Last Updated on September 20, 2021 by Admin 2

312-38 : Certified Network Defender : Part 12

  1. Which of the following IEEE standards adds QoS features and multimedia support?

    • 802.11b
    • 802.11e
    • 802.5
    • 802.11a
  2. What is the range for well known ports?

    • 49152 through 65535
    • 1024 through 49151
    • Above 65535
    • 0 through 1023
  3. Which of the following IEEE standards defines the demand priority access method?

    • 802.15
    • 802.3
    • 802.12
    • 802.11
  4. Which of the following is an example of a network providing DQDB access methods?

    • IEEE 802.3
    • IEEE 802.2
    • IEEE 802.4
    • IEEE 802.6
  5. Which of the following OSI layers formats and encrypts data to be sent across the network?

    • Transport layer
    • Network layer
    • Physical layer
    • Presentation layer
  6. Which of the following protocols is used in wireless networks?

    • CSMA
    • CSMA/CD
    • ALOHA
    • CSMA/CA
  7. Token Ring is standardized by which of the following IEEE standards?

    • 802.2
    • 802.4
    • 802.3
    • 802.1
  8. Which of the following protocols is used to report an error in datagram processing?

    • ARP
    • BGP
    • ICMP
    • DHCP
  9. Which of the following is a high-speed network that connects computers, printers, and other network devices together?

    • MAN
    • LAN
    • WAN
    • CAN
  10. Which of the following TCP/IP state transitions represents no connection state at all?

    • Closed
    • Closed
    • Close-wait
    • Fin-wait-1
  11. What is the range for private ports?

    • 49152 through 65535
    • 1024 through 49151
    • Above 65535
    • 0 through 1023
  12. Which of the following protocols supports source-specific multicast (SSM)?

    • DHCP
    • ARP
    • DNS
    • BGMP
  13. Which of the following standards is approved by IEEE-SA for wireless personal area networks?

    • 802.11a
    • 802.15
    • 802.16
    • 802.1
  14. Which of the following ranges of addresses can be used in the first octet of a Class A network address?

    • 0-127
    • 192-223
    • 224-255
    • 128-191
  15. Which of the following ranges of addresses can be used in the first octet of a Class B network address?

    • 224-255
    • 128-191
    • 0-127
    • 192-223
  16. Which of the following OSI layers defines the electrical and physical specifications for devices?

    • Data link layer
    • Presentation layer
    • Physical layer
    • Transport layer
  17. Which of the following protocols is a method for implementing virtual private networks?

    • SSL
    • PPTP
    • TLS
    • SNMP
  18. Which of the following layers provides communication session management between host computers?

    • Application layer
    • Internet layer
    • Transport layer
    • Link layer
  19. Which of the following flags is set when a closed port responds to an Xmas tree scan?

    • RST
    • ACK
    • PUSH
    • FIN
  20. Which of the following is a congestion control mechanism that is designed for unicast flows operating in an Internet environment and competing with TCP traffic?

    • Sliding Window
    • TCP Friendly Rate Control
    • Selective Acknowledgment
    • Additive increase/multiplicative-decrease
    Explanation:
    TCP-Friendly Rate Control (TFRC) is a congestion control mechanism that is designed for unicast flows operating in an Internet environment and competing with TCP traffic. Its goal is to compete fairly with TCP traffic on medium timescales, but to be much less variable than TCP on short timescales.
    TCP congestion control works by maintaining a window of packets that have not yet been acknowledged. This window is increased by one packet every round-trip time if no packets have been lost, and is decreased by half if a packet loss is detected. Thus, TCP’s window is a function of the losses observed in the network and the round trip time experienced by the flow.
    The idea behind TFRC is to measure the loss probability and round trip time and to use these as the parameters to a model of TCP throughput. The expected throughput from this model is then used to directly drive the transmit rate of a TFRC flow.
    Answer option D is incorrect. The additive increase/multiplicative-decrease (AIMD) algorithm is a feedback control algorithm used in TCP Congestion Avoidance. Its major goal is to achieve fairness and efficiency in allocating resources. AIMD combines linear growth of the congestion window with an exponential reduction when congestion takes place.
    The approach taken is to increase the transmission rate (window size), probing for usable bandwidth, until loss occurs. The policy of additive increase may, for instance, increase the congestion window by 1 MSS (Maximum segment size) every RTT (Round Trip Time) until a loss is detected. When loss is detected, the policy is changed to be one of multiplicative decrease, which may, for instance, cut the congestion window in half after the loss. A loss event is generally described to be either a timeout or the event of receiving 3 duplicate ACKs.
    Answer option C is incorrect. Selective Acknowledgment (SACK) is one of the forms of acknowledgment. With selective acknowledgments, the sender can be informed by a data receiver about all segments that have arrived successfully, so the sender retransmits only those segments that have actually been lost. The selective acknowledgment extension uses two TCP options:
    The first is an enabling option, “SACK-permitted”, which may be sent in a SYN segment to indicate that the SACK option can be used once the connection is established.
    The other is the SACK option itself, which can be sent over an established connection once permission has been given by “SACK-permitted”.
    Answer option A is incorrect. Sliding Window Protocols are a feature of packet-based data transmission protocols. They are used where reliable in-order delivery of packets is required, such as in the data link layer (OSI model) as well as in TCP.
    Conceptually, each portion of the transmission (packets in most data link layers, but bytes in TCP) is assigned a unique consecutive sequence number, and the receiver uses the numbers to place received packets in the correct order, discarding duplicate packets and identifying missing ones. The problem with this is that there is no limit of the size of the sequence numbers that can be required.