Checkpoint Exam: Physical, Data Link, and Network Layers Answers

Checkpoint Exam: Physical, Data Link, and Network Layers: Network Addressing and Basic Troubleshooting Module 1 – 3 Checkpoint Exam Answers

1. A network specialist has been hired to install a network in a company that assembles airplane engines. Because of the nature of the business, the area is highly affected by electromagnetic interference. Which type of network media should be recommended so that the data communication will not be affected by EMI?

UTP
STP
fiber optic
coaxial

Explanation: Optical fiber uses light to transmit signals. Therefore, fiber-optic cable is not affected by EMI or RFI.

2. Which physical layer network standard would use 8B/10B encoding?

1000BASE-T
IEEE 802.15
IEEE 802.11n
TIA/EIA-568

Explanation: In Manchester encoding, the transition occurs at the middle of each bit period. Manchester encoding is used in older Ethernet standards such as 10BASE-T. Ethernet 100BASE-X family uses 4B/5B encoding and 1000BASE-X uses 8B/10B encoding.

3. What are two characteristics of STP cable? (Choose two.)

If it is improperly grounded, the shield may act as an antenna and pick up unwanted signals.
It provides better noise protection than UTP cabling provides.
It is easy to install compared to UTP installation.
It is the most common network media.
It is primarily used as backbone cabling for corporate networks.

Explanation: STP provides better noise protection than does UTP cabling. However, compared to UTP cable, STP cable is significantly more expensive and difficult to install. If the cable is improperly grounded, the shield may act as an antenna and pick up unwanted signals.

4. In addition to the cable length, what two factors could interfere with the communication carried over UTP cables? (Choose two.)

size of the network
bandwidth
crosstalk
electromagnetic interference
signal modulation technique

Explanation: Copper media is widely used in network communications. However, copper media is limited by distance and signal interference. Data is transmitted on copper cables as electrical pulses. The electrical pulses are susceptible to interference from two sources:
– Electromagnetic interference (EMI) or radio frequency interference (RFI) – EMI and RFI signals can distort and corrupt the data signals being carried by copper media
– Crosstalk – Crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire interfering with the signal in an adjacent wire.

5. What is a primary role of the Physical layer in transmitting data on the network?

control data access to the media
provide physical addressing to the devices
create the signals that represent the bits in each frame on to the media
determine the path packets take through the network

Explanation: The OSI physical layer provides the means to transport the bits that make up a frame across the network media. This layer accepts a complete frame from the data link layer and encodes it as a series of signals that are transmitted to the local media.

6. How do goodput, throughput, and bandwidth relate to network data transmissions?

Goodput is always lower than throughput, which is generally lower than bandwidth.
Throughput is always lower than goodput, which is generally lower than bandwidth.
Goodput is always lower than bandwidth, which is generally lower than throughput.
Throughput is always lower than bandwidth, which is generally lower than goodput.

Explanation: Bandwidth is the capacity at which a medium can carry data, so it is always higher than throughput and goodput. Goodput is throughput minus traffic overhead for establishing sessions, acknowledgments, encapsulation, and retransmitted bits, so it is always lower than throughput.

7. Two network interns are working for a company that is installing new networks with both copper and fiber-optic cabling. The interns are reviewing information in preparation for the work. What is a property of a fiber-optic connector?

A Duplex Multimode LC connector is similar to an SC connector, but uses a duplex connector.
An LC connector is a widely-adopted LAN and WAN connector that uses a push-pull mechanism to ensure positive insertion.
A straight-tip connector locks securely with a “twist-on/twist-off” bayonet-style mechanism.
An LC connector is a smaller version of the straight-tip connector.

Explanation: Straight-tip connectors lock securely with a “twist-on/twist-off” bayonet-style mechanism. SC connectors are a widely-adopted LAN and WAN connector that uses a push-pull mechanism to ensure positive insertion. LC simplex connectors are a smaller version of the SC connector. A duplex multimode LC connector is similar to an LC simplex connector, but uses a duplex connector.

8. What is CSMA/CA on a network?

an access method that is used by wireless technology to avoid duplicate SSIDs
an access method that is used by wired Ethernet technology to avoid collisions
an access method that is used by wireless technology to avoid collisions
an access method that is used by any technology that has excessive collisions

Explanation: Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a wireless technology that allows only one device to transmit on a channel at a given moment and prevents collisions from occurring.

9. When troubleshooting network problems, where would a network administrator find the configuration information, such as the computer names and the IP addresses that are used?

physical topology diagram
DHCP server
DNS server
logical topology diagram

Explanation: A logical topology usually contains relevant network configuration information, such as the following:
– Device names
– Device IP addressing
– Network designations
– Configuration information

10. You are asked to document your school network. What type of topology diagram would you draw to show how devices are connected to the network?

physical topology diagram
logical topology diagram

Explanation: There are two types of topology diagrams. The logical topology uses icons to identify network devices and show how the devices are connected to the school network. The physical topology diagram shows where the network devices are actually located in each room of the school.

11. Although CSMA/CD is still a feature of Ethernet, why is it no longer necessary?

the development of half-duplex switch operation
the use of Gigabit Ethernet speeds
the use of CSMA/CA
the virtually unlimited availability of IPv6 addresses
the use of full-duplex capable Layer 2 switches

Explanation: The use of Layer 2 switches operating in full-duplex mode eliminates collisions, thereby eliminating the need for CSMA/CD.

12. Which statement describes an extended star topology?

End devices connect to a central intermediate device, which in turn connects to other central intermediate devices.
End devices are connected together by a bus and each bus connects to a central intermediate device.
Each end system is connected to its respective neighbor via an intermediate device.
All end and intermediate devices are connected in a chain to each other.

Explanation: In an extended star topology, central intermediate devices interconnect other star topologies.

13. In what communication mode does an Ethernet switch operate by default?

full-duplex
mesh
half-duplex
point-to-point

Explanation: Ethernet switches operate in full-duplex mode by default when powered on. Point-to-point and mesh are logical topologies.

14. A technician has been asked to develop a physical topology for a network that provides a high level of redundancy. Which physical topology requires that every node is attached to every other node on the network?

bus
star
hierarchical
mesh
ring

Explanation: The mesh topology provides high availability because every node is connected to all other nodes. Mesh topologies can be found in WANs. A partial mesh topology can also be used where some, but not all, end points connect to one another.

15. How do hosts ensure that their packets are directed to the correct network destination?

They send a query packet to the default gateway asking for the best route.
They always direct their packets to the default gateway, which will be responsible for the packet delivery.
They have to keep their own local routing table that contains a route to the loopback interface, a local network route, and a remote default route.
They search in their own local routing table for a route to the network destination address and pass this information to the default gateway.

Explanation: Hosts must maintain their own local routing table to ensure that network layer packets are directed to the correct destination network. This local table typically contains a route to the loopback interface, a route to the network that the host is connected to, and a local default route, which represents the route that packets must take to reach all remote network addresses.

16. What network address and subnet mask combination would be used to create a default static route that matches any IPv4 destination?

255.255.255.255 0.0.0.0
255.255.255.255 255.255.255.255
0.0.0.0 255.255.255.255
0.0.0.0 0.0.0.0

Explanation: For a route to be considered a default static route it must use a network ID and subnetmask combination that will match any destination IP address. The address and mask of 0.0.0.0 0.0.0.0 in a static route will create a route table entry that matches any destination.

17. What routing table entry has a next hop address associated with a destination network?

remote routes
directly-connected routes
local routes
C and L source routes

Explanation: Routing table entries for remote routes will have a next hop IP address. The next hop IP address is the address of the router interface of the next device to be used to reach the destination network. Directly-connected and local routes have no next hop, because they do not require going through another router to be reached.

18. Which feature on a Cisco router permits the forwarding of traffic for which there is no specific route?

route source
next-hop
outgoing interface
gateway of last resort

Explanation: A default static route is used as a gateway of last resort to forward unknown destination traffic to a next hop/exit interface. The next-hop or exit interface is the destination to send traffic to on a network after the traffic is matched in a router. The route source is the location a route was learned from.

19. If the default gateway is configured incorrectly on the host, what is the impact on communications?

The host is unable to communicate on the local network.
There is no impact on communications.
The host can communicate with other hosts on remote networks, but is unable to communicate with hosts on the local network.
The host can communicate with other hosts on the local network, but is unable to communicate with hosts on remote networks.

Explanation: A default gateway is only required to communicate with devices on another network. The absence of a default gateway does not affect connectivity between devices on the same local network.

20. A computer has to send a packet to a destination host in the same LAN. How will the packet be sent?

The packet will be sent directly to the destination host.
The packet will be sent to the default gateway first, and then, depending on the response from the gateway, it may be sent to the destination host.
The packet will be sent only to the default gateway.
The packet will first be sent to the default gateway, and then from the default gateway it will be sent directly to the destination host.

Explanation: If the destination host is in the same LAN as the source host, there is no need for a default gateway. A default gateway is needed if a packet needs to be sent outside the LAN.

21. Which portion of the network layer address does a router use to forward packets?

gateway address
host portion
network portion
broadcast address

Explanation: There are two parts to an a network layer address, the network and host portions. Routers are not concerned about delivering packets to hosts. Routers are concerned with delivering packets to the network that a destination host is a member of.

22. Why are two strands of fiber used for a single fiber optic connection?

They prevent crosstalk from causing interference on the connection.
The two strands allow the data to travel for longer distances without degrading.
They allow for full-duplex connectivity.
They increase the speed at which the data can travel.

Explanation: Light can only travel in one direction down a single strand of fiber. In order to allow for full-duplex communication two strands of fiber must be connected between each device.

23. What is a common characteristic of both CSMA/CD and CSMA/CA?

deterministic
nondeterministic
collision-free environment
used for both LAN and WAN

Explanation: All protocols based on CSMA are nondeterministic. Ethernet implements CSMA/CD and 802.11 (wireless, not Ethernet) implements CSMA/CA. Although there are a number of methods to avoid collisions, they may occur.

24. In which hybrid logical topology are some devices fully interconnected with all other devices, while some are not?

mesh
hub and spoke
partial mesh
point-to-point

Explanation: In a hybrid topology like a partial mesh topology, some devices are fully interconnected with all others while some are not.

25. Which statement describes the logical topology for a LAN?

It defines how computers connect to a LAN.
It depicts the locations of main routers and switches in a LAN.
It lists the number of computers, routers, and switches on the LAN.
It describes how computers access the LAN medium.

Explanation: A logical topology describes how the hosts access the network medium, whether the network is a broadcast network, a token passing network, or any other type of network.