What Does a Packet-Filtering Firewall Do?

Packets are forwarded between networks based on a set of rules enforcing access control policies. Not only examines packet headers for forwarding information, but includes rules about which packets to forward and which to drop.
May provide state full inspection (not ipchains)
Must provide some amount of application gateway support unless proxies are used to allow some forms of application traffic through.
May respond dynamically to trigger events
Logging

Packets are forwarded between networks based on a set of rules enforcing access control policies. Not only examines packet headers for forwarding information, but includes rules about which packets to forward and which to drop.