Introduction - Draytek Vigor2500V Manual

Firewall
Supplement B
URL Content Filtering
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.
6-17