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<HTML><HEAD><TITLE>Chapter 20 -- How Site Blocking Works</TITLE><META></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000EE" VLINK="#551A8B" ALINK="#CE2910"><H1><FONT SIZE=6 COLOR=#FF0000>Chapter 20</FONT></H1><H1><FONT SIZE=6 COLOR=#FF0000>How Site Blocking Works</FONT></H1><HR><P><CENTER><B><FONT SIZE=5><A NAME="CONTENTS">CONTENTS</A></FONT></B></CENTER><UL><LI><A HREF="#BlockingObjectionableSitesfromanIntranet">Blocking Objectionable Sites from an Intranet</A></UL><HR><P>Inside an intranet, it's easy to control the kinds of pages, information,pictures, and other data that people are accessing. The corporationcontrols what gets posted and what doesn't, and so nothing canget posted that the company believes would be objectionable. That'sfar from true out on the Internet, however. Objectionable contentmakes up a very small part of what's available on the Internet,and to find the objectionable content you have to do a bit ofdigging. Still, anyone who wants to find it can certainly getaccess to it.<P>Congress, among others, has tried to ban certain kinds of content-suchas pornography-from being available on the Internet. The realanswer to the problem, though, doesn't lie in legislation, becauseeven if such laws are held constitutional, anyone who truly understandsthe Internet and its technology also recognizes that the lawsare unenforceable. The real answer lies with technology itself:software that will allow people such as parents and intranet administrators to block access to those sites. A number of companies make andsell software that allows site blocking.<P>Many problems can occur if people from inside an intranet arevisiting pornographic or objectionable sites on the intranet.And in any event, companies would not want employees viewing thosekinds of sites on company time, using company hardware, software,and network resources.<P>To block objectionable sites on an intranet, the answer is notto put site-blocking software on each individual computer on thenetwork. It would be too unwieldy and expensive to do that. Instead,server-based site-blocking software is used. Site-blocking softwareon a proxy server examines the URLs sent to it and decides whetheror not to retrieve the requested page by reviewing databases thatlist objectionable sites and words.<P>One group working on the issue is PICS (Platform for InternetContent Selection). They are trying to develop industry standardsfor technology that would allow the content of all sites and documentson the Internet to be rated according to its sexual and violentcontent. They would also create standards that would allow softwareto be developed that would be able to block sites based on thoseratings.<P>Not all intranets need site-blocking software. However, intranetadministrators may want to know what kind of sites people on theintranet are visiting. They can use server-based software thatcan keep logs of what kinds of sites people are visiting on theInternet. This will help not only to decide whether site-blockingsoftware is needed, but also to know when more server resourcesare needed for the intranet. <H2><A NAME="BlockingObjectionableSitesfromanIntranet"><FONT SIZE=5 COLOR=#FF0000>Blocking Objectionable Sites from an Intranet</FONT></A></H2><P>Since intranets allow access to the Internet, intranet users canvisit objectionable sites on the Internet-sites with sexual, violent,or other kinds of distasteful content. This illustration showshow server-based blocking software might work, based on the SurfWatchproduct that can be used to block sites on individual computers.<OL><LI>Site-blocking software examines the URL of every request goingout of the intranet. URLs most likely to be unacceptable willbe accessing the Web (http); newsgroups (nntp); ftp (ftp); gopher(gopher); and Internet chat (irc). The software takes each ofthose five types of URLs and puts them each in their own separate"boxes." The rest of the intranet information goingout is allowed to go through.<LI>Every URL in each of the boxes is checked against a databaseof the URLs of objectionable sites. If the blocking software findsthat any of the URLs are from objectionable sites, it won't allowthat information to be passed on to the intranet. Products likeSurfWatch check thousands of sites, and list several thousandin their database that have been found to be objectionable.<LI>The site-blocking software next checks the URL against a databaseof words (such as "sex") that may indicate that thematerial being requested may be objectionable. If the blockingsoftware finds a matching pattern, it won't allow that informationto be passed on to the intranet.<LI>Site-blocking software can then use a third method of checkingfor objectionable sites, a rating system called PICS (Platformfor Internet Content Selection). If site-blocking software finds,based on the rating system, that the URL is for a site that maycontain objectionable material, it won't allow access to thatsite. Rules about passing or dropping can be configured to control.access to unrated sites.</OL><HR><CENTER><P><A HREF="ch19.htm"><IMG SRC="PC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="#CONTENTS"><IMG SRC="CC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="contents.htm"><IMG SRC="HB.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><A HREF="ch21.htm"><IMG SRC="NC.GIF" BORDER=0 HEIGHT=88 WIDTH=140></A><HR WIDTH="100%"></P></CENTER></BODY></HTML>⌨️ 快捷键说明
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