What is a Firewall?
A Firewall protects a company’s internal network and digital assets from cyber threats. It scrutinizes incoming and outgoing information, allowing or denying communication according to established rules.
Think of a firewall like a guard at the gate of your home, school or workplace. Firewalls stand at the gate, evaluating the information (like messages or files) that come in and go out. If the information looks good, the firewall lets it pass. If it looks suspicious or dangerous, the firewall blocks it and halts further activity.
Firewalls use different methods to read data packets and make decisions about what to allow or block. Some are simple and fast, like packet filtering, while others are more complex with a performance impact. Others are more sophisticated, such as a proxy firewall or next generation firewall, which can use advanced techniques like deep packet inspection and identity awareness to enhance protection.
In the late 1980s, Reid, Mogul, and Vixie each played roles at DEC in developing the technology that would eventually become the foundation for firewall systems. Their work led to circuit-level gateway firewalls, which can vet external connections by checking the transmission control protocol (TCP) handshake. However, because these firewalls do not check the actual packet content, malicious data can still make its way in or out of your network.
A more sophisticated option is a stateful inspection firewall, which reads data packets at various levels of the OSI model (layers 2-7). This type of firewall can inspect the entire context of a data transfer, not just the individual packet characteristics. It can also learn from the results of past interaction with different types of traffic and filter accordingly in future.