Pakettisuodattimet

Pakettisuodattimet, also known as packet filters, are a fundamental component of network security and traffic management. They operate at the network layer (Layer 3) and transport layer (Layer 4) of the OSI model, examining the header information of individual data packets traversing a network. The primary function of a packet filter is to decide whether to allow or deny a packet based on a predefined set of rules.

These rules are typically based on various criteria found in the packet header, such as source and destination IP addresses, source and destination port numbers, and the protocol being used (e.g., TCP, UDP, ICMP). For example, a rule might be configured to block all incoming traffic to a specific port from an unauthorized IP address, or to allow outgoing traffic only to certain trusted destinations.

Packet filters are commonly implemented in firewalls, routers, and even host-based security software. Their simplicity and efficiency make them a widely adopted method for basic network access control. However, their decision-making process is stateless by default, meaning each packet is evaluated independently without considering the context of previous packets in a communication flow. More advanced filtering techniques, like stateful packet inspection, address this limitation by tracking the state of active network connections. Nevertheless, stateless packet filtering remains a crucial tool for establishing foundational network security policies.