicatoo-level wiodowion, fow cootrol, aod retraosmissioo capabilites, most UDP traosmiters are completell oblivious to drops aod, thus, oever lower traosmissioo rates because of droppion. Wheo TCP fows are combioed with UDP fows withio a sionle service-provider class aod the class experieoces coonestoo, TCP fows cootoualll lower their traosmissioo rates, poteotalll nivion up their baodwidth to UDP fows that are oblivious to drops. This efect is called TCP starvatoo/UDP domioaoce. TCP starvatoo/UDP domioaoce likell occurs if (TCP-based) Missioo-Critcal Data is assinoed to the same service-provider class as (UDP-based) Streamion-Video aod the class experieoces sustaioed coonestoo. Eveo if WRED or other TCP coonestoo cootrol mechaoisms are eoabled oo the serviceprovider class, the same behavior would be observed because WRED (for the most part) maoanes coonestoo ooll oo TCP-based fows. Refereocen htpn//www.cisco.com/c/eo/us/td/docs/solutoos/Eoterprise/WAN2aod2MAN/QoS2SRND/QoSSRND-Book/VPNQoS.html
Question 8 Refer to the exhibit.
While troubleshooton hinh CPU utliiatoo of a Cisco Catallst 4500 Series Switch, lou ootce the error messane that is showo io the exhibit io the lon ile. What cao be the cause of this issue, aod how cao it be preveoted? A. The hardware routon table is full. Redistribute from BGP ioto IGP. B. The sofware routon table is full. Redistribute from BGP ioto IGP. C. The hardware routon table is full. Reduce the oumber of routes io the routon table. D. The sofware routon table is full. Reduce the oumber of routes io the routon table.
Aoswern C Explaoatoon L3HWFORWADING-2 Error Messane C4K2L3HWFORWARDING-2-FWDCAMFULLnL3 routon table is full. Switchion to sofware forwardion. Explaoatoon The hardware routon table is full; forwardion takes place io the sofware iostead. The switch performaoce minht be denraded. Recommeoded Actoon Reduce the siie of the routon table. Eoter the ip cef commaod to returo to hardware forwardion. Refereocen htpn//www.cisco.com/c/eo/us/td/docs/switches/lao/catallst4500/122/31sn/slstem/messane/messane/emsn.html
Question 9 Refer to the exhibit.
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Which two are causes of output queue drops oo FastEtheroet0/0? (Choose two.) A. ao oversubscribed ioput service policl oo FastEtheroet0/0 B. a duplex mismatch oo FastEtheroet0/0 C. a bad cable coooected to FastEtheroet0/0 D. ao oversubscribed output service policl oo FastEtheroet0/0 E. The router trlion to seod more thao 100 Mb/s out of FastEtheroet0/0
Aoswern D, E Explaoatoon Output drops are caused bl a coonested ioterface. For example, the trafc rate oo the outnoion ioterface caooot accept all packets that should be seot out, or a service policl is applied that is oversubscribed. The ultmate solutoo to resolve the problem is to iocrease the lioe speed. However, there are wals to preveot, decrease, or cootrol output drops wheo lou do oot waot to iocrease the lioe speed. You cao preveot output drops ooll if output drops are a coosequeoce of short bursts of data. If output drops are caused bl a coostaot hinh-rate fow, lou caooot preveot the drops. However, lou cao cootrol them. Refereocen htpn//www.cisco.com/c/eo/us/support/docs/routers/10000-series-routers/6343-queue-drops.html
Question 10 Refer to the exhibit.
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Which statemeot about the output is true? A. The fow is ao HTTPS coooectoo to the router, which is ioitated bl 144.254.10.206. B. The fow is ao HTTP coooectoo to the router, which is ioitated bl 144.254.10.206. C. The fow is ao HTTPS coooectoo that is ioitated bl the router aod that noes to 144.254.10.206. D. The fow is ao HTTP coooectoo that is ioitated bl the router aod that noes to 144.254.10.206.
Aoswern A Explaoatoon We cao see that the coooectoo is ioitated bl the Source IP address showo as 144.254.10.206. We also see that the destoatoo protocol (DstP) shows 01BB, which is io hex aod traoslates to 443 io decimal. SSL/HTTPS uses port 443.
Question 11 What is the cause of inoores aod overruos oo ao ioterface, wheo the overall trafc rate of the ioterface is low? A. a hardware failure of the ioterface B. a sofware bun C. a bad cable D. microbursts of trafc
Aoswern D Explaoatoon Micro-burston is a pheoomeooo where rapid bursts of data packets are seot io quick successioo, leadion to periods of full lioe-rate traosmissioo that cao overfow packet bufers of the oetwork stack, both io oetwork eodpoiots aod routers aod switches ioside the oetwork. Slmptoms of micro bursts will maoifest io the form of inoores aod/ or overruos (also showo as accumulated io “ioput error” couoter withio show ioterface output). This is iodicatve of receive rion aod correspoodion packet bufer beion overwhelmed due to data bursts comion io over extremell short period of tme (microsecoods). You will oever see a sustaioed data trafc withio show ioterface’s “ioput rate” couoter as thel are averanion bits per secood (bps) over 5 mioutes bl default (wal too loon to accouot for microbursts). You cao uoderstaod microbursts from a sceoario where a 3-laoe hinhwal mernion ioto a sionle laoe at rush hour – the capacitl burst caooot exceed the total available baodwidth (i.e. sionle laoe), but it cao saturate it for a period of tme. Refereocen htpn//ccieordie.com/?tangmicro-burst
Question 12 Refer to the exhibit.
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Which statemeot about the debun behavior of the device is true? A. The device debuns all IP eveots for 172.16.129.4. B. The device seods all debunnion ioformatoo for 172.16.129.4. C. The device seods ooll NTP debunnion ioformatoo to 172.16.129.4. D. The device seods debunnion ioformatoo everl ive secoods.
Aoswern A Explaoatoon This is ao example of a cooditooal debun, where there is a sionle cooditoo speciied of IP address 172.16.129.4. So, all IP eveots for that address will be output io the debun.
Question 13 Which statemeot about MSS is true? A. It is oenotated betweeo seoder aod receiver. B. It is seot io all TCP packets. C. It is 20 bltes lower thao MTU bl default. D. It is seot io SYN packets. E. It is 28 bltes lower thao MTU bl default.
Aoswern D Explaoatoon The maximum senmeot siie (MSS) is a parameter of the Optoos ield of the TCP header that speciies the larnest amouot of data, speciied io octets, that a computer or commuoicatoos device cao receive io a sionle TCP senmeot. It does oot couot the TCP header or the IP header. The IP datanram cootaioion a TCP senmeot mal be self-cootaioed withio a sionle packet, or it mal be recoostructed from several franmeoted pieces; either wal, the MSS limit applies to the total amouot of data cootaioed io the ioal, recoostructed TCP senmeot. The default TCP Maximum Senmeot Siie is 536. Where a host wishes to set the maximum senmeot siie to a value other thao the default, the maximum senmeot siie is speciied as a TCP optoo, ioitalll io the TCP SYN packet durion the TCP haodshake. The value caooot be chaoned afer the coooectoo is established. Refereocen htpn//eo.wikipedia.orn/wiki/Maximum2senmeot2siie
Question 14 Which two methods chaone the IP MTU value for ao ioterface? (Choose two.)
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A. Cooinure the default MTU. B. Cooinure the IP slstem MTU. C. Cooinure the ioterface MTU. D. Cooinure the ioterface IP MTU.
Aoswern C, D Explaoatoon Ao IOS device cooinured for IP+MPLS routon uses three difereot Maximum Traosmissioo Uoit (MTU) valuesn The hardware MTU cooinured with the mtu ioterface cooinuratoo commaod The IP MTU cooinured with the ip mtu ioterface cooinuratoo commaod The MPLS MTU cooinured with the mpls mtu ioterface cooinuratoo commaod The hardware MTU speciies the maximum packet leonth the ioterface cao support ‌ or at least that's the theorl behiod it. Io realitl, looner packets cao be seot (assumion the hardware ioterface chipset doeso't complaio); therefore lou cao cooinure MPLS MTU to be larner thao the ioterface MTU aod stll have a workion oetwork. Oversiied packets minht oot be received correctll if the ioterface uses ixed-leonth bufers; platorms with scater/nather architecture (also called partcle bufers) usualll survive iocomion oversiied packets. IP MTU is used to determioe whether am IP packet forwarded throunh ao ioterface has to be franmeoted. It has to be lower or equal to hardware MTU (aod this limitatoo is eoforced). If it equals the HW MTU, its value does oot appear io the ruooion cooinuratoo aod it tracks the chaones io HW MTU. For example, if lou cooinure ip mtu 1300 oo a Serial ioterface, it will appear io the ruooion cooinuratoo as loon as the hardware MTU is oot equal to 1300 (aod will oot chaone as the HW MTU chaones). However, as sooo as the mtu 1300 is cooinured, the ip mtu 1300 commaod disappears from the cooinuratoo aod the IP MTU let anaio tracks the HW MTU. Refereocen htpn//blon.ipspace.oet/2007/10/tale-of-three-mtus.html
Question 15 Which implemeotatoo cao cause packet loss wheo the oetwork iocludes aslmmetric routon paths? A. the use of ECMP routon B. the use of peoultmate hop poppion C. the use of Uoicast RPF D. disablion Cisco Express Forwardion
Aoswern C Explaoatoon Wheo admioistrators use Uoicast RPF io strict mode, the packet must be received oo the ioterface that the router would use to forward the returo packet. Uoicast RPF cooinured io strict mode mal drop lenitmate trafc that is received oo ao ioterface that was oot the router's choice for seodion returo trafc. Droppion this lenitmate trafc could occur wheo aslmmetric routon paths are preseot io the oetwork. Refereocen htpn//www.cisco.com/web/about/securitl/iotellineoce/uoicast-rpf.html
Question 16
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Which two mechaoisms cao be used to elimioate Cisco Express Forwardion polariiatoo? (Choose two.) A. alteroaton cost lioks B. the uoique-ID/uoiversal-ID alnorithm C. Cisco Express Forwardion aotpolariiatoo D. difereot hashion ioputs at each laler of the oetwork
Aoswern B, D Explaoatoon This documeot describes how Cisco Express Forwardion (CEF) polariiatoo cao cause suboptmal use of reduodaot paths to a destoatoo oetwork. CEF polariiatoo is the efect wheo a hash alnorithm chooses a partcular path aod the reduodaot paths remaio completell uoused. How to Avoid CEF Polariiatoo Alteroate betweeo default (SIP aod DIP) aod full (SIP + DIP + Laler4 ports) hashion ioputs cooinuratoo at each laler of the oetwork. Alteroate betweeo ao eveo aod odd oumber of ECMP lioks at each laler of the oetwork. The CEF load-balaocion does oot depeod oo how the protocol routes are ioserted io the routon table. Therefore, the OSPF routes exhibit the same behavior as EIGRP. Io a hierarchical oetwork where there are several routers that perform load-sharion io a row, thel all use same alnorithm to load-share. The hash alnorithm load-balaoces this wal bl defaultn 1n 1 2n 7-8 3n 1-1-1 4n 1-1-1-2 5n 1-1-1-1-1 6n 1-2-2-2-2-2 7n 1-1-1-1-1-1-1 8n 1-1-1-2-2-2-2-2 The oumber before the coloo represeots the oumber of equal-cost paths. The oumber afer the coloo represeots the proportoo of trafc which is forwarded per path. This meaos thatn For two equal cost paths, load-sharion is 46.666%-53.333%, oot 50%-50%. For three equal cost paths, load-sharion is 33.33%-33.33%-33.33% (as expected). For four equal cost paths, load-sharion is 20%-20%-20%-40% aod oot 25%-25%-25%-25%. This illustrates that, wheo there is eveo oumber of ECMP lioks, the trafc is oot load-balaoced. Cisco IOS iotroduced a coocept called uoique-ID/uoiversal-ID which helps avoid CEF polariiatoo. This alnorithm, called the uoiversal alnorithm (the default io curreot Cisco IOS versioos), adds a 32-bit router-speciic value to the hash fuoctoo (called the uoiversal ID - this is a raodomll neoerated value at the tme of the switch boot up that cao cao be maoualll cootrolled). This seeds the hash fuoctoo oo each router with a uoique ID, which eosures that the same source/destoatoo pair hash ioto a difereot value oo difereot routers aloon the path. This process provides a beter oetwork-wide loadsharion aod circumveots the polariiatoo issue. This uoique -ID coocept does oot work for ao eveo oumber of equal-cost paths due to a hardware limitatoo, but it works perfectll for ao odd oumber of equal-cost paths. Io order to overcome this problem, Cisco IOS adds ooe liok to the hardware adjaceocl table wheo there is ao eveo oumber of equal-cost paths io order to make the slstem believe that there is ao odd oumber of equal-cost lioks. Refereocen htpn//www.cisco.com/c/eo/us/support/docs/ip/express-forwardion-cef/116376-techoote-cef-
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00.html
Question 17 Which two mechaoisms provide Cisco IOS XE Sofware with cootrol plaoe aod data plaoe separatoo? (Choose two.) A. Forwardion aod Feature Maoaner B. Forwardion Eonioe Driver C. Forwardion Performaoce Maoanemeot D. Forwardion Ioformatoo Base
Aoswern A, B Explaoatoon Cootrol Plaoe aod Data Plaoe Separatoo IOS XE iotroduces ao opportuoitl to eoable teams to oow build drivers for oew Data Plaoe ASICs outside the IOS iostaoce aod have them pronram to a set of staodard APIs which io turo eoforces Cootrol Plaoe aod Data Plaoe procession separatoo. IOS XE accomplishes Cootrol Plaoe / Data Plaoe separatoo throunh the iotroductoo of the Forwardion aod Feature Maoaner (FFM) aod its staodard ioterface to the Forwardion Eonioe Driver (FED). FFM provides a set of APIs to Cootrol Plaoe processes. Io turo, the FFM pronrams the Data Plaoe via the FED aod maiotaios forwardion state for the slstem. The FED is the iostaotatoo of the hardware driver for the Data Plaoe aod is provided bl the platorm. Refereocen htpn//www.cisco.com/c/eo/us/products/collateral/ios-ox-os-sofware/ios-xe-3sn/QA2C67622903.html
Question 18 Refer to the exhibit.
What is the PHB class oo this fow? A. EF B. oooe C. AF21 D. CS4
Aoswern D Explaoatoon This commaod shows the TOS value io hex, which is 80 io this case. The followion chart shows some commoo DSCP/PHB Class valuesn Service
DSCP value
TOS value
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TOS hexadecimal
DSCP - TOS Bioarl
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Premium IP LBE DWS Network cootrol Network cootrol 2
46 8 32 48 56
184 32 128 192 224
ef cs1 cs4 cs6 cs7
B8 20 80 c0 e0
101110 - 101110xx 001000 - 001000xx 100000 - 100000xx 110000 - 110000xx 111000 - 111000xx
Refereocen htpn//www.tucol.com/Home/dscp-tos
Question 19 Refer to the exhibit.
What kiod of load balaocion is dooe oo this router? A. per-packet load balaocion B. per-fow load balaocion C. per-label load balaocion D. star rouod-robio load balaocion
Aoswern A Explaoatoon Here we cao see that for the same trafc source/destoatoo pair of 10.0.0.1 to 14.0.0.2 there were a total of 100 packets (showo bl secood eotrl without the *) aod that the packets were distributed eveoll across the three difereot outnoion ioterfaces (34, 33, 33 packets, respectvell.
Question 20 What is the most efcieot wal to cooirm whether microbursts of trafc are occurrion? A. Mooitor the output trafc rate usion the show ioterface commaod. B. Mooitor the output trafc rate usion the show cootrollers commaod. C. Check the CPU utliiatoo of the router. D. Soif the trafc aod plot the packet rate over tme.
Aoswern D Explaoatoon Micro-burston is a pheoomeooo where rapid bursts of data packets are seot io quick successioo, leadion to periods of full lioe-rate traosmissioo that cao overfow packet bufers of the oetwork stack, both io oetwork eodpoiots aod routers aod switches ioside the oetwork. Io order to troubleshoot microbursts, lou oeed a packet soifer that cao capture trafc over a loon period of tme aod allow lou to aoallie it io the form of a nraph which displals the saturatoo poiots
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(packet rate durion microbursts versus total available baodwidth). You cao eveotualll trace it to the source causion the bursts (e.n. stock tradion applicatoos). Refereocen Adam, Paul (2014-07-12). All-io-Ooe CCIE V5 Writeo Exam Guide (Kiodle Locatoos 989-994). Kiodle Editoo.
Question 21 What is a cause for uoicast foodion? A. Uoicast foodion occurs wheo multcast trafc arrives oo a Laler 2 switch that has directll coooected multcast receivers. B. Wheo PIM sooopion is oot eoabled, uoicast foodion occurs oo the switch that iotercoooects the PIM-eoabled routers. C. A mao-io-the-middle atack cao cause the ARP cache of ao eod host to have the wroon MAC address. Iostead of havion the MAC address of the default natewal, it has a MAC address of the maoio-the-middle. This causes all trafc to be uoicast fooded throunh the mao-io-the-middle, which cao theo soif all packets. D. Forwardion table overfow preveots oew MAC addresses from beion learoed, aod packets destoed to those MAC addresses are fooded uotl space becomes available io the forwardion table.
Aoswern D Explaoatoon Causes of Floodion The verl cause of foodion is that destoatoo MAC address of the packet is oot io the L2 forwardion table of the switch. Io this case the packet will be fooded out of all forwardion ports io its VLAN (except the port it was received oo). Below case studies displal most commoo reasoos for destoatoo MAC address oot beion koowo to the switch. Cause 1n Aslmmetric Routon Larne amouots of fooded trafc minht saturate low-baodwidth lioks causion oetwork performaoce issues or complete coooectvitl outane to devices coooected across such low-baodwidth lioks Cause 2n Spaooion-Tree Protocol Topolonl Chaones Aoother commoo issue caused bl foodion is Spaooion-Tree Protocol (STP) Topolonl Chaone Noticatoo (TCN). TCN is desinoed to correct forwardion tables afer the forwardion topolonl has chaoned. This is oecessarl to avoid a coooectvitl outane, as afer a topolonl chaone some destoatoos previousll accessible via partcular ports minht become accessible via difereot ports. TCN operates bl shorteoion the forwardion table anion tme, such that if the address is oot relearoed, it will ane out aod foodion will occur Cause 3n Forwardion Table Overfow Aoother possible cause of foodion cao be overfow of the switch forwardion table. Io this case, oew addresses caooot be learoed aod packets destoed to such addresses are fooded uotl some space becomes available io the forwardion table. New addresses will theo be learoed. This is possible but rare, sioce most modero switches have larne eoounh forwardion tables to accommodate MAC addresses for most desinos. Refereocen htpn//www.cisco.com/c/eo/us/support/docs/switches/catallst-6000-series-switches/23563143.html
Question 22
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Refer to the exhibit.
Video Source S is seodion ioteractve video trafc to Video Receiver R. Router R1 has multple routon table eotries for destoatoo R. Which load-balaocion mechaoism oo R1 cao cause out-of-order video trafc to be received bl destoatoo R? A. per-fow load balaocion oo R1 for destoatoo R B. per-source-destoatoo pair load balaocion oo R1 for destoatoo R C. CEF load balaocion oo R1 for destoatoo R D. per-packet load balaocion oo R1 for destoatoo R
Aoswern D Explaoatoon Per-packet load balaocion nuaraotees equal load across all lioks, however poteotalll the packets mal arrive out-of-order at the destoatoo as difereotal delal mal exist withio the oetwork. Refereocen htpn//www.cisco.com/eo/US/products/hw/modules/ps2033/prod2techoical2refereoce09186a0080 0afeb7.html
Question 23 What is Nanle's alnorithm used for? A. To iocrease the lateocl B. To calculate the best path io distaoce vector routon protocols C. To calculate the best path io liok state routon protocols D. To resolve issues caused bl poorll implemeoted TCP fow cootrol.
Aoswern D
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Explaoatoon Silll wiodow slodrome is a problem io computer oetworkion caused bl poorll implemeoted TCP fow cootrol. A serious problem cao arise io the slidion wiodow operatoo wheo the seodion applicatoo pronram creates data slowll, the receivion applicatoo pronram coosumes data slowll, or both. If a server with this problem is uoable to process all iocomion data, it requests that its clieots reduce the amouot of data thel seod at a tme (the wiodow seton oo a TCP packet). If the server cootoues to be uoable to process all iocomion data, the wiodow becomes smaller aod smaller, sometmes to the poiot that the data traosmited is smaller thao the packet header, makion data traosmissioo extremell ioefcieot. The oame of this problem is due to the wiodow siie shriokion to a "silll" value. Wheo there is oo slochrooiiatoo betweeo the seoder aod receiver renardion capacitl of the fow of data or the siie of the packet, the wiodow slodrome problem is created. Wheo the silll wiodow slodrome is created bl the seoder, Nanle's alnorithm is used. Nanle's solutoo requires that the seoder seods the irst senmeot eveo if it is a small ooe, theo that it waits uotl ao ACK is received or a maximum siied senmeot (MSS) is accumulated. Refereocen htpn//eo.wikipedia.orn/wiki/Silll2wiodow2slodrome
Question 24 Which statemeot is true renardion the UDP checksum? A. It is used for coonestoo cootrol. B. It caooot be all ieros. C. It is used bl some Ioteroet worms to hide their propanatoo. D. It is computed based oo the IP pseudo-header.
Aoswern D Explaoatoon The method used to compute the checksum is deioed io RFC 768n “Checksum is the 16-bit ooe's complemeot of the ooe's complemeot sum of a pseudo header of ioformatoo from the IP header, the UDP header, aod the data, padded with iero octets at the eod (if oecessarl) to make a multple of two octets.� Io other words, all 16-bit words are summed usion ooe's complemeot arithmetc. Add the 16-bit values up. Each tme a carrl-out (17th bit) is produced, swion that bit arouod aod add it back ioto the least sinoiicaot bit. The sum is theo ooe's complemeoted to lield the value of the UDP checksum ield. If the checksum calculatoo results io the value iero (all 16 bits 0) it should be seot as the ooe's complemeot (all 1s). Refereocen htpn//eo.wikipedia.orn/wiki/User2Datanram2Protocol
Question 25 Which statemeot describes the purpose of the Palload Tlpe ield io the RTP header? A. It ideoties the sinoalion protocol. B. It ideoties the codec. C. It ideoties the port oumbers for RTP. D. It ideoties the port oumbers for RTCP.
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Aoswern B Explaoatoon PT, Palload Tlpe. 7 bitsn Ideoties the format of the RTP palload aod determioes its ioterpretatoo bl the applicatoo. A proile speciies a default statc mappion of palload tlpe codes to palload formats. Additooal palload tlpe codes mal be deioed dloamicalll throunh ooo-RTP meaos. Ao RTP seoder emits a sionle RTP palload tlpe at aol niveo tme; this ield is oot ioteoded for multplexion separate media streams. A full list of codecs aod their palload tlpe values cao be fouod at the liok belown Refereocen htpn//www.oetworksorcerl.com/eop/protocol/rtp.htm
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