642-902 exam

CCCEEERRRTTT MMMAAAGGGIIICCC

Demo Edition

Implementing Cisco IP Routing

Exam: 642-902

642-902

1 http://www.certmagic.com

QUESTION: 1The Company WAN is displayed in the following diagram:

Traffic from Company4 to the Company Corporate Network is distributed between thelinks with unequal costs in the EIGRP network by configuring the variance command onCompany4 to 2. How many paths will participate in the load sharing?

A. 1B. 2C. 3D. 4E. 5F. 6

Answer: B

Explanation:If a path is not a feasible successor, the path is not used in load balancing. In this case theFD is 10, which means that only the paths with a total distance of 20 or less will bechosen. This leaves us only the paths from Company4-Company5-Company6 andCompany4-Company7-Company8.

Reference:CCNP Self-Study CCNP BSCI Exam certification guide p.485

QUESTION: 2Five Company routers are connected together as shown in the diagram below: Exhibit:

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You work as a network engineer at Company.com. You study the exhibit carefully.Company1 and Company2 are summarizing the 10.0.0.0/8 network and advertising it to allrouters. Which two EIGRP configurations will prevent unnecessary EIGRP updates frombeing sent and possibly causing 10.0.0.0/8 from being SIA on router Company1 orCompany2? (Select two)

A. Configure Company3, Company4, and Company5 as EIGRP stub routers.B. Configure an ACL on the interface of Company1 and Company2.C. Configure Company1 and Company2 as EIGRP stub routers.D. Configure summary routes on Company1 and Company2E. Configure static routing on Company3, Company4, and Company5

Answer: A, D

Explanation:A dual-homed remote will have two or more distribution (hub) routers. However, theprinciples of stub routing are the same as they are with a hub and spoke topology.

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It is not desirable for traffic from distribution router 2 to travel through any remote routerin order to reach network 10.3.1.0/24. If the links are sized to handle the load, it would beacceptable to use one of the backup routes. However, most networks of this type haveremote routers located at remote offices with relatively slow links. This problem can beprevented if proper summarization is configured on the distribution router and remoterouter. It is typically undesirable for traffic from a distribution router to use a remote routeras a transit path. A typical connection from a distribution router to a remote router wouldhave much less bandwidth than a connection at the network core. Attempting to use aremote router with a limited bandwidth connection as a transit path would generallyproduce excessive congestion to the remote router. The EIGRP Stub Routing feature canprevent this problem by preventing the remote router from advertising core routes back todistribution routers. Routes learned by the remote router from distribution router 1 will notbe advertised to distribution router 2. Since the remote router will not advertise core routesto distribution router 2, the distribution router will not use the remote router as a transit fortraffic destined for the network core.

Reference:http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a0080087026.html

QUESTION: 3Two Company EIGRP routers are attempting to establish themselves as neighbors. WhichEIGRP multicast packet type is responsible for neighbor discovery?

A. UpdateB. Query

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C. AcknowledgmentD. ReplyE. HelloF. None of the other alternatives apply

Answer: E

Explanation:Remember that simple distance vector routers do not establish any relationship with theirneighbors. RIP andIGRP routers merely broadcast or multicast updates on configuredinterfaces. In contrast, EIGRP routers actively establish relationships with their neighbors,much the same way that OSPF routers do.EIGRP routers establish adjacencies withneighbor routers by using small hello packets. Hellos are sent bydefault every fiveseconds. An EIGRP router assumes that as long as it is receiving hello packets fromknownneighbors, those neighbors (and their routes) remain viable. By formingadjacencies, EIGRP routers do thefollowing: Dynamically learn of new routes that jointheir network Identify routers that become either unreachable or inoperable Rediscoverrouters that had previously been unreachable

QUESTION: 4Company has chosen to use EIGRP for their network routing protocol. Which threestatements are true regarding EIGRP? (Select three)

A. By default, EIGRP uses the Dijkstra algorithm to determine the best path to adestination network based on bandwidth and delay.B. To speed convergence, EIGRP attempts to maintain a successor and feasible successorpath for each destination.C. EIGRP uses hellos to establish neighbor relationships.D. By default, EIGRP performs auto-summarization across classful network boundaries.E. EIGRP uses an area hierarchy to increase network scalability.

Answer: B, C, D

Explanation:The default behavior of EIGRP routers is to automatically summarize routes at thenetwork boundary.EIGRP routers maintain information regarding the successors and thefeasible successors to each network destination. This information is useful in theconvergence time whenever any of the links fail.EIGRP neighbors periodically use hellosto establish the relationship. Should any of the neighbors fail,triggered updates are sent toupdate the network regarding the topology change.

Incorrect Answer:

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A: The Dijkstra algorithm is used by link state routing protocols. EIGRP is considered tobe a hybrid routingprotocol.E: EIGRP networks are inherently flat, as each router is perceived as a peer to every otherEIGRP router. IS-ISand OSPF utilize hierarchical network topologies.

QUESTION: 5You need to configure EIGRP on all routers within the Company network. Which twostatements are Characteristics of the routing protocol EIGRP ? (Select two)

A. Updates are sent as broadcast.B. Updates are sent as multicast.C. LSAs are sent to adjacent neighbors.D. Metric values are represented in a 32-bit format for granularity.

Answer: B, D

Explanation:EIGRP routers establish adjacencies with neighbor routers by using small hello packets.These packets are sent to the multicast IP address of 224.0.0.10. Hellos are sent by defaultevery five seconds. An EIGRP router assumes that as long as it is receiving hello packetsfrom known neighbors, those neighbors (and their routes) remain viable. By formingadjacencies, EIGRP routers do the following:

• Dynamically learn of new routes that join their network

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• Identify routers that become either unreachable or inoperable• Rediscover routers that had previously been unreachable

QUESTION: 6You have been tasked with setting up summarization in the Company EIGRP network.Which two statements are true about EIGRP manual summarization? (Select two)

A. Manual summarization is configured on a per interface basis.B. When manual summarization is configured, auto-summarization is automaticallydisabled by default.C. The summary address is assigned an administrative distance of 10 by default.D. Manual summaries can be configured with the classful mask only.E. The summary address is entered into the routing table and is shown to be sourced fromthe Null0 interface.

Answer: A, E

Explanation:EIGRP automatically summarizes routes at the classful boundary, the boundary where thenetwork address endsas defined by class-based addressing. In most cases, autosummarization is a good thing, keeping the routing tables as compact as possible In thepresence of discontinuous sub networks, automatic summarization must be disabled forrouting to work properly. To turn off auto- summarization, use the followingcommand:Router(config-router)#no auto-summaryEIGRP also enables manualconfiguration of a prefix to use as a summary address. Manual summary routesareconfigured on a per-interface basis. The interface that will propagate the route summarymust first be selectedand then defined with the ip summary-address eigrp command, whichhas the following syntax:Router(config-if)#ip summary-address eigrp autonomous-system-number ip- address maskadministrative-distanceD 2.1.0.0/16 is a summary, 00:00:22,Null0Notice that the summary route is sourced from Null0, and not an actual interface.

QUESTION: 7Router Company14 is configured as an EIGRP stub router. What are three key conceptsthat apply when configuring the EIGRP stub routing feature in a hub and spoke network?(Select three)

A. Stub routers are not queried for routes.B. A hub router prevents routes from being advertised to the remote router.C. A stub router should have only EIGRP hub routers as neighbors.D. EIGRP stub routing should be used on hub routers only.E. Spoke routers connected to hub routers answer the route queries for the stub router.F. Only remote routers are configured as stubs.

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Answer: A, C, F

Explanation:The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improvesnetwork stability,reduces resource utilization, and simplifies stub router configuration.Stubrouting is commonly used in a hub and spoke network topology. In a hub and spokenetwork, one or moreend (stub) networks are connected to a remote router (the spoke) thatis connected to one or more distributionrouters (the hub). The remote router is adjacentonly to one or more distribution routers. The only route for IPtraffic to follow into theremote router is through a distribution router. This type of configuration is commonlyusedin WAN topologies where the distribution router is directly connected to a WAN. Thedistribution routercan be connected to many more remote routers. Often, the distributionrouter will be connected to 100 or moreremote routers. In a hub and spoke topology, theremote router must forward all nonlocal traffic to a distributionrouter, so it becomesunnecessary for the remote router to hold a complete routing table. Generally,thedistribution router need not send anything more than a default route to the remoterouter.When using the EIGRP Stub Routing feature, you need to configure the distributionand remote routers to useEIGRP, and to configure only the remote router as a stub. Onlyspecified routes are propagated from the remote(stub) router. The router responds toqueries for summaries, connected routes, redistributed static routes,external routes, andinternal routes with the message "inaccessible." A router that is configured as a stubwillsend a special peer information packet to all neighboring routers to reportitsstatusasastub router.

Reference:http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120limit/120s/120s15/eigrpstb.htm

QUESTION: 8You want to reduce the amount of EIGRP traffic across low speed links in the Companynetwork. Which is the most effective technique to contain EIGRP queries?

A. Using a hierarchical addressing schemeB. Configuring route filtersC. Establishing separate autonomous systemsD. Route summarizationE. None of the other alternatives apply

Answer: D

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Explanation:EIGRP automatically summarizes routes at the classful boundary, the boundary where thenetwork address endsas defined by class-based addressing. In most cases, autosummarization is a good thing, keeping the routingtables as compact as possibleIn thepresence of discontiguous subnetworks, automatic summarization must be disabled forrouting to workproperly. To turn off auto-summarization, use the followingcommand:Router(config-router)#no auto-summaryEIGRP also enables manualconfiguration of a prefix to use as a summary address. Manual summary routesareconfigured on a per-interface basis. The interface that will propagate the route summarymust first be selectedand then defined with the ip summary-address eigrp command, whichhas the following syntax:Router(config-if)#ip summary-address eigrp autonomous-system-number ip- address maskadministrative-distance

QUESTION: 9Routers Company1 and Company2 have formed an EIGRP neighbor relationship. In orderfor two routers to become EIGRP neighbors, which two values must match? (Select two)

A. K valuesB. DelayC. Autonomous systemD. Hello timeE. Hold timeF. Bandwidth

Answer: A, C

Explanation:Despite being compatible with IGRP, EIGRP uses a different metric calculation and hop-count limitation.EIGRP scales the IGRP metric by a factor of 256. That is because EIGRPuses a metric that is 32-bits long, andIGRP uses a 24-bit metric. By multiplying ordividing by 256, EIGRP can easily exchange information withIGRP.EIGRP also imposes amaximum hop limit of 224, which is slightly less than the 255 limit for IGRP.However,this is more than enough to support most of the largest internetworks. To becomethe neighbor K value shouldbe matched and should belongs to same AS.

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QUESTION: 10Company uses EIGRP as their internal routing protocol. Which three statements are trueabout EIGRP operation? (Select three)

A. The maximum metric for the specific routes is used as the metric for the summaryroute.B. When summarization is configured, the router will also create a route to null 0.C. The summary route remains in the route table, even if there are no more specific routesto the network.D. Automatic summarization across major network boundaries is enabled by default.E. Summarization is configured on a per-interface level.

Answer: B, D, E

Explanation:Using the ip summary-address eigrp summarization command will causes the creation ofan EIGRP summarydefault route to the null 0 interface with an administrative distance of5. Caution should be taken when usingthis as a default route. The low administrativedistance of this default route can cause this route to displacedefault routes learned fromother neighbors from the routing table. If the default route learned from theneighbors isdisplaced by the summary default route, or if the summary route is the only default routepresent,all traffic destined for the default route will not leave the router, instead, this trafficwill be sent to the null 0interface where it is dropped.By default, Cisco routers willautomatically summarize EIGRP routes across major network boundaries. WithEIGRP,

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You can configure a summary aggregate address for a specified interface. If there are anymore specificroutes in the routing table, EIGRP will advertise the summary address out theinterface with a metric equal tothe minimum of all more specific routes.

Incorrect Answer:A: The metric used in a summary route is the best metric from among the summarizedroutes, not themaximum (worst).C: When all of the specific routes used within a summary route are deleted from therouting table, the summaryroute will also be deleted.

QUESTION: 11A link failure in the Company network has caused the EIGRP routers to update theirrouting tables. What action does Company1, an EIGRP router, take when it cannot find afeasible successor for a network?

A. It examines the topology table for a next best path.B. It transitions from passive to active state for that network and queries its neighbors.C. It examines the routing and neighbor tables for the next best path.D. It transitions from active to passive state for that network and queries its neighbors.E. None of the other alternatives apply

Answer: B

Explanation:With EIGRP, A topology table entry for a destination can have one of two states. A routeis considered in thePassive state when a router is not performing a route recomputation.The route is in Active state when a routeris undergoing a route recomputation. If there arealways feasible successors, a route never has to go into Activestate and avoids a routerecomputation.When there are no feasible successors, a route goes into Active state and aroute recomputation occurs. A routerecomputation commences with a router sending aquery packet to all neighbors. Neighboring routers can eitherreply if they have feasiblesuccessors for the destination or optionally return a query indicating that theyareperforming a route recomputation. While in Active state, a router cannot change thenext-hop neighbor it isusing to forward packets. Once all replies are received for a givenquery, the destination can transition toPassive state and a new successor can be selected.

QUESTION: 12EIGRP performs automatic summarization at network boundaries. What administrativedistance is given to these EIGRP summary routes?

A. 1

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B. 90C. 95D. 0E. 5F. 170G. 255H. None of the other alternatives apply

Answer: E

Explanation:EIGRP automatically summarizes routes at the classful boundary, the boundary where thenetwork address endsas defined by class-based addressing. In most cases, autosummarization is a good thing, keeping the routingtables as compact as possibleIn thepresence of discontiguous subnetworks, automatic summarization must be disabled forrouting to workproperly. To turn off auto-summarization, use the followingcommand:Router(config-router)#no auto-summaryDefault Administrative Distance

QUESTION: 13You need to alter the metrics of certain EIGRP routes in the Company network. Whichtwo parameters are used by default to compute the EIGRP metric? (Select two)

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A. MTUB. BandwidthC. DelayD. ReliabilityE. LoadF. Interface up time

Answer: B, C

Explanation:Metrics are the mathematics used to select a route. The higher the metric associated with aroute, the lessdesirable it is. For EIGRP, the Bellman-Ford algorithm uses the followingequation and creates the overall24-bit metric assigned to a route:?? metric = [(K1bandwidth) + [(K2 bandwidth) (256 - load)] + (K3 delay)] [K5 (reliability + K4)]Theelements in this equation are as follows:?? By default, K1 = K3 = 1, K2 = K4 = K5 = 0.Therefore, by default, the metric formulareduces to:metric = (1 bandwidth) + (1delay)metric = bandwidth + delay

QUESTION: 14The Company network is using EIGRP as the network routing protocol. Which of thefollowing statements correctly describe features and characteristics of routing usingEIGRP? (Select three)

A. It sends periodic updates every 60 seconds.B. EIGRP uses DUAL to achieve rapid convergence.C. Adjacencies exist between master routers (MRs) in each domain.D. It uses multicast to discover other EIGRP routers on an internetwork.E. EIGRP provides support for multiple network layer protocols: IPX, AppleTalk, and IP.

Answer: B, D, E

Explanation:B: Enhanced IGRP uses the Diffusing Update based algorithm (DUAL).D: EIGRP use hello multicast packets for neighbor discovery/recovery.E: EIGRP supports IPX, Appletalk, and IP. Separate EIGRP instances can be created foreach routed protocol.

Incorrect Answer:A: EIGRP use triggered updates, not periodic updates.C: Each EIGRP router maintains a neighbor table that lists adjacent routers. However,there is no concept ofmaster router in EIGRP.

Reference:

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"Introduction to Enhanced IGRP (EIGRP)" Cisco website

QUESTION: 15While comparing the tables associated with EIGRP and OSPF, you notice somesimilarities. Which EIGRP table is similar to OSPF’s Link State Adjacency table?

A. Neighbor tableB. Routing tableC. Topology tableD. Successor tableE. None of the other alternatives apply

Answer: A

Explanation:Each EIGRP router maintains a neighbor table that lists adjacent routers. This table iscomparable to theneighbors (adjacency) database used by OSPF .

Incorrect Answer:B: The routing table of EIGRP would compare to the routing table of OSPFC: Both EIGRP and OSPF contain topology tables, which would compare to each other.D: EIGRP does not have a successor table. Successors are maintained in the routing andtopology tables ofEIGRP.

Reference:Building Scalable Cisco Networks (Cisco Press) page 250

QUESTION: 16Which of the following protocols is used in large networks working as service providers?

A. Intermediate System-to-Intermediate System protocol (IS-IS)B. Enhanced Interior Gateway Routing protocol (EIGRP)C. External Border Gateway protocol (eBGP)D. Open Shortest Path First protocol (OSPF)

Answer: A

QUESTION: 17Different types of EIGRP transmissions are sent between neighboring routers. Which threeof the following terms are known as ‘reliable packets’ in EIGRP? (Select three)

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A. HelloB. ACKC. ReplyD. QueryE. Update

Answer: C, D, E

Explanation:Updates are used to convey the reachability of destinations. When a new neighbor isdiscovered, update packetsare sent so the neighbor can build up its topology table. In thiscase, update packets are unicast. In other cases,such as a link cost change, updates aremulticast. Updates are always transmitted reliably.Queries and replies are sent whendestinations go into Active state. Queries are always multicast unless they aresent inresponse to a received query. In this case, it is unicast back to the successor that originatedthe query.Replies are always sent in response to queries to indicate to the originator that itdoes not need to go into Activestate because it has feasible successors. Replies are unicastto the originator of the query. Both queries andreplies are transmitted reliably.EIGRPreliable packets are: Update, Query and Reply.EIGRP unreliable packets are: Hello andAck.

Incorrect Answer:A, B: Hellos are multicast for neighbor discovery/recovery. They do not requireacknowledgment. A hello withno data is also used as an acknowledgment (ack). Acks arealways sent using a unicast address and contain anon-zero acknowledgment number.

Reference:Cisco BSCN version 1.0 study guide, pages 6-18.

QUESTION: 18Which one of the following statements best describes the way EIGRP advertises subnetmask information to its destination networks?

A. EIGRP advertises a prefix length for each destination network.B. EIGRP advertises a fixed length subnet mask for each destination network.C. EIGRP advertises only a classful subnet mask for each destination network.D. EIGRP, like IGRP and RIP, does not advertise a subnet mask for each destinationnetwork.

Answer: A

Explanation:

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EIGRP advertises a prefix length to each destination network. It supports VLSM whichallows subnet masks tobe automatically summarized at the network boundary, and EIGRPcan also be configured to summarize on anybit boundary at any interface.

Incorrect Answer:B: This is incorrect because EIGRP supports Variable Length subnet masks.C: This is incorrect because EIGRP is considered to be a classless protocol, not classful.D: EIGRP is more sophisticated then IGRP and RIP and actually does advertise a subnetmask to eachdestination network.

QUESTION: 19EIGRP was designed specifically not to use excessive bandwidth for routing updates andfunctions across WAN links. If EIGRP is configured on an interface, what is the maximumpercent of its bandwidth EIGRP would use, by default?

A. 10%B. 25%C. 50%D. 75%E. 100%

Answer: C

Explanation:By default, EIGRP will limit itself to using no more than 50% of the available bandwidth.The maximumbandwidth that can be used is a configurable parameter.

Reference:Cisco, Configuration Notes for the Enhanced Implementation ofEIGRP.http://www.cisco.com/warp/public/103/12.html

QUESTION: 20EIGRP supports Variable Length Subnet Masking (VLSM). Which two features of EIGRPare true regarding EIGRP support for VLSM? (Select two)

A. It advertises a routing maskB. It is a classful routing protocolC. It is a classless routing protocolD. It does not advertise a routing mask.

Answer: A, C

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Explanation:EIGRP includes the routing mask when it advertises routes. Subnet mask information mustbe included in allrouting updates for classless protocols. EIGRP is a classless protocol,meaning that is does not solely rely onthe network class in order to find the subnet mask.These two features enable EIGRP to support VLSM.

Incorrect Answer:B: Classful routing protocols do not support VLSM.D: The subnet mask must be included in the route to support VLSM.

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642-902 exam

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