If you're gearing up for interviews for Network Security Engineer, Firewall Engineer, or Cybersecurity Specialist positions, it's essential to incorporate the concept of firewalls into your approach.

This blog summarizes the most frequently asked firewall interview questions and answers, tailored to current cybersecurity trends and what the year 2026 holds.

1. What Do We Mean by Firewall?

A firewall works as an insurance policy by monitoring and filtering data traffic between trusted and untrusted networks, forcing security rules to dissociate unauthorized access, malware, and data exfiltration.

Firewalls can be hardware appliances, software-based, or cloud-hosted solutions. In modern enterprises, they act as the first line of defense and form a critical part of layered network security.

2: What's a Packet Filtering Firewall?

A packet-filtering firewall analyzes each packet by looking at the source and destination IP address, protocol, and port number. This packet-filtering firewall uses predefined filtering rules to determine if the packet should be allowed or dropped.

Packet-filtering firewalls offer speed but lack in many ways; they do not track the state of a connection or inspect application-level data.

3. What is the Difference Between Stateful and Stateless Firewalls?

A stateless firewall treats each packet individually and checks it against static rules without the context of any other packets. This is efficient and does not require memory overhead, but it does not understand what other packets are part of the ongoing connections.

A stateful firewall maintains a table of sessions relevant to activity. It knows whether a packet belongs to an ongoing session and hence provides a better line of defense against spoofing and session hijacking.

4. What Would Be the Main Function of a Firewall?

The primary function of a firewall is to manage network traffic according to policies and regulations. The primary functions of firewalls are:

Allowing or denying traffic according to policy. Allowing or denying incoming and outgoing network traffic according to policy. Tracking unauthorized attempts to access a network. A Firewall enables enforcement of network segmentation. Monitors behavior that might be malicious.

Next-generation firewalls provide security functions along with deep packet applications, threat intelligence, and intrusion prevention systems.

5. What Mode Does a Firewall Work in?

When a packet hits the firewall, it is subjected to a set of configured parameters such as source and destination IP addresses, port numbers, and applications.

If it meets a rule which allows it, it is permitted into the organization or out of the organization, but if it meets a deny rule, it is blocked.

Most commonly, ports are used for:

• HTTP (80),

• HTTPS (443),

• SSH (22),

• SMTP (25), and

• FTP (21).

Firewalls may also perform NAT (Network Address Translation) and deep packet inspection for enhanced visibility and control.

6. Can IPsec Replace Firewalls?

No. IPsec and firewalls perform different tasks, which are complementary.

The purpose of IPsec is to make sure that data between the devices will be encrypted and authenticated.

Firewalls are responsible for controlling the incoming and outgoing traffic in accordance with defined rules.

When used together, they form part of a robust network defense.

7. What is a VPN?

Virtual Private Network (VPN) creates an encrypted virtual tunnel between the user's local device and the remote network outside of this network over the internet. It offers security in data transmission between two data endpoints.

Most commonly, VPNs create secure remote access for employees, tunneling between sites, and such functionality is increasingly integrated into the modern firewall to manage secure connections.

8. What are the Types of Firewalls? 

The major types of firewalls that will exist in 2026 are:

• Packet-filtering firewalls

• Circuit-level gateways

• Application-level gateways (proxy firewalls)

• Stateful inspection firewalls

• Next-Generation Firewalls (NGFW)

• Cloud or host-based firewalls

Each type offers a diverse level of inspection and control that fits with the needs of the organization.

9. Which OSI Layers Do Firewalls Operate On? 

Firewalls operate at multiple levels within the OSI model:

• Layer three (network layer) - basically dealing with anything an IP can filter and routing decisions.

• Layer four (facilitating ether) - port and protocol filtering.

• Layer seven (for Application) - with content inspection and application control.

These next-generation firewalls work on all these layers for greater visibility and safety.

10. What Is a Transparent Firewall? 

Transparent firewalls accept Ethernet frames from the bridge and then filter them based on MAC addresses. Networks may be constructed without putting transparent firewalls in place or reconfiguring IPs or routing because it works with the current infrastructure. Integrating without the integration being understood makes these transparent firewalls desired.

11. What is Policy NAT? 

Policy NAT refers to a more granular control over how IP address translation appears to source and destination criteria.

Static Policy NAT – unalterable address mapping Dynamic Policy NAT – intermittently applied address translation based on conditions Policy NAT is popular within larger enterprises that may have different translation rules to apply for specific traffic.

12. What are the Default Timeout Values for TCP, UDP, and ICMP Sessions? 

The default session timeout period is simply:

• TCP: 60 minutes

• UDP: 2 mins

• ICMP: 2 seconds

Typical default values vary across vendors and can be adjusted in performance or security environments.

Firewall and Network Security Trends for 2026

Shifting trends in cyberspace are affecting the deployment and management of firewalls to an extent. These are:

• Zero Trust Security: Firewalls, as policy enforcement engines in a zero-trust architecture, check every connection.

• Encrypted Traffic Inspection: With most of the traffic being HTTPS, the firewalls inspect SSL/TLS streams for hidden threats.

• Security in Cloud and Hybrid Environments: Firewall solutions native to cloud and distributed environments are needed for multi-cloud and containerized environments.

• Automation and Orchestration: Infrastructure automation, configuration, and compliance checking are being carried out by Administrators through APIs and Infrastructure-as-Code (IaC).

• Artificial Intelligence and Machine Learning: With the increased application of AI, the firewall determines new attack patterns and auto-corrects policies.

• Microsegmentation: Isolating workloads limits lateral movement upon breaches.

Integration with Security Information and Event Manager (SIEM) and Extended Detection and Response (XDR): Firewall logs are now correlated in real-time with threat analysis via advanced detection and response systems.

Frequently Asked Questions

Q1. What is the firewall in networking?

A firewall is a system that controls and filters traffic between trusted networks and those that are untrusted, according to a defined set of security policies.

Q2. What are the main types of firewalls?

Packet-filtering, circuit-level, proxy, stateful inspection, next-generation firewalls, and cloud firewalls.

Q3. Name some popular firewall vendors.

Palo Alto Networks, Fortinet (FortiGate), Cisco Firepower, Check Point, and Sophos.

Q4. How does a firewall make traffic decisions?

By comparing the details of the packets against a rule set, it allows or blocks the passage of that traffic.

Q5. What are the deployment methods for firewalls?

Hardware appliances, software-based firewalls, and cloud-based firewall services.

Q6. Which OSI layers do firewalls operate on?

Layer 3 mainly. Layer 7 is used by next-generation firewalls.

Q7. Is a VPN a Layer 4 service?

No. The majority of VPNs operate at Layer 3, which is the network layer; they help create secure communication using tunneling protocols such as IPsec or SSL.

Q8. Do routers include firewall functions?

Most routers cover only very basic packet-filtering functions; dedicated firewalls provide an advanced level of protection and in-depth inspection.

Interview Preparation Tips for 2026

1. Expect real-world problem-solving questions on NAT, VPN, and traffic filtering.

2. Understand how to configure and troubleshoot firewall rules and policies.

3. Stay updated on next-generation firewall capabilities, automation, and cloud integration.

4. Understand zero-trust architecture and network segmentation.

5. Practice on one or more major platforms such as Palo Alto, Fortinet, or Cisco Firepower.

Conclusion

As the cybersecurity landscape evolves, it becomes important for each IT and security professional to learn how firewalls work and what part they play in modern network defenses. They are no longer just packet filtering machines; they are intellects fused with intrusion prevention and automation, and also cloud-native protection.

These days, for interview preparations in 2026, you would not only memorize some definitions but also gain concrete practical experience of how these technologies apply in real environments. The best candidates would understand the reason for each configuration and could readily adapt to fast-changing demands of hybrid and zero-trust networks.

NWKINGS has designed their instructor-led hands-on training module for those truly committed toward making their way in network security or firewall engineering. Their courses comprehensively cover the whole spectrum from basic networking technologies to advanced security technologies such as Next-Generation Firewalls, VPNs, IDS/IPS, and Cloud Security. This combined with realistic lab simulations and industry-recognized certifications will certainly prepare you to ace interviews and stand out among the candidates in the cybersecurity job market.

So, start your journey to become a certified Network Security Engineer today at NWKINGS by checking out their international standard training programs for yourself.