URL filtering provides visibility and control over web traffic on your network. For improved visibility into web content, you can configure the URL Filtering profile to log HTTP header attributes included in a web request. When a client requests a web page, the HTTP header includes the user agent, referer, and x-forwarded-for fields as attribute-value pairs and forwards them to the web server. When enabled for logging HTTP headers, the firewall logs the following attribute-value pairs in the URL Filtering logs:
Attribute Description
User-Agent The web browser that the user used to access the URL, for example, Internet Explorer. This information is sent in the HTTP request to the server.
Referer The URL of the web page that linked the user to another web page; it is the source that redirected (referred) the user to the web page that is being requested.
X-Forwarded-For (XFF) The option in the HTTP request header field that preserves the IP address of the user who requested the web page. If you have a proxy server on your network, the XFF allows you to identify the IP address of the user who requested the content, instead of only recording the proxy server’s IP address as source IP address that requested the web page.

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