Network Working Group                                          J. Postel
Request for Comments: 881                                            ISI
                                                           November 1983



                   The Domain Names Plan and Schedule
	
This RFC outlines a plan and schedule for the implementation of domain
style names throughout the DDN/ARPA Internet community.  The
introduction of domain style names will impact all hosts on the DDN/ARPA
Internet.

The Plan

   Introduction

      Domain style names are being introduced in the Internet to allow a
      controlled delegation of the authority and responsibility for
      adding hosts to the system.  This also allows a subdivision of the
      task of maintaining information about hosts.

      The subdivision will be based on administrative authority or
      organization boundaries (not necessarily network boundaries).
      Certain requirements will be placed on organizations wishing to be
      "top level" domains.  Initially, all the hosts in the Internet
      will be in the domain "ARPA".  As soon as is practical a second
      domain, "DDN", will be introduced.  Other domains may be added
      after that, provided the requirements listed below are met.

      Domain names will be supported in the long run by a system of
      special servers called "domain servers" which will be used to
      translate names to addresses.  While this system of domain servers
      is being created and programs are being converted to use them, the
      existing host tables will evolve to include domain style names.

      The domain server design also provides for mapping mailbox
      addresses to the host name of the mail server for that mailbox.
      This feature allows mailboxes to be related to an organization
      rather than to a specific host.

      This plan will be implemented in the ARPA community.  After the
      domain system is demonstrated in the ARPA community, the DDN
      Program Management Office (DDN-PMO) will determine the schedule
      for implementation of the domain system in the DDN community.
      This approach will cause some extra steps in the ARPA community
      implementation, and may limit communication between the ARPA and
      DDN communities in some ways.  The details and implications of
      this two phase approach are discussed more fully below.

   A Catch 22

      There is a problem in introducing domain style names: a great deal
      of software has to be changed.  Some groups would like to start
      using domain style names right away, and other groups don't want
      to see them or use them for a very long time.  Communication
      patterns are very complex and as soon as domain style names are
      allowed and used by a few groups they will start showing up almost
      everywhere.  This argues that everyone should be prepared for them
      before they are used at all.  However, we know that with people
      being people and with so many of people involved, the probability
      of everyone being ready in any reasonable time period is nearly
      zero.  The way out of this situation is to set up a reasonable
      schedule for experimenting with domain style names and authorizing
      their use.  People that get ready on schedule should have no
      problems with these names.

   Evolution of the Table

      Nearly all the hosts in the Internet now use some form of host
      table based on the master file "HOSTS.TXT" maintained by the
      Network Information Center (NIC).

      One way to introduce domain style names is to add to the entries
      in this table names in the domain style.  In particular, make the
      first name in each entry the official host name in the ARPA
      domain.

         For example, the current entry for USC-ISIF is:

            HOST : 10.2.0.52 : USC-ISIF,ISIF : DEC-1090T : TOPS20 :
            TCP/TELNET,TCP/SMTP,TCP/FTP,TCP/FINGER,UDP/TFTP :

         This could become:

            HOST : 10.2.0.52 : USC-ISIF.ARPA,USC-ISIF,ISIF : DEC-1090T :
            TOPS20 : TCP/TELNET,TCP/SMTP,TCP/FTP,TCP/FINGER,UDP/TFTP :

      For some hosts and programs this could be done today with no
      disruptions, but for others substantial problems could occur.  For
      example, with over five hundred entries in the table the addition
      of 500 names could exceed the space allocated to store the table
      in some programs.  (One could argue that these programs are going
      to blow up soon anyway as new host entries are added to the
      table.)  Another problem is that period (or dot, ".") is not now a
      legal character in host names and some programs may not be able to
      parse these new names.

      The plan is to make such a domain style name table available in
      parallel with the regular table for a few months, then to replace
      the regular table with this domain style table.  The dates for
      these changes is given in the schedule below.

      So far, no new domains have been introduced.  Only a table with
      all the entries having official names in the ARPA domain has been
      provided.  This should allow programs to be constructed to deal
      with domain style names in a general way without any special hacks
      to add or delete the string ".ARPA" to or from host names.

      The introduction of new domains is tied to the provision of domain
      servers by those domains.  As new domains meet the requirements
      and are authorized they will also be added to the host table.  No
      new domains will be added before master table is converted to the
      domain style entries.

      In the long run the Internet will become too complex and change
      too fast to keep a master table of all the hosts.  At some point
      the master table will be reduced to simply the entries for the
      domain servers for the top level domains.  By this time all normal
      translation of host names into addresses should take place by
      consulting domain servers.

   Conversion to Servers

      As soon as domain servers become available programs should be
      converted to use them to translate names into addresses.  The
      details of these procedures are given in RFCs 882 and 883.

      The general idea is that a host no longer keeps a complete host
      table but rather makes a request on the domain server each time a
      name must be translated to an address.  The code module in the
      host that implements the protocol to do this is called a
      "resolver".  The resolver may keep a cache of recently translated
      names and addresses for improved performance.

      Many hosts have a library function or system call that is used to
      access the host table to translate names to addresses.  It ought
      to be possible to replace this function or call with the resolver
      module such that most programs would not know which method was
      used to accomplish the name to address translation.

   Requirements on a Domain

      There are several requirements that must be met to establish a
      domain.  In general it must be responsibly managed.  There must be
      a responsible person to serve as a coordinator for domain related
      questions,  there must be a robust name service, it must be of at
      least a minimum size,  and the domain must be registered with the
      central domain administrator.

      Responsible Person:

         An individual must be identified who has authority for the
         administration of the names within the domain, and who takes
         responsibility for the behavior of the hosts in the domain in
         their interactions with hosts outside the domain.

         The operation of a name server should not be taken on lightly.
         There are some difficult problems in providing an adequate
         service, primarily the problems in keeping the data base up to
         date, and keeping the service operating.

         If some host in a domain somehow misbehaves in interactions
         with hosts outside the domain (e.g., consistently violates
         protocols), the responsible person for the domain must be able
         to take action to eliminate the problem.

      Domain Servers:

         A robust and reliable domain service must be provided.  One way
         of meeting this requirement is to provide at least two
         independent domain servers for the domain.  The data base can,
         of course, be the same.  The database can be prepared and
         copied to each domain server.  But, the servers should be in
         separate machines on independent power supplies, et cetera;
         basically as physically independent as can be and yet in the
         same domain.  They should have no common point of failure.

         One of the difficult problems in operating a domain server is
         the acquisition and maintenance of the data.  In this case the
         data is the host names and addresses.  In some environments
         this information changes fairly rapidly and keeping up-to-date
         data may be difficult.  This is one motivation for sub-domains.
         One may wish to create sub-domains until the rate of change of
         the data in a sub-domain domain server data base is easily
         managed.

         The concepts and implementation details of the domain server
         are given in RFCs 882 and 883.

      Minimum Size:

         The domain must be of at least a minimum size.  Several
         measures of size may be used in combination in making this
         test.  Measures may include: (a) the number of host computers
         in the domain, (b) the number of people with primary mailboxes
         in the domain, (c) the amount of traffic that crosses the
         boundary of the domain [packets/day or mail items/week].
         Specific threshold values for these measures will be
         established before new domains are authorized.

         There is no requirement to form a domain because some set of
         hosts is above the minimum size.

      Registration:

         The administrator must register the domain with the central
         authority.  The central authority must be satisfied that the
         requirements are met before authorization for the domain is
         granted.

         The administrator of a domain is required to make sure that
         host and sub-domain names within that jurisdiction conform to
         the standard name conventions and are unique with in that
         domain.

         If sub-domains are set up the administrator may wish to pass
         along some of his authority and responsibility to a sub-domain
         administrator.

   Mailbox Support

      The design of the domain servers provides two levels of support
      for mail.

      The first, called "agent binding", is that the right hand part of
      the typical mail box (Y in X@Y) can be mapped a host that will
      either accept the mail as the destination or accept the mail for
      forwarding.

      The second, called "mailbox binding", is to map the entire mailbox
      (X@Y) to a destination (this mechanism can also support some
      mailing list functions).

      Agent binding can be used to establish mailboxes that are based on
      an organization name rather than a host name.

         For example, an organization, "BLAT", with hosts "BLAT-20" and

         "BLAT-VAX" in the ARPA domain could set up mailboxes of the
         form "user@BLAT.ARPA" and use the domain server mechanisms for
         mapping these to the host that accepts the mail for the
         organization.

      Mailbox binding will allow different mappings for individual
      mailboxes of an organization or host to the destination host.  It
      will also provide for aliases and mailing groups.

         Mailbox binding requires adding information on individual
         mailboxes to the domain server database.  This could be a
         substantial increase in the database size and management
         responsibility.

   The ARPA Community and the DDN Community

      This plan will be put into effect in the ARPA community.

      The DDN community will adopt the domain style names, but will
      continue with the present scheme of a centrally maintained table
      copied periodically by each host.  Once the use of domain servers
      has been demonstrated by use in the ARPA community, the DDN-PMO
      will establish a schedule for implementing the domain system in
      the DDN community.

      This means that there may be a period of a year or more with the
      two communities using different schemes for distributing
      information about host names and addresses.

      Specifically:

         The NIC will maintain a table a "HOSTS.TXT" style table for use
         by DDN hosts.  This table will contain domain style names for
         all DDN hosts (e.g., USC-ISIA.DDN).  Since this is the only
         information DDN hosts will use to translate host names to
         Internet Addresses, this table must also contain names and
         addresses of ARPA community hosts of interest to DDN users
         (e.g., USC-ISIF.ARPA).

         There will be a domain server with data for the DDN domain.
         That is, hosts in the ARPA community that use the domain system
         of resolvers and servers will be able to access servers that
         have the data base covering the DDN community.

      It is quite likely that the table for the use of the DDN hosts
      will be incomplete with respect to coverage of the ARPA community
      and any new domains that are established.  One motivation for the
      domain system is the subdivision of name management to avoid the

      difficulty of keeping a global table of all hosts.  As the ARPA
      community moves to significant use of the domains system the
      maintenance of a global table for use by the DDN community will
      become very difficult.

      This means that DDN hosts might not be able to look up the names
      of some ARPA community hosts in their local tables.  In some cases
      this might result in an inability establish communication from a
      DDN hosts to such "unknown" ARPA community hosts.

         The most likely case is for a computer mail message sent from
         an ARPA community user on a host know to name servers but not
         in the central table to a user on a DDN community host that
         relies on a local copy of the central table.  When the DDN user
         attempts to answer this message his mail program will attempt
         to look up the host name.  This will fail, and the most likely
         result is that the mail program will tell the user that there
         is no such host!

      Please note that DDN community hosts are permitted (even
      encouraged) to implement the domain system in parallel with the
      ARPA community.  However, there is no requirement that they do so
      until called for in the schedule to be established by the DDN-PMO.

The Schedule

   04-Oct-83  The ARPANET/MILNET Logical Split

   02-Nov-83  Publish Domain Name Documents

      This Plan and Schedule (RFC-881), Domain Names - Concepts and
      Facilities (RFC-882), and Domain Names - Implementation
      Specification (RFC-883).

   16-Nov-83  Make Available Domain Style Host Table

      Create a copy a modified version of the HOSTS.TXT table named
      DHOSTS.TXT with an additional name (as the first name) in each
      entry of the form "official-host-name.ARPA".

   15-Dec-83  Final Specification of simple Query & Reply Protocol
   Available

      This specification covers the protocol procedures and message
      formats for the simple queries and replies to support translating
      host names to internet addresses only.

   15-Dec-83  Make Limited Domain Server & Resolvers Available

      An example limited domain server running on TOPS-20 and example
      limited resolvers running on each of TOPS-20 and VAX-Berkeley-Unix
      should be made available for testing and copying.  This simple
      version would be able to do queries and responses for host name to
      internet address translation only, and the servers would still use
      the global table.  This simple server would not refer the resolver
      to another server.  This simple server and these resolvers operate
      in datagram mode only.  However, this would allow user programs to
      begin to use the servers.

   01-Feb-84  Specification of Domain Requirements Available

      Detailed requirements for qualifying a set of hosts as a domain,
      and procedure for registering new domains is published.

   15-Feb-84  The ARPANET/MILNET Access Controls

      MILNET access controls installed in the MILNET/ARPANET gateways
      and TAC user access controls put into effect (see DDN MGT Bulletin
      16). [Date approximate.]

   07-Mar-84  Replace Main Host Table with Domain Style Host Table

      The DHOSTS.TXT becomes HOSTS.TXT.

   14-Mar-84  Final Specification of Query & Reply Protocol Available

      This specification covers the protocol procedures and message
      formats for the all queries and replies between resolvers and
      servers.

   14-Mar-84  Make Improved Domain Servers & Resolvers Available

      An example improved domain server running on TOPS-20 and example
      improved resolvers running on each of TOPS-20 and
      VAX-Berkeley-Unix should be made available for testing and
      copying.  This version should be able to do any of the defined
      query and response operations, and should support segmented data
      base by refering resolvers to other servers if necessary.  This
      server loads zone data from local master files only, and only at
      program start up.  This server and these resolvers operate with
      either datagram or reliable connection style communication.  This
      version does not support the data base update portion of the
      server protocol.

   04-Apr-84  Domain Servers for ARPA Domain Available

      Authoritative domain servers for the ARPA domain will be available
      for regular use.

   02-May-84  Introduce New Domains in the Main Host Table

      Add the DDN domain.  Most MILNET hosts will change to the DDN
      domain.  Authoritative domain servers for the DDN domain will be
      available for regular use.  HOSTS.TXT is updated.

   02-May-84  Establish a New Top Level Domains Only Table

      Start a new table, DOMAINS.TXT, that lists only the top level
      domains and the entries for their domain servers.

   16-May-84  Final Specification of Maintenance Protocol Available

      This specification covers the protocol procedures and message
      formats for the data base update exchanges between servers.

   16-May-84  Make Improved Domain Servers & Resolvers Available

      An example improved domain server running on TOPS-20 and example

      improved resolvers running on each of TOPS-20 and
      VAX-Berkeley-Unix should be made available for testing and
      copying.  This version should be able to do any of the defined
      query and response operations, and should support segmented data
      base by refering resolvers to other servers if necessary.  This
      server loads zone data from local master files and remote servers,
      and only at program start up.  This server and these resolvers
      operate with either datagram or reliable connection style
      communication.

   06-Jun-84  Permit the Introduction of New Domains

      Organizations meeting the requirements for establishing new
      domains will be allowed to begin use of new domain names.  New
      domains must be registered, meet the requirements (including
      running domain servers), and will be added to the HOSTS.TXT table.

   18-Jul-84  Final Specification of Complete Protocol Available

      This specification covers the protocol procedures and message
      formats for the complete domain names system.

   18-Jul-84  Make Full Domain Servers & Resolvers Available

      At this point an example domain server and an example resolver
      running on each of TOPS-20 and VAX-Berkeley-Unix should be made
      available for testing and copying.  This version should be able to
      do any of the defined query and response operations, and should
      support segmented data base by refering resolvers to other servers
      if necessary.  This version should support the data base update
      portion of the server protocol, including data aging and dynamic
      zone updating from remote servers.  This is a full implementation
      of the protocol.

   05-Sep-84  Discontinue the Full Host Table for the ARPA Community

      Stop maintaining the HOSTS.TXT table for the ARPA community.  The
      HOSTS.TXT table continues to be used in the DDN community with
      complete data for the DDN domain, however the data for the ARPA
      and other domains may no longer be complete or fully up to date.

   03-Oct-84  DDN-PMO Schedules DDN Implementation

      The DDN-PMO establishes the schedule for the implementation of the
      domain system in the DDN community.