ActualTests.Cisco.640-802.Exam.Q.and.A.08.15.08-DDU (1130589), страница 57
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There is concern that a lack of router resources is impedinginternetwork performance. As part of examining the router resources, the OSPFDRs need to be known. All the router OSPF priorities are at the default and therouter IDs are shown with each router.Which routers are likely to have been elected as DR? (Choose two)A. Certkiller -1B. Certkiller -2C. Certkiller -3D. Certkiller -4E. Branch-1F.
Branch-2Answer: D, FExplanation:Actualtests.com - The Power of Knowing640-802DR and BDR election is done via the Hello protocol. Hello packets are exchanged via IPmulticast packets (Appendix B) on each segment. The router with the highest OSPFpriority on a segment will become the DR for that segment. The same process is repeatedfor the BDR.
In case of a tie, the router with the highest RID will win. The default for theinterface OSPF priority is one. Remember that the DR and BDR concepts are permulti-access segment. Setting the OSPF priority on an interface is done using the ip ospfpriority interface command.A priority value of zero indicates an interface which is not to be elected as DR or BDR.The state of the interface with priority zero will be DROTHER. The following diagramillustrates the DR election:In the above diagram, RTA and RTB have the same interface priority but RTB has ahigher RID.
RTB would be DR on that segment. RTC has a higher priority than RTB.RTC is DR on that segment.The default RID is the highest IP address that is active in the router. Based on this info,router Certkiller -4 and Branch-2 will most likely be elected as the DR in their respectivenetworks.QUESTION 506:Certkiller is using OSPF in their WAN. What is the maximum number of hopsOSPF allows before it deems a network unreachable?A.
15B. 16C. 99D. 255E. UnlimitedF. None of the aboveAnswer: EExplanation:Actualtests.com - The Power of Knowing640-802OSPF is a link state protocol. Link state protocols do not use hops to mark networks asunreachable. Instead OSPF implements a steady state operation to its adjacent neighborsby sending and receiving small Hello packets periodically. When an OSPF router doesnot receive a Hello packet for a specified time period, it assumes that the neighbor isdown.
The router then runs the SPF algorithm to calculate new routes.Reference:Certkiller 640-801 Study Guide, Section 5.2 "Steady State Operation".Incorrect Answers:A. This is the maximum number of hops that a RIP network could use before the route isdeemed unreachable.B. When a RIP routes receives a routing update for a route that shows a hop count of 16,the route is considered to be unreachable. RIP routers use this to prevent packets fromlooping through the network indefinitely, but OSPF routers do not.QUESTION 507:On the topic of the OSPF hello protocol; which of the statements below are true?(Select two answer choices)A.
The OSPF Hello protocol provides dynamic neighbor discovery.B. The OSPF Hello protocol detects unreachable neighbors in 90 second intervals.C. The OSPF Hello protocol maintains neighbor relationships.D. The OSPF Hello protocol negotiates correctness parameters between neighboringinterfaces.E. The OSPF Hello protocol uses timers to elect the router with the fastest links at thedesignated router.F. The OSPF Hello protocol broadcast hello packets throughout the internetwork todiscover all routers that are running OSPF.Answer: A, CExplanation:The Hello PacketOSPF contains a protocol (the Hello protocol) that is used to establish and maintainrelationships between neighboring nodes. These relationships are called adjacencies.Adjacencies are the basis for the exchange of routing data in OSPF.It is through the use of this protocol, and packet type, that an OSPF node discovers theother OSPF nodes in its area.
Its name is intentionally significant; the Hello protocolestablishes communications between potential neighboring routers. The Hello protocoluses a special subpacket structure that is appended to the standard 24-octet OSPF header.Together, these structures form a hello packet.All routers in an OSPF network must adhere to certain conventions that must be uniformthroughout the network.
These conventions include the following:1. The network maskActualtests.com - The Power of Knowing640-8022. The interval at which hello packets will be broadcast (the hello interval)3. The amount of time that must elapse before a non responding router will be declareddead (that is, the router dead interval) by the other routers in the network4. All routers in an OSPF network must agree to use the same value for each of theseparameters; otherwise, the network might not operate properly.
These parameters areexchanged using hello packets. Together, they comprise the basis for neighborlycommunications. They ensure that neighbor relationships (known as adjacencies)are not formed between routers in different subnets and that all members of thenetwork agree on how frequently to stay in contact with each other.The hello packet also includes a listing of other routers (using their unique router IDs)that the source router has recently been in contact with. This field, the Neighbor field,facilitates the neighbor discovery process. The hello packet also contains several otherfields such as Designated Router and Backup Designated Router. These fields are usefulin maintaining adjacencies and support the operation of the OSPF network in bothperiods of stability and convergence.QUESTION 508:You are an administrator and you've just configured OSPF on a router with bothphysical and logical interfaces.
Which of the following factors determine the routerID?A. The lowest network number of any interface.B. The highest network number of any interface.C. The highest IP address of any logical interface.D. The middle IP address of any logical interface.E. The lowest IP address of any physical interface.F.
The highest IP address of any physical interface.G. The lowest IP address of any logical interface.Answer: CExplanation:Physical interface address is used only if there are no loopback addresses.Sybex 5th p. 308:"Router ID The Router ID (RID) is an IP address used to identify the router.Cisco chooses the Router ID by using the highest IP address of allconfigured loopback interfaces. If no loopback interfaces are configuredwith addresses, OSPF will choose the highest IP address of all activephysical interfaces."QUESTION 509:Under which network type circumstance would an OSPF router establish routerActualtests.com - The Power of Knowing640-802adjacencies while not performing the DR/BDR election process?A.
Point-to-pointB. BroadcastC. Non-broadcast multi-accessD. Backbone area 0E. None of the aboveAnswer: AExplanation:If there's a point to point connection, there's no need for a designated router or a backupdesignated router election since only two routers can exist on a point to point networksegment.Incorrect Answers:B, C. All OSPF routers in a broadcast and non-broadcast multi-access network gothrough the DR and BDR election process.D. The backbone area is not a network type, but a collection of OSPF networks links.Area 0 is reserved as the backbone area, and routers within area 0 may or may not gothrough the DR/BDR election process, depending on the network type.QUESTION 510:On the topic of OSPF routing; which of the following are the traits of an OSPFarea? (Select three)A.
Each OSPF area requires a loopback interface to be configured.B. Areas may be assigned any number from 0 to 65535.C. Area 0 is called the backbone area.D. OSPF networks do not require multiple areas.E. Multiple OSPF areas must connect to area 0.F. Single area OSPF networks must be configured in area 1.Answer: C, D, EExplanation:OPSF uses areas in a hierarchical fashion, and the backbone area is always area 0. Allother areas have at least one connection to area 0. If, for some reason, any area does nothave a direct connection to the backbone area 0, then an OSPF virtual link must beconfigured.
OSPF networks do not require multiple areas, as all routers can be containedwithin a single area. If an OSPF network is configured as a single area, then area 0 doesnot need to be used.Incorrect Answers:A. Loopback interfaces are often used in OSPF networks, so that the router ID can beActualtests.com - The Power of Knowing640-802configured. However, this is not a requirement.B. The area-id can be an integer between 0 and 4294967295.F.
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