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CCNA Routing and Switching v3.0

QUESTION 21

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?

 

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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

 

Correct 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 MAC header includes the router’s MAC address and the final destination’s MAC address or the MAC address of the next router in the path.

 

 

QUESTION 22

DRAG DROP

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Correct Answer:

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QUESTION 23

Refer to the exhibit. Which three statements correctly describe Network Device A? (Choose three.)

 

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A.

With a network wide mask of 255.255.255.128, each interface does not require an IP address.

B.

With a network wide mask of 255.255.255.128, each interface does require an IP address on a unique IP subnet.

C.

With a network wide mask of 255.255.255.0, must be a Layer 2 device for the PCs to communicate with each other.

D.

With a network wide mask of 255.255.255.0, must be a Layer 3 device for the PCs to communicate with each other.

E.

With a network wide mask of 255.255.254.0, each interface does not require an IP address.

 

Correct Answer: BDE

Explanation:

If Subnet Mask is 255.255.255.128 the hosts vary from x.x.x.0 – x.x.x.127 & x.x.x.128- x.x.x.255, so the IP Addresses of 2 hosts fall in different subnets so each interface needs an IP an address so that they can communicate each other.

If Subnet Mask is 255.255.255.0 the 2 specified hosts fall in different subnets so they need a Layer 3 device to communicate.

If Subnet Mask is 255.255.254.0 the 2 specified hosts are in same subnet so are in network address and can be accommodated in same Layer 2 domain and can communicate with each other directly using the Layer 2 address.

 

 

QUESTION 24

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.

 

Correct Answer: ADE

Explanation:

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

 

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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 provider’s network. Therefore a modem terminates an analog local loop is correct.

 

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QUESTION 25

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

 

clip_image009

 

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

 

Correct 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 26

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.

 

Correct 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 27

What parameter can be different on ports within an EtherChannel?

 

A.

speed

B.

DTP negotiation settings

C.

trunk encapsulation

D.

duplex

 

Correct Answer: B

Explanation:

For an etherchannel to come up, the speed, duplex and the trunk encapsulation must be the same on each end.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

QUESTION 28

DRAG DROP

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.

 

clip_image011

 

Correct Answer:

clip_image013

 

 

 

 

QUESTION 29

What are three benefits of implementing VLANs? (Choose three.)

 

A.

A higher level of network security can be reached by separating sensitive data traffic from other network traffic.

B.

A more efficient use of bandwidth can be achieved allowing many physical groups to use the same network infrastructure.

C.

A more efficient use of bandwidth can be achieved allowing many logical networks to use the same network infrastructure.

D.

Broadcast storms can be mitigated by increasing the number of broadcast domains, thus reducing their size.

E.

Broadcast storms can be mitigated by decreasing the number of broadcast domains, thus increasing their size.

F.

VLANs make it easier for IT staff to configure new logical groups, because the VLANs all belong to the same broadcast domain.

G.

Port-based VLANs increase switch-port use efficiency, thanks to 802.1Q trunks.

 

Correct Answer: ACD

Explanation:

Benefits of VLANs

VLAN is a network structure which allows users to communicate while in different locations by sharing one multicast domain and a single broadcast. They provide numerous networking benefits and have become popular in the market. For instance, it helps reduce administrative costs when users are geographically dispersed.

 

1. Inexpensive

The popularity of VLANs is due to the fact that changes, adds, and moves can be attained simply by making necessary configurations on the VLAN port. Time-consuming, re- addressing, and host reconfigurations is now a thing of the past, because network configuration can be made at ease when need arises.

 

2. Better manage
ment

A VLAN typically solve the scalability issues that exist in a large network by breaking the main domain into several VLAN groups or smaller broadcast configurations, thereby encourage better control of multicast traffic as well as broadcast domains.

 

3. Improves network security

High-security can be positioned in different VLAN groups to ensure that non-members cannot receive their broadcasts. On the other hand, a router is added and workgroups relocated into centralized locations.

 

4. Enhances performance

A more efficient use of bandwidth can be achieved allowing many logical networks to use the same network infrastructure.

 

5. Segment multiple networks

VLANs are typically used to achieve multiple purposes. They are popularly used to reduce broadcast traffic. Each VLAN creates a separate, smaller broadcast domain.

 

6. Better administration

VLANs facilitate grouping of multiple geographical stations. When VLAN users move to another physical location, the network does not have to be configured.

 

 

 

QUESTION 30

Refer to the topology shown in the exhibit. Which three ports will be STP designated ports if all the links are operating at the same bandwidth? (Choose three.)

 

clip_image014

 

A.

Switch A – Fa0/0

B.

Switch A – Fa0/1

C.

Switch B – Fa0/0

D.

Switch B – Fa0/1

E.

Switch C – Fa0/0

F.

Switch C – Fa0/1

 

Correct Answer: BCD

Explanation:

This question is to check the spanning tree election problem.

1. First, select the root bridge, which can be accomplished by comparing the bridge ID, the smallest will be selected. Bridge-id= bridge priority + MAC address. The three switches in the figure all have the default priority, so we should compare the MAC address, it is easy to find that SwitchB is the root bridge.

2. Select the root port on the non-root bridge, which can be completed through comparing root path cost. The smallest will be selected as the root port.

3. Next, select the Designated Port. First, compare the path cost, if the costs happen to be the same, then compare the BID, still the smallest will be selected. Each link has a DP. Based on the exhibit above, we can find DP on each link. The DP on the link between SwitchA and SwitchC is SwitchA’Fa0/1, because it has the smallest MAC address.

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