Packet filtering is the most basic firewall method. It inspects network packets and applies simple allow or block rules based on fields such as source and destination IP address, port, protocol, or direction. It usually does not understand whether a packet belongs to a valid session or what the application is trying to do.
This matters because packet filtering is a coarse but effective control for reducing exposure and enforcing network policy. Defenders use it to limit which hosts and services are reachable, block known-bad traffic, and segment networks into smaller trust zones. In attacks, adversaries often look for services left open by overly broad rules or try to pass through ports that are allowed because the filter cannot see deeper application behavior. Packet filtering is useful, but it is not enough on its own for web attacks, session-aware abuse, or complex threat detection.