Computer networks are interconnected systems of computers and devices that facilitate data communication and resource sharing. They enable seamless information exchange and access to shared resources such as printers, files, and internet connections.
To clear a computer network interview successfully, candidates should focus on understanding networking fundamentals like TCP/IP protocols, OSI model, routing, and subnetting. Practical experience with network troubleshooting tools and network security concepts is crucial.
Additionally, honing problem-solving skills and demonstrating a willingness to learn and adapt to new technologies will impress interviewers. Stay updated on the latest networking trends and be prepared to showcase your hands-on experience to stand out in the competitive job market.
Listed below are several commonly Computer Networks asked interview questions and answers regarding Computer networking:
Q1. What is the difference between a hub, a switch, and a router?
Q2. Explain the OSI model and its layers.
Q3. What is a VPN, and how does it ensure secure communication over an insecure network?
Q4. What is the difference between authentication and authorization in the context of network security?
Q5. What is TCP/IP, and how does it relate to the OSI model?
Q6. What is the difference between TCP and UDP?
Q7. What is DNS, and how does it work?
Q8. Explain the concept of defense in depth, and how it applies to network security.
Q9. Explain the concept of encryption and its role in securing network traffic.
Q10. What is the difference between a layer 2 switch and a layer 3 switch?
The blog is divided into three sections as mentioned below:
1. Basic Computer Networks Interview Questions
2. Intermediate Computer Networks Interview Questions
3. Advanced Computer Networks Interview Questions
Basic Computer Networks Interview Questions
1. What is the difference between a hub, a switch, and a router?
- A hub is a simple networking device that connects multiple devices in a network, broadcasting incoming data to all associated components.
- A switch is an intelligent device that receives incoming data and selectively forwards it to the appropriate device based on the destination MAC address.
- A router is a networking device responsible for interconnecting multiple networks and forwarding data packets between them using IP addresses as the basis for routing.
2. Explain the OSI model and its layers.
- The Open Systems Interconnection (OSI) model is a conceptual structure that standardizes the communication system’s functions into seven layers.
- The layers are Physical, Application, Data Link, Transport, Presentation, Session, and Network. Each layer serves a specific purpose in the communication process.
3. What is a VPN, and how does it ensure secure communication over an insecure network?
A Virtual Private Network is a secure, encrypted connection that allows users to access a private network over a public or insecure network, such as the Internet.
VPNs ensure secure communication by creating a secure tunnel between the user’s device and the private network, encrypting all data transmitted between them. This encryption prevents unauthorized access and protects the confidentiality and integrity of the data.
4. What is the difference between authentication and authorization in the context of network security?
- Authentication refers to the process of verifying the identity of a user or device, ensuring that they are who they claim to be. It typically involves providing credentials such as usernames, passwords, or digital certificates.
- Authorization, on the other hand, is the process of granting or denying access to specific resources or actions based on the authenticated user’s privileges. It determines what actions or data the user is allowed to access or manipulate.
5. What is TCP/IP, and how does it relate to the OSI model?
TCP/IP (Transmission Control Protocol/Internet Protocol) is a suite of protocols used for communication over the Internet.
TCP/IP is not an exact match to the OSI model, but it can be loosely mapped to the OSI layers as follows:
- Network interface layer (equivalent to the Physical and Data Link layers)
- Internet layer (equivalent to the Network layer)
- Transport layer (equivalent to the Transport layer)
- Application layer (equivalent to the Session, Presentation, and Application layers)
6. What is the difference between TCP and UDP?
- Transmission Control Protocol (TCP) is a connection-centric communication protocol designed to secure consistent and sequential transmission of data by forming a link between the sender and receiver.
- The User Datagram Protocol (UDP) is a connectionless communication protocol that enables swift but unreliable transmission of data without the need for establishing a connection beforehand. It is commonly used for applications that prioritize speed over reliability, such as video streaming and online gaming.
7. What is DNS, and how does it work?
The Domain Name System is a decentralized naming system that translates domain names (e.g., www.networking.com) into IP addresses.
When a user inputs a domain name into a web browser, the browser initiates a DNS query to a DNS server. Subsequently, the DNS server looks up the corresponding IP address associated with the domain name and sends it back to the browser. This process enables the browser to establish a connection with the relevant web server.
8. Explain the concept of defense in depth, and how it applies to network security.
Defense in depth refers to a security approach wherein a network is safeguarded through the implementation of multiple layers of security measures. Each layer provides a unique set of security controls, and if one layer is breached, other layers provide additional protection.
It applies to network security by combining various security mechanisms such as intrusion detection, prevention systems, firewalls, access controls, encryption, and regular security audits to create a robust defense against potential threats.
9. Explain the concept of encryption and its role in securing network traffic.
Encryption is the process of encoding data in such a way that only authorized parties can access and understand it. It transforms plaintext data into ciphertext using cryptographic algorithms and keys.
In the context of securing network traffic, encryption is essential to protect sensitive information from unauthorized access. By encrypting data before transmitting it over a network, even if intercepted, it remains unreadable to unauthorized users. Only those with the appropriate decryption key can access and decipher the data.
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10. What is the difference between a layer 2 switch and a layer 3 switch?
- A layer 2 switch functions at the data link layer of the OSI model and determines forwarding decisions by considering MAC addresses. It is primarily used for local network switching.
- A layer 3 switch, which is also referred to as a multilayer switch, functions at both the data link layer and the network layer of the OSI model. It possesses the capability to make forwarding decisions using both MAC and IP addresses, enabling efficient routing of traffic between various networks.
Intermediate Computer Networks Interview Questions
If you want to ace your next computer network interview, you need to be familiar with the basic and advanced concepts of computer networks. In this section, we will cover some of the most common and important computer network interview questions and answers that will help you learn about topology in computer networks, types of computer networks, protocols, security, and more.
11. What is the purpose of the Spanning Tree Protocol (STP) in network switches?
The Spanning Tree Protocol (STP) is used to prevent loops and ensure a loop-free topology in Ethernet networks. It allows switches to create a logical tree-like structure by selecting a root bridge and determining the shortest path to reach each switch in the network.
12. Explain the concept of routing and the role of a router in a network.
Routing is the process of forwarding data packets between different networks based on IP addresses.
A router is a networking device that connects multiple networks and makes intelligent routing decisions based on IP addresses to ensure data packets are delivered to their intended destinations.
13. What is the principle of least privilege, and how does it relate to network security?
The principle of least privilege (PoLP) is a security principle that ensures users and systems are given the least amount of access privileges necessary to fulfill their essential tasks. It limits potential damage by reducing the attack surface and preventing unauthorized access to sensitive resources. In the context of network security, applying the principle of least privilege involves assigning network permissions and user privileges based on specific roles and responsibilities, ensuring that users and systems have access only to the network resources required to fulfill their duties.
14. What is Secure Socket Layer (SSL)/Transport Layer Security (TLS), and how does it ensure secure communication over the internet?
Secure Socket Layer (SSL)/Transport Layer Security (TLS) is a cryptographic protocol used to secure communication over the internet. They establish an encrypted connection between a client and a server, ensuring the confidentiality and integrity of the data transmitted between them. SSL/TLS protocols authenticate the server’s identity using digital certificates and establish a secure channel through which data is encrypted and decrypted. This encryption prevents unauthorized access and protects sensitive information from interception or tampering.
15. What is a DDoS (Distributed Denial of Service) attack, and what measures can be taken to prevent or mitigate it?
A DDoS attack involves overwhelming a network or system with a flood of traffic from multiple sources, making it unavailable to legitimate users. Measures to prevent or mitigate DDoS attacks include implementing traffic filtering, rate limiting, and anomaly detection mechanisms; using load balancers and caching services; employing dedicated DDoS protection services; and increasing network bandwidth and server capacity.
16. Explain the difference between NAT and PAT.
- Network Address Translation (NAT) is a technique used to translate private IP addresses into public IP addresses, enabling multiple devices on a private network to share a single public IP address.
- Port Address Translation (PAT) is a variant of NAT that also translates port numbers, allowing multiple devices on a private network to share a single public IP address and port combination.
17. How does Dynamic Host Configuration Protocol (DHCP) work in assigning IP addresses to devices on a network?
DHCP is a network protocol that automates the process of assigning IP addresses to devices on a network.
When a device connects to a network, it sends a DHCP request. A DHCP server on the network responds to this request by offering an available IP address lease. If the device accepts the lease, it sends a DHCP request to the server, which confirms the assignment of the IP address. The device then configures its network settings with the assigned IP address, subnet mask, gateway, and other relevant information.
18. What do you understand by establishing a TCP connection (TCP handshake)?
The TCP handshake process involves three steps: SYN, SYN-ACK, and ACK.
- SYN (Synchronize): The client initiates the TCP connection by sending an SYN packet to the server, indicating its intention to establish a connection.
- SYN-ACK (Synchronize-Acknowledge): Upon receiving the SYN packet, the server responds with an SYN-ACK packet, acknowledging the client’s request and providing its initial sequence number.
- ACK (Acknowledge): The client acknowledges the server’s SYN-ACK packet by sending an ACK packet. This packet also contains the next sequence number the client expects to receive.
After the three-way handshake is completed, the TCP connection is established, and data transmission can begin.
19. Describe the purpose and functioning of an Intrusion Detection System (IDS) and Intrusion Prevention System (IPS).
An Intrusion Detection System (IDS) is a security utility designed to observe network traffic and system events, detecting any indications of unauthorized access, misuse, or malicious activities. It detects and alerts administrators about potential security incidents.
An Intrusion Prevention System (IPS) is an advanced version of an IDS that not only detects but also takes action to prevent malicious activities. It can automatically block or modify network traffic in real-time to mitigate potential threats.
IDS and IPS play crucial roles in network security by providing proactive monitoring and protection against unauthorized activities and intrusions.
20. What are the best practices for securing wireless networks?
The best practices for securing wireless networks are as follows:
- Implementing strong encryption (e.g., WPA2 or WPA3) to protect wireless communications
- Using strong and unique passwords for wireless network access
- Disabling or hiding the network’s SSID (service set identifier) to prevent unauthorized access
- Enabling MAC address filtering to allow only authorized devices to connect
- Regularly updating wireless access point firmware to address security vulnerabilities
- Configuring a separate guest network to isolate guest devices from the main network
- Monitoring network traffic for suspicious activities and implementing intrusion detection and prevention systems
Advanced Computer Networks Interview Questions
If you are preparing for a job interview that requires knowledge of computer networks, this blog will help you learn about advanced concepts of computer networks and how to answer common questions.
21. Explain the concept of network access control and the technologies used for its implementation.
- Network access control (NAC) is a security approach that enforces policies to control and manage access to network resources. It ensures that only authorized and compliant devices can connect to the network. NAC can be implemented through various technologies, such as the following:
- 802.1X Authentication: It provides port-based authentication, requiring users or devices to authenticate before accessing the network.
- Network Admission Control (NAC) Systems: They enforce security policies by verifying the compliance and health status of devices before granting access.
- Endpoint Security Solutions: They assess the security posture of devices and enforce security policies, such as antivirus and firewall requirements, before allowing network access.
- Network Segmentation and VLANs: Network segmentation and VLANs separate network traffic based on security requirements, allowing for granular access control and isolation of different groups or types of devices.
22. Explain the role of digital certificates and Certificate Authorities (CAs) in network security.
Digital certificates are electronic documents that verify the authenticity and integrity of entities, such as websites or individuals, in a networked environment. They are issued by trusted Certificate Authorities (CAs) and contain information such as the entity’s public key and identification details. Digital certificates are used for various purposes, including secure communication (e.g., SSL/TLS certificates), email encryption (e.g., S/MIME certificates), and code signing. CAs play a crucial role in network security by validating the identity of entities and ensuring the trustworthiness of digital certificates.
23. Describe the process of network vulnerability assessment and penetration testing.
- Network vulnerability assessment involves identifying and evaluating vulnerabilities in a network’s infrastructure. It typically includes scanning network devices, systems, and applications for known vulnerabilities, misconfigurations, and weaknesses.
- Penetration testing, on the other hand, simulates real-world attacks to assess the effectiveness of security controls and identify vulnerabilities that may not be detected through automated scans. Both processes help organizations identify and address potential security risks before they can be exploited by attackers.
24. What are the common types of network attacks, and how can they be mitigated?
Common types of network attacks are the following:
- Denial of Service (DoS) Attack: It floods a network or system with excessive traffic to make it unavailable. Mitigation involves implementing traffic filtering, rate limiting, and DoS protection mechanisms.
- Man-in-the-Middle (MitM) Attack: It intercepts and alters the communication between two parties. Mitigation involves using encryption (e.g., SSL/TLS), digital certificates, and secure communication channels.
- Malware Attack: It distributes malicious software to compromise systems. Mitigation includes using up-to-date antivirus software, regular patching, and user education.
- Phishing: It tricks users into revealing sensitive information. Mitigation involves user awareness training, email filtering, and multi-factor authentication.
- SQL injection, cross-site scripting (XSS), and other web application attacks: It exploits vulnerabilities in web applications. Mitigation includes secure coding practices, input validation, and regular security audits.
25. What is the difference between symmetric and asymmetric encryption?
In symmetric encryption, a single key is employed for both encryption and decryption, whereas asymmetric encryption involves a pair of keys: a public key for encryption and a private key for decryption. While symmetric encryption offers faster processing, it necessitates secure key distribution. On the other hand, asymmetric encryption provides enhanced security but operates at a slower pace.
26. Let's consider a company with the IP address range 192.168.0.0/24, which provides 254 usable IP addresses for devices on the network. However, the company needs to divide the network into smaller subnetworks to accommodate different departments. How will you respond to this situation?
In this case, subnetting allows the company to create smaller subnets within the main network. Let’s say the company wants to create four subnets, each accommodating 50 devices.
To subnet the network, the company can borrow additional bits from the host portion of the IP address. In this example, borrowing 2 bits will provide 4 subnets (2^2 = 4). The remaining 6 bits in the host portion will allow 62 usable IP addresses per subnet (2^6 – 2 = 62, accounting for the network address and broadcast address in each subnet).
After subnetting, the network might look as follows:
Network address: 192.168.0.0/26
First usable IP address: 192.168.0.1
Last usable IP address: 192.168.0.62
Broadcast address: 192.168.0.63
Network address: 192.168.0.64/26
First usable IP address: 192.168.0.65
Last usable IP address: 192.168.0.126
Broadcast address: 192.168.0.127
Network address: 192.168.0.128/26
First usable IP address: 192.168.0.129
Last usable IP address: 192.168.0.190
Broadcast address: 192.168.0.191
Network address: 192.168.0.192/26
First usable IP address: 192.168.0.193
Last usable IP address: 192.168.0.254
Broadcast address: 192.168.0.255
By subnetting the network, the company can allocate specific IP address ranges to different departments or teams while ensuring efficient utilization of IP addresses. Each subnet operates as a separate network segment, allowing for better network management, security, and control.
This scenario demonstrates how subnetting can divide a larger network into smaller, manageable subnets to meet the specific needs and requirements of an organization.
27. Let's assume that Company XYZ is a multinational organization with multiple branch offices located in different cities. The company needs to establish a secure and reliable network infrastructure to connect all its branch offices while ensuring efficient network utilization and fault tolerance. How will you respond to this situation?
Subnetting: The IT team at Company XYZ decides to implement subnetting to optimize IP address allocation and manage network traffic efficiently. They allocate separate subnets for each branch office, allowing for better organization and scalability.
By subnetting, they ensure that each branch office operates as a separate network segment, preventing broadcast storms and improving overall network performance.
Branch Office 1: Subnet 192.168.1.0/24
Branch Office 2: Subnet 192.168.2.0/24
Branch Office 3: Subnet 192.168.3.0/24
Spanning Tree Protocol (STP): Company XYZ also implements STP to ensure a loop-free network topology and provide redundancy in case of link failures. They connect the branch offices using redundant links to ensure high availability and fault tolerance.
STP is activated in the following ways:
- It identifies and blocks redundant paths, preventing loops in the network.
- If a link failure occurs, STP dynamically recalculates the best path and activates an alternate path, ensuring uninterrupted connectivity between the branch offices.
- STP maintains a loop-free topology, ensuring efficient network operation and preventing broadcast storms.
- By combining subnetting and STP, Company XYZ achieves an optimized and reliable network infrastructure. Subnetting allows for efficient IP address management and improved network performance, while STP ensures fault tolerance and prevents network loops, enhancing overall network reliability.
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28. Company ABC is a global organization with multiple branch offices located in different countries. The company wants to establish a secure and reliable network infrastructure to ensure seamless communication between all branch offices. They consider implementing the OSI model for their network architecture. Provide a detailed plan that outlines how each layer of the OSI model would be utilized in the network architecture, which should fulfill the company’s requirement. Support your answer with relevant justifications and explain the interplay between the layers to ensure a comprehensive network solution for Company ABC.
Following the bottom-to-top approach:
- When you connect your computer to a network using an Ethernet cable, the Physical layer is responsible for transmitting the electrical signals representing the data across the cable.
- When you send an email attachment, the Data Link Layer adds a header and footer to the data, forming a data frame. It then checks for errors during transmission and retransmits any corrupted frames.
- When you browse the internet, the Network Layer routes your data packets through various routers and switches to reach the destination server, regardless of the physical networks involved.
- When you download a large file, the Transport Layer breaks the file into smaller segments, ensures that all segments arrive in the correct order, and reassembles them on the receiving end.
- When you participate in a video conference, the Session Layer establishes a session between the video conferencing applications on your device and the remote device, allowing synchronized communication.
- When you compress a file before sending it, the Presentation Layer compresses the data into a common format that can be decompressed by the receiving application.
- When you send an email, the Application Layer uses the Simple Mail Transfer Protocol (SMTP) to transfer the email from your email client to the email server.