Using this method is often over-inclusive. It is impossible for a keyword blocking system to block all objectionable content without simultaneously blocking a large amount of useful information. In addition, much of the objectionable content on the Internet consists of pictures, which usually have no text to which keyword filtering would apply. Packet filtering denies access by allowing or blocking requests to specific IP addresses which define individual websites. Advantages of packet filtering include speed and simplicity.
Packet filters control the transmission of data based on information contained in the packet header.
The destination IP address and port number define the server and protocol used for a data transfer. However, they do not specify which page on the web server is being requested. In many cases, some portions of a website are acceptable while others are not. In addition, newer web servers can host multiple websites using one IP address and port number. This information is stored as data in the packet body, not in the header, and thus can not be used by a packet filter.