Basic Firewall Interview Questions and Answers

1. What is a firewall?
  • A firewall acts as a line of defense in a network. It acts as a barrier between a trusted and a non-trusted network.
  • It allows/blocks incoming or outgoing traffic on the basis of pre-configured policies or rules.
  • Firewalls are the oldest and the most frequently used network security solutions.
  • A firewall could be a free or a paid software solution.
  • A firewall also works to protect internal networks from each other.
2. What is a packet-filtering firewall?

A packet filtering firewall is one that examines the source and destination IP addresses, protocols such as User Diagram Protocol (UDP) and Transmission Control Protocol (TCP) as well as port addresses.

The packet is verified and secured if both IP addresses match each other.

 

3. What is the difference between stateful and stateless firewalls?

On the basis of their state, the packet filtering firewalls can be classified into two types:

  • Stateful packet filtering firewalls
  • Stateless packet filtering firewalls

 

Stateful packet filtering firewalls

  • A stateful firewall is located in Layer 3 and Layer 4 of the Open Systems Interconnection (OSI) model.
  • It keeps track of the state of network connections.
  • This means that it knows the current status of the process.
  • This firewall adds the traffic into a stable table once it is approved.
  • Stateful firewalls are able to detect fake messaging and unauthorized access.
  • They have a powerful memory as they remember the main aspects of network connections.
  • They have stronger attack mitigation.
Stateless packet filtering firewalls:
  • Stateless firewalls are also known as Access Control Lists (ACLs).
  • They are not aware of the current state of connection/incoming traffic.
  • ACLs are present in the network or physical layers and sometimes, in the transport layer.
  • The device accepts or rejects an incoming packer by checking if it matches the ACL rules or not.
  • Stateless firewalls are faster than stateful firewalls.
  • They perform better in heavy traffic as they do not dive deep into the information of a packet as stateful firewalls do.

4. What is the function of a firewall?

  • The function of a firewall is to protect sensitive enterprise systems, be it any basic firewall or an advanced Next Generation (NGFW) firewall as a FortiGate firewall.
  • A firewall is able to recognize harmful or malicious traffic.
  • It is able to block traffic from a particular IP address if it senses any malicious activity in them.
  • It acts as a filtering unit for legal and healthy traffic.
  • An advanced firewall can also look into the contents of data packets and look for malware signatures.
 
5. How does a firewall function?

A firewall filters traffic on the basis of a set of configurations or rules that are applied by a firewall administrator. It has the ability to permit or block any IP address, port number, web application, and network-layer protocols on the basis of these rules.

Some of the common ports are as follows?

  • 80 HTTP
  • 25 SMTP
  • 22 SSH
  • 23 Telnet
  • 443 HTTPS
  • 20 and 21 FTP
 
6. What do you understand by a VPN?
  • The full form of a VPN is Virtual Private Network (VPN).
  • It creates a safe and secure connection between the Internet and your device.
  • Once you are connected to the internet through a VPN, your data is sent via an encrypted virtual tunnel.
  • It also creates a connection between two private networks over the internet.

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8. What are the different types of firewalls in network security?

There are five types of firewalls in network security. These are as follows:

  • Packet filtering firewalls
  • Application-level gateway or Proxy firewalls
  • Circuit-level gateway firewalls
  • Stateful inspection firewalls
  • Next-Generation
  • firewalls (NGFW)
 
9. Firewalls work in which OSI layers?

A firewall works at these three layers in the OSI model, namely:

  • Layer 3 (Network layer)
  • Layer 4 (Transport layer)
  • Layer 7 (Application layer)

 

10. What is the function of a transparent firewall?
  • A firewall acts as a Layer 2 device like a bridge or switch in transparent mode.
  • It then forwards Ethernet frames on the basis of destination mac-address.
  • The best part about a transparent firewall is that it can be easily inserted in an already existing segment to control the traffic between two sides without readdressing or reconfiguring the devices.

 

11. What is Policy NAT?
  • Policy NAT stands for Policy Network Address Translation.
  • It allows you to NAT by giving both the source and destination addresses in an extended Access List (ACL).
  • We can also give source and destination ports.

There are two types in which Policy NAT is available:

  1. Static Policy NAT

  2. Dynamic Policy NAT

 
12. What is the default timeout value for TCP, UDP and ICMP sessions?
  • The default value for a TCP session is 60 minutes.
  • The default value for the UDP session is 2 minutes.
  • The default value for the ICMP session is 2 seconds

FAQ

01. What is a firewall in Networking?

A firewall acts as a line of defense in a network. It acts as a barrier between a trusted and a non-trusted network. It allows/blocks incoming or outgoing traffic on the basis of pre-configured policies or rules.

02. What are the types of firewalls?

Packet filtering firewalls Application-level gateway or Proxy firewalls Circuit-level gateway firewalls Stateful inspection firewalls Next-Generation firewalls (NGFW)

03. Give some examples of firewalls.?

The most popular firewalls in the market are the Palo Alto firewall, Checkpoint firewall, FortiGate firewall, etc.

04. How does a firewall function?

A firewall filters traffic on the basis of a set of configurations or rules that are applied by a firewall administrator.

05. What are the three types of firewall delivery methods?

Hardware-based firewalls, Software-based firewalls, Cloud/hosted firewalls

06. Is the firewall Layer 3 or Layer 4?

A firewall works in both Layer 3 and Layer 4. In fact, in the advanced OSI model, the firewalls work in Layer 7 as well.

07. Is VPN a Layer 4?

A VPN usually sits at Layer 3, the Network layer.

08. Does the firewall have a router?

Yes, a lot of routers have in-built routers. It is the core of a wireless network.

Firewall QNA

Q. What is the difference between a firewall and a router?

Ans. 

Firewall filters traffic based on security rules, while router forwards data packets between networks.

  • Firewall is used to block or allow traffic based on security rules, while router is used to forward data packets between networks
  • Firewall operates at the network layer (Layer 3) or above, while router operates at the network layer (Layer 3)
  • Firewall can inspect and filter traffic based on IP addresses, ports, protocols, and application types, while router primarily forwards packets based on IP addresses
  • Example: A firewall can block certain websites from being accessed by users, while a router forwards data packets between a local network and the internet

     

    Q. What is a next-generation firewall (NGFW), and what features does it offer?

Ans. 

A next-generation firewall (NGFW) integrates traditional firewall capabilities with advanced features for enhanced security.

  • Application awareness: NGFWs can identify and control applications regardless of port or protocol (e.g., blocking Facebook while allowing Skype).
  • Integrated intrusion prevention system (IPS): Provides real-time threat detection and prevention against known vulnerabilities.
  • Deep packet inspection: Analyzes the data within packets for malicious content, not just header information.
  • User identity awareness: Allows policies to be applied based on user identity rather than just IP addresses.
  • Advanced threat protection: Incorporates features like sandboxing to analyze suspicious files in a safe environment.

 

Q. What is the difference between a firewall and a gateway?

Ans. 

Firewall is a security system that monitors and controls incoming and outgoing network traffic, while a gateway is a node that connects two different networks.

  • Firewall is a security system that filters network traffic based on predetermined security rules.
  • Gateway is a node that acts as an entry and exit point for data between two networks.
  • Firewall can be a software program or a hardware device, while gateway is typically a hardware device.
  • Examples of firewalls include Cisco ASA, Palo Alto Networks, and Check Point, while examples of gateways include routers and switches.

 

Q. On which layers does a firewall operate?

Ans. 

Firewall works on multiple layers of OSI model

  • Firewall operates on layers 3 (network layer) and 4 (transport layer) of the OSI model
  • It can filter traffic based on IP addresses, ports, protocols, and other criteria
  • Firewalls can also perform deep packet inspection to detect and block malicious traffic
  • Examples of firewall software include Cisco ASA, pfSense, and Windows Firewall

 

Q. What is the difference between an application-level firewall and a stateful firewall?

Ans. 

Application level firewall filters traffic based on application layer protocols while stateful firewall filters based on connection state.

  • Application level firewall operates at layer 7 of OSI model while stateful firewall operates at layer 4.
  • Application level firewall can block specific applications while stateful firewall cannot.
  • Stateful firewall keeps track of connection state while application level firewall does not.
  • Examples of application level firewall include proxy servers and web application firewalls while examples of stateful firewall include Cisco ASA and Check Point Firewall.

 

Q. What are the different kinds of Firewalls?

Ans. 

Firewalls are network security systems that monitor and control incoming and outgoing network traffic based on predetermined security rules.

  • Types of firewalls include packet filtering firewalls, stateful inspection firewalls, proxy firewalls, and next-generation firewalls.
  • Packet filtering firewalls examine packets of data and decide whether to forward or discard them based on predetermined criteria.
  • Stateful inspection firewalls keep track of the state of active connections and make decisions based on the context of the traffic.
  • Proxy firewalls act as intermediaries between internal and external networks, filtering traffic based on application-layer data.
  • Next-generation firewalls combine traditional firewall functionality with additional features such as intrusion prevention, application awareness, and deep packet inspection.

 

Q. Tell me something about Firewalls

Ans. 

Firewalls are network security systems that monitor and control incoming and outgoing network traffic.

  • Firewalls can be hardware or software-based
  • They can be configured to block or allow specific types of traffic
  • Firewalls can prevent unauthorized access to a network
  • They can also be used to monitor network activity and detect potential threats
  • Examples of popular firewall software include Norton, McAfee, and Windows Firewall

 

Q. What is the use of a firewall, and what are its uses?

Ans. 

Firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

  • Firewall acts as a barrier between a trusted internal network and untrusted external network
  • It can prevent unauthorized access to a network
  • It can block malicious traffic and prevent malware from entering the network
  • It can also be used to restrict access to certain websites or applications
  • Examples of firewalls include hardware firewalls, software firewalls, and cloud-
  • based firewalls

     

    Q. What is the difference between a firewall and a next-generation firewall?

Ans. 

A firewall filters traffic based on predetermined rules, while a next generation firewall includes additional features like intrusion prevention and application awareness.

  • Firewall filters traffic based on IP addresses and ports
  • Next generation firewall includes intrusion prevention, application awareness, and deep packet inspection
  • NGFW can identify and block advanced threats like malware and ransomware
  • NGFW can provide more granular control over applications and users

     

    Q. What are firewalls and NAT?

  • Ans. 

    Firewall is a network security system that monitors and controls incoming and outgoing network traffic. NAT (Network Address Translation) is a process used to modify network address information in packet headers while in transit.

    • Firewall acts as a barrier between a trusted internal network and untrusted external network

    • Firewall can be hardware-based or software-based

    • NAT allows multiple devices on a local network to share a single public IP address

    • NAT can be used to hide the internal network structure from external networks

    • Example: A firewall can block unauthorized access to a network, while NAT can translate private IP addresses to public IP addresses for internet communication

     

    Q. How do you manage a network smoothly using a firewall?

    Ans. 

    A firewall can be used to manage network traffic and ensure smooth operation.

    • Define clear security policies and rules for the firewall

    • Regularly update and maintain the firewall software

    • Monitor network traffic and adjust firewall settings as needed

    • Implement intrusion detection and prevention systems

    • Train employees on safe browsing habits and network security

    • Use VPNs to secure remote access to the network

     

    Q. What is a firewall, and what are its security features?

    Ans. 

    A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

    • Acts as a barrier between internal network and external networks

    • Filters incoming and outgoing traffic based on set rules

    • Can be hardware-based or software-based

    • Can block unauthorized access while allowing legitimate traffic

    • Can be configured to log and report on network activity

Firewall QNA

  1. What is Network Security?

Network security is a process of securing IT infrastructure from unauthorized access, misuse, malfunction, modification, destruction, or improper disclosure. IT infrastructure includes firewalls, routers, switches, servers, and other devices, which help host the software applications. In simple terms, network security refers to all activities related to protecting the confidentiality, integrity, and availability of an organization’s software and hardware assets.

 

  1. What is a Network Firewall?

Network firewall protects your network from unauthorized access. It filters traffic based on the configuration set by the firewall administrator. The firewall basically performs two functions, block and permit traffic based on configuration.

 

  1. How does a firewall work?

Firewall filters network traffic based on the configuration set by the firewall administrator.  It can permit or block any port number, web application, and network-layer protocols based on configuration.

 

Common ports:

  • 80  HTTP
  • 443  HTTPS
  • 20 & 21  FTP
  • 23  Telnet
  • 22  SSH
  • 25  SMTP
  1. What can a firewall protect IT infrastructure inside your organization?

Firewalls are configured to protect IT infrastructure from any unauthorized access. It secures the network by implementing defined security policies, hiding and protecting your internal network addresses, and reporting threats and activities. It also provides audit logs related to network traffic to the firewall administrator, identifying the root cause of a security breach.

    1. What are the types of firewalls ?

    The National Institute of Standards and Technology (NIST , an organization) from the US, divides firewalls into three basic types: Packet filters, Stateful inspection, and Proxy.

    Packet filters permit or block packets based on port number, protocols source, and destination address.

    Stateful inspection works on the principle of the state of active connections between client and server. It uses the state information to allow or block network traffic.

    Proxy firewall combines stateful inspection technology to enable deep packet inspection. Here, the firewall act as a proxy; a client makes a connection with the firewall, and then the firewall makes a separate connection to the server on behalf of the client.

    1. What is a Host-based Firewall?
    • These are personal firewalls running on your desktops and laptops as a software.
    • Firewall software is generally included in your operating system and is also available externally as a 3rd party solution.
    • The main objective of the personal firewall is to stop unauthorized access to the network.
    • These firewalls are generally a “Stateful” firewall and block connection based on port numbers.
    • These firewalls are also used to block applications based on your configuration.
    • The best example is the Windows Firewall, which works based on port number, application, and other attributes.

Firewall QNA

Network Firewall Interview Questions and Answers for Freshers

Here are some basic firewall questions for interviews that are frequently asked for entry-level positions.

1. What is a network firewall? 

A network firewall is a critical security device or software that monitors and controls the flow of traffic between trusted internal networks and untrusted external networks, such as the Internet. It operates based on predefined security rules to permit or block data packets, thereby protecting the network from unauthorized access, malware, and other cyber threats. 

 

2. What is the role of a Network Firewall? 

A network firewall serves to protect your network from unauthorized access. It filters incoming and outgoing traffic according to rules set by the firewall administrator, primarily allowing or blocking traffic based on these configurations.

 

7. What is a VPN? 

A VPN, or Virtual Private Network, creates a secure tunnel to protect your data from unauthorized access. It safeguards private web traffic from interception, interference, and censorship, effectively establishing a connection between two private networks over the internet. 

 

8. What types of firewalls exist? 

According to the National Institute of Standards and Technology (NIST), firewalls are categorized into three main types:  

1. Packet Filters: These allow or deny packets based on port numbers, protocols, and source/destination addresses. 

2. Stateful Inspection: This method relies on the state of active connections to allow or block traffic based on established rules. 

3. Proxy Firewalls: These combine stateful inspection with deep packet inspection, acting as intermediaries that handle requests between clients and servers. 

 

13. What is Unified Threat Management (UTM)? 

Unified Threat Management, also known as all-in-one security appliances or web security gateways, combines various security features such as URL filtering, malware inspection, spam filtering, built-in routing/switching, firewall functions, and intrusion detection/prevention capabilities, often serving as a VPN endpoint. 

 

14. What are the limitations of network firewalls? 

While firewalls act as the first line of defense against external threats, they are not equipped to handle internal attacks. Their primary function is to protect the network perimeter, leaving internal systems vulnerable to harm from within

 

15. What is a packet filtering firewall? 

A packet-filtering firewall controls traffic by examining packet attributes such as source and destination addresses, port numbers, and protocol types. 

 

19. What is a Stateful Inspection Firewall? 

Stateful inspection firewalls represent an advanced approach to securing networks, integrating features from packet filtering, circuit-level gateways, and application-level gateways for enhanced protection. 

 

20. What are some common attack methods on networks? 

Common network attack methods include ping sweeps, port scans, email reconnaissance, IP spoofing, DDoS attacks, packet sniffing, DNS transfers, Trojan horses, backdoors, and spyware.

 

21. Can you explain the concept of IP spoofing? 

IP spoofing involves attackers masking their actual IP address by sending malicious traffic from a fabricated or “spoofed” IP address. This tactic complicates efforts by security experts and law enforcement to trace the actual attacker, particularly in cases like DDoS attacks. 

 

24. What is the purpose of a Network Firewall? 

 A network firewall serves to protect your network by controlling incoming and outgoing traffic based on predetermined security rules. It acts as a barrier against unauthorized access, allowing or blocking traffic as configured by the firewall administrator. 

 

25. How does a firewall function? 

A firewall functions by analyzing network traffic according to the settings specified by the administrator. It can permit or deny traffic based on criteria such as port numbers, protocols, and IP addresses, effectively managing access to and from the network. 

 

Who will Benefit the Most from These Questions?

Here are the job roles that will benefit the most by preparing for firewall interview questions:

1. Network Security Engineer: Responsible for implementing and managing firewall solutions to protect network infrastructure.

2. Firewall Engineer: Focuses specifically on configuring, maintaining, and troubleshooting firewalls in various environments.

3. Cybersecurity Analyst: Analyzes security threats and implements measures, including firewalls, to safeguard organizational data.

4. Security Consultant: Provides expert advice on firewall configurations and best practices to enhance clients’ security postures.

5. Systems Administrator: Manages network systems and ensures proper firewall configurations to protect against unauthorized access.

6. Penetration Tester: Evaluate the effectiveness of firewalls by simulating attacks and identifying vulnerabilities.

7. IT Support Specialist: Assists in troubleshooting firewall-related issues and ensuring network security for end-users.

FAQ

What is a firewall, and what is its primary function?

A firewall is a security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Its primary function is to establish a barrier between a trusted internal network and untrusted external networks, protecting the internal network from unauthorized access and threats.

Yes, implementing a network firewall is essential for safeguarding your network from unauthorized access and cyber threats. Firewalls monitor and filter incoming and outgoing traffic based on established security rules, providing a crucial line of defense against potential attacks.

Network security refers to the practice of protecting computer networks and their data from unauthorized access, misuse, or cyberattacks.

Firewalls offer several advantages, including protection against unauthorized access, prevention of malware and virus infiltration, and monitoring of network traffic. They enhance data privacy, improve compliance, and provide control over application usage, making them essential for robust network security.

What Difference Between Firewalls and Routers

Firewalls and routers are both essential components of an organization’s network infrastructure. However, they are different systems with very different functions.

A router is a tool for networking. Routers make up much of the backbone of the Internet, connecting networks together and routing traffic between them. A router has no security capabilities, it is solely intended to help a network packet travel from point A to point B.

Firewalls, on the other hand, are security solutions designed to help protect the organization against cyber threats. All traffic flowing through a firewall is inspected and evaluated against predefined rules. Based on these rules, the firewall will decide to either allow the packet to continue on to its destination or block the attempted connection.

What is a Router?

A router is a networking device used to help route traffic from source to destination. Routers have an upstream port and multiple downstream ports, and route traffic originating from one port to the appropriate destination port. This includes routing traffic between machines within the subnet and routing traffic between internal and external machines.

Routers primarily route traffic at Layer 3 (Network) of the OSI model, though they do operate at Layer 1 (Physical) and Layer 2 (Data Link) as well. A router will have IP addresses assigned to each of its ports and will route traffic to the appropriate port based on the destination address specified within a network packet.

Routers are the backbone of the Internet as well as of private, internal networks. When traveling from point A to point B, a network packet is likely to make multiple hops from one router to the next while traversing the Internet or a large private network.

What is a Firewall?

A firewall is a solution that defines and protects network boundaries. Firewalls are deployed at the edge of the network — where it connects to another network — and all traffic flows through the firewall for inspection and filtering. For instance organizations often have a perimeter firewall to segment internal networks and assets of an organization from the Internet.

Firewalls work based on predefined firewall rules. The rules use the packet’s header — and potentially its contents — to determine whether or not it should be permitted to enter or leave the network. For example, a firewall may be configured to block traffic to or from certain IP ranges, restrict inbound network connections, or prevent certain network protocols from entering or leaving the corporate network.

Firewalls are important to an organization’s cybersecurity program because they can block potential inbound threats and outbound data exfiltration. Firewalls come in a variety of forms, including stateless and stateful firewalls — which make decisions based solely on IP address and port in packet headers — and next-generation firewalls (NGFWs), which incorporate additional functions — such as an intrusion prevention system (IPS) — and can identify malicious content in the body of a network packet.

 Router vs firewall, a comparison table 

Aspect Router Firewall 
Primary Function Routes data packets between different networks.  Secures a network by applying rules that apply to the incoming and the outgoing traffic. 
Layer of Operation (OSI) Layer 3 (Network Layer) and Layer 4 (Transport Layer). Layer 4 (Transport Layer) and higher  Layer 7 (Application Layer). 
Packet Handling Forwards packets to destination IP addresses. Inspects packets and apply security policies. 
Security Features Basic security features (e.g., NAT, ACLs). Extensive security features (e.g., packet filtering, IPS). 
Performance Impact Optimized for high-speed data forwarding with minimal delay. It can introduce latency due to security checks which are additional to the data transfer.  
Configuration Complexity Complex for advanced routing protocols, straightforward for basics. Complex due to detailed security policies and rules. 
NAT (Network Address Translation) Performs NAT to share a single public IP address. Performs NAT with added focus on security. 
User Access Control Basic ACLs to permit or deny traffic. Detailed access control, user authentication, VPN support. 
VPN Support Some support for VPNs, limited security features. Robust VPN support with advanced security features. 
Logging and Monitoring Basic logging for network performance and routing issues. Extensive logging and monitoring of security incidents. 
Traffic Shaping and QoS Includes QoS features for traffic prioritization. May include QoS, but secondary to security functions. 
Placement in Network Network perimeter or between segments. Network boundaries for external and internal protection. 
Hardware vs. Software Usually hardware solution, but there are software implementations.  Usually software solution, but there are hardware implementations.  
Cost Generally less expensive. Often more expensive due to advanced security features. 
Usage Scenario Interconnecting networks, managing traffic flow. Protecting networks from threats, enforcing security policies. 
Advanced features Dual-band and even Tri-band Wi-Fi. This allows better performance, and optimized handling of multiple devices.  

Intrusion Detection and Prevention Systems (IDPS): Monitoring and preventing potential threats. 

Deep Packet Inspection (DPI): Examining the data part of a packet to enhance security.