Operation Manual

Protect Your Network
6-21
Chapter 6- B
URL Content Filtering
6-B.1 Introduction
The Internet contains a wide range of materials, some of which may be
offensive or even illegal in many countries. Unlike traditional media, the
Internet does not have any obvious tools to segregate materials based on
URL strings or content. URL content filtering systems are seen as tools that
would provide the cyberspace equivalent of the physical separations that
are used to limit access to some particular materials. In rating a site as
objectionable, and refusing to display it on the user's computer screen, URL
content filtering facilities can be used to prevent children from seeing
material that their parents find objectionable. In preventing access, the
URL content filtering facility acts as an automated version of the
convenience-store clerk who refuses to sell adult magazines to high-school
students. The URL content filtering facilities are also used by businesses
to prevent employees from accessing Internet resources that are either not
work related or otherwise deemed inappropriate.
The name of the URL content filtering comes from checking the content of
the URL strings. Traditional firewall inspects packets based on the fields of
TCP/IP headers, while the URL content filtering checks the URL strings or
the payload of TCP/IP packets. In the Vigor routers, the URL content
filtering facility inspects the URL string and some of HTTP data hiding in the
payload of TCP packets.