1. Introduction

   The Domain Name System (DNS) is the global hierarchical replicated
   distributed database system for Internet addressing, mail proxy, and
   other information.  Each node in the DNS tree has a name consisting
   of zero or more labels [STD13,RFC1591,RFC2606] that are treated in
   a case insensitive fashion.  This document clarifies the meaning of
   "case insensitive" for the DNS.  This clarification updates RFCs
   1034, 1035 [STD13], and [RFC2181].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].