1. A firewall marketing buzzword, stateful inspection implies that the firewall is remembering stuff from previous packets when making the decision whether or not to forward/block the current packet. Stateful inspection is needed to pass classic FTP as well as newer multimedia protocols (NetMeeting, RealAudio, etc.). Example: Class FTP has a separate control connection and data connection. When you connect to an FTP server and request a file, you tell the server to connect back to you. Since most firewalls allow outgoing connections to servers but block incoming connections, you will be able to connect to the FTP server, but you won't be able to retrieve the desired file. Stateful inspection looks at the outgoing connection and notices that you've requested the incoming connection. The firewall opens up a tiny hole allowing just that inbound connection, thus fixing the entire situation. From Hacking-Lexicon