Use of DNS Aliases for Network Services
RFC 2219
| Document | Type |
RFC - Best Current Practice
(October 1997; No errata)
Also known as BCP 17
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|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 2219 (Best Current Practice) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | (None) | ||
| Send notices to | (None) | ||
Network Working Group M. Hamilton
Request for Comments: 2219 Loughborough University
BCP: 17 R. Wright
Category: Best Current Practice Lawrence Berkeley Laboratory
October 1997
Use of DNS Aliases for Network Services
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Abstract
It has become a common practice to use symbolic names (usually
CNAMEs) in the Domain Name Service (DNS - [RFC-1034, RFC-1035]) to
refer to network services such as anonymous FTP [RFC-959] servers,
Gopher [RFC-1436] servers, and most notably World-Wide Web HTTP
[RFC-1945] servers. This is desirable for a number of reasons. It
provides a way of moving services from one machine to another
transparently, and a mechanism by which people or agents may
programmatically discover that an organization runs, say, a World-
Wide Web server.
Although this approach has been almost universally adopted, there is
no standards document or similar specification for these commonly
used names. This document seeks to rectify this situation by
gathering together the extant 'folklore' on naming conventions, and
proposes a mechanism for accommodating new protocols.
It is important to note that these naming conventions do not provide
a complete long term solution to the problem of finding a particular
network service for a site. There are efforts in other IETF working
groups to address the long term solution to this problem, such as the
Server Location Resource Records (DNS SRV) [RFC-2052] work.
1. Rationale
In order to locate the network services offered at a particular
Internet domain one is faced with the choice of selecting from a
growing number of centralized databases - typically Web or Usenet
News "wanderers", or attempting to infer the existence of network
services from whatever DNS information may be available. The former
approach is not practical in some cases, notably when the entity
seeking service information is a program.
Hamilton & Wright Best Current Practice [Page 1]
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
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