Computer Science/IT MCQs
Topic Notes: Computer Science/IT
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
21
Which protocol is used by 'Ping' and 'Traceroute'?
Answer:
ICMP
The Internet Control Message Protocol (ICMP) is used by network devices to send error messages and operational information. Ping uses ICMP 'Echo Request' and 'Echo Reply' messages, while Traceroute often uses ICMP 'Time Exceeded' messages (generated when TTL reaches 0) to map the path to a destination.
22
In the context of Optical Fiber communication, what is 'Four-Wave Mixing' (FWM)?
Answer:
A nonlinear effect where the interaction of three wavelengths produces a fourth wavelength.
Four-Wave Mixing (FWM) is a third-order nonlinear effect in optical fibers. When three signals of different frequencies propagate through a fiber, they interact to generate new signals at frequencies that can overlap with existing channels, causing crosstalk and signal degradation, particularly in Wavelength Division Multiplexing (WDM) systems.
23
In Software Defined Networking (SDN), what is the primary role of the Southbound API?
Answer:
Communication between the SDN controller and the network forwarding devices.
The Southbound API is the interface used by the SDN controller to communicate with and program the underlying network switches and routers (forwarding plane). OpenFlow is the most well-known example of a Southbound API, enabling the separation of the control plane from the data plane.
24
What is the primary vulnerability addressed by 'DNSSEC'?
Answer:
DNS cache poisoning and man-in-the-middle attacks.
DNS Security Extensions (DNSSEC) add digital signatures to DNS records. This allows a DNS resolver to verify that the information received from the DNS server is authentic and has not been tampered with. It prevents attackers from redirecting users to malicious websites via cache poisoning.
25
In a Chord Distributed Hash Table (DHT), if there are $N$ nodes in the system, what is the average number of hops required to resolve a query?
Answer:
$O(\log N)$
Chord uses a finger table to maintain routing information for nodes at exponential distances around the identifier circle. This structure allows the system to resolve lookups by halving the distance to the target in each step, resulting in a lookup efficiency of $O(\log N)$ hops, which is highly scalable for large distributed systems.
26
Which of the following describes the 'Poisson distribution' relevance in network traffic modeling?
Answer:
It is used for modeling packet arrivals in traditional voice-centric networks.
While Poisson distributions were historically used to model telephone call arrivals (random and independent), they are often poor models for modern computer network traffic, which tends to be 'self-similar' or 'bursty'. However, the Poisson process remains a fundamental mathematical model for simple queuing theory in networking.
27
What is 'Forward Error Correction' (FEC)?
Answer:
A technique where the sender adds redundant data so the receiver can correct errors without retransmission.
FEC is a signal processing technique where the sender includes extra (redundant) information in the message. This allows the receiver to detect and fix a certain number of bit errors caused by noise or interference on the transmission channel, reducing the need for time-consuming retransmissions.
28
In the BGP decision process, which attribute is checked first (highest priority)?
Answer:
Weight (Cisco specific) or Local Preference
The BGP path selection process follows a specific hierarchy. On Cisco routers, 'Weight' is checked first. In standard BGP implementations, 'Local Preference' is the first attribute evaluated. These attributes allow administrators to favor certain outbound paths over others before looking at path lengths or origin types.
29
Which of the following best describes 'VLAN Trunking' (802.1Q)?
Answer:
Connecting two switches and allowing traffic from multiple VLANs to pass over a single link.
VLAN Trunking allows multiple Virtual LANs to share a single physical connection between network devices (like switches). The 802.1Q standard adds a 'tag' to the Ethernet frame header to identify which VLAN the frame belongs to, ensuring the receiving switch can correctly route the traffic to the appropriate VLAN.
30
What is a 'Content-Addressable Memory' (CAM) table used for in a switch?
Answer:
To map MAC addresses to the physical ports on which they were seen.
A CAM table (often called a MAC address table) is used by high-speed switches to make forwarding decisions. When a frame arrives, the switch looks at the destination MAC address and checks the CAM table to determine which physical port that MAC address is associated with. If it's not in the table, the switch broadcasts the frame to all ports.