Which of the following is a distributed multi-access network that helps in supporting integrated communications using a dual bus and distributed queuing?
Correct Answer: C
In telecommunication, a distributed-queue dual-bus network (DQDB) is a distributed multi-access network that helps in supporting integrated communications using a dual bus and distributed queuing, providing access to local or metropolitan area networks, and supporting connectionless data transfer, connection-oriented data transfer, and isochronous communications, such as voice communications. IEEE 802.6 is an example of a network providing DQDB access methods. Answer option B is incorrect. A Token Ring network is a local area network (LAN) in which all computers are connected in a ring or star topology and a bit- or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time. The Token Ring protocol is the second most widely-used protocol on local area networks after Ethernet. The IBM Token Ring protocol led to a standard version, specified as IEEE 802.5. Both protocols are used and are very similar. The IEEE 802.5 Token Ring technology provides for data transfer rates of either 4 or 16 megabits per second. Answer option A is incorrect. The IEEE 802.2 standard defines Logical Link Control (LLC). LLC is the upper portion of the data link layer for local area networks. Answer option D is incorrect. Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) is an access method used by wireless networks (IEEE 802.11). In this method, a device or computer that transmits data needs to first listen to the channel for an amount of time to check for any activity on the channel. If the channel is sensed as idle, the device is allowed to transmit data. If the channel is busy, the device postpones its transmission. Once the channel is clear, the device sends a signal telling all other devices not to transmit data, and then sends its packets. In Ethernet (IEEE 802.3) networks that use CSMA/CD, the device or computer continues to wait for a time and checks if the channel is still free. If the channel is free, the device transmits packets and waits for an acknowledgment signal indicating that the packets were received.
Question 267
During a security awareness program, management was explaining the various reasons which create threats to network security. Which could be a possible threat to network security?
Correct Answer: A
Question 268
What should an administrator do while installing a sniffer on a system to listen to all data transmitted over the network?
Correct Answer: D
In the context of network sniffing, promiscuous mode is a specific setting for a network interface controller (NIC) that allows the NIC to pass all traffic it receives to the central processing unit, rather than just the frames that the NIC is specifically programmed to receive. This mode is essential for network sniffers, as it enables them to capture all network traffic, including packets not addressed to the NIC's MAC address. When a NIC is not in promiscuous mode, it will ignore packets not intended for its MAC address.
Question 269
Which of the following key features is used by TCP in order to regulate the amount of data sent by a host to another host on the network?
Correct Answer: D
Flow control is the process of regulating the amount of data sent by a host to another host on the network. The flow control mechanism controls packet flow so that a sender does not transmit more packets than a receiver can process. TCP uses a sliding window flow control protocol. In each TCP segment, the receiver specifies in the receive window field the amount of additional received data (in bytes) that it is willing to buffer for the connection. The sending host can send only up to that amount of data before it must wait for an acknowledgment and window update from the receiving host. Answer option A is incorrect. TCP uses a sequence number for identifying each byte of data. Answer option B is incorrect. TCP timestamp helps TCP to compute the round-trip time between the sender and receiver. Answer option C is incorrect. Congestion control concerns controlling traffic entry into a telecommunications network, so as to avoid congestive collapse by attempting to avoid oversubscription of any of the processing or link capabilities of the intermediate nodes and networks and taking resource reducing steps, such as reducing the rate of sending packets. It should not be confused with flow control, which prevents the sender from overwhelming the receiver.
Question 270
In which of the following attacks does an attacker use software that tries a large number of key combinations in order to get a password?
Correct Answer: B
In a brute force attack, an attacker uses software that tries a large number of key combinations in order to get a password. To prevent such attacks, users should create passwords that are more difficult to guess, i.e., by using a minimum of six characters, alphanumeric combinations, and lower-upper case combinations. Answer option D is incorrect. Smurf is an attack that generates significant computer network traffic on a victim network. This is a type of denial-of-service attack that floods a target system via spoofed broadcast ping messages. In such attacks, a perpetrator sends a large amount of ICMP echo request (ping) traffic to IP broadcast addresses, all of which have a spoofed source IP address of the intended victim. If the routing device delivering traffic to those broadcast addresses delivers the IP broadcast to all hosts, most hosts on that IP network will take the ICMP echo request and reply to it with an echo reply, which multiplies the traffic by the number of hosts responding. Answer option A is incorrect. Buffer overflow is a condition in which an application receives more data than it is configured to accept. It helps an attacker not only to execute a malicious code on the target system but also to install backdoors on the target system for further attacks. All buffer overflow attacks are due to only sloppy programming or poor memory management by the application developers. The main types of buffer overflows are: Stack overflow Format string overflow Heap overflow Integer overflow Answer option C is incorrect. A zero-day attack, also known as zero-hour attack, is a computer threat that tries to exploit computer application vulnerabilities which are unknown to others, undisclosed to the software vendor, or for which no security fix is available. Zero-day exploits (actual code that can use a security hole to carry out an attack) are used or shared by attackers before the software vendor knows about the mvulnerability. User awareness training is the most effective technique to mitigate such attacks.
