Conventional packet filtering only examines the header information for each packet to compare its source/destination IP and the port number against its access control list to make a decision on whether to allow or drop it. Deep packet inspection will not only consider the information contained in the header, but also the content contained within the payload of the packet. One real world scenario that it can be compared to is what is experienced at airport security. Packet filtering is similar to checking the luggage tag to validate that the originating and destination airport as well as the flight number all match up against their records. Deep packet inspection would be closer to x-raying the bag to view its contents to provide that there is nothing dangerous inside.