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URL content filter 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 related to job content 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.
Firewall Setup
6-6
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