ActualTests.Cisco.640-802.Exam.Q.and.A.08.15.08-DDU (1130589), страница 20
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This address is hardcoded, unique, and cannot be changed.The election process begins with every switch sending out BPDUs with a Root Bridge IDequal to its own Bridge ID as well as a Sender Bridge ID. The latter is used to identifythe source of the BPDU message. Received BPDU messages are analyzed for a lowerRoot Bridge ID value. If the BPDU message has a Root Bridge ID (priority) of the lowervalue than the switch's own Root Bridge ID, it replaces its own Root Bridge ID with theRoot Bridge ID announced in the BPDU. If two Bridge Priority values are equal, then thelower MAC address takes preference.QUESTION 166:Which of the protocols below, operates at Layer 2 of the OSI model, and is used tomaintain a loop-free network?A.
RIPB. STPActualtests.com - The Power of Knowing640-802C. IGRPD. CDPE. VTPF. None of the aboveAnswer: BExplanation:STP (spanning tree protocol) operates on layer 2 to prevent loops in switches andbridges.Incorrect Answers:A, C. RIP and IGRP are routing protocols, which are used at layer 3 to maintain a loopfree routed environment.D. CDP does indeed operate at layer 2, but it doest not provide for a loop free topology.CDP is used by Cisco devices to discover information about their neighbors.E.
VTP is the VLAN Trunking Protocol, used to pass VLAN information throughswitches. It relies on the STP mechanism to provide a loop free network.QUESTION 167:By default, which of the following factors determines the spanning-tree path cost?A. It is the individual link cost based on latencyB. It is the sum of the costs based on bandwidthC. It is the total hop countD. It is dynamically determined based on loadE.
None of the aboveAnswer: BExplanation:"The STP cost is an accumulated total path cost based on the available bandwidth of eachof the links."Reference: Sybex CCNA Study Guide 4th Edition (Page 323)Note: A path cost value is given to each port. The cost is typically based on a guidelineestablished as part of 802.1d. According to the original specification, cost is 1,000 Mbps(1 gigabit per second) divided by the bandwidth of the segment connected to the port.Therefore, a 10 Mbps connection would have a cost of (1,000/10) 100.To compensate for the speed of networks increasing beyond the gigabit range, thestandard cost has been slightly modified. The new cost values are:Actualtests.com - The Power of Knowing640-802You should also note that the path cost can be an arbitrary value assigned by the networkadministrator, instead of one of the standard cost values.Incorrect Answers:A, D: The STP process does not take into account the latency or load of a link.
STP doesnot recalculate the link costs dynamically.C. Hop counts are used by RIP routers to calculate the cost of a route to a destination.The STP process resides at layer 2 of the OSI model, where hop counts are notconsidered.QUESTION 168:What is the purpose of the spanning-tree algorithm in a switched LAN?A. To provide a monitoring mechanism for networks in switched environments.B. To manage VLANs across multiple switches.C. To prevent switching loops in networks with redundant switched paths.D. To segment a network into multiple collision domains.E.
To prevent routing loops in networks.Answer: CExplanation:STP is used in LANs with redundant paths or routes to prevent loops in a layer 2switched or bridged LAN.Incorrect Answers:A, B: The primary purpose of STP is to prevent loops, not for monitoring or managementof switches or VLANs.D. VLANs are used to segment a LAN into multiple collision domains, but the STPprocess alone does not do this.Actualtests.com - The Power of Knowing640-802E. Routers are used to prevent routing loops at layer 3 of the OSI model.
STP operates atlayer 2.QUESTION 169:Which two of the following values does STP take into consideration when it electsthe root bridge? (Select two answer choices)A. The BPDU version numberB. The access layer bridge settingC. The Bridge IDD. The spanning-tree update numberE. The bridge priorityF. The VLAN numberAnswer: C, EExplanation:The bridges elect a root bridge based on the bridge IDs in the BPDUs. The root bridge isthe bridge with the lowest numeric value for the bridge ID. Because the two part bridgeID starts with the priority value, essentially the bridge with the lowest priority becomesthe root. For instance, if one bridge has priority 100, and another bridge has priority 200,the bridge with priority 100 wins, regardless of what MAC address was used to create thebridge ID or each bridge/switch.Reference: CCNA Self-Study CCNA ICND Exam Certification Guide (Cisco Press,ISBN 1-58720-083-X) Page 39QUESTION 170:Which of the following are spanning tree port states? (Select three answer choices)A.
LearningB. SpanningC. ListeningD. ForwardingE. InitializingF. FilteringG. PermittingAnswer: A, C, DExplanation:There are 4 STP states that a bridge port can be in: Blocking, Listening, Learning, andActualtests.com - The Power of Knowing640-802Forwarding:QUESTION 171:What are the switch and bridge port characteristics of a layer two spanning-treenetwork that is fully converged?A.
All switch and bridge ports are in the forwarding state.B. All switch and bridge ports are in the stand-by state.C. All switch and bridge ports are assigned as either root or designated ports.D. All switch and bridge ports are in either the forwarding or blocking state.E. All switch and bridge are either blocking or looping.Answer: DExplanation:When a switch first comes up, it will be in the listening and learning states. This isneeded so that the switch learns the MAC addresses of the devices on the LAN, and tolearn where any loops in the network may exist. After this initial period of listening andlearning, the ports will be forwarding to the hosts, or blocking certain ports that create aloop in the network.
An example of this is shown below:Actualtests.com - The Power of Knowing640-802In the above figure, after the network has converged, spanning tree protocol puts eachport either in designated (Forwarding) or Non-designated (Blocking) state. So, Choice Dis correct.If you get a converged spanning-tree network, you have only two port states.Forwarding and Blocking. Forwarding: all traffic will be forwardedBlocking: all traffic to devices that will create a loop in a spanning-tree network will beblocked.
It is possible to get redundant paths in large switched and routed networks.QUESTION 172:The Certkiller LAN consists of 6 switches connected together as shown in thediagram below:What is the name of the potential problem of this switch setup, and what protocolcan prevents its occurrence. (Select only one answer choice)Actualtests.com - The Power of Knowing640-802A. Routing loops, hold down timersB. Switching loops, split horizonC. Routing loops, split horizonD.
Switching loops, VTPE. Routing loops, STPF. Switching loops, STPAnswer: FExplanation:The spanning-Tree Protocol (STP) prevents loops from being formed when switches orbridges are interconnected via multiple paths. Spanning-Tree Protocol implements the802.1D IEEE algorithm by exchanging BPDU messages with other switches to detectloops, and then removes the loop by shutting down selected bridge interfaces. Thisalgorithm guarantees that there is one and only one active path between two networkdevices.QUESTION 173:In a switched LAN network, what is the Spanning-Tree algorithm used for?A.
It is used to provide a mechanism for routing updates in switched environments.B. It is used to prevent routing loops in networks with redundant routes.C. It is used to prevent switching loops in networks with redundant switched routes.D. It is used to manage, the addition, deletion, and naming of VLANs across multipleswitches.E. It is used to segment a network into multiple collision domains.F. None of the above.G. All of the above are functions of STP.Answer: CExplanation:To avoid loops, all bridging devices, including switches, use STP. STP causes eachinterface on a bridging device to settle into a blocking state or a forwarding state.Blocking means that the interface cannot forward or receive data frames. Forwardingmeans that the interface can send and receive data frames.
By having a correct subset ofthe interfaces blocked, a single currently active logical path will exist between each pairof LANs. STP resides at the data link layer, so it is used to prevent loops within aswitched network. It is not used to prevent routing loops; that is the function of themechanisms within a routing protocol.Reference:CCNA Self-Study CCNA INTRO exam certification Guide (Cisco Press, ISBN1-58720-094-5) page 248.Actualtests.com - The Power of Knowing640-802QUESTION 174:In which Spanning-Tree states does a switch port learn MAC addresses? (Selecttwo)A. BlockingB.
ListeningC. ForwardingD. LearningE. RelayingAnswer: C, DExplanation:STP uses a couple of port states besides forwarding and blocking.1. Listening - Listens to incoming Hello messages to ensure that there are no loops, butdoes not forward traffic. This is an interim state between blocking and forwarding.2. Learning - Still listens to BPDUs, plus learns MAC addresses from incoming frames. Itdoes not forward traffic. This is an interim state between blocking and forwarding.3. Disabled - Administratively down.Reference: Cisco CCNA intro 640-821QUESTION 175:Three Certkiller switches are connected together as shown in the diagram below:Study the Exhibit carefully.
All switches have the default STP configuration and alllinks are Fast Ethernet. Which port on which switch will Spanning Tree place inblocking mode?A. Switch CK1 - Port Fa1/1B. Switch CK1 - Port Fa1/2C. Switch CK2 - Port Fa1/2D. Switch CK2 - Port Fa1/1Actualtests.com - The Power of Knowing640-802E. Switch CK3 - Port Fa1/1F. Switch CK3 - Port Fa1/2Answer: FExplanation:Switch CK1 will become the ROOT BRIDGE because it has the lowest MAC address.Its both ports will become designated ports so choice A and B are wrong.Next Election will be of ROOT PORTS.
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