200-125 CCNA Cisco Certified Network Associate CCNA (v3.0)

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Question 1

Refer to the exhibit.


Based on the information given, which switch will be elected root bridge and why?

  • A. Switch A, because it has the lowest MAC address
  • B. Switch A, because it is the most centrally located switch
  • C. Switch B, because it has the highest MAC address
  • D. Switch C, because it is the most centrally located switch
  • E. Switch C, because it has the lowest priority
  • F. Switch D, because it has the highest priority


Answer : E

Explanation: To elect the root bridge in the LAN, first check the priority value. The switch having the lowest priority will win the election process. If Priority Value is the same then it checks the MAC Address; the switch having the lowest MAC Address will become the root bridge. In this case, switch C has the lowest MAC Address so it becomes the root bridge.

Question 2

Refer to the exhibit. PC_1 is sending packets to the FTP server. Consider the packets as
they leave RouterA interface Fa0/0 towards RouterB. Drag the correct frame and packet
address to their place in the table.




Answer :

Question 3

Refer to the exhibit:


What will Router1 do when it receives the data frame shown? (Choose three.)

  • A. Router1 will strip off the source MAC address and replace it with the MAC address 0000.0c36.6965.
  • B. Router1 will strip off the source IP address and replace it with the IP address 192.168.40.1.
  • C. Router1 will strip off the destination MAC address and replace it with the MAC address 0000.0c07.4320.
  • D. Router1 will strip off the destination IP address and replace it with the IP address of 192.168.40.1.
  • E. Router1 will forward the data packet out interface FastEthernet0/1.
  • F. Router1 will forward the data packet out interface FastEthernet0/2.


Answer : A,C,F

Explanation: Remember, the source and destination MAC changes as each router hop along with the TTL being decremented but the source and destination IP address remain the same from source to destination.

Question 4

Refer to the graphic.


Host A is communicating with the server. What will be the source MAC address of the
frames received by Host A from the server?

  • A. the MAC address of router interface e0
  • B. the MAC address of router interface e1
  • C. the MAC address of the server network interface
  • D. the MAC address of host A


Answer : A

Explanation: Whereas switches can only examine and forward packets based on the contents of the MAC header, routers can look further into the packet to discover the network for which a packet is destined. Routers make forwarding decisions based on the packet's network- layer header (such as an IPX header or IP header). These network-layer headers contain source and destination network addresses. Local devices address packets to the router's MAC address in the MAC header. After receiving the packets, the router must perform the following steps: 1. Check the incoming packet for corruption, and remove the MAC header. The router checks the packet for MAC-layer errors. The router then strips off the MAC header and examines the network-layer header to determine what to do with the packet. 2. Examine the age of the packet. The router must ensure that the packet has not come too far to be forwarded. For example, IPX headers contain a hop count. By default, 15 hops is the maximum number of hops (or routers) that a packet can cross. If a packet has a hop count of 15, the router discards the packet. IP headers contain a Time to Live (TTL) value. Unlike the IPX hop count, which increments as the packet is forwarded through each router, the IP TTL value decrements as the IP packet is forwarded through each router. If an IP packet has a TTL value of 1, the router discards the packet. A router cannot decrement the TTL value to 1 and then forward the packet. 3. Determine the route to the destination. Routers maintain a routing table that lists available networks, the direction to the desired network (the outgoing interface number), and the distance to those networks. After determining which direction to forward the packet, the router must build a new header. (If you want to read the IP routing tables on a Windows 95/98 workstation, type ROUTE PRINT in the DOS box.) 4. Build the new MAC header and forward the packet. Finally, the router builds a new MAC header for the packet. The MA

Question 5

Which of the following describes the roles of devices in a WAN? (Choose three.)

  • A. A CSU/DSU terminates a digital local loop.
  • B. A modem terminates a digital local loop.
  • C. A CSU/DSU terminates an analog local loop.
  • D. A modem terminates an analog local loop.
  • E. A router is commonly considered a DTE device.
  • F. A router is commonly considered a DCE device.


Answer : A,D,E

Explanation: The idea behind a WAN is to be able to connect two DTE networks together through a DCE network. The networks DCE device (includes CSU/DSU) provides clocking to the DTE- connected interface (the routers serial interface).

A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device. A CSU/DSU is used between two digital lines - For more explanation of answer D, in telephony the local loop (also referred to as a subscriber line) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service providers network. Therefore a modem terminates an analog local loop is correct.

Question 6

Drag the cable type on the left to the purpose for which it is best suited on the right. (Not all
options are used.)




Answer :

Explanation:

To remember which type of cable you should use, follow these tips: - To connect two serial interfaces of 2 routers we use serial cable To specify when we use crossover cable or straight-through cable, we should remember: Group 1: Router, Host, Server Group 2: Hub, Switch One device in group 1 + One device in group 2: use straight-through cable Two devices in the same group: use crossover cable For example: we use straight-through cable to connect switch to router, switch to host, hub to host, hub to server and we use crossover cable to connect switch to switch, switch to hub, router to router, host to host)

Question 7

Refer to exhibit:


Which two destination addresses will be used by Host A to send data to Host C? (Choose
two.)

  • A. the IP address of Switch 1
  • B. the MAC address of Switch 1
  • C. the IP address of Host C
  • D. the MAC address of Host C
  • E. the IP address of the router's E0 interface
  • F. the MAC address of the router's E0 interface


Answer : C,F

Explanation: While transferring data through many different networks, the source and destination IP addresses are not changed. Only the source and destination MAC addresses are changed. So in this case Host A will use the IP address of Host C and the MAC address of E0 interface to send data. When the router receives this data, it replaces the source MAC address with its own E1 interfaces MAC address and replaces the destination MAC address with Host Cs MAC address before sending to Host C.

Question 8

Host 1 is trying to communicate with Host 2. The e0 interface on Router C is down.


Which of the following are true? (Choose two.)

  • A. Router C will use ICMP to inform Host 1 that Host 2 cannot be reached.
  • B. Router C will use ICMP to inform Router B that Host 2 cannot be reached.
  • C. Router C will use ICMP to inform Host 1, Router A, and Router B that Host 2 cannot be reached.
  • D. Router C will send a Destination Unreachable message type.
  • E. Router C will send a Router Selection message type.
  • F. Router C will send a Source Quench message type.


Answer : A,D

Explanation: Host 1 is trying to communicate with Host 2. The e0 interface on Router C is down. Router C will send ICMP packets to inform Host 1 that Host 2 cannot be reached.

Question 9

A network interface port has collision detection and carrier sensing enabled on a shared
twisted pair network. From this statement, what is known about the network interface port?

  • A. This is a 10 Mb/s switch port.
  • B. This is a 100 Mb/s switch port.
  • C. This is an Ethernet port operating at half duplex.
  • D. This is an Ethernet port operating at full duplex.
  • E. This is a port on a network interface card in a PC.


Answer : C

Explanation: Modern Ethernet networks built with switches and full-duplex connections no longer utilize CSMA/CD. CSMA/CD is only used in obsolete shared media Ethernet (which uses repeater or hub).

Question 10

Refer to the exhibit.


After HostA pings HostB, which entry will be in the ARP cache of HostA to support this
transmission?

  • A. Exhibit A
  • B. Exhibit B
  • C. Exhibit C
  • D. Exhibit D
  • E. Exhibit E
  • F. Exhibit F


Answer : A

Explanation: Host A knows host B is in another network so it will send the pings to its default gateway 192.168.6.1. Host A sends a broadcast frame asking the MAC address of 192.168.6.1. This information (IP and MAC address of the default gateway) is saved in its ARP cache for later use.

Question 11

Refer to the exhibit.


Host A pings interface S0/0 on router 3. What is the TTL value for that ping?

  • A. 252
  • B. 253
  • C. 254
  • D. 255


Answer : B

Explanation: From the CCNA ICND2 Exam book: Routers decrement the TTL by 1 every time they forward a packet; if a router decrements the TTL to 0, it throws away the packet. This prevents packets from rotating forever. I want to make it clear that before the router forwards a packet, the TTL is still remain the same. For example in the topology above, pings to S0/1 and S0/0 of Router 2 have the same TTL. The picture below shows TTL values for each interface of each router and for Host B. Notice that Host A initializes ICMP packet with a TTL of 255:

Question 12

For what two purposes does the Ethernet protocol use physical addresses? (Choose two.)

  • A. to uniquely identify devices at Layer 2
  • B. to allow communication with devices on a different network
  • C. to differentiate a Layer 2 frame from a Layer 3 packet
  • D. to establish a priority system to determine which device gets to transmit first
  • E. to allow communication between different devices on the same network
  • F. to allow detection of a remote device when its physical address is unknown


Answer : A,E

Explanation: Physical addresses or MAC addresses are used to identify devices at layer 2. MAC addresses are only used to communicate on the same network. To communicate on different network we have to use Layer 3 addresses (IP addresses) -> B is not correct. Layer 2 frame and Layer 3 packet can be recognized via headers. Layer 3 packet also contains physical address ->. On Ethernet, each frame has the same priority to transmit by default ->. All devices need a physical address to identify itself. If not, they cannot communicate ->. Topic 2, LAN Switching Technologies

Question 13

Cisco Catalyst switches CAT1 and CAT2 have a connection between them using ports
FA0/13. An 802.1Q trunk is configured between the two switches. On CAT1, VLAN 10 is
chosen as native, but on CAT2 the native VLAN is not specified.
What will happen in this scenario?

  • A. 802.1Q giants frames could saturate the link.
  • B. VLAN 10 on CAT1 and VLAN 1 on CAT2 will send untagged frames.
  • C. A native VLAN mismatch error message will appear.
  • D. VLAN 10 on CAT1 and VLAN 1 on CAT2 will send tagged frames.


Answer : C

Explanation: A native VLAN mismatch error will appear by CDP if there is a native VLAN mismatch on an 802.1Q link. VLAN mismatch can cause traffic from one vlan to leak into another vlan.

Question 14

Assuming the default switch configuration, which VLAN range can be added, modified, and
removed on a Cisco switch?

  • A. 1 through 1001
  • B. 2 through 1001
  • C. 1 through 1002
  • D. 2 through 1005


Answer : B

Explanation: Explanation VLAN 1 is the default VLAN on Cisco switch. It always exists and cannot be added, modified or removed. VLANs 1002-1005 are default VLANs for FDDI & Token Ring and they cant be deleted or used for Ethernet.

Question 15

Refer to the exhibit.


At the end of an RSTP election process, which access layer switch port will assume the
discarding role?

  • A. Switch3, port fa0/1
  • B. Switch3, port fa0/12
  • C. Switch4, port fa0/11
  • D. Switch4, port fa0/2
  • E. Switch3, port Gi0/1
  • F. Switch3, port Gi0/2


Answer : C

Explanation: In this question, we only care about the Access Layer switches (Switch3 & 4). Switch 3 has a lower bridge ID than Switch 4 (because the MAC of Switch3 is smaller than that of Switch4) so both ports of Switch3 will be in forwarding state. The alternative port will surely belong to Switch4. Switch4 will need to block one of its ports to avoid a bridging loop between the two switches. But how does Switch4 select its blocked port? Well, the answer is based on the BPDUs it receives from Switch3. A BPDU is superior to another if it has: 1. A lower Root Bridge ID 2. A lower path cost to the Root 3. A lower Sending Bridge ID 4. A lower Sending Port ID These four parameters are examined in order. In this specific case, all the BPDUs sent by Switch3 have the same Root Bridge ID, the same path cost to the Root and the same Sending Bridge ID. The only parameter left to select the best one is the Sending Port ID (Port ID = port priority + port index). In this case the port priorities are equal because they use the default value, so Switch4 will compare port index values, which are unique to each port on the switch, and because Fa0/12 is inferior to Fa0/1, Switch4 will select the port connected with Fa0/1 (of Switch3) as its root port and block the other port -> Port fa0/11 of Switch4 will be blocked (discarding role).

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