RFC 2219 (rfc2219) - Page 2 of 8

Use of DNS Aliases for Network Services

RFC 2219                      DNS Aliases                   October 1997


   Perhaps the most visible example of the latter approach at work is in
   the case of World-Wide Web HTTP servers.  It is common practice to
   try prefixing the domain name of an organization with "http://www."
   in order to reach its World-Wide Web site, e.g. taking "hivnet.fr"
   and arriving at "http://www.hivnet.fr."  Some popular World-Wide Web
   browsers have gone so far as to provide automatic support for this
   domain name expansion.

   Ideally, the DNS or some complementary directory service would
   provide a means for programs to determine automatically the network
   services which are offered at a particular Internet domain, the
   protocols which are used to deliver them, and other technical
   information.  Unfortunately, although much work has been done to
   develop said directory service technologies and to define new types
   of DNS resource record to provide this type of information, there is
   no widely agreed upon or widely deployed solution to the problem -
   except in a small number of cases.

   The first case is where the DNS already provides a lookup capability
   for the type of information being sought after.  For example: Mail
   Exchanger (MX) records specify how mail to a particular domain should
   be routed [RFC-974], the Start of Authority (SOA) records make it
   possible to determine who is responsible for a given domain, and Name
   Server (NS) records indicate which hosts provide DNS name service for
   a given domain.

   The second case is where the DNS does not provide an appropriate
   lookup capability, but there is some widely accepted convention for
   finding this information.  Some use has been made of Text (TXT)
   [RFC-1035] records in this scenario, but in the vast majority of
   cases a Canonical Name (CNAME) or Address (A) record pointer is used
   to indicate the host or hosts which provide the service.  This
   document proposes a slight formalization of this well-known alias
   approach.

   It should be noted that the DNS provides a Well Known Services (WKS)
   [RFC-1035] lookup capability, which makes it possible to determine
   the network services offered at a given domain name.  In practice
   this is not widely used, perhaps because of the absence of a suitable
   programming interface.  Use of WKS for mail routing was deprecated in
   the Host Requirements specification [RFC-1123] in favour of the MX
   record, and in the long term it is conceivable that SRV records will
   supersede both WKS and MX.








Hamilton & Wright        Best Current Practice