CCNA 1 Module 14 Quiz – Transport Layer (Answers)

1. Network congestion has resulted in the source learning of the loss of TCP segments that were sent to the destination. What is one way that the TCP protocol addresses this?

  • The source decreases the amount of data that it transmits before it receives an acknowledgement from the destination.
  • The source decreases the window size to decrease the rate of transmission from the destination.
  • The destination decreases the window size.
  • The destination sends fewer acknowledgement messages in order to conserve bandwidth.
Explanation: If the source determines that the TCP segments are either not being acknowledged or are not acknowledged in a timely manner, then it can reduce the number of bytes it sends before receiving an acknowledgment. This does not involve changing the window in the segment header. The source does not decrease the window that is sent in the segment header. The window in the segment header is adjusted by the destination host when it is receiving data faster than it can process it, not when network congestion is encountered.

2. Which two operations are provided by TCP but not by UDP? (Choose two.)

  • identifying the applications
  • acknowledging received data
  • tracking individual conversations
  • retransmitting any unacknowledged data
  • reconstructing data in the order received
Explanation: Numbering and tracking data segments, acknowledging received data, and retransmitting any unacknowledged data are reliability operations to ensure that all of the data arrives at the destination. UDP does not provide reliability. Both TCP and UDP identify the applications and track individual conversations. UDP does not number data segments and reconstructs data in the order that it is received.

3. What is the TCP mechanism used in congestion avoidance?

  • three-way handshake
  • socket pair
  • two-way handshake
  • sliding window
Explanation: TCP uses windows to attempt to manage the rate of transmission to the maximum flow that the network and destination device can support while minimizing loss and retransmissions. When overwhelmed with data, the destination can send a request to reduce the of the window. This congestion avoidance is called sliding windows.

4. What is a responsibility of transport layer protocols?

  • providing network access
  • tracking individual conversations
  • determining the best path to forward a packet
  • translating private IP addresses to public IP addresses

Explanation: There are three main responsibilities for transport layer protocols TCP and UDP:

  • Tracking individual conversations
  • Segmenting data and reassembling segments
  • Identifying the applications

5. How does a networked server manage requests from multiple clients for different services?

  • The server sends all requests through a default gateway.
  • Each request is assigned source and destination port numbers.
  • The server uses IP addresses to identify different services.
  • Each request is tracked through the physical address of the client.
Explanation: Each service provided by a server, such as email or file transfers, uses a specific port number. The source port number of a service request identifies the client that is requesting services. The destination port number identifies the specific service. Servers do not use address information to provide services. Routers and switches use addressing information to move traffic through the network.

6. Which two services or protocols use the preferred UDP protocol for fast transmission and low overhead? (Choose two)

  • FTP
  • DNS
  • HTTP
  • POP3
  • VoIP
Explanation: Both DNS and VoIP use UDP to provide low overhead services within a network implementation.​

7. What is the purpose of using a source port number in a TCP communication?

  • to notify the remote device that the conversation is over
  • to assemble the segments that arrived out of order
  • to keep track of multiple conversations between devices
  • to inquire for a nonreceived segment
Explanation: The source port number in a segment header is used to keep track of multiple conversations between devices. It is also used to keep an open entry for the response from the server. The incorrect options are more related to flow control and guaranteed delivery.

8. Which number or set of numbers represents a socket?

  • 01-23-45-67-89-AB
  • 21
Explanation: A socket is defined by the combination of an IP address and a port number, and uniquely identifies a particular communication.

9. Which two flags in the TCP header are used in a TCP three-way handshake to establish connectivity between two network devices? (Choose two.)

  • ACK
  • FIN
  • PSH
  • RST
  • SYN
  • URG
Explanation: TCP uses the SYN and ACK flags in order to establish connectivity between two network devices.

10. What happens if part of an FTP message is not delivered to the destination?

  • The message is lost because FTP does not use a reliable delivery method.
  • The FTP source host sends a query to the destination host.
  • The part of the FTP message that was lost is re-sent.
  • The entire FTP message is re-sent.
Explanation: Because FTP uses TCP as its transport layer protocol, sequence and acknowledgment numbers will identify the missing segments, which will be re-sent to complete the message.

11. What type of applications are best suited for using UDP?

  • applications that are sensitive to delay
  • applications that need reliable delivery
  • applications that require retransmission of lost segments
  • applications that are sensitive to packet loss
Explanation: UDP is not a connection-oriented protocol and does not provide retransmission, sequencing, or flow control mechanisms. It provides basic transport layer functions with  a much lower overhead than TCP. Lower overhead makes UDP suitable for applications which are sensitive to delay.

12. Which action is performed by a client when establishing communication with a server via the use of UDP at the transport layer?

  • The client sets the window size for the session.
  • The client sends an ISN to the server to start the 3-way handshake.
  • The client randomly selects a source port number.
  • The client sends a synchronization segment to begin the session.
Explanation: Because a session does not have to be established for UDP, the client selects a random source port to begin a connection. The random port number selected is inserted into the source port field of the UDP header.

13. Which transport layer feature is used to guarantee session establishment?

  • UDP ACK flag
  • TCP 3-way handshake
  • UDP sequence number
  • TCP port number
Explanation: TCP uses the 3-way handshake. UDP does not use this feature. The 3-way handshake ensures there is connectivity between the source and destination devices before transmission occurs.

14. What is the complete range of TCP and UDP well-known ports?

  • 0 to 255
  • 0 to 1023
  • 256 – 1023
  • 1024 – 49151
Explanation: There are three ranges of TCP and UDP ports. The well-know range of port numbers is from 0 – 1023.

15. What is a socket?

  • the combination of the source and destination IP address and source and destination Ethernet address
  • the combination of a source IP address and port number or a destination IP address and port number
  • the combination of the source and destination sequence and acknowledgment numbers
  • the combination of the source and destination sequence numbers and port numbers
Explanation: A socket is a combination of the source IP address and source port or the destination IP address and the destination port number.

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