Types of Firewalls and How They Work

There are several types of firewall. Stateful inspection firewalls filter packets at the network, transport, and application layers. They match packet headers against known trusted packets and evaluate them accordingly. While stateful inspection firewalls allow traffic through, they can be vulnerable to DoS attacks, which take advantage of existing connections. Listed below are the main types of firewalls and how they work. Listed below are a few examples of each type.

Firewalls work by matching network traffic against a list of firewall rules. Patches are applied from first to last. In the example above, a connection from an accounting employee to a system administrator would be rejected if the rules 2 didn’t match the destination IP address. However, the connection would be accepted if rule 3 was present. Since firewall chains cannot cover every possible situation, they must always include a default policy that includes an action and a rule.

A circuit-level firewall is positioned between the transport and application layers of the TCP/IP stack. This type of firewall operates at the session layer of the OSI model and inspects the data packets during the handshake. This means that it can detect potentially harmful data. If stateful inspection is used correctly, a firewall can reduce the risk of a DDoS attack by blocking malicious traffic. These are two common types of firewalls.

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