81. What is the role of the Physical Layer in the OSI model?
- To encrypt data before transmission
- To route packets between networks
- To transmit raw bits over a physical medium such as cables or radio waves
- To manage sessions between applications
Answer : C Explanation: The Physical Layer (Layer 1) is the lowest layer of the OSI model. It deals with the actual physical transmission of raw data bits (0s and 1s) over a physical medium such as copper cables, fiber optic cables, or wireless radio waves. It defines electrical, optical, and radio specifications including voltage levels, timing, cable types, connectors, and data rates. Examples include Ethernet cables, fiber optics, and Wi-Fi signals.
82. What is the difference between TCP/IP model and the OSI model?
- TCP/IP has 7 layers; OSI has 4 layers
- OSI has 7 layers and is a theoretical reference model; TCP/IP has 4 layers and is the practical model used on the internet
- OSI is used on the internet; TCP/IP is only used in academic environments
- They are identical models with different names
Answer : B Explanation: The OSI model has 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, Application) and is a theoretical reference framework used for understanding network communication. The TCP/IP model has 4 layers (Network Access, Internet, Transport, Application) and is the practical model that the internet actually runs on. The TCP/IP Application layer combines OSI’s Session, Presentation, and Application layers.
83. What is a VLAN (Virtual Local Area Network) and what are its benefits?
- A VLAN is a physical network segment that connects different buildings
- A VLAN logically segments a network into separate broadcast domains, improving security and performance
- A VLAN is a wireless network that spans multiple cities
- A VLAN is used exclusively for connecting routers together
Answer : B Explanation: A VLAN (Virtual Local Area Network) is a logical grouping of devices on the same or different physical switches into separate broadcast domains. Benefits include improved security (isolating sensitive departments like finance from general users), reduced broadcast traffic, easier network management, and flexibility to group users by function rather than physical location. VLANs are configured on managed switches and communicate with each other through Layer 3 routing.
84. What is network topology and what are its main types?
- Network topology refers to the speed of a network; types are fast, medium, and slow
- Network topology is the physical or logical arrangement of devices in a network; main types are Bus, Star, Ring, Mesh, and Tree
- Network topology refers to the number of devices in a network
- Network topology is the security level of a network; types are low, medium, and high
Answer : B Explanation: Network topology describes how devices in a network are arranged and connected — either physically (actual cable layout) or logically (how data flows). The five main types are: Bus (all devices on a single cable), Star (all devices connected to a central hub/switch), Ring (devices in a circular chain), Mesh (every device connected to every other device), and Tree (hierarchical combination of star topologies). Each has different advantages in terms of cost, reliability, and scalability.
85. What is a hub and how does it differ from a switch?
- A hub and switch are identical devices
- A hub broadcasts data to all connected ports; a switch intelligently forwards data only to the intended destination port
- A hub operates at Layer 3; a switch operates at Layer 1
- A hub is faster than a switch in all cases
Answer : B Explanation: A hub is a basic Layer 1 device that broadcasts incoming data to all connected ports regardless of the intended destination — causing unnecessary traffic and collisions. A switch is a Layer 2 device that learns MAC addresses and forwards frames only to the specific port of the intended recipient, dramatically reducing traffic and improving efficiency. Because of this, hubs are now obsolete and have been replaced by switches in all modern networks.
86. What is network congestion and how is it controlled?
- Network congestion occurs when a device runs out of storage; controlled by adding more hard drives
- Network congestion occurs when too much data overwhelms a network; controlled through flow control, traffic shaping, and queuing
- Network congestion is a type of cyber attack; controlled through firewalls
- Network congestion occurs only in wireless networks; controlled by adding more access points
Answer : B Explanation: Network congestion occurs when the volume of data traffic exceeds the network’s capacity to handle it, causing delays, packet loss, and reduced performance. It is controlled through mechanisms such as TCP flow control (adjusting transmission rate based on receiver capacity), traffic shaping (smoothing out bursts), queuing algorithms (prioritizing important traffic), and congestion avoidance algorithms like TCP’s AIMD (Additive Increase Multiplicative Decrease).
87. What is a repeater and at which OSI layer does it operate?
- A repeater filters network traffic — operates at Layer 3
- A repeater regenerates and amplifies weak signals to extend network range — operates at Layer 1
- A repeater connects different network protocols — operates at Layer 4
- A repeater assigns IP addresses — operates at Layer 2
Answer : B Explanation: A repeater is a Layer 1 (Physical Layer) device that receives a weak or degraded signal and regenerates/amplifies it to extend the transmission distance. It does not filter or interpret data — it simply boosts the signal. Repeaters are used in long cable runs where the signal would otherwise degrade below usable levels. In wireless networks, the equivalent device is a wireless range extender or access point in repeater mode.
88. What is the purpose of a DNS cache?
- To store all website files locally for offline access
- To temporarily store recently resolved DNS records to speed up future lookups
- To backup DNS server configurations
- To block malicious websites automatically
Answer : B Explanation: A DNS cache stores recently resolved domain name-to-IP address mappings locally on a device or DNS resolver. When you revisit a website, the device checks its DNS cache first before querying a DNS server, significantly reducing lookup time and network traffic. Each cached record has a TTL (Time to Live) value that determines how long it is kept before expiring. You can clear the DNS cache on Windows using the command “ipconfig /flushdns”.
89. What is the difference between symmetric and asymmetric encryption?
- Symmetric encryption uses two different keys; asymmetric uses one key
- Symmetric encryption uses the same key for encryption and decryption; asymmetric uses a public-private key pair
- Symmetric encryption is slower than asymmetric encryption
- Asymmetric encryption is only used for file storage; symmetric is used for network communication
Answer : B Explanation: Symmetric encryption uses the same key for both encrypting and decrypting data — it is fast but requires secure key exchange. Examples include AES and DES. Asymmetric encryption uses a mathematically linked key pair: a public key (shared openly) for encryption and a private key (kept secret) for decryption. Examples include RSA and ECC. HTTPS uses asymmetric encryption to exchange keys, then symmetric encryption for the actual data transfer.
90. What is a man-in-the-middle (MITM) attack?
- An attack where the attacker floods a server with traffic
- An attack where the attacker secretly intercepts and possibly alters communication between two parties
- An attack that targets the physical hardware of network devices
- An attack that sends fake DNS responses to redirect users
Answer : B Explanation: A Man-in-the-Middle (MITM) attack occurs when an attacker secretly positions themselves between two communicating parties, intercepting and potentially altering the communication without either party knowing. Common techniques include ARP spoofing, DNS spoofing, and SSL stripping. MITM attacks can steal credentials, session cookies, and sensitive data. HTTPS, VPNs, and certificate pinning are key defenses against MITM attacks.
