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Network Infrastructure Magazine | Wednesday, July 01, 2026
Fremont, CA: Even though it was first mentioned in security debates over thirty years ago, the network firewall remains a critical element in the business network security toolbox. Over time, the firewall has shown to be an effective method for filtering out hazardous traffic before it enters the network boundary. However, like with any vital technology, developments have increased the firewall's capabilities and implementation options.
The history of the firewall began when systems administrators realized outside attackers were breaking into their networks at the beginning of the contemporary internet age. Some kind of mechanism that scanned network data for unmistakable indicators of accidents was inevitable. Here are the five types of firewalls:
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Packet Filtering Firewall
Firewalls with packet filtering capabilities collaborate at the intersections where switches and routers are used. All incoming packets are compared to predetermined criteria, including permitted IP addresses, packet types, port numbers, and other details from the packet protocol headers rather than the firewall's routing messages. Troublesome packets are often lost without warning; that is, they are not transmitted and, as a result, are deleted.
Circuit-Level Gateway
Circuit-level gateways employ an alternative, comparatively expeditious method of detecting malicious content. Circuit-level gateways use a speedier method of detecting malicious content: they observe TCP handshakes and other initiation messages for network protocol sessions as they transpire between the local and remote hosts on the network. This allows them to ascertain whether the initiated session is authentic and whether the remote system is reliable. However, they do not personally examine the packets.
Application-Level Gateway
The single point of entrance and exit into and out of the network is this device, formally referred to as a proxy and occasionally called a proxy firewall. Application-level gateways filter packets based on several attributes, such as the HTTP request text, in addition to the service they are meant for, as indicated by the destination port.
Although they offer significant data protection, application-layer gateways can significantly negatively impact network speed and be challenging to maintain.
Stateful Inspection Firewall
State-aware devices inspect every packet but also monitor if the packet is part of a running TCP or other network session. This compromises network performance more than packet filtering or circuit monitoring alone, but it provides better security.
A further variation of stateful inspection is the multilayered inspection firewall, which considers the flow of transactions being processed across various protocol layers within the seven-layer Open Systems Interconnection (OSI) paradigm.
Next-Generation Firewall
A typical network gateway firewall (NGFW) integrates stateful inspection and packet inspection with some form of deep packet inspection (DPI) and additional network security systems like antivirus, malware filtering, and an IDS/IPS.
DPI examines the data that is contained in the packet, whereas packet inspection in conventional firewalls examines the packet's protocol header. When a packet payload is combined with other packets in an HTTP server reply, it may be detected by a DPI firewall whether or not the answer is valid HTML. It can also monitor the course of a web surfing session.
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