Table of Contents
Basic to Intermediate Interview Questions
1. Why is TCP preferred for file transfer applications while UDP is preferred for live streaming?TCP is preferred for file transfers because it guarantees delivery, maintains packet order, and checks for errors. UDP is preferred for live streaming because it sends data faster and does not wait for acknowledgements, which reduces delay.
2. Suppose a user enters a website URL in the browser. What happens before the webpage appears?
The browser first checks DNS to find the IP address of the website. After that, it establishes a connection with the server, sends an HTTP request, receives the response, and finally renders the webpage contents.
3. Why do devices need IP addresses even when they are connected to the same WiFi network?
Devices need IP addresses because the network must identify each device uniquely. Without IP addresses, data packets would not know where to reach.
4. A website loads images very slowly but text appears quickly. Which network issue may cause this?
This may happen because of limited bandwidth, packet loss, slow server response, or high network congestion affecting larger files.
5. What is the difference between collision and congestion?
Collision occurs when multiple devices try to transmit data at the same time on the same medium. Congestion occurs when network traffic becomes larger than the network capacity.
6. Why are switches generally preferred over hubs in modern networks?
Switches send data only to the required destination device, which improves efficiency and reduces unnecessary traffic. Hubs broadcast data to all connected devices.
7. If two computers have the same IP address in a network, what problem can occur?
This creates an IP conflict. The network becomes unable to identify the correct destination, and communication may fail.
8. Why is MAC address still needed if IP address already exists?
The IP address identifies the device logically across networks, while the MAC address identifies the physical hardware within the local network.
9. What is the role of ARP in networking?
ARP converts IP addresses into MAC addresses so that devices can communicate inside a local network.
10. Why is DNS considered important for internet usage?
DNS converts domain names into IP addresses so users can access websites using easy names instead of numerical addresses.
Application Based Interview Questions
11. A company has employees working remotely from different cities. Which technology would help them securely access the office network?A VPN would help because it creates an encrypted connection between remote users and the company network.
12. Suppose packets are reaching the destination but in the wrong order. Which protocol handles this issue?
TCP handles this problem because it arranges packets in the correct sequence before delivering them.
13. Why do online games usually prefer UDP instead of TCP?
Online games require low latency and faster communication. UDP reduces delay because it does not perform retransmission and acknowledgement checks.
14. If a network suddenly becomes slow after adding many users, what is the likely reason?
The network may be facing congestion because more users increase traffic and consume available bandwidth.
15. What happens if DNS stops working but the internet connection is active?
Users may not access websites using names such as example.com, but websites may still work if their IP addresses are entered directly.
16. Why do routers work at a different layer than switches?
Routers work at the network layer because they handle IP addresses and routing. Switches work at the data link layer because they forward frames using MAC addresses.
17. A packet travels through three routers before reaching the destination. What is happening here?
The packet is being forwarded across different networks. Each router decides the best path based on routing information.
18. Why are private IP addresses not directly accessible on the internet?
Private IP addresses are reserved for internal networks. They require NAT to communicate with public networks.
19. Why is subnetting used in organizations?
Subnetting divides large networks into smaller sections, which improves performance, security, and management.
20. What may happen if subnetting is not used in a large network?
The network may experience higher traffic, inefficient resource usage, and difficult management.
Slightly Difficult Interview Questions
21. Can two websites have the same IP address?Yes, multiple websites can share the same IP address using virtual hosting techniques.
22. Why does TCP use a three way handshake?
TCP uses a three way handshake to establish a reliable connection and confirm that both sender and receiver are ready.
23. What is the purpose of acknowledgement packets in TCP?
Acknowledgement packets confirm successful data delivery and help in retransmitting lost packets.
24. Why does packet switching perform better than circuit switching for internet communication?
Packet switching uses bandwidth efficiently because resources are shared dynamically rather than reserving fixed paths.
25. Suppose a packet gets lost during transmission. What happens in TCP and UDP?
TCP detects the loss and retransmits the packet. UDP does not retransmit and continues sending data.
26. Why is HTTP considered stateless?
HTTP does not remember previous requests automatically. Each request is treated independently.
27. What is latency and why is it important in networks?
Latency is the delay between sending and receiving data. Lower latency improves application performance, especially in gaming and video calls.
28. Why are firewalls used in networks?
Firewalls monitor incoming and outgoing traffic and help prevent unauthorized access.
29. What problem does NAT solve?
NAT allows multiple devices to share a single public IP address and helps conserve IP resources.
30. Why is IPv6 needed when IPv4 already exists?
IPv6 is needed because IPv4 addresses are limited and the number of internet connected devices keeps increasing.
Scenario Based Questions
31. A user can ping an IP address but cannot open the website using the domain name. What is the issue?The issue is most likely related to DNS because IP communication works but domain resolution fails.
32. Why might a video call lag even when internet speed appears high?
The issue may be caused by latency, jitter, packet loss, or network congestion rather than bandwidth alone.
33. A switch fails in an office network. What impact may occur?
Devices connected through that switch may lose communication with each other and network services may stop.
34. If packets continuously take longer routes, what could be the reason?
Routing tables may be outdated or network conditions may force alternative paths.
35. Why is bandwidth not always equal to actual speed experienced by users?
Bandwidth shows maximum capacity, but actual speed depends on congestion, latency, packet loss, and server performance.
36. What happens if the TTL value becomes zero?
The packet is discarded to prevent endless looping inside the network.
37. Why is load balancing used in network systems?
Load balancing distributes traffic across multiple servers so that no single server becomes overloaded.
38. How does caching improve network performance?
Caching stores frequently used data so repeated requests can be served faster.
39. Why is packet fragmentation sometimes required?
Fragmentation breaks large packets into smaller parts so they can pass through networks with smaller transmission limits.
40. What may happen if fragmentation becomes excessive?
Excessive fragmentation can increase overhead and reduce network efficiency.
Advanced Freshers Interview Questions
41. What is the difference between throughput and bandwidth?Bandwidth represents maximum network capacity, while throughput represents actual transmitted data.
42. Why does HTTPS provide better security than HTTP?
HTTPS encrypts communication using SSL or TLS, which protects transmitted information.
43. Why is congestion control important in TCP?
Congestion control prevents excessive traffic and helps maintain stable network performance.
44. What is jitter in networking?
Jitter is the variation in packet arrival time and can affect real time applications.
45. Why are ports required in networking?
Ports allow multiple services to run on the same device while keeping communication separate.
46. Can a device have multiple IP addresses?
Yes, a device can have multiple IP addresses if it uses different interfaces or network configurations.
47. Why is packet loss harmful for VoIP applications?
Packet loss reduces audio quality and may cause missing voice segments.
48. Why are routing protocols needed?
Routing protocols help routers exchange information and determine optimal paths.
49. What is the importance of QoS in networks?
Quality of Service prioritizes important traffic and improves performance for critical applications.
50. Why do interviewers ask application based networking questions?
Interviewers ask these questions because networking jobs require practical understanding, troubleshooting skills, and real world thinking instead of memorized definitions.
Final Tip for Freshers
For Computer Networks interviews, prepare in this order:- OSI Model and TCP/IP
- TCP vs UDP
- IP Addressing and Subnetting
- Routing and Switching
- DNS, HTTP, HTTPS
- ARP, NAT, VPN
- Congestion, Latency, Throughput
- Scenario based troubleshooting questions
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