Network Working Group R. Fielding Request for Comments: 2616 ...

From: webmaster@w3.orgThis header field MAY be used for logging purposes and as a means foridentifying the source of invalid or unwanted requests. It SHOULD NOTbe used as an insecure form of access protection. The interpretationof this field is that the request is being performed on behalf of theperson given, who accepts responsibility for the method performed. Inparticular, robot agents SHOULD include this header so that theperson responsible for running the robot can be contacted if problemsoccur on the receiving end.The Internet e-mail address in this field MAY be separate from theInternet host which issued the request. For example, when a requestis passed through a proxy the original issuer's address SHOULD beused.The client SHOULD NOT send the From header field without the user'sapproval, as it might conflict with the user's privacy interests ortheir site's security policy. It is strongly recommended that theuser be able to disable, enable, and modify the value of this fieldat any time prior to a request.14.23 HostThe Host request-header field specifies the Internet host and portnumber of the resource being requested, as obtained from the originalURI given by the user or referring resource (generally an HTTP URL,Fielding, et al. Standards Track [Page 128]RFC 2616 HTTP/1.1 June 1999as described in section 3.2.2). The Host field value MUST representthe naming authority of the origin server or gateway given by theoriginal URL. This allows the origin server or gateway todifferentiate between internally-ambiguous URLs, such as the root "/"URL of a server for multiple host names on a single IP address.Host = "Host" ":" host [ ":" port ] ; Section 3.2.2A "host" without any trailing port information implies the defaultport for the service requested (e.g., "80" for an HTTP URL). Forexample, a request on the origin server for would properly include:GET /pub/WWW/ HTTP/1.1Host: www.w3.org