ActualTests.Cisco.640-802.Exam.Q.and.A.08.15.08-DDU (1130589), страница 12
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Full-duplex Ethernet uses a loopback circuit to detect collisions. Half-duplex ethernetuses a jam signalE. None of the aboveAnswer: CQUESTION 100:A network administrator wants to control which user hosts can access the networkbased on their MAC address. What will prevent workstations with unauthorizedMAC addresses from connecting to the network through a switch?A. BPDUActualtests.com - The Power of Knowing640-802B.
Port securityC. RSTPD. STPE. VTPF. Blocking modeAnswer: BExplanation:UnderstandingHow PortSecurity Works:You can use port security to block input to an Ethernet, Fast Ethernet, or Gigabit Ethernetport when the MAC address of the station attempting to access the port is different fromany of the MAC addresses specified for that port.
Alternatively, you can use port securityto filter traffic destined to or received from a specific host based on the host MACaddress.When a secure port receives a packet, the source MAC address of the packet is comparedto the list of secure source addresses that were manually configured or autoconfigured(learned) on the port. If a MAC address of a device attached to the port differs from thelist of secure addresses, the port either shuts down permanently (default mode), shutsdown for the time you have specified, or drops incoming packets from the insecure host.The port's behavior depends on how you configure it to respond to a security violation.If a security violation occurs, the Link LED for that port turns orange, and a link-downtrap is sent to the Simple Network Management Protocol (SNMP) manager. An SNMPtrap is not sent if you configure the port for restrictive violation mode.
A trap is sent onlyif you configure the port to shut down during a security violation.Reference:http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_guide_chapter09186a008007fQUESTION 101:Actualtests.com - The Power of Knowing640-802The Certkiller internetwork shown in the diagram is experiencing network delays.On the basis of the information provided in the exhibit above, what is the problem?A. The connection between Switch1 and Switch2 should be half-duplex.B. The cable between Router1 and Switch1 should be a crossover.C.
The cable connecting Host A to Switch2 is too long.D. The server is on a different subnet than router interface Fa0/0.E. The cable between Switch1 and Switch2 should be straight-through.F. None of the aboveAnswer: CExplanation:According to IEEE specifications, the maximum segment length of an Ethernet cableshould not exceed 100 meters. The total distance between an Ethernet Transmitter andReceiver at the absolute end points of the network (maximum diameter from origin tofinal destination, if the wires were stretched out to form a straight line) should be nomore than100 Meters (328 ft., 109 yards, or about the length of a football field). Thislimitation results from the timing of the Ethernet signals on the cable and not necessarilythe cable characteristics, and is, therefore, a "hard" number.QUESTION 102:What is the IEEE standard associated with Gigabit Ethernet? (Select two answerchoices)A.
802.11B. 802.5C. 802.3abActualtests.com - The Power of Knowing640-802D. 802.3aeE. 802.3zF. 802.3uAnswer: C, EExplanation:The IEEE 802.3z standard describes 1000BASE-SX.The 1000BaseT standard was released in June 1999, defined by IEEE 802.3ab.Incorrect Answers:A.
This describes the standard used for wireless networks.B. This is the standard for token ring networks.D. On June 17, 2002 the IEEE 802.3ae specification for 10 Gigabit Ethernet wasapproved as an IEEE standard by the IEEE Standards Association (IEEE-SA) StandardsBoard.F. IEEE 802.3u describes the standard for 100BASE-TX.QUESTION 103:Which of the following can lead to the contribution of LAN traffic congestion?(Select all that apply)A. Too many hosts in a broadcast domainB.
Full duplex operationC. Broadcast stormsD. MulticastingE. SegmentationF. Low bandwidthAnswer: A, C, FExplanation:Choice A is correct because the more hosts on a broadcast domain, the more traffic that iscreated. Choice Ccontributes to congestion because broadcast storms can become veryproblematic, and lead to complete network saturation. Multicasts are similar tobroadcasts in their use on a LAN. Finally, if there is not enough bandwidth, trafficsessions can time out.
This leads to new transmissions and the re-sending of data, whichcan lead to more congestion.Incorrect Answers:B, E. These are incorrect because full duplex operation and segmented networks actuallyresult in less congestion.D. Multicasting can actually alleviate congestion issues, as single streams of informationcan reach multiple hosts at the same time, instead of using a series of point to pointconnections.Actualtests.com - The Power of Knowing640-802QUESTION 104:On a half-duplex Ethernet LAN, two hosts attempt to send data simultaneously,resulting in a collision.
Following this collision, what will the hosts do? (Select allvalid answers)A. The destination host sends a request to the source for retransmission.B. The jam signal indicates that the collision has been cleared.C. The hosts will attempt to resume transmission after a time delay has expired.D. An electrical pulse indicates that the collision has cleared.E. The router on the segment will signal that the collision has cleared.F. The hosts will do nothing, as the higher layers are responsible for data error correctionand re-transmission.Answer: CExplanation:When a host on an Ethernet LAN has information to send, the following steps are taken:1.
A device with a frame to send listens until Ethernet is not busy.2. When the Ethernet is not busy, the sender begins sending the frame.3. The sender listens to make sure that no collision occurred.4. Once the senders hear the collision, they each send a jamming signal, to ensure that allstations recognize the collision.5. After the jamming is complete, each sender randomizes a timer and waits that long.6. When each timer expires, the process starts over with step 1.QUESTION 105:Which of the following statements correctly describe the differences betweenhalf-duplex and full-duplex Ethernet? (Select two answer choices.)A. Full-duplex Ethernet uses CSMA/CD to prevent collisions.B.
Half-duplex Ethernet uses a loopback circuit to detect collisions.C. A full-duplex Ethernet card allows 20Mbps for data transmission.D. Full-duplex Ethernet makes use of two pairs of wires for data.E. An Ethernet hub can operate both half and full duplex simultaneously.Answer: B, DExplanation:Half-duplex Ethernet send and receives on the same line, so a loopback needs to be set todetect collisions. Alternatively, full-duple Ethernet doesn't have to because it uses twopairs of wire, one to send and the other to receive. Collisions are not possible on fullActualtests.com - The Power of Knowing640-802duplex Ethernet networks.Incorrect Answers:A. Full duplex uses both pairs of wires, so transmissions are sent on the first pair, anddata that is received come in on the other pair.
This prevents collisions.C. Full duplex allows for data to be sent and received at the same time. It will not doublethe amount of bandwidth at any given time. The speed of the Ethernet link will remain at10/100.E. Hubs are shared devices and can only support one mode, unlike switches.QUESTION 106:Why is full-duplex Ethernet superior to its single-duplex counterpart? (Select twoanswer choices.)A.
It uses inexpensive hubsB. It operates without collisionsC. It operates on switchesD. It provides faster data transferE. It utilizes fewer wiring pairsAnswer: B, DExplanation:Full duplex Ethernet allows concurrent sending and receiving, which allows the fullbandwidth to be used for both sending and receiving. The result is a collision freenetwork with increased throughput.Incorrect Answers:A, C. These are incorrect because full duplex doesn't require hubs or switches. Fullduplex operation can be used on switch and router ports, as well as PC hosts.E. This is incorrect because full duplex actually uses more wiring pairs.
In full duplex,both wire pairs are used. Half duplex uses only a single pair.QUESTION 107:When you compare the differences between half-duplex and full-duplex Ethernet,which of the following characteristics are exclusive to half-duplex? (Select twoanswer choices)A. Half-duplex Ethernet operates in a shared collision domain.B. Half-duplex Ethernet operates in an exclusive broadcast domain.C.
Half-duplex Ethernet has efficient throughput.D. Half-duplex Ethernet has lower effective throughput.E. Half-duplex Ethernet operates in an exclusive collision domain.Actualtests.com - The Power of Knowing640-802Answer: A, DExplanation:A single device could not be sending a frame and receiving a frame at the same timebecause it would mean that a collision was occurring. So, devices simply chose not tosend a frame while receiving a frame. That logic is called half-duplex logic.Ethernet switches allow multiple frames to be sent over different ports at the same time.Additionally, if only one device is connected to a switch port, there is never a possibilitythat a collision could occur. So, LAN switches with only one device cabled to each portof the switch allow the use of full-duplex operation. Full duplex means that an Ethernetcard can send and receive concurrently.Incorrect Answers:B.
Full duplex effectively doubles the throughput of half-duplex operation, because datacan be both sent and received at the full 10/100 speed.C, E. In half duplex operation, the network is shared between all devices in the collisiondomain.Reference: CCNA Self-Study CCNA INTRO exam certification Guide (Cisco Press,ISBN 1-58720-094-5) Page 62-63.QUESTION 108:Two stations on the Certkiller LAN transmit at the same time, resulting in acollision. What happens when a collision occurs on the network? (Choose all thatapply)A.
Each device on the Ethernet segment stops transmitting for a short time.B. A jam signal informs all devices that a collision occurred.C. When data transmission resumes, the devices that were involved in the collision havepriority to transmit.D. The devices that are involved in the collision stops transmitting for a short time.E. The collision invokes a random back-off algorithm.Answer: B, D, EExplanation:When a host on an Ethernet LAN has information to send, the following steps are taken:1. A device with a frame to send listens until Ethernet is not busy.2. When the Ethernet is not busy, the sender begins sending the frame.3.
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