Computer Networks MCQ Questions And Answers

Computer Networks MCQ Questions And Answers

31. Which protocol is responsible for translating human-readable domain names like www.google.com into IP addresses?

  1. DHCP
  2. FTP
  3. DNS
  4. ARP

Answer : C
Explanation: DNS (Domain Name System) is the protocol responsible for translating domain names into IP addresses. When you type www.google.com into your browser, a DNS server looks up the corresponding IP address so your device knows where to send the request. Without DNS, users would have to memorize numerical IP addresses to visit any website.

32. Which protocol automatically assigns IP addresses to devices when they connect to a network?

  1. SNMP
  2. DHCP
  3. FTP
  4. ICMP

Answer : B
Explanation: DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses, subnet masks, default gateways, and DNS server addresses to devices joining a network. Without DHCP, a network administrator would have to manually configure each device — a time-consuming task on large networks. DHCP makes network management far more efficient and scalable.

33. What is the default port number used by HTTP?

  1. 443
  2. 21
  3. 25
  4. 80

Answer : D
Explanation: HTTP (HyperText Transfer Protocol) uses port 80 by default. Port 443 is reserved for HTTPS, port 21 for FTP, and port 25 for SMTP. These fall under well-known ports (0–1023) assigned by IANA. Knowing default port numbers is a commonly tested concept in networking interviews and certification exams like CCNA and CompTIA Network+.

34. What is the key difference between TCP and UDP?

  1. TCP is connectionless; UDP is connection-oriented
  2. UDP guarantees reliable delivery; TCP does not
  3. TCP provides reliable, ordered, error-checked delivery; UDP is faster but does not guarantee delivery
  4. TCP works at the Network layer; UDP works at the Data Link layer

Answer : C
Explanation: TCP (Transmission Control Protocol) is connection-oriented — it establishes a connection via a three-way handshake and guarantees reliable, ordered data delivery using acknowledgments. UDP (User Datagram Protocol) skips the handshake, making it faster but unreliable. UDP is preferred for real-time applications like video streaming, VoIP, and online gaming where speed matters more than guaranteed delivery.

35. How many bits are used in an IPv6 address?

  1. 32-bit
  2. 64-bit
  3. 128-bit
  4. 256-bit

Answer : C
Explanation: IPv6 uses 128-bit addresses, written as eight groups of four hexadecimal digits separated by colons (e.g., 2001:0db8:85a3::8a2e:0370:7334). This provides approximately 3.4 × 10³⁸ unique addresses — solving the address exhaustion problem caused by IPv4’s limited 32-bit address space of roughly 4.3 billion addresses. IPv6 also brings improvements in routing efficiency, security, and auto-configuration.

36. Which networking device operates at Layer 2 of the OSI model and uses MAC addresses to forward data only to the intended destination?

  1. Hub
  2. Repeater
  3. Router
  4. Switch

Answer : D
Explanation: A switch operates at Layer 2 (Data Link Layer) and uses MAC addresses to intelligently forward frames only to the port connected to the intended recipient device. Unlike a hub — which broadcasts all incoming data to every connected port — a switch reduces unnecessary traffic and collisions, making the network significantly more efficient. Switches are the backbone of modern LAN infrastructure.

37. What is NAT (Network Address Translation) primarily used for in computer networks?

  1. To translate domain names into IP addresses
  2. To allow multiple devices on a private network to share a single public IP address
  3. To assign MAC addresses to network devices
  4. To encrypt all traffic between two network endpoints

Answer : B
Explanation: NAT (Network Address Translation) enables multiple devices on a private internal network to communicate with the internet through a single public IP address. This was critical in extending the life of the IPv4 address space. NAT also adds a layer of security by hiding internal IP addresses from external networks. It is implemented on routers and is a fundamental concept in both home networking and enterprise environments.

38. Which protocol is used to map a known IP address to its corresponding MAC address on a local network?

  1. RARP
  2. ICMP
  3. ARP
  4. DNS

Answer : C
Explanation: ARP (Address Resolution Protocol) resolves IP addresses to MAC addresses within a local area network. When a device needs to communicate with another device on the same LAN, it sends a broadcast ARP request asking “who has this IP address?” The device with that IP replies with its MAC address. ARP operates at the boundary of Layer 2 and Layer 3 of the OSI model and is essential for LAN communication.

39. What is the default subnet mask for a Class B IP address?

  1. 255.0.0.0
  2. 255.255.255.0
  3. 255.255.0.0
  4. 255.255.255.255

Answer : C
Explanation: Class B IP addresses (range 128.0.0.0 to 191.255.255.255) use the first two octets to identify the network and the remaining two for hosts, giving a default subnet mask of 255.255.0.0 (or /16 in CIDR notation). This supports up to 65,534 usable host addresses per network. Class A uses 255.0.0.0 and Class C uses 255.255.255.0.

40. Which of the following is NOT a private IP address range defined by RFC 1918?

  1. 10.0.0.0 – 10.255.255.255
  2. 172.16.0.0 – 172.31.255.255
  3. 192.168.0.0 – 192.168.255.255
  4. 200.1.0.0 – 200.255.255.255

Answer : D
Explanation: RFC 1918 defines three private IP address ranges not routable on the public internet: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These are used inside private networks such as homes and offices. The 200.x.x.x range belongs to public IP space and is fully routable on the internet. Private IP addresses must be translated using NAT before accessing the internet.

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