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rfc:rfc921

Network Working Group Jon Postel Request for Comments: 921 ISI

                                                          October 1984

Updates: RFC 897, RFC 881

        Domain Name System Implementation Schedule - Revised

Status of this Memo

 This memo is a policy statement on the implementation of the Domain
 Style Naming System in the Internet.  This memo is an update of
 RFC-881, and RFC-897.  This is an official policy statement of the
 IAB and the DARPA.  Distribution of this memo is unlimited.
 The intent of this memo is to detail the schedule for the
 implementation for the Domain Style Naming System.  The explanation
 of how this system works is to be found in the references.

The Current Situation

 There are three aspects to the domain style naming system, (1) the
 names themselves, (2) the method of translating names to addresses,
 and (3) the relationship between the Internet and the rest of the
 world.
 Names
    The names are being changed from simple names, or globally unique
    strings, to structured names, where each component name is unique
    only with respect to the superior component name.
    Simple Names
       Until recently, hosts in the DARPA research and DDN operational
       communities were assigned names in a flat or global name space
       of character strings.  There are some limits on these names.
       They must start with a letter, end with a letter or digit and
       have only letters or digits or hyphen as interior characters.
       Case is not significant.
          For example:  USC-ISIF
    Hierarchical Names
       Because of the growth of the Internet, structured names (or
       domain style names) have been introduced.  Each element of the
       structured name will be a character string (with the same
       constraints that previously applied to the simple names).  The

Postel [Page 1]

RFC 921 October 1984 Domain Implementation Schedule - Revised

       elements (or components) of the structured names are separated
       with periods, and the elements are written from the most
       specific on the left to the most general on the right.
          For example:  USC-ISIF.ARPA
    The Initial and Temporary Domain
       The introduction of these hierarchical names has been very
       limited.  Every current name in this new system has the form
       "old-simple-name.ARPA".  That is, the all the hosts are in a
       domain called "ARPA".  This is a temporary situation.  The
       current intention is for the ARPA domain to cease to exist.
       This means that all hosts will change their names as the domain
       style names come into full use.
 Name to Address Lookup
    Every host in the Internet is expected to have a way of
    translating the name of any other host into its Internet address.
    By and large, the name to address translation is done by looking
    up the information in a table of all hosts.
    The maintenance of this table is centralized at the Network
    Information Center (NIC).  Each host is expected to obtain a
    current copy of the table on a timely basis.  This table is called
    "HOSTS.TXT" [8] and is normally accessed via the Hostnames
    Server [9].
 Interface to the World
    A great deal of mail moves between the Internet and other
    "systems" that somehow transport mail among computers.  This is
    currently done by hiding some sort of "other-system" addressing
    information in the local-part of the mail address and using a
    mail-relay host in the host-part of the mailbox.
    For example,
       OBERST%EDUCOM.MAILNET@MIT-MULTICS.ARPA
       EDMISTON.CIC@CSNET-RELAY.ARPA

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RFC 921 October 1984 Domain Implementation Schedule - Revised

The Future Situation

 Names
    Hierarchical Names
       The use of the hierarchical names will be greatly expanded
       according to the rules established in the "Domain Requirements"
       memo (RFC-920) [5].
          For example:  F.ISI.USC.EDU
    There are several levels of development for use of the domain
    style names.
    First, there is the current simple substitution of the domain
    style names for the old style host names.  At this stage all
    domain style names directly translate to host addresses (using the
    NIC tables) and all domain style names have two components.  The
    mail system uses addresses of the form "local-part@host", where
    host is a domain style host name.
       For example:  USC-ISIF.ARPA  and  Postel@USC-ISIF.ARPA
       Here we expect that "USC-ISIF.ARPA" is the name of an Internet
       host and that we can send mail for "Postel" to the SMTP port on
       that host.  It may be that some backward host can still fake it
       by ignoring the ".ARPA" and looking up an address for
       "USC-ISIF" in some old style file.
    Second, there is an extension to more name components and more top
    level domains.  The mail system still uses addresses of the form
    "local-part@host", where host is a domain style host name.
       For example:  F.ISI.USC.EDU  and  Postel@F.ISI.USC.EDU
       Here we expect that "F.ISI.USC.EDU" is the name of an Internet
       host and that we can send mail for "Postel" to the SMTP port on
       that host.  It is likely that the NIC will enter these new
       domain style names in the centrally maintained table (i.e.,
       HOSTS.TXT) during the transition period.  It is unlikely that a
       backward host can hack this at all.
    Third, there is an extension to domain style names that may
    represent only organizations or administrative entities.  Finding
    a host that acts for such entities may require a level of

Postel [Page 3]

RFC 921 October 1984 Domain Implementation Schedule - Revised

    indirection in the search.  The mail system may use
    "local-part@domain-name", where the "domain-name" identifies a
    host (as before) or an organization.
       For example:  USC-ISI.EDU  and  Postel@USC-ISI.EDU
       Here we don't count on "USC-ISI. EDU" being the name of an
       Internet host.  When we want to send mail to "Postel" we ask
       the domain name server about sending mail to "USC-ISI.EDU".
       The server will tell us the name (and address) of a real
       Internet host that handles mail on this organizations behalf,
       for example, "F.ISI.USC.EDU = 10.2.0.52".  We then send mail
       for "Postel@USC-ISI.EDU" to the SMTP port on F.ISI.USC.EDU.
 Name to Address Lookup
    Every host in the Internet will be expected to have a way of
    translating the name of any other host into its Internet address.
    By and large, the name to address translation will be done by
    interacting with a lookup server.  There will be a number of
    servers that each hold a portion of the name to address
    information.
    The maintenance of the translation data base will be subdivided
    and distributed.
    The design and implementation details for this service are given
    in RFC-882 [2] and RFC-883 [3].
 Interface to the World
    Mail will continue to move between the Internet and other
    "systems".  This may be done by designating some sort of
    "other-system" representative organization in the domain server
    data bases that can indirect mail to a mail-relay host.
    For example,
       Oberst@EDUCOM.MAILNET
       When we want to send mail to "Oberst" we ask the domain name
       server about sending mail to "EDUCOM.MAILNET".  The server will
       tell us the name (and address) of a real Internet host that
       handles mail on this organizations behalf, for example,
       "MIT-MULTICS.ARPA = 10.0.0.6".  We then send mail for
       "Oberst@EDUCOM.MAILNET" to the SMTP port on MIT-MULTICS.ARPA.

Postel [Page 4]

RFC 921 October 1984 Domain Implementation Schedule - Revised

    For example,
       Edmiston@CIC.CSNET
       When we want to send mail to "Edmiston" we ask the domain name
       server about sending mail to "CIC.CSNET".  The server will tell
       us the name (and address) of a real Internet host that handles
       mail on this organizations behalf, for example,
       "CSNET-RELAY.ARPA = 10.4.0.5".  We then send mail for
       "Edmiston@CIC.CSNET" to the SMTP port on CSNET-RELAY.ARPA.

The Transition Situation

 Actually, the situation is a bit more complicated, of course.  Hosts
 are already using domain style names under the constraint that their
 domain style name is exactly their old style name with the string
 ".ARPA" appended.  The first transition step is to ensure that all
 hosts do this, and then to eliminate the use of old style names
 altogether.
 Please note carefully that two types of changes are being made:
    One is a change in the support mechanism for translating a host
    name to an internet address,
       that is from using local copies of a full centrally maintained
       table to dynamically accessing a distributed set of servers
       each posesing a portion of a data base maintained in a
       distributed fashion.
    The other is a change in the host names themselves,
       from a flat global space of unstructured strings to a
       hierarchical structure of names.
 There are two steps to the transition plan.
    First, change from old names to domain style names.
    Second, change from using central tables to using name servers.
 There are two communities that are taking slightly different courses
 in this transition.  The DARPA research community is making the full
 transition.  The DDN operational community is making the change in
 naming on the same schedule, but is not requiring hosts in the DDN
 operational community make the change to using servers at the same

Postel [Page 5]

RFC 921 October 1984 Domain Implementation Schedule - Revised

 time (they can if they want to).  The DDN PMO will establish a
 schedule for that change at a later time.  The NIC will maintain a
 central table of all DDN operational hosts.
 Interface to the World
    The interchange of mail with "other-systems" will have to continue
    pretty much as it has (except that RELAY-HOST is RELAY-HOST.ARPA)
    until organization names can be used.  Then representative
    organizations can be designated for each "other-system" in the
    domain server data bases that will then specify a mail-relay host.

All Hosts Change Names

 The impact of introducing the domain style names is that all hosts
 change their names at least once.  Hosts that move to new domains or
 subdomains may change their names several times.
 Hosts have an official (or primary) name and possibly several
 nicknames.  When mail is sent from a host, the official name is used
 in the mail header address fields.
 Suppose, that in the old days before domains were thought of, a host
 changed its name.  What is the impact on users of changing the name
 of a host?
    Mail that was sent before the name was changed can not be answered
    using mail program commands that automatically fill in the return
    address.  While it may be possible to use special tricks to fix up
    the "From" or the "To" users addresses, the "Cc" addresses are
    very difficult to correct.
       Suppose one host changed its name from FOO to BAR.  Mail that
       was sent from FRED@FOO to JOE@ABC can not be answered unless
       the change of name is known to the user or the mail program at
       ABC and the host name BAR substituted for FOO.  Mail that is
       sent to JOE@ABC from SAM@DEF with a cc to FRED@FOO can not be
       answered easily.
    Any mailing lists that have mailboxes with the host that changed
    names will now have incorrect entries.
 The point is that while the host that changed names may be able to
 use special tricks for a while to fix things up for the users, it is
 difficult for other hosts to do this.

Postel [Page 6]

RFC 921 October 1984 Domain Implementation Schedule - Revised

 A general trick is to make the old name a nickname for the host for
 some period of time.
 The introduction of domain style names means that all hosts change
 their names essentially at the same time.
 To lessen the havoc, there will be a period of time when both the old
 and the new names are allowed.  That is, the old names will be
 nicknames for a while.

Primary Names

 Currently, host have an official or primary names and may have
 several nicknames.  For example,
    Primary Name             Nicknames
    USC-ISIF.ARPA            USC-ISIF ISIF
    ADA-VAX.ARPA             ADA-VAX ISI-VAXB  AJPO  VAXB
 The data base is such than given any of the names for a host one can
 find the address, and given the address one can find the primary
 name.
 In the new domain style name system this property must be maintained.
 That is, given the Internet address of a host one must be able to
 find the primary name of that host.  This calls for careful
 management of the distributed database by those in charge of the
 domains and zones.

Postel [Page 7]

RFC 921 October 1984 Domain Implementation Schedule - Revised

The Revised Time Table

 There are three major phases to the implementation of the domain
 names system: (1) putting the machinery in place (servers,
 resolvers), (2) getting the data base installed, (3) changing the
 user programs (mailers, etc.).
    The machinery is now (at last) well along, there is a server for
    TOPS-20, and two different servers for Unix.  The data base now
    contains the ARPA domain and is initialized for the other top
    level domains.  Little has been done to change user programs to
    use the new procedures.
 Done
    Service Design and Specification:  The design and specification
    for the protocol and data base were published (RFC-882, RFC-883).
    Domain Requirements Specification:  The requirements for
    establishing a new domain are published as an RFC (RFC-920).
    Domain Style Names in Table:  Hosts are using their domain style
    names as their official and primary names.  The standard table of
    host names contains domain style names as the official and primary
    name.
    Servers for ARPA Domain:  Several domain name servers are in
    operation to supply host name to internet address translations,
    one of these servers is at the NIC.
 15 Dec 84  Domain Table
    A master table of top level domain names and their associated
    servers is established at the NIC.  Probably this information will
    be added to the HOSTS.TXT file as a new entry type.
 15 Jan 85  Begin New Domain Registration
    New domains may register according to the procedures and
    restrictions described in RFC-920 [5].
 15 Feb 85  Major Machinery Completed
    The principal servers are up and running, there are resolvers
    programmed and tested for the most popular systems (Unix 4.2bsd,
    TOPS-20).

Postel [Page 8]

RFC 921 October 1984 Domain Implementation Schedule - Revised

 15 May 85  Significant Use of Resolvers and Servers
    Programs (e.g., Mailers, Telnet, FTP) begin regular use of the new
    mechanisms (resolvers and servers).  This may be done by changing
    the programs to act as resolvers themselves and call on servers
    directly, or to provide system calls that include the resolver
    function to replace old system calls that accessed the host table.
 15 Jul 85  Implementation of the Domain Naming System Completed
    The goal is to complete the switch over to the domain style names
    and the use of the servers by this date.  All programs that
    translate host name to Internet addresses should now use
    procedures based on the use of the domain style names system of
    resolvers and servers and the distributed data base.
 15 Sep 85  Decommission Host Table
    At this point the master host table maintained by the NIC need no
    longer be complete for the DARPA research community.  A full table
    of the DDN operational hosts will be maintained by the NIC.
 15 Oct 85  DDN Plan for Domains Name Service
    The DDN PMO may establish a plan for the future support of name to
    address translations in the DDN community.

Postel [Page 9]

RFC 921 October 1984 Domain Implementation Schedule - Revised

Appendix : The Old Time Table

 Here we present the time table from the previous schedule (RFC-897)
 with some comments on what was and was not accomplished.
  1. - Nov 83 Plan and Schedule
    At this point the overall plan for the implementation of domain
    style names and name servers, and a schedule of events was
    published (RFC-881).  Also the design and specification for the
    protocol and data base were published (RFC-882, RFC-883).
       <This was done, but the schedule did not work.>
  1. - Nov 83 Initial Domain Style Host Name Table
    At this point a version of the host table which includes the
    domain style names is made available (DHOSTS.TXT).
       <This was done, on schedule.>
  1. - Feb 84 Domain Requirements Specification
    At this point the requirements for establishing a new domain are
    published as an RFC.
       <This topic was much discussed in the Namedroppers mailing
       list, but no RFC was published until Oct84 [5].>
 14 Mar 84  Begin using Domain Style Names
    At this point all hosts should start using their domain style
    names as their official and primary names.  The standard table of
    host names contains domain style names as the official and primary
    name (DHOSTS.TXT becomes HOSTS.TXT).
       <This was done, on schedule.>
 04 Apr 84  Server for ARPA Domain
    At this point several domain name servers are in operation to
    supply host name to internet address translations, one of these
    servers is at the NIC.
       <This was done, not on schedule, but by Sep84.>

Postel [Page 10]

RFC 921 October 1984 Domain Implementation Schedule - Revised

 04 Apr 84  Domain Table
    At this point a master table of top level domain names and their
    associated servers is established at the NIC.
       <Not done yet.>
 02 May 84  Stop using old style Names
    At this point the use of old style names must be completely phased
    out.
       <I think this is done.  Except that some hosts still use the
       OHOSTS.TXT file.>
 02 May 84  Certain New Domains
    At this point a few new domains may be established, in particular
    the DDN domain.
       <Not done yet.  Well, "DDN" won't be a top level domain
       according to the new rules (see [5]).>
 06 Jun 84  General & Multilevel Domains
    At this point additional new domains may be established, if they
    meet the requirements.  Domain style names may have more than two
    segments.
       <Not done yet.>
 18 Jul 84  Organizational Domains
    Domain style names may identify organizations.  Finding an address
    for a host may involve a level of indirection.
       <Not done yet.>
 05 Sep 84  Decommission Host Table
    At this point the master host table maintained by the NIC need no
    longer be complete for the DARPA research community.  A full table
    of the DDN operational hosts will be maintained by the NIC.
       <Not done yet.>

Postel [Page 11]

RFC 921 October 1984 Domain Implementation Schedule - Revised

 03 Oct 84  DDN Plan for Domains Name Service
    At this point the DDN PMO will establish a plan for the future
    support of name to address translations in the DDN community.
       <Not done yet.>

Postel [Page 12]

RFC 921 October 1984 Domain Implementation Schedule - Revised

References

 [1]  Postel, J., "The Domain Names Plan and Schedule", RFC-881, USC
      Information Sciences Institute, November 1983.
 [2]  Mockapetris, P., "Domain Names - Concepts and Facilities",
      RFC-882, USC Information Sciences Institute, November 1983.
 [3]  Mockapetris, P., "Domain Names - Implementation and
      Specification", RFC-883, USC Information Sciences Institute,
      November 1983.
 [4]  Postel, J., "Domain Name System Implementation Schedule",
      RFC-897, USC Information Sciences Institute, February 1984.
 [5]  Postel, J., and J. Reynolds, "Domain Requirements", RFC-920, USC
      Information Sciences Institute, October 1984.
 [6]  Mockapetris, P., "The Domain Name System", Proceedings of the
      IFIP 6.5 Working Conference on Computer Message Services,
      Nottingham, England, May 1984.  Also as ISI/RS-84-133,
      June 1984.
 [7]  Mockapetris, P., J. Postel, and P. Kirton, "Name Server Design
      for Distributed Systems", Proceedings of the Seventh
      International Conference on Computer Communication, Sidney,
      Australia, October 1984.  Also as ISI/RS-84-132, June 1984.
 [8]  Feinler, E., K. Harrenstien, Z. Su, and V. White, "DoD Internet
      Host Table Specification", RFC-810, Network Information Center,
      SRI International, March 1982.
 [9]  Harrenstien, K., V. White, and E. Feinler, "Hostnames Server",
      RFC-811, Network Information Center, SRI International,
      March 1982.

Postel [Page 13]

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