RFC881

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.

The Domain Names Plan and Schedule

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 Domain Names Plan and Schedule

  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.

The Domain Names Plan and Schedule

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.

The Domain Names Plan and Schedule

  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

The Domain Names Plan and Schedule

     "BLAT-VAX" in the ARPA domain could set up mailboxes of the
     form "[email protected]" 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

The Domain Names Plan and Schedule

  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 Domain Names Plan and Schedule

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.]

The Domain Names Plan and Schedule

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

The Domain Names Plan and Schedule

  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.