A URL filter is a Web content filter that is comprised of several filter rules. To construct a filter rule, either Allow or Deny a filter level, category type, category or a custom category. An Allow list bans all sites except those in the categories and URL lists defined in the Allow list. A Deny list allows all sites except the categories and URL lists defined in the Deny list.
URL filtering allows you to enable URL filtering on the device, create and apply a URL filter defining the banned and/or allowed URLs. When enabled, the URL filter is applied to all user-initiated URL requests to determine if the requested URL is banned or allowed. Only if allowed is the user‘s request (in the form of a HTTP request packet) forwarded to the Web server.
URL filters can be applied at any of the following points: the user‘s application (browser/ email reader), the network‘s gateway, at the Internet service provider (ISP) end, and also on a Web portal.
For wireless clients, the WLAN infrastructure is the best place to implement these filters. A URL filter is a set of whitelist and/or blacklist rules. The whitelist allows access only to those Websites and URLs specified in it. All other Websites and URLs, apart from those specified in the whitelist, are banned. On the other hand, the blacklist bans all Websites and URLs specified in it. All other Websites and URLs, apart from those specified in the blacklist, are allowed.
To simplify URL filter configuration, Websites have been classified into pre-defined category-types and categories. The system provides 14 category-types and 62 categories. To further simplify configuration, these 14 category-types have been grouped into five (5) pre-defined levels. (See Usage Guidelines section for the list of category-types, categories, and levels). The actual classification of URLs (on the basis of the pre-defined factors mentioned above) is done by the classification server. A local database also helps by caching URL records for a user-defined time period. The classification server host is specified in the Web filter policy. The Web filter policy also defines the URL database parameters. For more information, see web-filter-policy on page 597. The WiNG software also allows you to create URL lists. Each URL list contains a list of user-defined URLs. Use the URL list in a URL filter (whitelist or blacklist rule) to identify the URLs to ban or allow. For example, a URL list named SocialNetworking is created listing the following three sites: Facebook, Twitter, and LinkedIn. When applied to a URL filter‘s blacklist these three sites are banned. Where as, when applied to a whitelist only these three sites are allowed. For more information on configuring a URL list, see url-list on page 707.