25.2 Interview Questions

Introduction

This chapter gives you a collection of interview questions and model answers focused on networking fundamentals. The goal is not to memorize answers word for word, but to understand what the interviewer is really trying to test and to have clear, simple ways to explain concepts.

You can use this chapter to practice speaking your answers out loud. Start with short explanations, then add detail if the interviewer seems interested or asks follow‑up questions.

Basic Concept Questions

Interviewers often begin with simple questions to check that you understand the foundations and that you can explain them clearly.

What is a computer network?

A computer network is a group of devices that are connected so they can share data and resources. Resources can be files, printers, applications, or access to the internet. The connection can use cables or wireless signals.

Interviewers expect that you mention at least devices, connection, and sharing of resources or data. You do not need technical detail at this stage. Clear and simple language is better than long, complicated definitions.

What is the difference between a LAN and a WAN?

A Local Area Network, or LAN, is a network in a small geographic area, such as one office, one floor, or one building. It is usually owned, managed, and controlled by a single organization.

A Wide Area Network, or WAN, covers a large geographic area, such as a city, a country, or even the whole world. Often different parts of a WAN are owned or operated by different companies, including internet service providers.

You can add that LANs usually have higher speeds and lower latency than WANs.

What is bandwidth and what is latency?

Bandwidth describes how much data can be sent per unit of time. It is usually measured in bits per second, for example Mbps or Gbps. High bandwidth means you can send a lot of data each second.

Latency describes how long it takes for a piece of data to travel from one point to another. It is the delay, usually measured in milliseconds. Low latency means little delay.

A useful way to explain both at once is to compare a road. Bandwidth is like how many lanes the road has. Latency is like how long it takes to drive from point A to point B.

What is the OSI model and why is it useful?

The OSI model is a conceptual model that describes networking in 7 layers, from the physical transmission of bits up to applications that users work with. It is not a protocol itself. It is a way to break networking into pieces.

It is useful because it gives a common language to describe where a problem is, where a protocol works, and how different parts of the network interact. Many troubleshooting methods are based on moving layer by layer and checking what works and what does not.

If needed you can list the layers in order, but do not repeat full explanations of each layer here, because they are covered in other chapters.

Addressing and Protocol Questions

Interviewers want to know that you understand how devices find each other and communicate on a network.

What is an IP address?

An IP address is a logical address that identifies a device on an IP network. It has two main roles. It identifies the network where the device is located and it identifies the specific host on that network.

IPv4 addresses are usually written as four numbers separated by dots, for example 192.168.1.10. IPv6 uses a different, longer format, but the idea of logical addressing is the same.

What is the difference between a MAC address and an IP address?

A MAC address is a physical address that is usually burned into the network interface card. It works at the data link layer. It is used on a local network segment, for example on one Ethernet network.

An IP address is a logical address that works at the network layer. It can be changed by configuration. It is used to route traffic between networks.

You can add that MAC addresses are usually written in hexadecimal and stay the same most of the time, while IP addresses can change with DHCP or when a device moves between networks.

What is a subnet mask?

A subnet mask is a number that tells which part of an IPv4 address is the network portion and which part is the host portion. It is usually written in dotted decimal, like 255.255.255.0, or in prefix format, like /24.

The mask has bits set to 1 where the address belongs to the network part, and bits set to 0 where the address belongs to the host part.

What is a default gateway?

A default gateway is a router address configured on a host. The host sends traffic for remote networks to this router, when the host does not have a more specific route. The default gateway then forwards the traffic toward its destination.

You can say simply, “It is the router that a device uses to leave its local network.”

What is DNS and why is it important?

DNS, the Domain Name System, translates human readable names like www.example.com into IP addresses that computers use. It lets users remember names instead of numbers.

Without DNS, people would need to type IP addresses into their browsers directly. Many networking problems that appear as “the site is down” are actually due to DNS failures.

Switching and Ethernet Questions

These questions test if you understand basic local network behavior.

What is a switch and how is it different from a hub?

A hub repeats all incoming electrical signals out of all other ports. It does not understand addresses. All devices connected to a hub share the same collision domain.

A switch looks at MAC addresses in Ethernet frames. It learns which MAC address is available on which port. Then it forwards frames only out of the port that leads to the destination. This reduces unnecessary traffic and separates collision domains per port.

You can mention that hubs are very rare in modern networks, while switches are the normal choice.

What is a VLAN and why is it used?

A VLAN is a Virtual Local Area Network. It allows a single physical switch to act as if it has several separate logical networks. Devices in different VLANs do not communicate directly at layer 2, even if they are on the same switch.

VLANs are used to improve security, separate departments, and control broadcast domains. To pass traffic for multiple VLANs between switches, a trunk link is usually used.

What is MAC address learning?

A switch learns MAC addresses by reading the source MAC address of incoming frames and storing it in a table with the port number. When the switch later sees a frame with that MAC as the destination, it knows which port to use and can forward it directly.

If a destination MAC is unknown, the switch floods the frame out of all ports in that VLAN, except the one where it arrived.

Routing and Internet Questions

Here the interviewer checks if you understand how traffic moves beyond the local network.

What is routing?

Routing is the process of selecting paths in a network to send packets from a source to a destination across multiple networks. Devices that perform routing are called routers.

Routers keep routing tables. These tables describe which networks are reachable and which next hop to use.

What is the difference between a router and a switch?

A switch works mainly on MAC addresses at the data link layer and forwards frames inside the same IP network.

A router works on IP addresses at the network layer and forwards packets between different IP networks.

Many home devices combine both roles into one box. In interviews, however, you should keep the logical functions separate in your explanations.

What is a static route versus a dynamic route?

A static route is manually configured by an administrator. It does not change automatically when the network changes. It is simple and predictable, but not flexible.

A dynamic route is learned through a routing protocol. Routers exchange information and update their routing tables automatically. This allows for adaptation when links go down or come up.

You can mention typical dynamic routing protocols, but do not explain them fully here, as they are covered in other chapters.

What is a default route?

A default route is a route that matches any destination when no more specific route exists. It is usually written as 0.0.0.0/0 in IPv4.

Routers and hosts send traffic to the default route when they do not know a specific path to the destination network.

What is NAT and why is it used?

NAT, Network Address Translation, changes IP addresses in packet headers, usually at the edge of a network. It is most often used so many private internal addresses can share a smaller set of public addresses when accessing the internet.

NAT helps with IPv4 address shortage and adds a basic layer of hiding internal network structure. It is not a security solution by itself but it does limit direct access from the internet to internal devices in many typical configurations.

Transport and Application Questions

Interviewers often want to see if you can compare TCP and UDP and understand ports.

What is a port number?

A port number identifies a specific process or service on a device. IP addresses find the device, port numbers find the application on that device.

For example, web servers often listen on TCP port 80 for HTTP and TCP port 443 for HTTPS.

What is the difference between TCP and UDP?

TCP is a connection oriented protocol. It establishes a connection, provides reliable delivery, orders packets, and handles retransmissions if packets are lost.

UDP is a connectionless protocol. It sends packets without setting up a formal connection. It does not guarantee delivery or order. It has less overhead and is faster and simpler.

You can mention that things like web pages, file transfers, and emails usually use TCP, while voice, video, and simple queries like DNS often use UDP.

What is the three way handshake?

The three way handshake is the process TCP uses to establish a connection between two devices. The client sends a SYN, the server responds with SYN ACK, and the client finishes with an ACK. After these three messages, the connection is established and data can flow.

If you forget the details in the moment, you can at least say, “It synchronizes sequence numbers and confirms that both sides are ready to communicate.”

What is a socket?

A socket is the combination of an IP address and a port number, and also the transport protocol. It represents one end of a communication. A full connection between two devices has two sockets, one on each side.

Name Resolution and Web Questions

These questions link network concepts to things users see every day, such as websites.

What happens when you type a URL in a browser and press Enter?

This is a very common interview question. You do not need to give every tiny detail, but you should mention key steps.

First, the browser parses the URL and checks if it can use a cached DNS result. If not, the system uses DNS to resolve the domain name to an IP address.

Then the browser establishes a TCP connection to the server IP, usually on port 80 or 443. If HTTPS is used, a TLS handshake is performed to establish encryption.

After that, the browser sends an HTTP request to the server. The server processes it and returns an HTTP response, often containing HTML, images, scripts, and other resources. The browser renders the page using that data.

You can then say that many optimizations and additional steps can exist, such as caching, content delivery networks, and redirects.

What is HTTPS and how is it different from HTTP?

HTTP is a protocol used by web browsers and servers to exchange web pages and related data. It sends data in clear text.

HTTPS is HTTP over TLS. It encrypts the communication between client and server, which protects data from eavesdropping and tampering. It also allows the client to verify the identity of the server using digital certificates.

You do not need to explain the full TLS handshake in an interview at beginner level, unless the interviewer asks.

Wireless and Connectivity Questions

Some roles expect basic understanding of wireless networking behavior.

What is Wi Fi?

Wi Fi is a set of standards for wireless local area networking that use radio waves to transmit data. It allows devices to connect to a network and to the internet without cables, usually through an access point.

Wi Fi operates in specific frequency bands and uses channels within those bands.

Why might Wi Fi be slower than a wired connection?

Wi Fi often has higher interference, shared radio space, and more overhead for things like signaling and protection. Distance from the access point, walls, and other devices can reduce signal quality and effective throughput.

Wired Ethernet has more controlled conditions and usually supports higher and more stable speeds with lower latency.

Security and Access Control Questions

Interviewers test if you are aware of basic security concepts used in networks.

What is a firewall?

A firewall is a device or software that controls traffic based on a set of rules. It decides which traffic is allowed to enter or leave a network or host, based on factors like IP address, port, protocol, and sometimes application type.

You can add that firewalls help enforce security policies and reduce the attack surface.

What is the CIA triad?

The CIA triad is a simple model that describes three main goals of information security.

Confidentiality means preventing unauthorized access to data.

Integrity means preventing unauthorized modification of data and ensuring it is accurate.

Availability means ensuring authorized users can access data and services when they need them.

In interviews, often just naming and briefly defining these three is enough.

What is a VPN and why is it used?

A VPN, Virtual Private Network, creates an encrypted tunnel over a public network such as the internet. It lets users or sites communicate as if they were on the same private network.

VPNs are used to protect data in transit and to allow remote workers or branch offices to access internal resources securely.

Troubleshooting Questions

Interviewers want to see how you think, not just what you know.

How would you approach a user who cannot access a website?

Explain your method step by step. A simple approach is:

Check if the user has network connectivity at all. Can they reach any other site or ping a known IP address?

Check DNS. Can they resolve the website name to an IP address?

Check if others can reach the same website from a different device or network.

Check if the problem is specific to one browser or one device.

If you have access to tools, you might use ping, traceroute, and check logs on firewalls or proxies.

You should highlight that you move from basic to more complex checks and that you change only one thing at a time when testing.

What tools would you use for network troubleshooting?

For a beginner level answer you can mention ping to test reachability, traceroute to see the path and where it fails, and tools like netstat, tcpdump, or Wireshark to inspect connections and packets.

You do not need to provide full commands, but you should show you know what each tool is useful for.

Behavioral and Communication Questions

Networking roles are not only about technical skills. Interviewers also check how you communicate and learn.

How do you explain technical concepts to non technical users?

You can say that you avoid jargon, use analogies, and confirm understanding by asking questions. For example, you may compare networks to roads, mail systems, or water pipes.

You can also mention that you focus on what the user cares about, such as what they can expect and what they need to do, instead of deep internal details.

Tell me about a time you solved a network related problem.

If you are new and do not have a job history, you can use examples from labs, home networks, or studies. For example, fixing a home Wi Fi issue, troubleshooting an IP address conflict in a lab, or configuring a simple router.

Use a simple structure, such as situation, action, result. Describe briefly what the problem was, what you did, and what the outcome was.

Tips for Using These Questions

Use this chapter as a practice guide. Pick a question, close the book or screen, and try to say your answer aloud. Then check back and adjust your explanation. Focus on:

Being clear and concise.

Using correct terms but also being understandable.

Showing that you know why something is done, not just how.

You are not expected to know everything. In an interview, if you do not know, it is better to say so honestly and explain how you would find out, for example by checking documentation, lab testing, or asking a more experienced colleague.

With practice, these questions become opportunities to demonstrate both your knowledge and your way of thinking.