Most Asked Infosys Computer Networks Interview Questions

Understanding Networking Fundamentals: A Comprehensive Guide

In today's interconnected world, understanding networking fundamentals is crucial. Whether you're streaming your favorite show, playing online games, or simply browsing the web, networking underpins it all. This guide will walk you through essential networking concepts, equipping you with a solid foundation to navigate the digital landscape.

Explain the OSI model with its 7 layers.

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system without regard to its underlying internal structure and technology. It divides network communication into seven distinct layers, each with its specific responsibilities. Data passes through these layers sequentially, from the application layer down to the physical layer on the sending device, and then back up the layers on the receiving device. Here's a breakdown of each layer:

1. Application Layer: This is the top layer, where applications interact with the network. Examples include HTTP (web browsing), FTP (file transfer), SMTP (email), and DNS (domain name resolution).
2. Presentation Layer: Handles data formatting, encryption, and decryption. Ensures data is presented in a usable format for the application layer. Examples include SSL/TLS encryption and data compression.
3. Session Layer: Manages connections between applications. It establishes, manages, and terminates sessions between communicating devices. Examples include session establishment, management, and termination.
4. Transport Layer: Provides reliable end-to-end data delivery. This layer segments data into packets, ensures reliable transmission (TCP), or offers a connectionless approach (UDP). TCP and UDP are prominent protocols at this layer.
5. Network Layer: Responsible for logical addressing and routing. This layer uses IP addresses to direct data packets across networks. IP (Internet Protocol) is the key protocol here.
6. Data Link Layer: Deals with physical addressing and error detection on a single network segment. This layer uses MAC addresses to identify devices and ensures reliable data transfer within a local network. Examples include Ethernet and Wi-Fi protocols.
7. Physical Layer: The lowest layer, dealing with the physical transmission of data over the network medium (cables, wireless signals). It defines the electrical, mechanical, and procedural characteristics of the network. Examples include cables, connectors, and wireless signals.

Understanding how these layers interact is fundamental to grasping how networks function.

What is the difference between the OSI model and the TCP/IP model?

Both the OSI and TCP/IP models are used to describe network communication, but they differ significantly in their structure and approach. The OSI model is a theoretical model with seven layers, designed to be a comprehensive framework for understanding network communication. The TCP/IP model is a practical, four-layer model based on the actual implementation of the internet protocol suite. Key differences include:

• Number of Layers: OSI has seven layers, TCP/IP has four (Application, Transport, Internet, Network Access).
• Layer Functions: The functions of corresponding layers differ; for example, the OSI's Session, Presentation, and Application layers are often combined in the TCP/IP Application layer.
• Flexibility: OSI is more abstract and theoretically complete, while TCP/IP is more pragmatic and focuses on practical implementation.
• Real-world application: TCP/IP is the dominant model used in the internet, while the OSI model mostly serves as a pedagogical tool.

While OSI provides a detailed, layered view, TCP/IP is more closely aligned with how networks actually operate.

What is the difference between TCP and UDP?

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are both transport layer protocols, but they differ significantly in how they handle data transmission. TCP is a connection-oriented protocol, establishing a dedicated connection before transmitting data and guaranteeing reliable delivery. UDP is connectionless, sending data packets without establishing a connection, prioritizing speed over reliability.

Feature	TCP	UDP
Connection	Connection-oriented	Connectionless
Reliability	Reliable (guaranteed delivery)	Unreliable (no guaranteed delivery)
Speed	Slower	Faster
Overhead	Higher	Lower
Error Detection	Yes	No
Examples	Web browsing (HTTPS), file transfer (FTP)	Streaming video, online gaming

Choose TCP for applications requiring reliable data transfer, and UDP for speed-sensitive applications that can tolerate some data loss.

What is IP addressing? Differentiate IPv4 and IPv6.

IP addressing is a system used to assign unique numerical labels to devices connected to a computer network that uses the Internet Protocol for communication. These addresses allow devices to locate and communicate with each other. There are two main versions:

• IPv4 (Internet Protocol version 4): Uses 32-bit addresses, represented as four decimal numbers separated by dots (e.g., 192.168.1.1). It's running out of available addresses.
• IPv6 (Internet Protocol version 6): Uses 128-bit addresses, represented as eight groups of four hexadecimal digits separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). It provides a vastly larger address space, improved security, and better routing capabilities. It's the future of IP addressing, designed to handle the exploding number of internet-connected devices.

IPv6 is gradually replacing IPv4 due to its scalability and improved features.

What is DNS and how does it work?

DNS (Domain Name System) is the internet's phonebook. It translates domain names (like google.com) into IP addresses (like 172.217.160.142), which computers use to communicate. Without DNS, we'd have to remember complex IP addresses for every website we visit. DNS uses a hierarchical system of servers:

• Recursive resolvers: These are the servers your computer contacts first. They query other DNS servers to find the IP address.
• Root nameservers: These servers are at the top of the hierarchy, and they point to top-level domain (TLD) servers (like .com, .org, .net).
• TLD servers: These servers manage domain names within a specific TLD.
• Authoritative nameservers: These servers are managed by website owners and contain the actual IP address mapping for their domain.

When you type a domain name, your computer asks a recursive resolver, which then follows the hierarchy down to the authoritative nameservers to get the correct IP address.

What is DHCP and its role in networking?

DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses and other network configuration parameters to devices on a network. This eliminates the need for manual configuration, making network management much easier. A DHCP server manages a pool of IP addresses and leases them to devices on the network. When a device connects to the network, it sends a DHCP request. The server then assigns an available IP address, subnet mask, default gateway, and DNS server information. This lease has a specific duration, after which the device needs to renew it. The process of automatically assigning and managing network configurations simplifies network setup and administration.

What are the differences between a hub, switch, and router?

Hubs, switches, and routers are all networking devices used to connect multiple devices, but they operate differently:

• Hub: A simple device that broadcasts data received on one port to all other ports. This creates collisions and limits network performance. Hubs are largely obsolete.
• Switch: A more intelligent device that learns the MAC addresses of connected devices and forwards data only to the intended recipient, significantly improving network performance. Switches are commonly used in local area networks (LANs).
• Router: A device that connects different networks (e.g., your home network to the internet). It forwards data packets between networks based on their IP addresses and routing tables. Routers are essential for connecting multiple networks.

Switches improve upon the limitations of hubs by forwarding traffic only to the intended device; routers extend network connectivity across different network boundaries.

What is the ARP protocol and its function in networking?

ARP (Address Resolution Protocol) is a crucial protocol used in local area networks (LANs) to map IP addresses to MAC addresses. IP addresses identify devices on a network logically, while MAC addresses are physical hardware addresses. When a device wants to communicate with another device on the same LAN, it needs the recipient's MAC address. ARP allows the sending device to obtain the MAC address by broadcasting an ARP request containing the recipient's IP address. The device with that IP address responds with its MAC address. This mapping is essential for local communication.

What is the difference between HTTP and HTTPS?

Both HTTP (Hypertext Transfer Protocol) and HTTPS (Hypertext Transfer Protocol Secure) are used for communication on the web, but HTTPS offers enhanced security. HTTP is an unencrypted protocol, meaning data transmitted is visible to anyone who intercepts the communication. HTTPS uses SSL/TLS encryption to secure the communication, ensuring that data remains confidential. The key difference lies in security; HTTPS provides data encryption and integrity verification.

What is a firewall and what are its types?

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. It acts as a barrier between a trusted internal network and an untrusted external network (like the internet). Firewalls can be categorized in various ways:

• Hardware firewalls: These are physical devices, like routers with built-in firewall capabilities.
• Software firewalls: These are programs installed on computers or servers.
• Packet filtering firewalls: These examine individual data packets and block or allow them based on IP addresses, ports, and protocols.
• Stateful inspection firewalls: These inspect not only individual packets but also the context of the communication, considering the state of the connection.
• Application-level firewalls/Proxies: These examine the application-level data and can block specific applications or activities.

Choosing the appropriate firewall depends on your specific security needs and network architecture.

What is a VPN and what are its advantages?

A VPN (Virtual Private Network) creates a secure, encrypted connection over a public network like the internet. This allows you to connect to a private network remotely, as if you were physically connected. Advantages include:

• Enhanced security: Data transmitted through a VPN is encrypted, protecting it from eavesdropping.
• Increased privacy: VPNs mask your IP address, making it harder to track your online activity.
• Access to restricted content: VPNs can bypass geographical restrictions on websites and services.
• Secure public Wi-Fi: VPNs protect your data when using public Wi-Fi networks.

VPNs are valuable tools for enhancing online security and privacy.

Conclusion: This guide provided an overview of crucial networking fundamentals. Understanding these concepts is essential in today's digital age. From the OSI model to VPNs, mastering these basics will improve your understanding of how networks operate and enhance your overall digital literacy. Continue exploring these topics for a deeper understanding of networking's complexities.