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Versions: 00 01 02 rfc2219                                              
INTERNET-DRAFT                                           Martin Hamilton
draft-ietf-ids-dnsnames-00.txt                   Loughborough University
Expires in six months                                        Russ Wright
                                            Lawrence Berkeley Laboratory
                                                                May 1996

                Use of DNS Aliases for Network Services
                Filename: draft-ietf-ids-dnsnames-00.txt

Status of this Memo

      This document is an Internet-Draft.  Internet-Drafts are working
      documents of the Internet Engineering Task Force (IETF), its
      areas, and its working groups.  Note that other groups may also
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   It has become a common practice to use symbolic names (usually
   CNAMEs) in the Domain Name Service (DNS - [1,2]) to refer to network
   services such as anonymous FTP [3] servers, Gopher [4] servers, and
   most notably World-Wide Web HTTP [5] 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 programatically 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.  Distribution
   of this document is unlimited.  Comments should be sent to the IETF
   Integrated Directory Services mailing list, ietf-ids@umich.edu, or

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INTERNET-DRAFT                                                  May 1996

   directly to the authors.

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.

   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 such as TCP [6] and UDP [7] port numbers.

   Unfortunately, although much work has been done on developing "yellow
   pages" directory service technologies, and on attempting 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 [8], 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)
   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.

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INTERNET-DRAFT                                                  May 1996

   It should be noted that the DNS provides a Well Known Services (WKS)
   lookup capability, which makes it possible to determine the services
   offered by a particular host given its domain name.  In practice this
   is not widely used, and was deprecated in the Host Requirements
   specification [9].  In fact, WKS is really trying to solve a
   different problem - advertising the services provided by a particular
   machine, rather than which machines provide particular services for a
   domain as a whole.

2. A generic framework

   One approach to dealing with aliases for new protocols would be to
   define a standard set of DNS aliases for the most popular network
   services, and an accompanying review procedure for registering new
   protocols - such as has been attempted with Internet Media (MIME)
   Types [10].  We suggest that in the rapidly changing world of
   computer networking this may not be the most appropriate way of
   tackling the problem.

   The Internet Assigned Numbers Authority (IANA) maintains a registry
   of well known port numbers, registered port numbers, protocol and
   service names [11].  We propose that this list be used to determine
   the a default port number, transport protocol (e.g. TCP or UDP) and
   DNS alias for a given application protocol.


        Name      Port  Transport   Protocol
        finger    79    TCP         Finger [12]
        ftp       21    TCP         File Transfer Protocol
        gopher    70    TCP         Internet Gopher Protocol
        ldap      389   TCP/UDP     Lightweight Directory Access
                                      Protocol [13]
        ntp       123   UDP         Network Time Protocol [14]
        rwhois    4321  TCP         Referral WHOIS [15]
        whois     43    TCP         NICNAME/WHOIS [16]

   If it is not appropriate to use the information registered with IANA
   for a particular application protocol, we suggest the protocol
   specification should indicate why this is the case - and preferably
   propose an alternative mechanism.  For example, a Remote Procedure
   Call (RPC) based application protocol which does not use a fixed port
   number by default might determine which port to use by contacting a
   remote RPC portmapper.

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INTERNET-DRAFT                                                  May 1996

   We suggest that the DNS alias to be used for a service be taken
   initially from the IANA lists of well known port numbers (in the
   traditionally "restricted" rage 0 to 1023) and registered port
   numbers (1024 to 65535), with recourse to the list of protocol and
   service names if there is some confusion over the preferred alias.
   This might be necessary if, for example, the name associated with the
   IANA registered port number for a protocol contains the underscore
   character "_", the plus character "+", or the dot character "." -
   these are not legal as domain name components.

3. Special cases

   In addition to the character set problems outlined above, there are a
   small number of special cases which are not currently catered for in
   the IANA registry.  We propose that IANA maintain a list of these in
   addition to the existing assigned numbers information.

   Some common examples:

        Alias     Service
        archie    archie [17] (alias for "prospero")
        cso       CCSO nameserver [18] (alias for "csnet-ns")
        fsp       File Service Protocol [19]
        news      Usenet News via NNTP [20] (alias for "nntp")
        ns        DNS servers, and CCSO nameservers (aliases for
                                       "domain" and "csnet-ns")
        ph        CCSO (alias for "csnet-ns")
        wais      Wide Area Information Server [21] (alias for
        www       World-Wide Web HTTP (alias for "http")

4. (Ab)Use of the DNS as a directory service

   The widespread use of these common aliases effectively means that it
   is sometimes possible to "guess" the domain names associated with an
   organization's network services, though this is becoming more
   difficult as the number of organizations registered in the DNS

   It should be understood by implementors that the existence of a DNS
   entry such as


   does not constitute a registration of a World-Wide Web service.

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INTERNET-DRAFT                                                  May 1996

   There is no requirement that the domain name resolve to an IP address
   or addresses.  There is no requirement that a host be listening for
   HTTP connections, or if it is, that the HTTP server be running on
   port 80.  Finally, even if all of these things are true, there can be
   no guarantee that the World-Wide Web server will be prepared to honor
   requests from arbitrary clients.

   Having said this, the aliases do provide useful "hints" about the
   services offered.  We propose that they be taken in this spirit.

   The conventions described in this document are, essentially, only
   useful when the organization's domain name can be determined - e.g.
   from some external database.  A number of groups, including the IETF,
   have been working on ways of finding domain names given a set of
   information such as organization name, location, and business type.
   It is hoped that one or more of these will eventually make it
   possible to augment the basic lookup service which the DNS provides
   with a more generalised search and retrieval capability.

5. DNS server configuration

   In the short term, whilst directory service technology and further
   types of DNS resource record are being developed, domain name
   administrators are encouraged to use these common names for the
   network services they run.  They will make it easier for outsiders to
   find information about your organization, and also make it easier for
   you to move services from one machine to another.

   There are two conventional approaches to creating these DNS entries.
   One is to add a single CNAME record to your DNS server's
   configuration, e.g.

        ph.hivnet.fr. IN CNAME baby.hivnet.fr.

   Note that in this scenario no information about ph.hivnet.fr should
   exist in the DNS other than the CNAME record.  An alternative
   approach would be to create an A record for each of the IP addresses
   associated with ph.hivnet.fr, e.g.

        ph.hivnet.fr. IN A

   Recent DNS server implementations provide a "round-robin" feature
   which causes the host's IP addresses to be returned in a different
   order each time the address is looked up.

   Network clients are starting to appear which, when they encounter a
   host with multiple addresses, use heuristics to determine the address
   to contact - e.g. picking the one which has the shortest round-trip-

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INTERNET-DRAFT                                                  May 1996

   time.  Thus, if a server is mirrored (replicated) at a number of
   locations, it may be desirable to list the IP addresses of the mirror
   servers as A records of the primary server.  This is only likely to
   be appropriate if the mirror servers are exact copies of the original

6. Limitations of this approach

   Some services require that a client have more information than the
   server's domain name and (default) port number.  For example, an LDAP
   client needs to know a starting search base within the Directory
   Information Tree in order to have a meaningful dialogue with the
   server.  This document does not attempt to address this problem.

   In some cases, different aliases are in common use for the same
   service - e.g. "ph", "cso" and "ns" for the CCSO nameserver.  It
   might appear to be in everyone's interest to narrow the choice of
   alias down to a single name.  However, if current practice implies
   that a number of aliases are equally valid, it would be advisable to
   support them all.  This increases the likelihood of the service being

   <<contentious>> Given the confusion over the multiple use of the "ns"
   alias in particular, we could suggest/mandate that everyone move to a
   single name, e.g. the IANA registered "csnet-ns" or one of "cso" and
   "ph".  Should we be trying to do this ?  Discuss!  <</contentious>>

   Another problem is the use of a single alias to refer to multiple
   network services, e.g. "ns" is commonly used to refer to both hosts
   which run the CCSO nameserver, and DNS servers themselves.  In this
   particular case the DNS already provides a lookup capability for
   nameservers via the NS record.  As noted, implementations should be
   resilient in the event that the name does not point to the expected

7. Security considerations

   The DNS is open to many kinds of "spoofing" attacks, and it cannot be
   guaranteed that the result returned by a DNS lookup is indeed the
   genuine information.  Spoofing may take the form of denial of
   service, such as directing of the client to a non-existent address,
   or a passive attack such as an intruder's server which masquerades as
   the legitimate one.

   Work is ongoing to remedy this situation insofar as the DNS is
   concerned [22].  In the meantime it should be noted that stronger
   authentication mechanisms such as public key cryptography with large
   key sizes are a pre-requisite if the DNS is being used in any

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INTERNET-DRAFT                                                  May 1996

   sensitive situations.  Examples of these would be on-line financial
   transactions, and any situation where privacy is a concern - such as
   the querying of medical records over the network.  Strong encryption
   of the network traffic may also be advisable, to protect against TCP
   connection "hijacking" and packet sniffing.

8. Conclusions

   The service names registered with the IANA provide a sensible set of
   defaults which may be used as an aid in determining the hosts which
   offer particular services for a given domain name.

   This document has noted some exceptions which are either inherently
   unsuitable for this treatment, or already have a substantial
   installed base using alternative aliases.

9. Acknowledgements

   Thanks to Jeff Allen, Tom Gillman, Renato Iannella, Thomas
   Lenggenhager, Bill Manning, Andy Powell, Sri Sataluri, and <<your
   name here!!>> for their comments on draft versions of this document.

   This work was supported by grants from the UK Electronic Libraries
   Programme (eLib) and the European Commission's Telematics for
   Research Programme.

10. References

   Request For Comments (RFC) and Internet Draft documents are available
   from <URL:ftp://ftp.internic.net> and numerous mirror sites.

         [1]         P. V. Mockapetris. "Domain names - concepts and
                     facilities", RFC 1034.  November 1987.

         [2]         P. V. Mockapetris. "Domain names - implementation
                     and specification", RFC 1035.  November 1987.

         [3]         J. Postel, J. K. Reynolds.  "File Transfer Proto-
                     col", RFC 959.  October 1985.

         [4]         F. Anklesaria, M. McCahill, P. Lindner, D. Johnson,
                     D. Torrey & B. Albert.  "The Internet Gopher Proto-
                     col (a distributed document search and retrieval
                     protocol)", RFC 1436.  March 1993.

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INTERNET-DRAFT                                                  May 1996

         [5]         T. Berners-Lee, R. Fielding, H. Nielsen.  "Hyper-
                     text Transfer Protocol -- HTTP/1.0", RFC 1945.  May

         [6]         J. Postel.  "Transmission Control Protocol", RFC
                     793.  September 1981.

         [7]         J. Postel.  "User Datagram Protocol", RFC 768.
                     August 1980.

         [8]         C. Partridge.  "Mail routing and the domain sys-
                     tem", RFC 974.  January 1986.

         [9]         R. T. Braden.  "Requirements for Internet hosts -
                     application and support", RFC 1123. October 1989.

         [10]        J. Postel.  "Media Type Registration Procedure",
                     RFC 1590.  March 1994.

         [11]        J. Reynolds, J. Postel.  "ASSIGNED NUMBERS", RFC
                     1700.  October 1994.

         [12]        D. Zimmerman.  "The Finger User Information Proto-
                     col", RFC 1288. December 1992.

         [13]        W. Yeong, T. Howes, S. Kille.  "Lightweight Direc-
                     tory Access Protocol", RFC 1777.  March 1995.

         [14]        D. Mills.  "Network Time Protocol (Version 3)
                     Specification, Implementation", RFC 1305.  March

         [15]        S. Williamson & M. Kosters.  "Referral Whois Proto-
                     col (RWhois)", RFC 1714.  November 1994.

         [16]        K. Harrenstien, M. K. Stahl, E.J. Feinler.
                     "NICNAME/WHOIS", RFC 954.  October 1985.

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INTERNET-DRAFT                                                  May 1996

         [17]        A. Emtage, P. Deutsch. "archie - An Electronic
                     Directory Service for the Internet", Winter Usenix
                     Conference Proceedings 1992.  Pages 93-110.

         [18]        R. Hedberg, S. Dorner, P. Pomes.  "The CCSO
                     Nameserver (Ph) Architecture", Internet Draft.
                     February 1996.

         [19]        FSP software distribution:

         [20]        B. Kantor, P. Lapsley.  "Network News Transfer Pro-
                     tocol", RFC 977.  February 1986.

         [21]        M. St. Pierre, J. Fullton, K. Gamiel, J. Goldman,
                     B. Kahle, J. Kunze, H. Morris & F. Schiettecatte.
                     "WAIS over Z39.50-1988", RFC 1625.  June 1994.

         [22]        D. E. Eastlake 3rd, C. W. Kaufman.  "Domain Name
                     System Security Extensions", Internet Draft.  Janu-
                     ary 1996.

11. Authors addresses

   Martin Hamilton
   Department of Computer Studies
   Loughborough University of Technology
   Leics. LE11 3TU, UK

   Email: m.t.hamilton@lut.ac.uk

   Russ Wright
   Information & Computing Sciences Division
   Lawrence Berkeley National Laboratory
   1 Cyclotron Road, Berkeley
   Mail-Stop: 50B-2258
   CA 94720, USA

   Email: wright@lbl.gov

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INTERNET-DRAFT                                                  May 1996

             This Internet Draft expires 29th November, 1996.

                                                               [Page 10]