URL Filtering

URL Filtering allows to block websites according substring match in URL address, for example "microsoft". You can construct "black" or "white" lists of websites.

URL Filter may include unlimited number of URL Rules. URL Rule consists of URL-address or a part of URL-address. In case of URL Rule match, a web-request will be blocked. For example, URL Filter with URL Rules:

microsoft.com
facebook.com

will block all websites with strings microsoft.com or facebook.com in their URL-address.
 

Theory of WEB-requests

According RFC 3986, address of WEB-request include the followings parts:

  foo://username:password@example.com:8042/over/there/?name=ferret#nose
  \ /   \________________/\_________/ \__/\_________/  \_________/ \__/
   |           |               |        |     |             |       |
   |       userinfo         hostname  port URI-path          query   fragment
scheme

TrafMeter will search a match for URL rules in the part "hostname" and/or "URI-path" of WEB-requests.
 

Constructing the URL rules

Besides simple URL rules, which include parts of URL address (such as microsoft.com or facebook.com), you can use several modifiers to change a logic of URL Rules.

Symbol

Description

^

Beginning of the string (similar Regular Expressions). For example, ^forum.w3c.org will match only website http://forum.w3c.org but not http://www.forum.w3c.org

$

End of the string (similar Regular Expressions). For example, .gif$ will prevent loading all files with ".gif" extension.

*

Any symbol or sequence of the symbols. For example, www.*.com

+

Allows URL address, which will match the URL rule. You can use this symbol only at the beginning of the string.

#

Comment. All strings beginning with '#' will be ignored.

You can use the above modifiers only once in the URL rule.
 

How URL Filtering works

URL Filtering works in a transparent mode and there are no needs to specify any proxy server address in browsers on the client computers. URL Filtering analyses every captured TCP packet and tries to find HTTP request header inside. If HTTP request header is found and URL Filter matches a success, TrafMeter will create HTML page "access denied" and send it back to the client emulating the web server reply. In additional, TrafMeter sends TCP packet with FIN flag to properly close TCP connection.
 

Examples of URL Filters

URL Filter

Description

microsoft.com
intel.com
ibm.com
nokia.com

Will block web sites listed here

+forum*.js$
.js$

Will block all files with .js extension (javascript) except javascript from all sites beginning with 'forum'.

+.com$
+.net$
*

Will create "while" list of allowed sites "*.com/*.net" and block all other sites.

 

 Note