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RFC 1183

New DNS RR Definitions

Pages: 11
Updates:  10341035
Updated by:  5395586461956895

Top   ToC   RFC1183 - Page 1
Network Working Group                                        C. Everhart
Request for Comments: 1183                                      Transarc
Updates: RFCs 1034, 1035                                      L. Mamakos
                                                  University of Maryland
                                                              R. Ullmann
                                                          Prime Computer
                                                  P. Mockapetris, Editor
                                                            October 1990

                         New DNS RR Definitions

Status of this Memo

   This memo defines five new DNS types for experimental purposes.  This
   RFC describes an Experimental Protocol for the Internet community,
   and requests discussion and suggestions for improvements.
   Distribution of this memo is unlimited.

Table of Contents

   Introduction....................................................    1
   1. AFS Data Base location.......................................    2
   2. Responsible Person...........................................    3
   2.1. Identification of the guilty party.........................    3
   2.2. The Responsible Person RR..................................    4
   3. X.25 and ISDN addresses, Route Binding.......................    6
   3.1. The X25 RR.................................................    6
   3.2. The ISDN RR................................................    7
   3.3. The Route Through RR.......................................    8
   REFERENCES and BIBLIOGRAPHY.....................................    9
   Security Considerations.........................................   10
   Authors' Addresses..............................................   11


   This RFC defines the format of new Resource Records (RRs) for the
   Domain Name System (DNS), and reserves corresponding DNS type
   mnemonics and numerical codes.  The definitions are in three
   independent sections: (1) location of AFS database servers, (2)
   location of responsible persons, and (3) representation of X.25 and
   ISDN addresses and route binding.  All are experimental.

   This RFC assumes that the reader is familiar with the DNS [3,4].  The
   data shown is for pedagogical use and does not necessarily reflect
   the real Internet.
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1. AFS Data Base location

   This section defines an extension of the DNS to locate servers both
   for AFS (AFS is a registered trademark of Transarc Corporation) and
   for the Open Software Foundation's (OSF) Distributed Computing
   Environment (DCE) authenticated naming system using HP/Apollo's NCA,
   both to be components of the OSF DCE.  The discussion assumes that
   the reader is familiar with AFS [5] and NCA [6].

   The AFS (originally the Andrew File System) system uses the DNS to
   map from a domain name to the name of an AFS cell database server.
   The DCE Naming service uses the DNS for a similar function: mapping
   from the domain name of a cell to authenticated name servers for that
   cell.  The method uses a new RR type with mnemonic AFSDB and type
   code of 18 (decimal).

   AFSDB has the following format:

   <owner> <ttl> <class> AFSDB <subtype> <hostname>

   Both RDATA fields are required in all AFSDB RRs.  The <subtype> field
   is a 16 bit integer.  The <hostname> field is a domain name of a host
   that has a server for the cell named by the owner name of the RR.

   The format of the AFSDB RR is class insensitive.  AFSDB records cause
   type A additional section processing for <hostname>.  This, in fact,
   is the rationale for using a new type code, rather than trying to
   build the same functionality with TXT RRs.

   Note that the format of AFSDB in a master file is identical to MX.
   For purposes of the DNS itself, the subtype is merely an integer.
   The present subtype semantics are discussed below, but changes are
   possible and will be announced in subsequent RFCs.

   In the case of subtype 1, the host has an AFS version 3.0 Volume
   Location Server for the named AFS cell.  In the case of subtype 2,
   the host has an authenticated name server holding the cell-root
   directory node for the named DCE/NCA cell.

   The use of subtypes is motivated by two considerations.  First, the
   space of DNS RR types is limited.  Second, the services provided are
   sufficiently distinct that it would continue to be confusing for a
   client to attempt to connect to a cell's servers using the protocol
   for one service, if the cell offered only the other service.

   As an example of the use of this RR, suppose that the Toaster
   Corporation has deployed AFS 3.0 but not (yet) the OSF's DCE.  Their
   cell, named, has three "AFS 3.0 cell database server"
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   machines:,, and  These three machines would be listed in three
   AFSDB RRs.  These might appear in a master file as:   AFSDB   1   AFSDB   1   AFSDB   1

   As another example use of this RR, suppose that Femto College (domain
   name has deployed DCE, and that their DCE cell root
   directory is served by processes running on and  Furthermore, their DCE file servers also run
   AFS 3.0-compatible volume location servers, on the hosts and  These machines would be
   listed in four AFSDB RRs, which might appear in a master file as:   AFSDB   2   AFSDB   2   AFSDB   1   AFSDB   1

2. Responsible Person

   The purpose of this section is to provide a standard method for
   associating responsible person identification to any name in the DNS.

   The domain name system functions as a distributed database which
   contains many different form of information.  For a particular name
   or host, you can discover it's Internet address, mail forwarding
   information, hardware type and operating system among others.

   A key aspect of the DNS is that the tree-structured namespace can be
   divided into pieces, called zones, for purposes of distributing
   control and responsibility.  The responsible person for zone database
   purposes is named in the SOA RR for that zone.  This section
   describes an extension which allows different responsible persons to
   be specified for different names in a zone.

2.1. Identification of the guilty party

   Often it is desirable to be able to identify the responsible entity
   for a particular host.  When that host is down or malfunctioning, it
   is difficult to contact those parties which might resolve or repair
   the host.  Mail sent to POSTMASTER may not reach the person in a
   timely fashion.  If the host is one of a multitude of workstations,
   there may be no responsible person which can be contacted on that
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   The POSTMASTER mailbox on that host continues to be a good contact
   point for mail problems, and the zone contact in the SOA record for
   database problem, but the RP record allows us to associate a mailbox
   to entities that don't receive mail or are not directly connected
   (namespace-wise) to the problem (e.g., GATEWAY.ISI.EDU might want to
   point at HOTLINE@BBN.COM, and GATEWAY doesn't get mail, nor does the
   ISI zone administrator have a clue about fixing gateways).

2.2. The Responsible Person RR

   The method uses a new RR type with mnemonic RP and type code of 17

   RP has the following format:

   <owner> <ttl> <class> RP <mbox-dname> <txt-dname>

   Both RDATA fields are required in all RP RRs.

   The first field, <mbox-dname>, is a domain name that specifies the
   mailbox for the responsible person.  Its format in master files uses
   the DNS convention for mailbox encoding, identical to that used for
   the RNAME mailbox field in the SOA RR.  The root domain name (just
   ".") may be specified for <mbox-dname> to indicate that no mailbox is

   The second field, <txt-dname>, is a domain name for which TXT RR's
   exist.  A subsequent query can be performed to retrieve the
   associated TXT resource records at <txt-dname>.  This provides a
   level of indirection so that the entity can be referred to from
   multiple places in the DNS.  The root domain name (just ".") may be
   specified for <txt-dname> to indicate that the TXT_DNAME is absent,
   and no associated TXT RR exists.

   The format of the RP RR is class insensitive.  RP records cause no
   additional section processing.  (TXT additional section processing
   for <txt-dname> is allowed as an option, but only if it is disabled
   for the root, i.e., ".").

   The Responsible Person RR can be associated with any node in the
   Domain Name System hierarchy, not just at the leaves of the tree.

   The TXT RR associated with the TXT_DNAME contain free format text
   suitable for humans.  Refer to [4] for more details on the TXT RR.

   Multiple RP records at a single name may be present in the database.
   They should have identical TTLs.
Top   ToC   RFC1183 - Page 5

   Some examples of how the RP record might be used. A
                     MX    10
                     HINFO NeXT UNIX
                     WKS tcp ftp telnet smtp
                     RP TXT (
         "Louis A. Mamakos, (301) 454-2946, don't call me at home!" )

   In this example, the responsible person's mailbox for the host
   SAYSHELL.UMD.EDU is  The TXT RR at provides additional information and advice.

                    MX    10
                    HINFO MICROVAX-II UNIX
                    WKS udp domain
                    WKS tcp ftp telnet smtp domain
                    RP ops.CS.UMD.EDU.

                    MX    10
                    HINFO MICROVAX-II UNIX
                    WKS udp domain
                    WKS tcp ftp telnet smtp domain
                    RP petry.people.UMD.EDU.
                    RP ops.CS.UMD.EDU.
                    RP  .  TXT   "Louis A. Mamakos (301) 454-2946" TXT   "Michael G. Petry (301) 454-2946"
   ops.CS.UMD.EDU.       TXT   "CS Operations Staff (301) 454-2943"

   This set of resource records has two hosts, TRANTOR.UMD.EDU and
   TERP.UMD.EDU, as well as a number of TXT RRs.  Note that TERP.UMD.EDU
   and TRANTOR.UMD.EDU both reference the same pair of TXT resource
   records, although the mail box names ( and differ.

   Here, we obviously care much more if the machine flakes out, as we've
   specified four persons which might want to be notified of problems or
   other events involving TRANTOR.UMD.EDU.  In this example, the last RP
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   RR for TRANTOR.UMD.EDU specifies a mailbox (,
   but no associated TXT RR.

3. X.25 and ISDN addresses, Route Binding

   This section describes an experimental representation of X.25 and
   ISDN addresses in the DNS, as well as a route binding method,
   analogous to the MX for mail routing, for very large scale networks.

   There are several possible uses, all experimental at this time.
   First, the RRs provide simple documentation of the correct addresses
   to use in static configurations of IP/X.25 [11] and SMTP/X.25 [12].

   The RRs could also be used automatically by an internet network-layer
   router, typically IP.  The procedure would be to map IP address to
   domain name, then name to canonical name if needed, then following RT
   records, and finally attempting an IP/X.25 call to the address found.
   Alternately, configured domain names could be resolved to identify IP
   to X.25/ISDN bindings for a static but periodically refreshed routing

   This provides a function similar to ARP for wide area non-broadcast
   networks that will scale well to a network with hundreds of millions
   of hosts.

   Also, a standard address binding reference will facilitate other
   experiments in the use of X.25 and ISDN, especially in serious
   inter-operability testing.  The majority of work in such a test is
   establishing the n-squared entries in static tables.

   Finally, the RRs are intended for use in a proposal [13] by one of
   the authors for a possible next-generation internet.

3.1. The X25 RR

   The X25 RR is defined with mnemonic X25 and type code 19 (decimal).

   X25 has the following format:

   <owner> <ttl> <class> X25 <PSDN-address>

   <PSDN-address> is required in all X25 RRs.

   <PSDN-address> identifies the PSDN (Public Switched Data Network)
   address in the X.121 [10] numbering plan associated with <owner>.
   Its format in master files is a <character-string> syntactically
   identical to that used in TXT and HINFO.
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   The format of X25 is class insensitive.  X25 RRs cause no additional
   section processing.

   The <PSDN-address> is a string of decimal digits, beginning with the
   4 digit DNIC (Data Network Identification Code), as specified in
   X.121. National prefixes (such as a 0) MUST NOT be used.

   For example:

   Relay.Prime.COM.  X25       311061700956

3.2. The ISDN RR

   The ISDN RR is defined with mnemonic ISDN and type code 20 (decimal).

   An ISDN (Integrated Service Digital Network) number is simply a
   telephone number.  The intent of the members of the CCITT is to
   upgrade all telephone and data network service to a common service.

   The numbering plan (E.163/E.164) is the same as the familiar
   international plan for POTS (an un-official acronym, meaning Plain
   Old Telephone Service).  In E.166, CCITT says "An E.163/E.164
   telephony subscriber may become an ISDN subscriber without a number

   ISDN has the following format:

   <owner> <ttl> <class> ISDN <ISDN-address> <sa>

   The <ISDN-address> field is required; <sa> is optional.

   <ISDN-address> identifies the ISDN number of <owner> and DDI (Direct
   Dial In) if any, as defined by E.164 [8] and E.163 [7], the ISDN and
   PSTN (Public Switched Telephone Network) numbering plan.  E.163
   defines the country codes, and E.164 the form of the addresses.  Its
   format in master files is a <character-string> syntactically
   identical to that used in TXT and HINFO.

   <sa> specifies the subaddress (SA).  The format of <sa> in master
   files is a <character-string> syntactically identical to that used in
   TXT and HINFO.

   The format of ISDN is class insensitive.  ISDN RRs cause no
   additional section processing.

   The <ISDN-address> is a string of characters, normally decimal
   digits, beginning with the E.163 country code and ending with the DDI
   if any.  Note that ISDN, in Q.931, permits any IA5 character in the
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   general case.

   The <sa> is a string of hexadecimal digits.  For digits 0-9, the
   concrete encoding in the Q.931 call setup information element is
   identical to BCD.

   For example:

   Relay.Prime.COM.   IN   ISDN      150862028003217
   sh.Prime.COM.      IN   ISDN      150862028003217 004

   (Note: "1" is the country code for the North American Integrated
   Numbering Area, i.e., the system of "area codes" familiar to people
   in those countries.)

   The RR data is the ASCII representation of the digits.  It is encoded
   as one or two <character-string>s, i.e., count followed by

   CCITT recommendation E.166 [9] defines prefix escape codes for the
   representation of ISDN (E.163/E.164) addresses in X.121, and PSDN
   (X.121) addresses in E.164.  It specifies that the exact codes are a
   "national matter", i.e., different on different networks.  A host
   connected to the ISDN may be able to use both the X25 and ISDN
   addresses, with the local prefix added.

3.3. The Route Through RR

   The Route Through RR is defined with mnemonic RT and type code 21

   The RT resource record provides a route-through binding for hosts
   that do not have their own direct wide area network addresses.  It is
   used in much the same way as the MX RR.

   RT has the following format:

   <owner> <ttl> <class> RT <preference> <intermediate-host>

   Both RDATA fields are required in all RT RRs.

   The first field, <preference>, is a 16 bit integer, representing the
   preference of the route.  Smaller numbers indicate more preferred

   <intermediate-host> is the domain name of a host which will serve as
   an intermediate in reaching the host specified by <owner>.  The DNS
   RRs associated with <intermediate-host> are expected to include at
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   least one A, X25, or ISDN record.

   The format of the RT RR is class insensitive.  RT records cause type
   X25, ISDN, and A additional section processing for <intermediate-

   For example,      IN   RT   2    Relay.Prime.COM.
                      IN   RT   10   NET.Prime.COM.
   *       IN   RT   90   Relay.Prime.COM.

   When a host is looking up DNS records to attempt to route a datagram,
   it first looks for RT records for the destination host, which point
   to hosts with address records (A, X25, ISDN) compatible with the wide
   area networks available to the host.  If it is itself in the set of
   RT records, it discards any RTs with preferences higher or equal to
   its own.  If there are no (remaining) RTs, it can then use address
   records of the destination itself.

   Wild-card RTs are used exactly as are wild-card MXs.  RT's do not
   "chain"; that is, it is not valid to use the RT RRs found for a host
   referred to by an RT.

   The concrete encoding is identical to the MX RR.


   [1] Stahl, M., "Domain Administrators Guide", RFC 1032, Network
       Information Center, SRI International, November 1987.

   [2] Lottor, M., "Domain Administrators Operations Guide", RFC 1033,
       Network Information Center, SRI International, November, 1987.

   [3] Mockapetris, P., "Domain Names - Concepts and Facilities", RFC
       1034, USC/Information Sciences Institute, November 1987.

   [4] Mockapetris, P., "Domain Names - Implementation and
       Specification", RFC 1035, USC/Information Sciences Institute,
       November 1987.

   [5] Spector A., and M. Kazar, "Uniting File Systems", UNIX Review,
       7(3), pp. 61-69, March 1989.

   [6] Zahn, et al., "Network Computing Architecture", Prentice-Hall,

   [7] International Telegraph and Telephone Consultative Committee,
Top   ToC   RFC1183 - Page 10
       "Numbering Plan for the International Telephone Service", CCITT
       Recommendations E.163., IXth Plenary Assembly, Melbourne, 1988,
       Fascicle II.2 ("Blue Book").

   [8] International Telegraph and Telephone Consultative Committee,
       "Numbering Plan for the ISDN Era", CCITT Recommendations E.164.,
       IXth Plenary Assembly, Melbourne, 1988, Fascicle II.2 ("Blue

   [9] International Telegraph and Telephone Consultative Committee.
       "Numbering Plan Interworking in the ISDN Era", CCITT
       Recommendations E.166., IXth Plenary Assembly, Melbourne, 1988,
       Fascicle II.2 ("Blue Book").

  [10] International Telegraph and Telephone Consultative Committee,
       "International Numbering Plan for the Public Data Networks",
       CCITT Recommendations X.121., IXth Plenary Assembly, Melbourne,
       1988, Fascicle VIII.3 ("Blue Book"); provisional, Geneva, 1978;
       amended, Geneva, 1980, Malaga-Torremolinos, 1984 and Melborne,

  [11] Korb, J., "Standard for the Transmission of IP datagrams Over
       Public Data Networks", RFC 877, Purdue University, September

  [12] Ullmann, R., "SMTP on X.25", RFC 1090, Prime Computer, February

  [13] Ullmann, R., "TP/IX: The Next Internet", Prime Computer
       (unpublished), July 1990.

  [14] Mockapetris, P., "DNS Encoding of Network Names and Other Types",
       RFC 1101, USC/Information Sciences Institute, April 1989.

Security Considerations

   Security issues are not addressed in this memo.
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Authors' Addresses

   Craig F. Everhart
   Transarc Corporation
   The Gulf Tower
   707 Grant Street
   Pittsburgh, PA  15219

   Phone: +1 412 338 4467


   Louis A. Mamakos
   Network Infrastructure Group
   Computer Science Center
   University of Maryland
   College Park, MD 20742-2411

   Phone: +1-301-405-7836

   Email: louie@Sayshell.UMD.EDU

   Robert Ullmann 10-30
   Prime Computer, Inc.
   500 Old Connecticut Path
   Framingham, MA 01701

   Phone: +1 508 620 2800 ext 1736

   Email: Ariel@Relay.Prime.COM

   Paul Mockapetris
   USC Information Sciences Institute
   4676 Admiralty Way
   Marina del Rey, CA 90292

   Phone: 213-822-1511