CISCO CCNA - Book 1, Chapter 4
OSI Transport Layer Why there is a need for the transport layer The role of the transport layer as it provides the end-to-end transfer of data between applications The role of two TCP/IP transport layer protocols: TCP and UDP How the key functions of the transport layer protocol, including reliability, port addressing and segmentation, work How TCP and UDP handle the key functions When it is appropriate to use TCP or UDP and some examples of applications that use each protocol
Questions and Answers
- 1.
Based on the transport layer header shown in the diagram, which of the following statements describe the established session? (Choose two)
- A.
This is a UDP header
- B.
This contains a Telnet request
- C.
This contains a TFTP data transfer
- D.
The return packet from this remote host will have an Acknowledgement Number of 43693
- E.
This is a TCP header
Correct Answer(s)
B. This contains a Telnet request
E. This is a TCP headerExplanation
The given transport layer header is a TCP header because it contains a Telnet request. TCP is a connection-oriented protocol commonly used for Telnet, which is a remote login protocol. Therefore, the statement "This is a TCP header" is correct. Additionally, the established session can be inferred from the Telnet request, as Telnet establishes a session between a client and a server. Hence, the statement "This contains a Telnet request" is also correct.Rate this question:
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- 2.
Refer to the exhibit. What two pieces of information can be determined from the output that is shown? (Choose two)
- A.
The local host is using three client sessions
- B.
The local host is using web sessions to a remote server
- C.
The local host is listening for TCP connections using public addresses
- D.
The local host is using well-known port numbers to identify the source ports
- E.
The local host is performing the three-way handshake with 192.168.1.101:1037
Correct Answer(s)
A. The local host is using three client sessions
B. The local host is using web sessions to a remote serverExplanation
From the output shown, it can be determined that the local host is using three client sessions and is using web sessions to a remote server.Rate this question:
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- 3.
Refer to the exhibit. Host1 is in the process of setting up a TCP session with Host2. Host1 has sent a SYN message to begin session establishment. What happens next?
- A.
Host1 sends a segment with the ACK flag = 0, SYN flag = 0 to Host2
- B.
Host1 sends a segment with the ACK flag = 1, SYN flag = 0 to Host2
- C.
Host1 sends a segment with the ACK flag = 1, SYN flag = 1 to Host2
- D.
Host2 sends a segment with the ACK flag = 0, SYN flag = 1 to Host1
- E.
Host2 sends a segment with the ACK flag = 1, SYN flag = 0 to Host1
- F.
Host2 sends a segment with the ACK flag = 1, SYN flag = 1 to Host1
Correct Answer
F. Host2 sends a segment with the ACK flag = 1, SYN flag = 1 to Host1Explanation
After receiving the SYN message from Host1, Host2 will respond by sending a segment with the ACK flag set to 1 and the SYN flag set to 1. This segment is known as a SYN-ACK segment and it acknowledges the receipt of the SYN message from Host1 while also initiating its own synchronization request. This exchange of SYN and SYN-ACK segments is part of the TCP three-way handshake process, which is used to establish a reliable connection between two hosts.Rate this question:
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- 4.
Refer to the exhibit. In line 7 of this Wireshark capture, what TCP operation is being performed?
- A.
Session establishment
- B.
Segment retransmit
- C.
Data transfer
- D.
Session disconnect
Correct Answer
A. Session establishmentExplanation
In line 7 of the Wireshark capture, the TCP operation being performed is session establishment. This can be inferred from the context of the question, which is asking about a specific line in the capture. The term "session establishment" refers to the process of establishing a connection between two devices or hosts over a TCP/IP network.Rate this question:
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- 5.
Refer to the exhibit. Host A is using FTP to download a large file from Server 1. During the download process, Server 1 does not receive an acknowledgment from Host A for several bytes of transferred data. What action will Server 1 take as a result?
- A.
Create a Layer 1 jam signal
- B.
Reach a timeout and resend the data that needs to be acknowledged
- C.
Send a RESET bit to the host
- D.
Change the window size in the Layer 4 header
Correct Answer
B. Reach a timeout and resend the data that needs to be acknowledgedExplanation
If Server 1 does not receive an acknowledgment from Host A for several bytes of transferred data, it will reach a timeout and resend the data that needs to be acknowledged. This is a common mechanism in network communication protocols where if a sender does not receive an acknowledgment within a certain time period, it assumes that the data was not successfully received and retransmits it to ensure its delivery.Rate this question:
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- 6.
With TCP/IP data encapsulation, which range of port numbers identifies all well-known applications?
- A.
0 to 255
- B.
256 to 1022
- C.
0 to 1023
- D.
1024 to 2047
- E.
49153 to 65535
Correct Answer
C. 0 to 1023Explanation
The well-known applications in TCP/IP data encapsulation are identified by port numbers ranging from 0 to 1023. These port numbers are reserved for commonly used protocols and services such as HTTP (port 80), FTP (port 21), and SSH (port 22).Rate this question:
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- 7.
Why are port numbers included in the TCP header of a segment?
- A.
To indicate the correct router interface that should be used to forward a segment
- B.
To identify which switch ports should receive or forward the segment
- C.
To determine which Layer 3 protocol should be used to encapsulate the data
- D.
To enable a receiving host to forward the data to the appropriate application
- E.
To allow the receiving host to assemble the packet in the proper order
Correct Answer
D. To enable a receiving host to forward the data to the appropriate applicationExplanation
Port numbers are included in the TCP header of a segment to enable a receiving host to forward the data to the appropriate application. Port numbers act as identifiers for different applications running on a host. When a segment arrives at the receiving host, the port number in the TCP header helps the host determine which application or process should receive the data. This allows for proper delivery and processing of the data by the intended application.Rate this question:
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- 8.
Which OSI model layer is responsible for regulating the flow of information from source to destination, reliably and accurately?
- A.
Application
- B.
Presentation
- C.
Session
- D.
Transport
- E.
Network
Correct Answer
D. TransportExplanation
The transport layer of the OSI model is responsible for regulating the flow of information from source to destination, reliably and accurately. It ensures that data is transmitted correctly by breaking it into smaller packets, numbering them, and reassembling them at the destination. It also handles error detection and correction, ensuring that the data arrives intact and in the correct order.Rate this question:
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- 9.
Why is flow control used for TCP data transfer?
- A.
To synchronize equipment speed for sent data
- B.
To synchronize and order sequence numbers so data is sent in complete numerical order
- C.
To prevent the receiver from being overwhelmed by incoming data
- D.
To synchronize window size on the server
- E.
To simplify data transfer to multiple hosts
Correct Answer
C. To prevent the receiver from being overwhelmed by incoming dataExplanation
Flow control is used for TCP data transfer to prevent the receiver from being overwhelmed by incoming data. This is important because the sender may transmit data at a faster rate than the receiver can process it. Flow control mechanisms, such as TCP's sliding window protocol, allow the receiver to inform the sender about its available buffer space to avoid congestion and ensure that data is delivered at a manageable pace. By regulating the flow of data, flow control helps maintain reliable and efficient communication between the sender and receiver.Rate this question:
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- 10.
Which two options represent Layer 4 addressing? (Choose two)
- A.
Identifies the destination network
- B.
Identifies source and destination hosts
- C.
Identifies the communicating applications
- D.
Identifies multiple conversations between the hosts
- E.
Identifies the devices communicating over the local media
Correct Answer(s)
C. Identifies the communicating applications
D. Identifies multiple conversations between the hostsExplanation
Layer 4 addressing refers to the Transport layer of the OSI model. This layer is responsible for end-to-end communication between hosts and provides services such as segmentation, flow control, and error recovery. The options "identifies the communicating applications" and "identifies multiple conversations between the hosts" represent Layer 4 addressing because they both relate to the communication between applications running on different hosts and the management of multiple simultaneous conversations between these hosts.Rate this question:
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- 11.
What is dynamically selected by the source host when forwarding data?
- A.
Destination logical address
- B.
Source physical address
- C.
Default gateway address
- D.
Source port
Correct Answer
D. Source portExplanation
The source port is dynamically selected by the source host when forwarding data. The source port is a 16-bit number that identifies the specific application or process on the source host that is sending the data. It allows the destination host to correctly route the data back to the correct application or process. The source port is randomly chosen by the source host from the available port numbers, and it is used along with the destination IP address and port to establish a unique connection between the source and destination hosts.Rate this question:
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- 12.
What are two features of the User Datagram Protocol (UDP)? (Choose two)
- A.
Flow control
- B.
Low overhead
- C.
Connectionless
- D.
Connection-oriented
- E.
Sequence and acknowledgements
Correct Answer(s)
B. Low overhead
C. ConnectionlessExplanation
UDP has two main features: low overhead and connectionless.
Low overhead refers to the minimal amount of additional data that UDP adds to the original message. Unlike TCP, which adds a lot of control information, UDP only includes a small header, making it more efficient for transmitting small amounts of data.
Connectionless means that UDP does not establish a dedicated connection between the sender and receiver before transmitting data. This lack of connection setup and teardown processes makes UDP faster and more lightweight than connection-oriented protocols like TCP.
Therefore, the correct answer is low overhead and connectionless.Rate this question:
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- 13.
What mechanism is used by TCP to provide flow control as segments travel from source to destination?
- A.
Sequence numbers
- B.
Session establishment
- C.
Window size
- D.
Acknowledgements
Correct Answer
C. Window sizeExplanation
TCP uses the mechanism of window size to provide flow control as segments travel from source to destination. The window size represents the amount of data that the receiver is willing to accept before requiring acknowledgment from the sender. By adjusting the window size, TCP can regulate the rate at which data is sent, preventing congestion and ensuring that the receiver can handle the incoming data. This allows for efficient and reliable transmission of data between the source and destination.Rate this question:
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- 14.
Which transport layer protocol provides low overhead and would be used for applications which do not require reliable data delivery?
- A.
TCP
- B.
IP
- C.
UDP
- D.
HTTP
- E.
DNS
Correct Answer
C. UDPExplanation
UDP (User Datagram Protocol) is a transport layer protocol that provides low overhead and is used for applications that do not require reliable data delivery. Unlike TCP, UDP does not provide error checking, sequencing, or flow control mechanisms. This makes UDP faster and more efficient for applications such as real-time streaming, online gaming, and DNS queries, where occasional loss of data is acceptable. UDP is a connectionless protocol, meaning it does not establish a direct connection between the sender and receiver before transmitting data packets.Rate this question:
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- 15.
Which information is found in both the TCP and UDP header information?
- A.
Sequencing
- B.
Flow control
- C.
Acknowledgements
- D.
Source and destination port
Correct Answer
D. Source and destination portExplanation
Both TCP and UDP header information contain the source and destination port. The source port identifies the sending application or process, while the destination port identifies the receiving application or process. This information is crucial for establishing communication between the sender and receiver.Rate this question:
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- 16.
Which three features allow TCP to reliably and accurately track the transmission of data from source to destination? (Choose three)
- A.
Flow control
- B.
Urgent pointer
- C.
Best effort delivery
- D.
Session establishment
- E.
Connectionless services
- F.
Numbering and sequencing
Correct Answer(s)
A. Flow control
D. Session establishment
F. Numbering and sequencingExplanation
TCP uses flow control to ensure that the sender does not overwhelm the receiver with data, allowing for a smooth and efficient transmission. Session establishment is necessary for TCP to establish a connection between the source and destination, ensuring reliable communication. Numbering and sequencing allow TCP to keep track of the order of data packets, ensuring that they are received and assembled correctly at the destination.Rate this question:
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- 17.
During a TCP communication session, if the packets arrive to the destination out of order, what will happen to the original message?
- A.
The packets will not be delivered
- B.
The packets will be retransmitted from the source
- C.
The packets will be delivered and reassembled at the destination
- D.
The packets will be delivered and not reassembled at the destination
Correct Answer
C. The packets will be delivered and reassembled at the destinationExplanation
In TCP communication, if the packets arrive at the destination out of order, they will still be delivered and reassembled at the destination. TCP uses sequence numbers to ensure that packets are received in the correct order. If packets arrive out of order, the receiver will reassemble them based on their sequence numbers before delivering the original message. This ensures that the data is received accurately and in the correct order, even if the packets were not transmitted in order.Rate this question:
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- 18.
Which is an important characteristic of UDP?
- A.
Acknowledgement of data delivery
- B.
Minimal delays in data delivery
- C.
High reliability of data delivery
- D.
Same order data delivery
Correct Answer
B. Minimal delays in data deliveryExplanation
UDP (User Datagram Protocol) is a connectionless protocol that operates at the transport layer of the network. It is known for its low latency and minimal delays in data delivery. Unlike TCP, UDP does not provide acknowledgement of data delivery, high reliability, or guaranteed same order data delivery. Due to its lightweight nature, UDP is commonly used for applications that prioritize speed and real-time data transmission, such as video streaming or online gaming. Therefore, the correct characteristic of UDP mentioned in the answer is its minimal delays in data delivery.Rate this question:
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- 19.
After a web browser makes a request to a web server that is listening to the standard port, what will be the source port number in the TCP header of the response from the server?
- A.
13
- B.
53
- C.
80
- D.
1024
- E.
1728
Correct Answer
C. 80Explanation
When a web browser makes a request to a web server on the standard port, the source port number in the TCP header of the response from the server will be 80. The source port number is used to identify the sending application or process on the client side, and in this case, the web browser is the client application. Port 80 is the standard port for HTTP (Hypertext Transfer Protocol), which is the protocol used for transmitting web pages and other resources over the internet. Therefore, the response from the server will have a source port number of 80.Rate this question:
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- 20.
Which event occurs during the transport layer three-way handshake?
- A.
The two applications exchange data
- B.
TCP initializes the sequence numbers for the sessions
- C.
UDP establishes the maximum number of bytes to be sent
- D.
The server acknowledges the bytes of data received from the client
Correct Answer
B. TCP initializes the sequence numbers for the sessionsExplanation
During the transport layer three-way handshake, TCP initializes the sequence numbers for the sessions. This process is crucial for establishing a reliable connection between the client and the server. The sequence numbers ensure that the data packets are delivered in the correct order and that no packets are lost during transmission. By initializing the sequence numbers, TCP sets the foundation for a successful and efficient data transfer between the two parties involved.Rate this question:
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- 21.
Which port number is used by HTTP?
- A.
23
- B.
80
- C.
53
- D.
110
Correct Answer
B. 80Explanation
HTTP (Hypertext Transfer Protocol) is a protocol used for transmitting web pages over the internet. It operates on port number 80, which is specifically designated for HTTP communication. This port allows web browsers to establish a connection with web servers and retrieve the requested web pages. Therefore, the correct answer is 80.Rate this question:
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- 22.
Which port number is used with SMTP?
- A.
20
- B.
23
- C.
25
- D.
143
Correct Answer
C. 25Explanation
SMTP (Simple Mail Transfer Protocol) is a protocol used for sending email messages between servers. The correct answer is 25 because port number 25 is the standard port used for SMTP. This port is used by email clients to connect to the email server and send outgoing emails.Rate this question:
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- 23.
Which characteristics are part of TCP? (Choose two)
- A.
Reliable
- B.
Connectionless
- C.
No flow control
- D.
Resends anything not received
Correct Answer(s)
A. Reliable
D. Resends anything not receivedExplanation
TCP (Transmission Control Protocol) is a reliable transport protocol that ensures the delivery of data packets in the correct order and without errors. It achieves reliability by implementing various mechanisms such as acknowledgments, retransmissions, and error checking. The statement "Resends anything not received" aligns with TCP's behavior of retransmitting lost or corrupted packets to ensure they are successfully delivered. Therefore, the answer choice "Reliable" is correct as TCP guarantees the reliable delivery of data.Rate this question:
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- 24.
At the transport layer, which of the following controls is used to keep a transmitting host from overflowing the buffers of a receiving host?
- A.
Best effort
- B.
Encryption
- C.
Flow control
- D.
Congestion avoidance
Correct Answer
C. Flow controlExplanation
Flow control is used at the transport layer to prevent a transmitting host from overwhelming the buffers of a receiving host. It ensures that the transmitting host sends data at a rate that the receiving host can handle, preventing buffer overflow and potential data loss. Flow control techniques include techniques like sliding window protocols, where the receiving host acknowledges received data and specifies how much more data it can accept. By regulating the flow of data, flow control helps maintain reliable and efficient communication between the transmitting and receiving hosts.Rate this question:
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- 25.
End systems use port numbers to select the proper application. What is the lowest port number that can be dynamically assigned by the host system?
- A.
1
- B.
128
- C.
256
- D.
1024
Correct Answer
D. 1024Explanation
The lowest port number that can be dynamically assigned by the host system is 1024. Port numbers are used to identify specific processes or services running on an end system. Ports below 1024 are considered well-known ports and are typically reserved for specific services, such as HTTP (port 80) or FTP (port 21). Ports above 1024 can be dynamically assigned by the host system for temporary or less commonly used services.Rate this question:
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- 26.
During data transfer, what is the receiving host responsible for? (Choose the best two answers)
- A.
Encapsulation
- B.
Bandwidth
- C.
Segmentation
- D.
Acknowledgement
- E.
Reassembly
Correct Answer(s)
D. Acknowledgement
E. ReassemblyExplanation
During data transfer, the receiving host is responsible for two main tasks: acknowledgement and reassembly. Acknowledgement refers to the process of confirming the successful receipt of data packets from the sender. This ensures that the sender knows the data has been received correctly and can proceed with the next transmission. Reassembly, on the other hand, involves reconstructing the original data from the received packets. This is especially important when data is divided into smaller segments for transmission and needs to be reassembled in the correct order at the receiving end.Rate this question:
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- 27.
Why does TCP use a sequence number in the header?
- A.
To reassemble the segments into data
- B.
To identify the application layer protocol
- C.
To indicate the number of the next expected byte
- D.
To show the maximum number of bytes allowed during a session
Correct Answer
A. To reassemble the segments into dataExplanation
TCP uses a sequence number in the header to reassemble the segments into data. This is because TCP breaks the data into smaller segments for transmission and these segments can arrive out of order at the destination. The sequence number helps the receiver to rearrange the segments in the correct order and reconstruct the original data. By using the sequence number, TCP ensures reliable and ordered delivery of data.Rate this question:
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- 28.
Which of the following determines how much data a sending host running TCP/IP can transmit before it must receive an acknowledgement?
- A.
Segment size
- B.
Transmission size
- C.
Bandwidth
- D.
Window size
Correct Answer
D. Window sizeExplanation
The window size determines how much data a sending host running TCP/IP can transmit before it must receive an acknowledgement. The window size represents the amount of data that the receiving host is willing to accept before sending an acknowledgement back to the sender. It acts as a flow control mechanism, allowing the sender to adjust its transmission rate based on the receiver's capacity to receive data. A larger window size allows for more data to be transmitted before waiting for an acknowledgement, increasing the overall efficiency of the TCP connection.Rate this question:
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- 29.
What is the purpose of TCP/UDP port numbers?
- A.
To indicate the beginning of a three-way handshake
- B.
To reassemble the segments into the correct order
- C.
To identify the number of data packets that can be sent without acknowledgement
- D.
To track the different conversations crossing the network at the same time
Correct Answer
D. To track the different conversations crossing the network at the same timeExplanation
TCP/UDP port numbers are used to track the different conversations crossing the network at the same time. Each communication session between two devices on a network is assigned a unique port number, allowing multiple conversations to occur simultaneously. This helps in routing the incoming data packets to the correct application or service running on the receiving device. By using port numbers, the network can differentiate between different conversations and ensure that the data reaches the intended destination.Rate this question:
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- 30.
List three network applications that use TCP. Please separate each answer with a comma and a space.
Correct Answer
web, email, file transfer
web, file transfer, email
email, web, file transfer
email, file transfer, web
file transfer, email, web
file transfer, web, emailExplanation
The correct answer is email, web, file transfer.Rate this question:
- 31.
List three network applications that use UDP. Please separate each answer with a comma and a space.
Correct Answer
DNS, video, VoIP
DNS, VoIP, video
video, DNS, VoIP
video, VoIP, DNS
VoIP, DNS, video
VoIP, video, DNS - 32.
What is the protocol number for UDP?
- A.
1
- B.
3
- C.
6
- D.
17
Correct Answer
D. 17Explanation
The protocol number for UDP is 17.Rate this question:
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- 33.
Which acknowledgement number should be sent by the receiver shown in the exhibit?
Correct Answer
7Explanation
The receiver should send an acknowledgement number of 7. This means that the receiver has successfully received and processed all the data up to sequence number 7 from the sender. The acknowledgement number is used to confirm the successful transmission of data and to inform the sender about the next expected sequence number.Rate this question:
- 34.
What is the default DNS port number?
- A.
1025
- B.
53
- C.
110
- D.
143
Correct Answer
B. 53Explanation
The default DNS port number is 53. DNS (Domain Name System) is responsible for translating domain names into IP addresses. It uses port 53 for communication between DNS servers and clients. This port is designated specifically for DNS traffic and is the standard port used for DNS queries and responses.Rate this question:
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Oct 27, 2011Quiz Created by
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