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rfc: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.

Postel [Page 1]

RFC 881 November 1983 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.

Postel [Page 2]

RFC 881 November 1983 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.

Postel [Page 3]

RFC 881 November 1983 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.

Postel [Page 4]

RFC 881 November 1983 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

Postel [Page 5]

RFC 881 November 1983 The Domain Names Plan and Schedule

       "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

Postel [Page 6]

RFC 881 November 1983 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.

Postel [Page 7]

RFC 881 November 1983 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.]

Postel [Page 8]

RFC 881 November 1983 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

Postel [Page 9]

RFC 881 November 1983 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.

Postel [Page 10]

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