CCNA – Chapter 1

Question 1
Which layer in the OSI reference model is responsible for determining the availability of the receiving program and checking to see if enough resources exist for that communication?

A. transport
B. network
C. presentation
D. session
E. application

Answer : E

Explanation:

The application layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level.



Question 2
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:

In full-duplex switches CSMA/CD (carrier sense multiple access with collision detection) is disabled by default. The plain old bus topology and network hub does have CSMA/CD. Both networks are half duplex.





Question 3
A receiving host computes the checksum on a frame and determines that the frame is damaged. The frame is then discarded. At which OSI layer did this happen?

A. physical
B. session
C. data link
D. transport
E. network

Answer : C

Explanation:

The data link layer defines the format of data on the network. All of the data sent through the network are made into a frame which is performed at this level. The frame is a uniform way of sending the data along with address information and error checking capabilities. CRC is used for the error detection at this level. If at the receiving end the CRC fails at this level there is a request back to the sender for retransmission of this packet.



Question 4
Which of the following correctly describe steps in the OSI data encapsulation process? (Choose two)

A. The transport layer divides a data stream into segments and may add reliability and flow control information.
B. The data link layer adds physical source and destination addresses and an FCS to the segment.
C. Packets are created when the network layer encapsulates a frame with source and destination host addresses and protocol-related control information.
D. Packets are created when the network layer adds Layer 3 addresses and control information to a segment.
E. The presentation layer translates bits into voltages for transmission across the physical link.

Answer : A, D

Explanation:

A: The basic function of the transport layer is to accept data from the session layer, break up the data into smaller units if need be, and send these manageable data packets to the network layer. At the destination this layer is responsible for combining the packets into their original state.
D: The network layer basically handles all of the addressing issues. This layer addresses packets, determines the best path or route, and manages network problems such as data congestion.

Incorrect Answers:

B: The data link layer adds physical source and destination addresses and an FCS to the packet. Not segment.
C: Packets are created when network layer encapsulates a segment with source and destination addresses and protocol-related information. Not frame.
E: The physical layer translates bits into voltages for transmission across physical link. Not presentation layer.

Question 5
Refer to the exhibit.



What two results would occur if the hub were to be replaced with a switch that is configured with one Ethernet VLAN? (Choose two.)

A. The number of broadcast domains would remain the same.
B. The number of collision domains would increase.
C. The number of collision domains would decrease.
D. The number of broadcast domains would decrease.
E. The number of collision domains would remain the same.
F. The number of broadcast domains would increase.

Answer : A, B

Explanation:

The hub has only one broadcast domain and only one collision domain. Whereas Switch does have one broadcast domain and each port one collision domain.
If we replace switch with hub, then the broadcast domain remains same. But collision domain increased to 5 (according to the topology).



Question 6
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

As with other IEEE 802 LANs, each Ethernet station is given a 48-bit MAC address (physical address). The MAC addresses are used to specify both the destination and the source of each data packet. Ethernet establishes link level connections, which can be defined using both the destination and source addresses. On reception of a transmission, the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. Network interfaces normally do not accept packets addressed to other Ethernet stations. Adapters come programmed with a globally unique address.

Question 7
What is the first 24 bits in a MAC address called?

A. NIC
B. BIA
C. oui
D. vai

Answer : C

The first three octets (in transmission order) identify the organization that issued the identifier and are known as the Organizationally Unique Identifier (OUI). The following three (MAC-48 and EUI-48) or five (EUI-64) octets are assigned by that organization in nearly any manner they please, subject to the constraint of uniqueness.