A firewall is a cybersecurity tool that monitors incoming and outgoing network traffic and allows or blocks data packets according to a set of cybersecurity rules.

Firewalls are typically used to protect network nodes from egress and ingress data traffic, as well as specific applications. Firewalls protect networks from external attacks by utilising software, hardware, or cloud-based methods. A firewall’s primary goal is to block malicious traffic and data packets while allowing legitimate traffic to pass through.

To prevent attacks, firewalls examine inbound traffic based on predefined security rules and filter traffic from unsecured or suspicious sources. Traffic is guarded at a computer’s entry point called ports, where information is actually exchanged with external devices. Consider the case where the source address ‘’ is permitted to communicate with the destination address ‘’ via port 22. Port 22 is regarded as a point of data exchange in this context, and thus the firewall protects it from intruder attacks.

The firewall operation can be understood by using a simple analogy in which ‘IP addresses’ are treated as ‘houses,’ and ‘port numbers’ are treated as ‘rooms’ within the house. Only trusted people (source addresses) are permitted to enter the house (destination address) at all times in such a scenario. These people’s movement within the house is further filtered or restricted as shown below:

a) Depending on whether they are the owner or a guest, people entering the house only have access to certain rooms (destination ports).
b) The owner is permitted to enter any room (any port), whereas guests are restricted to a specific set of rooms (specific ports).

When a firewall is configured on a system or network, the rules for the type of activity that is permitted for an entire group of people are pre-defined. As a result, the entire firewall functionality is based on the monitoring job, which allows or blocks packets based on a set of security protocols.

Key Components of a Firewall

Network policy, advanced authentication, packet filtering, and application gateways are the four primary components of firewall architecture. Let’s take a closer look at each component.

1) Network policy
The design, installation, and operation of a firewall in a network is heavily influenced by two levels of network policy: higher-level policy and lower-level policy.

(a) The higher-level policy is an issue-specific network access policy that defines which services are allowed or explicitly denied from the restricted network, how they would be used, and the conditions for policy exceptions.
(b) The lower-level policy describes how the firewall will handle the higher-level policy’s access restriction and service filtration.

These policies are summarised below.

  • Service access policy
    The service access policy is concerned with internet-specific issues as well as all outside network accesses (i.e., dial-in policy, SLIP, and PPP connections). For a firewall to be effective, the service access policy must be realistic and sound, and it should be developed prior to the installation of a firewall. A realistic policy strikes a balance between protecting the network from known threats and allowing users access to network resources.

    A firewall can enforce a variety of service access policies. However, a typical policy may be to prohibit internet access to a site while allowing internet access to the site. Another common policy would be to allow internet access, but only to specific systems such as information servers and email servers. Firewalls frequently implement service access policies that grant some users internet access to specific internal hosts. This access, however, would be granted only if it was absolutely necessary and could be combined with advanced authentication.
  • Firewall design policy
    The firewall design policy is firewall-specific, defining the rules used to implement the service access policy. This policy cannot be designed in isolation from understanding firewall capabilities and limitations, as well as threats and vulnerabilities associated with TCP/IP. Firewalls typically follow one of two basic design policies: permit any service unless explicitly denied, or deny any service unless explicitly permitted.

    A firewall that implements the first policy by default allows all services to enter the site except those that the service access policy has identified as disallowed. The second policy adheres to the traditional access model used in all areas of information security, in which the second policy denies all services by default but then allows those that have been identified as allowed.

2) Advanced authentication
To combat weak traditional passwords, advanced authentication measures such as smartcards, authentication tokens, biometrics, and software-based mechanisms are being developed. While authentication methods differ, they all have one thing in common: passwords generated by advanced authentication devices cannot be reused by an attacker who has monitored a connection. Given the issues with passwords on the internet, an internet-accessible firewall that does not use or contains the hooks to use advanced authentication may be considered irrelevant in the current context.

One-time password systems are some of the more popular advanced authentication devices in use today. For example, a smartcard or authentication token generates a response that the host system can use instead of a traditional password. Because the token or card interacts with software or hardware on the host, each login generates a unique response. As a result, a one-time password is generated that, if monitored, an intruder cannot use to gain access to an account.

3) Packet filtering
A packet filtering router filters packets as they pass between the router’s interfaces to achieve IP packet filtering. IP packets can typically be filtered by source IP address, destination IP address, TCP/UDP source port, or destination port on a packet-filtering router.

Currently, not all packet filtering routers filter the source TCP/UDP port. However, more vendors are incorporating this capability. Some routers examine which network interfaces a packet arrived at and use this as an additional filtering criterion.

4) Application gateways
To address the shortcomings of packet filtering routers, firewalls must employ software applications to forward and filter connections for services such as TELNET and FTP. This type of application is known as a proxy service, and the host that runs it is known as an application gateway.

Types of Firewalls

Firewalls are classified into two types: host-based firewalls and network-based firewalls.

1) Host-based Firewalls
Each network node has a host-based firewall that controls all incoming and outgoing packets. It is a software application or set of applications that is included with the operating system. Each host’s firewall protects it from attacks and unauthorised access.

2) Network-based Firewalls
A network firewall performs network-level functions by utilising two or more network interface cards (NICs). In other words, these firewalls use firewall rules to filter all incoming and outgoing network traffic. A network-based firewall is typically a dedicated system that includes proprietary software.

3) Firewall classifications have evolved over time. In addition to the broad categories mentioned above, here are the five distinct types of firewalls that continue to play an important role in network security.

A) Packet filtering firewall
Packet filtering firewalls operate in parallel at junction points where devices like routers and switches perform their functions. These firewalls do not route packets, but instead compare each packet to a set of predefined criteria, such as allowed IP addresses, packet type, port number, and other aspects of packet protocol headers. Packets marked as problematic are dropped.

B) Circuit-level gateway
TCP handshakes and other network protocol session initiation messages are monitored across the network as they are established between local and remote hosts to determine whether the session being initiated is legitimate and whether the remote system is trusted. They do not examine the packets themselves. They do, however, provide a quick way to identify malicious content.

C) Stateful inspection firewall
State-aware devices inspect each packet and keep track of whether it is part of an existing TCP or other network session. This provision provides greater security than either packet filtering or circuit monitoring alone, but it has a greater impact on network performance.

The multilayer inspection firewall is another variant of stateful inspection that considers the flow of transactions in progress across multiple protocol layers of the seven-layer open systems interconnection (OSI) model.

D) Application-level gateway
A proxy, also known as a proxy firewall, combines some of the characteristics of packet filtering firewalls with those of circuit-level gateways. They filter packets based on the service (specified by the destination port) and certain other characteristics, such as the HTTP request string.

E) Next-generation firewall (NGFW)
NGFW combines packet inspection with stateful inspection, including deep packet inspection, as well as other network security systems such as intrusion detection/prevention, malware filtering, and antivirus.

In most conventional firewalls, packet inspection looks at the packet’s protocol header. Deep packet inspection, on the other hand, examines the actual data carried by the packet. A deep packet inspection firewall monitors a web browsing session. It can determine whether a packet payload, when combined with other packets in an HTTP server response, constitutes a valid HTML formatted response.

Key Benefits of Firewalls

Understanding the benefits of firewall security is the first step toward assisting businesses in growing in a secure manner in the ever-changing digital age. Firewalls are the first line of defence against external threats, malware, and hackers attempting to access data and systems. The following are some of the primary advantages of deploying a firewall in a network:

1) Block spyware
In today’s data-driven world, preventing spyware from gaining access and infiltrating a system is critical. As systems become more sophisticated and robust, the number of criminals attempting to gain access to them grows. One of the most common ways for unauthorized people to gain access is through the use of spyware and malware. These are computer programmed that are designed to infiltrate systems, take control of computers, and steal sensitive or critical data. Firewalls are an important line of defense against such malicious programmers.

2) Direct virus attacks
A virus attack can disrupt any enterprise’s digital operations more quickly and severely than expected. As the number of threats evolves and grows in complexity, it is critical that defenses are put in place to keep the systems healthy and operational at all times. Controlling the system’s entry points and preventing virus attacks are two of the most visible benefits of firewalls. Depending on the type of virus, the cost of damage from a virus attack on any system could be immeasurable.

3) Maintain privacy
Another advantage of using a firewall is that it promotes privacy. By working proactively to keep your data and your customers’ data safe, you create a privacy environment that your clients can rely on. Nobody wants their data stolen, especially when steps could have been taken to prevent the intrusion.

4) Network traffic monitoring
The ability to monitor network traffic is the foundation of all firewall security benefits. Data flowing into and out of your systems opens the door for threats to compromise your operations. Firewalls protect systems by monitoring and analyzing network traffic and applying pre-defined rules and filters. An enterprise can manage customized protection levels based on what is seen coming in and out of the firewall with a well-trained IT team.

5) Prevent hacking
Most businesses today follow the trend of digital operations, which invites more thieves and bad actors into the picture. With the rise of data theft and criminals holding systems hostage, firewalls have become even more critical, preventing hackers from gaining unauthorised access to data, emails, systems, and other resources. A firewall can either completely stop a hacker or deter them from choosing an easier target.

Key Applications of Firewall

The purpose of a firewall is to keep unauthorised connections and malicious software out of your network. Unwanted traffic can enter a network through software, hardware, or software-based cloud methods. As a result, it is critical for the firewall to leave its imprint on all possible network fronts vulnerable to external attacks. Firewall applications are broadly classified as follows:

1) Software-based applications
Instead of a separate piece of hardware, software-based applications secure data by using any type of firewall installed on a local device (or a cloud server). The advantage of a software-based firewall is that it can be used to create defence in depth by isolating individual network endpoints from one another.

Maintaining individual software firewalls on different devices, on the other hand, can be difficult and time-consuming. Furthermore, not every device on a network may be compatible with a single software firewall, necessitating the use of multiple software firewalls from various vendors to protect every node or device.

2) Hardware-based applications
Hardware firewalls employ a physical appliance that functions as a traffic router to intercept data packets and traffic requests before they reach the network’s servers. Physical appliance-based firewalls like this one excel at perimeter security by intercepting malicious traffic from outside the network before it reaches the company’s network endpoints.

The main weakness of a hardware-based firewall is that it is frequently easy for insider attacks to bypass it. Furthermore, the actual capabilities of a hardware firewall may differ depending on the manufacturer; some may have a more limited capacity to handle simultaneous connections than others.

3) Cloud-based applications
When a cloud solution is used to provide a firewall, it is referred to as a cloud firewall or firewall-as-a-service (FaaS). Cloud firewalls are similar to proxy firewalls in that a cloud server is frequently used in a proxy firewall configuration.

The benefit of cloud-based firewalls is that they are extremely easy to scale with any organisation. As the need grows, more capacity can be added to the cloud server to filter larger traffic loads. Cloud firewalls provide network architecture with perimeter security.

Top 7 Best Practices for Using a Firewall Protection in 2021

A firewall is the most important network security tool. Network firewall configuration can be a difficult task for administrators because they must strike the perfect balance between security and user performance. It is critical to protect the network from future security threats, malware that could exfiltrate sensitive data from your network to other locations, and to handle existing threats appropriately.

Here are the top seven firewall practises to follow in order to protect any network from an existing or potential threat:

1) Automation of firewall updates
Many processes have become faster and easier as technology has advanced. Firewall administrators may not always be able to constantly check for updates and perform software updates on a regular basis, putting the network at risk of security breaches.

Instead of manually updating the firewall, one can automate the process. An automated system can be set up to check for available updates and implement them as they become available. Such automation reduces the need for human intervention while also keeping the firewall secure and robust at all times.

2) Centralized management tool for multi-vendor firewalls
Many organisations have multi-vendor firewalls in place. Companies prefer firewalls manufactured by various companies that are installed in systems to provide additional layers of security. However, the architecture of firewalls offered by various vendors is typically different.

As a result, it is critical to centrally manage all of your firewalls in one location to ensure that they are all functioning properly. Using a centralised tool to manage multi-vendor firewalls can provide a unified view of firewall policies and rules from various manufacturers, allowing organisations to easily compare and manage firewall rules. Through this centralised management tool, the organisation can also perform security auditing and reporting, troubleshoot configuration issues, and support firewall migration.

3) Design and optimize network-specific firewall rules
To provide the expected security protection, the firewall rules must be well designed and optimised. Cleaning up any kind of unnecessary clutter in the firewall rule base can have a positive impact on network security.

In general, the firewall rule base contains redundant elements, duplicates, or unnecessary rules, which make the guidelines complex and ineffective. As a result, it is critical to streamline these rules in order to have a clear set of guidelines that can be better followed.

To clean up the firewall rule base, do the following:
a) Remove unnecessary shadowed rules, which may cause more critical rules to be overlooked.
b) Remove rules that clash.
c) Remove redundant or duplicate rules that slow down the firewall’s performance.
d) Errors or inconsistencies in firewall rules must be rectified because they can cause issues.
e) Remove obsolete or no longer in use rules, which might complicate firewall maintenance and provide a security risk if not updated.

4) Establish a firewall configuration change plan
For a variety of reasons, the network’s firewall will need to be upgraded from time to time. This is required to verify that the firewall conforms with new firewall rules and remains up to date in order to guard against new threats. However, in order to be seamless and secure, a change management plan must be in place. An unanticipated configuration change creates a security hole in the network that attackers can exploit.

The following elements must be included in a resilient firewall change management plan:

  • Define the goals of the necessary modifications.
  • List the risks associated with policy changes and their effects on the network.
  • Mitigation strategy to reduce the risks stated.
  • Audit trails that show who made the change, when it was done, and why.

5) Monitor user access and block traffic
It is strongly advised to block all network traffic by default. Allow just specified types of traffic to known services. This can aid in regulating who has access to the network and so preventing security breaches.

Because the firewall is your first line of defence against attacks, no one should be able to change its configuration. To ensure that only authorised administrators can update firewall configurations, user permission control is required. Furthermore, every modification made by an authorised administrator must be noted in the log for audits and compliance. Unwanted configuration modifications can thus be recognised, and configuration restoration can be performed in such cases.

Furthermore, firewall logs must be examined on a regular basis to detect any illegal firewall breaches from within or outside the network.

6) Periodic firewall security audits
Security audits are required to confirm that the firewall rules correspond to the network’s external security regulations and are compliant with organizational norms. Unauthorized firewall configuration changes can result in noncompliance. As a result, it is critical for administrators and IT security personnel to conduct frequent security audits to guarantee that no illegal changes have occurred. This will also keep you up to date on any necessary firewall adjustments and advise you of any potential threats posed by these changes.

When a new firewall is placed within a network, there is ongoing firewall migration activity, or bulk configuration changes are made on multi-vendor firewalls, security audits are crucial and required.

7) Regular firewall software update
Firewall companies deliver software upgrades on a regular basis. By introducing modest changes to existing software, these upgrades address any new potential security issues. It is critical to maintain the firewall software up to date since it ensures that the network remains secure and is not vulnerable to any security threats. As a result, it is necessary to periodically check to see if the firewall software has been updated to the most recent version.

In conclusion

A firewall is a cybersecurity solution that secures systems when they are connected to the internet. With so much dangerous content circulating around the internet and the exponential rise in cyber threats and hackers, it is critical to maintain systems secure. As a result, selecting the proper type of firewall that fits the organizational needs is critical to effectively secure the systems.

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