A firewall is a network security device or software that acts as a barrier between an internal network and external networks, such as the Internet. Its primary purpose is to monitor and control incoming and outgoing network traffic based on predetermined security rules. Here are the key aspects and functions of a firewall:
Traffic Filtering: Firewalls examine network packets and data flows based on specific criteria, such as source and destination IP addresses, ports, protocols, and packet contents. They analyze this information to determine whether to allow, block, or redirect the traffic. This filtering helps enforce security policies and protect the network from unauthorized access or malicious activities.
Packet-Level Firewall: Packet-filtering firewalls operate at the network and transport layers of the network stack. They inspect individual packets and make decisions based on preconfigured rules. These rules can specify which packets should be allowed or denied based on criteria such as IP addresses, ports, and protocols.
Stateful Inspection: Stateful inspection firewalls maintain information about the state of network connections. They not only examine individual packets but also track the state of connections, allowing them to make more intelligent decisions. For example, they can identify whether a packet is part of an established connection or a new connection attempt, enhancing the accuracy and security of traffic filtering.