Types of Firewall
Firewalls can be categorized based on their generation.
1. Packet Filtering Firewall
Packet filtering firewall is used to control network access by monitoring outgoing and incoming packets and allowing them to pass or stop based on source and destination IP address, protocols, and ports. It analyses traffic at the transport protocol layer (but mainly uses first 3 layers). Packet firewalls treat each packet in isolation. They have no ability to tell whether a packet is part of an existing stream of traffic. Only It can allow or deny the packets based on unique packet headers. Packet filtering firewall maintains a filtering table that decides whether the packet will be forwarded or discarded. From the given filtering table, the packets will be filtered according to the following rules:
- Incoming packets from network 192.168.21.0 are blocked.
- Incoming packets destined for the internal TELNET server (port 23) are blocked.
- Incoming packets destined for host 192.168.21.3 are blocked.
- All well-known services to the network 192.168.21.0 are allowed.
2. Stateful Inspection Firewall
Stateful firewalls (performs Stateful Packet Inspection) are able to determine the connection state of packet, unlike Packet filtering firewall, which makes it more efficient. It keeps track of the state of networks connection travelling across it, such as TCP streams. So the filtering decisions would not only be based on defined rules, but also on packet’s history in the state table.
3. Software Firewall
A software firewall is any firewall that is set up locally or on a cloud server. When it comes to controlling the inflow and outflow of data packets and limiting the number of networks that can be linked to a single device, they may be the most advantageous. But the problem with software firewall is they are time-consuming.
4. Hardware Firewall
They also go by the name “firewalls based on physical appliances.” It guarantees that the malicious data is halted before it reaches the network endpoint that is in danger.
5. Application Layer Firewall
Application layer firewall can inspect and filter the packets on any OSI layer, up to the application layer. It has the ability to block specific content, also recognize when certain application and protocols (like HTTP, FTP) are being misused. In other words, Application layer firewalls are hosts that run proxy servers. A proxy firewall prevents the direct connection between either side of the firewall, each packet has to pass through the proxy.
6. Next Generation Firewalls (NGFW)
NGFW consists of Deep Packet Inspection, Application Inspection, SSL/SSH inspection and many functionalities to protect the network from these modern threats.
7. Proxy Service Firewall
This kind of firewall filters communications at the application layer, and protects the network. A proxy firewall acts as a gateway between two networks for a particular application.
8. Circuit Level Gateway Firewall
This works as the Sessions layer of the OSI Model’s . This allows for the simultaneous setup of two Transmission Control Protocol (TCP) connections. It can effortlessly allow data packets to flow without using quite a lot of computing power. These firewalls are ineffective because they do not inspect data packets; if malware is found in a data packet, they will permit it to pass provided that TCP connections are established properly.
Introduction of Firewall in Computer Network
A firewall is a network security device that prevents unauthorized access to a network. It monitors both incoming and outgoing traffic using a predefined set of security to detect and prevent threats.
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