How to prepare for an interview as an aspiring network engineer? Basic knowledge

Greetings, colleagues! My name is ProstoKirReal and I am a network engineer.

The world of information technology is often united by one word – IT. When my friends ask me what I do for a living, I always ask again: is it easier for you to explain or more difficult? They always choose the easier way, and I have to say that I am an IT specialist.

But the IT world is vast and multifaceted. One of its aspects is network technologies and, in particular, the work of networkers. The profession of a network engineer is difficult and noisy, especially if you spend time in cold server rooms without seeing sunlight. But if you still want to learn the networking craft, the first thing you will face is an interview.

How to prepare for an interview

What do you need to know before your interview? Which areas need more time and attention to study, and what can be omitted? I will try to answer at least some of these questions, since there are many areas in the networking craft with their own characteristics.

During an interview for a network engineer position, you may be asked a variety of questions related to both technical knowledge and personal qualities and work experience. But if we have no or minimal experience, then what should we know first?

❯ Where should we go for interviews?

Avoid small companies

• Don't look at salaries at first.
• Pay attention to employee training.

Why should you avoid small companies?

As a rule, such companies need already qualified employees, which we will become over time. Even if a novice engineer is required, usually such companies are engaged in a specific area, for example, providing highly targeted equipment, working in networks such as process control systems, where specialized protocols and equipment are used. In general, even if we learn something, this experience may only be needed in one segment.

Look for large companies dealing in different areas, different types of networks and network devices. Ideally, this should be an integrator that solves various customer problems. In such a company there will always be a lot of experience, as well as directions, and they can be interesting.

Why shouldn't you look at salaries at the beginning of your journey?

Salary is important, of course, but career growth is more important. The faster you gain experience, the broader your horizons in network technologies and the better your understanding of how they work and what problems they solve, the more in demand you will be on the labor market.

Why pay attention to learning?

If the company does not have internal instructions, courses or training programs, you will not develop from experience alone. When you study a question yourself, it is always difficult to understand the material. For example, I can learn how to configure a certain dynamic routing protocol, but without understanding how this routing works, I will not be able to understand where the error may be or explain to a colleague why I made a certain setting here. It is important to find a mentor from whom you will not be ashamed to ask for help.

It is important to quickly and efficiently improve your competencies.

Location is also important

In small towns like mine, for example, it is not always possible to find a decent salary for the work performed. Remote work may also not be suitable, since you always gain experience faster in a team.

❯ Introduction to Networking

Key terms and concepts:

• LAN and WAN: the difference between local area network (LAN) and wide area network (WAN).
• Ethernet: What is Ethernet and how is it used to create networks.
• Network topologies: Description of different types of network topologies (star, ring, bus, etc.).

Technical issues

1.

Basics of network technologies:

• What is an IP address and how is it used?
• Explain the difference between TCP and UDP.
• What is NAT and why is it needed?

2.

Protocols and models:

• Describe the OSI model and the main functions of each layer.
• What is ARP and how does it work?
• Explain how DHCP works.

3.

Routing and switches:

• What is a router and how is it different from a switch?
• Describe the routing process in a network.
• What routing protocols do you know? Which one do you prefer and why?

4.

Network Security:

• What methods are used to secure networks?
• What is a VPN and how does it work?
• Describe the principles of firewalls.

Practical questions

1.

Troubleshooting:

• How would you diagnose a network connection problem?
• What tools do you use to monitor and troubleshoot your network?

1.

Equipment setup:

• Describe the process of setting up a new switch.
• What steps will you take to deploy a new router on your network?

They may also ask about personal qualities and experience. Answer honestly, getting a difficult job by deception will not lead to anything good.

❯ Answers to technical questions

Introduction to network technologies. Basic terms and concepts

LAN and WAN:

difference between local (LAN) and wide area (WAN) networks.

LAN (Local Area Network) is a local network that covers a small geographic area, such as a home, office, or small building. LAN provides high data transfer speeds and allows you to connect devices such as computers, printers and servers within the same network.

WAN (Wide Area Network) is a wide area network that covers a large geographic area, such as a city, a country, or even the whole world. A WAN connects multiple local area networks (LANs) and provides the ability to transmit data over long distances.

Ethernet: What is Ethernet and how is it used to create networks

Ethernet is the standard technology for creating local area networks (LANs). It describes how devices are physically connected, the data transfer method and data formats for network communication and allows the exchange of data between devices.

Main characteristics of Ethernet:

• Cables: The most common are twisted pair (Cat5e, Cat6) and fiber optic cables.
• Speed: Ethernet options include Fast Ethernet (100 Mbps), Gigabit Ethernet (1 Gbps), and 10 Gigabit Ethernet (10 Gbps).
• Frame format: Ethernet uses frames to transmit data, which include a header, data, and a checksum.
• Topologies: Ethernet networks can use a variety of topologies, including star, bus, and ring.
• Network topologies: description of various types of network topologies.

Network topology is the structure or arrangement of various elements (nodes, connections) of a computer network. The main types of topologies include:

1. Star (Star Topology): all devices are connected to a central node, such as a switch or router. Benefits include ease of management and problem isolation. Disadvantage – failure of the central node leads to a shutdown of the entire network.
2. Bus Topology: all devices are connected to one common communication line (bus). Benefits include ease of installation and cost-effectiveness. Disadvantage: If the main line is damaged, the entire network goes down, and as the number of devices increases, performance may degrade.
3. Ring Topology: all devices are connected in series, forming a ring. Benefits include even load distribution and ease of installation. The disadvantage is that the failure of one node can disrupt the entire network, although modern technologies such as FDDI offer failover mechanisms.
4. Mesh Topology: Each node is connected to several other nodes. Advantages include high reliability and fault tolerance since data can be transmitted over multiple paths. The disadvantage is the complexity and high cost of installation.
5. Tree Topology: a hierarchical topology where nodes are organized as a tree with a root node and branches. Advantages include scalability and ease of management. Disadvantages include that if the root node fails, the entire branch may be disabled.

These topologies can be combined to create hybrid networks, allowing you to take advantage of the benefits of each depending on your specific requirements and conditions.

Fundamentals of network technologies. What is an IP address and how is it used?

An IP address (Internet Protocol Address) is a unique address used to identify a device on a network. It allows devices to communicate over the Internet or local network.

Explain the difference between TCP and UDP

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are transport protocols used to transfer data over a network.

• TCP: Provides reliable data transmission by establishing a connection between the sender and the receiver. It ensures that all packets are delivered in the correct order and eliminates transmission errors. Examples of TCP use include web surfing (HTTP/HTTPS), file transfer (FTP), and email (SMTP).
• UDP: does not establish a connection and does not guarantee packet delivery. It is faster and is used for applications where transfer speed is important rather than reliability, such as video streaming, online gaming and voice over IP (VoIP) calls.

What is NAT and why is it needed?

NAT (Network Address Translation) is a method of translating IP addresses on a network. It is used to manage IP addresses and allows multiple devices on a local area network (LAN) to use a single external IP address to access the Internet.

Basic functions of NAT:

• Saving IP addresses: allows you to use one public IP address for multiple devices on a private network.
• Safety: hides internal IP addresses from external networks, making it difficult to directly access devices from the Internet.
• Routing: provides communication between devices on the local network and external resources on the Internet.

Protocols and Models: Describe the OSI model and the main functions of each layer

The OSI (Open Systems Interconnection) model is a conceptual model that describes network communication functions as seven layers. Each layer performs specific tasks and interacts with the layers above and below.

1. Physical Layer: defines the physical characteristics of connections, such as electrical signals, connectors, cables, and network interfaces.
2. Data Link Layer: ensures reliable data transfer between devices on the same network and controls access to the physical environment.
3. Network Layer: is responsible for routing data between different networks and managing IP addresses.
4. Transport Layer: provides reliable data transfer between hosts using protocols such as TCP and UDP.
5. Session Layer: manages the establishment, maintenance, and termination of communication sessions between applications.
6. Presentation Layer: is responsible for converting data into a format suitable for transmission and interpretation, including encryption and compression.
7. Application Layer: provides interaction with users and applications accessing network services such as email, file sharing and web services.

Routing and Switches: What is a Router and How is it Different from a Switch?

Router:

a device that connects multiple networks and controls the routing of data packets between them. It uses IP addresses to determine the best path for data transmission and can operate at layer 3 of the OSI model (network layer).

Switch:

a device that connects devices on the same local area network (LAN) and transfers data between them. It operates at the second layer of the OSI model (data link layer) and uses MAC addresses to transfer data to the desired device.

Network security. What methods are used to secure networks?

• Firewalls: control incoming and outgoing traffic, allowing or blocking it based on predefined rules.
• VPN (Virtual Private Network): provides a secure connection over the Internet by creating an encrypted tunnel between devices.
• Antivirus Software: Protects devices from malware.
• IDS/IPS (Intrusion Detection/Prevention Systems): detect and prevent attempts of unauthorized access or attacks on the network.
• Encryption: protects data by converting it into a format that is unreadable without the appropriate key.

What is a VPN and how does it work?

VPN (Virtual Private Network) is a technology that provides a secure connection over an unsecured network such as the Internet. It creates an encrypted tunnel between devices, which allows you to protect data from interception and unauthorized access.

Key VPN features:

• Confidentiality: Encrypts data to prevent it from being intercepted and read.
• Anonymity: hides the user's IP address by giving him a different IP address from the VPN server.
• Safety: Protects your connection when using unsecured networks such as public Wi-Fi.

Describe the principles of firewalls?

A firewall is a device or software that controls access to and from a network based on predefined security rules. Firewalls work by:

• Packet Filtering: Analyzes data packet headers and makes decisions to allow or block based on rules such as IP addresses, ports and protocols.
• Network Address Translation (NAT): hides internal IP addresses by converting them to one or more public addresses.
• Application-Level Gateway: Analyzes data at the application level, providing protection against application-level attacks.
• Stateful Inspection: monitors the state of active connections and makes decisions based on session state, which provides more accurate filtering.

❯ Practical Issues: Troubleshooting

How would you diagnose a network connection problem?

1. Checking the physical connection: Make sure all cables are properly connected and devices are turned on.
2. Checking network settings: Make sure the IP address, subnet mask and gateway are configured correctly.
3. Using network utilities: use the ping command to check the availability of other devices on the network and the tracert/traceroute command to trace the route of packets.
4. Checking device configuration: Check your routers and switches to ensure they are configured correctly.
5. Checking event logs: Examine event logs on network devices to identify errors or warnings.
6. Network scan: Use network scanners to check the availability and status of devices on the network.

What tools do you use to monitor and troubleshoot your network?

• Wireshark: network traffic analyzer for capturing and analyzing data packets.
• Ping: a utility for checking the availability of devices on the network.
• Traceroute/Tracert: A utility for tracking the route of data packets on a network.
• netstat: A utility for viewing active network connections and their status.
• Nmap: network scanner for detecting devices and checking their security.
• SNMP (Simple Network Management Protocol): A protocol for monitoring and controlling network devices.

We looked at the basic questions that are most often asked during an interview. Each organization may ask additional tricky questions; it will not be possible to answer everything in a short article.

I will give examples of such questions without explanation, I will leave them for your home study:

• What is subnet mask and reverse subnet mask?
• What are packet, datagram, frame and segment? How are they different from each other?
• What is the difference between an L3 switch and a router, and how is this or that equipment used?
• Why would a switch send a packet to the network with the smaller mask first?

❯ Conclusion

I hope this resource helps you prepare for your network engineer interview. Remember that in this profession it is important to constantly learn and develop. Good luck!

PS Required Certifications and Education

• CCNA (Cisco Certified Network Associate): The core knowledge and skills that this certification provides.
• CompTIA Network+: General networking concepts covered by this certificate.

Other certificates: CCNP, JNCIA, etc.

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