Network Firewall

What is Firewall in Networking?

A firewall is a security device that monitors network traffic. It protects the internal network by filtering incoming and outgoing traffic based on a set of established rules.

How Does a Firewall Work?

A firewall is placed on the hardware or software level of a system to secure it from malicious traffic. Depending on the setup, it can protect a single machine or a whole network of computers. The device inspects incoming and outgoing traffic according to predefined rules.

Communicating over the Internet is conducted by requesting and transmitting data from a sender to a receiver. Since data cannot be sent as a whole, it is broken up into manageable data packets that make up the initially transmitted entity. The role of a firewall is to examine data packets traveling to and from the host.

Types of Firewalls

Basically there are three types of firewalls – software firewalls, hardware firewalls, or both. The remaining types of firewalls specified in this list are firewall techniques which can be set up as software or hardware.

Software Firewalls

A software firewall is installed on the host device. Accordingly, this type of firewall is also known as a Host Firewall. Since it is attached to a specific device, it has to utilize its resources to work. Therefore, it is inevitable for it to use up some of the system’s RAM and CPU.

If there are multiple devices, you need to install the software on each device. Since it needs to be compatible with the host, it requires individual configuration for each. Hence, the main disadvantage is the time and knowledge needed to administrate and manage firewalls for each device.

On the other hand, the advantage of software firewalls is that they can distinguish between programs while filtering incoming and outgoing traffic. Hence, they can deny access to one program while allowing access to another.

Hardware Firewalls

Hardware firewalls are security devices that represent a separate piece of hardware placed between an internal and external network (the Internet). This type is also known as an Appliance Firewall.

Unlike a software firewall, a hardware firewall has its resources and doesn’t consume any CPU or RAM from the host devices. It is a physical appliance that serves as a gateway for traffic passing to and from an internal network.

They are used by medium and large organizations that have multiple computers working inside the same network. Utilizing hardware firewalls in such cases is more practical than installing individual software on each device. Configuring and managing a hardware firewall requires knowledge and skill, so make sure there is a skilled team to take on this responsibility.

Packet-Filtering Firewalls

When it comes to types of firewalls based on their method of operation, the most basic type is the packet-filtering firewall. It serves as an inline security checkpoint attached to a router or switch. As the name suggests, it monitors network traffic by filtering incoming packets according to the information they carry.

As explained above, each data packet consists of a header and the data it transmits. This type of firewall decides whether a packet is allowed or denied access based on the header information. To do so, it inspects the protocol, source IP address, destination IP, source port, and destination port. Depending on how the numbers match the access control list (rules defining wanted/unwanted traffic), the packets are passed on or dropped.

If a data packet doesn’t match all the required rules, it won’t be allowed to reach the system.

A packet-filtering firewall is a fast solution that doesn’t require a lot of resources. However, it isn’t the safest. Although it inspects the header information, it doesn’t check the data (payload) itself. Because malware can also be found in this section of the data packet, the packet-filtering firewall is not the best option for strong system security.

Packet-Filtering Firewalls
Packet-Filtering Firewalls

Circuit-Level Gateways

Circuit-level gateways are a type of firewall that work at the session layer of the OSI model, observing TCP (Transmission Control Protocol) connections and sessions. Their primary function is to ensure the established connections are safe.

In most cases, circuit-level firewalls are built into some type of software or an already existing firewall.

Like pocket-filtering firewalls, they don’t inspect the actual data but rather the information about the transaction. Additionally, circuit-level gateways are practical, simple to set up, and don’t require a separate proxy server.

Circuit-Level Gateways
Circuit-Level Gateways

Stateful Inspection Firewalls

A stateful inspection firewall keeps track of the state of a connection by monitoring the TCP 3-way handshake. This allows it to keep track of the entire connection – from start to end – permitting only expected return traffic inbound.

When starting a connection and requesting data, the stateful inspection builds a database (state table) and stores the connection information. In the state table, it notes the source IP, source port, destination IP, and destination port for each connection. Using the stateful inspection method, it dynamically creates firewall rules to allow anticipated traffic.

This type of firewall is used as additional security. It enforces more checks and is safer compared to stateless filters. However, unlike stateless/packet filtering, stateful firewalls inspect the actual data transmitted across multiple packets instead of just the headers. Because of this, they also require more system resources.

Stateful Inspection Firewalls
Stateful Inspection Firewalls

Proxy Firewalls

A proxy firewall serves as an intermediate device between internal and external systems communicating over the Internet. It protects a network by forwarding requests from the original client and masking it as its own. Proxy means to serve as a substitute and, accordingly, that is the role it plays. It substitutes for the client that is sending the request.

When a client sends a request to access a web page, the message is intersected by the proxy server. The proxy forwards the message to the web server, pretending to be the client. Doing so hides the client’s identification and geolocation, protecting it from any restrictions and potential attacks. The web server then responds and gives the proxy the requested information, which is passed on to the client.

Proxy Firewalls
Proxy Firewalls

Next-Generation Firewalls

The next-generation firewall is a security device that combines a number of functions of other firewalls. It incorporates packet, stateful, and deep packet inspection. Simply put, NGFW checks the actual payload of the packet instead of focusing solely on header information.

Unlike traditional firewalls, the next-gen firewall inspects the entire transaction of data, including the TCP handshakes, surface-level, and deep packet inspection.

Using NGFW is adequate protection from malware attacks, external threats, and intrusion. These devices are quite flexible, and there is no clear-cut definition of the functionalities they offer. Therefore, make sure to explore what each specific option provides.

Next-Generation Firewalls
Next-Generation Firewalls

Features that historically were handled by separate devices are now included in many NGFWs and include:

Intrusion Prevention Systems (IPS)

Whereas basic firewall technologies identify and block certain types of network traffic, IPSes use more granular security such as signature tracing and anomaly detection to prevent threats from entering networks. Once separate platforms, IPS functionality is more and more a standard firewall feature.

Deep packet inspection (DPI)

Deep packet inspection is a type of packet filtering that looks beyond where packets are coming from and going to and inspects their content, revealing, for example, what application is being accessed or what type of data is being transmitted. This information can make possible more intelligent and granular policies for the firewall to enforce. DPI could be used to block or allow traffic, but also restrict the amount of bandwidth particular applications are allowed to use. It could also be a tool for protecting intellectual property or sensitive data from leaving a secure network.

SSL/TLS termination

SSL-encrypted traffic is immune to deep-packet inspection because its content cannot be read. Some NGFWs can terminate SSL traffic, inspect it, then create a second SSL connection to the intended destination address. This can be used to prevent, for instance, malicious employees from sending proprietary information outside the secure network while also allowing legitimate traffic to flow through. While it’s good from a data-protection point of view, DPI can raise privacy concerns. With the advent of transport layer security (TLS) as an improvement on SSL, this termination and proxying can apply to TLS as well.


Incoming attachments or communications with outside sources can contain malicious code. Using sandboxing, some NGFWs can isolate these attachments and whatever code they contain, execute it and find out whether it’s malicious. The downside of this process is this can consume a lot of CPU cycles and introduce noticeable delay in traffic flowing through the firewall.

There are other features that could be incorporated in NGFWs. They can support taking in data gathered by other platforms an using it to make firewall decisions. For example, if a new malware signature has been identified by researchers, the firewall can take in that information and start filtering out traffic that contains the signature.

Gartner, which once used the term NGFW, now says that previous incarnations of firewalls are outmoded and that they now call NGFWs simply enterprise firewalls.

Cloud Firewalls

A cloud firewall or firewall-as-a-service (Faas) is a cloud solution for network protection. Like other cloud solutions, it is maintained and run on the Internet by third-party vendors.

Clients often utilize cloud firewalls as proxy servers, but the configuration can vary according to the demand. Their main advantage is scalability. They are independent of physical resources, which allows scaling the firewall capacity according to the traffic load.

Businesses use this solution to protect an internal network or other cloud infrastructures (Iaas/Paas).

Cloud Firewalls
Cloud Firewalls

Which Firewall Architecture is Right for Your Business?

When deciding on which firewall to choose, there is no need to be explicit. Using more than one firewall type provides multiple layers of protection. Also, consider the following factors:

  • The size of the organization. How big is the internal network? Can you manage a firewall on each device, or do you need a firewall that monitors the internal network? These questions are important to answer when deciding between software and hardware firewalls. Additionally, the decision between the two will largely depend on the capabilities of the tech team assigned to manage the setup.
  • The resources available. Can you afford to separate the firewall from the internal network by placing it on a separate piece of hardware or even on the cloud? The traffic load the firewall needs to filter and whether it is going to be consistent also plays an important role.
  • The level of protection required. The number and types of firewalls should reflect the security measures the internal network requires. A business dealing with sensitive client information should ensure that data is protected from hackers by tightening the firewall protection.

Published by Abdul Samad

Having 17+ years of extensive experience in IT industry, enabled to enhance the team performance and maximize customer satisfaction by strategically managing calls and implementing process improvements. Demonstrated ability to solve problems, meets challenging goals, and expedites delivery. Skilled MSSQL administrator guide team during the crisis situation. Apply Creative thoughts process in re-designing the workflow system to eliminate duplication of effort and increase productivity.

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