P. Mockapetris. <a href="http://www.ietf.org/rfc/rfc1034.txt"><cite>DOMAIN NAMES - CONCEPTS AND FACILITIES.</cite></a> November 1987. Internet RFC 1034. URL: <a href="http://www.ietf.org/rfc/rfc1034.txt">http://www.ietf.org/rfc/rfc1034.txt</a>