Introduction
Computer Networking is a fundamental cornerstone of Computer Science and Information Technology. Competitive examinations such as PPSC Lecturer Computer Science, FPSC, NTS, and network administrator recruitment tests regularly feature questions on network architectures, the OSI model, TCP/IP protocols, subnetting, and network security. This curated set contains 50 high-yield Computer Networks MCQs with verified answers and detailed explanations.
Section 1: Network Fundamentals & Topologies
Q1. What is the primary purpose of a computer network?
A) To increase hardware processing speed
B) To share resources, data, and services among connected devices
C) To run standalone software applications
D) To format hard drives
Correct Answer: B) To share resources, data, and services among connected devices
Explanation: Computer networks interconnect autonomous computing devices to exchange data and share peripheral resources efficiently.
Q2. Which network topology connects all nodes to a central central device such as a hub or switch?
A) Bus Topology
B) Ring Topology
C) Star Topology
D) Mesh Topology
Correct Answer: C) Star Topology
Explanation: In a star topology, all endpoint devices are directly connected via dedicated links to a central hub or switch.
Q3. Which topology provides maximum redundancy and high fault tolerance by connecting every node to every other node?
A) Star Topology
B) Mesh Topology
C) Tree Topology
D) Bus Topology
Correct Answer: B) Mesh Topology
Explanation: A full mesh topology connects every device to every other device ($n(n-1)/2$ links), providing complete redundancy.
Q4. In a Bus topology, what component is placed at both ends of the main backbone cable to absorb signal reflections?
A) Repeater
B) Terminator
C) Router
D) Attenuator
Correct Answer: B) Terminator
Explanation: Terminators prevent signal reflection back along the shared bus communication medium.
Q5. What type of network covers a small geographical area such as an office, room, or building?
A) WAN (Wide Area Network)
B) LAN (Local Area Network)
C) MAN (Metropolitan Area Network)
D) PAN (Personal Area Network)
Correct Answer: B) LAN (Local Area Network)
Explanation: LANs connect network equipment within a localized area such as a single home, office, or school building.
Q6. What type of network spans a city or town?
A) LAN
B) MAN
C) WAN
D) SAN
Correct Answer: B) MAN
Explanation: Metropolitan Area Networks (MAN) cover larger geographic areas than LANs, typically spanning a whole city.
Q7. Which transmission mode allows data communication in both directions simultaneously?
A) Simplex
B) Half-Duplex
C) Full-Duplex
D) Multiplex
Correct Answer: C) Full-Duplex
Explanation: Full-duplex permits concurrent bidirectional data transmission (e.g., telephone calls).
Q8. Walkie-talkies operate under which transmission mode?
A) Simplex
B) Half-Duplex
C) Full-Duplex
D) Auto-Duplex
Correct Answer: B) Half-Duplex
Explanation: Half-duplex supports bidirectional transmission, but only one direction at a time.
Q9. Television broadcasting is an example of which transmission mode?
A) Simplex
B) Half-Duplex
C) Full-Duplex
D) Multi-Simplex
Correct Answer: A) Simplex
Explanation: Simplex communication is strictly unidirectional; data travels only from transmitter to receiver.
Q10. What is the measure of the data transmission capacity of a network line?
A) Latency
B) Throughput
C) Bandwidth
D) Jitter
Correct Answer: C) Bandwidth
Explanation: Bandwidth measures the maximum volume of data that can pass through a channel per unit of time (bps).
Section 2: The OSI Reference Model
Q11. How many layers exist in the Open Systems Interconnection (OSI) reference model?
A) 4
B) 5
C) 7
D) 9
Correct Answer: C) 7
Explanation: The ISO OSI model consists of 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.
Q12. Which layer of the OSI model is responsible for routing packets across multiple networks?
A) Data Link Layer
B) Network Layer
C) Transport Layer
D) Session Layer
Correct Answer: B) Network Layer
Explanation: Layer 3 (Network Layer) handles logical IP addressing, packet forwarding, and path selection (routing).
Q13. What is the Protocol Data Unit (PDU) at Layer 2 (Data Link Layer)?
A) Bit
B) Frame
C) Packet
D) Segment
Correct Answer: B) Frame
Explanation: Data units are called Bits at Physical (Layer 1), Frames at Data Link (Layer 2), Packets at Network (Layer 3), and Segments/Datagrams at Transport (Layer 4).
Q14. Which OSI layer handles process-to-process communication and end-to-end reliability?
A) Network Layer
B) Transport Layer
C) Physical Layer
D) Application Layer
Correct Answer: B) Transport Layer
Explanation: Layer 4 (Transport Layer) manages end-to-end segmentation, flow control, and error recovery using TCP or UDP.
Q15. Encryption, decryption, and data compression are handled by which OSI layer?
A) Application Layer
B) Presentation Layer
C) Session Layer
D) Transport Layer
Correct Answer: B) Presentation Layer
Explanation: Layer 6 (Presentation Layer) formats, translates, encrypts, and compresses data for applications.
Q16. Which layer of the OSI model manages and terminates active communication sessions between applications?
A) Session Layer
B) Transport Layer
C) Data Link Layer
D) Physical Layer
Correct Answer: A) Session Layer
Explanation: Layer 5 (Session Layer) establishes, maintains, synchronizes, and closes dialogue sessions.
Q17. MAC (Media Access Control) address formatting operates at which OSI layer?
A) Layer 1 (Physical)
B) Layer 2 (Data Link)
C) Layer 3 (Network)
D) Layer 4 (Transport)
Correct Answer: B) Layer 2 (Data Link)
Explanation: MAC sublayer addressing operates within Layer 2 (Data Link Layer).
Q18. What is the hardware length of a standard MAC address?
A) 32 bits
B) 48 bits
C) 64 bits
D) 128 bits
Correct Answer: B) 48 bits
Explanation: MAC addresses are 48-bit (6-byte) hexadecimal values burned into Network Interface Cards (NICs).
Q19. At which OSI layer do network Switches primarily operate?
A) Physical Layer
B) Data Link Layer
C) Network Layer
D) Transport Layer
Correct Answer: B) Data Link Layer
Explanation: Layer 2 switches inspect destination MAC addresses in frame headers to forward traffic.
Q20. At which OSI layer do network Routers operate?
A) Data Link Layer
B) Network Layer
C) Transport Layer
D) Application Layer
Correct Answer: B) Network Layer
Explanation: Routers operate at Layer 3 (Network Layer) using IP addresses to route packets between networks.
Section 3: TCP/IP Protocols & Port Numbers
Q21. How many layers are in the updated TCP/IP protocol suite model?
A) 4
B) 5
C) 6
D) 7
Correct Answer: A) 4
Explanation: The classic TCP/IP model has 4 layers: Link, Internet, Transport, and Application.
Q22. Which protocol at the Transport layer provides connection-oriented, reliable transmission with flow control?
A) UDP
B) TCP
C) IP
D) ICMP
Correct Answer: B) TCP
Explanation: TCP (Transmission Control Protocol) establishes connections via a 3-way handshake and guarantees packet delivery.
Q23. Which protocol at the Transport layer is connectionless, unreliable, but low-overhead and fast?
A) TCP
B) UDP
C) FTP
D) ARP
Correct Answer: B) UDP
Explanation: UDP (User Datagram Protocol) transmits datagrams without establishing prior connections or retransmitting lost packets.
Q24. What mechanism does TCP use to establish a reliable connection between sender and receiver?
A) 2-way Handshake
B) 3-way Handshake
C) Sliding Window
D) Ping Request
Correct Answer: B) 3-way Handshake
Explanation: TCP establishes connection states using SYN, SYN-ACK, and ACK packet exchanges.
Q25. What is the default port number used by HTTP?
A) 21
B) 25
C) 80
D) 443
Correct Answer: C) 80
Explanation: Unencrypted HTTP traffic listens on TCP port 80.
Q26. What is the default port number used by HTTPS (Secure HTTP)?
A) 80
B) 443
C) 8080
D) 22
Correct Answer: B) 443
Explanation: Encrypted HTTPS traffic runs over SSL/TLS on TCP port 443.
Q27. Which protocol translates human-readable domain names into IP addresses?
A) DHCP
B) DNS
C) ARP
D) FTP
Correct Answer: B) DNS
Explanation: DNS (Domain Name System) maps hostnames to IP addresses using port 53.
Q28. Which protocol automatically assigns dynamic IP addresses to host devices on a network?
A) DNS
B) DHCP
C) NAT
D) SNMP
Correct Answer: B) DHCP
Explanation: Dynamic Host Configuration Protocol (DHCP) automatically assigns IP parameters to network devices.
Q29. Which protocol resolves an IP address to a physical MAC address?
A) RARP
B) ARP
C) ICMP
D) IGMP
Correct Answer: B) ARP
Explanation: Address Resolution Protocol (ARP) resolves known Layer 3 IP addresses into Layer 2 MAC addresses.
Q30. Which protocol is used by utilities like ping to report network errors and diagnostic messages?
A) IGMP
B) ICMP
C) SMTP
D) SNMP
Correct Answer: B) ICMP
Explanation: Internet Control Message Protocol (ICMP) handles network error reporting and diagnostic queries.
Section 4: IP Addressing & Subnetting
Q31. How many bits are in an IPv4 address?
A) 16 bits
B) 32 bits
C) 64 bits
D) 128 bits
Correct Answer: B) 32 bits
Explanation: IPv4 uses a 32-bit address space, usually formatted in dotted-decimal notation (e.g., 192.168.1.1).
Q32. How many bits are in an IPv6 address?
A) 32 bits
B) 64 bits
C) 128 bits
D) 256 bits
Correct Answer: C) 128 bits
Explanation: IPv6 uses 128 bits formatted as eight groups of four hexadecimal digits separated by colons.
Q33. What is the default subnet mask for a Class C IPv4 address?
A) 255.0.0.0
B) 255.255.0.0
C) 255.255.255.0
D) 255.255.255.255
Correct Answer: C) 255.255.255.0
Explanation: Class C uses 24 bits for the network component and 8 bits for host addresses.
Q34. What range of first-octet numbers defines a Class A IPv4 address?
A) 1 – 126
B) 128 – 191
C) 192 – 223
D) 224 – 239
Correct Answer: A) 1 – 126
Explanation: Class A IPs range from 1.0.0.0 to 126.255.255.255 (127.x.x.x is reserved for loopback).
Q35. What is the loopback IPv4 address used for testing local host TCP/IP stack functionality?
A) 0.0.0.0
B) 127.0.0.1
C) 192.168.0.1
D) 255.255.255.255
Correct Answer: B) 127.0.0.1
Explanation: 127.0.0.1 (localhost) sends traffic directly back to the local software network stack.
Q36. What class of IPv4 addresses is reserved for Multicast traffic?
A) Class B
B) Class C
C) Class D
D) Class E
Correct Answer: C) Class D
Explanation: Class D IP addresses (224.0.0.0 to 239.255.255.255) are assigned for multicast messaging.
Q37. Which of the following is a private IPv4 address range?
A) 8.8.8.8
B) 192.168.1.1
C) 1.1.1.1
D) 200.100.10.1
Correct Answer: B) 192.168.1.1
Explanation: RFC 1918 defines private IP spaces: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
Q38. What technology translates private local IP addresses to a single public IP address for internet routing?
A) DHCP
B) NAT (Network Address Translation)
C) DNS
D) VPN
Correct Answer: B) NAT (Network Address Translation)
Explanation: NAT maps internal private local addresses to a public external IP address.
Q39. What is the network prefix length notation for subnet mask 255.255.255.0?
A) /8
B) /16
C) /24
D) /32
Correct Answer: C) /24
Explanation: CIDR notation count bits set to 1: $8 + 8 + 8 = 24$, so it is represented as /24.
Q40. How many usable host IP addresses are provided by a /24 subnet?
A) 256
B) 254
C) 255
D) 128
Correct Answer: B) 254
Explanation: Total IP slots are $2^8 = 256$. Subtracting Network ID and Broadcast address leaves 254 usable host IPs.
Section 5: Network Hardware, Media & Security (41-50)
Q41. Which networking device operates at Layer 1 (Physical Layer) and blindly broadcasts received signals to all connected ports?
A) Switch
B) Router
C) Hub
D) Gateway
Correct Answer: C) Hub
Explanation: Legacy hubs operate at the Physical layer, broadcasting incoming frames across all ports indiscriminately.
Q42. Which connector type is standard for Ethernet twisted-pair copper cables?
A) RJ-11
B) RJ-45
C) BNC
D) SMA
Correct Answer: B) RJ-45
Explanation: RJ-45 is the standard 8-position, 8-contact connector used for Ethernet cabling.
Q43. Which transmission medium transfers data using light pulses instead of electrical signals?
A) Coaxial Cable
B) Unshielded Twisted Pair (UTP)
C) Fiber Optic Cable
D) Shielded Twisted Pair (STP)
Correct Answer: C) Fiber Optic Cable
Explanation: Fiber optic cables send light signals along glass strands, offering ultra-high bandwidth and immunity to EMI.
Q44. What collision handling technology is used by traditional wired Ethernet networks?
A) CSMA/CA
B) CSMA/CD
C) Token Passing
D) ALOHA
Correct Answer: B) CSMA/CD
Explanation: Wired Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
Q45. What collision avoidance technology is used by wireless Wi-Fi networks (IEEE 802.11)?
A) CSMA/CD
B) CSMA/CA
C) Polling
D) TDMA
Correct Answer: B) CSMA/CA
Explanation: Wireless media cannot detect collisions during transmission, using Collision Avoidance (CSMA/CA) instead.
Q46. Which security appliance monitors and filters incoming and outgoing network traffic based on predefined firewall rules?
A) Switch
B) Bridge
C) Firewall
D) Repeater
Correct Answer: C) Firewall
Explanation: Firewalls enforce security boundaries between trusted internal networks and untrusted external traffic.
Q47. What type of attack floods a targeted network server with overwhelming traffic to render it unavailable?
A) Man-in-the-Middle (MitM)
B) Denial of Service (DoS / DDoS)
C) Phishing
D) SQL Injection
Correct Answer: B) Denial of Service (DoS / DDoS)
Explanation: DoS/DDoS attacks exhaust server bandwidth or processing resources to disrupt service.
Q48. Which protocol encrypts remote terminal logins over port 22, replacing unencrypted Telnet?
A) FTP
B) SSH (Secure Shell)
C) SNMP
D) HTTP
Correct Answer: B) SSH (Secure Shell)
Explanation: SSH provides encrypted communication for command-line access on port 22.
Q49. What network software/hardware creates a secure, encrypted tunnel over a public network like the internet?
A) NAT
B) VPN (Virtual Private Network)
C) VLAN
D) Proxy
Correct Answer: B) VPN (Virtual Private Network)
Explanation: A VPN encrypts traffic across public networks to provide secure remote connectivity.
Q50. What technology logically segments a single physical switch into multiple isolated broadcast domains?
A) VPN
B) VLAN (Virtual LAN)
C) NAT
D) Subnetting
Correct Answer: B) VLAN (Virtual LAN)
Explanation: VLANs group switch ports into distinct logical broadcast domains regardless of physical location.
Conclusion
Mastering these 50 Computer Networks MCQs gives you a strong foundation across network layers, protocols, IP addressing schemes, and security fundamentals. Consistently practicing these high-frequency topics will boost your performance in competitive examinations like PPSC, FPSC, and NTS.
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