Top Network Firewall Interview Questions and Expert Answers for 2025

Network firewalls are a critical component of cybersecurity, protecting organizations from unauthorized access, threats, and cyberattacks. If you're preparing for a firewall-related job interview in 2025, knowing the right questions and their answers can set you apart. This guide covers some of the most common network firewall interview questions with expert answers to help you ace your next interview.

Basic Firewall Interview Questions

1. What is a network firewall?

A network firewall is a security device—either hardware or software—that monitors and controls incoming and outgoing network traffic based on predefined security rules. It acts as a barrier between trusted and untrusted networks to prevent unauthorized access.

2. How does a firewall work?

A firewall analyzes network packets and determines whether to allow or block them based on security rules. It can use packet filtering, stateful inspection, or deep packet inspection (DPI) to make decisions.

3. What are the main types of firewalls?

• Packet Filtering Firewalls – Examine individual packets and allow/block based on rules.
• Stateful Inspection Firewalls – Track active connections and filter traffic based on the connection state.
• Proxy Firewalls – Act as intermediaries between users and the internet, inspecting and filtering requests.
• Next-Generation Firewalls (NGFWs) – Combine traditional firewall functions with advanced security features like IDS/IPS and DPI.

Intermediate Firewall Interview Questions

4. What is the difference between a hardware firewall and a software firewall?

• Hardware Firewall: A physical device placed between a network and external connections; it is more effective for enterprises.
• Software Firewall: Installed on individual devices to control traffic for that specific system. It is more common for personal use or endpoint security.

5. What is Stateful Inspection in a firewall?

Stateful inspection, also known as dynamic packet filtering, keeps track of active connections and their states. Unlike simple packet filtering, it considers the entire context of a traffic session to make security decisions.

6. What are firewall rules, and how do they work?

Firewall rules define how traffic should be handled, typically based on criteria like:

• Source/Destination IP Address
• Source/Destination Port
• Protocol (TCP, UDP, ICMP, etc.)
• Action (Allow/Deny)

Firewalls evaluate these rules sequentially, and once a match is found, the appropriate action is taken.

7. What is the difference between an IDS and a firewall?

• Firewall: Prevents unauthorized access by filtering traffic based on rules.
• Intrusion Detection System (IDS): Monitors network activity for malicious behavior but does not block traffic.
• Intrusion Prevention System (IPS): Similar to IDS but can actively block threats.

Advanced Firewall Interview Questions

8. How do Next-Generation Firewalls (NGFWs) improve security?

NGFWs enhance security by integrating multiple features, including:

• Deep Packet Inspection (DPI)
• Application Layer Filtering
• Intrusion Prevention System (IPS)
• Advanced Malware Protection
• SSL Decryption

9. How does a firewall handle encrypted traffic (HTTPS/SSL)?

Firewalls use SSL decryption to inspect encrypted traffic by acting as an intermediary (man-in-the-middle). However, this requires proper certificate management to avoid security risks.

10. What are some common firewall configuration mistakes?

• Allowing unrestricted outbound traffic
• Misconfigured access control lists (ACLs)
• Using weak or default passwords
• Not updating firewall firmware
• Lack of proper logging and monitoring

11. What is Zero Trust Architecture, and how do firewalls fit into it?

Zero Trust Architecture (ZTA) assumes that no entity—inside or outside the network—should be trusted by default. Firewalls enforce strict access control policies to limit user and device access based on authentication and least-privilege principles.

12. How do firewalls protect against DDoS attacks?

Firewalls use features like rate limiting, anomaly detection, and connection tracking to identify and block excessive traffic from attackers. Some NGFWs include DDoS mitigation features that detect patterns of attacks and block malicious requests.
Scenario-Based Firewall Interview Questions

13. If a legitimate user is unable to access a resource, how would you troubleshoot the firewall settings?

• Check Firewall Logs – Identify if the traffic is being blocked.
• Review Firewall Rules – Ensure there are no conflicting rules.
• Test Connectivity – Use tools like ping, traceroute, or telnet.
• Check Stateful Inspection – Ensure the connection state is valid.
• Inspect NAT and Port Forwarding – Verify if address translation is configured correctly.

14. How would you implement a firewall rule to block all incoming traffic except for SSH (Port 22) and HTTPS (Port 443)?

A typical firewall rule would be:

• Allow TCP traffic on port 22 (SSH)
• Allow TCP traffic on port 443 (HTTPS)
• Deny all other incoming traffic

15. How can firewalls prevent insider threats?

Firewalls can help prevent insider threats by:

• Implementing User-Based Access Controls (UBAC)
• Logging and monitoring user activity
• Using Data Loss Prevention (DLP) mechanisms
• Enforcing Multi-Factor Authentication (MFA) for access

Final Tips for Firewall Interviews

• Stay updated on the latest cybersecurity threats and firewall technologies.
• Practice troubleshooting firewall issues using real-world scenarios.
• Understand how firewalls integrate with cloud security and Zero Trust frameworks.

With these network firewall interview questions and answers, you’ll be well-prepared to impress employers in 2025. For expert training and hands-on experience, consider learning from Network Kings, a trusted platform for IT and cybersecurity professionals. Good luck! 🚀