deep packet inspection

Deep Packet Inspection (DPI, also called complete packet inspection and Information eXtraction or IX) is a form of computer network packet filtering that examines the data part (and possibly also the header) of a packet as it passes an inspection point, searching for protocol non-compliance, viruses, spam, intrusions, or defined criteria to decide whether the packet may pass or if it needs to be routed to a different destination, or, for the purpose of collecting statistical information. There are multiple headers for IP packets; network equipment only needs to use the first of these (the IP header) for normal operation, but use of the second header (TCP, UDP etc.) is normally considered to be shallow packet inspection (usually called Stateful Packet Inspection) despite this definition.